Original article New quinoxaline 1, 4-di-N-oxides: Anticancer and hypoxia-selective therapeutic agents Magda M.F. Ismail a, * , Kamelia M. Amin b , Eman Noaman c , Dalia H. Soliman a , Yousry A. Ammar d a Department of Pharmaceutical Chemistry, Faculty of Pharmacy (Girls), Al-Azhar University, Cairo, Egypt b Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Cairo University, Cairo, Egypt c Department of Radiation Biology, Natural Center for Radiation Research and Technology, Atomic Energy Authority, Cairo, Egypt d Department of Chemistry, Faculty of Science, Al-Azhar University, Cairo, Egypt article info Article history: Received 19 December 2009 Received in revised form 6 February 2010 Accepted 21 February 2010 Available online 1 March 2010 Keywords: Quinoxaline 1,4-di-N-oxide Antitumor activity Hypoxia-selective cytotoxicity abstract A new series of quinoxaline 1,4-di-N-oxides was synthesized and evaluated for antitumor and hypoxic- selective cytotoxic activities. Antitumor activity against liver carcinoma (Hepg2) and brain tumor (U251) human cell lines were evaluated, among the tested compounds, 5b and 9b exhibited potential cytotoxic effect against Hepg2 with IC50 values of 0.77 and 0.50 mg/mL respectively, whereas, all the tested compounds lack antitumor activity against U251 human cell line. Moreover, compound 4 was the most potent hypoxia selective-cytotoxin on EAC cell line; IC50 2.5 mg/mL, potency 22 mg/mL, and was approxi- mately 5.4-times more selective cytotoxin (HCR > 40) than 3-amino-2-quinoxalinecarbonitrile1,4-dioxide (standard, HCR > 7.4). Compounds 8b and 9b were more selective than the standard. Ó 2010 Elsevier Masson SAS. All rights reserved. 1. Introduction Some quinoxaline 1,4-di-N-oxide derivatives have been synthesized and evaluated as direct antitumor against MCF7 (breast), NCI-H460 (lung) and SF268 (CNS) human cell lines [1]. In addition, antitumor agents can be made selective for tumors by virtue of high activity under hypoxic conditions [2]. The lead compound in this regard is tirapazamine, which acts as bio- reductive cytotoxic agent [3]. Extensive studies have been carried out on 3-amino-2-quinoxalinecarbonitrile 1,4-dioxide, indicated that, it is more susceptible to reductive activation than tirapaz- amine [4] and causes redox-activated DNA damage analogous to it [5]. Recently, we reported on the antitumor and hypoxia-selective cytotoxicity of certain quinoxaline 1,4-di-N-oxides [6]. As a continu- ation to our previous efforts aiming to enhance the potency and selective cytotoxicity, we designed a new series having an electron- withdrawing (Cl) or an electron-donating (OCH 3 ) group at C 7 and diverse substituents at position 2 and 3 of the quinoxaline 1,4-di-N- oxides nucleus. 2. Results and discussion 2.1. Chemistry Scheme 1 outlines the synthetic pathway used to obtain compounds 2e6. 3-Amino-2-quinoxalinecarbonitrile 1,4-dioxide, 2 [4] was prepared by reaction of 5(6)-chlorobenzofuroxane, 1a with malononitrile in presence of triethylamine [7]. Methylation of 2 using dimethylsulphate in dioxane afforded the 3-methylamino derivative 3, while acetylation of 2 with acetic anhydride furnished 3-diacetylaminoquinoxaline derivative, 4. Additionally, the reaction of 5(6)-methoxybenzofuroxane 1b with prepared styrenes yielded the 2-aryliminomethylquinoxaline derivatives 5a,b which were further reduced by lithium borohydride to give 2-arylaminomethyl- 7-methoxy-3-phenylquinoxaline-4-oxides 6a,b. Nitrosation [8] of the acid hydrazides 7a,b [9] with sodium nitrite in acetic acid afforded the acid azides 8a,b. The latter underwent Curtius rearrangement with various aromatic amines in N,N-dime- thylformamide (DMF) to yield the urea derivatives 9aee while urethans or carbamates 10a-e were produced by boiling 8a,b with different alcohols (Scheme 2). 2.2. Antitumor screening The antitumor screening is divided into two main parts. The first part is a preliminary screening of all the synthesized compounds against two human cell lines: liver carcinoma (Hepg2) and brain * Corresponding author. Tel.: þ20 2 22713531. E-mail address: magdafathi_111@hotmail.com (M.M.F. Ismail). Contents lists available at ScienceDirect European Journal of Medicinal Chemistry journal homepage: http://www.elsevier.com/locate/ejmech 0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ejmech.2010.02.052 European Journal of Medicinal Chemistry 45 (2010) 2733e2738