Synthesis of a New Substrate for Exo-galactofuranosidases, 4-Nitrocatechol 1-yl α-D-Galactofuranoside

摘要

Glycosylation of 4-nitrocatechol with tetra-O-acetyl a-D-galactofuranosyl bromide, by different methods (Koenigs-Knorr, Helferich, reaction with phenoxide) led to 4’-nitrocatechol 1’-yl f-D-(2,3,5,6-tetra-O-acetyl)galactofuranoside. Glycosylation donor, tetra-O-acetyl a-D-galactofuranosyl bromide, was obtained by bromination of penta-O-acetyl B-D-galactofuranose with hydrogen bromide in glacial acetic acid. B-D-Galactofuranose pentaacetate was synthesized by peracetylation of D-galactose in boiling pyridine followed by separation of the aimed product by fractional crystallization. The crystalline mass obtained was recrystallized from ethanol. Due to the fact that penta-O-acetyl B-D-galactofuranose has levorotary action, optical rotation was a constant guide along the preparation of the furanosic precursor. The aglycon, 4-nitrocatechol, was prepared by acidic hydrolysis of 2-hydroxy 5-nitrophenyl sulfate, synthesized at its turn by reacting 4-nitrophenol and potassium persulfate in a strongly alkaline environment conferred by potassium hydroxide. All intermediates and products were characterized chemically and by physical methods.