Bárbara Gigante

Synthesis and catalytic activity of a chiral periodic mesoporous organosilica (ChiMO)

A chiral vanadyl salen complex having two peripheral trimethoxysilyl groups has been used to obtain a chiral periodic mesoporous organosilica having MCM-41 periodicity and the two Si-CH2 groups anchored on the framework; this solid induces 30% enantioselectivity in the cyanosilylation of benzaldehyde.

A short synthesis of phenanthro[2,3-d]imidazoles from dehydroabietic acid. Application of the methodology as a convenient route to benzimidazoles

Abstract Methyl cis -deisopropyldehydroabietate was selectively nitrated at the 12-position by reaction with ‘claycop’, a montmorillonite clay impregnated with copper(II) nitrate. The 12-nitro compound was reduced to the corresponding amine and this was subjected to a combined acylation and ortho nitration. The compounds so produced were further converted into octahydro-1 H -phenanthro[2,3- d ]imidazoles by reductive cyclization. The same acylation- ortho nitration methodology was shown to provide a short synthesis of 2-substituted benzimidazoles from aniline.

Vanadyl salen complexes covalently anchored to an imidazolium ion as catalysts for the cyanosilylation of aldehydes in ionic liquids

Two vanadyl salen complexes having peripheral styryl substituents have been reacted with 1-methyl-3-(3-mercaptopropyl)-imidazolium chloride using azoisobutyronitrile as radical initiator. The resulting compounds contain at the same time a vanadyl salen complex and one imidazolium cation. In agreement with the expectations in view of their structure, these compounds were insoluble in conventional organic solvents, but completely miscible in imidazolium ionic liquids. These vanadyl salen complexes bonded to an imidazolium cation are highly active and reusable catalysts for the cyanosilylation of aldehydes. Moderate enantiomeric excesses were obtained using the chiral version of this complex.

On the activity of chiral chromium salen complexes covalently bound to solid silicates for the enantioselective epoxide ring opening

Abstract Two series of solid catalysts in which a chiral chromium salen complex has been anchored on aminopropyl-functionalized SiO 2 , ITQ-2 or MCM-41 have been prepared. In those catalysts in which anchoring of the complex was accomplished through coordination with the metal high enantiomeric excesses were obtained (up to 70% enantiomeric excess (e.e.)), but the complex leaches to the solution on a large extent. In contrast, for those other solids in which the complex is attached to the surface by covalent linkage to the ligand no leaching was observed, but the e.e. were modest (below 20%) compared to those obtained in homogeneous catalysis under comparable conditions (above 50%).

Antimicrobial activity of resin acid derivatives

The wide potential of resin acids as bioactive agents gave rise to a growing effort in the search for new applications of the natural forms and their derivatives. In some of these compounds, the antimicrobial activity is associated to the presence in the molecules of functional groups such as the hydroxyl, aldehyde, and ketone or to their cis or trans configurations. The resin acid family covers a spectrum of antimicrobial activities against several microorganisms, from bacteria to fungi, in which the mode of action was studied by electron microscopy. The morphological alterations are consistent with an unspecific mode of action causing inhibition of the fungal growth or damaging the fungal cells in parallel with a mechanism of resistance based on the retention of the compound by the lipid accumulation. The sterol composition of phytopathogenic fungi Botrytis cinerea and Lophodermium seditiosum treated with methyl cis-7-oxo-deisopropyldehydroabietate revealed the presence of ergosterol (M+ 396) and dihydroergosterol (M+ 398) in both cultures showing that this compound did not interfere with the ergosterol metabolic pathway of both fungi.

Ionic liquids as green solvents for the asymmetric synthesis of cyanohydrins catalysed by VO(salen) complexes

It has been found that the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate is a good substitute solvent for CH2Cl2 to conduct the enantioselective cyanosilylation of aldehydes to their silylated cyanohydrins, using trimethylsilyl cyanide as reagent and a Schiff base vanadyl complex as catalyst. The mass balances (>90%), conversions (>80%) and enantiomeric excess (88% < ee < 90%) were high and comparable to those achieved in CH2Cl2. The ionic liquid containing the catalyst can be reused at least four times without loosing activity.

Assessment of the negative factors responsible for the decrease in the enantioselectivity for the ring opening of epoxides catalyzed by chiral supported Cr(III)-salen complexes

In order to determine the influence of the inorganic support on the asymmetric induction, different chiral chromium(III)-salen complexes have been incorporated within the cavities of zeolites Y, EMT and into the interlamellar region of K-10 montmorillonite. These heterogeneous catalysts are able to promote the asymmetric ring opening of epoxides with trimethylsilylazide to afford chiral azido trimethylsilyl ethers and azido alcohols with modest enantiomeric excess that varies depending on the inorganic support. The factors that have been found to play a negative influence diminishing the enantioselectivity of the supported Cr(III)-salen catalyst compared to the unsupported complexes are the following: (i) the presence of adventitious acid sites, (ii) the encapsulation of no sufficiently stereogenic ligands and (iii) the change in the reaction mechanism from bimetallic to a single metal reaction mechanism.

Antimicrobial activity of diterpene resin acid derivatives

C-13 deisopropylated and/or C-7 oxidized resin acid derivatives were tested against various microorganisms to determine structural features responsible for biological activity and to determine the influence of the C-13 isopropyl group on antimicrobial activity. Test results show that methyl cis and trans 7-oxo-13-deisopropyldehydroabietate and a mixture of both isomers exhibited activity against fungi and bacteria.

Synthesis and fluorescence properties of [60] and [70]fullerene–coumarin dyads: Efficient dipole–dipole resonance energy transfer from coumarin to fullerene

New [60] and [70]fullerene–coumarin dyads were prepared by covalently linking a coumarin dye to a fullerene (C60 or C70) via a 1,3-dipolar cycloaddition reaction of azomethine ylides or by a cyclopropanation reaction of fullerenes with malonate derivatives. These dyads were spectroscopically characterized and their fluorescence properties studied. Fluorescence quenching of the coumarin fluorophore in the dyads results from efficient dipole–dipole resonance energy transfer from the coumarin moiety to the fullerene moiety.

Diels-Alder adducts of C-60 and resin acid derivatives: Synthesis, electrochemical and fluorescence properties

Abstract New, stable and quite soluble [2+4] mono-adducts of [60]fullerene with levopimaric acid derivatives were synthesised in high yields. These adducts were also obtained directly from pine rosin. Electrochemical behaviour and fluorescence properties, including the observation of thermal delayed fluorescence, are reported.