Microwave-promoted synthesis and biological activity of some 2-hetarylmethyl-4-(4-hetarylphenyl)-5-methyl-2,4-dihydro-3H-1,2,4-triazol-3-one derivatives

A series of fused and non-fused 1,2,4-triazole derivatives were prepared starting from ethyl 4-[1-(2-ethoxy-2-oxoethyl)-3-methyl-5-oxo-1,5-dihydro-4H-1,2,4-triazol-4-yl]benzoate. Firstly, both ethyl ester groups were simultaneously transformed into hydrazide groups, then into 4-amino-5-mercapto-4H-1,2,4-triazol-3-yl groups using both microwave-assisted and conventional methods. The latter products interacted with 2 equiv of phenacyl bromides, chloroacetone, or chloroacetic acid to form ring assemblies containing two [1,2,4]triazolo-[3,4-b][1,3,4]thiadiazine fragments. Cyclization using 2 equiv of carboxylic acids, urea, or CS2 leads to the corresponding [1,2,4]triazolo-[3,4-b][1,3,4]thiadiazole derivatives. The synthesized compounds were evaluated in regard to their antimicrobial, anti-lipase, and antiurease activities.