María M. Afonso

Oxidized multi-walled carbon nanotubes for the dispersive solid-phase extraction of quinolone antibiotics from water samples using capillary electrophoresis and large volume sample stacking with polarity switching

In this work, a new method for the determination of eleven quinolone antibiotics (moxifloxacin, lomefloxacin, danofloxacin, ciprofloxacin, levofloxacin, marbofloxacin, enrofloxacin, difloxacin, pefloxacin, oxolinic acid and flumequine) in different water samples using dispersive solid-phase extraction (dSPE) and capillary zone electrophoresis with diode-array detection was developed. Oxidized multi-walled carbon nanotubes (o-MWCNTs) were used for the first time as stationary phases for the off-line preconcentration by dSPE of the antibiotics. A 65 mM phosphate buffer at pH 8.5 was found adequate for analyte separation while large volume sample stacking with polarity switching of the analytes dissolved in water containing 10% (v/v) of acetonitrile was carried out in order to improve the sensitivity. dSPE parameters, such as sample volume and pH, o-MWCNT amount, volume and type of eluent in dSPE were optimized. Application of the developed method to the analysis of spiked Milli-Q, mineral, tap, and wastewater samples resulted in good recoveries values ranging from 62.3 to 116% with relative standard deviation values lower than 7.7% in all cases. Limits of detection were in the range of 28-94 ng/L. The proposed method is very fast, simple, repeatable, accurate and highly selective.

Iron(III) Tosylate in the Preparation of Dimethyl and Diethyl Acetals from Ketones and β -Keto Enol Ethers from Cyclic β -Diketones

Abstract An efficient method for conversion of ketones to their corresponding dimethyl and diethyl acetals and of cyclic β-diketones into β-keto enol ethers using Fe(OTs)3 as a catalyst is described.

Evaluation of two molecularly imprinted polymers for the solid-phase extraction of natural, synthetic and mycoestrogens from environmental water samples before liquid chromatography with mass spectrometry.

In this work, we have compared the selectivity of two commercial molecularly imprinted polymers (AFFINIMIP®SPE Estrogens and AFFINIMIP®SPE Zearalenone) for the extraction of 12 estrogenic compounds of interest (i.e. 17α-estradiol, 17β-estradiol, estrone, hexestrol, 17α-ethynylestradiol, diethylstibestrol, dienestrol, zearalenone, α-zearalanol, β-zearalanol, α-zearalenol and β-zearalenol) from different water samples. High-performance liquid chromatography coupled with ion trap mass spectrometry with electrospray ionization was used for their determination. Results showed that although both molecularly imprinted polymeric cartridges were specifically designed for different groups of analytes (natural estrogens like estradiol in the first case and zearalenone derivatives in the second) they nearly have the same extraction performance (with recovery values in the range 65-101%) for the same analytes in Milli-Q water because of the cross-reactivity of the polymer. However, when more complex water samples were analyzed, it was clear that the behavior was different and that the AFFINIMIP®SPE Estrogens showed less cross-reactivity than the other cartridge. Validation of the proposed methodology with both cartridges revealed that the extraction was reproducible and that the final limits of detection of the proposed method were in the low ng/L range.

Dispersive liquid–liquid microextraction of pesticides and metabolites from soils using 1,3-dipentylimidazolium hexafluorophosphate ionic liquid as an alternative extraction solvent

In this work, the use of the ionic liquid (IL) 1,3‐dipentylimidazolium hexafluorophosphate ([PPIm][PF6]) as an alternative extractant for IL dispersive liquid–liquid microextraction (IL‐DLLME) of a group of pesticides and metabolites (2‐aminobenzimidazole, carbendazim/benomyl, thiabendazole, fuberidazole, carbaryl, 1‐naphthol, and triazophos) from soils is described. After performing an initial ultrasound‐assisted extraction (USE), the IL‐DLLME procedure was applied for the extraction of these organic analytes from soil extracts. Separation and quantification was achieved by high‐performance liquid chromatography (HPLC) with fluorescence detection (FD). Calibration, precision, and accuracy of the described USE‐IL‐DLLME‐HPLC‐FD method using [PPIm][PF6] as an alternative extractant was evaluated with two soils of different physicochemical properties. Accuracy percentages were in the range 93–118% with RSD values below 20%. A comparison of the performance of [PPIm][PF6] versus that of the so‐common 1‐hexyl‐3‐methylimidazolium hexafluorophosphate ([HMIm][PF6]) was accomplished. Results indicate a comparable extraction efficiency with both ILs, being slightly higher with [HMIm][PF6] for the metabolite 2‐aminobenzimidazole, and slightly higher with [PPIm][PF6] for triazophos. In all cases, LODs were in the low ng/g range (0.02–14.2 ng/g for [HMIm][PF6] and 0.02–60.5 ng/g for [PPIm][PF6]). As a result, the current work constitutes a starting point for the use of the IL [PPIm][PF6] for further analytical approaches.

HETERO DIELS-ALDER VS MUKAIYAMA ALDOL PATHWAYS IN THE REACTION OF MONOACTIVATED DIENES AND ALDEHYDES. A LEWIS ACID STUDY

Abstract The effect of Lewis acid on the reaction of 2-monoactivated dienes and aldehydes was studied searching for more general reaction conditions than those previously published. It was found that BF 3 ·OEt 2 in diethyl ether gave the best yields of Dieis-Alder adducts with good endo/exo selectivities. The Mukaiyama aldol-Michael cyclization pathway which has been reported to occur with this Lewis acid in the reaction of diactivated dienes, does not seem to operate with the monoactivated ones. Other Lewis acids gave good yields of silylated aldol products, and a crossover experiment showed that the recently proposed silatropic-ene pathway does not occur under the conditions used.

A versatile approach to cyclic ethers. Synthesis of disubstituted oxepanes and oxocanes

Abstract A synthetic sequence for the preparation of α,α′-disubstituted cyclic ethers of various ring sizes and either relative stereochemistry (cis or trans) is presented. It is based on the hetero Diels Alder reaction of a monoactivated diene and an aldehyde, yielding a silylenol pyrone which is transformed into a linear ether. This ether is cyclized by an intramolecular nucleophilic substitution reaction to the desired cyclic ethers. The viability of this route is demonstrated by the preparation of two examples, an oxocane and an oxolane.

Synthesis and pharmacological activity of diterpenylnaphthoquinone derivatives.

New diterpenylquinones, combining a diterpene diacid and a naphthoquinone, were prepared from junicedric acid and lapachol. The new derivatives were assessed as gastroprotective agents by the HCl-EtOH-induced gastric lesions model in mice as well as for basal cytotoxicity on the following human cell lines: Normal lung fibroblasts (MRC-5), gastric epithelial adenocarcinoma (AGS), and hepatocellular carcinoma (Hep G2). Several of the new compounds were significantly active as antiulcer agents and showed selective cytotoxicity against AGS cells.

Study of an Unexpected Rearrangement of the α-Phenyl Pyrane Derivatives Prepared via Hetero-Diels−Alder Reaction of Acyclic Vinyl Allenes and Aldehydes

The Lewis acid catalyzed hetero-Diels-Alder reaction between acyclic vinyl allenes and aldehydes as heterodienophiles was studied. This reaction allows for the preparation of pyrane derivatives in good yields, high facial and regioselectivity and moderate endo/exo ratio. When benzaldehyde was used as the heterodienophile, rearranged products were obtained depending on the reaction conditions. DFT calculations were used to study the rearrangement, concluding that it is a highly selective ionic process, driven by the stability of the rearranged products.

Partial synthesis of germacranolides with pyran and furan-type rings

Abstract Pathways to synthesize germacranolides with ether bridges between C 1 and C 5 or C 3 and C 10 were described. A joint precursor was prepared using a readily available and inexpensive compound as starting material. The key step in the preparation of dihydropyranone-germacranolides proved to be a one-pot procedure involving several transformations, induced by the iodotrimethylsilane/acetonitrile system.

Synthesis of 2,5-Disubstituted Octahydroquinolin-4-ones via anIntramolecular Hetero Diels-Alder Reaction

A route for the preparation of 2,5-disubstituted octahydroquinolin-4-ones, synthetic precursors of the decahydroquinoline-type toxins, is presented. The key steps are an asymmetric epoxidation and an intramolecular hetero Diels-Alder reaction between an activated diene and an imine. The presence of an allylic stereogenic center induces some selectivity and thus only two cycloadducts are obtained in 70:30 ratio and good yield.