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.

4) The selective deacetylation of 4-O,5-N,7-O,8-O,9-O-pentaacetyl-2,3-didehydro-2-deoxyneuraminic acid (XI) with boron trifluoride ethearate in benzene/methanol gives the 4-deacetyl derivative (XII), which is treated with trifluoromethanesulfonic anhydride in dichloromethane and with sodium azide in DMF to obtain the 4-azido-4-deoxy derivative (XIII). The reduction of (XIII) with H2S in pyridine affords the corresponding 4-amino derivative (XIV), which is finally condensed with S-methylisothiourea in water and saponified through Dowex 50W x 8 in aqueous NH4OH.

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.

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.

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.

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.

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.

The synthesis of [11C]-labeled zanamivir useful in PET studies of drug deposition has been reported: The reaction of the known amino acid GR-121158X (I) with [11C]-cyanogen bromide in 0.1 M sodium borate gives the cyanoamino derivative (II), which is finally treated with a hot solution of NH4Cl and NH4OH in water.