Michel F. Tala

Antimicrobial activities of methanol extract and compounds from stem bark of Vismia rubescens

ETHNOPHARMACOLOGICAL RELEVANCE The plant, Vismia rubescens (Guttiferae) is popularly used in Cameroon and in several parts of Africa as febrifugal and for the treatment of various microbial infections (skin diseases, diarrhoea and venereal diseases). AIM OF THE STUDY This study was mapped out to evaluate the antimicrobial activities of the methanol extract and compounds from the stem bark of Vismia rubescens. MATERIALS AND METHODS Structures of the compounds obtained after column chromatography of the methanol-soluble fraction were determined by spectroscopy and in comparison with published data. The broth micro-dilution method was used to evaluate the antimicrobial activities against three bacteria species (Salmonella typhi, Staphylococcus aureus and Pseudomonas aeruginosa) and four yeast species (Candida albicans, Candida tropicalis, Candida parapsilosis and Cryptococcus neoformans). RESULTS Chemical analysis of the methanol extract from the stem bark of Vismia rubescens yielded five known compounds 1,4,8-trihydroxyxanthone (1), 1,7-dihydroxyxanthone (2), physcion (3), friedelin (4) and friedelanol (5). The crude extract and compounds 1, 2 and 3 exhibited both antibacterial and antifungal activities that varied between the microbial species (MIC=3.12-1000 microg/ml). Compounds 2 and 3 were the most active (MIC=3.12-100 microg/ml) while Staphylococcus aureus and Pseudomonas aeruginosa were sensitive to all the tested compounds. The antimicrobial activity of this plant as well as that of compounds 1 and 2 is being reported here for the first time. CONCLUSION These results provide promising baseline information for the potential use of this plant as well as some of the isolated compounds in the treatment of skin diseases and diarrhoea.

Laurentixanthone C: A New Antifungal and Algicidal Xanthone from Stem Bark of Vismia laurentii

Laurentixanthone C (1), a new xanthone, was isolated from the stem bark of Vismia laurentii (Guttiferae or Clusiaceae), in addition to the known compounds vismiaquinone (2), bisvismiaquinone (3), and dammaradienol (4). The structures were established based on spectroscopic studies, notably of the 2D NMR spectra. Preliminary results showed that 1 is algicidal and strongly antibacterial against the Gram-positive bacteria Bacillus megaterium and Chlorella fusca, respectively.

A new furan carboxamide and two potential precursors from a terrestrial streptomycete

Abstract Three new bioactive metabolites, 1,6-dihydroxy- 2-methyl-heptan-4-one (1), 4-hydroxy-1-(2-methyl-oxiranyl)- pentan-2-one (2), and 2-(2-hydroxy-propyl)-4-methylfuran- 3-carboxylic acid amide (3) were isolated from the terrestrial Streptomyces sp. isolate ANK245, along with the new microbial constituent p-vinylanisol (4a) and the known metabolites p-vinyl-phenol (4b) and phenethyl alcohol. Analysis of the nonpolar part of the extract by gas chromatography/mass spectrometry (GC-MS) provided further evidence for tetradecanoic acid, 9-octadecenoic acid, hexadecanoic acid, 2-methoxy-4-vinylphenol (4c), 4-hydroxy-3-methoxy-benzaldehyde, o-hydroxybiphenyl, and 1,5,9-trimethyl-4,8,13-cyclotetradecatrien-1,3-diol (5). Structures 1–3 of the new compounds were elucidated by nuclear magnetic resonance (NMR) and NMR spectroscopy, but mass spectrometry (MS) techniques and their absolute configuration were determined by density functional theory (DFT) calculations and Mosher derivatisation. Their antimicrobial and cytotoxic activities were evaluated in comparison with the crude bacterial extract.

Conocarpol, a new cycloartane triterpenoid from Diospyros conocarpa

Abstract A new cycloartane triterpenoid named conocarpol (1) was isolated from the stem bark of Diospyros conocarpa, together with the known compounds aridanin (2), lupeol (3), betulin (4), betulinic acid (5), stigmasterol (6), and stigmasterol 3-O-β-d-glucopyranoside (7). Their structures were established on the basis of 1D and 2D NMR spectroscopy as well as mass spectrometry. Aridanin (2) is reported for the first time in the family Ebenaceae, and conocarpol (1) represents the first cycloartane triterpene within this family.

Longiflorol, a bergenin α-d-apioside from the stem bark of Diospyros longiflora, and its antioxidant activity

Abstract Phytochemical investigation of the stem bark of Diospyros longiflora yielded longiflorol (1), a new bergenin α-d-apioside, together with bergenin (2) and five known compounds: lupeol (S1), betulin (S2), betulinic acid (S3), stigmasterol (S4) and stigmasterol glucoside (S5). Their structures were determined by one-dimensional (1D) and 2D nuclear magnetic resonance experiments along with electrospray ionization high-resolution mass spectrometry and extended density-functional theory calculations of chiroptical properties. Longiflorol (1) and bergenin (2) were evaluated for their DPPH (2,2-diphenyl-1-picrylhydrazyl) antioxidant activity, with the crude extract for comparison and ascorbic acid as standard. The results showed that the extract and 2 had good antioxidant activity, whereas 1 showed only moderate activity at high concentration (>2 mg mL−1).