Used in solid-phase peptide synthesis to incorporate selenocysteine, the 21st amino acid, into peptides. The Fmoc group allows for mild base deprotection, while the Trt (trityl) group protects the reactive selenol side chain during synthesis. This protection scheme is essential for preventing oxidation and unwanted side reactions. After chain assembly, the Trt group can be selectively removed under mild acidic conditions, enabling further modifications or formation of selenyl-sulfide bonds. Commonly applied in the preparation of selenopeptides for studies in redox biology, enzyme mimicry, and structural analysis using techniques like X-ray crystallography or NMR.