L-Leucine tert-butyl ester hydrochloride is primarily used in peptide synthesis as a building block. It serves as a protected form of L-leucine, where the tert-butyl group shields the carboxyl group, allowing selective reactions at other sites during peptide chain assembly. This compound is particularly valuable in solid-phase peptide synthesis (SPPS) and solution-phase peptide synthesis, enabling the creation of complex peptides with high precision. Additionally, it finds application in pharmaceutical research for developing peptide-based drugs, where controlled and efficient synthesis is crucial. Its stability and ease of deprotection make it a preferred choice in organic and medicinal chemistry.