Synthesis and Antimicrobial Activity of Some Pyrrolo[1,2,3-de]-1,4-benzothiazines,Part 2

Acid catalyzed cyclization reactions of both 3-alkyl- and 3-aryl-substituted N-/2,2-dialkoxyethyl)-3,4-dihydro-2H-1,4-benzothiazines ( 2 ) lead to 2,3-dihydro-pyrrolo[1,2,3-de]-1,4-benzothiazines ( 3 ). The pyrrolobenzothiazine structure was deduced on the basis of 2D ¹H NMR-NOESY experiments and fully determined by X-ray data. Compounds 3a-c showed poor antibacterial activity. However, the 3-phenyl-N-(2,2-dimethoxyethyl)-3,4-dihydro-2H-1,4-benzothiazine ( 2b′ ) showed antifungal activity against Aspergillus niger 16-fold greater than miconazole.