Design and synthesis of 4′-O-alkyl-chitobiosyl-4-methylumbelliferone as human chitinase fluorogenic substrates

•New probes are reported that report faithfully on chitotriosidase activity.•Transglycosylation is effectively prevented by sterically bulky appendages.•Central glucosazido building block to act as an effective acceptor and donor synthon.•trans-Selective glycosylations without the use of a neighbouring group.

The synthesis of three fluorogenic chitobiosyl derivatives, modified at the non-reducing 4′-OH with, either a methyl, an isopropyl or a cyclohexylmethyl substituent, is described. The 4′-capped 4-methylumbelliferyl chitobiosides are hydrolysed by the human chitinase CHIT1 following Michaelis–Menten kinetics and in contrast to unmodified chitobiosyl-4-methylumbelliferone do not undergo transglycosylation. The compounds are also relatively poor hexosaminidase substrates and thus provide useful alternatives to 4′-deoxychitobiosyl-4-methylumbelliferone, previously reported by us as fluorogenic substrate to monitor CHIT1 activity as a marker for Gaucher disease state.

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