Inactivation of Glucosamine‐6‐Phosphate Synthase by N 3 ‐Oxoacyl Derivatives of L ‐2,3‐Diaminopropanoic Acid

N 3 ‐Oxoacyl derivatives of L ‐2,3‐diaminopropanoic acid 1 – 4 , containing either an epoxide group or a conjugated double bond system, inactivate Saccharomyces cerevisiae glucosamine‐6‐phosphate (GlcN‐6‐P) synthase in a time‐ and concentration dependent manner. The results of kinetics studies on inactivation suggested a biphasic course, with formation of the enzyme–ligand complex preceding irreversible modification of the enzyme. The examined compounds differed markedly in their affinity to the enzyme active site. Inhibitors containing a phenyl ketone moiety bound much more strongly than their methyl ketone counterparts. The molecular mechanism of enzyme inactivation by phenyl ketone compounds 1 and 3 was elucidated by using a stepwise approach with 2D NMR, MS and UV–visible spectroscopy. A substituted thiazine derivative was identified as the final product of a model reaction between an epoxide compound, 1 , and L ‐cysteine ethyl ester (CEE); and the respective cyclic product, found as a result of reaction between 1 and CGIF tetrapeptide, was identical to the N‐terminal fragment of GlcN‐6‐P synthase. On the other hand, the reaction of a double‐bond‐containing compound, 3 , with CEE, CGIF and GlcN‐6‐P synthase led to the formation of a CS bond, without any further conversion or rearrangement. Molecular mechanisms of the reactions studied are proposed.