Amino acid protecting group
Twenty common amino acids can be divided into fatty 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 (His, Arg, Lys), thioacids (Cys, Met), alcoholic amino acids (Ser, Thr), sub-amino acids (Pro) according to the side chain.The protection of amino acids in the chemical synthesis of polypeptides is very important and directly determines the key to the success of synthesis.Common amino acids in 20 have multiple active side chains, which need protection. Generally, these protecting groups are stable in the synthesis process without side reactions, and can be completely quantitatively shed after the synthesis.Amino acids requiring protection in synthesis include Cys, Asp, Glu, His, Lys, Asn, Gln, Arg, Ser, Thr, Trp, Tyr.Groups to be protected: hydroxyl, carboxyl, amino, amino, amido, guanidine, anti-inflammation, imidazole, etc.Under special circumstances, amino acids such as Trp, Asn, Gln, Thr and Tyr are not protected.
Fig. 1 Three common amino-protecting group structures
Amino acid side chains have many protective groups, and the same side chain has a variety of protective groups, which can be selectively removed under different conditions, which is of great significance for the modification of cyclic peptides and polypeptides.In addition, the side chain protectors are closely related to the selected synthesis methods, and the strategies of Boc and Fmoc in the solid phase are also different. In a sense, polypeptide chemistry is the flexible use and combination of amino acid protectors.For the use of side chain protectors, please refer to the relevant chapters of Huang Weide's "Polypeptide Synthesis". Here, several protectors of Cys, Lys, Asp and their removal methods are briefly introduced.The most common protective groups of Cys are Trt, Acm and Mob, which can complete the synthesis of many pairs of disulfide bond polypeptides.The most common protection bases of Lys are Boc, Fmoc, Trt, Dde, Alloc, which provide many orthogonal protection strategies for solid synthetic cyclic peptides.The most common protection basis of Asp is OtBu, OBzl, OMe, OAll, OFm, which also provides a variety of orthogonal protection strategies.
Table 1 Common Protective Groups of Bright Groups
Table 2 Amino Common Protective Groups
Table 3 Common Protective Groups of Carboxyl Groups
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