Quinoline-Malononitrile-Based Aggregation-Induced Emission Probe for Monoamine Oxidase Detection in Living Cells.

A quinoline-malononitrile (QM)-based aggregation-induced emission probe was developed to detect MAOs in cells through an enzymatic reaction followed by ß-elimination. After being incubated at 37 °C, QM-NH2 responded to the MAO enzymes with great specificity and within just 5 min. This 5 min responsive mechanism was fast, with the limit of detection (LOD) at 5.49 and 4.76 µg mL-1 for MAO-A and MAO-B, respectively. Moreover, QM-NH2 displayed high enzyme specificity even in the presence of high concentrations of biological interferences, such as oxidizing and reducing agents, biothiols, amino acids, and glucose. Furthermore, QM-NH2 demonstrated biocompatibility as the cells retained more than 70% viability when exposed to QM-NH2 at concentrations of up to 20 µM. As a result, QM-NH2 was used to detect MAO-A and MAO-B in SH-SY5Y and HepG2 cells, respectively. After 1h incubation with QM-NH2, the cells exhibited enhanced fluorescence by about 20-fold. Moreover, the signal from cells was reduced when MAO inhibitors were applied prior to incubating with QM-NH2. Therefore, our research recommends using a QM probe as a generic method for producing recognition moieties for fluorogenic enzyme probes.

Controlling the Photocatalytic Activity and Benzylamine Photooxidation Selectivity of Bi2WO6 via Ion Substitution: Effects of Electronegativity.

Doping or ion substitution is often used as an effective strategy to improve photocatalytic activities of several semiconductors. Most frequently, the dopants provide extra states to increase light absorption, alter the electronic structure, or lower the carrier recombination. This work focuses on ion substitution in Bi2WO6, where the dopants modify band-edge potentials of the catalysts. Specifically, we investigate how the electronegativity (EN) of the dopant could be used to tune the band-edge potentials and how such changes influence the photocatalytic mechanism. Compared to Te that has a lower EN, I lowers the band-edge potentials. While substitutions with both ions enhance Rh B photodegradation and benzylamine photooxidation, the modified band potentials of I-doped Bi2WO6 influence the benzylamine photooxidation pathway, resulting in higher selectivity. Additionally, substitution of I7+ in the Bi2WO6 lattice improves the morphologies, decreases the band-gap energy, and reduces the carrier recombination. As a result, I-doped Bi2WO6 shows almost 3 times higher %conversion while maintaining 100% selectivity in the oxidative coupling of benzylamine. The findings here signify the importance of the choices of dopants on the photocatalytic reactions and would benefit the design of other related materials for such applications.

Design of a surrogate for high throughput screening of fatty aldehyde reductase engineering.

We designed and synthesized a fatty aldehyde surrogate containing a formyl thioester group, which can be reduced by fatty aldehyde reductase (FALR) with stoichiometric formaldehyde generation. It can be rapidly visualized and quantified using the Purpald assay. We demonstrated its successful application in the high throughput screening of FALR engineering.

Flavylium-Based Hypoxia-Responsive Probe for Cancer Cell Imaging.

A hypoxia-responsive probe based on a flavylium dye containing an azo group (AZO-Flav) was synthesized to detect hypoxic conditions via a reductase-catalyzed reaction in cancer cells. In in vitro enzymatic investigation, the azo group of AZO-Flav was reduced by a reductase in the presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH) followed by fragmentation to generate a fluorescent molecule, Flav-NH2. The response of AZO-Flav to the reductase was as fast as 2 min with a limit of detection (LOD) of 0.4 µM. Moreover, AZO-Flav displayed high enzyme specificity even in the presence of high concentrations of biological interferences, such as reducing agents and biothiols. Therefore, AZO-Flav was tested to detect hypoxic and normoxic environments in cancer cells (HepG2). Compared to the normal condition, the fluorescence intensity in hypoxic conditions increased about 10-fold after 15 min. Prolonged incubation showed a 26-fold higher fluorescent intensity after 60 min. In addition, the fluorescence signal under hypoxia can be suppressed by an electron transport process inhibitor, diphenyliodonium chloride (DPIC), suggesting that reductases take part in the azo group reduction of AZO-Flav in a hypoxic environment. Therefore, this probe showed great potential application toward in vivo hypoxia detection.

Microwave Heating Outperforms Conventional Heating for a Thermal Reaction that Produces a Thermally Labile Product: Observations Consistent with Selective Microwave Heating.

Microwave (MW) heating is more effective than conventional (CONV) heating for promoting a high-temperature oxidative cycloisomerization reaction that was previously reported as a key step in a total synthesis of the natural product illudinine. The thermal reaction pathway as envisioned is an inverse electron-demand dehydro-Diels-Alder reaction with in situ oxidation to generate a substituted isoquinoline, which itself is unstable to the reaction conditions. Observed reaction yields were higher at a measured bulk temperature of 200 °C than at 180 °C or 220 °C; at 24 hours than at earlier or later time points; and when the reaction solution was heated using MW energy as opposed to CONV heating with a metal heat block. Selective MW heating of polar solute aggregates is postulated to explain these observations.

Bioinspired Diastereoconvergent Synthesis of the Tricyclic Core of Palodesangrens via Diels-Alder Reaction, LiAlH4-Mediated Isomerization, and Acid-Mediated Cyclization.

The cyclohexene moiety of the tricyclic 6,7-diaryl-tetrahydro-6 H-benzo[ c]chromene core of palodesangrens could be assembled in a biomimetic and step-economical fashion by the Diels-Alder reaction between the electron-rich ( E)-1,3-butadienylarenes as the diene and the electron-deficient chalcones as the dienophile. During the reduction of ketone to the corresponding alcohol by LiAlH4, the mixture of endo and exo isomers underwent a novel diastereoconvergent LiAlH4-mediated isomerization to install the desired stereochemistry at C10a. Subsequent pyran ring closure under acidic conditions installed the stereochemistry at the remaining C6. Overall, the tricyclic core of palodesangrens could be prepared in three steps and up to 38% yield.

A convenient one-pot synthesis of N-substituted amidoximes and their application toward 1,2,4-oxadiazol-5-ones.

The first direct one-pot approach for the synthesis of N-substituted amidoximes from secondary amides or the intermediate amides has been developed. Through the Ph3P-I2-mediated dehydrative condensation, a variety of N-aryl and N-alkyl amidoximes (R1(C[double bond, length as m-dash]NOH)NHR2, where R1 or R2 = aryl, alkyl, or benzyl) were readily afforded under mild conditions and short reaction times. The synthetic application of the obtained amidoximes has also been demonstrated through the formation of 1,2,4-oxadiazolones via base-mediated carbonylative cyclization with 1,1'-carbonyldiimidazole.

Ultrasound-Assisted Solvent-Free Parallel Synthesis of 3-Arylcoumarins Using N-Acylbenzotriazoles.

An ultrasound-assisted one-pot acylation/cyclization reaction between N-acylbenzotriazoles and 2-hydroxybenzaldehydes has been developed for the synthesis of substituted 3-arylcoumarins. Using ultrasound not only allows rapid and clean conversion but also simplifies experimental setup and parallel workup leading to rapid generation of 3-arylcoumarin libraries under mild, solvent-free, and chromatography-free conditions.