A small library of 26 2,2′-[alkane-α,ω-diylbis(oxyphenylene)]bis-1H-benzimidazoles has been prepared and evaluated against Giardia intestinalis, Entamoeba histolytica, Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani, and Plasmodium falciparum. Among the tested compounds, eight derivatives (17, 19, 20, 24, 27, 30, 32 and 35) exhibited an anti-Plasmodium falciparum activity characterized by IC50 values in the range of 180–410 nM (0.11–0.21 μg/mL) and selectivity indexes (IC50 rat skeletal myoblasts L6 cells vs IC50P. falciparum K1 strain) varying between 92 and more than 450. Two of the eight novel drug leads, namely compounds 19 and 32, were also active against G. intestinalis and L. donovani with selectivity indexes of 122 and >164 respectively.Eight derivatives out of a newly prepared small library of twenty-six bisbenzimidazoles emerged as promising effective agents against Plasmodium falciparum. They were characterized by IC50 values ranging from 190 to 450 nM and selectivity indexes ranging from 92 to more than 450.

A series of alkanediamide-linked bisbenzamidines was synthesized and tested in vitro against a drug-sensitive strain of Trypanosoma brucei brucei, a drug-resistant strain of Trypanosoma brucei rhodesiense and Pneumocystiscarinii. Bisbenzamidines linked with longer alkanediamide chains were potent inhibitors of both strains of T. brucei. However, bisbenzamidines linked with shorter alkanediamide chains were the most potent compounds against P. carinii. N,N′-Bis[4-(aminoiminomethyl)phenyl] hexanediamide, 4 displayed potent inhibition (IC50 = 2–3 nM) against T. brucei and P. carinii, and was non-cytotoxic in the A549 human lung carcinoma cell line. The inhibitory bioactivity was significantly reduced when the amidine groups in 4 were moved from the para to the meta positions or replaced with amides.The synthesis and SAR of a series of alkanediamide-linked bisbenzamidines as potent inhibitors of Trypanosomal brucei and Pneumocystis carinii are described.

A series of 13 1,4-diarylpiperazines has been prepared, evaluated for antileishmanial activity and their binding affinity to DNA was measured. Among these compounds, 1,4-bis[4-(1H-benzimidazol-2-yl)phenyl]piperazine (14) emerged as the most active compound with an IC50 value of 0.41 μM which is about sevenfold more potent than pentamidine.

A series of pentamidine congeners has been synthesized and screened for their in vitro activity against Pneumocystis carinii. Among the tested compounds, bisbenzamidines linked by a flexible pentanediamide or hexanediamide chain (7 and 9) emerged as exceptionally potent agents that were more effective and less toxic than pentamidine in the assays described in this study.Modifications of the linker between the benzamidine moieties led to the discovery of several new highly potent anti-Pneumocystis carinii agents.

The synthesis, anti-Pneumocystis carinii activity and DNA binding properties of eight new N,N′-bis[4-(N-alkylamidino)phenyl]homopiperazines are reported. Compounds 2 and 8 were the most potent and caused about 70% inhibition of Pneumocystis carinii growth in a cell culture model at 1 μM concentrations.The synthesis, anti-Pneumocystis carinii activity and DNA binding properties of eight new N,N′-bis[4-(N-alkylamidino)phenyl]homopiperazines are reported.