Synthesis of depsipeptides from L-amino acids and lactones

By using the corresponding L -amino acid sodium as initiator, ɛ -caprolactone-depsipeptides CL-Ala and CL-Leu were prepared by the reactions of ɛ -caprolactone (CL) with L -alanine and L -leucine, respectively, and p -dioxanone-depsipeptide (PDO-Leu) was prepared by the reaction of p -dioxanone (PDO) with L leucine. Two poly( ɛ -caprolactone) oligomers (PCL-Ala and PCL-Leu) of different molecular weights with depsipeptide unit were synthesized by controlling the feed ratio of L -amino acid sodium and CL. The presence of the depsipeptide structure in these obtained products was confirmed by 1 H NMR spectra and the molecular weight of the poly( ɛ -caprolactone) oligomers was measured by gel permeation chromatography (GPC). These products contain a hydroxyl group and a carboxyl group in one molecule, which means they could act as bifunctional monomers for further polymerization to prepare high molecular weight polymers. By this way, the depsipeptide unit could be introduced into the polymers and the biodegradation rates of the novel polymers could be well controlled in vivo by the tailored molecular structures.