Isovitexin and Chlorogenic Acid from Juncus decipiens (Buchenau) Nakai Target Melanogenesis and Enhance Photoprotection

Background: Juncus decipiens , a medicinal plant with a long history of traditional use, has been reported to possess diverse biological activities; however, its potential in regulating melanogenesis and protecting against ultraviolet (UV)-induced damage has not yet been explored. Methods: A bio-guided fractionation strategy targeting melanin inhibition was employed. Among the solvent-partitioned fractions, the ethyl acetate (EtOAc) fraction exhibited the most potent anti-melanogenic activity with minimal cytotoxicity in B16 melanoma cells. Further fractionation and purification led to the isolation of two compounds, structurally characterized as isovitexin and chlorogenic acid using high-resolution mass spectrometry (HR-MS) and nuclear magnetic resonance (NMR) analyses. Results: Isovitexin significantly reduced melanin content in a dose-dependent manner and inhibited intracellular tyrosinase activity, indicating its direct role in suppressing melanogenesis. Additionally, isovitexin enhanced cell viability under UVB-induced stress in normal human dermal fibroblasts, suggesting photoprotective potential. Conclusion: These findings represent the first report of the anti-melanogenic and photoprotective activities of compounds isolated from J. decipiens , supporting its value as a source of natural, multifunctional agents for skin health applications.