Sulfur-Containing Phenolic Compounds from the Cave Soil-Derived Aspergillus fumigatus GZWMJZ-152

Six new sulfur-containing phenolic compounds (1–6) and their putative metabolic precursors (7–9) were isolated from the cave soil-derived fungus Aspergillus fumigatus GZWMJZ-152. Compound 1 represents an unusual benzophenone–diketopiperazine hybrid via a thioether linker, while compound 2 contains a naturally rare sulfoxide group. Both compounds 2 and 3 were initially isolated as racemic mixtures and then purified as the enantiomerically pure (+)-2, (−)-2, (+)-3, and (−)-3, respectively. Their structures, including absolute configurations, were elucidated by spectroscopic analysis, X-ray diffraction, and the calculations of electronic circular dichroism. The antioxidant activity of compounds 1–9 was evaluated based on oxygen radical absorbance capacity, 2,2-diphenyl-1-picrylhydrazyl radical scavenging, and the protective effect on the PC12 cell line against H₂O₂-induced damage. Compounds 5–7 and 9 showed radical-scavenging activity against 2,2-diphenyl-1-picrylhydrazyl free radicals with the IC₅₀ values of 3.45 ± 0.02, 23.73 ± 0.08, 18.90 ± 0.16, and 17.27 ± 0.15 μM, respectively. Compounds (±)-2, 4, 7, and 8 exhibited potent antioxidant capacity with oxygen radical absorbance capacity values of 1.73 ± 0.13, 1.65 ± 0.03, 6.14 ± 0.35, and 1.55 ± 0.04 μmol TE/μmol, respectively. Compounds (±)-2 and (±)-3 also exhibited protective effects on oxidative injury of PC12 cells induced by H₂O₂.