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-nonulopyranosonate (14) under Williamson reaction conditions gave the corresponding α-glycosides in good yields. Deprotection of these α-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-α-D-glycero-D-galacto-2-nonulopyranosidonic acid (7), a key intermediate for the synthesis of N-glycolylneuraminic acid.