Submitted to: Carbohydrate Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2025
Publication Date: 10/16/2025
Citation: Price, N.P., Vermillion, K.E, Jackson, M.A. 2025. A simplified NMR-based method to assign the absolute configuration of aldose monosaccharides. Carbohydrate Research. https://doi.org/10.1016/j.carres.2025.109696.
DOI: https://doi.org/10.1016/j.carres.2025.109696

Interpretive Summary: Sugars and polysaccharides (numerous sugars linked together) are abundant in plants and serve as an important source of energy and nutrition. In addition, they are used for producing important bioproducts, such as fuels and chemicals, using agricultural commodities (e.g., corn, soybean, sorghum, sugar crops). Many types of sugars have alternate structures that are mirror images of each other. Just like the right and left hand may seem identical, they interact with the environment in different ways. Knowing the exact structure of sugars is important for plant breeding, nutrition, pharmaceutical research, and bioproduct development. There are laboratory techniques that can differentiate between mirror images of sugars. However, these often require large amounts of sugar or numerous experimental steps. It is even more difficult to identify the exact structure of the sugar when it is part of larger polysaccharides. ARS researchers in Peoria, Illinois, developed a simple one-step method that can easily differentiate between mirror images of the sugars and can also characterize them as part of polysaccharides. This discovery will facilitate the development of new bioproducts from commodity crops, improving economic returns for farmers, enhancing market opportunities and adding value to American agricultural.

Technical Abstract: A straightforward, aqueous-based procedure is described to determine the absolute configuration of aldose monosaccharides, a critical task in carbohydrate analysis. This approach leverages the reaction of aldose monosaccharide enantiomers with L-cysteine, a readily-available chiral amino acid, to form cyclic thiazolidine diastereomers. These derivatives can be analyzed using Heteronuclear Single Quantum Coherence (HSQC) NMR spectroscopy, specifically looking at the H-1–C-1 proton-carbon single bond correlations. This NMR technique provides the necessary data to determine the absolute configuration of the parent monosaccharide. Several monosaccharide D-/L-enantiomeric pairs are analyzed as examples, and the technique is utilized to determine the compositional stereochemistry of complex polysaccharides (gellan and xanthan gums). We have also established the previously unknown stereochemistry of the arabinosyl residues found in frost grape polysaccharide (FGP) isolated from vines of the grape species, Vitis riparia Michx. The generalized method described is anticipated to be valuable to analytical carbohydrate chemists for the facile assignment of carbohydrate stereochemistry.