As we know, all carbohydrates contain at least one asymmetrical (chiral) carbon. Therefore, carbohydrates are all optically active. The absolute configuration of a carbohydrate unit is determined from the highest numbered chiral carbon in the chain and is denoted D (dexter in Latin means right) or L (laevus in Latin means left) from the direction of the hydroxyl group on the parent carbon in the Fischer projection. As a result, carbohydrates can exist in either one of two configurations, as determined by the orientation of the hydroxyl group about the asymmetric carbon furthest from the carbonyl. Most of the carbohydrates that are of physiological significance exist in the D configuration with a few exceptions. The carbohydrates with mirror-image configurations are in the L configuration. Although both D and L configurations possibly exist, most of the monosaccharides found in nature are in the D configuration. The structural characteristics of polysaccharides such as the absolute configuration can have an effect on their physicochemical properties.
Figure 1. Fischer projections of representative sugars - the configurational D or L stereogenic
The structural studies of polysaccharides usually start with a wet chemistry sugar analysis to elucidate the monosaccharide identities and their respective absolute configuration (D/L). The polysaccharide is hydrolyzed with a strong acid, e.g. trifluoroacetic acid (TFA) at 100-120 °C. The hydrolysis procedure is usually straightforward, but must sometimes be optimized depending on the tendency of the released monosaccharide units to degrade or not even hydrolyze from the polysaccharides in the first place.
The absolute configuration of the unique monosaccharide units can be determined by butanolysis of the hydrolysed polysaccharides followed by acetylation and Gas Chromatography–Mass Spectrometry (GC-MS) analysis or Gas-Liquid Chromatography (GLC) analysis. With knowledgeable experts and years of experience, Creative Proteomics offers accurate, reliable Absolute Configuration analysis service.
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