Question

Hot water extracts of ground willow and poplar bark are an effective pain reliever. Unfortunately, the liquid is so bitter that most people refuse it. The pain reliever in these infusions is salicin, a \(\beta\)-glycoside of D-glucopyranose and the phenolic - \(\mathrm{OH}\) group of 2-(hydroxymethyl) phenol. Draw a structural formula for salicin, showing the glucose ring as a chair conformation.

Short answer

Question: Draw the structural formula for salicin, which is a β-glycoside made up of D-glucopyranose and the phenolic -OH group of 2-(hydroxymethyl) phenol. Show the glucose ring in chair conformation and attach the phenolic -OH group at the appropriate position.

Step-by-step solution

Draw D-glucopyranose in the chair conformation

First, draw the glucose molecule in its chair conformation, as a cyclohexane ring structure. D-glucopyranose can be represented in the following format: - OH groups facing down: 1C and 3C positions. - OH groups facing up: 2C, 4C, and 6C positions.

Identify the attachment site for the phenolic -OH group

The attachment site for the β-glycoside linkage will be in the position 1 of the D-glucopyranose, resulting in a bonding at the oxygen atom of the phenolic -OH group.

Draw the 2-(hydroxymethyl) phenol molecule

Draw the structure of 2-(hydroxymethyl) phenol, which consists of a benzene ring with the phenolic -OH group in the 1 position and the hydroxymethyl group in the 2 position. Remember to show the double bond characteristic of the phenolic -OH group.

Create the β-glycoside linkage

Connect the oxygen atom of the phenolic -OH group in 2-(hydroxymethyl) phenol to the 1C position of D-glucopyranose to create the β-glycoside linkage. Be sure to indicate that this bond has a beta orientation.

Confirm the final structure

Check your final structure to ensure you have included: - The chair conformation of D-glucopyranose. - All the correct -OH group orientations in D-glucopyranose. - The correct structure for 2-(hydroxymethyl) phenol. - The β-glycoside linkage between D-glucopyranose and the phenolic -OH group in 2-(hydroxymethyl) phenol. After completing these steps, you should have a correct structural representation of salicin, showing the glucose ring in the chair conformation.

Key concepts

Understanding the Glucose Chair Conformation

When visualizing the structure of glucose, a fundamental shape to consider is the 'chair conformation'. Essential in organic chemistry and biochemistry, the chair conformation is an accurate representation of cyclic molecules like glucose, providing insights into their three-dimensional structure. Glucose, specifically β-D-glucopyranose, is often depicted in this conformation due to its stability and prevalence in nature.

In this architectural model, each carbon atom is bonded to other atoms in such a way that the overall shape of the molecule resembles a chair. This shape allows for easier identification of the position and orientation of functional groups. The hydroxyl (-OH) groups attached to the glucose molecule can either be axial, pointing vertically up or down, or equatorial, jutting out to the sides.

Importance of Axial and Equatorial Positions

Understanding the axial and equatorial positions is crucial because they influence the molecule's chemical properties and how it interacts with other molecules. In glucose's chair conformation, the -OH groups at positions 2, 4, and 6 are usually in the equatorial position, reducing steric hindrance and making the molecule more stable. Conversely, the -OH group at position 1, when linked to form a glycosidic bond, may be in an axial position, which plays a significant role in forming β-glycosidic linkages.

The β-Glycoside Linkage

Key to the structure of many important biomolecules is the β-glycoside linkage. It's a type of covalent bond that joins a carbohydrate to another molecule, which could be another carbohydrate or a different type of molecule entirely. In salicin, the β-glycoside linkage is what connects the glucose to the phenolic -OH group.

The 'beta' designation refers to the orientation of the glycosidic bond relative to the plane of the glucose ring. In beta linkages, the oxygen atom bonded to the anomeric carbon (position 1 in glucose) is positioned above the plane of the glucose ring, which is distinct from alpha linkages where the oxygen is below the plane.

Role in Molecular Stability and Function

The β-glycoside linkage dictates not only the structural stability of molecules like salicin but also their functionality. For instance, β-linkages are notoriously resistant to enzymatic breakdown, which is why they're commonly found in structural polysaccharides like cellulose. Whereas, alpha linkages, found in starch, are much more readily digested by enzymes. This characteristic plays a critical role in how substances, such as salicin, are metabolized and harnessed by living organisms.

Phenolic -OH Groups in Biochemistry

The phenolic -OH group is a functional unit comprised of a hydroxyl group (-OH) directly bound to an aromatic hydrocarbon ring, typically benzene. This kind of structure is found in an array of bioactive compounds, including salicin. Its presence confers unique chemical properties that are pivotal to the compound's biological activity.

Phenolic -OH groups are characterized by their relative acidity and ability to form hydrogen bonds, attributes that enhance the solubility of compounds in water and their interaction with various biological targets.

Impact on Molecular Reactivity and Interactions

The reactivity of phenolic -OH groups also allows them to participate in critical reactions, like the formation of β-glycoside linkages in molecules such as salicin. The hydroxymethyl group in 2-(hydroxymethyl)phenol adds an extra twist to this, enhancing the compound's overall hydrophilicity and reactivity. The presence of such functional groups is fundamental in biochemistry, as it determines how molecules like salicin will interact with enzymes and receptors in the body, ultimately influencing their therapeutic effects as pain relievers and beyond.