Deoxy‐nitrosugars. 16th Communication . Synthesis of N ‐acetyl‐4‐deoxyneuraminic acid

The synthesis of 5‐acetamido‐4‐deoxyneuraminic acid ( 1 ) is described. Acetylation of a mixture of the epimeric triols 4 and 5 gave the tetraacetates 7 and 8 ( Scheme 1 ). Ozonolysis of a mixture of these acetates followed by base‐promoted β‐elimination led to the ( E ) ‐configurated α,β‐unsaturated keto ester 10 , which was hydrogenated to give the saturated keto ester 11 . Saponification of 11 and hydrolytic removal of the benzylidene group followed by anion‐exchange chromatography gave the 5‐acetamido‐4‐deoxyneuraminic acid ( 1 , Scheme 1 and 2 ). De‐ O ‐acetylation (NaOMe/MeOH) of the keto ester 11 gave a mixture of the tert ‐butyl ester 12 and the methyl ester 13 , which were converted to tert ‐butyl N ‐acetyl‐4‐deoxyneuraminate ( 14 ) and to methyl N ‐acetyl‐4‐deoxyneuraminate ( 15 ), respectively. Hydrogenolysis of the benzylidene acetal 11 followed by de‐ O ‐acetylation gave the pentahydroxy ester 16 .