Original article Discovery of Tr € oger's base analogues as selective inhibitors against human breast cancer cell line: Design, synthesis and cytotoxic evaluation Bhaskar Reddy Manda a , Manjula Alla a, * , Roopa Jones Ganji b , Anthony Addlagatta b, * a Crop Protection Chemicals Division, CSIR-Indian Institute of Chemical Technology, Hyderabad 500 607, India b Centre for Chemical Biology, CSIR-Indian Institute of Chemical Technology, Hyderabad 500 607, India article info Article history: Received 3 February 2014 Received in revised form 11 August 2014 Accepted 12 August 2014 Available online 13 August 2014 Keywords: Tr€ oger's base VilsmeiereHaack reaction Amination Cytotoxicity abstract A library of structurally diverse Tr€ oger's base analogues has been constructed via unusual amination of methylene bridge employing VilsmeiereHaack conditions as well as by the incorporation of five and six membered heterocycles on the aromatic core of Tr€ oger's base framework. The constructed structurally diverse frameworks were evaluated for their cytotoxic activities against a panel of three human cancer lines A549 (lung adenocarcinoma), MDAMB-231 (breast) and SK-N-SH (neuroblastoma). From the ac- tivity profile obtained, a redesign of Tr€ oger's base analogues led to the construction of more potent molecular entities. The study led to development of a series of compounds with MDAMB-231 cell line specific cytotoxicity. Of the 30 compounds synthesized and evaluated, 7 compounds were found to possess cytotoxicity that is equivalent or better than standard drug doxorubicin against MDAMB-231 cell line while only one compound was found to be active against SK-N-SH cell line. © 2014 Elsevier Masson SAS. All rights reserved. 1. Introduction Tr€ oger's base, 2,8-dimethyl-6H,12H-5,11-methanodibenzo[b,f] [1,8]diazocine (Fig. 1), was first synthesized in 1887 by Julius Tr€ oger by the reaction of p-toluidine with methylal [CH 2 -(OCH 3 ) 2 ] in acidic conditions [1]. Its correct structure was determined by Spielman in 1935 and assigned as racemic [2]. Later a number of aromatic, heterocyclic Tr€ oger's bases with various functional groups were synthesized by using different methylene donors such as para- formaldehyde, hexamethylenetetramine (HMTA), dimethoxy- methane, or DMSO and by varying acidic media such as trifluoroacetic acid (TFA), HCl, or acetic acid [3]. The basic structure of Tr€ oger's base features a central bicyclic aliphatic diazocine unit fused with two arene rings, oriented approximately at right angles to each other (V shaped) [4]. Tr€ oger's base also has C 2 -symmetry and chirality that is provided by the two stereogenic bridgehead nitrogen atoms (inability to invert) of the diazocine ring. The unique geometry of Tr€ oger's base has been exploited for many applications in the field of supramolecular chemistry as molecular receptors [5], in development of molecular torsion balances [6], in asymmetric catalysis [7], and as chiral solvating agent [8]. Tr€ oger's base structural features were utilized in the design and development of DNA minor grove binders (Fig. 2). Tr€ oger's bases derived from heterocyclic aromatic amines like acridine [9], phe- nanthroline and proflavine [10] have shown good affinity for DNA. Among these, the geometry of acridine derived Tr€ oger's base gives rise to a helix shape which can be similar or opposite to the helicity of DNA, resulting in enantioselective binding to calf-thymus B-DNA [9a] and hence serves as a molecular probe. Racemic Tr€ oger's base containing phenanthroline units are known to cleave DNA in the presence of Cu 2þ ions [11]. Proflavine type Tr€ oger's base has also been used for enantiospecific binding to calf-thymus B-DNA se- quences containing both A.T and G.C base pairs. Veale et al. re- ported the synthesis and fluorescence imaging studies of 1,8- naphthalimide analogues of Tr€ oger's base and illustrated their rapid uptake by cancer cells [12]. However, limited studies have been reported on Tr€ oger's base derivatives as anticancer agents [13]. Earlier, our group has reported the VilsmeiereHaack reaction of Tr€ oger's base analogues resulting in an unusual functionalization of methylene bridge of the diazocine unit [14]. In our continued in- terest in developing small molecules as cytotoxic agents [15], we have expanded our chemistry on Tr€ oger's base scaffold in designing * Corresponding authors. E-mail addresses: manjula@iict.res.in, manjula_alla@yahoo.com (M. Alla), anthony@iict.res.in (A. Addlagatta). Contents lists available at ScienceDirect European Journal of Medicinal Chemistry journal homepage: http://www.elsevier.com/locate/ejmech http://dx.doi.org/10.1016/j.ejmech.2014.08.044 0223-5234/© 2014 Elsevier Masson SAS. All rights reserved. European Journal of Medicinal Chemistry 86 (2014) 39e47