Two Conformational Isomers of a Cyclopeptide from Annona squamosa

A novel cyclopeptide, squamin A(cyclo l -prolyl- l-(S -oxo)-methionyl- l -tyrosyl- l -glycyl- l -threonyl- l -valyl- l -alanyl- l -alanyl- l -isoleucyl was isolated from \%Annona squamosa\%. Another cyclopeptide, squamin B, a conformat