Study On Lipase-catalyzed Asymmetric Ammonolysis In Organic Solvent

Enzymatic ammonolysis of carboxylic ester with ammonia as the acyl acceptor is a novel reaction which was discovered in the mid of 1990s. This reaction not only provides a useful alternative for the synthesis of functional amides, but also can be used for the preparation of optically pure compounds. R-Phenylglycine and its derivatives are key intermediates for the semi-synthesis of β-lactam antibiotics. The possibility of applying enzymatic enantioselective ammonolysis to the preparation of R-phenylglycine was explored in this paper. Effects of reaction conditions, additives, imprinting with R-enantiomer and in situ racemizing of S-enantiomer on Novozym435-catalyzed enantioselective ammonolysis were investigated systematically.Lipase Novozym435 was screened from different enzyme sources because of its comparatively high catalytic activity and enantioselectivity; The reaction conditions have profound effects on the enzymatic enantioselective ammonolysis of racemic phenylglycine methyl ester: ammonium carbamate was selected from different ammonia sources; tert-butanol was thought to be the most suitable reaction medium by taking the reaction rate and enantioselectivity into account; the optimum initial water activity was found to be 0.75 and relatively high reaction rate and enantioselectivity could be attained within temperature of 20℃- 35℃. The ammonolysis kinetic constants of the two enantiomers of phenylglycine methy ester were V_max,.R=(?) 28mmol/L·h V_max,.S= 3.8 mmol/L·h ; K_m,R= 24.5mmol/L, K_m,S=70.5 mmol/L respectively.Enzymatic ammonolysis showed comparatively high catalytic activity and enantioselectiviy compared to the corresponding hydrolysis and alcoholysis, and lipase exhibited fairly high stability in this reaction media.Additives have complicated effects on the enzymatic ammonolysis of phenylglycine methyl ester: within the scope studied, 18-crown-6 could improve the ammonolysis rate, but lower the enantioselectivity to some degree; Bile salt and inorganic salt were found to show some negative effects on the enzymatic ammonolysis and among the surfactants tested, only Span80 could improve the enzymatic activity as well as the enantioselectivity to some extent.Imprinting with preferable enantiomer could enhance both enzymatic activity and enantioselectivity dramatically in this study. Ammonolysis rate was 8.2 mmol/L·h and the ratio of the ammonolysis rate of the two enantiomers could reach 40 with co-imprinted...