Isolation, absolute configurations and bioactivities of pestaphilones A–I: Undescribed methylated side chain containing-azaphilones from Pestalotiopsis oxyanthi

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 13C NMR calculations with DP4+ probability analysis, Rh2(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 C7 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 Rh2(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) μM to (35.21 ± 3.25) μM.