A novel (R)‐imine reductase (PlRIR) from Paenibacillus lactis was heterologously overexpressed in Escherichia coli, purified and characterized. The purified PlRIR exhibited relatively high catalytic efficiency (kcat/Km=1.58 s−1 mm−1) towards 2,3,3‐trimethylindolenine. A panel of 3H‐indoles and 3H‐indole iodides were reduced by PlRIR to yield the corresponding products with good‐to‐excellent enantioselectivity (66–98 % ee). In addition, PlRIR also possesses good activities toward other types of imines such as pyrroline, tetrahydropyridine, and dihydroisoquinoline, indicating a reasonably broad substrate acceptance. In a 100 mg scale preparative reaction, 100 mm 2,3,3‐trimethylindolenine was converted efficiently to afford (R)‐2,3,3‐trimethylindoline with 96 % ee and 81 % yield.

Baeyer‐Villiger monooxygenases (BVMOs) are remarkable biocatalysts for the Baeyer‐Villiger oxidation of ketones to generate esters or lactones. The regioselectivity of BVMOs is essential for determining the ratio of the two regioisomeric products (“normal” and “abnormal”) when catalyzing asymmetric ketone substrates. Starting from a known normal‐preferring BVMO sequence from Pseudomonas putida KT2440 (PpBVMO), a novel BVMO from Gordonia sihwensis (GsBVMO) with higher normal regioselectivity (up to 97/3) was identified. Furthermore, protein engineering increased the specificity constant (kcat/KM) 8.9‐fold to 484 s−1 mM−1 for 10‐ketostearic acid derived from oleic acid. Consequently, by using the variant GsBVMOC308L as an efficient biocatalyst, 10‐ketostearic acid was efficiently transformed into 9‐(nonanoyloxy)nonanoic acid, with a space‐time yield of 60.5 g L−1 d−1. This study showed that the mutant with higher regioselectivity and catalytic efficiency could be applied to prepare medium‐chain ω‐hydroxy fatty acids through biotransformation of long‐chain aliphatic keto acids derived from renewable plant oils.

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