What is a glycoside?

• A. A cyclic sugar with a full acetal at the anomeric carbon.
• B. An epimer of glucose.
• C. Any sugar with a protecting group.
• D. A cyclic sugar formed from an L-carbohydrate.

Answer: (A)

Verified step by step guidance

1. Understand the definition of a glycoside: A glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. This typically involves the anomeric carbon of the sugar forming an acetal linkage.
2. Identify the structure of a cyclic sugar: Cyclic sugars are formed when the carbonyl group of a sugar reacts with a hydroxyl group on the same molecule, creating a hemiacetal or hemiketal. In glycosides, this hemiacetal is converted to a full acetal.
3. Recognize the role of the anomeric carbon: The anomeric carbon is the carbon derived from the carbonyl carbon (C=O) in the sugar's open-chain form. In cyclic form, it is the carbon bonded to two oxygen atoms.
4. Differentiate between hemiacetal and acetal: A hemiacetal has one -OH group and one -OR group attached to the anomeric carbon, while a full acetal has two -OR groups. Glycosides have a full acetal at the anomeric carbon.
5. Evaluate the options: Based on the definition and structure of glycosides, identify that a glycoside is a cyclic sugar with a full acetal at the anomeric carbon, which matches the first option provided.