The total synthesis and structure-activity relationships of a highly cytotoxic depsipeptide kulokekahilide-2 and its analogs

We successfully completed the total synthesis of kulokekahilide-2, a cytotoxic depsipeptide from the Cephalaspiedean mollusk Phillinopsis speciosa. We have revised the absolute stereochemistry of kulokekahilide-2 to 21-L-Ala, 24-D-MePhe, 37-L-Ile, 43-D-Ala, 15-D-Hica, and 5S,6S,7S-Dtda. We also investigated the cause of the mis-assignment of the configuration in the originally proposed kulokekahilide-2 and concluded that methanolysis using MeONa caused partial racemization, which led to the mis-assignment. The structure activity relationships of kulokekahilide-2 and its analogs indicate the importance of an L-amino acid at position 21. (C) 2011 Elsevier Ltd. All rights reserved.