The structure and stereochemistry of phlogantholide-A,a diterpene from Phlogacanthus thyrsiflorus

The structure and stereochemistry of phlogantholide-A, a new diterpene lactone isolated from the leaves of Phlogacanthus thyrsiflorus has been determined as 2β,15,18-trihydroxy-ent-labd-8(17),13-dien-16-oic lactone by chemical and spectroscopic means.     

Labdane diterpenes from Cistus symphytifolius

The investigation of the aerial part of Cistus symphytifolius afforded, in addition to sitosterol, trimethoxykaempferol, cativic acid, labdenic acid, labdanolic acid and labdan-8α,15-diol, three new bicyclic diterpenes: cistadienic acid, cistenolic acid and labd-13(E)- ene-8α,15-diol. The structures of these were determined by spectral studies and correlations. CD spectral studies showed that cistenolic acid and salvic acid are enantiomeric compounds, so the stereochemistry of salvic acid (7α-hydroxy-labd-8(17)-ene-15-oic acid) should be changed to 7β-hydroxy-eperu-8(17)-ene-15-oic acid (7β-hydroxy-ent-labd-8(17)-ene-15-oic acid).     

Labdane diterpenoids from nolana rostrata

Six new labdane diterpenes, methyl 3-oxo-18-hydroxylabda-8(17),13E-dien-15-oate, methyl 2β,3β- dihydroxylabda-8(17),13E-dien-15-oate, 2-oxo-labda-8(17),13Z-dien-15-oic acid, 3-oxo-18-acetoxylabda-8(17),13Z- dien-15-oic acid, 3-oxo-18-hydroxylabda-8(17),13Z-dien-15-oic acid, 2β,3β-dihydroxylabda-8(17),13Z-dien-15-oic acid, and the known compound kaempferol-3,7,4′-trimethyl ether were isolated from the aerial parts of Nolana rostrata. The structures of the new compounds were elucidated by spectroscopic methods.     

Differential metabolism of diastereoisomeric diterpenes by Preussia minima,found as endophytic fungus in Cupressus lusitanica

The plant diastereoisomeric diterpenes ent-pimara-8(14)-15-dien-19-oic acid, obtained from Viguiera arenaria, and isopimara-8(14)-15-dien-18-oic acid, isolated from Cupressus lusitanica, were distinctly functionalized by the enzymes produced in whole cell cultures of the fungus Preussia minima, isolated from surface sterilized stems of C. lusitanica. The ent-pimaradienoic acid was transformed into the known 7β-hydroxy-ent-pimara-8(14)-15-dien-19-oic acid, and into the novel diterpenes 7-oxo-8 β-hydroxy-ent-pimara-8(14)-15-dien-19-oic and 7-oxo-9β-hydroxy-ent-pimara-8(14)-15-dien-19-oic acids. Isopimara-8(14)-15-dien-18-oic acid was converted into novel diterpenes 11α-hydroxyisopimara-8(14)-15-dien-18-oic acid, 7β,11α-dihydroxyisopimara-8(14)-15-dien-18-oic acid, and 1β,11α-dihydroxyisopimara-8(14)-15-dien-18-oic acid, along with the known 7β-hydroxyisopimara-8(14)-15-dien-18-oic acid. All compounds were isolated and fully characterized by 1D and 2D NMR, especially ¹³C NMR. The diterpene bioproduct 7-oxo-9β-hydroxy-ent-pimara-8(14)-15-dien-19-oic acid is an isomer of sphaeropsidin C, a phytotoxin that affects cypress trees produced by Shaeropsis sapinea, one of the main phytopathogen of Cupressus. The differential metabolism of the diterpene isomers used as substrates for biotransformation was interpreted with the help of computational molecular docking calculations, considering as target enzymes those of cytochrome P450 group.     

Microbial transformation of neoandrographolide by Mucor spinosus (AS 3.2450)

Microbial transformation of neoandrographolide (1), was performed by Mucor spinosus (AS 3.2450). Ten metabolites were obtained and identified as 14-deoxyandrographolide (2), 17,19-dihydroxy-8,13-ent-labdadien-16,15-olide (3), 3,14-dideoxyandrographolide (4), 7β-hydroxy-3,14-dideoxyandrographolide (5), 17,19-dihydroxy-7,13-ent-labdadien-16,15-olide (6), 8(17),13-ent-labdadien-16,15-olid-19-oic acid (7), 8α,17β-epoxy-3,14-dideoxyandrographolide (8), 8β,17,19-trihydroxy-ent-labd-13-en-16, 15-olide (9), phlogantholide-A (10), 19-[(β-d-glucopyranosyl)oxy]-19-oxo-ent-labda-8(17),13-dien-16,15-olide (11) by spectroscopic and chemical means. Among them, products 3, 5, 6, 8 and 9 were characterized as new compounds. The inhibitory effects of compounds 1–11 on nitric oxide production in lipopolysaccharide-activated macrophages were evaluated and their preliminary structure–activity relationships (SAR) were discussed.     

Diterpenoids and a sesquiterpene lactone from viguiera ladibractate

Eight known diterpene acids, ent-12-oxokaur-9(11),16-dien-19-oic acid, ent-12β-hydroxykaur-9(11),16-dien-19-oic acid, ent-isokaur-15(16)-en-17,19-dioic acid, ent-15α,16-epoxy-17-hydroxykaura-19-oic acid, ent-kaura-17,19-dioic acid, ent-kaur-16-en-19-oic acid, grandifloric acid, angeloyloxygrandifloric acid, as well as a new sesquiterpene lactone, ladibranolide, were isolated from Viguiera ladibractate. The stereochemistry of the sesquiterpene lactone was established by NOE experiments.     

Labdane diterpenes from an acacia species

Two new diterpenes, (13E)-labd-13-ene-3β,8α,15-triol and (13E)-3β,8α-dihydroxylabd-13-en-15-oic acid have been isolated from an unclassified Acacia sp. Chemical and spectroscopic evidence for their structure is presented. The known labdanes, sclareol, 13-epi-sclareol and (13E)-labd-13-ene-8α,15-diol were also isolated.     

Terpenes with antimicrobial activity from Cretan propolis

Five terpenes, the diterpenes: 14,15-dinor-13-oxo-8(17)-labden-19-oic acid and a mixture of labda-8(17),13E-dien-19-carboxy-15-yl oleate and palmitate as well as the triterpenes, 3,4-seco-cycloart-12-hydroxy-4(28),24-dien-3-oic acid and cycloart-3,7-dihydroxy-24-en-28-oic acid were isolated from Cretan propolis. Moreover, 18 known compounds were also isolated, seven of them for the first time as propolis components. All structures were established on the basis of spectroscopic analysis and chemical evidence. All isolated compounds were tested for antimicrobial activity against some Gram-positive and Gram-negative bacteria as well as against some human pathogenic fungi showing a broad spectrum of antimicrobial activity.     

Ent-kauren-19-oic acid derivatives from the stem bark of Croton pseudopulchellus Pax

Two new ent-kauren-19-oic acid derivatives, ent-14S*-hydroxykaur-16-en-19-oic acid and ent-14S*,17-dihydroxykaur-15-en-19-oic acid together with eleven known compounds ent-kaur-16-en-19-oic acid, ent-kaur-16-en-19-al, ent-12β-hydroxykaur-16-en-19-oic acid, ent-12β-acetoxykaur-16-en-19-oic acid, 8R,13R-epoxylabd-14-ene, eudesm-4(15)-ene-1β,6α-diol, (?)-7-epivaleran-4-one, germacra-4(15), 5E,10(14)-trien-9β-ol, acetyl aleuritolic acid, β-amyrin, and stigmasterol were isolated from the stem bark of Croton pseudopulchellus (Euphorbiaceae). Structures were determined using spectroscopic techniques. Ent-14S*-hydroxykaur-16-en-19-oic acid, ent-kaur-16-en-19-oic acid, ent-12β-hydroxykaur-16-en-19-oic acid, ent-12β-acetoxykaur-16-en-19-oic acid and 8R,13R-epoxylabd-14-ene were tested for their effects on Semliki Forest virus replication and for cytotoxicity against human liver tumour cells (Huh-7 strain) but were found to be inactive. Ent-kaur-16-en-19-oic acid, the major constituent, showed weak activity against the Plasmodium falciparum (CQS) D10 strain.     

Bioactive constituents of Helianthus tuberosus (Jerusalem artichoke)

In a cytotoxicity-guided study using the MCF-7 human breast cancer cell line, nine known compounds, ent-17-oxokaur-15(16)-en-19-oic acid (1), ent-17-hydroxykaur-15(16)-en-19-oic acid (2), ent-15β-hydroxykaur-16(17)-en-19-oic acid methyl ester (3), ent-15-nor-14-oxolabda-8(17),12E-dien-18-oic acid (4), 4,15-isoatriplicolide angelate (5), 4,15-isoatriplicolide methylacrylate (6), (+)-pinoresinol (7), (?)-loliolide (8), and vanillin (9) were isolated from the chloroform-soluble subfraction of a methanol extract of the whole plant of Helianthus tuberosus collected in Ohio, USA. This is the first time that diterpenes have been isolated and identified from this economically important plant. The bioactivities of all isolates were evaluated using the MCF-7 human breast cancer cell line as well as a soybean isoflavonoid defense activation bioassay. The results showed that two germacrane-type sesquiterpene lactones, 5 and 6, are cytotoxic agents. While compounds 2, 3, 5 and 6 blocked isoflavone accumulation in the soybean, the norisoprenoid (?)-loliolide (8) was somewhat stimulatory of these defense metabolites.     

Biotransformation of ent-pimaradienoic acid by cell cultures of Aspergillus niger

Microbial transformation stands out among the many possible semi-synthetic strategies employed to increase the variety of chemical structures that can be applied in the search for novel bioactive compounds. In this paper we obtained ent-pimaradienoic acid (1, PA, ent-pimara-8(14),15-dien-19-oic acid) derivatives by fungal biotransformation using Aspergillus niger strains. To assess the ability of such compounds to inhibit vascular smooth muscle contraction, we also investigated their spasmolytic effect, along with another five PA derivatives previously obtained in our laboratory, on aortic rings isolated from male Wistar rats. The microbial transformation experiments were conducted at 30 °C using submerged shaken liquid culture (120 rpm) for 10 days. One known compound, 7α-hydroxy ent-pimara-8(14),15-dien-19-oic acid (2), and three new derivatives, 1β-hydroxy ent-pimara-6,8(14),15-trien-19-oic acid (3), 1α,6β,14β-trihydroxy ent-pimara-7,15-dien-19-oic acid (4), and 1α,6β,7α,11α-tetrahydroxy ent-pimara-8(14),15-dien-19-oic acid (5), were isolated and identified on the basis of spectroscopic analyses and computational studies. The compounds obtained through biotransformation (2–5) did not display a significant antispasmodic activity (values ranging from 0% to 16.8% of inhibition); however the previously obtained diterpene, methyl 7α-hydroxy ent-pimara-8(14),15-dien-19-oate (8), showed to be very effective (82.5% of inhibition). In addition, our biological results highlight the importance to study the antispasmodic potential of a large number of novel diterpenes, to conduct further structure–activity relationship investigations.     

Clerodane diterpenes from Aristolochia species

The investigation of Aristolochia brasiliensis and A. esperanzae afforded 12 clerodane derivatives, including the following six novel ones: rel (5S, 8R, 9S, 10R)-2-oxo-ent-3-cleroden-15-oic acid, rel (5S, 8R, 9S, 10R)-2-oxo-ent-clerod-3,13-dien-15-oic acid methyl ester, (5R, 8R, 9S, 10R)-ent-3-cleroden-15-oic acid, rel (5S, 8R, 9S, 10R)-ent-clerod-3,13-dien-15-oic acid, (2S, 5R, 8R, 9S, 10R)-2-hydroperoxy-ent-3-cleroden-15-oic acid methyl ester and (2S, 5R, 8R, 9S, 10R)-2-hydroperoxy-ent-clerod-3,13-dien-15-oic acid methyl ester. The structures were assigned on the basis of spectral data and derivatization by chemical reactions. The occurrence of this type of diterpene has not previously been reported in Aristolochiaceae.     

Stereochemistry of strictic acid and related furano-diterpenes from conyza japonica and grangea maderaspatana

Extraction of Conyza japonica gave strictic acid, ent-2β-hydroxy-15,16-epoxy-3,13(16),14-clerodatrien-18-oic acid and 5,7-dihydroxy-3,8,4′-trimethoxyflavone. Extraction of Grangea maderaspatana gave (-)-hardwickiic acid, ent-15,16-epoxy-1,3,13(16),14-clerodatetraen-18-oic acid and 3-hydroxy-8-acetoxypentadeca-1,9,14-trien-4,6-diyne. The structure of ent-2β-hydroxy-15,16-epoxy-3,13(16),14-cleroclatrien-18-oic acid was deduced by spectroscopic methods and by partial synthesis from (-)-hardwickiic acid and the stereochemistries of strictic acid and (ent-15,16-epoxy-1,3,13(16),14-clerodatraen-18-oic acid were established by correlation with ent-2β-hydroxy-15,16-epoxy-3,13(16),14-clerodatrien-18-oic acid.     

New natural diterpene acids from Juniperus communis

Three new diterpene acids have been isolated from the leaves of Juniperus communis and their structures, elucidated by spectroscopic methods, were identified as 7-oxo-13-epi- pimara-8,15-dien-18-oic acid, 7α-hydroxysandaracopimaric acid and (14 S)-14,15-dihydroxylabda- 8(17),13(16)-dien-19-oic acid. Biflavonyls, fatty acids and diterpenoids with known structures were also isolated.     

Beyerene derivatives and other constituents from Petunia patagonica

Two new diterpenes of the beyerene type, ent-19-hydroxy-1 7-acetoxybeyer-15-ene and ent-beyer-15-en-17-oic acid, and two previously characterized kauranoids, ent-16β-hydroxy-17-acetoxykaurane and ent-16β,1 7-dihydroxy-kaurane, as well as two known flavonoids, luteolin-7,3′,4′-trimethyl ether and luteolin-7,3′-dimethyl ether, and a triterpenoid, oleanoic acid, were obtained from a chloroform extract of Petunia patagonica. The new structures were elucidated by spectral data and chemical transformations.     

Labdane diterpenoids from Cistus ladaniferus

Three new diterpenic acids have been isolated from Cistus ladaniferus: 6,8(17) labdadien-15-oic, 7-oxo-8-labden-15-oic and 6β-acetoxy-7-oxo-8-labden-15-oic acids, beside labdanolic, 6-oxocativic,7α-hydroxy-8(17)-labden-15-oic, 8α-methoxy-labda-15-oic and 8α-hydroxy-13(E)-labden-15-oic acids.     

Trihydroxy-C18-acids and a labdane from rudbeckia fulgida

Extraction of Rudbeckia fulgida furnished 13αH-labd-8(17)-en-15-al-19-oic acid, two new C₁₈-acids tentatively formulated as 9 (S*),12 (S*),13 (S*)-trihydroxyoctadeca-10(E),15 (Z)-dienoic acid and 9 (S*),12 (S*),13 (S*)-trihydroxyoctadec-10 (E)-enoic acid, several known C₁₄-polyacetylenes and several flavone glycosides.     

Diterpenoids from the pericarp of Platycladus orientalis

Eight labdane-type diterpenes, 7beta,13S-dihydroxylabda-8(17),14-dien-19-oic acid (1), 12R,15-dihydroxylabda-8(17),13E-dien-19-oic acid (3c), 12R,15-dihydroxylabda-8(17),13Z-dien-19-oic acid (3d), 12R,13R,14S-trihydroxylabda-12,15-epoxy-8(17)-en-19-oic acid (4a), 12S,13S,14R-trihydroxylabda-12,15-epoxy-8(17)-en-19-oic acid (4b), 15-hydroxy-12-oxolabda-8(17),13E-dien-19-oic acid (5), 14R,15-dihydroxylabda-8(17),12Z-dien-19-oic acid (7a) and 14S,15-dihydroxylabda-8(17),12Z-dien-19-oic acid (7b), along with 20 known diterpenoids, were isolated from the pericarp of Platycladus orientalis. Their structures were unambiguously elucidated by NMR spectroscopic and single crystal X-ray diffraction analyses, as well as via chemical correlation conversion. NMR spectroscopic data of known isomers 8c and 8d were reported as a supplement to existing data.     

Ent-kaurane derivatives from the root cortex of yacon and other three Smallanthus species (Heliantheae,Asteraceae)

The metabolites produced by the secretory canals of the root cortex from four Smallanthus species belonging to the yacon group were identified as ent-kaurane-type diterpenes. The dichloromethane root cortex extracts of the four species were treated with diazomethane and analyzed comparatively by GC–MS using a simple and rapid procedure which is very sensitive and reproducible permitting detection of minor components. In all cases, ent-16-kauren-19-oic acid (kaurenoic acid) methyl ester was the main component, differences being observed only in the minor components. The minor components identified were grandiflorenic acid methyl ester, ent-16-kauren-19-al, 16α,17-epoxy-15α-angeloyloxy-kauran-19-oic acid methyl ester and several O-acyl derivatives at C-15 or C-18 of kaurenoic acid. One of the minor components, 18-isobutyroyloxy-ent-kaur-16-en-19-oic acid is a new kaurenoic acid derivative. Grandiflorenic acid and 15-α-angeloyloxy-16,17-α-epoxy-ent-16-kauren-19-oic acid were present only in Smallanthus sonchifolius and Smallanthus siegesbeckius which showed very similar GC traces. The different GC profile of RC diterpenes from Smallanthus connatus and Smallanthus macroscyphus supports the view that they are different taxa. Some chemotaxonomic aspects of the genus Smallanthus and the subtribe Milleriinae are briefly discussed.     

Ent-labdane derivatives from gutierrezia grandis

Two new diterpenes, 3α-angeloyloxy-18-hydroxy-13-furyl-ent-labda-8(17)-ene and 3α-hydroxy-18-angeloyloxy- 13-furyl-ent-labda-8(17)-ene and an only recently reported third diterpene, 3α, 18-dihydroxy-13-furyl-ent-labda-8(17)-ene, were isolated from the leaves of Gutierrezia grandis. Their structures were determined by mass spectral, IR, ¹H NMR and ¹³C NMR data was well as chemical evidence.