Structural factors influencing the reaction rates of 4-aryloxy-7-nitrobenzofurazans with amino acids

An interesting observation was made when studying the SNAr reaction between several 4-aryloxy-7-nitrobenzofurazans (2) and several amino acids leading to the apparition of detectable fluorescence from the substitution products3. Acidic amino acids reacted very slowly=while basic amino acids react fastest with2 having an unsubstituted phenyl or a 4-formyl-phenyl Ar group. Amongst neutral amino acids, proline reacts fastest at room temperature after 100 min. With2 having a methoxy-subtituted Ar group.