The structural determination of a new steroidal metabolite from the brown alga Sargassum asperifolium

An investigation of the natural products chemistry of the brown alga Sargassum asperifolium from the red sea yielded a new steroidal metabolite, 24-vinyl cholest-4-ene-24-ol-3-one, saringosterone (3), a known steroidal metabolite, 24-vinyl cholest-5-ene-3b,24-diol, saringosterol (4), and known diterpene with a hydroazulene skeleton, dictyone (1). The identification of the isolated metabolites was established mainly by spectral methods and chemical transformation of the dictyone (1) to its acetate (2).     

Cytotoxic hydroazulene diterpenes from the brown alga Dictyota dichotoma

Two new hydroazulenoid (prenyl guaiane) diterpenes, dictyone acetate (2) and 3,4-epoxy 13-hydroxy pachydictyol A (4) were isolated from the petroleum ether fraction of the alcoholic extract of the brown alga, Dictyota dichotoma (Hudson) Lamouroux, which was collected from the Red Sea coasts at Hurgada, Egypt, together with three known ones, pachydictyol A (1), dictyone (3) and 11-hydroxypachydictyol A (dictyol E) (5). In addition, the steroidal compound, stigmasta-5,(E)-24(28)-dien-3-beta-ol (fucosterol) (6) was also isolated. The structures of the isolated compounds have been determined on the basis of spectroscopic evidences as well as physical and chemical correlation with known compounds. Compounds 1, 2, 3 and 5 showed moderate cytotoxic activity.     

Abietane diterpenes induce cytotoxic effects in human pancreatic cancer cell line MIA PaCa-2 through different modes of action

Abietane diterpenes, especially those containing quinone moieties, are often reported to have cytotoxic effects on cancer cell lines. They deserve greater attention because several cancer chemotherapeutic agents also possess the quinone structural feature. To date, very little is known about their cytotoxic molecular modes of action. In the present study, five diterpenes, 7 alpha-acetoxyroyleanone, horminone, royleanone, 7-ketoroyleanone and sugiol which have been previously isolated from the medicinal plant Peltodon longipes were shown to possess cytotoxic activity against the human pancreatic cancer cell line MIA PaCa-2. 7 alpha-Acetoxyroyleanone, horminone and royleanone were demonstrated to possess alkylating properties using the nucleophile 4-(4-nitrobenzyl)pyridine. However, no clear correlation between the alkylating properties and cytotoxicity of these diterpenes was observed. Furthermore, the relaxation activity of human DNA topoisomerases I and II was found to be influenced by these compounds, with 7-ketoroyleanone and sugiol being the most active. These two diterpenes preferentially inhibited topoisomerase I and exhibited lower IC₅₀ values than the classical topoisomerase I inhibitor camptothecin. Molecular docking studies revealed possible interactions of diterpenes with topoisomerase I, indicating that these compounds do not form the drug–enzyme–DNA covalent ternary complex as observed with camptothecin. A binding pocket located at the surface of the DNA-interaction site was proposed. Moreover, the ability of the five diterpenes to generate DNA-strand breaks in single cells was confirmed using the alkaline comet assay. As expected, these diterpenes also influenced cell cycle progression and arrested cells in different phases of the cell cycle, primarily the G1/G0 and S-phases. Interestingly, the diterpenes only exhibited a slight ability to induce apoptotic cell death and failed to generate intracellular reactive oxygen species. These results provide additional understanding of the cytotoxic effects of abietane diterpenes. Depending on their functional groups, we propose that abietane diterpenes utilise different mechanisms to induce cell death.     

Antifeedant/insecticidal terpenes from asteraceae and labiatae species native to Argentinean semi-arid lands

To validate the potential as added-value resources of Asteraceae and Labiatae species of Argentinean semi-arid lands, we have selected 13 of their major terpenoids belonging to several chemical classes and tested their insect antifeedant and toxic activity on the herbivorous insects Spodoptera littoralis and Leptinotarsa decemlineata. The antifeedant effects of the test compounds were structure- and species-dependent. The most active antifeedant to L. decemlineata was the eudesmane sesquiterpene gamma-costic acid (13), followed by the labdane diterpene 2alpha,3alpha-dihydroxycativic acid (8), the clerodane diterpenes 6-acetylteucjaponin B (5), bacchotricuneatin A (1), bartemidiolide (7), butanolide (4), and the sesquiterpenes ilicic acid (11) and tessaric acid (10) (eudesmane and eremophilane type, respectively). S. littoralis was only affected by the clerodanes and showed the strongest response to salviarin (3) and 5, followed by hawtriwaic acid (6) and 12-epi-bacchotricuneatin A (2). Orally injected S. littoralis larvae were negatively affected by 5. Most of the diterpenes had selective cytotoxic effects to insect-derived Sf9 cells with the clerodane 1 being the most active, followed by the eudesmane costic acid (12), the only cytotoxic sesquiterpene. None of these compounds was cytotoxic to mammalian CHO cells.     

In vitro cytotoxic activity of abietane diterpenes from Peltodon longipes as well as Salvia miltiorrhiza and Salvia sahendica

Phytochemical investigations of the n-hexane extract from the roots of Peltodon longipes (Lamiaceae) resulted in the isolation of 12 known abietane diterpenes (1-12). Structures were established on the basis of one and two dimensional nuclear magnetic resonance spectroscopic data ((1)H and (13)C, COSY, HSQC and HMBC), electron ionization mass spectrometric analysis (EIMS) as well as comparison with data from literature. These compounds, as well as eight known diterpenes (13-19) from Salvia miltiorrhiza, and two from Salvia sahendica (20 and 21) were evaluated for their cytotoxic effects in human pancreatic (MIAPaCa-2) and melanoma (MV-3) tumor cell lines using the MTT assay. Tanshinone IIa (13), 7α-acetoxyroyleanone (1), 1,2-dihydrotanshinone (16) and cryptotanshinone (14) had the highest cytotoxic effects in MIAPaCa-2, displaying IC(50) of 1.9, 4.7, 5.6, and 5.8 μM, respectively. Structure-activity relationships of abietane diterpenoid quinones are discussed.     

Novel cytotoxic diterpenes from the stem of dysoxylum kuskusense

Three novel diterpenes, dysokusones A (1), B (2), and C (3), were isolated from the stem of Dysoxylum kuskusense as cytotoxic substances. The structures were established by spectroscopic examinations. Compounds 1, 2, and 3 were cytotoxic toward HL-60(TB) cells with EC₅₀ values of 2.25, 6.35, and 2.37 μM, respectively. Compound 1 also displayed cytotoxicity against K-562 and NCI-H522 cells with EC₅₀ values of 5.04 and 4.80 μM, respectively.     

ent-Beyerane diterpenoids from the heartwood of Excoecaria parvifolia

Chromatographic fractionations of the toluene extract of the heartwood of Excoecaria parvifolia collected in Australia resulted in the isolation of 12 beyerane diterpenes (1-12), and the triterpene, lupeol. Four of the isolated diterpenoids (5-7 and 12) have unusual structures: ent-3-oxa-beyer-15-en-2-one, (5); ent-15,16-epoxy-2-hydroxy-19-norbeyer-1,4-dien-3-one (6); methyl ent-2,4-seco-15,16-epoxy-4-oxo-3,19-dinorbeyer-15-en-2-oate (7); and ent-2,17-dihydroxy-19-norbeyer-1,4,15-trien-3-one (12). The structures were established by spectroscopic analyses, NMR data comparisons with similar diterpenes, and chemical correlations. All the diterpenes are assumed to have the same absolute configuration as the co-occurring (+)-stachenol (4). Diosphenol 2 and nor-lactone 5 exhibited significant potency in bioassays for cytotoxic activity against leukemia cells (L1210). Plausible biosynthetic pathways are proposed to explain the origin of the diterpene metabolites.     

Effects of sesquiterpenes and triterpenes from the rhizome of Alisma orientale on nitric oxide production in lipopolysaccharide-activated macrophages: absolute stereostructures of alismaketones-B 23-acetate and -C 23-acetate

The methanolic extract from a Chinese herbal medicine, the rhizome of Alisma orientale, was found to exhibit inhibitory activity of nitric oxide (NO) production in lipopolysaccharide (LPS)activated macrophages. Novel triterpenes, alismaketones-B 23-acetate and -C 23-acetate, were isolated from the active extract together with eight sesquiterpenes and eighteen protostane-type triterpenes. The absolute stereostructures of new triterpenes were characterized on the basis of chemical and physicochemical evidence, which included the chemical correlations with known triterpenes. The guaiane-type sesquiterpenes (alismol, orientalols A and C) and protostane- and seco-protostane-types triterpenes (alisols C monoacetate, E-23-acetate, F, H, I, L-23-acetate, and M-23-acetate, alismaketones-B 23-acetate and -C 23-acetate, alismalactone 23-acetate, and 3-methylalismalactone 23-acetate) inhibited LPS-induced NO production (IC50 = 8.4-68 microM). Other triterpenes (alisols A, A monoacetate, B, B monoacetate, E, G, K-23-acetate, and N-23-acetate and 11-deoxyalisol B) also showed the potent inhibitory activity, but they showed cytotoxic effects more than 30 microM (MTT assay). In addition, alismol and alisol F were found to suppress iNOS induction.     

Bioactive compounds from sclerotia extract of Poria cocos that control adipocyte and osteoblast differentiation

Poria cocos Wolf confers edible sclerotia also known as ‘Indian bread’ in North America, that have been used for the treatment of various diseases in Asian countries. As part of our ongoing aim to identify biologically new metabolites from Korean edible mushrooms, we investigated the ethanol (EtOH) extract of the sclerotia of P. cocos by applying a comparative LC/MS- and bioassay-based analysis approach, since the EtOH extract reciprocally regulated adipocyte and osteoblast differentiation in mouse mesenchymal stem cells (MSCs). Bioassay-based analysis of the EtOH extract led to the successful isolation of two sterols, ergosterol peroxide (1) and 9,11-dehydroergosterol peroxide (2); three diterpenes, dehydroabietic acid (3), 7-oxocallitrisic acid, (4) and pimaric acid (5); and two triterpenes, dehydroeburicoic acid monoacetate (6) and eburicoic acid acetate (7) from the active hexane-soluble fraction. The isolated compounds (1–7) were examined for their effects on the regulation of MSC differentiation. The two sterols (1 and 2) were able to suppress MSC differentiation toward adipocytes. In contrast, the three diterpenes (3–5) showed activity to promote osteogenic differentiation of MSC. These findings demonstrate that the EtOH extract of P. cocos sclerotia is worth consideration as a new potential source of bioactive compounds effective in the treatment of osteoporosis in the elderly, since the extract contains sterols that inhibit adipogenic differentiation as well as diterpenes that promote osteogenic differentiation from MSCs.     

Casearin X,Its Degradation Product and Other Clerodane Diterpenes from Leaves of Casearia sylvestris: Evaluation of Cytotoxicity against Normal and Tumor Human Cells

An EtOH extract of the leaves of Casearia sylvestris afforded new clerodane diterpene, casearin X, together with the known compounds casearins B, D, L, and O, and caseargrewiin F. Casearin X degraded to the corresponding dialdehyde when stored in CDCl₃. The diterpenes isolated were cytotoxic to human cancer cell lines, with caseargrewiin F being the most active and the new clerodane, casearin X, the second active compound with IC₅₀ values comparable to the positive control doxorubicin. All isolated diterpenes showed lower activities against normal human cells than against cancer cell lines, which might indicate a possible selective action on cancer cells. Casearin X dialdehyde was not cytotoxic to cancer cells indicating that the occurrence of these CO groups at C(18) and C(19) is incompatible with the cytotoxic activity.     

Cytotoxic ent-abietane diterpenes from Gelonium aequoreum

Seventeen ent-abietane diterpenes, including gelomulides K-X (1-14), and three known compounds, were isolated from a dichloromethane-soluble extract of Gelonium aequoreum through bioassay-guided fractionation. Their structures were identified by spectroscopic methods, and stereochemistry was confirmed by X-ray crystallographic analysis, CD spectral data, and Mosher's method. The isolates were evaluated for in vitro cytotoxic activity, and compounds 1 and 3 showed moderate cytotoxicity against lung (A549), breast (MDA-MB-231 and MCF7), and liver (HepG2) cancer cell lines.     

Abietane Diterpenes from Hyptis suaveolens

Investigation of the constituents of the whole plant of Hyptis suaveolens led to the isolation of three new abietane diterpenes, isosuaveolic acid ( 1 ), 8α,9α‐epoxysuaveolic acid ( 2 ), and 14‐O‐methylsuaveolic acid ( 3 ), together with eleven known compounds. The structures of 1 – 3 were established by spectroscopic methods and chemical correlations. Some isolates were tested for their antimycobacterial and cytotoxic activities.     

Novel diterpenoids with potent inhibitory activity against endothelium cell HMEC and cytotoxic activities from a well-known TCM plant Daphne genkwa

Twelve highly oxygenated novel daphnane-type diterpenoids genkwanines A-L (1-12), together with four known diterpenes (13-16), were isolated from the bud of Daphne genkwa, a well-known traditional Chinese medicine (TCM). The new structures were elucidated on the basis of spectral methods, especially 2D NMR spectra (HMQC, HMBC, NOESY). Inhibitory activity against endothelium cell HMEC proliferation and cytotoxic activities against two tumor cell lines were assessed for all the compounds 1-16, and found to be significant and structure related. A number of compounds showed very potent cytotoxic activities against two tumor cell lines at the IC50 levels of 0.15-8.40 microM, and most interestingly, five of the compounds 4, 8, 10, 13, and 14 exhibited strong activity to inhibit the endothelium cell HMEC at the IC50 levels of 2.90-15.0 microM.     

Norlathyrane Diterpenes from the Root of Euphorbia kansuensis

Phytochemical investigation of the EtOH extract obtained from the root of the Euphorbia kansuensis Proch . grown in China resulted in the isolation of two novel norlathyrane diterpenes, named ekanpenoids A and B ( 1 and 2 , resp.). Their structures were established by extensive 1D‐ and 2D‐NMR spectroscopy, as well as other spectra. The isolated diterpenes exhibited potent cytotoxic activities against the HeLa and Hep‐G2 cell lines with the IC₅₀ values ranging from 3.6 to 9.7 μg/ml.     

Multidrug resistant cancer cells susceptibility to cytotoxic taxane diterpenes from Taxus yunnanensis and Taxus chinensis

Twelve taxane diterpenes (1-12), which were isolated previously from the EtOH extract of the aerial parts of Taxus yunnanensis or Taxus chinensis, were evaluated for cytotoxicity against the multidrug resistant cancer cells KB-VIN and KB-7d. Compounds and showed significant cytotoxicity in these cell lines. Compounds and also demonstrated significant activity against KB-7d. The biflavonoid isolated from T. yunnanensis was only marginally cytotoxic against the A549 (lung) cell line, but a simple methoxylated analogue (14) was inactive.     

Synthesis of 1-O-monoacyl or 12-O-monoacyl, 1-,12-O-diacyl-, and 11,12-dehydrated excisanin A 7,14-acetonides and their cytotoxic activity

1-O-Monoacyl, 12-O-monoacyl, 1-,12-O-diacyl, and 11,12-dehydrated excisanin A 7,14-acetonides were synthesized from excisanin A isolated from Rabdosia excisa. The structure and cytotoxic activity relationships (SAR) of the natural parent ent-kaurene diterpenes and these semisynthetic analogues were studied by using P388 murine leukemia cells.     

The cytotoxic norditerpene dilactones of Podocarpus milanjianus and Podocarpus sellowii

The cytotoxic norditerpene dilactones nagilactone F and its new congener nagilactone G have been isolated from the bark constituents of Podocarpus milanjianus and Podocarpus sellowii. The diterpenes totarol, 19-oxototarol and macrophyllic acid were also isolated.     

Diterpenes from the bark and seeds of Colophospermum mopane

The CHCl3 extract of the bark and seeds of Colophospermum mopane gave three new diterpenes, dihydrogrindelic acid and dihydrogrindelaldehyde and methyl labd-13E-en-15-oate. The structures were assigned on the basis of detailed spectroscopic data analyses. The aldehyde showed significant cytotoxic activity against a human breast cancer cell line.     

Synthesis and cytotoxic activity of novel C7-functionalized spongiane diterpenes

Based on two lead cytotoxic spongiane diterpenes, a new series of C7-oxygenated derivatives were synthesized and evaluated for their antitumor activity in vitro against the cancer cell lines HeLa and HEp-2. In general, introduction of either hydroxyl or acetoxy groups at C-7 did not improve the resultant cytotoxicity, while the presence of a butyrate ester led to more active compounds (CC(50)=4.0-9.5 microM).     

In vitro cytotoxicity of Tanshinones isolated from Salvia miltiorrhiza Bunge against P388 lymphocytic leukemia cells

The cytotoxic effect of four tanshinones isolated from the dried root of Salvia miltiorrhiza Bunge (Lamiaceae) were studied in vitro using P388 lymphocytic leukemia cells. Tanshinone I and tanshinone IIA were shown to be quite strongly cytotoxic against the cells (86.76% and 56.05% cell inhibition at 25 microg/ml). Dihydrotanshinone I and cryptotanshinone, which lack of saturation at C-15, showed little cytotoxicity (13.71% and 39.21% cell inhibition at 25 microg/ml). The results also revealed a structure activity relationship. We suggest that the unsaturation at C-15 and saturation on ring A may be critical structural components for cytotoxicity in these diterpenes.