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Abstract
Nineteen compounds isolated from Calophyllum inophyllum, C. inophylloide, Garcinia opaca and G. bancana (Family: Guttiferae) were investigated for their platelet-activating factor (PAF) receptor binding inhibitory effects using rabbit platelets. Among them, five xanthones and a biflavonoid exhibited significant inhibitory effects. The compounds, 6-deoxyjacareubin, 2-(methylbut-2-enyl)-1,3,5-trihydoxyxanthone and 2-(3-methylbut-2-enyl)-1,3,5,6-tetrahydroxyxanthone isolated from C. inophyllum inhibited 3 H-PAF binding to rabbit platelets with IC 50 values of 4.8, 29.0 and 44.0 µM, respectively. The IC 50 values of macluraxanthone and 1,3,5-trihydroxy-6,6' dimethylpyrano(2',3':6,7)-4-(1,1-dimethylprop-2-enyl)xanthone from G. opaca were 11.0 and 21.0 µM, respectively, and amentoflavone from C. inophylloide exhibited a IC 50 value of 8.3 µM.