Used in solid-phase peptide synthesis, particularly for constructing fluorescently labeled peptides. The Mca (methylcoumarin-4-acetic acid) group acts as a fluorescent probe, enabling detection and tracking of peptide interactions in biological systems. Commonly applied in protease substrate studies, where cleavage of the peptide by enzymes releases the fluorescent Mca tag, allowing real-time monitoring of enzymatic activity. The Fmoc group provides orthogonal protection, compatible with standard synthesis protocols, making it ideal for stepwise assembly of complex peptide sequences.