Copper-Catalyzed Anomeric O-Arylation of Carbohydrate Derivatives at Room Temperature

Anion-Bridged Dual Hydrogen Bond Enabled Concerted Addition of Phenol to Glycal

A noncovalent organocatalytic concerted addition of phenol to glycal is developed for the stereoselective and regioselective construction of biologically important phenolic 2-deoxyglycosides, featuring wide substrate tolerance. The method relies on an anion-bridged dual hydrogen bond interaction which is experimentally proved by Nuclear Magnetic Resonance (NMR), Ultraviolet and visible (UV-vis), and fluorescence analysis. Experimental evidence including kinetic analysis, Kinetic Isotope Effect (KIE) studies, linear free energy relationship, Hammett plot, and density functional theory (DFT) calculations is provided for a concerted mechanism where a high-energy oxocarbenium ion is not formed. In addition, the potential utility of this method is further demonstrated by the synthesis of biologically active glycosylated flavones. The benchmarking studies demonstrate significant advances in this newly developed method compared to previous approaches.

Furofuran Lignans for Plant Protection: Discovery of Sesamolin and Its Derivatives as Novel Anti-Tobacco Mosaic Virus and Antibacterial Agents

Natural products have been a valuable source of efficient and low-risk pesticides. In this work, a series of novel sesamolin derivatives A0-A31 and B0-B4 were designed and synthesized via structural simplification of furofuran lignan phrymarolin II, and their antiviral and antibacterial activities were systematically evaluated. The bioassay results showed that compound A24 displayed remarkable inactivation activity against tobacco mosaic virus (TMV) with an EC₅₀ value of 130.4 μg/mL, which was superior to that of commercial ningnanmycin (EC₅₀ = 202.0 μg/mL). The antiviral mode of action assays suggested that compound A24 may obstruct self-assembly by binding to TMV coat protein (CP), thus resisting the TMV infection. In addition, compound A25 possessed prominent antibacterial activities, especially against Ralstonia solanacearum with an EC₅₀ value of 43.8 μg/mL, which is better than those of commercial bismerthiazol and thiodiazole copper. This research lays a solid foundation for the utilization of furofuran lignans in crop protection.

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.

The Palladium-Catalyzed Glycosylation of Halotropones

A range of mono- and disaccharides, including glucose derivative 10, has been cleanly coupled, in the presence of a Pd catalyst, with various halogenated and structurally distinctive tropones, including "parent" compound 11, to afford the corresponding α- and β-anomeric forms of the tropolone glycosides, e.g., 12 and 13, respectively. Varying the ligand used influences the anomer distribution significantly and such that either the α- or β-form predominates. Notable chemo- and regioselectivities are observed when dihalogenated troponoids are employed as coupling partners.

Total Synthesis and Anti-Tobacco Mosaic Virus Activity of the Furofuran Lignan (±)-Phrymarolin II and Its Analogues

Phrymarolin II, a furofuran lignan isolated from Phryma leptostachya L., features a 3,7-dioxabicyclo[3.3.0]octane skeleton. Herein, we report an alternative total synthesis of (±)-phrymarolin II (2), which was performed in 9 steps from commercially available sesamol. The key steps of the synthesis included a zinc-mediated Barbier-type allylation and a copper-catalyzed anomeric O-arylation. Our total synthesis allowed the synthesis of analogues of (±)-phrymarolin II. Most derivatives displayed good to excellent in vivo activity against tobacco mosaic virus (TMV). (±)-Phrymarolin II (2) and compounds (±)-31d and (±)-31g exhibited similar or higher activity than commercial ningnanmycin, which indicated that phrymarolin lignans are a promising new class of plant virus inhibitors.

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 aryl ethers of carbohydrates via reaction with arynes: selective O-arylation of trans-vicinal dihydroxyl groups in carbohydrates

A new method for the O-arylation of carbohydrates under metal-free conditions using arynes as an aryl source has been developed. This approach works well with mono, di and trihydroxy compounds. Preferential O-arylation takes place at primary over secondary and equatorial over axial. Site-selective O-arylation was achieved with the substrate having trans vicinal diequatorial hydroxyls.

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.