Intramolecular Pd-Catalyzed Arylation of 1-Amidosugars: A New Route to N-Glycosyl Quinolin-2-ones

Pd-Catalyzed Coupling of Bromo-N- (β-glucopyranosyl)quinolin-2-ones with Amides: Synthesis of N-glucosyl-6BrCaQ Conjugates with Potent Anticancer Activity

A series of N-glycosyl- 6BrCaQ conjugates was synthesized through a Pd-catalyzed cross-coupling reaction between brominated N-glycosyl quinolin-2-one derivatives and various nitrogen nucleophiles. Antiproliferative assays revealed that this new series of analogues represents a promising class of antitumor compounds as illustrated by the high biological activity observed for several derivatives towards different cancer cell lines compared to the non-glycosylated congeners.

Mechanistic Study of the Copper(II)-Mediated Site-Selective O-Arylation of Glycosides with Arylboronic Acids

Glycosides having multiple free OH groups have been shown to undergo site-selective O-arylations in the presence of arylboronic acids and copper(II) acetate. Herein, a mechanistic analysis of these Chan-Evans-Lam-type couplings is presented based on reaction kinetics, mass spectrometric analysis of reaction mixtures, and substituent effect studies. The results establish that the formation of a substrate-derived boronic ester accelerates the rate-determining transmetalation step. Intramolecular transfer of the aryl group from the boronic ester is ruled out in favor of a pathway in which the key pre-transmetalation assembly is generated from a boronic ester, a copper complex, and a second equivalent of arylboronic acid.

Synthesis of N-Glycosides by Silver-Assisted Gold Catalysis

The synthesis of N-glycosides from stable glycosyl donors in a catalytic fashion is still challenging, though they exist ubiquitously in DNA, RNA, glycoproteins, and other biological molecules. Herein, silver-assisted gold-catalyzed activation of alkynyl glycosyl carbonate donors is shown to be a versatile approach for the synthesis of purine and pyrimidine nucleosides, asparagine glycosides and quinolin-2-one N-glycosides. Thus synthesized nucleosides were subjected to the oxidation-reduction sequence for the conversion of Ribf- into Araf- nucleosides, giving access to nucleosides that are otherwise difficult to synthesize. Furthermore, the protocol is demonstrated to be suitable for the synthesis of 2'-modified nucleosides in a facile manner. Direct attachment of an asparagine-containing dipeptide to the glucopyranose and subsequent extrapolation to afford the dipeptide disaccharide unit of chloroviruses is yet another facet of this endeavor.

Recent advances in the direct O-arylation of carbohydrates

Methods for the O-arylation of hydroxyl and hemiacetal groups in carbohydrates via C(sp2)-O bond formation are discussed. Such methods provide an alternative disconnection to the traditional approach of nucleophilic substitution between a sugar-derived electrophile and a phenol or phenoxide nucleophile. They have led to new opportunities for stereoselectivity, site-selectivity and chemoselectivity in the preparation of O-aryl glycosides and carbohydrate-derived aryl ethers, compounds that are useful for a broad range of applications in medicinal chemistry, glycobiology and organic synthesis.

Synthesis of N-Glycosyl-2-oxindoles by Pd-Catalyzed N-Arylation of 1-Amidosugars

An efficient intramolecular Pd-catalyzed N-arylation of o-iodo-amidosugars for the synthesis of N-glycosylated oxindoles has been reported. The coupling reaction takes place in toluene and involves Pd(OAc)₂/RuPhos catalytic systems in the presence of K₂CO₃. This versatile approach was extended successfully to the synthesis of other N-glycosylated heterocycles.

Copper-mediated anomeric O-arylation with organoboron reagents

Copper-mediated couplings of arylboroxines with glycosyl hemiacetals furnish O-aryl glycosides via Csp2-O bond formation. The method enables the anomeric O-arylation of protected pyranose and furanose derivatives, and is tolerant of functionalized arylboroxine partners. Whereas mixtures of anomers are formed from glucopyranose, galactopyranose and arabinofuranose hemiacetals, the α-anomer is generated selectively from mannopyranose and mannofuranose-derived substrates.

Synthesis of aryl-thioglycopeptides through chemoselective Pd-mediated conjugation

We describe herein a Pd-catalyzed methodology for the thioglycoconjugation of iodoaryl peptides and aminoacids. This operationally simple process occurs under semi-aqueous conditions and displays wide substrate scope. The strategy has been successfully applied to both the thioglycosylation of unprotected peptides and the generation of thioglyco-aminoacid building blocks, including those suitable for solid phase peptide synthesis. To demonstrate the broad potential of this technique for late stage functionalization, we successfully incorporated challenging unprotected β-S-GlcNAc- and α-S-GalNAc-derivatives into very long unprotected peptides. This study opens the way to new applications in chemical biology, considering the well-recognized advantages of S-glycosides over O-glycosides in terms of resistance towards both enzymatic and chemical degradation.

Convergent Synthesis of N,S-bis Glycosylquinolin-2-ones via a Pd-G3-XantPhos Precatalyst Catalysis

Buchwald-Hartwig-Migita cross-coupling of 1-thiosugars with α- or β-3-iodo-N-glycosylquinolin-2-ones has been accomplished under mild and operationally simple reaction conditions through the use of a Pd-G3 XantPhos palladacycle precatalyst. This new methodology has been successfully applied to a variety of α- or β-mono-, di-, and poly-thiosugar derivatives to efficiently synthesize a series of α- or β-N,S-bis-glycosyl quinolin-2-ones, which are difficult to synthesize by classical methods.

Efficient Buchwald-Hartwig-Migita Cross-Coupling for DNA Thioglycoconjugation

An efficient method for the thioglycoconjugation of iodinated oligonucleotides by Buchwald-Hartwig-Migita cross-coupling under mild conditions is reported. The method enables divergent synthesis of many different functionalized thioglycosylated ODNs in good yields, without affecting the integrity of the other A, C, and G nucleobases.

Controllable Activation of Pd-G3 Palladacycle Precatalyst in the Presence of Thiosugars: Rapid Access to 1-Aminobiphenyl Thioglycoside Atropoisomers at Room Temperature

A controllable method for the functionalization of XantPhos Pd-G3 precatalyst with thiosugars and thiols has been established. Under mild and operationally simple reaction conditions through just mixing of precatalyst and thiosugars (α- or β-mono-, di- and poly-thiosugar derivatives) in water at 25 °C for 20 min, a series of 1-aminobiphenyl thioglycosides that are difficult to synthesize by classical methods has been synthesized in very high yields.