Chemistry of the Androconial Secretion of the Ithomiine Butterfly Oleria onega
Résumé
Ithomiine butterflies use pyrrolizidine alkaloids (PAs) as precursors for male
pheromones, such as dihydropyrrolizines or lactones. In contrast to most other ithomiine genera,
none of these compounds have ever been detected in Oleria species. The absence of these
compounds is thought to be the result of limited access to PA-containing plants. Here we
investigate the contents of the androconia of Oleria onega caught in the wild when PA containing
plants were abundant. Although the PA lycopsamine was detected in the hairpencils, none of the
other known PA-derived compounds were present. Instead, the unsubstituted core of the PA necine
base, 1-methylene-1H-pyrrolizine (13), a very unstable compound, was found. The identity of this
compound was proven by synthesis. Although its formation in nature appears very likely, 13 is
also formed during GC analysis of PAs, making its natural formation ambiguous. Nevertheless, its
reactivity makes it a good candidate for a signaling compound, because its rapid degradation can
be used for transporting spatial and time information. In addition, several other compounds, likely
used in intraspecific communication, were identified. All these compounds are reported for the
first time as natural products or from insects. These include 9-hydroxynonanoic acid (21) and (Z)-
9-hydroxy-6-enoic acid (18), as well as their condensation products with 11-hexadecenoic- and
octadecenoic acids. Furthermore, self-condensation products, such as (Z)-9-[(9-hydroxynon-6-
enoyl)oxy]- and 9-[(9-hydroxynonanoyl)oxy]nonanoic acid and non-6-enoic acids (35, 36, 38, 40)
were identified, together with the known compounds 2-heptadecanol (39) and 6,10,14-
trimethylpentadecan-2-ol (37). In summary, O. onega appears to lack enzymes to produce
dihydropyrrolizines. In stark contrast to other ithomiine genera, a unique blend of oxidized fatty
acids seems to be used instead.
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