The interaction of 4-hydrazinylthieno[2,3-d]pyrimid ines with dicarboxylic acids anhydrides has been st udied. It was found that for ethyl 4-hydrazinyl-5-methylthieno[2, 3-d]pyrimidine-6-carboxylate this reaction proceeds with the Dimroth rearrangement even in the mild conditions. The most suitable conditions for this reaction was boiling in the glacial acetic acid media. Using 1,1’-carbonyldiimi dazole as the coupling reagent the series of 3-[8- (ethoxycarbonyl)-9-methy lthieno[3,2-e][1,2,4]triaz olo[1,5-c]pyrimidin-2-yl]propanoic acid amides were synthesized. The compounds obtained showed the mode rate antimicrobial activity.