Platelet-Activating Factor (PAF) Antagonistic Activity of a New Biflavonoid from Garcinia nervosa var. pubescens King

The methanol extract of the leaves of Garcinia nervosa var. pubescens King, which showed strong inhibitory effects on platelet-activating factor (PAF) receptor binding, was subjected to bioassay-guided isolation to obtain a new biflavonoid, II-3,I-5, II-5,II-7,I-4',II-4'-hexahydroxy-(I-3,II-8)-flavonylflavanonol together with two known flavonoids, 6-methyl-4'-methoxyflavone and acacetin. The structures of the compounds were elucidated by spectroscopic methods. The compounds were evaluated for their ability to inhibit PAF receptor binding to rabbit platelets using (3)H-PAF as a ligand. The biflavonoid and acacetin showed strong inhibition with IC(50) values of 28.0 and 20.4 µM, respectively. The results suggest that these compounds could be responsible for the strong PAF antagonistic activity of the plant.