Chemical and Pharmaceutical Bulletin p. 2051 - 2060 (1996)
Update date:2022-08-04
Topics:
Kuroita, Takanobu
Marubayashi, Nobuhiro
Sano, Mitsuharu
Kanzaki, Kouji
Inaba, Kenichi
Kawakita, Takeshi
A series of 3,4-dihydro-2H-1,4-benzoxazine-8-carboxamide derivatives was synthesized and evaluated for serotonin-3 (5-HT3) receptor antagonistic activities by means of assays of 5-HT3 receptor binding and the ability to antagonize the von Bezold-Jarisch reflex in rats. Replacement of the 1,4- benzoxazine ring with a 1,4-benzthiazine ring or seven-membered ring (i.e., 1,5-benzoxepine or 1,5-benzthiepine) resulted in decreased affinity for 5- HT3 receptor. Introduction of substituents at the 2 position of the 1,4- benzoxazine ring increased the antagonistic activities (dimethyl > methyl > dihydro > phenyl). The compounds bearing a 9-methyl-9-azabicyclo[3.3.1]non- 3-yl moiety as the basic part of 3,4-dihydro-2H-1,4-benzoxazine-8-carboxamide derivatives were equipotent to those bearing 1-azabicyclo[2.2.2]oct-3-yl moiety. The 9-methyl-9-azabicyclo[3.3.1]non-3-yl moiety was confirmed to adopt a boat-chair conformation on the basis of both NMR studies and X-ray analysis. In this series, endo-6-chloro-3,4-dihydro-N-(9-methyl-9- azabicyclo[3.3.1]non-3-yl)-2,2,4-trimethyl-2H-1,4-benzoxazine-8-carboxamide showed the highest affinity for 5-HT3 receptors (K(i) = 0.019 nM), and a long-lasting 5-HT3 receptor antagonistic activity as evidenced by antagonism to the von Bezold-Jarisch reflex in rats. Such a long-lasting 5-HT3 receptor antagonism would be attributed to the introduction of both two methyl groups at the 2 position of the benzoxazine ring and the 9-methyl-9- azabicyclo[3.3.1]non-3-yl moiety, which adopts the boat-chair conformation.
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Doi:10.1007/BF01431114
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