From mother's milk to structural insights: 1H-15N NMR analysis of Lewis X antigen-bearing oligosaccharides isolated from human milk

Human milk oligosaccharides (HMOs) are complex unconjugated glycans abundant in breast milk, with vital roles in infant nutrition and health. The structural elucidation of HMOs remains challenging due to their diverse compositions and isomeric complexities. This study presents a novel approach employing 1H-15N NMR correlations to pinpoint and characterize HMOs, LNH, LNnH, and their fucosylated derivatives including those of bearing the Lewis X motif. Isolated from human milk, these hexa-, hepta-, and octasaccharides were extensively analysed by NMR. This enabled their first complete 1H, 13C and 15N resonance assignments. Using 1H-15N HSQC experiments, the distinctive 1H-15N correlations of GlcNAc units within the HMOs provided structural fingerprints, allowing for unequivocal differentiation of isomeric structures and fucosylation patterns. Results demonstrate the potential of 1H-15N NMR spectroscopy in decoding complex HMO structures, offering new perspectives on their detailed structural characterization and contributing to a deeper understanding of their potential benefits.