Dependence of DNA Sequence Selectivity and Cell Cytotoxicity on Azinomycin A and B Epoxyamide Stereochemistry Robert S. Coleman,* ,² Robert L. Woodward, ² Amy M. Hayes, ² Erika A. Crane, ² Anna Artese, ‡ Francesco Ortuso, ‡ and Stefano Alcaro* ,‡ Department of Chemistry, The Ohio State UniVersity, 100 West 18th AVenue, Columbus, Ohio 43210, and Dipartimento di Scienze Farmaco-Biologiche, UniVersita ` di Catanzaro “Magna Græcia”, 88021 Roccelletta di Borgia, Catanzaro, Italy coleman@chemistry.ohio-state.edu Received February 15, 2007 ABSTRACT Evaluation of the importance of C18/C19 stereochemistry of azinomycin A/B epoxyamide partial structures with respect to DNA alkylation sequence selectivity is reported using a unique assay with a DNA oligomer containing imbedded normal (5′-GGC-3′/3′-CCG-5′) and inverted (5′-CGG-3′/3′-GCC-5′) azinomycin consensus cross-linking sequences. Both species were found to have unique selectivity profiles and alkylate DNA in a manner distinct from azinomycin B. Computational docking experiments support altered binding modes for the enantiomers. The importance of natural products as lead compounds for anticancer drug development is evident in the fact that more than half of existing agents are natural products or derivatives thereof, 1 and a wide variety of bioactive natural products are currently in clinical trials as anticancer agents. 2 Many such compounds exert their action by covalent modification 3 or cross-linking of duplex DNA 4 and provide the basis for much of cancer chemotherapy. The azinomycins 5 are Streptomyces metabolites isolated in 1986 that show good levels of in vitro cytotoxicity and effective, potent in vivo antitumor activity. 6 Azinomycin B was subsequently demonstrated to covalently cross-link double-stranded DNA by reaction of the N7 positions of suitably disposed purine bases with the electrophilic C10 and C21 carbons. 7,8 Recent studies have further supported this finding, demonstrating that nuclear DNA is the relevant molecular target of the natural product. 9 There has also been ² The Ohio State University. ‡ Universita ` di Catanzaro. (1) Newman, D. J.; Cragg, G. M.; Snader, K. M. J. Nat. Prod. 2003, 66, 1022. (2) Newman, D. J.; Cragg, G. M. J. Nat. Prod. 2004, 67, 1216. (3) Gates, K. S. DNA and Aspects of Molecular Biology. In Compre- hensiVe Natural Products Chemistry; Barton, D., Nakanishi, K., Meth-Cohn, O., Eds.; Pergamon Press: Amsterdam, NY, 1999; Vol. 7, pp 491-552. (4) Rajski, S. R.; Williams, R. M. Chem. ReV. 1998, 98, 2723. (5) (a) Nagaoka, K.; Matsumoto, M.; Oono, J.; Yokoi, K.; Ishizeki, S.; Nakashima, T. J. Antibiot. 1986, 39, 1527. (b) Yokoi, K.; Nagaoka, K.; Nakashima, T. Chem. Pharm. Bull. 1986, 34, 4554. (6) Ishizeki, S.; Ohtsuka, M.; Irinoda, K.; Kukita, K.; Nagaoka, K.; Nakashima, T. J. Antibiot. 1987, 40, 60. In vitro cytotoxicity: IC50 ) 0.07 μg/mL (1a) and 0.11 μg/mL (1b) against L5178Y cells. In vivo antitumor activity: 193% ILS at 16 μg/kg of 1b (3/7 survivors) against P388 leukemia; 161% ILS at 32 μg/kg of 1b (5/8 survivors) against Erlich carcinoma. In the same system, mitomycin C exhibited a 204% ILS at 1 mg/kg against P388 leukemia. (7) (a) Armstrong, R. W.; Salvati, M. E.; Nguyen, M. J. Am. Chem. Soc. 1992, 114, 3144. (b) Fujiwara, T.; Saito, I.; Sugiyama, H. Tetrahedron Lett. 1999, 40, 315. (c) Zang, H.; Gates, K. S. Biochemistry 2000, 39, 14968. (d) Coleman, R. S.; Perez, R. J.; Burk, C. H.; Navarro, A. J. Am. Chem. Soc. 2002, 124, 13008. ORGANIC LETTERS 2007 Vol. 9, No. 10 1891-1894 10.1021/ol070395s CCC: $37.00 © 2007 American Chemical Society Published on Web 04/14/2007