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1. Boc peptide synthesis
The Boc method is a classical peptide solid phase synthesis method in which Boc is used as a protecting group for the amino acid α-amino group, benzyl alcohol is used as a side chain protecting group, and Boc removal is usually carried out using trifluoroacetic acid (TFA). When the polypeptide is synthesized, the Boc-protected N-α-amino acid has been covalently cross-linked to the resin, the TFA excises the Boc protecting group, and the N-terminus is neutralized with a weak base.
Prolongation of the peptide chain is carried out by activation and coupling of dicyclohexylcarbodiimide (DCC), and finally the synthesized target polypeptide is dissociated from the resin by strong acid hydrofluoric acid (HF) method or trifluoromethanesulfonic acid (TFMSA). . In the Boc polypeptide synthesis method, in order to facilitate the next step of polypeptide synthesis, the acid is deprotected repeatedly, and some side reactions are brought into the experiment, for example, the polypeptide is easily cleaved from the resin, and the amino acid side chain is unstable under acidic conditions. 
2. Fmoc peptide synthesis method
Carpino and Han developed a new method for solid phase synthesis of peptides based on Boc peptide synthesis - Fmoc peptide synthesis.
Fmoc polypeptide synthesis uses Fmoc as a protecting group for the amino acid a-amino group. The advantage is that it is stable under acidic conditions, is not affected by reagents such as TFA, and can be deprotected by mild alkali treatment, so the side chain can be protected by a Boc protecting group which is easily removed by acid.
The final excision of the peptides can be quantified from the resin using TFA/dichloromethane (DCM), avoiding the use of strong acids. At the same time, compared with the Boc method, the Fmoc method has mild reaction conditions, few side reactions, high yield, and the Fmoc group itself has characteristic ultraviolet absorption, which is easy to monitor and control the reaction. The Fmoc method is more and more widely used in the field of peptide solid phase synthesis. 
The synthesis of a polypeptide is a process in which amino acids are repeatedly added, usually from the C-terminus to the N-terminus (amino terminus). The principle of solid phase synthesis of peptide is to connect the first amino acid C-terminus of the peptide of interest to the solid phase carrier through a covalent bond, and then use the N-terminus of the amino acid as a starting point for synthesis, after deprotection of the amino group and excess of activated The two amino acids are reacted, the peptide chain is terminated, and the operation is repeated to achieve the desired length of the synthetic peptide chain. Finally, the peptide chain is cleaved from the resin, and purified to obtain the target polypeptide.