褪黑素（MT）受体主要包括MT1和MT2两种亚型，是多种疾病的潜在治疗靶点。MT受体激动剂成药前景广阔，然而当前报道的激动剂主要为人工合成化合物，结构类似，受体选择性（特别是MT1）不理想。立足我国丰富的中药资源，发现类型多样的MT受体天然激动剂具有较高的可行性。我们首次揭示赤芍和牡丹皮具有MT受体激动活性，并从活性部位分离得到一对新颖降二萜和系列活性单萜，首次发现蒎烷型单萜芍药内酯苷在1mM浓度下，对MT1和MT2受体的激动率分别为120%和89%，EC50值分别为76和117μM，提示五元内酯环是重要活性位点。本研究将在前期基础上，借助活性跟踪和LCMS分析继续开展赤芍和牡丹皮中活性成分的导向分离，综合运用有机合成、肝微粒体转化、肠道菌群代谢等手段，构建MT受体天然/类天然激动剂化合物库，对高活性化合物开展抗抑郁药效评价，为基于MT受体的新型抗抑郁先导化合物的发现奠定化学和药理学基础。

Melatonin (MT) receptors mainly including MT1 and MT2 subtypes are the action sites of the endogenous hormone, melatonin. MT1 and MT2 receptors widely distributed in the central nervous system and peripheral tissues are promising targets for treating central nervous system diseases (e.g. depression, anxiety, sleep disorders), type 2 diabetes mellitus, tumors and pains. With the MT1 and MT2 receptors being cloned in the mid-1990s, hundreds of ligands were synthesized and evaluated for agonistic activities. Currently, several MT receptor-mediated drugs, e.g., ramelteon, tasimelteon, and agomelatine have been on the market for the treatment of depression and sleep disorders. However, the currently reported melatonin receptor agonists are almost synthetic compounds which show highly structural similarity with melatonin. Therefore, naturally derived melatonin receptor agonists with diverse skeletons are urgently needed. Traditional Chinese herbs have been used for medicinal purposes in China for thousands of years, which are fascinating sources for drug discovery. In our previous investigation, the total extracts of Chi-Shao (Paeonia veitchii) and Mu-Dan-Pi (P. suffruticosa) were revealed with agonistic activities on MT1 and MT2 receptors. Subsequent bioassay- and LCMS-guided investigation resulted in two novel norditerpenes, (±)-paeoveitol and a series of pinane-type monoterpenes from the active parts of P. veitchii. In particular, albiflorin showed potent activities on both MT1 and MT2 receptors, with agonistic rates of 120.5 and 89.2% at the concentration of 1mM, according to the assay on HEK293 cell line in vitro. The following dose-effect studies provided the EC50 values of 75.8 and 116.9 μM for MT1 and MT2 receptors, respectively. The preliminary structure–activity relationships study indicated the importance of the lactone unit. In this project, systematically bioassay and LCMS guided isolation will be applied to reveal the active constituents of Chi-Shao and Mu-Dan-Pi. Furthermore, diverse derivatives will be synthesized by chemical modification, liver microsomes and intestinal microbiota to establish the drug-like libraries. The most potent compounds will be further evaluated for anti-depressant efficacy in vivo. The successful implementation of this project (if granted) will provide scientific basis for the discovery of new anti-depressant leading compounds from natural resources.