Chapter 20: Problem 34
Pregabalin, marketed as Lyrica, is an anticonvulsant drug that is also effective in treating chronic pain. The IUPAC name of pregabalin is (S)-3-(aminomethyl)-5-methylhexanoic acid. (An aminomethyl group is \(-\mathrm{CH}_{2} \mathrm{NH}_{2}\).) Draw the structure of pregabalin.
Short Answer
Expert verified
Pregabalin's structure is a hexanoic acid backbone with methyl and aminomethyl groups at the 5th and 3rd carbons, respectively, following (S)-stereochemistry.
Step by step solution
01
Understanding the IUPAC Name
The IUPAC name (S)-3-(aminomethyl)-5-methylhexanoic acid indicates the structure and configuration of pregabalin. The '(S)' denotes the stereochemistry, which is based on the priority rules of atoms attached to the chiral center. The '3-(aminomethyl)' group tells us that an aminomethyl group (-CH₂NH₂) is attached to the 3rd carbon, and '5-methyl' indicates a methyl group (-CH₃) is attached to the 5th carbon of the hexanoic acid chain.
02
Sketching the Hexanoic Acid Backbone
Start by drawing hexanoic acid, which is a six-carbon chain with a carboxylic acid functional group (-COOH) at one end. The structure will look like this:
H₃C-CH₂-CH₂-CH₂-CH₂-COOH
Ensure the carbon atoms are connected linearly, with the 6th carbon being part of the carboxylic acid (-COOH).
03
Adding the Methyl Group
Introduce the methyl group at the 5th carbon of the hexanoic acid chain. Thus, the backbone now appears as:
H₃C-CH(CH₃)-CH₂-CH₂-CH₂-COOH
04
Adding the Aminomethyl Group
Attach the aminomethyl group (-CH₂NH₂) at the 3rd carbon. This will alter the structure to:
H₃C-CH(CH₃)-CH(NH₂)-CH₂-CH₂-COOH
05
Applying Stereochemistry
As per the '(S)' configuration, check the priorities of the substituents around the chiral center (the third carbon in this case). Arrange the groups to follow the (S)-configuration when viewed from a suitable perspective, ensuring the carboxylic acid, aminomethyl group, hydrogen, and carbon chain are correctly placed in three-dimensional space.
06
Finalizing the Structure
Combine all the information from the previous steps to complete the three-dimensional structure of pregabalin with the proper configuration and attachments. Ensure all bonds and angles look correct in a chemical sketch.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
IUPAC nomenclature
The IUPAC nomenclature is a standardized system for naming chemical compounds, making it universally understood. For instance, pregabalin's IUPAC name is (S)-3-(aminomethyl)-5-methylhexanoic acid, which is not just a name but an informative description.
- The '(S)' refers to the stereochemistry, indicating the spatial arrangement of atoms around the chiral center.
- The '3-(aminomethyl)' segment specifies that an aminomethyl group, represented as (-CH₂NH₂), is attached to the third carbon of the main chain.
- '5-methyl' signifies a methyl group (-CH₃) is attached at the fifth carbon.
- Lastly, 'hexanoic acid' describes the core structure as a six-carbon chain ending with a carboxylic acid group (-COOH).
Chiral Center
A chiral center, often pivotal in organic molecules, is a carbon atom bonded to four distinct atoms or groups. Pregabalin, for example, has a chiral center at the third carbon in the chain.
- Identifying the chiral center is crucial because it impacts the molecule's 3D shape, which affects its interaction with biological systems.
- The different arrangements of atoms around the chiral center lead to molecules that can be non-superimposable mirror images of each other, known as enantiomers.
Stereochemistry
Stereochemistry explores the spatial arrangement of atoms within a molecule, crucial for understanding a compound's behavior and function. In pregabalin, the stereochemistry is denoted by (S)- before its IUPAC name.
- The '(S)' indicates the specific 3D orientation of atoms around the chiral center, determined using Cahn-Ingold-Prelog priority rules.
- These rules rank the substituents based on atomic number, atomic mass, and connectivity, guiding the (R)- and (S)-notations.
Hexanoic Acid
Hexanoic acid forms the backbone of pregabalin, a straight chain made of six carbon atoms ending in a carboxylic acid group (-COOH).
- Each carbon atom is sequentially bonded, which provides the main structure for attaching different functional groups.
- In pregabalin, the hexanoic acid backbone allows for the introduction of the aminomethyl and methyl groups at specific carbon positions, critical for its biological effectiveness.
Aminomethyl Group
The aminomethyl group, written as (-CH₂NH₂), is a significant substituent in the structure of pregabalin. It brings both structural and functional contributions to the molecule.
- Its presence signifies a primary amine, which can engage in hydrogen bonding, affecting the drug's solubility and absorption.
- Attached at the third carbon of the hexanoic acid chain, it is crucial for pregabalin's interaction with receptors in the nervous system, underpinning its effectiveness in pain management and as an anticonvulsant.