A tailor-made NaDESs development strategy for the enhanced extraction of hydroxynaphthoquinones from Alkanna tinctoria roots.

Abstract

The natural hydroxynaphthoquinone enantiomers (HNQs) are well-described pharmaceutical and cosmeceutical agents especially present in European Alkanna tinctoria (L.) Tausch roots [1]. In this work, eco-friendly natural deep eutectic solvents (NaDESs) were developed for the selective extraction of these compounds. An extensive screening was performed using more than sixty tailor-made NaDESs. The impact of the intrinsic physicochemical properties on the HNQs extraction efficiency as well as the specificity towards the different enantiomeric pairs was thoroughly investigated. As a result of a multivariate analysis, the most relevant mixture with the highest extraction efficiency was composed of levulinic acid and glucose (LeG) using a ratio of 5:1 (w/w) and 20% of water (w/w). Further optimization of the extraction efficiency was attained by response surface methodology, using a temperature of 45°C, a solid-to-liquid ratio of 30 mg/mL, and an extraction time of 50 min. A maximum extraction output of 41.72±1.04 mg/g was reached for HNQs, comparable to that of the commonly used organic solvents. A solid-phase extraction step was also proposed for the recovery of HNQs and for NaDESs recycling. Our results revealed NaDESs as a highly customizable class of green solvents with remarkable capabilities for the extraction of HNQs.