Synthesis and identification of azocoumarin derivatives toward imaging of α-synuclein aggregates in the brain

To identify α-synuclein aggregation in synucleinopathies is still challenging, due to the lack of specific probes for α-synuclein aggregates with efficient brain uptake. In this work, compact molecules based on coumarin scaffold were synthesized and evaluated for detection and bioimaging of α-synuclein aggregates in the brain. Among the developed compounds, azocoumarin 5 containing push-pull electronic architecture featured selective fluorescence enhancement towards α-synuclein aggregates in comparison to other β-sheet protein species (β-amyloid, tau). In addition, azocoumarin [¹⁸F]Cou-NNF was succesfully developed, and demonstrated its potential as radiotracer for imaging brain α-synuclein aggregates, owing to its favorable affinity for α-synuclein aggregates accompanied with efficient brain uptake and little defluorination in vivo. Overall, compact azocoumarin provides an effective lead structure for developing α-synuclein probes, and N=N bond shows promise in enhancing selective affinity for α-synuclein aggregates.