Selective radical synthesis of β- C -disaccharides

Synthesis of monoglycosides, bisglycosides and open-chain ketoacetals from sugar derived exocyclic enol ethers

Pent-4-enofuranoside derivatives have been converted to glycosides and open-chain ketoacetals on treatment with various alcohols under acidic conditions.

2-Methylenetetrahydropyrans: efficient partners in the carbonyl ene reaction

The carbonyl ene reaction of 2-methylenetetrahydropyrans provides a rapid, high yielding route for the preparation of β-hydroxydihydropyrans under mild conditions. This process provides a new entry for the synthesis of 2-substituted tetrahydropyrans and for the direct introduction of oxygen heterocycles into molecular frameworks.

Zeolites and other silicon-based promoters in carbohydrate chemistry

Silicon-based materials, namely zeolites, clays, and silica gel have been widely used in organic synthesis, allowing mild reaction conditions and environmentally friendly methodologies. These heterogeneous catalysts are easy to handle, possess nontoxic and noncorrosive character and offer the possibility of recovery and reuse, thus contributing to clean and sustainable organic transformations. Moreover, they present shape-selective properties and provide stereo- and regiocontrol in chemical reactions. Herein, we survey the most significant applications of silicon-based materials as catalysts in carbohydrate chemistry, to mediate important transformations such as glycosylation, sugar protection and deprotection, and hydrolysis and dehydration. Emphasis is placed on their promising synthetic potential in comparison with conventional catalysts.

New reactions of 2-methylenetetrahydropyrans. A three component coupling protocol for the synthesis of tetrahydropyranyl ketides

Three component coupling of a 2-methylenetetrahydropyran, an activated aldehyde or ketone and a secondary nucleophile provides an efficient preparation of tetrahydropyranyl ketides, a unit common to many complex natural products.

Conformational behaviour of glycomimetics: NMR and molecular modelling studies of the C-glycoside analogue of the disaccharide methyl β-d-galactopyranosyl-(1→3)-β-d-glucopyranoside

The conformational behaviour of the C-glycoside beta-C-Gal-(1-->3)-beta-Glc-OMe (1) has been studied using a combination of molecular mechanics and NMR spectroscopy (proton-proton coupling constants and nuclear Overhauser effects). It is shown that the C-disaccharide populates two distinctive conformational families in solution, the normal syn-psi conformation, which is the predominating conformation of parent O-glycoside 2, and the anti-psi conformation, which has not been detected for the O-disaccharide.

The use of levoglucosenone and isolevoglucosenone as templates for the construction of C-linked disaccharides

Because of their functionalities (enone, ketone, and acetal) and their bicyclic structure (steric factors), levoglucosenone (1,6-anhydro-3,4-dideoxy-beta-D-glycero-hex-3-enopyran-2-ulose) and isolevoglucosenone (1,6-anhydro-2,3-dideoxy-beta-D-glycero-hex-3-enopyran-4-ulose) are useful templates for the convergent and combinatorial synthesis of (1-->2), (1-->3), and (1-->4)-linked C-disaccharides in reactions combining them with sugar-derived carbaldehydes. Synthetic methods relying on conjugate nucleophilic additions of these enones, their combination with aluminum reagents and aldehydes (Baylis-Hillman reaction) and modified Takai-Hiyama-Nozaki-Kishi couplings of enol triflates derived from them with sugar-derived aldehydes are reviewed. Highly stereoselective methods have thus been developed. These allow the generation of disaccharide mimetics with a high molecular diversity.

Convenient approach to higher carbon sugars. First synthesis of the free C12-sugar: D-erythro-L-manno-D-manno-dodecose

The model synthesis of a C12-aldose was initiated from the easily available dimethyl(benzyl 2,3,4-tri-O-benzyl-alpha-D-manno-heptopyranos-6-ulos-7-yl)phosphonate and 2,3:4,5-di-O-isopropylidene-D-arabinose.