Gallic Acid Synthesized As A Precursor 1,2,4 - Triazoles And Antibacterial And Antiviral Activity Study

The present study focuses on the development of highly efficient, broad-spectrum andenvironmentally friendly green pesticides with low toxicity. Heterocyclic compounds in general,and fluorinated heterocyclic compounds in particular, play an important role in the design of novelpesticides due to their bio-activities and structural diversities. Among this class of compounds,1,2,4-triazole derivatives have received widespread attention as potential antitumor, herbicidal,fungicidal, insecticidal, antiviral and plant growth regulatory regents. Therefore, potential of thesecompounds in pesticide application is worthy of further investigation. For the purpose ofidentifying new target compounds capable of combatting diseases against pathogen or viral attack,we designed and synthesized three different classes of 1,2,4-triazole derivatives from Gallic acid,a nature product with good biological activity. The structures of the target molecule are shown inScheme 1.The synthetic methods, structure and biological activities of theses compounds were studied,structure activity relationship were established and preliminary action mechanism for anti-TMVactivity was ascertained.1. General procedure for synthesis of desired compounds3,4,5-Trimethoxybenzoic acid, obtained by methylation of gallic acid with dimethyl sulfate,was treated with thiocarbohydrazide to afford 4-amino-5-(3,4,5-trimethoxyphenyl)-2H-1,2,4-triazole-3(4H)-thione.1,2,4-Triazole-3(4H)-thione Schiff baseâ… was then synthesized by the condensation reactionof the intermediate 4-amino-5-(3,4,5-trimethoxyphenyl)-2H-1,2,4-triazole-3(4H)-thione (M) withdifferent substituted aldehydes. Alkylation of the Schiff base 1,2,4-Triazole-3(4H)-thioneâ… withalkyl halides was carried out to obtain novel Schiff base containing thioether moiety.Target compoundâ…¢was finally obtained by reduction of compoundâ…¡with sodium borohydride. The structures of all the compounds were confirmed by IR, MS, ¹H NMR, ¹³C NMRspectra and elemental analyses.2. Characterization of crystalsIn order to further confirm the structure of the desired compound, 4 single crystals weregenerated for structure eluvidation. The results showed that the double bonds C=N and C=C werepresent in a trans (E) geometric configuration mode. The alkylation of compoundâ… occurred atsulphur atom instead of nitrogen in the ring.Crystalâ…¡₅₄ belongs to monoclinic system with space group P2₁/n. As mentioned, theconfiguration of double bond of C=N is trans. The bond length of N4-C12 is 1.278(2)(?), which isshorter than the two double bonds C=N(N2-C8=1.313(2)(?), N1-C7=1.319(2)(?)) in 1,2,4-triazolering. The bond length of N1-N2 is shorter than that of the N3-N4 out of the ring. There isconsiderable conjugation between sulfur atom and 1,2,4-triazole ring are intermolecularinteraction within (?).Crystalâ…¡₅₉ belongs to monoclinic system with space group P2₁/c. The configuration ofdouble bond of C=N is trans. The bond length of N4-C10 is 1.252(3)(?), which is shorter than thetwo double bonds C=N(N2-C9= 1.299(3)(?), N1-C17=1.306(3)(?)) in 1,2,4-triazole ring. The bondlength of [1.392(3)(?)] is shorter than that of the N3-N4[1.405(2)(?)] out of the ring. There isconsiderable conjugation between sulfur atom and 1,2,4-triazole ring are intermolecularinteraction within (?).Crystalâ…¡₇ belongs to monoclinic system with space group C2/c. The configurations ofdouble bond C=N and C=C are trans. The bond length of C14-N4 is 1.282(4)(?), which is shorterthan that of the two double bonds C=N(N2-C11=1.315(4)(?), N1-C10= 1.316(4)(?)) in 1,2,4-triazolering. The bond length of N1-N2[1.388(4)(?)] is shorter than that of N3-N4[1.414(3)(?)] out of thering due to the conjugation of the atomic orbital in ring. There is considerable conjugationbetween sulfur atom and 1,2,4-triazole ring are intermolecular interaction within (?).Crystalâ…¡₃₂ belongs to monoclinic system with space group P2₁/c. The configuration ofdouble bond of C=N is trans. The bond length of C20-N6 is 1.272(5)(?), which is shorter than thatof the two double bonds C=N[N3-C9=1.331(5)(?), N4-C10=1.325(5)(?)]. The bond length ofN3-N4[1.378(2)(?)] is shorter than that of N5-N6 [1.419(3)(?)] out of the ring due to the conjugationof the atomic orbital in ring. There is considerable p-Ï€conjugation between sulfur atom and 1,2,4-triazole ring are intermolecular interaction within (?).3. Optimization of reaction condition4-Amino-5-(3,4,5-trimethoxyphenyl)-2H-1,2,4- triazole-3(4H)-thione was obtained throughan improved synthetic method under solvent-free conditions by reacting 3,4,5-trimethoxybenzoicacid with thiocarbohydrazide. In this one-pot reaction, the number of synthetic steps and reactiontime were reduced, and the yield of the products was increased from 35% to 61%. In addition, byadopting a different work-up procedure for thiocarbohydrazide and compoundâ…¢, the yields ofthese compounds were significantly enhanced.4. Mechanism of formation and characterization of side productWhen alkylation, e.g. ethyl 2-chloroacetate or 1-(chloromethyl)-4-nitrobenzene wasemployed in the alkylation of Schiff baseâ… , [1,2,4]triazolo[3,4-b][1,3,4]thiadiazine derivativeswere obtained instead of the expected product-â…¡. The resulting novel fused heterocycliccompounds obtained by simple alkylation might be associated with some biological activity, Theformation of side product was explained by a probable reaction of the Schiff base with the halideto generate, the conresponding sulfide that could subsequently undergo a base catalyzedintramoledecular ring close by the attack of methylene on imine carbon, three such[1,2,4]triazolo[3,4-b][1,3,4] thiadiazine derivatives (â…£₁,â…£₂,â…£₃) were synthesised through thisroute, and the structures were confirmed by IR, MS,¹H NMR,¹³C NMR spectra and elementalanalyses.5. Antifungal activitiesThe antifungal activities of some title compounds to Gibberella zeae, Botrytis cinerea andSclerotinia sclerotiorum were tested by the mycelial growth rate method. The results showed thatsome of them exhibited antifungal activities to a certain degree. At the concentration 50μg/mL,the title compoundâ…¢₁₃ inhibited Fusarium graminearum, Cytospora mandshurica, Fusariumoxysporum at 43.9%, 44.3%, 42.3%, respectively, with values similar to that of Hymexazol(53.9%, 55.3%, 54.1% respectively).The compoundsâ…¢₄,â…¢₈ showed good inhibition rates toGibberella zeae at 50μg/mL.6. The treatment activity for CMV in vivoThe anti-CMV activities of some title compounds were tested at the concentration of 50μg/mL. The results showed that the title compounds had treatment activities for CMV in vivo to a certain degree, e. g., the treatment activities for CMV of compoundsâ…¡₇,â…¡₃₁,â…¡₃₀,â…¡₂₃ were 48.6%,47.6%, 48.9%, 47.7%, respectively, which were in the same rage as that of Ningnanmycin (66.5%).Structure-activity relationship indicated that fluorine atom exerts some influence on the anti-CMVactivity.7. The treatment activity for TMV in vivoThe anti-TMV activities of some title compounds were tested at the concentration of 50μg/mL. The results showed that the title compounds had treatment activities for TMV in vivo to acertain degree, e. g., the treatment activities for TMV of compoundsâ…¡₂,â…¡₃₄,â…¡₄₈,â…¡₂₇ were 48.3%,43.2%, 45.3%, 43.2%, respectively, which were in the same range as that of Ningnanmycin(58.2%).8. Action mechanism for anti-TMV activityFrom the systemic acquired resistance (SAR) signal conduction mechanism about responsesof treated tobacco to TMV, the tobacco plants treated by selected compounds can from relatedsignal as resistance mechanism, which starting a series resistance factor of tobacco plants,promoting defense enzymes and systemic resistance.To the best of our knowledge, there is no commercial antiviral agent containing 1,2,4-triazolemoiety, so the work lays solid foundation for further studies and application of 1,2,4-triazolederivatives for the development of anti plant-virus agent.