Synthesis, antimicrobial activity and molecular docking of di- and triorganotin (IV) complexes with thiosemicarbazide derivatives

Six organotin (IV) complexes with two ligands derived from 2,3-butanedione and thiosemicarbazide have been synthesized and fully characterized by several spectroscopic techniques, including Sn-119 NMR and single crystal X-ray diffraction. Reactions of the ligand diacetyl-2-(thiosemicarbazone)-3-(3-hydroxy-2-naphthohydrazone), (LH2)-H-1, with SnR2Cl2 (R = Me, Bu, Ph) lead to the obtaining of complexes 1-3 with general formula [SnR2L1] (R = Me 1, R = Bu 2, R = Ph 3), in which the ligand is doubly deprotonated and behaves as a N2SO donor, whereas from the reactions of diacetyl-2-thiosemicarbazone, HATs, with the same organotin precursors any complex could be isolated. By contrast, reaction of HATs with SnR3Cl induces the ligand cyclization to form a 1,2,4-triazine-3-thione that binds to the metal as a monoanionic donor in a mono or bidentate manner to form compounds 4-6 with formula [SnR3L2] (R = Me 4, R = Bu 5, R = Ph 6). The antimicrobial activity of the ligands and the six complexes was tested towards bacteria and fungi, including clinical isolated strains. The results show that the ligands are devoid of activity, except HATs that displays activity against Bacillus subtilis. Conversely, the complexes exhibit good antimicrobial properties against Gram positive and negative bacteria, yeasts and moulds. The best results are obtained for complexes [SnBu3L2] 5 and [SnPh3L2] 6, indicating that their more lipophilic nature could play an important role in the ease of microbial cell penetration. In some cases, these complexes display similar or higher activity than that of ampicillin and miconazole, used as antibacterial and antifungal positive controls, respectively. Docking study with DHPS protein (S. aureus) has shown that out of six drugs, the compound 6 has the best binding affinity (-8.5 Kcal/mol).