SYNTHESIS OF FLUORESCENT 4-METHYL-7-THIOCOUMARYL S-GLYCOSIDES OF SIALIC-ACID

Condensation of 4-methyl-7-thiocoumarin sodium salt with methyl 5-N-acetyl-4,7,8,9-tetra-O-acetyl-2-chloro-2,3,5-trideoxy-D-glycero-D-galacto-2-nonulopyranosonate (2), methyl 5-N-(O-acetylglycolyl)-4,7,8,9-tetra-O-acetyl-2-chloro-2,3,6-trideoxy-D-glycero-D-galacto-2-nonulopyranosonate (11), and methyl 4,5,7,8,9-penta-O-acetyl-2-chloro-2,3-dideoxy-D-glycero-D-galacto-2-nonylopyranosonate (14) under Williamson reaction conditions gave the corresponding alpha-glycosides in good yields. Deprotection of these alpha-glycosides gave three new fluorogenic substrates, the 4-methylcoumarin-7-yl S-glycosides of N-acetylneuraminic acid, N-glycolylneuraminic acid, and 3-deoxy-D-glucose-D-galacto-2-nonulopyranosonic acid (KDN). Furthermore, we have developed a facile method for preparation of benzyl 5-amino-3,5-dideoxy-alpha-D-glycero-D-galacto-2-nonulopyranosidonic acid (7), a key intermediate for the synthesis of N-glycolylneuraminic acid.