Microwave assisted stereospecific synthesis of d-erythro-l-gluco-nonulose

A convenient, highly efficient synthesis of d-erythro-l-gluco-nonulose from a new 2-C-(hydroxymethyl) branched-chain aldose is presented. The nucleophilic addition of the appropriately protected aldose to formaldehyde afforded 2-C-(hydroxymethyl)-d-erythro-l-manno-octose. The branched sugar bearing a CH₂OH group at C-2 provides access to a nine-carbon sugar in a single step through a stereospecific isomerization. The isomerization exploited the catalytic effect of molybdate ions and microwave irradiation. The structure of the product was analyzed by NMR spectra and quantum-chemical DFT calculations. DFT-computed proton–proton coupling constants were found to be comparable with the experimentally obtained coupling constants and agreed with the pyranose form of this branched-chain aldose.     

1-C-Alkyl imino-d-xylitol and -l-arabinitol derivatives obtained via nucleophilic addition to pentose-derived N-tert-butanesulfinyl imines: sugar- versus chiral auxiliary-induced stereoselectivity

The stereoselective synthesis of 1-C-alkyl iminosugars in the d-xylo and l-arabino series as potential drugs for the treatment of lysosomal diseases has been achieved. The key step involves nucleophilic addition to pentodialdofuranose-derived imines generated using enantiopure tert-butanesulfinamide. Depending on the pentofuranose configuration and structure, the stereoselectivity of this reaction was found to be controlled either by the sugar moiety or by the stereogenic sulfur center.     

Anomeric spiroannelated 1,4-diazepine 2,5-diones from furano exo-glycals: towards a new class of spironucleosides

The first synthesis of 1,4-diazepine 2,5-dione peptides containing a β-amino acid in which the β carbon is also the anomeric carbon of a furanoid sugar is described. These new anomeric spirosugars obtained with a stereoselective control in the d-gulo, d-manno, d-allo and d-ribo series can be regarded as the first members of a new class of spironucleosides. In the course of our study, two symmetrical tetrameric cyclopeptides comprising two identical sugar β-amino acid and α-amino acid residues were also isolated, these structures could be of interest as new potential host molecules.     

Short and highly stereoselective total synthesis of d-ribo-configured ureido sugars

An highly stereoselective, flexible and very short synthetic approach to d-ribo-configured ureido monosaccharides of the aldose, aldonic acid and alditol series has been performed starting from the 5-(alditol-1-C-yl)-hydantoin intermediates, obtained via aldol-type addition reaction of hydantoin based building blocks to enantiomerically pure aldehydes. A study to assess the stereoselectivity of this reaction has been undertaken and a very high increase of diastereoselectivity was observed depending on the hydantoin protecting group. The imidazolidinone ring elaboration of 5-(alditol-1-C-yl)-hydantoin intermediates to give ureido sugar derivatives was studied.     

Highly efficient and selective biocatalytic acylation studies on triazolylsugars

Different acid anhydrides (of C₂ to C₇ aliphatic fatty acids and benzoic acid) have been used to study the selective acylation of primary/secondary hydroxyl groups in 2-phenyl-4-(d-threo-1′,2′,3′-trihydroxypropyl)-2H-1,2,3-triazole, 2-phenyl-4-(d-erythro-1′,2′,3′-trihydroxypropyl)-2H-1,2,3-triazole, 2-phenyl-4-(d-arabino-1′,2′,3′,4′-tetrahydroxybutyl)-2H-1,2,3-triazole and 2-phenyl-4-(d-lyxo-1′,2′,3′,4′-tetrahydroxybutyl)-2H-1,2,3-triazole in the presence of Candida antarctica lipase B in diisopropyl ether. Among the different acid anhydrides, butanoic anhydride was found to be the most efficient acylating agent (for butanoylation); for acetylation, vinyl acetate gave the best results. The reactions with both these acylating agents were highly selective and efficient yielding exclusively the monoacylated products in 95-99% yields in 1-5 h.     

Diastereoselective synthesis of 5-(alditol-1-C-yl)-hydantoins and their use as precursors of polyhydroxylated-α-amino acids

The synthesis of 5-(alditol-1-C-yl)-hydantoin derivatives was performed via diastereoselective aldol-type addition of 1,3-dibenzyl-hydantoin to enantiopure aldehydo sugars. Starting from the d-ribo-configured 5-(alditol-1-C-yl)-hydantoin template, the synthesis of (2R,3S,4R)-3,4,5-trihydroxynorvaline was carried out.     

Synthesis of highly oxygenated decalins from sugar allyltins: an access to sulfur and phosphorus derivatives

A sugar allyltin derivative (with the d-gluco-configuration) was converted into d-xylo-dienoaldehyde and then into several bicyclic highly oxygenated compounds. The proposed methodology allows for a convenient synthesis of such derivatives containing heteroatoms other than oxygen. Molecular docking studies employing AutoDock 4.2 and AutoDock Vina were conducted in order to evaluate their activity as glycosidase inhibitors.     

Synthesis of new carbohydrate-derived ketones as organocatalysts in the enantioselective epoxidation of arylalkenes. Part 2: Chiral ketones from sugars

A range of new, somewhat complex, stereochemically varied, and structurally related carbohydrate-derived ketones were synthesised by a simple method from the carbohydrate precursor (d-gluco and d-galacto derivatives). The common skeleton possesses the keto function sited on a seven-membered ring fused to positions 2 and 3 of the sugar moiety. Their chirality transfer capability in the dioxirane-mediated epoxidation of arylalkenes was evaluated.     

Synthesis and glycosidase inhibitory activity of pseudo-di-(or tri-)saccharides

The synthesis of pseudo-di-(or tri-)saccharides with a d-mannoazepane or a l-gulopiperidine skeleton either N-linked to a d-gluco-C-furanoside or to d-mannitol, and evaluation of their inhibitory activities against α- or β-d-glucosidase, α-d-mannosidase and α-l-fucosidase are described.     

Polyhydroxylated N-(thio)carbamoyl piperidines: nojirimycin-type glycomimetics with controlled anomeric configuration

N-(Thio)carbamoyl d-xylo-nojirimycin derivatives have been prepared by intramolecular rearrangement of sugar thiourea precursors under basic conditions. The stereochemistry at the aminoketal stereocentre is under stereoelectronic control, with the diastereomer having the pseudoanomeric group in axial orientation being obtained in all cases.     

Short synthesis of hydroxylated thiolane and selenolane rings from mono-benzylated pentitols and aldoses dithioacetals bis-thionocarbonates as bis-electrophilic substrates

1-O-Benzylpentitols (with d-arabino, d-lyxo, d,l-xylo and d,l-ribo configurations) and aldoses dibenzyldithioacetals (with l-arabino, d-lyxo, d-xylo, d-ribo, d-galacto, d-gluco and d-manno configurations) were directly and efficiently transformed into their cyclic bis-thionocarbonate derivatives (61-73%) by reaction with diimidazolyl thione (Im₂CS) in 1,4-dioxane. These bis-electrophilic adducts react regioselectively with Na₂S·9H₂O or Se/NaBH₄ to lead regioselectively to the corresponding thiolane and selenolane rings in good yields for a short synthesis (47-65%).     

A common and stereoselective strategy for the synthesis of N,O,O,O-tetra-acetyl d-ribo-(2S,3S,4R)-phytosphingosine and 2-epi-jaspine B

A common and stereoselective strategy for the synthesis of N,O,O,O-tetra-acetyl d-ribo-(2S,3S,4R)-phytosphingosine and 2-epi-jaspine B was achieved by using Grignard addition on N-benzyl sugar lactamine and Wittig olefination as key steps.     

Trihydroxy-2-thiaquinolizidine derivatives as a new class of bicyclic glycosidase inhibitors

Trihydroxy-2-thiaquinolizidines, a new class of bicyclic dideoxy-iminohexitol glycosidase inhibitor derivatives with nominally the d-gluco, l-ido, d-manno and l-gulo configurations were synthesized. X-ray analyses indicated that the preferred conformation for d-gluco and d-manno derivatives was a flat trans-fused system. Unlike deoxynojirimycin, the compound with d-gluco configuration was selective for α-glucosidases (yeast and rice) and showed no inhibitory activity towards β-glucosidase (almond), α-galactosidase (green coffee beans), α-galactosidase (E. coli) and α-mannosidase (jack bean), while the l-ido derivative was specific for β-glucosidase (almond).     

Lead tetraacetate-iodine oxidation of 23-spirostanols

Reactions of 23R- and 23S-23-spirostanols in the 25R and 25S series with lead tetraacetate-iodine were studied. The reactions carried out at low temperature afforded d-seco-iododialdehydes and C₂₂ lactones, while similar reactions performed in refluxing tetrachloromethane yielded 20-chlorolactones and their 21-acetoxy derivatives irrespective of the hydroxyl group configuration at C-23. The reaction mechanisms are discussed.     

A new diorganozinc-based enantioselective access to truncated d-ribo-phytosphingosine

The use of a trans α,β-epoxyaldehyde as a precursor of d-ribo-phytosphingosines was studied. The highly stereoselective alkylation of the aldehyde with a diorganozinc reagent was ensured through double asymmetric induction. The regioselective opening of the epoxide in turn gives access to an azide from which a C₁₀ phytosphingosine can be easily prepared.     

An efficient approach to d-threo-3-hydroxyaspartic acid for the synthesis of novel l-threo-oxazolines as selective blockers of glutamate reversed uptake

An efficient, stereoselective synthetic strategy to d-threo-3-hydroxyaspartic acid was developed. Starting from l-(2S,3S)-N-benzoyl-3-hydroxyaspartic acid dimethyl ester by a Deoxo-fluor-catalyzed cyclization reaction, an inversion of configuration at the β-center (erythro isomer), was observed. A base-induced epimerization reaction led to the d-trans-isomer, which was hydrolyzed to give d-threo-3-hydroxyaspartic acid with excellent stereoselectivity and overall yield. Starting from d-threo-3-hydroxyaspartic acid, l-threo-oxazolines can be stereoselectively synthesized.     

Stereoselective synthesis of C-glycosylphosphonates from their ketols. Reconsideration of an abandoned route

Isosteric phosphonate analogues of glycosyl 1-phosphates have been obtained by addition of LiCH₂P(O)(OMe)₂ to glyconolactones followed by Et₃SiH–TMSOTf reductive dehydroxylation of the resultant ketols. The compounds prepared include four β-linked pyranose derivatives (d-galacto, 2-azido-2-deoxy-d-galacto, d-gluco, d-manno) and one β-linked furanose derivative (d-manno). In the latter case the ketol was activated as its 2-acetate. In agreement with an observation in another laboratory, the dehydroxylation of a model ketol phosphonate failed with the use of Et₃SiH–BF₃·Et₂O.     

Spectrochemical properties of noncubic transition metal complexes in solutions—IV. Energy levels of tetragonal distorted chromium(III) complexes in aqueous solutions

A general method for the analysis of the d-d transition energies observed in the ligand field spectra of chromium(III) complexes with D_4h or C_4υ symmetry is described and used to derive the crystal field and angular overlap parameters for the complexes of known stereochemistry. Examples are also presented. The spectrum of the diamminetetrakis(isothiocyanato)chromate(III) ammonium in aqueous solution is reported. The spectra of the miscellaneous systems have been studied theoretically using a crystal field model and an angular overlap model.     

Convergent syntheses of C(1→3)-linked disaccharides starting from isolevoglucosenone

Nucleophilic addition (Nu⁻M⁺) to isolevoglucosenone 1 generates enolates stereospecifically (exo face addition) that can be reacted with sugar-derived aldehydes to give C(1→3)-linked disaccharide precursors with high diastereoselectivity. Limitations of the method arising from unfavorable aldolate stability can be overcome by using Et₂AlI as the nucleophile. This leads to products of Baylis–Hillmann condensations. One example is presented and has led to the preparation of 2,3-anhydro-3-C-[(1S)-2,6-anhydro-d-glycero-d-gulo-heptitol-1-C-yl]-β-d-gulo-pyranose 5.     

Synthesis and glycosidase inhibitory activity of aminocyclitols with a C6- or a C7-ring

The synthesis of carbasugars and various aminocyclitols, related to voglibose and acarbose used in the treatment of non-insulino-dependant diabetes, is described from C₂-symmetrical bis-epoxides derived from d-mannitol. The methodology involves two key steps: a domino alkylation-cyclization with 2-lithio-1,3-dithiane derivatives, and reduction or reductive amination with a primary amine. These compounds have been evaluated as inhibitors of several glycosidases, and this study indicates notably that the l-ido or d-manno 1-aminocycloheptane-3,4,5,6-tetrol are inhibitors of α-d-glucosidase with K_i in the micromolar range.