Synthesis and evaluation of α-glucosidase and tyrosinase inhibitory activities of ester derivatives of usnic acid

Abstract

Introduction: Usnic acid isolated from lichen was a potential bioactivity compound. It has a broad spectrum bioactivity, including antiviral, anti-inflammatory, anticancer… However, low solubility in water limited its application. Many researchs have done to overcome the restriction. Recent results showed that usnic acid derivatives bearing triazole, enamine, pyrazole and benzylidene groups had strong antiviral and anticancer activities. Thus, investigation of usnic acid derivatives synthesis was an attractive aspect due to the diversity of bioactivities of usnic acid derivatives.
 Methods: Usnic acid was isolated from lichen, six ester derivatives of usnic acid were synthesized from usnic acid with acetyl chloride and benzoyl chloride under stirring at room temperature. The products were evaluated α-glucosidase and tyrosinase inhibitory activities.
 Results: All the ester derivatives were created with good yields. All derivatives exhibited the same or higher activity comparing with usnic acid. Ester of usnic acid bearing benzoyl group showed excellent α-glucosidase activity with IC50 26.7±0.57 and 68.8±0.15 µM.
 Conclusion: Among the ester derivatives, UE1 and UE6 were reported as as new compounds. Interestingly, all products displayed the same or higher biological activity than the starting material, usnic acid when evaluated against α-glucosidase and tyrosinase.

A Comparative Survey of Anti-Melanoma and Anti-Inflammatory Potential of Usnic Acid Enantiomers—A Comprehensive In Vitro Approach

“…At the highest tested dose of 250 µg/mL, (+)usnic acid revealed 5.22% and 9.1% tyrosinase inhibition, (−)-usnic acid 1.4% and 4.09%, while IC 50 values for the control kojic acid were 1.1 µg/mL and 44.9 µg/mL, for monoand diphenolase activity, respectively. Similar observations were recently described for (+)-usnic acid, with no anti-tyrosinase activity up to 50 [23] and 200 µM [24], while no information was available on the activity of its left-handed enantiomer.…”