Abstract
Fifteen subspecies of the wood tiger moth, Arctia plantaginis (Lepidoptera: Erebidae: Arctiinae), have been recorded in the Northern Hemisphere. An analysis of crude pheromone extracts by GC equipped with an electroantennographic (EAG) detector showed four EAG-active components (Comps. I–IV) that were commonly involved in the pheromone glands of two subspecies inhabiting Japan and Finland. Comp. I is a major component (>75%) and the others are minor components (3% - 15%). Their mass spectra, measured by GC/MS, revealed the chemical structures of C21 unsaturated hydrocarbons as follows: 3,6,9-triene for Comp. I, 4,6,9-triene for Comp. II, 1,3,6,9-tetraene for Comp. III, and 2,4,6,9-tetraene for Comp. IV. Comps. I and III are known Type II pheromone compounds, and their retention times coincide with those of the authentic standards with all Z configurations. As a next step, the extract was analyzed by GC/FT-IR to determine the configuration of Comps. II and IV. Their IR spectra showed two characteristic C-H bending absorptions around 990 and 945 cm-1 due to the conjugated dienyl moieties; thus, Z and E configurations were assigned to the double bonds at the 2- and 4-positions, respectively. Their Z double bonds at the 6- and 9-positions are indicated by no absorptions around 970 cm-1, due to the isolated double bonds with E configurations. Finally, the structures of Comps. II and IV were confirmed by synthesis using a double Wittig reaction. The synthetic (4E,6Z,9Z)-4,6,9-triene and (2Z,4E,6Z,9Z)-2,4,6,9-tetraene showed strong EAG activity, and their chemical data coincided well with those of the natural Comps. II and IV, indicating the correctness of the structure determination by GC/FT-IR analysis and its usefulness for Type II pheromone compounds.
Highlights
Lepidopteran sex pheromones, which have been identified from more than 670 species, are mainly sorted into two types according to their chemical structures [1] [2] [3]
The extract was analyzed by gas chromatography (GC)/FT-IR to determine the configuration of Comps
To increase the information about the Japanese species, we started to investigate a sex pheromone of the wood tiger moth, Arctia plantaginis, which belongs to Arctiini
Summary
Lepidopteran sex pheromones, which have been identified from more than 670 species, are mainly sorted into two types according to their chemical structures [1] [2] [3]. Sex pheromones of 23 species in the tribe Arctiini have been reported, and the pheromones of 16 of these species are composed of Type II compounds [5]. GC-EAD can differentiate biologically active compounds from others in the crude extract, and chemical structures of the pheromone candidates are identified by GC/MS [8] The sensitivity of both instruments is so high that a pheromone gland extract of one female sometimes provides enough information to clarify the chemical cues when compared with published data of known compounds. Geometrical isomers of alkenyl compounds with a straight chain usually show different infrared (IR) spectra, and their configurations can be determined by examining the absorptions of C-H stretching and bending at the double bond. We successfully applied the same instrument to determine the structure of novel Type II compounds occurring in the pheromone glands of the wood tiger moth
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