Large Macrocyclic Lactones as Specific Cuticular Lipids of <i>Eueides</i> Butterflies

Linear long-chain hydrocarbons are common constituents of the outer cuticle of most insects. These cuticular hydrocarbons form the first barrier to the environment, preventing desiccation, but also play important roles in communication among many insects, transporting, for example, information on species, sex, or physiological state. <i>Eueides</i> is a genus of heliconiine butterflies, a group known for their complex mimicry systems. We report here the identification and synthesis of large macrocyclic lactones from the cuticles of five <i>Eueides</i> species, which largely replace the hydrocarbons. These lactones have chain lengths of 23-34 and ring sizes of 17-29. They occur in <i>Eueides</i> but not in other closely related genera such as <i>Heliconius</i>, <i>Dryas</i>, <i>Dryadula</i>, <i>Agraulis,</i> or <i>Dione</i>. Each species has a specific mixture of macrocyclic lactones. These unique bouquets may be used in species recognition, as visual cues may be unreliable in mimicry rings. We identified 43 different compounds using GC/MS, GC/IR, and enantioselective synthesis via ring-closing metathesis and Jacobsen hydrolytic kinetic resolution. The absolute configuration could not be determined because these lactones were not separable by gas chromatography on chiral phases.