STRUCTURE-BASED DESIGN OF A GENERAL-CLASS OF MECHANISM-BASED INHIBITORS OF THE SERINE PROTEINASES EMPLOYING A NOVEL AMINO ACID-DERIVED HETEROCYCLIC SCAFFOLD

We describe in this paper the structure-based design of a general clas s of heterocyclic mechanism-based inhibitors of the serine proteinases that embody in their structure a novel peptidomimetic scaffold (1,2,5 -thiadiazolidin-3-one 1,1-dioxide), Sulfone derivatives of this class (I) were found to be time-dependent, potent, and highly efficient irre versible inhibitors of human leukocyte elastase, cathepsin G, and prot einase 3. The partition ratios for a select number of inhibitors were found to range between 0 and 1. We furthermore demonstrate that these inhibitors exhibit remarkable enzyme selectivity that is dictated by t he nature of the P-1 residue and is consistent with the known substrat e specificity reported for these enzymes. Thus, inhibitors with small hydrophobic side chains were found to be effective inhibitors of elast ase, those with aromatic side chains of cathepsin G, and those with a basic side chain of bovine trypsin. Taken together, the findings cited herein reveal the emergence of a general class of stable mechanism-ba sed inhibitors of the serine proteinases which can be readily synthesi zed using amino acid precursors. Biochemical and high-field NMR studie s show that the interaction of this class of inhibitors with a serine proteinase results in the formation of a stable acyl complex(es) and t he release of benzenesulfinate, formaldehyde, and a low molecular weig ht heterocycle. The data are consistent with initial formation of a Mi chaelis-Menten complex, acylation of Ser(195), and tandem loss of the leaving group. The initial HLE-inhibitor complex reacts with water gen erating formaldehyde and a stable HLE-inhibitor complex. Whether the i nitial HLE-inhibitor complex also reacts with His(57) to form a third complex is not known at this point. The desirable salient parameters a ssociated with this class of inhibitors, including the expeditious gen eration of structurally diverse libraries of inhibitors based on I, su ggest that this class of mechanism-based inhibitors is of general appl icability and can be used in the development of inhibitors of human an d viral serine proteinases of clinical relevance.