Scheme 1.

Enzymatic cleavage of the chromogenic or fluorogenic N-acetyl-β-D-glucosaminide substrates, 1 – 9, by HEX(NAG) releases an optical reporter that produces a detectable change in signal. Substrates 1 - 3 are chromogenic and substrates 4 - 9 are fluorogenic. The * shown on optical reporters 6 and 7 are reminders that there is a self-immolative linker between the N-acetyl-β-D-glucosaminide and the optical reporter. The lower box depicts the structural difference between GlcNAc and GalNAc, and the substrate selectivities of GH3, GH20 and GH84 glycosyl hydrolase families.