Fluorescence labeled ligands have been gaining importance as molecular tools, enabling receptor–ligand-binding studies by various fluorescence-based techniques. Aiming at red-emitting fluorescent ligands for the hH₂R, a series of squaramides labeled with pyridinium or cyanine fluorophores (19–27) was synthesized and characterized. The highest hH₂R affinities in radioligand competition binding assays were obtained in the case of pyridinium labeled antagonists 19–21 (pK_i: 7.71–7.76) and cyanine labeled antagonists 23 and 25 (pK_i: 7.67, 7.11). These fluorescent ligands proved to be useful tools for binding studies (saturation and competition binding as well as kinetic experiments), using confocal microscopy, flow cytometry, and high content imaging. Saturation binding experiments revealed pK_d values comparable to the pK_i values. The fluorescent probes 21, 23, and 25 could be used to localize H₂ receptors in HEK cells and to determine the binding affinities of unlabeled compounds.

中文翻译：

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荧光 H2 受体方酸酰胺型拮抗剂：合成、表征和应用。

荧光标记的配体作为分子工具越来越重要，可以通过各种基于荧光的技术进行受体-配体结合研究。针对hH ₂ R 的发红光荧光配体，合成并表征了一系列用吡啶鎓或花青荧光团 ( 19 – 27 )标记的方酸酰胺。最高HH ₂在放射性配体竞争结合测定- [R亲和力在吡啶标记的拮抗剂的情况下，得到19 - 21（对ķ_我：7.71-7.76）和花青标记拮抗剂23和25（对ķ_我: 7.67, 7.11)。这些荧光配体被证明是使用共聚焦显微镜、流式细胞术和高内涵成像进行结合研究（饱和和竞争结合以及动力学实验）的有用工具。饱和结合实验揭示了与 p K _i值相当的p K _d值。所述荧光探针21，23，和25可以被用来定位ħ _2种受体在HEK细胞，并确定未标记的化合物的结合亲和力。