This compound, (R)-2-((((9H-Fluoren-9-yl)methoxy)carbonyl)(methyl)amino)hexanoic acid, known as Fmoc-N-methyl-D-norleucine, is a specialty protected amino acid building block for solid-phase peptide synthesis (SPPS). The fluorenylmethoxycarbonyl (Fmoc) group protects the N-methylated amino group of the D-norleucine residue (with a butyl side chain), enabling selective deprotection with mild acids like piperidine while stable to basic coupling conditions. It facilitates the precise incorporation of N-methylnorleucine units into complex peptides, which offer enhanced stability and unique conformations for research, pharmaceuticals, and biotechnology.