Remarkable Effect of D-Sorbitol on the Second Stage in the PLE-Catalyzed Hydrolyses of a σ-Symmetric Diester,<i>cis</i>-Cyclohex-4-ene-1,2-bis(methyl acetate)
Enantioselective hydrolysis of cis-cyclohex-4-ene-1,2-bis(methyl acetate) with porcine liver esterase (PLE) in the presence of D-sorbitol afforded a chiral monoester in a highly enantioselective manner. During the enzymatic hydrolyses, D-sorbitol efficiently accelerate the second stage; hydrolysis of the resultant minor monoester toward the dicarboxylic acid leaving the desired major monoester.
The chiral mono-thiol diester, 1 or 2, is converted to the corresponding enantiomeric cyclised products,(–)-7 and (+)-7 or (–)-9, and (+)-9, depending on whether LDA or AlCl3–Et3N is used.
The chiral bicyclic β-keto ester (14), which is synthesised by our methods involving stereoselective differentiation between two identical groups in the diamide (4) of (R)-4-methoxycarbonyl-1,3-thiazolidine-2-thione and regiocontrolled Dieckmann-type cyclisation of half-thiol diester (11), has been successfully converted into (+)-carbacyclin (2).