About
312
Publications
22,969
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
4,464
Citations
Publications
Publications (312)
Introduction
The ¹³C-NMR data described for perezone (1), a 3-hydroxy p-quinone stated as the first natural product isolated as crystals in the New World, and rigidone (2), a 4-hydroxy o-quinone isolated from a coral species, are essentially the same. Some years ago, we described, using theoretical calculations, that a 4-hydroxy-1,2-quinone is more...
Diosgenin (1a) is used as a raw starting material for the synthesis of steroid hormones and contraceptives and is probably one of the most commercially important steroidal sapogenins. The literature on 1a is extensive, and topics range from its isolation from a variety of natural sources to its chemical modifications and therapeutic properties as a...
Evaluation of DFT calculated vibrational parameters for the IR and VCD spectra similarity of perezone (1) and dihydroperezone (2) was undertaken. Conformational sets were obtained using different search engines, and the parameters needed for spectra prediction were obtained using several combinations of commonly employed functionals and basis sets,...
Inverse epimers are uncommon in nature and a lack of study of their vibrational circular dichroism (VCD) behavior seems evident. This is relevant, among other facts, since in the case of epimers, VCD has been capable of determining the absolute configuration (AC) of 1 stereogenic center in a molecule having 10 stereogenic centers. The case of pipit...
Accurate chemical shift and coupling constant for 1- and 2-naphthyl derivatives were decipher by iterative full spin analysis. Each of the seven magnetically nonequivalent H2–H8 atoms in 1-naphthyl derivatives, or of the H1, H3–H8 atoms in 2-naphthyl derivatives were unambiguously identified by analyzing their intra- and inter-ring coupling constan...
Although tremetone [5-acetyl-2-(1-methylvinyl)-2,3-dihydrobenzofuran] has only one stereogenic center, the absolute configuration (AC) determination of its naturally occurring 11-acyloxy derivatives 1 and 2 by vibrational circular dichroism (VCD) turned out to be difficult. Similarity-based comparison of the experimental VCD spectrum of 11-coumaryl...
The occurrence of racemic and enantiomerically enriched (scalemic) mixtures of secondary metabolites in their natural sources is a rare phenomenon. The unprecedent case of enantiomeric variations from levorotatory to dextrorotatory, and back to levorotatory, passing through an almost racemic mixture, was recently documented for areolal, the major e...
The use of IR individual scaling factors (ISF) for the correction of DFT-calculated frequencies, and its effect on IR and VCD similarity functions, has been evaluated using (+)-(R)-3-methylcyclopentanone as a probe molecule. Contrary to using a single scaling factor to improve spectra matching, this approach sequentially searches for the optimal sc...
Diastereoisomeric stigmasterol oxiranes 4, 5, 8, and 9 are known phytosterol oxidation products (POPs) that have been evaluated for their cytotoxicity, although the results are of limited significance since, in most cases, they were evaluated as mixtures. Consequently, to establish biological activity hierarchy of these oxides, it is critical to ev...
Fusidic acid (1a) is a commercial antibiotic widely used in therapy for methicillin-resistant Staphylococcus aureus infections. Although the history of spectroscopic and conformational characteristics of 1a is long and old, the complete ¹H NMR parameters set assignment remains incomplete due to the large signal superposition in most conventionally...
A known kaurenoic acid (1), together with a new kaurane derivative named 3α-isobutyryloxykaurenoic acid (2), was isolated from the roots of Lasianthaea aurea, a plant endemic to Mexico. The compounds were characterized using their physical and spectroscopic data. In order to verify the structure and absolute configuration of 2, the derived methyl e...
The partial or total hydrolysis of (3R,4S,5S,6S,9R,10R,11R)-9,13-diangeloyloxylongipinan-1-one (1), isolated from the roots of Stevia viscida, gave alcohols 2 or 3, respectively, which were subjected to molecular rearrangements with boron trifluoride etherate. Compound 2 afforded (3R,4R,5R,6S,9R,10S,11S)-11,13-oxyneomorelian-1-one (10) and (4S,5R,6...
Since epoxythymols occur in Nature either as scalemic mixtures or as pure enantiomers, the knowledge of their chiral composition and of the absolute configuration (AC) of the dominant enantiomer turns out to be mandatory. This task has already been faced using 1,1-bis-2-naphthol (BINOL), as a chiral solvating agent in accurate 1H NMR quantification...
Although demonstrated in 1975, vibrational circular dichroism (VCD) finally started to popularize during this century as a reliable tool to determine the absolute configuration (AC) of organic molecules. This research field continues to be a very dynamic one, in particular for the study of natural products which are a unlimited source of chiral mol...
The four new briarane diterpenoids 2-butyryloxybriarane B-3 ( 2 ), 9-acetylbriarenolide S ( 3 ), briarenolide W ( 4 ), and 12-isobriarenolide P ( 5 ), along with briarane B-3 ( 1 ) and the five known diterpenes 6–10 were isolated from the gorgonian coral Briareum asbestinum collected from the Mexican Caribbean Sea . The structures were elucidated b...
The minimum chemical modification that can be incorporated into an organic molecule is the replacement of a hydrogen atom for a deuterium atom. This change is not altering the pharmacological properties of a molecule, although it provides the possibility of making specific spectroscopic evaluations. Thus, in the present study, we explore how a ster...
The medicinal aromatic plant Senecio filaginoides DC, which is very widespread in the Patagonia region, was harvested at the vegetative, flowering, and fructification stages. The materials were extracted by hydrodistillation, yielding in average 0.34% v/w of essential oils with a pleasant sweet and greenish scent. A total of 56 components were iden...
The aerial parts of Ageratina vernalis provided the new germacranolide 1,10-epoxydeltoidin A (3), together with the known pentacyclic triterpenoid hopane-6α,22-diol (1), and the also known germacranolides deltoidin A (2) and 15-hydroxydeltoidin A (4). In addition, pTsOH catalyzed cyclization of 2 afforded the new guaianolide 5. The absolute configu...
As it is difficult to study polyhydroxylated natural products by vibrational circular dichroism (VCD) due to their very limited solubility in infrared transparent solvents, 7-O-β-D-glucopyranosylchrysin (1), isolated from Mimosa rosei, was acetylated to provide 7-O-(2′',3′',4′',6′'-tetraacetyl-β-D-glucopyranosyl)-5-acetylchrysin (2). Density functi...
In search to find levels of density functional theory (DFT) for the accurate prediction of vibrational circular dichroism (VCD) spectra of cacalolides, we undertook the evaluation of isomeric quinols. To gain compounds that provide experimental VCD spectra for comparative purposes to the calculated spectra, we prepared the hexanes extracts of the r...
The genus Schizanthus (Solanaceae) comprises 12 accepted species primarily endemic to Chile. It is characterized by the presence of numerous tropane alkaloids found as ester derivatives of isomeric acids like angelic, senecioic, or tiglic, as well as mesaconic, itaconic, and citraconic acids, leading to numerous positional and configurational isome...
Five new and three known longipinane derivatives were obtained and their molecular interactions with α,β-tubulin were evaluated using in vitro and in silico assays. Alkaline hydrolysis of the natural longipinane diester 3, isolated in high yields from the roots of Stevia serrata, gave (3R,4S,5S,7S,8R,9S,10R,11R)-longipinan-7,8,9-triol-1-one (1). Co...
The tricyclic sesquiterpene (1R,3R,4S,5S,7S,8S,9S,10R,11R)-7,8-diangeloyloxylongipinan-1,9-diol, or rasteviol (7), underwent multiple Wagner-Meerwein molecular rearrangements and several hydride shifts when treated with Et2O-BF3 to generate the six new compounds (1R,3R,4S,5R,7S,8S,9S,10R,11S)-7,8-diangeloyloxy-1,9-epoxyjiquilpane (8), (1R,3R,4S,5R,...
The exceptional case of a natural compound that shows drastic absolute configuration variations within the same species was examined. Sequential samples of areolal (1) isolated from Piptothrix areolare showed dextrorotatory (ee 32%), almost racemic (ee 4%), levorotatory (ee 82%), and again dextrorotatory (ee 10%) values. Enantiomeric compositions o...
Both DNA barcoding and phylogenetic data of the studied botanical material suggested the existence a new population of Galphimia glauca. Their leaves afforded three new nor-3,4-seco-friedelanes named galphimines M-O, together with known galphimines D, E, G, and I. Galphimines M and N possess bicyclic orthoacetates which are the first examples of or...
The M06–2X, B3LYP, ωB97XD and B97D functionals with the 6–311++G(2d,2p) and DGDZVP basis sets were used to describe the stationary points of minimum energy of the potential energy surface of perezone. The inability of theoretical methods to predict a consistent conformational order, including the effects of zero point energy and dielectric constant...
The epimeric diterpenes (+)‐(1S,3E,7E,11S,12S)‐verticilla‐3,7‐dien‐12‐ol (1), isolated from Bursera suntui, and (+)‐(1S,3E,7E,11S,12R)‐verticilla‐3,7‐dien‐12‐ol (2), isolated from Bursera kerberi, gave the same Wagner‐Meerwein rearrangement product (−)‐(1E,4Z,8Z,11S,12R)‐phomacta‐1,(15)4,8‐triene (3). The Et2O:BF3‐induced transformations evidence t...
Although podocephalol (1) and its derived acetate 2 were found in Lasianthaea podocephala four decades ago, and 1 was later detected in the essential oils of several vegetal species, its absolute configuration (AC) and conformational preferences remained to be established. The structures of ar‐himachalene 1, now isolated from Lasianthaea aurea, and...
The known diterpenoids horminone (1) and taxoquinone (2) as a mixture, and pure 6,7-dehydroroyleanone (7) were isolated from the aerial parts of not yet studied Salvia concolor Lamb. Although 1 and 2 are known, the ¹ H Nuclear Magnetic Resonance (NMR) data of their acetyl derivatives 4 to 6 are only partially described. Moreover, the ¹³ C NMR data...
The bark of the roots of Piscidia carthagenensis afforded the known insecticides rotenone (1) and millettone (2), as well as the new rotenoid piscicartone (3). The structure of 3 followed from nuclear magnetic resonance studies, while its absolute configuration (AC) was determined by vibrational circular dichroism (VCD) measurements in comparison w...
The aerial parts of Salvia clinopodioides afforded abietanes 1a, 2a, and 3 (clinopodiolides A-C), two of which possess an unusual lactol moiety at C-19-C-20, together with an icetexane named clinopodiolide D (4a). Their structures were established by spectroscopic means, mainly 1H and 13C NMR, including 1D and 2D homo- and heteronuclear experiments...
β-Sitosteryl (S)-ibuprofenate (2), stigmasteryl (S)-ibuprofenate (3), ergosteryl (S)-ibuprofenate (4), and cholesteryl (S)-ibuprofenate (5) were prepared in 70-75% yields by Steglich esterification and were characterized by 1D and 2D NMR, as well as by MS. The new esters were evaluated in in vivo pain models of antinociception and anti-inflammation...
The roots of Stevia nepetifolia afforded the new longipinene derivative (4R,5S,7S,8S,9S,10R,11R,2 ' S,2 '' S)-(+)-7,8-di(alpha-methylbutyryloxy)-9-hydroxylongipin-2-en- 1-one (1), together with the known 7-angeloyloxy-8-(a-methylbutyryloxy)9-hydroxylongipin-2-en- 1-one (2), 7,8-diangeloyloxy-9-hydroxylongipin-2-en-1-one (3), valeranone, 2,3-epoxybi...
A series of functionalized sesquiterpenoids derived from benzocyclooctene, including natural parvifoline (1), isoparvifoline (3), epoxyparvifoline (5), epoxyisoparvifoline (7), 8,12-oxyparfivoline (9), 8,14-oxyparvifoline (11), and the respective benzoyl derivatives 2, 4, 6, 8, 10, and 12, were prepared and tested for their inhibitory effect on the...
A biomimetic transformation of p-menthene glucosides into aromatic monoterpenoids that alluded to mechanisms for essential oil metabolism, which lines up with the precepts of molecular economy, is described. Acid treatment of (-)-(3 S,4 S,6 R)-3,6-dihydroxy-1-menthene 3- O-β-d-glucopyranoside (1) and (-)-(3 S,4 R,5 R,6 S)-3,5,6-trihydroxy-1-menthen...
The 750 MHz 1H NMR spectrum of cholesteryl benzoate (1b) could be assigned completely, which means all chemical shifts and all coupling constants, including some long-range values, were established. This task was possible by extracting many approximate coupling constant values in the overlapped spectrum region from an HSQC experiment, and using the...
A methodology to determine the enantiomeric excess and the absolute configuration (AC) of natural epoxythymols was developed and tested using five constituents of Ageratina glabrata. The methodology is based on enantiomeric purity determination employing 1,1′-bi-2-naphthol (BINOL) as a chiral solvating agent combined with vibrational circular dichr...
Detailed literature inspections regarding the diterpenoids icetexone (1) and conacytone (3) reveal that the absolute configuration (AC) of these natural occurring compounds is not rigorously proven, despite they were originally isolated in 1976. This task is now completed by single-crystal X-ray diffraction Flack and Hooft parameters determination...
From the aerial parts of Salvia ballotiflora, eleven diterpenoids were isolated; among them, four icetexanes and one abietane (1–5) are reported for the first time. Their structures were established by spectroscopic means, mainly ¹H- and ¹³C-NMR, including 1D and 2D homo- and hetero-nuclear experiments. Most of the isolated diterpenoids were tested...
The synthesis of acetyldioxanes 4 and 9a starting from (-)-(1R)-myrtenal is described. The products were treated with a representative series of nucleophilic reagents (RMgX, RLi, NaBH4 and LiAlH4) to assess the effect of the substituent at C-3 on the stereochemical outcome. It was observed that the nucleophiles preferred the re-face of the CO group...
From the aerial parts of Salvia ballotiflora, eleven diterpenoids were isolated, among them, four icetexanes, and one abietane (1–5), which are first reported. Their structures were established by spectroscopic means, mainly 1H and 13C NMR, including 1D and 2D homo- and hetero-nuclear experiments. Most of the isolated diterpenoids were tested for t...
Two new dioxomorpholines, 1 and 2, three new derivatives, 3–5, and the known compound PF1233 B (6) were isolated from a marine-facultative Aspergillus sp. MEXU 27854. Their structures were established by 1D and 2D NMR and HRESIMS data analysis. The absolute configuration of 1 and 2 was elucidated by comparison of experimental and DFT-calculated vib...
The absolute configuration (AC) of the naturally occurring ocimenes (−)-(3S,5Z)-2,6-dimethyl-2,3-epoxyocta-5,7-diene (1) and (−)-(3S,5Z)-2,6-dimethylocta-5,7-dien-2,3-diol (2), isolated from the essential oils of domesticated specimens of Artemisia absinthium, followed by vibrational circular dichroism (VCD) studies of 1, as well as from the aceton...
A convenient approach for the absolute configuration assignment of secondary alcohols in the (8R,1′R,2′S,5′R)-15,25, (8S,1′R,2′S,5′R)-15,25, (8R,1′R)-21–24, and (8S,1′R)-21–24 ester series, and of primary amines in the (8R,1′R)-32–37 and (8S,1′R)-32–37 amide series, by means of ¹H NMR and VCD spectroscopy, using 2-cyano-2-indolylpropanoic acid as a...
Vibrational circular dichroism (VCD) emerged during the last decade as a reliable tool for the absolute configuration (AC) determination of organic compounds. The principles, instrumentation, and methodology applied prior to early 2013 were recently reviewed by us. Since VCD is a very dynamic field, the aim of this review is to update VCD advances...
The 1,3-dipolar cycloaddition of diazomethane to the sesquiterpene lactones, parthenin, coronopilin, and psilostachyin, gave their respective spiropyrazolines with complete chemoselectivity, while the diastereoselectivity in favour of the (11. S)-stereoisomer was 86-98%. Similarly, mexicanin I acetate, helenalin, and helenalin acetate provided the...
The structure of the dimeric eudesmanolide hydroxy-bis-dihydrofarinosin (1) from Encelia farinosa followed after contrasting their 1H and 13C NMR spectra with those of encelin (6), hydroxy-bis-dihydroencelin (3), and farinosin (4). Structure 1 was verified by single crystal X-ray diffraction analysis, which further provided the streochemistry of th...
The absolute configuration of jatropholone A 1 and B 2, including the possibility to observe the vibrational circular dichroism (VCD) capacity to differentiate between two epimeric compounds in the presence of an inherently dissymmetric chromophore, which normally dominates VCD and electronic circular dichroism (ECD) spectra, followed after compari...
The aerial parts of Ageratina glabrata afforded (−)-(3S,4R,5R,6S)-3,5,6-trihydroxy-1-menthene 3-O-β-d-glucopyranoside (1) and (−)-(3S,4S,6R)-3,6-dihydroxy-1-menthene 3-O-β-d-glucopyranoside (3). Acid hydrolysis of 1 yielded (+)-(1R,4S,5R,6R)-1,5,6-trihydroxy-2-menthene (5) and (+)-(1S,4S,5R,6R)-1,5,6-trihydroxy-2-menthene (6), while hydrolysis of 3...
A convenient and reliable approach for the absolute configuration assignment of oxindole derivatives 2a–m by vibrational circular dichroism (VCD) measurements and evaluation of the VCD bisignated couplet resulting from the interaction of the C2 and C9 carbonyl groups is presented. The absolute configuration assignments were further tested by 1H NMR...
The absolute configuration of the natural occurring isomers of 6β-benzoyloxy-3α-tropanol (1) has been established by the combined use of chiral high-performance liquid chromatography with electronic circular dichroism detection and optical rotation detection. For this purpose (±)-1, prepared in two steps from racemic 6-hydroxytropinone (4), was sub...
The naturally occurring eudesmanolide farinosin () is now fully characterized for the first time despite its original isolation almost half a century ago. The early assumed relative stereochemistry and absolute configuration were confirmed by vibrational circular dichroism together with evaluation of the Hooft X-ray parameters. The molecular confor...
Novel steganes (−)-(P,8R,8′R)-5′-desmethoxystegane 4, (−)-(P,7R,8R,8′R)-5′-desmethoxysteganol 5, (−)-(P,7R,8R,8′R)-5′-desmethoxysteganacin 6, and (−)-(P,8R,8′R)-5′-desmethoxysteganone 7 were synthesized from (+)-(M,8R,8′R)-5′-desmethoxyisostegane 2, which in turn was obtained from natural (−)-(8R,8′R)-5′-desmethoxyyatein 1 together with the novel (...
The aqueous extract of the leaves of Ageratina cylindrica afforded six new ent-kaurenoic acid glycosides together with the known diterpenoid paniculoside V, the flavonoid astragalin, chlorogenic acid, and l-chiro-inositol. The structures were elucidated mainly by NMR and MS methods, and the absolute configuration was established by vibrational circ...
Vibrational circular dichroism (VCD) emerged during the last decade as a reliable tool for the absolute configuration (AC) determination of organic compounds. The principles, instrumentation, and methodology applied prior to early 2013 were recently reviewed by us. Since VCD is a very dynamic field, the aim of this review is to update VCD advances...
The absolute configuration of the diterpenoid 9,12-cyclomulin-13-ol (1), a constituent of Azorella and Laretia species, has been established by vibrational circular dichroism spectroscopy in combination with density functional theory calculations. The obtained normal diterpene absolute configuration confirms that of azorellanol (2), which was deter...
A formal synthesis of the natural product (−)-flustramine B (3) is described, together with an easy and reliable approach for the absolute configuration assignment of a series of (3R,14S)- and (3S,14S)-oxindolylacetylphenyloxazolidinones 4, 6, 13a–c, and amides (+)- and (−)-14 by evaluation of the vibrational circular dichroism bisignated couplet r...
This work reports the antiproliferative activity of seco-oxacassanes 1–3, isolated from Acacia schaffneri, against human colon (HT-29), lung (A-549), and
melanoma (UACC-62) cancer cell lines, as well as against their non-malignant counterparts CCD-841 CoN, MRC-5, and VH-10, respectively, using the
sulforhodamine B test. While compounds 1 and 3 were...
The 3'R,4'R absolute configuration (AC) of the angular-type pyranocoumarins (-)-3',4'-di-O-acetylkhellactone (2), (-)-4'-O-acetyl-3'-O-angeloylkhellactone (3), (+)-3'-O-acetyl-4'-O-isobutyroylkhellactone (4), and (-)-3'-O-angeloyl-4'-O-senecioylkhellactone (5), isolated from the aerial parts of Prionosciadium thapsoides, was assigned by vibrational...
Thymol (2-isopropyl-5-methylphenol) is an aromatic molecule typically distributed in the genera Thymus and Origanum, which possesses both pharmacological and industrial relevance. This review highlights thymol derivatives with a stereogenic or prostereogenic center, which are distributed in 42 genera of the Asteraceae family whose chemotaxonomy is...
The absolute configurations of natural esquelane derivatives 1 and 2, the main components of a commercially available fragrance, as well as their synthetic derivatives 3–7 were revised by using the vibrational circular dichroism (VCD) spectroscopy of 2 and 6 in combination with density functional theory calculations at the B3LYP/DGDZVP level of the...
The absolute configuration of was deduced by vibrational circular dichroism together with the evaluation of the Flack and Hooft X-ray parameters. Vibrational circular dichroism exciton coupling, using the carbonyl group signals, confirmed the absolute configuration of . In addition, sodium borohydride reduction of the 11,13-double bond of 6-epi-des...
The most widely used physical methods for the chemical analysis of natural products are currently well established, although in the case of vibrational circular dichroism (VCD), this is not yet the case. The first VCD experiments were performed only about 40 years ago, and it took some 20 additional years for the development of sufficiently sensiti...
The new prenylated phloroglucinol α-pyrones 1-3 and the new dibenzofuran 4, together with the known 23-methyl-6-O-demethylauricepyrone (5), achyrofuran (6), and 5,7-dihydroxy-3,8-dimethoxyflavone (gnaphaliin A), were isolated from the aerial parts of Achyrocline satureioides. Their structures were determined by 1D and 2D NMR spectroscopic studies,...
A complex mixture of lomatin C-3′ esters and (−)-O-angeloyllomatin 1 was isolated from the seeds of Prionosciadium thapsoides. Since a literature search revealed that some lomatin C-3′ monoesters have positive specific rotations, while others had negative values, the absolute configuration of all of the molecules was determined to be (R) by exciton...
The stems of Bursera multijuga afforded (-)-(1S,3E,7R,8R,11E)-7,8-epoxycembra-3,11-dien-1-ol (1) and its acetate 2, together with cembrene A (3), nephthenol (4), and cembrenol (5). The structures of 1 and 2 were elucidated by 1D and 2D NMR, HRESIMS, and X-ray diffraction. The conformational preference of flexible 1 was studied by molecular modeling...
The insect antifeedant and toxic activity of hydroxyperezone (1), its derivatives 2-9, along with 3-hydroxy- (10) and 6-hydroxythymoquinone (11) were studied against Spodoptera littoralis, Leptinotarsa decemlineata, and Myzus persicae. The antifeedant tests showed that L. decemlineata was the most sensitive insect, followed by M. persicae, while S....
Aromadendranes belong to a class of sesquiterpenes present in higher plant essential oils and marine animals. Although the biological activities include antifungal, antibacterial, antiviral, plant growth regulatory, antifeedant, repellent and cytotoxic, there is only one precedent for spasmolytic effects. In a previous report we have shown that the...
The antifeedant effect of six cacalolides and six eremophilanolides was tested against the herbivorous insects Spodoptera littoralis, Leptinotarsa decemlineata, and Myzus persicae. The test compounds included several natural products isolated from Senecio madagascariensis (14-isovaleryloxy-1,2-dehydrocacalol methyl ether, 4), S. barba-johannis (13-...
The diastereoselectivity of diazomethane addition to the conjugated double bond of alpha,beta-unsaturated sesquiterpene lactones was explored using zaluzanin A (1) as a model. Thus, the absolute configuration of 1 was assured by X-ray diffraction analysis including evaluation of Flack and Hooft parameters, and by vibrational circular dichroism spec...
Chemical investigation of the aerial parts of Senecio polypodioides lead to the isolation of the new eudesmanoid 1β-angeloyloxyeudesm-7-ene-4β,9α-diol (1) and the known dirhamnosyl flavonoid lespidin (3), while from roots, the known 7β-angeloyloxy-1-methylene-8α-pyrrolizidine (5) and sarracine N-oxide (6), as well as the new neosarracine N-oxide (8...
Chemical investigation of the hexanes extracts of Ageratina jocotepecana afforded (-)-(5S,9S,10S,13S)-labd-7-en-15-oic acid (1), methyl (-)-(5S,9S,10S,13S)-labd-7-en-15-oate (2), (+)-(5S,8R,9R,10S,13R)-8-hydroxylabdan-15-oic acid (3), and (-)-(5S,9S,10S,13Z)-labda-7,13-dien-15-oic acid (5). The coexistence of (13R)- and (13S)-labdanes in this membe...
Chiral resolution of (+/-)-3alpha,6beta-dicinnamoyloxytropane (1) and (+/-)-3alpha,6beta-di(1-methyl-1H-pyrrol-2-ylcarbonyloxy)tropane (2), prepared by esterification of (+/-)-3alpha,6beta-tropanediol (3), was achieved using an amylose-derived HPLC stationary phase and normal phase conditions. The corresponding vibrational circular dichroism (VCD)...
Chiral resolution of (+/-)-3 alpha,6 beta-dicinnamoyloxytropane (1) and (+/-)-3 alpha,6 beta-di(1-methyl-1H-pyrrol-2-ylcarbonyloxy)tropane (2), prepared by esterification of (+/-)-3 alpha,6 beta-tropanediol (3), was achieved using an amylose-derived HPLC stationary phase and normal phase conditions. The corresponding vibrational circular dichroism...
The reliability of vibrational circular dichroism (VCD) spectroscopy to discriminate four diastereomeric cedranol acetates by means of their absolute configuration is examined. The usage of CompareVOA software to quantify comparisons of the measured infrared (IR) and VCD spectra with the corresponding simulated spectra at the B3LYP/DGDZVP and B3PW9...
The alkaloid extract from the roots of Chromolaena pulchella provided two new pyrrolizidine alkaloids, elucidated as (-)-supinidine triviridiflorate (1) and (-)-supinidine diviridiflorate (2) based on their physical and spectroscopic properties. Their absolute configuration was determined by chemical correlation with (-)-supinidine (3) and (+)-viri...
Careful reevaluation of the 1H and 13C NMR spectroscopic data of filifolinol acetate (4) led to the reassignment of the C-10 and C-11 signals, as well as the gem-dimethyl signals. Single crystal X-ray analysis provided an independent structural confirmation of 4, and comparison of the experimental vibrational circular dichroism spectrum with calcul...
The dichloromethane extract from the leaves of Caesalpinia platyloba provided cassane diterpenes whose structures were determined as (-)-(5S,6R,8S,9S,10R,14R)-6-acetoxyvouacapane (1), (-)-(5S,6R,8S,9S,10R,12Z,14R)-6-acetoxycassa-12,15-diene (3), and (-)-(5S,6R,8S,9S,10R,13E)-6-acetoxycassa-13,15-diene (4). Compound 1 was chemically correlated with...
Oxidation of 2-methylindoles 12a-f with dimethyldioxirane (DMD) revealed that N-unprotected 12b,f and protected N-carbamate 2-methylindole 12c afforded indoxyls 16b,c and o-(N-propionyl)aminobenzoic acid 17f as the main products, while N-alkyl- or N-aryl-2-methylindoles 12a,d,e gave 1,5′-diphenyl- 4′,5′-dihydro-3′H-spiro[indole-2,2′-pyrano[3,2-b]in...
An unprecedented macrocyclic dimeric diterpene containing a C2 symmetry axis was isolated from Acacia schaffneri . This compound, named schaffnerine, was characterized as (5S,7R,8R,9R,10S,13Z,17S,5'S,7'R,8'R,9'R,10'S,13'Z,17'S)-7,8:7,17':16,17:17,7':7',8':16',17'-hexaepoxy-7,8-seco-7',8'-seco-dicassa-13,13'-diene (1) from its spectroscopic data. Co...
Chiral HPLC coupled to electronic circular dichroism and laser optical rotation detection (HPLC-ECD-OR) permitted the on-line chiroptical characterization of both enantiomers of racemic flavanone (1) as ECD(-)310-OR(-)670-flavanone and ECD(+) 310-OR(+)670-flavanone for the first and second eluted peaks, respectively. Calculation of the ECD spectrum...
The aerial parts of Stevia tomentosa afforded a new guaianolide which was characterized by physical and spectroscopic data as (−)-1,5:3,4-diepoxyguaia-10(14)-en-12,8-olide (1). The absolute configuration of this unusual compound containing two β-oriented epoxide groups in the five-membered carbocyclic ring, one located at the C-1 and C-5 ring junct...
Complete assignment of the (1) H NMR chemical shift and coupling constant values of perezone (1), O-methylperezone (2) and 6-hydroxyperezone (3) was carried out by total-line-shape-fitting calculations using the PERCH iterative spectra analysis software (PERCH Solutions Ltd., Kuopio, Finland). The resulting simulated spectra for the three compounds...
The absolute configuration (AC) of (+)-2R,7R,15R,17S,19S-10-demethoxy-12-hydroxy-17,19-epoxygeissovelline (1), a main aspidospermatan-type indoline alkaloid from Geissospermum reticulatum, was established by vibrational circular dichroism (VCD), facilitating deduction of the AC of all structurally related alkaloids isolated from this plant.
1,2,3,4,6-Penta-O-acetyl-α-d-glucopyranose and the corresponding [1-(2) H], [2-(2) H], [3-(2) H], [4-(2) H], [5-(2) H], and [6,6-(2) H(2) ]-labeled compounds were prepared for measuring deuterium/hydrogen-induced effects on (13) C chemical shift (n) Δ (DHIECS) values. A conformational analysis of the nondeuterated compound was achieved using densit...
A general protocol for the synthesis of 3,1-benzoxazin-2-ones 18 from 3-hydroxyoxindoles 16 in a two steps sequence through phenylsuccinates or phenylpropionates 17 is described. Best reaction conditions for ring opening of 16 to succinates or propionates 17 were achieved using alcohol/silica gel, while cyclization of 17 to benzoxazinones 18 was ea...
New (1R)-(–)-myrtenal-derived macrocycles 5a and 5b were efficiently used as chiral auxiliaries in the diastereoselective nucleophilic addition of several nucleophiles (RMgX, RLi, LiAlH4, and NaBH4). We observed that the diastereoselectivity depended on the nucleophile, with the stereoselectivity order being RMgX (>99:1 dr) > RLi (7:3 dr) > AlLiH4...
The aerial parts of Arracacia tolucensis (Kunth) Hemsl. (Apiaceae) provided the new visamminol derivative (S)-(+)-4′-O-angeloylvisamminol (1), along with the known angular pyranocoumarin 2. Analysis of HMBC NMR correlations did not allow distinction of the linear dihydrofurochromone 1 from pyranochromone 5. The structure and S absolute configuratio...
Herein we describe a straightforward method for the determination of the absolute configuration of 3-indolyl(bromo)acetate 7, 3-indolyl(alkoxy)acetates 8a–f and 3-indolyl(amino)acetate 8g, based on 1H NMR spectral analysis. The conformational preferences for two diastereomeric esters were calculated by DFT, which matched very well with the experime...
The study of Raney-Ni catalyzed chemo- and regioselective hydrogenolysis of diastereomeric nitrile-substituted spirocyclopropyloxindoles is presented. The chemoselectivity outcome of the reaction is remarkably influenced by the relative stereochemistry of the nitrile-substituted spirocyclopropyloxindoles. Chemo- and high regioselective cyclopropane...
Both enantiomers of 3α,6β-dibenzoyloxytropane (1) have been prepared from optical active 6β-hydroxyhyoscyamines establishing their absolute configurations as (−)-(3R,6R) and (+)-(3S,6S)-dibenzoyloxytropane. Independent stereochemical confirmation was obtained by vibrational circular dichroism measurements, since bands characteristic of (3R,6R) and...
The absolute configuration of alga meroditerpenoids (_)-taondiol diacetate (1b) and (+)-epitaondiol diacetate (2c) are assigned by vibrational circular dichroism (VCD). The spectra of (2S,3S,6R,7R,10R,11R,14S)-1b and (2S,3S,6S,7S,10R,11R,14S)-2c enantiomers, calculated at the B3LYP/DGDZVP and at the B3LYP/DGDZVP2 levels of theory, respectively, mat...
Lupane triterpenoids 2 and 5-12 and oleanene derivatives 13 and 14 were prepared from lupeol (1), betulin (3), and germanicol (4). They were tested for anti-HIV activity, and some structure-activity relationships were outlined. The 20-(S) absolute configuration of epoxylupenone (8) was assessed by comparison of the observed and DFT-calculated vibra...
