Synthesis of N-formyl- and N-succinyl-D-neuraminic acid on the specificity of neuraminidase.

The sialic acids are important constituents of numerous glycoproteins, glycolipids, and oligosaccharides. Little is known about their functional signifp cance for the biological effect of these complex substances. In many instances removal of sialic acid is accompanied by a loss of biological activity [I] . So far only N-acetylneuraminic acid (lactaminic acid) and N-glykolylneuraminic acid were found in nature together with 0-acetylated derivatives. The terminal sialyl moiety seems always to be bound to the next carbohydrate unit by an ar-ketosidic bond. Ample evidence has now been accumulated that only this type of linkage is split by the various neuraminidase enzymes. We were interested in obtaining a sialic acid with two anionic sites in the molecule and chose the succinyl group as N-substituent. Furthermore it seemed worthwhile to prepare a sialic acid with a Cl residue at the amino group. In this communication we describe the synthesis of N-formyl and N-succinyl-D-neuraminic acid and of their corresponding benzyl &ketosides. In addition we wish to report the result of the interaction between Vibrio cholerae neuraminidase and the above mentioned ketosides. It was found that the benzyl-ketoside of N-succinylneuraminic acid is not split at all by the enzyme. This result could be expected, since the N-butyryl group also abolishes the property to serve as substrate PIOn the other hand the enzyme cleaves the corresponding ketoside of N-formylneuraminic acid. However, compared to the naturally occurring 3-O-N-