High‐Resolution 1H‐NMR Spectroscopy of Free and Glycosidically Linked O‐ Acetylated Sialic Acids

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Abstract
A number of naturally occurring and synthetic, partially O‐acetylated derivatives of N‐acetylneuraminic and N‐glycoloylneuraminic acids have been investigated by 360‐MHz 1H‐NMR spectroscopy. O‐Acetylation causes strong downfield shifts for the resonances of neighbouring sugar‐skeleton protons. The chemical shifts of these resonances, together with their characteristic multiplet shapes, can be used for localisation of the position of O‐acetyl substituents in the molecule. The number of such substituents in the molecule can be inferred from the number of acetyl‐methyl singlets, which also have characteristic resonance positions.This method for determination of the number and position of O‐acetyl substituents in sialic acid residues is very powerful for structural analysis of underivatized carbohydrate chains derived from glycoconjugates. This is demonstrated for the oligosaccharide N‐acetyl‐4‐O‐acetylneuraminosyl‐(α2→3)‐lactose isolated from echidna milk

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