Synthesis and biological activity of thiazolo[3′,2′ : 2,3]-as-triazino[5,6-b]indoles and isomeric thiazolo[2′,3′ : 3,4]-as-triazino[5,6-b]indoles

9/7-Bromo-2,3-dihydro-8-methoxy-5H-as-triazino[5,6-b]indole-3-thiones 3a,b on condensation with 4-chlorophenacyl bromide give 9/7-bromo-3-[4-chlorophenylthio]-8-methoxy-5H-as-triazno[5,6-b]indole hydrobromides 4a,b which on PPA catalysed cyclization furnish 6/8-bromo-3-[4-chlorophenyl-7-methoxythiazolo[3',2' : 2,3]-as-triazino[5,6-b]indoles 9a,b and not angular isomeric 6/8-bromo-1-[4-chlorophenyl]-7-methoxythiazolo[2',3' : 3,4]-as-triazino [5,6-b] indoles 6a,b. The unequivocal synthesis of the latter have also been accomplished. The antimicrobial potential of the compounds 6 and 9 have also been evaluated.