β-N-Heterocyclic Cyclobutane Carboximides: Synthesis through a Tandem Base-Catalyzed Amidation/aza-Michael Addition Protocol and Facile Transformations

A stereoselective one-pot double derivatization of cyclobutene-1-carboxylic acid via a mild organic base catalyzed amidation/aza-Michael addition of benzo[d]oxazol-2(3H)-ones has been developed. This unprecedented tandem reaction provides access to novel β-N-heterocyclic cyclobutane carboximide derivatives with a trans geometry. The carboximide moiety reacts smoothly with nucleophiles, allowing access to diverse derivatives of trans-β-N-heterocyclic cyclobutanecarboxylic acid, including peptidomimetic structures.     

High performance liquid chromatographic separation of cholesterol oxidation products

Summary A fast, sensitive, high performance liquid chromatographic method for the simultaneous determination of cholesterol hydroperoxides and other major oxysterols, using two different detection systems (ultraviolet at 210 nm and light scattering), is here described. The hydroperoxy derivatives were obtained by cholesterol photoxidation, isolated by thin layer chromatography and joined with a standard mixture of 10 oxysterols (epoxy, hydroxy and keto derivatives). Aliquots were directly injected onto a 5-μm particle size, 25×0.46 cm i.d. Spherisorb S5 CN normal phase column, usingn-hexane/anhydrous ethanol (97:3, v/v) as mobile phase and a flow rate of 0.8 mL min⁻¹. This method allowed, in a single isocratic analysis, the separation and quantification of the primary and secondary cholesterol oxidation products in 30 minutes. The light scattering detector was particularly useful for the determination of nonderivatized 5,6-epoxides and cholestane-3β,5α,6β-triol. The sensitivity of both detectors was very similar for most of the oxysterols, except for the 5,6-epoxides and the 7-ketocholesterol. The method suitability for the determination of cholesterol oxidation products in food matrices was successfully tested on a saponified lipid extract from egg yolk powder.     

Development of a rapid method to determine phenolic and other polar compounds in walnut by capillary electrophoresis-electrospray ionization time-of-flight mass spectrometry

The aim of this work was to develop a capillary electrophoresis-mass spectrometry (CE-MS) method to identify and quantify phenolic and other related polar compounds in walnut samples. The extraction capacity of several solvent mixtures of phenolic compounds from walnut by conventional solid-liquid extractions was tested, and CE and electrospray ionization MS parameters were optimized. The finalized procedure is able to determine many well-known phenolic compounds present in walnuts and provide relevant information about the presence of minor polar compounds. A new compound in walnut ((2E,4E)-8-hydroxy-2,7-dimethyl-2,4-decadiene-1,10-dioic acid 6-O-beta-d-glucopiranosyl ester, [M-H](-) 403.161m/z) with a structure similar to glansreginins was also identified. Phenolic compounds correspond to 14-28% of total polar compounds quantified. Aglycone and glycosylated ellagic acid represent the principal components and account for 64-75% of total phenols in walnuts. However, the sum of glansreginins A, B and (2E,4E)-8-hydroxy-2,7-dimethyl-2,4-decadiene-1,10-dioic acid 6'-O-beta-d-glucopiranosyl ester was in the range of 72-86% of total quantified compounds. In addition, this is the first time that separation by CE with detection by electrospray ionization time-of-flight MS has been applied to the analysis of phenolic and other polar compounds in walnut samples, providing results in less than 15min.     

Photon channelling in foams

Experiments by Gittings, Bandyopadhyay and Durian (Europhys. Lett. 65, 414 (2004)) demonstrate that light possesses a higher probability to propagate in the liquid phase of a foam due to total reflection. The authors term this observation photon channelling which we investigate in this article theoretically. We first derive a central relation in the work of Gitting et al. without any free parameters. It links the photon's path-length fraction f in the liquid phase to the liquid fraction ɛ. We then construct two-dimensional Voronoi foams, replace the cell edges by channels to represent the liquid films and simulate photon paths according to the laws of ray optics using transmission and reflection coefficients from Fresnel's formulas. In an exact honeycomb foam, the photons show superdiffusive behavior. It becomes diffusive as soon as disorder is introduced into the foams. The dependence of the diffusion constant on channel width and refractive index is explained by a one-dimensional random-walk model. It contains a photon channelling state that is crucial for the understanding of the numerical results. At the end, we shortly comment on the observation that photon channelling only occurs in a finite range of ɛ.     

Chemical composition and in vitro activity of plant extracts from Ferula communis and Dittrichia viscosa against postharvest fungi

F. communis and D. viscosa are perennial Mediterranean weeds that have been used for different therapeutic purposes in traditional pharmacopeia. Plant extracts were obtained from air dried D. viscosa young shoots (DvA) and F. communis aerial part (FcA) and roots (FcR) with n-hexane. The chemical compositions of the extracts were analyzed by HPLC-DAD, LC-MS (ESI) and LC-Q-TOF techniques. Two sesquiterpene lactones (inuviscolide, tomentosin) and three sesquiterpene acids (costic acid, hydroxycostic acid, ilicic acid) were identified from the D. viscosa extract, while in F. communis extracts three daucane sesquiterpenes (acetoxyferutinin, oxojaeskeanadioyl anisate, fertidin) and one coumarin (ferulenol) derivates were found. Biological activities of plant extracts were studied in in vitro experiments on the colonies and conidia of Botryotinia fuckeliana, Penicillium digitatum, P. expansum, Monilinia laxa, M. fructigena and Aspergillus spp. Extracts showed varying degree of antifungal activities on colony growth and conidia germination. The extract from FcA showed the least effect, while DvA extract had the strongest fungitoxic effects. FcR extract presented a fungitoxic effect on the colony growth, but it was not able to inhibit the conidia germination. These distinctions can be attributed to the differences in chemical composition of plant extracts.     

High precision delta(17)O isotope measurements of oxygen from silicates and other oxides: method and applications

The use of infrared laser-assisted fluorination to release oxygen from milligram quantities of silicates or other oxide mineral grains is a well-established technique. However, relatively few studies have reported the optimisation of this procedure for oxygen-17 isotope measurements. We describe here details of an analytical system using infrared (10 μm) laser-assisted fluorination, in conjunction with a dual inlet mass spectrometer of high resolving power ( approximately 250) to provide (17)O and (18)O oxygen isotope measurements from 0.5-2 mg of silicates or other oxide mineral grains. Respective precisions (1) of typically 0.08 and 0.04 per thousand are obtained for the complete analytical procedure. Departures from the mass-dependent oxygen isotope fractionation line are quantified by Delta(17)O; our precision (1) of such measurements on individual samples is shown to be +/-0.024 per thousand. In turn, this permits the offset between parallel, mass-dependent fractionation lines to be characterised to substantially greater precision than has been possible hitherto. Application of this system to investigate the (17)O versus (18)O relationship for numerous terrestrial whole-rock and mineral samples, of diverse geological origins and age, indicates that the complete data set may be described by a single, mass-dependent fractionation line of slope 0.5244+/- 0.00038 (standard error). Copyright 1999 John Wiley & Sons, Ltd.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Chromatographic techniques for the determination of alkyl-phenols, tocopherols and other minor polar compounds in raw and roasted cold pressed cashew nut oils

Anacardium occidentale belongs to the family Anacardiaceae and is principally grown in tropical America (Mexico, Peru, Brazil, etc.) and India. Cashew nuts contain low amounts of hydroxy alkyl phenols that come from an oily liquid present in their shell and that is known as cashew-nut shell liquid. This paper reports the alkyl phenols composition of cold pressed raw and roasted cashew nut oil. First of all, cashew nut shell liquid was used for a basic fractionation of the alkyl phenol classes by preparative TLC and definitively identified by GC-MS and GC-FID. Anacardic acids were the major alkylphenols contained in both oils followed by cardol, cardanol and 2-methylcardol compounds, respectively. Raw and roasted oils did not show different compositions except for cardanols. The oil produced from roasted cashew nut reported a higher concentration of cardanols. Furthermore, tocopherols and other minor polar compounds were determined by HPLC-FLD and HPLC-DAD-MS, respectively. Tocopherol content varied in a range of 171.48-29.56mg/100g from raw to roasted cashew nut oil, being β-tocopherol the one which presented a higher decrease (93.68%). Also minor polar compounds in cashew oil decreased after roasting from 346.52 to 262.83mg/kg.     

CZE separation of strawberry anthocyanins with acidic buffer and comparison with HPLC

Anthocyanins, the major colourants of strawberries, are polar pigments that are positively charged at low pH. Herein, we have assessed a new analytical method for the separation of anthocyanins using CZE. Acidic buffer solutions (pH <2) were employed in order to maintain pigments in the cation flavylium form and achieve high molar absorptivity at 510 nm. These spectral properties enabled us to identify strawberry anthocyanins in a preliminary stage by detection in the visible range, although the method was optimised at 280 nm to obtain the best S/N. The effects of buffer composition highlighted the necessity of adding an organic modifier to the running buffer to obtain a suitable separation. The electrophoretic method permitted the separation of the three main anthocyanins of strawberry extracts, namely pelargonidin 3-glucoside (Pg-glu), pelargonidin 3-rutinoside and cyanidin 3-glucoside. The electrophoretic results, expressed as retention time and separation efficiency of the major anthocyanin (Pg-glu), were compared to those achieved in HPLC, the analytical technique traditionally used for the investigation of anthocyanins in vegetable matrix. The content of Pg-glu in strawberries (cv. Camarosa), calculated with HPCE and HPLC methods, resulted respectively in 11.41 mg/L and 11.37 mg/L.     

Determination of wine aroma compounds by dehydration followed by GC/MS

A new extraction method for the analysis of the volatile fraction of white and red wines has been developed and validated. A dehydration step with MgSO4 separated an aroma compounds-rich alcoholic-glycerine layer. Spiked samples showed good recoveries in the range between 75 and 120% with CVmax% of 17, except for 2-phenylethanol and y-butyrolactone for which recoveries in red wines were under 60%, and for monoethylsuccinate, where recoveries averaged 50 and 60% in white and red wines, respectively. Method repeatability and intermediate precision showed good CVmax% with minimum and maximum values between 7.7 and 24, and between 18.7 and 25.0, respectively. The average determination coefficients were greater than 0.99 with CVmax% of 13. The instrumental LOD and LOQ were, in all cases, under 0.05 mg/L, except for 2,3 butanediol (0.20 mg/L). Overall, the presence of wine matrix affected aroma compounds responses in GC/MS analysis. These observations indicate that the use of a matrix-matched calibration curve is mandatory to obtain reliable quantitative data.