Functional poly(2-oxazoline)s by direct amidation of methyl ester side chains

摘要

Poly(2-alkyl/aryl-2-oxazoline)s (PAOx) are biocompatible pseudopolypeptides that have received significant interest for biomedical applications in recent years. The growing popularity of PAOx in recent years is driven by its much higher chemical versatility compared with the gold standard in this field, poly(ethylene glycol) (PEG), while having similar beneficial properties, such as stealth behavior and biocompatibility. We further expand the PAOx chemical toolbox by demonstrating a novel straightforward and highly versatile postpolymerization modification platform for the introduction of side-chain functionalities. PAOx having side chain methyl ester functionalities is demonstrated to undergo facile uncatalyzed amidation reactions with a wide range of amines, yielding the corresponding PAOx with side-chain secondary amide groups containing short aliphatic linkers as well as a range of side-chain functionalities including acid, amine, alcohol, hydrazide, and propargyl groups. The PAOx with side-chain methyl ester groups can be prepared by either partial hydrolysis of a PAOx followed by the introduction of the methyl ester via modification of the secondary amine groups with methyl succinyl chloride or by the direct copolymerization of a nonfunctional 2-oxazoline monomer with a 2-methoxycarbonylethyl-2-oxazoline. Thus, this novel synthetic platform enables direct access to a wide range of side-chain functionalities from the same methyl-ester-functionalized poly(2-oxazoline) scaffold.