ABSTRACT
For an oligosaccharide of unknown structure, much structural information can be obtained from the anomeric region of the proton spectrum. As discussed earlier, a variety of different structural features are possible in carbohydrates, and the anomeric proton chemical shifts and coupling constants are highly sensitive to these structural details. Features such as the type and sequence of monosaccha rides (e.g., mannose or glucose), the degree of branching, the nature of the linkage
between adjacent sugars (e.g., l~>4 or l-^6), and the stereochemistry of the sugar (e.g., a or β anomers) all affect the anomeric Ή chemical shifts. Furthermore, in a pyranose ring, the H1/H2 coupling constant is large when the two protons are diaxial but small for axial-equatorial or diequatorial configurations. Consequently, this anomeric coupling constant is always small for mannose. For other pyranose sugars, the anomeric coupling constant is small for the a anomer and large for the β anomer. A variety of monomers and oligomers of known structure have been characterized by Ή NMR, and the Ή parameters for many types of structures are known [149-157]. Hence, the anomeric shifts and coupling constants measured for a sugar of unknown structure can be used, in combination with other analyti cal techniques, as an aid in determination of the primary structure. This approach has been used successfully to determine the structure of many different carbohy drate moieties [158-170], and computer algorithms and databases have been de signed to assist in the process [171-173].
