4’-Acetylchrysomycin A and its co-metabolite, 4’-acetylchrysomycin B, were isolated during a screen for antitumor agents. Acetylation of chyrsomycin A reduces cytotoxicity, although both are highly potent (IC50s 64 μg ml-1 for 4'-acetylchrysomycin A and B, respectively.