Oxidation of isatin and its 5-substituted analogs with potassium permanganate in anhydrous acetonitrile gave indolo[2,1- b]quinazoline-6,12-dione (tryptanthrin) and its 2,8-dimethyl-, 2,8-dibromo-,...

Reaction of 5-methyl-, 5-bromo-, and 5-iodoisatins with phosphoryl chloride gave the corresponding 2,8-disubstituted indolo[2,1-b]quinazoline-6,12-diones in moderate yield. 5,7-Dichloroisatin failed to react with POCl₃. Treatment of an equimolar mixture of isatin and 5-bromoisatin with POCl₃ afforded indolo[2,1-b]-quinazoline-6,12-dione (tryptanthrin), 2,8-dibromoindolo[2,1-b]quinazoline-6,12-dione, and two isomeric monobromo-substituted tryptanthrin derivatives, the 2-bromo isomer prevailing.

Reactions of tryptanthrin with acetone, cyclopentanone, hexan-2-one, 4-methylpentan-2-one, 4-hydroxy-4-methylpentan-2-one, cyclohexanone, and butan-2-one in the presence of potassium carbonate afforded racemic phaitanthrin A and other addition products to the ketone group of tryptanthrin with high yields. Thermal dissociation, some chemical transformations, and antimicrobial activity of some adducts were studied, and inhibitory effect against gram-positive bacteria was found for particular derivatives.