Aspartame is L-$\alpha$-aspartyl-L-phenylalanine methyl ester. The dipeptide is formed by an amide bond between the $\alpha$-carboxyl group of aspartic acid and the $\alpha$-amino group of phenylalanine. The C-terminal carboxyl group (on the phenylalanine side) is then methylated to give the methyl ester.

Key structural features that identify the correct option:

1. Free $\alpha$-amino group on the aspartate end.

2. The free $\beta$-carboxyl (side-chain -CH${}_2$-COOH) remains on aspartate.

3. Amide (peptide) bond connecting aspartate's $\alpha$-COOH to phenylalanine's $\alpha$-NH.

4. Methyl ester (-COOMe) on phenylalanine's $\alpha$-carbon.

Option (B) matches all four features.