Highly stereoselective synthesis of imino-C-di- and trisaccharides as hydrolytically stable glycomimetics

A new straightforward route to glycomimetics containing a piperidine unit is reported. The key step of the methodology is the intramolecular 1,3-dipolar cycloaddition of easily accessible glycosyl alkenyl nitrones. The reaction takes place in most cases with a complete selectivity in favor of the exo–exo adduct, which facilitates the synthesis of all-cis piperidines bearing the glycosyl units. The direct transformation of adducts into the final imino-C-di and trisaccharide analogues is achieved in one step using simple reagents. Inhibition properties against two glycosidases have been tested but no positive results have been found.     

Generalized anomeric effect in action: synthesis and evaluation of stable reducing indolizidine glycomimetics as glycosidase inhibitors

A series of aminoketalic castanospermine analogues incorporating a stereoelectronically anchored axial hydroxy group at the pseudoanomeric stereocenter (C-5) have been synthesized to satisfy the need for glucosidase inhibitors that are highly selective for alpha-glucosidases. The polyhydroxylated bicyclic system was built from readily available hexofuranose derivatives through a synthetic scheme that involved (i) the construction of a five-membered cyclic (thio)carbamate or (thio)urea moiety at the nonreducing end and (ii) the intramolecular nucleophilic addition of the heterocyclic thiocarbamic nitrogen atom to the masked aldehyde group of the monosaccharide. A biological screening of the resulting reducing 2-oxa- and 2-azaindolizidines against several glycosidase enzymes is reported.     

Stereoselective synthesis of conformationally constrained cyclohexanediols: a set of molecular scaffolds for the synthesis of glycomimetics

The practical, stereoselective synthesis of the three diastereoisomeric 1,2-trans-dicarboxy-4,5-cyclohexanediols 1-3 (DCCHDs) is described, starting from a common precursor, easily available in both enantiomeric forms. The regioselective derivatization of all functional groups of 1 is also reported. The three DCCHDs are locked in a single chair conformation and thus can be used to mimic vicinally disubstituted monosaccharides of any relative configuration.     

Synthesis of sulfonamide-bridged glycomimetics

A flexible and short synthesis of sulfonamide-bridged di-, tri-, tetra-, and octasaccharide glycomimetics was accomplished by reaction of glycosyl thioacetates with amino sugar substrates. The chemistry to incorporate the sulfonamide linker in place of a native O-glycosidic bond was broadly scoped, allowing access to head-to-head (1?1) and head-to-tail (1→2), (1→3), (1→4), and (1→6) sulfonamide-bridged glycomimetics. The synthesis proceeds with retention of configuration at the anomeric center and is compatible with variable stereochemical arrangements and with acid- and base-labile protecting groups.     

An approach to the synthesis of isolongifolene

An efficient synthesis of 7, 7-dimethyltricyclo [6.2.1.0^1,6] undeca-2, 5-dien-4-one 2, an advanced intermediate for the synthesis of the tricyclic sesquiterpene isolongifolene 1, has been carried out utilising Ar₁-5 participation reaction as the key step.     

An approach to the synthesis of stenine

A type 2 N-acylnitroso intramolecular Diels-Alder reaction followed by reductive N-O bond cleavage formed the B and C rings of the Stemona alkaloid stenine. Further elaboration provided the functionalized tricyclic core.     

Novel approach to the synthesis of istaroxime

Istaroxime 1, a novel cardiotonic agent with high efficiency and low toxicity was synthesized from dehydroepiandrosterone 2 using a novel approach that included epoxidation, ring-opening, substitution, and oximation. The new protocol without gas protection was milder than the reported approaches. The overall yield of the method was 24.1%.     

An approach to the synthesis of the phomoidrides

The phomoidrides are a structurally fascinating family of natural products which possess moderate inhibitory activity against Ras farnesyl transferase and squalene synthase. Since their discovery they have inspired a great deal of attention from synthetic chemists. Our own work, culminating in an efficient synthesis of the fully elaborated tetracyclic core of phomoidrides B and D, is described herein. The synthesis relies on a late stage tandem reaction involving a novel carbonylation reaction that delivers the strained bicyclic pseudoester system, which strain in turn drives a highly efficient silyloxy-Cope rearrangement that delivers the tetracyclic core of phomoidrides B and D. Several examples of this powerful tandem reaction are presented that document its tolerance of significant structural variation. The application of this methodology to the synthesis of a phomoidride D precursor lacking only the maleic anhydride is described, and the prospects for the completion of a total synthesis are discussed.     

A Pauson-Khand approach to the synthesis of ingenol

[reaction: see text] Pauson-Khand cyclization of dioxanone photoadduct 21 leads to the formation of a single product in good yield. However, retro-aldol fragmentation of the pentacyclic cyclopentenone 22 leads to the formation of 23, with cis C-8/C-10 intrabridgehead stereochemistry, unlike the target compound ingenol 1, which possesses C-8/C-10 trans intrabridgehead stereochemistry.     

New approach to the synthesis of 2-carbamoylbenzothiazoles

The reactions of substituted anilines with chloroacetamide and sulfur in the presence of triethylamine afforded monothiooxamides. When treated with K₃Fe(CN)₆, the latter underwent cyclization to form 2-carbamoylbenzothiazoles. The reactions were accompanied by the formation of the corresponding thiooxanilic acids, which also underwent cyclization to form benzothiazole-2-carboxylic acids.     

An approach to the synthesis of pseudomonic acids

The synthesis of the cis-fused γ-lactone 2,7-dioxabicyclo-[4,3,0]non-4-en-8-one (3) by two routes is reported. Its stereoselective conversion to a key intermediate for pseudomonic acid synthesis is described.     

New approach to the synthesis of trifluoromethylvinyl sulfides

Nucleophilic substitution reaction of halogen atom in β-chloro-and β-bromo-β-trifluoromethylstyrenes by thiolates was studied. Stereo-and regioselectivity of the reaction with respect to the electronic and sterical properties of substituents in the aromatic ring of starting styrenes was investigated. Regioisomer with geminal trifluoromethyl and alkyl-or arylthio groups was found to be formed predominantly or exclusively. The reaction proceeds stereoselectively in nearly quantitative yields. On this basis, a new convenient stereoselective method for the synthesis of trifluoromethylvinyl sulfides was elaborated. Dedicated to Academician V. A. Tartakovsky in honor of his 75th anniversary. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1469–1475, August, 2007.     

New approach to the synthesis of deoxynucleoside-phosphoramidite derivatives

A new method for the synthesis of deoxyribonucleoside-phosphoramidite via an intermediate, 5′-0-dimethoxytritylthymidine-3′-0-diisopropylamino-phosphorochloridite, is reported. By using this method, several deoxyribonucleoside phosphoramidite derivatives with different protecting groups at phosphorus including PS and PN bond besides PO bond were synthesized.