Testudinariol A and B, two unusual triterpenoids from the skin and the mucus of the marine mollusc Pleurobrancus testudinarius

The skin of the Notaspidea mollusc Pleurobranchus testudinarius contains a very unusual triterpenoid, testudinariol-A (1), which is also the main liposoluble component of the defensive mucous secretion. The structure, and the absolute stereochemistry, of I has been assigned on the basis of extensive spectral and chemical studies. The structural work on a minor co-occurring metabolite, testudinariol-B (2), led to the epimer of 1 at C-10.