Abstract:

Chiral amines with bioactivities are important chiral auxiliaries, and also key intermediates for the synthesis of many natural products and chiral drugs. Among the top 200 drugs for market revenues in 2019, more than 30% contain chiral amine structures. Therefore, the development of efficient and effective methods to synthesize chiral amine compounds is of interest for research. Due to its high efficiency, environmental friendliness and economic competitiveness, more attention has been paid on the enzyme-catalyzed production of chiral amines by academia and industry. Imine reductases (IREDs) reviewed in this article are a class of NAD(P) H-dependent oxidoreductases that catalyze asymmetric reduction of imines to chiral amines. The reduction of C\underset{}{̿}N bonds constitutes a physiological reaction present in a number of biosynthetic pathways, leading to a variety of metabolites. The imine reductases have excellent characteristics such as high catalytic efficiency, strong regioselectivity and stereoselectivity, etc., which stand out among many other methods for the synthesis of chiral amines, and attract attention and enthusiasm of many researchers. In the past decade, with the rapid development of bioinformatics, structural biology, high-throughput screening approaches and the continuous expansion of the gene databases, many imine reductases with different functions have been identified. Significant achievements have been made in the discovery of IREDs, protein engineering and multi-enzyme cascade applications, among which some successful modification cases have industrial application potentials. This review summarizes the structural characteristics, catalytic mechanisms and applications of IREDs, with emphasis on their protein engineering and applications in multi-enzyme cascade reactions, as well as the bottleneck, breakthrough and progress in asymmetric catalytic chiral amine biosynthesis. In addition, the challenges and potentials of the enzymatic synthesis of chiral amine compounds for industrial production, and the importance of novel artificial biosynthesis pathway design to overcome these challenges are highlighted.

Key words: imine reductase, chiral amine, biocatalysis, protein engineering, biosynthesis

摘要：

手性胺存在于许多生物活性物质中，是重要的手性助剂，同时也是合成天然产物及手性药物的关键中间体。2019年零售额前200名的药物中，含有手性胺结构的药物超过三成，因此发展高效、便捷合成手性胺化合物的方法是研究的重要方向。通过酶催化方法制备手性胺化合物，因具有高效性、环境友好性、经济效率高等优点，获得了学术界及工业界的广泛关注。本文所综述的亚胺还原酶（IREDs）是一类NAD（P）H依赖的氧化还原酶，可催化亚胺的不对称还原合成手性胺。IREDs具有催化效率高、区域及立体选择性强等优异的特性，在众多合成手性胺方法中脱颖而出，吸引了科研工作者的研究目光。近年来，随着生物信息学、结构生物学、高通量筛选方法的飞速发展和数据库的不断扩充，鉴定了许多不同功能的IRED，并在IRED的发现、分子改造、底物谱扩展和多酶级联应用等方面均取得了显著的成果，其中不乏一些具有工业应用价值。本文概述了IRED的结构特征及作用机理，着重介绍了IRED的分子改造和在多酶串联反应中的应用，以及在不对称催化手性胺生物合成中遇到的瓶颈、获得的突破和进展。此外还对酶法合成手性胺化合物实现工业化生产所面临的挑战及巨大潜力，以及新颖的人工生物合成途径设计对克服这些挑战的重要性进行了展望。

关键词: 亚胺还原酶, 手性胺, 生物催化, 酶工程, 生物合成