Study On The Acylation Of Phenol Glycosides Catalyzed By Whole-Cell Catalysts In Non-Aqueous Phase

Plant phenol glycosides such as arbutin,saildroside and phlorizin,are kinds of the important natural products that widely exists in plants.It has been used in many traditional industries such as functional food,nutraceutical,pharmaceutical,and cosmetics because of their countless bioactivities,including antioxidant,anti-inflammatory,antibacterial,whitening and anoxia-resisting activities.Unfortunately,the low lipophilicity,unsatisfactory stability and low bioavailablity of phenol glycosides limited their further applications in the functional food,pharmaceutical,and cosmetics industries.Previous studies reported the acylation of phenol glycosides can improve its liposoluble and thus improve its bioavailability.However,so far,no studies have been reported on whole-cell-catalyzed acylation of phenol glycosides（arbutin,salidroside,piceid and pholrizin）.Herein,whole-cell catalyzed acylation of arbutin were investigated and the effects of several key factors on the biocatalytic reaction were studied.The mechanisms underlying of the effect of the reaction time on the formation of the mono-and diester in the reaction of acylation of arbutin were revealed.Moreover,the structure recognization of the cells on acyl donors with different carbon chain lengths and various phenol glycosides were studied;in addition,the effects of the orgin of strains and reaction medium on the conversion rate,regioselectivity,the time of reaction to reach equilibrium and the ratio of mono-and diester of products were also revealed.Among fiftheen strains,the whole cell catalyst of Candida parapsilosis ACCC 20221 tested the highest activity of the reaction of propanylation of arbutin.In all pure organic solvents studied,the highest conversion rate reached in THF,at the most suitable molar ratio of VP/arbutin（mM/mM）15:1 and whole cell dosage 30 mg/mL,after 24 h,the conversion rate can reach 98.3%.In order to improve the soluilibity of arbutin,the feasibility of biorganic solvent systems were studied,and results showed comparing with pure organic solvent systems,biorganic solvent systems significantly increases the soluilibity of arbutin with a high conversion rate（>85%）,especially in the biorganic solvent system of pyridine/isooctane（1:1,V/V）,after 24 h,the conversion rate can reach 97.2%,however,the soluilibity of arbutin was five times than in THF.The structurs of the purified products were analyzed by MS and ¹³C NMR spectrums,and results showed two products of mono-and diesters of arbutin were obtained in the reaction of acylation of arbutin catalyzed by Candida parapsilosis ACCC 20221.For the monoesters,only occurred at 6’-carbon atom of arbutin,and the acylation sites of diester were C3’and C6’of the sugar moiety of arbutin.For Candida parapsilosis ACCC 20221,the 6’carbon atom of the sugar moiety of arbutin was the dominant site and then was the C3’of the sugar moiety of arbutin.Investigation of time course of synthesis of the two products showed that controllable synthesis of mono-or diesters of arbutin can be achieved by controlling reaction time when whole cells were used as cataltysts.The recoginization of whole cell catalysts to the acylation substates were investigated.By choose of a series of acyl donors with different carbon chain length（C2-C18）.Results showed with the increase of carbon chain length,both the initial rate and conversion rate of the reaction decreased,and the highest conversion was obtained with vinyl propionate as acyl donor.The 6’-regioselectivity of the reaction increased with the increase of carbon chain length of acyl donor,and the propotion of monoester in tye final products was changed from83.5%to>99%.The log p value of products increased along with the increase of fatty acid chain length,indicating the improved liposolublity of the esters,Effects of the polyphenol structures on the whole cell catalyzed reaction were also investigated by choosing a serial of polyphenols with similar structure or function of arbutin using Candida parapsilosis ACCC20221 and Aspergillus oryzae GIM 3.5232 as catalysts.The results showed two whole-cell catalysts have the ability to catalyze the propanoylation of phenolic glycosides,especially the whole-cell catalyst of Candida parapsilosis ACCC 20221.By Candida parapsilosis ACCC20221,the conversion rate of salidroside,arbutin,piceid and phlorizin were 99.7%,98.3%,83.5%and 40.5%,respectively.And the synthesis of mono-or diesters of salidroside is controllable by choosing a suitable whole-cell catalysts,organic solvents and controlling reaction time.Researches present in this dissertation provides a facile and efficient biocatalytic method for acylation modification of polyphenols using whole-cells as a catalyst,which may provide a therotical reference for the further development of phenolic glycosides.