A cytotoxic sesquiterpene and unprecedented sesquiterpene-bisbibenzyl compounds from the liverwort Schistochila glaucescens

Extracts of the New Zealand liverwort Schistochila glaucescens were cytotoxic. Bioactivity-directed isolation led to the new sesquiterpene lactone glaucescenolide as the main cytotoxic component with an IC50 of 2.3 μg/ml against P388 leukaemia cells. Also isolated were three known bisbibenzyls, neomarchantins A and B and marchantin C , which were also cytotoxic (P388 IC50s 8–18 μg/ml). Two new compounds GBB A and B are the first examples of a bisbibenzyl connected to a sesquiterpene moiety. A biosynthetic route to , and , via a shared intermediate, furanosesquiterpene , is proposed.