Chemoenzymatic synthesis of an N-acetylneuraminic acid analogue having a carbamoylmethyl group at C-4 as an inhibitor of sialidase from influenza virus

5,9-Diacetamido-2,6-anhydro-O-4-carbamoylmethyl-3,5,9-trideoxy-d-glycero-d-galacto-non-2-enonic acid (1) was synthesized via a key intermediate 2 through the Neu5Ac aldolase [E.C.4.1.3.3]-catalyzed aldol reaction of 2-acetamido-2,6-dideoxy-6-azido-d-glucose with sodium pyruvate operating under alkaline conditions (pH 10.5) in order to accelerate epimerization C-2 of N-acetyl-d-glucosamine (d-GlcNAc) derivatives. Compound 1 showed inhibitory activity against sialidase.