Improved enzymatic synthesis of a highly potent oligosaccharide antagonist of L-selectin

The polylactosamine sLex beta1-3'(sLex beta1-6')LacNAc beta1-3'(sLex beta1-6')LacNAc beta1-3'(sLex beta1-6')LacNAc (7) (where sLex is Neu5Ac alpha2-3Gal beta1-4(Fuc alpha1-3)GlcNAc and LacNAc is Gal beta1-4GlcNAc) is a nanomolar L-selectin antagonist and therefore a potential anti-inflammatory agent (Renkonen et al. (1997) Glycobiology, 7, 453). Here we describe an improved synthesis of 7. The octasaccharide LacNAc beta1-3'LacNAc beta1-3'LacNAc beta1-3'LacNAc (4) was converted into the triply branched undecasaccharide LacNAc beta1-3'(GlcNAc beta1-6')LacNAc beta1-3'(GlcNAc beta1-6')LacNAc beta1-3'(GlcNAc beta1-6')LacNAc (5) by incubation with UDP-GlcNAc and the midchain beta1,6-GlcNAc transferase activity of rat serum. Glycan 5 was enzymatically beta1,4-galactosylated to LacNAc beta1-3'(LacNAc beta1-6')LacNAc beta1-3'(LacNAc beta1-6')LacNAc beta1-3'(LacNAc beta1-6')LacNAc (6). Combined with the enzymatic conversion of 6 to 7 (Renkonen et al., loc. cit.) and the available chemical synthesis of 4, our data improve the availability of 7 for full assessment of its anti-inflammatory properties.