2-(Benzothiazol-2-yl)-phenyl-β-d-galactopyranoside derivatives as fluorescent pigment dyeing substrates and their application for the assay of β-d-galactosidase activities

2-(Benzothiazol-2-yl)-phenyl-β-d-galactopyranoside derivatives were synthesized as novel artificial fluorescent pigment dyeing substrates for β-d-galactosidase. The substrates, which exhibited non-fluorescence or weak fluorescence in solution phase, were smoothly hydrolyzed by β-d-galactosidase from Aspergillus oryzae and yielded a water-insoluble strong fluorescent pigment. The difference of fluorescent intensity exhibited a linear relationship with the amount of enzyme.