Synthesis and Biological Evaluation of 2-Indolyloxazolines as a New Class of Tubulin Polymerization Inhibitors. Discovery of A-289099 as an Orally Active Antitumor Agent Qun Li,* Keith W. Woods, Akiyo Claiborne, Stephen L. Gwaltney, II, Kenneth J. Barr, Gang Liu, Laura Gehrke, R. Bruce Credo, Yu Hua Hui, Jang Lee, Robert B. Warner, Peter Kovar, Michael A. Nukkala, Nicolette A. Zielinski, Stephen K. Tahir, Michael Fitzgerald, Ki H. Kim, Kennan Marsh, David Frost, Shi-Chung Ng, Saul Rosenberg and Hing L. Sham Cancer Research, Abbott Laboratories, Abbott Park, IL 60064-6101, USA Received 12 October 2001; accepted 16 November 2001 Abstract—A series of indole containing oxazolines has been discovered as a result of structural modifications of the lead compound A-105972. The compounds exert their anticancer activity through inhibition of tubulin polymerization by binding at the colchicine site. A-289099 was identified as an orally active antimitotic agent active against various cancer cell lines including those that express the MDR phenotype. The anticancer activity, pharmacokinetics, and an efficient and enantioselective synthesis of A-289099 are described. # 2002 Elsevier Science Ltd. All rights reserved. Tubulin binding agents have generated considerable interest among cytotoxic agents, due in part to the suc- cess of the taxanes in clinical oncology. 1,2 However, emerging resistance to antimitotic agents such as pacli- taxel has limited their ultimate effectiveness. 3 Renewed interest has been generated by the hope that non-MDR substrates that interact with tubulin at sites different from those of vinca alkaloids and taxanes can be dis- covered. 4 Recently, compounds which bind to tubulin at the colchicine binding site, as represented by com- bretastatin A4, demonstrate promising activity against various cancer cell lines, including those that express the MDR phenotype. 1,5 The relatively simple structures of these compounds may provide the added advantage of being orally active. We recently identified the oxadiazoline A-105972 as a colchicine site binder with an IC 50 of 3.4 mM against tubulin polymerization. 6 As a part of our continuing efforts to identify more stable and orally active com- pounds, we report here our investigation of indole-based oxazolines, which led to the discovery of A-289099 (5b-S) as a potent and orally active antimitotic agent. 7 The racemic oxazolines (5) were synthesized by coupling of the amino alcohol 1 7 with either the acids (2) in a two-step transformation or the nitriles (3) in a one-step reaction as shown in Scheme 1. The required acids (2) or nitrile (3n) were prepared from known starting materials 8 10 as indicated in Scheme 2. Synthesis of the pure enantiomers of 5b proved to be more challenging. Literature methods for the synthesis of optically active 5-aryl oxazolines are limited. We eventually developed the enantioselective oxazoline synthesis shown in Scheme 3. Thus, styrene 14 was enantioselectively dihydroxylated according to the procedure of Ramacciotti et al. 11 using AD-mix-a to give S-diol 15. Monotosylation of 15 followed by nucleophilic displacement of the tosylate with sodium azide provided 16. Reduction of azide 16 under hydro- 0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0960-894X(01)00759-4 Bioorganic & Medicinal Chemistry Letters 12 (2002) 465–469 *Corresponding author. Fax: +1-847-935-5165; e-mail: qun.li@ abbott.com