Heterocyclic systems containing bridgehead nitrogen atom:: Synthesis and bioactivity of 2,3-dihydro-4H-[1,3]thiazino[3′,2′:2,3]as-triazino[5,6-b]indole and quinoxalino [2′,3′:4,5]thiazolo[3,2-b]indolo[2,3-e]-as-triazine and their isomeric systems

2,3-Dihydro-7-methyl-5H-as-triazino [5,6-b]indole-3-thione 2 on condensation with 1,3-dibromopropane and 2,3-dichloroquinoxaline gives the cyclized products, 2,3-dihydro-9-methyl-4H-[1,3]thiazino[3',2':2,3]-as-triazino[5,6-b]indole 4 and 10-methylquinoxa-lino[2',3':4',5']thiazolo[3,2-b]indolo[2,3-e]-as-triazine 6 respectively and not the angular isomers, 2,3-dihydro-9-methy1-1H-[1,3]thiazino[2',3':3,4]-as-triazino[5,6-b]in-dole 3 and 2-methylquinoxalino[2'3':4,5]thiazolo[2,3-c]indolo[2,3-e]as-triazine 5. The unequivocal synthesis of the latter 3 and 5 have been accomplished by reaction of 6-methylisatin-3-thiosemicarbazone 1 with 1,3-dibromopropane and 2,3-dichloroquinoxalines, respec-tively. The antibacterial and antifungal activity of the synthesized compounds have also been evaluated.