The types of cyclic peptides can be divided into homocyclic peptides and heterocyclic peptides according to their skeleton structure.
The main chain of homocyclic peptide is bridged by amide bond, and its structure is simple; in addition to amide bond, heterocyclic peptide has ester bond, ether bond, thioester bond and other bridging structures.
Factors affecting the synthesis of cyclopeptides in solid phase synthesis
Selection of linear peptide
No matter what strategy is used, the yield of different linear peptides will change according to the structure of linear peptides.
If the steric hindrance of the chain peptide sequence compound is large, and there is a large repulsion between the N-terminal and the C-terminal, the intramolecular cyclization of the compound is more difficult, and the coupling reagent with high activity is needed to activate the functional groups. Effect of temperature and solvent
Generally speaking, the higher the temperature, the more favorable the linear peptide to overcome the twisting tension of Ti high cyclization efficiency, but too high temperature will also increase the side effects. Therefore, lowering the temperature at the beginning, adding the condensation reagent and then increasing to room temperature can improve the yield of Gao cyclic peptide to a certain extent.
In solid-state synthesis, due to the different swelling properties of resin in different solvents, it is very important to select the solvent with high Ji property and good swelling property for the synthesis of cyclic peptide.
Influence of closed loop position on cyclization reaction
In the synthesis strategy of cyclic peptide, the determination of the closed-loop site often determines the success or failure of synthesis.
In general, it is necessary to avoid the close loop between n-alkyl, a, a-disubstituted or β substituted amino acids with high steric hindrance.
In addition, the position of intramolecular hydrogen bond also determines the position of closed loop to a certain extent.
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