Despite the simple structures of 3,4‐fused tricyclo coumarins, their fluorescence properties have not been studied extensively. We have synthesized triazolo[c]coumarins using Huisgen cycloaddition and investigated their fluorescence properties. The Huisgen cycloaddition was found to proceed in excellent yields when subjected to heating under solvent‐free conditions. As is generally known, fluorescence is enhanced with an increase in the electron‐donating group at the 7‐position. The 7‐NEt2‐triazolo[c]coumarin derivatives showed useful fluorescence, and their relative fluorescence quantum yields in aprotic polar organic solvents were high. It revealed that fluorescence properties of triazolo[c]coumarins depended on the regio isomer. The electron distribution was hardly extended to alkyl side chain on triazole from the molecular orbital calculation by density functional theory (DFT) and time‐dependent DFT (TD‐DFT). This result suggests that the trend of fluorescence properties is similar to the present result even when various substituents are introduced on triazole.

Covalent ligands are generally filtered out of chemical libraries used for high-throughput screening, because electrophilic functional groups are considered to be pan-assay interference compounds (PAINS). Therefore, screening strategies that can distinguish true covalent ligands from PAINS are required. Hydrogen/deuterium−exchange mass spectrometry (HDX−MS) is a powerful tool for evaluating protein stability. Here, we report a covalent modifier screening approach using HDX−MS. In this study, HDX−MS was used to classify peroxisome proliferatoractivated receptor γ (PPARγ) and vitamin D receptor ligands. HDX−MS could discriminate the strength of ligand−protein interactions. Our HDX−MS screening method identified LT175 and nTZDpa, which can bind concurrently to the PPARγ ligand-binding domain (PPARγ−LBD) with synergistic activation. Furthermore, iodoacetic acid was identified as a novel covalent modifier that stabilizes the PPARγ−LBD.