Question

Draw the structure of ( \(S\) )-proline.

Short answer

(S)-proline is an amino acid with a cyclic structure, drawn with the correct (S) configuration at its chiral center.

Step-by-step solution

Understand the Structure of Proline

Proline is an amino acid, and it specifically has a unique cyclic structure among standard amino acids. It contains a five-membered ring involving its nitrogen atom, distinguishing its structure. Begin by visualizing this cyclic structure.

Identify Chiral Centers

Proline has a chiral center at the carbon atom that is part of both the aliphatic ring and the amino acid backbone. This chiral center will determine whether the proline is the (R) or (S) enantiomer.

Assign R or S Configuration

The (S)-enantiomer configuration requires assigning priorities to the substituents attached to the chiral center according to the CIP (Cahn-Ingold-Prelog) rules. For proline, the substituents are the hydrogen, nitrogen in the ring, and the carboxyl group. Arrange them in order of priority.

Visualize the S Configuration

To achieve the (S) configuration, imagine viewing the chiral center with the lowest priority group (hydrogen) pointing away. The remaining groups should follow a counterclockwise arrangement from highest to lowest priority when looking from highest to lowest.

Draw (S)-Proline

Draw the cyclic structure of proline including the NH group, COOH group, and side chain. Make sure to place the substituents according to the proper (S) configuration with the highest priority substituent starting the counterclockwise arrangement.

Key concepts

Amino Acids

Amino acids are essential building blocks of proteins. They play vital roles in almost every biological function.
These organic compounds consist predominantly of:

• an amino group (-NH₂)
• a carboxyl group (-COOH)
• an alpha carbon to which they are both attached
• an R group or side chain specific to each amino acid

Proline is unique among standard amino acids due to its nitrogen being part of a five-membered ring.
This ring formation makes proline a secondary amine, rather than the primary amine structure typical of other amino acids. This structural difference influences the protein's flexibility and function. Proline can often introduce kinks into a polypeptide chain, affecting protein folding and stability.
The cyclic nature of proline is significant in defining its properties, as it adopts a stiff conformation, impacting interactions within proteins. Understanding proline's unique structure is crucial in biochemistry because of its influence on protein architecture.

Chiral Centers

Chiral centers in molecules are like spatial hubs that confer a 'handedness' to their structure. A chiral center typically involves a carbon atom connected to four different atoms or groups.
In proline, despite its cyclic nature, it does indeed possess such a chiral center. This center is located at the carbon attached to the ring, the carboxyl group, and the side chain.

• Chirality introduces the concept of enantiomers, or mirror-image isomers, into chemistry.
• Enantiomers have the same molecular formula but are not superimposable on each other, similar to left and right hands.

This difference is crucial in biochemistry as enantiomers can have drastically different effects in biological systems. Some enzymes and receptors in the body can distinguish between these, affecting everything from taste to metabolic reactions.
Recognizing the presence of a chiral center is step one in understanding how to assign stereochemistry, especially why proline's unique configuration matters.

Stereochemistry

Stereochemistry involves the study of different spatial arrangements of atoms in molecules and their effects on the chemical behavior.
Specifically, in amino acids, stereochemistry plays a vital role in determining biological activity.
The configuration of stereocenters, like the one found in proline, is often categorized as (R) or (S) based on the priority of the attached groups according to the Cahn-Ingold-Prelog (CIP) rules.

• To assign an (S)-configuration, visualize the molecule so that the lowest priority group is pointing away from you.
• The arrangement of the remaining groups should be counterclockwise as you read them from highest to lowest priority.

Proline's (S) configuration can impact how it interacts within protein structures and with other biomolecules. This orientation affects protein folding and, consequently, biological function.
Understanding and visualizing stereochemistry in three-dimensional space is critical for working confidently in fields like pharmacology and materials science. It's key to predicting how molecules will interact in the dynamic environment of the body.