An Artificial Cofactor Catalyzing the Baylis-Hillman Reaction with Designed Streptavidin as Protein Host*.

Horst Lechner,M Breuning,Birte Höcker,Vincent R Emann

doi:10.1002/cbic.202000880

Abstract

An artificial cofactor based on an organocatalyst embedded in a protein has been used to conduct the Baylis‐Hillman reaction in a buffered system. As protein host, we chose streptavidin, as it can be easily crystallized and thereby supports the design process. The protein host around the cofactor was rationally designed on the basis of high‐resolution crystal structures obtained after each variation of the amino acid sequence. Additionally, DFT‐calculated intermediates and transition states were used to rationalize the observed activity. Finally, repeated cycles of structure determination and redesign led to a system with an up to one order of magnitude increase in activity over the bare cofactor and to the most active proteinogenic catalyst for the Baylis‐Hillman reaction known today.

Highlights

An artificial cofactor based on an organocatalyst embedded in a protein has been used to conduct the Baylis-Hillman reaction in a buffered system
There are several examples using streptavidin as the host for these cofactors, since its natural ligand biotin binds strongly (Kd ~ 10À 15 M) and is easy to modify with catalysts at the carboxylic acid group
Streptavidin is a known thermo- and solvent stable protein, which is another advantage in the development of new catalysts

Summary

Introduction

An artificial cofactor based on an organocatalyst embedded in a protein has been used to conduct the Baylis-Hillman reaction in a buffered system. We describe here the use of an artificial cofactor employing the well-known biotin-streptavidin system to catalyze a Baylis-Hillman reaction. The protein was expressed, purified and, after adding 4, its activity tested in the Baylis-Hillman model reaction with p-nitrobenzaldehyde 1 and cyclopentenone 2 as the substrates (Figure 1A).

Results

Conclusion