Abietanes and a novel 20-norabietanoid from Plectranthus cyaneus (Lamiaceae)

Antioxidative-activity-guided fractionation of extracts of the aerial parts of the title plant yielded the two novel abietanoid diterpenoids 11,20-dihydroxysugiol (= 11,12,20-trihydroxyabieta-8,11,13-trien-7-one; 3) and 1,11-epoxy-6,12-dihydroxy-20-norabieta-1(10),5,8,11,13-pentaen-7-one (4) in addition to 11-hydroxysugiol (= 12-O-demethylcryptojaponol = 11,12-dihydroxyabieta-8,11,13-trien-7-one; 2) and the main constituent carnosolon (= 6,20-epoxy-6,11,12-trihydroxyabieta-8,11,13-trien-7-one; 1). The structures were established on the basis of spectroscopic, chiroptic, and X-ray crystallographic evidence.