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Antioxidant Properties of Natural and Synthetic Chromanol Derivatives: Study by Fast Kinetics and Electron Spin Resonance Spectroscopy
Abstract
[structure: see text] Chromanol-type compounds act as antioxidants in biological systems by reduction of oxygen-centered radicals. Their efficiency is determined by the reaction rate constants for the primary antioxidative reaction as well as for disproportionation and recycling reactions of the antioxidant-derived radicals. We studied the reaction kinetics of three novel chromanols: cis- and trans-oxachromanol and the dimeric twin-chromanol, as well as ubichromanol and ubichromenol, in comparison to alpha-tocopherol and pentamethylchromanol. The antioxidant-derived radicals were identified by optical and electron spin resonance spectroscopy (ESR). The kinetics of the primary antioxidative reaction and the disproportionation of the chromanoxyl radicals were assessed by stopped-flow photometry in different organic solvents to simulate the different polarities associated with biomembranes. Furthermore, the reduction of the chromanoxyl radicals by ubiquinol and ascorbate was measured after laser-induced one-electron chromanol oxidation in ethanol and in a micellar system, respectively. The rate constants showed that twin-chromanol had better radical scavenging properties than alpha-tocopherol and a significantly slower disproportionation rate of its corresponding chromanoxyl radical. In addition, the radical derived from twin-chromanol is reduced by ubiquinol and ascorbate at a faster rate than the tocopheroxyl radical. Finally, twin-chromanol can deliver twice as many reducing equivalents, which makes this compound a promising new candidate as artificial antioxidant in biological systems.
... Their low toxicity in association with their broad pharmacological properties has enthused chemists to search for new medicinal agents. A large number of chromene and benzochromene derivatives have been designed with attractive biological properties, such as antimicrobial activities [1][2][3][4], anti-influenza drug discovery programmes [5], anti-inflammatory effects [6,7], antioxidant properties [8], Alzheimer's disease treatments [9,10], and the prevention of sugar cataracts that can instigate human blindness [11]. The variety and significance of the properties of the chromene and fused chromene derivatives have been emphasized in several reviews and articles for the manufacturing of potent antitumor agents [12][13][14]. ...
... On the other hand, the 1 H NMR spectra of 4 and 6 showed the singlet signals of the amino, methine, and methoxy protons at δ 7.05, δ 4.79, δ 3.72, δ 3.71 and δ 7.72, δ 4.99, δ 3.73, δ 3.66 ppm, respectively. In addition, the methylene, the methyl protons resonated at δ 4.02 and δ 1.16 ppm for compound 6 while the 13 C NMR spectra of 4 and 6 showed signals (7)(8)(9)(10) was achieved via the reaction of β-enaminonitrile (4) with different nucleophilic reagents, namely, acetic anhydride, benzaldehyde, triethyl orthoformate, and N,N-dimethylformamide dineopentyl acetal (DMF-DPA), while the ammonolysis of compound 9, via the stirring of bubbling ammonia gas in MeOH at ambient temperature for 1 h, resulted in the production of an open chain 2-aminomethyleneamino-4-(3,4-dimethoxyphenyl)-6-methoxy-4H-benzo[h]chromene-3-carbonitrile (11) as shown in Scheme 2. ...
... Synthetic protocol of 2-substituted β-enaminonitrile (7)(8)(9)(10)(11). Compounds 4 and 9 are successful precursors for the synthesis of an assortment of novel heterocyclic derivatives based on 4H-benzo[h] chromene. ...
Novel β-enaminonitrile/ester compounds (4, 6) and an imidate of 4 (9) were utilized as key scaffolds for the synthesis of newly 2-substituted 4H-benzo[h]chromene (7, 8, 10, 11, 13, 14) and 7H-benzo[h]chromeno[2,3-d]pyrimidine derivatives (15-19). The spectral data confirmed the successful isolation of the desired compounds. The targeted compounds were assessed for their in vitro anticancer activity against mammary gland breast cancer cell line (MCF-7), human colon cancer (HCT-116), and liver cancer (HepG-2), while doxorubicin, vinblastine, and colchicine were utilized as standard references drugs. Some of the examined compounds displayed high growth inhibitory activity against the three different cell lines. For example, the aminoimino derivative (18) exhibited excellent antitumor activity versus all cancer cell lines with IC50 values = 0.45 µg/mL, 0.7 µg/mL, and 1.7 µg/mL. Among the tested molecules, compounds 9, 15, and 18 were selected for further study regarding their effects on cell cycle analysis, apoptosis assay, caspase 3/7 activity, and DNA fragmentation. We found that these three potent cytotoxic compounds induce cell cycle arrest at the S and G2/M phases, which causes apoptosis. Furthermore, these compounds significantly inhibit the invasion and migration of the different tested cancer cells. Finally, the SAR survey highlighted the antitumor activity of the new molecules that was remarkably influenced by the hydrophilicity of substituent as well the fused rings at certain positions.
... Bislang wurde der Photoionisierungsansatz offenbar nur verwendet, um mit UV-C-und UV-B-Strahlung Phenoxyradikale von Tocopherol-Derivaten zu erzeugen und ihre nachgelagerten Reaktionen mit dem Monoanion des wasserlöslichen Co-Antioxidans Ascorbat zu studieren. [29,65] Andere Co-Antioxidantien enthalten häufig phenolische Grundstrukturen und absorbieren dadurch bei diesen Ionisierungswellenlängen (266 bzw. 308 nm) oder sind dort sogar selbst photoionisierbar [66,67] . ...
... Zwei Herangehensweisen zur Realisierung dieser indirekten Methode haben sich etabliert. Einerseits kann ein in Abwesenheit von Antioxidantien persistentes Radikal [65,[170][171][172][173][174] (oder in seltenen Fällen auch PbO 2 als chemisches Oxidationsmittel) [65,170] mit dem gewünschten Antioxidans vermischt werden (z.B. durch Strömungsmethoden), wobei in diesem Fall eine Stabilität von AO • im Millisekundenbereich oder länger Grundvoraussetzung ist. Andererseits kann das für die Erzeugung von AO • nötige oxidierende Radikal durch die Einwirkung externer Stimuli (z.B. ionisierende Strahlung, [62,124,128,129,[175][176][177][178] Licht [65,131,167,168,177,179] oder Wärme [180] ) in situ erzeugt werden (siehe Abb. ...
... Zwei Herangehensweisen zur Realisierung dieser indirekten Methode haben sich etabliert. Einerseits kann ein in Abwesenheit von Antioxidantien persistentes Radikal [65,[170][171][172][173][174] (oder in seltenen Fällen auch PbO 2 als chemisches Oxidationsmittel) [65,170] mit dem gewünschten Antioxidans vermischt werden (z.B. durch Strömungsmethoden), wobei in diesem Fall eine Stabilität von AO • im Millisekundenbereich oder länger Grundvoraussetzung ist. Andererseits kann das für die Erzeugung von AO • nötige oxidierende Radikal durch die Einwirkung externer Stimuli (z.B. ionisierende Strahlung, [62,124,128,129,[175][176][177][178] Licht [65,131,167,168,177,179] oder Wärme [180] ) in situ erzeugt werden (siehe Abb. ...
Aqueous photoionizations produce the hydrated electron, which is a super reductant with versatile chemical applications (e.g. reductive decomposition of pollutants). However, all previous procedures had to rely on UV-C radiation, inherently making a solar application impossible. In this thesis, some photoionization mechanisms were elucidated that require ionization wavelengths of the terrestrial solar spectrum and consume only the cheap sacrificial donor ascorbate. The most efficient photoionization can even be driven by green light and proceeds via an aryl radical anion as key intermediate. Moreover, investigations of the cyclic electron donor photoionization have shown that this mechanism is capable of generating the phenoxy radical of the famous radical scavenger resveratrol and of repairing it by co-antioxidants. With this approach, detailed findings on the biologically important repair of the resveratrol radical both in homogeneous solution and in supramolecular systems have been obtained.
... Chromene (benzopyran) is one of the privileged medicinal scaffold which appears as an integral part of many natural compounds and originated great attention due to their wide ranging of biological properties such as anti-HIV [12], anticancer [13], antimicrobial [14,15], antitumor [16], antiviral [17], anti-inflammatory [18] and antioxidant [19] activities. Among naturally occurring chromene heterocycles, molecules like Dehydrolupinifolinol (I), Eriosemaone A (II), Karanjachromene (III), and (+)-Calanolide A (IV) were reported as anti-tubercular agents (Fig. 1) [20][21][22][23]. ...
... Among naturally occurring chromene heterocycles, molecules like Dehydrolupinifolinol (I), Eriosemaone A (II), Karanjachromene (III), and (+)-Calanolide A (IV) were reported as anti-tubercular agents (Fig. 1) [20][21][22][23]. On the other hand, Indole derivatives have inspired chemists due to their natural origin and diverse pharmacological properties [24] including anticonvulsant [25], antidepressant [14], antihistamine [16], anti-tubercular [17], antidiabetic [18], analgesic, anti-inflammatory [19], anthelmintic [20], and antiallergic [26], activities. Recently, many researchers have reported indole incorporated analogues as anti-tubercular agents (V-IX) (Fig. 2) [27][28][29][30][31]. ...
As part of an ongoing effort to develop new anti-tubercular agents, a series of novel indole-fused spirochromene hybrids (7a–l) were efficiently synthesized in excellent yields by the popular ‘Fisher–Indole synthesis’ approach. The structure elucidation of the target compounds was carried out by different spectral techniques including ¹H-NMR, ¹³C-NMR, ESI Mass, and FTIR analysis. Additionally, the proposed structure of 7i was proved by single-crystal X-ray analysis. These compounds (7a–l) were screened for in vitro anti-tubercular activity against Mycobacterium tuberculosis H37Rv (ATCC 27294) strain. The results showed that most of the targets exhibited promising antimycobacterial activity with MICs of 1.56–6.25 μg/mL and weak cytotoxicity (19.93–32.16% at 50 μg/mL). Among them, compound 7l was found to be the most active compound (MIC of 1.56 μg/mL) with a good safety profile (32.16% at 50 μg/mL).
Graphic abstract
... Consequently, hypothermic storage warrants M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT strategies to alleviate these deleterious effects of hypothermia and rewarming, while reliably and consistently maintaining the key characteristics of cells, including viability, phenotype, and, in the case of ASC, differentiation potential. Substituted 6-chromanols represent a novel class of pharmacological compounds that preserve cell viability under a number of conditions [19][20][21]. Here, we describe the identification of a 6-chromanol derivate (SUL-109), a single molecule cell culture additive, as a preservation agent that protects human ASC from hypothermia and rewarming damage without affecting their subsequent differentiation capacity. Louis, MI) and 2 mM L-glutamine (Life Technologies #25030, Carlsbad, CA). ...
... We explored the mechanisms-of-action by which SUL-109 could protect the ASC from damage encountered during hypothermic preservation and rewarming and found that the protective effects were not derived from the ROS-scavenging capability of 6-chromanols [19,20,49], as antioxidant capacity did not associate with cell survival. Rather, SUL-109 increases the activity of mitochondrial complexes I and IV, thereby maintaining the mitochondrial membrane potential, ATP production and minimalizing ROS generation. ...
... 14 Although several reports have addressed radical scavenging by cyclodextrin-complexed ResOH, 7,9,[15][16][17] nothing whatsoever is known about the repair of ResO at the water-cyclodextrin interface. Even for a-tocopherol (vitamin E), the best-investigated lipophilic antioxidant, kinetic and mechanistic studies on the repair of its phenoxy radical have focused exclusively on homogeneous solutions 14,[18][19][20][21][22][23] and model membranes. [19][20][21][22][23][24] This lack of information concerning reactions across the water-cyclodextrin phase boundary-despite the widespread use of both cyclodextrins and antioxidants in food processing-prompted us to examine them using HAsc À as the repairing agent for ResO . ...
... Even for a-tocopherol (vitamin E), the best-investigated lipophilic antioxidant, kinetic and mechanistic studies on the repair of its phenoxy radical have focused exclusively on homogeneous solutions 14,[18][19][20][21][22][23] and model membranes. [19][20][21][22][23][24] This lack of information concerning reactions across the water-cyclodextrin phase boundary-despite the widespread use of both cyclodextrins and antioxidants in food processing-prompted us to examine them using HAsc À as the repairing agent for ResO . ...
Repair reactions of phenoxy radicals by co-antioxidants are key parts of radical scavenging cascades in nature. Yet, kinetic and mechanistic studies of such repairs are scarce, particularly at biologically relevant interfaces. For the popular red-wine polyphenol resveratrol, we present the first example of repairing a cyclodextrin-complexed phenoxy radical by a water soluble co-antioxidant (ascorbate), a reaction of practical importance given the fact that both antioxidants and cyclodextrins are large-scale food additives. To prepare the phenoxy radical from its parent compound inside the cavities of native or hydroxypropyl-substituted α- and β-cyclodextrins, we employed laser photoionization with UV-A (355 nm), which does not rely on additional reagents, and therefore leaves the repair completely undisturbed. A global fit of the intensity dependence pinpoints the cyclodextrin influences on the biphotonic resveratrol ionization as a shift of the ground-state absorption spectrum and a longer life of the first excited state due to the suppression of the geometrical isomerization by the rigid containers, whereas the actual electron ejection from an upper excited state is almost medium-independent. The exchange of the phenoxy radical between the cyclodextrin interior and the aqueous bulk is immeasurably slow on the timescale of its repair by the ascorbate monoanion. Kinetic H/D isotope effects and activation entropies identify the repair at the cyclodextrin-water interface as a concerted proton-electron transfer with no mechanistic difference to homogeneous aqueous solution. The activation enthalpies reveal a steric repulsion between ascorbate and cyclodextrin that indicates a deeper embedding of the less hydrophilic phenoxy radical in the macrocycle compared to the parent compound, with the observed structure-rate relationships explainable on the basis of the cavity diameter and depth.
... 56 The compound showed antioxidant properties that were superior to that of the truncated tocopherol model compound in several test systems. 58 Since it contained two chromanol moieties, twin-tocopherol 33 gave all reactions characteristic of tocopherol twice, most notably ortho-quinone methide formation. Each one of the two ''twin parts'' in 33 was able to undergo a reaction similar to the spiro dimerization of tocopherol. ...
... 70 3-Oxa-chromanols have recently been tested for their antioxidative properties, as they represent an interesting novel class of phenolic antioxidants. 58 EPR measurements of the radicals derived from 3-oxa-chromanol derivatives revealed similar stabilities as compared to the a-tocopheroxyl radical (2), producing well-resolved multiline spectra, the hyperfine coupling constants for the methyl substituents at the aromatic ring being quite similar to those of 2. Distinct effects of the configuration on the long-range couplings into the heterocyclic ring were observed. 27a,70 The oxidation behavior of 3-oxa-chromanols was mainly studied by means of the 2,4-dimethyl-substituted compound 2,4,5,7,8-pentamethyl-4H-benzo[1,3]dioxin-6ol (59) applied as mixture of isomers; 27a it showed an extreme dependence on the amount of coreacting water present. ...
Introduction α-Tocopherol and Its Derived o-QM: General Aspects Chemo- and Regioselectivity in the o-QM Formation from Tocopherol Reactions of the “Common” Tocopherol-Derived Ortho-Quinone Methide 3 Formation of Tocopherol-Derived o-QMs Involving Other Positions Than C-5A Future Prospects Acknowledgments References
... For the reaction of DPPH Å with a-TOH in n-hexane a rate constant around 10,000 L mol À1 s À1 (Table 2) was obtained, which is in the expected range from other studies. 17,18 In contrast, TNH 2 and T 3 NH 2 derivatives reacted more than hundred times slower with DPPH Å than a-TOH in n-hexane (Table 2). ...
... Endpoint determinations are carried out after 30 min or even longer times giving little kinetic but rather stoichiometric information. 17,[29][30][31][32][33] This is in contrast to the physiological situation in which in most cases an excess of antioxidants is present. By the stopped flow technique, the direct reaction kinetics of the antioxidant with the model radical with little interference of subsequent reaction steps is obtained. ...
The antioxidant activity of vitamin E (VE) homologs α, γ and δ-tocotrienamines (4b-6b), never studied before, and α, γ and δ-tocopheramines (4a-7a) was investigated by means of different total antioxidant capacity (TAC) tests. In all the test model systems, compounds 4a-7a and 4b-6b showed similar or higher TAC values than the parental vitamin E forms and their physiological metabolites. α-Homologs of VE amines showed markedly higher activity than the VE congeners in the TEAC test, which is tailored for liposoluble antioxidants, while γ-homologs of the amine analogs showed higher activity in the FRAP tests. Kinetics analysis of the reaction with DPPH(·) showed higher second order rate k for 4a than for α-tocopherol (1a). α-Tocopherolquinone 1f was the common main oxidation product for both 1a and α-tocopheramine (4a) exposed to ferric ions or DPPH(·), and the implied oxidative deamination of 4a was accompanied by a nitration reaction of phenolic substrates that were added to the reaction medium. Possible mechanisms of these reactions were studied.
... Some compounds such as ubichromenol, pennicitrinone C andpennicitrinol B (Fig. 6) also exhibited antioxidant activity when tested through model radical DPPH for evaluation of radical scavenging properties. Ubichromenol was found to be a weak antioxidant [55] and the compound was inactive, when obtained from Penicillium citrinum B-57, however, compounds 4, 6-8 showed IC 50 values ranging from 10.6 to 58.7 µM [56]. Some synthetic chromenes and their derivatives also show anti-inflammatory and antioxidant properties. ...
Chromene is a naturally abundant heterocyclic compound found in alkaloids, tocopherols, terpenes and other compounds. Its derivatives can be used as a scaffold that exhibits pharmacological activity in the human body. Chromene drugs and related bioactive molecules are the prime focus of this reference. It presents 13 thoroughly researched chapters that comprehensively cover all aspects about the molecule. Starting with a detailed introduction to its role and importance in drug discovery, the book goes into the details of chromene structure, synthesis and pharmacology. Readers can gain knowledge of different commercial medicines based on chromene and its pharmacological activity against different diseases. The elaborate topics in the book will help researchers working on chromene based drugs.
Key highlights of the book include:
- Complete coverage of chromene's role in nature and drug development with references to historical background and current developments
- References to commercial and preclinical drugs and patents of interest
- Explanation of chromene bioacivity in different diseases (antioxidant, antidiabetic, antinflammatory, antibacterial and antifungal activities, antitumour, immunomodulatory activity)
- Explanation of chromene activity against SARS-Cov2
... As a classical phenolic antioxidant, PG acts as a trap of radicals and halts or minimizes autoxidative processes (Gregor et al. 2005). In this radical scavenger function it has often been used also in cellulose science, mostly to stabilize the polymer during processing against chain degradation and unwanted oxidation/autoxidation. ...
Propyl gallate (PG, gallic acid propyl ester, Tenox®) is a very frequently used stabilizer and antioxidant in food and material applications, also used on large scale in the Lyocell process to stabilize the cellulose spinning dopes. In the present study we have investigated the fate of PG under classical Lyocell conditions (cellulose dissolved in N-methylmorpholine-N-oxide monohydrate at temperatures above 80 °C) by means of multiple analytical techniques, including NMR, GPC, and MS-hyphenated chromatography. It is demonstrated that propyl gallate is quickly hydrolyzed to gallate or, as a side reaction, aminolyzed to gallic acid morpholide. The products of the antioxidative action of gallic acid and propyl gallate, namely ellagic acid and its bis(ortho-quinone), are very easily adsorbed to cellulosic surfaces and are chiefly responsible for the discoloration of Lyocell spinning dopes and the resulting fibers. However, gallic acid morpholide and its parent compound gallic amide, while both having good antioxidant activity similar to propyl gallate itself, do neither form ellagic acid nor the bis(ortho-quinone) and are thus significantly superior to the conventionally used propyl gallate with regard to chromophore generation and resulting brightness loss. Also gallate moieties in tannins can be converted into the amide or morpholide to be further used as Lyocell stabilizers, which might open the way both to new Lyocell stabilizers and to a niche utilization for tannins.
Graphical abstract
... Hydroxychavicol is one of the major phenolic compounds which were reported to possess antinitrosation, anti-mutagenic, and anticarcinogenic effects; besides this, it has an enormous potency to act as an antioxidant, antiinflammatory, anti-platelet and antithrombotic agent without impairing hemostatic function [33] . 4-Chromanol has antioxidant activity [34,35] . Eugenol found in the present study has antibacterial and antifungal activities [36] . ...
The present study aims at finding out the optimum parameters for the extraction of components fromBetel leaves possessing medicinal applications using ethanol solvent by Soxhlet apparatus. The optimumconditions for the extract were calculated based on the extract yield by varying four parameters: materialquantity (A: 2–4 g), solvent quantity (B: 250–300 ml), mantle temperature (C: 65–75 °C) and extractiontime (D: 1–3 hours) and optimized using a four factor three level Box–Behnken response surfacedesign (BBD) coupled with desirability function methodology. Results showed that temperature and extractiontime had significant effect on yield of extract. Optimum conditions for highest yield of extract(10.94%) are as follows: material quantity (2 g), solvent quantity (281.4 ml), temperature (72 °C) and time(3 hours). The extract at the maximum yield condition was analyzed for phytocomponents by FTIR andGC–MS. The results indicated the presence of Hydroxy chavicol (69.46%), 4-Chromanol (24%) and Eugenol(4.86%), which possess wide application including as antioxidant, anti-inflammatory, anti-platelet and antithrombotic,antibacterial and antifungal agents.
... Among the most significant heterocyclics are the substituted chromenes and benzochromenes, owing to their antimicrobial [1][2][3][4][5], antiviral, anti-HIV, antileishmanial, antianaphylactic [6][7][8], anticancer [9][10][11][12][13][14][15][16], anti-inflammatory [17,18] and antioxidant [19] applications. β-enaminonitriles containing 4H-benzo[h]chromene systems have been used in cancer treatment approaches; therefore, they are described as prospective cancer pharmaceuticals' targets. ...
β-Enaminonitriles bearing 9-hydroxy-1H-benzo[f]chromene moiety was synthesized. The targeted compounds were evaluated for their anti-proliferative activity against three human tumor cell lines, PC-3, SKOV-3 and HeLa, and the active cytotoxic compounds were further evaluated against cancer cells, MCF-7/ADR, and two normal cell lines, HFL-1 and WI-38. Few compounds were assigned to be the most potent derivatives against PC-3, SKOV-3 and HeLa cell lines in comparison with Vinblastine and Doxorubicin. Several compounds possessed a relatively good potency against MCF-7/ADR cells as compared with Doxorubicin and were tested as a P-gp inhibitor. Moreover, the halogenated substituents, 2,4-F2, 2,3-Cl2, 2,5-Cl2 and 3,4-Cl2; have good potency against P-gp-mediated MDR in MCF-7/ADR as compared with Doxorubicin. Meanwhile, Rho123 accumulation assays revealed that few compounds effectively inhibited P-pg and efflux function. In addition, certain derivatives induced apoptosis and an accumulation of the treated MCF-7/ADR cells in the G1, S and G1/S phases.
... The mode of action through which SUL-109 and other 6chromanol derivates exert their effects on cell protection include scavenging of ROS [23,24], as well as maintenance of the mitochondrial network and activation of mitochondrial complexes I and IV, thereby preserving ATP production and avoiding ROS formation [7,13]. Although SUL-109 is predicted to have an antioxidant function, based on its chemical formulation, the protection of ADSCs during hypothermia could be largely contributed to the effect of SUL-109 on the mitochondrial complexes [7]. ...
The newly developed 6-hydroxychromanol SUL-109 was shown to provide protection during hypothermic storage of several cell lines, but has not been evaluated in hematopoietic stem cells (HSCs). Hypothermic preservation of HSCs would be preferred over short-term cryopreservation to prevent cell loss during freezing/thawing and be particularly useful for short-term storage, e.g., during conditioning of patients or transport of HSC transplants.
Here, we cultured human CD34+ UCB cells and lineage depleted (Lin--) Balb/c BM cells up to 7 days in serum-free HSC expansion medium with hematopoietic growth factors. SUL-109 containing cultures were stored at 4oC for 3-14 days. UCB cells were tested for viability, cell cycle and reactive oxygen species (ROS). DMSO-cryopreserved Lin-- BM cells or Lin-- BM cells maintained for 14 days at 4oC were transplanted into RAG2-/- Balb/c mice and engraftment was followed for 6 months. Addition of SUL-109, which was easy and non- toxic, during hypothermic storage of expanded CD34+ UCB cells provided a significant improvement in cell survival of the immature CD34+/CD38- fraction after 7 days of hypothermic storage through scavenging of hypothermia-induced ROS and was able to preserve multilineage capacity of human CD34+ UCB cells up to 14 days of cold storage. In addition SUL-109 protected murine BM lineage negative cells from 14 days of hypothermic preservation and retained their engraftment potential after transplantation in immune-deficient RAG2-/- mice.
In conclusion, SUL-109 is a promising novel chemical to be used as a protective agent during cold storage of human and murine HSCs to prevent hypothermia-induced apoptosis and to promote cell viability. Biology of Blood and Marrow Transplantation (2020).
... Chromene molecules are one of the most demanded compounds that are recognized as one type of 'privileged medicinal scaffolds' due to their unique pharmacological and biological activities [6][7][8][9][10][11][12][13]. Derivatives of these molecules exhibit tremendous medicinal behaviors such as antimicrobial and antifungal [12,[14][15][16], antiproliferation [9][10][11]13,[17][18][19], antioxidant [6,20], antispasmolytic, estrogenic [21], antileishmanial [22], hypotensive [8], vascular-disrupting activity [23], and blood platelet antiaggregating effects [24]. In addition, these molecules have been used in the enhancement of cognitive functions for the treatment of neurodegenerative symptom [25], as well as treating Alzheimer's disease [26] and Schizophrenia disorder [27]. ...
This report presents the development of a novel and primary model of sulfonamide compounds encompassing a chromene azo motif with the intent of becoming applicable for drug candidates in the cases of drug-resistant pathogens. The novel molecules (7a-n) have been synthesized via a two-step reaction. First, 4-((2, 4-dihydroxyphenyl)diazenyl)benzenesulfonamide (3a-e) were obtained through the reaction of their corresponding diazotized 4-aminobenzenesulfonamides (1a-e) with resorcinol, followed by the heterocyclization of 3a-e with arylidenemalononitriles (6a-d). Upon structural identification, the newly synthesized compounds were evaluated for their antibacterial and antifungal activities. Moreover, their cytotoxic screening was performed against three cancer cell lines: HCT-116, HepG-2, and MCF-7. Further examinations were comprised of the inhibitory effect analyses of the novel sulfonamide/chromene derivatives against the HDAC classes and the Tubulin polymerization in order to discern the prime antitumor drug candidates.
... [4][5][6] Although TB drug development has made substantial progress in the past decade and different drug classes are in development, there is still a need of novel potent chemical entities provided with promising antimycobacterial activities. 7 Chromene (benzopyran), an important class of benzo-fused oxaheterocycles is an integral part of many bioactive compounds exhibiting a wide range of biological properties including anti-HIV, [8][9][10] anticancer, 11,12 antimicrobial, 13,14 antitumor, 15 antiviral, 16 anti-inammatory 17 and antioxidant 18 activities. Among naturally occurring chromene heterocycles, molecules like dehydrolupinifolinol (I), eriosemaone A (II), karanjachromene (III), (+)-calanolide A (IV) and benzofurochromene (V) were reported as anti-tubercular agents ( Fig. 1). ...
A facile and convenient approach has been designed for the synthesis of novel prototypes that possess the advantage of the two pharmacophores of chromene and 1,2,3-triazole in a single molecular backbone, were evaluated against Mycobacterium tuberculosis H37Rv strain. The new analogues 1,2,3-triazole-fused spirochromenes were accomplished in four step synthetic strategy utilizing click chemistry ([3 + 2] Huisgen cycloaddition) in the ultimate step. The synthesized compounds were established based on the spectral data and X-ray crystal structure for 7a. Among the compounds tested against Mycobacterium tuberculosis H37Rv strain, some products exhibited potent antimycobacterial activity with minimum inhibitory concentration (MIC) values ranging from 1.56 to 6.25 μg mL−1. Compounds exhibiting good in vitro potency in the MTB MIC assay were further examined for cytotoxicity in a RAW 264.7 cells. Compounds 7a, 7d, 7i (MIC: 1.56 μg mL−1) and 7k, 7m (MIC: 3.125 μg mL−1) exhibited promising hits.
... Hydroxychavicol is one of the major phenolic compounds which were reported to possess antinitrosation, anti-mutagenic, and anticarcinogenic effects; besides this, it has an enormous potency to act as an antioxidant, antiinflammatory, anti-platelet and antithrombotic agent without impairing hemostatic function [33] . 4-Chromanol has antioxidant activity [34,35] . Eugenol found in the present study has antibacterial and antifungal activities [36] . ...
The present study aims at finding out the optimum parameters for the extraction of components from Betel leaves possessing medicinal applications using ethanol solvent by Soxhlet apparatus. The optimum conditions for the extract were calculated based on the extract yield by varying four parameters: material quantity (A: 2–4 g), solvent quantity (B: 250–300 ml), mantle temperature (C: 65–75 °C) and extraction time (D: 1–3 hours) and optimized using a four factor three level Box–Behnken response surface design (BBD) coupled with desirability function methodology. Results showed that temperature and extraction time had significant effect on yield of extract. Optimum conditions for highest yield of extract (10.94%) are as follows: material quantity (2 g), solvent quantity (281.4 ml), temperature (72 °C) and time (3 hours). The extract at the maximum yield condition was analyzed for phytocomponents by FTIR and GC–MS. The results indicated the presence of Hydroxy chavicol (69.46%), 4-Chromanol (24%) and Eugenol (4.86%), which possess wide application including as antioxidant, anti-inflammatory, anti-platelet and antithrombotic, antibacterial and antifungal agents.
... 5 Among synthetic compounds related to vitamin E, highly efficient antioxidants such as the synthetic twin chromanol (Twin) and related compounds were identified. 6 An increasing number of reports demonstrated that antioxidants including vitamin E-related chromanols showed different effects at the cellular, tissue, and whole organism level, although their reaction rates with radicals were similar. 7,8 This raised questions about the bioactivity of such vitamin E derivatives, which is not related to the antioxidant activity. ...
... The scavenging of stable DPPH radicals is a widely used method to evaluate antioxidant activities because of its simplicity and accuracy (20). It is known that the DPPH radical is considered to be a model of a stable lipophilic radical (21). Therefore, the DPPH radicals assay is a suitable model system for testing the effects of lipophilic antioxidants, and the results of this assay provide information about the protective effects of the antioxidants in the oxidation of lipids. ...
In this study, lipophilic tomato waste extracts (obtained from the Knjaz,
Bačka, Saint Pierre, Rutgers and Novosadski niski genotypes) were analyzed to
determine their lycopene and β-carotene content, as well as their kinetics of
antiradical activity. The kinetic behaviour of lipophilic tomato waste
extracts and standard antioxidant compound (BHA) were investigated using the
2,2-diphenyl-1-picrylhydrazyl (DPPH) radical test. In addition, correlations
between the contents of lycopene and β-carotene content and antiradical
activity of lipophilic tomato waste extracts were also sought. The content of
lycopene in tomato waste extracts ranged from 4.29 ± 0.14 mg/g for Rutgers
waste exract to 22.64 ± 0.86 mg/g for Knjaz waste extract, while the content
of β-carotene varied from 2.48 ± 0.09 mg/g for Novosadski niski waste exract
to 15.93 ± 0.56 mg/g for Knjaz waste extract. Based on the time required for
the DPPH radical-extract reaction to reach steady state, the investigated
lipophilic extracts, as well as BHA can be classified as the antioxidants
with slow (steady state ≥ 150 min) antiradical behaviour. A comparison of the
efficient concentrations at different kinetic times (EC50,t) for the
lipophilic tomato waste extracts and BHA showed that the DPPH antiradical
activity decreased in the order of BHA > Knjaz > Bačka > Saint Pierre >
Rutgers > Novosadski niski. The results of the correlation analysis suggest
that lycopene is the main individual carotenoid responsible for the EC50,t
values of the tomato waste extracts towards the stable DPPH radical.
[Projekat Ministarstva nauke Republike Srbije, br. TR 31044]
... The last of these was found to be a promising new candidate as an artificial antioxidant in biological systems. [11] all-rac-α-Selenotocopherol has been synthesized and found to be a slightly less potent antioxidant than α-tocopherol, in keeping with the value of the OH bond dissociation energy, which was found to be approximately 1 kcal mol -1 higher than that of α-tocopherol. [12] Moreover, phenolic compounds with one or two nitrogen atoms in the aromatic ring (e.g., 3-pyridinols, [13] 6amino-3-pyridinols, [13] 5-pyrimidinols [14] and analogues) are extremely effective chain-breaking antioxidants in homogeneous organic solutions, a tetrahydro-1,8-naphthyridin-3ol being almost 30 times more effective than α-tocopherol at inhibiting lipid peroxidation. ...
Treatment of dimethylhydroquinone dimethyl ethers (ortho and meta isomers) with glycopyranose pentaacetates (D-gluco, D-galacto) in the presence of SnCl4 and F3CCO2Ag selectively afforded the corresponding C-β-D-glycosyl derivatives by aromatic electrophilic substitution. Oxidation of the dimethoxybenzene moiety with ceric ammonium nitrate delivered C-β-D-glycosyl-dimethylbenzoquinones, which were reduced with Na2S2O4 to the corresponding C-β-D-glycosyl-dimethylhydroquinones. ZnCl2-catalyzed cyclization either with methylbut-2-en-1-ol (prenyl alcohol) or with all-racemic phytol led to acetyl-protected C-β-D-glycosyl chromanols or C-β-D-glycosyl tocopherols, the sugar residues of which were deacetylated under base catalysis conditions. These new molecules were evaluated as antioxidants in terms of their ability to inhibit the peroxidation of linoleic acid in SDS micelles. The position of the C-glucosyl moiety on the phenolic nucleus emerges as the critical structural determinant of their activity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
... Although there is some uncertainty about the actual value of e for the hydrocarbon region of a bilayer, a value *2.1 seems to be reasonable [33][34][35]. In fact, benzene is frequently used in both experimental [36][37][38] and theoretical [39][40][41] investigations to represent non-polar regions. The solvent cage effects have been included according to the corrections proposed by Okuno [42], taking into account the free volume theory [43]. ...
The ·OH and ·OOH radical scavenging activity of N-acetylcysteine amide (NACA) has been studied using density functional theory, specifically the M05-2X functional. All possible
reaction sites have been considered, and the branching ratios have been estimated. The efficiency of different mechanisms
of reaction has been evaluated, and it has been concluded that NACA reacts exclusively by hydrogen atom transfer (HAT). The
overall reactivity of NACA toward OH radicals is proposed to be diffusion-controlled in both non-polar and polar media. The
values of the overall rate coefficients are 3.80×109 and 1.36×109 L mol−1s−1 for benzene and aqueous solutions, respectively. The reactivity of NACA toward ·OOH, on the other hand, is much lower but still higher than those of melatonin and caffeine. HAT from the –SH site is proposed
to be the channel accounting for most of the radical scavenging activity of NACA in aqueous solution. In non-polar environments,
two channels of reaction were found to similarly contribute to the overall reactivity of NACA toward OH radicals. They are
those corresponding to hydrogen atom transfer from –CH2 and –SH sites.
KeywordsNACA–Oxidative stress–Free radicals–Antioxidant–Scavenger–Rate constant–Mechanisms
... 5 Among synthetic compounds related to vitamin E, highly efficient antioxidants such as the synthetic twin chromanol (Twin) and related compounds were identified. 6 An increasing number of reports demonstrated that antioxidants including vitamin E-related chromanols showed different effects at the cellular, tissue, and whole organism level, although their reaction rates with radicals were similar. 7,8 This raised questions about the bioactivity of such vitamin E derivatives, which is not related to the antioxidant activity. ...
Synthetic chromanol derivatives (TMC4O, 6-hydroxy-2,2,7,8-tetramethyl-chroman-4-one; TMC2O, 6-hydroxy-4,4,7,8-tetramethyl-chroman-2-one; and Twin, 1,3,4,8,9,11-hexamethyl-6,12-methano-12H-dibenzo[d,g][1,3]dioxocin-2,10-diol) share structural elements with the potent inhibitor of the mitochondrial cytochrome (cyt) bc(1) complex stigmatellin. Studies with isolated bovine cyt bc(1) complex demonstrated that these compounds partially inhibit the mammalian enzyme. The aim of this work was to comparatively investigate these toxicological aspects of synthetic vitamin E derivatives in mitochondria of different species. The chromanols and atovaquone as reference compound were evaluated for their inhibition of the cyt bc(1) activity in mitochondrial fractions from bovine hearts, yeast, and Leishmania. In addition, compounds were evaluated in vitro for their inhibitory activity against whole-cell Leishmania and mouse peritoneal macrophages. In these organisms, the chromanols showed a species-selective inhibition of the cyt bc(1) activity different from that of atovaquone. While in atovaquone the side chain mediates species-selectivity, the marked differences for TMC2O and TMC4O in cyt bc(1) inhibition suggests that direct substitution of the chromanol headgroup will control selectivity in these compounds. Low micromolar concentrations of TMC2O (IC(50) = 9.5 ± 0.5 μM) inhibited the growth of Leishmania, and an esterified TMC2CO derivative inhibited the cyt bc(1) activity with an IC(50) of 4.9 ± 0.9 μM. These findings suggest that certain chromanols also exhibit beyond their antioxidative properties antileishmanial activities and that TMC2O derivatives could be useful toward the development of highly active antiprotozoal compounds.
A class of 4H-benzo[h]chromene (4a-h) and 1H-benzo[f]chromene (6a-h) derivatives linked to carboxamide/carbothioamide at the 3/2-positions were designed and synthesized with the intent of cultivating efficacious antitumor agents. The pursued benzochromenes were successfully authenticated via the employment of an array of spectral assays. Subsequently, an antiproliferative evaluation against a selected line of tumorous cells (MCF-7, HepG-2, and PC-3) were performed in-vitro for the novel benzochromenes (4a-h and 6a-g) with the superior cytotoxically-active molecules subjected to additional assessment against the non-cancerogenic cells (HFL-1 and WI-38). Compounds 4a, 6b, 6c, 6d, 6f, and 6g demonstrated high efficiency towards MCF-7, HepG-2, and PC-3 cell lines, analogous to that of Vinblastine, Doxorubicin, and feeble efficacy against normal cell lines. The inhibition activity of the selected molecules (4a, 6b, 6c, 6d, 6f, and 6g) was detected in the G2/M phase of the cell cycle, which similarly instigated the suppression of the topoisomerase I & II enzymes in order to yield this result. Additionally, the derivatives submitted for the topoisomerase inhibition appraisal were similarly subjugated to examinations regarding the inhibition of tyrosine kinase receptors EGFR and VEGFR-2, in which the results were successively contrasted against the reference kinase inhibitor Sorafenib. Lastly, the molecular docking assay of the highly potent and efficacious derivatives in correlation with the active enzymatic and kinase sites was addressed.
Background: Several studies have been conducted on 4-H chromene compounds because of their intriguing pharmacological and biological properties. Various new natural compounds having a chromene foundation have been reported over the past 20 years.
Objective: In the present study, we reported the acute oral toxicity, antioxidant activity, and molecular docking study of the most active 4H-chromene derivative2-(4-Bromo-phenoxy)-N-[6-chloro-4-(4-chlorophenyl)-3-cyano-4H-chromen-2-yl]-acetamide (A9).
Method: The acute oral toxicity was carried out as per OECD 423 guidelines. For investigating the antioxidant activity, various biochemical parameters in colon tissue like SOD, CAT, MDA, PC and GSH and also enzyme levels, such as ALT, AST, ALP, and LDH, were measured in this experiment.
Results: Acute oral toxicity study indicated that the A9 ligand was found to be safer in animals. Additionally, the A9 ligand had significant antioxidant properties at various doses and was not found to be harmful to the liver. Due to its stronger binding energy and the appropriate interactions that induce inhibition, the A9 ligand's antioxidant function was also validated by additional molecular docking research.
Conclusion: This compound can be exploited as a lead molecule in further research.
Keywords: 4H-chromene, acute oral toxicity, antioxidant activity, molecular docking, estimation, cytochrome P450.
Conjugated cyano cyclo‐olefins modified as highly regioselective dipolarophiles in 1,3‐dipolar cycloaddition with NaN3 to synthesize corresponding fused 1,2,3‐triazole and 1H‐tetrazole derivatives. The first example of catalytic 1,3‐dipolar cycloaddition of NaN3 with 2H‐chromene‐3‐carbonitriles and subsequent elimination/cyclization of cyano functionality is designated. In presence of catalytic amount of p‐TSA or AgNO3, 2H‐chromene‐3‐carbonitriles react with NaN3 discretely producing 2,4‐dihydrochromeno[3,4‐d][1,2,3]triazoles or 5‐(2H‐chromen‐3‐yl)‐1H‐tetrazoles respectively, in good to excellent yields (i. e. 51–88% or 85–97%) with high regioselectivity and wide substrate scope adequacy.
Reaction of 7‑methoxy-2-naphthol with appropriate aromatic aldehydes and 2-cyano-ethanethioamide provided the corresponding 3-amino-1-aryl-9‑methoxy-1H-benzo[f]chromene-2-carbothioamide. The structures of these compounds were established on the basis of IR, ¹H NMR, ¹³C NMR, MS data and elemental analysis. Furthermore, the anti-proliferative properties were evaluated against the human cancer cell lines MCF-7, HepG-2 and PC-3 in comparison to the positive controls Vinblastine and Doxorubicin, employing the viability assay. The obtained results confirmed that some of the tested molecules revealed strong and selective cytotoxic activities against the three cancer cell lines. Moreover, various molecular descriptors, frontier molecular orbitals (FMO), Mulliken analysis and electronic properties were studied to probe the biological activity behavior of the synthesized 1H-benzo[f]chromene-2-carbothioamide derivatives. The effect of electron withdrawing groups (EWGs) and electron donating groups (EDGs) was also explored on the structural parameters and electronic nature of compounds. The energy gaps, reactivity descriptors values and molecular docking studies exhibited that some 1H-benzo[f]chromene-2-carbothioamide derivatives would be active biological compounds.
Aim: The present study involves to design, synthesis and evaluate the anticancer activity of 4H-chromene derivatives (PKB 1-10) on human breast cancer MCF-7 cell line. Materials and Methods: 4H-chromene derivatives (PKB 1-10) were designed by docking, in silico ADME and predicted toxicity studies. These designed compounds were then synthesized by acid catalyzed Michael Addition of phenols to benzylidene oxobutanoates. These compounds were characterized by 1 H NMR, 13 C NMR, FTIR and melting point. Then all synthesized compounds were tested for anticancer activity on MCF-7 cell line. Results: Compounds PKB-4 and PKB-10 showed better docking scores than standard drug, Adriamycin. In silico ADME and toxicity studies were also found significant for most of the compounds. The majority of the compounds displayed promising to potent anticancer activity on MCF-7 cell line. Conclusion: It may be concluded that most of the compounds showed significant docking and in silico ADME and toxicity profiles. Compounds have excellent anticancer potential and could be considered as novel anticancer agents for more investigation.
Alkoxybenzenes and alkoxynaphthalenes, as nucleophiles, have drawn great attention from organic chemists over the decades. Due to their high ring strain, those particular classes of molecules are often used in synthesis by utilizing their properties to undergo facile Friedel–Crafts alkylations. Different isomeric and low or densely substituted alkoxybenzenes are used for synthesis according to the structure of the target molecule. Isomeric methoxybenzenes, are the most commonly used molecule in this regard. This review aims to comprehensively cover the instances of different alkoxy-benzenes/naphthalenes used as nucleophiles for ring opening.
3-Amino-1-aryl-1H-benzo[f]chromene-2-carbonitrile derivatives were synthesized from three-component reaction of arylaldehyde, malononitrile and 2-naphthol in the presence of 1, 4-bis(4-ferrocenylbutyl)piperazine as a new catalyst. Cytotoxic potencies of the compounds were tested on HT-29 cells. 3-Amino-1-(4-fluorophenyl)-1H-benzo[f]chromene-2-carbonitrile (4c) was more active among these compounds and was selected for further studies. Apoptosis was investigated by acridine orange/ethidium bromide (AO/EtBr) double staining and flow cytometry. The qRT-PCR was used to analyze the expression of pro- and anti-apoptotic genes. The binding attributes of 4c with calf thymus DNA (ctDNA) was examined using multi-spectroscopic measurements. We found that 4c had potent cytotoxic activity against HT-29 cells with an IC50 value of 60 µM through induction of cell cycle arrest in the sub-G1 phase and apoptosis. RT-PCR analysis demonstrated down-regulation of Bcl-2 expression, while the expression of Bax, caspase-3, -8 and -9 genes was up-regulated in HT-29 cells incubated with 4c compared with control cells. These studies revealed that 4c interacts with DNA through groove binding mode with the intrinsic binding constant (Kb) of 3 × 102 M-1. Thus, 4c is a valuable candidate for further evaluation as a new series of potent chemotherapeutic family in colon cancer treatment.
In this thesis, we investigated the impact of hyperglycemia on adipose tissue-derived stromal cells (ASC) as a prelude to their use in the future therapeutic treatment of diabetic retinopathy (DR). Ultrastructure analyses of co-cultured ASC-endothelial cells featured the pericytic role of ASC in the maintenance of the vascular architecture under normal and high glucose conditions. The ROS-induced mitochondrial dysfunction and hyperglycemia-induced apoptosis partially influenced the pericytic functions of ASC. Injected ASC into an angiogenic mouse models, were detected at pericytic positions on newly formed vessels. Our recommendation is to preculturing of ASC under ‘chronic’ hyperglycemia, before injecting into a hyperglycemic environment to reduce their expression of pro-inflammatory and pro-angiogenic genes. ASC-conditioned medium (ASC-Cme) delivered from ASC cultured in chronically HG, protected bovine retinal endothelial cells (BREC) from hyperglycemia-induced apoptosis and inflammatory activation. This effect on BREC was evoked by the ROS-neutralizing capacity of ASC-Cme in culture that was associated with a reduced NF-κB activation which showed as a downmodulation of HG-upregulated pro-inflammatory genes in BREC. Towards using ASC for treatment of DR, we present a new hypothermic storing technique of cells in their own culture medium to well-maintain and transport the prepared cells to their clinical destination. The new pharmacologic compound, (6-hydroxyl-2,5,7,8-tetramethylchroman-2-yl)(4-(2-hydroxyethyl)piperazin-1-yl) methanone (SUL-109) shields ASC during cell preservation from hypothermic cell death without influencing their multi-potency capacity and proliferation through maintenance of the mitochondrial membrane potential and promoting the activation of mitochondrial complexes I and IV, consequently sustaining ATP production and preventing the overproduction of ROS under hypothermic conditions.
Repair reactions of lipophilic phenoxy radicals by hydrophilic co-antioxidants at model membranes are important for understanding the factors that govern the interactions between radical scavengers in biological systems. By using near-UV photoionization, we have selectively generated the phenoxy radical of the famous antioxidant resveratrol inside anionic (SDS), cationic (DTAC), or neutral (TX-100) micelles, as well as in homogeneous aqueous solution, and have compared its repairs in these media by the water-soluble co-antioxidants ascorbic acid and ascorbate monoanion. With all surfactants, these reactions are dynamic processes at the micelle-water interface. Whereas for the combinations ascorbate monoanion / ionic micelle the repair rates can be rationalized by the Coulombic interactions, unexpected effects were observed with the neutral ascorbic acid and the charged micelles: for the anionic micelles, this repair is three times faster than in homogeneous solution, and two orders of magnitude faster than for the cationic micelles. Given that the repair by a concerted proton-electron transfer demands a coplanar arrangement of the resveratrol phenoxy centre sticking out into the Stern layer and the co-antioxidant hydroxy moiety approaching from the aqueous bulk, we explain these results by ion-dipole interactions: only at a negatively charged micellar surface does the direction of the large dipole moment of ascorbic acid lead to an orientation favourable for the repair.
Noncovalent sulfur···oxygen interactions can increase the stability of chalcogen ortho-substituted phenoxyl radicals. This effect contributes to transforming the 7-hydroxybenzo[b]thiophene moiety in a privileged structural motif to enhance the activity of phenolic antioxidants. A cascade of five consecutive electrophilic reactions occurring in one pot afforded potent and biocompatible α-tocopherol-like antioxidants.
Compounds incorporating the chromene scaffold are largely present in natural products and display a wide variety of biological activities. Their low toxicity combined to the broad pharmacological properties have inspired medicinal chemists in the search for new therapeutic agents.
This review covers the literature between 1993 and on the biological activity of 2H- and 4H-chromenes, both from natural and synthetic origin. Includes a section that identifies a selection of chromene-based natural products, followed by recent literature on bioactive natural chromenes and the corresponding source, covering plants and fruits. Synthetic chromenes are equally important and a separate section addresses the use of these derivatives as new leads for drug discovery. Different biological targets were identified, namely those associated with anticancer, antimicrobial, anti-inflammatory, antithrombotic and antipsychotic activities.
Piper betle (Linn), a member of family Piperaceae is an edible plant. The leaves of Piper betle have been traditionally used in India for prevention of oral diseases. In the present study, the antibacterial activity against Streptococcus mutans for aqueous and ethanol extract of Piper betle leaves was studied by agar cup diffusion method. Minimum inhibitory concentration of extracts against Streptococcus mutans was detected by tube dilution method. GCMS[gas chromatography and mass spectroscopy] analysis of aqueous and ethanol extracts was carried out to detect the phytochemicals present in it. Both aqueous and ethanol extract inhibited the growth of Streptococcus mutans. Zone of inhibition of ethanol extract [20.6±1.12mm] was larger compared to aqueous extract [18.3±0.53].The MIC value for the aqueous and ethanol extract was 10mg/ml and 5mg/ml respectively. GCMS analysis revealed the presence of six compounds in each of the extract. The predominant compound in aqueous extract was 4 chromanol while phenol-2-methoxy-4(- 2propenyl) acetate was found in ethanol extract.
The commercial development of plants as sources of antioxidants that can be used to enhance the properties of foods, for nutritional purposes and preservation as well as for prevention of oxidation-related diseases, is currently of major interest. Rosehip (Rosa canina L.) is a rich source of vitamin C and polyphenols.
Phytochemicals in rosehip tea were separated into three fractions: Fr1 (vitamin C, 39.17 mg kg(-1)), Fr2 (flavonoids, 451.05 µg kg(-1)) and Fr3 (phenolic acids, 504.69 µg kg(-1)). Quercetin and ellagic acid were the most abundant polyphenolic compounds. Rosehip fractions, primarily rosehip flavonoids (EC(50) = 49 mg L(-1)), showed high antioxidant activity towards 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH(•)). Cell growth effects of rosehip fractions were assessed in HeLa, MCF7 and HT-29 cell lines, with the lowest IC(50) values being determined for rosehip flavonoids, (80.63, 248.03 and 363.95 mg L(-1) respectively). However, the vitamin C fraction did not inhibit the growth of tested tumour cells.
The results of this study confirm that vitamin C and flavonoids are responsible for the antioxidant activity of rosehip tea, while only polyphenols contribute to its antiproliferative activity.
Several 6-chromanol derivatives with various substituents (one or two amino, acetylamino, chloro or nitro substituents at the 5-, 7-, 8- or 5,7- positions on the phenyl ring of 2,2-dimethyl-6-chromanol) were synthesized, and their second order rate constants (k) for a reaction that demonstrates radical scavenging activity (reaction with the galvinoxyl radical) were determined. Three monoacetylamino compounds, 8-nitro compound, and 5,7-diamino, 5,7-diacetylamino, and 5,7-dinitro compounds were newly synthesized. Log k was plotted against the Hammett sigma (σm) or Taft sigma (σ*) constants for the compounds containing each of the four substituents to obtain their reaction constants (ρ) from the slopes. The σ plots representing radical scavenging activity showed a linear correlation with negative ρ values for all compounds with substituted positions. The results indicate that the electron-donating effect of the amino and acetylamino groups on the chroman ring enhanced radical scavenging activity, whereas the electron-withdrawing effect of the chloro and nitro groups decreased this activity. Furthermore, the magnitude of ρ for the substituted compounds increased in the following order with respect to the substitution position: meta-substituted (–3.71 for 6a-d), ortho-monosubstituted (–0.86 for 4a-d, –0.87 for 5a-d), and ortho-disubstituted (–0.47 for 7a-d). The greater ρ magnitudes for the meta-substituted compound indicated that the radical scavenging reactions were more sensitive to inductive substituent effects than for the ortho-substituent compounds. The ρ values for ortho-mono- and ortho-disubstituted compounds were smaller than that for the meta-substituted compound, despite the fact that the k values for the ortho-substituted compounds were higher than those for the meta-substituted compounds. Thus, electron-donating groups in ortho-substituted 6-chromanols accelerate the reaction rate through resonance stabilization in addition to the inductive substituent effect.
Measurements of aroxyl radical (ArO•)-scavenging rate constants (ksAOH) of antioxidants (AOHs) (α-, β-, γ-, and δ-tocopherols (TocHs) and -tocotrienols (Toc-3Hs)) were performed in ethanol solution, using stopped-flow spectrophotometry. ksAOH values of α-, β-, γ-, and δ-Toc-3Hs showed a good agreement with those of the corresponding α-, β-, γ-, and δ- TocHs. ksAOH values were measured not only for each AOH, but also for the mixtures of two AOHs ((i) α-TocH and β-, γ-, or δ-TocH and (ii) α-TocH and α-, β-, γ-, or δ-Toc-3H). A synergistic effect that the ksAOH value increases by 12% for γ-TocH (or by 12% for γ-Toc-3H) was observed for the solutions including α-TocH and γ-TocH (or γ-Toc-3H). On the other hand, a cancel effect that the ksAOH value decreases (a) by 7% for β-TocH (or 11% for β-Toc-3H) and (b) by 24% for δ-TocH (or 25% for δ-Toc-3H) was observed for the solutions including two kinds of AOHs. However, only a synergistic effect may function in edible oils, because contents of β- and δ-TocHs (and β- and δ-Toc-3Hs) are much less than those of α- and γ-TocHs (and α- and γ-TocH-3s) in many edible oils. UV-vis absorption of α-Toc•, which had been produced by reaction of α-TocH with ArO•, decreased remarkably under the coexistence of α-TocH and β-, γ-, or δ-TocH (or β-, γ-, or δ-Toc-3H), indicating that the prooxidant effect of α-Toc• is suppressed by the coexistence of the other TocHs and Toc-3Hs.
The analysis of the activation parameters for the formal H‐atom transfer reaction between 2,2,5,7,8‐pentamethyl‐6‐chromanol (ChrOH) and 2,2‐diphenyl‐1‐picrylhydrazyl (dpph•) reveals that these parameters are effective probes of the actual reaction mechanism. Indeed, the A factors measured in various polar and apolar solvents are localized in three distinct domains according to whether the reaction occurs via outer‐sphere electron transfer (ET) from the anion ChrO− or hydrogen atom transfer (HAT). For instance, A = 5.9 × 105 M−1 s−1 and E a = 2.5 kcal mol−1 in cyclohexane where the reaction proceeds by HAT, whereas in methanol, ethanol, and their mixtures with water where there is a substantial ET contribution A > 109 M−1s−1 and E a > 7 kcal mol−1. Interestingly, in nonhydroxylic polar solvents, A∼ 107 M−1s−1 and the E a values reflect the H‐bond accepting ability of the solvent in agreement with the “standard” kinetic solvent effects on HAT reactions. Addition of small quantities of pyridine accelerates the reaction rates in these solvents. This suggests that the H‐bonded complex (ChrOH···Py) is able to react via intermolecular ET with dpph•. It is known, in fact, that pyridine lowers the oxidation potential of phenols by ∼0.5 V and the ΔG ET of ChrOH + dpph• consequently decreases by about 10 kcal mol−1. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 524–531, 2012
Changes in the free radical components of rice bran oil before and after bleaching using a modified kaolin were investigated by electron paramagnetic resonance (EPR) spectroscopy. Before bleaching the EPR spectrum of the oil consisted of a single weak peak with g-value and linewidth similar to those of melanoidins, common colored components of seeds and husks. After bleaching, this was replaced by an EPR spectrum with 1H hyperfine structure characteristic of the α-tocopheroxyl radical, thus indicating some vitamin E oxidation during the bleaching process. This radical was exceptionally stable compared to its half-life in biological or simple chemical systems. The high stability of the α-tocopheroxyl radical indicates that reactions in the bleached oil are extremely slow, and that this oil has exceptional stability properties.
In order to understand the dynamics of antioxidant actions of vitamin E (α-, β-, γ-, and δ-tocopherols, TocH) in biological systems, kinetic study of the formation and decay reactions of vitamin E radicals (α-, β-, γ-, and γ- tocopheroxyls, Toc •) has been performed in organic solvents, using stopped-flow spectrophotometry. By mixing α-, β-, γ-, and δ-TocH with aryloxyl radical (ArO •) in ethanol, the peaks of the UV-vis absorption due to α-, β-, γ-, and δ-Toe• radical appeared rapidly at ca. 430-340 nm, showed maxima, and then decayed gradually. The second-order rate constants (κ a and 2κ d) for the formation and decay (that is, bimolecular disproportionation) reactions of a-Toe were determined by comparing the observed curves with the simulation ones obtained by the numerical calculation of differential equations related to the above reactions. From the results, the wavelengths of absorption maxima (λ maxi) and molar extinction coefficients (ε) (i = 1-4) of the optical spectra were determined for α-Toc• radical. Notable solvent effects have been observed for the reaction rates (κ f and 2κ d) and absorption spectra (λ maxi and ε i) of α-Toc• radical. The scheme of the formation and decay reactions of α-, β-, γ-, and δ-Toc• radicals has been discussed based on the results obtained.
Refluxing trimethylhydroquinone 2 in 10:1 dodecane/CH2Cl2 with linalool 3b (two-fold excess) and camphor-sulfonic acid, then treating the crude condensation product (consisting of a mixture of the chromanols 1b and 1c, alongside the tricyclic compounds 9 and 10) sequentially with Ac2O and m-CPBA afforded, after removal by column chromatography of the 9/10 acetates, a mixture of the regioisomeric epoxides 1jOAc and 1kOAc (ratio 9:1, total 60%). Treatment of this mixture with Al(O-i-Pr)(3) followed by CuI-catalysed Wurtz coupling of the acetates of the resulting allylic alcohols with citronellylmagnesium chloride 12a, and finally hydrogenation then provided the title acetate (overall 46% from 2).
Novel phenolic antioxidants: 2a (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-yl)methyl 3-methoxy-4-hydroxycinnamate, 2b (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-yl)methyl 3,5-dimethoxy-4-hydroxycinnamate, 2c (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-yl)methyl 3,4-dihydroxycinnamate, and 3 (6-hydroxy-2,5,7,8-tetramethylchroman-2-yl)methyl (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-carboxylate) have been prepared
in good yields and fully characterized by 1H and 13C NMR, and HRMS. Their radical scavenging activities have been evaluated by DPPH and ORAC assays. Each of the synthesized
antioxidants exhibited significantly higher radical scavenging activities than trolox and α-tocopherol. These novel antioxidants
efficiently protected canola oil triacylglycerides (CTG) during accelerated storage and frying. Compounds 2c and 3 were significantly more efficient than α-tocopherol protecting CTG under accelerated storage. All new antioxidants were more
efficient than α-tocopherol under frying conditions and present significantly higher thermal stability.
The hydroxyl radical-scavenging activity of the amino-substituted alpha-tocopherol analogues was much higher than that of alpha-tocopherol. Aminochromanoxyl radicals generated from 5- and 7-aminochromanol were successfully detected in aqueous solution at room temperature during ESR measurements. The stability of the aminochromanoxyl radicals leads to a significant enhancement of the radical-scavenging activity.
The measurements of the UV-vis absorption spectra of α-, β-, γ-, and δ-tocopheroxyl (α-, β-, γ-, and δ-Toc(•)) radicals were performed by reacting aroxyl (ArO(•)) radical with α-, β-, γ-, and δ-tocopherol (α-, β-, γ-, and δ-TocH), respectively, in acetonitrile solution including three kinds of alkali and alkaline earth metal salts (LiClO(4), NaClO(4), and Mg(ClO(4))(2)) (MX or MX(2)), using stopped-flow spectrophotometry. The maximum wavelengths (λ(max)) of the absorption spectra of the α-, β-, γ-, and δ-Toc(•) located at 425-428 nm without metal salts increased with increasing concentrations of metal salts (0-0.500 M) in acetonitrile and approached some constant values, suggesting (Toc(•)···M(+) (or M(2+))) complex formations. Similarly, the values of the apparent molar extinction coefficient (ε(max)) increased drastically with increasing concentrations of metal salts in acetonitrile and approached some constant values. The result suggests that the formations of Toc(•) dimers were suppressed by the metal ion complex formations of Toc(•) radicals. The stability constants (K) were determined for Li(+), Na(+), and Mg(2+) complexes of α-, β-, γ-, and δ-Toc(•). The K values increased in the order of NaClO(4) < LiClO(4) < Mg(ClO(4))(2), being independent of the kinds of Toc(•) radicals. Furthermore, the K values increased in the order of δ- < γ- < β- < α-Toc(•) radicals for each metal salt. The alkali and alkaline earth metal salts having a smaller ionic radius of the cation and a larger charge of the cation gave a larger shift of the λ(max) value, a larger ε(max) value, and a larger K value. The result of the DFT molecular orbital calculations indicated that the α-, β-, γ-, and δ-Toc(•) radicals were stabilized by the (1:1) complex formation with metal cations (Li(+), Na(+), and Mg(2+)). Stabilization energy (E(S)) due to the complex formation increased in the order of Na(+) < Li(+) < Mg(2+) complexes, being independent of the kinds of Toc(•) radicals. The calculated result also indicated that the metal cations coordinate to the O atom at the sixth position of α-, β-, γ-, and δ-Toc(•) radicals.
A kinetic study of regeneration reaction of α-tocopherol (α-TocH) by ubiquinol-10 has been performed in the presence of four kinds of alkali and alkaline earth metal salts (LiClO(4), NaClO(4), NaI, and Mg(ClO(4))(2)) in methanol and acetonitrile solutions, using double-mixing stopped-flow spectrophotometry. The second-order rate constants (k(r)'s) for the reaction of α-tocopheroxyl (α-Toc•) radical with ubiquinol-10 increased and decreased notably with increasing concentrations of metal salts in methanol and acetonitrile, respectively. The k(r) values increased in the order of no metal salt < NaClO(4) ~ NaI < LiClO(4) < Mg(ClO(4))(2) at the same concentration of metal salts in methanol. On the other hand, in acetonitrile, the k(r) values decreased in the order of no metal salt > NaClO(4) ~ NaI > LiClO(4) > Mg(ClO(4))(2) at the same concentration of metal salts. The metal salts having a smaller ionic radius of cation and a larger charge of cation gave a larger k(r) value in methanol, and a smaller k(r) value in acetonitrile. The effect of anion was almost negligible in both the solvents. Notable effects of metal cations on the UV-vis absorption spectrum of α-Toc• radical were observed in aprotic acetonitrile solution, suggesting complex formation between α-Toc• and metal cations. On the other hand, effects of metal cations were negligible in protic methanol, suggesting that the complex formation between α-Toc• and metal cations is hindered by the hydrogen bond between α-Toc• and methanol molecules. The difference between the reaction mechanisms in methanol and acetonitrile solutions was discussed on the basis of the results obtained. High concentrations of alkali and alkaline earth metal salts coexist with α-TocH and ubiquinol-10 in plasma, blood, and many tissues, suggesting the contribution of the metal salts to the above regeneration reaction in biological systems.
Pentamethyl-6-chromanol (PMCol), a chromanol-type compound related to vitamin E, was proposed as an anticancer agent with activity against androgen-dependent cancers. In repeat dose-toxicity studies in rats and dogs, PMCol caused hepatotoxicity, nephrotoxicity, and hematological effects. The objectives of this study were to determine the mechanisms of the observed toxicity and identify sensitive early markers of target organ injury by integrating classical toxicology, toxicogenomics, and metabolomic approaches. PMCol was administered orally to male Sprague-Dawley rats at 200 and 2000 mg/kg daily for 7 or 28 days. Changes in clinical chemistry included elevated alanine aminotransferase, total bilirubin, cholesterol and triglycerides-indicative of liver toxicity that was confirmed by microscopic findings (periportal hepatocellular hydropic degeneration and cytomegaly) in treated rats. Metabolomic evaluations of liver revealed time- and dose-dependent changes, including depletion of total glutathione and glutathione conjugates, decreased methionine, and increased S-adenosylhomocysteine, cysteine, and cystine. PMCol treatment also decreased cofactor levels, namely, FAD and increased NAD(P)+. Microarray analysis of liver found that differentially expressed genes were enriched in the glutathione and cytochrome P450 pathways by PMCol treatment. Reverse transcription-polymerase chain reaction of six upregulated genes and one downregulated gene confirmed the microarray results. In conclusion, the use of metabolomics and toxicogenomics demonstrates that chronic exposure to high doses of PMCol induces liver damage and dysfunction, probably due to both direct inhibition of glutathione synthesis and modification of drug metabolism pathways. Depletion of glutathione due to PMCol exposure ultimately results in a maladaptive response, increasing the consumption of hepatic dietary antioxidants and resulting in elevated reactive oxygen species levels associated with hepatocellular damage and deficits in liver function.
The measurement of the UV-vis absorption spectrum of α-tocopheroxyl (α-Toc(•)) radical was performed by reacting aroxyl (ArO(•)) radical with α-tocopherol (α-TocH) in acetonitrile solution including four kinds of alkali and alkaline earth metal salts (MX or MX(2)) (LiClO(4), LiI, NaClO(4), and Mg(ClO(4))(2)), using stopped-flow spectrophotometry. The maximum wavelength (λ(max)) of the absorption spectrum of the α-Toc(•) at 425.0 nm increased with increasing concentration of metal salts (0-0.500 M) in acetonitrile, and it approached constant values, suggesting an [α-Toc(•)-M(+) (or M(2+))] complex formation. The stability constants (K) were determined to be 9.2, 2.8, and 45 M(-1) for LiClO(4), NaClO(4), and Mg(ClO(4))(2), respectively. By reacting ArO(•) with α-TocH in acetonitrile, the absorption of ArO(•) disappeared rapidly, while that of α-Toc(•) appeared and then decreased gradually as a result of the bimolecular self-reaction of α-Toc(•) after passing through the maximum. The second-order rate constants (k(s)) obtained for the reaction of α-TocH with ArO(•) increased linearly with an increasing concentration of metal salts. The results indicate that the hydrogen transfer reaction of α-TocH proceeds via an electron transfer intermediate from α-TocH to ArO(•) radicals followed by proton transfer. Both the coordination of metal cations to the one-electron reduced anions of ArO(•) (ArO:(-)) and the coordination of counteranions to the one-electron oxidized cations of α-TocH (α-TocH(•)(+)) may stabilize the intermediate, resulting in the acceleration of electron transfer. A remarkable effect of metal salts on the rate of bimolecular self-reaction (2k(d)) of the α-Toc(•) radical was also observed. The rate constant (2k(d)) decreased rapidly with increasing concentrations of the metal salts. The 2k(d) value decreased at the same concentration of the metal salts in the following order: no metal salt > NaClO(4) > LiClO(4) > Mg(ClO(4))(2). The complex formation between α-Toc(•) and metal cations may stabilize the energy level of the reactants (α-Toc(•) + α-Toc(•)), resulting in the decrease of the rate constant (2k(d)). The alkali and alkaline earth metal salts having a smaller ionic radius of cation and a larger charge of cation gave larger K and k(s) values and a smaller 2k(d) value.
Contrary to concepts handed down in the literature from the early days of vitamin E research, one-electron oxidation of vitamin E does not involve 5a-C-centered radicals. A combined approach of analytical techniques, in particular electron paramagnetic resonance spectroscopy (EPR), organic synthesis of special derivatives, isotopic labeling, kinetic studies, and computational chemistry was used to re-evaluate the one-electron and two-electron oxidation chemistry of alpha-tocopherol (alpha-toc). EPR in combination with 5a-13C-labeled compounds provided no indication of the involvement of 5a-C-centered radicals. Oxidation of special tocopherol derivatives were used to disprove the occurrence of 5a-C-centered one-electron intermediates. Additionally it was shown that those vitamin E reactions that were commonly evoked to plead for the involvement of C-centered tocopheryl radicals actually proceeded via heterolytic, i.e., non-radical, intermediates. The results will help to clear widely spread misunderstandings about the chemistry of vitamin E and will have mechanistic implications for the synthesis of tocopherol-based supramolecular structures and 5a-substituted alpha-tocopherol derivatives.
Many, if not most, redox reactions are coupled to proton transfers. This includes most common sources of chemical potential energy, from the bioenergetic processes that power cells to the fossil fuel combustion that powers cars. These proton-coupled electron transfer or PCET processes may involve multiple electrons and multiple protons, as in the 4 e–, 4 H+ reduction of dioxygen (O2) to water (eq 1), or can involve one electron and one proton such as the formation of tyrosyl radicals from tyrosine residues (TyrOH) in enzymatic catalytic cycles (eq 2). In addition, many multi-electron, multi-proton processes proceed in one-electron and one-proton steps. Organic reactions that proceed in one-electron steps involve radical intermediates, which play critical roles in a wide range of chemical, biological, and industrial processes. This broad and diverse class of PCET reactions are central to a great many chemical and biochemical processes, from biological catalysis and energy transduction, to bulk industrial chemical processes, to new approaches to solar energy conversion. PCET is therefore of broad and increasing interest, as illustrated by this issue and a number of other recent reviews.
Novel antioxidants, derivatives of trolox, and selected phenolic acids have been prepared in good yields and fully characterized by (1)H NMR, (13)C NMR, and MS. Their antioxidant activities have been assessed by DPPH and ORAC assays, and during frying and accelerated storage tests. Novel phenolic compounds exhibited higher radical scavenging activities than both trolox and α-tocopherol. Trolox hydroxybenzoate showed a significantly higher protection than α-tocopherol under storage conditions. All new antioxidants performed better than α-tocopherol under frying conditions. Moreover, their outstanding thermal stability makes them more valuable than α-tocopherol for frying applications.
A kinetic study of the reaction between vitamin C (L-ascorbic acid, AsH2) and a tocopheroxyl radical (7-tert-butyl-5-isopropyltocopheroxyl) in Triton X-100 micellar solution has been performed using stopped-flow spectrophotometry. The second-order rate constants (k2) obtained showed notable pH dependence with a broad maximum around pH 8. For instance, the k2 values obtained were 26 M-1 S-1 at pH 3, 322 M-1 S-1 at pH 7, and 273 M-1 S-1 at pH 10. A good correlation between the rate constants and the mole fraction of ascorbate monoanion (AsH-) was observed, showing that ascorbate (AsH-) can regenerate the tocopherol from tocopheroxyl in biological systems. Furthermore, the results indicate that reduced ascorbic acid (AsH2) does not have the ability to regenerate the tocopherol in aqueous solution. On the other hand, it was found that AsH2 can reduce the tocopheroxyl to tocopherol in benzene/ethanol (2:1) mixtures, although the rate of reaction is only approximately 15% of that observed in micellar solution at pH 7.
The maximum possible bimolecular rate of electron transfer to ubiquinone (coenzyme Q with six isoprenoid units in the side chain) is likely to be that from solvated electrons, now determined by pulse radiolysis to be 1.7 x 10¹⁰m⁻¹ sec⁻¹. ·CH2O⁻ radicals also reduce ubiquinone, with k = 2.0 x 10⁹m⁻¹ sec⁻¹. The reduction product in both cases is the ubisemiquinone free radical anion, ε445 nm = 7200 m⁻¹ cm⁻¹. In acid solutions reduction is produced only by ·CH2OH radicals with k = 1.4 x 10⁹m⁻¹ sec⁻¹. The reduction product is the neutral ubisemiquinone free radical, ε420 nm = 3000 m⁻¹ cm⁻¹. Neutral ubisemiquinone free radicals disproportionate with k = 4.8 x 10⁷m⁻¹ sec⁻¹. In neutral solution ubiquinone is reduced both by solvated electrons and by ·CH2OH radicals: formation of the neutral ubisemiquinone is followed by deprotonation to yield the anion, with k = 1.0 x 10⁴ sec⁻¹. The pK of the semiquinone free radical is 6.45 ± 0.15.
Three selectively labeled propynes were prepared either with deuterium or carbon-13 at position 3 and doubly labeled with carbon-13 at positions 1 and 2 by an alkylation reaction from the corresponding labeled or unlabeled monolithio acetylides and dimethylsulfates. Their lithiation with nBuLi gave the corresponding propynyllithium derivatives which reacted with dimethyl squarate to afford the corresponding propargylic alcohols. These were thermolysed in p-xylene to furnish [5-D3-methyl]-, [5-13C-methyl]-, and [5,6-13C2-2,5-cyclohexadienyl]ubiquinone. The farnesyl side chain was introduced onto the labeled quinones with farnesyl trimethyltin under BF3 catalysis to provide [5-D3-methyl]-, [5-13C-methyl]-, and [5,6-13C2-2,5-cyclohexadienyl]ubiquinone 3 (6c, 6b, 6a, respectively).
α-Tocopherol appears to have been selected as nature's major lipid-soluble, chain-breaking antioxidant because it has a number of superior properties when compared with most synthetic phenolic antioxidants: one of these properties is shown to be very low reactivity of α-tocopheroxyl towards oxygen.
Condensation of trimethylhydroquinone with aldehydes provides 2,4-disubstituted 5,7,8-trimethyl-4H-benzo[1,3]dioxin-6-ols in a straightforward one-pot reaction. These compounds are 3-oxa-derivatives of α-tocopherol (vitamin E) and represent an interesting novel class of phenolic antioxidants. The formation reaction proceeds according to a two-step mechanism consisting of electrophilic substitution and acetalization, and provides the product as a cis/trans-mixture of diastereomers.
The kinetics of bimolecular decay of α-tocopheroxyl free radicals (T.) was studied by ESR mainly in ethanol and heptanol solvents. A second-order kinetic law was observed during the whole course of reaction (-d[T.]d t = 2 k[T.]2) and the following rate constants were determined with good accuracy in the temperature range 281–321 K: ethanol: log(2 k) = 8.2 ± 0.5 — (6.6±0.7 kcal/mol)/(2.3 RT) M−1·s−1; heptanol: log(2 k)=6.1±0.4-(4.3±0.6 kcal/mol)/(2.3 RT) M−1.s−1. The global rate constant clearly increases with solvent polarity.
In order to study the inhibition of oxidation by vitamin E, the formation and reaction of chromanoxyl radicals and hindered phenoxyl radicals were examined by ESR. t-Butoxyl radical abstracted the phenolic hydrogens of α-, β-, γ-, and δ-tocopherols, 2,4,6-tri-t-butylphenol (TBP), and 2,6-di-t-butyl-4-methylphenol (BMP) to give corresponding phenoxyl radicals which were stable enough to be observed by ESR. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) also induced the formation of chromanoxyl and phenoxyl radicals. The ESR spectra of chromanoxyl radicals were recorded and their hyperfine coupling constants were determined. The phenoxyl radicals from TBP and BMP disappeared quite rapidly when excess t-butyl hydroperoxide was added, whereas α-chromanoxyl radical from α-tocopherol remained considerably. α-Chromanoxyl radical and phenoxyl radicals reacted with p-t-butylbenzenethiol to regenerate α-tocopherol and corresponding phenols respectively. The implications of these results are discussed.
Es wurde die Umsetzung von Cystem bei erhöhtem Druck studiert. Die Anwendung eines Druckes won ca. 10 atü ist einerseits nötig, um die Reaktionskomponenten flüssig zu halten; andererseits ergibt sie bis zu einem gewissen Grad eine Reaktionsbeschleunigung. Reaktionsdauer, Reaktionstemperatur sowie Salpetersäurekonzentration und molares Verhältnis von Salphetersäure zu Cyclohexan stehen in Wechselwirkung zueinander. Während mit zunehmender Reaktionsdauer Nitrocyclohexan abgebaut wird, begünstigt eine Temperaturerhöhung die Bildung dieser Verbindung. Die Reaktionsgeschwindigkeit ist u.a. direkt proportional zur Salpetersäurekonszentration und indirekt proportional zum Volumen der wässerigen Phase.
Tocopheroxyl model radicals have been prepared by the reaction between tocopherol models and stable phenoxyl radical in ethanol under nitrogen atmosphere. Optical spectra were recorded, and wavelength of absorption peaks (λmax) and molar extinction coefficients (ε) were correctly determined.
ESR measurements were performed for the coenzyme Q1, chromanoxyl and chromenoxyl radicals obtained by oxidizing the phenol precursors with PbO2 in toluene, and the proton hyperfine splittings were correctly determined.
The decay kinetics of triplet excited probes (meso-tetraphenylporphyrin or anthracene) in unilamellar phospholipid bilayer membranes was studied using nanosecond laser-induced transient absorption spectroscopy. Two decay modes, quenching by molecular oxygen and triplet−triplet annihilation, were investigated as a function of temperature. The rates of both processes were sensitive to the phase of the membrane and underwent a significant change at the temperature corresponding to the main phase transition. The analysis of triplet annihilation data obtained in dimyristoylphosphatidylcholine or dipalmitoylphosphatidylcholine unilamellar vesicles, and mixtures thereof, demonstrates that the phase transition can be analyzed in these systems with an accuracy matching that of other techniques, including calorimetry; this accuracy applies to the determination of critical temperatures as well as to the estimation of transition cooperativity. Triplet quenching by molecular oxygen is shown to be largely determined by diffusion of oxygen from the bulk medium to the membrane. Triplet decay is thus a suitable probe of fluidity as well as of diffusional processes in unilamellar bilayers.
The 100-MHz 13C NMR spectrum of (2R,4′R,8′R)-α-tocopherol (natural vitamin E) has been completely assigned with the aid of a number of selectively deuteriated (2R,4′R,8′R)-α-tocopherols. The 13C NMR spectrum of (2RS,4′RS,8′RS)-α-tocopherol (all-racemic, synthetic vitamin E) has also been measured. Many of the individual carbons in this all-racemic mixture of eight α-tocopherol stereoisomers give more than one resonance with eight of the carbons (2-CH3, 2′, 3′, 4′, 4′-CH3, 5′, 8′, and 9′) giving the maximum number of four resonances from each of the four enantiomeric pairs; these resonances have also been assigned. The structurally related 5′-hydroxy-2-(4′,8′,12′-trimethyltridecyl)-2,4,6,7- tetramethyl-2,3-dihydrobenzofuran (HTDBF) has been synthesized for the first time in the 2R,4′R,8′R and 2S,4′R,8′R configurations and their 13C resonances have been assigned. In its all-racemic form this compound also shows up to four resonances from a single carbon. Related observations have been made with phytol and isophytol. A careful examination of these chirally induced chemical shift differences for the individual carbon atoms, Δ, reveals a bond-alternation effect with maxima at a separation of one, three, and five bonds from the closest chiral center and with the maximum at a five-bond separation being greater than that at a three-bond separation. For example, the total Δ, ∑Δ, averaged over the number of carbon aroms, n, which are separated from the nearest chiral center by the same number of bonds has been conservatively calculated for α-tocopherol to be 54, 106, 43, 66, 40, and 75 ppb at separations from the closest chiral center of zero, one, two, three, four, and five bonds, respectively. For HTDBF the corresponding ∑Δ/n values are 45, 67, 12, 0, 0, and 20 ppb. We attribute these remarkable long-range (five-bond) effects to differences in 1,6 nonbonded repulsions for different enantiomeric pairs and consider that it provides direct evidence for the operation of Newman's classic "rule of six".
Several new tocopherol derivatives have been synthesized, and second-order rate constants, ks, for H atom abstraction by substituted phenoxyl radicals (PhO•) have been measured spectrophotometrically by the stopped-flow method as a model reaction of tocopherols with unstable free radicals (LOO•, LO•, and HO•) in biological systems. Vitamin K1-chromanol (1) and K1-chromenol (2) were found to be 6.9 and 4.5 times more active than α-tocopherol, which has the highest antioxidant activity among natural tocopherols. Thus, these compounds have the highest antioxidant activity among phenolic antioxidants including natural tocopherols, tocopherol derivatives, and related phenols in solution. Two new tocopherol derivatives with five-membered heterocyclic rings were also found to be 1.8 and 1.1 times more active than the α-tocopherol. However, both the ubichromanol (3) and ubichromenol (4) having two methoxy substituents at the aromatic ring were only ca. 10% as reactive as α-tocopherol. From detailed analysis of the temperature dependence of ks values in the tocopherols, the activation energy, Eact, for the reaction has been determined. Half-peak oxidation potentials, Ep/2, for tocopherol compounds have also been measured with cyclic voltammetry.
Rate constants which have been reported for the bimolecular self-reaction of alpha-tocopheroxyl radicals vary by about 5 orders of magnitude. We have found that the observed bimolecular rate constant can vary by about a factor of 7 during a single, but typical experiment, e.g., in chlorobenzene at 37 degrees C from ca. 7 x 10(3) M(-1) s(-1) initially to ca. 1 x 10(3) M(-1) s(-1) finally. The overall reaction involves a disproportionation with the transfer of a hydrogen atom from the 5-methyl group of one radical to the phenoxyl oxygen atom of the other radical forming alpha-tocopherol and an o-quinone methide. In the slow regime (which corresponds to the true reaction of two alpha-tocopheroxyl radicals) this disproportionation has a deuterium kinetic isotope effect of 3.7. The bizarre kinetic behavior observed with alpha-tocopheroxyl radicals has been traced to a very minor impurity which will be present in any normal sample of alpha-tocopherol. The impurity in question is a bisphenol in which two alpha-tocopherol moieties have become linked through their 5-methyl carbon atoms. This bisphenol is a ''natural'' impurity in alpha-tocopherol since it will be formed upon exposure of alpha-tocopherol to air. The coupling of two o-quinone methide molecules yields a spiro-dimer which is then reduced to the bisphenol, probably by unoxidized alpha-tocopherol.
The H-atom donating activities of 2,6-di-tert-butyl-4-methylphenol (BHT), 2,6-di-tert-butyl-4-methoxyphenol (DBHA), 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC), and 3,5-di-tert-butylcatechol (DTBC) toward the nitrogen-centered 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical were measured by stopped flow methods in hexane, 1-propanol, tert-butyl alcohol, and acetone. Decreases in these activities on transferring from hexane to the hydrogen bond accepting (HBA) solvents, the kinetic solvent effect (KSE), are attributed to hydrogen bonding from the phenolic group. Steric hindrance accounts for a lower decrease observed for the highly hindered BHT and DBHA compared to PMHC. The catechol, DTBC, a very active H-atom donor to DPPH in hexane, showed a dramatic loss of activity in HBA solvents, especially acetone. Higher H-atom donating activities of BHT, DBHA, and PMHC were observed toward the oxygen-centered radical of 2,6-di-tert-butyl-4-(4‘-methoxyphenyl)phenoxyl (DBMP), and the decreases in activity in the HBA solvents paralleled those found with DPPH. Thus the KSE was found to be independent of the nature of the abstracting radical for DPPH and DBMP. The inhibition of the oxygen uptake (IOU) method was used to determine the antioxidant activities (kinh) of α-tocopherol, PMHC, catechol, and DTBC during free radical autoxidation of styrene and mixtures of styrene and tert-butyl alcohol. The kinh of α-tocopherol and PMHC dropped to one-tenth of the values with increasing tert-butyl alcohol content due to the HBA activity of the alcohol compared to styrene.
A systematic study on the effect of various substituents at the 7- and/or 8-position on the redox properties of isoalloxazines (flavins) is reported. The redox properties of these flavin derivatives were studied by cyclic voltammetry in 100 mM, pH 7.4 HEPES and 200 mM, pH 10 borate buffers. The magnitude and direction of the effect was dependent on the nature and location of the substituent. The redox potentials of the substituted flavins were correlated with the Hammett σ value of the substituents.
Photolysis of diphenyldiazomethane in RS-2-butanol in solution between room temperature and −115°C gives ether as the only volatile product. Photolysis of in polycrystalline (S)-2-butanol at −196° gives as well as the 5 products derived from formal CH insertion of the carbene into the matrix. Tertiary alcohol was formed in 15% yield and was shown to be enantiomerically pure.
Rate constants, k1, for H-atom abstraction by peroxyl radicals from α-tocopherol and 35 structurally related phenols have been measured at 30°C by the inhibited autoxidation of styrene (IAS) method. An independent laser-flash kinetic EPR method was used with ten of these phenols which gave k1 values at 24°C that were in satisfactory agreement with the values found by the IAS method. The structures of several phenols were determined by X-ray analysis. The EPR spectral parameters for the phenoxyl radicals derived from many of these phenols were also measured. The relative magnitudes of k1 values for phenols that are structurally closely related and have an oxy substituent para to the hydroxyl group can be correlated with the degree of stabilization of the phenoxyl radical. Stabilization depends on two factors: (i) the extent of orbital overlap between the 2p type lone pair on the para oxygen atom and the aromatic π electron system and (ii) the electron-donating or withdrawing character of the group bonded to the para oxygen atom. Orbital overlap depends on the dihedral angle, θ, between the direction of the 2p orbital on the para oxygen and a line perpendicular to the aromatic plane. It can be estimated from the X-ray structures. Along the series 4-methoxytetramethylphenol (VIc), 6-hydroxy-2,2,5,7,8-pentamethylchromene, 6-hydroxy-2,2,5,7,8-pentamethylchroman, and 2,3-dihydro-5-hydroxy-2,2,4,6,7-pentamethylbenzofuran (IIIb), k1 increases from 3.9 × 105, 2.5 × 106, 3.8 × 106, to 5.7 × 106 M-1 s-1, as θ decreases from 89, 38, 17, to 6°. Compound IIIb is the most active antioxidant being 1.8 times more active than α-tocopherol. For 2-substituted 6-hydroxy-2,5,7,8-tetramethylchromans log (k1/M-1 s-1) can be correlated with the σI constant of the 2-substituent, ρI = -1.25. For these compounds and for some 2,6-dimethylphenols log (k1/M-1 s-1) can also be correlated with the extent of stabilization of the corresponding phenoxyl radicals as measured by the unpaired spin density at the two ortho methyl groups. Some additional kinetic and spectroscopic data are presented. It is also shown that the perpendicular methoxy group in VIc is not deactivating relative to a hydrogen atom but is, instead, about as activating as a methyl group.
Rate constants have been measured at 25 degrees C in 13 solvents (S) for abstraction of the phenolic hydrogen atom from alpha-tocopherol (TOH) by tert-butoxyl (BO.), k(TOH/BO)(S), and by 2,2-diphenyl-1-picrylhydrazyl (DPPH.), k(TOH/DO)(S), and in eight solvents for abstraction of the phenolic hydrogen atom from phenol by cumyloxyl, k(PhOH/CumO)(S), and DPPH., k(PhOH/DPPH)(S). Over the range of solvents examined k(TOH/BO)(S) and k(TOH/DPPH)(S) vary by a factor of Ca. 65, and k(PhOH/CumO)(S) and k(PhOH/DPPH)(S) vary by a factor of ca. 120. in accordance with a prediction(5) the kinetic solvent effect is essentially identical for the same substrate and is independent of the attacking radical. That is, for almost any pair of solvents, A and B (k(TOH/BO)(A)/k(TOH/BO)(B))/(k(TOH/DPPH)(A)/k(TOH/DPPH)(B)) approximate to 1.0. The same applies with phenol as the substrate. Exceptions to this 1:1 relationship occur when one of the reactions becomes partly diffusion-controlled and in the solvent tert-butyl alcohol in which DPPH. shows a larger reactivity than would be expected. The absolute magnitudes of the alkoxyl and DPPH rate constants in the same solvent differ by a factor of over 1 000 000 (10(6)) for alpha-tocopherol and by 10 000 000 000 (10(10)) for phenol! We have therefore confirmed, under extreme conditions, a new, unifying principle for free radical chemistry in solution.
The synthesis of racemic all-trans-ζ1- (I) and -ϵ-tocopherol (II) is described. Comparison with the corresponding natural specimens proved the all-trans-configuration of the side chain of ζ1-and ϵ-tocopherol isolated from wheat bran.
Introduction
Kinetics and Mechanism
Efficiencies of Phenolic Antioxidants
Chemical Calculations on Phenols
Future Prospects for Antioxidants
This paper presents the synthesis and characterization by mass spectrometry and NMR spectroscopy of [2-13C]- and [3-13C]ubiquinone-0 and of [5-13C]- and [6-13C]ubiquinone-10. A scheme based on the synthetic approach to [5-13C]ubiquinone-10 has been worked out for the synthesis of ubiquinones 13C-labeled at any individual position and at every combination of positions in the quinone ring. The [5-13C]- and [6-13C]ubiquinone-10 isotopomers were incorporated into the QA-site of the photosynthetic reaction center of Rhodobacter sphaeroides R-26. Magic angle spinning NMR subsequently revealed an unperturbed 6-position, while the signal of the 5-position was absent. These results corroborate the recently reported detection of an asymmetric binding of QA with a dynamic perturbation involving the 4-carbonyl functionality.
The antiradical activities of various antioxidants were determined using the free radical, 2,2-Diphenyl-1-picrylhydrazyl (DPPH*). In its radical form. DPPH* has an absorption band at 515 nm which dissappears upon reduction by an antiradical compound. Twenty compounds were reacted with the DPPH* and shown to follow one of three possible reaction kinetic types. Ascorbic acid, isoascorbic acid and isoeugenol reacted quickly with the DPPH* reaching a steady state immediately. Rosmarinic acid and δ-tocopherol reacted a little slower and reached a steady state within 30 min. The remaining compounds reacted more progressively with the DPPH* reaching a steady state from 1 to 6 h. Caffeic acid, gentisic acid and gallic acid showed the highest antiradical activities with a stoichiometry of 4 to 6 reduced DPPH* molecules per molecule of antioxidant. Vanillin, phenol, γ-resorcylic acid and vanillic acid were found to be poor antiradical compounds. The stoichiometry for the other 13 phenolic compounds varied from one to three reduced DPPH* molecules per molecule of antioxidant. Possible mechanisms are proposed to explain the experimental results.
The oxidative modification of low density lipoprotein (LDL) is thought to be an important factor in the initiation and development of atherosclerosis. Antioxidants have been shown to protect LDL from oxidation and to inhibit atherosclerosis development in animals. Potent synthetic antioxidants are currently being tested, but they are not necessarily safe for human use. We here characterize the antioxidant activity of IRFI005, the active metabolite of Raxofelast (IRFI0016) that is a novel synthetic analog of vitamin E under clinical development, and demonstrate that it prevents oxidative modification of LDL. IFI005 inhibited the oxidative modification of LDL, measured through the generation of MDA, electrophoretic mobility and apo B100 fluorescence. During the oxidation process IRFI005 was consumed with the formation of the benzoquinone oxidation product. The powerful antioxidant activity of IRFI005 is at least in part mediated by a chain breaking mechanism as it is an efficient peroxyl radical scavenger with a rate constant k(IRFI005 + LOO°) of 1.8 × 106 M−1s−1. 4. IRFI005 substantially preserved LDL-associated antioxidants, α-tocopherol and carotenoids, and when co-incubated with physiologic levels of ascorbate provoked a synergistic inhibition of LDL oxidation. Also the co-incubation of IRFI005 with Trolox caused a synergistic effect, and a lag phase in the formation of the trolox-benzoquinone oxidation product. A synergistic inhibition of lipid peroxidation was also demonstrated by co-incubating IRFI005 and α-tocopherol incorporated in linoleic acid micelles. These data strongly suggest that IRFI005 can operate by a recycling mechanism similar to the vitamin E/ascorbate system.
Intermediate free radicals formed in the first oxidation step of tocopherols (vitamin E) are detectable at ambient temperature by electron spin resonance (ESR), even in commercial samples without previous treatment. Oxidation with diphenylpicrylhydrazyl or photolysis (400 nm) of pure or dissolved tocopherols yield high resolution ESR spectra showing 7 (α- and ζ2-tocopherol), 5 (β- and γ-tocopherol), or 3 (δ-tocopherol and tocol) main lines and further hyperfine structure. The g-factor, g = 2.0046 ± 0.0002, is almost independent of temperature, solvent, and methyl substitution. The radicals are chromanoxyls generated by abstraction of hydrogen from the 6-hydroxyl group. They differ from known phenoxyls by nonequivalent protons at C-5 and C-7; spin density is about 20% higher at C-5. Coupling constants are (5-CH) = 6.0 Oe, (5-CCH3) = 5.8 Oe, (7-CH) = 5.o Oe, ah(7-CCH3) = 4.8 Oe. The length of the side chain only indirectly influences the ESR spectra via the state of aggregation of the tocopherols. The lifetime of α-tocopheroxyl radicals generated in the pure substance by ultraviolet irradiation at ambient temperature is about 10 min and decreases in the order α-, ζ2-, gg-, β-, δ-tocopherol and tocol.
The reactions of DPPH with Cl2, NO2 and F2 were studied. In the para-phenyl position substituted diphenylpicrylhydrazines were formed. Besides this, the reaction of halogens led to products which were nitro-substituted in the para-phenyl position. Thus, it was shown that the reactions of halogens and halogen radicals with DPPH include a substitution at the picryl group of DPPH and its derivatives under liberation of NO2.By ESR in situ spectroscopy and computational analysis of spectra, nitro-, dinitro-, fluoro- and difluoro-diphenylpicrylhydrazyls were identified as transient intermediates. In the formation of these species nitrogen dioxide and fluorine act as oxidants for the corresponding substituted hydrazines.
We have shown previously that atomic values for physicochemical properties are an important guide for correlating the observed biological activity of the ligands to their chemical structure (Ghose, A. K.; Pritchett, A.; Crippen, G. M. J. Comput. Chem. 1988, 9, 80-90, and references cited therein). The objective of the present work is to (i) report the hydrophobicity and the molar refractivity for phosphorus and selenium atoms at different structural environments that are ubiquitous in biologically active systems, (ii) refine the atomic values of the various elements reported earlier to satisfy the largely extended data set, and (iii) suggest a method for selecting the best superposition of different molecules on a reference structure using these atomic physicochemical properties. The octanol-water partition coefficient was used to scale the atomic hydrophobicity. The hydrophobicity values of 120 atom types were evaluated from 893 compounds. The observed and calculated octanol-water partition coefficient showed a correlation coefficient of 0.926 and a standard deviation of 0.496. The atomic refractivity values were evaluated from the molar refractivities of 538 compounds; the corresponding correlation coefficient and standard deviation were 0.999 and 0.774, respectively. The atomic values were tested by predicting the respective properties for a large number of compounds. The superposition method has been applied to certain naturally occurring nucleoside antibiotics. The algorithm presented here shows various important superpositions of two or more molecules with minimum physical assistance to avoid any personal bias.
In an earlier article 8 the need was demonstrated for atomic physicochemical properties for three dimensional structure directed quantitative structure-activity relationships, and it was shown how atomic parameters can be developed for successfully evaluating the molecular octanol-water partition coefficient, which is a measure of hydrophobicity. In this work we report more refined atomic values of octanol-water partition coefficients derived from nearly twice the number of compounds. Carbon, hydrogen, oxygen, nitrogen, sulfur and halogens are divided into 110 atom types of which 94 atomic values are evaluated from 830 molecules by least squares. These values gave a standard deviation of 0.470 and a correlation coefficient of 0.931. These parameters predicted the octanol-water partition coefficient of 125 compounds with a standard deviation of 0.520 and a correlation coefficient of 0.870. There is only a correlation coefficient of 0.432 between the atomic octanol-water partition coefficients and the atomic contributions to molar refractivity over the 93 atom types used for both the properties. This suggests that both parameters can be used simultaneously to model intermolecular interactions. We evaluated the CNDO/2 gross atomic charge distribution over several molecules to check the validity of our classification. We found that the charge density on the heteroatoms in conjugated systems is strongly affected by the presence of similar atoms in the conjugation which suggests it should be incorporated as a separate parameter in evaluating the partition coefficient. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/38278/1/540090111_ftp.pdf
VITAMIN E (α-tocopherol) and vitamin C (ascorbic acid) react
rapidly with organic free radicals, and it is widely accepted that the
antioxidant properties of these compounds are responsible in part for
their biological activity1-5. Tissue vitamin C levels are
often considerably greater than those of vitamin E, for example in liver
the values are approximately 2 mM and 0.02 mM, respectively.
Nevertheless, vitamin E is considerably more lipophilic than vitamin C,
and in biomembranes has been found to be the more potent antioxidant,
particularly with respect to lipid peroxidation; penetration to a
precise site in the membrane may be an important feature of the
protection against highly reactive radicals6. Tappel has
suggested that the two vitamins act synergistically, vitamin E acting as
the primary antioxidant and the resulting vitamin E radical then
reacting with vitamin C to regenerate vitamin E7. We now
report direct observation of this interaction, which we feel may be an
important feature in the maintenance of vitamin E levels in tissues.
Incubation of phosphatidylcholine liposomes containing the biological antioxidant alpha-tocopherol (alpha-TH) with xanthine, xanthine oxidase, and FeCl2 caused alpha-TH oxidation to alpha-tocopherol quinone (alpha-TQ) and 8a-hydroperoxytocopherone (2). In addition, 4a,5-epoxy-8a-hydroperoxytocopherone (3), 7,8-epoxy-8a-hydroperoxytocopherone (4), and their respective hydrolysis products 2,3-epoxy-alpha-tocopherol quinone (6) and 5,6-epoxy-alpha-tocopherol quinone (7) also were formed. alpha-TQ was the major product at less than 20% alpha-TH oxidation, whereas epoxides were the predominant products when alpha-TH was more extensively oxidized. 8a-(Alkyldioxy)tocopherones 1, which are formed when peroxyl radicals oxidize alpha-TH in other systems and which are precursors to alpha-TQ, were not found. 8a-Hydroxytocopherone (5), rather than 8a-(alkyldioxy)tocopherones 1, appeared to be the precursor to alpha-TQ. Approximately 30% of the alpha-TH consumed was regenerated by treatment of samples with ascorbic acid or nordehydroguaiaretic acid (NDGA) at pH 3, but not at pH 7. The stability of the ascorbic acid- and NDGA-reducible species and pH dependence for regeneration matched those of 8a-hydroxytocopherone (5) and contrasted with the properties of the tocopheroxyl radical (alpha-T.). Incubation of liposomes containing alpha-TH with the diphenylpicrylhydrazyl (DPPH) radical, which oxidizes alpha-TH to alpha-T. in high yield, formed an ascorbic acid-reducible species with properties identical to those of compound 5. The results indicate that phospholipid peroxyl radicals oxidize alpha-T. to epoxides, 8a-hydroperoxytocopherone (2), and the tocopherone cation (alpha-T+), which hydrolyzes to 5, the immediate precursor to alpha-TQ.(ABSTRACT TRUNCATED AT 250 WORDS)
The oxidation of the heme iron of metmyoglobin by H2O2 yields an oxo ferryl complex (FeIV = O), similar to Compound II of peroxidases, as well as a protein radical; this high oxidation state of myoglobin is known as ferrylmyoglobin. The interaction of Trolox, a water-soluble vitamin E analog, with ferrylmyoglobin entailed two sequential one-electron oxidations of the phenolic antioxidant with intermediate formation of a phenoxyl radical and accumulation of a quinone end product. These oxidation reactions were linked to individual reductions of ferrylmyoglobin to metmyoglobin, as indicated by the value of the relationship [metmyoglobin]formed/[Trolox]consumed: 1.92 +/- 0.28. The Trolox-mediated reduction of ferrylmyoglobin to metmyoglobin could proceed directly, i.e., electron transfer from the phenolic-OH group in Trolox to the oxoferryl moiety, or indirectly, i.e., sequential electron transfer from Trolox to a protein radical to the oxoferryl moiety. The former mechanism is supported by the finding that the high oxidation heme iron is reduced under conditions where the tyrosyl residues are blocked by o-acetylation and when hemin is substituted for myoglobin. The latter mechanism is consistent with the following observations: (a) the EPR signal ascribed to the protein radical is suppressed by Trolox, with the concomitant appearance of the EPR spectrum of the Trolox phenoxyl radical and (b) the rate of ferrylmyoglobin reduction by Trolox is decreased with increasing number of tyrosyl residues in the proteins of horse myoglobin (titrated by o-acetylation) and sperm whale myoglobin. The apparent discrepancy between these observations can be reconciled by considering that both electrophilic centers in ferrylmyoglobin--the oxoferryl heme moiety and the protein radical--function independently of each other and that recovery of ferrylmyoglobin by Trolox could be effected through the tyrosyl residues, albeit at slower rates. The mechanistic aspects of these results are discussed in terms of the two main redox transitions in the myoglobin molecule encompassing valence changes of the heme iron and electron transfer of the tyrosyl residue in the protein and linked to the two sequential one-electron oxidations of Trolox.
Laser flash photolysis of alpha-tocopherol in methanol and in aqueous micellar solutions has been shown to produce the alpha-tocopheroxyl radical. The reaction between the alpha-tocopheroxyl radical and ascorbate in positively charged hexadecyltrimethylammonium chloride (HTAC) micelles occurred with a second order rate constant of 7.2 x 10(7) M-1.s-1, whereas in negatively charged sodium dodecyl sulphate (SDS) micelles the rats constant was only 3.8 x 10(4) M-1.s-1. The alpha-tocopheroxyl radical was found to be relatively long-lived in HTAC micelles (t1/2 greater than or equal to 5 min), allowing the slow disappearance of the alpha-tocopheroxyl radical by reaction with glutathione to be observed.
The occurrence of reactive oxygen species, known as pro-oxidants, is an attribute of normal aerobic life. The steady-state formation of pro-oxidants is balanced by a similar rate of their consumption by antioxidants that are enzymatic and/or nonenzymatic. "Oxidative stress" results from imbalance in this pro-oxidant-antioxidant equilibrium in favor of the pro-oxidants. A number of diseases are associated with oxidative stress, being the basis of antioxidant therapy. Current evidence in clinical research does not show unequivocal distinction between causal or associative relationships of pro-oxidants to the disease process.
Ubiquinones and tocopherols (vitamin E) are intrinsic lipid components which have a stabilizing function in many membranes attributed to their antioxidant activity. The antioxidant effects of tocopherols are due to direct radical scavenging. Although ubiquinones also exert antioxidant properties the specific molecular mechanisms of their antioxidant activity may be due to: (i) direct reaction with lipid radicals or (ii) interaction with chromanoxyl radicals resulting in regeneration of vitamin E. Lipid peroxidation results have now shown that tocopherols are much stronger membrane antioxidants than naturally occurring ubiquinols (ubiquinones). Thus direct radical scavenging effects of ubiquinols (ubiquinones) might be negligible in the presence of comparable or higher concentrations of tocopherols. In support of this our ESR findings show that ubiquinones synergistically enhance enzymic NADH- and NADPH-dependent recycling of tocopherols by electron transport in mitochondria and microsomes. If ubiquinols were direct radical scavengers their consumption would be expected. Further proving our conclusion HPLC measurements demonstrated that ubiquinone-dependent sparing of tocopherols was not accompanied by ubiquinone consumption.
An antioxidant is a substance that, when present at low concentrations compared to those of an oxidizable substrate, significantly delays or prevents oxidation of that substrate. Many substances have been suggested to act as antioxidants in vivo, but few have been proved to do so. The present review addresses the criteria necessary to evaluate a proposed antioxidant activity. Simple methods for assessing the possibility of physiologically-feasible scavenging of important biological oxidants (superoxide, hydrogen peroxide, hydroxyl radical, hypochlorous acid, haem-associated ferryl species, radicals derived from activated phagocytes, and peroxyl radicals, both lipid-soluble and water-soluble) are presented, and the appropriate control experiments are described. Methods that may be used to gain evidence that a compound actually does function as an antioxidant in vivo are discussed. A review of the pro-oxidant and anti-oxidant properties of ascorbic acid that have been reported in the literature leads to the conclusion that this compound acts as an antioxidant in vivo under most circumstances.
Plasma membranes were purified from flagella of porcine cauda epididymal sperm and proteolytic regulation of bicarbonate-sensitive adenylate cyclase was studied. It was found that the epididymal sperm plasma membrane contained a trypsin-like proteinase which inactivated adenylate cyclase. Bicarbonate activates adenylate cyclase as reported previously, but, at the same time, the anions enhance the inactivation of the enzyme by the membrane-bound trypsin-like proteinase. This phenomenon is not due to the direct activation of the proteinase, but closely related to the activation of adenylate cyclase by bicarbonate. It was also found that seminal proteinase inhibitors blocked the inactivation of adenylate cyclase and maintained the bicarbonate activation of the enzyme at high level. Actually, bicarbonate keeps adenylate cyclase fully active in ejaculated sperm, because membrane-bound proteinase is completely inhibited by the seminal proteinase inhibitors. These results suggest that the interactions between membrane-bound proteinase and seminal proteinase inhibitor are involved in the regulation of the bicarbonate-sensitive adenylate cyclase system.
The effect of mixtures of phospholipids (PL) and natural antioxidants (AO)--tocopherol (TP), ubiquinone, ubichromenol, vitamin K, on the value of induction periods and on the rate of initiated oxidation of model substrates (++methyl oleate, mixtures of fatty acid methyl ethers, ethylbenzene) was studied at 60 degrees C. The possibility of synergism of different AO in the presence of PL has been established. It has been shown that the action of bioantioxidants in lipids may be increased 2.5-3.5 times. The dependences of TP and PL synergistic effect values on the concentration of the mixture components were studied. It has been shown that the synergistic++ effect grows proportionally to the amount of TP (in the interval studied up to 5 X 10(-3)M). At a constant concentration of TP the dependence of the value of induction periods increases linearly with the growth of PL concentration at the interval of 0.0-0.2%, and further it does not depend on the amount of PL. It has been shown that the synergism value does not depend on oxidation conditions and the nature of the oxidized substrate.
Kinetic study of the reaction between tocopheroxyl (vitamin E radical) and ubiquinol-10 (reduced ubiquinone, n = 10) has been performed. The rates of reaction of ubiquinol with alpha-tocopheroxyl 1 and seven kinds of alkyl substituted tocopheroxyl radicals 2-8 in solution have been determined spectrophotometrically, using a stopped-flow technique. The result shows that the rate constants decrease as the total electron-donating capacity of the alkyl substituents on the aromatic ring of tocopheroxyls increases. For the tocopheroxyls with two alkyl substituents at ortho positions (C-5 and C-7), the second-order rate constants, k1, obtained vary in the order of 10(2), and decrease predominantly, as the size of two ortho-alkyl groups (methyl, ethyl, isopropyl and tert-butyl) in tocopheroxyl increases. On the other hand, the reaction between tocopheroxyl and ubiquinone-10 (oxidized ubiquinone) has not been observed. The result indicates that ubiquinol-10 regenerates tocopherol by donating a hydrogen atom of the 1-OH and/or 4-OH group to the tocopheroxyl radical. For instance, the k1 values obtained for alpha-tocopheroxyl are 3.74 x 10(5) M-1.s-1 and 2.15 x 10(5) M-1.s-1 in benzene and ethanol solution at 25 degrees C, respectively. The above reaction rates, k1, obtained were compared with those of vitamin C with alpha-tocopheroxyl reported by Packer et al. (k2 = 1.55 x 10(6) M-1.s-1) and Scarpa et al. (k2 = 2 x 10(5) M-1.s-1), which is well known as a usual regeneration reaction of tocopheroxyl in biomembrane systems. The result suggests that ubiquinol-10 also regenerates the tocopheroxyl to tocopherol and prevents lipid peroxidation in various tissues and mitochondria.
The events accompanying the inhibitory effect of alpha-tocopherol and/or ascorbate on the peroxidation of soybean L-alpha-phosphatidylcholine liposomes, which are an accepted model of biological membranes, were investigated by electron paramagnetic resonance, optical and polarographic methods. The presence of alpha-tocopherol radical in the concentration range 10(-8)-10(-7) M was detected from its EPR spectrum during the peroxidation of liposomes, catalysed by the Fe3+-triethylenetatramine complex. The alpha-tocopherol radical, generated in the phosphatidylcholine bilayer, is accessible to ascorbic acid, present in the aqueous phase at physiological concentrations. Ascorbic acid regenerates from it the alpha-tocopherol itself. A kinetic rate constant of about 2 X 10(5) M-1 X s-1 was estimated from the reaction as it occurs under the adopted experimental conditions. The scavenging effect of alpha-tocopherol on lipid peroxidation is maintained as long a ascorbic acid is present.
We found previously that [d]-alpha-tocopherol (alpha-T) and [d]-gamma-tocopherol (gamma-T) are lipid antioxidants (thiobarbituric acid test) in model systems containing arachidonic acid (AA), cumene hydroperoxide, and Fe3+ and in smooth muscle cell (SMC) cultures challenged with AA. We now show that [d]-alpha-tocopherylquinone (alpha-TQ), [d]-delta-tocopherylquinone (delta-TQ), and [d]-gamma-tocopherylquinone (gamma-TQ) are antioxidants at low concentrations and prooxidants at high concentrations in the model system. Prooxidant activity is greater with gamma-TQ than either alpha-TQ or delta-TQ. Low concentrations of alpha-TQ, delta-TQ, and gamma-TQ are also antioxidants in SMC cultures challenged with AA. Unlike alpha-TQ, partially substituted gamma-TQ and glutathione (GSH) form a Michael adduct which has been purified and characterized. We found previously that alpha-T, gamma-T, and alpha-TQ are mitogenic in SMC. We now report that both delta-TQ and gamma-TQ but not alpha-TQ show concentration-dependent cytotoxicity (changes in morphology, propidium iodide stain) in SMC cultures. Cytotoxicity is greater with gamma-TQ than delta-TQ. An acute lymphoblastic leukemia (ALL) cell line shows greater chemosensitivity (MTT and Neutral Red assays) to gamma-TQ than to either doxorubicin (DOX) or vinblastine (VLB). An ALL cell line resistant to both DOX and VLB retains the same chemosensitivity to gamma-TQ as the drug-sensitive ALL cell line. ALL cell lines are unaffected by either alpha-TQ or the GSH Michael adduct of gamma-TQ. These data show that partially substituted tocopheryl quinones capable of forming Michael adducts are potential chemotherapeutic agents for multidrug-resistant cancer cells.
The etiology of neurodegenerative diseases remains enigmatic; however, evidence for defects in energy metabolism, excitotoxicity, and for oxidative damage is increasingly compelling. It is likely that there is a complex interplay between these mechanisms. A defect in energy metabolism may lead to neuronal depolarization, activation of N-methyl-D-aspartate excitatory amino acid receptors, and increases in intracellular calcium, which are buffered by mitochondria. Mitochondria are the major intracellular source of free radicals, and increased mitochondrial calcium concentrations enhance free radical generation. Mitochondrial DNA is particularly susceptible to oxidative stress, and there is evidence of age-dependent damage and deterioration of respiratory enzyme activities with normal aging. This may contribute to the delayed onset and age dependence of neurodegenerative diseases. There is evidence for increased oxidative damage to macromolecules in amyotrophic lateral sclerosis, Huntington's disease, Parkinson's disease, and Alzheimer's disease. Potential therapeutic approaches include glutamate release inhibitors, excitatory amino acid antagonists, strategies to improve mitochondrial function, free radical scavengers, and trophic factors. All of these approaches appear promising in experimental studies and are now being applied to human studies.
The reaction by which the antioxidant capacity of alpha-tocopherol is sustained by recycling of the alpha-tocopheroxyl radical in membranes or lipoproteins by aqueous ascorbate has been studied by laser flash photolysis in model micellar and membrane systems. In bilayers of dimyristoylphosphatidylcholine at 35 degrees C the measured second-order rate constant was 3 x 10(5) M s-1, or about five times slower than previously reported in a solvent system. The rate of reaction was decreased on addition of negatively charged lipid (dipalmitoylphosphatidic acid) and increased by addition of positively charged lipid (didodecyldimethylammonium bromide). These effects of bilayer charge were suppressed by increasing the ionic strength of the aqueous medium. Micellar charge also had an effect on the pH dependence of the reaction rate. Arrhenius data showed that the enthalpy of activation was effectively zero for the reaction in solution between ascorbate and radicals of water-soluble tocopherol analogues, but was positive in membrane and micellar systems. In all cases the entropy of activation was strongly negative. The kinetic deuterium isotope ratio varied between 3 and 8. The data strongly support a concerted electron and proton transfer mechanism for the reaction between alpha-tocopheroxyl radical and ascorbate.
A computer program has been developed for fitting EPR data with multiple free radicals as formed in biochemical and chemical spin-trapping systems. Simulation of these spectra requires as many as 40 independent parameters, creating a chaotic analysis environment. Accurate simulation of these systems is essential for correct identification of the free radicals, which often show only slight differences in spin-Hamiltonian parameters. This method consists of rule-based perturbations with trial and error calculations and has proven successful in several applications. Details of the algorithm, example data, and a discussion of the difficulties of this analysis are presented in this report.
Free radicals vary widely in their thermodynamic properties, ranging from very oxidizing to very reducing. These thermodynamic properties can be used to predict a pecking order, or hierarchy, for free radical reactions. Using one-electron reduction potentials, the predicted pecking order is in agreement with experimentally observed free radical electron (hydrogen atom) transfer reactions. These potentials are also in agreement with experimental data that suggest that vitamin E, the primary lipid soluble small molecule antioxidant, and vitamin C, the terminal water soluble small molecule antioxidant, cooperate to protect lipids and lipid structures against peroxidation. Although vitamin E is located in membranes and vitamin C is located in aqueous phases, vitamin C is able to recycle vitamin E; i.e., vitamin C repairs the tocopheroxyl (chromanoxyl) radical of vitamin E, thereby permitting vitamin E to function again as a free radical chain-breaking antioxidant. This review discusses: (i) the thermodynamics of free radical reactions that are of interest to the health sciences; (ii) the fundamental thermodynamic and kinetic properties that are associated with chain-breaking antioxidants; (iii) the unique interfacial nature of the apparent reaction of the tocopherol free radical (vitamin E radical) and vitamin C; and (iv) presents a hierarchy, or pecking order, for free radical electron (hydrogen atom) transfer reactions.
The enzymatic features and molecular species of the inhibitory action of menadione on lipid peroxidation in rat liver microsomes were examined. In an ascorbate-supported system or a NADH-supported reconstituted system containing NADH-cytochrome b5 reductase and cytochrome b5, menadione was not an inhibitor of lipid peroxidation at pH 7.5, while some antioxidant ability was observed at lower pH ranges. Lipid peroxidation in the presence of menadione in the NADH-supported reconstituted system at pH 7.5 was markedly inhibited by adding lipoamide dehydrogenase. NAD(P)H-supported lipid peroxidation in microsomes with increased DT-diaphorase activity from 3-methylcholanthrene-treated rats was highly susceptible to menadione. These inhibitions were abolished by dicoumarol, an inhibitor of DT-diaphorase. Cumene hydroperoxide-dependent lipid peroxidation in microsomes, with desferal and NADP+ to prevent nonheme iron-dependent reactions and oxygen radical generation, was inhibited by menadione in the presence of NADPH, and the inhibition was also more effective in the microsomes with increased DT-diaphorase activity. Menadiol reacted with 1,1-diphenyl-2-picrylhydrazyl (DPPH) in ethanol at a molar ratio of DPPH/menadiol at 1.9. In an iron-supported reconstituted enzymatic or a nonenzymatic system at pH 7.5, menadiol showed an antioxidant effect at an early stage, followed by a prooxidant effect, which was prevented by SOD, probably by protecting menadiol autooxidation. These results show that menadione exerts an antioxidant effect through participation of microsomal DT-diaphorase by generating menadiol with a radical scavenging ability, while menadiol also has a prooxidant property.