Showing papers on "Glycal published in 2006"
TL;DR: With an excess of diphenyl sulfoxide, glycal formation can be completely suppressed and excellent yields are obtained for coupling to a wide range of primary, secondary, and tertiary acceptors.
74 citations
TL;DR: Treatment with Ti(Oi-Pr)4 leads to an unusual kinetic epoxide-opening spirocyclization (spirocycloisomerization) with retention of configuration at the anomeric carbon, and together, these reactions provide comprehensive access to systematically stereochemically diversified spiroketals.
Abstract: A Ti(Oi-Pr)4-mediated kinetic spiroketalization reaction has been developed for the stereocontrolled target- and diversity-oriented synthesis of spiroketals. In contrast to most existing methods for spiroketal synthesis, this reaction does not rely upon thermodynamic control over the stereochemical configuration at the anomeric carbon. Stereochemically diverse glycals are first alkylated at the C1-position to introduce a hydroxyl-bearing side chain, then epoxidized stereoselectively. Treatment with Ti(Oi-Pr)4 leads to an unusual kinetic epoxide-opening spirocyclization (spirocycloisomerization) with retention of configuration at the anomeric carbon. The reaction is proposed to proceed via a chelation-controlled mechanism and has been used to form five-, six-, and seven-membered rings with stereochemically diverse substituents. This approach may also be useful for the related intermolecular beta-mannosidation reaction. This Ti(Oi-Pr)4-mediated spirocyclization is stereochemically complementary to our previously reported MeOH-induced spirocyclization, which proceeds with inversion of configuration, and together, these reactions provide comprehensive access to systematically stereochemically diversified spiroketals.
53 citations
TL;DR: The major glucose-derived product exhibited crystal packing with C- H...O and C-H...pi (arene) interactions and the major galactose- derived product, a low molecular mass organogelator (LMOG), formed a rare type of micro tubular gel assembly in n-hexane.
45 citations
TL;DR: Aryl ether C- glycoside scaffolds have been prepared from tri-O-acetyl-D-glucal by C-glycosylation followed by allylic substitution with phenols mediated by Pd(0) to create highly substituted tetrahydrofurans.
45 citations
TL;DR: A catalytic dihydroxylation reaction on glycals has been developed using a bimetallic oxidizing system to furnish sugar 1,2-diols in a highly stereoselective manner.
Abstract: A catalytic dihydroxylation reaction on glycals has been developed using a bimetallic oxidizing system to furnish sugar 1,2-diols in a highly setreoselective manner.
38 citations
TL;DR: A stereo-defined synthesis of two diastereomers of polyhydroxypyrrolidines from 3,4,6-tri-O-benzyl-d -glucal 4 involving a cleavage-recyclization strategy is reported in this article.
36 citations
TL;DR: A new and highly efficient methodology for the construction of synthetically important highly O-functionalized enantiopure 2,3,4-trisubstituted tetrahydrofurans with three contiguous stereocenters is reported.
30 citations
TL;DR: In this paper, β-Aryl-C-2-deoxynucleosides are obtained from known glycals by an epoxidation−glycosylation−deoxygenation sequence.
29 citations
TL;DR: Among these six compounds, 4'-cyano (28) and 4'-ethynyl (29) analogues were found to show inhibitory activity against HIV-1 with ED50 values of 7.6 and 0.74 microM, respectively.
Abstract: Motivated by our recent finding that 4‘-ethynylstavudine (4) is a promising anti-human immunodeficiency virus type 1 (HIV-1) agent, we synthesized its 4‘-thio analogue, as well as other 4‘-thiostavudines having a carbon substituent at the 4‘-position, as racemates in this study. Methyl 3-oxo-tetrahydrothiophen-2-carboxylate (5) was used as a starting material to construct the requisite 4-thiofuranoid glycal (13). Introduction of a thymine base was carried out by an electrophilic addition reaction to 13 using N-iodosuccinimide (NIS) and bis(trimethylsilyl)thymine. The desired β-anomer (16β) obtained as a major product in this reaction underwent ready elimination with activated Zn to give the 4‘-carbomethoxy derivative (18). By using 18 as a common intermediate, 4‘-carbon-substituted (CH2OH, CO2Me, CONH2, CHCH2, CN, and C⋮CH) 4‘-thiostavudines were prepared. Among these six compounds, 4‘-cyano (28) and 4‘-ethynyl (29) analogues were found to show inhibitory activity against HIV-1 with ED50 values of 7.6 and...
27 citations
TL;DR: Neodysiherbaine A, a neuroexitotoxin occurring in a Micronesian marine sponge Dysidea herbacea, was synthesized from tri-O-acetyl-D-glucal with excellent stereocontrol.
Abstract: Neodysiherbaine A, a neuroexitotoxin occurring in a Micronesian marine sponge Dysidea herbacea, was synthesized from tri-O-acetyl-D-glucal with excellent stereocontrol. The method established enables us to obtain gram quantities of neodysiherbaine A and its related compounds.
26 citations
TL;DR: Rapid-mixing chemical quench experiments were conducted to determine the nature of the intermediate formed upon proton abstraction in the reaction catalyzed by the enzyme from Pseudomonas aeruginosa, and colorimetric and HPLC analysis of quenched samples indicated that shortened oligosaccharides containing an unsaturated sugar residue form as transient intermediates in the epimerization reaction.
Abstract: C5-mannuronan epimerase catalyzes the formation of α-l-guluronate residues from β-d-mannuronate residues in the synthesis of the linear polysaccharide alginate. The reaction requires the abstraction of a proton from C5 of the residue undergoing epimerization followed by re-protonation on the opposite face. Rapid-mixing chemical quench experiments were conducted to determine the nature of the intermediate formed upon proton abstraction in the reaction catalyzed by the enzyme from Pseudomonas aeruginosa. Colorimetric and HPLC analysis of quenched samples indicated that shortened oligosaccharides containing an unsaturated sugar residue form as transient intermediates in the epimerization reaction. This suggests that the carbanion is stabilized by glycal formation, concomitant with cleavage of the glycosidic bond between the residue undergoing epimerization and the adjacent residue. The time dependence of glycal formation suggested that slow steps flank the chemical steps in the catalytic cycle. Solvent isoto...
TL;DR: A direct enantioselective pathway that delivers exclusively the beta-anomer of a 4'-spironucleoside has been successfully developed and quantitatively furnishes the targeted, previously elusive anomer.
Abstract: A direct enantioselective pathway that delivers exclusively the β-anomer of a 4‘-spironucleoside has been successfully developed. The key starting material is the enantiomerically pure dihydroxy lactone 19, which has proven amenable to conversion to glycal 22 via the chloro acetonide. This intermediate is then capped as the 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) glycal. The latter can enter into N-iodosuccinimide-promoted glycosidation with persilylated thymine. Only the β anomer is formed. Ensuing deiodination and desilylation proceed quantitatively to furnish the targeted, previously elusive anomer.
TL;DR: In this article, an efficient, consecutive approach for the construction of synthetically valued, enantiomerically pure, trisubstituted THF domains 3 -10 in a stereoselective manner starting from glycal derived allylic alcohols under Sharpless asymmetric epoxidation (SAE) conditions is reported.
Abstract: A highly efficient, consecutive approach for the construction of synthetically valued, enantiomerically pure, trisubstituted THF domains 3 – 10 in a stereoselective manner starting from glycal derived allylic alcohols 1a – 1d under Sharpless asymmetric epoxidation (SAE) conditions is reported. The reaction involves the intramolecular asymmetric ring opening (ARO) of in situ formed enantiopure 2,3-epoxy alcohols followed by protection of the diol.
TL;DR: In this article, the synthesis of densely functionalized acyclic long chain terminal alkenic alcohols was achieved by reductive opening of glycal derived 2,3-epoxy-1-iodides, with commercial zinc dust alone in a short reaction time with excellent yields involving a simple reaction procedure.
TL;DR: New 2-deoxy-and 2-6-dideoxy-a-L-arabinohexopyranosides of betulinic acid and 28-oxoallobetulin methyl esters were synthesized by the glycal method as discussed by the authors.
Abstract: New 2-deoxy-and 2,6-dideoxy-a-L-arabinohexopyranosides of betulinic acid and 28-oxoallobetulin methyl esters were synthesized by the glycal method
TL;DR: New glycoglycerolipids, derivatives of 2-deoxysugars bearing one or two fatty acid chains bearing oneor two fatty Acid chains have been synthesised and the influence of the structure of glycal derivatives in glycosylation reactions is discussed.
TL;DR: In this paper, the peracetylated N-acetylneuraminic acid glycal was obtained from the reaction mixture by simple filtration and subsequent evaporation of the solvent.
Abstract: Treatment of the readily available peracetylated N-acetylneuraminic acid glycosyl chloride [methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-2-chloro-2,3,5-trideoxy-β-D-glycero-D-galactononulopyranosonate)] with anhydrous Na 2 HPO 4 in refluxing MeCN quantitatively affords the peracetylated N-acetylneuraminic acid glycal [methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2,6-anhydro-D-glycero-D-galacto-non-2-enonate], which can be isolated from the reaction mixture by simple filtration and subsequent evaporation of the solvent. No glycal formation was detected at room temperature even after prolonged treatment with Na 2 HPO 4 . The method proposed is experimentally simple and allows ready preparation of substantial amounts of the title compound, which is an important intermediate in sialic acid chemistry.
TL;DR: In this article, a palladium mediated modified protocol has been developed for the glycosidation of an aromatization prone xylo-furanoid glycal for the synthesis of D-D4FC.
Abstract: D-D4FC ( 1 ) is an anti-HIV agent currently under phase II clinical trial (Pharmaset Inc) Its molecular architecture is suitable for a Ferrier rearrangement kind of operation on a furanoid glycal to fix the position of the double bond and the relative stereochemistry Despite the fact that classical Ferrier rearrangement does not work on furanoid glycals, a palladium mediated modified protocol has been developed for the glycosidation of an aromatization prone xylo-furanoid glycal ( 5 ) for the synthesis of D-D4FC
TL;DR: Exo-Glycals are unsaturated sugars that have a double bond attached to the anomeric center outside the sugar ring as mentioned in this paper, which is useful for the synthesis of C-glycosides and compounds containing quaternary carbons, provided that the olefin can be properly reduced or functionalized.
Abstract: It is well known that carbohydrates play an indispensable role in a variety of essential biological activities, such as cell-cell adhesion, bacteria and virus infections, and tumor metastasis. Among an increasing number of sugars and sugar mimetics that have been designed and synthesized for the purpose of drug discovery, C-glycosides are considered to be one of the best choices on account of their stability and resemblance as they differ from normal glycosides only in glycosidic linkages. exo-Glycals are unsaturated sugars that have a double bond attached to the anomeric center outside the sugar ring. These carbohydrate molecules are useful for the synthesis of C-glycosides and compounds containing quaternary carbons, provided that the olefin can be properly reduced or functionalized. This review places special emphasis on two aspects of exo-glycals including general methods of preparation and synthetic applications for making biologically important molecules. The first half discusses the methods of addition/elimination and Ramburg-Backlund rearrangement that offer many beneficial features including a wide range of double bond substitutions, limited reaction steps, easy operation and good overall yields. The rest of the article demonstrates a number of synthetic studies using exoglycals as the starting materials. The target molecules can be categorized into three groups, namely C-glycosides, enzyme inhibitors and bioactive natural products.
TL;DR: In this paper, the formation of sialic acid glycosides with a trifluoromethanesulfonic anhydride is reported, which can be used for coupling to a wide range of primary, secondary, and tertiary acceptors.
Abstract: The formation of sialic acid glycosides with a thiosialic acid derivative, diphenyl sulfoxide, and trifluoromethanesulfonic anhydride is reported. With an excess of diphenyl sulfoxide, glycal formation can be completely suppressed and excellent yields are obtained for coupling to a wide range of primary, secondary, and tertiary acceptors.
TL;DR: In this paper, a new and highly efficient methodology for the construction of synthetically important highly O-functionalized enantiopure 2,3,4-trisubstituted tetrahydrofurans with three contiguous stereocenters is reported.
Abstract: A new and highly efficient methodology for the construction of synthetically important highly O-functionalized enantiopure 2,3,4-trisubstituted tetrahydrofurans with three contiguous stereocenters is reported.
TL;DR: Palladium acetate catalyzed C -glycosidation of peracetylated glycals with arylboronic acids in acetonitrile (CH 3 CN) yields the desired 1-substituted 2,3-unsaturated glycal as well as a byproduct corresponding to the ring-opened pyran, present in varying proportions depending on the reaction conditions used as discussed by the authors.
Abstract: Palladium acetate catalyzed C -glycosidation of peracetylated glycals with arylboronic acids in acetonitrile (CH 3 CN) yields the desired 1-substituted 2,3-unsaturated glycal as well as a byproduct corresponding to the ring-opened pyran, present in varying proportions depending on the reaction conditions used. The byproduct is not formed when toluene/EtOH is used as reaction solvent.
TL;DR: In this article, 2-C -acetoxymethyl glycal derivatives react with aliphatic alcohols in the presence of InCl 3 to furnish the corresponding 2-c -methylene glycosides in excellent yields and with exclusive α-selectivity.
Abstract: 2- C -Acetoxymethyl glycal derivatives react with aliphatic alcohols in the presence of InCl 3 (30 mol %) to furnish the corresponding 2- C -methylene glycosides in excellent yields and with exclusive α-selectivity except for the methyl 2- C -methylene glycosides, which are formed in ∼2:1 anomeric ratio in favour of the α-anomer. The reaction of 2- C -acetoxyglycals with phenols, however, produces the corresponding chiral carbohydrate-derived pyranobenzopyran derivatives via initial Ferrier rearrangement followed by tandem cyclization in excellent yields and moderate to high stereoselectivities in favour of the corresponding 10a- R -pyrano[2,3- b ][1]benzopyran derivatives.
TL;DR: In this paper, a methanol-induced kinetic spiroketalization reaction has been developed for the stereocontrolled target and diversity-oriented synthesis of Spiroketals.
Abstract: A methanol-induced kinetic spiroketalization reaction has been developed for the stereocontrolled target- and diversity-oriented synthesis of spiroketals. In contrast to existing methods for spiroketal synthesis, this reaction does not depend on thermodynamic product stability or require axial attack of an oxygen nucleophile. Stereodiverse glycals are alkylated at the C1 position with side chains bearing protected hydroxyl groups. After alcohol deprotection, the glycal is epoxidized stereoselectively, then the side chain hydroxyl is spirocyclized with inversion of configuration at the anomeric carbon by addition of excess MeOH at -63 degrees C. This spirocyclization reaction appears to proceed by MeOH hydrogen-bonding catalysis and has been used to form five- and six-membered rings with stereoisomeric substituents. In some cases, the stereocomplementary spiroketals can be also obtained by classical acid-catalyzed equilibration.
TL;DR: In this paper, the synthesis of densely functionalized acyclic long chain terminal alkenic alcohols was achieved by reductive opening of glycal derived 2,3-epoxy-1-iodides, with commercial zinc dust alone in a short reaction time with excellent yields involving a simple reaction procedure.
Abstract: The synthesis of densely functionalized acyclic long chain terminal alkenic alcohols was achieved by reductive opening of glycal derived 2,3-epoxy-1-iodides, with commercial zinc dust alone in a short reaction time with excellent yields involving a simple reaction procedure and easy work-up. A mechanism involving an organometallic intermediate is proposed.