Nepetaefolinol and two related diterpenoids from Leonotis nepetaefolia

Abstract

Nepetaefolinol, a new diterpenoid from L. nepetaefolia, is identified as 9,13-epoxy-6β-hydroxy-8α-labdane-16,15:19,20-diolactone (1) on the basis of chemical and spectroscopic evidence. The related enone (5) undergoes a ring B aromatisation to give the phenol 7,13,15-trihydroxy-20-norlabda-5(10),6,8-triene-16,19-dioic acid 16,15-lactone 19-methyl ester (6) on treatment with mild base. Two new minor components of the extract are leonotinin [8β,17:15,16-diepoxy-9-hydroxylabda-13(16), 14-dien-19,6β-olactone](7) and 8β,17:9,13-diepoxylabdane-16,15:19,6β-diolactone (10).