Parasitic diseases such as Human African Trypanosomiasis (HAT), Chagas disease and Leishmaniasis cause thousands of fatalities each year. Current chemotherapy is based on drugs discovered over 60 years ago that are expensive and difficult to administer. The drug-pipeline is virtually dry and the trickle of inhibitors that are in development are largely based on those that are already in use. Parasite resistance to these drugs is developing, underlining the urgent need for novel anti-parasitic drug therapies. This study focused on the identification of novel small molecular inhibitors with anti-parasitic activities against Trypanosoma brucei spp. (HAT), Trypanosoma cruzi spp. (Chagas disease) and Leishmania infantum spp. (Leishmaniasis) with a particular focus on combining broadspectrum activity with parasite-specificity. A two-pronged approach was used to develop an effective chemotherapy through the optimisation of known inhibitors of glycophosphatidylinositol (GPI)-anchor biosynthesis and improving the specificity of iron chelators. GPI anchor biosynthesis is a pathway essential for survival to all three parasites. Here, a rhodanine-N-acetic acid derivative served as the starting point for the development of a library of 379 thiazolidine-4-one and pyrazolone analogues. These were systematically screened against three species of parasitic protozoa and a mammalian cell line in order to identify inhibitors which demonstrate low-�M anti-parasitic activity and a good selectivity profile. Further target identification studies on the effect of these new inhibitors using in vitro assays confirmed inhibition of GPI anchor biosynthesis as a mode of action. This provides further evidence that the GPI anchor is a druggable target for the development of novel anti-parasitic agents against T. brucei, T. cruzi and L. infantum. Taken together, this work indicates that drugs targeting one feature common to all three protozoa can provide anti-parasitic activity with low toxicity against mammalian cells.