Sulfenyl transfer rearrangement of sulfenimines (thiooximes). A novel synthesis of 7.alpha.-methoxycephalosporins and 6.alpha.-methoxypenicillins

Inactivation of alanine racemase by beta-chloro-L-alanine released enzymatically from amino acid and peptide C10-esters of deacetylcephalothin

The reactions of a set of amino acid and peptidyl C10-esters of deacetylcephalothin (1-5) have been examined with purified enzymes in vitro. Each of the compounds examined is a substrate for the Escherichia coli TEM-2 beta-lactamase, and enzyme-catalyzed hydrolysis of the lactam bond gives release of an amino acid or a peptidyl fragment from a cephem nucleus. 7 beta-(2-Thienylacetamido)-3-[[(beta-chloro-L-alanyl)oxy]methyl]-3- cephem-4-carboxylate (4) gives time-dependent inactivation of E. coli JSR-O alanine racemase in a process that requires beta-lactamase for the initial liberation of beta-chloro-L-alanine from the cephalosporin. Alanine racemase is similarly inactivated by 7 beta-(2-thienylacetamido)-3-[[[(beta-chloro-L-alanyl)-beta-chloro- L- alanyl]oxy]methyl]-3-cephem-4-carboxylate (1), but this inhibition requires the sequential action of both beta-lactamase and alanine aminopeptidase. Analysis of the enzymatic transformations of 7 beta-(2-thienylacetamido)-3-[[[(beta-chloro-L-alanyl)-L- alanyl]oxy]methyl]-3-cephem-4-carboxylate (3), monitored by high-field 1H NMR, reveals that (1) beta-lactamase releases the dipeptide beta-chloro-L-alanyl-L-alanine from 3 and (2) leucine aminopeptidase effects stoichiometric hydrolysis of the dipeptide to beta-chloro-L-alanine and L-alanine. These biochemical findings are discussed with reference to the mechanism of antibacterial action of 1 against beta-lactamase-producing, penicillin-resistant microorganisms [Mobashery, S., Lerner, S. A., & Johnston, M. (1986) J. Am. Chem. Soc. 108, 1685].

beta-Lactamase inhibitors

In summary, Table XVI shows the inhibition profiles of representative beta-lactamases from each major class of Richmond and Sykes. Either resistance (R) or sensitivity (S) is given as a general guide to the type of compounds likely to inhibit each class. Thus the (qualitative) statements regarding the effectiveness of clavulanic acid can be taken to represent those for the penam sulfones and similarly for MM4550 and the other olivanic acids, carpetimycins, PS series, and asparenomycins. This can also be said of cloxacillin and the other aromatic carboxamido penicillins. Compounds are also included which are specifically or particularly inhibitory to certain beta-lactamases.

Inactivation of RTEM beta-lactamase from Escherichia coli by clavulanic acid and 9-deoxyclavulanic acid

The interaction of the TEM-2 beta-lactamase with 9-deoxyclavulanic acid (3) and with both extensively labeled (2) and specifically labeled (1) clavulanic acid has been studied. The close similarity between 9-doexyclavulanate and clavulanate in kinetics, spectroscopic, and protein chemical terms show that the allyl alcohol group of clavulanate is irrelevant to its action as a beta-lactamase inactivator. Use of the radiolabeled samples of clavulanate shows that, of three irreversibly inactivated forms of the enzymes, two contain the whole clavulanate skeleton and the third only retains the carbon atoms of the original beta-lactam ring. These findings allow the complex interaction between clavulanic acid and the beta-lactamase to be defined more narrowly in chemical terms.

Inactivation of the RTEM beta-lactamase from Escherichia coli. Interaction of penam sulfones with enzyme

The characteristics of the reaction of a number of mechanism-based inactivators of the RTEM beta-lactamase have suggested that a common mechanistic pathway may be followed by many of these compounds. These ideas have been tested by the synthesis and evaluation of some penam sulfones as beta-lactamase inactivators. The sulfones of poor beta-lactamase substrates are, as predicted, potent inactivators of the enzyme. A unique serin residue (Ser-70) is labeled by quinacillin sulfone, and it is likely that this serine acts nucleophilically in the normal hydrolytic reaction of the beta-lactamase to form an acyl-enzyme intermediate.