21-Hydroxyoligomycin A is an oligomycin antibiotic co-isolated with nemadectins from the thermotolerant Streptomyces soil isolate S451. Originally considered a nemadectin compound, 21-Hydroxyoligomycin A is structurally distinct and synthesized by a separate pathway from the nemadectins. 21-Hydroxyoligomycin A has been described to demonstrate nematocidal, antifungal, and antitumor effects.