Boc-Ser-OtBu (N-(tert-butoxycarbonyl)-L-serine tert-butyl ester) is a protected derivative of L-serine widely used in peptide synthesis. The Boc group protects the α-amino function, while the tert-butyl ester protects the carboxyl group, leaving the side-chain hydroxyl group free. This design enables selective incorporation into peptide chains during multi-step syntheses like solid-phase peptide synthesis (SPPS), preventing unwanted side reactions and ensuring precise control over reactivity. It is essential for producing complex peptides and pharmaceuticals, with protecting groups removable under mild acidic conditions.