Muscarinic receptor agonists are characterized by apparently strict restraints on their tertiary or quaternary amine and their distance to an ester or related center. On the basis of the active state crystal structure of the muscarinic M₂ receptor in complex with iperoxo, we explored potential agonists that lacked the highly conserved functionalities of previously known ligands. Using structure-guided pharmacophore design followed by docking, we found two agonists (compounds 3 and 17), out of 19 docked and synthesized compounds, that fit the receptor well and were predicted to form a hydrogen-bond conserved among known agonists. Structural optimization led to compound 28, which was 4-fold more potent than its parent 3. Fortified by the discovery of this new scaffold, we sought a broader range of chemotypes by docking 2.2 million fragments, which revealed another three micromolar agonists unrelated either to 28 or known muscarinics. Even pockets as tightly defined and as deeply studied as that of the muscarinic reveal opportunities for the structure-based design and the discovery of new chemotypes.

中文翻译：

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基于结构的新M ₂受体激动剂的设计和发现

毒蕈碱受体激动剂的特征在于，它们的叔胺或季胺及其与酯或相关中心的距离显然受到严格限制。基于毒蕈碱M ₂受体与吡咯酮复合的活性状态晶体结构，我们探索了缺乏先前已知配体高度保守的功能的潜在激动剂。使用结构引导的药效团设计，然后对接，我们在19种对接和合成的化合物中发现了两种激动剂（化合物3和17），它们与受体非常吻合，并被预测会在已知的激动剂中形成保守的氢键。结构优化导致化合物28的效价比其母体3高4倍。由于发现了这种新型支架，我们对接了220万个片段，寻求了更广泛的化学型，这揭示了另外三种与28种毒蕈碱或已知毒蕈碱无关的微摩尔激动剂。甚至像毒蕈碱一样严格定义和深入研究的口袋也揭示了基于结构的设计和发现新化学型的机会。