A pyrazolo[1,5-a]pyridine-fused pyrimidine based novel fluorophore and its bioapplication to probing lipid droplets.

A new fluorescent core skeleton containing pyrazolo[1,5-a]pyridine-fused pyrimidine, called fluoremidine (FD), was discovered. FD analogues were prepared via a one-pot silver-catalyzed cascade cyclization. An N,N-dimethylamino group at the R(1)- and R(2)-positions plays important roles in controlling fluorescence brightness and emission wavelength. An N-acetyl group at the R(3) position contributes to red shifting of the emission wavelength. FD shows excellent solvatochromism with turn-on fluorescence in the lipophilic environment, which was utilized to design a fluorescent probe, FD13, for visualizing lipid droplets in living cells.