Structural Elucidation of 2-(6-(Diethylamino)benzofuran-2-yl)-3-hydroxy-4 H -chromen-4-one and Labelling of Mycobacterium aurum Cells

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-4 H -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.