Five New Cantharidin Derivatives from the Insect Mylabris cichorii L. and Their Potential against Kidney Fibrosis In Vitro

Five new monoterpenoids including three 1-hydroxymethyl-2-methyl cantharimide-type derivatives (1, 2, and 5) and two 1,2-dimethyl cantharimide-type derivatives (3 and 4), together with three known compounds (6–8) were isolated from the insect Mylabris cichorii Linnaeus. The structures of these new compounds, including their absolute configurations, were characterized by detailed analysis of NMR, chemical derivatization, and quantum chemical ECD calculations. All of the compounds were tested for their biological activity against kidney fibrosis. The results revealed that compounds 2, 4, and 7 could inhibit kidney fibrosis in vitro at 40 μM by inhibiting the expression of fibronectin and collagen I in TGF-β1-induced NRK-52e cells.