Conversion of Isatins to Tryptanthrins, Heterocycles Endowed with a Myriad of Bioactivities

Tryptanthrin and Its Derivatives in Drug Discovery: Synthetic Insights

Tryptanthrin is a golden-yellow, naturally occurring alkaloid that can be obtained from multiple sources and through different synthetic methodologies. This tetracyclic compound displays several relevant biological activities. The potential of this tetracyclic alkaloid has been widely explored, and several researchers have focused their attention on expanding the variety of tryptanthrin derivatives by using a range of synthetic strategies. In this short review, we aim to address recent developments in the synthesis of the tryptanthrin core, as well as the development of new strategies employed by synthetic organic chemists to obtain novel tryptanthrin derivatives with potential biological activity, using different tools from the chemists’ toolbox, such as photocatalysis, solvent-free approaches, and multicomponent reactions.

Sulfonated tryptanthrin anolyte increases performance in pH neutral aqueous redox flow batteries

Aqueous organic redox flow batteries (AORFBs) hold great promise as low-cost, environmentally friendly and safe alternative energy storage media. Here we present aqueous organometallic and all-organic active materials for RFBs with a water-soluble active material, sulfonated tryptanthrin (TRYP-SO₃H), working at a neutral pH and showing long-term stability. Electrochemical measurements show that TRYP-SO₃H displays reversible peaks at neutral pH values, allowing its use as an anolyte combined with potassium ferrocyanide or 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt monohydrate as catholytes. Single cell tests show reproducible charge-discharge cycles for both catholytes, with significantly improved results for the aqueous all-organic RFB reaching high cell voltage (0.94 V) and high energy efficiencies, stabilized during at least 50 working cycles.

Divergent Synthesis of Methylisatoid and Tryptanthrin Derivatives by Ph3P-I2-Mediated Reaction of Isatins with and without Alcohols

A novel phosphonium-mediated reaction of isatins is described. In the presence of alcohol, the reaction proceeds to furnish C-12 modified tryptanthrin derivatives. Without alcohol, self-dimerization of isatins gives rise to tryptanthrin and its analogs. This divergent and step-economic approach provides a facile access to diverse indoloquinazoline structures including the natural alkaloids, methylisatoid and cephalanthrin B, in high yields from simple precursors under mild and metal-free reaction conditions.

Regorafenib analogues and their ferrocenic counterparts: synthesis and biological evaluation

New ferrocene analogues of regorafenib have been prepared and their biological activity was evaluated in kinase and cellular assays.