Anomers
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| α- D -glucopyranose - anomer of β- D -glucopyranose | β- D -glucopyranose - anomer of α- D -glucopyranose |
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| α- D -Ribopyranose - anomer of β- D -ribopyranose | β- D -Ribopyranose - anomer of α- D -Ribopyranose |
| Examples of α and β anomers: locants ( red ), anomeric center at C1 ( blue arrow ), reference atom ( green arrow ), CIP configuration ( gray ) |
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In the case of carbohydrates and other glycosides, anomers (Greek áno̅ = above) are a special type of isomers - more precisely: diastereomers - which only differ in the configuration at the anomeric center .
The anomeric center is a center of chirality that arises from the prochiral carbonyl carbon atom of the open-chain form during the formation of the cyclic half or full acetal / ketal of a carbohydrate . It is adjacent to the ring oxygen of sugars (in the pyranose or furanose form). The resulting diastereomers are referred to as anomers.
The configuration at the anomeric center is described by the stereo descriptors α and β, the α-anomer being that isomer in which the absolute configuration of the anomeric carbon atom according to the CIP rules is opposite to the configuration of the reference atom, the highest numbered chiral center . This definition applies to both D and L sugar. In the Fischer projection of the α- D carbohydrates, the oxygen atom at the anomeric center is on the same side of the main chain as the hydroxyl group of the reference atom. Consequently, in the case of β anomers, the hydroxyl group of the reference atom of the D carbohydrates is on the opposite side of the main chain.
Web links
Individual evidence
- ↑ Entry on anomers . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.A00373 Version: 2.3.3.
- ↑ Olaf Kühl: Organic Chemistry , Wiley-VCH, Weinheim, 2012, p. 222, ISBN 978-3-527-33199-4 .