Diphenylemestrins A-E: diketopiperazine-diphenyl ether hybrids from Aspergillus nidulans

A chemical investigation of secondary metabolites (SMs) from Aspergillus nidulans resulted in the identification of five novel dioxopiperazine (DKP)-diphenyl ether hybrids, designated as diphenylemestrins A-E (1-5). These compounds 1-5 represent the first known dimers combining DKP and diphenyl ether structures, with compound 4 featuring an uncommon dibenzofuran as the diphenyl ether component. The structural elucidation and determination of absolute stereochemistry were accomplished through spectroscopic analysis and electronic circular dichroism (ECD) calculations. Notably, diphenylemestrin C (3) exhibited moderate cytostatic activity against NB4 cells, with a half maximal inhibitory concentration (IC₅₀) value of 21.99 μmol·L^-1, and induced apoptosis at higher concentrations.