酵母脂肪酶分子进化及催化合成(S)-1,4-苯并二口恶烷*

Objective: 1,4-Benzodioxane is an important chiral intermediate for antihypertensive (Proroxan and Doxazosin), antidepressant (MCK-242) and other drugs, and it displays a broad spectrum of applications in the pharmaceutical field. Currently, in spite of high-yield advantage of chemical synthesis, there are some problems of environmental pollution and low production safety. Using lipase to catalyze synthesis of 1,4-benzodioxane provides a new pathway of green synthesis of 1,4-benzodioxane. However, natural enzymes face the dilemma of poor enantioselectivity. Therefore, molecular evolution was performed on Candida antarctica lipase B, and a technical route for the catalytic synthesis of 1,4-benzodioxane was established. Methods: Firstly, the key amino acid residues involved in substrate binding and conversion in the active center of Candida antarctica lipase B were analyzed, and saturation mutagenesis libraries on the interaction sites were constructed. Improved mutants with high efficiency and high enantioselectivity were then obtained using HPLC detection. Furthermore, catalytic synthesis conditions of mutant D223N/A225K were systematically optimized. Results: The results indicated that the mutants mainly derived from the pairwise site D223/A225 (such as D223N/A225K and D223G/A225W) were biased towards the synthesis of (S)-isoforms, while most of the mutants derived from the pairwise site E188/I189 (such as E188D/I189M) showed a bias for the synthesis of (R)-isoforms. Compared with WT, the ee_s value of the best mutant D223N/A225K to synthesize (S)-1,4-benzodioxane was increased from 11.9% to 29.3%. After systematic optimization of the reaction conditions, an ee_s value of (93.9±0.16)% and a conversion rate of (47.5±2.33)% were achieved using mutant D223N/A225K to catalyze kinetic resolution of methyl (R,S)-2,3-dihydro-1,4-benzodioxin-2-carboxylate in n-butanol/phosphate buffered saline (20∶80, V/V) biphasic solvent at 37℃ for 50 min. Conclusion: An efficient kinetic resolution of methyl (R,S)-2,3-dihydro-1,4-benzodioxin-2-carboxylate was successfully achieved by molecular evolution and optimization of conditions, which provides a new example for the creation of new enzymes by protein engineering technology, and also provides a theoretical and technical foundation for the efficient synthesis of (S)-1,4-benzodioxane molecules by enzymatic methods.