Designing metal chelates of halogenated sulfonamide Schiff bases as potent nonplatinum anticancer drugs using spectroscopic, molecular docking and biological studies

In this contribution, five Ni(II) complexes have been synthesized from sulfonamide-based Schiff bases (SB(1)–SB(5)) that comprise bromo or iodo substituents in the salicylidene moiety. The chemical structures of these compounds were extensively elucidated by different analytical and physicochemical studies. All ligands act as bidentate chelators with ON binding mode yielding octahedral, square planar, or tetrahedral geometries. The phenolic OH at δ 12.80 ppm in the free Schiff base SB(2) vanishes in the (1)H NMRspectrum of diamagnetic complex [Ni(SB(2)–H)(2)] favoring the OH deprotonation prior to the chelation with Ni(II) ion. The appearance of twin molecular ion peaks ([M − 1](+) and [M + 1](+)) is due to the presence of bromine isotopes ((79)Br and (81)Br) in the mass spectra of most cases. Also, the thermal decomposition stages of all complexes confirmed their high thermal stability and ended with the formation of NiO residue of mass 6.42% to 14.18%. Besides, antimicrobial activity and cytotoxicity of the ligands and some selected complexes were evaluated. Among the ligands, SB(4) showed superior antimicrobial efficacy with MIC values of 0.46, 7.54, and 0.95 µM against B. subtilis, E. coli, and A. fumigatus strains, respectively. The consortium of different substituents as two bromine atoms either at positions 3 and/or 5 on the phenyl ring and a thiazole ring is one of the reasons behind the recorded optimal activity. Moreover, there is a good correlation between the cytotoxicity screening (IC(50)) and molecular docking simulation outcomes that predicted a strong binding of SB(2) (16.0 μM), SB(4) (18.8 μM), and SB(5) (6.32 μM) to the breast cancer protein (3s7s). Additionally, [Ni(SB(4)–H)(2)] (4.33 µM) has nearly fourfold potency in comparison with cisplatin (19.0 μM) against breast carcinoma cells (MCF-7) and is highly recommended as a promising, potent, as well as low-cost non-platinum antiproliferative agent after further drug authorization processes.