Aspartame, an artificial sweetener, is a dipeptide aspartyl phenylalanine methyl ester. The structure of aspartame is

Structures of phenylalanine and aspartic acid are given below.

The correct option is Option B.

Step-by-Step Explanation:

1. Understand the components of Aspartame:
Aspartame is an artificial sweetener chemically known as L-aspartyl-L-phenylalanine methyl ester. It is a dipeptide derivative composed of two amino acids:
• L-aspartic acid
• L-phenylalanine (esterified at its carboxyl terminal with methanol to form a methyl ester)

2. Structures of the starting materials (as shown in the question):
• Aspartic acid has the chemical formula:
${\text{H}}_2\text{N}-\text{CH}\left({\text{CH}}_2\text{COOH}\right)-\text{COOH}$
It contains a side-chain carboxylic acid group ($-{\text{CH}}_2\text{COOH}$).

• Phenylalanine has the chemical formula:
${\text{H}}_2\text{N}-\text{CH}\left({\text{CH}}_2{\text{C}}_6{\text{H}}_5\right)-\text{COOH}$
In phenylalanine methyl ester, the carboxyl group ($-\text{COOH}$) is replaced by a methyl ester group ($-{\text{COOCH}}_3$):
${\text{H}}_2\text{N}-\text{CH}\left({\text{CH}}_2{\text{C}}_6{\text{H}}_5\right)-{\text{COOCH}}_3$

3. Identify the Peptide Linkage:
In aspartame, the peptide bond ($-\text{CONH}-$) is formed specifically between the α-carboxyl group of aspartic acid and the α-amino group of phenylalanine methyl ester. This means:
• The side-chain carboxylic acid group ($-{\text{CH}}_2\text{COOH}$) of the aspartyl residue remains free and does not participate in peptide bond formation.
• The linkage is represented by:
${\text{H}}_2\text{N}-\text{CH}\left({\text{CH}}_2\text{COOH}\right)-\text{CONH}-\text{CH}\left({\text{CH}}_2{\text{C}}_6{\text{H}}_5\right)-{\text{COOCH}}_3$

4. Matching with the Options:
• Option B correctly depicts the structure where the peptide bond is formed using the α-carboxyl carbon of aspartic acid, leaving the $-{\text{CH}}_2\text{COOH}$ group free, and the C-terminal phenylalanine residue is esterified as $-{\text{COOCH}}_3$.