Sialic acids are involved in numerous biological processes, including cell-cell recognition, cell differentiation, and viral infection'. They are principally found in plasma membranes of animal cells at the non-reducing terminus of the carbohydrate moieties of glycoproteins and glycolipids, where they appear to function as receptors for the biomolecules which initiate the aforementioned processe9. Of the thirty or so naturally occurring siaiic acids, the most prevalent in animal cells is N-acetylneuraminic acid3 (NeuAc, l), a nine-carbon amino sugar acetylated at the 5 position. The solution structure of 1 and other sialic acids have been extensively studied. However, to comprehend fully the biological function of these molecules we must also determine their conformational properties as they exist in nature, that is at water-membrane interfaces. Deuterium n.m.r. has been of tremendous value in the study of conformational properties of molecules at membrane surfaces4. Applications of deuterium n.m.r. include the use of simple deuterium-labeled carbohydrates and glycolipids in media that mimic a biological membrane environments. Because of the low natural abundance of deuterium, enrichment is a prerequisite for application of these methods. The development of a mild and efficient deuteration procedure for sialic acids, along the lines of those for other carbohydrates, is therefore important. Here we extend the applicability of a Raney nickel-catalyzed hydrogen-deuterium exchange method to include the carboxylatecontaining sialic acids, a class of compounds not heretofore been shown to undergo exchange by this method.
Friebolin et al6 have reported the deuteration of sialic acid at C-3 upon treatment with NaOH in D,O, and Julina et a1.7 have reported the synthesis of 6deuteriosialic acid. Both of these methods have their merits. However, neither of them are suitable for the direct deuteration of sialic acid-containing glycosides and hence are not useful for labeling natural products. Also, conformational analysis