Qiong-You Wu

Design, syntheses and 3D-QSAR studies of novel N-phenyl pyrrolidin-2-ones and N-phenyl-1H-pyrrol-2-ones as protoporphyrinogen oxidase inhibitors.

The characteristics of low application rates, good crop selectivity, low residue and environmental safety exhibited by Protoporphyrinogen oxidase (PPO, EC 1.3.3.4)-inhibiting herbicides have attracted a world-wide research interests. As continuation of our research work on the development of new PPO inhibitors, a series of mono-carbonyl analogues of cyclic imides, N-phenyl pyrrolidin-2-ones and N-phenyl-1H-pyrrol-2-ones, were designed and synthesized based on previously established DFT-QSAR results. The PPO inhibition activities of 29 newly synthesized compounds were tested and a predictive comparative molecular field analysis (CoMFA) model was established with the conventional correlation coefficient r(2)=0.980 and the cross-validated coefficient q(2)=0.518. According to the CoMFA model, the substituent effects on the PPO inhibition activity were explained reasonably. Further greenhouse assay showed that 2-(4-chloro-2-fluoro-5-propoxy-phenyl)-2,3,4,5,6,7-hexahydro-isoindol-1-one (C(6), k(i)=0.095μM) and 2-(5-allyloxy-4-chloro-2-fluorophenyl)-2,3,4,5,6,7-hexahydro-isoindol-1-one (C(7), k(i)=0.12μM) displayed excellent post-emergency herbicidal activity at the concentration of 150g.ai/ha against seven tested weeds. Due to their high PPO inhibition effect and broad spectrum herbicidal activity, these two compounds have the potential for further study on crop selectivity and field trial. These results confirmed once again that only one of the carbonyl groups of cyclic imides is essential to the PPO inhibition activity.

Synthesis and Antifungal Activity of Novel Sclerotiorin Analogues

Sclerotiorin 1, first isolated from Penicillium sclerotiorum, has weak antifungal activity and belongs to the azaphilone-type family of natural products. Several series of sclerotiorin analogues were designed and synthesized with the aim of discovering novel fungicides with improved activity. The syntheses involved two key steps, cycloisomerization and then oxidation, and used a simple and efficient Sonogashira cross-coupling reaction to construct the required functionalized precursor. With sclerotiorin as a control, the activities of the newly synthesized analogues were evaluated against seven fungal pathogens, and several promising candidates (compounds 3a₁, 3d₂, 3e₂, 3f₂ and 3k₂) with greater activity and simpler structures than sclerotiorin were discovered. In addition, preliminary structure-activity relationships were studied, which revealed that not only the chlorine or bromine substituent at the 5-position of the nucleus but also the phenyl group at the 3-position and the substituent pattern on it contributed crucially to the observed antifungal activity. Analogues with a methyl substituent at the 1-position have reduced levels of activity, while those with a free hydroxyl group in place of acetoxy at the quaternary center of the bicyclic ring system retain activity.

Design and syntheses of novel N-(benzothiazol-5-yl)-4,5,6,7-tetrahydro-1H-isoindole-1,3(2H)-dione and N-(benzothiazol-5-yl)isoindoline-1,3-dione as potent protoporphyrinogen oxidase inhibitors.

Discovery of protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors has been one of the hottest research areas in the field of herbicide development for many years. As a continuation of our research work on the development of new PPO-inhibiting herbicides, a series of novel N-(benzothiazol-5-yl)-4,5,6,7-tetrahydro-1H-isoindole-1,3(2H)-diones (1a-p) and N-(benzothiazol-5-yl)isoindoline-1,3-diones (2a-h) were designed and synthesized according to the ring-closing strategy of two ortho-substituents. The bioassay results indicated that some newly synthesized compounds exhibited higher PPO inhibition activity than the control of sulfentrazone. Compound 1a, S-(5-(1,3-dioxo-4,5,6,7-tetrahydro-1H-isoindol-2(3H)-yl)-6-fluorobenzothiazol-2-yl) O-methyl carbonothioate, was identified as the most potent inhibitor with k(i) value of 0.08 μM, about 9 times higher than that of sulfentrazone (k(i) = 0.72 μM). Further green house assay showed that compound 1b, methyl 2-((5-(1,3-dioxo-4,5,6,7-tetrahydro-1H-isoindol-2(3H)-yl)-6-fluorobenzothiazol-2-yl)thio)acetate, exhibited herbicidal activity comparable to that of sulfentrazone even at a concentration of 37.5 g ai/ha. In addition, among six tested crops, wheat exhibited high tolerance to compound 1b even at a dosage of 300 g ai/ha. These results indicated that compound 1b might have the potential to be developed as a new herbicide for weed control of wheat field.

Quantitative structure-activity relationships of 1,3,4-thiadiazol-2(3H)-ones and 1,3,4-oxadiazol-2(3H)-ones as human protoporphyrinogen oxidase inhibitors.

Protoporphyrinogen oxidase (Protox, EC 1.3.3.4) has attracted great interest during the last decades due to its unique biochemical characteristics and biomedical significance. As a continuation of our research work on the development of new PPO inhibitors, 23 new 1,3,4-thiadiazol-2(3H)-ones bearing benzothiazole substructure were designed and synthesized. The in vitro assay indicated that the newly synthesized compounds 1a-w displayed good inhibition activity against human PPO (hPPO) with K(i) values ranging from 0.04μM to 245μM. To the knowledge, compound 1a, O-ethyl S-(5-(5-(tert-butyl)-2-oxo-1,3,4-thiadiazol-3(2H)-yl)-6-fluorobenzothiazol-2-yl)carbonothioate, with the K(i) value of 40nM, is so far known as the most potent inhibitor against hPPO. Based on the molecular docking and modified molecular mechanics/Poisson-Boltzmann surface area (MM-PBSA) calculations, the quantitative structure-activity relationships of 1,3,4-thiadiazol-2(3H)-ones and 1,3,4-oxadiazol-2(3H)-one derivatives were established with excellent correlation relationships (r(2)=0.81) between the calculated and experimental binding free energies. Some important insights were also concluded for guiding the future rational design of new hPPO inhibitors with improved potency.

Recent Developments in the Synthesis and Applications of Isatins

Isatin (1H-indole-2,3-dione, Figure 1) was first obtained by Erdman and Laurent in 1841 as a product from the oxidation of indigo by nitric and chromic acids.1 Since then, isatin and its derivatives have become important heterocycles. They are found in nature and are present in numerous bioactive compounds, which can act as inhibitors of apoptosis,2,3 anticonvulsants,4 antiviral,5,6 anti-bacterial and antifungal7 agents. For example, 5-(3′methylbuten-2′-yl)isatin and 6-(3′-methylbuten-2′-yl)isatin, which were, respectively, isolated from Chaetomium globosum and Streptomyces albus, have been described as novel antifungal compounds.8–11 Indirubin has been shown to be the active ingredient of Danggui Longhui Wan, a mixture of plants that has been used in traditional Chinese medicine to treat chronic diseases for many years and is also found in Chinese medicinal herbs Isatis indigotica and Strobilanthes cusia.12–15 Methisazone and the β-thiosemicarbazone of isatin (IBT) have also been described as smallpox chemoprophylactic agents (Figure 1).6,12 Besides, the versatility of isatins has also led to extensive studies on the use of isatin and its derivatives in organic synthesis.16–30 This review summarizes the recent progress of the preparative methodologies of isatins and their applications in the syntheses of natural products and biologically important heterocyclic compounds for the period of 2000 to 2013.

Atom-economic dehydrogenative amide synthesis via ruthenium catalysis

Recently, a class of dehydrogenative transformations for amide bond formation have been developed. These transformations are atom-economic and environmentally-benign processes with their respective starting materials of alcohols and amines, aldehydes and amines, as well as symmetrical esters and amines, showing a promising prospect for applications. These unique protocols have been reported using various ruthenium-based catalytic systems. However, challenges still exist in this area. For example, existing catalytic systems usually suffer from low efficiency, high catalyst loading, and lack of structural diversity.

Discovery of 1,2,4-triazole-1,3-disulfonamides as dual inhibitors of mitochondrial complex II and complex III

Respiratory chain succinate-ubiquinone oxidoreductase (SQR or complex II) and ubihydroquinone-cytochrome (cyt) c oxidoreductase (cyt bc1 or complex III) have been demonstrated as the promising targets of numerous antibiotics and fungicides. As a continuation of our research work on the development of new fungicides, a series of 1,2,4-triazole-1,3-disulfonamide derivatives with dual functions targeting both SQR and cyt bc1 were designed and synthesized by coupling diverse diphenyl ether moieties with triazolesulfonamide units. These newly synthesized compounds were characterized by elemental analyses, 1H NMR and ESI-MS spectrometry. The in vitro assay indicated that most of the synthesized compounds displayed good inhibition against porcine succinate-cytochrome reductase (SCR) with IC50 values ranging from 3.2 to 81.8 μM, revealing much higher activity than that of the commercial control amisulbrom whose IC50 value is 93.0 μM. Further evaluation against the respective SQR and cyt bc1 indicated that most compounds exhibited SQR-inhibiting activity as well as cyt bc1-inhibiting activity, but the inhibition potency against SQR is much higher than that against cyt bc1, showing that the SCR inhibition might be contributed greatly by the SQR inhibition. The further antibacterial evaluation against Xanthomonas oryzae pv. oryzae revealed that four compounds showed excellent potency at the concentration of 20 μg mL−1. In particular, compounds 6h and 6j exhibited much better antibacterial activity than the commercial control bismerthiazol in terms of their EC50. Impressively, 6j has an EC90 of 33.62 μg mL−1, more than 10-fold higher than that of bismerthiazol.

Hexahydrophthalimide–benzothiazole hybrids as a new class of protoporphyrinogen oxidase inhibitors: synthesis, structure–activity relationship, and DFT calculations

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) has attracted continuous interest during the last few decades not only because of its unique biochemical characteristics but also because of its biomedical significance. As a continuation of our research work on the development of new PPO inhibitors, N-(benzothiazol-5-yl)-hexahydro-2H-isoindole-1,3-dithione (1a–j) and N-(benzothiazol-5-yl)-octahydro-3-thioxoisoindol-1-one derivatives (2a–i) were designed and synthesized. These newly prepared compounds were characterized by elemental analyses, 1H NMR and ESI-MS spectroscopy. The in vitro assay indicated that these compounds displayed good inhibition activity against human PPO (hPPO) with Ki values ranging from 0.38 μM to 6.83 μM. Notably, most of the monothionated products (1a–j) displayed a higher or comparable PPO-inhibition activity compared with the commercial control sulfentrazone. The comparison of the dihedral angles of the representative compound with that of acifluorfen (ACF) complexed with hPPO clearly indicated that the dihedral angle between the thionyl amide or carbonyl amide ring and the benzothiazole ring was closely related to the variation of the PPO inhibition activity of different types of inhibitors.

Design, synthesis and fungicidal activity of novel sclerotiorin derivatives.

Sclerotiorin, a chlorine‐containing azaphilone‐type natural product, was first isolated from Penicillium sclerotiorum and has been reported to exhibit weak fungicidal activity. Optimization of the substituents at the 3‐ and 5‐positions of the sclerotiorin framework was investigated with the aim of discovering novel fungicides with improved activity. The design of sclerotiorin analogues involved replacing the diene side chain with a phenyl group or an aromatic‐ or heteroaromatic‐containing aliphatic side chain. The designed compounds were synthesized by cycloisomerization and subsequent oxidation of suitable 2‐alkynylbenzaldehydes, in which a variety of substituents were introduced using a Sonogashira coupling reaction. The structures of these newly prepared compounds were confirmed by 1H and 13C NMR spectroscopy, HRMS and single‐crystal X‐ray analysis. The antifungal activity of the synthesized compounds was evaluated against seven phytopathogenic species. Compounds 3, 9g and 9h were found to have a broad spectrum of fungicidal activity, and these structurally simpler products can be recognized as lead compounds for further optimization.

Design, synthesis and insecticidal activity of novel 1,1‐dichloropropene derivatives

BACKGROUND Pyridalyl is a highly active insecticide against lepidopterous larvae, with a novel chemical structure not related to any other existing insecticide. To discover new pyridalyl analogues with high activity against resistant pests, a series of 1,1-dichloropropene derivatives bearing structurally diverse substituted heterocycle rings in place of the pyridine ring of pyridalyl were designed and synthesised. RESULTS All of the title compounds were confirmed by (1)H NMR, (13)C NMR and high-resolution mass spectra. Two representative compounds (Ic and IIa) were further characterised by X-ray diffraction analysis. In addition, bioassays showed that most of the newly synthesised compounds displayed good insecticidal activity against Prodenia litura. Further determination of LD50 values and field trials identified compound IIa as the most promising candidate, which produced a much better 14 day control effect against diamondback moths and longer duration of efficacy than pyridalyl, indicating its potential for further development as a new insecticide for the control of lepidopteran insects. CONCLUSION Compound IIa has great potential for further development as a new insecticide for the control of lepidopteran insects.