Synthesis of d-ribo-C-nucleoside analogues by dehydration of new d-allo-pentitol-1-yl heterocycles

Indium-mediated allylation in carbohydrate synthesis: A short and efficient approach towards higher 2-acetamido-2-deoxy sugars

Higher aminosugars are interesting targets in carbohydrate synthesis since these compounds play important roles in biological systems. However, their availability from natural sources is limited. Thus, in order to investigate their biological function, the development of facile and adaptable routes to this class of compounds is of fundamental importance. Our synthetic route towards these target molecules makes use of readily accessible pentoses and hexoses, which are subjected to indium-mediated two-carbon chain elongation. Subsequent ozonolysis and treatment with base yields α,β-unsaturated aldehydes, which are stereoselectively epoxidized using Jørgenson’s protocol. After Wittig chain elongation the obtained allylic epoxides were regio- and stereoselectively opened with trimethylsilyl azide under palladium catalysis. Finally, a suitable deprotection protocol, starting with acidic acetate cleavage and ozonolysis was established. Peracetylation of the products simplifies purification and subsequent azide reduction followed by final deacetylation using methanolic sodium methoxide furnishes the title compounds.

Acid-catalyzed dehydrative cyclization of 4-(D-galacto -pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole. synthesis and anomeric configuration of D-lyxo-C-nucleoside analogs

Dehydration of 4-(D-galacto-pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole with 20% methanolic sulfuric acid afforded the anomeric pairs of nucleosides, 4-(alpha-D-lyxopyranosyl)-2-phenyl-2H-1,2,3-triazole (major component) and its beta-anomer, as well as 4-(alpha-D-lyxofuranosyl)-2H-1,2,3-triazole and its beta-anomer. The four anomeric C-nucleosides were separated by chromatography, and their structure and anomeric configuration were determined by periodate oxidation, acylation, and NMR spectroscopy as well as mass spectrometry. The anomeric assignment from optical rotation was not in agreement with final structure assignment and represented a violation of the Hudson isorotation rules. NOE studies and X-ray diffraction measurements confirmed the anomeric configuration.