David Ngnokam

Geranylated flavonoids from Dorstenia poinsettifolia

Abstract Two new geranylated flavonoids, poinsettifolins A and B, were isolated from the extracts of the herb Dorstenia poinsettifolia , and the structures were determined with NMR spectroscopy and mass spectrometry. In addition, the flavone 5,7,4-trihydroxy-8-prenylflavone (licoflavone C), the chalcones 4,2′,4′-trihydroxy-3′-prenylchalcone (isobavachalcone) and isobavachromene, the triterpene butyrospermol, and the carotenoid lutein were isolated.

Diterpenoids from Neoboutonia glabrescens (Euphorbiaceae).

Glabrescin, a daphnane diterpenoid, neoboutonin, a degraded diterpenoid with a novel skeleton, and neoglabrescins A and B, two rhamnofolane derivatives, have been isolated from the stem bark of Neoboutonia glabrescens Prain (Euphorbiaceae), together with the known tigliane derivative, baliospermin, and the known daphnane, montanin. Other constituents include squalene, 3-acetylaleuritolic acid, oleanolic acid and sitosterol, and the phenolic compounds 9-methoxy-1,7-dimethylphenanthrene and 2,3,8-tri-O-methylellagic acid. The structures were assigned on the basis of spectral studies and comparison with published literature data. The structures of neoglabrescins A and B were derived for their acetylated derivatives and, in the case of neoglabrescin A, confirmed by X-ray crystallographic analysis.

Cycloartane glycosides from leaves of Oxyanthus pallidus.

From the MeOH extract of leaves of Oxyanthus pallidus, three cycloartane glycosides, named pallidiosides A-C, were isolated together with two known compounds, oleanolic acid and 3-O-β-D-glucopyranosyl-β-sitosterol. The structures of pallidiosides A-C were assigned on the basis of spectral studies and comparison with published literature data. The known compounds were identified by means of Co TLC and confirmed by their physical constants.

Leptocarposide: a new triterpenoid glycoside from Ludwigia leptocarpa (Onagraceae).

A new triterpenoid bidesmoside (leptocarposide) possessing an acyl group in their glycosidic moiety (1), together with the known luteolin‐8‐C‐glucoside (2) and 1‐O‐β‐d‐glucopyranosyl‐(2S,3R,8E)‐2‐[(2′R)‐2‐hydroxypalmitoylamino]‐8‐octadecen‐1,3‐diol (3) was isolated from the n‐butanol‐soluble fraction of whole plant of Ludwigia leptocarpa (Nutt) Hara (Onagraceae). Structure of compound 1 has been assigned on the basis of spectroscopic data (1H and 13C NMR, 1H‐1H COSY, HSQC, HMBC, and ROESY), mass spectrometry, and by comparison with the literature. This compound was further screened for its potential antioxidant properties by using the radical scavenging assay model 2,2‐diphenyl‐1‐picrylhydrazyl and reveals non‐potent antioxidant activities, while compound 2 shows SC50 of 0,038 mM. Copyright

Evaluation of plant extracts for tomato late blight control in Cameroon

Abstract Late blight caused by Phytophthora infestans is the most important disease of tomato in Cameroon. Three experiments are conducted to assess the fungitoxicity of methylene chloride/methanol leaf extracts of seven plants on P. infestans development. The extracts (3%) are evaluated for sporangial germination inhibition, latent and incubation periods, lesion size and late blight severity on tomato plants. Inoculated leaflets and plants are incubated in the greenhouse at 21°C during the day and 18°C during the night, with a 12 h photoperiod and for 7 days. Sporangial germination is significantly inhibited by Tephrosia vogelli and Entandrophragma angolense extracts, while disease progression is highly limited by Ageratum houstonianum, Tephrosia vogelli, Clausena anisata and Entandrophragma angolense extracts. The fungitoxic effects of some of the extracts is comparable to synthetic fungicides, metalaxyl and maneb, used as positive controls, indicating their potential as components of an integrated pathogen management programme for tomato late blight. Eucalyptus saligna, Deinbollia saligna and Garcinia smeathmannii extracts have low efficiency.

New friedelane triterpenes from Lepidobotrys staudtii

Abstract Three new dihydroxy-3-friedelanone triterpenes were isolated from the leaves and the stem bark of the Cameroonian medicinal plat Lepidobotrys staudtii. Structure elucidation by spectroscopic techniques showed that they are 2α,29-dihydroxy-3-friedelanone (1a), 2β,21α-dihydroxy-3-friedelanone (2a) and 6β,21α-dihydroxy-3-friedelanone (3). In addition, the known monohydroxy-3-friedelanones 4, 5, 6 and 7 were obtained.

Owariensisone: a new iridolactone from the whole plant of Brillantaisia owariensis P. Beauv

Abstract From the whole plant of Brillantaisia owariensis P. Beauv, a new iridolactone, owariensisone (1) together with six known compounds (nepetin-7-O-glucoside, choline, sucrose, mannitol, xylitol, 1-O-palmitoyl-2-eicosanoyl-3-O-(6-amino-6-deoxy)-β-d-glucopyranosyl-glycerol) were isolated. Structures of these compounds were established by direct interpretation of their spectral data, mainly HR-TOFESIMS, 1-D NMR (1H and 13C) and 2-D NMR (1H-1H COSY, HSQC, HMBC, NOESY, TOCSY and DOCSY) and by comparison with the literature.