Volatile Natural Deep Eutectic Solvents (VNADESs) for Extraction of Shikonin Derivatives from Echium vulgare Roots and Evaluation of Biological Activity

What if the greenest solvent for extracting precious plant pigments could simply evaporate away? Scientists are turning to volatile natural deep eutectic solvents to unlock shikonins from a humble weed.

Shikonins are vibrant naphthoquinones with a palette of biological activities, but their usual extraction relies on harsh nonpolar solvents. Now, researchers are exploring a greener path using volatile natural deep eutectic solvents (VNADESs) made from thymol, camphor, menthol, and benzyl alcohol. These solvents promise efficiency without the toxic footprint.

In this study, extracts from Echium vulgare roots were analyzed with advanced mass spectrometry, revealing eight shikonin derivatives. The VNADES-based extracts matched the traditional hexane extracts in shikonin content. However, attempts to remove the VNADES via freeze-drying caused significant loss of the precious compounds.

The selected VNADES extract (TBa 2:8) showed lower cytotoxicity than hexane extract, making it potentially safer. Its antioxidant activity varied by assay, but it uniquely reduced intracellular ROS and NO levels—something hexane couldn't do. Yet hexane still won on antimicrobial strength.

The takeaway: VNADESs are a promising green alternative for shikonin extraction, but removing them without losing the goods remains a tricky puzzle.

Key Points

• VNADESs match hexane in extracting shikonin derivatives.
• Freeze-drying causes significant shikonin loss.
• TBa 2:8 shows lower cytotoxicity and reduces ROS/NO.