An unexpected side reaction was observed in peptoids containing a C-terminal carboxamide with a 2-aminoethyl side chain. The reaction proceeded via cyclization and release of NH₃, resulting in C-terminal oxopiperazine formation, analogous to pyroglutamate formation from N-terminal glutamine in peptides. Reaction conditions that promote oxopiperazine formation were developed. In particular, the addition of organic bases accelerated the cyclization, thus providing a simple strategy for the post-synthetic C-terminal capping of peptoids.

中文翻译：

---

Oxopiperazine封顶：通过C末端环化形成含oxopiperazine的类肽

在含有带有2-氨基乙基侧链的C-末端羧酰胺的类肽中观察到了意外的副反应。该反应通过环化和NH _3的释放进行，导致C-末端氧代哌嗪的形成，类似于从肽中的N-末端谷氨酰胺形成焦谷氨酸。开发了促进氧哌哌嗪形成的反应条件。特别地，有机碱的添加加速了环化，从而为类肽的合成后的C-末端加帽提供了简单的策略。