N-Acetylneuraminic acid (5-acetamido-3,5-dideoxy-D-glycero-D-galacto-2-nonulosonic acid: NeuAc) is a sugar component of oligosaccharides in glycoproteines and ganglyosides which play important roles in biological functions such as recognition and differentiation of cells. We previously succeeded to synthesize 3-deoxy-D-manno-2-octulosonic acid (KDO) via the condensation of a triflate (4) with methyl glyoxylate dithioacetal (3). In the present study, the NeuAc derivative 5 was successfully synthesized by an application of the the same methodology via the coupling reaction of 3 with epoxide 6 which possesses all asymmetric carbon atoms of NeuAc. We first prepared the mannosamine derivative 8 either from D-glucose by substitution of the hydroxyl group at C_2 with an amino group with inversion or from N-acetyl-D-glucosamine by epimerization at C_2. Epoxide 6 was then obtained by stereoselective oxidation of alkene 7 which was derived from the mannosamine derivative 8 by Wittig reaction. The condensation of the epoxide 6 with the dithioacetal 3 was proceeded with an internal exchange of the ester to give a lactone 5 with the desired NeuAc skeleton. We are now investigating the deprotection of 5 into NeuAc 1.
