Macrocyclic peptides have received increasing attention throughout the pharmaceutical industry as attractive scaffolds for the development of new therapeutics. Here, we describe the development of a new proline‐to‐cysteine (PTC) peptide cyclization reaction. Peptide sequences flanked by an N‐terminal proline and a C‐terminal cysteine were reacted with α,α′‐dibromo‐m‐xylene to furnish cyclic peptides bearing a tertiary amine embedded within the macrocycle backbone. Macrocyclization proceeded efficiently in solution and on‐resin with peptides of different sequence lengths (5‐10 amino acids) and amino acid compositions. This approach was also applied for peptide bicyclization. Liquid chromatography mass spectrometry (LC‐MS)/MS analysis of a fingerprint ion related to the PTC linkage that was present throughout the substrate scope expedited confirmation of the product cyclic topologies. Conformational studies by variable‐temperature NMR revealed PTC macrocycles can adopt a rigid structure and display an intramolecular hydrogen‐bonding pattern that differs significantly from their cysteine‐to‐cysteine linked counterparts, further highlighting the value of this alternative cyclization approach. Due to its compatibility with library‐based peptide display and selection technologies, the described approach could offer significant utility in drug discovery campaigns.

中文翻译：

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脯氨酸至半胱氨酸环化生成构象受限的环肽

作为用于开发新疗法的有吸引力的支架，大环肽已在整个制药工业中受到越来越多的关注。在这里，我们描述了新的脯氨酸到半胱氨酸（PTC）肽环化反应的发展。肽序列侧接由N末端脯氨酸和一个C-末端半胱氨酸用α反应，α'二溴米二甲苯提供环肽，该环肽带有嵌入大环骨架内的叔胺。在溶液中和在树脂上使用不同序列长度（5-10个氨基酸）和氨基酸组成的肽有效地进行了大环化。该方法也适用于肽双环化。液相色谱质谱（LC-MS）/ MS分析与整个基板范围内存在的PTC键相关的指纹离子，可加快产品循环拓扑的确认时间。通过变温NMR进行的构象研究表明，PTC大环可以采用刚性结构并显示出分子内氢键模式，该模式与半胱氨酸-半胱氨酸连接的分子明显不同，这进一步凸显了这种替代环化方法的价值。