Synthesis of chloro-substituted analogs of Thiazole orange – Fluorophores for flow cytometric analyses

► Synthesis of chloro-containing analogs of Thiazole orange has been reported. ► Spectral properties of the dyes in presence of dsDNA have been investigated. ► The ability of dyes to stain live or apoptotic cells were examined by flow cytometry. ► The dyes are suitable for detection of apoptosis at low concentrations (1 × 10 −11 M). Synthesis, absorption and fluorescence properties of a series of asymmetrical monomethine cyanine dyes, chloro-containing analogs of Thiazole orange, are reported. Their staining ability was studied by flow cytometry. The saturating concentrations of each dye that gives a stable staining intensity have been determined. The ability of dyes B9, B11, B13 to stain live macrophages and apoptotic splenocytes was investigated. Positive signal in nucleus of adherent macrophages detected by fluorescent microscopy showed good specificity of B9, B11 and B13 dyes for DNA. In apoptotic assay cells positive for Annexin V were stained more brightly with the dyes B9, B11 and B13 than with propidium iodide. Despite that B13 showed high DNA selectivity it induces apoptosis of splenocytes and it is not suitable for detection of dead cells. The other synthesized chloro-containing analogs of Thiazole orange B9 and B11 can be successfully used for flow cytometric analyses of DNA content in live cells and for analyses of cell apoptosis.