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 Gram-negative 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 line [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.
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