Different reaction routes found in acid-catalyzed glycosylation of endo- and exo-glycals: competition between Ferrier rearrangement and protonation

Synthesis of C,N-Glycosides via Brønsted Acid-Catalyzed Azidation of exo-Glycals

The reaction of exo-glycals with azidotrimethylsilane in the presence of a Brønsted acid leads to the generation of the corresponding C,N-glycosyl azides. The majority of these glycosylation reactions proceed at room temperature with short reaction times. In addition, the targeted products were obtained in high yields with exclusive diastereoselectivity to the α-anomer in pyranose-based derivatives. Carbohydrate units based on mannose, galactose, arabinose, and ribose were also shown to proceed in high yields.

Efficient carbon-Ferrier rearrangement on glycals mediated by ceric ammonium nitrate: Application to the synthesis of 2-deoxy-2-amino-C-glycoside

A carbon-Ferrier rearrangement on glycals has been performed by using ceric ammonium nitrate to obtain products in moderate to good yields with high selectivity. The versatility of this method has been demonstrated by applying it to differently protected glycals and by employing several nucleophiles. The obtained C-allyl glycoside has been utilized for the synthesis of a orthogonally protected 2-amino-2-deoxy-C-glycoside.

Synthesis and anti-inflammatory activity of N-phthalimidomethyl 2,3-dideoxy- and 2,3-unsaturated glycosides

3,4,6-Tri-O-acetyl-D-galactal, 3,4,6-tri-O-acetyl-D-glucal and 3,6,2',3',4'6'-hexa-O-acetyl-D-lactal were reacted with N-hydroxymethylphthalimide and boron trifluoride etherate to produce the corresponding phthalimidomethyl unsaturated glycosides via Ferrier rearrangement. When the galactal derivative was used, a non-Ferrier rearrangement product was also isolated as a minor product under classical Ferrier conditions. Phthalimidomethyl deoxy glycosides were readily prepared by hydrogenation of the unsaturated glycosides. Following deacetylation, the anti-inflammatory activities of these compounds were tested on mice and three were found to possess potent activity compared to hydrocortisone sodium succinate (HSS).

Inter- and intramolecular glycosylation of exo-glycals promoted by metallic Lewis acids

exo-Glycosyl carbonates were employed for inter- and intramolecular glycosylation reactions. A number of metallic Lewis Acids and solvents were examined to enhance the reactivity. The optimum conditions were found to be the use of AlCl3 in 1-nitropropane. The method was demonstrated to be useful for the intermolecular glycosyl transfer of several nucleophiles, including simple alcohols, sugars, and amino acid derivatives; however, intramolecular glycosylations were not successful.