Synthesis Of Novel Thiourea Derivatives And Research Of Their Control Effects On Plant Pathogens And Viruses

Thiourea derivatives and 1,3,4-thiadiazoles have broad biological activities such as anti-virus,anti-fungi,anti-bacterials,insecticidal,herbicidal activities and regulating activity for plant growth.Especially,thioureas have advantages of low residue,low toxicity and a cute toxicity to mammals as pesticides,and 1,3,4-thiadiazoles have good tissue permeability and variety structure modified easily,therefore they have been playing the important role in green and new pesticides innovation.At present,dozens of new thiourea and 1,3,4-thiadiazole pesticides have been successfully developed by international corporation,but no drugs have been developed to combine the advantages of these two compounds.In order to obtain the new high activity,wide-spectrum,low toxicity,low residue and environmentally friendly green pesticide,we designed and synthesized 20 thiourea derivatives containing 1,3,4-thiadiazole and thioether via the method of linking active sub-structures.The structure of the target molecule was shown in Fig.1.The reactive conditions,structures and biological activities of the target compounds were studied,structure-activity relationship was summarized and preliminary mechanism of action for anti-TMV was ascertained.1.General procedure for synthesis of target compoundsThe intermediates?(?1-?8),2-amino-5-alkylthio-1,3,4-thiadiazoles,were prepared via two steps which began with compound 1,thiosemicarbazide.The intermediates?2,allyl isothiocyanate was synthesized from the nucleophilic substitution reaction of halohydrocarbon with potassium rhodanide;The intermediate?3,4-trifluoro-methylphenyl isothiocyanate was gained from the reaction of 4-trifluoromethyl-phenyl amine with phosgene.Target compounds 1-20 were synthesized in good yield through one pot reaction of intermediates?(?1-?3: ethyl,allyl,4-trifluoromethylphen-yl)with intermediates ?(?1-?8).The structures of compounds 1-20 all were confirmed by IR,1H-NMR,13C-NMR and HRMS data.2.The reaction conditions were optimizedThe reaction conditions were optimized in the last step,which the title compound was obtained by the reaction of intermidiate?with intermidiate?.The best result was gained when intermidiate?and intermidiate? with molar ratio(1.5:1)were dissolved in the mixed solvent of DMF and acetonitrile(1:1)and refluxed for 10 h,a light yellow solid in good yield 72.4%-88% was obtained,which could be further purified by recrystallization in ethanol(or mixed solvent DMF: ethanol=1:1).3.Title compounds had anti-fungi effect in vitroThe antifungal activity of the target compounds 1-20 against Curvularia lunata,Cotton Fusarium Wilt,P.parasitica var nicotianae and Fusarium spp.were tested by the mycelial growth rate method.The results showed that most of the compounds 1-20 exhibit better antifungal activities.At 200 ?g/m L,compounds 3?7?8?11?14?15?16?17and18 showed very good inhibitory activities against Curvularia lunata,and the growth inhibitory rates(%)of these compounds were comparable with Grade A(inhibitory rate: 90%-100%);compounds 7?8?11?14?15 and 18 exhibited significant inhibitory effects against Cotton Fusarium Wilt.;and compounds 8?11?15-18 exhibited excellent antifungal activities against P.P.var.Nicotianae.;whereas compounds 8?15?16 and 18 exhibited excellent inhibitory activities against Fusarium spp..In addition,some compounds showed broad spectrum antifungal activities.Among of the compounds,compound 15 showed the best inhibitory effects with the tested fungi.The best antifungal activity was presented by compound 15,which was found to be sixteen times more active against Fusarium spp.(EC50: 6.22 ?g/m L)than triadimefon(EC50: 102.18 ?g/m L).The preliminary analysis of structure-activity indicated that allyl group or aromatic ring(R2: allyl,benzyl,2-fluoro-6-chlorobenzyl,2-chloro-5-methylene pyridine)exerted some influence on the inhibitory activities.4.Title compounds had antiviral effect(1)Anti-TMV activity in vivoThe curative and protective efficacies of title products 1-20 in vivo against TMV at the concentration of 0.5 mg/m L were determined by means of half-leaf.The results showed that some compounds possessed good anti-TMV effect,such as the curative rates against TMV of compounds 8?14?15 and 16 were 45.2%,45.9%,47.9% and 53.5%,respectively;the protection rates were 68.2%,74.9%,75.6% and 75.3%,respectively.Their curative and protection activities were near or exceed that of the commercial control Ningnanmycin(Curative rate 46.3%,Protection rate 67.8%).(2)Analysis of structure-activity relationship and action mechanism for anti-TMV activityAnalysis of structure-activity relationship indicated that allyl,6-chloro-pyridin-3-yl and 2-fluoro-6-chloro-benzyl exerted some influence on the anti-TMV activity.From the systemic acquired resistance(SAR)signal conduction mechanism about responses of treated tobacco to TMV,the tobacco plants treated by selected compounds can from related signal as resistance mechanism,which starting a series resistance factor of tobacco plants,promoting defense enzymes and systemic resistance.