Research On Stereoselective Synthesis Of 2,6-dideoxy Glycosides

2,6-Dideoxyglycosides are common carbohydrate components of many bioactive natural products.Removal or modification of the deoxyglycoside components usually changes the biological properties of the natural products.Since the non-availability of neighboring-group participation from substituents at C-2,and the enhanced conformational flexibility derived from the reduced number of substituents make it difficult to achieve glycosidation in a stereoselective manner,thus it tends to provide a mixture of ?-/?-anomers.In this thesis,we attempted to explore efficient methods for stereoselective synthesis of 2,6-dideoxyglycosides.5-Hydroxymethylfurfural(HMF),as a versatile organic intermediate and fossil fuel,is expected to become a new sustainable material to solve the energy crisis.HMF also can be used in the Ferrier-type reaction of glycals to provide 2,3-unsaturated-O-glycosides.In this thesis,we attempted to find an efficent and environmentally benign catalyst to catalyze the Ferrier-type reaction of HMF with glycals.This thesis was composed of four parts:1.Research on stereoselective synthesis of a-2,6-dideoxy glycosides.2.Research on stereoselective synthesis of?-2,6-dideoxy glycosides.3.Research on stereoselective synthesis of?-2,6-dideoxy-aryl-C-glycosides.4.Research on the Ferrier-type reaction of HMF with glycals.1.We have developed an efficient method for stereoselective synthesis of a-2,6-dideoxyglycosides using steady peracylprotected 2,6-dideoxyglucose as donor and I2+Et3SiH as catalytic system.This method was applied to a wide range of acceptors,including primary alcohols,secondary alcohols,benzyl alcohol,allyl alcohol,propargyl alcohol,halogenated alcohols,sterols,and sugar derivatives.Besides,other advantages such as mild reaction conditions,high efficiency(up to 99%)and short reaction time(5min),have also been shown.2.An efficient and convenient approach for stereoselective synthesis of ?-linked 2,6-dideoxyglycosides has been developed through one-pot glycosylation strategy.The glycosidation promoted by easily available silver nitrate,provided the corresponding 2,6-dideoxyglycosides and oligosaccharide with good to excellent yields(52-84%)and preponderant ?-configuration(?/? = 2.3:1 to 11:1).3.We have demonstrated herein an efficient and fast protocol for the stereoselective construction of ?-2,6-dideoxy-aryl-C-glycosides under the catalysis of I2+Et3SiH.The present procedure offers several advantages,such as mild reaction conditions,short reaction time(15min),high yields and excellent stereoselectivities.4.In this report,we have demonstrated a new and efficient method for the synthesis of 2,3-unsaturated-O-glycosides from HMF and glycals using FeCl3·6H2O/C(2:3)as catalyst.The advanteges of the procedure are as follows:highly yielding,simple operation,and the catalyst of FeCl3·6H2O/C(2:3)can be repeatedly used.