Fmoc-D-Cys(4-MeBzl)-OH is primarily used in peptide synthesis, particularly in solid-phase peptide synthesis (SPPS). It serves as a protected derivative of D-cysteine, ensuring the thiol group remains stable during the peptide chain assembly process. The Fmoc (fluorenylmethyloxycarbonyl) group acts as a temporary protecting group for the amino group, while the 4-MeBzl (4-methylbenzyl) group protects the thiol functionality. This compound is essential for introducing D-cysteine residues into peptides, which is important for creating peptides with specific chiral properties or enhanced stability. Its application is particularly valuable in the development of therapeutic peptides, research on peptide structure-function relationships, and the synthesis of peptides with disulfide bonds, which are critical for many biological activities.