Classification of Amino Acids

The 20 common amino acids can be divided into several categories according to their side chains: aliphatic amino acids (Ala, Gly, Val, Leu, Ile,), aromatic amino acids (Phe, Tyr, Trp, His), amide or carboxyl side chain amino acids ( Asp, Glu, Asn, Gln), basic side chain amino acids (Lys, Arg), sulfur-containing amino acids (Cys, Met), alcohol-containing amino acids (Ser, Thr), imino amino acids (Pro).

Fmoc Protected Amino Acids

The protection of amino acids in the chemical synthesis of polypeptides is very critical, which directly determines the key to the success of the synthesis. Because many of the common 20 amino acids have active side chains and need to be protected, it is generally required that these protecting groups are stable during the synthesis process, without side reactions, and can be completely and quantitatively removed after the synthesis.

Protected amino acids are the most basic raw materials for solid-phase peptide synthesis . Amino acids all contain alpha amino and carboxyl groups, and some of the 20 amino acids also contain side-chain active groups, such as hydroxyl, amino, guanidino and heterocyclic groups. These active groups need to be protected during the peptide reaction, and the protective groups are removed after the target peptide is synthesized.The most frequently used protected amino acid raw material is the Fmoc protected amino acids. 

Solid-phase Peptide Synthesis

The artificial synthesis of peptides is controlled by the synthesis of different amino acids in a certain order. One difficulty in achieving controlled synthesis is that the reagents required for peptide grafting reactions can simultaneously interact with other functional groups that do not participate in peptide grafting, such as the free amino group of the N-terminal amino acid residue, the free carboxyl group of the C-terminal residue, and some active groups in the side chain, especially the SH group, which can all interact with peptide grafting reagents.

In order to obtain synthetic peptides with specific sequences, a directed synthesis method of gradual condensation is needed. Before peptide synthesis, these functional groups must first be blocked or protected to avoid interacting with peptide reagents and generating unnecessary peptide bonds or other bonds. After the peptide bond is formed, the protective group is removed.

Main Design Ideas for Solid-phase Synthesis of Peptides

Firstly, the carboxyl group of the carboxyl terminal amino acid of the peptide chain to be synthesized is covalently linked to an insoluble polymer resin. Then, the amino acid bound to the solid phase carrier is used as an amino component to remove the protective group and react with an excess activated carboxyl component to lengthen the peptide chain.

This step can be repeated multiple times, including condensation, washing, deprotection, neutralization, and washing, followed by the next round of condensation, and finally reaching the desired synthesized peptide chain length.

Amino Acids that Need To Be Protected

Include: Cys, Asp, Glu, His, Lys, Asn, Gln, Arg, Ser, Thr, Trp, Tyr. Groups that need to be protected: hydroxyl, carboxyl, mercapto, amino, amido, guanidine, indole, imidazole, etc. Wherein Trp can also be unprotected, because indole is relatively stable in nature. Of course, under special circumstances, some amino acids may not be protected, such as Asn, Gln, Thr, Tyr.

Fluorene methoxycarbonyl (Fmoc)

This protective group is stable to acids and can be removed with a 50% dichloromethane solution of amines such as concentrated ammonia water or dioxane methanol 4 mol/L NaOH.

Fluorene methoxycarbonyl has strong UV absorption. It can be used for peptide synthesis in both liquid and solid phases by pairing with protective groups removed with acids. The advantages of fluorene methoxycarbonyl are:

1) Fmoc amino acids are particularly stable to acids, using acids to remove Boc and Z groups, and Fmoc amino acids also have good stability.

2) Fmoc amino acids can be removed from Fmoc groups using ordinary amines.

The Fmoc group is introduced into amino acids in the presence of NaHC03 or Na2C03 through the following reactions, as shown in the figure:

Removal of Amino Acid Protecting Groups

There are many protecting groups for amino acid side chains. The same side chain has many different protecting groups, which can be selectively removed under different conditions. This is of great significance in the modification of cyclic peptides and polypeptides. Moreover, the side chain protecting group is closely related to the selected synthesis method. The liquid phase and the solid phase are different, and the BOC and FMOC strategies in the solid phase are also different. In a sense, peptide chemistry is the flexible use and matching of amino acid protecting groups.

Fmoc Amino Acids - Omizzur

Omizzur Biotech supply 1000+ Fmoc amino acids in peptide synthesis, Boc/Cbz, N-methyl amino acids, amino acid derivatives,unnatural amino acids,and high-purity peptide coupling, group protecting reagents, etc. All are available from stock , price with market advantage. Our products include but are not limited to the following varieties,if any needs, please contact the customer service center , our customer service staff will quickly feedback within 2 hours.

Omizzur is currently recruiting local high-quality partners,  has rich incentive policies for manufacturers or local dealers. Contact us to discuss cooperation matters now .