1. The basic principle of peptide synthesis?
Solid phase peptide synthesis is a major breakthrough in peptide synthesis chemistry. Its biggest feature is that it does not need to purify the intermediate products, and the synthesis process can be carried out continuously, which lays a foundation for the automation of peptide synthesis. At present, the automatic peptide synthesis is basically solid-phase synthesis. The basic process is as follows:
Based on Fmoc protective group, the carboxyl-group of the C-terminal amino acid of the target peptide to be synthesized is first connected with an insoluble polymer resin in the form of covalent bond, and then the amino group of this amino acid is used as the starting point of peptide synthesis to form peptide bond with the activated carboxyl-group of other amino acids, and the peptide can be obtained by repeating this process. According to the different amino acid composition of peptides, the post-treatment methods of peptides are different, and the purification methods are also different.
2. If the solubility of the peptide we synthesized is not good, is there a problem with the peptide?
It is difficult to accurately predict the solubility of a peptide and what the appropriate solvent is. If the peptide is difficult to dissolve, the idea that there is a problem peptide synthesis is not correct.
3. What is the peptide status? How to save?
The peptide we provide is powdered, generally gray white, with different composition. The color of peptide powder is different. The peptide generally needs to be kept away from light for long-term storage, and should be kept at - 20 degrees, and can be kept at 4 degrees in the short term. If it is transported in a short time, it can be transported at room temperature.
4. What are the impurities in non HPLC purified peptides?
Impurities in crude peptide:Some raw materials of non full-length peptide and peptide post-treatment, such as DTT, TFA, and salt.
5. What are the impurities in the peptides purified by HPLC?
The peptides purified by HPLC still have some impurities, including short peptides and trace TFA.
6. How to determine the solubility of peptides from peptide sequences?
(1) If the peptide contains a high proportion of highly hydrophobic amino acids such as Leu, Val, IIE, Met, Phe and Trp, the peptide is difficult to dissolve in aqueous solution or impossible to dissolve at all. Whether these amino acids are purified or synthesized, there may be problems.
(2) Generally, the proportion of hydrophobic amino acids is less than 50%, and 4 consecutive AA cannot be hydrophobic. The proportion of charged amino acids (positive charge K, R, H, N-terminus, negative charge D, E, C-terminus) reaches 20%. If the N or C-terminal of peptide is short, the solubility can also be improved if polar amino acids can be increased.
7. Why are peptides containing Cys, met, or Trp difficult to synthesize?
Peptides containing Cys, Met, or Trp are difficult to synthesize, and it is difficult to obtain high-purity products. Mainly because these groups are unstable and easy to oxidize. The use and storage of these peptides need special attention to avoid repeatedly opening the cover.
8. Why are the synthetic yield or purity of some peptides relatively low?
For example, when Val, ile, Tyr, Phe, Trp, Leu, Gln, and Thr are adjacent or repeated, the peptide chain cannot be fully stretched and dissolved in the synthesis process, and the synthesis efficiency decreases. In the following cases, the synthesis efficiency and purity of the product are relatively low, such as repeated Pro, Ser, repeated Asp etc.
9. What are the ways to improve the synthesis of difficult sequence peptides?
In solid-phase peptide synthesis, the problems of peptide synthesis failure or low synthesis efficiency are often encountered. The main reason is due to the peptide sequence, because some peptide sequences are formed on the resin β-Folding changes the swelling property of the resin, and it is possible to bury the active site of the reaction in the resin, which makes the reaction difficult. At present, the main methods reported are as follows: 1. Use mixed solvent, DMSO / DMF, 6N-Guanidine/DMF solution. 2. Increase the reaction temperature or use microwave method. 3. Use high separation liquid salt, LiCl, NaClO4, etc. 4. Use PEG-PS resin with better swelling performance and reduce the resin load (0.05-0.2mmol/g).
