Investigations on fungicides

The systemic anti-mildew activity shown by homologous series of alkoxy-, alkylamino- and alkylthio-trichloroethyl formamides when applied to the roots of wheat or cucumber seedlings has been measured. In general the thio compounds were much less active than their oxy and amino analogues. The alkyl grouping giving most activity varied from one series to another and with test method. In cucumber plants the most prolonged protection against mildew was given by the sec-butoxy and sec-butylamino compounds. When inoculated disks of cucumber leaf tissue were floated upon solutions of the compounds, smaller differences in anti-mildew activity were found than when application was made through the roots.     

Isosteric probes provide structural requirements essential for detoxification of the phytoalexin brassinin by the fungal pathogen Leptosphaeria maculans

Brassinin is a plant defense metabolite with antimicrobial activity produced de novo by a variety of Brassica species in response to stress, that is, a phytoalexin. The inhibition of brassinin oxidase (BO), a brassinin-detoxifying enzyme produced by the phytopathogenic fungus Leptosphaeria maculans, is a target in our continuing search for novel crop protection agents. To probe the substrate specificity of BO, in particular the mechanism of the detoxification step, several analogues of brassinin, including functional group isosteres ((mono/dithio)carbamate, urea, and thiourea) and homologue methyl tryptaminedithiocarbamate, were investigated using fungal cultures and purified BO. It was concluded that the essential structural features of substrates of BO were: (i) an -NH at the (mono/dithio)carbamate, urea or thiourea group; (ii) a methylene bridge between indole and the functional group; (iii) a methyl or ethyl group attached to the thiol moiety of the (mono/di)thiocarbamate group. A general stepwise pathway for the oxidation of brassinin was proposed that accounts for the structural requirements of detoxification of brassinin analogues in L. maculans. All compounds that were BO substrates appeared to be oxidized in mycelial cultures to aldehydes, except for the two most polar compounds N'-(3-indolylmethyl)-N'-methylurea and methyl N'-(3-indolylmethyl)carbamate. The substrate specificity of BO suggests that selective inhibitors can be designed for the potential control of L. maculans.     

Conformational states of N-acylalanine dithio esters: correlation of resonance Raman spectra with structures

The conformational states of N-acylalanine dithio esters, involving rotational isomers about the RC(=O)NH--CH(CH3) and NHCH(CH3)--C(=S) bonds, are defined and compared to those of N-acylglycine dithio esters. The structure of N-(p-nitrobenzoyl)-DL-alanine ethyl dithio ester has been determined by X-ray crystallographic analysis; it is a B-type conformer with the amide N atom cis to the thiol sulfur. Raman and resonance Raman (RR) measurements on this compound and for the B conformers of solid N-benzoyl-DL-alanine ethyl dithio ester and N-(beta-phenylpropionyl)-DL-alanine ethyl dithio ester and its NHCH(CD3)C(=S) and NHCH(CH3)13C(=S) analogues are used to set up a library of RR data for alanine-based dithio esters in a B-conformer state. (Methyloxycarbonyl)-L-phenylalanyl-L-alanine ethyl dithio ester crystallizes in an A-like conformational state wherein the alanine N atom is nearly cis to the thiono S atom (C=S) [Varughese, K.I., Angus, R.H., Carey, P.R., Lee, H., & Storer, A.C. (1986) Can. J. Chem. 64, 1668-1673]. RR data for this solid material in its isotopically unsubstituted and CH(C-D3)C(=S) and CH(CH3)13C(=S) forms provide information on the RR signatures of alanine dithio esters in A-like conformations. RR spectra are compared for the solid compounds, for N-(p-nitrobenzoyl)-DL-alanine, N-(beta-phenylpropionyl)-DL-alanine, and (methyloxycarbonyl)-L-phenylalanyl-DL-alanine ethyl dithio esters, and for several 13C=S- and CD3-substituted analogues in CCl4 or aqueous solutions. The RR data demonstrate that the alanine-based dithio esters take up A, B, and C5 conformations in solution.(ABSTRACT TRUNCATED AT 250 WORDS)     

COMPARATIVE EFFECTS OF TWO PHOTOSENSITIVE COMPOUNDS ON SUPEROXIDE DISMUTASE ACTIVITY IN SPODOPTERA LITURA LARVAE*

Abstract Superoxide dismutase activity was detected in the fourth instar larvae of cutworm Spodoptera litura and effects of the two photosensitive compounds, α-terthienyl and the synthesized compound 1-phenyl-4–(3, 4-methylene dioxy) phenyl-diacetylene (signified as compound No. 5), on superoxide dismutase activity, were compared under the specified condition. Results indicated that the near ultraviolet irradiation (300–400 nm) almost had no effect on superoxide dismutase activity in vivo in the control larvae but could decrease superoxide dismutase activity in vitro. After treatment with photosensitive compounds and near ultraviolet irradiation, superoxide dismutase activity in vitro could be enhanced by the two chemicals, with α-terthienyl more effective, while in vivo it was hardly affected by the latter compound but could be inhibited by α-terthienyl. This suggested that the larvae treated by a-terthienyl were more susceptible to light than that by the latter compound whenever in vivo or in vitro. The possible mechanisms of action of the two photo-activated compounds were discussed.     

Studies on the Mode of Action of Organophosphorus Fungicide,Kitazin

Studies were conducted on the influence of Kitazin analogues on the incorporation of ¹⁴C-glucosamine into the mycelial cell wall fraction of Pyricularia oryzae. Compounds of thiolates and phosphates, both having in vitro inhibitory activities toward the mycelial growth, inhibited the incorporation, whereas those of thionates and dithioates, either having no fungitoxicity, did not inhibit the incorporation. Mycelia of P. oryzae treated with Kitazin-P (S-benzyl O,O′-diisopropyl phosphrothioate; IBP) accumulated about twice as much an amino sugar derivative as untreated ones. Mycelia treated with thiono or dithio analogues, which have no fungitoxicity, showed no accumulation. The accumulated substance gave a identical spot with authentic UDP-N-acetyl glucosamine on paper chromatograms developed with four solvent systems.     

Investigations on fungicides

A series of pyrazole derivatives, which are structural analogues of the systemic fungicide, carboxin (5,6-dihydro-2-methyl-i,4-oxathiin-3-carboxani-lide), have been synthesized and their antifungal properties investigated. 3,5-dimethylpyrazole-i-carboxanilides, although active in vitro and in leaf disk tests, showed no systemic antifungal activity. Certain 3,5-dimethylpyra-zole-4-carboxanilides, however, and their corresponding 1 -methyl derivatives, showed good activity in spore germination tests and high activity against wheat and broad bean rusts in vivo. In several instances, systemic antifungal activity was of the same order as that of carboxin, although generally accompanied by higher levels of phytotoxicity. 1 -Phenyl derivatives were essentially inactive. Substitution in the anilide ring by 3-methyl, 2-methyl or 3-chloro groups resulted in enhanced systemic activity, while 4-chloro, 4-ethoxy, 2-nitro and 3,4-dichloro substituents reduced activity.     

Investigations on fungicides: XIV. Fungitoxicity of N-(2,2,2–trichloro-1–methoxyethyl)-formamide and related compounds

From a study of forty compounds related to the systemic fungicide N,N'-bis(1–formamido-2,2,2–trichloroethyl)-piperazine, known as triforine (CELAW524), it was found that a new compound, N-(2,2,2–trichloro-1–methoxyethyl)-formamide, controls Erysiphe graminis on wheat when applied to the roots in sand. A number of N-(2,2,2–trichloro-1–aryloxyethyl)-form-amides and alkyl N-(2,2,2–trichloro-1–arylaminoethyl)-carbamates protect broad beans against Uromyces fabae and wheat against Erysiphe graminis; some of these formamides show slight activity when applied to plant roots.     

Novel indole-based melatonin analogues substituted with triazole,thiadiazole and carbothioamides: studies on their antioxidant,chemopreventive and cytotoxic activities

Melatonin (MLT) is a well-known free-radical scavenger, involving in the prevention of cellular damage that can lead to cancer, ageing and a variety of neurodegenerative diseases. Research on MLT-related compounds has been required to optimise the maximum pharmaceutical activity with the lowest side effects. In our ongoing research, we have synthesized new indole-based MLT analogues as potential antioxidant agents by modifying the MLT molecule. In this study, we build on previous findings, through the synthesis, characterization and in vitro antioxidant profiling of a series of new indole-based MLT analogues which possess triazole, thiadiazole and carbothioamides on the third position on the indole ring. In vitro antioxidant activity was investigated by evaluating their reducing effect against oxidation of a redox sensitive fluorescent probe and their radical scavenging activity was assessed via the DPPH assay. In addition, in vitro cytotoxic effects of newly synthesized compounds were investigated in CHO-K1 cells using the MTT assay.     

Inhibition of auxin transport by isoquinolinedione herbicides

2-(p-carbethoxyphenyl)-1,3(2H,4H)-isoquinolinedione (CEPIQ), an experimental herbicide, caused effects on geotropism, which are often indicative of an effect on auxin transport, in a whole plant herbicidal screen. However, it showed little or no activity in an in vitro binding assay in corn coleoptiles for the auxin-transport inhibitor,N-1-naphthylphthalamic acid (NPA). Other active isoquinolinedione analogues of this compound did, however, exhibit significant in vitro activity. Direct measurements of auxin transport in corn coleoptiles were undertaken in an attempt to resolve the apparent discrepancy between herbicidal and binding activities. In all cases examined, compounds that were highly active on whole plants were good inhibitors of auxin transport, and compounds that were weak as herbicides showed little or no effect on auxin transport. Therefore, it is concluded that the mode of action of these isoquinolinedione herbicides is the inhibition of auxin transport. Ring-opened analogues of several isoquinolinediones were synthesized and assayed in both the transport and binding assays, in order to test whether compounds in this class express their herbicidal activity by undergoing ring-opening in vivo, yielding products that are more straightforward analogues of NPA with free carboxyl groups. The homophthalamic acids had little or no activity in both assays. On the other hand, thep-ethyl- andp-ethoxy-phenyl phthalamic acids showed auxin transport inhibition comparable to the parent isoquinolinediones, but with markedly increased binding activity. These results support the possible role of ring-opening in the generation of biological activity. However, thep-carbethoxyphenyl phthalamic acid, analogous to CEPIQ, was very weak in both assays. Thus, ring-opening in vivo cannot alone account for the biological activity of this class of compounds.     

3,5-Dialkyl-4-hydroxybenzylidenemalononitrile; A New Group of Fungicidal and Acaricidal Agents

Several 3,5-dialkyl-4-hydroxybenzylidenemalononitriles and related compounds were tested for their fungicidal and acaricidal activities. The influence of structural variation on biological activity was studied by preparing and using a total of 22 compounds of benzylidenemalononitrile analogues.

Amongst the compounds tested 3,5-di-tert-butyl and amyl-4-hydroxybenzylidenemalononitrile were most effective against fungus, Piricularia oryzae Car. and mite, Tetranychus telarius L.     

Investigations on fungicides: The systemic fungicidal activity of certain N-carboxymethyl dithiocarbamic acid derivatives

The systemic activity of thirty-three N-substituted S-esters derived from dithiocarbamic acid was investigated by assessing their ability to reduce the infection of broad-bean seedlings by Botrytis fabae and of wheat seedlings by Erysiphe graminis, following application to the roots or cut shoots of the host. Marked systemic activity against mildews was shown by the N-carboxymethyl dithiocarbamates, by S-carboxymethyl-N, N-dimethyl-dithiocarbamate (G₃₃) and by procaine and 6-azauracil. The effect was not very host-specific since most compounds showing high activity in wheat also showed activity in pea, cucumber and, to a smaller extent, apple. All the materials tested showed a much lower level of systemic activity in broad-bean seedlings against B. fabae. Measurements were also made of the uptake, translocation, phytotoxicity and the stability within plant tissues of some of these compounds. The degree of systemic activity which they show is discussed in relation to these and other properties of the compounds.     

INVESTIGATIONS ON FUNGICIDES II. ARYLOXY- AND ARYLTHIO-ALKANECARBOXYLIC ACIDS AND THEIR ACTIVITY AS FUNGICIDES AND SYSTEMIC FUNGICIDES

A wide range of aryloxyacetic acids and corresponding acids with alkyl groups in the side chain, their arylthio- analogues and the antibiotic griseofulvin have been assessed in the plate test for fungistatic effect on six fungi, and as systemic fungicides against Botrytis fabae in broad beans and Alternaria solani in tomatoes. The results indicate that in general, arylthio- derivatives are more fungicidal than their aryloxy- analogues. The systemic fungicidal performance of x-(2-chlorophenylthio)propionic acid in the tomato test at 1–100 p. p. m. was found to be of the same order as that shown by griseofulvin at 50–500 p. p. m. Variable results were obtained with griseofulvin in the tornato test and its performance in the bean test was consistently poor. Further evidence is presented which indicates that the protection conferred by certain compounds may not be due to activity per se .     

Synthesis and antiviral evaluation of novel open-chain analogues of neplanocin A

Novel acyclic nucleoside analogues were designed and synthesized as open-chain analogues of neplanocin A. The coupling of the allylic bromide with purine bases using cesium carbonate afforded a series of novel acyclic nucleosides. The synthesized compounds Ia – II were evaluated for their antiviral activity against various viruses such as HIV, HSV-1, HSV-2, and ECMV.     

1,2,4-Triazoloazine derivatives as a new type of herpes simplex virus inhibitors

A new class of inhibitors of herpes simplex virus replication was found. The compounds under study are derived from condensed 1,2,4-triazolo[5,1-c][1,2,4]triazines and 1,2,4-triazolo[1,5-a]pyrimidines, structural analogues of natural nucleic bases. Antiherpetic activity and cytotoxicity of the compounds were studied. The corresponding triphosphates of several active compounds were prepared and tested as inhibitors of DNA synthesis catalyzed by herpes simplex virus polymerase. The potential mechanism of their action is blocking of DNA dependent DNA polymerase, a key enzyme of viral replication.     

DIHYDROMUSCIMOL, THIOMUSCIMOL AND RELATED HETEROCYCLIC COMPOUNDS AS GABA ANALOGUES

A series of heterocyclic GABA analogues related to muscimol (5-aminomethyl-3-isoxazolol) were tested as depressants of the firing of GABA sensitive neurones on the cat spinal cord, and as inhibitors of the sodium-independent binding of GABA to rat brain membranes. Furthermore, the compounds were examined as inhibitors of GABA uptake into rat brain slices and as inhibitors of the activities of the GABA-metabolizing enzymes L-glutamate 1-carboxylyase and GABA:2-oxoglutarate aminotransferase. Dihydromuscimol [(RS)-4,5-dihydromuscimol] and thiomuscimol (5-aminomethyl-3-isothiazolol) were approximately equipotent to muscimol as bicuculline-sensitive depressants of neuronal firing and as inhibitors of GABA binding. The structurally related compounds isomuscimol (3-aminomethyl-5-isoxa-zolol) and azamuscimol (5-aminomethyl-3-pyrazolol) were much weaker than muscimol as GABA agonists. The affinity of the compounds for GABA receptor sites in vitro is in agreement with their relative potency as GABA receptor agonists in vivo. The rat brain synaptic membranes used for the GABA receptor binding studies were prepared by two procedures, which were shown to have a pronounced influence on the observed potency of the inhibitors of GABA binding. The compounds were weak or inactive as inhibitors of the uptake of GABA into rat brain slices and of the activity of GABA: 2-oxoglutarate aminotransferase in vitro. Azamuscimol and 2-methylaza-muscimol were moderately potent inhibitors.of the activity of L-glutamate 1-carboxylyase in vitro. This inhibition by azamuscimol was timedependent following pseudo-first-order kinetics, consistent with azamuscimol acting as a catalytic inhibitor. The structure of the heterocyclic rings of these zwitterionic compounds is a factor of critical importance for interaction with GABA receptors. The present structure-activity analysis demonstrates that heterocyclic GABA analogues having a high degree of delocalization of the negative charges have low affinity for the GABA receptors.     

Effect of drought stress,abscisic acid,and abscisic acid analogues on the efficacy of diclofop-methyl and tralkoxydim

The effects of drought stress, abscisic acid (ABA), and four ABA analogues on diclofop-methyl and tralkoxydim efficacy were investigated in oat (Avenu sativa). Drought stress conditions (6% soil moisture content) reduced the efficacy of diclofop-methyl at 350 g ha^–1, but not at 700 g ha^–1. Similarly, tralkoxydim efficacy was reduced by drought stress at 62.5 and 125 g ha^–1, but not at 250 g ha^–1. ABA (100 m), applied as a root drench 2 days before the herbicide, protected oat plants against all rates of diclofop-methyl and against low rates of tralkoxydim. Two ABA analogues protected oat plants from diclofop-methyl injury, whereas two others had no effect. Foliage applications of ABA were much less effective than root applications in protecting against herbicide injury. Protection by ABA and the two active analogues was dependent on the relative time of application with respect to the herbicides. Optimal protection by ABA and analogue I was obtained when they were applied between 2 days before and 1 day after diclofop-methyl application. Analogue IV protected plants when applied between 3 days before and 1 day after diclofop-methyl application. Partial protection against tralkoxydim activity by ABA was observed when it was applied between 1 day before and 1 day after herbicide application. Analogue I did not afford any protection against tralkoxydim, and analogue IV afforded partial protection when applied the same day or 1 day after tralkoxydim. The results indicate that protection against these postemergence herbicides, similar to that conferred by water stress, can be induced by ABA and structural analogues that apparently mimic the action of ABA.Abbreviations SMC soil moisture content - ABA abscisic acid     

4′-Aza-3′,5′-dihomothymidine and Derivatives

Abstract

A series of 3′-branched 4′-azanucleoside analogues have been prepared. These compounds comprise three asymmetric atoms, two carbons and one nitrogen. They constitute nucleoside analogues imparted with a “flickering configuration”, the nitrogen inversion replacing a D-L epimerization of their natural congeners. The 1′,3′-cis and 1′,3′-trans isomers have been separated and their configuration established by ¹H NMR and the X-ray diffraction structure of one crystalline example. The configurations of the frozen invertomers were assessed by low temperature ¹H NMR experiments assisted by molecular mechanics simulations. None of these compounds exhibited any significant in vitro antiviral activity.     

Synthesis,molecular docking,and antioxidant activity of new fluorescent tetrafluoroterphenyl analogues

Nucleophilic aromatic substitution (S_NAr) chemistry has been applied to develop many functionalized pentafluorobenzene derivatives. Those compounds are highly specific at the para position of the fluorinated ring. Therefore, they are typical adducts for the preparation of antioxidant molecular systems. In this context, we report the use of S_NAr chemistry as a suitable and simple approach for the synthesis of fluorescent antioxidant perfluorinated materials bearing ether bonds in various para-substituted alkoxy chains and with high purity and excellent yields. The fluoroterphenyl core was prepared via alkylation, Cu(I)-assisted decarboxylation, and cross-coupling using the potassium salt of fluorobenzoate, followed by the reaction with different alcohols. The structures of the synthesized fluoroterphenyl adducts were investigated using FT-IR, ¹H NMR, ¹³C NMR, and ¹⁹F NMR spectroscopy. The emission spectra and absorption spectra showed solvatochromism. The newly prepared tetrafluoroterphenyl analogues were investigated by antioxidant examination using the 2,2-diphenyl-1-picrylhydrazyl assay. Results were compared with ascorbic acid and butylated hydroxytoluene as references, and revealed that the tetrafluoroterphenyl analogues containing a decyl chain had the highest activity, with an IC₅₀ value of 22.36 ± 0.19 g/ml. The produced tetrafluoroterphenyl analogues were used in molecular docking strategies with a Protein Data Bank protein ID 5IKQ. The antioxidant investigations and docking results were convergent.     

Cytokinin and anticytokinin activity of some 4-substituted 1H-pyrazoles and 8-aza analogues of adenine

Using specific bioassays i.e. radish cotyledon expansion, betacyanin synthesis in Amaranthus caudatus, and senescence retardation of isolated leaf explants, six 4-substituted 1-H pyrazoles and five 8-aza adenine analogues were tested for their cytokinin- and anticytokinin activity. Most of the pyrazole derivatives showed some cytokinin-like activity and enhanced the effect of 10^–5 M BA. 8-Aza substituted adenines were found to be cytokinin antagonists; in the bioassays used they were inactive when applied alone but blocked the action of 10^–5 M BA when applied simultaneously.     

DNA Breaking Reaction with Catecholamines

Breaking activity of catecholamines and their structural analogues on λ DNA were investigated by agarose slab gel electrophoresis. Since λ DNA has a homogenous molecular size, it is a favorable material to detect the activity of DNA breaking reagent. Among the compounds tested, those having enediol group were only active, though their activities remarkably differed owing to their side chains. The profile of the breaking reaction was studied in detail by the use of one of the catecholamines, epinephrine.