合成路线1

Glycosylation of sugar (I) with the idopyranosyl fluoride (II) by means of BF3.Et2O and molecular sieves in dichloromethane gives the disaccharide fragment (III), which is then converted into acetonide (V) by saponification of the ester functions with t-BuOK, followed by reaction with 2,2-dimethoxypropane (IV) in DMF and acidification with p-toluensulfonic acid. Methylation of acetonide (V) with MeI and NaH in DMF/MeOH provides the disaccharide (VI), which is then treated with HOAc to yield the 4',6'-diol (VII). Selective silylation of the diol (VII) with tert-butyldimethylsilyl chloride (TBDMSCl) in pyridine leads to the 6'-O-TBDMS derivative (VIII), which is condensed with levulinic acid (IX) by means of dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP) in dioxane to give the ester (X). Compound (X) is then submitted to simultaneous Jones oxidation and TBDMS removal with CrO3 and H2SO4/H2O in acetone to provide the iduronic acid derivative (XI), which is converted into the key intermediate (XII), first by esterification with MeI and KHCO3 in DMF and then by removal of the 4'-O-levulinoyl protecting group with HOAc and hydrazine hydrate in pyridine.