C-aryl Glycosides Research Articles

Synthesis of Aryl C-Glycosides via Iron-Catalyzed Cross Coupling of Halosugars: Stereoselective Anomeric Arylation of Glycosyl Radicals.

We have developed a novel diastereoselective iron-catalyzed cross-coupling reaction of various glycosyl halides with aryl metal reagents for the efficient synthesis of aryl C-glycosides, which are of significant pharmaceutical interest due to their biological activities and resistance toward metabolic degradation. A variety of aryl, heteroaryl, and vinyl metal reagents can be cross-coupled with glycosyl halides in high yields in the presence of a well-defined iron complex, composed of iron(II) chloride and a bulky bisphosphine ligand, TMS-SciOPP. The chemoselective nature of the reaction allows the use of synthetically versatile acetyl-protected glycosyl donors and the incorporation of various functional groups on the aryl moieties, producing a diverse array of aryl C-glycosides, including Canagliflozin, an inhibitor of sodium-glucose cotransporter 2 (SGLT2), and a prevailing diabetes drug. The cross-coupling reaction proceeds via generation and stereoselective trapping of glycosyl radical intermediates, representing a rare example of highly stereoselective carbon-carbon bond formation based on iron catalysis. Radical probe experiments using 3,4,6-tri-O-acetyl-2-O-allyl-α-d-glucopyranosyl bromide (8) and 6-bromo-1-hexene (10) confirm the generation and intermediacy of the corresponding glycosyl radicals. Density functional theory (DFT) calculations reveal that the observed anomeric diastereoselectivity is attributable to the relative stability of the conformers of glycosyl radical intermediates. The present cross-coupling reaction demonstrates the potential of iron-catalyzed stereo- and chemoselective carbon-carbon bond formation in the synthesis of bioactive compounds of certain structural complexity.

Synthesis of C-Aryl Glycosides by Glycosyl C(sp3)–C(sp2) Stille Cross-Coupling

Synthesis of C-Aryl Glycosides by Glycosyl C(sp3)–C(sp2) Stille Cross-Coupling

Glycosyl Stille Cross-Coupling with Anomeric Nucleophiles – A General Solution to a Long-Standing Problem of Stereocontrolled Synthesis of C-Glycosides

Aryl C-glycosides are common structural motifs found in bioactive natural products and commercially available drugs. Despite their importance, most chemical methods to prepare C-glycosides have relied on the nucleophilic addition/substitution of a glycosyl electrophile, which result in variable anomeric selectivities and yields. Furthermore, these methods are not compatible with saccharides containing free hydroxyl groups. Here, we describe a direct cross-coupling reaction of anomeric nucleophiles (anomeric stannanes) and aryl halides. This method is the first general approach to the synthesis of aryl C-glycosides resulting in exclusive anomeric selectivities for both anomers for a broad range of aryl and carbohydrate coupling partners (including unprotected saccharides).1 Introduction2 Synthesis of Anomeric Stannanes3 Glycosyl Stille Cross-Coupling4 Future Outlook5 Summary

Highly Stereospecific Cross-Coupling Reactions of Anomeric Stannanes for the Synthesis of C-Aryl Glycosides.

We demonstrate that configurationally stable anomeric stannanes undergo a stereospecific cross-coupling reaction with aromatic halides in the presence of a palladium catalyst with exceptionally high levels of stereocontrol. In addition to a broad substrate scope (>40 examples), this reaction eliminates critical problems inherent to nucleophilic displacement methods and is applicable to (hetero)aromatics, peptides, pharmaceuticals, common monosaccharides, and saccharides containing free hydroxyl groups.

Stereoselective Synthesis of 2-(β-C-Glycosyl)glycals: Access to Unusual β-C-Glycosides from 3-Deoxyglycals.

A novel method for the highly stereoselective synthesis of β-(1→2)-C-saccharides employing 3-deoxy- and 3-C-branched glycals as hermaphroditic substrates is revealed. The generality of the C-C bond formation reaction between the two sugar units is evaluated. The developed methodology is successfully applied to the synthesis of biologically significant subunits that are present in various natural products, which include mixed C-disaccharides with adjacent THP-THF rings, C-aryl glycosides, and highly functionalized β-C-glycosides.

ChemInform Abstract: Studies Toward the Total Synthesis of Pluraflavin A.

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.

Synthesis of rigid p-terphenyl-linked carbohydrate mimetics.

An approach to β-D-2-aminotalose- and β-D-2-aminoidose-configured carbohydrate mimetics bearing a phenyl substituent is described. Unnatural divalent rigid p-terphenyl-linked C-aryl glycosides with 2.0 nm dimension are available using Suzuki cross-couplings. The key compound, a p-bromophenyl-substituted 1,2-oxazine, was prepared by a stereoselective [3 + 3]-cyclization of a D-isoascorbic acid-derived (Z)-nitrone and lithiated TMSE-allene. The Lewis acid-induced rearrangement of this heterocycle provided the corresponding bicyclic 1,2-oxazine derivative that may be regarded as internally protected amino sugar analogue. After subsequent reduction of the carbonyl group, the resulting bicyclic compound was used for Suzuki cross-couplings to form biphenyl aminopyran or p-terphenyl-linked dimers. Hydrogenolysis afforded new unnatural aminosugar mimetics. Zinc in the presence of acid or samarium diiodide were examined for the N–O bond cleavage in order to obtain the rigid p-terphenyl-linked C-glycosyl dimers.

Studies toward the total synthesis of pluraflavin A.

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.

ChemInform Abstract: A Diversity Oriented One‐Pot Synthesis of Novel Iminosugar C‐Glycosides.

AbstractThe reaction proceeds with complete regio‐ and stereoselectivity.

Stereoselective C-glycosylation of furanosyl halides with arylzinc reagents

Abstract Were are reporting a highly diastereoselective, transition-metal-free approach of C-aryl glycosides in the pyranoside and furanoside series by the direct coupling of glycosyl halides with diarylzinc reagents in a toluene/di-n-butyl ether solvent mixture.

A diversity oriented one-pot synthesis of novel iminosugar C-glycosides

A mild and highly efficient one-pot method has been developed for the stereoselective synthesis of structurally diverse novel iminosugar C-aryl glycosides. The generality of this methodology is demonstrated with a wide variety of aryl nucleophiles and amines. The synthetic potential of this methodology is further shown in the domino synthesis of iminosugar based hybrid molecules.

ChemInform Abstract: Chemical Synthesis of N‐Aryl Glycosides

AbstractReview: 88 refs.

Preparation of L-vancosamine-related glycosyl donors

An improved practical synthesis of L-vancosamine-related glycosyl donors is described. The key steps include (1) stereoselective addition of methylcerium reagent to oximino ether and (2) stereoselective hydrogenation of exocyclic unsaturated glycoside in the presence of Wilkinson catalyst with C(5) inversion to give L-vancosamine derivatives. Three glycosyl donors were prepared, and their reactivities in the aryl C-glycoside formation were compared. Conversion of primary amine and azide to the corresponding N,N-dimethyl derivative is also described.

Chemical Synthesis of N-Aryl Glycosides

Along with the O- and C-aryl glycosides, N-aryl glycosides represent an important class of carbohydrate and heterocyclic aryl conjugates that possess diverse applications and implications of biological interest. However, most of the synthetic efforts have been directed toward the preparation of O- and C-aryl glycosides. This review focuses on the various strategies that have been employed to synthesize N-aryl glycosides, most of which developed in the past 20 years. Besides having their unique applications, these N-aryl glycosides can also be treated as the analogs of O- and C-aryl glycosides. Wide ranges of reaction conditions are discussed for the optimum conditions.

Design and stereoselective synthesis of a C-aryl furanoside as a conformationally constrained CHIR-090 analogue

The UDP-3-O-[(R)-3-hydroxymyristoyl]-N-acetylglucosamine deacetylase (LpxC) is a promising target for the development of novel antibiotic substances against multidrug-resistant Gram-negative bacteria.The C-aryl glycoside 3 was designed as conformationally constrained analogue of the potent LpxC-inhibitor CHIR-090.The chiral pool synthesis of 3 started with d-mannose. The C-aryl glycoside 8 was synthesized stereoselectively by nucleophilic attack of 4-iodine-substituted phenyllithium and subsequent reduction with Et3SiH. The ester 10 was obtained in a one-pot diol cleavage, CrO3 oxidation, and esterification. A Sonogashira reaction of the aryl iodide 11 led to the alkyne 17 which was transformed with H2NOH into the hydroxamic acid 3.

Secondary metabolites from a marine-derived fungus Aspergillus carneus Blochwitz

Prenylated indole alkaloids, carneamides A-C (1–3), quinazolinone derivatives, carnequinazolines A-C (5–7), aryl C-glycosides, carnemycin A, B (8, 9) and a drimane sesquiterpenoid (10), together with known compounds (11–21) were isolated from the marine-derived fungus Aspergillus carneus (Trichocomaceae) KMM 4638. The antimicrobial and cytotoxic activities of the several alkaloids were examined.

Regio- and Stereoselective Synthesis of 2-Deoxy-C-aryl Glycosides via Palladium Catalyzed Decarboxylative Reactions

An efficient and versatile approach for the synthesis of 2-deoxy-C-aryl glycosides is reported. This strategy is based on a palladium-catalyzed decarboxylative Heck coupling reaction of benzoic acids and glycals. A wide variety of glycals and benzoic acids have been screened, and all these reactions could afford the desired C-aryl glycoside products in moderate to good yields with exclusive regio- and stereoselectivities.

Total synthesis and structure revision of deacetylravidomycin M

Total synthesis of the unnatural enantiomer of deacetylravidomycin M was accomplished. The key steps include, (1) aryl C-glycosidation of the azido-bearing fucosyl acetate 2 by using catalytic Sc(OTf) 3, (2) the [2+2] cycloaddition reaction of alkoxybenzyne bearing an azido sugar to ketene silyl acetal, and (3) the ring expansion reaction of alkoxybenzocyclobutenone. The synthesis revealed that the natural product is not the proposed amine, but the corresponding N-oxide.

Studies toward the syntheses of pluramycin natural products. The first total synthesis of isokidamycin

We report the first total synthesis of the complex C-aryl glycoside isokidamycin, the epimer of the naturally-occurring pluramycin antibiotic kidamycin. The synthesis features a highly efficient Diels–Alder reaction between a substituted naphthyne and a glycosylated furan to form the anthracene core bearing a pendent angolosamine C-glycoside. The regiochemical outcome of the Diels–Alder reaction was controlled by employing a disposable silicon tether to link the reactive naphthyne and the glycosyl furan, rendering the cycloaddition intramolecular. The benzopyranone moiety of the aromatic nucleus was appended by cyclization of a functionalized vinylogous amide onto an advanced anthrol intermediate. The vancosamine amino glycoside was introduced by an O→ C-glycoside rearrangement that produced the β-anomer. Subsequent refunctionalizations then led to isokidamycin.

Epimeric Monosaccharide−Quinone Hybrids on Gold Electrodes toward the Electrochemical Probing of Specific Carbohydrate−Protein Recognitions

Carbohydrates represent one of the most significant natural building blocks, which govern numerous critical biological and pathological processes through specific carbohydrate-receptor interactions on the cell surface. We present here a new class of electrochemical probes based on gold surface-coated epimeric monosaccharide-quinone hybrids toward the ingenious detection of specific epimeric carbohydrate-protein interactions. Glucose and galactose, which represent a pair of natural monosaccharide C4 epimers, were used to closely and solidly conjugate with the 1,4-dimethoxybenzene moiety via a single C-C glycosidic bond, followed by the introduction of a sulfhydryl anchor. The functionalized aryl C-glycosides were sequentially coated on the gold electrode via the self-assembled monolayer (SAM) technique. X-ray photoelectron spectroscopy (XPS) was used to confirm the SAM formation, by which different binding energies (BE) between the glucosyl and the galactosyl SAMs on the surface, probably rendered by their epimeric identity, were observed. The subsequent electrochemical deprotection process readily furnished the surface-confined quinone/hydroquinone redox couple, leading to the formation of electrochemically active epimeric monosaccharide-quinone SAMs on the gold electrode. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) used for the detection of specific sugar-lectin interactions indicated that the addition of specific lectin to the corresponding monosaccharide-quinone surface, i.e., concanavalin A (Con A) to the glucosyl SAM and peanut agglutinin (PNA) to the galactosyl SAM, resulted in an obvious decrease in peak current, whereas the addition of nonspecific lectins to the same SAMs gave very minor current variations. Such data suggested our uniquely constructed gold surface coated by sugar-quinone hybrids to be applicable as electrochemical probes for the detection of specific sugar-protein interactions, presumably leading to a new electrochemistry platform toward the study of carbohydrate-mediated intercellular recognitions.