Development of Potent Serotonin-3(5-HT₃) Receptor Antagonists. II. Structure-Activity Relationships of N-(1-Benzyl-4-methylhexahydro-1H-1, 4-diazepin-6-yl)carboxamides

Abstract

Our studies on 4-amino-5-chloro-2-ethoxybenzamides led to the discovery that the N-(1, 4-dimethylhexahydro-1H-1, 4-diazepin-6-yl)benzamide 9 and the 1-benzyl-4-methylhexahydro-1H-1, 4-diazepine analogue 10 are potent serotonin-3 (5-HT₃) receptor antagonists. Structure-activity relationship (SAR) studies on the influence of the aromatic nucleus of 9 and 10 upon inhibition of the von Bezold-Jarisch reflex in rats are described. Heteroaromatic rings such as pyrrole, thiophene, furan, pyridine, pyridazine, 1, 2-benzisoxazole, indole, quinoline, and isoquinoline rings showed weak 5-HT₃ receptor antagonistic activity. Within this series, use of the 1H-indazole ring as an aromatic moiety led to a substantial increase of the acitivity; the 1H-indazolylcarboxamides 54, 57, 97, and 102 showed potent 5-HT₃ receptor antagonistic activity. The optimal compound identified via extensive SAR studies was N-(1-benzyl-4-methylhexahydro-1H-1, 4-diazepin-6-yl)-1H-indazole-3-carboxamide (54), whose effect was superior to that of the corresponding benzamide 10 and essentially equipotent to those of ondansetron (1) and granisetron (4).