Table 2. In Vitro Antitrypanosomal Evaluation of 3-Chloro-4-(dimethylamino)phenyl-2-thiohydantoin Derivatives (SAR of R₃–R₄).

compd	R3	R4	T.brucei EC50 (nM)a
1	H	H	346
38	4-Cl	H	853
39	4-F	H	52
40	3-F	H	968
41	4-Me	H	1553
42	4-OMe	H	>20000
43	4-CF3	H	>20000
44	4-CN	H	17818
45	4–C(O)OEt	H	>20000
46	3-pyridyl	H	3000
47	4-F	3-F	313
48	4-F	2-F	63
49	5-F	2-F	9260
50	4-F	3-CN	>20000
51	4-F	2-Cl	46
52	4-F	2-OMe	191
53	4-F	2-NO2	350
54	4-F	2-CF3	924

^aConcentration of compounds required to inhibit growth by 50% (EC₅₀) of T. brucei brucei strain BF427. Pentamidine isethionate was included as a control for all of the T. brucei EC₅₀ assays with average ± SEM: 1.15 ± 0.09 nM (n = 32).