The subtilisin Carlsberg catalysed transesterification of N-acetyl phenylalanine methyl ester (1), N-acetyl phenylalanine ethyl ester (2), N-trifluoroacetyl phenylalanine methyl ester (3) and N-trifluoroacetyl phenylalanine ethyl ester (4) was studied in supercritical carbon dioxide. The water content of the reaction affects the reactivity of the system; for the transesterification of the methyl esters with ethanol the optimum concentration of water was determined to be about 0.74 M, while for the transesterification of the ethyl esters with methanol the optimum concentration of water was about 1.3 M. The conversion is also dependent upon the concentration of alcohol; for ethanol, 2% v/v gives the maximum conversion, whilst for methanol, only 0.8-1.2% v/v is required. This is probably due to a difference in the solubility of the substrates in the two alcohol/supercritical carbon dioxide mixtures. The reaction is highly stereoselective, in all cases no evidence for reaction of the D-isomer could be detected by chiral gas chromatography.
在超临界二氧化碳中,研究了枯草芽孢杆菌嘉士伯催化 N-乙酰基苯丙氨酸甲酯(1)、N-乙酰基苯丙氨酸乙酯(2)、N-三氟乙酰基苯丙氨酸甲酯(3)和 N-三氟乙酰基苯丙氨酸乙酯(4)的酯交换反应。反应中的水含量会影响体系的反应活性;在甲酯与乙醇的酯交换反应中,水的最佳浓度约为 0.74 M,而乙酯与甲醇的酯交换反应中,水的最佳浓度约为 1.3 M。这可能是由于底物在两种酒精/超临界二氧化碳混合物中的溶解度不同。反应具有高度的立体选择性,在所有情况下,手性气相色谱法都检测不到 D 异构体的反应。