Efficient and convenient synthesis, characterization, and antimicrobial evaluation of some new tetracyclic 1,4-benzothiazines

In the present study, 20 new tetracyclic 1,4-benzothiazines (<b>4a</b>–<b>4 t</b>) were conveniently synthesized in good yields and characterized by different spectral and physical techniques. The in vitro antimicrobial evaluation of the synthesized benzothiazine derivatives was performed by serial dilution against two Gram-positive bacteria [<i>Bacillus subtilis</i> (MTCC 441) and <i>Staphylococcus epidermidis</i> (MTCC 6880)], two Gram-negative bacteria [<i>Escherichia coli</i> (MTCC 1652) and <i>Pseudomonas aeruginosa</i> (MTCC 424)], and two fungal strains [<i>Candida albicans</i> (MTCC 227) and <i>Aspergillus niger</i> (MTCC 8189)]. The derivatives <b>4 l</b> and <b>4 t</b> were found to be more potent than standard drug, i.e., fluconazole, against <i>A. niger</i> and <i>C. albicans</i>, respectively.