Semisynthesis Of Myricetin From Dihydromyricetin

Myricetin is widely distributed in plants, having a variety of pharmacological activities, is the precursor of many lead drugs, also can be used directly as drugs. However, in natural plants with low content of myricetin, extraction and separation technology is difficult, leading to market products in short supply of myricetin, and the price is high. Studies prove that the dihydromyricetin amount to more than 30% in Ampelopsis Grossedentata, abundant sources of resources. In this paper, according to the characteristics of dihydromyricetin structure similar with myricetin, using chemical conversion method semisynthetics myricetin. The main contents are as follows:(1)UV spectrophotometry and high performance liquid chromatography(HPLC) methods were established to detect myricetin. The detection wavelength of UV was at 375 nm, standard curve equation: C=14.328A-0.1871, r=0.9998, there was a good liner relation within the range of 3.52~10.56 μg/mL. The method had good precision, stable and high repeatability. Chromatographic conditions: Hypersil BDS C18 column, mobile phase consisted of acetonitrile: 0.1% phosphoric acid=24:76(v/v), flow rate was 1.0 mL/min, column temperature was 25℃, detection wavelength was 375 nm. Standard curve equation: C=1.49×10-5S-2.40471, r=0.9997, there was a good liner relation within the range of 40.0~120.0 μg/mL. The method had good precision, stable and high repeatability.(2)Myricetin was semisynthesized using dihydromyricetin as raw materials by the reaction steps including base-catalyzed ring opening generation chalcone, Algar-Flynn-Oyamada(AFO) reaction, HCl solution to adjust the pH and other reaction steps. Single factor experiments on the reaction parameters were optimized. Under the optimum reactin conditions [Dihydromyricetin 0.520 g, H2O(30mL) as the solvent, adding 15% H2O2 0.68 mL and 16% NaOH aqueous solution 5.5mL in order], verification tests myricetin average yield was 16.21%(n=3), RSD=1.78%.(3)Using dihydromyricetin as raw materials, dissolving by pyridine and heating to reflux was semisynthesized myricetin. Response surface design was optimized myricetin synthesis parameters, the optimal reaction parameters as follows: volume fraction 66.6%, temperature 90.36℃ and solid-liquid ratio 20.88:1(mg:mL). The predicted reaction yield was 76.48%, while the actual measured average yield was 76.63%(n=4), RSD=1.39%.(4)Decolorization processes of myricetin crude were studied. Based on the single factor experiment, taking myricetin decolorization rate and retention rate as index, selecting decolorization temperature, amount of acticarbon, pH and decolorization time to optimize the best condition for the the process of decolorization, orthogonal experimental design was designed with four factors and three level. The optimum decolorization conditions were A3B3C1D1: decolorization temperature 35℃, active carbon dosage 0.08 g, with pH 3.0 and decolorization time 10 min. The order of influence factor was active carbon dosage ? decolorization temperature > pH> decolorization time.(5)Crystallization processes of myricetin were studied. Taking methanol and ethanol as the crystallization solvent, crystallized myricetin purity was 99.21% and 98.89%, the yield was 48.82% and 50.26% respectively. Using methanol and ethanol concentration gradient crystallization method, crystallized myricetin purity was 99.26% and 98.89%, the yield was 69.0% and 71.0% respectively.(6)The structure of synthetic myricetin was investigated by proton nuclear magnetic resonance spectroscopy(1H-NMR), nuclear magnetic resonance spectroscopy of carbon(13C-NMR), infrared spectroscopy(IR), ultraviolet spectroscopy(UV) and high performance liquid chromatography(HPLC) methods.(7)UV spectrophotometry method was established to detect peroxide value, it has not significantly different from the national standard method. Myricetin on DPPH·scavenging capacity and antioxidant capacity of edible oil were compared, the results showed that the synthetic myricetin and myricetin standard had similar ability with antioxidant capacity and DPPH·scavenging capacity.