Three new gallic acid sugaresters from Elaeagnus oxycarpa Schlechtend leaves and their antioxidant and tyrosinase inhibitory activities

Five compounds were isolated and purified from the water extract of Elaeagnus oxycarpa Schlechtend leaf by multi-dimensional reversed-phase preparative liquid chromatographic system based on the separation and enrichment model. Their structures were identified by spectral analysis such as NMR, MS, UV, IR and by comparison with literature information as 2, 4(1H, 3H)-pyrimidinedione (1), elaeagnussugarester B (2), elaeagnussugarester A (3), elaeagnussugarester C (4), gallic acid (5). Compounds 2-4 are new compounds, compound 1 was isolated from Elaeagnus oxycarpa Schlechtend for the first time. The antioxidant and anti-tyrosinase activities of these compounds were evaluated by using the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical method, the 2, 2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radical method, the potassium ferricyanide reduction method and the colorimetric method with L-tyrosine as substrate. The results showed that compounds 2-5 have good antioxidant activities and inhibitory effect on tyrosinase. Compound 4 exhibited the most strong antioxidant activities, with IC₅₀ = 3.59 ± 0.06 μmol·L^-1 for DPPH free radical scavenging ability, IC₅₀ = 10.04 ± 0.20 μmol·L^-1 for ABTS free radical scavenging ability, and total reduction capacity of compound 4 was better than vitamin C respectively. Compound 3 possessed better inhibitory effect on tyrosinase with IC₅₀ = 0.25 ± 0.06 mmol·L^-1.