失眠是现代社会常见病，现有药物有一定疗效但副作用明显，不能满足临床需要。褪黑素(MT)受体激动剂是新型镇静催眠药物研究热点，可避免苯二氮卓类药物的依赖性和戒断症状。已有MT受体激动剂均为合成化合物，结构类似，亟需开发结构类型多样的天然来源激动剂。中药钩藤镇静催眠疗效确切，当前研究主要针对降压活性和生物碱成分，未见其关于MT受体活性报道。我们首次发现钩藤提取物具MT1受体激动活性，并从一活性部位分离得到系列活性黄烷醇，特别是儿茶素和3-O-甲基儿茶素对MT1受体的激动率为287.97%和157.35%，且剂量依赖性好，EC50分别为12.9和29.4μM，值得深入研究。本研究在此基础上，通过活性跟踪和LCMS分析继续开展钩藤活性成分的导向分离和结构优化，以期发现MT1/MT2受体高活性/高选择性激动剂，进行动物体内镇静催眠药效评价，为天然来源新型镇静催眠先导化合物的发现提供化学和药理学基础。

Insomnia is a symptom characteristic by difficulty initiating and maintaining sleep and associated with daytime consequences. Many factors can cause insomnia which is typically secondary to medical, psychiatric, circadian, or sleep disorders, and can also be a primary disorder. Sedative and hypnotic medicines are the main therapeutic means for insomnia in clinical, however their efficacy is unsatisfied due to the obvious side effects including dependence and withdrawal syndrome. Increasing clinical evidences suggest that melatonin receptor (MT1 and MT2) agonists represent a novel therapeutic approach for the treatment of sleep disturbances. However, the currently reported melatonin receptor agonists are exclusively synthetic compounds which show highly structural similarity with melatonin. Therefore, naturally derived melatonin receptor agonists with diverse skeletons are urgently needed. Gou-Teng (Uncaria rhynchophylla) is a famous traditional Chinese herb used for the treatment of convulsion, hypertension, epilepsy, eclampsia, and cerebral diseases. The main chemical constituents of Gou-Teng are indole alkaloids, flavonoids, triterpenoids and organic acids, of which the indole alkaloids as the characteristic constituents are correspondent to the hypotensive effect. In contrast, the sedative and hypnotic constituents of Gou-Teng are still disputed. Our previous investigation manifested that the total extract of U. rhynchophylla showed agonistic effect on MT1 receptor with an agonistic rate of 100.48 % (400 μg/mL). In order to clarify the active constituents, the subsequent investigation resulted in five flavanols, three triterpenoids, and two steroids from A-1-3, and eight indole alkaloids from A-2. The following bioassay on HEK-293 cell line in vitro indicated that the flavanols showed high agonistic effect on MT1 receptor, of which catechin (1) and 3-O-methylcatechin (3) exhibited the highest agonistic rates with the EC50 values of 12.90 and 29.40 μM. Preliminary structure-activity relationship (SAR) investigation suggested that the 2,3-cis form was prior to the trans-form. This is the first time to characterize the agonistic effects of Gou-Teng and the correspondent active constituents. Therefore, further investigation on Gou-Teng will be very significant for searching natural melatonin receptor agonists. In this project, systematically bioassay and LCMS guided isolation, chemical modification and SAR investigation will be conducted on the active constituents of Gou-Teng, by which the high active and selective leading compounds (MT1/MT2 agonists) will be further evaluated for the sedative and hypnotic efficacy in vivo. The successful implementation of this project (if granted) will provide scientific basis for developing natural melatonin receptor agonists as new sedative and hypnotic leading compounds.