Trypanocidal labdane diterpenoids from the seeds of Aframomum aulacocarpos (Zingiberaceae)

New Labdanes with Antimicrobial and Acaricidal Activity: Terpenes of Callitris and Widdringtonia (Cupressaceae)

In spite of the evidence for antimicrobial and acaricidal effects in ethnobotanical reports of Callitris and Widdringtonia, the diterpene acids from Widdringtonia have never been described and no comparison to the Australian clade sister genus Callitris has been made. The critically endangered South African Clanwilliam cedar, Widdringtonia wallichii (syn. W. cedarbergensis), of the Cederberg Mountains was once prized for its enduring fragrant timbers and an essential oil that gives an aroma comparable to better known Mediterranean cedars, predominantly comprised by widdrol, cedrol, and thujopsene. In South Africa, two other ‘cedars’ are known, which are called W. nodiflora and W. schwarzii, but, until now, their chemical similarity to W. wallichii has not been investigated. Much like Widdringtonia, Callitris was once prized for its termite resistant timbers and an ‘earthy’ essential oil, but predominantly guaiol. The current study demonstrates that the essential oils were similar across all three species of Widdringtonia and two known non-volatile diterpene acids were identified in leaves: the pimaradiene sandaracopimaric acid (1) and the labdane Z-communic acid (2) with a lower yield of the E-isomer (3). Additionally, in the leaves of the three species, the structures of five new antimicrobial labdanes were assigned: 12-hydroxy-8R,17-epoxy-isocommunic acid (4), 8S-formyl-isocommunic acid (5), 8R,17-epoxy-isocommunic acid (6), 8R-17R-epoxy-E-communic acid (7), and 8R-17-epoxy-E-communic acid (8). Australian Callitris columellaris (syn. C. glaucophylla) also produced 1 and its isomer isopimaric acid, pisiferal (9), and pisiferic acid (10) from its leaves. Callitris endlicheri (Parl.) F.M.Bailey yielded isoozic acid (11) as the only major diterpene. Diterpenes 4–6, pisiferic acid (10), spathulenol, and guaiol (12) demonstrated antimicrobial and acaricidal activity.

Previously undescribed fridooleanenes and oxygenated labdanes from the brown seaweed Sargassum wightii and their protein tyrosine phosphatase-1B inhibitory activity

Previously undescribed fridooleanene triterpenoids 2α-hydroxy-(28,29)-frido-olean-12(13), 21(22)-dien-20-propyl-21-hex-4'(Z)-enoate, 2α-hydroxy-(28,29)-frido-olean-12(13), 21(22)-dien-20-prop-2(E)-en-21-butanoate and oxygenated labdane diterpenoids 2α-hydroxy-8(17), (12E), 14-labdatriene, 3β, 6β, 13α-tri hydroxy 8(17), 12E, 14-labdatriene were purified from the ethyl acetate-methanol and dichloromethane fractions of the air-dried thalli of Sargassum wightii (Sargassaceae), a brown seaweed collected from the Gulf-of-Mannar of Penninsular India. Inhibitory potential of Δ12 oleanenes towards protein tyrosine phosphatase-1B, the critical regulator of insulin-receptor activity were found to be significantly greater (IC50 0.1 × 10-2 and 0.09 × 10-2 mg/mL, respectively) than the standard sodium metavanadate (IC50 0.31 × 10-2 mg/mL). Fridooleanene triterpenoids displayed greater antioxidant activities (IC50DPPH 0.16-0.18 mg/mL) than the commercially available antioxidants, butylated hydroxytoluene and α-tocopherol (IC50DPPH 0.25 and 0.63 mg/mL, respectively). In general, the oxygenated labdane diterpenoids displayed significantly lesser antioxidant and tyrosine phosphatase-1B inhibitory properties than those exhibited by the fridooleanenes. Bioactivities of the titled compounds were primarily determined by the electronic and lipophilic parameters and not by the steric descriptors. Molecular docking simulations and kinetic studies were employed to describe the tyrosine phosphatase-1B inhibitory mechanism. The previously undescribed fridooleanene triterpenoids might be used as potential anti-hyperglycaemic pharmacophore leads to reduce the risk of elevated postprandial glucose levels.

A New Labdane Diterpene from Rauvolfia Tetraphylla Linn. (Apocynaceae)

The air-dried stems and branches of Rauvolfia tetraphylla afforded a new labdane diterpene characterised as 3β-hydroxy-labda-8(17),13(14)-dien-12(15)-olide on the basis of spectroscopic studies including UV, IR, MS and NMR (1H, 13C and HMQC); this is the first report of a new terpenoid constituent from R. tetraphylla, an important medicinal plant widely known for the source of a variety of alkaloids.

Phenol esters and other constituents from the stem barks of Stereospermum acuminatissimum

A new ester, 2-(4'-hydroxyphenyl)ethyl dotriacontanoate (1), and a new inseparable mixture of octacosan-1,28-dioldiferulate and triacontan-1,30-dioldiferulate (2) were isolated from the stem barks of Stereospermum acuminatissimum, along with 24 known compounds including 4 triterpenoids, 11 anthraquinones, 2 lignans, 3 phenylpropanoids, 2 4-hydroxyphenethyl esters, 1 methoxyphenol, and 1 iridoid. The structures of the new metabolites were determined with the help of spectroscopic data including extensive 2D NMR spectroscopy. The known compounds were identified by comparison of their physical and spectroscopic data with those reported in the literature. The compounds were tested against Candida albicans ATCC 24433, C. albicans ATCC 90028, Candida glabrata ATCC 90030, Candida krusei ATCC 6258, and Candida parapsilosis ATCC 22019. Some of them were moderately active.