SAR study of bicyclo[4.1.0]heptanes as melanin-concentrating hormone receptor R1 antagonists: Taming hERG Original Research Article

To improve the ex vivo potency of MCH inhibitor 1a and to address its hERG liability, a structure–activity study was carried out, focusing on three regions of the lead structure. Introduction of new side chains with basic nitrogen improved in vitro and ex vivo bindings. Many potent compounds with Ki < 10 nM were discovered (compounds 6a–j) and several compounds (14–17) had excellent ex vivo binding at 6 h and 24 h. Attenuating the basicity of nitrogen on the side chain, and in particular, introduction of a polar group such as aminomethyl on the distal phenyl ring significantly lowered the hERG activity. Further replacement of the distal phenyl group with heteroaryl groups in the cyclohexene series provided compounds such as 28l with excellent ex vivo activity with much reduced hERG liability.