Total Synthesis of Callipeltin B and M, Peptidyl Marine Natural Products

Total synthesis of callipeltins B and M, peptidyl cytotoxic agents isolated from marine sponges, by the combination of Fmoc solid-phase peptide synthesis and cyclization and global deprotection in the solution phase is described. Eight amino acids, including several unusual amino acids, were assembled on a solid support, and effective TFA-mediated deprotection was employed to reach callipeltin M. Callipeltin B was accomplished via the macrolactonization between the side chain of D-aThr and the C-terminus carboxylic acid of protected callipeltin M.