合成路线1

1) The esterification of N-acetylneuraminic acid (I) with methanol/HCl gives the corresponding methyl ester (II), which is acetylated with acetic anhydride, pyridine and dimethylaminopyridine (DMAP) yielding the pentaacetate (III). The reaction of (III) with trimethylsilyl trifluoromethanesulfonate in ethyl acetate affords the 2,3-didehydro derivative (IV), which is treated with trimethylsilyl azide in butanol to give the 4-azido derivative (V). The selective deacetylation of (V) with sodium methoxide in methanol yields N-acetyl-4-azido-2,4-dideoxy-2,3-didehydroneuraminic acid methyl ester (VI), which is reduced with H2 over Lindlar catalyst (Pd-Pb) in water and treated with Dowex 8x2 resin to afford the N-acetyl-4-amino-2,4-dideoxy-2,3-didehydroneuraminic acid (VII). The reaction of (VII) with BrCN and sodium acetate in methanol gives the corresponding 4-cyanoamino derivative (VIII), which is converted into the final product by reaction with ammonium formate in aqueous NH4OH. 2) The amino derivative (VII) can be converted directly into the final product by reaction with amidinosulfonic acid (X), NaOH and K2CO3 in water. 3) The amino derivative (VII) can also be converted directly into the final product by reaction with pyrazole-1-carboxamidine (XI) and triethylamine in water.