SYNTHESIS OF A NEW SUBSTRATE FOR EXO-GALACTOFURANOSIDASES, 2-HYDROXY-4-NITROBENZENE 1-YL β-D-GALACTOFURANOSIDE

摘要

1,2,3,5,6-Penta-O-acetyl β-D-galactofuranose was synthesized by pcracetylation of D-galactose in boiling pyridine followed by fractional crystallization. The first crops of crystals were 1,2,3,5,6-penta-O-acetyl β-D-galactopyranose, then mother liquor was concentrated and seeded with some crystals of 1,2,3,5,6-penta-O-acctyl β-D-galactofuranose. The crystalline mass obtained was recrystallized from ethanol. Optical rotation was a constant guide along the preparation of the furanosic precursor, due to the fact that only pentaacetate-B-furanose is levorotatory of the four D-galactose pentaacetate isomers. Bromination of penta-O-acetyl β-D-galactofuranose with hydrogen bromide produced the glycosylation donor, 1-bromo 1-deoxy 2,3,5,6-tetra-O-acetyl α-D-galactofuranose. The aglycon, 1,2-dihydroxy 4-nitrobcnzene, was prepared by acidic hydrolysis of 2-hydroxy 5-nitrophenyl sulfatc, synthesized at its turn by reacting 4-nitrophenol and potassium persulfate in a strongly alkaline solution conferred by potassium hydroxide. All intermediates and products were structurally characterized by chemical and physical methods.