Design of Glycosyltransferase Inhibitors: Targeting the Biosynthesis of Glycosaminoglycans by Phosphonate-Xyloside

β-1,4-Galactosyltransferase 7 (β4GalT7) is a key enzyme in the biosynthesis of glycosaminoglycans (GAG) that transfers the first galactose unit to xylose in the linker region. Searching for new inhibitors of the GAG biosynthesis, we used saturation transfer difference (STD) nuclear magnetic resonance (NMR) spectroscopy to evaluate the binding interactions between β4GalT7 and several pentosides in the presence of UDP donors. These investigations verified the glycosylation specificity of β4GalT7 and revealed that the naphthalene and the uridine moieties were significant contributors to the binding of the acceptor and the donor, respectively, while the galactose part was less important. Based on these findings, we set out to investigate conjugates of UDP and naphthoxylosides to function as transition state analogues. These compounds were synthesized using a one-pot procedure and tested as inhibitors in a β4GalT7 assay. Interestingly, one truncated analogue, a bisphosphonate-xyloside construct, showed a significant inhibition (IC₅₀: 188 μM). These findings open for the design of a new class of inhibitors of the GAG biosynthesis.