Synthesis charactrization, in vitro antimicrobial and antioxidant activites of chalcone derivatives of 4-hydroxyacetophenone
This study synthesizedsome phenolic chalcone-ninhydrin adducts via microwave-irradiation of phenolic chalcones with ninhydrin. This was with a view to improving the chemotherapeutic property of chalcones. The chalcones were prepared by reacting 4-hydroxyacetophenone with an equivalent mole of sevensubstituted benzaldehydesto afford the corresponding chalcones (1a, 2a, 3a, 4a, 5a, 6a and 7a). The resulting phenolic-chalcones were reacted with ninhydrin by pulse microwave-irradiationof the reactants in glacial acetic acid for 8 min to give the following compounds 1b, 2b, 3b, and 4b, except the reaction of 7a with ninhydrin which was achieved by refluxing in glacial acetic acid for 6 hours to yieldninhydrin adduct of the chacone7b.The compounds were screened for antioxidant activities which included2,2-diphenyl-2-picrylhydrazyl hydrate (DPPH) and (ferric reducing antioxidant power)FRAP assays. They were also screened in-vitro against nine strains of Gram-positive and five Gram-negative bacteria, to determine their zones of inhibition, minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC). The structures of some of the synthesized compounds were investigated and confirmed using nuclear magnetic resonance (NMR) experiments (1H, 13C, and distortionless enhancement by polarization transfer (DEPT). Some of the compounds were also subjected to infra-red spectroscopic analysis and mass spectrometry to corroborate the information obtained from the NMR experiments. The spectroscopic analysis showed that the expected structures of the chalcones were obtained and that the ninhydrin adducts were either di- or tri-substituted adducts.Compound 7a demonstrated the best DPPH radical scavenging ability with an IC50 value of 0.0240 mg/ml which was lower than the standard (ascorbic acid, 0.0250 mg/ml).In the FRAP assay, however, compound 4b demonstrated the best activity with an ascorbic acid equivalent of (AAE) of 0.470 mg. Therefore,compounds 7a and 7b exhibited a comparable radical scavenging ability to the ascorbic acid used as standard drug than the other compounds against the DPPH, while compound 4b exhibited an excellent ferric reducing antioxidant ability using the FRAP assays. All the bacterial strains were sensitive to compound 5a except Pseudomonasaeruginosa,which was also not susceptible to the standard drugs, streptomycin and ampicillin. Compound 5a exhibited the best activity against the Gram-negative bacteria and also had the lowest MIC values than ampicillin. The study concluded that compounds 4a, 7a and 7b could serve as good antioxidant agents and compound 5aexhibited an excellent antimicrobial property.