A metallo-β-lactamase-type alkylsulfatase was found to catalyze the enantioselective hydrolysis of sec-alkylsulfates with strict inversion of configuration. This catalytic event, which does not have an analog in chemocatalysis, yields homochiral (S)-configurated alcohols and nonreacted sulfate esters. The latter could be converted into (S)-sec-alcohols as the sole product in up to >99% ee via a chemoenzymatic deracemization protocol on a preparative scale.
In search of highly enantioselective microbial sec-alkyl sulfatase activity, a broad screening among bacteria, fungi and Archaea revealed several Ralstonia and Pseudomonas spp. as valuable sources, whereas fungi were completely inactive. In particular, Pseudomonas sp. DSM 6611 was able to hydrolyse the (R) enantiomers of a broad range of rac-sec-alkyl
Strategies for the chemoenzymatic transformation of a racemate into a single stereoisomeric product in quantitative yield have been developed. A range of industrially relevant α-hydroxycarboxylic acids was deracemized in a stepwise fashion via lipase-catalysed enantioselective O-acylation, followed by mandelate racemase-catalysed racemization of the remaining non-reacted substrate enantiomer. Alternatively, aliphatic α-hydroxycarboxylic acids were enzymatically isomerized using whole resting cells of Lactobacillus spp. Enantioselective hydrolysis of rac-sec-alkyl sulphate esters was accomplished using novel alkyl sulphatases of microbial origin. The stereochemical path of catalysis could be controlled by choice of the biocatalyst. Whereas Rhodococcus ruber DSM 44541 and Sulfolobus acidocaldarius DSM 639 act through inversion of configuration, stereo-complementary retaining sulphatase activity was detected in the marine planctomycete Rhodopirellula baltica DSM 10527.
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