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Six coumarin derivatives [three 4-phenylcoumarins (Mammea A/AA, Mammea A/BA and MAB 3), two 4-n-propylcoumarins (Mammea B/BB and Mammea B/BA) and one 4-n-pentylcoumarin (Mammea C/OB)], 1,5-dihydroxyxanthone and 1-methoxy-5-hydroxyxanthone have been isolated from the stem bark of Mammea africana Sabine collected in Cameroon. Although known, the structures of the coumarin derivatives were confirmed by spectral analysis, including two-dimensional nuclear magnetic resonance. All the coumarin compounds showed noteworthy cytotoxicity against the human 9-KB cell line. Both of the 4-n-propylcoumarins were also found to exhibit significant activity against Staphylococcus aureus.

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There has been a recent increase in the research efforts on secondary metabolites of the genus Allanblackia.1-3) Our interest was stimulated by the fact that, many of the secondary metabolites from this genus such as xanthones, biflavonoids, benzophenones and pentacyclic triterpenes exhibited a wide range of biological and pharmacological activities, including cytotoxic, anti-inflammatory, antimicrobial, antifungal and HIV inhibitory activities.2,4,5) Allanblackia monticola STANER L.C., which belongs to the plant family Clusiaceae, is a large forest tree found throughout the west and south province of Cameroon, where it is used as medicinal plant to treat several diseases including, respiratory infections, diarrhoea and toothache. 6) In a previous paper, we have reported the isolation and structural elucidation of a novel polyisoprenylated xanthone, allanxanthone B, along with the known compounds: tovophyllin A, rubraxanthone, garciniafuran, lupeol and stigmasterol from the CH 2 Cl 2 -MeOH (1 : 1) extract of the stem bark of this plant. 7) In the present paper, we report the isolation and characterization of seven compounds isolated from the MeOH extract of this plant, including a new triprenylated xanthenedione, designated allanxanthone C (1), together with the known compounds norcowanin (2), 8) mangostin (3), 9) tovophyllin A (5), 10) garciniafuran (6), 11) rubraxanthone (7) 12) and stigmasterol-3-O-b-D-glucopyranoside (4).13) The structure of known compounds were identified from their spectral data and confirmed by comparison with those published in the literature. We also report on the antiplasmodial, cytotoxic and antimicrobial activities of the methanol extract and some isolated compounds.Extensive column chromatography of a methanol extract of the stem bark of A. monticola led to the isolation allanxanthone C (1).Allanxanthone C (1) was obtained as a sticky yellow oil. It reacts positively to ferric chloride test, suggesting the presence of a phenolic groups. Its molecular formula, C 28 H 32 O 6 , was deduced from the high resolution Electro Spray Ionisation-Time of Flight (ESI-TOF) mass spectrometry which showed the pseudomolecular ion [MϩH] ϩ at m/z 465.5545 (Calcd for 465.5580). The IR spectrum of 1 confirmed the presence of phenolic group (3350 cm Ϫ1 ) and suggested the presence of conjugated carbonyl group (1674 cm Ϫ1) and xanthone carbonyl group (1643 cm Ϫ1).14) The 1 H-NMR and Heteronuclear Single Quantum Coherence (HSQC) spectra of allanxanthone C (1) showed the presence of a hydrogenbonded hydroxyl at d 13.50 (1H, s, 8-OH) and two singlet protons at d 6.55 (1H, s, H-4) and d 6.45 (1H, s, H-5), d 109.5 (d, C-4) and 93.5 (d, C-5). The presence of a set of signals at d 4.74 (2H, t, Jϭ7.6 Hz, H-2Љ), 3.43 (2H, dd, Jϭ7.60, 13.6 Hz, H-1Љ), 2.73 (2H, dd, Jϭ7.6, 13.6 Hz, H-1Љ) and 1.47 (12H, s) was typical of a gem bis(3-methylbut-2-enyl) groups linked to a sp 3 carbon atom (d 56.9, C-1). Further study of the methanol extract of the stem bark of Allanblackia monticola STANER L.C. resulted in the isolati...

Tubastarea sp., a stony coral (Dendrophylliidae) from the Great Hanish in the Archipelago of the Hanish Islands, Yemen, contains, in addition to the known aplysinopsin (1) and 6-bromo-3'-deimino-3'-oxoaplysinopsin (2), the new bis(indole) alkaloid (3). The structures of compounds (1-3) were elucidated by interpretation of spectral data. Compound 3 inhibits the growth of Plasmodium falciparum (chloroquine-resistant strain) with an IC(50) 1.2 microg mL(-1).

Bioassay-guided fractionation of a root bark extract of Symphonia globulifera has yielded, in addition to stigmasterol, two new xanthones with isoprenoid units, named globulixanthones A (1) and B (2). The structures of these compounds have been elucidated by spectroscopic means. They possess significant cytotoxicity in vitro against the KB cell line.

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