Biochemical Synthesis of Several Chiral Insecticide Intermediates and Mechanisms of Action of Relevant Enzymes

Abstract

  Efficient biochemical processes were developed for the synthesis of several chiral alcohol and acid intermediates of insecticides by a combination of strictly stereoselective hydrolytic enzyme-catalyzed reactions and subsequent chemical transformations with inversion or racemization of the chiral center of the undesired antipodes. The whole amounts of starting racemic mixtures are converted to desired stereoisomers in the processes, which are generally applicable to the industrial productions of various chiral secondary alcohols and α-substituted acids once a highly stereospecific enzyme is obtained for the target compounds. The alcohols reported here are: 1-(4-phenoxyphenoxy)-2-propanol, 1; 4-hydroxy-3-methyl-2-(2’-propynyl)-2-cyclopentenone, 2; and α-cyano-3-phenoxybenzyl alcohol, 3. The acids are 2, 2-dimethyl-3-(2-methyl-1-propenyl)-cyclopropanecarboxylic acid (chrysanthemic acid), 4; and 2-(4-chlorophenyl)-3-methylbutyric acid, 5. In addition, the mechanism of action of Pseudomonas cepacia lipase (PCL), the most effective enzyme for the resolution of 1, and the recombinant Arthrobacter globiformis esterase (AES) for 4 was studied from the reaction kinetics. The site-directed mutagenesis techniques were also used for AES. The results indicated that the stereoselectivity of PCL is caused by the position and direction of a medium-sized substituent at the chiral center of the alcohol moiety in the rate-determining breakdown of a tetrahedral intermediate in the acylation of the enzyme and that the catalytic site of AES has the characteristics of the penicillin-recognizing enzymes in which Ser 59 in the concensus motif Ser-X-X-Lys plays a vital role as a nucleophile during acylation and Lys 62 acts as a general base.