Isolation and Identification of Two Sialic Acids from the Jelly Coat of Sea Urchin Eggs

Two sialic acids were isolated from the jelly coat of the eggs of the sea urchin Pseudocentrotus depressus. Both were subjected to chemical assay, thin layer chromatography, infrared absorption study, and enzymatic treatment. The results indicate that one of the sialic acids is identical with N-glycolylneuraminic acid. The other sialic acid is a completely new type and was deduced to be N-acetoglycolyl-4-methyl-4,9-dideoxy neuraminic acid from the following data. (a) Elemental analyses inferred an empirical formula of C14H23NO9. (b) From each mole of the isolated sialic acid, 2.14 moles of C-methyl, 1.14 moles of glycolyl, and 0.93 mole of acetyl group (0.87 mole of O-acetyl group) were derived. (c) Uptake of periodate was observed to be 2 moles per mole of the sialic acid, whereas 3 moles were taken up per mole of N-glycolylneuraminic acid under the same conditions. Oxidation of 1 mole of the sialic acid liberated 0.88 mole of acetaldehyde. (d) Its reaction with thiobarbituric acid yielded only 39.6% of the color obtained by the direct Ehrlich procedure. (e) The sialic acid was not cleaved by N-acetylneuraminic acid aldolase. (f) Infrared spectrum studies of the sialic acid indicated the presence of methyl and O-acetyl ester groups.