Cytotoxic cassane diterpenoids from the seeds of Caesalpinia sappan

Five new cassane-type diterpenoids, named 11-oxophanginin A (1), caesalsappanins O-Q (2-4) and phanginin U (5), were isolated from the seeds of Caesalpinia sappan. Compound 4 is the first example of cassane-type diterpenoid with a 19,20-epoxide linkage and a methoxy group at C-16.