Semiochemicals containing lepidopteran sex pheromones: Wonderland for a natural product chemist

Abstract

Since the first identification of bombykol, sex pheromones of about 700 moth species have been elucidated. Additionally, field evaluations of synthetic pheromones and their related compounds have revealed the male attraction of another 1,300 species. These pheromones and attractants are listed on the web-sites, "Pheromone Database, Part I." Pheromone components are classified according to their chemical structures into two major groups (Types I and II) and miscellaneous. Based on our previous review published in 2004, studies reported during the last two decades are highlighted here to provide information on the structure characteristics of newly identified pheromones, current techniques for structure determination, new enantioselective syntheses of methyl-branched pheromones, and the progress of biosynthetic research. Besides the moth sex pheromones, various pheromones and allomones from many arthropod species have been uncovered. These semiochemicals are being collected in the "Pheromone Database, Part II." The chemical diversity provides a wonderland for natural product chemists.

Keywords: Lepidoptera; SN2 reaction; chemical ecology; diagnostic ions; epoxidase; structural diversity.

Fig. 1. Formulas and abbreviations of representative lepidopteran sex pheromones, Type I, Type II, and other compounds.

Fig. 2. Taxonomy and pheromone studies of insects in the superfamily of Noctuoidea. The numbers before and after + in parentheses in each group indicate the total number of species whose female sex pheromone and male attractant have been reported, respectively. Each mark after the group name indicates that some species within the group produces a pheromone component of Type I (☆ with a common functional group, ★ with a novel functional group), Type II (▲), or others (※). (This figure is a significant revision of Fig. 2 in Ref. due to the change in the classification of Noctuoidea).

Fig. 3. Sex pheromones identified from female lichen moths.

Fig. 4. Infrared spectra obtained by GC/FT-IR of the pheromone components of Monema flavescens, (A) and (C), and synthetic geometric isomers, (B) and (D), and band chromatograms of pheromone extracts; M. flavescens (E) and Parasa lepida (F).

Fig. 5. Preparation of epoxy derivatives from E4,Z6,Z9-trienes (A), Z6,Z9,E11-trienes (B), and Δ1,Z3,Z6,Z9-tetraenes (C), and their diagnostic fragment ions for the GC/MS analysis. See mass spectra of Suppl. Fig. S4 for the epoxydienes from E4,Z6,Z9-21:H, Supplemental Fig. S5 for the epoxydienes from Z6,Z9,E11-21:H, and Supplemental Fig. S6 for the epoxytrienes from Δ1,Z3,Z6,Z9-21:H.

Fig. 6. Notable chiral synthons for enantioselective syntheses of methyl-branched pheromones (A) and new synthetic approaches using chiral propylene oxide, (B) and (C).

Fig. 7. Biosynthetic pathways for methyl-branched pheromones of Arctiinae moths (A), the gypsy moth (B), the smaller tea tortrix (C), the storage mite (D), and the lichen moth (E). The pathways of (C) and (E) are putative.