Design and Synthesis of Potent and Selective Inhibitors of Integrin VLA-4 Sompong Wattanasin,* Beat Weidmann, Didier Roche, Stewart Myers, Amy Xing, Qin Guo, Michael Sabio, Peter von Matt, Ronald Hugo, Susan Maida, Philip Lake and Marla Weetall Novartis Institute for Biomedical Research, Novartis Pharmaceuticals Corporation, 556 Morris Avenue, Summit, NJ 07901, USA Received 16 July 2001; accepted 28 August 2001 Abstract—The synthesis and identification of a novel series of inhibitors of integrin VLA-4 are described. Their in vitro activity and selectivity against closely related integrins are also presented. # 2001 Elsevier Science Ltd. All rights reserved. Antagonism of cell surface receptors belonging to the integrin superfamily is a new paradigm for drug dis- covery in transplantation and cancer, as well as in other diseases. 1 Integrin VLA-4 is an attractive therapeutic target: blockade of integrin VLA-4 by monoclonal antibodies (mAbs) has shown clear-cut efficacy in ani- mal models of autoimmune disease, asthma, inflamma- tion, and acute and chronic rejection of allogeneic grafts. 2,3 VLA-4 antagonists act to block leukocyte migration as well as leukocyte activation on the cell types thought to mediate these diseases. VLA-4 is expressed on memory T cells, memory B cells, NK cells, monocytes and macrophages. Although orally active antagonists of the platelet integrin receptor are in advanced development, 1d a lack of similar progress is evident in the discovery of orally active low molecular weight (LMW) antagonists of the important leukocyte integrins such as VLA-4, despite their validation as tar- gets by mAbs. Because of the importance of this integ- rin and its implication in various disease processes, efforts toward the design and synthesis of orally bioa- vailable LMW inhibitors have intensified in recent years. 4 Herein, we describe the identification of potent and selective inhibitors of VLA-4 based on the known bisarylurea series 5 of LDV peptidomimetics. Although potent inhibition in the low nanomolar range was achieved with the progenitor members of the series, such as 1 and 2, 5 concerns with their peptidic features led us to make various structural modifications (Scheme 1). We have successfully generated antagonists that retain nM potency, but are structurally simpler than the original leads. Scheme 2 outlines the general approach to aza analo- gues 3–6. Thus, t-butyl carbazate was reductively alky- lated to give 15. Coupling of 15 with the isocyanate 16, which was derived from racemic ethyl 3-amino-3-phe- nylpropanoate, gave 17. Deprotection of the t-BOC group, acylation with the bisarylurea acid 18 5c and hydrolysis of the ethyl ester finally resulted in the aza analogue 3. Aza analogues 4 and 5 were similarly pre- pared from racemic ethyl 3-amino-4-hexenoate and ethyl valine, respectively. The aza analogue 6 was pre- pared as shown in Scheme 2. Sequential alkylation of t- butyl carbazate with ethyl bromoacetate and allyl bro- mide gave 19. Removal of the t-BOC protecting group followed by coupling with N-t-BOC-l-leucine and deprotection afforded 20. Acylation with the bisarylurea acid 18 and hydrolysis of the ester gave 6. The general route to b-aminoacid analogues (7–10) is illustrated by the synthesis of 7 in Scheme 3. Con- densation of 18 with 1,1-dimethylethyl (3R)-3-amino-5- methylhexanoate followed by removal of the t-butyl ester with trifluoroacetic acid provided 21. Standard coupling of the acid 21 with 1,1-dimethylethyl (3S)-3- 0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0960-894X(01)00586-8 Bioorganic & Medicinal Chemistry Letters 11 (2001) 2955–2958 *Corresponding author. Fax: +1-908-277-4885; e-mail: sompong. wattanasin@pharma.novartis.com