N-(Arylacetyl)-biphenylalanines as Potent VLA-4 Antagonists Bing Li, a, * Stephen E. de Laszlo, a Theodore M. Kamenecka, a Ihor E. Kopka, a Philippe L. Durette, a Thomas Lanza, Jr., a Malcolm MacCoss, a Sharon Tong, a Richard A. Mumford, b Ermengilda D. McCauley, b Gail Van Riper, b John A. Schmidt b and William K. Hagmann a a Department of Medicinal Chemistry, Merck Research Laboratories, Rahway, NJ 07065, USA b Department of Inflammation and Rheumatology Research, Merck Research Laboratories, Rahway, NJ 07065, USA Received 28 January 2002; accepted 6 May 2002 Abstract—A series of potent N-(aralkyl-, arylcycloalkyl-, and heteroaryl-acyl)-4-biphenylalanine VLA-4 antagonists was prepared by rapid analogue methods using solid-phase chemistry. Further optimization led to several highly potent compounds (IC 50 < 1 nM). Evaluation of rat pharmacokinetic revealed generally high clearance. # 2002 Elsevier Science Ltd. All rights reserved. VLA-4 (a 4 b 1 ; CD49d/CD29) is a heterodimeric integrin expressed on the surface of lymphocytes. 1 Its ligands include vascular cell adhesion molecule-1 (VCAM-1), which is expressed on activated endothelial cells at sites of inflammation and produced in response to inflammatory cytokines, and an alternatively spliced (CS-1) domain of fibronectin (FN). The adhesion of lymphocytes to VCAM-1 and subsequent migration to extravascular spaces appear to be critical steps in the inflammatory response. 2 Several reports have demonstrated that blocking this interaction in animals with a 4 antibodies or VLA-4 antagonists can have therapeutic utility in a variety of disease models, including models of airways hyperresponsiveness, inflammatory bowel disease, multiple sclerosis, and arthritis. 36 VLA-4 has been shown to bind to the sequences -Ile-Asp-Ser- (-IDS-) in the C-D loop of VCAM-1 and -Leu-Asp-Val- (-LDV-) in the CS-1 domain of FN. 7,8 It is believed that the center aspartic acid makes an essential binding contact with VLA-4. In our search for unique antagonists of VLA-4, we and others have reported series of substituted acylated and sulfonylated phenyl- alanine derivatives as potent VLA-4 antagonists. 3,914 Substituted biphenylalanines emerged as one potency enhancing pharmacophore for both VLA-4 and the related integrin, a 4 b 7 . 12,14 Acyl components could be relatively small and include N-benzylpyroglutamate, substituted benzoyls, and tetrahydrofuroyl. In our search for unique leads that retained potency and had improved pharmacokinetic characteristics, a solid- phase chemistry strategy for the synthesis of single compounds was pursued. (l)-2 0 -Methoxy-4-biphenyl- alanine had been identified as a potency enhancing acid component and was initially chosen to load on the resin. For the acyl component, commercially available car- boxylic acids were chosen from among substituted aryl acetyls. The corresponding benzoyl derivatives have previously been disclosed. 15 The acids were incorporated via amide bond coupling to the derivatized resin to afford the desired products after cleavage from the resin (Scheme 1). (l)-4-Iodophenyl- alanine t-butyl ester was reacted with FmocCl in the presence of diisopropylethylamine to give N-Fmoc-(l)- 4-iodophenylalanine t-butyl ester which was reacted with 2-methoxyphenylboronic acid under Suzuki aryl coupling conditions to yield (l)-4-(2 0 -methoxy)- biphenylalanine t-butyl ester. 16 The ester was removed by treatment with trifluoroacetic acid to afford the free acid which was subsequently loaded onto a Wang resin using standard conditions. 12 Approximately 3 g of the free acid gave about 3 g of loaded resin which was enough to prepare  100 compounds. The N-Fmoc protecting group on the resin-loaded amino acid was 0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0960-894X(02)00366-9 Bioorganic & Medicinal Chemistry Letters 12 (2002) 2141–2144 *Corresponding author. Fax: +1-732-594-6090; e-mail: bing_li@ merck.com