Antimicrobial and antileishmanial xanthones from the stem bark of Allanblackia gabonensis (Guttiferae).

The phytochemical study of stem bark of Allanblackia gabonensis has resulted in the isolation and characterisation of one new xanthone derivative, named allanxanthone D, together with 10 known compounds, including 6 xanthones derivatives, allanxanthone A, 1,5-dihydroxyxanthone, 1,7-dihydroxyxanthone and 1,3,6,7-tetrahydroxy-2-(3-methylbut-2-enyl)xanthone, forbexanthone, 6-deoxyisojacareubin, one polyisoprenylated benzophenone, guttiferone F, one flavanol, epicathechin, two phytosterols, beta-sitosterol and campesterol. The structures of these compounds were established on the basis of one- and two-dimensional NMR homo- and hetero-nuclear evidence. These compounds were evaluated for their activity against Leishmania amazonensis in vitro and antimicrobial activities against a range of Gram negative and Gram positive bacteria.

Antimicrobial activity of the methanolic extract and of the chemical constituents isolated from Newbouldia laevis.

The methanolic extract (NLB) and ten compounds isolated from the root bark of Newbouldia laevis Seem, namely chrysoeriol (1), newbouldiaquinone (2), 2-acetylfuro-1,4-naphthoquinone (3), 2-hydroxy-3-methoxy-9,10-dioxo-9,10-dihydroanthracene-1-carbaldehyde (4), lapachol (5), beta-sitosterol-3-O-beta-D-glucopyranoside (6), oleanolic acid (7), canthic acid (8) newbouldiamide (9) and 2-(4-hydroxyphenyl)-ethyltrioctanoate (10), were tested for in vitro antimicrobial activity. Twenty one microorganisms belonging to six Gram-positive and twelve Gram-negative bacterial species as well as three yeasts from Candida species were tested for their susceptibility to NLB and the pure isolated compounds based on the Agar Hole Diffusion test and the Liquid Dilution method. The Hole Diffusion assay indicated that NLB and compound 7 were active against all tested pathogens while other compounds showed selective activity with the antimicrobial spectra varying from 76% (compound 10) to 95 % (compound 6). Minimal inhibitory concentrations (MIC) also illustrated the important antimicrobial activity of NLB and of the isolated compounds. MIC values obtained varied from 9.76 to 312.50 microg/ml for NLB, and 0.038 to 9.76 microg/ml for pure compounds against most of the tested microorganisms. The antimicrobial activities of compounds 2, 4 and 9 are described here extensively for the first time. The results indicate a promising basis for the use of Newbouldia laevis and some of its active principles in the treatment of infectious diseases.