7.16 C–X Bond Formation: Hydroxynitrile Lyases: From Nature to Application

Abstract

The natural function of hydroxynitrile lyases (HNLs) is the cleavage of cyanohydrins. By serendipity they are also able to catalyze the reverse synthesis reaction. Thus, they are valuable biocatalysts for the stereoselective C–C bond formation by condensation of HCN with carbonyl compounds. The resulting cyanohydrins serve as versatile building blocks for a broad range of chemical and enzymatic follow-up reactions. In the last 30years, a large number of (R)- and (S)-selective HNLs have been discovered. They differ substantially concerning their sequence, structure, and substrate scope. Enzyme engineering and reaction optimization can be employed to enhance the yield and stability of recombinant HNLs and broaden their substrate scope, resulting in tailor-made enzymes for large-scale manufacturing of cyanohydrins with improved yield and enantiomeric excess. This chapter will focus on the newest discoveries, developments, and applications of HNLs for the synthesis of highly functionalized, chiral compounds.