A novel series of 4-substituted 1-{[4-(10,15,20-triphenylporphyrin-5-yl)phenyl]methylidene}thiosemicarbazide, 4a-4n, was synthesized in 9-21% yield by the condensation of 4-(10,15,20-triphenylporphyrin-5-yl)benzaldehyde (3) with various substituted thiosemicarbazides in presence of catalytic amount of AcOH. These compounds were assayed for in vitro antiamoebic activity, and the results showed that out of 14 compounds 9 were found with IC(50) values lower than metronidazole corresponding to 1.05- to 4.7-fold increase in activity. MTT Assay showed that all the compounds are nontoxic to human kidney epithelial cell line. 4-(m-Toluidinyl)-1-{[4-(10,15,20-triphenylporphyrin-5-yl)phenyl]methylidene}thiosemicarbazide (4h) showed the highest antiamoebic activity with least cytotoxicity. Some of the compounds were screened for their antimalarial activities and ability to inhibit beta-haematin formation, but none of them showed an activity better than chloroquine and quinine. Only one compound out of six showed an activity comparable to standard drug.
In an endeavour to develop efficacious antiprotozoal agents 2-[4-(7-chloroquinolin-4-yl)piperazin-1yl]acetamide derivatives were synthesized and screened in vitro against the HM1:IMSS strain of E. histolytica and 3D7 strain of P. falciparum. Among the twenty-seven synthesized compounds, eleven evinced propitious anti-amoebic activity with IC50 values ranging from 0.41 to 1.80 µM) lower than the standard drug metronidazole (IC50 1.80 µM). All the compounds inhibited the in vitro growth of P. falciparum (IC50 range: 0.30-33.52 µM). Compounds A22 and A25 were found to be the most active antimalarial derivatives, and compound A16 the most active in inhibiting β-haematin formation; however compound A25 displayed the more favourable safety profile. The crystal structure for the compounds A7, A8, A12 and A21 was also determined. The molecular docking of crystal resolved inhibitors with PfDHFR allowed identification of stabilizing interactions within enzyme active site. These compounds affirm potential for further derivatives to enhance antiprotozoal activity whilst retaining their safety profile.
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