SYNTHESIS AND EVALUATION OF NEW ELASTASE INHIBITORS .1. 1,1-DIOXOCEPHEM-4-THIOLESTERS

Several 7alpha-chloro and 7alpha-methoxy cephalosporin thiolester sulphones variously substituted at the C-3' position were synthesized from 7-amino-3-deacetoxycephalosporanic acid (7-ADCA). The compounds are time-dependent inhibitors of human leukocyte elastase (HLE) with effective K(i) ranging from micro- to nanomolar values, and second order rate constant reaching 10(6) M-1s-1; they also inhibit porcine pancreatic elastase with similar, though not identical efficiency. Compared to the corresponding cephem esters, the thiolesters of the 7-Cl series inhibit HLE up to 10 times as fast. Complete enzyme inactivation is achieved when a leaving group at C-3' (OAc or S-Het) is present, at the expense however of stability towards hydrolytic beta-lactam cleavage. In the 7-OMe series the thiolester compounds are far more stable and retain good efficiency for irreversible enzyme inhibition, superior to that displayed by the corresponding ester compounds. Three representative compounds (including one ester and two thiolesters) are shown to be effective inhibitors of HLE in the presence of insoluble elastin.