合成路线1

The azido acetamide intermediate (XXVII) can be prepared by several alternative methods. Alkylation of the benzyl glycoside of N-acetyl-3,6-di-O-benzyl-α-D-glucosamine (XXVIII) with iodomethane and NaH in DMF followed by catalytic benzyl group hydrogenolysis of the resulting 4-methoxy derivative (XXIX) with H2 over Pd/C yields N-acetyl-4-O-methylglucosamine (XXX), which by subsequent incubation with N-acetylneuraminic acid aldolase (N-Ac-NAA) in the presence of sodium pyruvate (XXXI) and NaN3 at pH 10-11 gives the nonuropyranosoic acid derivative (XXXII). Acid (XXXII) is esterified with MeOH in the presence of acidic cation exchange resin (Dowex 50x8) to give methyl ester (XXXIII), which by acetylation with Ac2O in pyridine and successive treatments with HCl and DBU leads to the non-2-enopyranosonate (XXXIV). Finally, compound (XXXIV) is converted to the azido acetamide intermediate (XXVII) by treatment with boron trifluoride etherate and one equivalent of MeOH in CH2Cl2 followed by NaN3 and Dowex 50x8 resin (1, 7, 8). Scheme 4.
Alternatively, solvolysis of the cyclic carbonate (XX) with methanolic NaOMe yields diol (XXXV), which is then acetylated with AcOH by means of Et3N and DMAP in EtOAc to give diacetate (XXXVI). Ring opening of oxazoline (XXXVI) with Me3SiN3 in the presence of (i-PrO)4Ti in t-BuOH furnishes the 4-azido-5,6-dihydropyran derivative (XXVII) (3). Scheme 4.