Koenigs-Knorr Synthesis of Natural and Potential Metabolites of Cholesteryl Hexosides

Abstract

The following glycosides of cholesterol have been synthesized: a-D-galactofuranoside, �-D-glucopyranoside, bis-sulfo-3,6-b-D-glucopyranoside. 1-a-Bromides of protected sugars were used as glycosylation donors: tetra-O-benzoyl-D-galactofuranosyl and tetra-O-acetyl-D-glucopyranosyl. Peracylated sugars, i. e., precursors of sugar bromides, were synthesized in conditions that preferentially facilitated the envisaged ring: room temperature for pyranosic ring, high temperature for furanosic one. Constantly, cadmium carbonate was used as promotor. As a general scheme of work, glycosylation mixture was submitted to Zemplen saponification and the obtained glycolipids have been separated by characteristic methods. The glucoside of cholesterol was sulfated with chlorosulfonic acid in pyridine. Neutral or acidic glycolipids were characterized per se by chromatographic and chemical means as well as by IR spectroscopy. Sulfatide and galactocerebroside of rat brain and ganglioside GM4 of rooster testis were used as reference compounds. Alternatively, the synthesized glycosides were peracetylated and their 1H and 13C NMR spectra registered. New NMR spectroscopic data are presented for cholesteryl-a-D-galactofuranoside and -bis-sulfo-6-b-D-glucopyranoside.