Fmoc / t-Bu Solid Phase Synthesis

The Fmoc method is a new method for solid phase synthesis of peptides developed by Carpino and Hart based on the Boc method.

The fundamental difference between the Fmoc/t-Bu(9-fluorenylmethoxycarbonyl/tert-butoxy) strategy and the Boc/Bzl strategy is the use of alkali-removable Fmoc is a protecting group for α-amino group, the side chain is protected by t-Bu which can be removed by TFA, and the solid phase carrier Wang resin with acid-sensitive linking arm is used, and the final step of the synthesis is removed by TFA. Han Xiang et al. successfully synthesized the 32-peptide thymosin α 1 by Fm oc solid phase method, starting from Fm oc-Asn(Trt)-W angResin, Boc protecting the side chain amino group of Lys, and tert-butyl ester group (O-t-Bu Protecting the side chain carboxyl group of Asp and Glu, t -Bu protects the side chain hydroxyl group of Ser and Thr, and trityl group (Trt) protects the side chain amide group of Asn, and the total synthesis yield is 33.2%, and the purity is >98.8%.

The Fmoc protected amino acid is sensitive to bases, especially secondary amines, and can be removed with piperidine at room temperature. Under these conditions, Z-based, Boc-based or other amino protecting groups are unaffected.

The Fmoc protecting group is stable to acid and can be removed under mild alkaline conditions. It can be used orthogonally to acid-sensitive side chain protecting groups, and has the advantages of mild reaction conditions, less side reactions, and high yield. 

Purification of the product is also facilitated when the polyaryl analog of the Fmoc protecting group is attached to the N-terminus of the polypeptide and protein. At the same time, the Fmoc group has characteristic ultraviolet absorption and is easy to monitor and control the reaction, so it is more and more popular. 

Moreover, with the development of the peptide synthesis industry, the cost of Fmoc to protect amino acid raw materials is greatly reduced, and the Fmoc method has gradually replaced the Boc method and is widely used in solid phase synthesis.