Using benzylidene imidazolone core, we created ap anel of color-shifted fluorogenic ligandsf or FAST protein withoutc ompromise to the binding efficiency and the utility for live-cellp rotein labeling. Thiss tudy highlights the potential of benzylidene imidazolones derivatives for rapid expansion of ap allet of live-cellf luorogenic labelingt ools.

(2-Aminobenzylidene)-imidazolones were used as substrates for [1,5]-hydride shift triggered cyclization under promotion by TiCl4 at room temperature.

An efficient and high-yielding strategy to prepare “unsymmetrical” 4-aryl-isoxazol-3,5-dicarboxylic acid derivatives from nitroacetic esters and aromatic aldehydes has been developed. The strategy is based on the isolation and usage of the previously missed intermediate of the Dornow reaction5-hydroxy-6-oxo-4-aryl-6H-1,2-oxazine-3-carboxylates. In addition, the mechanism of the Dornow reaction was partially revised.

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2-(2-(Benzylthio)benzylidene)malonates can undergo the 1,5hydride shift triggered cyclization resulting in thiachromanes in 45-84 % yield. Boron trifluoride as a reaction promotor is the key to success. DFT calculations revealed that the reaction proceeds via a chelate BF2 complex, which was confirmed by NMR-analysis. Experimental and theoretical comparison of nitro-gen, sulfur and carbon analogues revealed that sulfur derivatives have the highest activation barrier for the hydride transfer due to the unfavorable transition state geometry, which explains the lack of previous reports on 1,5-hydride shifts in (alkylthio)styrenes.

In this work, we have shown that the introduction of a trifluoromethyl group into the me-ta-position of arylidene imidazolones (GFP chromophore core) leads to a dramatic increase in their fluorescence in nonpolar and aprotic media. The presence of a pronounced solvent-dependent gradation of fluorescence intensity makes it possible to use these substances as fluorescent polarity sensors. In particular, we showed that one of the created compounds could be used for selective labeling of the endoplasmic reticulum of living cells.