This study aims to synthesize some novel pyrazolo[1,5- a]pyrimidine derivatives, and investigate their biological activities. These compounds exhibited good to high antioxidant activities [2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capabilities]. Among them, Ethyl 5-(2-ethoxy-2-oxoethyl)-7- hydroxy-2-methylpyrazolo[1,5-a]pyrimidine-3-carboxylate (3h) showed the highest antioxidant activity [Half-maximal Inhibitory Concentration (IC50)=15.34 μM] compared to ascorbic acid (IC50=13.53 μM) as a standard compound. Their antibacterial activities were investigated against two Gram-positive bacteria (Bacillus subtilis, and Staphylococcus aureus) and two Gramnegative bacteria (Pseudomonas aeruginosa, and Escherichia coli). The results showed that Ethyl 7-hydroxy-5- phenylpyrazolo[1,5-a]pyrimidine-3-carboxylate (3i) has the best antibacterial activity against Gram-positive B. subtilis [Zone of Inhibition (ZOI)=23.0�1.4 mm, Minimum Inhibitory Concentration (MIC)=312 μM]. Also, the cytotoxicity of these compounds was assessed against breast cancer cell lines [human breast adenocarcinoma (MCF-7)], which 7-Hydroxy-2-methyl-5- phenylpyrazolo[1,5-a]pyrimidine-3-carbonitrile (3f) displayed the most cytotoxicity (IC50=55.97 μg/mL), in contrast with Lapatinib (IC50=79.38 μg/mL) as a known drug.
