H-Hyp-Obzl.HCl is the hydrochloride salt of 4-hydroxy-L-proline benzyl ester, a key building block in peptide synthesis. It features a free amino group (as HCl salt), a free hydroxyl group on the pyrrolidine ring, and a benzyl-protected carboxylic acid. This protection strategy allows selective N-terminal coupling in solid-phase or solution-phase peptide synthesis, enabling the incorporation of hydroxyproline residues into complex peptides. Hydroxyproline is crucial for structural elements like turns and collagen-like sequences. The compound is vital for producing bioactive peptides, enzyme substrates, inhibitors, and peptide-based therapeutics in medicinal chemistry and biotechnology research.