Heteroaryl urea inhibitors of fatty acid amide hydrolase: Structure–mutagenicity relationships for arylamine metabolites Mark S. Tichenor a,⇑ , John M. Keith a , William M. Jones a , Joan M. Pierce a , Jeff Merit a , Natalie Hawryluk a , Mark Seierstad a , James A. Palmer a , Michael Webb a , Mark J. Karbarz a , Sandy J. Wilson a , Michelle L. Wennerholm a , Filip Woestenborghs b , Dominiek Beerens b , Lin Luo a , Sean M. Brown a , Marlies De Boeck b , Sandra R. Chaplan a , J. Guy Breitenbucher a a Janssen Research and Development, L.L.C., 3210 Merryfield Row, San Diego, CA 92121, United States b Janssen Research and Development, A Division of Janssen Pharmaceutica N.V., Turnhoutseweg 30, B-2340 Beerse, Belgium article info Article history: Received 29 August 2012 Revised 8 October 2012 Accepted 15 October 2012 Available online 22 October 2012 Keywords: Fatty acid amide hydrolase FAAH Urea Heteroaryl amine Mutagenic Ames II abstract The structure–activity relationships for a series of heteroaryl urea inhibitors of fatty acid amide hydrolase (FAAH) are described. Members of this class of inhibitors have been shown to inactivate FAAH by covalent modification of an active site serine with subsequent release of an aromatic amine from the urea electro- phile. Systematic Ames II testing guided the optimization of urea substituents by defining the structure– mutagenicity relationships for the released aromatic amine metabolites. Potent FAAH inhibitors were identified having heteroaryl amine leaving groups that were non-mutagenic in the Ames II assay. Ó 2012 Elsevier Ltd. All rights reserved. Fatty acid amide hydrolase (FAAH) is responsible for degrading a family of fatty acid amide signaling molecules including the endogenous cannabinoid receptor (CB1/CB2) agonist anandamide. 1 Modulating the cannabinoid system by FAAH inhibition is an attractive approach for treating a variety of conditions associated with cannabinoid receptor function including pain, anxiety, and depression. Elevating levels of anandamide by inhibiting its degradation is anticipated to have an improved side effect profile relative to exogenous cannabinoid receptor agonists such as D 9 -tetrahydrocannabinol (THC) that cause cognitive and motor impairment. Genetic knockout mice lacking FAAH have anandamide levels that are elevated 15-fold relative to wild-type animals and exhibit an analgesic phenotype but are otherwise healthy, 2 providing a rationale for the therapeutic value of FAAH inhibition. 3 The majority of FAAH modulators that have been reported in the literature are mechanism-based inhibitors that inactivate the en- zyme by forming a covalent bond with active site serine-241 (Fig. 1), 4–7 although an increasing number of recent publications have described compounds that inhibit FAAH by noncovalent mechanisms. 8–11 Covalent modification 12 is an effective approach for modulating FAAH activity because nearly complete enzyme inhibition is required before anandamide levels are significantly elevated. 13,14 Phenyl carbamate inhibitors exemplified by URB-597 (1) were reported to be effective in animal models of analgesia and anxiety. 15,16 However, the clinical utility of URB-597 may be limited 0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.bmcl.2012.10.076 ⇑ Corresponding author. Tel.: +1 858 320 3512; fax: +1 858 450 2089. E-mail address: mticheno@its.jnj.com (M.S. Tichenor). O NH 2 O H N O 1, URB-597 2, SA-47 4, PF-04457845 N H N O N N O N CF 3 3, Takeda-25/JNJ-1661010 N H N O N S N N 6, OL-135 O N O N N Me N N H O O H N O Me N H N O N N O Cl 5, JNJ-40355003 Figure 1. Representative FAAH inhibitors. Bioorganic & Medicinal Chemistry Letters 22 (2012) 7357–7362 Contents lists available at SciVerse ScienceDirect Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl