Inhibition of L- and P-selectin by a rationally synthesized novel core 2-like branched structure containing GalNAc-Lewisx and Neu5Acalpha2- 3Galbeta1-3GalNAc sequences

The selectins interact in important normal and pathological situations withcertain sialylated, fucosylated glycoconjugate ligands containing sialylLewisx(Neu5Acalpha2-3Galbeta1-4(Fucalpha1-3)GlcN Ac). Much effort has goneinto the synthesis of sialylated and sulfated Lewisxanalogs as competitiveligands for the selectins. Since the natural selectin ligands GlyCAM-1 andPSGL-1 carry sialyl Lewisxas part of a branched Core 2 O-linked structure,we recently synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(SE-3Galbeta1+++-3)GalNAc1alphaOMe and found it to be a moderately superior ligand for Land P-selectin (Koenig et al. , Glycobiology 7, 79-93, 1997). Other studieshave shown that sulfate esters can replace sialic acid in some selectinligands (Yeun et al. , Biochemistry, 31, 9126-9131, 1992; Imai et al. ,Nature, 361, 555, 1993). Based upon these observations, we hypothesizedthat Neu5Acalpha2-3Galbeta1-3GalNAc might have the capability ofinteracting with L- and P-selectin. To examine this hypothesis, wesynthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(Neu5Acalpha2+++-3Galbeta1-3)- GalNAc alpha1-OB, which was found to be 2- to 3-fold betterthan sialyl Lexfor P and L selectin, respectively. We also report thesynthesis of an unusual structure GalNAcbeta1-4(Fucalpha1-3)GlcNAcbeta1-OMe (GalNAc- Lewisx-O-methyl glycoside), which also proved tobe a better inhibitor of L- and P-selectin than sialyl Lewisx-OMe.Combining this with our knowledge of Core 2 branched structures, we havesynthesized a molecule that is 5- to 6-fold better at inhibiting L- andP-selectin than sialyl Lewisx-OMe, By contrast to unbranched structures,substitution of a sulfate ester group for a sialic acid residue in such amolecule resulted in a considerable loss of inhibition ability. Thus, thecombination of a sialic acid residue on the primary (beta1-3) arm, and amodified Lexunit on the branched (beta1-6) arm on an O-linked Core 2structure generated a monovalent synthetic oliogosaccharide inhibitorsuperior to SLexfor both L- and P-selectin.