X-ray Diffraction, Solution Structure, and Computational Studies on Derivatives of (3-<i>sec</i>-Butyl-2,3-dihydro-1<i>H</i>-isoquinolin-4-ylidene)acetic Acid: Compounds with Activity as Calpain Inhibitors

A thorough experimental and computational study of derivatives of (3-sec-butyl-2,3-dihydroisoquinolin-4-ylidene)acetic acid was performed. Some of these compounds are calpain inhibitors and could be useful as therapeutic agents, since this enzyme is a Ca2+-dependent cysteine protease involved in a wide variety of metabolic and physiological processes, whose over-activation is associated to several pathological conditions. To gain a better understanding of the structure−activity relationships, a structural analysis was carried out with 1H and 13C NMR spectroscopy and DFT calculations together with the X-ray diffraction data of three compounds. The solid state structures showed that the crystal packing as well as the intermolecular interactions depend on the substituent nature of the COOR group. Also, the reactivity of the exocyclic double bond was theoretically evaluated, finding that the more reactive compound is the most potent inhibitor of calpain (IC50 = 25 nM).本研究对(3-仲丁基-2,3-二氢异喹啉-4-亚基)乙酸的衍生物开展了系统的实验与计算研究。其中部分化合物属于钙蛋白酶（calpain）抑制剂，有望作为治疗制剂应用；因该酶属于钙依赖型半胱氨酸蛋白酶，参与诸多代谢与生理过程，其过度激活与多种病理状态密切相关。为深入解析结构-活性关系（structure-activity relationships），本研究结合三种化合物的X射线衍射数据，通过氢谱（¹H NMR）、碳谱（¹³C NMR）核磁共振波谱法以及密度泛函理论（Density Functional Theory，DFT）计算开展了结构分析。固态结构分析结果表明，晶体堆积方式与分子间相互作用均取决于COOR基团的取代基性质。此外，本研究还对环外双键的反应活性开展了理论评估，结果发现反应活性越强的化合物，其钙蛋白酶抑制活性越高，其中活性最优的化合物半最大抑制浓度（IC₅₀）为25 nM。