Biomolecules · Question 4

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

1. [figure]
2. [figure]
3. [figure]
4. [figure]

Answer

(2) [figure]

Solution

Aspartyl-phenylalanine methyl ester: Asp is the N-terminal residue, Phe is the C-terminal residue (as its methyl ester).

The α-COOH of Asp forms the peptide (amide) bond with the -NH2 of Phe-OMe; the side-chain -CH2COOH of Asp stays free; both residues keep the natural L-configuration.

[figure] + [figure] -H2O [figure]

(A) uses the side-chain (β) carboxyl of Asp for the amide bond; (C) is Phe–Asp (wrong sequence); (D) has the ester on the Asp side chain and a free COOH on Phe.

Only (B) fits.

Answer: (B)