Acetylaszonalenin (LL-S490β) is a benzodiazepine metabolite first isolated from an uncharacterised strain of Aspergillus by Ellestad and co-workers at American Cyanamid (now Pfizer) in 1973 in the search for biologically active secondary metabolites. Acetylaszonalenin was re-discovered by Kimura and co-workers as a co-metabolite of aszonalenin in 1982. The biological role and pharmacology of acetylaszonalenin have received little attention to date.