Cytotoxic clerodane diterpenes from Glossocarya calcicola

Three clerodane diterpenes were isolated and identified from leaf extract of Glossocarya calcicola. Compound 1 has been 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, to which we have assigned the trivial name calcicolin-A. The other two compounds had the same skeletal structure and C-12 substituent but in compound 2, the C-1 esterifying group becomes 2-methylbut-2(E)-enoic acid and in 3 it becomes 2-methylbutanoic acid. Although anti-insect activity was not observed for G. calcicola, cytotoxicity against insect and human carcinoma cell lines was detected.