SYNTHESIS OF 5-AMINO-5-DEOXY-D-MANNOPYRANOSE AND 1,5-DIDEOXY-1,5-IMINO-D-MANNITOL, AND INHIBITION OF α- AND β-D-MANNOSIDASES

Article abstract of DOI:10.1016/0008-6215(84)85084-3

The title compounds and the corresponding L-gulo derivatives were synthesised in 6 steps from benzyl 2,3:5,6-di-O-isopropylidene-α-D-mannofuranoside.The K_i values, determined from inhibition studies with α-D-mannosidases from jack beans, almonds, and calf liver, and β-D-mannosidase from Aspergillus wentii, ranged from 70 to 400 μM for the mannitol derivative and from 1.2 to 20 μM for 5-amino-5-deoxy-D-mannopyranose, i.e., inhibition is E2-E4-fold stronger than with D-mannose.Marked enhancement of inhibition with increasing pH is ascribed to the ionisation of a carboxyl group at the active site, forming an ion pair with the protonated inhibitor.The inhibition equilibrium between the jack-bean enzyme and the mannose derivative was approached slowly with k_app 2.0E5 M^-1.min^-1.The mannose-derived inhibitor was also inhibitory against β-D-glucosidases from almonds and Asp. wentii, with K_i values only 20-150-times larger than those for the inhibition of these enzymes by 5-amino-5-deoxy-D-glucopyranose.This moderate discrimination in binding of D-gluco and D-manno derivatives is in marked contrast to the high specificity shown by the glucosidase in catalysing the hydrolysis of mannosidases.A similar low specificity with respect to binding, combined with highly specific catalysis, was also seen with the mannosidases acting on inhibitors and substrates with the D-gluco configuration.