Regiospecific synthesis of pyrido[3,4-b]- and pyrido[4,3-b]carbazole-5,11-dione derivatives. Evaluation of their in vitro antifungal or antiprotozoological activities.

Hetero Diels-Alder reactions between 2- or 3-bromocarbazolequinones 1a or 1b and azadiene 5 afford regiospecifically pyrido3,4-b]- and pyrido4,3-b]carbazole-3,5,11-triones 6a and 6b. The regiochemistry of the cycloadditions is controlled by the position of the bromine atom at C-2 or C-3 of the bromoquinone. The corresponding N- and O-methyl derivatives 7 and 8 are prepared. Structural assignment of the regioisomers is made by 1H-NMR nuclear Overhauser effect difference experiments performed on a diacetoxy derivative of pyrido4,3-b]carbazole 9b. The in vitro antifungal and antiprotozoological activities of some prepared derivatives have been evaluated against Candida albicans, Candida krusei, Cryptococcus neoformans and Trichomonas vaginalis. None of the tested compounds have shown significant activity towards the yeasts or protozoa.