Antifungal Xanthones from Calophyllum brasiliensis Heartwood

Abstract

The heartwood of the tropical tree Calophyllum brasiliensis is known to be highly resistant to fungi and termites. To determine whether resistance to wood-rotting fungi could be caused by bioactive secondary metabolites, a chemical and biological study was carried out. Hexane, acetone, methanol, and water extracts were prepared. The yield of the extracts ranged from 0.04% (hexane) to 4.81% (acetone). Methanol, acetone, and water extracts (5 mg/ml = 0.5%) inhibited the mycelial growth of the brown rot fungus Postia placenta by 83%, 59%, and 21%, respectively. Chromatographic separation of the acetone and methanol extracts afforded five prenylated xanthones: 6-desoxyjacareubin (I), 1,5-dihydroxy-2-(3,3-dimethylallyl)-3-methoxy-xanthone (II), jacareubin (III) and 1,3,5-trihydroxy-2-(3,3-dimethylallyl)-xanthone (IV) and 1,3,5,6-tetrahydroxy-2-(3,3-dimethylallyl)-xanthone (V). Xanthones III, IV, and especially V, were the most abundant constituents of both extracts and inhibited at 0.25 mg/ml the mycelial growth of P. placenta. Inhibitory activity ranged from 55.5% (V) to 68.8% (III and IV mixture). Acetylation of xanthones did not induce a sharp change in the extent of fungistasis compared with parent compounds. The above results suggest that C. brasiliensis xanthones actually play a defensive role against wood decay fungi.