New labdane-type diterpenoids from Croton oblongifolius and their cytotoxic activity

Abstract

Eight new labdane-type diterpenoids (1-3) and (5-9) and hardwickiic acid(4), a clerodane, were isolated from the stem bark of Croton oblongifolius. Their structures were established to be 3-oxygenated ent-manoyl oxide derivatives with a 8,13-epoxytricyclic ring system and hydroxylabdandienes on the basis of spectroscopic and X-Ray crystallographic analysis. The absolute stereochemistry of the core labdane skeleton was deduced to be (5S,8S,9S,10R,13S) from the X-Ray crystallographic analysis of the p-bromobenzoate of ent-3α-hydroxymanoyl oxide (3) and mutual chemical correlation. Cytotoxicity of these compounds was tested against a panel of human tumor cell lines. © 2005 The Japan Institute of Heterocyclic Chemistry.