Altering the Sex Pheromone Cyclo(l-Pro-l-Pro) of the Diatom Seminavis robusta towards a Chemical Probe

As a major group of algae, diatoms are responsible for a substantial part of the primary production on the planet. Pennate diatoms have a predominantly benthic lifestyle and are the most species-rich diatom group, with members of the raphid clades being motile and generally having heterothallic sexual reproduction. It was recently shown that the model species Seminavis robusta uses multiple sexual cues during mating, including cyclo(l-Pro-l-Pro) as an attraction pheromone. Elaboration of the pheromone-detection system is a key aspect in elucidating pennate diatom life-cycle regulation that could yield novel fundamental insights into diatom speciation. This study reports the synthesis and bio-evaluation of seven novel pheromone analogs containing small structural alterations to the cyclo(l-Pro-l-Pro) pheromone. Toxicity, attraction, and interference assays were applied to assess their potential activity as a pheromone. Most of our analogs show a moderate-to-good bioactivity and low-to-no phytotoxicity. The pheromone activity of azide- and diazirine-containing analogs was unaffected and induced a similar mating behavior as the natural pheromone. These results demonstrate that the introduction of confined structural modifications can be used to develop a chemical probe based on the diazirine- and/or azide-containing analogs to study the pheromone-detection system of S. robusta.

Mg-Catalyzed OPPenauer Oxidation—Application to the Flow Synthesis of a Natural Pheromone

The so-called OPPenauer oxidation is well known for its ability to oxidize valuable alcohols into their corresponding aldehydes or ketones. In particular, it has proven to be extremely successful in the oxidation of sterols. On the other hand, its application—in the original formulation—to the obtainment of ketones outside the field of steroids met a more limited success because of less favorable thermodynamics and side reactions. To circumvent these issues, the first example of magnesium-catalyzed OPPenauer oxidation is described. The oxidation of primary and secondary alcohol was performed using pivaldehyde or bromaldehyde as the oxidant and cheap magnesium tert-butoxide as catalyst. Decent to excellent yields were obtained using reasonable catalytic charge. The synthesis of a pheromone stemming from the Rhynchophorus ferrugineus was obtained by tandem addition-oxidation of 2-methylpentanal and the process was successfully applied to continuous flow on a multigram scale.

Evidence of Pheromone Catabolism Via β-Oxidation in the European Corn Borer (Lepidoptera: Crambidae)

Experiments were conducted using tritiated European corn borer, Ostrinia nubilalis (Hübner), pheromone, (Z)-[11,12-3H2]-11-tetradecen-1-ol acetate, a tritiated fluorinated analog of the European corn borer pheromone, 2-fluoro-(Z)-[11,12-3H2]-11-tetradecen-1-ol acetate, and methyl-4-bromocrotonate (MBC) to determine if pheromone catabolism proceeds on the moth's antennae via the β-oxidation pathway of fatty acid degradation. When antennae were treated with tritiated natural pheromone plus MBC (a precursor of the known β-oxidation inhibitor, 4-bromocrotonic acid), catabolism of the pheromone was significantly inhibited. When the 2-fluoro pheromone analog was applied alone to antennae, it was hydrolyzed to the corresponding alcohol but was not degraded. MBC had no effect on catabolism of the 2-fluoro analog, and 2-fluoro substitution inhibited entrance of the compound into β-oxidation. These results demonstrate that β-oxidation is the primary oxidative pathway by which pheromone is degraded on the antennae of European corn borer moths.

SENSITIVITY OF BLUEBERRY LEAFTIER MOTHS (LEPIDOPTERA: TORTRICIDAE) (KEARFOTT) TO THEIR OWN SEX PHEROMONE: MATING BIOASSAY, ELECTROANTENNOGRAM, AND TRAP ATTRACTANCY STUDIES

A mating suppression bioassay, an electroantennogram study, and a lure attractancy study demonstrated the sensitivity of the Croesia curvalana (Kft.) moth to the female sex pheromone. Mating suppression of 98% was achieved with source concentrations of 30 μg of either (E)- and (Z)-11-tetradecenal (95:5) or the natural pheromone blend of (E)- and (Z)-11-tetradecenal (90:10) + (E)- and (Z)-11-tetradecenyl acetate (85:15) (aldehyde:acetate = 9:1), and was 60% with a source concentration of 0.6 μg. Source concentrations of the minor component acetate, ranging from 15 to 0.6 μg, produced mating suppressions of from 78 to 38%. Male antennae responded to source concentrations of 2 × 10−10 mg (E)- and (Z)-11-tetradecenal (90:10) and antennal saturation occurred at 2 × 10−4 mg. Little female response was found at any age. Polyvinyl chloride lures releasing 1–2 ng/h captured males at approximately the same rate as did virgin moths. Release rates as low as 8 ng/h reduced trap capture from the 4 ng/h release rate found to be most effective under prevailing environmental conditions using Pherocon 1C traps. Results from these studies suggest C. curvalana could be a candidate for pheromone-based field mating suppression.