A Chemoenzymatic Synthon Strategy for Synthesizing -Acetyl Analogues of -Acetylated W Capsular Polysaccharide Oligosaccharides.

-Acetylated sialic acid has been found in the serogroup W (NmW) capsular polysaccharide (CPS) and is a required structural component of clinically used NmW CPS-based polysaccharide and polysaccharide-conjugate vaccines. The role of sialic acid -acetylation in NmW CPS, however, is not clearly understood. This is partially due to the lack of a precise control of the percentage and the location of -acetylation which is labile and susceptible to migration. We explore chemoenzymatic synthetic strategies for preparing -acetylated analogues of -acetylated NmW CPS oligosaccharides which can serve as structurally stable probe mimics. Substrate specificity studies of NmW CPS polymerase (NmSiaD) identified 4-azido-4-deoxy--acetylmannosamine (ManNAc4N) and 6-azido-6-deoxy--acetylmannosamine (ManNAc6N) as suitable chemoenzymatic synthons for synthesizing -acetyl analogues of NmW CPS oligosaccharides containing 7--acetyl--acetylneuraminic acid (Neu5,7Ac) and/or 9--acetyl--acetylneuraminic acid (Neu5,9Ac). The synthesis was achieved by NmSiaD-dependent sequential one-pot multienzyme (OPME) strategy with in situ generation of the corresponding sugar nucleotides from simple monosaccharides or derivatives to form N-oligosaccharides which were converted to the desired NAc-oligosaccharides by an efficient one-step chemical transformation.