A series of N-benzyl-1-(5-aryl-1,3,4-oxadiazol-2-yl)-1-(1H-pyrrol-2-yl)methanamines were synthesized via one-pot reaction of appropriate benzylamine, pyrrole-2-carbaldehyde, (N-isocyanimino)triphenylphosphorane, and a carboxylic acid. The anti-tumor potential of title compounds was tested against several cancer cell lines by using MTT assay. Some tested compounds including 5e, 5p and 5q exhibited comparable or better cytotoxic activity against A549, HT29 or HT1080 cells in comparison to the reference drug doxorubicin. Also, the cytotoxic activity of compounds 5d and 5n against MCF-7 was better than that of doxorubicin. Compound 5n with IC50 value of 4.3 μM was 4-fold more potent than doxorubicin. The structure-activity relationship study revealed that the introduction of halogen atoms on both 5-phenyl ring and N-benzyl part improved the cytotoxic activity against all tested cell lines.

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Reactions of benzoic acid derivatives and (E)-cinnamic acid derivatives with N, N-dialkyl carbodiimide proceed smoothly at room temperature and in neutral conditions to afford N-acylurea derivatives in high yields. The reaction proceeds smoothly and cleanly under mild conditions and no side reactions were observed.

The 1 : 1 imine intermediate 7 generated by the addition of a primary amine 2 to chloroacetone (1) is trapped by (isocyanoimino)triphenylphosphorane (4) in the presence of an aromatic carboxylic acid 3 and leads to the formation of the corresponding iminophosphorane intermediate 9 (Scheme 2). The 1,3,4-oxadiazole derivatives 5 are then formed via an intramolecular aza-Wittig reaction of the iminophosphorane intermediate 9. The reactions were completed under neutral conditions at room temperature. The fully substituted 1,3,4-oxadiazole derivatives 5 were produced in high yields (Table).