Comparative chemical composition and antioxidant activity of Calamintha nepeta (L.) Savi subsp. glandulosa (Req.) Nyman and Calamintha grandiflora (L.) Moench (Labiatae)

The two studied Calamintha species showed different polyphenolic content and sterol composition. Calamintha grandiflora possessed twice the polyphenolic content of Calamintha nepeta subsp. glandulosa, while the latter contained a higher number of sterols. Among them, stigmast-5-en-3β-ol was found to be the major constituent. The methanolic extract of C. grandiflora was more potent than the C. nepeta subsp. glandulosa methanolic extract in a DPPH assay, while the activity of the C. grandiflora EtOAc fraction was weaker than its C. nepeta subsp. glandulosa counterpart. Fractions of C. nepeta subsp. glandulosa showed higher activity using a β-carotene bleaching test. The petrol ether fraction of C. grandiflora showed significant inhibition of NO production.     

Electron paramagnetic resonance studies on oxidative polymerization mechanism of furan derivatives

The oxidative polymerization of furan, 3-methylfuran and 2,2′,5′,2″-terfuran, induced by iodine in organic solvents having different donicity, was investigated by time-resolved electron paramagnetic resonance (EPR) spectroscopy. The reaction was monitored starting from the onset of the process and radical species arising from the monomers in early stages of the polymerization reaction were detected. The comparison between experimental and theoretical hyperfine coupling constants, obtained by simulated EPR spectra and theoretical ab initio calculations, respectively, allowed one to structurally characterize the above radical species, thus enabling mechanistic conclusions about oxidative coupling. Moreover, the analysis of the time evolution of EPR spectrum during the oxidative polymerization process was used for evaluating the relative amount of localized and mobile radical species along the polymer backbone, thus getting preliminary information about conjugation extent and electroconducting properties of the final material. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1901–1910, 1998     

Quantification of 13 priority polycyclic aromatic hydrocarbons in human urine by headspace solid-phase microextraction gas chromatography-isotope dilution mass spectrometry

Polycyclic aromatic hydrocarbons (PAHs) are common environmental pollutants in both living and working environments. The aim of this study was the development of a headspace solid-phase microextraction gas chromatography-isotope dilution mass spectrometry (HS-SPME/GC-IDMS) method for the simultaneous quantification of 13 PAHs in urine samples. Different parameters affecting PAHs extraction by HS-SPME were considered and optimized: type/thickness of fiber coatings, extraction temperature/time, desorption temperature/time, ionic strength and sample agitation. The stability of spiked PAHs solutions and of real urine samples stored up to 90 days in containers of different materials was evaluated. In the optimized method, analytes were absorbed for 60 min at 80 °C in the sample headspace with a 100 μm polydimethylsiloxane fiber. The method is very specific, with linear range from the limit of quantification to 8.67 × 10³ ng L⁻¹, a within-run precision of <20% and a between-run precision of <20% for 2-, 3- and 4-ring compounds and of <30% for 5-ring compounds, trueness within 20% of the spiked concentration, and limit of quantification in the 2.28-2.28 × 10¹ ng L⁻¹ range. An application of the proposed method using 15 urine samples from subjects exposed to PAHs at different environmental levels is shown.     

New isosteres of (R)-2-methylhomoserine and (R)-2-methylaspartic acid by alkylation of a chiral imine leading stereoselectively to a quaternary stereogenic center

Imines obtained from either chiral 3-amino-4-silyloxymethylpyrrolidin-2-one 5a or 5b underwent alkylation to give, in good yield and total stereoselection, the corresponding 3,3,4-trisubstituted pyrrolidin-2-ones 8a–d where both the amino and the silyloxymethyl groups lie cis to each other, as shown by ¹H NMR spectroscopic data and NOE experiments. By removal of both the imino group and the chiral inducer from 8b, the pyrrolidin-2-one 12, an isostere of (R)-2-methylhomoserine 2 and the pyrrolidin-2-one 14, an isostere of (R)-2-methylaspartic acid 4 were obtained straightforwardly.     

Allylic Functionalization of 2,5- and 2,4-Cyclo-Hexadiene-1,3-Dicarboxylates

A series of 2,4- and 2,5-cyclohexadiene-1,3-dicarboxylates were functionalized at the allylic position via oxidation (SeO₂, PDC/t-BuOOH) and halogenation (NBS). The regiochemical outcome for different substrates and reactions was studied and the importance of factors such as reaction mechanism, steric hindrance and reaction intermediates stability was discussed.

     

Determination of several synthetic cathinones and an amphetamine‐like compound in urine by gas chromatography with mass spectrometry. Method validation and application to real cases

Most routine practices for drugs‐of‐abuse testing do not include screening procedures for new psychoactive substances, despite their increasing diffusion, preventing clear knowledge of the real consumption of these drugs in the populations. To make up for this shortcoming, a gas chromatography with mass spectrometry method was developed for the simultaneous determination of 18 synthetic cathinones and one amphetamine‐like compound in human urine. The sample preparation was based on liquid–liquid extraction under alkaline condition followed by derivatization with trifluoroacetic anhydride. The separation of the 19 analytes was achieved in less than 10 min. The whole methodology was validated according to national and international guidelines. Selectivity, linearity range, limit of detection and limit of quantitation, precision and accuracy were evaluated. For all the analytes, the calibration curve was linear in the 100–1000 ng/mL concentration range. The limits of detection ranged from 10 to 30 ng/mL and limits of quantitation from 30 to 100 ng/mL. Precisions were in the ranges 0.1–10.4%, and 1.0–12.1% for low (100 ng/mL) and high (1000 ng/mL) concentration, respectively. The accuracy, expressed as bias% was within ±20% for all the analytes. The present method was successfully applied to urine samples originating from autopsies, drug abuse/withdrawal controls, clinical investigations, roadside controls, driving re‐licensing, and workplace testing.     

Last ten years (2008–2018) of chiral ligand‐exchange chromatography in HPLC: An updated review

Chiral ligand‐exchange chromatography is one of the elective strategies for the direct enantioresolution of small chelating compounds: amino acids, diamines, amino alcohols, diols, small peptides, etc. Unlike other methods, the interaction between chiral selector and analyte enantiomers is mediated by a cation, thus producing diastereomeric ternary complexes. Two main approaches are conventionally applied in chiral ligand‐exchange chromatography. The first relies upon chiral stationary phases where the chiral selector is either covalently immobilized or physically adsorbed onto suitable packing materials (coated phases). In the second approach, chiral molecules are added to the eluent, thus generating chiral eluent systems. Among the advantages of chiral ligand‐exchange chromatography, the generation of UV/vis‐active metal complexes, and the use of commercially available or easy‐to‐synthesize chiral selectors, in combination to rather inexpensive achiral columns for coated phases and chiral eluents, are noteworthy. Besides amino acids and amino alcohols, other species have proven suitable for chiral ligand‐exchange chromatography applications. Recently, the use of either chiral ionic liquids or micellar liquid chromatography systems as well as the successful off‐column formation of diastereomeric complexes have expanded the selectivity profiles and application fields. All of these issues are touched in the review, shedding light to the contributions appeared in the last decade.     

Anticancer Potential of Diiron Vinyliminium Complexes

Invited for the cover of this issue is the group of Fabio Marchetti at the Università di Pisa and Paul J. Dyson at Ecole Polytechnique Fédérale de Lausanne (EPFL). Read the full text of the article at 10.1002/chem.201902885 .     

Development and validation of HPLC methods for the analysis of phenethylamine and indoloquinazoline alkaloids in Evodia species

The aim of this study was to evaluate the chromatographic performance of a PEG stationary phase, in comparison with those of C18 columns, for the HPLC analysis of phenethylamine ((+/-)-synephrine) and indoloquinazoline (rutaecarpine and evodiamine) alkaloids in methanolic extracts of fruits of Evodia rutaecarpa (Juss.) Benth. and E. rutaecarpa (Juss.) Benth. var. officinalis (Dode) Huang (i.e., E. officinalis Dode) (Rutaceae family). The method was validated and showed good linearity, precision, accuracy, sensitivity, and specificity. The highest content of both phenethylamine and indoloquinazoline alkaloids was found in methanolic fruit extracts of E. rutaecarpa, and it was closely related to the degree of maturity. E. officinalis fruits displayed low amounts of both types of alkaloids. Furthermore, an enantioselective HPLC method for the enantioseparation of (+/-)-synephrine from Evodia fruits was applied, by using a protein-based chiral stationary phase with cellobiohydrolase (CBH) as the chiral selector (Chiral-CBH). Isolation of synephrine from Evodia aqueous fruit extracts was carried out by strong cation-exchange SPE. The results of the application of the method to the analysis of Evodia samples showed that (-)-synephrine was the main component while (+)-synephrine was present in low concentration.