New labdane diterpenoids from the liverwort <i>Scapania undulata</i>

Scapanin A, a diterpenoid isolated from the liverwort Scapania undulata (L.) Dum., and originally named 'scapanin', is shown to be (11S,12Z)-8α,12-epoxy-5α,11-dihydroxylabda-12,14-dien-1-one (4). Nine other new ladbane derivatives, (19) (scapanin B), (24), (29), (35), and (39)–(43), and a novel rearranged labdane (44) (scapanin G) have also been isolated from S. undulata. The structures were elucidated on the basis of 1H and 13C n.m.r. studies, chemical transformations, and X-ray crystal-structure determinations of the diol (25) and 14,15-dihydroscapanin A (7). The absolute configurations of scapanin A (4) and the alcohol (41) were assigned from the c.d. spectra of their derivatives (14) and (45) respectively.