The quinazoline class was exploited to search for a new translocator protein (TSPO) fluorescent probe endowed with improved affinity and residence time (RT). Computational studies on an “in-house” collection of quinazoline derivatives, featuring highly steric demanding groups at the amide nitrogen, suggested that, despite their molecular extension, these ligands are still easily lodged in the TSPO binding site. Binding assays supported this hypothesis, highlighting a low nanomolar/subnanomolar affinity of these ligands, together with a higher RT of the representative compound 11 with respect to our previously reported indole-based fluorescent probe. Thanks to the amenability of the amide nitrogen atom to be substituted with bulky groups, we developed quinazoline-based imaging tools by fluorescently labeling the scaffold at this position. Probes with relevant TSPO affinity, favorable spectroscopic properties, and improved RT were identified. The results from fluorescence microscopy showed that these probes specifically labeled the TSPO at the mitochondrial level in the U343 cell line.

中文翻译：

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利用4-苯基喹唑啉支架开发用于转运蛋白（TSPO）的高亲和力荧光探针

利用喹唑啉类来寻找一种新的易位蛋白（TSPO）荧光探针，该探针具有改善的亲和力和停留时间（RT）。对喹唑啉衍生物“内部”集合的计算研究表明，酰胺氮上具有高度空间要求的基团，尽管它们具有分子延伸性，但这些配体仍很容易沉积在TSPO结合位点。结合分析支持了这一假设，突出了这些配体的纳摩尔/亚纳摩尔亲和力低，以及代表性化合物11的RT较高关于我们先前报道的基于吲哚的荧光探针。由于酰胺氮原子可以被庞大的基团取代，我们通过在此位置进行荧光标记来开发基于喹唑啉的成像工具。确定了具有相关TSPO亲和力，良好的光谱特性和改进的RT的探针。荧光显微镜的结果表明，这些探针在U343细胞系的线粒体水平上特异性标记了TSPO。