Synthesis and biological activity of 7-alkylidenecephems.
Several 7-alkylidenecephalosporins were synthesized and biologically evaluated as beta-lactamase inhibitors. The three beta-lactamase enzymes used in this study included two type C beta-lactamases, derived from Enterobacter cloacae P99 and E. cloacae SC12368, and one type A beta-lactamase, derived from Escherichia coli WC3310. Of the cephalosporins prepared, compound 7e, the sodium salt of 7-[(Z)-(2'-pyridyl)methylene]cephalosporanic acid sulfone, was found to have excellent inhibitory properties against both type C enzymes. Also, compound 7f, the sodium salt of 7-[(Z)-(tert-butoxycarbonyl)methylene]cephalosporanic acid sulfone showed high activity as an inhibitor of the type A enzyme. The inhibition kinetics of 7e were further explored. The IC50 value of 7e indicated that this compound was approximately 20-fold more active than tazobactam against the enzyme derived from E. cloacae P99 and 167-fold more active than tazobactam against the enzyme derived from E. cloacae SC12368. A plot of enzymatic activity vs incubation time with stoichiometric amounts of inhibitor reveals a rapid deactivation of the enzyme followed by an extremely slow reactivation. 7e exhibited a second-order rate constant of k3' = 5.3 x 10(6) L/mol.min, and a partition ratio of approximately 20:1 inhibitor:enzyme was determined for this inhibitor. After separation of excess inhibitor with Sephadex filtration, a rate constant of enzyme reactivation was measured at kreactiv = 1.0 x 10(-3) s-1. Following 24 h of incubation of enzyme with a large excess of inhibitor and sephadex filtration to remove excess inhibitor, the enzyme was able to recover only 43% of its original activity, indicating an irreversible component to the inhibition. Potential mechanisms of inhibition for both 7e and 7f are suggested.
Buynak
J D
JD
Department of Chemistry, Southern Methodist University, Dallas, Texas 75275.
Wu
K
K
Bachmann
B
B
Khasnis
D
D
Hua
L
L
Nguyen
H K
HK
Carver
C L
CL
D000900:Anti-Bacterial Agents / Q000138:chemical synthesis* / Q000494:pharmacology*; D002511:Cephalosporins / Q000138:chemical synthesis* / Q000494:pharmacology*; D002850:Chromatography, Gel; D016972:Enterobacter cloacae / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D014753:Vinyl Compounds / Q000138:chemical synthesis* / Q000494:pharmacology*; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000187:drug effects / Q000378:metabolism
D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D014753:Vinyl Compounds; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases