Chemistry of the Androconial Secretion of the Ithomiine Butterfly Oleria onega

摘要

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 occurrence uncertain. Nevertheless, its reactivity makes it a good candidate for a signaling compound, because its rapid degradation can be used to convey spatial and temporal information. In addition, several other compounds, likely used in intraspecific communication, were identified. All of 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.