Microplate assay for screening the antibacterial activity of Schiff bases derived from substituted benzopyran-4-one

Schiff bases (SB1–SB3) were synthesized from the condensation of 6-formyl-7-hydroxy-5-methoxy-2-methylbenzopyran-4-one with 2-aminopyridine (SB1), p-phenylenediamine (SB2) and o-phenylenediamine (SB3), while Schiff bases (SB4–SB6) were synthesized by condensation of 5,7-dihydroxy-6-formyl-2-methylbenzopyran-4-one with 2-aminopyridine (SB4), p-phenylenediamine (SB5) and o-phenylenediamine (SB6). Schiff bases were characterized using elemental analysis, IR, UV–Vis, 1H NMR, 13C NMR and mass spectroscopy. These compounds were screened for antibacterial activities by micro-plate assay technique. Escherichia coli and Staphylococcus capitis were exposed to different concentrations of the Schiff bases. Results showed that the antibacterial effect of these Schiff bases on Gram-negative bacteria were higher than that on Gram-positive bacteria moreover, the Schiff bases containing substituent OCH3 on position five have higher antibacterial activity than that containing hydroxy group on the same position.

Schiff bases synthesized by condensation of benzopyran-4-one with diamines. Their antibacterial effect on Gram-negative bacteria were higher than that on Gram-positive. Schiff bases containing substituent OCH3 on position 5 have higher antibacterial activity than that containing hydroxy group. There is a charge transfer interaction between Schiff bases and LPS layers in Gram-negative bacteria.Figure optionsDownload as PowerPoint slideHighlight
► Schiff bases were prepared by condensation of benzopyran-4-one with diamines.
► Chemical structures were confirmed by elemental and spectroscopic analysis.
► Antibacterial activities of Schiff bases were assessed by micro-plate assay.