Synthesis, Antimicrobial and Antioxidant Activities of 3-Alkyl(aryl)-4-(3-methoxy-4-hydroxybenzylideneamino)-4,5-dihydro-1H-1,2,4-triazol-5-one Derivatives

It is known that Schiff bases and Mannich bases containing 1,2,4-triazol-5-one rings have significant antioxidant and antimicrobial activities. Therefore, in this study, we synthesized compounds containing Mannich bases and examined their antioxidant and antimicrobial activities. In the study, we first synthesized 3-alkyl(aryl)-4-(3-methoxy-4-hydroxybenzylideneamino)-4,5-dihydro-1H-1,2,4-triazol-5-one (3) compounds, which are Schiff bases, have been obtained from reacting with 3-methoxy-4-hydroxybenzaldehyde (2) of 3-Alkyl(aryl)-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-one (1) compounds. Then, synthesized Schiff bases have been obtained 8 pieces of 1-(morpholin-4-yl-methyl)-3-alkyl(aryl)-4-(3-methoxy-4-hydroxybenzylideneamino)-4,5-dihydro-1H-1,2,4-triazol-5-one (4) compounds from reaciton with morpholine and 7 pieces of 1-(4-piperidinecarboxamide-1-yl-methyl)-3-alkyl(aryl)-4-(3-methoxy-4-hydroxybenzylideneamino)-4,5-dihydro-1H-1,2,4-triazol-5-one (5) compounds from reaction with 4-piperidinecarboxamide in formaldehyde environment according to the Mannich reaction. Structural analyses of fifteen newly synthesized compounds were characterized using 13C-NMR, 1H-NMR and IR spectroscopic methods. Additionally, the in-vitro antioxidant properties of the synthesized fifteen Mannich bases were investigated using metal chelation activity, reducing power methods, and free radical scavenging activity, and the results were compared with the standard antioxidants used. While the compounds synthesized in the antioxidant study did not show reducing activity, they showed low free radical scavenging activity compared to the standards. In the continuation of the antioxidant study, we observed that the synthesized compounds formed chelates with high iron ions due to the presence of -OH, -NR2, -O-, C=O, -NH2 groups. In the last part of the study, the in vitro antimicrobial effects of the synthesized compounds against six different microorganisms (Bacillus cereus, Bacillius subtilis, Pseudomonas aeruginosa, Klebsiella pneumonia, Escherichia coli, and Staphylococcus aureus) were determined using the agar well technique. We observed that the antimicrobial activity of the synthesized compounds varied depending on the type of substituent (R = a - h).