Abstract:

Natural product is an important source of small-molecule drugs and probes, the synthesis of which is challenging, and has long attracted much more attention in the field of organic chemistry. With the continuous advancement of chromatographic techniques for separation and spectroscopic methods for structural analysis, the pace of discovering tiny bioactive natural products is accelerating, concomitantly leading to an increase in the diversity and complexity of the newly identified structures. However, to meet the demand of the quantity needed for the study of their structure-activity relationships, target identification, in vivo activity evaluation, etc., growing challenges in the requirement for the synthetic efficiency, economy, and scalability of natural products are emerging. Synthetic practices in a chemoenzymatic way have provided multi-dimensional visions for natural product research, which emerged as a hot research topic in recent years. On the one hand, enzymatic catalysis has provided highly efficient and selective synthetic methodologies that would complement traditional synthetic methods. On the other hand, the introduction of enzyme-catalyzed reactions would bring a new mode of strategic design for synthesis, enabling the rapid and diverse synthesis of natural products with high efficiency. In this context, how to integrate the enzyme-catalyzed reactions into the synthesis of natural products is the key to a successful chemoenzymatic synthesis. We herein summarized three roles played by the applications of enzyme-catalyzed reactions in the current practices of chemoenzymatic synthesis of natural products. ①The involvement of biocatalysis would introduce a chiral center or a key functional group into the starting material, or supply complex synthetic precursors (e.g., polysubstituted (hetero)aromatics, chiral pools, etc.) via in vitro enzyme-catalyzed reactions or fermentation, hence advancing the starting line of synthesis; ②Late-stage enzyme-catalyzed chemo-, regio-, and stereoselective modifications of substrates with heavily substituted functional groups or inert positions of complex skeletons; ③The strategic application of enzymatic catalysis as a key carbon-carbon bond-forming step in the construction of the skeleton of natural product. Finally, we have discussed the current challenges and future trends of the chemoenzymatic synthesis of natural products in three facets, including the design of synthetic strategy, the development of synthetic methods, as well as persons involved in the research. Thus, the integration of interdisciplinary methods and technologies, including chemical synthesis and biocatalysis, would invigorate the synthesis of natural products.

Key words: natural product, chemoenzymatic synthesis, biocatalysis, biosynthesis, late-stage functionalization

摘要：

天然产物是小分子药物和探针的重要来源，其合成研究一直以来是有机合成中一个备受关注而又极具挑战性的领域。随着色谱分离技术和结构分析技术的不断发展，微量活性天然产物的发现速度不断加快，其结构的多样性和复杂性也不断增加，而对其构效关系，靶标鉴定，体内活性等方面的研究则需要供应足够量的天然产物，因而对天然产物的合成在效率、经济性和规模等方面都提出了更高的要求。化学-酶法的方式为天然产物的合成研究提供了多维的视角，一方面提供了高效高选择性的酶催化合成方法，另一方面，酶催化反应的引入可以给原先合成策略的设计模式带来突破，并快速，高效地实现天然产物的多样化合成，从而成为近期研究的热点。其中酶催化反应如何有机地整合到天然产物的合成中便成为目前化学-酶法合成成功的关键，本文从当前天然产物化学-酶法的合成实践中总结了酶催化反应所发挥的三方面作用：①对合成起点的改变，即酶催化反应可以在合成原料中引入关键的手性中心或官能团，以体外酶促或体内发酵的方式提供复杂的合成前体，如多取代芳（杂）环，手性池等；②合成后期通过酶催化方式对多官能团底物或复杂骨架的惰性位置进行化学、区域和立体选择性的官能团化；③酶催化反应作为关键步骤在母核骨架构建中关键碳碳键形成方面的策略性应用。最后，本文从合成策略的设计，合成方法的开发，以及研究人员思维等三个方面讨论了化学-酶法策略在当下所面临的挑战和未来的发展趋势。在此背景下，化学合成与生物催化等多学科手段的深度交叉融合将为天然产物的合成科学带来新的活力。

关键词: 天然产物, 化学-酶法合成, 生物催化, 生物合成, 后期官能团化