The development of unnatural tripeptides as highly enantioselective organocatalysts for the asymmetric aldol reaction of isatins was achieved. H-Pro-Gly-d-Ala-OH with the d-alanine residue as the C-terminal amino acid residue expressed the best enantioselectivity. The H-Pro-Gly-d-Ala-OH-catalyzed reaction of isatins gave various aldol adducts with up to 93% yield and up to 97% ee. Investigation of the transition state via DFT calculation revealed that high optical purity was realized by the d-alanine controlled steric environment.

中文翻译：

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非天然三肽作为Isatins不对称醛醇缩合反应的高度对映选择性有机催化剂

实现了非天然三肽作为靛红的不对称醛醇缩合反应的高度对映选择性有机催化剂的开发。以d-丙氨酸残基为C末端氨基酸残基的H-Pro-Gly- d -Ala-OH表现出最佳的对映选择性。H-Pro-Gly- d -Ala-OH催化的靛红反应生成的各种羟醛加合物的收率高达93％，ee高达97％。通过DFT计算对过渡态的研究表明，通过d-丙氨酸控制的空间环境实现了高光学纯度。