Exploring the carbohydrate-binding sites of myelin-associated glycoprotein (MAG) and its ligands by a integrated dynamic approach

Based on previous SAR studies of ganglioside GQ1bα, an octasaccharide, the
tetrasaccharide core, α-Sia-2,3-β-Gal-1,3-(α-Sia-2,6)β-GalNAc, was found to be an
important component for the activity against MAG. In particular within the
tetrasaccharide core, the terminal α(2,3)-linked sialic acid was found to be an important
pharmacophore. To improve binding properties, sialic acid derivatives were synthesized.
Lead optimization was performed using the Topliss Operational Scheme.
The bioaffinities of above compounds for MAG were measured by a hapten inhibition
assay. Additional STD NMR, Biacore and molecular modeling studies provided more
information about the binding epitopes.
On the basis of all information available the lead compound was used to identify second
binding site ligands using NMR. A library of 60 compounds was screened for hit
identification. Second site ligands were identified using a spin labeled Tempo-derivative
of sialic acid. A total of 5 hits were identified from which the best was taken for further
studies.
The in-situ click chemistry approach was applied to identify the best inhibitor for MAG.
The identified inhibitor was synthesized by linking the second site ligand to the first site
ligand using the click chemistry approach. A compound with a nanomolar activity for
MAG was identified as compared to the best compound with a higher micromolar
activity.