Synthesis, Characterization And Antibacterial Activity Of Glucosides Of1,2,4-Triazolo[3,4-b]-1,3,4-thiadiazoles

Studies in recent years have indicated that many Condensed Heterocyclic Compounds have excellent and broad biological activity, especially the 1,2,4-triazolo [3,4-b]-1,3,4-thiadiazole derivatives with the unique biological activity such as anti-bacterial,anti-inflammatory, anti-cancer and anti-spasm. Sugar-modified triazole compounds have drawn extensive attention for their favorable biological activity of low toxicity, excellent solubility and other prominent features. Therefore, three series of 3-alkyl/aryl-6-S-(2’,3’,4’,6’-tetra-O-acetyl-β-D-glcopyranosyl)-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles(A1~A10), 3-alkyl/aryl-6-S-(2’,3’,4’,6’-tetra-O-acetyl-β-L-arabinosyl)-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles(B1~B10) and 3-alkyl/aryl-6-S-(tetrahydroxy-β-D-glcopyranosyl)-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles(C1~C10) were rationally designed and synthesized respectively based on the combination of 1,2,4-triazolo[3,4-b]-1, 3,4-thiadiazole and glucosides according to the principle of superposition of bioactive substructures and the results of molecular modeling design.Firstly, substituted methyl benzoate or fatty acid were used as raw materials to prepare the compounds 3-substituted-4-amino-5-sulfhydryl-1,2,4-triazoles by hydrazinolysis, salify and cycliztion. Secondly, compounds 3-substituted-6-thione-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles were obtained by the reaction of 3-substituted-4-amino-5-sulfhydryl-1,2,4-triazoles and CS2 in KOH solution. Then compounds 3-alkyl/aryl-6-S-(2’,3’,4’,6’-tetra-Oacetyl-β-D-glcopyranosyl)-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole(A1~A10) and 3-alkyl/aryl-6-S-(2’,3’,4’,6’-tetra-O-acetyl-β-D-glcopyranosyl)-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole(B1~B10) were obtained by the nucleophilic substitution reaction of intermediate 3-substituted-6-thione-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles and 2′,3′,4′,6′-tetra-O-acetyl-α-Dglucopyranosyl or 2′,3′,4′-tetra-O-acetyl-α-L-arabinosyl in reaction system of KOH, acetone and water. Finally, target compounds 3-alkyl/aryl-6-S-(tetrahydroxy-β-D-glcopyranosyl)-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles(C1~C10) were synthesized by removing the acetyl in system of methylene chloride, methanol and sodium methoxide. The results show that the mixed system mentioned above is the better system for hydrolytic reaction to remove acetyl. The reaction conditions are described below: the volume ratio of methanol and methylene chloride is 1: 1, the corporeal quantity ratio of sodium methoxide and the glycoside is 1: 1, the reaction temperature is below 20 ℃ and the reaction time is 20~30 min. The structures of all the compounds were confirmed by 1H NMR, 13 C NMR and IR.The preliminary bioassay was carried out based on the U.S. National Clinical Laboratory Standards Committee(NCCLS) Minimal Inhibitory Concentration regulation. The in vitro antimicrobial activity data show that all target compounds possess efficient antibacterial activities against Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Moniliaalbican, especially the Monilia albican. Compound C6 shows excellent activity against Monilia albican, which is more effective than those of the reference drug fluconazole and triclosan. The compounds B3, C3 and C6 have the lower MIC values on the four tested strains which show the strong antimicrobial activity and great development potential.The structure activity relationship of the synthesized compounds show that the antibacterial activity of the compounds with acetyl removed has significantly enhanced. To compare the antimicrobial activity of S-glcopyranosyl and S-arabinosyl, the introduction of S-arabinosyl is more conducive to increase the antimicrobial activity. The introduction of hydroxy moiety on the phenyl ring improves the biological activity.The results of molecular docking clarify that the interaction rules between target compounds and Escherichia coli Fab I is consistent with that between antibacterial agent triclosan and Escherichia coli Fab I. The binding free energy between Fab I and compounds C1~C10 are lower than those of compounds A1~A10. Therefore, compounds C1~C10 have the potential to be Fab I inhibitors, that is the important significant for the development of new antibacterial agent.