Molecular networking-guided isolation of linearly fused prenylated indole diketopiperazine alkaloids from a marine-derived fungus Aspergillus sp. MG35-18 and their anti-inflammatory effects.

This study described the isolation and structural characterization of four novel linearly fused prenylated indole diketopiperazine alkaloids (1-4) alongside four known analogues from the marine-derived fungus Aspergillus sp. MG35-18, guided by LC-MS/MS-based molecular networking. These compounds are characterized with a rare [3,2-f] indole-pyrano fused ring system. Structural elucidation was achieved through HR-ESI-MS and comprehensive 1D and 2D NMR analyses, including 1H, 13C, 1H1H COSY, HSQC, and HMBC spectroscopy. Furthermore, the stereochemistry of new compounds 1-4 was determined via NOESY correlations, electronic circular dichroism (ECD) calculation, Marfey's method and comparison with literature data. Subsequent anti-inflammatory activity assessments revealed that compounds 4-8, particularly 6, exhibited significant inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) overproduction in murine macrophage RAW264.7 cells at 20 μM. Moreover, no cytotoxicity was observed at the tested concentration. Notably, compound 6 demonstrated potent inhibitory effects on LPS stimulated release of NO, interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) in a dose-dependent manner, suggesting its promising anti-inflammatory potential.