A novel highly Potent 5-HT3 antagonist and Tropisetron analogue (I) is described with an increased efficacy to inhibit cisplatin induced emesis in fertets. Four novel structural classes of kinetic benzamide bioisostetes (8-11) are presented. 5-HT derivatives L2_14 are described as astroproe gands of the recently discovered 5-HT4 receptor.