Fmoc-L-2-cyanophenylalanine is a non-natural, protected amino acid derivative. Its structure features an L-configuration, a 9-fluorenylmethoxycarbonyl (Fmoc) protecting group on the alpha-amino group, and a cyanide (-CN) substituent at the ortho position of the phenylalanine side chain's phenyl ring. This specific substitution introduces unique electronic and steric properties compared to canonical phenylalanine. This compound is primarily employed as a specialized building block in solid-phase peptide synthesis (SPPS) using the Fmoc strategy. The cyanophenylalanine residue serves as a versatile spectroscopic probe and a reactive handle in peptide chemistry. It is notably used to incorporate the non-natural amino acid p-cyanophenylalanine, a sensitive infrared probe for studying protein structure and dynamics, into synthetic peptides and proteins. The ortho-substituted variant offers alternative conformational and reactivity profiles for research purposes. As a protected amino acid with a modified aromatic side chain, it falls under the category of peptide synthesis intermediates and specialized organic synthesis blocks. Its use is predominantly confined to research laboratories focused on peptide engineering, biophysical studies, and the development of novel bioactive peptides or protein mimics.