SYNTHESIS, STRUCTURE, AND CONFORMATION OF THE DILACTONE DERIVATIVE OF GD1B GANGLIOSIDE

Treatment of GD1b, β-Gal-(1→3)-β-GalNAc-(1→4)-[α-Neu5Ac-(2→8 )-α-Neu5Ac-(2→3)]-β-Gal-(1→4)-β-Glc-(1→1) -Cer, with dicyclohexylcarbodi-imide in anhydrous methyl sulfoxide affords 95-98% of GD1b-dilactone. The carboxyl groups of the two sialic acid units are involved in ester linkages, as proved by ammoniolysis and reduction which gave derivatives containing the amide of sialic acid and N-acetylneuraminulose, respectively. 1H-N.m.r. spectroscopy showed that the lactone rings involved position 9 of the inner sialic acid and position 2 of the inner galactose and that the disialosyl chain is extended toward the -β-Gal-(1→4)-β-Glc- portion of the ganglioside moiety.