Synthesis and Biological Properties of N ‐Acetyl‐4‐deoxy‐ D ‐neuraminic Acid

N ‐Acetylneuraminic acid ( 1 ) can be transformed into the methyl α‐ D ‐ketoside 2 which, by reaction with methanesulfonyl chloride, yields the corresponding 4‐ O ‐mesylate 3 and the 4,7‐di‐ O ‐mesylate 4 as a by‐product. Compound 3 reacts with Nal giving the 4‐deoxy‐4‐iodo compound 5 with equatorial orientation of the I‐atom. As second product, the dihydrooxazole 6 is produced. Catalytic hydrogenation of 5 is followed by ester cleavage and removal of the isopropylidene group yielding the methyl α‐ D ‐ketoside 8 which affords the title compound, N ‐acetyl‐4‐deoxyneuraminic acid ( 9 ), by reaction with fowl plague virus sialidase. Further biochemical activities of 8 and 9 are reported.