Synthesis, cytotoxicity and anti-inflammatory activity of piperine derivatives

Cancer is a significant leading cause of mortality worldwide which has been struggled in the clinical over the years. Parallelly, chronic inflammation becomes one of the risk factors to cause cancer. In searching for new potential anti-cancer and anti-inflammatory agents, an amide, ester, and dimer series of piperine derivatives were synthesized and screened for their anti-cancer and anti-inflammatory activities. Piperine (1) was isolated from fruits of Piper longum L. and hydrolyzed under reflux conditions to obtain piperic acid (2) as a starting material for the synthesis. The conversion of piperic acid to an amide series (3a-j) was involving an azabenzotriazole tetramethyl uronium hexafluorophosphate (HATU) coupling agent in the presence of N,N-diisopropylethylamine (DIPEA) as a catalyst. Ester series derivatives (4a-c) were carried out by Fischer and Steglich esterification. Meantime, dimer series (5-8) were prepared by SiO2-mediated Diels-Alder reaction. Preliminary screening of anti-cancer activity of the compounds was performed toward six human cancer cell lines; lung A549, liver HepG2 and Huh-7, colorectal HCT-116 and HT-29 and breast MCF-7 cancer cells by MTT assay. At the same time, the anti-inflammatory activity was evaluated by nitric oxide (NO) inhibition assay of LPS-activated macrophage J774.A1 cells. Among the compounds tested, the dimeric derivative 6 exhibited potent activity against Huh-7 (IC50: 5.6 µM) and A549 (IC50: 5.7 µM), while the dimer 7 revealed a significant activity with an IC50 value of 6.5 µM towards A549 cells. Almost all compounds in the amide series showed moderate activity to inactive, with the exception of compound 3j, which showed significant activity against HCT-116 with an IC50 value of 8.6 µM. Only compound 4c from the ester series showed moderate activity against HT-29 (IC50: 19.9 µM). Whilst for the anti-inflammatory activity evaluation, only the dimer with N-substituted cyclopentane 5 possessed a potent NO inhibition on J774.A1 cells with an IC50 value of 7.2 µM with no significant toxicity. Further, western blot analysis revealed that the anti-inflammatory activity of compound 5 was mediated by selective suppression of iNOS expression.