Characterization and structure of a sialic acid-containing hexasaccharide isolated from human pregnancy urine.

A hexasaccharide containing sialic acid has been isolated from the urine of pregnant women. It contains D-glucose, N-acetyl-D-glucosamine, and sialic acid in the proportions of 2:1:1:2. Its structure, established by methylation analysis, enzymic digestion, and potassium borohydride reduction, is that of lacto-N-tetraose with one of the residues of sialic acid linked alpha-(2 leads to 3) to the terminal nonreducing residue of D-galactose, and the other sialic acid residue linked alpha-(2 leads to 6) to the N-acetyl-D-glucosamine residue. This hexasaccharide is related to human pregnancy, as it has not been found in nonpregnant, normal-woman urine and is present in human milk.