Synthesis and Structure Reassessment of Psammopemmin A

We have isolated meridianins A, B, C, and E from the Antarctic tunicate Synoicum sp. In the process of verifying the structure of these compounds it was noted that the physical data reported for meridianins bore a striking resemblance to that of psammopemmins. The psammopemmins are alkaloids bearing similar structures to the meridianins, but reported from the Antarctic sponge Psammopemma sp. To verify the structure originally proposed for psammopemmin A, the compound was synthesized. By comparing the H-1 and C-13 NMR data of reported and synthetic psammopemmin A with that of meridianin A, we infer that the correct structure of psammopemmin A isolated from Psammopemma sp. is actually that of meridianin A.