Six new diterpenoids from Suregada multiflora

Six new diterpenoids were isolated from a CH(2)Cl(2)-MeOH extract of the bark of Suregada multiflora. The structures were established on the basis of one- and two-dimensional NMR and other spectroscopic studies and chemical derivatizations. Two compounds, suregadolides C (1) and D (2), were identified as new diterpene lactones of two antipodal series, containing a cyclopropane ring bridging C-3 and C-4 of the basic abietane skeleton. Suremulide A (3) was found to be a new abietene diterpene lactone. Bannaringaolide A (4), a diterpene lactone, based on a novel carbon skeleton with a seven-membered ring, possibly formed by the rearrangement of the exocyclic C-17 in ring C of an ent-pimarane framework, has also been isolated. A kaurane triol, suremulol A (5), and a kaurane diol, suremulol B (6), were also identified as new metabolites.