Mechanism of inhibition of human leukocyte elastase by two cephalosporin derivatives

Abstract

The cephalosporin derivatives L 658758 [1-[[3-(acetoxymethyl)-7 alpha-methoxy-8-oxo-5-thia-1-azabicyclo [4.2.0]oct-2-en-2-yl]carbonyl]proline S,S-dioxide] and L 659286 [1-[[7 alpha-methoxy-8-oxo-3-[[(1,2,5,6-tetrahydro-2-methyl-5,6-dioxo- 1,2,4-triazin-3-yl)thio]methyl]-5-thia-1-aza-(6R)-bicyclo[4.2.0]-o ct-2-en-2-yl]carbonyl]pyrrolidine S,S-dioxide] are mechanism based inhibitors of human leukocyte elastase (HLE). The mechanism involves initial formation of a Michaelis complex followed by acylation of the active site serine. The group on the 3'-methylene is liberated during the course of these reactions, followed by partitioning of an intermediate between hydrolysis to regenerate active enzyme and further modification to produce a stable HLE-inhibitor complex. The partition ratio of 2.0 obtained for the reaction with L 658758 approaches that of an optimal inhibitor. These compounds are functionally irreversible inhibitors as the recovery of activity after inactivation is slow. The half-lives at 37 degrees C of the L 658758 and L 659286 derived HLE-I complexes were 9 and 6.5 h, respectively. The complexes produced by both inhibitors are similar chemically since the thermodynamic parameters for activation to regenerate active enzyme are essentially identical. The free energy of activation for this process is dominated primarily by the enthalpy term. The stability of the final complexes likely arises from Michael addition on the active site histidine to the 3'-methylene.

Synthesis and Preliminary Biological Evaluation of 3′-Substituted Cephem Sulfones as Potential β-Lactamase Inhibitors

“…[6] In their outstanding study, they proposed acetate elimination from the 3Ј-position of their derivatives as the necessary step towards irreversible inactivation of the enzyme. This last observation parallels the work of Doherty on the inhibition of human leukocyte elastase by cephalosporin sulfone esters, [7] as well as Pratt's study on the importance of the 3Ј-leaving group in the inhibition of PC1 β-lactamase of Staphylococcus aureus by cephalosporin sulfide derivatives. [8] Several years ago we published a paper where, inter alia, hydrolysis under biomimetic conditions (methanolic triethylamine) of deacetoxycephalosporin sulfone derivatives were studied.…”

Strategies for the inhibition of serine proteases

“…Figures 12 and 13 show the proposed mechanisms for the inhibition of HNE by a 7a-methoxysubstituted derivative and PPE by the 7a-chloro-substituted compound, respectively. Since the original discovery, a vast number of analogues of monocyclic and bicyclic b-lactams [222,224,227,228], derivatives of cephalosporins [229 -234], penems Figure 12. Proposed mechanism of inhibition of HNE by 7-methoxy-substituted cephems [222].…”

Novel Natural Product 5,5-trans-Lactone Inhibitors of Human α-Thrombin: Mechanism of Action and Structural Studies

“…Classes of irreversible inhibitor include -lactam elastase inhibitors (12)(13)(14), isocoumarins (15), isatoic anhydrides (16), enol lactones (17), ynenol lactones (18), 6-chloro-2-pyrones (19), and the chloromethyl ketone R-thrombin inhibitor PPACK, 3 which forms an adduct to His57 (20). Boronate, trifluoromethyl ketone, and aldehyde inhibitors have been reported to form reversible covalent adducts to Ser195 that mimic the catalytic tetrahedral intermediate (21)(22)(23)(24).…”