Asymmetric Reductive Carbocyclization Using Engineered Ene Reductases.

Kathrin Heckenbichler,Lea Alexandra Brandner,Rolf Breinbauer,Peter Macheroux,Karl Gruber,Anna Schweiger,Marina Toplak,Alexandra Binter

doi:10.1002/anie.201802962

Abstract

Ene reductases from the Old Yellow Enzyme (OYE) family reduce the C=C double bond in α,β‐unsaturated compounds bearing an electron‐withdrawing group, for example, a carbonyl group. This asymmetric reduction has been exploited for biocatalysis. Going beyond its canonical function, we show that members of this enzyme family can also catalyze the formation of C−C bonds. α,β‐Unsaturated aldehydes and ketones containing an additional electrophilic group undergo reductive cyclization. Mechanistically, the two‐electron‐reduced enzyme cofactor FMN delivers a hydride to generate an enolate intermediate, which reacts with the internal electrophile. Single‐site replacement of a crucial Tyr residue with a non‐protic Phe or Trp favored the cyclization over the natural reduction reaction. The new transformation enabled the enantioselective synthesis of chiral cyclopropanes in up to >99 % ee.

Highlights

Ene reductases from the Old Yellow Enzyme (OYE) family reduce the C=C double bond in a,b-unsaturated compounds bearing an electron-withdrawing group, for example, a carbonyl group
Going beyond its canonical function, we show that members of this enzyme family can catalyze the formation of CÀC bonds. a,b-Unsaturated aldehydes and ketones containing an additional electrophilic group undergo reductive cyclization
The two-electron-reduced enzyme cofactor flavin mononucleotide (FMN) delivers a hydride to generate an enolate intermediate, which reacts with the internal electrophile

Summary

Introduction

Ene reductases from the Old Yellow Enzyme (OYE) family reduce the C=C double bond in a,b-unsaturated compounds bearing an electron-withdrawing group, for example, a carbonyl group. Engineered and artificial metalloenzymes have been developed for biocatalytic CÀ C bond formations, including olefin cyclopropanation,[3] Suzuki coupling,[4] Diels–Alder reaction,[5] and others.[6] we report a new type of enzymatic CÀC-bond formation in which a combination of substrate design and protein engineering enabled asymmetric reductive cyclization using ene reductases.

Results

Conclusion