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Herein we describe a reaction of ortho-carbonylated alkynyl-substituted arylaldehydes with common primary amines that can provide functionalized isoindolinone and 3-hydroxylindenamine products in high yields. Depending on the substituent size of primary amines, two distinct reaction pathways were exploited selectively, that are, an initial aza-conjugate addition followed by hydrogen transfer to access isoindolinone framework and a unique oxa-conjugate addition followed by Petasis-Ferrier rearrangement to afford indenamine derivatives. In the presence of Et3N, the reaction property of small primary amines was changed, proceeding to afford 3-hydroxylindenamine derivatives efficiently. These products contain interesting substructures that exist in many natural products and bioactive molecules. The reaction features contain the use of transition-metal-free catalysts, simple operation, broad substrate scope, and product diversity. [ABSTRACT FROM AUTHOR]

In this work, we have developed an efficient method for the rapid extraction and separation of triterpene acids from 37 different varieties of raspberry via ultrasound-assisted dispersive liquid-liquid microextraction (UA-DLLME). The triterpene acids were then determined by high-performance liquid chromatography (HPLC) with fluorescence detection using benzimidazo-[2,1-b]quinazolin-12(6H)-one-5-ethyl-p-toluenesulfonate (BQETS) as the labeling agent. Five triterpene acids, including asiatic acid (AA), maslinic acid (MA), corosolic acid (CA), oleanolic acid (OA) and betulinic acid (BA), were extracted by UA-DLLME using chloroform and acetone as the extracting and dispersing solvents, respectively. After extraction and nitrogen flushing, the extracts were simultaneously characterized by HPLC based on pre-column derivatization using BQETS, a new labeling agent synthesized in our laboratory. Several key parameters affecting the extraction efficiency and derivatization yields were investigated and optimized by response surface methodology (RSM) combined with Box-Behnken design (BBD). The method was further validated for linearity (correlation coefficient R > 0.9979), precision (RSD = 0.23-2.45 %), and recovery (RSD = 90-106.5 %). The limits of detection (LODs) and the limits of quantification (LOQs) were determined to be within the range of 1.83-7.69 µg/L and 6.06-25.47 µg/L, respectively. This is the first report of the use of BQETS as a pre-column derivatization agent for the determination of triterpene acids in real samples. The proposed method has been applied to the determination of five triterpene acids in 37 different raspberry varieties with significantly increased sensitivity compared to other methods. The results obtained indicate that the contents of triterpene acids vary significantly across different raspberry varieties. [ABSTRACT FROM AUTHOR]

Herein we demonstrate a gold-catalyzed regio- and stereo-selective cycloisomerization of bis(o-alkynyl benzyl alcohols). By this protocol, the synthesis of dihydroisobenzofuran derivatives can be achieved in good yields. The reaction features a continuous alkyne/alkene-directed 5-exo-dig cyclization and a Prins-type cyclization for the formation of three cycles. [ABSTRACT FROM AUTHOR]

An efficient sensor was developed for highly sensitive and selective determination of melamine based on Ag nanoclusters (Ag NCs) capped by hyperbranched polyethyleneimine (PEI) molecules with different molecular weights. The fluorescence of the Ag NCs could be quenched by Hg2+ and recovered by melamine. The molecular weights of PEI had an appreciable effect on the sensitivity, and Ag NCs capped by PEI with a molecular weight of 600 were more sensitive; the linear range of melamine was from 0.1 to 30 μM with a detection limit 30 nM. Moreover, this Ag NCs–Hg2+ system displayed excellent selectivity over common interferences such as metal ions, amino acids, sugars and nitrogen-containing organic molecules. Benefiting from the high selectivity, good recoveries ranging from 96% to 101% were obtained in food samples, including milk, infant formula, and dog food. More importantly, Ag NC-doped agarose hydrogels were fabricated easily to construct a visual device for the detection of melamine in food samples. [ABSTRACT FROM AUTHOR]

A method for preparing multisubstitutedN-(tosylamino)pyrrole derivatives through AuCl3-catalyzed cycloisomerization of theβ-alkynyl hydrazone compounds was described. The reaction could be carried out in one pot from theβ-ketoesters to give the cyclized products in moderate to excellent yields with low catalyst loadings. [ABSTRACT FROM AUTHOR]

The authors describe dual-emission carbon nanodots containing blue emitters (BE; peak emission at 385nm under 315 nm excitation) and yellow emitters (YE; peak emission at 530 nm under 365nm excitation), and how they can be applied to direct and indirect determination of tetracyclines (TCs). The direct detection scheme is based on the finding that tetracycline (TET), oxytetracycline, chlortetracycline and doxycycline quench the two emissions of the carbon dots. While direct determination is rapid and convenient, it cannot differentiate between TCs. The indirect detection scheme, in contrast, is based on the finding that Al (III) ions enhance the fluorescence of the YE in the carbon dots, and that they cause a blue shift in emission. It is, however, known that TET forms a strong complex with Al (III), and this can inhibit the interaction between Al (III) and the YE, so that the fluorescence of YE is not enhanced and blue-shifted by Al (III) in the presence of TET. This finding is exploited in a fluorescence turn-on/off assay for TET that can distinguish TET from other TCs. The linear range of indirect determination for TET extends from 1 nM to 30 μM, and the limit of detection is 0.52 nM. The indirect method was successfully applied to the determination of TET in spiked milk, fish and pork, and recoveries ranged from 91.7 to 102 %. [ABSTRACT FROM AUTHOR]

Rationale Quantitative analysis of cholesterol and its metabolic steroid hormones plays a vital role in diagnosing endocrine disorders and understanding disease progression, as well as in clinical medicine studies. Because of their extremely low abundance in body fluids, it remains a challenging task to develop a sensitive detection method. Methods A hyphenated technique of dual ultrasonic-assisted dispersive liquid-liquid microextraction (dual-UADLLME) coupled with microwave-assisted derivatization (MAD) was proposed for cleansing, enrichment and sensitivity enhancement. 4′-Carboxy-substituted rosamine (CSR) was synthesized and used as derivatization reagent. An ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method was developed for determination of cholesterol and its metabolic steroid hormones in the multiple reaction monitoring mode. Results Parameters of dual-UADLLME, MAD and UHPLC-MS/MS were all optimized. Satisfactory linearity, recovery, repeatability, accuracy and precision, absence of matrix effect and extremely low limits of detection (LODs, 0.08-0.15 pg mL−1) were achieved. Conclusions Through the combination of dual-UADLLME and MAD, a determination method for cholesterol and its metabolic steroid hormones in human plasma, serum and urine samples was developed and validated with high sensitivity, selectivity, accuracy and perfect matrix effect results. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An unprecedented access to strained tetracyclic bridgehead alkenes by reaction of easily accessible ortho-alkynylarylaldehydes with conjugated dienes is described. The process involves a chemo- and stereo-selective, gold-catalyzed, tandem intermolecular [3+2] cycloaddition/Prins-type ring-closing reaction that allows generating structural complexity in a straightforward manner. This approach for the preparation of anti-Bredt compounds is synthetically superior to those previously reported: the procedure is easy to implement, operates under mild experimental conditions, is efficient, and exhibits a good substrate scope. [ABSTRACT FROM AUTHOR]