Articles cis-2,5-Dicyanopyrrolidine Inhibitors of Dipeptidyl Peptidase IV: Synthesis and in Vitro, in Vivo, and X-ray Crystallographic Characterization Stephen W. Wright,* Mark J. Ammirati, Kim M. Andrews, Anne M. Brodeur, Dennis E. Danley, Shawn D. Doran, Jay S. Lillquist, Lester D. McClure, R. Kirk McPherson, Stephen J. Orena, Janice C. Parker, Jana Polivkova, Xiayang Qiu, Walter C. Soeller, Carolyn B. Soglia, Judith L. Treadway, Maria A. VanVolkenburg, Hong Wang, Donald C. Wilder, and Thanh V. Olson Pfizer Global Research and DeVelopment, Eastern Point Road, Groton, Connecticut 06340 ReceiVed January 4, 2006 Inhibitors of the glucagon-like peptide-1 (GLP-1) degrading enzyme dipeptidyl peptidase IV (DPP-IV) have been shown to be effective treatments for type 2 diabetes in animal models and in human subjects. A novel series of cis-2,5-dicyanopyrrolidine R-amino amides were synthesized and evaluated as inhibitors of dipeptidyl peptidase IV (DPP-IV) for the treatment of type 2 diabetes. 1-({[1-(Hydroxymethyl)cyclopentyl]amino}- acetyl)pyrrolidine-2,5-cis-dicarbonitrile (1c) is an achiral, slow-binding (time-dependent) inhibitor of DPP- IV that is selective for DPP-IV over other DPP isozymes and proline specific serine proteases, and which has oral bioavailability in preclinical species and in vivo efficacy in animal models. The mode of binding of the cis-2,5-dicyanopyrrolidine moiety was determined by X-ray crystallography. The hydrochloride salt of 1c was further profiled for development as a potential new treatment for type 2 diabetes. Type 2 diabetes (formerly non-insulin-dependent diabetes mellitus) is a severe and increasingly prevalent disease. 1 Diabetics may suffer debilitating cardiovascular, eye, kidney, and nerve damage and are at risk of premature handicap and death due to these and other diabetic complications, which are the result of glucose toxicity caused by their hyperglycemia. A progressive reduction in insulin sensitivity and insulin secretion are hallmarks of the disease, which eventually result in failure of the pancreatic islet cells and dependence on exogenous insulin. The incretin hormone glucagon-like peptide 1 (GLP-1) is a potent stimulator of endogenous insulin release. GLP-1 has beneficial effects on islet -cell function and insulin sensitivity without induction of hypoglycemia. 2 Unfortunately, GLP-1 is rapidly degraded in vivo. Inhibition of GLP-1 degradation by dipeptidyl peptidase IV (DPP-IV) has emerged as a promising approach for the treatment of Type 2 diabetes 3 and has been aggressively pursued by numerous laboratories. 4 We sought to identify novel inhibitors of DPP-IV that were structurally distinct from the wide variety of inhibitors previously reported by other groups. In particular, we wanted to explore an achiral cis-2,5- dicyanopyrrolidine template, to learn if such compounds were active as inhibitors of DPP-IV. Molecular modeling based on published DPP-IV enzyme-inhibitor crystal structures 5 sug- gested that the cis-2,5-dicyanopyrrolidine template was not a good starting point for compound design. However, it is well- known that binding site residues can move to accommodate a ligand, and 4,5-methano-bridged inhibitors of DPP-IV have been reported. 6 Therefore, we opted to test the idea that a cis-2,5- dicyanopyrrolidine template might inhibit DPP-IV. This paper reports the results of our investigation. Synthesis. The compounds were prepared by parallel syn- thesis according to the procedure outlined in Scheme 1, in which the preparation of 1c is illustrated for example. Coupling of the bromoacetamide 2 with an excess (g3 equiv) of the appropriate primary amine was carried out in acetonitrile at 20 °C. On the basis of previously reported work detailing the stability of nitrile-containing inhibitors of DPP-IV, we elected to employ only amines bearing a quaternary R-carbon center. 7 The products were converted to their hydrochloride salts by treatment with 1 equiv of hydrogen chloride in methanol following purification by silica gel chromatography. The requisite bromoacetamide 2 was prepared by the route shown in Scheme 2. Strecker reaction of 2,5-dimethoxytetrahy- drofuran and aminodiphenylmethane with KCN in 0.1 M aqueous citric acid solution afforded a precipitate containing * To whom correspondence should be addressed. Telephone: 860-441- 5831; fax: 860-715-4483; email: stephen.w.wright@pfizer.com. Scheme 1. Preparation of cis-2,5-Dicyanopyrrolidine Inhibitors a a Conditions: (a) 1-(Hydroxymethyl)cyclopentylamine (3 equiv), MeCN, 20 °C, 18 h. Scheme 2. Preparation of Bromoacetamide 2 a a Conditions: (a) 2,5-Dimethoxytetrahydrofuran, KCN, 0.1 M aqueous citric acid, 20 °C, 72 h; (b) BrCH2COBr, MeCN, 70 °C, 16 h. 3068 J. Med. Chem. 2006, 49, 3068-3076 10.1021/jm0600085 CCC: $33.50 © 2006 American Chemical Society Published on Web 05/02/2006