Cascade Biocatalysis for Regio- and Stereoselective Aminohydroxylation of Styrenyl Olefins to Enantiopure Arylglycinols

Abstract

Chiral β-amino alcohols are privileged scaffolds frequently found in pharmaceutically active molecules and natural products. Aminohydroxylation of olefins is one of the most powerful strategies to access chiral vicinal amino alcohols. However, the direct regio- and stereoselective aminohydroxylation of olefins to unprotected enantioenriched β-amino alcohols remains a long-standing challenge. Herein, we report that a novel one-pot four-enzyme [styrene monooxygenase (SMO)/epoxide hydrolase (EH)/alcohol dehydrogenase (ADH)/ω-transaminase (TA)] biocatalytic cascade efficiently catalyzes the direct transformation of readily available styrenyl olefins into unprotected 2-amino-2-phenyl ethanols in good yields and excellent enantioselectivity. In vitro cascade biocatalysis aminohydroxylation of styrenyl olefins was first investigated by the combined four enzymes (SMO/EH/ADH/TA) with a trace amount of NADH (0.02 mM) and pyridoxal-5′-phosphate (0.1 mM), affording both enantiomers of β-amino alcohols 5a–j in 13.9–98.7% conversions and 86–99% ee. Whole-cell-based cascade biocatalysis was achieved by using the constructed recombinant Escherichia coli pairwise combinations and single tailor-made whole-cell biocatalyst without an additional NADH cofactor; (R)- and (S)-β-amino alcohols 5a–j could be obtained in 14.6–99.7% conversions and 86–99% ee. Moreover, the preparative experiments of this new cascade biocatalysis were demonstrated by the single tailor-made whole-cell biocatalyst [E. coli (CGS-DEM) and E. coli (CGS-DEB)] with the substrates 1a–b and 1h in an aqueous-organic two-phase system, affording chiral β-amino alcohols [(R)- or (S)-5a–b, h] in good yields (50.9–64.3%) and excellent ee (>99%).