Showing papers on "Glycal published in 2014"
TL;DR: A first direct route to difluoromethylated alkynes is reported, albeit with low yields, in a copper-mediated fluorofunctionalization of alkenes and alkynes.
Abstract: A copper-mediated fluorofunctionalization of alkenes and alkynes has been developed. This method provides ready access to trisubstituted difluoromethylated olefins (from dihydropyrans, glycal derivatives, or terminal alkynes) or to tetrasubstituted olefins (from disubstituted alkynes). The products were obtained in good to high yields with acceptable E/Z selectivities. Finally, a first direct route to difluoromethylated alkynes is reported, albeit with low yields.
49 citations
TL;DR: In this article, an iterative and α-selective glycosylation method for 2-deoxyglycosyl and 2,6-dideoxythioglycoside donors based on the DMF modulation concept is described.
31 citations
TL;DR: The synthetic use of the KDO donor was demonstrated in the preparation of β-KDO-containing oligosaccharides and showed excellent disastereoselectivity of glycosylation in a CH2Cl2-CH3CN solvent mixture.
27 citations
TL;DR: The fluorinated exo-glycals proved to be potent inhibitors as compared with a series of C-glycosidic analogues of UDP-Galf, thus demonstrating the double beneficial effect of the exocyclic enol ether functionality and the fluorine atom.
Abstract: Two complementary methods for the synthesis of fluorinated exo-glycals have been developed, for which previously no general reaction had been available. First, a Selectfluor-mediated fluorination was optimized after detailed analysis of all the reaction parameters. A dramatic effect of molecular sieves on the course of the reaction was observed. The reaction was generalized with a set of biologically relevant furanosides and pyranosides. A second direct approach involving carbanionic chemistry and the use of N-fluorobenzenesulfonimide (NFSI) was performed and this method gave better diastereoselectivities. Assignment of the Z/E configuration of all the fluorinated exo-glycals was achieved based on the results of HOESY experiments. Furthermore, fluorinated exo-glycal analogues of UDP-galactofuranose were prepared and assayed against GlfT2, which is a key enzyme involved in the cell-wall biosynthesis of major pathogens. The fluorinated exo-glycals proved to be potent inhibitors as compared with a series of C-glycosidic analogues of UDP-Galf, thus demonstrating the double beneficial effect of the exocyclic enol ether functionality and the fluorine atom.
25 citations
TL;DR: The Pd-π-allyl intermediate in an electron-rich glycal system with poor reactivity is employed as an efficient glycosyl donor and may provide an access to complex oligosaccharides.
Abstract: The Pd-π-allyl intermediate in an electron-rich glycal system with poor reactivity is employed as an efficient glycosyl donor. Starting from glucal derived carbonate, various O-glycosides were formed via a palladium-catalyzed reaction through a tandem decarboxylation, proton abstraction, and nucleophilic addition, in good yields with excellent selectivity. Iterative glycosylation with the same strategy may provide an access to complex oligosaccharides.
22 citations
TL;DR: Compounds resulting from ring expansion (oxepanes), ring contraction (tetrahydrofurans), or branched pyranoses, by incorporation of nucleophiles, can be obtained from 6-O-benzyl, 6-hydroxy, or 6-Silyl derivatives, respectively.
Abstract: Novel substrates that combine dicobalt hexacarbonyl propargyl (Nicholas) and pyranose-derived allylic (Ferrier) cations have been generated by treatment of hexacarbonyldicobalt (C-1)-alkynyl glycals with BF3 (.) Et2 O. The study of these cations has resulted in the discovery of novel reaction pathways that have shown to be associated to the nature of O-6 substituent in the starting alkynyl glycals. Accordingly, compounds resulting from ring expansion (oxepanes), ring contraction (tetrahydrofurans), or branched pyranoses, by incorporation of nucleophiles, can be obtained from 6-O-benzyl, 6-hydroxy, or 6-O-silyl derivatives, respectively. The use of a 6-O-allyl alkynyl glycal led to a suitable funtionalized oxepane able to experience an intramolecular Pauson-Khand cyclization leading to a single tricyclic derivative.
19 citations
TL;DR: Attempts to install the dimethylamino group of the C-disaccharide suggest that introduction of an azide group by displacement and subsequent reduction may pave the way to the total synthesis of pluraflavin A.
Abstract: A synthetic strategy towards the potent cytostatic agent pluraflavin A has been developed. Formation of the enantioenriched anthrapyran core bearing a halogen atom enabled the introduction of the α C-aryl glycoside by Stille cross-coupling and subsequent hydrogenation of the aryl glycal. Chemo- and stereoselective O-glycosylations of α oliose and β 3-epi vancosamine residues afforded a fully glycosylated aromatic core. Attempts to install the dimethylamino group of the C-disaccharide suggest that introduction of an azide group by displacement and subsequent reduction may pave the way to the total synthesis of pluraflavin A.
19 citations
TL;DR: In this article, an efficient total synthesis of 18 membered macrolactone, (+)-Aspicilin (lichen macrolide) has been achieved in 12 linear steps with 10.2% overall yield from carbohydrate based building block D-glucal.
Abstract: An efficient total synthesis of 18 membered macrolactone, (+)-Aspicilin (lichen macrolide) has been achieved in 12 linear steps with 10.2% overall yield from carbohydrate based building block D-glucal. Highlights of the strategy include preparation of 2-deoxysugar from protected glycal 14, two-carbon Wittig olefination of the Swern oxidised intermediate 7, union of ‘carbohydrate based’ fragment 5 and a long chain (C-11) chiral alcohol 6 by Yamaguchi esterification and finally ring closing metathesis of the resulting compound 4.
18 citations
TL;DR: A review of 1,2-cyclopropyl car-bohydrates can be found in this article, where a wide variety of products are obtained depending on the functionality attached to the cyclopropane and the promoter (Lewis acid, Br o nsted acid, halophile or base).
Abstract: Addition of a carbene to a glycal is the prominent method for the synthesis of 1,2-cyclopropyl car- bohydrates. This incorporation of a cyclopropane into a carbohydrate scaffold enables divergent reactivity, with the two main classes being ring expansion and cleavage to 2- C -branched carbohydrates. A wide variety of products are obtained depending on the functionality attached to the cyclopropane (none or ester or hal- ogens) and the promoter (Lewis acid, Br o nsted acid, halophile or base) used in the reaction. This article reviews progress in the synthesis and reactions of 1,2-cyclopropyl carbohydrates since 2000 and discloses efforts by our group in the area.
16 citations
TL;DR: A novel metal-free strategy for a rapid and α-selctive C-alkynylation of glycals was developed that can access C-glycosides in a single step from a variety of acetylenes, i.e., arylacetylenes and most importantly aliphatic alkynes.
Abstract: A novel metal-free strategy for a rapid and α-selctive C-alkynylation of glycals was developed. The reaction utilizes TMSOTf as a promoter to generate in situ trimethylsilylacetylene for C-alkynylation. Thanks to this methodology, we can access C-glycosides in a single step from a variety of acetylenes , i.e., arylacetylenes and most importantly aliphatic alkynes.
15 citations
TL;DR: In this article, the synthesis of two new stereoisomers of steviamine, namely 1,8a-di-epi-(+)-steviamines and 2,3-di-,epi-,−)-stebiamines, was reported, starting from tri-O-benzyl-D-glucal.
TL;DR: A regio- and stereo-controlled, one-pot amidoglycosylation of alcohols has been achieved using O-acetylated glycals, trichloroethoxysulfonamide, and iodosobenzene in the presence of a rhodium(II) catalyst.
Abstract: A regio- and stereo-controlled, one-pot amidoglycosylation of alcohols has been achieved using O-acetylated glycals, trichloroethoxysulfonamide, and iodosobenzene in the presence of a rhodium(II) catalyst. The reaction would proceed via stereoselective intermolecular aziridination of the glycal.
TL;DR: A mild, catalytic, and efficient protocol has been developed for the synthesis of 2,3-unsaturated glycosides or ‘pseudo-glycals’ using Zn(OTf)2 using various acceptors including alcohols, phenols, thiols, and sugar aglycones.
Abstract: A mild, catalytic, and efficient protocol has been developed for the synthesis of 2,3-unsaturated glycosides or ‘pseudo-glycals’ using Zn(OTf)2. Stereoselective glycosylation of glycal donor with various acceptors comprising of alcohols, phenols, thiols, and sugar aglycones proceeds smoothly to afford the corresponding 2,3-unsaturaed glycosides in good to excellent yields.
TL;DR: A facile and stereoselective method for Ferrier glycosylation was developed using ruthenium(III) chloride using the glycal donor reacted smoothly with several acceptors comprising different functionalities to afford corresponding 2,3-unsaturated glycosides in good to excellent yields.
Abstract: A facile and stereoselective method for Ferrier glycosylation was developed using ruthenium(III) chloride. Using this protocol, the glycal donor reacted smoothly with several acceptors comprising different functionalities to afford corresponding 2,3-unsaturated glycosides in good to excellent yields.
TL;DR: In this paper, a dihydropyranonucleoside was synthesized as a potential anti-HIV agent, which was converted into a di-PMB derivative in several steps.
Abstract: As a part of our ongoing studies of structure–activity relationships regarding cyclohexenyl nucleosides, we were prompted to synthesize a dihydropyranonucleoside as a potential anti-HIV agent. The synthesis of a glycal moiety started from but-2-enediol, which was converted into a di-PMB derivative in several steps. The introduction of an allyl group followed by ring-closing metathesis gave a dihydropyran derivative. After isomerization of the double bond catalyzed by Wilkinson’s catalyst, the resulting glycal, 2,3-bis[(4-methoxybenzyloxy)methyl]-3,4-dihydro-2 H -pyran, was subjected to an oxidative glycosylation reaction mediated by hypervalent iodine. Treatment of 2,3-bis[(4-methoxybenzyloxy)methyl]-3,4-dihydro-2 H -pyran with (PhSe) 2 /PhI(OAc) 2 /TMSOTf (cat.) gave the desired pyranyluracils as a mixture of anomers that were converted into the final target, dihydropyranocytidine, after several manipulations and separation of the anomers.
TL;DR: The epimerization methodology was subsequently combined with acylating enzymes in a dynamic kinetic asymmetric transformation (DYKAT), giving stereoselective acylation to the desired stereoisomers 12, 13, and 15.
Abstract: Epimerization of a non-anomeric stereogenic center in carbohydrates is an important transformation in the synthesis of natural products. In this study an epimerization procedure of the allylic alco ...
TL;DR: The Suzuki—Miyaura cross-coupling of diHydropyranylphosphates with various arylboronate esters affords the corresponding arylated dihydropyrans including C-arylated glycal (V).
Abstract: The Suzuki—Miyaura cross-coupling of dihydropyranylphosphates with various arylboronate esters affords the corresponding arylated dihydropyrans including C-arylated glycal (V).
TL;DR: In this article, a mild and atom-economic rhenium(V)-catalyzed stereoselective synthesis of β-D-digitoxosides from 6-deoxy-Dallals has been described.
Abstract: A mild and atom-economic rhenium(V)-catalyzed stereoselective synthesis of β-D-digitoxosides from 6-deoxy-D-allals has been described. This β-selective glycosylation was achieved probably because of the formation of corresponding α-digitoxosides disfavored by 1,3-diaxial interaction. In addition, this method has been successfully applied to the synthesis of digitoxin trisaccharide glycal for the direct synthesis of digitoxin and C1'-epi-digitoxin.
TL;DR: The glycal donor reacts smoothly with several acceptors comprising different functionalities to provide unsaturated glycosides, disaccharides, and amino acid glycoconjugates in good to high yields.
Abstract: The glycal donor reacts smoothly with several acceptors comprising different functionalities to provide unsaturated glycosides, disaccharides, and amino acid glycoconjugates in good to high yields.
TL;DR: In this article, a highly stereoselective rapid C-glycosylation reaction was developed between glycal and unactivated alkynes in the presence of coppertriflate and ascorbic acid at low catalyst loading and at room temperature.
Abstract: A highly stereoselective rapid C-glycosylation reaction has been developed between glycal and unactivated alkynes in the presence of coppertriflate and ascorbic acid at low catalyst loading and at room temperature. A wide variety of glycals and aryl acetylenes participate in the reaction smoothly. TfOH generated during the reduction of Cu(OTf)2 by ascorbic acid may be the active catalyst for the glycosylation.
01 Jan 2014
30 Sep 2014
TL;DR: In this paper, an efficient total synthesis of 18 membered macrolactone, (+)-Aspicilin (lichen macrolide) has been achieved in 12 linear steps with 10.2% overall yield from carbohydrate based building block D-glucal.
Abstract: An efficient total synthesis of 18 membered macrolactone, (+)-Aspicilin (lichen macrolide) has been achieved in 12 linear steps with 10.2% overall yield from carbohydrate based building block D-glucal. Highlights of the strategy include preparation of 2-deoxysugar from protected glycal 14, two-carbon Wittig olefination of the Swern oxidised intermediate 7, union of ‘carbohydrate based’ fragment 5 and a long chain (C-11) chiral alcohol 6 by Yamaguchi esterification and finally ring closing metathesis of the resulting compound 4.
01 Jan 2014
TL;DR: The Li-enolates of the methylene active compounds [(II) and (V)] react stereoselectively with the d-glycal-derived vinyl aziridines [(I) and(V)] to the title highly functionalized pyrrole derivatives in a unique manner as discussed by the authors.
Abstract: The Li-enolates of the methylene active compounds [(II) and (V)] react stereoselectively with the d-glycal-derived vinyl aziridines [(I) and (V)] to the title highly functionalized pyrrole derivatives in a unique manner.
TL;DR: Depending on the C3 stereochemistry of the glycal substrate this method yields either diastereomerically pure products or mixtures of diastreomers.
Abstract: Depending on the C3 stereochemistry of the glycal substrate this method yields either diastereomerically pure products or mixtures of diastereomers.