A γ-glutamylcysteine synthetase inhibitor (100% inhibition at a concentration of 10 μM in an enzyme assay); selective for γ-glutamylcysteine synthetase, lacking activity at glutamine synthetase at concentrations up to 500 μM; reduces renal glutathione in mice without inducing abnormal behavior or convulsions at a dose of 32 mmol/kg; eliminates T. brucei from the bloodstream of infected mice via depletion of intratrypanosomal glutathione and induction of oxidative stress at a dose of 4 mmol/kg; an isomeric mixture of L-buthionine-S-sulfoxime, L-buthionine-R-sulfoxime, D-buthionine-S-sulfoxime, and D-buthionine-R-sulfoxime