6H-Isoindolo[2,1-a]indoles (5, 7, 10, 13), 5,6-dihydroindolo[2, 1-a]isoquinolines (20, 21), and 6,7-dihydro-5H-benzo[c]azepino[2, 1-a]indoles (23, 25, 27, 30) have been prepared as melatonin analogues to investigate the nature of the binding site of the melatonin receptor. The affinity of analogues was determined in a radioligand binding assay using cloned human mt(1) and MT(2) receptor subtypes expressed in NIH 3T3 cells. Agonist and antagonist potency was measured using the pigment aggregation response of a clonal line of Xenopus laevis melanophores. The 2-methoxyisoindolo[2, 1-a]indoles (7a-d) showed much higher binding affinities than the parent isoindoles (5a-e), and whereas 7a-c were agonists in the functional assay, 7d and 5a-e were antagonists. The 2-ethoxyisoindolo[2,1-a]indoles (10a-d) showed reduced binding affinities compared to their methoxy analogues, while the 5-chloro derivative 13 showed a considerable reduction in binding affinity and potency compared to 7a. The 10-methoxy-5,6-dihydroindolo[2, 1-a]isoquinolines (21a-c) had higher binding affinities than the corresponding parent indoloisoquinolines (20a-c) in the human receptor subtypes, and the parent compounds were antagonists whereas the 10-methoxy derivatives were agonists in the functional assay. The N-cyclobutanecarbonyl derivatives of both the parent (20d) and 10-methoxyl (21d) series had similar binding affinities and were both antagonists with similar potencies. The 11-methoxy-6, 7-5H-benzo[c]azepino[2,1-a]indoles (25a-d) had higher binding affinities than the corresponding parent compounds (23a-d) at the MT(2) receptor but similar affinities at the mt(1) site; all of the compounds were antagonists in the functional assay. Changing 11-methoxy for 11-ethoxy decreased the binding affinity slightly, and this was more evident at the MT(2) receptor. All of the derivatives investigated had either the same or a greater affinity for the human MT(2) receptor compared to the mt(1) receptor (range 1:1-1:132). This suggests that the mt(1) and MT(2) receptor pockets differ in their ability to accommodate alkyl groups in the indole nitrogen region of the melatonin molecule. Two compounds (7c and 25c) were tested in functional assays on recombinant mt(1) and MT(2) melatonin receptors. Compound 7c is a potent agonist with some selectivity (44-fold) for the MT(2) receptor, while 25c is an MT(2)-preferring antagonist. Increasing the carbon chain length between N-1 of indole and the 2-phenyl group from n = 1 through n = 3 leads to a fairly regular decrease in the binding affinity, but, remarkably, when n = 3, it converts the methoxy compounds from melatonin agonists to antagonists. The Xenopus melatonin receptor thus cannot accommodate an N-n-alkyl chain attached to a 2-phenyl substituent with n > 2 in the required orientation to induce or stabilize the active receptor conformation.

中文翻译：

---

映射褪黑激素受体。6.衍生自6H-异吲哚并[2,1-a]吲哚，5,6-二氢吲哚并[2,1-a]异喹啉和6,7-二氢-5H-苯并[c] azepino [2]的褪黑素激动剂和拮抗剂，1-a]吲哚。

6H-异吲哚并[2,1-a]吲哚（5，7，10，13），5,6-二氢吲哚并[2，1-a]异喹啉（20，21）和6,7-二氢-5H-苯并[c] azepino [2，1-a]吲哚（23，25，27，30）已制成褪黑激素类似物，以研究褪黑激素受体结合位点的性质。使用在NIH 3T3细胞中表达的克隆的人mt（1）和MT（2）受体亚型在放射性配体结合测定中确定类似物的亲和力。使用非洲爪蟾（Xenopus laevis）黑色素细胞克隆系的色素聚集反应来测量激动剂和拮抗剂的效力。2-甲氧基异吲哚并[2,1-a]吲哚（7a-d）与母体异吲哚（5a-e）相比具有更高的结合亲和力，而7a-c在功能测定中是激动剂，7d和5a-e是拮抗剂。2-乙氧基异吲哚[2，与它们的甲氧基类似物相比，1-a]吲哚（10a-d）的结合亲和力降低，而与7a相比，5-氯衍生物13的结合亲和力和效价大大降低。在人类受体亚型中，10-甲氧基-5,6-二氢吲哚并[2,1-a]异喹啉（21a-c）的结合亲和力高于相应的母体吲哚异喹啉（20a-c），并且母体化合物是拮抗剂10-甲氧基衍生物是功能测定中的激动剂。母体（20d）和10-甲氧基（21d）系列的N-环丁烷羰基衍生物具有相似的结合亲和力，并且都是具有相似效力的拮抗剂。11-甲氧基-6，7-5H-苯并[c]氮杂环庚烷[2，1-a]吲哚（25a-d）在MT（2）受体处的结合亲和力高于相应的母体化合物（23a-d），但在mt（1）位点具有相似的亲和力；在功能测定中，所有化合物均为拮抗剂。将11-甲氧基更改为11-乙氧基会稍微降低结合亲和力，这在MT（2）受体上更为明显。与mt（1）受体相比，所有研究的衍生物对人MT（2）受体的亲和力相同或更高（范围1：1-1：132）。这表明mt（1）和MT（2）受体口袋在褪黑激素分子的吲哚氮区域中容纳烷基的能力不同。在重组mt（1）和MT（2）褪黑激素受体的功能测定中测试了两种化合物（7c和25c）。化合物7c是一种有效的激动剂，对MT（2）受体具有一定的选择性（44倍），而25c是首选MT（2）的拮抗剂。从n = 1到n = 3增加吲哚的N-1和2-苯基之间的碳链长度会导致键合亲和力有规律地下降，但是，当n = 3时，它会转化为甲氧基化合物从褪黑激素激动剂到拮抗剂。因此，非洲爪蟾褪黑激素受体不能适应以n> 2的方向连接到2-苯基取代基上的Nn-烷基链，诱导或稳定活性受体构象的方向是必需的。它将褪黑激素激动剂中的甲氧基化合物转化为拮抗剂。因此，非洲爪蟾褪黑激素受体不能适应以n> 2的方向连接到2-苯基取代基上的Nn-烷基链，诱导或稳定活性受体构象的方向是必需的。它将褪黑激素激动剂中的甲氧基化合物转化为拮抗剂。因此，非洲爪蟾褪黑激素受体不能适应以n> 2的方向连接到2-苯基取代基上的Nn-烷基链，诱导或稳定活性受体构象的方向是必需的。