BIOCHEMISTRY OF SPHINGOLIPIDS .19. STUDIES ON AN EPIMERIZATION PHENOMENON IN OLIGOSACCHARIDE OF PHYTOGLYCOLIPID

Phytoglycolipids from various plant seeds yield on alkaline hydrolysis a mixture of oligosaccharides which on further acid hydrolysis give a common trisaccharide, glucosamidoglucuronidoinositol. In a more detailed study of the trisaccharide fraction from com a relatively water-insoluble material was isolated amounting to 15% of the total. This material has now been identified as glucosamidoiduronidoinositol. In a study of the possible origin of the insoluble trisaccharide it was discovered that glucosamidoglucuronidoinositol and glucuronidoinositol are partially epimerized to the corresponding iduronido derivatives in yields of 15 and 27%, respectively, by treatment with hot Ba(OH)2solution. These findings are in accord with the facile 50% epimerization of unsubstituted glucuronic acid to iduronic acid. Phytoglycolipid (tri- and tetrasaccharide mixture) was esterified and reduced thus converting the hexuronic acid moiety to hexose. Hydrolysis of the reduced material yielded glucose but no idosan. Nitrous acid degradation of the tri- and tetrasaccharide mixture (obtained by alkaline hydrolysis) gave glucosylinositol but no idosylinositol was obtained. Therefore it can be concluded that iduronic acid is not present in phytoglycolipids but is an artifact produced by the alkaline treatment used in hydrolysis of the glycolipid. The facile eperimization of glucuronido derivatives under alkaline conditions is a matter of concern in dealing with various glucuronic acid containing polymers. © 1969, American Chemical Society. All rights reserved.