SYNTHESIS OF A NEW NANOMOLAR SACCHARIDE INHIBITOR OF LYMPHOCYTE ADHESION - DIFFERENT POLYLACTOSAMINE BACKBONES PRESENT MULTIPLE SIALYL-LEWIS-X DETERMINANTS TO L-SELECTIN IN HIGH-AFFINITY MODE

Lymphocyte infiltration is a hallmark of acute rejections in solid org an transplants, such as cardiac allograft, We have previously shown th at lymphocyte extravasation to cardiac grafts undergoing rejection is largely due to interactions between lymphocyte L-selectin and its sial yl Lewis x (sLex) decorated ligands, Our previous work demonstrated fu rther that an enzymaticaIly synthetized tetravalent sLex glycan of a b ranched polylactosamine backbone is a highly efficient inhibitor of L- selectin-dependent lymphocyte adhesion to graft endothelium, To improv e the availability of multivalent sLex glycans for anti-inflammatory i ndications, we now report enzymatic synthesis of another tetravalent s Lex glycan that can be potentially produced on a large scale, and show that even the new saccharide is a nanomolar inhibitor of L-selectin-d ependent lymphocyte adhesion, The novel antagonist is sLex beta 1-3'(s Lex beta 1-6')LacNAc beta 1-3'(sLex beta 1-6' )LacNAc beta 1-3' (sLex beta 1-6')LacNAc (8) (where LacNAc is the disaccharide Gal beta 1-4Glc NAc and sLex is the tetrasaccharide Neu5A-c alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc). Its five-step synthesis was started from the octame ric polylactosamine LacNAc beta 1-3'(GlcNAc beta 1-6')LacNAc beta 1-3' (GlcNAc beta 1-6')La (3), which in turn is accessible in one step from the hexasaccharide LacNAc beta 1-3'LacNAc beta 1-3'LacNAc. Importantl y, the hexasaccharide primer has been synthesized chemically (Alais an d Veyrieres, Tetrahedron Lett,, 24, 5223, 1983), Hence, our data outli ne a route to glycan 8, consisting of a combination of chemical and en zymatic methods of oligosaccharide synthesis, In addition, our data sh ow that polylactosamine backbones are able to present multiple sialyl Lewis x determinants to L-selectin in high-affinity mode, without a re quirement for uniqueness in the backbone structure.