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Condensed tannins: Co-occurrence of procyanidins, prodelphinidins and profisetinidins in the heartwood of Acacia baileyana
Abstract
The flavonoids and condensed tannins of the heartwood of Acacia baileyana var. purpurea are described. In conformity with other Acacia species, the hydroxylation pattern of the flavonoids is of the resorcinol type but, in sharp contrast, the tannins are heterogeneous consisting of a mixture of the resorcinol and phtoroglucinol series. Dimeric proanthocyanidins of the phloroglucinol type were absent and this exception to the general observation that they invariably co-occur with the polymers may be explained by the relative nucleophilicity of the aromatic A-rings.
... The 50% MeOH and 70% acetone eluates were polyphenol-rich fractions. 13 C-NMR analyses revealed that 50% MeOH and 70% acetone eluates mainly contained procyanidin-and prodelphinidin-type condensed tannins [29,30] (Figure 3). Yield and content are expressed as weight percentage based on ASE2 (/ASE2), nonvolatile compounds (/NVC) and each fraction (/Each Fr.). ...
... The 50% MeOH and 70% acetone eluates were polyphenol-rich fractions. 13 C-NMR analyses revealed that 50% MeOH and 70% acetone eluates mainly contained procyanidin-and prodelphinidin-type condensed tannins [29,30] (Figure 3). ...
Researching the beneficial health properties of wood byproducts can prevent wastage by turning them into valuable resources. In this study, the virucidal activity of two extracts from Abies sachalinensis byproducts, ASE1, and ASE2, against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was investigated. ASE1 is rich in monoterpenoid volatile compounds, whereas ASE2 contains nonvolatile polyphenols. SARS-CoV-2 solutions were mixed with ASE1 or ASE2, and viral titer reduction was evaluated. At their original acidic pH, ASE2 showed stronger virucidal activity than ASE1. The virucidal activity of ASE2 was also significantly enhanced when pH was increased to neutral or basic, which was not the case for ASE1. At a neutral pH, ASE2 induced statistically significant viral titer reduction in 1 min. HCl and NaOH solutions, which had a pH close to that of acidic and basic ASE2 test mixtures, respectively, exhibited no virucidal activity against SARS-CoV-2. Among the SARS-CoV-2 variants, Omicron showed the highest vulnerability to ASE2. Western blotting, RT-PCR, and electron microscopic analysis revealed that neutral ASE2 interacts with SARS-CoV-2 spike proteins and moderately disrupts the SARS-CoV-2 genome and viral envelope. These findings reveal the virucidal potential of ASE2.
... The NMR and optical data of 4 matched with those of (-)-butin. [4] Thus, the structure of 4 was assigned as shown. 3 (c 0.1, MeOH). ...
... Thus, the structure of 5 was assigned as (-)-fustin. [4] Compound 6 was isolated as yellow amorphous powder. Its molecular formula C15H10O5 was deduced based on the HRESIMS ion at m/z 271.0613 [M+H] + (calcd. ...
From the stem barks of Swintonia griffithii , six flavonoids: (–)‐naringenin ( 1 ), (–)‐eriodictyol ( 2 ), (+)‐taxifolin ( 3 ), (–)‐butin ( 4 ), (–)‐fustin ( 5 ), and 3′,4′,7‐trihydroxyflavone ( 6 ) were isolated. Their structures were determined based on the spectroscopic interpretation and compared with those of reported data. In the tyrosinase inhibitory activity test, (+)‐taxifolin ( 3 ) and 3′,4′,7‐trihydroxyflavone ( 6 ) exhibited potent effect with the IC 50 values of 20.9 and 56.7 μ M, respectively.
... mg/g DM) reported for five Acacia species (Rubanza et al., 2005), a dominant browse species in the semi-arid tropics. Flavonoids in Acacia species with uncommon characteristics of the resorcinol-type hydroxylation pattern in the A-ring constituted in profisetinidins and prorobinetinidins (Foo, 1984) were only detected in A. etbaica and S. singueana. The presence of PC and PD in PA-containing browse confirmed their wide distribution in plants (Foo, 1984). ...
... Flavonoids in Acacia species with uncommon characteristics of the resorcinol-type hydroxylation pattern in the A-ring constituted in profisetinidins and prorobinetinidins (Foo, 1984) were only detected in A. etbaica and S. singueana. The presence of PC and PD in PA-containing browse confirmed their wide distribution in plants (Foo, 1984). Mueller-Harvey et al. (1987) detected myricetin, quercetin and kaempferol in C. farinosa and R. natalensis. ...
... Meanwhile, the highest value of TVC was found in the inner heartwood part of clone 16 alone with 218,21 mg GAE/g ± 25,14 mg CE/g. The total phenolic content of A. auriculiformis has been reported to be five times higher than A. mangium and flavonoids and proanthocyanidins (condensed tannin) are found to be the most dominant phenolic compound founds in Acacia heartwood extractive (Foo 1984. The higher phenolic content of A. auriculiformis was suspected to be contributing to its better resistance against heart rot and termites ) mainly due to the monomeric flavonoids, specifically, 3,4',7,8-tetra-hydroxy flavanone and teracacidin, found in greater amount in A. auriculiformis (Drewes and Roux 1966, Pietarinen et al. 2004. ...
Breeding strategy of Acacia hybrid is being developed by Center for Forest Biotechnology and Tree Improvement Indonesia and has produced three superior clones in growth (Clone 16, 25, and 44). Understanding the extractives of the new clones might determine future development steps to improve its resistance to diseases especially heartrot. The objective of this study was to investigate the extractive content in three radial directions (SW = sapwood; OHW = outer heartwood; IHW = inner heartwood); total phenolic, flavonoid, flavanol contents (colorimetric assay); and antioxidant activity (1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging assay). Extractions were done with three different solvents in successive (n-hexane = H; methanol = M; hot water = W), yielded 0,69 % – 1,70 %; 1,51 % – 10,86 %; and 0,51 % – 1,16 % of extractive contents, respectively. The total phenolic content (TPC) from TPC-H, TPC-M, and TPC-W ranged between 3,68 mg of gallic acid equivalent (GAE)/g – 10,41 mg GAE/g; 76,83 mg GAE/g – 448,35 mg GAE/g; and 43,28
mg GAE/g – 198,92 mg GAE/g, respectively; the total flavonoid content (TFC) from TFC-H, TFC-M, and TFC-W between 4,23 mg of quercetin equivalent (QE)/g – 41,51 mg QE/g; 29,55 mg QE/g – 133,71 mg QE/g;
and 7,70 mg QE/g – 29,37 mg QE/g, respectively; total flavanol content (TVC) from TVC-H, TVC-M, and TVC-W ranged between 28,74 mg of catechin equivalent (CE)/g – 66,90 mg CE/g; 83,39 mg CE/g – 247,18
mg CE/g; and 7,08 mg CE/g – 29,21 mg CE/g, respectively. Furthermore, the antioxidant activity was found to be significantly affected by the radial factor with the strongest activity exhibited by inner heartwood extract with an IC50 value of 255,77 μg/ml (gallic acid IC50 showed a value of 39,00 μg/ml). Among clones, clone 16 was determined to have the highest extractive, total flavonoid as well as flavanol contents. Thus, clone 16 was hypothesized to be more resistance against heart rot disease.
... They contain a relatively high content of probinetinidin and profisetinidin-type condensed tannins. A study of condensed tannins of A. baileyana suggested that other prodelphinidin-and procyanidin polymers can be present even when the molliscacidin is the monomer present (Foo 1984). ...
Acacia sensu lato (Fabaceae: Mimosoideae) was recently retypified and divided into five genera worldwide: Acacia, Acaciella, Mariosousa, Senegalia and Vachellia. Acacia sensu stricto is now considered to be a large genus of predominantly Australian origin comprising seven sections: Acacia, Alatae, Botrycephalae, Juliflorae, Lycopodiifoliae, Plurinerves and Pulchellae. This review presents an overview of the current taxonomy of A. sensu stricto and the natural products isolated and identified from it. Further, the traditional uses of different species and known bioactivities of isolated natural products are summarised. The flavonoids and tannins are the best studied classes of natural products from Acacia with characteristic hydroxylation patterns of flavonoids isolated from the heartwood of species positioned in different sections of the genus. These compounds display a range of activities including antioxidant, enzyme inhibitory and antimicrobial effects. Peltogynoid compounds, differing from other flavonoids by the presence of a fourth ring, have been isolated from a small group of species, however, their biological activities remain to be defined. Only a limited number of terpenes and steroids have been identified, but complex triterpenoid saponins with various bioactivities are present across various sections. Despite their economic importance and the traditional use, only a limited number of species have been thoroughly studied for their chemical composition. Further investigation of the sections Alatae and Lycopodiifoliae would be of interest for bioactive compound research as these sections are largely unexplored.
... In previous studies, we have generated a range of transgenic plants that ectopically express genes encoding various transcription factors and biosynthetic enzymes involved in PA biosynthesis, and have reported that these plants produce PAs in their aerial organs [4,5]. However, these studies relied on histochemical staining for initial screening of tannin-containing tissues, use of the acid-butanol method for determining PA levels [6], and thin-layer chromatography for determination of oligomer size [7]. HPLC-MS can be used to detect and quantify small oligomers of PA, but they need to be relatively pure [8]. ...
Proanthocyanidins (PAs) are oligomeric plant natural products mostly derived from epicatechin and/or catechin monomers. In studies aimed at engineering PAs into plant tissues that do not naturally make these compounds, we have expressed PA biosynthetic and regulatory genes in tobacco, alfalfa (Medicago sativa) and the model legume Medicago truncatula. Because engineered tannins may be produced in small quantities and it is often necessary to screen many independent plant lines, we have developed an improved, highly sensitive method to quantify and determine the composition of oligomeric PAs in plant extracts. The method involves normal-phase HPLC separation of semi-purified PAs followed by post-column reaction with the PA-specific reagent DMACA (dimethylaminocinnamaldehyde). This procedure allows for accurate and sensitive quantification of individual oligomeric PAs and, unlike currently used methods, does not require exhaustive sample preparation and clean-up. Compositional data are shown for genetically engineered PAs in tobacco and alfalfa.
... The solvent system pair consists of t-butanol-acetic acid-water (3:1:1) for development in the first direction and 6- percent acetic acid for development in the second direction. 3 ,5,18,19,41,42 The relative separations of procyanidin oligomers by this technique is shown infigure 1 . A definite advantage of the cellulose plates is that they can be cut into small sizes (e.g., 7.6 or 10 sq. ...
Current trends in chromatographic isolation and analyses of proanthocyanidins are reviewed. Preparative isolations by low pressure column chromatography can be carried out using a variety of gel types. Often, repeated separations are required to obtain pure compounds, and it has been found advantageous to alternate each separation with a different gel type. Counter-current separation methods have seen limited application; however, with the development of new apparatus, the situation could change in the future. Paper and thin layer cellulose chromatography remain widely used for qualitative analyses of lower molecular weight oligomers. Quantitative analyses of oligomers can be carried out by high performance liquid chromatography with a variety of reversed-phase columns. Molecular weight profiles of either derivatized or underivatized proanthocyanidins can now be obtained by gel permeation chromatography.
Phenolic compounds are important constituents of red wine, contributing to its sensory properties and antioxidant activity. Owing to the diversity and structural complexity, study of these compounds was mainly limited, during the last three decades, on their low-molecular-mass compounds or simple phenolic compounds. Only in recent years, much attention has been paid to highly polymerized polyphenols in grape and red wines. The reason for this is largely due to the development of analytical techniques, especially those of HPLC-ESI-MS, permitting the structural characterization of highly polymerized polyphenols. Furthermore, the knowledge on the biological properties of polymeric polyphenols of red wine is very limited. Grape polyphenols mainly consist of proanthocyanidins (oligomers and polymers) and anthocyanins, and low amount of other phenolics. Red wine polyphenols include both grape polyphenols and new phenolic products formed from them during winemaking process. This leads to a great diversity of new polyphenols and makes wine polyphenol composition more complex. The present paper summarizes the advances in the research of polymeric polyphenols in grape and red wine and their important role in Enology. Scientific results indicate that polymeric polyphenols, as the major polyphenols in grape and red wine, play a major role in red wine sensory properties, color stability and antioxidant activities.
The effect of browse species tannins (using polyethylene glycol, PEG 6000) on in vitro gas production (GP), methane (CH4), ammonia (NH3), volatile fatty acids (VFA) and in vitro organic matter digestibility (IVOMD) were studied. Approximately 0.5 g of air-dried A. etbaica, C. farinosa, C. tomentosa, D. angustifolia, D. cinerea, E. racemosa, M. angolensis, M. senegalensis, R. natalensis and S. singueana leaves were used as substrates in an automated in vitro system. Proanthocyanidin (PA) contents were quantified using the modified HCl-butanol method and the PA composition analysed by ultra performance liquid chromatography using a diode array detector coupled with electrospray ionization mass spectrometry (UPLC-DAD-ESI-MS/MS). Substrates were inoculated for 72 h in buffered rumen fluid (2:1, v/v), pooled from three goats fed a grass silage and concentrate diet, on three separate occasions. Each substrate was incubated in triplicate with or without inclusion of PEG 6000 and GP measured. During incubation, head space gas samples were taken at 0, 3, 6, 9, 12, 24, 30, 48, 54, and 72 h and analysed for CH4. Volatile fatty acids, NH3 and IVOMD were determined after 72 h of incubation. Data from three runs were averaged for analysis. Addition of PEG increased (P < 0.0001) GP, CH4, NH3 and total VFA indicating that PA were mainly involved in reducing methanogenesis but also digestibility. Prodelphinidins were found to be the major PA affecting fermentation. Also the contribution of quercetin, myricetin and kaempferol derivatives in CH4 reduction were evident. Changes in the molar proportions of VFA with PEG addition indicated that PA affected fermentation pathways. The absence of PEG effect on IVOMD was due to artefacts from the tannin-PEG complexes interfering with the incubation residue measurement. Overall, the effect of tannin-containing browse on in vitro fermentation characteristics was mainly due to PA with the possible minor effects of other phenolic and non-phenolic compounds.
In Polhill-Raven (1981) wurden die Mimosoideen durch folgende Autoren bearbeitet:
Einleitung der Subfamilie, 143–152: T. S. Elias.
The chemical basis of wood durability, together with the nature, synthesis and localization of tannins in wood tissues are reviewed. Most durable woods, particularly those of angiosperms, are rich in tannins. The presence of tannins in durable woods may be explained partly by their toxicity to microorganisms resulting from some of their fundamental physico-chemical properties, but also by their high solubility in water which may be necessary for wood cells to accumulate such large amounts of low toxicity compounds.
Structural complexity in the condensed tannins (polymeric proanthocyanidins) is centered principally on variations in hydroxylation patterns of the flavan chain extender units, the stereochemistry at the three chiral centers of the heterocyclic ring, the location and type of interflavanoid bond, and the structure of the terminal unit. Superimposed on these basic structural features are derivatizations such as O-methylation, C- and O-glycosylation, and O-galloylation. Because of the strong nucleophilicity of the resorcinolic or phloroglucinolic A-rings, some unusual conjugates linked through the C-6 or C-8 positions have also been found. A further level of structural diversity results from facile rearrangements of these compounds. Although great progress has been made in elucidation of the structure of oligomeric proanthocyanidins, our knowledge of the structure of higher polymers rests primarily on interpretations of their 13C-NMR spectra.
The condensed tannins, together with hydrolyzable tannins (gallic acid metabolites, described in Sect. 7.2) constitute the vegetable tannins, which have the essential characteristic of binding proteins and, less familiarly, polysaccharides. It is this feature of their chemistry that has been of continuing fascination for scientists, and has provided much of the impetus for their study. Recent work has shown that a minor role in plants probably involves their broad-spectrum antibiotic properties (see Sect. 7.7.5) and this is also likely to involve their binding characteristics (see Sect. 7.7.2.3).
The aim of the work was to study the effect of tannin rich extract of phenolics from faba bean seed hulls on glucose and methionine absorption from the small intestine of rats. The extract obtained by extraction of faba bean seed hulls with 70% aqueous acetone contained, after lyophylization, 49.5% proanthocyanidins. The presence of proanthocyanidin oligomers was confirmed chromatographically. In biological experiments, the effect of the extract obtained and of chemically pure tannins on the absorption of glucose, methionine and water in the small intestine of rat was determined using gut perfusion and everted sacs method. Proanthocyanidins from the Nadwislanski faba bean seed hulls administered to the rat gut in the amount corresponding to the content of these compounds in daily diet with 20-40% faba beans content had no significant effect on glucose or methionine absorption but they increased water absorption. Significant lowering of glucose and methionine absorption took place when perfusion fluid was supplemented with analogical amount of chemically pure tannins.
The proanthocyanidins of Acaciella angustissima (Mill.) Britton & Rose foliage have antinutritional and antimicrobial effects as proanthocyanidin- containing extracts reduced intake and weight gain of weanling rats when added to conventional diets and caused changes in fecal bacterial diversity and metabolic activity. Purified fractions of A. angustissima were shown to be more inhibitory to rat fecal bacteria than Schinopsis spp. (quebracho) proanthocyanidin extracts. In this study, it was determined that A. angustissima proanthocyanidins consist largely of 5-deoxyflavan- 3-ols and proanthocyanidin dimers through hexamers, based on guibourtinidol, fisetinidol, and robinetinidol, with a predominance of fisetinidol units. These are accompanied by smaller amounts of higher oligomers (heptamers-decamers) and deoxyflavan-3-ols, dimers and trimers containing a p-hydroxybenzoate ester moiety.
The biflavonoids and proanthocyanidins constitute the two major classes of oligomeric flavonoids found in plants (126, 136). The biflavonoids are oxidative coupling products leading to biflavones, flavanone-flavones, and biflavanones. These compounds always carry carbonyl functions at the C-4 positions (126). In contrast, the proanthocyanidins are products of the reduction of flavanonols such as flavan-3,4-diols or oligomeric flavan-3-ols with an interflavanoid bond at C-4 being coupled to a terminating flavan-3-ol (136). Natural compounds that are crossed products between these two classes, such as a flavan-3-ol linked through C-4 to a flavanone or a flavanone oxidatively coupled to a flavan-3-ol, are extremely rare. The unusual biflavonoid larixinol, isolated from Larix gmelini, a condensation product of dihydrokaempferol and (−)-epiafzelechin, comes closest to a representative of the crossed flavanone-flavan-3-ol biflavanoids (336). It is likely, therefore, that this classification of oligomeric flavanoids into two categories will undoubtedly be used for some time to come.
The object of this study was to elucidate the relationship between the chemical structure of purified condensed tannin polymers from tree species and their radical scavenging characteristics. By means of (13)C-NMR spectrometry and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), four kinds of proanthocyanidins were identified: prorobinetinidins, profisetinidins, procyanidins, and prodelphinidins. The tannins were submitted to radical scavenging assays with DPPH and galvinoxyl radicals and from the time-course of the reactions was concluded: 1) Tannins with pyrogallol type B-ring scavenge radicals in the beginning faster than those with catechol type B-ring. 2) Tannins with catechol type Bring needs more time to scavenge the same amount of radicals as those with pyrogallol type B-ring. 3) The IC(50) values of tannins with catechol type B-ring decrease after longer reaction times with the galvinoxyl radical. 4) Radical scavenging with DPPH radical proceeds faster than that for the galvinoxyl radical.
A tannin–phenolic resin (40 wt% of tannin, characterized by 1H nuclear magnetic resonance (NMR) and 13C NMR, Fourier transform infrared, thermogravimetry, differential scanning calorimetry) was used to prepare composites reinforced with sisal fibers (30–70 wt%). Inverse gas chromatography results showed that the sisal fibers and the tannin–phenolic thermoset have close values of the dispersive component and also have predominance of acid sites (acid character) at the surface, confirming the favoring of interaction between the sisal fibers and the tannin–phenolic matrix at the interface. The Izod impact strength increased up to 50 wt% of sisal fibers. This composite also showed high storage modulus, and the lower loss modulus, confirming its good fiber/matrix interface, also observed by SEM images. A composite with good properties was prepared from high content of raw material obtained from renewable sources (40 wt% of tannin substituted the phenol in the preparation of the matrix and 50 wt% of matrix was replaced by sisal fibers).
Five flavan dimers which showed lipase-inhibiting effects were isolated from fruits of Cassia nomame (Leguminosae). Structures of two new compounds among them were determined to be (2S)-3′,4′,7-trihydroxyflavan-(4β → 8)-catechin and (2S)-3′,4′,7-trihydroxyflavan-(4α → 8)-catechin. Fouf flavan dimers structurally related to these two compounds were also synthesized for spectral comparison. Among 10 flavan dimers tested for lipase-inhibitory activity, (2S)-3′,4′,7-trihydroxyflavan-(4α → 8)-catechin showed the most potent inhibitory effect. A partially purified fraction composed of oligomeric flavans with Mn 1020 also showed a noticeable inhibitory effect.
A reversed-phase liquid chromatographic method was developed for the simultaneous quantification of 10 major flavonoids, namely butin, (3R)-4'-methoxy-2',3,7-trihydroxyisoflavanone, liquiritigenin, melanettin, violanone, vistitone, formononetin, dalbergin, sativanone and medicarpin in the heartwood of Dalbergia odorifera, an important traditional Chinese medicine. Samples were extracted with 60% methanol. The optimal conditions of separation and detection were achieved on an Agilent Zorbax SB-C18 column (250 mm x 4.6 mm, 5 microm) with a gradient of acetonitrile and 0.3% (v/v) aqueous acetic acid, at a flow rate of 0.8 ml/min, detected at 275 nm. The complete separation was obtained within 55 min for the 10 target compounds. All calibration curves showed good linearity (r2>0.999) within test ranges. The assay was reproducible with overall intra- and inter-day variation of less than 3%. The mean recovery of the method was 100+/-10%, with R.S.D. less than 5%. The current assay method was considered to be suitable for the quality control of D. odorifera samples and could be readily utilized for the determination of the active principles present in this medicinal herb.
In a continuation of investigations of proanthocyanidins of the roots of Rhodiola pamiroalaica, we have isolated proanthocyanidins RP-3 and RP-4. Their compositions, structures, and relative configurations have been investigated: RP-3 is 7-O-(6-O-galloyl-beta-D-Glcp)-3-O-galloyl-(-)-epigallocatechin-(4 beta-8)-[(-)epicatechin-(4 beta-8)-(3-O-galloyl-(-)-epigallocatechin)](2)-(4 beta-8)-[5-O-(beta-D-Glcp) (6) under right arrow O-beta-D-Glcp)-(+)-catechin], and RP-4 is 7-O-(6-O-galloyl-beta-D-Glcp-3-O-galloyl-(-)-epigallocatechin-(4 beta-8)-[3-O-galloyl-(-)-epicatechin]-(4 beta-8)-[3-O-galloyl-(-)-epigallocatechin]-(4 beta-8)-[3-O-galloyl-(-)-epicatechin]-(4 beta-8)-[3-O-galloyl-5-(beta-D-Glcp-(6) under right arrow O-beta-D-Glcp)-(-)-epigallocatechin.
This review discusses the possibilities of using carbon-13 nuclear magnetic resonance spectroscopy in the investigation of flavan-3-ols, proanthocyanidins, and their derivatives, and reports differences in the spectral behavior of monomers, oligomers and their derivatives and features of the spectra of high-molecular-mass proanthocyanidins.
The structures of two compounds previously isolated fromRhodiola semenovii, rhodokhinoside (I) and rhodikhim (II), have been established.
Condensed tannins have formaldehyde gas-scavenging ability. Tannins consisting of phloroglucinol-type A-rings, such as prodelphinidin and procyanidin, had higher formaldehyde-scavenging ability than those consisting of resorcinol-type A-rings, such as prorobietinidin and profisetinidin. This ability was markedly improved by ammonia treatment. The increase in formaldehyde-scavenging ability was especially notable in the case of condensed tannins with a high ratio of pyrogallol-type B-rings, such as prorobietinidin and prodelphinidin. To clarify the factors affecting improvement of the formaldehyde-scavenging ability by ammonia treatment, the reaction behavior of condensed tannins during ammonia treatment was studied. Analyses using 13C-NMR and on-line methylation pyrolysis/gas chromatography/mass spectrometry revealed that on treatment of condensed tannins with ammonia, amino-substitution at C-4′ of the pyrogallol-type B-ring occurred to form a 4′-amino-3′,5′-dihydroxybenzene-type B-ring. It can be assumed that the introduction of a 4′-amino-3′,5′- dihydroxybenzene-type B-ring into the tannin molecule results in improved formaldehyde-scavenging ability.
In addition to their nutritive value, foods provide health benefits or have a role in disease prevention since they contain a wide range of phytochemicals which represent functional or bioactive components. These bioactive molecules present in foods are based on a variety of chemical structures, from carotenoids, through sterols and fatty acids, to different types of polyphenols. In this review, the polyphenols which are common constituents of vascular plants are explored. They are also common constituents of fruits and vegetables, teas and cocoas. The extractable polyphenols, obtainable by solvent extraction of the forest biomass, are of special interest as they are readily available form different types of forest and wood transformation residues. Flavonoids, cinnamic acid derivatives and proanthocyanidins, which share a part of their biosynthetic pathway with lignins, and therefore are associated with "woody" character of the plants, are reviewed along with some non-flavonoids important as food constituents such as stilbenes and hydrolysable tannins. The foods rich in these polyphenols are reviewed along with the forest sources of the same classes of molecules. The emphasis is put on residues of wood transformation such as bark and knotwood as these materials represent particularly rich resources for bioactive polyphenol classes. One of the most notorious bioactive properties of polyphenols is their antioxidant activity. The most important results on antioxidant capacity of forest trees extracts are presented and compared to those obtained for the extracts from healthy foods rich in polyphenols. These results are discussed also in relation to total phenol content of the studied extracts. Finally, the results on the application of selected types of polyphenols or extracts from forest biomass in prevention and/or treatment of diseases which are related to oxidative stress, cardiovascular disease, Alzheimer and cancer, are presented. It is clear from all discussed results, that the forest biomass in general and the residues of wood transformation in particular, represent the important natural resources of bioactive polyphenols. These residues have a real potential to be used as raw materials for the development of food supplements and/or functional foods which can enhance the animal and human health by disease prevention. They are also applicable for cosmetics and pharmaceutical products development, but their application in disease prevention remains more straightforward.
The aim of the work was to study the binding, degradation and metabolism of dietary condensed tannins in the gastrointestinal tract of an omnivore. Young pods of carob ( Ceratonia siliqua L) were radiolabelled by in vivo feeding of ¹⁴ CO 2 , trans ‐[U‐ ¹⁴ C]cinnamate or L ‐[U‐ ¹⁴ C]phenylalanine. [ ¹⁴ C]Proanthocyanidins (condensed tannins) were extracted with acetone/water (3:1 v/v), isolated on Sephadex LH‐20 and fed to rats by gavage. After 4 and 18 h, 90–94% of the gavaged ¹⁴ C was in the gut contents and/or faeces. Much of the gavaged ¹⁴ C (57%), predominantly that originally in tannins of high degree of polymerisation (DP), became insolubilised, mainly in the form of protein–tannin complexes. Some of the [ ¹⁴ C]tannins that remained soluble decreased in DP, especially in the small intestine and caecum. A further fraction (12% of the ¹⁴ C gavaged) underwent chemical modifications in the gut to form soluble, non‐tannin compounds. Small proportions of the ¹⁴ C were found in the liver (1.0–1.5%), urine (1–2%) and ¹⁴ CO 2 (1–2%). We conclude that proanthocyanidins are not inert within the gut but undergo various modifications which may affect the nutrition of the animal.
© 2001 Society of Chemical Industry
In humans, steroid 5α-reductase is involved in the development of benign prostatic hyperplasia (BPH). We tested the steroid
5α-reductase inhibitory activity of the 70% acetone extract of woody plants. The tannin polymer prepared from the 70% acetone
extract showed the highest steroid 5α-reductase inhibitory activity. Furthermore, the steroid 5α-reductase inhibitory activity
of tannins was not affected by the addition of superoxide dismutase or catalase. It was concluded that the steroid 5α-reductase
inhibitory activity of condensed tannin was caused by binding to the steroid 5α-reductase, rather than from the peroxide/superoxide
produced by tannins. The tannins, prepared from tree barks, with potential for steroid 5α-reductase inhibitory activity might
be advantageous in therapy for steroid 5α-reductase diseases such as BPH or prostate cancer.
Two oligomeric proanthocyanidin glycosides have been isolated from the roots ofRhodiola pamiroalaica and their structures and relative configurations have been established:
7 - O - galloyl - b- DGlcp\xleftarrow6O - b- D - Glcp\xleftarrow6O - b- D - Glcp] - ( + ) - gallocatechin - (4a- 8) - ( - ) - epicatechin - (4b- 8) - ( + ) - catechin - (4a- 8) - 5 - O - [6 - O - galloyl - b- D*Glcp\xleftarrow6O - b- D - Glcp\xleftarrow6 O - b- D - Glcp] - ( + ) - catechin \begin{gathered}7 - O - galloyl - \beta- DGlcp\xleftarrow{6}O - \beta- D -\hfill \\Glcp\xleftarrow{6}O - \beta- D - Glcp] - ( + ) - gallocatechin - (4\alpha- 8) \hfill \\ - ( - ) - epicatechin - (4\beta- 8) - ( + ) - catechin -\hfill \\(4\alpha- 8) - 5 - O - [6 - O - galloyl - \beta- D*Glcp\xleftarrow{6}O - \beta- D - Glcp\xleftarrow{6} \hfill \\O - \beta- D - Glcp] - ( + ) - catechin \hfill \\ \end{gathered}
— RP-1 - and
7 - O - [O - D - Glcp\xleftarrow6O - b- D - Glcp - ] - ( - ) - epicatechin - (4b- 6) - 7 - O - b- D - Glcp - ( - ) - epicatechin - (4b- 6) - 3 - O - galloyl - ( - ) - epigallo - catechin - (4b- 6) - 3 - O - galloyl - ( - ) - epigallocatechin - (4b- 6) - 3 - O - galloyl - 5 - O - b- D - Glcp - (
The heartwood of Acacia mangium is vulnerable to heart rot and this is the first study to investigate the role of heartwood extractives in its susceptibility.
Acacia auriculiformis was compared with A. mangium because it is rarely associated with heart rot. The heartwood extracts of both species were dominated by three flavonoids
(2,3-trans-3,4′,7,8-tetrahydroxyflavanone, teracacidin, and 4′,7,8,-trihydroxyflavanone), which were purified and identified by nuclear
magnetic resonance spectroscopy. The latter compound has not been previously reported in A. mangium and evidence for melacacidin is also newly reported. The mass spectrometric (MS) behavior of these compounds is given, for
example teracacidin does not form molecular ions by either electrospray ionization or atmospheric-pressure chemical ionization.
The nature of Acacia tannins was compared to quebracho tannin (composed of profisetinidins) using oxidative cleavage to enable MS detection but
a negative reaction was obtained for both, which suggests the Acacia tannins may also be of the 5-deoxy proanthocyanidin type. The concentration of flavanones was less when A. mangium heartwood was decayed but the amount of proanthocyanidins was only slightly reduced and therefore these compounds may be
more resistant to degradation by heart rot fungi. We found that the total phenol content of A. auriculiformis was about fivefold that of A. mangium, and, while preliminary, this provides evidence for a role played by phenolic extractives in heart rot resistance of these
Acacia species.
The bark of the tree Burkea africana is used medicinally in large areas of sub-Saharan Africa. The constituents responsible for its putative activity are not well known. We have investigated the bark of B. africana for antioxidant and radical scavenging activity. A hydroethanol bark extract showed high activity, and most of this activity was located in semipolar fractions of the extract. From chromatographic purification and spectroscopical structure studies, we conclude that the active constituents are proanthocyanidins. Two major components appear to be fisetinidol-(4alpha- --> 8)-catechin 3-gallate and bis-fisetinidol-(4alpha- --> 6, 4alpha- --> 8)-catechin 3-gallate. The latter compound is a new natural product. Smaller amounts of monomeric flavan-3-ols (catechin, epicatechin and fisetinidol) were also found.
Condensed tannins of commercial importance are described. They are comprised of repeating flavan-3-ol units linked through 4,6 and terminal 4,8 bonds. The terminal unit invariably differs from the remainder in phenolic substitution. The tannins represent gradational mixtures falling mainly within the mass range 500 - 3000. Knowledge of the composition and physical properties of those natural extracts in which tannins occur, of the organized structure of tannins, of the differential reactivity of their nucleophilic centers, and of their phenolic substitution has assisted in extending the scope of their industrial application to include a range of phenolic wood adhesives, precipitants and depressants. Other tannin reactions of potential industrial interest are briefly described. The variety of successful applications developed hitherto underscores the versatility of condensed tannins as industrial raw material.
Examination of heartwoods from 14 species of Acacia collected from arid
zones of Australia gave flavonoids in which the main components showed phenolic
hydroxylation patterns typical of the subsections of the genus. In each case the
main flavonoids were accompanied by minor components possessing hydroxylation
patterns different from those of the main constituents. 3-Methoxyflavones were
widely distributed in the species examined, and 8-methoxflavan-3,4-diols were
detected in two species. Methylated flavonoids isolated include 7,8,4'-trihydroxy-3-
methoxyflavone, 7,8,3',4'-tetrahydroxy-3-methoxyilavone, 7,3',4'-trihydroxy-3,8-
dimethoxyflavone, and 7,3',4'-trihydroxy-8-methoxyflavonol. Attention is drawn
to the similar chromatographic and light-absorption properties of fisetin, 8-methoxy-
fisetin, and 7,8,4'-trihydroxyflavonol.
Examination by paper chromatography of the flavonoid content of the heartwoods and barks of sixty-one species of Acacia native to Australia, permits broad subdivision into four groups, depending on variations of the phenolic hydroxyl pattern (3′,4′,7-trihydroxy; 4′,7-dihydroxy; 3′,4′,7,8-tetrahydroxy or 4′,7,8-trihydroxy). Although these chemical subdivisions do not correspond with the broad morphological grouping of Australian Acacia into Phyllodineae and Bipinnatae, certain correlations are evident. All species of Botryocephaleae and Racemosae contain 3′,4′,7-trihydroxyflavonoids, associated in rare instances with 4′,7-dihydroxyflavonoids. Similarly most Plurinerves and Juliflorae contain 3′,4′,7,8-tetrahydroxyflavonoids, but with notable exceptions amongst certain of the Juliflorae which contain only 4′,7,8-trihydroxyflavonoids.
The relative contributions of nucleophilicity and steric hindrance in determining the course of the reaction during the formation of ‘angular’ trif
Comparisons of acid- and base-catalysed reactions of epicatechin-(4β)-phenyl sulphide and leucocyanidin show that condensations proceed more rapidly at alkaline than at acidic pH so the biosynthesis of condensed tannins may occur through a quinone methide rather than a carbocation intermediate.
The Australian acacias have been examined in considerable detail, via extensive morphological
and anatomical observation and numerical analyses involving 171 species. This work has provided
further evidence of the need -to divide Australian Acacia taxonomically into two main series,
associating the bipinnate-leaved Botryocephalae closely with the uninerved phyllodinous species and
separating them from the Pulchellae. It has also made available a large body of morphological and
anatomical data, suitable for generating special purpose keys and potentially useful for other
purposes.
IR studies of four proanthocyanidin dimers and all four 4-(2′,4′,6′-trihydroxyphenyl) derivatives of the flavan monomer units of proanthocyanidin
The four theoretically possible diastereoisomeric 4 → 8 linked procyanidin dimers with two 2,3-cis-flavanoid units, epicatechin-(4β→ 8)-epicatechin (6), epicatechin-(4β→ 8)-ent-epicatechin (8), ent-epicatechin-(4α→ 8)-epicatechin (7), and ent-epicatechin-(4α→ 8)-ent-epicatechin (2), have been synthesized together with the 2,3-trans diastereoisomers catechin-(4α→ 8)-catechin (14) and catechin-(4α→ 8)-ent-catechin (15). The preferred rotamer conformations of the deca-acetate derivatives of (6), (8), (14), and (15) in chloroform were deduced from their 13C n.m.r. and high-field 1H n.m.r. spectra. The 1H n.m.r. spectra of the preferred conformers of the pairs of acetate derivatives of (6) and (15), and (8) and (14), were qualitatively similar as the relative configuration about the interflavanoid bond of one pair has a meso-relationship to the other.
Homogeneous polymeric proanthocyanidins have been isolated from 22 plant sources and all are based on a C(4)–C(8)[or C(6)] linked polyflavan-3-ol structure. 13C N.m.r, spectroscopy in 2[H6]acetone–water is used to calculate the ratio of procyanidin to prodelphinidin monomer units, the average heterocyclic ring stereochemistry of the monomers, and the ratio of monomers to chain-terminating units. The majority of polymers isolated in this study possess monomers with predominantly a 2,3-cis stereochemistry [the same configuration as (–)-epicatechin]. The number-average molecular weight, calculated from monomer to terminal unit ratios, of the polymers is 1 500–5 000. The structure of the chain-terminating group is established by thiolysis degradation and g.l.c. analysis of the products.
Evidence based on the results of feeding experiments with labelled (3H,14C) cinnamic acids is presented to show that the various procyanidin dimers are biosynthesised from two metabolically distinct units. One is the flavan-3-ol [(+)-catechin (10) or (–)-epicatechin (9)] and the other is the C-4 carbocation (7) or (8). It is postulated that the carbocations are derived by protonation of the flav-3-en-3-ol (6) and are intermediates in the reduction to the flavan-3-ols (9) and (10). The relationship of procyanidin biosynthesis to anthocyanidin formation in certain plants is briefly discussed.
The u.v. spectra of 5-and 7-hydroxyflavan-4-ols in acid solution are interpreted in terms of the π-π* transition of quinone methide intermediates; the enhanced reactivity of 4-substituted 7-hydroxyflavans compared to 4-substituted 7-methoxyflavans supports this mechanism which may be operative in the biozynthesis of polyflavonoids (e.g. condensed tannins).
13C N.m.r. chemical shifts have been assigned to 40 natural and synthetic proanthocyanidins, related flavan-3-ols, and their peracetate derivatives. These data may be used to draw structural inferences from the related spectra of proanthocyanidin polymers.
Chemical and other data concerning the location and site of formation of heartwood extractives are discussed. The biological conditions in the transition zone adjacent to the heartwood boundary are briefly described and some properties of extractives are given. The classes of polyphenolic compounds found in the wood of Eucalyptus species are listed together with the details of ellagic acid derivatives which are the most common class in this genus.