113 research outputs found
Solvent-Free Approaches in Carbohydrate Synthetic Chemistry: Role of Catalysis in Reactivity and Selectivity
Owing to their abundance in biomass and availability at a low cost, carbohydrates are
very useful precursors for products of interest in a broad range of scientific applications. For
example, they can be either converted into basic chemicals or used as chiral precursors for the
synthesis of potentially bioactive molecules, even including nonsaccharide targets; in addition, there
is also a broad interest toward the potential of synthetic sugar-containing structures in the field of
functional materials. Synthetic elaboration of carbohydrates, in both the selective modification of
functional groups and the assembly of oligomeric structures, is not trivial and often entails
experimentally demanding approaches practiced by specialized groups. Over the last years, a large
number of solvent-free synthetic methods have appeared in the literature, often being endowed
with several advantages such as greenness, experimental simplicity, and a larger scope than
analogous reactions in solution. Most of these methods are catalytically promoted, and the catalyst
often plays a key role in the selectivity associated with the process. This review aims to describe the
significant recent contributions in the solvent-free synthetic chemistry of carbohydrates, devoting a
special critical focus on both the mechanistic role of the catalysts employed and the differences
evidenced so far with corresponding methods in solution
Towards the semi-synthesis of phosphorylated mimics of glycosaminoglycans: Screening of methods for the regioselective phosphorylation of chondroitin
Glycosaminoglycan (GAG) mimics carrying phosphate rather than sulfate anionic groups have been poorly
investigated, in spite of their interesting perspectives. While some GAG-mimicking phosphorylated polymers
have been reported, to the best of our knowledge no phosphorylated polysaccharides having the same backbone
of natural sulfated GAGs have been accessed yet. To fill this gap, in this work two standard phosphorylation
protocols and two recently reported procedures have been screened on a set of polysaccharide species composed
by microbial sourced chondroitin and three partially protected, semi-synthetic derivatives thereof. A detailed
structural characterization by 1H, 13C and 31P NMR spectroscopy revealed the higher versatility of the innovative,
biomimetic reaction employing monopotassium salt of phosphoenolpyruvate (PEP–K) with respect to
standard phosphorylating agents (phosphoric acid or phosphorus oxychloride). Indeed, PEP-K and H3PO4 gave
similar results in the regioselective phosphorylation of the primary hydroxyls of unprotected chondroitin, while
only the former reacted on partially protected chondroitin derivatives in a controlled, regioselective fashion,
affording chondroitin phosphate (CP) polysaccharides with different derivatization patterns. The reported results
represent the first, key steps towards the systematic semi-synthesis of phosphorylated GAGs as a new class of
GAG mimics and to the evaluation of their biological activities in comparison with native sulfated GAGs
Resonating bipolarons
Electrons coupled to local lattice deformations end up in selftrapped
localized molecular states involving their binding into bipolarons when the
coupling is stronger than a certain critical value. Below that value they exist
as essentially itinerant electrons. We propose that the abrupt crossover
between the two regimes can be described by resonant pairing similar to the
Feshbach resonance in binary atomic collision processes. Given the
intrinsically local nature of the exchange of pairs of itinerant electrons and
localized bipolarons, we demonstrate the occurrence of such a resonance on a
finite-size cluster made out of metallic atoms surrounding a polaronic ligand
center.Comment: 7 pages, 4 figures, to be published in Europhysics Letter
Bottom-Up Approach to Eumelanin Photoprotection: Emission Dynamics in Parallel Sets of Water-Soluble 5,6-Dihydroxyindole-Based Model Systems
Assemblage of oligosaccharides via one-pot multiglycosidations
conferenza plenaria su invito personalmente presentata, ABSTRACT LP-
Nuove metodiche per la sintesi di derivati saccaridici. Un accesso efficace ed oligosaccaridi e nuovi coniugati glicosteroidici di interesse biologico
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