N-anthraniloylation converts peptide p-nitroanilides into fluorogenic substrates of proteases without loss of their chromogenic properties

By simple substitution of an N-acyl group for the anthraniloyl(o-aminobenzoyl) group, chromogenic p-nitroanilide substrates are converted into highly sensitive fluorogenic substrates of proteases. The fluorescence of the anthraniloyl group is completely quenched by the p-nitroanilide moiety in the intact substrates and is released during their enzymatic hydrolysis. The approach is exemplified by the synthesis of anthraniloyl-Phe p-nitroanilide, anthraniloyl-Lys p-nitroanilide, and anthraniloyl-Gly-Gly-Phe p-nitroanilide as substrates for chymotrypsin, trypsin, and alkaline mesentericopeptidase, respectively. The kinetic parameters of these substrates are slightly better than those of similar derivatives bearing other acyl groups, suggesting that the enhanced sensitivity is completely due to the method of measurement. Since the conversion does not affect the chromogenic properties of the substrates, the same compounds can be used as usual p-nitroanilide substrates as well.