Four cyclic peptides, diandrine A-D (1-4), were isolated from the MeOH extract of Formosan Drymaria diandra. Their structures were elucidated by chemical and spectroscopic analyses as cyclo(-Gly(1)-Pro(2)-Trp(3)-Pro(4)-Tyr(5)-Phe(6)-), cyclo(-Gly(1)-Pro(2)-Leu(3)-Pro(4)-Leu(5)-Trp(6)-Ser(7)-Ser(8)-) cyclo(Gly(1)-Gly(2)-Pro(3)-Tyt(4)-Trp(5)-Pro(6)-), and cyclo(Gly(1)-Gly(2)-Pro(3)-Tyr(4)-Trp(5)-Pro(6)-), respectively. Compounds 3 and 4 were stable conformational isomers. Cyclopeptide 1 showed a selective inhibitory effect on collagen-induced platelet aggregation with an IC50 value of 44.2 lot.
