The main viral protease (Mpro) of SARS-CoV-2 provides an excellent target for antivirals, due to its essential and conserved function in the viral replication cycle. We reported in this study, the SARS-CoV-2 main protease inhibitory effect of twelve compounds isolated from D. caloneura and P. erinaceus together with four derivatives. Among the effectively tested samples, two derivatized compounds displayed significant improvement on the activity from the starting material, friedelin (1) through the acetoreduced (2) to the acetoxy product (3) with respective IC50 values of 42.89, 29.69 and 19.39 µg/mL. The latter displayed the highest activity although lower as compared to that of baicalein, the positive control with IC50 0.41 µg/mL. The molecular docking study showed that an increase in the number of hydrogen bonds between compounds and active site of Mpro resulted in increased inhibition.

中文翻译：

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大戟科植物Discoglypremna caloneura (Pax) Prain和豆科紫檀(Pterocarpus erinaceus Poir)茎皮中的SARS-CoV-2主要蛋白酶抑制剂及其分子对接研究

SARS-CoV-2 的主要病毒蛋白酶 (Mpro) 由于其在病毒复制周期中的重要且保守的功能，为抗病毒药物提供了极好的靶标。我们在这项研究中报道了从 D. caloneura 和 P. erinaceus 中分离的 12 种化合物以及 4 种衍生物对 SARS-CoV-2 主要蛋白酶的抑制作用。在有效测试的样品中，两种衍生化合物显示出从起始材料木聚糖 (1) 通过乙酰还原 (2) 到乙酰氧基产物 (3) 的活性显着改善，IC50 值分别为 42.89、29.69 和 19.39 µg/mL 。后者显示出最高的活性，但与阳性对照黄芩素相比较低，IC50 为 0.41 µg/mL。分子对接研究表明，化合物与 Mpro 活性位点之间氢键数量的增加导致抑制作用增强。