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 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 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 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.     

The approach to the synthesis of novel amino-C-glycosides

Stereoselective 1,3-dipolar cycloadditions of exo-glycals 1 to nitrones 2, 5 and 8 were investigated under the catalysis of Lewis acid or in a refluxing benzene or toluene solution, and afforded the corresponding cycloadducts of ketosyl spiro-isoxazolidines. The reductive cleavage of the N-O bond in the isoxazolidine ring and debenzylation by the catalytic hydrogenation [Pd(OH)₂/C] were approached using the glucose-type cycloadducts 6b and 6e to alkyl-C-glycoside derivatives 12, providing a new access to a novel alkyl-C-glycoside containing an amino group on the side alkyl chain.     

Thiomidoyl approach to the synthesis of α-sialosides

Novel sialosyl donors, S-benzoxazolyl (SBox) and S-thiazolyl (STaz) sialosides, have been synthesized and applied to the stereoselective synthesis of α-sialosides. It was also demonstrated that it is possible to selectively activate SBox sialyl donor over ethyl thioglycoside, allowing the direct synthesis of disaccharide donors that could be used in subsequent glycosylations without further manipulations.     

An asymmetric approach to the synthesis of trans-dihydrindandione

A three-step asymmetric approach to the synthesis of (3aS,7aS)-3a,4-dihydro-7a-methyl-1,5(7aH)-indandione in 60% enantiomeric excess is described.     

A new approach to the synthesis of telluranthene

A series of new methods of synthesizing telluranthrene are proposed, based on the use of poly(o-phenylene)ditelluride and its precursors. The best yields of telluranthene are obtained by the reactions of the disodium salt of o-ditellurolobenzene with o-diiodobenzene (50–62%) and of poly(o-phenylene)ditelluride with butyllithium.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1424–1427, October, 1991.