Synthesis, biological screening of novel long chain derivatives of 1,3-disubstituted-1H-pyrazol-5(4H)-one and 2-substituted-3H-1,4-phthalazin-1,4-dione: Structure-activity relationship studies

The main purpose of this study is to synthesize novel heterocyclic derivatives of fatty acids which are also biologically important. The simple, efficient and one-pot synthesis of two novel series of 1-long chain alkanoyl/alkenoyl/hydroxyalkenoyl-3-methyl-1H-pyrazol-5(4H)-ones 2(a–e) and 2-long chain alkenoyl/hydroxyalkenoyl-3H-phthalazin-1,4-diones 3(b–e) is achieved by the reaction of ethylacetoacetate/phthalic anhydride and long chain alkyl/alkenyl/hydroxyalkenyl hydrazides 1(a–e). Although some methods are available for the synthesis of phthalazindiones and pyrazolones, the development of a new synthetic method for the efficacious build up of heterocycles (phthalazindiones and pyrazolones) substituted with long alkanoyl/alkenoyl/hydroxyalkenoyl chain is an interesting challenge in the field of synthesis of novel compounds of fatty acids that includes heterocyclization and derivatization of fatty acids. Compounds 2(a–e) were synthesized by the cyclization reaction between ethylacetoacetate and long alkyl/alkenyl/hydroxyalkenyl chain hydrazides 1(a–e). Compounds 3(b–e) were synthesized by the reaction of phthalic anhydride and long alkenyl/hydroxyalkenyl chain hydrazides 1(b–e) in absolute ethanol/glacial AcOH. Structures of all the newly synthesized compounds have been elucidated by means of IR, 1H NMR, 13C NMR and MS. Newly synthesized compounds were evaluated for in vitro antibacterial and antifungal activities and their structure–activity relationship studies have been carried out.