Tin(IV) compounds of tridentate thiosemicarbazone Schiff bases: Synthesis, characterization, in-silico analysis and in vitro cytotoxicity

Twelve tin(IV) compounds (5–16) derived from four tridentate thiosemicarbazone Schiff bases of 4-methyl-3-thiosemicarbazide with 2-hydroxy-3-methoxybenzaldehyde (1, 2) and 4-phenyl-3-thiosemicarbazide with 2,3-dihydroxybenzaldehyde (3, 4) of the general formulae [R2Sn(Ln)] and [Sn(Ln)2] (where R = Ph or Me; Ln = 1, 2, 3 and 4) were synthesized and characterized by elemental analysis, IR, UV–vis, mass spectrometry and multinuclear NMR (1H, 13C and 119Sn) spectroscopy. X-ray crystallographic data was obtained for 11′, a 2:1 co-crystal between Ph2Sn(L2) (11) and 3-methoxysalicylaldehyde azine, and Me2Sn(L2) (12) where L2H2 is 2-(2-hydroxy-3-methoxybenzylidene)-N-phenylhydrazinecarbothioamide. The analysis revealed distinct coordination geometries for 11 and 12 approaching trigonal–bipyramidal. In the crystal of 11′, supramolecular dimers arising from amine N H…S(thiolate) hydrogen bonding and {…HNCS}2 synthons are evident; π(chelate ring)…π(oxidobenzylidene) stacking is also apparent. In the crystal of 12, supramolecular, helical chains are generated by a combination of amine N H…O(phenoxide) hydrogen bonding and Sn…S secondary bonding. The cytotoxic activity of the compounds against a panel of ten cancer cell lines, [HT29 (colon), U87 and SJ-G2 (glioblastoma), MCF-7 (breast), A2780 (ovarian), H460 (lung), A431 (skin), DU145 (prostate), BE2-C (neuroblastoma) and MIA (pancreas), and one normal cell line, MCF-10A (normal breast)] were investigated. The thiosemicarbazone Schiff bases 1 and 4 as well as the diphenyltin(IV) compounds showed a strong ability to inhibit the growth of cancer cells, with particular selectivity against HT29, MCF-7, A2780, A431, BE2-C, SJ-G2 and MIA cell lines. The structure–activity relationship of all these compounds were studied by evaluating the effect of alkyl and aryl groups attached on the thiosemicarbazone backbone, the methoxy/hydroxyl groups present at the meta-position of the phenyl ring and alkyl or aryl groups bound to the tin center.