Synthetic Studies on Sialoglycoconjugates. 4: Synthesis of 5-Acetamido-3,5-Dideoxy-d-Galacto-2-Octulosonic Acid Derivatives and Analogs

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Abstract
5-Acetamido-3.5-dideoxy-D-galacto-2-octulosonic acid derivatives and the α-2-thioanalog (14) were synthesized. Methyl [2-(trimethylsilyl)ethyl 5-acetamido-3,5-dideoxy-α-D-galacto-2-octulopyranosid]onate (8), prepared from methyl [2-(trimethylsilyl)ethyl 5-acetamido-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosid]onate (1) via 8,9-O-isopropylidenation, O-acetylation, O-deisopropylidenation, metaperiodate oxidation, and sodium borohydride reduction, was converted, by selective bromination, into the 8-bromo derivatives (9). Compound 12, derived from 8 via O-acetylation and boron trifluoride etherate treatment, was converted to the 2-chloro derivative (13), which underwent displacement with potassium thioacetate, to yield methyl 5-acetamido-4,7,8-tri-O-acetyl-2-S-acetyl-2-thio-α-D-galacto-2-octulopyranosonate (14).