Combinatorial evolution of site- and enantioselective catalysts for polyene epoxidation
作者:Phillip A. Lichtor、Scott J. Miller
DOI:10.1038/nchem.1469
日期:2012.12
Selectivity in the catalytic functionalization of complex molecules is a major challenge in chemical synthesis. The problem is magnified when there are several possible stereochemical outcomes and when similar functional groups occur repeatedly within the same molecule. Selective polyene oxidation provides an archetypical example of this challenge. Historically, enzymatic catalysis has provided the only precedents. Although non-enzymatic catalysts that meet some of these challenges became known, a comprehensive solution has remained elusive. Here, we describe low molecular weight peptide-based catalysts, discovered through a combinatorial synthesis and screening protocol, that exhibit site- and enantioselective oxidation of certain positions of various isoprenols. This diversity-based approach, which exhibits features reminiscent of the directed evolution of enzymes, delivers catalysts that compare favourably to the state-of-the-art for the asymmetric oxidation of these compounds. Moreover, the approach culminated in catalysts that exhibit alternative-site selectivity in comparison to oxidation catalysts previously described. Aspartic acid-based catalysts that are selective for oxidation of either the 2,3 position or the 6,7 position of certain isoprenols have been discovered. The catalysts emerged from a diversity-based approach employing the one-bead-one-compound libraries. The site-selectivity of the catalysis seems to derive from the hydroxyl group in the substrate, although the details of this are not yet known.
复杂分子的催化功能化选择性是化学合成中的一大挑战。当存在多种可能的立体化学结果且同一分子中重复出现类似官能团时,这个问题变得更加严重。选择性多烯氧化为这一挑战提供了一个典型的例子。历史上,酶催化提供了唯一的先例。尽管一些满足这些挑战的非酶催化剂已经被认识到,但全面的解决方案仍然难以实现。在此,我们描述了一种基于低分子量肽的催化剂,这些催化剂是通过组合合成和筛选协议发现的,能够对各种异戊醇的某些位置进行位点和对映体选择性氧化。这种基于多样性的策略,具有与酶的定向进化类似的特征,提供了与这些化合物的不对称氧化的最新技术相当的催化剂。此外,该方法最终得出的催化剂在与之前描述的氧化催化剂相比时展现了替代位点的选择性。我们发现了选择性氧化某些异戊醇的2,3位或6,7位的基于天冬氨酸的催化剂。这些催化剂来源于采用一珠一配体库的多样性基础方法。催化的位点选择性似乎源自底物中的羟基,但其具体细节尚不清楚。