Several indole derivatives and analogues comprising a range of related structural classes were designed, synthesized and tested as ligands for the 5-HT4 receptor. Within each series, binding experiments showed compounds with good affinity demonstrating high percentage displacement values at 1 αM. The most potent of these (20) had a pKi of 8.54 demonstrating very good affinity. These indole analogues were combined with 55 ligands ...