Common modifications in peptide synthesis

There are many contents of peptide labeling and modification, which are widely used in the research of peptide drugs, peptide biology, peptide antibodies and peptide reagents. At present, biotin labeling, fluorescence labeling (FAM, FITC, etc.) and phosphorylation modification are widely used.

Biotin labeling

Biotin avidin system (BAS) is a new type of biological reaction enhancement system. It was applied in immunology and developed rapidly in the late 1970s. Due to its high affinity and multi-stage enhancement effect between biotin and affinity, as well as its organic combination with immunoassay techniques such as fluorescein, enzyme and isotope, the specificity and sensitivity of various microimmunolysis assays have been further improved. There are mainly biotin n N-hydroxysuccinimide ester (bnhs) and biotin p-nitrophenol ester (pbnp) which are used to label the amino groups of polypeptides.

Among them, bnhs is commonly used. Of course, biotin can also be directly labeled because it has a free carboxyl group in its structure; HBTU / HOBt / NMM method is used for condensation (due to the low solubility of biotin, DMSO / DMF mixed solvent is used to increase the solubility).

Fluorescent labeling

Fluorescent labeling is simple and non radioactive. Therefore, fluorescent labeling has been widely used in biological research. The fluorescent labeling method is related to the structure of fluorescent reagent. The method used for free carboxyl group is the same as peptide condensation reaction, and HBTU / HOBt / NMM method is also used.

N-labeled FITC peptide forms fluorescein through cyclic effect, usually accompanied by the removal of the latter amino acid, but can be avoided when there is a spacer or when the target peptide is cut off from the resin by a non acidic environment.

Synthesis of phosphopeptide

Phosphopeptides play an important role in the process of life. Phosphorylation is located on these peptides, Ser, THR, Tyr. At present, phosphorylated amino acids are commonly used in the synthesis of phosphopeptides.

In general, HBTU / HOBt / NMM method is used to connect phosphorylated amino acids. However, at present, there are some objections to the use of this method to synthesize phosphorylation, especially in the synthesis of polyphosphate peptides or long peptides, the connection efficiency is low, and the purity of Zu ì end products is very low. For this kind of phosphate peptide, we consider to adopt the post phosphorylation method.

The synthesis process is to selectively remove the protection basis of amino acid side chain after the peptide is synthesized. For Tyr, thr can be directly reacted with unprotected amino acids, while ser can be quantitatively removed by Fmoc ser (TRT) at 1% TFA / DCM. After phosphorylation, bisbenzylphosphide amide and tetrazole were used to form phosphoramides and tetrazoles, which were connected to hydroxyl groups, and then oxidized to phosphoryl groups in peroxyacid to complete the reaction.

Common modification and marking

N-terminal labeling or modification, N-terminal acetylation (AC), N-terminal biotin labeling (biotin), C-terminal biotin labeling (lysine side chain connection), c-fitc (lysine side chain connection), disulfide ring peptide (S-S), peptide sh ǒ u-tailamide ring, Lys (me), Lys (me2), Lys (me3), map complex antigen peptide.

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