Conformational differences between O- and C-glycosides: the alpha-O-man-(1-->1)-beta-Gal/alpha-C-Man-(1-->1)-beta-Gal case--a decisive demonstration of the importance of the exo-anomeric effect on the conformation of glycosides

The conformational behavior of alpha-O-Man-(1-->1)-beta-Gal (1) and its C-analogue (2) has been studied using J/NOE NMR data, molecular mechanics, molecular dynamics, and ab initio calculations. The population distribution around the glycosidic linkages of 1 and 2 is rather different, especially for the alpha-Man linkage. A lower limit for the exo-anomeric effect in water has been experimentally determined.     

Synthesis of the non-classical acetogenin mucocin: a modular approach based on olefinic coupling reactions

A three component modular synthesis of the potent antitumor agent mucocin, based on olefinic coupling reactions, is described. A cross-metathesis on tetrahydropyran and tetrahydrofuran alkene components was used to assemble a stereochemically complex, non-adjacently-linked bicyclic ether. The latter was elaborated to a sulfone and partnered with a butenolide aldehyde component in a Julia-Kocienski olefination to provide the mucocin framework, which was converted to the natural product after hydrogenation and alcohol deprotection.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

An iodoetherification-dehydroiodination strategy for the synthesis of complex spiroketals from dihydroxyalkene precursors

Dihydroxyalkenes or their monoprotected alcohol derivatives are transformed to 5,5- and 5,6-spiroketals through a sequence involving an initial iodocyclization, followed by a silver triflate mediated spiroketalization step on the derived hydroxy-iodoether.     

Synthesis of beta-C-galacto-pyranosides with fluorine on the pseudoanomeric substituent

[reaction: see text] beta-C-galacto-Pyranosides with CHF and CF2 substitutes for the glycosidic oxygen were prepared through a four-step sequence starting from a central 1-thio-1,2-O-isopropylidene acetal alcohol and different alpha-fluoro- and alpha,alpha-difluoro acids. The key step in the synthesis is the oxocarbenium cyclization of an intermediate enol ether-thioacetal to a C1-substituted glycal.     

A convergent strategy for the synthesis of beta-carba-galacto-disaccharides

[reaction in text] A convergent strategy for the synthesis of beta-carba-galacto-disaccharides is illustrated by the preparation of 1 and 4, from a central "glycone" component 22, and the corresponding "aglycone" segments, monosaccharide alcohols, 23a or 23b. The key step is the formation of the carbasugar ring via an oxocarbenium ion-enol ether cyclization.     

Highly functionalized trans-2,5-disubstituted tetrahydrofurans from ribofuranoside templates: precursors to linked polycyclic ethers

Iodoetherification of C5 allylated ribo-furanosides leads to trans-2,5-disubstituted tetrahydrofurans with high selectivity. The application of this reaction to the synthesis of complex polycyclic ethers is illustrated in the preparation of a truncated, tricyclic analog of monensin A.     

Allylated monosaccharides as precursors in triple reductive amination strategies: synthesis of castanospermine and swainsonine

The feasibility of the triple-reductive amination reaction for the synthesis of complex indolizidine frameworks is illustrated by application to the potent glycosidase inhibitors castanospermine and swainsonine. The target compounds were obtained from known carbohydrate precursors in yields of 23 and 14%, over nine and 13 steps, respectively. The iodoetherification reaction of allylated monosaccharides was shown to be a practical reaction for the synthesis of the tricarbonyl precursors for the key triple reductive amination reactions.