Selective Monoacylation of Diols by Substrate Assisted Catalysis in T40A Candida antarctica Lipase B

The selectivity towards diols over monoesters in the esterification of diols catalysed by lipase B from Candida antarctica (CALB) was improved by the single point mutation T40A in the enzyme’s oxyanion hole. Substrate‐assisted catalysis was suggested from molecular modelling of the tetrahedral intermediate in esterification of 1,2‐ethanediol catalysed by T40A CALB. The non‐reacting hydroxyl group of the diol forms a hydrogen bond to the oxyanion in the transition state, replacing that deleted in mutation. Monoester yields in transacylation reactions were monitored over time to compare the selectivities for wild‐type and T40A CALB. The results showed increased selectivities towards the diols tested over their corresponding monoesters as a result of the T40A mutation with substrate‐assisted catalysis as a plausible explanation. Transition state mutates! Deletion of one hydroxyl group in the oxyanion hole through T40A‐mutation of lipase B from Candida antarctica enables substrate‐assisted catalysis of diols. The hydroxyl group that is not attacking the acyl enzyme can play the role of the deleted hydroxyl group in the oxyanion hole and restore stabilization of the transition state. The monoester formed cannot react further to form the diester, which increases the monoester yield.