Substituted 2-Aminopyridines as Inhibitors of Nitric Oxide Synthases William K. Hagmann, a, * Charles G. Caldwell, a Ping Chen, a Philippe L. Durette, a Craig K. Esser, a Thomas J. Lanza, a Ihor E. Kopka, a Ravi Guthikonda, a Shrenik K. Shah, a Malcolm MacCoss, a Renee M. Chabin, b Daniel Fletcher, d Stephan K. Grant, b Barbara G. Green, b John L. Humes, c Theresa M. Kelly, b Sylvie Luell, d Roger Meurer, d Vernon Moore, d Stephen G. Pacholok, c Tony Pavia, b Hollis R. Williams c and Kenny K. Wong b a Department of Medicinal Chemistry, Merck Research Laboratories Rahway, NJ 07065, USA b Department of Biochemistry, Merck Research Laboratories Rahway, NJ 07065, USA c Department of In¯ammation Research, Merck Research Laboratories Rahway, NJ 07065, USA d Department of Pharmacology Merck Research Laboratories Rahway, NJ 07065, USA Received 22 May 2000; accepted 28 June 2000 AbstractÐA series of substituted 2-aminopyridines was prepared and evaluated as inhibitors of human nitric oxide synthases (NOS). 4,6-Disubstitution enhanced both potency and speci®city for the inducible NOS with the most potent compound having an IC 50 of 28 nM. # 2000 Elsevier Science Ltd. All rights reserved. In recent years, nitric oxide (NO) has emerged as one of the most interesting, and seemingly ubiquitous, mediators of normal and pathophysiological processes. 1 À3 In mammalian cells, NO is produced by the oxidation of l-Arginine by nitric oxide synthase (NOS). There are three isoforms of NOS: the constitutively expressed neuronal NOS (n-NOS) and endothelial cell NOS (e-NOS) and the inducible NOS (i-NOS). n-NOS is believed to have a role in the production of NO as a neurotransmitter. e-NOS is found primarily in vascular endothelium where it regulates blood pressure and vascular tone. i-NOS expression is induced in activated macrophage and other cell types by numerous in¯am- matory stimuli including endotoxin (LPS) and cytokines (e.g. IL-1) and has a role in host defense and possibly chronic in¯ammatory conditions. Transgenic mice that have the NOS genes knocked-out con®rm many of the biological roles of the respective NOS isoforms. 4 À8 The induction of i-NOS by in¯ammatory stimuli and the prolonged production of copious amounts of NO by some activated in¯ammatory cells strongly suggest a role for i-NOS in both host defense and tissue destruction associated with acute and chronic in¯ammation. As such, i-NOS may have a role in a variety of diseases including septic shock, arthritis, and in¯ammatory bowel disease. The objective of our program was to identify potent and selective inhibitors of i-NOS with appropriate pharmacological properties. Several groups have identi®ed 2-aminopyridines as NOS inhibitors. A detailed report of the in vitro and in vivo properties of 2-amino-4-methylpyridine 3 has appeared. 9,10 The structure±activity relationship for a variety of substi- tuted 2-aminopyridines is described herein. Synthesis of 2-Aminopyridines The synthesis of 2-aminopyridine derivatives has been extensively reviewed. 11 À13 Several of the compounds in Tables 1 and 2 are also commercially available. Among the methods employed to prepare some of the com- pounds described, the Chitchibabin reaction, Hofmann, Curtius, Lossen and Neber-type rearrangements, and halogen replacements were employed. 14 The synthesis of 2-aminopyridine from pyridine-N-oxides has also been described (Scheme 1). 15 Pyridine-N-oxides were treated with 4-chloro-2,2-dimethyl-1,3(2H)-benzoxazine to give 3-(2-pyridyl)-1,3-benzoxazinones. Subsequent treatment with strong acid aorded the 2-aminopyridine. 0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0960-894X(00)00389-9 Bioorganic & Medicinal Chemistry Letters 10 (2000) 1975±1978 *Corresponding author. Tel.: +1-732-594-7249; fax: +1-732-594- 5966; e-mail: william_hagmann@merck.com