Concise total synthesis of flavone C-glycoside having potent anti-inflammatory activity

The total synthesis of anti-inflammatory active flavone C-glycoside isolated from oolong tea extract is achieved. Introducing a C-glucosyl moiety to an aryl system and constructing a fused tetracyclic ring characteristic to this natural product were conducted based on the O-to-C rearrangement of sugar moiety and the successive intramolecular Mitsunobu reaction, respectively. This concise and efficient synthetic pathway is applicable to the large-scale synthesis of target flavone and for constructing a large library of related compounds.     

Intramolecular metal-catalyzed amination of pseudo-anomeric C-H bonds

Intramolecular metal-catalyzed amination of a pseudo-anomeric C-H bond in a C-glycoside is reported. Treatment of α,β-C-carbamoyloxymethyl- or β-C-sulfamoyloxymethyl glycosides with Rh₂(OAc)₄, PhI(OAc)₂, and MgO provided original spirooxazolidines or spirooxathiazolidines in reasonable yields. No correlation between ‘anomeric’ stereochemistry and insertion efficiency was found for the conversion of carbamate derivatives whereas amination reactions of the corresponding sulfamate esters were found to be strongly dependent on the anomeric configuration.     

Facile synthesis of salmochelin S1, S2, MGE, DGE, and TGE

Salmochelin S1, S2, MGE, DGE, and TGE were prepared through amide bond connection of an aryl C-glucosyl acyl chloride (Ar¹COCl) and serine ester amines, followed by hydrogenolysis of the per-benzylated precursors. Each synthesis employed a highly diastereoselective Ni-catalyzed Negishi approach to the aryl C-glycoside subunit.     

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.     

Hydrogen atom transfer experiments provide chemical evidence for the conformational differences between C- and O-glycosides

The regioselectivity of the hydrogen atom transfer (HAT) reaction promoted by alkoxyl radicals generated from 3-hydroxypropyl α-d-mannopyranoside derivative (O-glycoside) and 2,6-anhydro-d-glycero-d-manno-decitol derivative (C-glycoside) is studied. The O-glycoside model abstracts preferentially the hydrogen atom at C-5 (1,8-HAT) while the C-glycoside abstracts the hydrogen atom at C-1 (1,6-HAT) but no abstraction at C-5 could be detected. These results are explained by the stereoelectronic control exerted by the exo-anomeric effect in the O-glycoside.     

Synthesis of thio-C-glycosides from 2′-carbonylalkyl C-glycosides by a tandem β-elimination and intramolecular hetero-Michael addition

2′-Carbonyl 5-S-acetyl-C-glycofuranosides and 2′-carbonyl 4-S-acetyl-C-glycopyranosides were converted in good yields to respective 5-thio-C-glycopyranosides and 4-thio-C-glycofuranosides under base treatment. The transformation was resulted from β-elimination on 2′-carbonyl C-glycoside to form α,β-conjugated aldehyde (or ketone) and following intramolecular hetero-Michael addition by the thiol group.     

Synthesis and evaluation of C-glycosides as hydrotropes and solubilizing agents

This work presents expeditious synthesis of C-glycoside amphiphiles in aqueous media from unprotected di- or mono-saccharides. A Horner-Wadsworth-Emmons/Michael addition/Barbier allylation sequence led to C-glycosides that exhibit hydrotropic properties. The hydrotropic and solubilizing properties of these homoallylic alcohols including a β-C-glycoside moiety as well as additional β-C-glycosidic ketones with a short (C₇) alkyl chain are also described and compared with those of commercial O-glucoside references.     

Synthesis of 1,2,3-triazolylpyranosides through click chemistry reaction

We have developed an efficient method for the synthesis of functionalized C-glycosyl 1,2,3-triazoles through a Cu(I)-promoted azide–alkyne 1,3-dipolar cycloaddition between a TMS-protected C-alkynyl-glycoside and organic azides. The reaction was accelerated by ultrasound irradiation and the addition of a base was not necessary to obtain the 1,2,3-triazole product. Moreover, further manipulation of the products led to chiral molecules with a C-glycoside linkage.     

Total synthesis of (−)-centrolobine: β-C-glycoside formation via a tandem Grignard addition and stereoselective hemi-ketal reduction

It has been demonstrated that an aryl-β-C-glycoside can be efficiently constructed via a sequence consisting of Brown asymmetric allylation, ring-closing metathesis, hydrogenation, nucleophilic addition, and stereoselective Et₃SiH reduction. The antibiotic natural product (−)-centrolobine was synthesized in this manner utilizing only five steps with an overall 53% yield.     

A concise synthesis of (3S,4S,5R)-1-(α-d-galactopyranosyl)-3-tetracosanoylamino-4,5-decanediol, a C-glycoside analogue of immunomodulating α-galactosylceramide OCH

A concise and convergent synthesis of the C-glycoside analogue 2b of immunomodulating α-galactosylceramide OCH 1b starting from readily available 2,3,4,6-tetra-O-benzyl-d-galactose 3 and l-arabinose 6 is described. The synthesis features the nucleophilic addition of an α-ethynyl sugar 5 to the phytosphingosine-precursor aldehyde 9 and would be applicable to a variety of C-glycoside analogues of interest.     

Design and synthesis of a phenyl C-glycoside derivative of Spliceostatin A and its biological evaluation toward prostate cancer treatment

We designed and synthesized a novel phenyl C-glycoside analogue of Spliceostatin A, which is potent splicing inhibitor and has anti-cancer activities. We successfully synthesized its right phenyl C-glycoside sugar fragment in shorter steps compared to previous synthetic methods for Spliceostatin A and revealed an appropriate fragment combination with a Julia-coupling reaction. Regarding biological activity, the Ph-C-glycoside analogue of Spliceostatin A showed repressed cell proliferation in three prostate cancer cell lines and suppressed AR-V7 expression.     

Synthesis and anti-tumor activity of β-C-glycoside analogs of the immunostimulant KRN7000

A ring-closing metathesis approach was employed for the synthesis of a β-C-glycoside analog of the immunostimulant KRN7000. The protected C-glycosyl amino acid derivative 18 was converted to amino-olefin 20, and osmylation served to install the diol unit as a mixture of separable syn and anti isomers. Deprotection to the hydroxy-amine 21 was followed by N-acylation and debenzylation to deliver the target compound 5.     

The conformational behaviour of α,β-trehalose-like disaccharides and their C-glycosyl,imino-C-glycosyl and carbagalactose analogues depends on the chemical nature of the modification: an NMR investigation

The conformational behaviour of β-O-Gal-(1→1)-α-Man 4 and the C-glycoside, carbaglycoside and aza-C-glycoside mimics 1–3 has been studied using J/NOE NMR data, molecular mechanics and molecular dynamics. It is shown that the population distributions around the glycosidic linkages of the different analogues depend on the chemical nature of the acetal or pseudoacetal residue.     

An amide orthoesterification route to N-(1′-alkylthioglucopyranosyl)indoles

The addition of 3-methylindolylmagnesium bromide to tetra-O-benzyl-α-d-gluconothionolactone yields the expected indole N-gluconothioamide as its hemiorthothioamide tautomer. The thiol function is alkylated to yield the corresponding orthothioamide, a 1′-alkylthio-substituted N-glycoside. Alternatively, the 1′-alkylthio-N-glycoside can be accessed from the corresponding indole N-gluconamide via a boron trifluoride-etherate mediated orthoesterification with ethanethiol. Radical reduction of the orthothioamide yields the N-glycosides in 2:1 stereoselectivity in favor of the β-N-glycoside, while reduction via the oxonium ion leads to an improved 6:1 selectivity.     

Highly stereoselective addition of organozinc reagents to pentopyranose derived glycals: effect of protecting group and assignment of C-glycoside stereochemistry

The nucleophilic addition of ethyl 3-propionylzinc iodide to a variety of differently protected pentopyranose derived d-glycals 6a-g proceeds with good to high levels of diastereoselectivity to provide the corresponding β-C-glycosides 7. The stereochemistry of the para-nitrobenzoate derivative 7d has been confirmed by X-ray crystallography, and the stereochemistry of the other β-C-glycoside products has been correlated to 7d. The stereochemical outcome observed supports the earlier suggestion by Isobe that through-space effects are important in stabilising and controlling the reactivity of the intermediate oxonium species represented by 11.     

Facile synthesis of 2-(β-C-glucopyranosyl)-β-amino acid: a new class of glycopeptide building block

A convenient preparation of both stereoisomers of a (2R)/(2S)-2-C-glycosylated β-amino acid is described. β-C-Glycoside was formed by the reaction of α-acetobromoglucose with carbanion of cyanoacetate. The steric bulk of the C-glycoside moiety does not hinder amino acid coupling, showing the utility of this carbohydrate-containing building block for glycopeptide synthesis.     

Synthesis of 4,8-anhydro-d-glycero-d-ido-nonanitol 1,6,7-trisphosphate as a novel IP3 receptor ligand using a stereoselective radical cyclization reaction based on a conformational restriction strategy

4,8-Anhydro-d-glycero-d-ido-nonanitol 1,6,7-trisphosphate (9), designed as a novel IP₃ receptor ligand having an α-C-glycosidic structure, was synthesized via a radical cyclization reaction with a temporary connecting allylsilyl group as the key-step. Phenyl 2-O-allyldimethylsilyl-3,4-bis-O-TBS-1-seleno-β-d-glucopyranoside (10a), conformationally restricted in the unusual ¹C₄-conformation, was treated with Bu₃SnH/AIBN to form the desired α-cyclization product 16a almost quantitatively. On the other hand, when a conformationally unrestricted O-benzyl-protected 2-O-allyldimethylsilyl -1-selenoglucoside 15 was used as the substrate, the radical reaction was not stereoselective and gave a mixture of the α-and β-products. From 16a, the target C-glucoside trisphosphate 9 was synthesized via phosphorylation of the hydroxyls by the phosphoramidite method. During the synthetic study, an efficient procedure for the oxidative C-Si bond cleavage, via a nucleophilic substitution at the silicon with p-MeOPhLi followed by Fleming oxidation, was developed. The C-glycoside 9 was found to be a full agonist for Ca²⁺ mobilization, although its activity was weaker than that of the natural ligand IP₃. Thus, the α-C-glucosidic structure was shown to be a useful mimic of the myo-inositol backbone of IP₃.     

Recent Advances on Natural Aryl-C-glycoside Scaffolds: Structure,Bioactivities, and Synthesis—A Comprehensive Review

Aryl-C-glycosides, of both synthetic and natural origin, are of great significance in medicinal chemistry owing to their unique structures and stability towards enzymatic and chemical hydrolysis as compared to O-glycosides. They are well-known antibiotics and potent enzyme inhibitors and possess a wide range of biological activities such as anticancer, antioxidant, antiviral, hypoglycemic effects, and so on. Currently, a number of aryl-C-glycoside drugs are on sale for the treatment of diabetes and related complications. This review summarizes the findings on aryl-C-glycoside scaffolds over the past 20 years, concerning new structures (over 200 molecules), their bioactivities—including anticancer, anti-inflammatory, antioxidant, antivirus, glycation inhibitory activities and other pharmacological effects—as well as their synthesis.     

Synthesis of the C17-C25 subunit of lasonolide A utilizing a Tsuchihashi-Yamamoto type rearrangement

An efficient synthesis of the C₁₇-C₂₅ subunit resident in (−)-lasonolide A is reported herein. The key reaction features that were utilized include a Tsuchihashi-Yamamoto type rearrangement and Molander-Reformatsky SmI₂ mediated intramolecular aldol reaction sequence. Lastly, a diastereoselective target oriented β-C-glycoside formation sequence via an oxocarbenium reduction completed the stereochemistry required for the completion of the C₁₇-C₂₅ segment of (−)-lasonolide A.     

A d-ribose-derived α-amino nitrile as a versatile intermediate for the collective synthesis of piperidine-type iminosugar C-glycosides

Iminosugar C-glycosides are valuable entities in medicinal chemistry. Herein we disclose a collective synthesis approach to such compounds, in a route that features a remarkably stable, fully characterised, ribose-derived iminium salt as a key intermediate. Addition of organometallic reagents to this key intermediate delivers a variety of iminosugar C-glycoside products in high yields and with excellent stereocontrol.