Trehalose conjugates of 3-hydroxychromone (3HC) dyes have previously been utilized as fluorescence labels to detect metabolically active mycobacteria with a view to facilitating point-of-care detection of mycobacterial pathogens, especially Mycobacterium tuberculosis. We subjected the 3HC dye 2-(6-(diethylamino)benzofuran-2-yl)-3-hydroxy-4H-chromen-4-one (3HC-2) to a combined X-ray crystallography and density functional theory (DFT) study, and conducted preliminary fluorescence labelling experiments with the model organism Mycobacterium aurum. In the crystal, 3HC-2 exhibits an s-cis conformation of the chromone and the benzofuran moieties about the central C–C bond. According to DFT calculations, the s-cis conformer is about 1.8 kcal mol−1 lower in energy than the s-trans conformer. The solid-state supramolecular structure features hydrogen-bonded dimers and π…π stacking. Fluorescence microscopy revealed fluorescence of M. aurum cells treated with the dye trehalose conjugate 3HC-2-Tre in the GFP channel. It was concluded that s-cis is the preferred conformation of 3HC-2 and that the generally considered non-pathogenic M. aurum can be labelled with the fluorescence probe 3HC-2-Tre for convenient in vitro drug screening of new antimycobacterial agents.

中文翻译：

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2-(6-(Diethylamino)benzofuran-2-yl)-3-hydroxy-4H-chromen-4-one 的结构解析和金分枝杆菌细胞的标记

3-羟基色酮 (3HC) 染料的海藻糖缀合物先前已被用作荧光标记来检测代谢活跃的分枝杆菌，以促进分枝杆菌病原体，特别是结核分枝杆菌的即时检测。我们对 3HC 染料 2-(6-(diethylamino)benzofuran-2-yl)-3-hydroxy-4H-chromen-4-one (3HC-2) 进行了组合的 X 射线晶体学和密度泛函理论 (DFT)研究，并用模式生物金分枝杆菌进行了初步的荧光标记实验。在晶体中，3HC-2 显示出色酮和苯并呋喃部分围绕中心 C-C 键的顺式构象。根据 DFT 计算，s-cis 构象异构体的能量比 s-trans 构象异构体低约 1.8 kcal mol−1。固态超分子结构具有氢键二聚体和 π…π 堆叠特征。荧光显微镜显示在 GFP 通道中用染料海藻糖缀合物 3HC-2-Tre 处理的金黄色葡萄球菌细胞的荧光。得出的结论是，s-cis 是 3HC-2 的首选构象，通常认为非致病性的 M. aurum 可以用荧光探针 3HC-2-Tre 标记，以便于体外药物筛选新的抗分枝杆菌药物。