Synthesis of a block copolymer of L-lactide and depsipeptide with pendant thiol groups

Abstract

In order to develop a new type of lactic acid copolymer having pendant reactive groups as a biodegradable biomaterial, the synthesis of an AB-type diblock copolymer of L-lactide (L-LA) and depsipeptide with pendant thiol groups was investigated. Cyclodepsipeptide consisting of glycolic acid (Glc) and β-methoxybenzyl L-cystine (Cys), cyclo[Glc-Cys(MBzl)], was polymerized in tetrahydrofuran (THF) solution using potassium ethoxide as an initiator. The terminal hydroxyl group of the poly[Glc-Cys(MBzl)] obtained was converted to potassium alkoxide by K/naphthalene. L-LA was polymerized in THF using the polymer alkoxide as a macro-initiator to obtain poly[Glc-Cys(MBzl)]-block-polyLA showing two melting temperatures (Tms). Through subsequent deprotection of the methoxybenzyl groups, the objective biodegradable amphiphilic AB-type block copolymer, poly(Glc-Cys)-block-polyLA, was obtained. The accumulation ability of thiol groups located on the surface of the block copolymer film was evaluated to be higher than that of the random copolymer film.