SYNTHESIS OF 5-N-THIOACYLATED AND 9-N-THIOACYLATED SIALIC ACIDS

N-Thioacylation of neuraminic acid methyl alpha-glycoside (5) with O-ethyl thioformate (1), methyl dithioacetate (2), and methyl dithiopropionate (3) afforded N-thioformyl, N-thioacetyl, and N-thiopropionyl neuraminic acid derivatives 6a-c in high yield. Cleavage of the glycosides was accomplished either by acid hydrolysis or by sialidase treatment. Alternatively, 5-N-thioacylneuraminic acids were produced from the corresponding N-thioacyl-D-mannosamines 7a-c and pyruvate employing N-acetylneuraminate pyruvate lyase. The sialidase-resistant methyl alpha-thioglycoside of N-thioacetylneuraminic acid (10) was also prepared. N-Acetyl-9-deoxy-9-thioacetamido neuraminic acid (19) was obtained either directly by reaction of N-acetyl-9-amino-9-deoxyneuraminic acid (17) with methyl dithioacetate (2) or via its methyl alpha-glycoside 18. Compound 17 was produced from the methyl a-glycoside of 9-O-tosylated methyl ester 12 via the azide 13. -For the 5-N-thioacyl sialic acids 6a-c and 8a-c as well as for the 9-deoxy-9-thioacetamido derivatives 18 and 19 some biological properties are reported.