The inhibiting effects of several spermidine and spermine derivatives on T. cruzi trypanothione reductase were assessed. Spermidine and spermine derivatives containing hydrophobic aromatic substituents were found to be competitive inhibitors of trypanothione reductase. The most effective compounds tested were N~,NLbis(2 naphthylmethyl)spermidine, N*,/v~-bis(2-naphthylmethyl)spermine and N~,/CLbis(3-phenylpropyl)spermine.Trypanosoma cruzi is a protozoan parasite causing Chagas disease which currently infects 16-18 million people leading to more than 45,000 deaths each year. 1 The disease occurs predominantly in Central and South America, however about 100,000 people in the USA are also infected, probably due to transfusion of blood products originating from South America. ~ Current treatment of T. cruzi and other trypanosome infections is difficult and often ineffectual in controlling the chronic phase of these diseases. 3 Therefore effective antitrypanosomal drugs are needed. A promising strategy for the development of new drugs is to design compounds which interfere with the mechanisms by which trypanosomes maintain the levels of reduced glutathione necessary for defense against oxidative stress. 4'S'6 Levels of reduced glutathione in most organisms are maintained by the action ofglutathione reductase. Trypanosomes do not contain glutathione reductase, but contain a unique enzyme, trypanothione reductase (TR). 7 TR is a NADPH-dependent, FAD-containing enzyme which reduces the disulfide group of N~,~ bis(glutathionyl)spermidine (trypanothione). 7 It is presumed that in trypanosomes, glutathione (and possibly other thiols t) is reduced nonermymatically by a thiobdisulfide exchange reaction with reduced trypanothione. 9 Given that the antioxidant defenses of trypanosomes are based on the action of TIL inhibitors of TR are potential antitrypanosomal agents.In this paper we describe the synthesis and inhibiting effects of several novel spermidine and spermine derivatives on T. cruzi TR. The compounds N~,N~-bis(2-naphthylmethyl)spermidine (3), N~,N~-bis(2-naphthyl methyl)spermine (7) and N~,A~-bis(3-phenylpropyl)spermine (6) were found to be competitive inhibitors (K~ values of 9.5, 5.5 and 3.5 p.M, respectively) with potencies of a similar magnitude to the most effective competitive inhibitor described previously, t° These compounds are easily synthesized and could furthermore be modified to produce potentially more effective or irreversible inhibitors of TR.