Lignans and [11]-chaetoglobosins from Pseudeurotium bakeri and their immunosuppressive activity

Two previously unreported lignans (1-2) and four undescribed [11]-chaetoglobosins (3-6) were obtained from the culture extract of an endophytic fungus Pseudeurotium bakeri P1-1-1. Their structures with absolute configurations were determined by spectroscopic data analysis, single-crystal X-ray diffraction, electronic circular dichroism (ECD) calculations, the modified Mosher's method, and Mo₂(OAc)₄-induced electronic circular dichroism (ICD) experiments. Compounds 5 and 6 showed moderate cytotoxic effects against seven human cancer cell lines. Compounds 2-4 exhibited immunosuppressive activities on concanavalin A-induced T cell proliferation with IC₅₀ values of 3.7, 3.4, and 14.5 μM, and on lipopolysaccharide-induced B cell proliferation with IC₅₀ values of 4.1, 3.9, and 14.2 μM, respectively. Further investigation revealed that 2 and 3 induced apoptosis in activated T cells in a dose-dependent manner.