Efficient synthesis of C-terminal modified peptide ketones for chemical ligations

Synthesis of a C-terminal modified peptide with an α-amido methylketone was efficiently carried out using a backbone-amide-type linker loading with a monofunctionalized diamine, provided that no base such as piperidine or diisopropylethylamine or a reducing agent such as triisopopylsilane was used for the synthetic pathway. The ketoxime-forming chemoselective ligation between a methylketone and an aminooxy was quantitative in 5 h at pH 2.

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