Fmoc-S-benzyl-D-cysteine is widely used in peptide synthesis, particularly in solid-phase peptide synthesis (SPPS). It serves as a protected form of D-cysteine, where the Fmoc (fluorenylmethyloxycarbonyl) group protects the amino group, and the S-benzyl group protects the thiol side chain. This protection is crucial to prevent unwanted reactions during the peptide assembly process. It is especially valuable in the synthesis of peptides containing cysteine residues, as it ensures the correct formation of disulfide bonds, which are essential for the structural integrity and function of many peptides and proteins. Additionally, its D-configuration makes it useful in the creation of peptides with specific stereochemical properties, often employed in research and drug development to study chiral interactions and biological activity.