Inhibition of L- and P-selectin by a rationally synthesized novel core 2-like branched structure containing GalNAc-LewisX and Neu5Acα2-3Galβ1-3GalNAc sequences

The selectins interact in important normal and pathological situations with certain sialylated, fucosylated glycoconjugate ligands containing sialyl Lewis(x) (Neu5Ac alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc), Much effort has gone into the synthesis of sialylated and sulfated Lewis(x) analogs as competitive ligands for the selectins, Since the natural selectin ligands GlyCAM-1 and PSGL-1 carry sialyl Lewis(x) as part of a branched Core 2 O-linked structure, we recently synthesized Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-6(SE-3Gal beta 1-3)GalNAc1 alpha OMe and found it to be a moderately superior ligand for L and P-selectin (Koenig ef al,, Glycobiology 7, 79-93, 1997), Other studies have shown that sulfate esters can replace sialic acid in some selectin ligands (Yeun ef al,, Biochemistry, 31, 9126-9131, 1992; Imai et al,, Nature, 361, 555, 1993), Based upon these observations, we hypothesized that Neu5Ac alpha 2-3Gal beta 1-3Gal-NAc might have the capability of interacting with L- and P-selectin, To examine this hypothesis, we synthesized Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-6(Neu5Ac alpha 2-3Gal beta 1-3)-Gal-NAc alpha 1-OB, which was found to be 2- to 3-fold better than sialyl Le(x) for P and L selectin, respectively. We also report the synthesis of an unusual structure GalNAc beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-OMe (GalNAc-Lewis(x)-O-methyl glycoside), which also proved to be a better inhibitor of L- and P-selectin than sialyl Lewis(x)-OMe. Combining this with our knowledge of Core 2 branched structures, we have synthesized a molecule that is 5- to 6-fold better at inhibiting L- and P-selectin than sialyl Lewis(x)-OMe, [GRAPHICS] By contrast to unbranched structures, substitution of a sulfate ester group for a sialic acid residue in such a molecule resulted in a considerable loss of inhibition ability, Thus, the combination of a sialic acid residue on the primary (beta 1-3) arm, and a modified Le(x) unit on the branched (beta 1-6) arm on an O-linked Core 2 structure generated a monovalent synthetic oliogosaccharide inhibitor superior to SLe(x) for both L- and P-selectin.