Phenolic bis-styrylbenzenes as β-amyloid binding ligands and free radical scavengers

Starting from bisphenolic bis-styrylbenzene DF-9 (4), β-amyloid (Aβ) binding affinity and specificity for phenolic bis-styrylbenzenes, monostyrylbenzenes, and alkyne controls were determined by fluorescence titration with β-amyloid peptide Aβ_1-40 and a fluorescence assay using APP/PS1 transgenic mouse brain sections. Bis-styrylbenzene SAR is derived largely from work on symmetrical compounds. This study is the first to describe Aβ binding data for bis-styrylbenzenes unsymmetrical in the outer rings. With one exception, binding affinity and specificity were decreased by adding and/or changing the substitution pattern of phenol functional groups, changing the orientation about the central phenyl ring, replacing the alkene with alkyne bonds, or eliminating the central phenyl ring. The only compound with an Aβ binding affinity and specificity comparable to 4 was its 3-hydroxy regioisomer 8. Like 4, 8 crossed the blood-brain barrier and bound to Aβ plaques in vivo. By use of a DPPH assay, phenol functional groups with para orientations seem to be a necessary, but insufficient, criterion for good free radical scavenging properties in these compounds.