2,N ⁶ -Disubstituted Adenosine Analogs with Antitrypanosomal and Antimalarial Activities

Abstract

A library of 2,N 6 -disubstituted adenosine analogs was synthesized and the analogs were tested for their antiprotozoal activities. It was found that 2-methoxy and 2-histamino and N 6 -m-iodobenzyl substitutions generally produced analogs with low levels of antiprotozoal activity. The best antiplasmodial activity was achieved with large aromatic substitutions, such as N 6 -2,2-diphenylethyl and naphthylmethyl, which could indicate a mechanism of action through aromatic stacking with heme in the digestive vacuole of Plasmodium spp. The activities against Trypanosoma cruzi trypomastigotes and Leishmania donovani amastigotes were generally low; but several analogs, particularly those with cyclopentylamino substitutions, displayed potent activities against Trypanosoma brucei rhodesiense and T. b. brucei bloodstream forms in vitro. The most active were 2-cyclopentylamino-N 6 -cyclopentyladenosine (compound NA42) and 2-cyclopentylamino-N 6 -cyclopentyladenine (compound NA134), with the nucleobase an order of magnitude more potent than the nucleoside, at 26 ؎ 4 nM. It was determined that the mode of action of these purines was trypanostatic, with the compounds becoming trypanocidal only at much higher concentrations. Those 2,N 6 -disubstituted purines tested for their effects on purine transport in T. b. brucei displayed at best a moderate affinity for the transporters. It is highly probable that the large hydrophobic substitutions, which bestow high calculated octanol-water coefficient values on the analogs, allow them to diffuse across the membrane. Consistent with this view, the analogs were as effective against a T. b. brucei strain lacking the P2 nucleoside transporter as they were against the parental strain. As the analogs were not toxic to human cell lines, the purine analogs are likely to act on a trypanosomespecific target.

Evaluation of Nucleoside Hydrolase Inhibitors for Treatment of African Trypanosomiasis

“…This was apparent from the biphasic inhibition curve displayed in the Alamar blue assay (Fig. 3A), similar to the previously defined curve for the trypanostatic adenosine analogue NA-42, where the first IC 50 corresponds to the concentration inducing growth arrest and the second IC 50 corresponds to the concentration inducing a parasitocidal effect (34). We thus examined the rate at which trypanosomes are killed by UAMC-00363 by using an in vitro lysis assay as described previously, with phenylarsine oxide as a positive control (28).…”

Potent Trypanocidal Curcumin Analogs Bearing a Monoenone Linker Motif Act on Trypanosoma brucei by Forming an Adduct with Trypanothione

“…Sensitivity of trypanosome cultures to curcumin and its analogs was determined using the redox-sensitive indicator dye Alamar blue (resazurin sodium salt; Sigma-Aldrich, St. Louis, MO), as described by Rodenko et al (2007). The assay was performed in white 96-well plates, each of which contained 2 Â 10 5 cells and the appropriate drug (at doubling dilution) in 200 ml HMI-9/FBS.…”

“…The diamidine trypanocides pentamidine and diminazene (both from Sigma-Aldrich) were used as controls. Drug sensitivity assays with human embryonic kidney cells were performed similarly using a resazurin-based assay, exactly as described previously (Rodenko et al, 2007;Changtam et al, 2010a).…”

SAR Studies of Diphenyl Cationic Trypanocides: Superior Activity of Phosphonium over Ammonium Salts

“…10,11 TbAT1-KO is a trypanosome strain lacking a functional P2-transporter and is resistant to diminazene. 12 The B48 strain is a mutant derived from the TbAT1-KO strain 13 with a nonfunctional high affinity pentamidine transporter (HAPT).…”