Table 5. Selectivity over inhibition of human mitochondrial protein synthesis and brain plasma ratio.

Compound number	Human mitochondrial protein synthesis EC50 (nM)	Selectivity index a	Brain/plasma ratio at 60 min (%)
Compounds with 1,3-dihydro-imidazol-2-one linker
15	42 b	26	9.6
16	290 b	85	0.1
17	430 b	143	0
18	175 b	30	0
20	195 b	38	5.5
26	39 b	39	0
27	75 b	42	0
Compounds with fused ring linker
39	507	145	0
40	478	154	0.5
42	1750	203	0.6
43	316	45	0

^aSelectivity index is defined as EC₅₀ against human mitochondrial protein synthesis divided by EC₅₀ against T. brucei parasite growth.

^bAs reported previously.19 Control for mitochondrial protein synthesis inhibition EC₅₀ assay average ± SEM: chloramphenicol (7.9 ± 1.6 μM, n = 9).