Neoantimycin is a rare and unusual ring-extended member of the antimycin class. Neoantimycin is produced by a Streptomyces species unrelated to antimycin-producing strains. Literature references to neoantimycin are limited but the recent discovery of the closely related metabolite, prunustatin A, as a selective GRP78 molecular chaperone down-regulator highlights the potential of this class as research probes.