Quantitative Standards of 4‐O‐Acetyl‐ and 9‐O‐Acetyl‐N‐Acetylneuraminic Acid for the Analysis of Plasma and Serum

N‐Acetylneuraminic acid (sialic acid, Neu5Ac) is one of a large, diverse family of nine‐carbon monosaccharides that play roles in many biological functions such as immune response. Neu5Ac has previously been identified as a potential biomarker for the presence and pathogenesis of cardiovascular disease (CVD), diabetes and cancer. More recent research has highlighted acetylated sialic acid derivatives, specifically Neu5,9Ac(2), as biomarkers for oral and breast cancers, but advances in analysis have been hampered due to a lack of commercially available quantitative standards. We report here the synthesis of 9‐O‐ and 4‐O‐acetylated sialic acids (Neu5,9Ac(2) and Neu4,5Ac(2)) with optimisation of previously reported synthetic routes. Neu5,9Ac(2) was synthesised in 1 step in 68 % yield. Neu4,5Ac(2) was synthesised in 4 steps in 39 % overall yield. Synthesis was followed by analysis of these standards via quantitative NMR (qNMR) spectroscopy. Their utilisation for the identification and quantification of specific acetylated sialic acid derivatives in biological samples is also demonstrated.