Question

Aspartame, marketed for use as a nonnutritive sweetener under such trade names as Equal, NutraSweet, and Canderel, is the methyl ester of a simple dipeptide. Identify the two amino acids present in aspartame, and show all the products of digestion, assuming that both amide and ester bonds are hydrolyzed in the stomach.

Short answer

The amino acids in aspartame are phenylalanine and aspartic acid; digestion releases phenylalanine, aspartic acid, and methanol.

Step-by-step solution

Identify the Structure of Aspartame

Aspartame is a methyl ester of a dipeptide composed of two amino acids, phenylalanine and aspartic acid. The chemical structure of aspartame is as follows: it has a backbone consisting of these two amino acids linked by an amide bond, with an additional methyl ester group at one end.

Hydrolysis of Amide Bonds

The digestion of aspartame involves breaking the amide bond between phenylalanine and aspartic acid. Hydrolysis cleaves the amide bond, resulting in the separation of the two amino acids. The products from this step are free phenylalanine and aspartic acid.

Hydrolysis of the Ester Bond

In addition to the amide bond, aspartame also contains an ester bond due to the methyl ester group. Hydrolysis of this bond releases methanol and converts the ester group in aspartame into a free carboxylic group. Thus, the aspartic acid in the structure becomes free aspartic acid with an unmodified carboxylic group.

Combine the Products from Hydrolysis

Combining the results from both hydrolysis processes, the complete products of aspartame digestion are phenylalanine, aspartic acid, and methanol. Aspartic acid is released in its free form, and phenylalanine is unaffected by the ester hydrolysis.

Key concepts

Dipeptide structure

Aspartame is made up of a dipeptide structure. Dipeptides consist of two amino acids, which are the building blocks of proteins, linked together by a specific type of covalent chemical bond known as an amide bond, also called a peptide bond.
The dipeptide in aspartame is composed of phenylalanine and aspartic acid. These amino acids are connected by an amide bond, forming a backbone for the dipeptide chain.
In aspartame, a methyl ester group is attached to the dipeptide, specifically to the carboxylic acid end of aspartic acid. This esterification modifies the molecule's properties and is part of why aspartame is sweet.

• Phenylalanine: An essential amino acid that is needed for normal growth and functioning.
• Aspartic acid: A non-essential amino acid involved in the synthesis of proteins and the urea cycle.

Understanding this structure is key to knowing how aspartame behaves in our bodies.

Hydrolysis process

The hydrolysis process is crucial in the body's digestion of aspartame. Hydrolysis involves breaking chemical bonds by adding water molecules. In the case of aspartame, both the amide bond and the ester bond are subject to hydrolysis during digestion.

First, the amide bond between phenylalanine and aspartic acid is cleaved. This process releases these two amino acids in their free forms. This step is important because it ensures that our bodies can utilize the amino acids separately, which is necessary for various bodily functions.

• Amide Bond Cleavage: Water molecules attack the amide bond, causing it to break and separating phenylalanine and aspartic acid.

Following this, the ester bond in the methyl ester group is hydrolyzed. This reaction converts the ester into a free carboxylic acid group on aspartic acid and releases methanol into the body.

• Ester Bond Cleavage: Involves water reacting with the ester bond, transforming the ester into an alcohol and carboxylic acid.

The complete hydrolysis of aspartame results in the release of phenylalanine, aspartic acid, and methanol.

Amino acids

Amino acids are organic molecules that combine to form proteins. They play a crucial role in almost all biological processes in the body.

In the context of aspartame digestion, the amino acids of interest are phenylalanine and aspartic acid.

• Phenylalanine is essential because the body cannot produce it on its own; it must be obtained through diet.
• Aspartic acid is non-essential because the body can produce it from other substances.

Both amino acids are vital for protein synthesis, tissue repair, and nutrient absorption. Upon digestion of aspartame, phenylalanine and aspartic acid are absorbed into the bloodstream and utilized by the body.

Phenylalanine is particularly important because it serves as a precursor for neurotransmitters like dopamine and norepinephrine. It underscores the importance of these amino acids, not just as components of a dipeptide like aspartame but as fundamental nutrients indispensable for health.