A novel series of 2-substituted-aminomethyl-8 phenyl-pyrazolo[3,4-d][1,3,4]thiadiazolo[3,2-a]pyrimidin-4 (1H)-ones have been synthesized by treating 2-chloromethyl-8-phenyl-pyrazolo[3,4-d][1,3,4]thiadiazolo[3,2-a] pyrimidin-4(1H)-one with various nucleophiles. The chloromethyl derivative was prepared by treating 2-amino-3 mercapto pyrazolo[3,4-d]pyrimidine with one carbon donor, chloroacetic acid. The intermediate 2-amino-3 mercapto pyrazolo[3,4-d]pyrimidine was prepared by a novel, eco-friendly route starting from 2-amino-3-carbethoxy-1-phenyl-pyrazole. The target compounds exhibited broad-spectrum antibacterial activity (Kirby Bauer's Method).