Towards a Green and Sustainable Valorization of Salix amplexicaulis : Integrating Natural Deep Eutectic Solvents and Microwave-Assisted Extraction for Enhanced Recovery of Phenolic Compounds

Combining advanced extraction technologies with non-pollutant solvents represents a sustainable approach toward valorizing medicinal plants and aligns with the principles of green chemistry. This study aimed to evaluate the efficiency of microwave-assisted extraction (MAE) combined with natural deep eutectic solvents (NADES) to extract bioactive compounds from the underexplored leaves and bark of Salix amplexicaulis Bory & Chaub. Additionally, the potential of NADES as sustainable alternatives to conventional solvents was assessed through a comparative evaluation of MAE-NADES with MAE–water and traditional ethanol maceration. NADES based on lactic acid–glycerol, lactic acid–glucose, glycerol–glucose, and glycerol–urea were synthesized by heating and stirring. Willow extracts were characterized by HPLC-DAD, resulting in the identification and quantification of seven phenolic acids and four flavonoids. Lactic acid–glucose (5:1)-based NADES extracted the highest number of phenolics in the greatest amount from the bark and leaves of S. amplexicaulis . MAE-NADES offers a fast, cost-effective preparation, high extraction efficiency, and environmentally friendly properties, opening new perspectives on the valorization of S. amplexicaulis in the pharmaceutical field. Furthermore, NADES provide a promising alternative to water and toxic organic solvents for extracting bioactives.