Synthesis and characterization of styryl-BODIPY derivatives for monitoring in vitro Tau aggregation

New synthetic strategy to synthesize α-methyl BODIPY derivatives from dipyrromethanes is reported. The method involves regioselective formylation of dipyrromethane followed by modified Wolff-Kishner reduction. The photophysical, electrochemical and computational studies of α-methyl BODIPY derivatives have been investigated in detail. The α-methyl BODIPY derivative was utilized further to prepare biologically important functionalized styryl-BODIPY library in high yield using microwave assisted Knoevenagel condensation. These synthesized dye derivatives were screened to find a potential candidate to track real-time in vitro tau protein fibrillization. Quinoxaline functionalized styryl-BODIPY derivative (5i) exhibited significant fluorescence enhancement upon binding to tau fibrils. Furthermore, tau-5i conjugate was systematically characterized by emission, aggregation kinetics, fluorescence microscopy and Atomic Force Microscopy techniques. Cell culture studies proved that compound 5i was cell permeable and non-toxic to live cells. In addition, a mechanism by which 5i interacts with tau fibrils has been elucidated which can be potentially exploited to further develop reporting dyes and inhibitors for tau aggregates.