Chiral methyl-branched pheromones

Insect pheromones are some of the most interesting natural products because they are utilized for interspecific communication between various insects, such as beetles, moths, ants, and cockroaches. A large number of compounds of many kinds have been identified as pheromone components, reflecting the diversity of insect species. While this review deals only with chiral methyl-branched pheromones, the chemical structures of more than one hundred non-terpene compounds have been determined by applying excellent analytical techniques. Furthermore, their stereoselective syntheses have been achieved by employing trustworthy chiral sources and ingenious enantioselective reactions. The information has been reviewed here not only to make them available for new research but also to understand the characteristic chemical structures of the chiral pheromones. Since biosynthetic studies are still limited, it might be meaningful to examine whether the structures, particularly the positions and configurations of the branched methyl groups, are correlated with the taxonomy of the pheromone producers and also with the function of the pheromones in communication systems.

A plant factory for moth pheromone production

Moths depend on pheromone communication for mate finding and synthetic pheromones are used for monitoring or disruption of pheromone communication in pest insects. Here we produce moth sex pheromone, using Nicotiana benthamiana as a plant factory, by transient expression of up to four genes coding for consecutive biosynthetic steps. We specifically produce multicomponent sex pheromones for two species. The fatty alcohol fractions from the genetically modified plants are acetylated to mimic the respective sex pheromones of the small ermine moths Yponomeuta evonymella and Y. padella. These mixtures are very efficient and specific for trapping of male moths, matching the activity of conventionally produced pheromones. Our long-term vision is to design tailor-made production of any moth pheromone component in genetically modified plants. Such semisynthetic preparation of sex pheromones is a novel and cost-effective way of producing moderate to large quantities of pheromones with high purity and a minimum of hazardous waste.

Synthesis of the sex pheromone of the citrus mealybug, Pseudococcus cryptus

The sex pheromone of the citrus mealybug (Pseudococcus cryptus), [(1R,3R)-3-isopropenyl-2,2-dimethylcyclobutyl]methyl 3-methyl-3-butenoate, was synthesized from (+)-alpha-pinene in five operational steps in a 43% overall yield. The synthetic pheromone was identical with the natural pheromone in (1)H-NMR and mass spectroscopic properties, and showed almost the same pheromonal activity as the natural pheromone.

Synthesis of the four components of the female sex pheromone of the painted apple moth, Teia anartoides

Four pheromone components of the female painted apple moth (Teia anartoides), an Australian insect pest, were synthesized. These were (Z)-6-henicosen-11-one (1), (6Z, 8E)-6,8-henicosadien-11-one (2), (Z)-cis-9,10-epoxy-6-henicosene (3), and (Z)-cis-9,10-epoxy-6-icosene (4). 2-Dodecanone was converted to 1 and 2, and both the enantiomers of 3 and 4 were synthesized from the enantiomers of 4-tert-butyldimethylsilyloxy-cis-2,3-epoxy-1-butanol.

New synthesis of serricornin, the female sex pheromone of the cigarette beetle

Serricornin [(4S,6S,7S)-7-hydroxy-4,6-dimethyl-3-nonanonel, the female sex pheromone of Lasioderma serricorne, was synthesized by starting from (2S,4S)-2,4-dimethyl-1,5-pentanediol that had been obtained by lipase-catalyzed enantiomer separation of its racemate.

Synthesis of the enantiomers of some methyl-branched cuticular hydrocarbons of the ant, Diacamma sp

The enantiomers of 3-methylpentacosane, 3-methylheptacosane, 3-methylnonacosane, 13-methylheptacosane, and 5-methylheptacosane were synthesized by starting from the enantiomers of 2-methylbutyl bromide or citronellol. These methyl-branched alkanes are the characteristic components of the cuticular hydrocarbons of queen of the ant, Diacamma sp..

Organic synthesis and chemical ecology

The roles of organic synthesis in chemical ecology are discussed, with many examples. The structure, including the absolute configuration, of a semiochemical (signal substance) can be established by enantioselective synthesis. Only through synthesis can a semiochemical be obtained in an amount sufficient for decisive biological evaluation. Rigorous enantioselective synthesis of semiochemicals to provide their pure enantiomers has shown that they are not always enantiomerically pure. Synthesis of the stereoisomers of semiochemicals has clarified their structure-bioactivity relationships to reveal the unprecedented diversity in the stereochemical aspects of pheromone communications.