Popular Science Tips: Late-maturing Peptide Bond Synthesis - Enzyme-Promoted Synthesis

Liquid-synthesized peptides are more complex than solid-synthesized ones.However, liquid phase is more widely used than solid synthesis.Many special modified groups or periodate molecules can not be synthesized by solid phase, but can be linked with peptides by liquid synthesis method. The common liquid synthesis method of peptide bond, carbodiimide shrinkage agent method, is introduced.

Carbodiimide condensant method

Commonly used condensants are diisopropylamine (DIC), dicyclic own carbodiimide (DCC) and 1-(3-dimethylaminopropylamine)-3-ethylcarbodiimide (EDCI).

The use of such condensants usually requires the addition of acylation catalysts or activators, such as DMAP, HOBt, etc.Because the acid in the first stage of reaction is unstable to the intermediate formed by carbodiimide, if the acylation catalyst is not used to convert into the corresponding active ester or active amide, it will itself be rearranged into the corresponding stable urea derivative, which will not only produce unnecessary by-products, but also affect the recovery rate of the product.

Reduction activators: There are several commonly used reduction activators, and currently DMAP has been used to catalyze acylation reactions in each.When the catalytic effect of DMAP is poor, 4-PPY can be used, and related literatures have reported that the catalytic ability is much better than that of DMAP.

Among the three commonly used shrinkage agents, DIC and DCC are inexpensive.

In general, when DCC and DMAP are used together, dicyclic urea, another product of DCC reaction, has a small solubility in general organic phase, but has a slight solubility. Therefore, dicyclic urea, which is difficult to completely remove by common purification methods, recrystallization, column analysis and so on, has a smaller solubility in ether than other solvents. Therefore, after treating the solvent of this reaction, the solvent of evaporation reaction is generally added.Ethyl ether filters most of the bicyclic own ureas before further treatment.Diisopropylurea produced by DIC (usually used in conjunction with Hobt) has good solubility in general organic solvents, so it is generally used in solid synthesis.

At present, EDCI is widely used in biochemistry, and its main feature is that the urea generated after the reaction is water-soluble and easy to wash out. Generally, EDCI is combined with HOBt (note: this reaction is generally indispensable for HOBt, otherwise the shrinkage rate may be too low).When the a-position resistance of the acid is large or the electron-attracting group is connected, the reaction stays at the step of active ester (the active ester has a strong mass spectrum signal and can be detected by MS or LC-MS).

Hobt Structural Formula

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