Synthesis of Nonsymmetrically Substituted 2,3-Dialkoxyphenazine Derivatives and Preliminary Examination of Their Cytotoxicity

Abstract

Fourteen new 2,3-dialkoxyphenazine derivatives with two different alkoxy groups bearing R1 and R2 alkyl chains, defined as −CH2CH(CH3)2 and −(CH2)n−1CH3 for n = 1, 2, 4, 6, 8, and 10, were prepared via regioselective synthesis. The applied synthetic protocol is based on the following reactions: the Buchwald-Hartwig coupling of a nonsymmetrically substituted 4,5-dialkoxy-2-nitroaniline with a 1-bromo-2-nitrobenzene derivative featuring additional tert-butyl, trifluoromethyl or two methoxy groups; the reduction of bis(2-nitrophenyl)amine; and a final step of tandem-like oxidation that leads to the preparation of a heterocyclic phenazine system. The regioselectivity of these steps and the molecular structure of the compounds under investigation were confirmed by nuclear magnetic resonance and additionally by single-crystal X-ray diffraction performed for some examples of 5 and 6 phenazine series. For 7-(tert-butyl)-3-isobutoxy-2-(octyloxy)phenazine (5f), 3-(hexyloxy)-2-isobutoxy-7-(trifluoromethyl)phenazine (6e), and 2,3-bis(hexyloxy)-7,8-dimethoxyphenazine (7), viability and cytotoxicity assays were performed on the LoVo human colon adenocarcinoma cell line, with 5f confirmed to exhibit cytotoxicity.