Trypanocidal activity of melamine-based nitroheterocycles

Abstract

A series of nitroheterocyclic compounds were designed with linkages to melamine or benzamidine groups that are known substrates of the P2 aminopurine and other transporters in African trypanosomes of the brucei group. Several compounds showed in vitro trypanotoxicity with 50% inhibitory concentrations in the submicromolar range. Although most compounds interacted with the P2 transporter, as judged by their ability to inhibit adenosine transport via this carrier, uptake through this route was not necessary for activity since TbAT1-null mutant parasites, deficient in this transporter, retained sensitivity to these drugs. One compound, a melamine-linked nitrofuran, also showed pronounced activity against parasites in mice. Studies into the mode of action of this compound indicated that neither reductive, nor oxidative, stress were related to its trypanocidal activity ruling out a genotoxic effect in T. brucei, distinguishing it from some other, mammalian cell toxic, trypanocidal nitroheterocycles.

FIG. 1.

Uptake of triazines and benzamidines into T. brucei. The left-hand side of the diagram shows the known routes of uptake of diamidines and melaminophenyl arsenicals into T. brucei. P2 is the product of the TbAT1 gene and encodes an unusual transporter capable of nucleoside and nucleobase uptake. It recognizes a motif also present on diamidine- and melamine-based drugs. These are shown on the right hand side of the diagram. Pentamidine enters via two additional transporters: HAPT1 and LAPT1. The uptake routes of selected triazine- and benzamidine-derived drugs is depicted.

FIG. 2.

Preparation of compounds from 2,4-diamino-6-chlorotriazines by displacement of the chlorine by hydrazine, followed by condensation with the appropriate nitrofuraldehyde.

FIG. 3.

Synthesis of benzamidine derivatives of the imidazoles. Lettered arrows: a, (BOC)₂O, NaOH, THF/H₂O; b, chloroacetyl chloride, Et₃N, MeCN; c, 2-nitroimidazole, Et₃N, MeCN; d, 4-nitroimidazole, Et₃N, MeCN; e, TFA, anisole, DCM.