NMR-STUDIES OF THE (R)-1-ACETAMIDO-2-(4-FLUOROPHENYL)ETHANE-1-BORONICACID COMPLEX

The interaction of (R)-l-acetamido-2-(4-fluorophenyl)ethane-1-boronic acid with alpha-chymotrypsin at pH 4 was studied by a variety of F-19- NMR experiments. It was demonstrated that this compound forms a comple x with a 1:1 stoichiometry, probably because the boronic acid acts as a 'transition state' inhibitor of the enzyme. Analysis of fluorine T1 relaxation behavior and F-19{H-1} NOE data shows that the rate constan t for dissociation of the complex is 1.3 s-1 and that the motion of th e 4-fluoroaromatic ring within the complex can be characterized by an overall rotational correlation time of 13 ns and a correlation time fo r rotation about its local C2 axis of 110 ns. Enzyme-induced fluorine chemical shifts, fluorine relaxation times, line width data and 2D F-1 9{H-1} NOE results suggest that the structure of the complex in the vi cinity of the fluoroaromatic ring is similar to that found in a closel y similar acylated enzyme. However, the dynamics of 4-fluoroaromatic r ing motions are different in the two systems, with the ring being slig htly more mobile in the boronic acid complex than in the acylenzyme.