Synthesis and characterization of a fluorescent probe for α-tocopherol suitable for fluorescence microscopy

Previously prepared fluorescent derivatives of α-tocopherol have shown tremendous utility in both in vitro exploration of the mechanism of ligand transfer by the α-tocopherol transfer protein (α-TTP) and the intracellular transport of α-tocopherol in cells and tissues. We report here the synthesis of a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) containing α-tocopherol analog having extended conjugation with an alkenyl thiophene group that extends the absorption and emission maxima to longer wavelengths (λex=571nm and λem=583nm). The final fluorophore thienyl-ene-BODIPY-α-tocopherol, 2, binds to recombinant human α-TTP with a Kd=8.7±1.1nM and is a suitable probe for monitoring the secretion of α-tocopherol from cultured Mcf7#189 cells.