An expeditious route to N-glycolylneuraminic acid based on enzyme-catalyzed reaction

A new preparative way of N-glycolylneuraminic acid (NeuGc), one of the important family of sialic acids, from N-acetylglucosamine (GlcNAc) via N-acetylmannosamine (ManNAc) was established based on the combination of chemical and enzymatic reactions. In a kinetic study of the key enzymatic reaction for this process, aldolase-catalyzed synthesis of sialic acid, an inhibitory effect of gluco-isomer on the enzymatic reaction was quantitatively clarified, and the importance of isomerically pure substrate with manno-configuration for aldolase-catalyzed reaction was suggested. A newly developed method, selective degradation of GlcNAc contaminating in the substrate by use of Rhodococcus rhodochrous IFO 15564 provided pure ManNAc to avoid such inhibitory effect of the gluco-isomer for aldolase. Starting from pure ManNAc, via mannosamine hydrochloride, acetoxyacetyl chloride was applied for introducing a protected form of glycolyl group to give N-acetylglycolylmannosamine. For the removal of acetyl protective group, a lipase from Aspergillus niger was effectively used under a mild and neutral condition to afford N-glycolylmannosamine (ManNGc), the substrate of aldolase. NeuGc was prepared in 25% yield and 7 steps from GlcNAc.