Used in peptide synthesis to introduce a lysine residue with a photolabile nicotinoyl protecting group, enabling light-controlled deprotection during solid-phase synthesis. The Fmoc group allows for standard base-sensitive cleavage, while the nicotinoyl moiety on the side chain provides orthogonal protection that can be removed with UV light, making it valuable for spatial and temporal control in the synthesis of complex peptides and protein domains. Commonly applied in the preparation of bioactive peptides, enzyme substrates, and peptide arrays where selective deprotection is required.