Synthesis and photophysical properties of 3-[2-(pyridyl)benzoxazol-5-yl]-l-alanine derivatives

The syntheses of N-(tert-butyloxycarbonyl)-3-[2-(4-pyridyl)benzoxazol-5-yl]-l-alanine methyl ester and N-(tert-butyloxycarbonyl)-3-[2-(2-pyridyl)benzoxazol-5-yl]-l-alanine methyl ester using different oxidizing agents (NBS, lead tetraacetate, Mitsunobu reaction) in oxidative cyclization of Schiff base are described. The compounds obtained are fluorescent. The position of the emission band and the fluorescence quantum yield depend on solvent polarity. The fluorescence decays of all the compounds studied are heterogeneous.