Synthesis of sequential polydepsipeptides utilizing a new approach for the synthesis of depsipeptides

Sequential polydepsipeptides were synthesized by the depsipeptide active ester method using a new approach for the direct synthesis of N-protected depsipeptide free acids from hydroxy acids. The method uses synthesis of Boc-didepsipeptides by reaction of free hydroxy acids with Boc-amino acid N-hydroxysuccinimide esters catalyzed by 4-dimethylaminopyridine and chain elongation of the free depsipeptides by the reaction with Boc-amino acid N-hydroxysuccinimide esters in an organic solvent system of acetonitrile-tetrahydrofuran. The Boc-depsipeptide free acids were activated as their N-hydroxysuccinimide esters, which were polymerized after removal of the Boc-protecting group.