Synthesis and characterization of the fluorescence utility of two Visible-Light-Absorbing tryptophan derivatives

We synthesize N alpha-Boc-4-dicyanovinyltryptophan OMe (4DCV-Trp) and characterize its photophysical properties in different solvents. We find that the maximum absorption wavelength of 4DCV-Trp is at ca. 430 nm in water, and that its fluorescence spectrum exhibits a large Stokes shift (e.g., ca. 150 nm in water). Furthermore, solventdependent studies reveal a positive, linear correlation between the frequency of 4DCV-Trp's fluorescence maximum and the solvent polarity index, suggesting that 4DCV-Trp could serve as a polarity reporter of proteins. In addition, we synthesize 4-nitrotryptophan and validate its utility as a fluorescence quencher of a blue fluorescent amino acid, 4-cyanotryptophan.