Fmoc-Amino Acids for Peptide Synthesis

Fmoc-Amino Acids for peptide synthesis were first reported by Carpino in 1970 (Carpino, L.A. and Han, G.Y. J. Am. Chem. Soc. 1970, 92, 5748). The Fmoc-Amino Acid group is removed from Fmoc-amino acids under basic conditions, thus allowing very acid labile resins such as 2-Cl-Trt to be used. Generally, peptide synthesis and cleavage conditions are milder with Fmoc amino acids than Boc amino acids. The Fmoc group is usually removed from Fmoc amino acids using piperidine, which removes the Fmoc group and reacts with the deprotection byproduct to prevent undesired side reactions and byproducts. When deprotection is sluggish, DBU can be used to accelerate the reaction. As DBU does not react the fulvene byproduct formed during deprotection, piperidine is often added as a scavenger to remove fulvene. DBU promotes aspartimide formation, however, and should not be used when aspartic acid residues are present.