Well-Designed Hydrophobic Deep Eutectic Solvents As Green and Efficient Media for the Extraction of Artemisinin from Artemisia annua Leaves

The green and efficient extraction of bioactive compounds from plant biomass is an important area of interest in the pharmaceutical industries. Hydrophilic deep eutectic solvents (DESs) have been considered as green alternatives to conventional solvents for bioactive compound extraction. In this study, we aimed to provide a practical example demonstrating the tunability of hydrophobic DESs as designer solvents to efficiently extract bioactive compounds from plant biomass. Artemisinin, known as the only drug effective in the treatment of malaria, was chosen for extraction from Artemisia annua leaves. A hydrophobic DES named N81Cl-NBA that was tailor-made from methyl trioctyl ammonium chloride and 1-butanol at a molar ratio of 1:4 showed the highest extraction yield. With N81Cl-NBA-based ultrasound-assisted extraction (UAE), the main factors affecting the extraction yield were statistically optimized using a central composite design combined with a response surface methodology. The optimal conditions were obtained as follows: solvent/solid ratio 17.5:1, ultrasonic power 180 W, temperature 45 °C, particle size 80 mesh, and extraction time 70 min. Under these conditions, an extraction yield of 7.9936 ± 0.0364 mg/g was obtained, which was distinctly higher than that obtained using the conventional organic solvent petroleum ether. Moreover, the recovery of the target artemisinin from the N81Cl-NBA extraction solution was achieved by AB-8 macroporous resin with a recovery yield of 85.65%. N81Cl-NBA could be reused at least two times without a significant decrease in extraction yield. This study suggests that not only hydrophilic DESs but also hydrophobic DESs are truly designer solvents that can be used as green and safe extraction solvents for pharmaceutical applications.