Condensed bridgehead nitrogen heterocyclic systems:: synthesis and evaluation of antimicrobial activity of thiazolo [3′,2:2,3]-as-triazino [5,6-b] indole and related systems

8-Ethyl-5H-2,3-dihydro-1,2,4-triazino [5,6-b] indole-3-thione 2 on condensation with 1,2-dibromoethane, 1,3-dibromopropane and 2,3-dichloroquinoxaline gives the cyclized products, 7-ethyl-2,3-dihydrothiazolo [3',2':2,3] [1,2,4] triazino [5,6-b] indole 3, 8-ethyl4H-2,3-dihydro [1,3] thiazino [3',21:2,3] [1,2,4] triazino [5,6-b] indole 4 and 9-ethyl quinoxalino [2',3':4,5] thiazolo [3,2-b] indolo [2,3-e]-as-triazine 5 respectively and not the angular isomers, 6,7,8. The unequivocal synthesis of the latter 6,7 and 8 has been accomplished by reaction of 5-ethylisatin 3-thiosemicarbazone 1 with 1,2-dibromoethane, 1,3-dibromopropane and 2,3-dichloroquinoxaline, respectively. The antibacterial and antifungal activities of the synthesized compounds have also been evaluated.