Green Chemistry-Based Extraction and Process Optimization of Onosma elegantissima: Exploring Its Bioactive Compounds and Pharmacological Potential

Onosma elegantissima is an endemic and understudied plant of the Kozani Regional Unit (Greece), with poorly established traditional use. However, the well-documented pharmacological potential of the genus has prompted further investigation. Furthermore, green solvent-based extraction procedures have gained emerging scientific interest due to their high efficiency/selectivity and environmentally friendly approach. Therefore, our study aimed to establish the optimal extraction protocol to obtain extracts with high therapeutic value using two green solvent-based techniques: hydrothermal and deep eutectic solvent (DES) extraction. Our results demonstrate that hydrothermal extraction for 90 min at 80 °C yielded extracts exhibiting total phenolic content (35.19 mg GAE/g dw), approximately threefold higher compared to DES extracts (10.03 mg GAE/g dw), and significantly higher antioxidant capacity. The flavonoid concentration (8.39 mg RE eq/g) measured was at the same level for both types of extracts (7.34 mg RE eq/g). The DES extract showed slightly higher anti-inflammatory potential, though. Additional assays were performed to evaluate antimicrobial activity and in vitro antidiabetic capacity. The bioactive compounds of optimized extracts were identified by HPLC, revealing that the most dominant compound recovered was chlorogenic acid in the DES extract and neochlorogenic acid in the hydrothermal extract. To complement the phytochemical analysis, molecular docking was used as a reproducible, hypothesis-generating screen to prioritize future enzyme inhibition assays for HPLC-detected phenolic constituents and literature-related comparators; docking was not used as evidence of biological activity. Conclusively, Onosma elegantissima’s first biological study revealed significant antioxidant activity.