Azido amino acids are versatile building blocks in peptide synthesis. They are utilized in click chemistry, the copper catalyzed cycloaddition of an azido function with a alkyne. Click chemistry is quick, does not require special selective deprotection schemes and it does not produce byproducts. Click chemistry is especially well suited for forming staples and other cyclic peptide structures and for conjugating peptides with tags or other biomolecules. Fmoc-Lys(N 3 )-OH and Fmoc-Nva(N 3 )-OH can also be utilized as protected derivatives of lysine and ornithine respectively. The azido group is stable under acid or basic conditions but can be readily reduced to the primary amine. The azido group is stable to TFA and piperidine. Standard synthesis and cleavage protocols may be used for azido-containing peptides.