Meglumine-based Sustainable Three-component Deep Eutectic Solvent Applicable for the Synthesis of Pyrazolo[5,1-b]quinazoline-3-carboxylates as a Sensing Probe for Cu2+ Ions.

An unprecedented meglumine-based three-component deep eutectic solvent (3c-DES) (MegPAc) was synthesized using meglumine, p-toluenesulfonic acid (PTSA), and acetic acid as a renewable, and non-toxic solvent. The exploitation of the MegPAc as an eco-friendly reaction media to construct a selective and sensitive small organic molecular sensing probe, namely, pyrazolo[5,1-b]quinazoline-3-carboxylates (PQCs) was executed. Captivatingly, the MegPAc served the dual role of solvent and catalyst, and it delivered the title components with 69-94 % yields within 67-150 minutes. Furthermore, a UV-visible study unfolds the selective detection of Cu2+ ions with our synthetic probe 4 ba and resulted in hypsochromic shift due to electrostatic interactions. Additionally, 1H NMR titration study and density functional theory (DFT) calculations were performed to attest the binding mechanism of sensing probe 4 ba and Cu2+ ions. Worthy of mention, this protocol unveils the efficacy of meglumine-based 3c-DES for the first time as a bio-renewable system to synthesize the PQCs.