Synthesis, X-ray crystal and monoamine oxidase inhibitory activity of 4,6-dihydrobenzo[c]pyrano[2,3-e][1,2]thiazine 5,5-dioxides: In vitro studies and docking analysis

We report the synthesis and biological evaluation of two new series of 2-amino-6-benzyl-4-phenyl-4,6-dihydrobenzo[c]pyrano[2,3-e][1,2]thiazine-3‑carbonitrile 5,5-dioxides and 2-amino-6-methyl-4-phenyl-4,6-dihydrobenzo[c]pyrano[2,3-e][1,2]thiazine-3‑carbonitrile 5,5-dioxides. The synthetic methodology involves a multistep reaction starting with methyl anthranilate which was coupled with methane sulfonyl chloride. The product of the reaction was subjected to N-benzylation and N-methylation reactions followed by ring closure with sodium hydride resulting in the formation of respective 2,1-benzothiazine 2,2-dioxides. These 2,1-benzothiazine precursors were subjected to multicomponent reaction with malononitrile and substituted benzaldehydes for the synthesis of two new series of pyranobenzothiazines (6a-r and 7a-r). The synthesized compounds were screened as selective inhibitors of monoamine oxidase A and monoamine oxidase B. The in vitro results suggested that compound 6d and 7q are the selective inhibitors of monoamine oxidase A, however, the selective and potent inhibitors of monoamine oxidase B included compounds 6h and 7r. Moreover, some dual inhibitors were noticed like 7l having more inhibitory activity towards both the isozymes. Moreover, the binding modes of the selective and potent inhibitors of monoamine oxidase A and B were investigated by molecular docking analysis. The results suggested that the synthetic derivatives may be potential towards the monoamine oxidase isozymes.