Synthesis and antimicrobial evaluation of dibenzo[b,e]oxepin-11(6H)-one O-benzoyloxime derivatives

A series of dibenzo[b,e]ox(thi)epin-11(6H)-one O-benzoyloximes has been synthesized and structurally elucidated by means of IR, ¹H-NMR, ¹³C-NMR, MS, and elemental analysis. The newly developed compounds were screened at concentrations of 200-25 μg/mL for their antibacterial activity against Gram+ve organisms such as Methicillin-Resistant Staphylococcus Aureus (MRSA), Gram-ve organisms such as Escherichia coli (E. coli), and at the same concentration range for their antifungal activity against fungal strain Aspergillus niger (A. niger) by the cup plate method. Ofloxacin and ketoconazole (10 μg/mL) were used as reference standards for antibacterial and antifungal activity, respectively. The dibenzo[b,e]oxepines 6a-c and 6e-h showed low antimicrobial activity (MIC 125-200 μg/mL) compared to the reference substances, whereas a major improvement (MIC 50-75 μg/mL) was achieved with the synthesis of the corresponding bromomethyl derivative 6d. Moreover, replacement of oxygen by its bioisosteric sulfur led to isomeric dibenzo[b,e]thi-epine derivatives 6g,h which significantly exhibited higher antimicrobial activity (MIC 25-50 μg/mL) against all tested culture strains used in the present study, demonstrating that a change of chemical class from dibenzo[b,e]oxepine to dibenzo[b,e]thiepine significantly improves the antimicrobial activity. Further variation, such as the oxidation of the thiepine sulfur to the corresponding isomeric dibenzo[b,e]thiepine 5,5-dioxide derivative 9, comparatively failed to exhibit high activity (MIC 200 μg/mL) against S. aureus, E. coli or A. niger.