ROB WILSON
Codexis Inc., Redwood City, CA, USA

Abstract

Oxidations are among the more commonly used reactions in the chemical industry, but current methods of asymmetric oxidation are limited by a number of challenges, including safety, selectivity, side-reactions and over-oxidation. These issues can be overcome by utilizing biocatalysts that are optimized for the reaction of interest through directed evolution. Enzyme-mediated reactions can also offer numerous cost, efficiency, safety and environmental advantages over traditional chemical approaches. Biocatalysis is well proven at bench-scale, but incorporating enzymes into industrial-scale pharmaceutical manufacturing has in the past often been perceived to be difficult. Here we describe the development of a novel Baeyer-Villiger monooxygenase (BVMO) enzyme that has been evolved for high performance and subsequently scaled to commercial manufacture of a leading drug for gastro-esophageal reflux disease. Our findings demonstrate that biocatalytic oxidation using BVMOs can eliminate the selectivity issues that can be problematic for asymmetric oxidations, and these versatile enzymes can be manipulated for a variety of different oxidation reactions.

INTRODUCTION

Chiral sulfoxides are important molecules for a number of pharmaceutical compounds, including esomeprazole (Nexium, for treatment of gastro-esophageal reflux), and armodafinil (Nuvigil, for treatment of narcolepsy) (1). They are typically synthesized through asymmetric sulfur oxidation but this is non-trivial, chemically, and current oxidation techniques are known to have significant limitations that can lead to reduced product quality or make processing complicated (1-3). Traditionally, manufacturing of chiral sulfoxides involves either resolution or the use of Kagan-Sharpless asymmetric catalysts (4). Both of these approaches have drawbacks: the maximum theoretical yield from resolutions is 50%, causing significant yield loss; the Kagan-Sharpless method requires chiral auxillaries and peroxides, making it atom intensive. Furthermore, the Kagan-Sharpless method is not perfectly enantioselective and also tends to over-oxidize the desired sulfoxides to sulfones, resulting in yield and purity issues (1-3).

In recent years, chemists have begun adopting biocatalysis for alternative synthetic routes. Enzymes can be optimized for specific ...