Studies on the Novel Diterpenoids of the Formosan Soft Coral Cespitularia sp.

by Lin, Jyun-jhou

Five new compounds were isolated from the soft coral Cespitularia sp.collected in Green Island, Taiwan. They are G8-7-7-A (1), G8-9-15-30-A(2), G8-10-B (3), G8-7-6-A (4) and G8-7-5-A (5). All of them belong to diterpenes with three methyl groups at C-16, C-17 and C-18, and an exocyclic double bond between C-4 and C-18. Compounds 1 and 2 are bicycle norditerpenes. G8-7-7-A (1) possesses a 6/13 ring and has an endocyclic double bond between C-7 and C-8. It also contains a hydroxyl group at C-6, a ketone group at C-12 and a lactone ring between C-10 and C-11. G8-9-15-30-A (2) is different from 1 at the lactone ring position. The lactone ring of 2 is between C-10 and C-12, and the ketone group is at C-11. So compound 2 possesses a 6/14 bicyclic ring system. Compounds 3-5 are cespitularin diterpenes, which belong to a 5/6/12 tricyclic ring. They all have an endocyclic double bond between C-7 and C-8. G8-10-B (3) contains an £\-hydroxy-£],£^-epoxy-£_-acetoxy furan and a hydroxyl group at C-6. The only difference between compounds 3 and 4 are substiuents at C-20. The C-20 position of 4 is an acrylic group, while compound 3 has an acetoxyl group at C-20. G8-7-5-A (5) contains an £^-hydroxy-£\,£]-unsaturated-£^-lactone function and a ketone group at C-6. Their structures were elucidated by mass, IR, 1D and 2D NMR spectroscopic analysis.