Draw a Haworth projection for the disaccharide gentibiose, given the following information: (a) It is a dimer of glucose. (b) The glycosidic linkage is \(\beta(1 \rightarrow 6)\) (c) The anomeric carbon not involved in the glycosidic linkage is in the \(\alpha\) configuration.

Understanding the structure of D-glucose is essential for drawing disaccharides like gentibiose. D-glucose is a monosaccharide with six carbon atoms (hexose) and is commonly found in its ring form, called a pyranose. In the ring form, the first carbon (known as the anomeric carbon) is bonded to the fifth carbon, creating a six-membered ring with one oxygen atom. Each carbon has hydroxyl groups (-OH) and hydrogen atoms attached.

To visualize D-glucose, draw a hexagon and place an oxygen at one vertex. This will be the oxygen connecting the first and fifth carbons. You then add hydroxyl groups and hydrogen atoms based on the D-glucose configuration. For example:

• Carbon 1: Downward -OH group
• Carbon 2: Upward -OH group
• Carbon 3: Downward -OH group
• Carbon 4: Upward -OH group
• Carbon 5: Connected to the CH2OH group

By understanding this basic structure, you can build more complex molecules.

A glycosidic linkage is a type of covalent bond that connects carbohydrate (sugar) molecules to each other or to another group. In the case of gentibiose, this bond forms between two glucose molecules. Glycosidic bonds are categorized by the carbon atoms involved and the orientation (α or β) of the bond.

For gentibiose, the bond is a β(1 → 6) linkage. This means:

• A hydroxyl group on the first carbon (C1) of one glucose (with β configuration, meaning the -OH group is upward) connects to the hydroxyl group on the sixth carbon (C6) of the second glucose molecule.

By recognizing how these linkages work, you can understand the bonding patterns in more complex sugars.

The anomeric carbon is the central carbon where ring closure occurs in glucose. In the Haworth projection of glucose, this is usually Carbon 1, and its configuration is crucial in determining the type of glycosidic linkage.

For gentibiose, the anomeric carbon not involved in the glycosidic bond is in the α configuration. This means the hydroxyl (-OH) group attached to this carbon is positioned downward in the Haworth projection.

This downward orientation differentiates the α form from the β form, where the hydroxyl group would be upward. The configuration of the anomeric carbon significantly impacts the molecule's reactivity and how it interacts with other molecules.

The β(1 → 6) linkage is a specific type of glycosidic bond found in gentibiose. Understanding this linkage is crucial for visualizing the structure properly.

In the β(1 → 6) linkage:

• The anomeric carbon (C1) of the first glucose is in the β configuration, so its hydroxyl group is oriented upward.
• This hydroxyl group bonds with the hydroxyl group on the C6 carbon of the second glucose unit.
• The second glucose unit must have its sixth carbon (C6) oriented upwards to facilitate this bond.

This arrangement ensures the correct structural formation of gentibiose, making it distinctive and stable.

The Haworth projection is a way to depict the 3D structure of sugar molecules in a flat, 2D manner. This projection makes it easier to visualize complex sugars like gentibiose.

In a Haworth projection, the ring structure and the substituent groups are displayed as follows:

• Draw a hexagon to represent the ring structure.
• Place oxygen at one vertex (usually the top right).
• Add carbon atoms at the other vertices and number them in a clockwise direction.
• Include the hydroxyl and other groups, placing them up or down based on their specific configuration.

Using the Haworth projection, you can clearly see the β(1 → 6) glycosidic linkage in gentibiose, along with the specific orientations of the hydroxyl groups, making it a valuable tool for understanding sugar structures.