Sonnet P E, Baillargeon M W
U.S. Department of Agriculture, Eastern Regional Research Center, Philadelphia, Pennsylvania 19118.
Lipids. 1991 Apr;26(4):295-300. doi: 10.1007/BF02537140.
Hydrolyses of racemic methyl-branched octanoic acid thiolesters are described using six commercial lipases as catalysts. Branching at positions 2, 4 and 5 greatly reduced activity; branching at the 3-position virtually eliminated activity. The reactivities of the racemic branched thiolesters relative to the unbranched ester were very similar for each lipase preparation examined. In reactions involving configurationally pure 2-methyloctanoic acids, the S-enantiomer reacted faster both in esterification of aliphatic alcohols and in hydrolyses of aliphatic alcohol esters with all of the lipases examined. Stereobiases in hydrolyses of the octanoic acid esters branched at other positions were low and variable. In sharp contrast to the hydrolyses of the thiolesters of 2-methyloctanoic acid, two aryl esters of 2-methyloctanoic acid catalyzed by R. miehei lipase hydrolyzed with a bias for the R-configuration. A view of the ester-enzyme complex is offered to explain the relative rates of reaction of the racemic esters.
本文描述了使用六种商业脂肪酶作为催化剂对外消旋甲基支链辛酸硫酯进行的水解反应。在2、4和5位的支链极大地降低了活性；在3位的支链几乎消除了活性。对于所检测的每种脂肪酶制剂，外消旋支链硫酯相对于直链酯的反应活性非常相似。在涉及构型纯的2-甲基辛酸的反应中，S-对映体在脂肪醇的酯化反应以及与所有所检测脂肪酶进行的脂肪醇酯水解反应中反应速度都更快。在其他位置支链的辛酸酯水解中的立体选择性较低且变化不定。与2-甲基辛酸硫酯的水解形成鲜明对比的是，米黑根毛霉脂肪酶催化的2-甲基辛酸的两种芳基酯水解时对R-构型有偏向性。本文提供了酯-酶复合物的视图来解释外消旋酯的相对反应速率。
