Exploring the Synthesis, Structure and Bioactivity of Pyrimidine Carboxylic Acid-Derived Organic Antimony (V) Complexes: Cytostatic and Antimicrobial Evaluations

Eight new organoantimony complexes, R3SbL2 (R = Ph, p-MePh; L = L1, L2) and (R3Sb)2OL2 (R = Ph, m-MePh; L = L1, L2), [Ph3Sb(C5H3N2O2)2] (1), [(Ph3Sb)2O(C5H3N2O2)2] (2), [(p-tol)3Sb(C5H3N2O2)2] (3), [(m-tol)6Sb2O(C5H3N2O2)2] (4), [Ph3Sb(C5H3N2O2)2] (5), [(Ph3Sb)2O(C5H3N2O2)2] (6), [(p-tol)3Sb(C5H3N2O2)2] (7) and [(m-tol)6Sb2O(C5H3N2O2)2] (8), were designed and synthesized by the reaction of 4-pyrimidine carboxylic acid (HL1) or 5-pyrimidine carboxylic acid (HL2) with organoantimony precursors. All the complexes were characterized by elemental analysis, FT-IR, NMR (1H and 13C), and single crystal X-ray diffraction analysis. Crystal structure results reveal that the central antimony atom of all the complexes displays a triangular biconical geometry. Among them, complexes 1, 3, 5 and 7 show a monomeric structure, while complexes 2, 4, 6 and 8 have a dimeric structure with oxygen bridges. The in vitro cytostatic activities of the eight complexes against a human alveolar basal epithelial lung cancer cell lines (A549) and hepatocellular carcinoma cell lines (HepG-2) were investigated, and the results showed that the organoantimony derivatives with the tolyl groups (3, 4, 7, 8) exhibited higher in vitro cytostatic activities compared with those with the phenyl groups (1, 2, 5, 6). At the same time, bacteriostatic tests were conducted to assess the inhibitory effects of complexes 1-8 against three prevalent plant pathogenic fungi and one bacterium. The results revealed that complex 4 exhibited significant fungicidal activities, on the other hand, complex 3 exhibited higher antibacterial activity against MRSA. These results will provide significant guidance for the further exploration of potential efficient biological activity complexes.