Ultrasonic-Assisted Biphasic Aqueous Extraction of Polyphenols from Vaccinium Dunalianum Leaves: Optimization, Antioxidant, and Tyrosinase Inhibition Activities.

To optimize the ultrasonic-assisted biphasic aqueous extraction conditions for polyphenolic compounds from Vaccinium dunalianum Wight leaves and investigate their antioxidant and tyrosinase inhibition activities, single-factor experiments were conducted to investigate the effects of ethanol volume fraction (%), ammonium sulfate mass fraction (%), solid-liquid ratio (g/mL), ultrasonic temperature (°C), and ultrasonic time (min) on polyphenolic content during extraction. Based on these experiments, three key factors influencing extraction were selected for response surface methodology (RSM) optimization. The results indicated that under conditions of 26% ethanol, 20% ammonium sulfate, a solid-liquid ratio of 1:30, and extraction for 35 minutes at 50°C, the polyphenol content reached 61.62 mg/g. The relative contents of 6'-O-caffeoylarbutin, ß-arbutin, and chlorogenic acid were 34.45%, 4.56%, and 31.06%, respectively. The DPPH· and ABTS+· scavenging rates were above 95% and 96%, respectively, and the ferric reducing ability exhibited a significant dose-effect relationship. The inhibition rates of monophenolase and diphenolase activities of tyrosinase were 43.84% and 35.73%, respectively. The optimized process for ultrasonic-assisted biphasic aqueous extraction of polyphenols from Vaccinium dunalianum Wight leaves demonstrated significant antioxidant and tyrosinase inhibition activities.

6'-O-Caffeoylarbutin from Quezui Tea: A Highly Effective and Safe Tyrosinase Inhibitor.

Tyrosinase is vital in fruit and vegetable browning and melanin synthesis, crucial for food preservation and pharmaceuticals. We investigated 6'-O-caffeoylarbutin's inhibition, safety, and preservation on tyrosinase. Using HPLC, we analyzed its effect on mushroom tyrosinase and confirmed reversible competitive inhibition. UV_vis and fluorescence spectroscopy revealed a stable complex formation with specific binding, causing enzyme conformational changes. Molecular docking and simulations highlighted strong binding, enabled by hydrogen bonds and hydrophobic interactions. Cellular tests showed growth reduction of A375 cells with mild HaCaT cell toxicity, indicating favorable safety. Animal experiments demonstrated slight toxicity within safe doses. Preservation trials on apple juice showcased 6'-O-caffeoylarbutin's potential in reducing browning. In essence, this study reveals intricate mechanisms and applications of 6'-O-caffeoylarbutin as an effective tyrosinase inhibitor, emphasizing its importance in food preservation and pharmaceuticals. Our research enhances understanding in this field, laying a solid foundation for future exploration.

Design, synthesis, and inhibitory activity of hydroquinone ester derivatives against mushroom tyrosinase.

Tyrosinase is a widely distributed copper-containing enzyme found in various organisms, playing a crucial role in the process of melanin production. Inhibiting its activity can reduce skin pigmentation. Hydroquinone is an efficient inhibitor of tyrosinase, but its safety has been a subject of debate. In this research, a scaffold hybridization strategy was employed to synthesize a series of hydroquinone-benzoyl ester analogs (3a-3g). The synthesized compounds were evaluated for their inhibitory activity against mushroom tyrosinase (mTyr). The results revealed that these hydroquinone-benzoyl ester analogs exhibited inhibitory activity against mTyr, with compounds 3a-3e displaying higher activity, with compound 3b demonstrating the highest potency (IC50 = 0.18 ± 0.06 µM). Kinetic studies demonstrated that the inhibition of mTyr by compounds 3a-3e was reversible, although their inhibition mechanisms varied. Compounds 3a and 3c exhibited non-competitive inhibition, while 3b displayed mixed inhibition, and 3d and 3e showed competitive inhibition. UV spectroscopy analysis indicated that none of these compounds chelated with copper ions in the active center of the enzyme. Molecular docking simulations and molecular dynamics studies revealed that compounds 3a-3e could access the active pocket of mTyr and interact with amino acid residues in the active site. These interactions influenced the conformational flexibility of the receptor protein, subsequently affecting substrate-enzyme binding and reducing enzyme catalytic activity, in line with experimental findings. Furthermore, in vitro melanoma cytotoxicity assay of compound 3b demonstrated its higher toxicity to A375 cells, while displaying low toxicity to HaCaT cells, with a dose-dependent effect. These results provide a theoretical foundation and practical basis for the development of novel tyrosinase inhibitors.