Wen-Chao Yang

A Coumarin-Based Fluorescent Probe for Selective and Sensitive Detection of Thiophenols and Its Application

The development of probes for specific thiophenol detection is of great importance, due to the toxicity of thiophenols and their derivatives in the environment. In the present study, a novel fluorescent probe was rationally designed for detecting thiophenols via an intramolecular charge transfer mechanism. The developed probe selectively and sensitively distinguished thiophenols from aliphatic thiols. It displayed a large Stokes shift (145 nm) and >280-fold fluorescence enhancement. Moreover, the new probe not only displayed excellent cell permeability for the successful detection of thiophenol in HEK293 cells but also quantitatively measured thiophenols in water samples with good recovery (more than 90%), indicating that it has promising prospects for application for thiophenol sensing in environmental and biological sciences.

Computational Discovery of Picomolar Qo Site Inhibitors of Cytochrome bc1 Complex

A critical challenge to the fragment-based drug discovery (FBDD) is its low-throughput nature due to the necessity of biophysical method-based fragment screening. Herein, a method of pharmacophore-linked fragment virtual screening (PFVS) was successfully developed. Its application yielded the first picomolar-range Q(o) site inhibitors of the cytochrome bc(1) complex, an important membrane protein for drug and fungicide discovery. Compared with the original hit compound 4 (K(i) = 881.80 nM, porcine bc(1)), the most potent compound 4f displayed 20 507-fold improved binding affinity (K(i) = 43.00 pM). Compound 4f was proved to be a noncompetitive inhibitor with respect to the substrate cytochrome c, but a competitive inhibitor with respect to the substrate ubiquinol. Additionally, we determined the crystal structure of compound 4e (K(i) = 83.00 pM) bound to the chicken bc(1) at 2.70 Å resolution, providing a molecular basis for understanding its ultrapotency. To our knowledge, this study is the first application of the FBDD method in the discovery of picomolar inhibitors of a membrane protein. This work demonstrates that the novel PFVS approach is a high-throughput drug discovery method, independent of biophysical screening techniques.

Syntheses of coumarin–tacrine hybrids as dual-site acetylcholinesterase inhibitors and their activity against butylcholinesterase, Aβ aggregation, and β-secretase

Exploring small-molecule acetylcholinesterase (AChE) inhibitors to slow the breakdown of acetylcholine (Ach) represents the mainstream direction for Alzheimers disease (AD) therapy. As the first acetylcholinesterase inhibitor approved for the clinical treatment of AD, tacrine has been widely used as a pharmacophore to design hybrid compounds in order to combine its potent AChE inhibition with other multi-target profiles. In present study, a series of novel tacrine-coumarin hybrids were designed, synthesized and evaluated as potent dual-site AChE inhibitors. Moreover, compound 1g was identified as the most potent candidate with about 2-fold higher potency (Ki=16.7nM) against human AChE and about 2-fold lower potency (Ki=16.1nM) against BChE than tacrine (Ki=35.7nM for AChE, Ki=8.7nM for BChE), respectively. In addition, some of the tacrine-coumarin hybrids showed simultaneous inhibitory effects against both Aβ aggregation and β-secretase. We therefore conclude that tacrine-coumarin hybrid is an interesting multifunctional lead for the AD drug discovery.

A Highly Sensitive and Selective Fluorescent Probe for Thiophenol Designed via a Twist-Blockage Strategy

A benzoquinolizine coumarin-based fluorescent probe was developed for detecting thiophenols, demonstrating the superior fluorescence properties caused by the decay of the twisting effect of N,N-diethylamino group of coumarin. It discriminated thiophenols from various analytes including aliphatic thiols with good selectivity and displayed ∼700-fold fluorescence intensity enhancement and a remarkable limit of detection (4.5 nM). The new probe also can be applied to quantitative determine the concentrations of thiophenol in water samples and living cells.

Design, synthesis, and bioevaluation of benzamides: novel acetylcholinesterase inhibitors with multi-functions on butylcholinesterase, Aβ aggregation, and β-secretase.

Alzheimers disease (AD) is a multifactorial syndrome with several target proteins contributing to its etiology. In this study, we conducted a structure-based design and successfully produced a series of new multi-site AChE inhibitors with a novel framework. Compound 2e, characterized by a central benzamide moiety linked to an isoquinoline at one side and acetophenone at the other, was the most potent candidate with K(i) of 6.47nM against human AChE. Particularly, it showed simultaneous inhibitory effects against BChE, Aβ aggregation, and β-secretase. We therefore conclude that compound 2e is a very promising multi-function lead for the treatment of AD.

Synthesis and Herbicidal Activity of Triketone–Quinoline Hybrids as Novel 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD) is one of the most important targets for herbicide discovery. In the search for new HPPD inhibitors with novel scaffolds, triketone-quinoline hybrids were designed and subsequently optimized on the basis of the structure-activity relationship (SAR) studies. Most of the synthesized compounds displayed potent inhibition of Arabidopsis thaliana HPPD (AtHPPD), and some of them exhibited broad-spectrum and promising herbicidal activity at the rate of 150 g ai/ha by postemergence application. Most promisingly, compound III-l, 3-hydroxy-2-(2-methoxy-7-(methylthio)quinoline-3-carbonyl)cyclohex-2-enone (Ki = 0.009 μM, AtHPPD), had broader spectrum of weed control than mesotrione. Furthermore, compound III-l was much safer to maize at the rate of 150 g ai/ha than mesotrione, demonstrating its great potential as herbicide for weed control in maize fields. Therefore, triketone-quinoline hybrids may serve as new lead structures for novel herbicide discovery.

Efficient synthesis and antiproliferative activity of novel thioether-substituted flavonoids

As widely occurring natural products, flavonoids are an important source for drug discovery, due to their structural diversity and broad-spectrum biological activity. In this work, a library of novel, thioether-substituted flavonoids with diverse heterocyclic groups was synthesized via a microwave-assisted procedure with the advantages of good yields, short times, mild conditions and ready isolation of the products. Their antiproliferative activities were evaluated against six cancer cell lines, HCCLM-7, Hela, MDA-MB-435S, SW-480, Hep-2, and MCF-7 by the MTT-based assay. Compared with the positive control 5-fluorouracil, three compounds, 6a, 6b and 6j were successfully identified as the most promising candidates, due to their higher potency and broad-spectrum bioactivity with IC50 values in the range of 0.43 μM-6.7 μM.

Detection of Intracellular Selenol-Containing Molecules Using a Fluorescent Probe with Near-Zero Background Signal

Selenocysteine (Sec), encoded as the 21st amino acid, is the predominant chemical form of selenium that is closely related to various human diseases. Thus, it is of high importance to identify novel probes for sensitive and selective recognition of Sec and Sec-containing proteins. Although a few probes have been reported to detect artificially introduced selenols in cells or tissues, none of them has been shown to be sensitive enough to detect endogenous selenols. We report the characterization and application of a new fluorogenic molecular probe for the detection of intracellular selenols. This probe exhibits near-zero background fluorescence but produces remarkable fluorescence enhancement upon reacting with selenols in a fast chemical reaction. It is highly specific and sensitive for intracellular selenium-containing molecules such as Sec and selenoproteins. When combined with flow cytometry, this probe is able to detect endogenous selenols in various human cancer cells. It is also able to image endogenous selenol-containing molecules in zebrafish under a fluorescence microscope. These results demonstrate that this molecular probe can function as a useful molecular tool for intracellular selenol sensing, which is valuable in the clinical diagnosis for human diseases associated with Sec-deficiency or overdose.

Synthesis and herbicidal evaluation of triketone-containing quinazoline-2,4-diones.

Exploring novel 4-hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD) inhibitors is one of the most promising research directions in herbicide discovery. To discover new triketone herbicides with broad-spectrum weed control as well as excellent crop selectivity, a series of (total 52) novel triketone-containing quinazoline-2,4-dione derivatives were synthesized and further bioevaluated. The greenhouse testing indicated that many of the newly synthesized compounds showed better or excellent herbicidal activity against broadleaf and monocotyledonous weeds at the dosages of 37.5-150 g of active ingredient (ai)/ha. The structure and activity relationship in this study indicated that the triketone-containing quinazoline-2,4-dione motif has possessed great impact on herbicide activity and may be used for further optimization. Among the new compounds, III-b and VI-a-VI-d displayed a broader spectrum of weed control than mesotrione. In addition, the compound III-b also demonstrated comparatively superior crop selectivity to mesotrione, thus possessing great potential for weed control in the field.

Design, synthesis and herbicidal activity of novel quinazoline-2,4-diones as 4-hydroxyphenylpyruvate dioxygenase inhibitors

BACKGROUND 4-Hydroxyphenylpyruvate dioxygenase (HPPD) (EC 1.13.11.27) has been identified as one of the most promising target sites for herbicide discovery. To discover novel HPPD inhibitors with high herbicidal activity and improved crop selectivity, a series of novel triketone-containing quinazoline-2,4-dione derivatives possessing a variety of substituents at the N-1 position of the quinazoline-2,4-dione ring were designed and synthesised. RESULTS The results of in vitro tests and greenhouse experiments indicated that some analogues showed good HPPD inhibitory activity, with promising broad-spectrum herbicidal activity at a rate of 150 g AI ha(-1) . Most surprisingly, compound 11 h, 1-ethyl-6-(2-hydroxy-6-oxocyclohex-1-enecarbonyl)-3-(o-tolyl)quinazoline-2,4(1H,3H)-dione, showed the highest HPPD inhibition activity, with a Ki value of 0.005 μM, about 2 times more potent than mesotrione (Ki  = 0.013 μM). Further greenhouse experiments indicated that compounds 11d and 11 h displayed strong and broad-spectrum post-emergent herbicidal activity even at a dosage as low as 37.5 g AI ha(-1) , which was superior to mesotrione. More importantly, compounds 11d and 11 h were safe for maize at a rate of 150 g AI ha(-1) , and compound 11d was safe for wheat as well. CONCLUSION The present work indicated that the triketone-containing quinazoline-2,4-dione motif could be a potential lead structure for further development of novel herbicides.