Pavel Šebek

First semi-synthetic preparation of sex pheromones

Here we describe the first construction of a genetically modified plant (GMP) with the ability to produce moth sex pheromone precursors. Previously prepared (Svatos et al., Czech Patent Appl. 2000/0125) N. tabacum GMP transformed with a plasmid encoding cabbage looper moth (Trichoplusia ni, Hubner, Lepidoptera, Noctuidae) acyl-CoA Δ11-(Z)-desaturase (Knipple et al., Proc. Natl. Acad. Sci. USA, 1998, 95, 15287) showed a substantial presence (ca. 6%) of the potential pheromone precursor, methyl (11Z)-hexadec-11-enoate (1). The ester 1 was isolated in bulk (6.5% of extracted lipids) from a greenhouse cultivated transgenic tobacco and the corresponding acetate, which are principal components of a large number of sex pheromones, was semi-synthetically prepared from the in planta produced pheromone precursor. The attractiveness of the prepared blends for moth, Mamestra brassica was proved in field trials.

New mimics of the acetate function in pheromone-based attraction

Several analogues of (Z)-8-dodecenyl acetate (1a), the major pheromone component of the Oriental fruit moth, Cydia molesta, with chloroformate and lactone functional groups in place of the acetate moiety, were synthesized and investigated for their biological activity at four evaluation levels, i.e. by electroantennography (EAG), electrosensillography (ESG), short-range sexual stimulation and activation in the flight-tunnel. We found very strict requirements on the shape as well as on the electron distribution of the acetate group for a productive interaction with the receptor. The behavioral results showed that, among the analogues investigated, the chloroformate 1b, alken-4-olide 2a and also dodecyl acetate (1c) possess significant (60-85%) inhibitory activities. Based on electrophysiological evidence demonstrating that (i) only 1b is competing with the major pheromone component 1a for the same receptor sites on the male antennal sensilla, (ii) 1c elicits moderate EAG but no ESG responses and (iii) 2a does not produce any electrophysiological response at all, three possible inhibitory mechanisms by which these analogues are acting could be distinguished.

Substituted 2,4,4,6-tetraphenyl-4H-selenopyrans: preparation, photocolouration and 4H-selenopyran ring geometry; an X-ray and DFT calculation study

1,5-Diaryl-3,3-diphenylpentane-1,5-diones 3a–d react with Al2Se3–HCl–AcOH reagent to give the 2,6-diaryl-4,4-diphenyl-4H-selenopyrans 4a–d in satisfactory yields while the same procedure starting from 1,5-diketone 5 affords small amounts of spiroheterocycle 6. 2,4,4,6-Tetraphenyl-4H-selenopyran 4a can be brominated or nitrated at positions 3 and 5 to give substituted derivatives 7–9. Dibromo derivatives 4c and 7 were converted with copper(I) cyanide to dicyano derivatives 4e and 10,11, respectively. Similarly to 4H-pyrans 1 and 4H-thiopyrans 2, the 1-selena analogues 4a–d and 8 exhibit solid state photocolouration which was investigated in terms of dispersive first-order reaction kinetics. The influence of selenium heteroatom on the geometry of the heterocyclic ring of molecules 4a,c and 6 is discussed on the basis of X-ray structure determinations, quantum DFT and semiempirical PM3 calculations.