Showing papers on "Glycal published in 2010"
TL;DR: A sulfamate ester group was introduced at different positions of glycal to act as a nitrene source and, moreover, to allow the study of the relative reactivity of the nitrene transfer from different sites of the glycal molecule.
Abstract: We carried out a principle study on the reaction mechanism of rhodium-catalyzed intramolecular aziridination and aziridine ring opening at a sugar template. A sulfamate ester group was introduced at different positions of glycal to act as a nitrene source and, moreover, to allow the study of the relative reactivity of the nitrene transfer from different sites of the glycal molecule. The structural optimization of each intermediate along the reaction pathway was extensively done by using BPW91 functional. The crucial step in the reaction is the Rh-catalyzed nitrene transfer to the double bond of the glycal. We found that the reaction could proceed in a stepwise manner, whereby the N atom initially induced a single-bond formation with C1 on the triplet surface or in a single step through intersystem crossing (ISC) of the triplet excited state of the rhodium-nitrene transition state to the singlet ground state of the aziridine complexes. The relative reactivity for the conversion of the nitrene species to the aziridine obtained from the computed potential energy surface (PES) agrees well with the reaction time gained from experimental observation. The aziridine ring opening is a spontaneous process because the energy barrier for the formation of the transition state is very small and disappears in the solution calculations. The regio- and stereoselectivity of the reaction product is controlled by the electronic property of the anomeric carbon as well as the facial preference for the nitrene insertion, and the nucleophilic addition.
50 citations
TL;DR: Thirteen new 1,2,3-triazoles (5a-e, 15a-d, 17a-b, 19, and 21) were synthesized by 'click' reaction of sugar-derived azides with commercially available acetylenes and tested in vitro for their biological activity.
44 citations
TL;DR: A 1-adamantyl thioglycoside derivative of KDN, derived from N-acetylneuraminic acid, carrying a 3,4-O-carbonate protecting group is a highy efficient and α-selective KDN donor on activation with NIS and TfOH in dichloromethane and acetonitrile at −78 °C.
Abstract: A 1-adamantyl thioglycoside derivative of KDN, derived from N-acetylneuraminic acid, carrying a 3,4-O-carbonate protecting group is a highy efficient and α-selective KDN donor on activation with NIS and TfOH in dichloromethane and acetonitrile at −78 °C. Glycosylations conducted with this protecting group do not suffer from competing glycal formation. Seven examples are given, including the use of galactose 3- and 6-hydroxy groups.
33 citations
TL;DR: Substituted dihydropyrans, easily accessed from a commercially available glycal, undergo acid-catalyzed rearrangement to provide highly functionalized isochroman and dioxabicyclooctane scaffolds.
27 citations
TL;DR: In this paper, a new modular synthesis of diverse 2,4-disubstituted pyrimidin-5-yl C-2′-deoxyribonucleosides by sequential regioselective reactions of 2,6-dichloropyrimidine with glycal was developed.
25 citations
TL;DR: NMR time course studies demonstrate that uridine phosphorylase can catalyze the hydrolysis of the fluorinated nucleosides in the absence of phosphate or sulfate, without the release of intermediates or enzyme inactivation.
Abstract: Uridine phosphorylase is a key enzyme in the pyrimidine salvage pathway This enzyme catalyzes the reversible phosphorolysis of uridine to uracil and ribose 1-phosphate (or 2{prime}-deoxyuridine to 2{prime}-deoxyribose 1-phosphate) Here we report the structure of hexameric Escherichia coli uridine phosphorylase treated with 5-fluorouridine and sulfate and dimeric bovine uridine phosphorylase treated with 5-fluoro-2{prime}-deoxyuridine or uridine, plus sulfate In each case the electron density shows three separate species corresponding to the pyrimidine base, sulfate, and a ribosyl species, which can be modeled as a glycal In the structures of the glycal complexes, the fluorouracil O2 atom is appropriately positioned to act as the base required for glycal formation via deprotonation at C2{prime} Crystals of bovine uridine phosphorylase treated with 2{prime}-deoxyuridine and sulfate show intact nucleoside NMR time course studies demonstrate that uridine phosphorylase can catalyze the hydrolysis of the fluorinated nucleosides in the absence of phosphate or sulfate, without the release of intermediates or enzyme inactivation These results add a previously unencountered mechanistic motif to the body of information on glycal formation by enzymes catalyzing the cleavage of glycosyl bonds
21 citations
TL;DR: An efficient synthesis of the N-(tert-butyloxycarbonyl)-O-triisopropylsilyl-D-pyrrolosamine glycal of lomaiviticin A and lomaIViticin B is described.
16 citations
TL;DR: 2-Azido- 4-benzylamino-4-N-,3-O-carbonyl-2,4,6-trideoxy-d-galactopyranosyl trichloroacetimidate (14) was conveniently prepared by regioselective introduction of an N-benzyl carbamate at O-3 of 6-deoxy- d-glucal 6, followed by mesylation atO-4.
16 citations
TL;DR: A new spirocyclization was developed for the synthesis of 1,7-dioxaspiro[5.5]undecanes and 1-oxa-7-thiaspiro and provided the corresponding products in good to excellent yields.
15 citations
TL;DR: Molybdenum catalysts are efficient and selective catalysts for the tandem epoxidation/alcoholysis or epoxide/hydrolysis of glucal and galactal derivatives as mentioned in this paper.
Abstract: Molybdenum catalysts are efficient and selective catalysts for the tandem epoxidation/alcoholysis or epoxidation/hydrolysis of glucal and galactal derivatives. In glucal derivatives the selectivity is mainly controlled by the allylic substituent at position 3 of the glycal, obtaining in general the products derived from the initial formation of the α-epoxide (gluco) when this hydroxy group is protected, while products derived from the β-epoxide (manno) are mainly obtained when it is unprotected. In galactal derivatives the estereoselectivity is always high to give the α-epoxide (galacto) and independent of the protecting groups.
14 citations
TL;DR: (4E,8E,10E)-9-Methyl-4,8,10-sphingatrienine, a core component of marine sphingolipids, was synthesised for the first time using a copper(I)-mediated 1,2-metallate rearrangement of a lithiated glycal as a key step.
Abstract: (4E,8E,10E)-9-Methyl-4,8,10-sphingatrienine, a core component of marine sphingolipids, was synthesised for the first time using a copper(I)-mediated 1,2-metallate rearrangement of a lithiated glycal as a key step. It was converted to phalluside-1, a cerebroside isolated from the ascidian Phallusia fumigate. By an analogous route, (4E,8E)-9-methyl-4,8-sphingadiene was synthesised and converted to Sch II, a cerebroside that induces fruiting body formation in the basidiomycete Schizophyllum commune.
TL;DR: The ZnCl2-mediated glycosidation of an α-1,2-epoxide, prepared by epoxidation of a glycal with 3,3-dimethyldioxirane, with an incoming glycal acceptor is not a priori, as advocated by Danishefski et al, a stereospecific process as discussed by the authors.
Abstract: The ZnCl2-mediated glycosidation of an α-1,2-epoxide, prepared by epoxidation of a glycal with 3,3-dimethyldioxirane, with an incoming glycal acceptor is not a priori, as advocated by Danishefski et al, a stereospecific process.
TL;DR: In this article, the stereoselectivity of NIS-mediated electrophilic glycosidation was examined by employing 2,4-bis-O-(trimethylsilyl)thymine and three different silyl-protected erythro-furanoid glycals 12, 16, and 18.
TL;DR: Highly functionalized 1-exo-alkylidene-2,3-anhydro-, and 1'-halo-1-exosodium-2-anHydrofuranoses can be prepared in four or five steps, respectively, from D -mannose.
TL;DR: Gamma-aminobutyric acid analogs based on sugar scaffolds were prepared in six to nine steps starting from D-glucal and D-galactal starting from the Vilsmeier-Haack reaction that affords the corresponding GABA analog.
TL;DR: In this paper, the synthesis of (+)-cacospongionolide B was achieved by highly stereoselective C-glycosidation of a glycal derived from D-arabinose with 3-furyl boronic acid in the presence of a palladium catalyst.
Abstract: Total synthesis of (+)-cacospongionolide B was achieved. The synthesis involved highly stereoselective C-glycosidation of a glycal derived from D-arabinose with 3-furyl boronic acid in the presence of a palladium catalyst and B-alkyl Suzuki-Miyaura coupling of in situ generated alkylborane prepared by the reaction of vinyl trans-decalin with alkenyl triflate.
TL;DR: The addition of primary and secondary aliphatic amines to glycal-derived allyl epoxides is completely 1,2-regio- and anti-stereoselective as discussed by the authors.
TL;DR: In this paper, the electrochemical bromination of 3,4,6-tri-O-acetyl-d -glucal has been investigated in DMSO by cyclic voltammetry and preparative-scale electrolyses.
TL;DR: The nucleophilic 1,2-addition of lithiated glycal 9b to functionalized quinone 7 provided, after reductive aromatization, C-aryl glycoside 11b.
Abstract: Nucleophilic 1,2-addition of lithiated glycal 9b to functionalized quinone 7 provided, after reductive aromatization, C-arylglycoside 11b. Treatment with mCPBA afforded the tricyclic papulacandin framework. Alternatively, hydroboration gave the chaetiacandin nucleus.
TL;DR: A mild and efficient Zn(II)-mediated electrophilic selenocyclization reaction of readily available and stable 3,4-O-isopropylidene-protected hydroxyalkenyl sulfides to 2-deoxy-2-phenylselenenyl-1-thio-glycosides is described.
TL;DR: In this article, bridging nucleoside analogues were prepared by cycloaddition reactions between pyranose glycals and barbiturate-derived, reactive thionoimides in modest yields.
Abstract: Novel bridging nucleoside analogues were prepared by cycloaddition reactions between pyranose glycals and barbiturate-derived, reactive thionoimides in modest yields. In all of the reactions conducted, the major cycloadducts obtained were the bottom faced adducts resulting from endo addition to the glycal. The adducts were stable to a variety of acidic reaction conditions and several of the compounds showed moderate activities against HIV-1 in primary human lymphocytes. One compound displayed anti-herpes simplex virus type-1 activity in Vero cells. Cytotoxicity measurements were also obtained.
TL;DR: In this article, a general and convenient synthesis of carbohydrate 2-C-analogs by addition of malonates to glycals is described, which is applicable to glyals derived from hexoses and pentoses and is characterized by easily available precursors.
Abstract: A general and convenient synthesis of carbohydrate 2-C-analogs by addition of malonates to glycals is described. The method is applicable to glycals derived from hexoses and pentoses and is characterized by easily available precursors. The reactions are mediated by manganese(III) or cerium(IV) and proceed via intermediarily generated malonyl radicals. All additions exhibit a very high degree of regioselectivity, since only 2-C-branched sugars were obtained. This result can be best rationalized by favorable orbital interactions between the SOMO of the malonyl radical and the HOMO of the double bond. Variation of the steric demand of the malonate or the glycal allows the stereoselectivities to be increased up to >98%. Highest selectivities were obtained with tri-O-acetyl-d-galactal and di-O-acetyl-d-arabinal, where the attack occurs exclusively from one face of the carbohydrate. For all cerium(IV)-mediated reactions, methyl glycosides are formed as main products in 73−89% yield, which can be isolated in ana...
TL;DR: Electrospray ionization/tandem mass spectrometric study of hexoses and pentoses using lead cationization and the distinction of underivatized monosaccharides using ESI-MS of their ammonium adducts is reported.
Abstract: Glycals, 1,2-unsaturatedderivatives of pentoses or hexoses, are versatile building blocks for the synthesis of numerous biologically active compounds; therefore, they have attained significant attention in the field of bioorganic and medicinal chemistry. Tandem mass spectrometric studies of glycals derived from various sugars are of fundamental importance from the viewpoint of synthetic strategies leading to higher analogues. Among themass spectrometry based techniques, electrospray ionization tandemmass spectrometry (ESI-MS/ MS) has been extensively used in the structural elucidation of carbohydrates and differentiation of monosaccharide diastereomers such as hexoses, hexosamines and N-acetylhexosamines. For example, Leary and coworkers have shown that stereoisomeric hexasoamines and N-acetylhexosamines can be differentiated when they were derivatized with [Zn(diethylenetriamine)(Cl)], [Ni(1,3-diaminopropane)3]Cl2 or [Co(diaminopropane)2Cl2]Cl and subjected to ESI-MS studies. Madhusudanan et al. have reported CIDMS/MS studies of the ammonium adducts of hexoses and the fragmentation patterns were used to differentiate diastereomers of monosasccharides. Salpin and Tortajada have reported an electrospray ionization/tandem mass spectrometric study of hexoses and pentoses using lead cationization. Recently, Zhu and Sato reported the distinction of underivatized monosaccharides using ESI-MS of their ammonium adducts. Banoub et al. reported the highand low-energy fast-atom bombardment (FAB) tandemmass spectrometry of a series of anomeric and regioisomeric 20deoxyribofuranoseyl imidazole nucleosides. Chauvin et al. differentiated the regioisomeric esters of sucrose by ion spray tandem mass spectrometry. While there exist several mass spectral studies on monosaccharides as discussed above, there are no reports on differentiation of diastereomers of glycals derived from monosaccharides. This has prompted us to investigate some glycal derivatives, 3,4-di-O-benzyl-Lidal (1) and 3,4-di-O-benzyl-D-glucal (2), and methyl-3,4-diO-benzyl-L-iduronicacid (3) and methyl 3,4-di-O-benzyl-Dglucuronicacid (4) (Scheme 1), by ESI-MS/MS. Electrospray ionization (ESI) mass spectra of glycals (Scheme 1) were recorded using a LCQ ion trap mass spectrometer (Thermo Finnigan, San Jose, CA, USA), equipped with an ESI source. The data acquisition was under the control of Xcalibur software (Thermo Finnigan). The typical source conditions were: spray voltage, 5 kV; capillary voltage, 15–20V; heated capillary temperature, 2008C; tube lens offset voltage, 20V; sheath gas (N2) pressure, 30 psi; and heliumwas used as damping gas. For the ion trap mass analyzer, the automatic gain control (AGC) settings were 2 10 counts for a full-scan mass spectrum and 2 10counts for a full product ion mass spectrum with a maximum ion injection time of 200ms. In the collisioninduced dissociation (CID)-MS/MS multistage-scan mode, the precursor ion of interest was first isolated by applying an appropriate waveform across the end-cap electrodes of the ion trap to resonantly eject all trapped ions, except those ions of the m/z ratio of interest. The isolated ions were then subjected to a supplementary AC signal to resonantly excite them and so cause CID. The collision energies used were 20– 40 eV. The excitation time used was 30ms. All spectra were recorded under identical experimental conditions for isomers and average of 25–30 scans. All the samples were infused into the ESI source at a flow rate of 5mL/min by using instrument’s syringe pump. Accurate mass measurements were obtained using a quadrupole time-of-flight (QqTOF) mass spectrometer (QSTAR XL, Applied Biosystems/MDS Sciex, Foster City, USA), equippedwith an ESI source. The data acquisition was under the control of Analyst QS software (Foster City, CA, USA). The typical source conditions were: capillary voltage, 5 kV; focusing potential, 260V; declustering potential 60V; resolution 8000 (full-width at half-maximum). Ultrahigh-purity nitrogen was used as the curtain gas and collision gas, whereas zero air was used as the nebulizer. The [MþNa]þ ions were selected as precursors by the quadrupole and allowed to collide with nitrogen gas in the collision cell. The product ions were then detected by a time-of-flight (TOF) analyzer. The samples were infused into the ESI source at a flow rate of 10mL/min using an in-built syringe pump. Compounds 1–4 were synthesized using procedures reported in the literature. These compounds were purified and characterized by IR, H NMR and mass spectrometry. The experimental procedures and their analytical data are provided as Supporting Information. The diastereomers after RAPID COMMUNICATIONS IN MASS SPECTROMETRY Rapid Commun. Mass Spectrom. 2010; 24: 2776–2780 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/rcm.4691
TL;DR: In this paper, the first example of direct intermolecular conversion of a glycal to a mannosamine derivative is presented, which leads to a proposal for the generation of glucosamine derivatives from glycals and triazolinediones.
Abstract: Triazolinediones react with tri-O-acetyl-D-glucal to pro- vide the corresponding diazetidines as single stereoisomers possess- ing the mannosamine configuration at C2. The diazetidines undergo facile ring opening with alcohol and amine nucleophiles. While this methodology is not fully developed, it is the first example of direct intermolecular conversion of a glycal to a mannosamine derivative. Computational analysis provides mechanistic insight that in turn leads to a proposal for the generation of glucosamine derivatives from glycals and triazolinediones.
TL;DR: High functionalised β-enamino ketones were obtained by this method using two differently N-substituted amino glycals and a variety of alkyl- and arylamines.
TL;DR: A furanose-derived 2,3-anhydro-exo-glycal, readily available from D-mannose in four steps, has proven to be a useful substrate in the preparation of a variety of highly functionalized C-1 glycals.
Abstract: A furanose-derived 2,3-anhydro-exo-glycal, readily available from D-mannose in four steps, has proven to be a useful substrate in the preparation of a variety of highly functionalized C-1 glycals. Upon treatment with Pd0 it affords a π-allyl palladium complex that can react with nucleophiles such as amines, ethyl malonate, or vinylstannanes. On the other hand, umpolung of the π-allyl palladium complex with Et2Zn facilitates its reaction with electrophilic aldehydes and ketones.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
TL;DR: In this paper, a convenient procedure for the synthesis of C-glycoside was developed via cycloaddition of dichloroketene, generated in situ, to glycal and dechlorination of the cycloadduct using zinc and acetic acid.
Abstract: A convenient procedure for the synthesis of C-glycoside was developed via cycloaddition of dichloroketene, generated in situ, to glycal and dechlorination of the cycloadduct using zinc and acetic acid.