- Synthesis and Conformational Analysis of 2-O-Silyl Protected Nucleosides from Unprotected Nucleobases and Sugar Epoxides
-
Synthesis of orthogonally protected 2-silyl nucleosides were achieved by trans opening of sugar epoxides with nucleobases catalyzed by trimethylsilyltrifluoromethanesulfonate using hexamethyldisilazane both as solvent and silylating agent. Both α and β nu
- Ahmed, Ajaz,Katoch, Meenu,Mukherjee, Debaraj,Rasool, Faheem,Singh, Gurpreet
-
-
- A Short Sequence for the Iterative Synthesis of Fused Polyethers
-
A simple and efficient four-step sequence for the synthesis of fused polyether arrays has been developed. Cyclic ethers are installed by sequential alkynyl ether formation, carbocupration, ring-closing metathesis and hydroboration with acidic workup. Cruc
- Elustondo, Frédéric,Chintalapudi, Venkaiah,Clark, J. Stephen
-
-
- 2-: O-Benzyloxycarbonyl protected glycosyl donors: A revival of carbonate-mediated anchimeric assistance for diastereoselective glycosylation
-
By reviving an old idea, we demonstrate that alkoxycarbonyl groups can be used in glycosylation reactions to achieve full stereocontrol through participation of a carbonate moiety at O-2. Various benzyloxycarbonyl-protected glycosyl donors were prepared and used for efficient 1,2-trans glycosylation of base-labile compounds and the synthesis of glycosyl esters.
- Weber, Julia,Svatunek, Dennis,Krauter, Simon,Tegl, Gregor,Hametner, Christian,Kosma, Paul,Mikula, Hannes
-
supporting information
p. 12543 - 12546
(2019/10/28)
-
- An Isolable and Bench-Stable Epoxidizing Reagent Based on Triazine: Triazox
-
A new triazine-based oxidizing reagent, 2-hydroperoxy-4,6-diphenyl-1,3,5-triazine (Triazox), has been developed. The reagent can be synthesized from inexpensive starting materials and is a bench-stable solid that is isolable in pure form. Epoxidation of alkenes possessing acid-sensitive functionalities using Triazox proceeded in good to excellent yields. The accompanying nonacidic triazinone coproduct can be easily removed by filtration. These features indicate that Triazox is a practically useful oxidizing reagent.
- Yamada, Kohei,Igarashi, Yuki,Betsuyaku, Tatsuki,Kitamura, Masanori,Hirata, Koki,Hioki, Kazuhito,Kunishima, Munetaka
-
supporting information
p. 2015 - 2019
(2018/04/16)
-
- METHOD FOR PRODUCING GLYCYRRHIZINIC ACID AND GALACTURO GLYCYRRHIZINIC ACID, AND INTERMEDIATE USED FOR THE PRODUCTION METHOD
-
PROBLEM TO BE SOLVED: To provide a synthesis method that makes it possible to produce high-purity glycyrrhizinic acid or galacturo glycyrrhizinic acid, simply and in high yields. SOLUTION: A production method includes performing glycosylation of position-3 hydroxy group of glycyrrhetinic acid, then performing selective galactosylation or glycosylation at position-2', and through deprotection, performing selective oxidation of a primary hydroxy group. SELECTED DRAWING: None COPYRIGHT: (C)2018,JPOandINPIT
- -
-
Paragraph 0024; 0026
(2018/07/28)
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- Glycosyl Cross-Coupling of Anomeric Nucleophiles: Scope, Mechanism, and Applications in the Synthesis of Aryl C-Glycosides
-
Stereoselective manipulations at the C1 anomeric position of saccharides are one of the central goals of preparative carbohydrate chemistry. Historically, the majority of reactions forming a bond with anomeric carbon has focused on reactions of nucleophiles with saccharide donors equipped with a leaving group. Here, we describe a novel approach to stereoselective synthesis of C-aryl glycosides capitalizing on the highly stereospecific reaction of anomeric nucleophiles. First, methods for the preparation of anomeric stannanes have been developed and optimized to afford both anomers of common saccharides in high anomeric selectivities. We established that oligosaccharide stannanes could be prepared from monosaccharide stannanes via O-glycosylation with Schmidt-type donors, glycal epoxides, or under dehydrative conditions with C1 alcohols. Second, we identified a general set of catalytic conditions with Pd2(dba)3 (2.5 mol%) and a bulky ligand (JackiePhos, 10 mol%) controlling the β-elimination pathway. We demonstrated that the glycosyl cross-coupling resulted in consistently high anomeric selectivities for both anomers with mono- and oligosaccharides, deoxysugars, saccharides with free hydroxyl groups, pyranose, and furanose substrates. The versatility of the glycosyl cross-coupling reaction was probed in the total synthesis of salmochelins (siderophores) and commercial anti-diabetic drugs (gliflozins). Combined experimental and computational studies revealed that the β-elimination pathway is suppressed for biphenyl-type ligands due to the shielding of Pd(II) by sterically demanding JackiePhos, whereas smaller ligands, which allow for the formation of a Pd-F complex, predominantly result in a glycal product. Similar steric effects account for the diminished rates of cross-couplings of 1,2-cis C1-stannanes with aryl halides. DFT calculations also revealed that the transmetalation occurs via a cyclic transition state with retention of configuration at the anomeric position. Taken together, facile access to both anomers of various glycoside nucleophiles, a broad reaction scope, and uniformly high transfer of anomeric configuration make the glycosyl cross-coupling reaction a practical tool for the synthesis of bioactive natural products, drug candidates, allowing for late-stage glycodiversification studies with small molecules and biologics.
- Zhu, Feng,Rodriguez, Jacob,Yang, Tianyi,Kevlishvili, Ilia,Miller, Eric,Yi, Duk,O'Neill, Sloane,Rourke, Michael J.,Liu, Peng,Walczak, Maciej A.
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p. 17908 - 17922
(2017/12/26)
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- Ionic liquids as phase transfer catalysts: Enhancing the biphasic extractive epoxidation reaction for the selective synthesis of β-O-glycosides
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Ionic liquids promoted the direct epoxidation of glycals acting as PTC. 1,2-anhydrosugars were prepared by the oxidation of glycals under biphasic conditions with dimethydioxirane generated in situ from oxone/acetone and amphiphilic IL's as catalysts. β-O
- Santiago, Cintia C.,Lafuente, Leticia,Bravo, Rodolfo,Díaz, Gisela,Ponzinibbio, Agustín
-
p. 3739 - 3742
(2017/09/02)
-
- α-C-Glycosides via syn Opening of 1,2-Anhydro Sugars with Organozinc Compounds in Toluene/n-Dibutyl Ether
-
The diastereoselective addition of organozinc species to 1,2-anhydro sugars in toluene/n-dibutyl ether solvent is reported. Compared to the existing methods, the reaction proceeds at 0 °C, and only a slight excess of nucleophile is required to achieve good yields. Scope was assessed with different O-protected glycals along with various nucleophiles (aryl, alkynyl). This methodology was applied to the synthesis of the α-anomer of canagliflozin.
- Wagschal, Simon,Guilbaud, Johan,Rabet, Pauline,Farina, Vittorio,Lemaire, Sébastien
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p. 9328 - 9335
(2015/09/28)
-
- Glycosyl dithiocarbamates: β-selective couplings without auxiliary groups
-
In this article, we evaluate glycosyl dithiocarbamates (DTCs) with unprotected C2 hydroxyls as donors in β-linked oligosaccharide synthesis. We report a mild, one-pot conversion of glycals into β-glycosyl DTCs via DMDO oxidation with subsequent ring opening by DTC salts, which can be generated in situ from secondary amines and CS2. Glycosyl DTCs are readily activated with Cu(I) or Cu(II) triflate at low temperatures and are amenable to reiterative synthesis strategies, as demonstrated by the efficient construction of a tri-β-1,6-linked tetrasaccharide. Glycosyl DTC couplings are highly β-selective despite the absence of a preexisting C2 auxiliary group. We provide evidence that the directing effect is mediated by the C2 hydroxyl itself via the putative formation of a cis-fused bicyclic intermediate.
- Padungros, Panuwat,Alberch, Laura,Wei, Alexander
-
p. 2611 - 2624
(2014/04/17)
-
- Convenient synthesis of 1,3-dithiolane-2-thiones: Cyclic trithiocarbonates as conformational locks
-
A series of novel 1,3-dithiolane-2-thiones, or cyclic trithiocarbonates, has been prepared by a new simple procedure: a treatment of the corresponding epoxides with the commercially available potassium ethyl xanthogenate, KSC(S)OEt. The stereochemistry of the products was determined by 1H NMR and in some cases by single-crystal X-ray data. Cyclohexane-based 1,3- dithiolane-2-thiones revealed a trans-fusion of the carbo- and hetero-cycles. The products obtained from the mono-substituted cyclohexene oxides demonstrated an axial position of the substituents. Thus the epoxide transformation into trithiocarbonate can be used as a method for locking cyclic compounds in unstable conformations.ARKAT-USA, Inc.
- Dotsenko, Irina A.,Zhao, Qinliang,Franz, Andreas H.,Batoon, Patrick,Samoshina, Nataliya M.,Samoshin, Vyacheslav V.
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-
- Practical and efficient large-scale preparation of dimethyldioxirane
-
An improved procedure for large-scale and also commercially viable preparation of dimethyldioxirane (DMDO), a common and widely used oxidation agent in organic synthesis, was developed using a conventional laboratory plant. All reaction parameters were optimized, and the stability of a freshly prepared solution of DMDO in acetone was monitored over an extended period of time to ensure long-term use after preparation, transport, and storage. This discontinuous approach, suitable for batch processing, is of interest basically to research laboratories but also to suppliers in the research and fine chemicals market.
- Mikula, Hannes,Svatunek, Dennis,Lumpi, Daniel,Gloecklhofer, Florian,Hametner, Christian,Froehlich, Johannes
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p. 313 - 316
(2013/04/24)
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- Glycal assembly by the in situ generation of glycosyl dithiocarbamates
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Glycal assembly offers an expedient entry into β-linked oligosaccharides, but epoxyglycal donors can be capricious in their reactivities. Treatment with Et2NH and CS2 enables their in situ conversion into glycosyl dithiocarbamates, which can be activated by copper triflate for coupling with complex or sterically congested acceptors. The coupling efficiency can be further enhanced by in situ benzoylation, as illustrated in an 11-step synthesis of a branched hexasaccharide from glucals in 28% isolated yield and just four chromatographic purifications.
- Padungros, Panuwat,Alberch, Laura,Wei, Alexander
-
supporting information; experimental part
p. 3380 - 3383
(2012/09/22)
-
- Armed-disarmed effect on the stability of cysteine thioglucosides
-
Thioglucosides of cysteine show variable stability depending on the nature of the protecting groups on the glycosyl donor. Armed protecting groups (benzyl) lead to products that decompose readily while disarmed protecting groups (acetyl) lead to more stable products. Since this armed/disarmed effect of the protecting group on the stability of the thioglucosides is more pronounced for cysteine with an unprotected carboxylic group, the proposed mechanism is that decomposition is initiated by an intramolecular protonation of glycosyl sulfide and subsequent displacement of the sulfide by adventitious nucleophiles.
- Nokwequ, Mbulelo G.,Nkambule, Comfort M.,Gammon, David W.
-
-
- Stereoelectronic factors in the stereoselective epoxidation of glycals and 4-deoxypentenosides
-
Glycals and 4-deoxypentenosides (4-DPs), unsaturated pyranosides with similar structures and reactivity profiles, can exhibit a high degree of stereoselectivity upon epoxidation with dimethyldioxirane (DMDO). In most cases, the glycals and their corresponding 4-DP isosteres share the same facioselectivity, implying that the pyran substituents are largely responsible for the stereodirecting effect. Fully substituted dihydropyrans are subject to a "majority rule", in which the epoxidation is directed toward the face opposite to two of the three groups. Removing one of the substituents has a variable effect on the epoxidation outcome, depending on its position and also on the relative stereochemistry of the remaining two groups. Overall, we observe that the greatest loss in facioselectivity for glycals and 4-DPs is caused by removal of the C3 oxygen, followed by the C5/anomeric substituent, and least of all by the C4/C2 oxygen. DFT calculations based on polarized-π frontier molecular orbital (PPFMO) theory support a stereoelectronic role for the oxygen substituents in 4-DP facioselectivity, but less clearly so in the case of glycals. We conclude that the anomeric oxygen in 4-DPs contributes toward a stereoelectronic bias in facioselectivity whereas the C5 alkoxymethyl in glycals imparts a steric bias, which at times can compete with the stereodirecting effects from the other oxygen substituents.
- Alberch, Laura,Cheng, Gang,Seo, Seung-Kee,Li, Xuehua,Boulineau, Fabien P.,Wei, Alexander
-
experimental part
p. 2532 - 2547
(2011/06/19)
-
- Stereoselective synthesis of β-Phenylselenoglycosides from glycals and rationalization of the selenoglycosylation processes
-
β-Phenylselenoglycosides have been efficiently and stereoselectively synthesized by direct oxidative glycosylation of benzenselenolate (PhSe -) with glycals. A rationalization of the presently described β-selectivity and the opposite α-selectivity reported by Danishefsky in the ring-opening of epoxy glycals with benzeneselenol (PhSeH) is proposed.
- Di Bussolo, Valeria,Fiasella, Annalisa,Balzano, Federica,Uccello Barretta, Gloria,Crotti, Paolo
-
supporting information; experimental part
p. 4284 - 4287
(2010/08/06)
-
- Synthesis of fused pyran-carbahexopyranoses as glycosidase inhibitors
-
Synthesis of polyhydroxylated oxabicyclo[4,4,0]decanes, which constitute a new family of annulated carbasugars, has been accomplished in a stereoselective manner by employing readily available 1,2-anhydro-3,4,6-tri-O-benzyl-α-d-glycopyranoses.
- Doddi, Venkata Ramana,Kancharla, Pavan K.,Reddy, Y. Suman,Kumar, Amit,Vankar, Yashwant D.
-
body text
p. 606 - 612
(2009/05/11)
-
- Gold(I)-catalyzed glycosidation of 1,2-anhydrosugars
-
(Chemical Equation Presented) Being able to increase the yield by >20% compared to the conventional use of anhydrous zinc chloride (>1 equiv) as a promoter, Ph3PAuOTf is disclosed to be a superior catalyst for the well-established glycosylation reaction with 1,2-anhydrosugars as donors.
- Li, Yao,Tang, Pingping,Chen, Youxi,Yu, Biao
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p. 4323 - 4325
(2008/09/21)
-
- The exo-deoxoanomeric effect in the conformational preferences of C-glycosides
-
Rotational studies of a series of β-d-C-glycopyranosides were carried out by CD and NMR spectroscopy. The populations around the C-glycosidic bond were strongly dependent on the structure of the C-aglycon, the exo-syn rotamer population increasing with th
- Mayato, Carlos,Dorta, Rosa L.,Vazquez, Jesus T.
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p. 931 - 948
(2008/02/03)
-
- New insights into the conformational properties of α-C-glucosides
-
A series of alkyl α-d-C-glucopyranosides were synthesized and their conformational properties analyzed by CD and NMR spectroscopy. The conformational analysis revealed that the hydroxymethyl group populations (torsion angle ω, O1-C1-C2-O2) and those aroun
- Mayato, Carlos,Dorta, Rosa L.,Vazquez, Jesus T.
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p. 2803 - 2811
(2008/03/28)
-
- Direct epoxidation of d-glucal and d-galactal derivatives with in situ generated DMDO
-
A multi-gram epoxidation of 3,4,6-tri-O-benzyl-d-glucal and d-galactal with dimethyldioxirane (DMDO) generated in situ from Oxone/acetone in a biphasic system (CH2Cl2-aqueous NaHCO3) resulted in the formation of
- Cheshev, Pavel,Marra, Alberto,Dondoni, Alessandro
-
p. 2714 - 2716
(2007/10/03)
-
- Synthesis and evaluation of α-helix mimetics based on a trans-fused polycyclic ether: sequence-selective binding to aspartate pairs in α-helical peptides
-
Inspired by the topological similarity between ladder-like cyclic ether skeletons and α-helical peptides, a trans-fused 6/6/6/6 tetracyclic ether containing two hydroxyl groups separated by a distance of 4.8 A? was designed as a scaffold for a nonpeptidic
- Oguri, Hiroki,Tanabe, Shintaro,Oomura, Akifumi,Umetsu, Mitsuo,Hirama, Masahiro
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p. 5801 - 5805
(2007/10/03)
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- 1,2-Anhydrosaccharides and 1,2-cyclic sulfites as saccharide donors in convergent synthesis of glucopyranosyl-, mannopyranosyl- and ribofuranosylbenzocamalexin
-
A convergent synthesis of 1-(β-o-glucopyranosyl)-, 1-(α-D-mannopyranosyl)- and 1-(β-D-ribofuranosyl) benzocamalexin was elaborated as an alternative route to the linear approach based on the indoline-indole method. 1,2-Anhydrosaccharides and 1,2-cyclic sulfites as saccharide donors were used in the key glycosylation step. Coupling with benzocamalexin resulted in moderate to excellent yields of nucleoside analogs, depending on the saccharide donor, catalyst and solvent used.
- Humenik, Martin,Kutschy, Peter,Kovacik, Vladimir,Bekesova, Slavka
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p. 487 - 506
(2007/10/03)
-
- Carbohydrate prodrugs of fluorooxindoles
-
The present invention provides novel prodrug derivatives of fluorooxindoles having the general Formula I wherein the wavy bond () represents the racemate, the (R)-enantiomer or the (S)-enantiomer, and R1, R2, R3, R4
- -
-
Page/Page column 9
(2010/02/08)
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- Synthesis of a staurosporine analogue possessing a 7-azaindole unit instead of an indole moiety
-
The synthesis of a new staurosporine analogue possessing a 7-azaindole unit instead of an indole moiety is described. This synthesis could be achieved by coupling a sugar moiety previously tosylated in 2′ position to the azaindolocarbazole aglycone. Nucle
- Messaoudi, Samir,Anizon, Fabrice,Pfeiffer, Bruno,Golsteyn, Roy,Prudhomme, Michelle
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p. 4643 - 4647
(2007/10/03)
-
- First total synthesis of structurally unique flavonoids and their strong anti-inflammatory effect
-
The first total synthesis of structurally unique flavonoids 1a and 1b is described. These compounds showed very strong anti-inflammatory effect against delayed hypersensitivity in a mouse model.
- Nakatsuka, Takashi,Tomimori, Yoshiaki,Fukuda, Yoshiaki,Nukaya, Haruo
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p. 3201 - 3203
(2007/10/03)
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- The β-glucuronyl-based prodrug strategy allows for its application on β-glucuronyl-platinum conjugates
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The use of platinum drugs in antitumour therapy is well established. An important drawback of these chemotherapeutics is the lack of selectivity for tumour cells, usually resulting in severe toxic side effects. A glucuronyl-platinum conjugate was designed and synthesised to test the compatibility of platinum compounds with β-glucuronidase-based prodrug therapy. Instantaneous cleavage of the β-glucuronic bond in the glucuronyl-platinum conjugate was observed upon addition of β-glucuronidase resulting in PtII(dach)(4-hydroxybenzylmalonate) and glucuronic acid.
- Tromp, Reynier A.,Van Boom, Stella S.G.E.,Timmers, C. Marco,Van Zutphen, Steven,Van Der Marel, Gijsbert A.,Overkleeft, Herman S.,Van Boom, Jacques H.,Reedijk, Jan
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p. 4273 - 4276
(2007/10/03)
-
- Total synthesis of mannosyl tryptophan and its derivatives
-
Glycosylation is one of the most important post- or co-translational modifications of proteins, which affects the biological activities of the parent proteins by influencing the higher-order structure. Recently, a highly novel variant of glycoproteins tha
- Manabe, Shino,Marui, Yoshihiko,Ito, Yukishige
-
p. 1435 - 1447
(2007/10/03)
-
- Zinc-mediated synthesis of α-C-glycosides from 1,2-anhydroglycosides
-
α-C-Glycosides have been prepared by the addition of organozinc reagents to glycal epoxides. Dialkyl and diaryl zinc reagents in the presence of CF3COOH provide the corresponding α-glycosides in 53-82% yields. Organozinc chlorides RZnC1 formed
- Xue, Song,Han, Kai-Zhen,He, Lin,Guo, Qing-Xiang
-
p. 870 - 872
(2007/10/03)
-
- Chemoselective ligation applied to the synthesis of a biantennary N-linked glycoform of CD52
-
We report here a strategy for the synthesis of N-linked glycopeptide analogues that replace the glycosidic linkages extending from the core pentasaccharide with thioethers amenable to construction by chemoselective ligation. The key building block, a pent
- Pratt, Matthew R.,Bertozzi, Carolyn R.
-
p. 6149 - 6159
(2007/10/03)
-
- C-Glycosides to fused polycyclic ethers
-
This manuscript describes the synthesis of fused polycyclic ethers from the coupling of C-glycoside forming reactions with ring closing metathesis and acid mediated annulation reactions.
- Allwein, Shawn P.,Cox, Jason M.,Howard, Brett E.,Johnson, Henry W.B.,Rainier, Jon D.
-
p. 1997 - 2009
(2007/10/03)
-
- Samarium diiodide-mediated reductive coupling of epoxides and carbonyl compounds: A stereocontrolled synthesis of C-glycosides from 1,2-anhydro sugars
-
Sugar mimics: 1,2-anhydro sugars can be cross-coupled with aldehydes and ketones under very mild conditions and using a wide range of protecting groups to give C-glycosides in good yield in a radical reaction mediated by SmI2 (see scheme; A = n
- Chiara, Jose Luis,Sesmilo, Esther
-
p. 3242 - 3246
(2007/10/03)
-
- Oligosaccharide synthesis with glycosyl phosphate and dithiophosphate triesters as glycosylating agents
-
Described is an efficient one-pot synthesis of α- and β-glycosyl phosphate and dithiophosphate triesters from glycals via 1,2-anhydrosugars. Glycosyl phosphates function as versatile glycosylating agents for the synthesis of β-glucosidic, β-galactosidic,
- Plante,Palmacci,Andrade,Seeberger
-
p. 9545 - 9554
(2007/10/03)
-
- A short route to nucleoside diphosphate activated D- and L-hexoses
-
Leloir transferases utilise nucleoside diphosphate sugars, which are notoriously difficult to synthesise and handle. Starting off from D- or L-configurated glycals, a facile synthesis of nucleotide sugars by epoxidation and direct coupling with uridine di
- Ernst, Christiane,Klaffke, Werner
-
p. 2973 - 2975
(2007/10/03)
-
- para-Chlorophenyl carbonate as a versatile hydroxyl protecting group
-
The p-chlorophenyl carbonate (CPC) group can be readily applied and rapidly removed in the presence of various protecting groups including pivaloyl and benzoyl esters. Additionally, the CPC group is stable under a variety of glycosylation conditions and yields solely β-linked glycosides when used as a C2 participating group.
- Love,Seeberger
-
p. 317 - 322
(2007/10/03)
-
- Aluminum- and boron-mediated c-glycoside synthesis from 1,2-anhydroglycosides.
-
[reaction: see text]This letter describes a single flask strategy to the synthesis of alpha-C-glycosides from glycals. This protocol couples a glycal epoxidation reaction with a C-2 alkoxy-directed carbon-carbon bond-forming reaction.
- Rainier,Cox
-
p. 2707 - 2709
(2007/10/03)
-
- Synthesis of D-glycopyranosyl azides from 1,2-anhydrosugars using lithium azidohydridodiisobutylaluminate
-
1,2-Anhydrosugars were transformed regio- and stereoselectively into the corresponding D-glycopyranosyl azides in high yield by treatment with lithium azidohydridodiisobutylaluminate in THF.
- Lee, Goo Soo,Min, Hye Kyung,Chung, Bong Young
-
p. 543 - 544
(2007/10/03)
-
- Synthesis of laminin hexasaccharide analogue
-
The synthesis of laminin hexasaccharide analogue di-O-[Gal-β-(1→4)-Glc-β]-(1→2)-(1→6)-man-α- (1→6)-man-α-Me derivative (1) was achieved with 1,2-anhydromannopyranose benzyl ether (3) as the key intermediate. Coupling of 3 with methyl 2,3,4-tri-O-benzyl-α-D-mannopyranoside (4) promoted by ZnCl2 gave methyl 2,3,4-tri-O-benzyl-6-O-(3,4,6-tri-O-benzyl-α-D-mannopyranosyl)-α-D- mannopyranoside (2a). Selective 6-O-debenzylation of 2b with ZnCl2-Ac2O-HOAc followed by coupling with acetobromolactopyranose afforded 1.
- Ding, Xianglan,Kong, Fanzuo
-
p. 915 - 922
(2007/10/03)
-
- Ruthenium meso-tetrakis(2,6-dichlorophenyl)porphyrin complex immobilized in mesoporous MCM-41 as a heterogeneous catalyst for selective alkene epoxidations
-
A ruthenium complex of meso-tetrakis(2,6-dichlorophenyl)porphyrin, [RuII(TDCPP)(CO)(EtOH)], is immobilized into mesoporous MCM-41 molecular sieves; the supported Ru catalyst can effect highly selective heterogeneous alkene epoxidations using 2,6-dichloropyridine TV-oxide as terminal oxidant. Aromatic and aliphatic alkenes can be efficiently converted to their epoxides in good yields and selectivities, and cis-alkenes such as czs-stilbene, cis-β-methylstyrene, and cis-β-deuteriostyrene are epoxidized stereospecifically. Oxidation of cycloalkenes, e.g., norbornene and cyclooctene, can be carried out effectively using the heterogeneous Ru-catalyzed reaction while these alkenes are unreactive in the zeolite-based titanium silicate (TS-l)-catalyzed conditions (Murugavel, R.; Roesky, H. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 477). On the other hand, the Ru/M-41(m) catalyst displays size selectivity in the (+)-limonene oxidation where the terminal C=C bond (vs internal trisubstituted C=C bond) becomes more readily oxidized. Bulky 3,4,6-tri-O-benzyl-D-glucal has failed to react under the heterogeneous Ru-catalyzed conditions, whereas the smaller acetyl derivative is converted to a 3:1 mixture of α- and β-glycal epoxides. The Ru/M-41(m) catalyst can be used repeatedly, and 67% of its initial activity is retained after 11 691 turnovers (three runs). The loss of activity is attributed to catalyst leaching and/or deactivation. On the basis of Hammett correlation (ρ+ = -0.72, R = 0.997) and product studies (cyclohexene and crs-alkenes as the substrates), a reactive dioxorutheniumCVI) porphyrin intermediate is not favored. An oxoruthenium(V) complex or oxoruthenium(IV) porphyrin cation radical could be the key intermediate for this highly selective epoxidation reaction.
- Liu, Chun-Jing,Yu, Wing-Yiu,Li, Shou-Gui,Che, Chi-Ming
-
p. 7364 - 7369
(2007/10/03)
-
- A highly convergent total synthetic route to glycopeptides carrying a high-mannose core pentasaccharide domain N-linked to a natural peptide motif
-
N-Linked glycopeptides were synthesized by condensation of a high-mannose anomeric amine bearing a pentasaccharide with aspartic-acid-containing tri- and pentapeptides through the agency of IIDQ. The pentasaccharide portion, corresponding to the 'core' re
- Danishefsky, Samuel J.,Hu, Shuanghua,Cirillo, Pier F.,Eckhardt, Matthias,Seeberger, Peter H.
-
p. 1617 - 1628
(2007/10/03)
-
- Coupling of glycal derived thioethyl glycosyl donors with glycal acceptors. An advance in the scope of the glycal assembly
-
Glycals were converted into thioethyl glycosyl donors through 1,2-anhydrosugar intermediates. Various participating groups in the C-2 position were examined for formation of β-glucosyl, β-galactosyl, and α-mannosyl linkages. A number of disaccharides was
- Seeberger, Peter H.,Eckhardt, Matthias,Gutteridge, Clare E.,Danishefsky, Samuel J.
-
p. 10064 - 10072
(2007/10/03)
-
- A Stereoselective and Preparative Entry to 1,2-Anhydrosugars through Oxidation of Glycals with Perfluoro-cis-2,3-dialkyloxaziridines
-
Perfluoro-cis-2,3-dialkyloxaziridines 1 perform the direct epoxidation of glycals 2 to give cleanly corresponding 1,2-anhydrosugars 3 with medium to complete diastereoselection; elaboration of these glycals to glycosyl fluorides and lipid conjugates is al
- Cavicchioli, Marcello,Mele, Andrea,Montanari, Vittorio,Resnati, Giuseppe
-
p. 901 - 902
(2007/10/02)
-
- STEREOSELECTIVE GLYCOSIDIC COUPLING REACTIONS OF FULLY BENZYLATED 1,2-ANHYDRO SUGARS WITH N-TOSYL- OR N-BENZYLOXYCARBONYL-L-SERINE METHYL ESTER
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The glycosidic coupling reaction of 1,2-anhydro-3,4,6-tri-O-benzyl-β-D-mannopyranose (7), 1,2-anhydro-3,4,6-tri-O-benzyl-α-D-galactopyranose (21), and 1,2-anhydro-3,4-di-O-benzyl-α-D-xylopyranose (18) with N-tosyl- (10) or N-benzyloxycarbonyl- (11) L-serine methyl ester provides a new stereocontrolled synthesis of 1,2-trans linked glycopeptides.The 1,2-anhydro sugars are shown to react smoothly with 10 or 11 in the presence of Lewis acid (ZnCl2 or AgOTf) as well as powdered 4 Angstroem molecular sieves in CH2Cl2 at room temperature to afford glycosyl serine derivatives with high stereoselectivity and high yield in less than 30 min.An improved method using 2-O-acetyl-3,4,6-tri-O-benzyl-α-D-mannopyranosyl chloride (6) as the key intermediate for ring closure was applied for the synthesis of 1,2-anhydro-3,4,6-tri-O-benzyl-β-D-mannopyranose.
- Du, Yuguo,Kong, Fanzuo
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p. 341 - 352
(2007/10/02)
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- Diastereoselective Bromination of Allyl Glycosides Using Tetrabutylammonium Tribromide
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Both (R) and (S)-2,3-dibromo-1-propanol with e.e. up to 60percent have been obtained by diastereoselective addition of Br2 to allyl glucosides and galactosides having only one unprotected hydroxyl group at C-2 or C-6 using tetrabutylammonium tribromide, followed by hydrolysis.The absolute configuration is shown to depend on the position of the free hydroxyl and on the configuration at the anomeric centre.
- Bellucci, Giuseppe,Chiappe, Cinzia,D'Andrea, Felicia
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p. 221 - 230
(2007/10/02)
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- Synthesis of a Methyl Heptaglucoside with Phytoalexin Elicitor Activity Based on Oxidative Coupling of Glucals
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Several suitable building blocks for the construction of the phytoalexin elicitor α-methyl-32,34-di-β-D-glucopyranosylgentiopentaoside (2) were readily accessible by oxidative coupling of glucals.Block coupling of trimeric phenylsele
- Timmers, Cornelis M.,Marel, Gijsbert A. van der,Boom, Jacques H. van
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p. 161 - 164
(2007/10/02)
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- First synthesis of a digitalis saponin. Demonstration of the scope and limitations of a convergent scheme for branched oligosaccharide synthesis by the logic of glycal assembly
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The synthesis of complex glycosides, with branching at C2, is demonstrated. The key element involves the use of a 1,2-oxirane donor. Upon glycosylation, a C2 hydroxyl is exposed to serve as the acceptor in the next glycosylation. Bra
- Randolph, John T.,Danishefsky, Samuel J.
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p. 5693 - 5700
(2007/10/02)
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- A simple and highly diastereoselective preparation of glycal epoxides using the MCPBA-KF complex
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Glycals are converted ro the corresponding epoxides in high yields by a diastereoselective one-step epoxidation using the m-chloroperoxybenzoic acid-KF complex in anhydrous dichloromethane.
- Bellucci, Giuseppe,Catelani, Giorgio,Chiappe, Cinzia,D'Andrea, Felicia
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p. 8433 - 8436
(2007/10/02)
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- A note on the solid-phase synthesis of oligosaccharides by the Danishefski approach
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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.
- Timmers, C. M.,Marel, G. A. van der,Boom, J. H. van
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p. 609 - 610
(2007/10/02)
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