ent-12-Oxolabda-8,13(16)-dien-15-oic acid and ent-8β,12α-epidioxy-12β-hydroxylabda-9(11),13-dien-15-oic acid γ-lactone: two new diterpenes from the aerial parts of Premna oligotricha.

Two novel ent-labdane diterpenes have been isolated from the aerial parts of Premna oligotricha(Verbenaceae). Primarily through NMR studies one was identified as ent-12-oxolabda-8,3(16)dien-15-oic acid. Similar analysis of the second diterpene was unable to distinguish between two possible structures, ent-8β,12α-epidioxy-12β-hydroxylabda-9(11),13-dien-15-oic acid γ-lactone and ent-8β,12α-epoxy-12β-hydroperoxylabda-9(11),13-dien-15-oic acid δ-lactone. The structure of the second diterpene was established as the γ-lactone by an X-ray diffraction study