Abstract A new class of 4-arylhydrazono-1-benzothiazolyl-3-methylpyrazolin-5-ones (3a–j) and 4-arylazo-1-benzothiazolyl-3, 5-dimethylpyrazoles (4a–j) were designed as pharmacophore hybrids between pyrazolinone/pyrazole and benzothiazole moiety. The target molecules were efficiently synthesized by the cyclization of various oxobutyrates/pentane-2, 4-dione derivatives with 6-chloro-2-hydrazinobenzothiazole in ...