Job/Unit: O43549 /KAP1 Date: 28-01-15 17:09:02 Pages: 9 FULL PAPER DOI: 10.1002/ejoc.201403549 Synthesis of Antitumor Carbazole-Amonafide Structural Hybrids Alex Rozovsky, [a,b] Elena Regozin, [a] Mor Oron-Herman, [b] Amnon Albeck, [c] and Gary Gellerman* [a] Keywords: Medicinal chemistry / Drug design / Antitumor agents / Nitrogen heterocycles / DNA / Cross-coupling A facile synthesis of new antitumor [4,5-bc]carbazole- amonafide derivatives is described. These compounds repre- sent a new class of structural hybrids that contain the medici- nally important carbazole and amonafide cores. The synthe- sis involves a Suzuki–Miyaura coupling of bromoamonafide with arylboronic acid reagents followed by the introduction Introduction A useful approach to design new DNA intercalating and topoisomerase poisoning compounds combines structural units from existing agents to enhance productive interac- tions within the enzyme-drug-DNA ternary complex. [1] This type of rational drug design led to the development of azatoxin (Figure 1), a drug that displays potent activity against topoisomerase II and mammalian cells and was subjected to preclinical development. [2] Azatoxin is a structural hybrid of the topoisomerase II targeted drugs etoposide and ellipticine [3] and contains fragments of the epipodophyllotoxin ring system of etoposide (interacts with both the minor groove of DNA and the enzyme), [4] which is fused to the planar indole ring of ellipticine (intercalates in DNA). [5] The search for new planar DNA intercalating drugs led to the development of benzocyclobutacarbazoles by joining the benzocylobutene and indole units. Several compounds of this type are described in the literature, and their antipro- liferative activities have been tested against murine L1210 leukemia cells. [2b] Xu and co-workers designed and evalu- ated new compounds that possess intercalating and photo- cleaving properties with five-membered thio-heterocyclic fused naphthalimides that have aminoalkyl side chains at the imide moiety. [6] [a] Department of Biological Chemistry, Ariel University Center of Samaria, Ariel 40700, Israel E-mail: garyg@ariel.ac.il www.ariel.ac.il [b] The Advance Technologies Center, The Chaim Sheba Medical Center, The Hashomer 52621, Israel [c] The Julius Spokojny Bioorganic Chemistry Laboratory, Department of Chemistry, Bar-Ilan University, Ramat Gan 52900, Israel Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejoc.201403549. Eur. J. Org. Chem. 0000, 0–0 © 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 of an azide group and subsequent regiospecific thermal nitrene insertion to yield carbazole-amonafide hybrids in good yields. Preliminary antiproliferative assays against can- cer and benign cell lines identified compounds with selective antitumor activity that exhibited submicromolar IC 50 values. Figure 1. Azatoxin as a structural hybrid of etoposide and ellip- ticine. Since the discovery of ellipticine and the synthesis of its derivatives, [7] much attention has been given to the anti- tumor activity of carbazoles (benzo[b]indoles). [8] Their structures provide an enormous chemical heterogeneity, which covers pure substituted carbazoles as well as complex annulated molecules. Nevertheless, depending on the precise structure and substitution pattern, there is also a small group of DNA binding carbazoles that do not intercalate but selectively bind in the minor groove of DNA. [9] Intercalators comprise a large group of compounds that share the common structural feature of a flat polycyclic and aromatic chromophore. The optimal size for an intercalat- ing chromophore is a tricyclic or tetracyclic ring system. [10]