Research on potentially bioactive aza and thiaza polycyclic compounds containing a bridgehead nitrogen atom. 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.