Centre de Biophysique Moléculaire, CNRS UPR 4301, Rue Charles Sadron, 45071, Orléans cedex 2, France.
Org Biomol Chem. 2020 Oct 21;18(40):8199-8208. doi: 10.1039/d0ob01737j.
We herein report a robust upgraded synthetic protocol for the synthesis of N-Hnb-Cys crypto-thioester peptides, useful building blocks for segment-based chemical protein synthesis through native chemical ligation. We recently observed the formation of an isomeric co-product when using a different solid support than the originally-reported one, thus hampering the general applicability of the methodology. We undertook a systematic study to characterize this compound and identify the parameters favouring its formation. We show here that epimerization from l- to d-cysteine occurred during the key solid-supported reductive amination step. We also observed the formation of imidazolidinones by-products arising from incomplete reduction of the imine. Structural characterization combined with the deciphering of underlying reaction mechanisms allowed us to optimize conditions that abolished the formation of all these side-products.
我们在此报告了一种强大的升级合成方案，用于合成 N-Hnb-Cys 加密硫酯肽，这是通过天然化学连接进行基于片段的化学蛋白质合成的有用构建块。我们最近观察到，当使用不同于最初报道的固相载体时，会形成一种异构副产物，从而阻碍了该方法的普遍适用性。我们进行了一项系统研究来表征这种化合物并确定有利于其形成的参数。我们在这里表明，在关键的固载还原胺化步骤中，l-半胱氨酸发生了向 d-半胱氨酸的差向异构化。我们还观察到亚胺不完全还原产生的咪唑烷酮副产物的形成。结构表征结合对反应机制的揭示使我们能够优化条件，从而消除了所有这些副产物的形成。
