Comparison and prediction of the retention in micellar electrokinetic chromatography and microemulsion electrokinetic chromatography for disubstituted benzenes

Retention index (I), rather than retention factor (k), was found to be a more reasonable parameter for comparison of the relative affinity of disubstituted benzenes in MEEKC and MEKC, due to independent of I with the SDS surfactant concentration. MEKC and MEEKC may give similar or different I values, depending on types of moieties. With known I and K_ow for alkylbenzenes as references in MEKC and MEEKC, the values of K_ow for disubstituted benzenes can be estimated from the observed I values, where K_ow is the octanol–water distribution constant. In addition, a group additive approach can be used to predict I for disubstituted benzenes with different moieties from the average observed I for the disubstituted benzenes with same moieties. However, electronic effects and/or intramolecular interaction may result in the different observed I from prediction.     

Convenient synthetic route to a dehydrorotenoid via selective intramolecular aldol condensation of 1,2-diaryl diketone

Synthesis of dehydrorotenoid (1) was successfully achieved via an intramolecular aldol reaction of the corresponding 1,2-diaryl diketone intermediate. The 1,2-diaryl diketone was prepared using a ruthenium-catalyzed oxidation of the corresponding substituted diaryl acetylene. Treatment of this 1,2-diketone with l-proline induced a selective intramolecular aldol condensation reaction, forming the desired benzopyranone over the alternative benzofuran. Deprotection, cyclization, and dehydration gave the target compound in good overall yield.     

Hydrogen bonding in labdane diterpenoids, labda-7,12(E),14-triene-17-oic acid and labda-12(Z),14,17-triene-18-oic acid

Two labdane diterpenoids, labda-7,12(E),14-triene-17-oic acid (1) and labda-12(Z),14,17-triene-18-oic acid (2), C₂₀H₃₀O₂, have been isolated from Croton oblongifolius. Both 1 and 2 crystallized in the monoclinic system, space group C2, with cell dimensions of a = 21.912(1) Å, b = 7.4002(4) Å, c = 11.5079(7) Å, = 101.999(1)^o and a = 21.308(2) Å, b = 11.9067(9) Å, c = 7.5606(6) Å, = 100.763(1)^o, respectively. Compound 1, a rare example of carboxylic group bound to a cyclohexene ring, forms an infinite intermolecular hydrogen-bonded polymer [O1 O2(–x + 1/2, y + 1/2, –z + 2) 2.697(2) Å], whereas molecules of compound 2 are linked to form an asymmetric hydrogen-bonded dimer [O1 O2(–x, y, –z) 2.657(3) Å].     

Gas Chromatographic Fingerprint Analysis for the Comparison of Seized Cannabis Samples

Cannabis sativa L. is widely used as recreational illegal drugs. Illicit Cannabis profiling, comparing seized samples, is challenging due to natural Cannabis heterogeneity. The aim of this study was to use GC–FID and GC–MS herbal fingerprints for intra (within)- and inter (between)-location variability evaluation. This study focused on finding an acceptable threshold to link seized samples. Through Pearson correlation-coefficient calculations between intra-location samples, ‘linked’ thresholds were derived using 95% and 99% confidence limits. False negative (FN) and false positive (FP) error rate calculations, aiming at obtaining the lowest possible FP value, were performed for different data pre-treatments. Fingerprint-alignment parameters were optimized using Automated Correlation-Optimized Warping (ACOW) or Design of Experiments (DoE), which presented similar results. Hence, ACOW data, as reference, showed 54% and 65% FP values (95 and 99% confidence, respectively). An additional fourth root normalization pre-treatment provided the best results for both the GC–FID and GC–MS datasets. For GC–FID, which showed the best improved FP error rate, 54 and 65% FP for the reference data decreased to 24 and 32%, respectively, after fourth root transformation. Cross-validation showed FP values similar as the entire calibration set, indicating the representativeness of the thresholds. A noteworthy improvement in discrimination between seized Cannabis samples could be concluded.     

Chiral separation in capillary electrophoresis using dual neutral cyclodextrins: theoretical models of electrophoretic mobility difference and separation selectivity

Simple equations and theoretical models, related to enantioselectivity (kappa) and C, have been developed for prediction of electrophoretic mobility difference (Deltamu) and separation selectivity (alpha) for enantiomers in CE using dual CDs, where alpha and kappa are defined as the ratio of mu and the ratio of binding constant (K) for enantiomers to each CD, respectively, C the CD concentration, and the average K for enantiomers and each CD. Experiments were carried out using dual CDs as beta-CD and dimethyl-beta-cyclodextrin (DM-beta-CD) and test analytes as five pairs of amphetamine drug enantiomers. A change in observed Deltamu and alpha of enantiomers in dual CDs was found to be in excellent agreement with the theoretical models. For example, in comparison with single CD1, dual CDs can enhance Deltamu and alpha up to the maximum value when enantiomers migrate with the same order in CD1 and CD2, and have the value of rho > 1.0, where rho is the enantioselectivity ratio for CD2 to CD1, while worse Deltamu and alpha are obtained for enantiomers with rho < 1.0.     

Electron Transfer from Thioethers

Abstract

Oxidation of thioethers is greatly facilitated by neighboring group participation by carboxylate, alcohol, and thioether moieties.     

Microemulsion electrokinetic chromatography for separation and analysis of curcuminoids in turmeric samples

Microemulsion EKC (MEEKC) was developed for quantitative analysis of curcuminoids, such as curcumin (C), demethoxycurcumin (D), and bis-demethoxycurcumin (B). MEEKC separation of curcuminoids was optimized, and a change in resolution was explained using a modified equation for resolution in MEEKC without electroosmosis. The suitable MEEKC conditions for separation of curcuminoids were obtained to be the microemulsion buffer containing 50 mM phosphate buffer at pH 2.5, 1.1% v/v n-octane as oil droplets, 180 mM SDS as surfactant, 890 mM 1-butanol as cosurfactant, and 25% v/v 2-propanol as organic cosolvent; applied voltage of -15 kV; and separation temperature 25 degrees C. Achieved baseline resolution of C:D and D:B was obtained with R(s) -2.4 and analysis time within 18 min. In addition, high accuracy and precision of the method were obtained. This MEEKC method was used for quantitative determination of individual curcuminoids in medicinal turmeric capsules and powdered turmeric used as coloring additive in food, with simple sample preparation such as solvent extraction, dilution, and filtration, and without cleaning up by SPE.     

Diaporthichalasin, a novel CYP3A4 inhibitor from an endophytic Diaporthe sp.

A novel CYP3A4 inhibitor, diaporthichalasin, together with pycnidione were isolated from an endophytic fungus, Diaporthe sp. Their structures were elucidated on the basis of spectral data and the structure of diaporthichalasin was confirmed by X-ray crystallographic analysis. Diaporthichalasin exhibited significantly potent inhibition of CYP3A4 with an IC₅₀ value of 0.626 μM, while the IC₅₀ value of pycnidione was 465 μM.