Structure-Activity Relationship Study on Ligands Activating the Voltage-Gated Potassium Channel K_V7.1

K_V7.1 agonists are promising therapeutic agents for the treatment of hypertension, arrhythmia and preterm labor. The 3-(indol-3-ylmethyl) substituted 1,4-benzodiazepine (R)-L3 has been reported as a potent K_V7.1 activator. In this study, (R)-L3 was systematically modified at eight positions including the configuration at 3-position. For the synthesis of the designed 1,4-benzodiazepines 8 and 12, 2-aminobenzophenones 4 were reacted with amino acid derived 1,3-oxazolidinediones 7 or 11. The required 2-aminobenzophenones 4 were obtained regioselectively by Sugasawa reaction of anilines 2 and 3 with various substituted benzonitriles, using BCl₃ and AlCl₃. Racemization during deprotonation and alkylation of secondary lactams 8 and 12 was not observed. However, racemization occurred during conversion of lactam 8b into thiolactam 17. The enantiomers of thiolactam rac-17 and triazole rac-18 were separated by chiral HPLC. The ion channel modulatory activity of the resulting 1,4-benzodiazepines was evaluated by two-electrode voltage-clamp (TEVC) experiments. These TEVC experiments showed that (3R)-configuration and the indolylmethyl moiety at 3-position are essential for K_V7.1 activation. High activity was observed for secondary lactam 8b and methylated lactam 9b, but larger N-substituents reduced the channel activation. The thioamide (R)-17 and the triazole (R)-18 did not significantly activate the K_V7.1 channel. Replacement of the F-atom in 2-position of the 5-phenyl moiety by a proton or other halogen atoms reduced the K_V7.1 activity. However, the 9-hydroxy derivative 9i appeared to exhibit higher agonistic activity (+68% activity increase at 1 µM) than (R)-L3 (9b, +45% at 1 µM). Moreover, higher phase I metabolic stability was observed for phenol 9i.