Cytotoxic nor-chamigrane and chamigrane endoperoxides from a basidiomycetous fungus.

A new nor-chamigrane endoperoxide, merulin A (1), and two new chamigrane endoperoxides, merulins B and C (2, 3), were isolated from the culture broth extract of an endophytic fungus of Xylocarpus granatum. Their structures were elucidated on the basis of spectroscopic, mainly NMR and MS, data. X-ray crystallographic analysis confirmed the structure of 1. Compounds 1 and 3 displayed significant cytotoxicity against human breast (BT474) and colon (SW620) cancer cell lines.