Novel Diketopiperazine Dihydroorotate Dehydrogenase Inhibitors Purified from Traditional Tibetan Animal Medicine Osteon Myospalacem Baileyi

Traditional Tibetan medicine provides an abundant source of knowledge on human ailments and their treatment. As such, it is necessary to explore their active single compounds used to treat these ailments to discover lead compounds with good pharmacologic properties. In this present work, animal medicine, Osteon Myospalacem Baileyi extracts have been separated using a two‐dimensional preparative chromatographic method to obtain single compounds with high purity as part of the following pharmacological research. Five high‐purity cyclic dipeptides from chromatography work were studied for their dihydroorotate dehydrogenase inhibitory activity on recombinant human dihydroorotate dehydrogenase enzyme and compound Fr. 1‐4 was found to contain satisfying inhibition activity. The molecular modeling study suggests that the active compound Fr. 1‐4 may have a teriflunomide‐like binding mode. Then, the energy decomposition study suggests that the hydrogen bond between Fr. 1‐4 and Arg136 can improve the binding mode to indirectly increase the van der Waals binding energy. All the results above together come to the conclusion that the 2, 5‐diketopiperazine structure group can interact with the polar residues well in the active pocket using electrostatic power. If some proper hydrophobic groups can be added to the sides of the 2, 5‐diketopiperazine group, it is believed that better 2, 5‐diketopiperazine dihydroorotate dehydrogenase inhibitors will be found in the future. In this article, we found a natural dihydroorotate dehydrogenase (DHODH) inhibitor by multi‐dimensional chromatography and in vitro Homo sapiens recombinant dihydroorotate dehydrogenase inhibition assay. Then, the binding mode of this compound with its receptor DHODH was studied. It is found that the binding mode of this compound was very similar with that of positive control teriflunomide. This compound could serve as a lead compound and more diketopiperazine skeleton DHODH inhibitors could be found.