Natural and Synthetic Xanthones as Monoamine Oxidase Inhibitors: Biological Assay and 3D‐QSAR

Fifty‐nine xanthones (=9H‐xanthen‐9‐ones) of natural or synthetic origin were investigated for their inhibitory activity toward monoamine‐oxidase A (MAO‐A) and MAO‐B. The compounds demonstrated reversible, time‐independent activities, with selectivity toward MAO‐A. The most active inhibitor had an IC₅₀ of 40 nM . Electron absorption spectroscopy revealed the formation of a 1 : 1 charge‐transfer complex between lumiflavine and xanthones. 3D‐QSAR Studies according to the CoMFA/GOLPE procedure provided information on the relationship between steric and electrostatic fields and MAO‐A inhibition. The ALMOND procedure yielded additional topographical information on structural factors favoring activity.     

2,2,5,5,8,8‐Hexa­methyl‐2,3,5,6,7,8‐hexa­hydro­imidazo­[1,2‐a]­pyrazine‐3,6‐dione,a bicyclic product of α‐amino­isobutyric acid condensation

The title compound, C₁₂H₁₉N₃O₂, is an unusual product of silica‐catalyzed intermolecular condensation of α‐amino­isobutyric acid. The mol­ecule has three types of C—N bonds: a double bond, a cis‐amide bond and single bonds, two of which are typical and two having intermediate lengths due to π‐electron delocalization between C=N and C=O groups. The cis‐amide moieties interact to form dimers via hydrogen bonds which stack in parallel layers.     

Studies on pyrrolidinones. Synthesis of 4,5-fused-3-hydroxypyridinyl-2-propionic acid derivatives

The synthesis of some condensed indolizinediones derived from pyroglutamic acid is described. Treatment of these ketones in HCl, HBr or MeONa/MeOH furnished aryl propionic acid derivatives. During the ketone transformations, two sequential processes could take place in competitive manner to provide heterocyclic systems bearing carboxylic acid or hydroxycarboxylic acid function. Easy synthesis of amides indicates that potential DNA-intercalating heterocyclic systems fused on γ-carboline and isoquinoline nucleus could be obtained from these series.     

Luminescence properties of pHEMA-TiO2 gels based hybrids materials

Photoluminescence (PL) of photochromic pHEMA-TiO₂ gels-based hybrids was studied by means of time- and energy-resolved spectroscopy at temperatures between 300 K and 10 K. The PL band at 485 nm is assigned to S0←T1 transition of methoxyphenol (organic molecule added to the commercial monomer hydroxyethyl methacrylate, HEMA and used as an inhibitor of spontaneous polymerisation) in the polymer environment, while the PL band at 600 nm is assigned to the self-trapped exciton onto octahedral TiO₆ site of the inorganic component. The mechanisms of the excited states population are discussed. In particular it is shown that both singlet-triplet energy transfer in methoxyphenol and methoxyphenol–TiO₂ charge transfer are strongly affected by the material composition and temperature. The hypothesis about the photoexcited holes annihilation with the trapped electrons is confirmed to be one of main mechanisms limiting the Ti³⁺ centres concentration.     

Giant Rabi splitting in metal/semiconductor nanohybrids

We present strong coupling regime between localized plasmon in lithographed nanoparticles and excitons in an organic semiconductor. The lithographed nanoparticles allow a very good control of the particle size and environment, thereby avoiding a large inhomogeneous broadening of the plasmonic resonances which could partially mask the plasmon/exciton hybridization. The nanoparticles diameter ranges from 100 to 200 nm. A giant Rabi splitting energy of 450 meV is obtained, and typical behaviors of mixed states, i.e. anticrossing of their energies and crossing of their linewidths, are observed. Three-dimensional finite-difference time-domain simulations and coupled oscillator calculations are used to analyze and corroborate the experimental results.     

A convenient route towards novel H8-1,1′-bis-(dibenzofuran-2-ol) derivatives and evaluation of their use as chiral auxiliaries

A novel bidentate ligand, H₈-BIFOL, was successfully prepared and resolved starting from readily available reagents. The reactivity and selectivity was evaluated in the alkynylation of benzaldehyde, resulting in ee’s up to 56%.