Abstract
Nine undescribed side chain containing azaphilones, pestaphilones A-I, were isolated from the Anoectochilus roxburghii endophytic fungus Pestalotiopsis oxyanthi. The structures of these isolates were identified by spectroscopic data, electronic circular dichroism (ECD) calculations and comparisons, quantum-chemical C-13 NMR calculations with DP4+ probability analysis, Rh-2(OCOCF3)(4)-induced ECD, acetonide formation, selective oxidation reaction and X-ray crystallographic data. Structurally, pestaphilones A-I were the first azaphilones characteristically formed via a methyl group at C-9 in the C-7 side chain. More importantly, a selective oxidation reaction was firstly set up to resolve the absolute configuration of flexible side chain containing azaphilones, and an acetonide formation based Rh-2(OCOCF3)(4)-induced ECD experiment was performed to identify the configurations of the oxygenated pyranoquinone core in the azaphilones. In bioassay, pestaphilones A-F displayed potential immunosuppressive activity in concanavalin A (Con A)-induced T lymphocyte proliferation, with IC50 values ranging from (9.36 +/- 1.14) mu M to (35.21 +/- 3.25) mu M.
NSTL
Elsevier