A thienoquinoxaline and a styryl-quinoxaline as new fluorescent probes for amyloid-β fibrils

Simple and easy to prepare quinoxaline derivatives proved able to stain amyloid fibers such as aggregated lysozyme and Aβ(1-40)-peptide by a fluorescence “turn on” mechanism. Thienoquinoxaline 1 allowed the detection of lysozyme and Aβ(1-40) fibers at λ=555 and 532nm, respectively, with excitation at λ=450nm. Styryl-quinoxaline 2 stained lysozyme and Aβ(1-40) fibers with fluorescence at λ=579 and 567nm, respectively, upon excitation at λ=453nm. The apparent Kd values for Aβ(1-40) fibers were 77 and 294nM for 1 and 2, respectively. The sensitivity of the aggregates detection assay with these new dyes was higher than that of thioflavin T. Considering their unique fluorescence properties compared to other dyes reported in the field, they can be considered as additional staining tools for the detection and studies of peptide/protein aggregation.