N-Me-Leu-OMe·HCl, chemically known as N-Methyl-L-leucine methyl ester hydrochloride, is a protected amino acid derivative. It features a leucine backbone with an N-methylated amine group and a methyl ester-protected carboxylic acid, making it a versatile building block in peptide chemistry. The hydrochloride salt form enhances its stability and solubility in various organic solvents. This compound is primarily used as a key intermediate in the solid-phase and solution-phase synthesis of modified peptides and peptidomimetics. The N-methylation alters the peptide's conformational properties, increasing metabolic stability, membrane permeability, and resistance to proteolytic degradation. These characteristics are crucial for developing peptide-based therapeutics, particularly in oncology and metabolic disease research. As a specialized synthon, it is employed to introduce the N-methyl-leucine residue into peptide sequences, a modification often found in bioactive natural products and drug candidates. Its applications extend to the preparation of peptide libraries for drug discovery and as a standard in analytical method development for peptide analysis.