Selective cytotoxicity of organotin(IV) compounds with 2,3-dihydroxybenzyldithiocarbazate Schiff bases

A series of tridentate ONS Schiff bases were synthesised via condensation by reacting 2,3-dihydroxybenzaldehyde with S-2-methylbenzyldithiocarbazate (S2MBDTC) ( 1 ), S-4-methylbenzyldithiocarbazate (S4MBDTC) ( 2 ) and S-benzyldithiocarbazate (SBDTC) ( 3 ) in an equimolar ratio (10 mmol). The Schiff bases were then reacted with diphenyltin(IV) and dimethyltin(IV) dichloride in an equimolar ratio (1 mmol) yielding six new organotin(IV) compounds ( 4 – 9 ). All the compounds were successfully characterised by elemental analysis, FT-IR, multinuclear NMR, UV–Vis, mass spectroscopy and molar conductivity. The molecular geometries for five compounds, 3 , 5 , 6 , 8 and 9 , have been established by X-ray crystallography. The five-coordinate geometry for each of the diorganotin molecules was defined by two carbon atoms from the tin-bound substituents as well as three donor atoms derived from the dinegative, tridentate dithiocarbazate ligands, namely thiolate-S, phenoxide-O and imine-N atoms. The resultant five-coordinate C 2 NOS geometries were intermediate between ideal square pyramidal and trigonal bipyramidal geometries. The diphenyltin(IV) compounds ( 4 – 6 ) exhibited particularly promising and selective cytotoxicity against the A2780 (ovarian), BE2-C (neuroblastoma), SJ-G2 (glioblastoma) and MIA (pancreas) cancer cell lines. The interactions of the compounds ( 4 – 9 ) with calf thymus (CT-DNA) were evaluated using an electronic absorption method, and 7 , 8 , 9 were found to have good DNA binding affinity. The molecular docking studies of compounds ( 4 – 9 ) with DNA revealed that the compounds interacted with duplex DNA via hydrogen bonding, hydrophobic and electrostatic interactions. Graphic abstract