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chemical synthesis of peptides, including liquid and solid in two ways. Liquid-phase synthesis of BOC and z now mainly used two methods of protection, is now mainly used in peptide synthesis, such as aspartame, peptide, oxytocin, and solid-phase synthesis, has protected many options, low cost, many advantages of synthetic scale easy to zoom in. Compared with the solid-phase synthesis and liquid-phase synthesis of the main disadvantage is that little synthesis, generally concentrated in less than 10 amino acid peptide synthesis, synthesis of intermediates need to be purified, long hours, heavy workload. Now using FMOC solid-phase synthesis method and the BOC method, synthesis it has convenient, quick, easy to automate, but also easier to about 30 amino acid peptide synthesis of.
1.1. Amino acid protecting group
20 kinds of amino acids, according to side chain can be divided into several categories: aliphatic amino acid (Ala,Gly,Val,Leu,Ile) is an aromatic amino acid (Phe,Tyr,Trp,His), glutamine or carboxyl side chains of amino acids (Asp,Glu,Asn,Gln), basic side chains of amino acids (Lys,Arg), sulfur-containing amino acids (Cys,Met), alcohol-containing amino acids (Ser,Thr), Imino acids (Pro). Protected amino acids in peptide synthesis is critical, it directly determines the synthesis can be the key to success. Because many of the 20 common amino acids are reactive side chains, the need for protection, the General requirements, the protecting group in the synthesis process of stable, no adverse reaction, synthesis after the removal of all quantitative. Protection is required in the synthesis of amino acids include: Cys,Asp,Glu,His,Lys,Asn,Gln,Arg,Ser,Thr,Trp,Tyr. Need for protection groups: hydroxyl, carboxyl, sulfhydryl, amine, amide, Guanidine, indole, imidazole, and so on. Trp with or without protection, because the nature of indole is stable. In special cases, of course, some amino acids with or without protection, like, Asn,Gln, and Thr,Tyr.

Figure 1 3 kinds of common structure of amino protecting groups
amino acid side-chain protecting groups is very large, with a side chain has a variety of different protection based, selective removal under different conditions, which in terms of cyclic peptides and peptide modification is of very important significance. Synthesis of side-chain protecting groups and choice there is a close relationship, liquid and solids are not the same, solid phase of BOC and FMOC strategy is not the same, from a certain point of view, peptide chemistry is the use of amino acid protecting group and match. On the use of side-chain protecting groups, refer to the solid-phase organic synthesis of Wang Dexin – principles and applications of the fourth chapter of the Guide, we introduced several protection and elimination methods of Cys,Lys,Asp. Cys there are three most common protecting groups, Trt,Acm,Mob, the three protection can complete a number of disulfide peptides synthesis. Lys most common protecting groups are: Boc,Fmoc,Trt,Dde,Allyl, for solid-phase synthesis of peptides provides a lot of orthogonal protection strategies. Asp the most common protecting groups are: Otbu,OBzl,OMe,OAll,OFm, also offers a variety of orthogonal protection strategies.