H-Phg-OtBu.HCl is a hydrochloride salt of the tert-butyl ester of phenylglycine, serving as a protected amino acid building block in peptide synthesis. It incorporates the phenylglycine residue into peptide chains while the tert-butyl group protects the carboxylic acid, preventing side reactions during peptide bond formation and offering stability across various conditions. This makes it ideal for assembling complex peptides with precise sequences. Additionally, it is used in preparing pharmaceutical intermediates for drugs targeting specific biological pathways, playing a key role in high-purity organic synthesis for advanced medicinal compounds.