摘要
Diels-Alder反应被认为是合成复杂天然产物的最有效的方法之一,一直以来都深受化学家的关注.而杂原子参与的HDA(Hetero-Diels-Alder)反应是合成各种天然杂环的重要工具,其中以氧杂DA反应和氮杂DA反应最为常见.酶催化HDA反应以其绿色温和、高效、高选择性等优势受到人们广泛关注.随着杂环天然产物中酶催化HDA反应的不断发现,对HDA相关酶的立体选择性、底物特异性的研究也不断深入,有效促进了人们对这一类酶序列与功能关系的了解,为其挖掘和改造奠定了基础.本文集中对目前已知的酶催化HDA反应合成杂环天然产物的成果进行概述,主要包括吡喃类化合物和吲哚生物碱生物合成中涉及的酶促HDA反应,以期通过对途径和催化机理的分析,为发展新的相关生物催化剂用于合成非天然的杂环产物提供思路.
Abstract
The Diels-Alder reaction is a chemical process where a conjugated diene reacts with a dienophile to form cyclohexene.This reaction can generate up to four adjacent chiral centers and two carbon-carbon bonds simultaneously,making it an effective method to form C—C bonds.Therefore,it has attracted wide attention.Hetero-Diels-Alder(HDA)reactions,which involve heteroatoms,are an important tool for synthesizing natural heterocyclic rings.HAD reaction types are classified according to the heteroatoms involved,with the most common types being oxa Diels-Alder reaction and aza Diels-Alder reaction.At present,non-enzyme catalysts have been successfully applied to catalyze HDA reactions,which are catalyzed by chemical catalysts such as Lewis acids,metal ions,and organic molecules can do.However,compared to chemical catalysis,enzyme-catalyzed HDA reactions are favored due to their green,mild,efficient,and highly selective properties.With the discovery of enzyme-catalyzed HDA reactions in natural product biosynthetic pathways,uncovering the stereoselectivity and substrate specificity of HDA-related enzymes promotes our understandings of the relationship between sequences and functions.Additionally,it lays the foundation for further mining and modification of enzymes.However,there are several challenges need to be tackled.Firstly,although a few HDA enzymes have been studied,the vast majority are remained to be isolated and characterized.Secondly,the catalytic mechanisms of most reported HDA enzymes are not clear,and more information about their structures,key residues and catalytic processes remains to be uncovered.Thirdly,all reported cases present rather narrow substrate spectra,and the stereoselectivity is rather poor.Here,we summarize the currently known enzyme-catalyzed HDA reactions in heterocyclic natural product biosynthetic pathways,focusing mainly on those involved in the biosynthesis of pyridines and indole alkaloids.By summarizing and analyzing the entire biocatalytic pathways and catalytic mechanisms,we expect to guide further research and engineering of HAD enzymes to improve their activity and selectivity.We also hope to inspire the development of new biocatalysts for the synthesis of non-natural heterocyclic products.
基金项目
国家自然科学基金(22077029)
国家自然科学基金(22034002)
湖南省自然科学基金杰出青年项目(2021JJ10034)
NETL
NSTL
万方数据