Rapid analysis of phthalic acid esters in environmental water using fast elution gas chromatography with mass spectrometry and adaptive library spectra

A method for the fast determination of the components in a complex sample by using gas chromatography with mass spectrometry was developed and used for the quantitative analysis of phthalic acid esters in environmental water. In the method, the adaptively corrected mass spectra were used to compensate for the differences between the library spectra and the measured ones in the experiment. The correction was obtained by the iterative transformation of the library spectra using iterative target transformation factor analysis, and the resolution was performed by non‐negative immune algorithm using the corrected spectra. Rapid analysis of 16 phthalic acid esters in water samples was achieved using fast elution gas chromatography with mass spectrometry measurements. The results show that the mass spectra and chromatographic profiles of the phthalic acid esters can be obtained from the overlapping signal of 13 min elution, and accurate quantitative analysis can be obtained. The recoveries of the phthalic acid esters obtained by standard addition are between 90.3 and 107.4%, and the relative standard deviations obtained in repeated measurements are less than 9%.     

Synthesis of New Brassinosteroid 24-Norcholane Type Analogs Conjugated in C-3 with Benzoate Groups

The metabolism of brassinosteroid leads to structural modifications in the ring skeleton or the side alkyl chain. The esterification and glycosylation at C-3 are the most common metabolic pathways, and it has been suggested that conjugate brassinosteroids are less active or inactive. In this way, plants regulate the content of active brassinosteroids. In this work, the synthesis of brassinosteroid 24-norcholane type analogs conjugated at C-3 with benzoate groups, carrying electron donor and electron attractant substituents on the aromatic ring, is described. Additionally, their growth-promoting activities were evaluated using the Rice Lamina Inclination Test (RLIT) and compared with that exhibited by brassinolide (used as positive control) and non-conjugated analogs. The results indicate that at the lowest tested concentrations (10⁻⁸–10⁻⁷ M), all analogs conjugated at C-3 exhibit similar or higher activities than brassinolide, and the diasteroisomers with S configuration at C-22 are the more active ones. Increasing concentration (10⁻⁶ M) reduces the biological activities of analogs as compared to brassinolide.     

Zinc‐Catalyzed Borylation of Primary,Secondary and Tertiary Alkyl Halides with Alkoxy Diboron Reagents at Room Temperature

A new catalytic system based on a Zn^II NHC precursor has been developed for the cross‐coupling reaction of alkyl halides with diboron reagents, which represents a novel use of a Group XII catalyst for C? X borylation. This approach gives borylations of unactivated primary, secondary, and tertiary alkyl halides at room temperature to furnish alkyl boronates, with good functional‐group compatibility, under mild conditions. Preliminary mechanistic investigations demonstrated that this borylation reaction seems to involve one‐electron processes.     

Dehydrogenative Meyer–Schuster‐Like Rearrangement: A Gold‐Catalyzed Reaction Generating an Alkyne

Easily accessible propargylic esters are converted to the inverted alkynyl ketones in an oxidative gold‐catalyzed reaction. Gagosz’s catalyst in combination with PhI(OAc)₂ is the best system for this conversion and 18 examples with yields up to 80 % are reported. The results indicate that the triple bond in the product is formed by elimination from a vinylgold intermediate. In a formal sense the new conversion overall is a dehydrogenative Meyer–Schuster rearrangement.     

CuII/TEMPO‐Promoted One‐Pot Synthesis of Highly Substituted Pyrimidines from Amino Acid Esters

A novel, Cu(OAc)₂/TEMPO promoted one‐step approach for the preparation of fully substituted pyrimidines from readily available amino acid esters has been described. In this reaction, the amino acid esters act as the only N?C sources for the construction of corresponding pyrimidines. The mechanism of this process includes oxidative dehydrogenation, the generation of an imine radical, and a formal [3+3] cycloaddition. This methodology proves to be a high atom‐economic and straightforward strategy for the synthesis of pyrimidines and diverse substrates which are substituted by various functional groups have been afforded in moderate to good yield.     

Kinetic Resolution of Racemic Mandelic Acid Esters by N,N′‐Dioxide–Scandium‐Complex‐Catalyzed Enantiomer‐Selective Acylation

A simple and efficient acylative kinetic resolution of racemic mandelic acid esters was accomplished with a chiral N,N’‐dioxide–scandium(III) complex under mild and base‐free reaction conditions. A variety of mandelic acid esters performed well in the reaction, obtaining both acylated products (up to 49% yield, 97% ee) and recovered substrates (up to 49% yield, 95% ee) in high enantioselectivities with perfect selectivity factors (up to 247). The enantioselective recognition and catalytic models were also proposed for the catalytic KR reaction.     

N-杂环卡宾催化对硝基苯甲醛的氧化酯化

以空气为氧化剂,研究了在N-杂环卡宾催化下,对硝基苯甲醛与9种醇的氧化酯化反应。考察了不同卡宾前体、卡宾前体的用量以及溶剂对收率和反应速率的影响。结果表明,当以对硝基苯甲醛摩尔分数10%的溴化3-乙基-4-甲基-5-羟乙基噻唑鎓盐为催化剂,过量的原料醇为溶剂时,可以有效地催化氧化对硝基苯甲醛进行酯化反应,收率为36%~64%,但当使用与对硝基苯甲醛等摩尔比的醇时,收率仅为9%~29%。     

Stereocontrolled Synthesis of 1,5‐Stereogenic Centers through Three‐Carbon Homologation of Boronic Esters

Allylic pinacol boronic esters are stable toward 1,3‐borotropic rearrangement. We developed a Pd^II‐mediated isomerization process that gives di‐ or trisubstituted allylic boronic esters with high E selectivity. The combination of this method with lithiation–borylation enables the synthesis of carbon chains that bear 1,5‐stereogenic centers. The utility of this method has been demonstrated in a formal synthesis of (+)‐jasplakinolide.     

Determination of phthalate esters in liquor samples by vortex‐assisted surfactant‐enhanced‐emulsification liquid–liquid microextraction followed by GC–MS

A novel method using vortex‐assisted surfactant‐enhanced‐emulsification liquid–liquid microextraction has been developed for the extraction of phthalate esters (PAEs) in Chinese liquor samples prior to analysis by GC–MS. In the proposed method, a high‐density extraction solvent (carbon tetrachloride) was dispersed into samples with the aid of a surfactant (Triton X‐100) and vortex agitation, resulting in a short extraction equilibrium (30 s). After centrifugation, a single microdrop of solvent was easily collected for GC–MS analysis. Key factors that affected the extraction efficiency were optimized. Under the optimum conditions, linearity was found in the range from 0.05 to 50 μg/L. Coefficients of determination varied from 0.9938 to 0.9971. LODs, based on an S/N of 3, ranged from 4.9 to 13 ng/L. Enrichment factors varied from 140 to 184. Reproducibility and recoveries were assessed by testing a series of three liquor samples that were spiked with different concentration levels. Finally, the proposed method was successfully applied to the determination of PAEs in 16 Chinese liquor samples. In this work, high‐density‐solvent vortex‐assisted surfactant‐enhanced‐emulsification liquid–liquid microextraction was applied for the first time for the extraction of PAEs in Chinese liquor samples and was proved to be simple, rapid, and sensitive.