Synthesis of Isofagomine Derivatives as New Fluorescence pH Indicators/Glycosidase Inhibitors

Inhibitor protonation of azasugars of the isofagomine type when bound to enzyme can be investigated using photon induced electron transfer (PET) quenching of an attached fluorophore. For this purpose, Isofagomine, iso-d-galacto-fagomine, and iso-l-gulo-fagomine were converted toN-(10-chloroanthracenenyl-9-alkyl) derivatives where the alkyl group contained one, two, or three methylene groups. The new derivatives displayed pH dependent fluorescence; as the ammonium forms they were fluorescent, while 90-99 % of the fluorescence was quenched in the amine forms. The 3 isofagomine derivatives were competitive inhibitors ofT. Maritima Iota-glucosidase withK(i)values from 0.37-4.6 tau M. Similarly, the iso-d-galacto-fagomines inhibitedA. Niger Iota-galactosidase withK(i)values from 63-2000 nm. When bound to the enzymes the inhibitors displayed between 1-15 % fluorescence.