N-Methyl-aspartic acid derivative used in peptide synthesis as a protected building block for incorporating N-methylated residues. The tert-butyl group protects the carboxylic acid side chain, while the methyl ester masks the C-terminus, and the N-methylation on the alpha-amino group enables selective coupling reactions without side-chain interference or unwanted reactivity at the nitrogen. This allows stepwise assembly of complex peptides with modified backbone properties. Commonly employed in solid-phase synthesis and pharmaceutical research for developing bioactive peptides with improved stability, specificity, and pharmacological profiles.