Oligosaccharides and their Structural Diversity (Infobox 1 - Nursing, Gut Bacteria, and the Immune System)

Carbohydrates (sugars) are among the most important classes of naturally occurring biomacromolecules. They are composed of monosaccharides (see Fig. 1) that can be connected together to form oligo- and polysaccharides.

Figure 1. Structures of monosaccharides.

Figure 2 depicts the smallest oligosaccharides, the disaccharides: lactose (milk sugar, 1), maltose (malt sugar, 2), and sucrose (table sugar, 3). In maltose, the monosaccharides are connected by an α-1,4-glycosidic bond, in lactose, they are connected by a β-1,4-glycosidic bond.

Figure 2. Structures of disaccharides.

The oligo- and polysaccharides are made up of standard monomer units. These are five- or six-membered heterocyclic rings that contain hemiacetals or acetals. These are referred to as furanoses (five-membered ring) and pyranoses (six-membered ring).

In the case of sucrose (3), glucopyranose and fructofuranose are bound O-glycosidically through the two anomeric C atoms (the chiral centers adjacent to the oxygen atom in the ring) [1].

References

[1] T. K. Lindhorst, Essentials of Carbohydrate Chemistry and Biochemistry, Wiley-VCH, Weinheim, Germany, 2007. ISBN: 978-3-527-31528-4

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