39 Synthetic Studies on Sialic Acid Derivatives and Their Stereochmistry
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The N-acetylneuraminic acid (NANA) having the widest biological disribution related sialic acid is α-glycoside linkage to glycoprotein and glycolipid of neuronal and other cell menbranes. We obtaned appreciable amounts of NANA that can be isolated under mild aqueous hydrolytic conditions from edible birds'nest in high yield and without contamination of another acylneuraminic acid by utilizing a modified procedure of Czarniecki and Thornton. CD spectra of NANA and its derivatives show two bands. The main band, centered below 200nm, is attributed to the acetamido groug. Weak band between 225-240nm arise from the n-π^*trasition of the carboxy chromophore, α-glycosides of NANA show a negative band, while β-glycosides give to a positive band. The conformation of NANA and its derivatives were established from the observed Cotton effect of the carboxy chromophore by application of the planar rule. NANA derivatives were prepared by the condensation of 2-chloro-4,7,8,9-penta-O-acetylneuraminic acid methyl ester (9) with 2,3-isopropylidene-D-ribonolactone, 1,2,3,4,-tetra-O-acetyl-β-D-glucopyranose, 2',3'-isopropylideneuridine, 5-fluoro-2',3'-isopropylidine, and Z-serine metyl ester respectively, according to the Koning-Korr technique.
