Conformationally restricted thrombin inhibitors resistant to proteolytic digestion

A new type of thrombin exo-site inhibitor has been designed with enhanced inhibitory potency and increased metabolic stability. With the aid of the model of the structure of the thrombin-hirudin fragment complex [Yue, S.-Y., DiMaio, J., Szewczuk, Z., Purisima, E. O., Ni, F., & Konishi, Y. (1992) Protein Eng. 5, 77-85], cyclic analogs of the hirudin fragment (hirudin55-65) were designed and synthesized. In these analogs, the side chains of appropriately substituted residues, 58 and 61, were joined in order to restrict the conformation of the inhibitor. An analog with an 18-membered lactam ring showed higher antithrombin activity (IC50 = 0.57 microM) than the corresponding analogs with 17- or 16-membered rings and was 2-fold more potent than its linear counterpart. Even 4-fold greater enhancement was obtained when a shorter fragment, hirudin 55-62, was cyclized. This cyclization not only improved the potency but, more importantly, dramatically increased the resistance to proteolytic digestion. Remarkable enhancement of stability to proteolysis was observed for peptide bonds located in the exocyclic linear peptide segments. These results are discussed using molecular modeling.

Abstract sourced from PubMed (NCBI) for the cited record. See the original publication for the authoritative version.

Cyclic analogs of the hirudin 55-65 fragment were designed as thrombin exosite inhibitors; an 18-membered lactam ring doubled antithrombin potency versus its linear form and cyclization markedly increased resistance to proteolytic digestion.

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