Bromo-Substituted Diazenyl-pyrazolo[1,5-a]pyrimidin-2-amines: Sonogashira Cross-Coupling Reaction, Photophysical Properties, Bio-interaction and HSA Light-Up Sensor.

A convenient synthesis of a broad series of thirteen examples of alkyne-spacer derivatives 2 from the well-known Sonogashira cross-coupling reaction on diazenyl-pyrazolo[1,5-a]pyrimidin-2-amine compounds 1 is reported. The reactivity of heterocycles 1 due the presence of selected electron-donor (EDG) and electron-withdrawing (EWG) groups attached to different alkynes was evaluated. Also, the reactional versatility due the position variation of the bromo atom at the scaffolds 1 was also investigated. In general, derivatives presented strong absorption bands at the 250-500 nm optical window and UV to cyan emission properties. Also, the redox analysis was recorded by electrochemical cyclic voltammetry technique. For HSA biomacromolecule assays, spectroscopic studies by UV-Vis, steady-state and time-resolved emission fluorescence, and molecular docking calculations evidenced the ability of each compound to establish interactions with human serum albumin (HSA). Finally, the behavior presented for this new class of heterocycles makes them a promising tool as optical sensors for albumins.