Identification and synthesis of volatile compounds from pheromone glands of tropical frogs

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Volatile chemical signals of Amphibia are currently not well investigated. The chemistry of gular and femoral glands of the African frog families Mantellidae and Hyperoliidae will be in the focus of the project. Males of both families possess such glands that contain volatile compounds. The chemistry of these often complex gland bouquets is unusual. Macrocyclic lactones dominate in the Mantellidae, while sesquiterpenes are the major components of the hyperoliid gular glands. Many of these compounds are new and have unprecedented structures. In the project the structural elucidation of the gland constituents will be performed using organic-analytical methods and the derived structural proposals will be verified by synthesis. The low amounts of material and the complex bouquets often prohibit the use of common nuclear magnetic resonance (NMR) spectroscopic methods for structural elucidation. Therefore, different methods will be used that have not been combined in this manner before for structure verification of gland constituents. Besides classical methods like gas chromatography/mass spectrometry (GC/MS) and microderivatizations of extracts, highly sensitive gas chromatography/infrared spectroscopy (GC/FT-IR) and calculation of infrared spectra by density functional theory methods (DFT) will be used. In addition, sesquiterpene hydrocarbons will be transformed reductively or oxidatively and the resulting material will be compared to derivatized extracts. This procedure will lead to structural proposals that have to be verified by organic synthesis. The follow-up synthesis will deliver material for behavioral testing and for other biological assays. During the first funding period especially mantellids were investigated. The hyperoliids will be the major focus of the second funding period. The gular glands of these frogs are only innervated during the breeding season. This opens the possibility to perform transcriptomic analysis of these glands to look for putative sesquiterpene cyclases. These cylases will then be heterologously expressed in cooperation to enable characterization of so far poorly investigated vertebrate sesquiterpene cyclases.About 80 species of both families were investigated during the first funding period and several new structures were identified and synthesized. These results are the basis for the second funding period. After structural identification of many of the unknown gland constituents, a comparative analysis will give insight into evolution, function and diversification of the communication chemistry in these highly diversified, species rich frog families.