3,4-Dehydro-L-proline is a non-proteinogenic amino acid derivative characterized by a pyrrolidine ring with a double bond between the 3 and 4 positions. It serves as a conformationally constrained proline analog, where the double bond restricts the ring's flexibility and influences the peptide backbone's conformational preferences. This compound is primarily utilized in biochemical and pharmaceutical research as a specialized building block for peptide synthesis. Its incorporation into peptides is studied to probe the role of proline in protein structure, stability, and function, and to design novel peptide-based therapeutics or probes with modified biological activity and metabolic stability. It acts as a tool to understand collagen biosynthesis and stability, as proline and its hydroxylated forms are critical components of collagen. While its main application is in life science research, its defined structure also makes it a valuable chiral synthon or intermediate in organic synthesis for constructing complex heterocyclic systems or natural product analogs, hence its secondary classification as an organic synthesis building block.