ORGN 448

Two didemnin binding proteins have been isolated by affinity chromatography using an affinity ligand attached to the didemnin A side chain. This modification on a side chain that makes a substantial contribution to the biological activity may have eliminated molecular targets that did not recognize the immobilized didemnin derivative.

In order to search for other receptor proteins, a simple ascidian metabolite, tamandarin B, is being functionalized with a nucleophilic site for derivatization remote from the critical side chain. The synthetic approach to [Lys³]tamandarin B will be presented.