Quantification of the extent of attenuation of the rate of turnover chemistry of the TEM-1 beta-lactamase by the alpha-1R-hydroxyethyl group in substrates

The 6 alpha-1R-hydroxyethyl group of imipenem, a clinically used carbapenem antibacterial agent, is believed to displace the hydrolytic water from its optimal position in the active site of class A beta-lactamases. This interaction renders the molecule a poor substrate for these bacterial enzymes, hence preserving the antibacterial property of the antibiotic. The extent of the contribution of the 6 alpha-1R-hydroxyethyl group in substrates toward stabilization of the antibiotic to the hydrolytic action of class A TEM-1 beta-lactamase was studied by the synthesis and evaluation of two penicillanic acid derivatives, 6 alpha-(1R-hydroxyethyl)penicillanic acid (2) and 6 beta-(1R-hydroxyethyl)penicillanic acid (3). The kinetic evaluation of the enzymic hydrolysis of these two penicillanic acid derivatives indicated that the 6 alpha-1R-hydroxyethyl group imparts as much as 10(4)-fold to the hydrolytic stability of the beta-lactam substrate.