Benzohydrazide as a good precursor for the synthesis of novel bioactive and anti-oxidant 2-phenyl-1,3,4-oxadiazol-aminoacid derivatives: Structural determination, biological and anti-oxidant activity

The synthesis and biological assessment of 2,5-disubstituted-1,3,4-oxadiazole derivatives from benzo hydrazide and amino acids as novel potential antioxidant and antibacterial agents have been reported. The structures of the new compounds were characterized by physicochemical properties and spectral methods. The synthesized compounds were screened for their in vitro antibacterial activity against three Gram-positive bacterial strains, namely Staphylococcus aureus ATCC 25923, Bacillus cereus ATCC 14579, Listeria innocua ATCC 33090, and two Gram-negative bacterial strains, namely Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922, and antifungal activity against Candida albicans ATCC 10231 in comparison with Amoxicillin, Tetracycline, Gentamicin and Oxacillin as standards. Most of the compounds have excellent efficacy, and some of them, such as 5i, 5g, 5d, 5c, and 5j can inhibit their activity better or very close to that of Amoxicillin, Tetracycline, Gentamicin, Oxacillin used as standards. Compounds 5b and 5i provided good results against L. innocua with inhibition values of IZ = 14 mm and IZ = 22 mm, respectively, while the rest of the compounds and antibiotics were unable to inhibit it. Compounds 5c, 5d, 5g and 5j showed excellent activity against C. albicans with values between 31 mm and 34 mm. These results were better than all the standards used. The MIC value (25 µg/ml) for derivatives 5(c-e), 5g and 5(i-j) against B. cereus represent the best activity of the tested compounds. All the target compounds were also screened for radical scavenging antioxidant activities by DPPH, FRAP, and TAC assays and found to be excellent antioxidant agents. According to the results, it was observed that most derivatives synthesized showed excellent activity with a concentration of 250 µg/ml as an antioxidant agent (76 % < RSA < 95.5 %) which gave an inhibition percentage that was better or very close to that of ascorbic acid and better than BHT.