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Updated: Jun 9, 2026

Synthesis and Mass Spectrometry Analysis of Oligo-peptoids
Published on: February 21, 2018
Oligo(4-aminopiperidine-4-carboxylic acid): an unusual basic oligopeptide with an acid-induced helical conformation
Joon-il Cho1, Masahiro Tanaka, Sota Sato
1Department of Chemistry and Biotechnology, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Abstract:
In sharp contrast with helical polypeptides carrying basic side chains, Api(8), a basic oligopeptide containing the non-natural achiral amino acid 4-aminopiperidine-4-carboxylic acid (Api), adopts a helical conformation only in acidic media. Alkaline titration of a protonated Api(8) oligomer appended with a leucine derivative at its N-terminus showed that disruption of its helical conformation occurs in a pH range of 7-10. NMR studies indicated that the piperidine groups in Api(8), when nonprotonated, possibly interact with the proximal amide protons in the peptide backbone and hamper the formation of the H-bonding network responsible for the helical conformation. The helical structure is induced not only by protonation but also by acylation of the piperidine groups.
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