The flowers of Edgeworthia gardneri are consumed as an herbal tea in Tibet with potential health benefits. To complement the current knowledge regarding the chemical composition and antihyperglycemic activity of the flower of E. gardneri, two new phenolics, gardnerol A and B (1 and 2), along with 19 known phenolics were isolated from the flower of E. gardneri. All isolates were evaluated for their inhibitory activity against α-glucosidase. Compound 5, identified as the major constituent of the flower of E. gardneri, showed a significant α-glucosidase inhibitory activity and acted as a competitive inhibitor. The oral administration of compound 5 at a dose of 300 mg/kg significantly reduced the postprandial blood glucose levels of normal and streptozotocin (STZ)-induced diabetic mice. Furthermore, compound 5 significantly decreased the fasting blood glucose levels in STZ-induced diabetic mice.
Tyrosinase is a key enzyme in melanin biosynthesis, and is also involved in the enzymatic browning of plant-derived foods. Tyrosinase inhibitors are very important in medicine, cosmetics and agriculture. In order to develop more active and safer tyrosinase inhibitors, an efficient approach is to modify natural product scaffolds. In this work, two series of novel tyrosinase inhibitors were designed and synthesized by the esterification of cinnamic acid derivatives with paeonol or thymol. Their inhibitory effects on mushroom tyrosinase were evaluated. Most of these compounds (IC: 2.0 to 163.8 μM) are found to be better inhibitors than their parent compounds (IC: 121.4 to 5925.0 μM). Among them, ()-2-acetyl-5-methoxyphenyl-3-(4-hydroxyphenyl)acrylate (), ()-2-acetyl-5-methoxyphenyl-3-(4-methoxyphenyl)acrylate () and ()-2-isopropyl-5-methylphenyl-3-(4-hydroxyphenyl)acrylate () showed strong inhibitory activities; the IC values were 2.0 μM, 8.3 μM and 10.6 μM, respectively, compared to the positive control, kojic acid (IC: 32.2 μM). Analysis of the inhibition mechanism of , and demonstrated that their inhibitory effects on tyrosinase are reversible. The inhibition kinetics, analyzed by Lineweaver-Burk plots, revealed that acts as a non-competitive inhibitor while and are mixed-type inhibitors. Furthermore, docking experiments were carried out to study the interactions between and mushroom tyrosinase.
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