Stereocenter, anomeric, hemiacetal

When a monosaccharide forms a cyclic hemiacetal (or hemiketal), the carbonyl carbon becomes a stereocenter. Thus, cyclization leads to formation of two possible stereoisomers. These isomers are called anomers, and the former carbonyl carbon is called the anomeric carbon. The isomer with the anomeric OH (shown in blue) pointed down is the alpha anomer. The isomer with the anomeric OH (shown in blue) pointed up is the beta anomer. (Figure 12.14)... 

Anomers Sugar hemiacetals, diastereomers with [Pg.254]

The new stereocenter resulting from cyclic hemiacetal formation is referred to as an anomeric carbon. The stereoisomers thus formed are called anomers. 

The keto forms of carbohydrates exist in eqnilibrinm with the corresponding five-membered (furanoses) or six-membered (pyranoses) cyclic hemiacetals. The new stereocenter formed by cyclization is called the anomeric carbon, and the two anomers are designated a and /3. 

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