Enzymatic Synthesis Of Polyesters From Ketones

Enzymatic polymerization, which benefits from high efficiency, mild reaction conditions, satisfactory biocompatibility along with high stereo-preference and chemoselectivity, has increasingly been the focus of intense research in the scientific community for the past decades. Polyester is one of the most important synthetic polymers and the most powerful tool for obtaining polyesters is ring-opening polymerization (ROP), especially the one catalyzed by lipase, which is highly efficient and free from undesired by-products, with cyclic lactones as the starting material. However the substrates of ROP, lactones, which can not be purchased directly, are usually obtained through Baeyer-Villiger oxidation (BVO) of ketones. In this thesis, a novel synthesis strategy of polyester from simple ketones was provided, and three routes for synthesis of polyester from simple ketones were investigated. The first one was chemo-Baeyer-Villiger oxidation/lipase-catalyzed ROP route, and the second one was single lipase-catalyzed Baeyer-Villiger oxidation/ROP one-pot process, the last one was cyclohexanone monooxygenase(CHMO)-catalyzed BVO oxidation/lipase-catalyzed ROP route. Detailed results were described as following.In the first section, metachloroperbenzoic acid (MCPBA) was used to catalyze the oxidation of substituted cyclohexanones, and six substituted caprolactones were successfully prepared, their structures were characterized by FTIR, GC, and NMR techniques. Furthermore, the ring-opening reaction and subsequent polymerization of these lactones were studied, including the stereoselectivity. The structures of these polyesters were confirmed by FTIR, NMR and GPC techniques. The polyesters’ molecular weights were ranged from300to17500.In the next section, a novel enzymatic one-pot cascade procedure for the synthesis of substituted polyesters starting from ketone has been developed, under the catalysis of Candida antarctica lipase B (CAL-B). Reactions parameters of the separated BVO reaction, the ROP polymerization, and one-pot cascade procedure including CAL-B-catalyzed BVO and ROP reactions were systematically investigated. As a result,6corresponding lactones could be effectively prepared. And then, corresponding polyesters were obtained through one-pot cascade procedure. The structures of lactones and their polyesters were characterized by NMR, IR and GPC techniques. The polyesters’ molecular weights were ranged from400to12800.Finally, the stereoselective oxidation of substituted cyclohexanones which was catalyzed by cyclohexanone monooxygenase(CHMO) was also explored preliminarily. As the best example,4-Methylcaprolactone was obtained with90%yield,99%ee value. The subsequent enzymatic ring-opening polymerization of4-Methylcaprolactone also has been done to provide a polyester with molecular weight at17520.