Spirohexenolide A is a spirotetronate isolated from Streptomyces platensis by Burkart and co-workers in 2013 as a potent antitumor agent. The original strain of S. platensis did not produce spirohexenolide A but the metabolite emerged on subsequent mutagenesis and media optimisation. Spirohexenolide A is a previously unknown tetracyclic metabolite with a 15-membered macrocyclic tetronic acid, most closely related to the 13-membered macrocyclic tetronic acids, tetromycins A and B. Spirohexenolide A was recently reported to modulate the action of human macrophage migration inhibitor factor (hMIF).