New sesquiterpene dilactones from Mikania micrantha

Four new sesquiterpene dilactones, mikamicranolide (1), 11beta,13-dihydromikamicranolide (2), 3alpha-hydroxy-11beta,13-dihydrodeoxymikanolide (3), and 2beta,3beta-dihydroxy-11beta,13-dihydrodeoxymikanolide (4), were isolated from the whole plants of Mikania micrantha. Their structures were elucidated on the basis of spectroscopic analysis. Compounds 1 and 2 possess an unusual rearranged 12,8-germacranolide sesquiterpene skeleton.