Carbohydrates as Synthetic Tools in Organic Chemistry

Dehydrogenation versus deprotonation of disaccharide molecules in vacuum: a thorough theoretical investigation

Dehydrogenation and deprotonation of sucrose and trehalose molecules in vacuum is theoretically studied by using ab initio calculations in the framework of the density functional theory. The differences in the structural, electronic, energetic and vibrational properties of dehydrogenated and deprotonated molecules are discussed, depending on the site from which the hydrogen atom or the proton has been removed. The dehydrogenated molecules are found to be stable, regardless of which hydrogen atom is removed. This contrasts with the instability of the deprotonated molecules, where break-ups or structural reorganizations of the molecule are observed in 20-30% of the cases, but only when the hydrogen atom whose proton is removed was bonded to a carbon atom. Considering the stability and possible rearrangements of the hydrogen network of the deprotonated/dehydrogenated molecule, the formation of additional hydrogen-bridge bonds compared with the nominal molecule appears to be more pronounced for the deprotonated molecules than for the dehydrogenated ones. Moreover, our calculations show that the hydrogen-transfer energy barriers are usually larger for the deprotonated molecules than for the dehydrogenated ones. Finally, compared with the nominal molecule, the vibrational frequency spectrum is shifted to lower frequencies for both the dehydrogenated and the deprotonated molecules.

Design and Synthesis of New α-hydroxy β-fluoro/β-trifluoromethyl and Unsaturated Phosphonates from Carbohydrate-Derived Building Blocks via Pudovik and Horner–Wadsworth–Emmons Reactions

Herein, we present the application of fluorinated carbohydrate-derived building blocks for α-hydroxy β-fluoro/β-trifluoromethyl and unsaturated phosphonates synthesis. Pudovik and Horner–Wadsworth–Emmons reactions were applied to achieve this goal. The proposed pathway of the key reactions is supported by the experimental results, as well as quantum chemical calculations. The structure of the products was established by spectroscopic (1D, 2D NMR) and spectrometric (MS) techniques. Based on our data received, we claim that the progress of the Pudovik and HWE reactions is significantly influenced by the acidic protons present in the molecules as assessed by pKa values of the reagent.

Extending the Martini 3 Coarse-Grained Force Field to Carbohydrates

Carbohydrates play an essential role in a large number of chemical and biochemical processes. High structural diversity and conformational heterogeneity make it problematic to link their measurable properties to molecular features. Molecular dynamics simulations carried out at the level of classical force fields are routinely applied to study the complex processes occurring in carbohydrate-containing systems, while the usefulness of such simulations relies on the accuracy of the underlying theoretical model. In this article, we present the coarse-grained force field dedicated to glucopyranose-based carbohydrates and compatible with the recent version of the Martini force field (v. 3.0). The parameterization was based on optimizing bonded and nonbonded parameters with a reference to the all-atom simulation results and the experimental data. Application of the newly developed coarse-grained carbohydrate model to oligosaccharides curdlan and cellulose displays spontaneous formation of aggregates of experimentally identified features. In contact with other biomolecules, the model is capable of recovering the protective effect of glucose monosaccharides on a lipid bilayer and correctly identifying the binding pockets in carbohydrate-binding proteins. The features of the newly proposed model make it an excellent candidate for further extensions, aimed at modeling more complex, functionalized, and biologically relevant carbohydrates.

Synthesis and Applications of Carbohydrate-Based Organocatalysts

Organocatalysis is a very useful tool for the asymmetric synthesis of biologically or pharmacologically active compounds because it avoids the use of noxious metals, which are difficult to eliminate from the target products. Moreover, in many cases, the organocatalysed reactions can be performed in benign solvents and do not require anhydrous conditions. It is well-known that most of the above-mentioned reactions are promoted by a simple aminoacid, l-proline, or, to a lesser extent, by the more complex cinchona alkaloids. However, during the past three decades, other enantiopure natural compounds, the carbohydrates, have been employed as organocatalysts. In the present exhaustive review, the detailed preparation of all the sugar-based organocatalysts as well as their catalytic properties are described.

Screening of simple carbohydrates as a renewable organocatalyst for the efficient construction of 1,3-benzoxazine scaffold

A convenient protocol for the two component preparation of 1,3-benzoxazines by using several protected and unprotected carbohydrate molecules as organocatalysts have been developed which is broadly applicable to condensation reaction between variety of Mannich bases and paraformaldehyde. This study revealed that fructose have much higher catalytic activity than the other carbohydrates and can be an alternative to metal-containing catalysts as a green renewable organocatalyst for efficient and rapid construction of 1,3-benzoxazine skeleton. In this context, 21 benzoxazine compounds were successfully synthesized and spectral characterizations of these compounds were carried out by spectroscopic methods and elemental analysis. Furthermore, density functional theory (DFT) calculations have been performed to study the detailed mechanism of organocatalyst assisted synthesis of the benzoxazine monomers. The results obtained from these calculations showed that the more realistic reaction pathway involves formation of a phenolate based intermediate which loses a water molecule to form benzenaminium ion. Subsequently, this ion provides the formation of the corresponding benzoxazines with good yields through the intramolecular ring closure step.

Evolution of phosphorus-thioether ligands for asymmetric catalysis

In the early 1990s chiral P-thiother ligands emerged as promising ligands in the field of asymmetric catalysis, with the development of many P-thioether ligand families. However, only a few of them have shown a broad reaction and substrate scope. So, compared with other heterodonor ligands such as the widely studied P-N ligands, their impact in asymmetric catalysis was not realised until recently. This has been mainly attributed to the difficulty of controlling the configuration at the sulfur atom when coordinated to the metal. More recently, it has been found that this problem could be solved by a rigorous choice of the ligand scaffold, a process usually aided by mechanistic studies. This allowed the recent discovery of new P-thioether ligand families with a broader versatility, both in reactions and in substrate/reagent scope. This feature article aims to highlight those new P-thioether ligand libraries and the relationship between the structure and catalytic performance.

Nutritional Status of Tomato (Solanum lycopersicum) Fruit Grown in Fusarium-Infested Soil: Impact of Cerium Oxide Nanoparticles

In this study, the impact of cerium oxide nanoparticles on the nutritional value of tomato (Solanum lycopersicum) fruit grown in soil infested with Fusarium oxysporum f. sp. lycopersici was investigated in a greenhouse pot study. Three-week old seedlings of Bonny Best tomato plants were exposed by foliar and soil routes to nanoparticle CeO₂ (NP CeO₂) and cerium acetate (CeAc) at 0, 50, and 250 mg/L and transplanted into pots containing a soil mixture infested with the Fusarium wilt pathogen. Fruit biomass, water content, diameter, and nutritional content (lycopene, reducing and total sugar) along with elemental composition, including Ce, were evaluated. Fruit Ce concentration was below the detection limit in all treatments. Foliar exposure to NP CeO₂ at 250 increased the fruit dry weight (67%) and lycopene content (9%) in infested plants, compared with the infested untreated control. Foliar exposure to CeAc at 50 mg/L reduced fruit fresh weight (46%) and water content (46%) and increased the fruit lycopene content by 11% via root exposure as compared with the untreated infested control. At 250 mg/L, CeAc increased fruit dry weight (94%), compared with the infested untreated control. Total sugar content decreased in fruits of infested plants exposed via roots to NP CeO₂ at 50 mg/kg (63%) and 250 mg/kg (54%), CeAc at 50 mg/kg (46%), and foliarly at 50 mg/L (50%) and 250 mg/L (50%), all compared with the infested untreated control. Plants grown in Fusarium-infested soil had decreased fruit dry weight (42%) and lycopene content (17%) and increased total sugar (60%) and Ca content (140%), when compared with the noninfested untreated control (p ≤ 0.05). Overall, the data suggested minimal negative effects of NP CeO₂ on the nutritional value of tomato fruit while simultaneously suppressing Fusarium wilt disease.

Reduction of sugar derivatives to valuable chemicals: utilization of asymmetric carbons

Recent progress on non-furfural routes from sugar derivatives to valuable chemicals including chiral chemicals was reviewed.

Epoxides of d-fructose and l-sorbose: A convenient class of "click" functionality for the synthesis of a rare family of amino- and thio-sugars

The strained epoxide ring of oxirane-derived furanoside and pyranoside of d-fructose are regioselectively opened by various primary and secondary amines as well as azide to yield C4-alkylamino-C4-deoxy and the corresponding azido derivatives. The epoxide ring of a furanoside derived from l-sorbose, a C-5 epimer of d-fructose also afforded C4-amino and C4-azido analogues. All three epoxides generated piperazine linked disaccharides. These epoxides are also easily opened by p-tolylthiol to access thiosugars. One such thiosugar was converted to vinylsulfone-modified fructofuranoside and subjected to nucleophillic addition. A suitably designed vinyl sulfone-modified fructofuranoside having a leaving group at C-6, act as an efficient substrate for MIRC (Michael Initiated Ring Closure) reactions to construct cyclopropane skeleton in d-fructose. The strategy is general in nature and provides an easy access to cyclopropanated sugar derivatives. Thus, the easily accessible "spring loaded" epoxides of d-fructose and l-sorbose have been used as pivotal starting point for the synthesis of hitherto unknown modified carbohydrates.

Use of chiral auxiliaries in the asymmetric synthesis of biologically active compounds: A review

This review article describes the use of some of the most popular chiral auxiliaries in the asymmetric synthesis of biologically active compounds. Chiral auxiliaries derived from naturally occurring compounds, such as amino acids, carbohydrates, and terpenes, are considered essential tools for the construction of highly complex molecules. We highlight the auxiliaries of Evans, Corey, Yamada, Enders, Oppolzer, and Kunz, which led to remarkable progress in asymmetric synthesis in the last decades and continue to bring advances until the present day.

A readily accessible and modular carbohydrate-derived thioether/selenoether-phosphite ligand library for Pd-catalyzed asymmetric allylic substitutions

A large library of thioether/selenoether-phosphite ligands have been tested in the Pd-catalyzed asymmetric allylic substitution reaction. The presented ligands are derived from cheap and available carbohydrates and they are air-stable solids and easy to handle. Their highly modular nature has made it possible to achieve excellent enantioselectivities in the substitution of a range of hindered and unhindered substrates (ees up to 99% and 91%, respectively). In addition, twelve C-, N- and O-nucleophiles can be efficiently introduced, independently of their nature. Among the whole library, ligands that contain an additional chiral centre in the alkyl backbone chain next to the phosphite group and an enantiopure biaryl phosphite group provided the best enantioselectivities. In general, there is a cooperative effect between these two chiral elements, and therefore, a matched combination between them is necessary to achieve the highest enantioselectivities. However, in the case of cyclic substrates, this cooperative effect is less pronounced and advantageously, both enantiomers of the product can be obtained by setting up the desired configuration of the biaryl phosphite group. Studies of the key Pd-π-allyl intermediates allowed us to better understand the enantioselectivities obtained experimentally.

Hexamethylene-1,6-bis(N-d-glucopyranosylamine) as a novel corrosion inhibitor for oil and gas industry: electrochemical and computational analysis

Experimental and theoretical studies on hexamethylene-1,6-bis(N-d-glucopyranosylamine) as a novel inhibitor against sweet corrosion useful for oil and gas industry.

Asymmetric organocatalytic synthesis of tertiary azomethyl alcohols: key intermediates towards azoxy compounds and α-hydroxy-β-amino esters

A series of peracylated glycosamine-derived thioureas have been synthesized and their behavior as bifunctional organocatalysts has been tested in the enantioselective nucleophilic addition of formaldehyde tert-butyl hydrazone to aliphatic α-keto esters for the synthesis of tertiary azomethyl alcohols. Using the 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-β-d-glucosamine derived 3,5-bis-(trifluoromethyl)phenyl thiourea the reaction could be accomplished with high yields (75-98%) and moderate enantioselectivities (50-64% ee). Subsequent high-yielding and racemization-free tranformations of both aromatic- and aliphatic-substituted diazene products in a one pot fashion provide a direct entry to valuable azoxy compounds and α-hydroxy-β-amino esters.

Corrosion inhibition of mild steel in 1M HCl by D-glucose derivatives of dihydropyrido [2,3-d:6,5-d'] dipyrimidine-2, 4, 6, 8(1H,3H, 5H,7H)-tetraone

D-glucose derivatives of dihydropyrido-[2,3-d:6,5-d']-dipyrimidine-2, 4, 6, 8(1H,3H, 5H,7H)-tetraone (GPHs) have been synthesized and investigated as corrosion inhibitors for mild steel in 1M HCl solution using gravimetric, electrochemical, surface, quantum chemical calculations and Monte Carlo simulations methods. The order of inhibition efficiencies is GPH-3 > GPH-2 > GPH-1. The results further showed that the inhibitor molecules with electron releasing (-OH, -OCH3) substituents exhibit higher efficiency than the parent molecule without any substituents. Polarization study suggests that the studied compounds are mixed-type but exhibited predominantly cathodic inhibitive effect. The adsorption of these compounds on mild steel surface obeyed the Langmuir adsorption isotherm. SEM, EDX and AFM analyses were used to confirm the inhibitive actions of the molecules on mild steel surface. Quantum chemical (QC) calculations and Monte Carlo (MC) simulations studies were undertaken to further corroborate the experimental results.

CO/O2 assisted oxidative carbon-carbon and carbon-heteroatom bond cleavage for the synthesis of oxosulfonates from DMSO and olefins

Selective carbon–carbon and carbon–heteroatom bond cleavage was achieved in a one reaction system.

Selective carbon–carbon and carbon–heteroatom bond cleavage was achieved in a one reaction system. With this strategy a novel Pd/Cu-catalyzed aerobic oxidative oxosulfonation of olefins with DMSO has been developed. Preliminary mechanistic investigations indicated that CO/O₂ assisted the bond cleavage and the leaving groups from the starting materials were trapped by O₂ and underwent a hydroxylation process.

Carbohydrates as enantioinduction components in stereoselective catalysis

Carbohydrate derivatives are readily available chiral molecules, yet they are infrequently employed as enantioinduction components in stereoselective catalysis. In this review, synthetic approaches to carbohydrate-based ligands and catalysts are outlined, along with example applications in enantioselective catalysis. A wide range of carbohydrate-based functionality is covered, and key trends and future opportunities are identified.

Novel glyconanoconjugates: synthesis, characterization and bioapplications

The impressive properties of nanoparticles (NPs) have caused them to gain considerable attention for biological applications such as cancer therapy.

Carbohydrates in diversity-oriented synthesis: challenges and opportunities

Carbohydrates are attractive building blocks for diversity-oriented synthesis due to their stereochemical diversity and high density of polar functional groups.

Recent advances in multicomponent reactions involving carbohydrates

Being an attractive class of naturally occurring molecules with fascinating properties, sugars and their derivatives have wide applications in different fields especially in drug discovery.

Glyconanosynthons as powerful scaffolds and building blocks for the rapid construction of multifaceted, dense and chiral dendrimers

The arsenal of available carbohydrates can be manipulated to provide versatile building blocks toward the syntheses of complex and chiral dendrimers.