Objective: The main objective of this work was to synthesize and evaluate the novel 2,3-dihydro-1,3,4-oxadiazole and 4,5-dihydro-1,2,4-triazole derivatives for cytotoxic activities. Methods: The 2,3-dihydro-1,3,4-oxadiazole derivatives 4a-h were synthesized by cyclization of N'-(substituted-benzylidene) isonicotinohydrazide 3a-e in refluxing acetic anhydride. The 2,3-dihydro-1,3,4-oxadiazole derivatives 4a-h were converted into the corresponding 4,5-dihydro-1,2,4-triazoles 5a-h using ammonia.

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... l the synthesized compounds were identified, depending on the physical and spectral data. Title compounds were assessed for their cytotoxic activity against human cancer cell line (MCF-7) by using Sulforhodamine B (SRB) colorimetric assay. Results: All the synthesized compounds showed characteristic peaks in FTIR, 1HNMR and Mass spectral analysis. The results of the in vitro cytotoxic activity revealed that the compound 4c exhibited equipotent cytotoxic activity with an IC50 value of 8.04 µM when compared with that of standard drug doxorubicin (IC50= 8.02 µM). The reminder compounds have shown good to moderate cytotoxic activities when compared with that of a reference standard. Conclusion: We synthesized a series of title compounds in quantitative yields. Most derivatives showed moderate to good cytotoxic activity.