A fluorogenic substrate for the detection of lysosomal enzyme N-acetyl-α-D-galactopyranosiaminidase (NAGA), which is driving the pathogenesis of Schindler disease. Also substrate for endo-α-N-acetylgalactosaminidase (O-glycosidase), which cleaves O-linked core 1 and core 3 disaccharides from glycoproteins.