Synthesis, Antioxidant and Antimicrobial Activities of Metal Complexes of 2-thiouracil-hydroxyquinoline Derivatives

Introduction: Metal ions are cofactors found in antioxidant enzymes such as superoxide dismutase (SOD), and are essential in catalytic mechanisms for scavenging the free radicals. Therefore, synthetic compounds containing metal ions coordination are designed for SOD mimic and other biological activities. Objective: This study aimed to synthesize metal (Ni, Cu, Mn) complexes of mixed ligands of 2-thiouracil (2TU) with 8-hydroxyquinoline (8HQ) (1-3) and with 2-hydroxyquinoline (2HQ) (4-6), and to determine antioxidant and antimicrobial activities. Results: The metal complexes 1-6 elicited SOD activity with IC50 of 1.20-500.26 μM, particularly, complex 5 (2TU-Cu-2HQ) showed the highest SOD activity with IC50 of 1.20 μM. In addition, complexes 1 (2TU-Ni-8HQ), 5 and 2 (2TU-Cu-8HQ) displayed radical scavenging activity (RSA) with IC50 of 174.86, 196.54 and 431.65 μM, respectively, whereas the complexes 3, 4 and 6 were shown to be inactive. Furthermore, the metal complex 3 (2TU-Mn-8HQ) exhibited good antimicrobial activity with the minimal inhibitory concentration (MIC) range of 11.07-708.64 μM against gram positive and gram negative bacteria as well as diploid fungus, followed by metal complexes 2 (MIC of 23.68-757.70 μM) and 1 (MIC of 350.67-701.35 μM). Interestingly, among the similar mixed ligands with different metal ions of complexes 1 (Ni), 2 (Cu) and 3 (Mn), the complex 3 has the highest SOD (IC50 = 3.50 μM) and antimicrobial activities, but Cu complex (5) of 2TU and 2HQ showed higher SOD and RSA activities than Ni (4) and Mn (6) complexes. Conclusion: This finding reveals novel transition metal complexes with a potential for further development as medicinal compounds.