A drug targeting motif for glycosidase inhibitors: an iminosugar–boronate shows unexpectedly selective β-galactosidase inhibition

Boronic acids were tethered to iminosugars in compounds such as 8 and 13 in order to increase their affinity for cell surfaces where glycoprotein processing enzymes are operative. Surprisingly, this modification diminished α-mannosidase inhibition while increasing β-galactosidase inhibitory activity (8: Ki=2.0×10−4 M versus E. coli β-galactosidase). The presence of a boronate in 8 and 13 has a profound impact on the specificity of this inhibition.