Recent advances in catalytic approaches for the synthesis of 3-substituted indoles: mechanisms and strategies

This review provides a comprehensive overview of recent advances in the synthesis of 3-substituted indoles, highlighting various catalytic methodologies employed to improve the reaction efficiency, selectivity, and sustainability. This article discusses base-catalyzed methods, amino acid catalysts, Brønsted acid catalysts, and Lewis acids and their unique roles in enhancing the synthesis of these valuable compounds. Additionally, the application of ionic liquids, surfactants, and heteropolyacid-based catalysts was explored for their green chemistry benefits, demonstrating reduced environmental impact and improved reaction outcomes. Electrochemical approaches using simple electrodes and phase-transfer catalysts are also examined as eco-friendly and efficient alternatives. This review underscores the broad versatility and applicability of these catalytic systems in synthesizing 3-substituted indoles, which are important intermediates in pharmaceuticals, material sciences, and natural product synthesis while emphasizing the need for continued innovation toward more sustainable and efficient synthesis methods.

Catalyst-free visible-light-induced condensation to synthesize bis(indolyl)methanes and biological activity evaluation of them as potent human carboxylesterase 2 inhibitors

A mild strategy for visible-light-induced synthesis of bis(indolyl)methanes was developed using aromatic aldehydes and indole as substrates. This reaction could be performed at room temperature under catalyst- and additive-free conditions to synthesize a series of bis(indolyl)methanes in good to excellent yields. In addition, all synthesized bis(indolyl)methanes together with β-substituted indole derivatives synthesized according to our previous work, were evaluated for their inhibitory effect against human carboxylesterase (CES1 and CES2). Primary structure–activity relationship analysis of all tested compounds showed that the modifications of β-substituted indole at the β-site with another indolyl group led to a significant enhancement of the inhibitory effect on CES2, and the bisindolyl structure is essential for CES2 inhibition. These results demonstrated that these bis(indolyl)methanes are potent and selective CES2 inhibitors, which might be helpful for medicinal chemists to design and develop more potent and selective CES2 inhibitors for biomedical applications.

Bis(indolyl)methanes were synthesized by a green protocol. Primary structure–activity relationship analysis showed that the bisindolyl structure is essential for CES2 inhibition.