Peptides reduction using immobilized

Small molecules containing disulfide bonds (such as cystine-containing peptides) may be reduced and isolated simply by removing the immobilized reductant. Separation of reduced molecules from reductant is much more difficult if a soluble reducing agent is used with low-molecular-weight disulfides. 

Amine-Reactive Methods Amine groups is often used for the immobilization of proteins and peptides. Specific methods are cyanogen bromide method, reductive amination, N-hydroxysuccinimide technique, and carbonyldiimidazole method. 

Several linkers have been developed that rely on the formation of highly stabilized aromatic carbocations. The most frequently used are the eponymous Sieber amide linker 36 [3] and Barany s 3-XAL linker 6 [4]. Both are based on a 3-methoxyxanthine scaffold, which owing to the highly stabilized nature of the xan-thenium ion can provide primary amides on treatment with 1% TFA in DCM, making them excellent tools for the synthesis of protected peptide carboxamides. The Sieber amide resin has also been used to prepare secondary amides via reductive alkylation of the amino group, acylation of the resultant amine and cleavage with dilute TFA [88]. Brill et al. [67] have effected transamination of trifluoroacety-lated Sieber amide resin in good yield. This approach offers considerable potential for the immobilization of amines on this support. 

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