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 Lewisx (Neu5Acα2–3Galβ1–4(Fucα1–3)GlcNAc). Much effort has gone into the synthesis of sialylated and sulfated Lewisx analogs as competitive ligands for the selectins. Since the natural selectin ligands GlyCAM-1 and PSGL-1 carry sialyl Lewisx as part of a branched Core 2 O-linked structure, we recently synthesized Galβ1–4(Fucα1–3)GlcNAcβ1–6(SE-3Galβ1–3)GalNAc1αOMe and found it to be a moderately superior ligand for L and P-selectin (Koenig et al., Glycobiology 7, 79–93, 1997). Other studies have shown that sulfate esters can replace sialic acid in some selectin ligands (Yeun et al., Biochemistry, 31, 9126–9131, 1992; Imai et al., Nature, 361, 555, 1993). Based upon these observations, we hypothesized that Neu5Acα2–3Galβ1–3GalNAc might have the capability of interacting with Land P-selectin. To examine this hypothesis, we synthesized Galβ1–4(Fucα1–3)GlcNAcβ1–6(Neu5Acα2–3Galβ1–3)-GalNAcα1-OB, which was found to be 2to 3-fold better than sialyl Lex for P and L selectin, respectively. We also report the synthesis of an unusual structure GalNAcβ1–4(Fucα1– 3)GlcNAcβ1-OMe (GalNAc-Lewisx-O-methyl glycoside), which also proved to be a better inhibitor of Land P-selectin than sialyl Lewisx-OMe. Combining this with our knowledge of Core 2 branched structures, we have synthesized a molecule that is 5to 6-fold better at inhibiting Land P-selectin than sialyl Lewisx-OMe,