Biol. Pharm. Bull. 29(1) 177—179 (2006)

clude some 500 species and are widespread in temperate and tropical climates. Phyllanthus species have attracted the attention of researchers for their hepatoprotective properties; an aqueous extract of Phyllanthus amarus was demonstrated to exert antihepatitis B virus effects to varying degrees. In 2003, various constituents isolated from Phyllanthus species were screened for anti-human hepatitis B virus in vitro. However, little or no attention has been paid to constituents isolated from Phyllanthus niruri L. for other biological studies, thus prompting us to isolate constituents that might have antiplatelet aggregatory effects, as previously detected in the crude extract of P. niruri. Furthermore, we isolated methyl brevifolincarboxylate (compound 1) as a constituent responsible for the antiplatelet aggregatory effects. Interestingly, 1 (Fig. 1) was also isolated from Phyllanthus urinaria L. and other Phyllanthus species, although no mention was made of its biological activities. Therefore, we investigated the vasorelaxant effects of 1 on rat aortic rings in connection with the receptor-operated Ca channel.