Discovery of Tetrasubstituted Pyrazines As Semiochemicals in a Sexually Deceptive Orchid

Abstract

Sexually deceptive orchids employ mimicry of insect sex pheromones to exploit a diverse group of pollinators. The chemical structures of five semiochemicals (1-3, 7, 8) produced by populations of the warty hammer orchid, Drakaea livida, pollinated by a thynnine wasp in the genus Catocheilus were elucidated. With the exception of (2,5-dimethylpyrazin-3-yl)methyl 3-methylbutanoate (7), all active compounds were tetrasubstituted pyrazines, including hydroxymethyl (1) and ester (2 and 3) trimethylpyrazine derivatives. Male Catocheilus wasps were responsive to all of these compounds in GC-EAD experiments.

Allelochemicals in Plant–Insect Interactions

“…The flowers have been found to release 2-ethyl-5-propylcyclohexane-1,3-dione, called chiloglottone (29), which is responsible for attracting male wasps and is also produced by female wasps as a sex pheromone. 141 In addition to sex pheromone analogues, certain orchid species mimic insect alarm pheromones in their floral scents. Although both wasps are attracted to dummies scented with chiloglottone, N. cryptoides more preferred those located at higher position from the ground than N. monticola did.…”

Mismatch in the distribution of floral ecotypes and pollinators: insights into the evolution of sexually deceptive orchids

“…Given that long‐range attraction in sexually deceptive orchids is achieved by floral odour (Kullenberg, ; Stoutamire, ; Borg‐Karlson, ; Phillips et al ., ) and there is no perceptible difference in floral morphology or colour to human eyes, we predict that population‐level differences in pollinator attraction are underpinned by differences in floral odour composition. Evidence supporting this prediction is found in Drakaea livida , where two recently discovered ecotypes appear to exhibit different floral odour composition, with different chemical compound being detected by their respective pollinator species (as measured by GC‐EAD; Bohman et al ., ,b). However, the attraction of Z. gilesi to both ecotypes of D. concolor indicates that there is some overlap in the floral odour composition of the ecotypes.…”

“…All species of Drakaea are pollinated exclusively by the sexual deception of thynnine wasps (Hopper & Brown, ; Phillips et al ., ). In Drakaea glyptodon , pollinator attraction is achieved using a specific blend of three alkylpyrazines and one hydroxymethyl pyrazine (Bohman et al ., ), with structurally related pyrazines also found in Drakaea livida (Bohman et al ., ,b). In Drakaea, the pollination process requires both attraction to the flower and an attempt by the wasp to fly off with the hinged insectiform labellum (Fig.…”

Oxidation of hydroxymethylpyrazines and hydroxylated phenyl compounds in a gas chromatography inlet

“…In several species the key compounds were identied as hydroxymethylpyrazines -a largely new group of natural products. [32][33][34][35] In the process of identifying these compounds, we also found various amounts of the corresponding aldehyde compounds in some analyses. When the compounds were prepared synthetically in the laboratory, and aer purication with semi-preparative high pressure liquid chromatography (HPLC), and subsequent analyses by GC-MS, various amounts of aldehydes were still present.…”

“…[32][33][34][35], and 7-8 from Sigma-Aldrich Australia. For structures of compounds 1-8 see The purity of all compounds were conrmed to >98% by HPLC, and these compounds are known to be stable when stored as solutions in acetonitrile or dichloromethane at room temperature for weeks (unpublished data).…”