Search Results (6)

Various substituted D-hexopypyranosides units with nitrogen-containing functionalities are present in many important natural compounds and pharmaceutical substances. Since their complex structural diversity contributes to a broad spectrum of biological functions and activities, these derivatives are frequently studied. This review covers syntheses of D-hexopyranosides with vicinal nitrogen-containing functionalities since the 1960s, when the first articles emerged. The syntheses are arranged according to the positions of substitutions, to form a relative configuration of vicinal functionalities, and synthetic methodologies. Full article

Large quantities (>3 g) of a new series of alkyl uronates were synthesized in two steps from commercial methyl hexopyranosides. Firstly, several tens of grams of free methyl α-d-glucopyranoside were selectively and quantitatively oxidized into corresponding sodium uronate using 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO)-catalyzed oxidation. Hydrophobic chains of different length were then introduced by acid-mediated esterification with fatty alcohols (ethyl to lauryl alcohol) leading to the desired alkyl glucuronates with moderate to good yields (49%–72%). The methodology was successfully applied to methyl α-d-mannopyranoside and methyl β-d-galactopyranoside. Physicochemical properties, such as critical micelle concentration (CMC), equilibrium surface tension at CMC (γ_cmc), solubility, and Krafft temperature were measured, and the effect of structural modifications on surface active properties and micelle formation was discussed. Full article

In the course of our studies on the regioselective carbon-oxygen bond cleavage of the benzylidene acetal group of hexopyranosides with a reducing agent, we found that a combination of a Lewis acid and a reducing agent triggered a ring-opening reaction of the pyranose ring of methyl α-D-allopyranosides. The formation of an acyclic boronate ester by the attachment of a hydride ion at C-1 indicated that the unexpected endocyclic cleavage of the bond between the anomeric carbon atom and the pyranose ring oxygen atom proceeded via an oxacarbenium ion intermediate produced by the chelation between O5/O6 of the pyranoside and the Lewis acid, followed by nucleophile substitution with a hydride ion at C1. Full article

The kinetics of CO₂ uptake by the cis-[Cr(C₂O₄)(BaraNH₂)(OH₂)₂]⁺ complex cation and the acid hydrolysis of the cis-[Cr(C₂O₄)(BaraNH₂)OCO₂]⁻ complex anion (where BaraNH₂ denotes methyl 3-amino-2,3-dideoxy-b-D-arabino-hexopyranoside) were studied using the stopped-flow technique. The reactions under study were investigated in aqueous solution in the 288–308 K temperature range. In the case of the reaction between CO₂ and cis-[Cr(C₂O₄)(BaraNH₂)(OH₂)₂]⁺ cation variable pH values (6.82–8.91) and the constant ionic strength of solution (H⁺, Na⁺, ClO₄⁻ = 1.0) were used. Carbon dioxide was generated by the reaction between sodium pyruvate and hydrogen peroxide. The acid hydrolysis of cis-[Cr(C₂O₄)(BaraNH₂)OCO₂]⁻ was investigated for varying concentrations of H⁺ ions (0.01–2.7 M). The obtained results enabled the determination of the number of steps of the studied reactions. Based on the kinetic equations, rate constants were determined for each step. Finally, mechanisms for both reactions were proposed and discussed. Based on the obtained results it was concluded that the carboxylation (CO₂ uptake) reactions of cis-[Cr(C₂O₄)(BaraNH₂)(OH₂)₂]⁺ and the decarboxylation (acid hydrolysis) of the cis-[Cr(C₂O₄)(BaraNH₂)OCO₂]⁻ are the opposite of each other. Full article

In an effort to synthesize a key intermediate, for synthesis of a variety of telithromycin derivatives a new by-product has been formed at the third stage of the synthetic scheme. The starting material, Clarithromycin, on treatment with hydrochloric acid and on benzoylation resulted in the formation of (3R,4S,5S,6R,7R,9R,11R,12R,13S,14R)-14-ethyl-4,12,13-trihydroxy-7-methoxy- 3,5,7,9,11,13-hexamethyl-2,10-dioxooxacyclotetradecan-6-yl 3,4,6-trideoxy- 3-(dimethylamino)-2-O-(phenylcarbonyl)-β-D-xylo-hexopyranoside (2). Oxidation of this gave (3R,5R,6R,7R,9R,11R,12R,13S,14R)-14-ethyl-12,13-dihydroxy- 7-methoxy-3,5,7,9,11,13-hexamethyl-2,4,10-trioxooxacyclotetradecan-6-yl 3,4,6-trideoxy-3-(dimethylamino)-2-O-(phenylcarbonyl)-β-D-xylo-hexopyranoside (3), and also an unexpected by-product 4 in equivalent amounts. The O21–H hydroxyl group in 3 was mesylated with dimethyl sulphoxide (DMSO) in pyridine leading to the precursor (3R,5R,6R,7R,9R,11R,12R,13S,14R)-14-ethyl- 12,13-dihydroxy-7-methoxy-3,5,7,9,11,13-hexamethyl-12-(methylsulfinyl)- 2,4,10-trioxooxacyclotetradecan-6-yl 3,4,6-trideoxy-3-(dimethylamino)-2-O- (phenylcarbonyl)-β-D-xylo-hexopyranoside (5), which on further treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in acetone and methylene chloride resulted in the formation of intermediate 6. The by-product 4 and the intermediate 6 were isolated and characterized as (1S,2R,5R,7R,8R,9R)-2- ethyl-9-methoxy-1,5,7,9,11,13-hexamethyl-4,6-dioxo-3,15-dioxabicyclo[10.2.1]- pentadeca-11,13-dien-8-yl 3,4,6-trideoxy-3-(dimethylamino)-2-O-(phenylcarbonyl)- β-D-xylo-hexopyranoside (4) and (3R,5R,6R,7R,9R,11E,13S,14R)-14- ethyl-13-hydroxy-7-methoxy-3,5,7,9,11,13-hexamethyl-2,4,10-trioxooxacyclotetradec- 11-en-6-yl 3,4,6-trideoxy-3-(dimethylamino)-2-O-(phenylcarbonyl)-β-Dxylo- hexopyranoside (6) respectively by 2D NMR and single crystal X-ray diffraction. Full article