Carboline derivatives based on natural pityriacitrin as potential antifungal agents

Carboline alkaloids are a class of important heterocyclic natural products, which usually present extensive bioactivities. During the course of our research for active compounds from natural products, the pityriacitrin and pityriacitrin B belonged carboline alkaloids have been isolated from a Chinese Burkholderia sp. NBF227, which indicated potential antifungal activities. So, in order to develop these carboline alkaloids as potential fungicidal agents, a series of pityriacitrin derivatives were investigated for their antifungal activities against Phytophthora capsici, Sclerotinia sclerotiorum, Botrytis cinerea and Rhizoctonia solani, and the results demonstrated that compounds 4, 10 and 19 displayed broad-spectrum antifungal activities. In addition, in vivo bioassay also indicated that compounds 4 and 10 could protect the pepper leaves and grape fruits against infection by P. capsici and B. cinerea, respectively. The possible mechanism of antifungal action for these compounds was also explored.     

Discovery of γ-lactam derivatives containing 1,3-benzodioxole unit as potential anti-phytopathogenic fungus agents

A series of γ-lactam analogs containing 1,3-benzodioxole moiety were designed, and these derivatives were synthesized from the lead compound of lactam via a structural diversity-oriented synthesis, their structures were confirmed by ¹HNMR,¹³CNMR, ESI-MS spectrum. Their antifungal activities were evaluated against four serious and typically crop-threatening agricultural fungi, including Rhizoctonia solani, Alternaria tenuis Nees, Gloeosporium theae-sinensis, and Fusarium graminearum. Some of these derivatives exhibited activity against Alternaria tenuis Nees higher than that of commercial fungicides carbendazim, such as compounds 7a, 7b, and 7i, compared with the blank control, some of these derivatives showed good antifungal activities against Gloeosporium theae-sinensis and Fusarium graminearum. The systematic study provides evidences for further structural modification and application of lactam analogues as antifungal agents for agriculture.     

Design,synthesis and antifungal evaluation of novel pyrazole carboxamides with diarylamines scaffold as potent succinate dehydrogenase inhibitors

Sixteen novel pyrazole carboxamides with diarylamines scaffold were designed, synthesized and characterized in detail via ¹H NMR, ¹³C NMR and ESI-HRMS. Preliminary bioassays showed that some of the target compounds exhibited good antifungal activity against Rhizoctonia solani, Fusarium oxysporum, Phytophthora infestans and Fusarium graminearum. Among them, compound 1c exhibited the highest antifungal activities against R. solani in vitro with EC₅₀ value of 0.005?mg/L, superior to the commercially available fungicide fluxapyroxad (EC₅₀?=?0.033?mg/L). And compound 1c (IC₅₀?=?0.034?mg/L) showed higher inhibition abilities against succinate dehydrogenase than fluxapyroxad (IC₅₀?=?0.037?mg/L). This study suggests that compound 1c could be regarded as a potential succinate dehydrogenase inhibitor.     

Synthesis and antifungal activity of imidazo[1,2-b]pyridazine derivatives against phytopathogenic fungi

A series of 3,6-disubstituted imidazo[1,2-b]pyridazine derivatives have been synthesized and characterized with spectroscopic analyses. The antifungal activities of these compounds against nine phytopathogenic fungi were evaluated by the mycelium growth rate method. The in vitro antifungal bioassays indicated that most of compounds displayed excellent and broad-spectrum antifungal activities. Especially, compounds 4a, 4c, 4d, 4l and 4r exhibited 1.9–25.5 fold more potent than the commercially available fungicide hymexazol against Corn Curvalaria Leaf Spot (CL), Alternaria alternate (AA), Pyricularia oryzae (PO) and Alternaria brassicae (AB) strains. Structure-activity relationship analysis showed that the enhanced antifungal activity is significantly affected by the substituents on the benzene ring and pyridazine ring.     

Synthesis of novel fenfuram-diarylether hybrids as potent succinate dehydrogenase inhibitors

Twelve novel fenfuram-diarylether hybrids were designed, synthesized and characterized by ¹H NMR and MS. Their in vitro antifungal activities were evaluated against five phytopathogenic fungi by mycelial growth inhibition method. Most compounds showed significant antifungal effect on Rhizoctonia solani and Sclerotinia sclerotiorum. Compound 1c exhibited the most potent antifungal effect on R. solani with an EC₅₀ value of 0.242 mg/L, superior to the commercial fungicide boscalid (EC₅₀ = 1.758 mg/L) and the lead fungicide fenfuram (EC₅₀ = 7.691 mg/L). Molecular docking revealed that compound 1c featured a higher affinity for succinate dehydrogenase (SDH) than fenfuram. Furthermore, it was shown that the 2-chlorophenyl group of compound 1c formed a π-π stacking with D/Tyr-128 and a Cl-π interaction with B/His-249, which made compound 1c more active than fenfuram against SDH.     

Synthesis and molecular docking study of some 3,4-dihydrothieno[2,3-d]pyrimidine derivatives as potential antimicrobial agents

In continuation of our research program aiming at developing new potent antimicrobial agents, new series of substituted 3,4-dihydrothieno[2,3-d]pyrimidines was synthesized. The newly synthesized compounds were preliminary tested for their in vitro activity against six bacterial and three fungal strains using the agar diffusion technique. The results revealed that compounds 7, 8a, 10b, 10d and 11b exhibited half the potency of levofloxacine against the Gram-negative bacterium, Pseudomonas aeruginosa, while compounds 5a, 8b, 10c and 12 displayed half the potency of levofloxacine against Proteus Vulgaris. Whereas, compounds 7, 10b, 10d and 11b showed half the activity of ampicillin against the Gram-positive bacterium, B. subtilis. Most of the compounds showed high antifungal potency. Compounds 3, 6, 7, 9b, 10a, 11a, 11b, 15 and 16 exhibited double the potency of clotrimazole against A. fumigatus. While compounds 3, 4, 5a, 5b, 9b, 10a, 10b, 10c, 13, 15, 16 and 18 displayed double the activity of clotrimazole against R. oryazae. Molecular docking studies of the active compounds with the active site of the B. anthracis DHPS, showed good scoring for various interactions with the active site of the enzyme compared to the co-crystallized ligand.     

Design,synthesis and antifungal activity of amide and imine derivatives containing a kakuol moiety

In continuation of our program to discover new potential antifungal agents, a series of amide and imine derivatives containing a kakuol moiety were synthesized and characterized by the spectroscopic analysis. By using the mycelium growth rate method, the target compounds were evaluated systematically for antifungal activities in vitro against four plant pathogenic fungi, and structure–activity relationships (SAR) were derived. Compounds 7d, 7e, 7h, 7i and 7r showed obvious inhibitory activity against the corresponding tested fungi at 50 μg/mL. Especially, compounds 7e and 7r displayed more potent antifungal activity against B. cinerea than that of thiabendazole (a positive control). Moreover, compound 7e also exhibited good activity against A. alternata with EC₅₀ values of 11.0 µg/mL, and the value was slightly superior to that of thiabendazole (EC₅₀ = 14.9 µg/mL). SAR analysis showed that the ether group was a highly sensitive structural moiety to the activity and the type as well as position of substituents on benzene ring could make some effects on the activity.     

Design,synthesis, DNA assessment and molecular docking study of novel 2-(pyridin-2-ylimino)thiazolidin-4-one derivatives as potent antifungal agents

A series of novel 2-imino-4-thiazolidinone derivatives 4a,b was synthesized through reaction of unsymmetrical thioureas 3a,b with chloroacetic acid. Condensation of 4a,b with aromatic aldehydes 5a-eyielded the corresponding 5-arylidene derivatives 6a-j. In addition, the reaction of 4a,b with 4-arylazo-3-hydroxybenzaldehydes 8a-c furnished the respective mono-arylazo-4-thiazolidinones10a-f. All the newly synthesized compounds were confirmed by their elemental analysis and spectral data. The antifungal activity of the newly synthesized compounds was assessed and the compounds 6d, 6e, 6i, 6j, 9a,b and 10a-frevealedhigher antifungal activity towards Alternaria solani than to the standard Ridomil gold plus. Moreover, the DNA toxicity of 4-thiazolidinone derivatives 6d, 9a, 10b, 10c and 10f on the nucleic acid of Alternaria solani (KT354939) was performed and the results showed qualitatively more than 70% cleavage. Also, compounds 6i, 6j, 9b, 10c and 10f were docked inside the active site of 1ZOYenzyme and suitable binding with the active site of amino acids, were displayed according to their bond lengths, angles and conformational energy.     

Discovery of benzotriazole-azo-phenol/aniline derivatives as antifungal agents

A series of benzotriazole-azo-phenol/aniline derivatives were prepared and evaluated for their antifungal activities against six phytopathogenic fungi such as Fusarium graminearum, Fusarium solani, Alternaria alternate, Valsa mali, Botrytis cinerea, and Curvularia lunata. Among them, compounds IIf, IIn, and IIr showed a broad-spectrum of potent antifungal activities. Especially some compounds displayed 3.5–10.8 folds more potent activities than carbendazim against A. alternata and C. lunata. Notably, compounds IIc, IIm, and IIr exhibited good protective and therapeutic effects against B. cinerea at 200?μg/mL. Their structure-activity relationships were also discussed.     

Design,synthesis and antifungal activity of novel fenfuram-diarylamine hybrids

Ten novel fenfuram-diarylamine hybrids were designed and synthesized. And their antifungal activities against four phytopathogenic fungi have been evaluated in vitro and most of the compounds demonstrated a significant antifungal activities against Rhizoctonia solani and Sclerotinia sclerotiorum. Compound 5e exhibited the most potent antifungal activity against R. solani with an EC₅₀ value of 0.037 mg/L, far superior to the commercially available fungicide boscalid (EC₅₀ = 1.71 mg/L) and lead fungicide fenfuram (EC₅₀ = 6.18 mg/L). Furthermore, scanning electron microscopy images showed that the mycelia on treated media grew abnormally with tenuous, wizened and overlapping colonies compared to the negative control. Molecular docking studies revealed that compound 5e featured a higher affinity for succinate dehydrogenase (SDH) than fenfuram. Furthermore, it was shown that the 3-chlorophenyl group in compound 5e formed a CH-π interaction with B/Trp-206 and a Cl-π interaction with D/Tyr-128, rendering compound 5e more active than fenfuram against SDH.     

Discovery of novel pyrrolo[2,3-b]pyridine derivatives bearing 4-oxoquinoline moiety as potential antitumor inhibitor

A series of pyrrolo[2,3-b]pyridine derivatives bearing 4-oxoquinoline moiety were designed, synthesized and evaluated for the anti-proliferative on three cancer cell lines (A549, HepG2 and MCF-7) in vitro. Most of the compounds showed moderate to high potency. Some excellent compounds were tested for the inhibitory activity of c-Met kinase. Compound 34 (c-Met IC₅₀ = 17 nM) was investigated the selectivity against Flt-3, c-Kit, VEGFR-2, ALK, PDGFR-β and RON. Structure-activity relationship studies indicated that hydrogen, fluorine atom, and mono-electron-withdrawing groups (mono-EWGs, such as R² = F) on R, R¹ and R², respectively, were beneficial for the anti-proliferative activities of the target compounds. Besides, we have took further study on the combined mode between compound 34 and c-Met kinase through molecular docking.     

Design,synthesis, and biological evaluation of 4-chloro-2H-thiochromenes featuring nitrogen-containing side chains as potent antifungal agents

A series of 4-chloro-2H-thiochromenes featuring nitrogen-containing side chains were designed, synthesized and tested in vitro for their antifungal activities. The results of preliminary antifungal tests showed that most target compounds exhibited good inhibitory activities against Candida albicans, Cryptococcus neoformans, Candida tropicalis. Notably, compounds 10e and 10y showed most potent activity in vitro against a variety of fungal pathogens with low MICs. Meanwhile, low cytotoxicity on mammalian cells has been observed for compounds 10e and 10y in the tested concentrations by the MTT assay. Therefore, the 4-chloro-2H-thiochromenes with nitrogen-containing groups provide new lead structures in the search for novel antifungal agents.     

Synthesis of novel dihydrotriazine derivatives bearing 1,3-diaryl pyrazole moieties as potential antibacterial agents

Three novel series of dihydrotriazine derivatives bearing 1,3-diaryl pyrazole moieties were designed, synthesized and evaluated in terms of their antibacterial and antifungal activities. Most of the synthesized compounds showed potent inhibition of several Gram-positive bacterial strains (including multidrug-resistant clinical isolates) and Gram-negative bacterial strains with minimum inhibitory concentration values in the range of 1–64?µg/mL. Compounds 4b and 4c presented the most potent inhibitory activity against Gram-positive bacteria (S. aureus 4220, MRSA 3167, QRSA 3519) and Gram-negative bacteria (E. coli 1924), with minimum inhibitory concentration values of 1 or 2?µg/mL. Compared with previous studies, these compounds exhibited a broad spectrum of inhibitory activity. The cytotoxic activity of the compounds 4a, 4b, 4c and 11n were assessed in L02 cells. In vitro enzyme study implied that compound 4c exerted its antibacterial activity through DHFR inhibition.     

Synthesis,characterization, anti-inflammatory and anti-proliferative activity against MCF-7 cells of O-alkyl and O-acyl flavonoid derivatives

A series of O-alkyl and O-acyl flavonoid derivatives was synthesized in high efficiency. Alkylation and acylation of 5-hydroxyflavonoids showed that the low reactivity hydroxyl group, 5-OH, well reacted with strong reagents whereas with weaker reagents, the different products were obtained dependently on structural characteristic of ring C of respective flavonoid. In order to evaluate anti-inflammatory activity, all compounds were tested for in vitro inhibition of bovine serum albumin denaturation and in vivo inhibition of carrageenan-induced mouse paw edema. Among them, the compounds 3, 3b, 4b and 4c demonstrated more effective anti-inflammatory activity than standard drugs (diclofenac sodium and ketoprofen) in both tests. Meanwhile, the flavonoids 2, 2c, 3a and 4b displayed anti-proliferative activity against MCF-7 cell lines. Triacetyl derivative of hesperetin 4b inducing degradation of DNA in MCF-7 cells was observed.     

Synthesis,antioxidant, antifungal,molecular docking and ADMET studies of some thiazolyl hydrazones

Some thiazolyl hydrazones were synthesized by one pot reaction of thiophene-2-carbaldehyde or 2, 4-dichlorobenzaldehyde, thiosemicarbazide and various phenacyl bromides which were preliminarily screened for in vitro antioxidant and antifungal activities. Excellent DPPH and H₂O₂ radical scavenged antioxidant activities were observed with almost all the tested compounds. Compounds 4a, 4b, 4c, 4e, 4f and 4i showed comparable DPPH scavenged antioxidant potential (90.26–96.56%) whereas H₂O₂ scavenged antioxidant activity (90.98–92.08%) was noticeable in case of 4a and 4f; showing significant antioxidant potential comparable with the standard ascorbic acid (95.3%). In vitro antifungal activity of synthesized compounds against fungal species Candida albicance, Aspergillus niger and Aspergillus flavus was found to be moderate to good as compared with the standard fluconazole and MIC values were found in the range of 3.12–25 μg/mL. Molecular docking studies revealed that the compounds 4a, 4b and 4c have a potential to become lead molecules in drug discovery process. In silico ADMET study was also performed for predicting pharmacokinetic and toxicity profile of the synthesized antioxidants which expressed good oral drug like behaviour and non-toxic nature.     

Synthesis,in vitro antimicrobial and cytotoxic activities of novel pyrimidine–benzimidazol combinations

A series of novel 4-substituted-2-{[(1H-benzo[d]imidazol-2-yl)methyl] thio}-6-methylpyrimidine derivatives were designed, synthesized and evaluated for their cytotoxic activities against four human cancer cell lines and inhibitory activities against five type culture strains in vitro. Some of synthetic pyrimidine–benzimidazol combinations showed good inhibitory activities against Stenotrophomonas maltophilia, especially compounds 7b and 7c. Compounds 7a and 7d exhibited enhanced activities against MGC-803 in vitro, when compared to 5-Fu.     

Discovery of novel andrographolide derivatives as cytotoxic agents

The natural diterpenoid andrographolide (1) exhibits various biological activities. Seventeen derivatives of 1 were prepared via esterification and etherification of 14-dehydroxy-11,12-didehydroandrographolide (2). Most derivatives demonstrated significant inhibition against tumor cell growth. The most active compounds, 3b and 3c, had GI₅₀ values of 1.46–9.19 μM against A549, DU145, KB and KB-Vin tumor cells. In an immunocytochemical study, treatment with compound 3c disrupted microtubule dynamics in PC-3 cells, but caused no accumulation of metaphase cells, which is a phenotype dissimilar from that of 1. This difference suggests that structural modification of 1 resulted in a shift in the underlying molecular mechanism.     

Natural products as sources of new fungicides (IV): Synthesis and biological evaluation of isobutyrophenone analogs as potential inhibitors of class-II fructose-1,6-bisphosphate aldolase

Several recently identified antifungal compounds share the backbone structure of acetophenones. The aim of the present study was to develop new isobutyrophenone analogs as new antifungal agents. A series of new 2,4-dihydroxy-5-methyl isobutyrophenone derivatives were prepared and characterized by ¹H, ¹³C NMR and MS spectroscopic data. These products were evaluated for in vitro antifungal activities against seven plant fungal pathogens by the mycelial growth inhibitory rate assay. Compounds 3, 4a, 5a, 5b, 5e, 5f and 5g showed a broad-spectrum high antifungal activity. On the other hand, for the first time, these compounds were also assayed as potential inhibitors against Class II fructose-1,6-bisphosphate aldolase (Fba) from the rice blast fungus, Magnaporthe grisea. Compounds 5e and 5g were found to exhibit the inhibition constants (Ki) for 15.12 and 14.27?μM, respectively, as the strongest competitive inhibitors against Fba activity. The possible binding-modes of compounds 5e and 5g were further analyzed by molecular docking algorithms. The results strongly suggested that compound 5g could be a promising lead for the discovery of new fungicides via targeting Class II Fba.     

Microwave assisted nano (ZnO–TiO2) catalyzed synthesis of some new 4,5,6,7-tetrahydro-6-((5-substituted-1,3,4-oxadiazol-2-yl)methyl)thieno[2,3-c]pyridine as antimicrobial agents

Combined nano zinc oxide and titanium dioxide [nano (ZnO–TiO₂)] has been reported first time for the synthesis of novel series of 4,5,6,7-tetrahydro-6-((5-substituted-1,3,4-oxadiazol-2-yl)methyl)thieno[2,3-c]pyridine. All the synthesized compounds (7a–7m) are novel and were screened for their antimicrobial activity against four different strains like Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis and antifungal activity was determined against two strains Candida albicans and Aspergillus niger. SAR for the newly synthesised derivatives has been developed by comparing their MIC values with ampicillin, ciprofloxacin and miconazole for antibacterial and antifungal activities, respectively. Among the synthesized compounds, 2,6 dichlorophenyl analogue (7f), 4 fluorophenyl analogue (7k) and 2,6 dichlorophenyl analogue (7l) shows promising antibacterial as well as antifungal activity whereas thiophene substituted compound (7j) shows promising antibacterial activity.     

Design,synthesis and antibacterial activities of thiouracil derivatives containing acyl thiourea as SecA inhibitors

A series of novel thiouracil derivatives containing an acyl thiourea moiety (7a–7x) have been synthesized by structural modification of a lead SecA inhibitor, 2. All the compounds have been evaluated for their antibacterial activities against Bacillus amyloliquefaciens, Staphylococcus aureus, and Bacillus subtilis. Compounds 7c, 7m, 7u, 7v exhibited promising activities against above bacteria. Such four compounds were further tested for their inhibitory activity against SecA ATPase, and the results showed that compounds 7c and 7u had higher inhibitory activities than that of compound 2. Molecular docking work suggests that compound 7u might bind at a pocket close to the ATPase ATP-binding domain.