Conversion of aldonic acids to their corresponding 2-keto-3-deoxy-analogs by the non-carbohydrate enzyme dihydroxy acid dehydratase (DHAD)

Abstract

Aldonic acids containing four to six carbon atoms were tested as potential substrates of dihydroxy acid dehydratase (DHAD), an enzyme from the biosynthetic pathway of branched chain amino acids. Novel assay systems for observing the course of DHAD catalysed reactions were developed in order to adapt the enzyme to extended practical applications. Kinetic studies for the new substrates ( 12 13 ) as well as inhibitor kinetics for the substrate analogue 3-deoxy-aldonic acids ( 25, 27 and 29) were performed. These gave indications for the restrictions of substrate modifications and contributed to the understanding of the individual effects. Finally l-threonic acid ( 12) and d-erythronic acid ( 13) could be successfully applied as substrates for DHAD and this led to the chemoenzymatic synthesis of their 2-keto-3-deoxy-analogue ( 20) in a preparative scale.