Spiro-substituted piperidines as neurokinin receptor antagonists. II. Syntheses and NK2 receptor-antagonistic activities of N-[2-aryl-4-(spiro-substituted piperidin-1'-yl)butyl]carboxamides.

In the course of our research on spiro-compounds as neurokinin receptor antagonists, N-[2-aryl-4-(spiro-substituted piperidin-1'-yl)butyl]carboxamides were designed, based on YM-35375 (3) as a lead compound, and evaluated for NK2 receptor-antagonistic activities. Some derivatives inhibited the binding of radio-labeled neurokinin A to the NK2 receptor with IC50 values at the level of 10(-9) M. Among these compounds, (+/-)-1'-[4-(N-benzoyl-N-methylamino)-3- (3,4-dichlorophenyl)butyl]spiro[benzo[c]thiophene-1(3H), 4'-piperidine] 2-oxide (58, YM-38336) showed 10 times more potent NK2 receptor binding affinity than compound 3 (IC50 values of 8.9 and 84 nM, respectively). It showed more potent inhibitory activity (ID50 20 micrograms/kg (i.v.)) against [beta-Ala8]-NKA(4-10)-induced bronchoconstriction in guinea pigs than compound 3 (ID50 41 micrograms/kg (i.v.)). This compound was also effective intraduodenally in the same model, exhibiting an ID50 value of 0.41 microgram/kg.