Artificial imine reductases based on the Biotin-(Strept)avidin technology : genetic optimization and applications towards "in vivo" transition metal catalysis

Abstract

The present PhD Thesis summarizes the scientific work performed in the research group of Prof. Dr. Ward from 2010-14 at the university of Basel. The main topic of the Ward group is the design of artificial metalloenzymes for asymmetric catalysis. These hybrid catatlysts result from the incorporation of a catalytically active transition metal complex within a host protein and thus combine properties of both traditional homogenous and biocatalysis. Moreover, the genetic tuneability of the protein scaffold allows to trigger the performance of an incorporated transition metal catalyst by modification of the second coordination sphere. The high affinity of the vitamin biotin towards the eucaryotic protein avidin (Avi) and its procaryotic counterpart streptavidin (Sav) offers an attractive strategy for the creation of artificial metalloenzymes. The conjugation of biotin with a catalytically active transition metal complex leads to an efficient incorporation of the latter within strept(avidin). This approach was applied extensively in the Ward group to obtain effective hybrid catalysts for a variety of reactions. The present work deals with the enantioselective reduction of prochiral imines to amines by artificial transfer hydrogenases (ATHase) which result from the incorporation of piano stool complexes of ruthenium, rhodium and iridium within Sav. The Thesis is divided into four chapters. The first chapter provides an introduction into the topic of artificial metalloenzymes and illustrates their potential in asymmetric catalysis. A review article summarizes the most recent achievments of this research field. The following two chapters present the research performed in context of several projects which resulted in four scientific publications. A brief introduction into the respective topic is given in each chapter. The author's contribution to each publication is highlighted in a preamble. An appendix at the end of each chapter presents additional results which did not appear in the corresponding publications. Chapter two describes the genetic optimization of the ATHase and gives mechanistic insights in its operating mode. Chapter three focuses on attempts to implement transition metal catalysis in vivo. This would open fascinating perspectives to enable directed evolution of artificial metalloenzymes. Detailed procedures of experiments described in the appendices are given in chapter four.