LC–MS/MS-guided discovery of japonamides C and D, two new cyclohexadepsipeptides, from the Nicotiana tabacum-derived endophytic fungus Aspergillus japonicus TE-739D

Endophytic fungi belonging to the <i>Aspergillus</i> genus have received substantial attention due to their notable secondary metabolic potential. In this study, chemical investigations using LC-MS/MS-based molecular networking on the endophytic fungus <i>Aspergillus japonicus</i> TE-739D led to the discovery of two new cyclohexadepsipeptides, namely japonamides C (<b>1</b>) and D (<b>2</b>), along with three known cyclodipeptides (<b>3</b>-<b>5</b>). Their structures, including the absolute configurations of the amino acid residues, were elucidated through spectroscopic data analysis and an optimized Marfey's method. The newly discovered compounds, japonamides C (<b>1</b>) and D (<b>2</b>), were screened for broad-spectrum cell proliferation inhibitory activity against 20 different human cell lines. The results indicated that both compounds displayed broad-spectrum antiproliferative activity against MKN-45, HCT116, TE-1, 5,637, CAL-62, and A-637 cells, with inhibition rates ranging from 55.0 to 72.3%. Moreover, the antibacterial activity of compounds <b>1</b>-<b>5</b> against two Gram-positive bacteria and two Gram-negative bacteria was also evaluated.