J. Antonio Palenzuela

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.

Quinoline alkaloids from Psychotria glomerulata

Abstract Three new quinoline alkaloids have been isolated from the aerial parts of Psychotria glomerulata from Panama. The major alkaloid, glomerulatine A, was identified as 8-8a,8′-8′ a tetradehydro(−)-calycanthine on the basis of spectral data including 1 H, 13 C, COSY-45, HMBC, HMQC and ROESY techniques. Computerized 1 H NMR analysis was used to establish that glomerulatine A possessed the calycanthine- and not the iso-calycanthine-type structure. Two minor alkaloids, glomerulatines B and C, were also isolated and on the basis of spectroscopic evidence it is proposed that they are 8-8a,8′-8′a-tetrahydro-N′-demethyl(−)-calycanthine and 8-8a-didehydro-(−)-calycanthine, respectively.

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.

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.

A-type Proanthocyanidins from Prunus spinosa. Configurational Studies from CD and NMR Data

Abstract Two new A-type proanthocyanidins were isolated from Prunus spinosa. Its structures were elucidated by spectroscopy. We also included configurational studies based on DC and NMR data.

Acid cyclization of 5-ketogermacren-6,12-olides. A reactivity and conformational study

Abstract The acid cyclization of three related 5-ketogermacren-6,12-olides has been studied. All products have been identified and their stereochemistries established. The conformation of the germacrenolides and of the protonated derivatives have been studied in order to provide an explanation for the stereochemical course of the reaction.