Bohumír Koutek

Volatiles released from oak, a host tree for the bark beetle Scolytus intricatus

Volatile compounds emitted in different phases of oak (Quercus robur) development (bark, unopened buds, young developing leaves, and blossoms) were analyzed with the aim of finding possible host-plant attractants for the European oak bark beetle, Scolytus intricatus. Complex mixtures of aliphatic, aromatic, and terpenoid compounds were identified in the samples. (E)-2-Hexenal and hexanal dominated in samples of bark. In buds, (Z)-3-hexenyl acetate formed a substantial part of the mixture. In both leaves and blossoms (E,E)-alpha-farnesene was the main component.Volatiles released from oak twigs and branches during both the maturation feeding and construction of maternal galleries by Scolytus intricatus were also analyzed. Most compounds found in the samples from females and males maturation feeding were identical. High contents of anisole, (E)-beta-ocimene, alpha-copaene, one unidentified sesquiterpenic hydrocarbon C(15)H(24) and beta-caryophyllene were found in both samples of twigs attacked by beetles. During the construction of maternal galleries by bark beetles in oak logs, monoterpene hydrocarbons such as p-cymene, (E)-beta-ocimene, and gamma-terpinene, and sesquiterpenes alpha-copaene and beta-caryophyllene were released in large quantities. No new compound appeared when males were added to the log with feeding females.

Comparison of methods employing gas chromatography retention data to determine vapour pressures at 298 K

Validity of five models suggested for expressing the relationship between vapour pressures and GC retention times measured on a non-polar capillary column were tested on a common set of compounds [five homologous series of the type H-(CH2)n-Y, where Y denotes Cl, Br, CHO, OCOCH3 and COOCH3, and n varies from 6 to 14]. Standard methods of statistical analysis, as well as vapour pressure values obtained independently from direct vapour pressure measurements were used as validity criteria. For the 40-compound data set examined, the methods provided vapour pressures agreeing within 9.2-24.7% (average absolute percent error) with direct experimental data.

Profiling and characterization of volatile secretions from the European stink bug Graphosoma lineatum (Heteroptera: Pentatomidae) by two-dimensional gas chromatography/time-of-flight mass spectrometry.

An efficient method combining the headspace solid-phase microextraction (HS-SPME) sampling procedure and comprehensive two-dimensional gas-chromatography/time-of-flight mass spectrometry (GC×GC/TOF-MS) was established to study the volatile secretion components of stink bugs (Heteroptera: Pentatomidae). The combined power of this approach is illustrated by the identification of fifty-seven compounds in the secretion of a European stink-bug representative, Graphosoma lineatum. (E)-4-oxohex-2-enal and (E)-dec-2-enal were found to be the major components in the adult bug secretions followed by lower amounts of n-alkenal (C₅-C₁₂), n-alkenyl acetate (C₅-C₁₁), n-alkane (C₁₁-C₁₇) homologs, dienals and other compounds. More than thirty known compounds have been identified that had not been described before in G. lineatum adults. Of these compounds, (E)-4-oxohex-2-enal is of particular interest, since its isolation and identification, while calling some previous reports into question, clearly demonstrates a potential ability of our approach to yield artifact-free secretion profiles.

Gas chromatographic determination of vapour pressures of pheromone-like compounds IV. Acetates, a reinvestigation

Abstract The equilibrium vapour pressures P and enthalpies of vaporization ΔH for an acetate series with carbon numbers varying from 10 to 18 were determined using a GC technique. The P and ΔH quantities at 298.15 K were calculated for more than 100 (un)saturated linear-chain compounds based on the experimental retention time measurements of the test acetates and five reference alkane standards with known vapour pressures. The advantage of utilizing several standards in the GC based vapour pressure determinations was demonstrated by comparison with previously published data. Additionally, empirical equations were developed for correlating 1n P and ΔH with the number of carbon atoms ( N ) and double bond positions (Δ) in the chain. It was shown that with these two-parameter equations the vapour pressures of acetates can be predicted with a considerable degree of confidence. In the case of E 2-, E 3- and Z 4-alkenyl acetate isomers, however, anomalies in retention time/vapour pressure-structure relationships were observed, indicating specific types of polar interactions.

Analysis of European oak bark beetle (Scolytus intricatus) extracts using hyphenated and chiral chromatography techniques

Two bioactive compounds, viz. 4-methylheptan-3-ol (I) and 4-methylheptan-3-one (II) have been identified in European oak bark beetle (Scolytus intricatus) extracts by gas chromatography coupled with mass spectrometric and electroantennographic detector systems. Further examination of these compounds using gas chromatography on chiral stationary phases, as well as a comparison with optically active standards proved the absolute configuration of the identified compounds to be (3R,4S)-I and (S)-II. The discovery of (3R,4S)-I and (S)-II as insect-produced compounds in both sexes of S. intricatus constitutes the first reported occurrence in this species.

Chemical constituents of Stereum subtomentosum and two other birch-associated basidiomycetes: an interspecies comparative study.

Metabolites of the wood‐rotting fungus Stereum subtomentosum Pouzar (Basidiomycetes, order Russulales, family Stereaceae) occuring on birch (Betula pendula Roth) trees were phytochemically investigated for the first time. Three main metabolite chemotypes present in MeOH extracts of the fruit bodies, viz. steroids, fatty acids, and water‐soluble sugars, were fractionated, isolated, and identified by 1D/2D NMR‐spectroscopic analyses, NMR data comparisons, and chemical correlations combined with GC/MS experiments. Thirteen compounds including two 5α,8α‐epidioxy steroids, α,α′‐trehalose, D‐arabinitol, D‐mannitol, and saturated/unsaturated fatty acids, were identified. Differences among S. subtomentosum and two other birch‐associated fungal species, Trametes versicolor (L.: Fr.) Pilát, and Piptoporus betulinus (Bull.: Fr.) P. Karst (Basidiomycetes, order Polyporales, family Polyporaceae) were evaluated as regards the richness and abundance relationships in metabolite profiling.

The role of beetle and host volatiles in host colonization in the European oak bark beetle, Scolytus intricatus (Ratzeburg) (Col., Scolytidae)

Abstract:u2002 To understand the role of chemical signals involved in Scolytus intricatus (Ratzeburg) (Col., Scolytidae) host colonization, the attractiveness of intact and beetle colonized host material was investigated in the field and in the laboratory. In the field, chemical signals operating at long range were investigated by means of sticky traps. In the laboratory, close‐range chemical interactions were investigated with an arena olfactometer. Field experiments showed no differences in the attractiveness between infested and non‐infested host material. On the contrary, laboratory experiments revealed higher attractiveness of infested host and beetle‐produced frass in comparison with intact host and mechanically produced sawdust respectively. Laboratory data also disclosed the attractiveness of beetle extracts of both sexes. Our data show that: (1) host kairomones play an important role during host colonization, and that (2) S. intricatus does not use a sex‐specific secondary attractant system. Differences between results of field and laboratory trials are discussed.

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.

Intital water content and lipase-mediated ester formation in hexane

Lipase biocatalysis was investigated as a tool for the production of esters by two model reactions, esterification of 1-butanol with 2-methyl-1-pentanoic acid and irreversible transesterification between 2-methyl-1-pentanol and vinyl acetate. The reactions were carried out in hexane using lipases from Candida cylindracea and porcine pancreas. The initial water content influenced both the yield of the ester and the enantioselectivity of the reaction (esterifica-tions) or the ester formation only (transesterifications).

A convenient synthesis of trans-sabinene hydrate from (−)-3-thujol via a highly selective ene reaction of singlet oxygen

trans-Sabinene hydrate (1), was synthesized from (−)-3-thujol (2) in four steps. The key step was the selective formation of trans-2-hydroxy-3-thujene (6) by photooxygenation of a 3:1 mixture of 2- and 3-thujenes (4 and 5) obtained from (−)-3-thujol mesylate (3). Hydrogenation of 6 gave compound 1 in 46% overall yield.