Used in solid-phase peptide synthesis as a protected amino acid building block, particularly for incorporating unsaturated side chains into peptide structures. The Fmoc group allows for mild base-labile protection, compatible with stepwise elongation on resin. The allyl and pentenoyl moieties provide sites for post-assembly modifications, such as ring-closing metathesis, enabling the formation of cyclic peptides or constrained architectures. Commonly applied in the synthesis of bioactive peptide analogs and peptidomimetics where structural rigidity or specific side-chain functionality is required.