Hydrolase-catalyzed stereoselective preparation of protected α,α-dialkyl-α-hydroxycarboxylic acids

The title compounds were prepared by a Passerini multi-component reaction and subjected to enzymatic kinetic resolution using 40 enzymes known to be active towards esters of tertiary alcohols. This identified a protease (P1), a thermophilic esterase (PestE) and an esterase of metagenome origin (esterase 8) as the most active and enantioselective biocatalysts. After further optimization of reaction conditions, two compounds were prepared in preparative scale using esterase 8 yielding (+)-1-(tert-butylamino)-2-methyl-1-oxobutyl-2-yl acetate with 93%ee and (−)-1-(tert-butylamino)-2-trifluoro-methyl-1-oxobutyl-2-yl acetate with 47%ee.