Monooxygenases in Stereoselective Sulfoxidation

Because CHMOs can also be used as catalysts in the enantioselective air oxidation of some prochiral thioethers (173-175,183-185), directed evolution of the CHMO from Acinetobacter sp. NCIMB 9871 was applied in the case of difficult substrates such as 24 (105). The WT CHMO leads to an ee of only 14%. 

Two mutants (1-D10-F6 and 1-K15-C1) are (R)-selective, whereas the other three variants (1-C5-H3, 1-H8-A1, and 1-J8-C5) induce the opposite enantioselectivity in favor of (S)-25. Sequencing studies show that between one and four amino acid exchanges occurred. In general, the mutants are different from those that were previously identified as hits in the BV reaction of prochiral cyclohexanone 

Selected Mutant CHMOs from Acinetobacter sp. NCIMB 9871 for the Enantioselective Air-Oxidation of Thio-Ether 24 (24h 23-25° C) Using Whole Cells (105) 

Mutant Amino acid exchanges Yield of 25 (%) Configuration ee (%) Sulfone as side product (%) 

Only 5% ee results when using the enzyme extract. 

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