A synthetic dodecanolide library for the identification of putative semiochemicals emitted by mantellid frogs

Aliphatic macrolides are used by various organisms as semiochemicals or pheromones, e.g. by the endemic Madagascan frog family Mantellinae. Volatile, methyl-branched aliphatic macrolides occur in various species, but their identification by MS is difficult, while isolation is not possible due to the low amounts produced. Therefore, we synthesized a library of methyl-branched 11-dodecanolides to identify unknown macrolides secreted by Gephyromantis moseri, a mantelline frog restricted to the rainforest and characterized by largely terrestrial habitats. The syntheses used metal-organic epoxide opening and ring-closing-metathesis as key steps. All library members 2-, 4-, 6-, 8-, and 10-methyl-11-dodecanolide were thus identified as part of the secretion by comparison of their mass spectra and their gas chromatographic retention indices. These compounds comprise new natural products.