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J. Med. Chem. 2007, 50, 3528-3539
Novel Vanilloid Receptor-1 Antagonists: 3. The Identification of a Second-Generation Clinical Candidate with Improved Physicochemical and Pharmacokinetic Properties Hui-Ling Wang,*,† Jodie Katon, Chenera Balan,† Anthony W. Bannon,‡ Charles Bernard,† Elizabeth M. Doherty,† Celia Dominguez,† Narender R. Gavva,‡ Vijay Gore,† Vu Ma,† Nobuko Nishimura,† Sekhar Surapaneni,§ Phi Tang,† Rami Tamir,‡ Oliver Thiel,† James J. S. Treanor,‡ and Mark H. Norman† Department of Chemistry Research and DiscoVery, Department of Neuroscience, and Department of Pharmacokinetics and Drug Metabolism, Amgen Inc., One Amgen Center DriVe, Thousand Oaks, California 91320-1799 ReceiVed February 19, 2007
Based on the previously reported clinical candidate, AMG 517 (compound 1), a series of related piperazinylpyrimidine analogues were synthesized and evaluated as antagonists of the vanilloid 1 receptor (VR1 or TRPV1). Optimization of in vitro potency and physicochemical and pharmacokinetic properties led to the discovery of (R)-N-(4-(6-(4-(1-(4-fluorophenyl)ethyl)piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (16p), a potent TRPV1 antagonist [rTRPV1(CAP) IC50 ) 3.7 nM] with excellent aqueous solubility (g200 µg/mL in 0.01 N HCl) and a reduced half-life (rat t1/2 ) 3.8 h, dog t1/2 ) 2.7 h, monkey t1/2 ) 3.2 h) as compared to AMG 517. In addition, compound 16p was shown to be efficacious at blocking a TRPV1-mediated physiological response in vivo (ED50 ) 1.9 mg/kg, p.o. in the capsaicininduced flinch model in rats) and was also effective at reducing thermal hyperalgesia induced by complete Freund’s adjuvant in rats (MED ) 1 mg/kg, p.o). Based on its improved overall profile, compound 16p (AMG 628) was selected as a second-generation candidate for further evaluation in human clinical trials as a potential new treatment for chronic pain. Introduction The vanilloid receptor-1 (VR1 or TRPV1) is a nonselective cation channel belonging to the transient receptor potential (TRP) super family that plays a role as an integrator of multiple pain-producing stimuli.1 Over the past several years, TRPV1 has emerged as an exciting target for the treatment of chronic pain,2 and we have reported the identification and SAR development of several novel classes of TRPV1 antagonists, including cinnamides,3 thiazoles,4 benzimidazoles,5 and pyrimidines.6,7 Investigations into the latter class of compounds have been particularly fruitful and have provided us with a rich supply of TRPV1 antagonists for further study. In parts 1 and 2 of this series, we described the structureactivity relationship (SAR) investigations leading to the discovery of the pyrimidine class of TRPV1 antagonists.6,7 These studies led to the identification of our first TRPV1 clinical candidate AMG 517 (1, Figure 1). AMG 517 was chosen for evaluation in human clinical trials based on its potent efficacy in pharmacological models and its excellent safety profile. As this promising candidate progressed into clinical development, we sought to identify a second-generation TRPV1 antagonist with an improved profile. The two areas that we felt AMG 517 could be improved upon were its half-life and solubility. In preclinical studies, AMG 517 was found to be extremely stable in vitro and in vivo and was shown to have very long halflives in multiple species (rat t1/2 ) 31 h, dog t1/2 ) 41 h, monkey t1/2 ) 62 h).7 Based on this preclinical pharmacokinetic data, allometric projections predicted a human half-life of 60-120 h and significant accumulation upon multiple-dose administration. In addition, AMG 517 was found to have low aqueous solubility ( 10, and extracted with
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Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15
toluene (3 × 50 mL) and EtOAc (50 mL). The combined organic phases were washed with brine (100 mL), dried over sodium sulfate, filtered, and concentrated in vacuo to afford (R)-1-(1-(4-fluorophenyl)ethyl)piperazine (23; 10.4 g, 91%) as a pale brown solid. Mp: 70-71 °C. 1H NMR (400 MHz, CDCl3): δ 7.26-7.30 (m, 2 H), 6.95-7.06 (m, 2 H), 3.33 (q, J ) 6.8 Hz, 1 H), 2.82-2.88 (m, 4 H), 2.40-2.50 (m, 1 H), 2.28-2.37 (m, 2 H), 2.01-2.09 (m, 2 H), 1.33 (d, J ) 6.8 Hz, 3 H). MS (ESI, pos. ion) m/z: 209 (M + 1). (S)-1-(1-(4-Fluorophenyl)ethyl)piperazine (24). Method A: Analogous to the method A in the preparation of compound 23, (S)-tert-butyl 4-(1-(4-fluorophenyl)ethyl)piperazine-1-carboxylate (22; 420 mg, 1.4 mmol) provided (S)-1-(1-(4-fluorophenyl)ethyl)piperazine (24) as a TFA salt. MS (ESI, pos. ion) m/z: 209 (M + 1). Method B: Analogous to the method B in the preparation of compound 23, N,N-bis(2-chloroethyl)-4-methylbenzenesulfonamide 25 (21.0 g, 134 mmol), (S)-1-(4-fluorophenyl)ethanamine (9.0 g, 120 mmol) provided (S)-1-(1-(4-fluorophenyl)ethyl)piperazine (24; 7.4 g, 56% over two steps) as a pale-yellow solid. 1H NMR (400 MHz, CDCl3): δ 7.26-7.30 (m, 2 H), 6.95-7.06 (m, 2 H), 3.33 (q, J ) 6.8 Hz, 1 H), 2.82-2.88 (m, 4 H), 2.40-2.50 (m, 1 H), 2.28-2.37 (m, 2 H), 2.01-2.09 (m, 2 H), 1.33 (d, J ) 6.8 Hz, 3 H). MS (ESI, pos. ion) m/z: 209 (M + 1). (R)-N-(4-(6-(4-(1-(4-Fluorophenyl)ethyl)piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (16p). A mixture of N-(4-(6-chloropyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (9; 3.0 g, 9.4 mmol), (R)-1-(1-(4-fluorophenyl)ethyl)piperazine (23; 2.0 g, 9.8 mmol, from the procedure described for compound 23, method B), and Na2CO3 (2.4 g, 9.4 mmol) in DMF (30.0 mL) was heated at 90 °C for 5.5 h. The reaction mixture was transferred dropwise to a flask containing H2O (240 mL) and stirred vigorously for 30 min. The resulting precipitate was collected by filtration and washed with H2O (1 × 50 mL and 2 × 25 mL) followed by hexanes (3 × 50 mL). The resulting solid was dried under vacuum to provide the title compound as an off-white solid (4.1 g, 88%). 1H NMR (400 MHz, DMSO-d6): δ 12.41 (s, 1 H), 8.06 (s, 1 H), 7.84 (dd, J ) 7.8, 0.8 Hz, 1 H), 7.27-7.40 (m, 3 H), 7.11-7.22 (m, 3 H), 6.32 (s, 1 H), 3.57 (br s, 4 H), 3.50 (q, J ) 6.8 Hz, 1 H), 2.402.48 (m, 2 H), 2.30-2.38 (m, 2 H), 2.15 (s, 3 H), 1.31 (d, J ) 6.7 Hz, 3 H). MS (ESI, pos. ion) m/z: 493 (M + 1). Anal. (C25H25FN6O2S): C, H, N. (S)-N-(4-(6-(4-(1-(4-Fluorophenyl)ethyl)piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (16q). This material was prepared according to the procedure described for compound 16p from N-(4-(6-chloropyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (9; 430 mg, 1.4 mmol) and (S)-1-(1-(4fluorophenyl)ethyl)piperazine (24; 280 mg, 1.4 mmol, from the procedure described for compound 24, method A). The title compound was obtained as an off-white solid (271 mg, 41%). 1H NMR (400 MHz, DMSO-d6): δ 12.41 (s, 1 H), 8.06 (s, 1 H), 7.84 (dd, J ) 7.8, 0.8 Hz, 1 H), 7.27-7.40 (m, 3 H), 7.11-7.22 (m, 3 H), 6.32 (s, 1 H), 3.57 (br s, 4 H), 3.50 (q, J ) 6.8 Hz, 1 H), 2.40-2.48 (m, 2 H), 2.30-2.38 (m, 2 H), 2.15 (s, 3 H), 1.31 (d, J ) 6.7 Hz, 3 H). MS (ESI, pos. ion) m/z: 493 (M + 1). Anal. (C25H25FN6O2S): C, H, N. N-(4-(6-(4-(1-(4-Fluorophenyl)ethyl)piperazin-1-yl)pyrimidin4-yloxy)benzo[d]thiazol-2-yl)acetamide (17a). A mixture of N-(4(6-(piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]thiazol-2-yl)acetamide (16a; 200 mg, 0.54 mmol) and 4′-fluoro-acetophenone (0.1 mL, 0.81 mmol) in THF (2 mL) at room temperature was treated with titanium tetra-isopropoxide (0.47 mL, 1.6 mmol) under nitrogen and then stirred at 75 °C for 16 h. The reaction mixture was cooled to -48 °C and then treated with sodium borohydride (60 mg, 1.6 mmol) followed by MeOH (1.0 mL). The resulting mixture was allowed to warm to room temperature over 3.5 h. The reaction mixture was diluted with EtOAc (50 mL) and washed with aqueous 1 N NaOH (2 × 50 mL). The organic layer was dried over Na2SO4, filtered, and concentrated under vacuum. The crude material was purified by silica gel chromatography (gradient: 0-5% MeOH/CH2Cl2) to provide the title compound as a white solid (5 mg, 2%). Mp: 241-242 °C. 1H NMR (400 MHz, DMSO-d6): δ
Wang et al.
12.41 (s, 1 H), 8.06 (s, 1 H), 7.84 (dd, J ) 7.8, 0.8 Hz, 1 H), 7.27-7.40 (m, 3 H), 7.11-7.22 (m, 3 H), 6.32 (s, 1 H), 3.57 (br s, 4 H), 3.50 (q, J ) 6.8 Hz, 1 H), 2.40-2.48 (m, 2 H), 2.30-2.38 (m, 2 H), 2.15 (s, 3 H), 1.31 (d, J ) 6.7 Hz, 3 H). MS (ESI, pos. ion) m/z: 493 (M + 1). Anal. (C25H25FN6O2S): C, H, N. N-(4-(6-(4-(1-(2-Fluorophenyl)ethyl)piperazin-1-yl)pyrimidin4-yloxy)benzo[d]thiazol-2-yl)acetamide (17b). This material was prepared according to the procedure described for compound 17a from N-(4-(6-(piperazin-1-yl)pyrimidin-4-yloxy)benzo[d]thiazol-2yl)acetamide (16a; 60 mg, 0.16 mmol) and 2′-fluoro-acetylphenone (0.03 mL, 0.24 mmol). The title compound (29 mg, 37%) was obtained as a pale-yellow solid. Mp: 203-204 °C. 1H NMR (400 MHz, DMSO-d6): δ 12.43 (s, 1 H), 8.06 (s, 1 H), 7.85 (d, J ) 7.8 Hz, 1 H), 7.48 (t, J ) 7.4 Hz, 1 H), 7.32 (t, J ) 8.0 Hz, 2 H), 7.14-7.26 (m, 3 H), 6.33 (s, 1 H), 3.86 (q, J ) 7.0 Hz, 1 H), 3.58 (br s, 4 H), 2.42-2.48 (m, 2 H), 2.35-2.42 (m, 2 H), 2.15 (s, 3 H), 1.36 (d, J ) 6.7 Hz, 3 H). MS (ESI, pos. ion) m/z: 493 (M + 1). Anal. (C25H25FN6O2S): C, H, N.
Acknowledgment. The authors thank Paul Reider, Randy Hungate, Jean-Claude Louis, and Chris Fibiger for their support in this research program. Thanks also go to James Davis, Gal Hever, Rongzhen Kuang, Jue Wang, Dawn Zhu, Shoushu Jiao, and Ella Magal for conducting the in vivo pharmacology, Helming Tan and Maggie Reed for the solubility determination, and Wesley Barnhart for his excellent technical assistance in conducting the HPLC chiral separation. Finally, we acknowledge all of our colleagues on the TRPV1 research team (pharmaceutics, toxicology, PKDM, process research and development, analytical support, clinical development). Supporting Information Available: Elemental analysis data for final compounds 12-15, 16a-q, and 17a,b. This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) (a) Caterina, M. J.; Schumacher, M. A.; Tominaga, M.; Rosen, T. A.; Levine, J. D.; Julius, D. The Capsaicin Receptor: A HeatActivated Ion Channel in the Pain Pathway. Nature 1997, 389, 816824. (b) Montell, C.; Birnbaumer, L.; Flockerzi, V.; Bindels, R. J.; Bruford, E. A.; Caterina, M. J.; Clapham, D. E.; Harteneck, C.; Heler, S.; Julius, D.; Kojima, I.; Mori, Y.; Penner, R.; Prawitt, D.; Scharenberg, A. M.; Schultz, G.; Shimizu, N.; Zhu, M. X. A Unified Nomenclature for the Superfamily of TRP Cation Channels. Mol. Cell 2002, 9, 229-231. (c) Clapham, D. TRP Channels as Cellular Sensors. Nature 2003, 426, 517-524. (d) Szallasi, A.; Blumberg, P. M. Vanilloid (Capsaicin) Receptors and Mechanisms. Pharmacol. ReV. 1999, 51, 159-212. (2) For reviews see: (a) Appendino, G.; Munoz, E.; Fiebich, B. L. TRPV1 (Vanilloid Receptor, Capsaicin Receptor) Agonists and Antagonists. Expert Opin. Ther. Pat. 2003, 13 (12), 1825-1837. (b) Szallasi, A.; Appendino, G. Vanilloid Receptor TRPV1 Antagonists as the Next Generation of Painkillers. J. Med. Chem. 2004, 47 (11), 1-7. (c) Roberts, L.; Connor, M. TRPV1 Antagonists as a Potential Treatment for Hyperalgesia. Recent Pat. CNS Drug DiscoVery 2006, 1, 65-76. (d) Geppetii, P.; Materazzi, S.; Nicoletti, P. The Transient Receptor Potential Vanilloid 1: Role in Airway Inflammation and Disease. Eur. J. Pharmacol. 2006, 533, 207-214 and references therein. (3) Doherty, E. M.; Fotsch, C.; Bo, Y.; Chakrabarti, P.; Chen, N.; Gavva, N.; Han, N.; Kelly, M. G.; Kincaid, J.; Klionsky, L.; J.; Liu, Q.; Ognyanov, V. I.; Tamir, R.; Wang, Q.; Zhu, Z.; Norman, M. H.; Treanor, J. J. S. Discovery of Potent, Orally Available Vanilloid Receptor-1 Antagonists. Structure-Activity Relationship of N-Aryl Cinnamides. J. Med. Chem. 2005, 48, 71-90. (4) Xi, N.; Bo, Y.; Doherty, E. M.; Fotsch, C.; Gavva, N.; Han, N.; Hungate, R. W.; Klionsky, L.; Liu, Q.; Tamir, R.; Xu, S.; Treanor, J. J. S.; Norman, M. H. Synthesis and Evaluation of Thiazole Carboxamides as Vanilloid Receptor 1 (TRPV1) Antagonists. Bioorg. Med. Chem. Lett. 2005, 15, 5211-5217. (5) Ognyanov, V. I.; Balan, C.; Bannon, A. W.; Bo, Y.; Dominguez, C.; Fotsch, C.; Gore, V. K.; Klionsky, L.; Ma, V. M.; Qian, Y.-X.; Tamir, R.; Wang, X.; Xi, N.; Xu, S.; Zhu, D.; Gavva, N. R.; Treanor, J. J. S.; Norman, M. H. Design of Potent, Orally Available Antagonists of Transient Receptor Potential Vanilloid 1. StructureActivity Relationships of 2-(Piperazin-1-yl)-1H-benzimidazoles. J. Med. Chem. 2006, 49 (12), 3719-3742.
AMG 628, a Second-Generation Clinical Candidate (6) Norman, M. H.; Fotsch, C.; Doherty, E. M.; Bo, Y.; Chen, N.; Chakrabarti, P.; Gavva, N. R.; Nishimura, N.; Nixey, T.; Ognyanov, V. I.; Rzasa, R.; Stec, M.; Surapaneni, S.; Tamir, R.; Viswanadhan, V.; Zhu, J.; Treanor, J. J. S. Novel Vanilloid Receptor-1 Antagonists: 1. Conformationally Restricted Analogues of trans-Cinnamides. J. Med. Chem. 2007, 50, 3497-3514. (7) Doherty, E. M.; Bannon, A. W.; Bo, Y.; Chen, N.; Dominguez, C.; Falsey, J. Fotsch, C.; Gavva, N. R.; Katon, J.; Nixey, T.; Ognyanov, V. I.; Pettus, L.; Rzasa, R.; Stec, M.; Surapaneni, S.; Tamir, R.; Zhu, J.; Treanor, J. J. S.; Norman, M. H. Novel Vanilloid Receptor-1 Antagonists: 2. Structure-Activity Relationships of 4-Oxopyrimidines Leading to the Selection of a Clinical Candidate. J. Med. Chem. 2007, 50, 3515-3527. (8) Tan, H.; Semin, D.; Wacker, M.; Cheetham, J. An Automated Screening Assay for Determination of Aqueous Equilibrium Solubility Enabling SPR Study During Drug Lead Optimization. JALA 2005, 10 (6), 364-373. (9) Goodman, A. J.; Stanforth, S. P.; Tarbitb, B. Desymmetrization of Dichloroazaheterocycles. Tetrahedron 1999, 55, 15067-15070. (10) Eastwood, P. R. A Versatile Synthesis of 4-Aryl Tetrahydropyridines via Palladium-Mediated Suzuki Cross-Coupling with Cyclic Vinyl Boronates. Tetrahedron Lett. 2000, 41, 3705-3708. (11) The ratio was determined by the relative integrations of pyrimidime protons, 7.05 vs 7.12 ppm and 8.58 vs 8.62 ppm, in the 1H NMR spectrum.
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 15 3539 (12) (a) Opalka, C. J.; D’Ambra, T. E.; Facoone, J. J.; Bodson, G.; Cossement, E. A Novel Synthesis of the Enantiomers of an Antihistamine Drug by Piperazine Formation from a Primary Amine. Synthesis 1995, 766. (b) Pflum, Derek, A.; Krishnamurthy, D.; Zhengxu, H.; Senanayke, S. A. Asymmetric Synthesis of Cetirizine Dihydrochloride. Tetrahedron Lett. 2002, 43, 923-926. (c) Bazzicalupi, C.; Bencini, A.; Fusi, V.; Micheloni, M.; Paoletti, P.; Valtancoli, B. Synthetic Route to Produce Giant-Size Azamacrocycles. J. Org. Chem. 1994, 59, 7508-7510. (13) The IC50 values of compound 16p were greater than 4 mM at blocking TRP channels (hTRPV3, mTRPV1, rTRPM8, hTRPA1) that are structurally related to TRPV1. (14) (a) Wang, H.-L.; Balan, C.; Doherty, E. M.; Falsey, J. R.; Gore, V. K.; Katon, J.; Norman, M. H. Preparation of 4-heteroaryloxy-6piperazinopyrimidines as vanilloid receptor ligands. US 2005/ 0176726 A1, 2005. (b) Balan, C.; Chen, N.; Doherty, E. M.; Gore, V; K.; Norman, M. H.; Wang, H.-L. Preparation of 4-heteroaryloxy6-piperazinopyrimidines and 2-heteroaryloxy-4-piperazinopyridines as vanilloid receptor ligands. US 2005/0182067 A1, 2005. (15) Poindexter, G. S.; Bruce, M. A.; Leboullec, K. L.; Monokovic, I. Use of 2-Oxazolidinones as Latent Aziridine Equivalents. III. Preparation of N-Substituted Piperazines. Tetrahedron Lett. 1994, 35, 7331-7334.
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