(2R,3S)-N-tert-Butoxycarbonyl-3-amino-1-chloro-2-hydroxy-4-phenylbutane (1b) is key for the synthesis of the antiviral drug atazanavir. It can be obtained via the stereoselective bioreduction of (3S)-3-(N-Boc-amino)-1-chloro-4-phenyl-butanone (1a) with short-chain dehydrogenase/reductase (SDR). However, the stereoselective bioreduction of this hydrophobic and bulky substrate still remained a challenge because of the steric hindrance effect and low mass transfer rate. In this study, SDR isolated from Novosphingobium aromaticivorans (NaSDR) having low activity to 1a, which was engineered to enhance catalytic efficiency through active pocket iterative saturation mutagenesis (ISM). The obtained mutant (muSDR) (G141V/I195L) had 3.57 times higher k(cat) than the wild type (WT) towards 1a. Molecular docking analysis revealed considerable differences in the distance between the substrate and catalytic residues in WT and mutant SDR. Moreover, muSDR reduced 15 ketones with excellent enantioselectivity, indicating broad substrate acceptance. After optimization of expression and reaction conditions, the conversion was completed in a scale-up reaction (500mL) using 50% toluene with 500mM substrate without additional NADH. These results show that muSDR may be a valuable biocatalyst for future industrial applications.
[1]Shanghai Univ Med & Hlth Sci, Sch Pharm, Pudong New Area, 279 Zhouzhu Highway, Shanghai 201318, Peoples R China.
[2]Shanghai Univ Med & Hlth Sci, Microbial Pharmacol Lab, Pudong New Area, 279 Zhouzhu Highway, Shanghai 201318, Peoples R China.
[3]Shanghai Inst Pharmaceut Ind, State Key Lab New Drug & Pharmaceut Proc, 285 Gebaini Rd, Shanghai 200040, Peoples R China.
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