De novo synthesis of tryptanthrin and its derivatives from indole: engineering a sustainable photocatalytic strategy.

Tryptanthrin is a natural alkaloidal molecule [IUPAC name 6,12-dihydro-6,12-dioxoindolo-(2,1-b)-quinazoline], possessing an indoloquinazoline moiety. Since first being discovered in 1979, it and its analogs generated great interest in the fields of medicinal chemistry, life science, and materials science. Protocols for synthesizing tryptanthrins with the features of facile, eco-friendly, and mild reaction conditions remain an underdeveloped area. This new protocol, leveraging Rose Bengal as a photo-catalyst and commercially available substituted indoles as starting materials, enables selective synthesis under mild reaction conditions, expanding the substrate scope, complementing existing methods, and investigating the possible reaction mechanism. This approach emphasizes eco-friendliness, cost-effectiveness, and scalability, making it suitable for diverse applications. This innovation holds promise for synthesizing tryptanthrin-based bioactive compounds and materials relevant to chemistry and beyond.