José Antonio Morales-Serna

Photoproduction of H2O2 and hydroxyl radicals catalysed by natural and super acid-modified montmorillonite and its oxidative role in the peroxidation of lipids

The reactivity of both natural montmorillonite and montmorillonite modified with super acids (CF3SO3H and HClO4) to generate hydrogen peroxide (H2O2) and hydroxyl radicals (˙OH) under both darkness and UV-light irradiation was investigated using EPR spin-trapping spectroscopy. We used the free-radical trapping action of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) to indicate the production of ˙OH from natural and modified clays. The recognition and characterisation of the formed DMPO–OH adduct established that super acid montmorillonites were able to generate hydroxyl radicals at 25 °C in the presence of O2 and H2O. When natural and acid montmorillonite were irradiated with UV light, hydroxyl radical generation was greater than under dark conditions. In addition, the peroxidation of lipids in biological matrices with natural and super acid montmorillonite was studied using a thiobarbituric acid reactive substances (TBARS) assay, which demonstrated that only ˙OH generated from the super acid montmorillonite induced the oxidative degradation of lipids. This study reports, for the first time, the generation of ˙OH and the peroxidation of lipids by a typical super acid-modified Mexican montmorillonite.

Homoisoflavanones from Agave tequilana Weber

Three homoisoflavanones were isolated from the “piña” and leaves of Agave tequilana Weber. The compounds were identified as: 5,7-dihydroxy-3-(4-methoxybenzyl)-chroman-4-one (1), 7-hydroxy-3-(4-hydroxybenzyl)-chroman-4-one (2) and 4’-demethyl-3,9-dihydro-punctatin (3). This is the first phytochemical study carried out to Agave tequilana Weber.

Cu–Al mixed oxide catalysts for azide–alkyne 1,3-cycloaddition in ethanol–water

Cu(Al)O mixed oxides, which are obtained by the calcination of Cu–Al layered double hydroxide (LDH), promote the formation of 1,2,3-triazoles from an alkyne–azide cycloaddition reaction (Huisgen-type reaction) with excellent yields using an EtOH–H2O mixture as the solvent under microwave heating. The yield of the reaction is the result of both heterogeneous and homogeneous catalytic processes, as a consequence of capturing Cu(II) from the material by sodium ascorbate. Although the appropriate reaction conditions were employed (EtOH–H2O, 80 °C, MW, 10 min), the reconstruction of LDH by the so-called memory effect was not observed.

Synthesis of azanucleosides through regioselective ring-opening of epoxides catalyzed by sulphated zirconia under microwave and solvent-free conditions.

New azanucleosides were obtained using sulphated zirconia (ZS) as catalyst in the nucleophilic oxirane ring opening reaction of 1-allyl-3-(oxiran-2-ylmethyl)pyrimidine-2,4(1H,3H)-dione and 1-allyl-5-methyl-3-(oxiran-2-ylmethyl)-pyrimidine-2,4(1H,3H)-dione, with (S)-prolinol. The new templates were obtained with good yields following a route which exploits the reactivity of epoxides in the presence of sulphated zirconia as catalyst. The key step was carried out using microwave and solvent-free conditions and proceeds with high selectivity.

Efficient activity of magnesium–aluminium hydrotalcite in the synthesis of amides

The synthesis of amides by coupling benzotriazole esters and amines can be achieved conveniently in moderate to excellent yields (50–95%) using a commercial, synthesized, calcined or reconstructed Mg–Al hydrotalcite instead of one of the classic bases (tertiary amines). The experimental results demonstrated that commercial and synthesized hydrotalcite can be quantitatively recovered from the reaction by simple filtration and reused for a number of cycles and that the reconstructed hydrotalcite is the most active form for the amide bond formation. Finally, to test the scope of the protocol for the synthesis of biologically relevant molecules, the total synthesis of Sansalvamide A was carried out.

Three new diarylbutane lignans from the resin of Bursera fagaroides

Three new diarylbutane lignans, named 9-acetyl-9′-pentadecanoil-dihydroclusin (1), 2,3-demethoxy-secoisolintetralin monoacetate (4) and dihydroclusin monoacetate (5), have been isolated from the resin of Bursera fagaroides, together with two known ones, 2,3-demethoxy-secoisolintetralin diacetate (2) and dihydroclusin diacetate (3). The complete structure assignments were obtained by means of 1H and 13C NMR spectra.

Effects of Bentonite on p-Methoxybenzyl Acetate: A Theoretical Model for Oligomerization via an Electrophilic-Substitution Mechanism

Tonsil Actisil FF, a commercial bentonitic clay, promotes the formation of a series of electrophilic-aromatic-substitution products from para-methoxybenzyl acetate in carbon disulfide. The molecules obtained correspond to linear isomeric dimers, trimers, tetramers and a pentamer, according to their spectroscopic data. A clear indication of the title mechanistic pathway for the oligomerization growth was obtained from the analysis of a set of computational-chemistry calculations using the density-functional-theory level B3LYP/6-311++G(d,p). The corresponding conclusions were based on the computed dipole moments, the HOMO/LUMO distributions, and a natural-populations analysis of the studied molecules.

Oligomerization of 3,5-dimethyl benzyl alcohol promoted by clay: experimental and theoretical study.

Linear oligomerization of 3,5-dimethyl benzyl alcohol is induced by a montmorillonite clay (Tonsil Optimum Extra), producing 1,3,5,7-tetramethyl-9,10-dihydro-anthracene, which, by loss of protons results in the product 1,3,5,7-tetramethylanthracene. It was also found that the compounds 4-(3´,5´-dimethylbenzyl)-1,3,5,7-tetramethyl-9,10-dihydroanthracece and 4-(3´,5´-dimethylbenzyl)-1,3,5,7-tetra-methylanthracene were formed from 1,3,5,7-tetramethyl-9,10-dihydroanthracene. 1,3,5,7-Tetramethylanthryl radical cation was formed from 1,3,5,7-tetramethyl-9,10-dihydroanthracene; it was characterized by Electronic Paramagnetic Resonance (EPR). On the other hand, a theoretical analysis was performed, allowing the rationalization of the observed products and some of the key reaction steps.

Reaction control in heterogeneous catalysis using montmorillonite: switching between acid-catalysed and red-ox processes

The use of montmorillonite, modified with a super-acid (CF3SO3H), in the presence of hydroquinone as a radical scavenger and under a nitrogen atmosphere, induced the formation of tetrasubstituted furans as the major product from benzoins. In the absence of a radical scavenger, the only products obtained were 1,2-diketones.

Synthesis of cycloveratrylene macrocycles and benzyl oligomers catalysed by bentonite under microwave/infrared and solvent-free conditions.

Tonsil Actisil FF, which is a commercial bentonitic clay, promotes the formation of cycloveratrylene macrocycles and benzyl oligomers from the corresponding benzyl alcohols in good yields under microwave heating and infrared irradiation in the absence of solvent in both cases. The catalytic reaction is sensitive to the type of substituent on the aromatic ring. Thus, when benzyl alcohol was substituted with a methylenedioxy, two methoxy or three methoxy groups, a cyclooligomerisation process was induced. Unsubstituted, methyl and methoxy benzyl alcohols yielded linear oligomers. In addition, computational chemistry calculations were performed to establish a validated mechanistic pathway to explain the growth of the obtained linear oligomers.