The R- and S-enantiomers of the 4, 5, 6, 7-tetrahydro-1H-benzimidazole derivatives 3-8 were prepared by optical resolution. Each R-isomer, except for 3, was almost two orders of magnitude more potent than its S-isomer as a 5-hydroxytryptamine (5-HT3) receptor antagonist, as judged from the effect on the von Bezold-Jarisch reflex (B. J. reflex) in rats, the contraction of isolated guinea-pig colon and the receptor-binding affinity. The (-)-(R)-5-[(1-methyl-1H-indol-3-yl)carbonyl] derivative 6R·HCl (remosetron=YM060) and (-)-(R)-5-[(1-indolinyl)carbonyl] derivative 4R·HCl (YM114=KAE-393) given p.o. were hundreds of times more potent than 1 (ondansetron) and 2 (granisetron) in their inhibitory effects on cisplatin-induced emesis in ferrets and restraint stress-induced increases in fecal pellet output in rats. Three-dimensional molecular modeling studies suggested that the 'chiral selection' of the enantiomers might be influenced by the steric repulsion between the aromatic ring part and the conformationally resricted 4, 5, 6, 7-tetrhydro-1H-benzimidazole ring in "equatorial-twist" conformation. In our pharmacophore model for the 5-HT3 receptor antagonist, a basic center exsts at the left side of the aromatic-carbonyl plane when viewing from the aromatic part with the carbonyl oxygen atom upwards, whereas the "handedness" is ambiguous in the previously proposed model.
通过光学解析法制备了 4、5、6、7-四氢-1H-
苯并咪唑衍
生物 3-8 的 R-和 S-对映体。从对大鼠冯贝佐尔德-贾里施反射(B. J. reflex)、离体豚鼠结肠收缩和受体结合亲和力的影响来看,除 3 外,每种 R-异构体作为 5-羟
色胺(5-HT3)受体拮抗剂的效力都比其 S-异构体高出近两个数量级。与 1(
昂丹司琼)和 2(格拉司琼)相比,它们对
顺铂诱导的雪貂性呕吐和束缚应激诱导的大鼠粪便排出量增加的抑制作用要强数百倍。三维分子建模研究表明,对映体的 "手性选择 "可能受到芳香环部分与构象受限的 4, 5, 6, 7-四氢-1H-
苯并咪唑环在 "赤道-扭转 "构象之间的立体斥力的影响。在我们的 5-HT3 受体拮抗剂药代动力学模型中,从羰基氧原子向上的芳香环部分看,基本中心位于芳香-羰基平面的左侧,而在以前提出的模型中,"手性 "是模糊的。