Antonio Franconetti

Palladium-Catalyzed Direct Stereoselective Synthesis of Deoxyglycosides from Glycals

Abstract Palladium(II) in combination with a monodentate phosphine ligand enables the unprecedented direct and α‐stereoselective catalytic synthesis of deoxyglycosides from glycals. Initial mechanistic studies suggest that in the presence of N‐phenyl‐2‐(di‐tert‐butylphosphino)pyrrole as the ligand, the reaction proceeds via an alkoxy palladium intermediate that increases the proton acidity and oxygen nucleophilicity of the alcohol. The method is demonstrated with a wide range of glycal donors and acceptors, including substrates bearing alkene functionalities.

Use of gold nanoparticles as crosslink agent to form chitosan nanocapsules: study of the direct interaction in aqueous solutions.

A systematic study of the interaction between free anionic gold nanoparticles and chitosan in a solution is presented. A spectroscopic study of the interaction between 10nm gold nanoparticles and low molecular weight chitosan is reported as a function of the concentration and pH of the polymer in a solution. Zeta potential measurements and TEM images indicate the effective aggregation of the nanoparticles in the presence of chitosan. At the same time, anionic gold nanoparticles act as crosslink agents to form chitosan nanocapsules with an average molecular size of 260nm. The changes of the surface plasmon band due to the adsorption of the polymer on the nanoparticle surface allow using of the citrate gold nanoparticles as sensors of the polymer for analytical purposes. The limit of detection for chitosan biopolymer is 69nM. The optimum pH for the interaction between the biopolymer and the nanoparticles is found at a value of 6.4, obtained from spectrophotometric measurements and applying a deconvolution analysis of the experimental data. A simple model based on molecular surface electrostatic interactions is proposed to understand the pH dependence of the investigated system.

Synthesis of hyperpolarizable biomaterials at molecular level based on pyridinium–chitosan complexes

Potential NLO-phore materials based on chitosan are described for the first time in this study. A series of fluorescent and quaternized pyridinium–chitosan derivatives have been synthesized by reaction of this polymer with easily available tunable pyrylium tetrafluoroborate salts. Among other spectroscopic techniques, 19F NMR, 13C CPMAS NMR and 2D diffusion experiments, were used to confirm the structures of the new pyridinium–chitosan complexes that show high fluorescence intensity. Degrees of N-substitution were achieved lower than 4.3%, allowing the original physicochemical properties of the biopolymer to be preserved. DFT calculations have been performed to investigate the molecular features related to the NLO properties in these compounds. NLO behavior was found to be clearly dependent on the nature and location of the substituent into the pyridinium core. Theoretical data reveal a large permanent dipolar moment, polarizabilities and hyperpolarizabilities making these molecules promising candidates as supramolecular devices exhibiting NLO properties with potentially enhanced solvatochromic properties.

Monitoring Glycan–Protein Interactions by NMR Spectroscopic Analysis: A Simple Chemical Tag That Mimics Natural CH–π Interactions

Detection of molecular recognition processes requires robust, specific, and easily implementable sensing methods, especially for screening applications. Here, we propose the difluoroacetamide moiety (an acetamide bioisoster) as a novel tag for detecting by NMR analysis those glycan-protein interactions that involve N-acetylated sugars. Although difluoroacetamide has been used previously as a substituent in medicinal chemistry, here we employ it as a specific sensor to monitor interactions between GlcNAc-containing glycans and a model lectin (wheat germ agglutinin). In contrast to the widely employed trifluoroacetamide group, the difluoroacetamide tag contains geminal (1) H and (19) F atoms that allow both (1) H and (19) F NMR methods for easy and robust detection of molecular recognition processes involving GlcNAc- (or GalNAc-) moieties over a range of binding affinities. The CHF2 CONH- moiety behaves in a manner that is very similar to that of the natural acetamide fragment in the involved aromatic-sugar interactions, providing analogous binding energy and conformations, whereas the perfluorinated CF3 CONH- analogue differs more significantly.

Fluorescent imino and secondary amino chitosans as potential sensing biomaterials.

A variety of fluorescent imino and secondary amino chitosans were synthesized under very mild conditions by reaction of the biopolymer amino functions with aromatic aldehydes in an acidified methanolic suspension. Simultaneous reactions of several aldehydes with chitosan were successfully carried out, and kinetic studies showed that 1-pyrenecarboxaldehyde reacts the fastest among them. An unprecedented study on the evaluation of the degree of N-substitution (DS, ranging from 31.7% to 12.0%) for the chitosan Schiff bases by using solid state CPMAS (13)C NMR is performed. A linear correlation between the DS obtained for the secondary amino chitosans by (1)H NMR (55.3-10.2%) and those obtained by CPMAS (13)C NMR (34.4-13.8%) has allowed us to calculate an empirical correlation factor that could be applied on chitosan-based aromatic systems. The new chiral-labelled chitosan derivatives exhibit a stable fluorescent behaviour, which was used to explore solvent sensoring applications.

Defective graphene as a metal-free catalyst for chemoselective olefin hydrogenation by hydrazine

A series of defective graphenes containing or not containing N, B, S and other heteroatoms exhibited general activity as metal-free catalysts for the hydrogenation of CC double bonds by hydrazine in the presence of oxygen. The best-performing graphene was the one obtained from the pyrolysis of alginate and subsequent exfoliation by sonication. The material was reusable in three consecutive runs without decay in its catalytic activity, and it exhibited 99% chemoselectivity for CC double bonds vs. nitro group hydrogenation in contrast with conventional Pd supported on carbon, which was almost unselective. Theoretical calculations using a model for defective graphene for styrene hydrogenation showed adsorption of the substrate by π–π stacking, resulting in activation of the double bond and direct interaction of cis-diimide with the CC group.

Fluoroacetamide Moieties as NMR Probes for molecular recognition of GlcNAc‐containing sugars: Modulation of the CH‐π Stacking Interactions by Different Fluorination Patterns

Abstract We herein propose the use of fluoroacetamide and difluoroacetamide moieties as sensitive tags for the detection of sugar–protein interactions by simple 1H and/or 19F NMR spectroscopy methods. In this process, we have chosen the binding of N,N′‐diacetyl chitobiose, a ubiquitous disaccharide fragment in glycoproteins, by wheat‐germ agglutinin (WGA), a model lectin. By using saturation‐transfer difference (STD)‐NMR spectroscopy, we experimentally demonstrate that, under solution conditions, the molecule that contained the CHF2CONH‐ moiety is the stronger aromatic binder, followed by the analogue with the CH2FCONH‐ group and the natural molecule (with the CH3CONH‐ fragment). In contrast, the molecule with the CF3CONH‐ isoster displayed the weakest intermolecular interaction (one order of magnitude weaker). Because sugar–aromatic CH–π interactions are at the origin of these observations, these results further contribute to the characterization and exploration of these forces and offer an opportunity to use them to unravel complex recognition processes.

Engineering active sites on reduced graphene oxide by hydrogen plasma irradiation: mimicking bifunctional metal/supported catalysts in hydrogenation reactions

H2 plasma has been used to generate carbon vacancies on reduced graphene oxide to increase its catalytic activity as a hydrogenation catalyst. A relationship between the power of the plasma treatment and the exposure time with the activity of the material was observed for CC double bond hydrogenation. The activity data in the case of 1-octene, showing skeletal isomerization besides hydrogenation, indicate that H2 plasma treatment can introduce hydrogenating and acid sites rendering a bifunctional catalyst that is reminiscent of the activity of noble metals supported on acid supports.

Enantioselective sulfoxidations employing the thermostable cyclohexanone monooxygenase from Thermocrispum municipale

The recently discovered cyclohexanone monooxygenase from Thermocrispum municipale (TmCHMO) was employed in the preparation of different optically active sulfoxides. This novel Baeyer-Villiger monooxygenase (BVMO) shows a similar substrate specificity and selectivity when compared with the prototype CHMO from Acinetobacter calcoaceticus. Interestingly, TmCHMO is able to catalyse the asymmetric sulfoxidations at relatively high temperatures, substrate concentrations and in the presence of organic solvents while maintaining or even increasing its selectivity. This shows that this newly found biocatalyst is a promising catalyst for the synthesis of optically active sulfoxides.

Carbohydrates: potential sweet tools against cancer

Cancer, one of the most devastating degenerative diseases nowadays, is one of the main targets in Medicinal Chemistry and Pharmaceutical industry. Due to the significant increase in the incidence of cancer within world population, together with the complexity of such disease, featured with a multifactorial nature, access to new drugs targeting different biological targets connected to cancer is highly necessary. Among the vast arsenal of compounds exhibiting antitumor activities, this review will cover the use of carbohydrate derivatives as privileged scaffolds. Their hydrophilic nature, together with their capacity of establishing selective interactions with biological receptors located on cell surface, involved in cell-to-cell communication processes, have allowed the development of an ample number of new templates useful in cancer treatment. Their intrinsic water solubility has allowed their use as of pro-drug carriers for accessing more efficiently the pharmaceutical target. The preparation of glycoconjugates in which the carbohydrate is tethered to a pharmacophore has also allowed a better permeation of the drug through cellular membranes, in which selective interactions with the carbohydrate motifs are involved. In this context, the design of multivalent structures (e.g. gold nanoparticles) has been demonstrated to enhance crucial interactions with biological receptors, like lectins, glycoproteins that can be involved in cancer progression. Moreover, the modification of the carbohydrate structural motif, by incorporation of metal complexes, or by replacing their endocyclic oxygen, or carbon atoms with heteroatoms has led to new antitumor agents. Such diversity of sugar-based templates with relevant antitumor activity will be cover in this review.