Oligo- and Polypeptide Synthesis

Histidine is one of the most problematic building blocks in peptide synthesis. Imidazole ring of His is easily A-acylated. Undesired side reactions such as racemization, formation of cyclic imidazolides and A-guanylations of the imidazole ring have been observed. These problems may be avoided by reversible masking of the imidazole function such as benzyl (Bzl), 2,4-nitropheyl (Dnp), benzyloxymethyl (Bom), tert-butoxycarbonyl (Boc), triphenyhnethyl (Trt), diphenylmethyl (Dpm), pyridyldi-phenyhnethyl (Pdpm), 4-toluenesulfonyl (Tos), allyl (Al) and allyloxymethyl (Alom). 

Orthogonal protection is required for the diamino carboxylic acid (Lys) and aminodi-carboxylic acids (Asp and Glu). The e-amino group of Lys is more basic and more 

Peptide coupiing (Addition of next N-protected amino acid) 

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