Synthesis and Evaluation of Glycosyl Luciferins.

Measuring glycosidase activity is important to monitor any aberrations in carbohydrate hydrolase activity, but also for the screening of potential glycosidase inhibitors. To this end, synthetic substrates are needed which provide an enzyme-dependent read-out upon hydrolysis by the glycosidase. Herein, we present two new routes for the synthesis of caged luminescent carbohydrates, which can be used for determining glycosidase activity with a luminescent reporter molecule. The substrates were validated with glycosidase and revealed a clear linear range and enzyme-dependent signal upon the in situ generation of the luciferin moiety from the corresponding nitrile precursors. Besides, we showed that these compounds could directly be synthesized from unprotected glycosyl-α-fluorides in a two-step procedure with yields up to 75 %. The intermediate methyl imidate appeared a key intermediate which also reacted with d-cysteine to give the corresponding d-luciferin substrate rendering this a highly attractive method for synthesizing glycosyl luciferins in good yields.