Photoprotective Effects of Two New Morin-Schiff Base Derivatives on UVB-Irradiated HaCaT Cells.

Ultraviolet (UV) radiation harms the skin, causing oxidative damage, inflammation, and disruption of the skin's barrier function. There is considerable interest in identifying new natural ingredients with antioxidant and anti-inflammatory properties to serve as adjuvants in sunscreens. The flavonoid morin (1) can undergo structural modifications to enhance its biological properties. The aim of this study was to synthesize two new morin-Schiff base derivatives, morin oxime (2) and morin semicarbazone (3), comparing their photoprotective effects with that of the parent compound on UVB-exposed HaCaT keratinocytes. The chemical structure of the novel compounds was revealed based on spectroscopic data analysis. Our findings demonstrated that derivatives 2 and 3 enhanced the light absorption capability in the UV-visible (vis) range compared to 1. Tested compounds exhibited a higher scavenger capacity than Trolox. Moreover, pre-treatment with all compounds protected HaCaT cells from UVB-induced cell death. Compound 3 demonstrated the strongest antioxidant effect, reducing reactive oxygen species (ROS) generation and, subsequently, malondialdehyde (MDA) levels. Additionally, compounds 2 and 3 exhibited greater anti-inflammatory effects than compound 1, significantly reducing interleukin (IL)-6 production levels at all tested concentrations. These findings have demonstrated, for the first time, a promising photoprotective activity of two new Schiff base derivatives and suggest their use as natural sunscreen ingredients.

Chiral NMR analysis reveals the environmental dependence of areolal scalemization in Piptothrix areolare.

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 epoxythymol of Piptothrix areolare. In an attempt to shed some light to understand the reasons for such an unusual behavior, herein, we evaluated this phenomenon by correlating the areolal enantiomeric purity with several environmental variables, including temperature, humidity, rain precipitation, wind speed, and radiation during over 1 year of the plant life cycle. The specific rotation and enantiomeric excess determined by 1 H-NMR-BINOL measurements provided the scalemic variations of areolal samples isolated from the roots collected from the same location along a 427-day period. The 1 H-NMR-BINOL methodology provided better sensitivity to enantiomeric variations than specific rotation measurements. Statistical data, including matrix correlation analysis, exploratory analysis by heatmap plotting, and the principal component analysis (PCA), suggested direct correlation of the scalemic variation with humidity, rain precipitation, and radiation variables with the best PCA explanation (78.4%) and noncritical or poor correlations in PCA explained in 60.2% and 48.4%, respectively. When variations in the optical activity parameter of any metabolite are observed, the search for scalemic mixtures along their host plant life cycle should be undertaken. Herein, this phenomenon could be associated with interactions with soil microorganisms and with evolutionary aspects of Piptothrix areolare which belongs to Asteraceae, one of the most successfully adaptable plant families.

Methodology for the Absolute Configuration Determination of Epoxythymols Using the Constituents of Piptothrix areolare.

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 quantifications to determine the enantiomeric ratio, and vibrational circular dichroism (VCD) to evidence the AC of the dominant enantiomer. We now explore the use of electronic circular dichroism (ECD) to determine the AC of an epoxythymol for which time-expensive DFT calculations would be required unless the AC of a related molecule is already known, from either VCD studies or single-crystal X-ray diffraction analysis, since one could correlate the ECD Cotton effect with the AC because in ECD only chromophores and their neighborhoods are evidenced. This method is now applied by using the epoxythymols from Piptothrix areolare. Known areolal (1) and 10-cinnamoyloxy-8,9-epoxythymol isobutyrate (2) were isolated from the roots, while known 7-acetoxy-10-cinnamoyloxy-8,9-epoxythymol isobutyrate (3) and 10-cinnamoyloxy-7-hydroxy-8,9-epoxythymol isobutyrate (4), as well as the new enantiopure 7-acetoxy-10-cinnamoyloxy-6-hydroxy-8,9-epoxythymol isobutyrate (5) and 10-cinnamoyloxy-8,9-epoxy-6-hydroxy-7-northymol isobutyrate (6), were obtained from the extract of the flowers. Chemical correlation of epoxythymols 1 and 3 was achieved. Compounds 1-4 were obtained as scalemic mixtures, and 5 and 6 as the pure (8S) enantiomers. In addition, the new 10-cinnamoyloxy-7-oxo-8,9-dehydrothymol isobutyrate (7) was isolated from the roots. The structures of 5-7 followed from NMR and HRMS data, while enantiomeric compositions of 1-6 were determined by 1H NMR-BINOL measurements. The AC determination for 2-6 was done by ECD using a sample of 1 to reference the ECD Cotton effect. In turn, the AC of 1 was determined by VCD and extensive DFT calculations. The ECD-BINOL methodology turned out to be some 500 times more sensitive than that combining VCD and 1H NMR-BINOL.

Configurational Variation of a Natural Compound within Its Source Species. The Unprecedented Case of Areolal in Piptothrix areolare.

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 of this epoxythymol derivative were determined from individual plant specimens collected from the same geographical location over a 46-day period, which were processed using the same extraction and isolation methods. Detection of this unusual phenomenon was possible by analysis of NMR data recorded in the presence of BINOL as a chiral solvating agent. The absolute configuration of (-)-(8S)-areolal followed from vibrational circular dichroism data of an enantiomerically enriched sample, while single-crystal X-ray diffraction and supramolecular analyses revealed interactions that diminish the crystal entropy in rac-1. These results might be related with environmental factors and biochemical processes, suggesting the need of strict evaluations of enantiomeric composition of natural products that could be considered for human applications.

TiCl4 catalyzed cleavage of (25R)-22-oxo-23-spiroketals. Synthesis of sapogenins with furostanol and pyranone E rings on the side chain.

The regioselective opening of the F ring of 22-oxo-23-spiroketals 7a-d using TiCl4 in acetic anhydride yielded the novel furostanols 11a-d along with cholestanic derivatives 8a-d with pyranone E ring. The structures of the new derivatives thus obtained were established using one- (DEPT) and two-dimensional 1H, 13C NMR experiments (COSY, HSQC, HMBC, NOESY). The 22α-hydroxyl orientation in compounds 11a-d was proposed by comparison of the 13C chemical shifts with those of other aglycone members of this family, and confirmed by combined NOESY and X-ray diffraction analysis of compound 11a.

Conformational, configurational, and supramolecular studies of podocephalol acetate from Lasianthaea aurea.

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 its derived acetate 2, were herein confirmed by extensive 1D and 2D nuclear magnetic resonance (NMR) studies, while the conformational preferences of the cycloheptene was established by density functional theory (DFT) calculations, which in combination with vibrational circular dichroism measurements provided the (R) absolute configuration of the molecules. The structure and AC were further verified through the Flack and Hooft parameters calculations derived from single crystal X-ray diffraction data of 2. In addition, careful evaluation of the crystal data allowed observing supramolecular layers cell package, an uncommon property in natural terpenes that might have potential applications. A transmission electron microscopy analysis of crystal of 2 was also possible, providing its physical characteristics at the micrometric scale.

Fruits of wild and semi-domesticated Diospyros tree species have contrasting phenological, metabolic, and antioxidant activity profiles.

BACKGROUND: In contrast to commercial Diospyros species, Mesoamerican fruit-producing species are scarcely known, particularly wild species that might harbor desirable traits suitable for breeding. Thus, metabolomic, chemical, and antioxidant profiles of fruits harvested from cultivated Diospyros digyna and wild Diospyros rekoi trees during consecutive winter seasons were obtained. Fruits were harvested in habitats having marked differences in soil quality, climate, and luminosity. RESULTS: D. digyna fruits were larger and less acid than D. rekoi fruits, whereas antioxidant activity tended to be higher in D. rekoi fruits. Phenolic, flavonoid, and sugar contents also varied significantly between species. Metabolomic analysis allowed the pre-identification of 519 and 1665 metabolites in negative and positive electrospray ionization (ESI) modes, respectively. Principal component analysis of the positive ESI data explained 51.8% of the variance and indicated clear metabolomic differences between D. rekoi and D. digyna fruits that were confirmed by direct-injection ESI mass spectrometry profiles. Twenty-one discriminating metabolites were detected in fruits of both species; D. digyna fruits differentially accumulated lysophospholipids, whereas discriminating metabolites in D. rekoi fruits were chemically more diverse than those in D. digyna fruits. CONCLUSION: Domesticated D. digyna fruits have improved physicochemical fruit traits compared with wild D. rekoi fruits, including larger size and lower acidity. The metabolomic and chemical composition of their respective fruits were also significantly different, which in D. rekoi was manifested as a notable season-dependent increase in antioxidant capacity. Therefore, wild D. rekoi can be considered as an important genetic resource for the improvement of commercial Diospyros fruit quality. © 2019 Society of Chemical Industry.

Parvifoline Derivatives as Tubulin Polymerization Inhibitors.

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 in vitro α,ß-tubulin polymerization process. The structural analysis and characterization of the new compounds 5-7 and 9-12 were achieved by 1D and 2D NMR spectroscopy, mass spectrometry, and X-ray diffraction analysis of 6, 7, and 9. Preparation of 9 and 12 involved molecular rearrangements of the epoxide group with transannular 1,5-hydride shifts. At 10 µM compounds 1, 5, and 8 inhibited the polymerization of the α,ß-tubulin heterodimer by 24%, 49%, and 90% as compared to colchicine. These compounds were subjected to docking analysis that supported their interactions in a colchicine binding site located in the α-tubulin subunit, in the pocket formed by Phe296, Pro298, Pro307, His309, Tyr312, Lys338, Thr340, Ile341, and Gln342. Competitive inhibition assays with colchicine were also performed for the three compounds, which supported their binding at the colchicine secondary site in α-tubulin. Also, evaluations of their cytotoxicity on MCF7 breast carcinoma, HeLa cervix carcinoma, and HCT 116 colon carcinoma cell lines were carried out and showed that 8 is active against the HeLa and HCT 116 cell lines with IC50 3.3 ± 0.2 and 5.0 ± 0.5 µM, respectively.

Biomimetic Transformation of p-Menthene Glucosides into p-Cymenes and Carvotanacetone.

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-ß-d-glucopyranoside (1) and (-)-(3 S,4 R,5 R,6 S)-3,5,6-trihydroxy-1-menthene 3- O-ß-d-glucopyranoside (2), from Ageratina glabrata, yielded p-cymene (7) and carvacrol (9). The stable oxidized intermediates (+)-(3 S,4 S,6 R)-3,6-dihydroxy-1-menthene (3), (+)-(1 S,4 S,6 R)-1,6-dihydroxy-2-menthene (4), (+)-(1 R,4 S,6 R)-1,6-dihydroxy-2-menthene (5), (+)-(4 S,6 R)-yabunikkeol (6), (+)-(4 S)-carvotanacetone (8), (+)-(1 S,4 S,5 R,6 R)-1,5,6-trihydroxy-2-menthene (15), (+)-(1 R,4 S,5 R,6 R)-1,5,6-trihydroxy-2-menthene (16), and the new (+)-(4 S,5 R,6 S)-1(7),2-menthadiene (17) permitted establishment of the reaction mechanisms. The reactivity of the hydroxy groups of 4 and 5, as well as those of 15 and 16, was compared by acetylation reactions and supported by DFT calculations, revealing diminished reactivity in 4 and 15 due to the cis configuration of their hydroxy groups at C-1 and C-6. In addition, p-cymene (7) was detected as one of the major constituents of the essential oil of A. glabrata, which matches well with the biomimetic study.

Methodology for the Absolute Configuration Determination of Epoxythymols Using the Constituents of Ageratina glabrata.

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 dichroism (VCD) measurements and calculations. The conformational searching included an extensive Monte Carlo protocol that considered the rotational barriers to cover the whole conformational spaces. (+)-(8S)-10-Benzoyloxy-6-hydroxy-8,9-epoxythymol isobutyrate (1), (+)-(8S)-10-acetoxy-6-methoxy-8,9-epoxythymol isobutyrate (4), and (+)-(8S)-10-benzoyloxy-6-methoxy-8,9-epoxythymol isobutyrate (5) were isolated as enantiomerically pure constituents, while 10-isobutyryloxy-8,9-epoxythymol isobutyrate (2) was obtained as a 75:25 (8S)/(8R) scalemic mixture. In the case of 10-benzoyloxy-8,9-epoxythymol isobutyrate (3), the BINOL methodology revealed a 56:44 scalemic mixture and the VCD measurement was beyond the limit of sensitivity since the enantiomeric excess is only 12%. The racemization process of epoxythymol derivatives was studied using compound 1 and allowed the clarification of some stereochemical aspects of epoxythymol derivatives since their ACs have been scarcely analyzed and a particular behavior in their specific rotations was detected. In more than 30 oxygenated thymol derivatives, including some epoxythymols, the reported specific rotation values fluctuate from -1.6 to +1.4 passing through zero, suggesting the presence of scalemic and close to racemic mixtures, since enantiomerically pure natural constituents showed positive or negative specific rotations greater than 10 units.

Absolute Configuration of Menthene Derivatives by Vibrational Circular Dichroism.

The aerial parts of Ageratina glabrata afforded (-)-(3S,4R,5R,6S)-3,5,6-trihydroxy-1-menthene 3-O-ß-d-glucopyranoside (1) and (-)-(3S,4S,6R)-3,6-dihydroxy-1-menthene 3-O-ß-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 yielded (+)-(3S,4S,6R)-3,6-dihydroxy-1-menthene (10), (+)-(1R,4S,6R)-1,6-dihydroxy-2-menthene (11), and (+)-(1S,4S,6R)-1,6-dihydroxy-2-menthene (12). The structures of the new compounds 1, 2, 5-9, and 11 were defined by 1D and 2D NMR experiments, while the absolute configurations of the series of compounds were determined by comparison of the experimental vibrational circular dichroism (VCD) spectra of the 1,6-acetonide 5-acetate derived from 6 and of the 1,6-acetonide derived from 12 with their DFT-calculated spectra. In addition, Flack and Hooft X-ray parameters of 10 permitted the same conclusion. The results further led to the absolute configuration reassignment of 10 isolated from Brickellia rosmarinifolia, Mikania saltensis, Ligularia muliensis, L. sagitta, and Lindera strychnifolia, as well as of 11 from Cacalia tangutica, as ent-11.

Chemical composition of the essential oil from Ageratina jocotepecana and its repellent effect on drywood termite incisitermes marginipennis / Composición química del aceite esencial de Ageratina jocotepecana y su efecto repelente en termitas de madera seca incisitermes marginipennis

Essential oils obtained from new plant species with metabolomes unexplored or poorly known are a natural resource to find molecules with deterrent (irritant) effect. The aim of this study was to evaluate the chemical composition and the termite repellent activity of the essential oils from Ageratina jocotepecana. The repellent effect was determined by the pine drywood termite Incisitermes marginipennis behavior of to sense the contact of the tunnel wall in the wooden colony in the presence of an irritant obstacle caused by essential oils. Gas chromatographic analysis of the essential oils from flower, leaf, and stem showed quantitative and qualitative differences in components. Twenty-eight volatile components were identified by their mass spectra (MS). beta-caryophyllene, carvacrol, spathulenol, and terpinen-4-ol were the four major components, of them in relation 0.1 M citronellol, the 0.1 M carvacrol was the best repellent of the termite. Essential oils from A. jocotepecana exhibited a termite repellent effect due to their major components. Additionally, more research about the termite repellent action of carvacrol is still needed.

Los aceites esenciales obtenidos de nuevas especies de plantas con metabolomas inexplorados o poco conocidos son un recurso natural para encontrar moléculas con efecto disuasivo (irritante). El propósito del estudio fue evaluar la composición química de los aceites esenciales de Ageratina jocotepecana y su actividad repelente de termitas. El efecto repelente fue determinado por el comportamiento de las termitas de la madera seca de pino Incisitermes marginipennis de sentir el contacto de la pared del túnel en la colonia de madera en la presencia de un obstáculo irritante causado por los aceites esenciales. El análisis de cromatografía de gases de los aceites esenciales de flores, hojas y tallo mostró diferencias cuantitativas y cualitativas en componentes. Veintiocho componentes volátiles fueron identificados por sus espectros de masas (MS). beta-cariofileno, carvacrol, spathulenol y terpinen-4-ol fueron los cuatro componentes mayoritarios, de ellos en relación con 0,1 M citronelol el control positivo, el carvacrol 0,1 M fue el mejor repelente de la termita. Además, más investigación sobre la acción repelente de termitas de carvacrol se necesita realizar.

Regio- and stereoselective cleavage of steroidal 22-oxo-23-spiroketals catalyzed by BF3·Et2O.

The regioselective opening of the F ring of 22-oxo-23-spiroketals using BF3·OEt2 in acetic anhydride yielded novel cholestanic frameworks with pyranone E ring 20-23. The structures of the new derivatives of botogenin, diosgenin, hecogenin and tigogenin thus obtained were established using one and two dimensional (1)H, (13)C experiments (DEPT, COSY, HETCOR, HMBC). The X-ray diffraction analysis unequivocally confirmed the R configuration at C-23 in the starting 22-oxo-23-spiroketal 18 and the Z configuration of the C23-C24 double bond in the reaction product 20.

Crystal structure of N-[(E)-(1,3-benzodioxol-5-yl)-methyl-idene]-4-chloro-aniline.

In the title compound, C14H10ClNO2, obtained by the condensation of 4-chloro-aniline and piperonal, the five-membered ring is almost planar (r.m.s. deviation = 0.023 Å) and the dihedral angle between the aromatic rings is 43.22 (14)°. In the crystal, a short O⋯Cl contact of 3.173 (2) Šis observed. The mol-ecules are arranged into corrugated (010) layers.

Absolute configuration of (13R)- and (13S)-labdane diterpenes coexisting in Ageratina jocotepecana.

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 member of the Asteraceae family was demonstrated by vibration circular dichroism measurements of ester 2 and methyl (+)-(5S,8R,9R,10S,13R)-8-hydroxylabdan-15-oate (4) in comparison to the DFT B3LYP/DGDZVP-calculated spectra. In addition, transformation of 1 and 3 with HClO4 in MeOH yielded epimeric methyl (+)-(5S,10S,13S)-labd-8-en-15-oate (6) and methyl (+)-(5S,10S,13R)-labd-8-en-15-oate (7), respectively, confirming the presence of C-13 epimers in this plant. Diterpene 1 showed remarkable antibacterial activity against Bacillus subtilis (MIC 0.15 mg/mL) and Staphylococcus aureus (MIC 0.78 mg/mL), while diterpene 3 exhibited moderate activities against the same organisms.

Cassane diterpenes from Caesalpinia platyloba.

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 (-)-(5S,6R,8S,9S,10R,14R)-6-hydroxyvouacapane (2), (+)-(5S,8S,9S,10R,14R)-6-oxovouacapane (5), and (+)-(5S,6S,8S,9S,10R,14R)-6-acetoxyvouacapane (6), the last one previously isolated from Dipteryx lacunifera. The absolute configurations of all six diterpenes 1-6 were established by comparison of DFT calculated vibrational circular dicroism spectra of 1, 2 and 5 with those obtained experimentally. In addition, several reported chemical shifts for 2 and 5 were reassigned based on two-dimensional NMR measurements.

Supinidine viridiflorates from the roots of Chromolaena pulchella.

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 (+)-viridifloric acid (4).

Regioselective cleavage of 22-oxo-23-spiroketals. Novel cholestanic frameworks with pyranone and cyclopentenone E rings on the side chain.

The regioselective opening of the F ring of 22-oxo-23-spiroketals using a saturated solution of HCl in acetic anhydride yielded novel cholestanic frameworks with pyranone or cyclopentenone E rings. The structures of the new derivatives of sarsasapogenin, diosgenin and hecogenin thus obtained were established using one and two dimensional (1)H, (13)C experiments (DEPT, COSY, HETCOR, HMBC, ROESY, and NOESY). The X-ray analysis for compound 11b confirmed the 23R configuration for the new stereogenic center.

Transkingdom signaling based on bacterial cyclodipeptides with auxin activity in plants.

Microorganisms and their hosts communicate with each other through an array of signals. The plant hormone auxin (indole-3-acetic acid; IAA) is central in many aspects of plant development. Cyclodipeptides and their derivative diketopiperazines (DKPs) constitute a large class of small molecules synthesized by microorganisms with diverse and noteworthy activities. Here, we present genetic, chemical, and plant-growth data showing that in Pseudomonas aeruginosa, the LasI quorum-sensing (QS) system controls the production of three DKPs--namely, cyclo(L-Pro-L-Val), cyclo(L-Pro-L-Phe), and cyclo(L-Pro-L-Tyr)--that are involved in plant growth promotion by this bacterium. Analysis of all three bacterial DKPs in Arabidopsis thaliana seedlings provided detailed information indicative of an auxin-like activity, based on their efficacy at modulating root architecture, activation of auxin-regulated gene expression, and response of auxin-signaling mutants tir1, tir1 afb2 afb3, arf7, arf19, and arf7arf19. The observation that QS-regulated bacterial production of DKPs modulates auxin signaling and plant growth promotion establishes an important function for DKPs mediating prokaryote/eukaryote transkingdom signaling.

Absolute configuration of labdanes and ent-clerodanes from Chromolaena pulchella by vibrational circular dichroism.

The aerial parts of Chromolaena pulchella biosynthesize two groups of diterpenes belonging to opposite enantiomeric series, specifically, the furanoid ent-clerodanes (5R,8R,9S,10R)-(-)-hardwikiic acid (1), methyl (5R,8R,9S,10R)-(-)-hardwikiate (2), (5S,8R,9S,10R)-(-)-hautriwaic acid lactone (3), methyl (5R,8R,9S,10R)-(-)-nidoresedate (4) and methyl (8R,9R)-(-)-strictate (5), as well as the labdanes (5S,8R,9R,10S)-(+)-(13E)-labd-13-ene-8,15-diol (6) and (5S,8R,9R,10S)-(+)-isoabienol (7). The absolute configuration of the two groups of diterpenes was unambiguously assigned by comparison of the vibrational circular dichroism spectra of 3 for ent-clerodanes, and of 7 for labdanes with their theoretical spectra obtained by density functional theory calculations. The results support a biogenetic proposal to diterpenes found in the studied botanical species.