Asymmetric ring opening of racemic epoxides to enantiopure β-amino alcohols via a cascade biocatalysis system.

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 longstanding 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 βamino alcohols [(R)-or (S)-5a−b, h] in good yields (50.9−64.3%) and excellent ee (>99%).

Apigenin prevented the DDC-induced abnormal lipid metabolism, liver damage and liver fibrosis by reducing inflammation and oxidative stress. Apigenin might be a potential drug for the treatment of cholestatic liver diseases.

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Optically active β-amino alcohols are very useful chiral intermediates frequently used in the preparation of pharmaceutically active substances. Here, a novel cyclohexylamine oxidase (ArCHAO) was identified from the genome sequence of Arthrobacter sp. TYUT010-15 with the R-stereoselective deamination activity of β-amino alcohol. ArCHAO was cloned and successfully expressed in E. coli BL21, purified and characterized. Substrate-specific analysis revealed that ArCHAO has high activity (4.15 to 6.34 U mg À 1 protein) and excellent enantioselectivity toward the tested β-amino alcohols. By using purified ArCHAO, a wide range of racemic β-amino alcohols were resolved, (S)-β-amino alcohols were obtained in > 99 % ee. Deracemization of racemic β-amino alcohols was conducted by ArCHAO-catalyzed enantioselective deamination and transaminase-catalyzed enantioselective amination to afford (S)-β-amino alcohols in excellent conversion (78-94 %) and enantiomeric excess (> 99 %). Preparative-scale deracemization was carried out with 50 mM (6.859 g L À 1) racemic 2-amino-2-phenylethanol, (S)-2-amino-2-phenylethanol was obtained in 75 % isolated yield and > 99 % ee.