Abstract
Iridolactone, isolated from Iridomyrmex nitidus Mayr., is shown to be the lactone of α-(2-hydroxymethyl-3-methylcyclopentyl)propionic acid and is identical with isoiridomyrmecin. Structural and configurational relationships of iridomyrmecin and of isoiridomyrmecin with the nepetalinic acids are discussed.