21-Hydroxyoligomycin A is a rare member of the oligomycin class isolated as a co-metabolite of nemadectin, hence its original naming as nemadectin omega. Only limited literature references to this metabolite are available. However, in-house testing suggests that 21-hydroxyoligomycin has a more selective action against mammalian tumor cell lines than oligomycin A, exhibiting only weak antifungal and nematocidal activity.