Efficient, solventless N-Boc protection of amines carried out at room temperature using sulfamic acid as recyclable catalyst

A simple, rapid, and efficient protocol for the chemoselective N-Boc protection of amines using sulfamic acid as catalyst is described. N-Boc protection of various structurally diverse aliphatic, aromatic, alicyclic, and heterocyclic amines (1°, 2°, 3°) was carried out with (Boc)₂O using sulfamic acid as catalyst (5 mol %) at room temperature under solventless conditions. The advantages of this method are simplicity, shorter reaction times (1-15 min), a cost-effective catalyst, and excellent isolated yields (90-100%); it is also environmentally benign. Moreover, the combined use of ultrasound and sulfamic acid achieves a synergic effect that is especially marked in the N-Boc protection of deactivated (sterically hindered and electron-deficient) amines. The catalyst possesses distinct advantages: ease of handling, cleaner reactions, high activity, and excellent chemoselectivity.     

Development and in-house validation of a robust and sensitive solid-phase extraction liquid chromatography/tandem mass spectrometry method for the quantitative determination of aflatoxins B1, B2, G1, G2, ochratoxin A, deoxynivalenol, zearalenone, T-2 and HT-2 toxins in cereal-based foods

A sensitive and robust liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for the simultaneous determination of aflatoxins (B(1), B(2), G(1), G(2)), ochratoxin A, deoxynivalenol, zearalenone, T-2 and HT-2 toxins in cereal-based foods. Samples were extracted with a mixture of acetonitrile/water (84:16, v/v) and cleaned up through a polymeric solid-phase extraction column. Detection and quantification of the nine mycotoxins were performed by reversed-phase liquid chromatography coupled with electrospray ionization triple quadrupole mass spectrometry (LC/ESI-MS/MS), using fully (13)C-isotope-labelled mycotoxins as internal standards. The method was validated in-house for five different cereal processed products, namely barley, oat and durum wheat flours, rye- and wheat-based crisp bread. Recoveries and repeatability of the whole analytical procedure were evaluated at contamination levels encompassing the EU maximum permitted levels for each tested mycotoxin. Recoveries ranged from 89 to 108% for deoxynivalenol, from 73 to 114% for aflatoxins, from 85 to 114% for T-2 and HT-2 toxins, from 64 to 97% for zearalenone, from 74 to 102% for ochratoxin A. Relative standard deviations were less than 16% for all tested mycotoxins and matrices. Limits of detection (signal-to-noise ratio 3:1) ranged from 0.1 to 59.2 μg/kg. The trueness of the results obtained by the proposed method was demonstrated by analysis of reference materials for aflatoxins, deoxynivalenol, zearalenone. The use of inexpensive clean-up cartridges and the increasing availability of less expensive LC/MS/MS instrumentation strengthen the potential of the proposed method for its effective application for reliable routine analysis to assess compliance of tested cereal products with current regulation.     

Pyrroloquinoxaline hydrazones as fluorescent probes for amyloid fibrils

Here we describe the identification and preliminary characterization of a new class of pyrrolo(imidazo)quinoxaline hydrazones as florescent probes for Aβ(1-42) fibrils. All the newly developed compounds were able to bind amyloid fibrils formed in vitro and some of them displayed an increase of their fluorescence upon binding. When tested on brain tissue preparations presenting Aβ deposits, the described hydrazones selectively stained amyloid structures and did not display aspecific binding. The hydrazones did not show antifibrillogenic activity and electron microscopy analysis revealed that they do not interfere with fibrils structure. The described pyrrolo(imidazo)quinoxalines could be useful for studying amyloid structures in vitro. Moreover, their experimentally proven ability to cross the blood-brain barrier in mouse opens the possibility of developing these compounds as potential amyloid imaging agents for in vivo applications.     

Crystal structure of the trigonal form of isotactic polypropylene as an example of density-driven polymer structure

Propene-hexene copolymers crystallize in a new polymorphic form of isotactic polypropylene when the concentration of hexene is higher than nearly 10-15 mol %. The hexene units are included in the crystals, inducing an increase of density that allows crystallization of 3-fold helical chains in a trigonal unit cell according to the space group R3c or Rc, where the helical symmetry of the chains is maintained in the crystal lattice. The structure of this new form is similar to those of isotactic polybutene and polystyrene and does not crystallize in polypropylene homopolymer because it would have too low density. The crystal structure of isotactic polypropylene is therefore no longer an exception to the principles of polymer crystallography, but the new structure represents the fulfillment of these principles and indicates that the packing of polymer molecules is mainly driven by density.     

Chromatographic Separation of Breynia retusa (Dennst.) Alston Bark,Fruit and Leaf Constituents from Bioactive Extracts

Breynia retusa (Dennst.) Alston (also known as Cup Saucer plant) is a food plant with wide applications in traditional medicine, particularly in Ayurveda. Extracts obtained with four solvents (dichloromethane, methanol, ethyl acetate and water), from three plant parts, (fruit, leaf and bark) were obtained. Extracts were tested for total phenolic, flavonoid content and antioxidant activities using a battery of assays including 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), cupric reducing antioxidant capacity (CUPRAC), total antioxidant capacity (TAC) (phosphomolybdenum) and metal chelating. Enzyme inhibitory effects were investigated using acetylcholinesterase (AChE), butyrylcholinesterase (BChE), tyrosinase, α-amylase and α-glucosidase as target enzymes. Results showed that the methanolic bark extract exhibited significant radical scavenging activity (DPPH: 202.09 ± 0.15; ABTS: 490.12 ± 0.18 mg Trolox equivalent (TE)/g), reducing potential (FRAP: 325.86 ± 4.36: CUPRAC: 661.82 ± 0.40 mg TE/g) and possessed the highest TAC (3.33 ± 0.13 mmol TE/g). The methanolic extracts were subjected to LC-DAD-MSⁿ and NMR analysis. A two-column LC method was developed to separate constituents, allowing to identify and quantify forty-four and fifteen constituents in bark and fruits, respectively. Main compound in bark was epicatechin-3-O-sulphate and isolation of compound was performed to confirm its identity. Bark extract contained catechins, procyanidins, gallic acid derivatives and the sulfur containing spiroketal named breynins. Aerial parts mostly contained flavonoid glycosides. Considering the bioassays, the methanolic bark extract resulted a potent tyrosinase (152.79 ± 0.27 mg kojic acid equivalent/g), α-amylase (0.99 ± 0.01 mmol acarbose equivalent ACAE/g) and α-glucosidase (2.16 ± 0.01 mmol ACAE/g) inhibitor. In conclusion, methanol is able to extract the efficiently the phytoconstituents of B. retusa and the bark is the most valuable source of compounds.     

Aziridines versus vinyl carbamates from the direct amination of electron-withdrawing group-substituted trifluoromethyl enoates

Aza-MIRC (Michael-initiated ring closure) and C-H insertion products were obtained in the reactions of trifluoromethylated olefins with different nosyloxycarbamates by changing base and solvent. Aza-Michael addition products were not isolated. The presence and the position of the trifluoromethyl group allow control of the outcome of the reactions.     

High-performance liquid chromatography analysis of polyacetylenes and polyenes in Echinacea pallida by using a monolithic reversed-phase silica column

In this study, a RP-HPLC method for the analysis of polyacetylenes and polyenes in Echinacea pallida roots and phytopharmaceuticals was developed. The reference compounds used for quantification were isolated from the plant material and their structures were determined on the basis of the analysis of UV, IR, NMR and MS data. The complete structure elucidation of three compounds, namely 8-hydroxy-tetradec-(9E)-ene-11,13-diyn-2-one (1), tetradec-(8Z)-ene-11,13-diyn-2-one (6) and pentadec-(8Z)-en-2-one (9) is described. In the analysis of the n-hexane extracts of E. pallida roots, the comparison between conventional and monolithic columns showed that the elution order in both cases is identical and the selectivity is equivalent. However, the retention times achieved by the monolithic column are shorter, resulting in a faster separation (20 min). Therefore, the analyses were carried out on a Chromolith Performance RP-18e (100 mm x 4.6 mm i.d.), with a gradient mobile phase composed by H(2)O and ACN at the flow rate of 2 mL/min. The column was thermostatted at 20 degrees C. The photodiode array detector monitored the eluent at 210 nm. The validation procedure confirmed that this technique affords reliable analysis of these components and is appropriate for the quality control of complex matrices, such as E. pallida roots and phytopharmaceuticals.     

Validation of a dissociation enhanced lanthanide fluorescence immunoassay for the screening of 17beta-estradiol in bovine serum according to European Union decision 2002/657/EC

A validation study was carried out in order to evaluate the performances of a dissociation enhanced lanthanide fluorescence immunoassay (DELFIA) for rapid screening of 17 beta-estradiol in bovine serum. This validation was performed according to European Union (EU) Decision 2002/657/EC, which establishes criteria and procedures for determination of detection capability (CCbeta), selectivity/specificity, and applicability/ruggedness/stability for qualitative screening tests. To determine these performance characteristics, 20 blank serum samples of cattle were collected and spiked with 17 beta-estradiol at 40 pg/mL, corresponding to the maximum residue limit permitted by Italian legislation. According to the EU Decision CCbeta criterion, spiked samples must have <5% probability to be classified as a false negative. 17 beta-Estradiol was detected in each spiked sample, and the CCbeta results were <40 pg/mL. There was also no observed interference effect due to chemically related substances or from the matrix. Moreover, slight variations of some critical factors in the DELFIA procedure, deliberately introduced for ruggedness evaluation, did not result in any negative effect on the 17beta-estradiol detection. The proposed method is suitable for qualitative screening analysis of 17 beta-estradiol according to EU performance requirements.     

An interior point Newton‐like method for non‐negative least‐squares problems with degenerate solution

An interior point approach for medium and large non‐negative linear least‐squares problems is proposed. Global and locally quadratic convergence is shown even if a degenerate solution is approached. Viable approaches for implementation are discussed and numerical results are provided. Copyright © 2006 John Wiley & Sons, Ltd.     

Characterization of durum wheat high molecular weight glutenin subunits Bx20 and By20 sequences by a molecular and proteomic approach

Wheat high molecular weight glutenin subunit variation is important because of its great influence on glutenin polymer structure, that is related to dough technological properties. Among the different subunits, the pair Bx20 and By20 is known to have a negative effect on quality, but the reasons are not clear: Bx20 has two cysteines, which theoretically make this subunit a chain extender of the glutenin polymer, just like the other Bx subunits, showing four cysteines, two of which should be involved in intra‐molecular disulfide bonds. By20 has never been characterized so far at molecular level. Here we report the nucleotide sequences of Bx20 and By20 genes isolated from the durum wheat cultivar ‘Lira 45’ and the validation of the corresponding deduced amino acid sequences by using MALDI‐TOF and LC‐MS/MS. Four nucleotide differences were identified in the Bx20 gene with respect to the deduced sequence present in NCBI, causing two amino acid substitutions. For the By20 subunit, nucleotide and amino acid sequences revealed a great similarity to By15, both at gene and protein levels, showing five nucleotide changes generating two amino acid differences. No evidence of post‐translational modifications has been found. Hypotheses are formulated in regard to relationships with technological quality. Copyright © 2016 John Wiley & Sons, Ltd.