Study On Glycosylation Of Quercetin Based On Dextransucrase

Flavonoids, which has a combination of properties includinganti-inflammatory,antibacterial, antiviral, antioxidant, anti-tumor, anti radiation,immune regulation and many other activities, widely exists in nature. It has become theresearch focus of natural drug development both at home and abroad. One majordisadvantage associated with the use of flavonoid aglyconesis is its poor solubility inwater. Glycosylation not only improves the water solubility of flavonoid aglycones，butalso improves their physicochemical properties. This paper explores the synthesis ofquercetin glycoside by using sucrose as glucose glycosyl donor, quercetin as glycosylreceptor and applying the transglycosylation of dextransucrase.Firstly, this paper studies the enzyme catalytic reaction system, determined the30%DMSO-70%acetic acid calcium acetate buffer (0.02mol/L, pH=5.4) as the enzymecatalytic reaction system. This reaction system, not only maintains the activity ofenzyme, but also solves the poor water solubility of quercetin.Secondly, study the separation and purification of enzyme catalyzed product. Afterthe process of alcohol precipitation and extraction, then separate and purify quercetinglucoside by combining AB-8macroporous resin column and Sephadex LH-20colum.The purity of quercetin glucoside is more than98%.Thirdly, study the conditions of catalytic reaction, through the investigation of theeffect of reaction time, reaction speed, activity of enzyme, reaction volume, sucroseconcentration on quercetin glucoside conversion rate. The optimal conditions ofenzyme catalyzed synthesis of quercetin glucoside were determined. Quercetinglucoside conversion rate was increased from28%to39.5%. The optimizedparameters are in a mixture of DMSO/Acetic acid calcium acetate buffer at thetemperature of25degrees by using10%of sucrose as glucose glycosyl donor,quercetin as glucose glycosyl receptor and40U/mL dextransucrase, the stirring speedis150r/min, and the reaction could lead to high conversion of quercetin glycoside, upto39.5%.Finally, the structure of quercetin glucoside was suggested by mass spectrometryand nuclear magnetic resonance hydrogen spectrum. The product was characterizedand confirmed as a quercetin mono-glycoside, and the molecular weight of the productis464. The most likely structure is quercetin-4’-ɑ-O–glucopyranoside.The results of this study laid the foundation for the glycosylation of flavonoids.