New cassane diterpenes from Caesalpinia bonduc (Fabaceae)

New cassane diterpenes, neocaesalpins A and B, were isolated from the seeds of Caesalpinia bonduc (Fabaceae) and their structures were deduced on the basis of the spectroscopic evidence. These compounds are characterized as having an alpha,beta-butenolide moiety whereas caesalpins, a group of diterpenes previously known from the same plant and related species, possess the furan ring. The possible biogenetic scheme for formation of an alpha,beta-butenolide was postulated as the furan ring undergoing peroxidation followed by isomerization to give rise to the hemiketal lactone.