Cytotoxic clerodane diterpenes from Glossocarya calcicola

Three novel compounds were isolated from Glossocarya calcicola Domin. Calcicolin-A (1), was characterised as (rel)-10βH-trans-12ξ-(2-methylbut-2(E)-enoyl)-1β-(isobutanoyl)-6α,13ξ-dihydroxyclerodan-4(20),8(18)-dien-7,15-dione-15,16-oxide. Calcicolin-B (2) and -C (3) possessed the same skeletal structure but differed in the C-1 esterifying group. In 2, the C-1 group becomes 2-methylbut-2(E)-enoic acid and in 3 it becomes 2-methylbutanoic acid. Compounds 2 and 3 showed greatest cytotoxic activities against insect and mammalian cell lines.