**Xiangxian Ying 1,\*, Jie Zhang 1, Can Wang 1, Meijuan Huang 1, Yuting Ji 1, Feng Cheng 1, Meilan Yu 2, Zhao Wang <sup>1</sup> and Meirong Ying 3,\***


Academic Editor: Stefano Serra Received: 11 November 2018; Accepted: 27 November 2018; Published: 28 November 2018

**Abstract:** The recombinant carbonyl reductase from *Rhodococcus erythropolis* WZ010 (ReCR) demonstrated strict (*S*)-stereoselectivity and catalyzed the irreversible reduction of *N*-Boc-3 piperidone (NBPO) to (*S*)-*N*-Boc-3-hydroxypiperidine [(*S*)-NBHP], a key chiral intermediate in the synthesis of ibrutinib. The NAD(H)-specific enzyme was active within broad ranges of pH and temperature and had remarkable activity in the presence of higher concentration of organic solvents. The amino acid residue at position 54 was critical for the activity and the substitution of Tyr54 to Phe significantly enhanced the catalytic efficiency of ReCR. The *k*cat/*K*<sup>m</sup> values of ReCR Y54F for NBPO, (*R*/*S*)-2-octanol, and 2-propanol were 49.17 s−<sup>1</sup> mM<sup>−</sup>1, 56.56 s−<sup>1</sup> mM<sup>−</sup>1, and 20.69 s−<sup>1</sup> mM<sup>−</sup>1, respectively. In addition, the (*S*)-NBHP yield was as high as 95.92% when whole cells of *E. coli* overexpressing ReCR variant Y54F catalyzed the asymmetric reduction of 1.5 M NBPO for 12 h in the aqueous/(*R*/*S*)-2-octanol biphasic system, demonstrating the great potential of ReCR variant Y54F for practical applications.

**Keywords:** (*S*)-*N*-Boc-3-hydroxypiperidine; carbonyl reductase; asymmetric reduction; rational design; *Rhodococcus erythropolis*
