Environmentally benign and sustainability-optimized extraction of alkaloids from Tetradium ruticarpum using custom-designed deep eutectic solvents.

This study presents, for the first time, the development of a green and efficient hydrophobic deep eutectic solvents-based ultrasound-assisted extraction (HDEs-UAE) method for the extraction of alkaloids from Tetradium ruticarpum, thereby effectively overcoming the limitations associated with conventional solvents and traditional extraction techniques. A total of 35 distinct DESs were synthesized, and their successful formation was confirmed through ¹H NMR and FT-IR spectroscopic analyses. Among them, the hydrophobic DES-21 (Menthol-Formic acid, Mol-FA) exhibited superior extraction efficiency and enabled the simultaneous extraction of seven alkaloid-based bioactive compounds in a single step, significantly outperforming conventional solvents such as water, methanol, and ethyl acetate. The extraction process and associated parameters, including the molar ratio of Mol:FA, ultrasonic power, extraction temperature, extraction time, and liquid-to-solid ratio, were systematically investigated and optimized using response surface methodology. The optimal conditions were established as an ultrasonic power of 300 W, an extraction temperature of 30 °C, an extraction time of 39.7 min, a liquid-to-solid ratio of 19.7 mL/g, and a molar ratio of 1:2 (Mol:FA), achieving a maximum total alkaloid extraction yield of 70.56 mg/g. The extraction mechanism was systematically investigated through complementary analytical techniques, including SEM, FT-IR, and density functional theory (DFT) calculations. Notably, DFT calculations and non-covalent interaction (NCI) analyses reveal that the enhanced extraction efficiency is attributable to the exergonic stability of the DES-21-EVOD complex, along with the increased availability of hydrogen-bond donors and acceptors provided by DES-21. In conclusion, the proposed HDESs-UAE method, characterized by its simplicity and environmental benignity, offers a highly efficient and sustainable approach for the extraction of bioactive alkaloid compounds from traditional Chinese medicine.