Lead optimisation starting from the previously reported selective quinoline NK3 receptor antagonists talnetant 2 (SB-223412) and 3 (SB-222200) led to the identification of 3-aminoquinoline NK3 antagonist 10 (GSK172981) with excellent CNS penetration. Investigation of a structurally related series of sulfonamides with reduced lipophilicity led to the discovery of 20 (GSK256471). Both 10 and 20 are high affinity, potent NK3 receptor antagonists which despite having different degrees of CNS penetration produced excellent NK3 receptor occupancy in an ex vivo binding study in gerbil cortex.
