Synthesis and herbicidal activity of novel pyrazolo[3,4-d]pyrimidin-4-one derivatives containing aryloxyphenoxypropionate moieties

Synthesis and herbicidal activities of 2-((3-pyridinyl-2-oxo-2,3-dihydrobenzo[d]thiazol-6-yl)oxy)propionates

BACKGROUND

The discovery of lead compounds is fundamental to herbicide innovation, yet the limited availability of valuable lead compounds has impeded their progress in recent years. The study presents a novel molecular scaffold that exhibits remarkably potent herbicidal activity.

RESULTS

Through a scaffold-hopping strategy, a highly potent lead compound for herbicides, namely 3-(2-pyridinyl)-benzothiazol-2-one, was unexpectedly discovered during attempts to structurally modify haloxyfop, a commercial aryl-oxy-phenoxy-propionate herbicide. To investigate the structure-activity relationship (SAR) of the newly discovered herbicidal chemicals, a series of 2-(2-oxo-3-(pyridin-2-yl)-2,3-dihydrobenzo[d]thiazol-6-yloxy)propanoic acid derivatives, I-01 ~ I-27, were designed and synthesized. SAR analysis revealed that trifluoromethyl at the 5-position of pyridine is crucial for herbicidal activity, whereas additional fluorine or Cl atom at the 3-position of pyridine significantly enhances activity. Carboxylic ester derivatives exhibit superior herbicidal activity compared with amide derivatives. Moreover, the activity of carboxylic ester derivatives decreases with C chain extension, but the introduction of O atoms in the side chain benefits activity enhancement. Pot experiments conducted in a glasshouse demonstrated that I-01 and I-09 exhibited potent postemergence herbicidal activity against broadleaf weeds, and completely inhibited growth of Amaranthus retroflex, Abutilon theophrasti and Portulaca oleracea at a dosage of 75 g ha-1.

CONCLUSION

Despite the initial goal of scaffold-hopping not being achieved, we have successfully identified a novel molecular scaffold exhibiting exceptional herbicidal activity, thereby presenting innovative prospects for herbicide development. © 2024 Society of Chemical Industry.

Synthesis, Herbicidal Activity, and Molecular Mode of Action Evaluation of Novel Aryloxyphenoxypropionate/Amide Derivatives Containing a Quinazolinone Moiety

To develop aryloxyphenoxypropionate herbicides with a novel structure and improved activity, a total of 39 aryloxyphenoxypropionate/amide derivatives containing quinazolinone moiety were synthesized and further bioevaluated. The bioassay results in the greenhouse showed that most of the target compounds had good herbicidal activity under postemergence conditions, of which, QPP-I-6 displayed excellent herbicidal activity against Echinochloa crusgalli, Digitaria sanguinalis, Spartina alterniflora, Eleusine indica, and Pennisetum alopecuroides with inhibition rates >90% at a dosage of 187.5 g ha-1. More importantly, QPP-I-6 displayed higher crop safety to Gossypium hirsutum, Glycine max, and Arachis hypogaea than the commercial herbicide quizalofop-p-ethyl. Studying the molecular mode of action by phenotypic observation, membrane permeability evaluation, transcriptomic analysis, and in vivo ACCase activity evaluation reveals that QPP-I-6 is a novel ACCase inhibitor. The present work demonstrates that QPP-I-6 can serve as a lead compound for further developing novel ACCase-inhibiting herbicides.

Novel pyrimidin-4-one derivatives as potential T3SS inhibitors against Xanthomonas campestris pv. campestris

BACKGROUND

Cruciferous black rot is caused by Xanthomonas campestris pv. campestris (Xcc) infection and is a widespread disease worldwide. Excessive and repeated use of bactericide is an important cause of the development of bacterial resistance. It is imperative to take new approaches to screening compounds that target virulence factors rather than kill bacterial pathogens. The type III secretion system (T3SS) invades a variety of cells by transporting virulence effector factors into the cytoplasm and is an attractive antitoxic target. Toward the search of new T3SS inhibitors, an alternative series of novel pyrimidin-4-one derivatives were designed and synthesized and assessed for their effect in blocking the virulence.

RESULTS

All of the target compounds were characterized by proton (1 H) nuclear magnetic resonance (NMR), carbon-13 (13 C) NMR, fluorine-19 (19 F) NMR and high-resolution mass spectrometry (HRMS). All compounds were evaluated using high-throughput screening systems against Xcc. The results of the biological activity test revealed that the compound SPF-9 could highly inhibit the activity of xopN gene promoter and the hypersensitivity (HR) of tobacco without affecting bacterial growth. Moreover, messenger RNA (mRNA) level measurements showed that compound SPF-9 inhibited the expression of some representative genes (hrp/hrc genes). Compound SPF-9 weakened the pathogenicity of Xcc to Raphanus sativus L.

CONCLUSION

Compound SPF-9 has good potential for further development as a novel T3SS inhibitor against Xcc. © 2023 Society of Chemical Industry.

Synthesis and properties of sildenafil isostere

A series of novel pyrazolo[3,4-d]pyrimidin-4-one derivatives were synthesized and evaluated for their anti-phosphodiesterase-5 (PDE-5) activity. A total of 28 compounds, containing alkyl and aryl groups at the 1-N and 3-C positions on the pyrazole ring, and also bearing different alkyl substituents on the piperazine ring were synthesized. Four compounds (4d, 5d, 6d, and 5o) were found to have better inhibitory activity against PDE-5 (IC₅₀  < 10 nM). All four of the most active compounds contain a phenyl ring at the N1 position. Compounds containing a 3,5-dimethylpiperazinyl group show better activity than others. These results suggest that compound 5o can be used as a lead structure for developing new inhibitors of PDE-5.

One-Pot Acid-Promoted Synthesis of 6-Aminopyrazolopyrimidines from 1H-Pyrazol-5-yl-N,N-dimethylformamidines or 5-Amino-1H-pyrazole-4-carbaldehydes with Cyanamide

A convenient and efficient one-pot acid-promoted synthesis of 6-aminopyrazolo[3,4-d]pyrimidine has been developed by treatment of 1H-pyrazol-5-yl-N,N-dimethylformamidines or 5-amino-1H-pyrazole-4-carbaldehydes with cyanamide (NH₂C≡N) in an acid-mediated solution. This synthetic route involves four steps of deprotection, imination, the key acid-promoted heterocyclization, and aromatization. On the basis of optimized studies, methanesulfonylchloride is considered to be the best solvent. Furthermore, the microwave-assisted synthetic technique was also carried out to improve the major product 6-aminopyrazolo[3,4-d]pyrimidines in this method. Moreover, our proposed mechanism was confirmed in this study, which demonstrates that N-[(5-amino-1,3-diaryl-1H-pyrazol-4-yl)methylene]cyanamide is the intermediate.

Synthesis, crystal structure, insecticidal activities, molecular docking and QSAR studies of some new phospho guanidines and phospho pyrazines as cholinesterase inhibitors

Novel phospho guanidine and phospho pyrazine derivatives were synthesized and characterized by ³¹P, ¹³C, ¹HNMR and IR spectroscopy to obtain novel and human-safe insecticides. Compound 35 [(C₄H₄N₂NH)₂P(O)(C₆H₆)] was investigated by X-ray crystallography. The inhibitory effects of synthesized compounds were evaluated on human and insect acetylcholinesterase (AChE) using in vitro Ellman method. A few of these compounds, which had low human toxicity, were selected for assessing the killing effects (in vivo) on the elm leaf beetle (X.luteola). The in vitro and in vivo results indicated that compounds bearing both phosphoryl groups and aromatic systems were found to possess a good selectivity for the inhibition of insect AChE over human AChE; up to 550-fold selectivity was achieved for compound 19. Docking studies were performed to explain reasons for the selective behavior of AChE inhibitors. Additionally, the quantitative structure-activity relationship (QSAR) and density functional theory (DFT) results of AChEs demonstrated that the size, shape, dipole moment, and ability to form hydrogen bond played the main role in both models. In addition, the aromatic π - π interactions and charge of the amide nitrogen had a major effect on insecticidal activity of the compounds. The present research can be helpful to gain a better understanding of the interactions between the insect AChE and its inhibitors and introduces compounds which are capable of becoming human-safe insecticides.

One-Flask Synthesis of Pyrazolo[3,4-d]pyrimidines from 5-Aminopyrazoles and Mechanistic Study

A novel one-flask synthetic method was developed in which 5-aminopyrazoles were reacted with N,N-substituted amides in the presence of PBr₃. Hexamethyldisilazane was then added to perform heterocyclization to produce the corresponding pyrazolo[3,4-d]pyrimidines in suitable yields. These one-flask reactions thus involved Vilsmeier amidination, imination reactions, and the sequential intermolecular heterocyclization. To study the reaction mechanism, a series of 4-formyl-1,3-diphenyl-1H-pyrazol-5-yl-N,N-disubstituted formamidines, which were conceived as the chemical equivalent of 4-(iminomethyl)-1,3-diphenyl-1H-pyrazol-5-yl-formamidine, were prepared and successfully converted into pyrazolo[3,4-d]pyrimidines. The experiments demonstrated that the reaction intermediates were the chemical equivalents of 4-(iminomethyl)-1,3-diphenyl-1H-pyrazol-5-yl)formamidines. The rate of the reaction could be described as being proportional to the reactivity of amine reactants during intermolecular heterocyclization, especially when hexamethyldisilazane was used.

Synthesis and Biological Evaluation of N- Pyrazolyl Derivatives and Pyrazolopyrimidine Bearing a Biologically Active Sulfonamide Moiety as Potential Antimicrobial Agent

A series of novel pyrazole-5-carboxylate containing N-triazole derivatives 3,4; different heterocyclic amines 7a–b and 10a–b; pyrazolo[4,3-d]pyrimidine containing sulfa drugs 14a,b; and oxypyrazolo[4,3-d]pyrimidine derivatives 17, 19, 21 has been synthesized. The structure of the newly synthesized compounds was elucidated on the basis of analytical and spectral analyses. All compounds have been screened for their in vitro antimicrobial activity against three gram-positive and gram-negative bacteria as well as three fungi. The results revealed that compounds 14b and 17 had more potent antibacterial activity against all bacterial strains than reference drug Cefotaxime. Moreover compounds 4, 7b, and 12b showed excellent antifungal activities against Aspergillus niger and Candida albicans in low inhibitory concentrations but slightly less than the reference drug miconazole against Aspergillus flavus.

Synthesis of Several New 1-arylpyrazolo[3,4-d]Pyrimidines Containing an Amide Moiety

A series of novel 1-arylpyrazolo[3,4-d]pyrimidine derivatives, containing an amide moiety, was synthesised by condensation of different acids with 1-(2,4-dichlorophenyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine. This intermediate was prepared from 5-amino-1-(2,4-dichlorophenyl)-1H-pyrazole-4-carbonitrile by condensation with triethyl orthoformate and then cyclisation with ammonium hydroxide solution in tetrahydrofuran at room temperature. In addition, the molecular structure of a 1-arylpyrazolo[3,4-d]pyrimidine containing an amide moiety was determined by single crystal X-ray diffraction.

Synthesis of New Derivatives of Pyrazolo[4,3-e][1,2,4]Triazolo[4,3-c]Pyrimidine

A number of new derivatives of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidine have been synthesised by cyclocondensation of several hydrazino derivatives of pyrazolo[3,4-d]pyrimidine with either orthoesters or carbon disulfide in pyridine followed by alkylation to obtain the desired products. The structures of all the newly synthesised products have been thoroughly elucidated.

Vilsmeier reagent-mediated synthesis of 6-[(formyloxy)methyl]-pyrazolopyrimidines via a one-pot multiple tandem reaction

Vilsmeier reagent-mediated synthesis of pyrazolopyrimidines.

Design, synthesis, biological activities and 3D-QSAR of new N,N'-diacylhydrazines containing 2,4-dichlorophenoxy moieties

A series of new N,N'-diacylhydrazine derivatives were designed and synthesized. Their structures were verified by 1H-NMR, MS and elemental analysis. The herbicidal activities and plant growth regulating activity of these N,N'-diacylhydrazines were evaluated. The herbicidal activity results showed that most of these N,N'-diacyl-hydrazines showed excellent in vivo activities against Echinochloa crus-galli, Digitaria sanguinalis, Brassica napus, Amaranthus retroflerus. Most of them exhibited higher herbicidal activities against dicotyledonous weeds than monocotyledonous weeds. To further investigate the structure-activity relationship, comparative molecular field analysis (CoMFA) was performed on the basis of herbicidal activity data. Both the steric and electronic field distributions of CoMFA are in good agreement in this work.

Design, synthesis, antifungal activities and 3D-QSAR of new N,N'-diacylhydrazines containing 2,4-dichlorophenoxy moiety

A series of new N,N'-diacylhydrazine derivatives were designed and synthesized. Their structures were verified by 1H-NMR, mass spectra (MS) and elemental analysis. The antifungal activities of these N,N'-diacylhydrazines were evaluated. The bioassay results showed that most of these N,N'-diacylhydrazines showed excellent antifungal activities against Cladosporium cucumerinum, Corynespora cassiicola, Sclerotinia sclerotiorum, Erysiphe cichoracearum, and Colletotrichum orbiculare in vivo. The half maximal effective concentration (EC50) of one of the compounds was also determined, and found to be comparable with a commercial drug. To further investigate the structure-activity relationship, comparative molecular field analysis (CoMFA) was performed on the basis of antifungal activity data. Both the steric and electronic field distributions of CoMFA are in good agreement in this study.

Synthesis and herbicidal activity of substituted pyrazole isothiocyanates

Isothiocyanates and substituted pyrazoles were combined to form a series of novel isothiocyanates with highly effective herbicidal activity. The target compounds were analyzed by elemental analysis, ¹H-NMR, EI-MS and IR spectroscopy. The synthesized compounds, particularly compounds 3-1 and 3-7, exhibited good herbicidal activities against four weeds. The EC₅₀ values of compound 3-1 against Echinochloa crusgalli L., Cyperus iria L., Dactylis glomerata L., and Trifolium repens L. were 64.32, 65.83, 62.42, and 67.72 µg/mL, respectively. The EC₅₀ values of compound 3-7 against E. crusgalli L., C. iria L., D. glomerata L., T. repens L. were 65.33, 64.90, 59.41 and 67.41 µg/mL, respectively. Compounds 3-1 and 3-7 may be further optimized as lead compounds for new herbicides.

Evaluation of electrophilic heteroaromatic substitution: synthesis of heteroaromatic-fused pyrimidine derivatives via sequential three-component heterocyclization

A new sequential three-component heterocyclization was developed by reacting aromatic and heterocyclic substrates, including aminobenzenes, 1-aminonaphthalene, 2-aminopyrazines, 5-aminopyrazoles, 3-aminopyridine, 5-aminopyrimidine, 5-aminoquinoline, and 8-aminoquinoline, with formamide in the presence of PBr(3). The reaction gave the corresponding pyrazolo[3,4-d]pyrimidines in good yields (59-96%), except for aminobenzenes and 3-aminopyridine. A plausible reaction mechanism involving amidination, electrophilic substitution imination, and oxidative cyclization in three steps was proposed to account for the heterocyclization. The reactivity of the reaction was found proportional to the electrophilicity of the aromatic or heterocyclic substrate.

Ultrasound promoted synthesis of bis(substituted pyrazol-4-ylcarbonyl)-substituted thioureas

A series of novel bis(substituted pyrazol-4-ylcarbonyl)-substituted thioureas have been synthesized by the reactions of substituted pyrazol-4-ylcarbonyl isothiocyanates with different diamines under ultrasound irradiation and classical heating method at 20-25 °C. In general, substantial improvement in rates and modest yields increases were observed when reactions were carried out under sonication, compared with the classical heating method. The structures of these compounds have been elucidated by elemental and spectral (IR, ¹H-NMR) analysis.

Synthesis and antifungal activities of novel 5-amino-6-arylamino-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one derivatives

A novel approach was developed to regioselectively synthesize new 5-amino-6-arylamino-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one 5 derivatives via a tandem aza-Wittig and annulation reactions of iminophosphorane 2, aromatic isocyanates, and hydrazine in 52-92% isolated yields. The compounds 5 reacted with triethyl orthoformate to give 1,8-2H-pyrazolo[3,4-d][1,2,4]triazolo[1,5-a]pyrimidin-4-ones 6 in good yields (62-94%). Their structures were clearly confirmed by spectroscopy data (IR, (1)H NMR, MS), elemental analysis, or X-ray diffraction crystallography. The results of preliminary bioassay indicated that the compounds 5 and 6 possessed high antifungal activity against Botrytis cinerea Pers and Sclerotinia sclerotiorum. Compounds 5 showed much better antifungal activities when R was Me instead of PhCH 2. Especially, compounds 6c, 6g, and 6i inhibited Sclerotinia by 100% at the concentration of 50 mg/L and by 83, 83, and 82% at the dosage of 10 mg/L, respectively.