In this paper, we describe the synthesis of the 5-styryltetrazolo[1,5-c]quinazolines substituted at the 9-position with a 4-fluorophenyl ring directly or via a conjugated π-spacer (C=C or C≡C bond) based on the 6-bromo-4-chloro-2-styrylquinazoline scaffold. The structures of the synthesized compounds were characterized based on a combination of ¹H-NMR, 13C-NMR, IR and high resolution mass spectral data as well as microanalyses. The tetrazoloquinazolines were evaluated for potential in vitro cytotoxicity against the human breast adenocarcinoma (MCF-7) and cervical cancer (HeLa) cells. The anti-proliferative assays demonstrated that the 9-bromo-5-styryltetrazolo[1,5-c]quinazoline 3a and 9-bromo-5-(4-fluorostyryl)tetrazolo[1,5-c]quinazoline 3b exhibit significant cytotoxicity against both cell lines. A carbon-based substituent at the 9-position resulted in complete loss of cytotoxicity against both cell lines except for the 5,9-bis((E)-4-fluorostyryl)tetrazolo[1,5-c]quinazoline 4e, which was found to exhibit comparable cytotoxicity to that of Melphalan (IC50 = 61 μM) against the MCF-7 cell line with IC50 value of 62 μM. Molecular docking against tubulin (PDB:1TUB) showed that compounds 3a, 3b and 4e bind to the tubulin heterodimer. Binding involves hydrogen bonding for 3a and 3b and halogen interactions for 4e.
Keywords: 9-bromo-5-styryltetrazolo[1,5-c]quinazoline; 9-carbo–substituted 5-styryltetrazolo[1,5-c]quinazolines; cross-coupling; cytotoxicity; molecular docking.