Daniela Tofani

Noncovalent Organocatalysis: A Powerful Tool for the Nucleophilic Epoxidation of α-Ylideneoxindoles

A novel asymmetric nucleophilic epoxidation for α-ylideneoxindole esters has been successfully devised, resulting in enantioenriched spiro compounds with two new contiguous stereocenters. The employed (S)-α,α-diphenylprolinol functions as a bifunctional catalyst, creating a complex H-bond network in conjunction with a substrate and an oxidant.

Fatty acid hydroxytyrosyl esters: structure/antioxidant activity relationship by ABTS and in cell-culture DCF assays.

A large series of hydroxytyrosyl esters of C2-C18 fatty acids with increasing lipophilicity was prepared by a new highly efficient method based on acylation of methylorthoformate-protected hydroxytyrosol. All products were tested for relative antioxidant effect using ABTS assays in ethanolic medium and DCF assays in L6 cells. No linear correlation between lipophilicity and antioxidant effect was found. ABTS assays showed a growing antioxidant capacity, with respect to hydroxytyrosol, only for medium-sized ester chains (C4-C10) and a nearly constant capacity for the higher homologues. This has been rationalized by molecular dynamics experiments in terms of partial shielding of the catecholic hydroxyls by long-chain esters. A similar and dose-dependent pattern was observed in DCF assays in L6 cells, but a sharp antioxidant activity drop resulted for long-chain esters, probably due to membrane entrapment.

Synthesis and Structure/Antioxidant Activity Relationship of Novel Catecholic Antioxidant Structural Analogues to Hydroxytyrosol and Its Lipophilic Esters

A large panel of novel catecholic antioxidants and their fatty acid or methyl carbonate esters has been synthesized in satisfactory to good yields through a 2-iodoxybenzoic acid (IBX)-mediated aromatic hydroxylation as the key step. The new catechols are structural analogues of naturally occurring hydroxytyrosol (3,4-DHE). To evaluate structure/activity relationships, the antioxidant properties of all catecholic compounds were evaluated in vitro by ABTS assay and on whole cells by DCF fluorometric assay and compared with that of the corresponding already known hydroxytyrosyl derivatives. Results outline that all of the new catechols show antioxidant capacity in vitro higher than that of the corresponding hydroxytyrosyl derivatives. Less evident positive effects have been detected in whole cells experiments. Cytotoxicity experiments, using MTT assay, on a representative set of compounds evidenced no influence in cell survival.

Singlet oxygen degradation of lignin

Abstract Lignin obtained by steam explosion of straw, beech (a hardwood plant), and pine (a softwood plant) was isolated and characterized by using standard methods. The irradiation of lignins with visible light in the presence of oxygen and of a singlet oxygen sensitizer (Rose Bengal) induced several modifications in the lignin structures that were monitored by using gel permeation chromatography (GPC) and UV spectroscopy. We observed a remarkable reduction of the mass distribution by GPC when monitoring at 280 nm and the shift of the residual chromatograms to mass values lower than the native lignins. These data are in agreement with a depolymerization reaction of lignins. The UV spectra showed that all the chemical species of lignins undergo several modifications during the irradiation reaction. Thus, the E 1 band reduced its absorbance and underwent a hypsochromic shift. The E 2 , and the B band were greatly reduced during the irradiation.

HSAB Driven chemoselectivity in alkylation of uracil derivatives. A high yielding preparation of 3-alkylated and unsymmetrically 1,3-dialkylated uracils

Abstract A qualitative hardness scale (N 1 3 4 ) has been found for the conjugated bases of 2-methoxy-4(3H)-pyrimidinones 1–3 and applied to high yielding chemoselective N 3 methylation, ethylation and benzylation reactions. Removal of the 2-methoxy group followed by a second alkylation affords unsymmetrically 1,3-disubstituted uracils.

Graft Copolymers of lignin from straw with 1-Ethenylbenzene: Synthesis and Characterization

The synthesis of copolymers between lignin from steam-exploded straw and 1-ethenylbenzene is described. Beforehand, lignin from steam-exploded straw was fully characterized by using elemental analysis, ultraviolet spectroscopy, gel permeation chromatography (GPC), Fourier transform infrared (FTIR), and both 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. Using a previously described procedure utilizing calcium chloride and hydrogen peroxide as reagents the synthesis of the copolymers was performed. FTIR of the copolymers showed the presence of both lignin and polystyrene. GPC analysis showed the presence of a fraction with high molecular weights. These results were confirmed from both viscosity data and differential calorimetry.

β,γ-Unsaturated α-amino ester derivatives by amination of γ-silylated α,β-unsaturated esters

Abstract The reactions of γ-silylated α,β-unsaturated esters 3a-e and 6 with NsONHCO 2 Et and CaO, produce β,γ-unsaturated N -(ethoxycarbonyl) α-amino esters 4a-e and 8 , isolated in 38–66 % yield, through addition of (ethoxycarbonyl)aminic function on the double bond and silyl group elimination. The reactivity increases in presence of α-substituents.

Desymmetrisation of meso-methylcyclooctanones. Highly enantioselective synthesis of C8 syn-isoprenoid and syn, syn-deoxypropionate subunits from a bicyclo[3.3.1]nonane precursor

Abstract The methyl esters of 3 R ,7 S -dimethyl- and 3 R ,5 R ,7 S -trimethyl-8-hydroxyoctanoic acids have been prepared in good yields and with e.e. >98% by chemical elaboration of the known exo , exo -3,7-dimethylbicyclo[3.3.1]nonan-9-one, the key step involving the desymmetrisation of the intermediate meso -ketones cis -3,7-dimethyl- and cis , cis -3,5,7-trimethyl-cyclooctanone through the corresponding chiral enolates generated by the lithium amide of the (+)bis[( R )-(1-phenylethylamine)]. The very high enantioselectivity observed might be related to the conformational features of the eight-membered ring.

Stereochemistry in reactions of chiral cyclic allylsilanes with (ethoxycarbonyl)nitrene. A new route to chiral N-substituted allylamines

Abstract The S E . reactions of chiral cyclic allylsilanes with (ethoxycarbonyl)nitrene generated by α- elimination of NsONHCO 2 Et with Et 3 N permit us to obtain chiral N -substituted allylic amines in good diastereomeric excess when stereoelectronic and conformational factors allow the anti attack.

Photochemical approach to the synthesis of naturally occurring thienylacetylenes

Abstract Three naturally occurring thienylacetylenes are synthesized through a photochemical coupling of 5-iodo-2-thienyl derivatives and 5-trimethylsilyl-2-thienylacetylene.