Aede de Groot

Qualitative and quantitative variation among volatile profiles induced by Tetranychus urticae feeding on plants from various families.

Many plant species are known to emit herbivore-induced volatiles in response to herbivory. The spider mite Tetranychus urticae Koch is a generalist that can feed on several hundreds of host plant species. Volatiles emitted by T. urticae-infested plants of 11 species were compared: soybean (Glycine max), golden chain (Laburnum anagyroides), black locust (Robinia pseudo-acacia), cowpea (Vigna unguiculata), tobacco (Nicotiana tabacum), eggplant (Solanum melalonga), thorn apple (Datura stramonium), sweet pepper (Capsicum annuum), hop (Humulus lupulus), grapevine (Vitis vinifera), and ginkgo (Ginkgo biloba). The degree to which the plant species produced novel compounds was analyzed when compared to the odors of mechanically damaged leaves. Almost all of the investigated plant species produced novel compounds that dominated the volatile blend, such as methyl salicylate, terpenes, oximes, and nitriles. Only spider mite-infested eggplant and tobacco emitted a blend that was merely quantitatively different from the blend emitted by mechanically damaged or clean leaves. We hypothesized that plant species with a low degree of direct defense would produce more novel compounds. However, although plant species with a low direct defense level do use indirect defense to defend themselves, they do not always emit novel compounds. Plant species with a high level of direct defense seem to invest in the production of novel compounds. When plant species of the Fabaceae were compared to plant species of the Solanaceae, qualitative differences in spider mite-induced volatile blends seemed to be more prominent in the Fabaceae than in the Solanaceae.

Leaf surface compound fromBrassica oleracea (Cruciferae) induces oviposition byPieris brassicae (Lepidoptera: Pieridae)

SummaryChemicals present on the surface of cabbage (Brassica oleracea L.) leaves were extracted by dipping these leaves for 3 s in dichloromethane followed by a 3 s dip in methanol. When offered in dual choice bioassays using green paper cards as a substrate, the methanol extract stimulated oviposition activity byPieris brassicae L. (Lepidoptera: Pieridae) females. The oviposition stimulant was isolated using medium pressure liquid chromatography, reversed-phase HPLC, ion-pair HPLC and ion exchange chromatography. Using1H-NMR spectroscopy, the stimulant could be identified as glucobrassicin (3-indolyl-methyl-glucosinolate). When pure glucobrassicin was offered at a dose identical to that in the crude methanol extract, butterflies did not discriminate between these two substrates in a dual choice test. It is argued that a high sensitivity for indole glucosinolates as host recognition factors may confer an adaptive value for these specialist crucifer feeders. The nutritional significance of their precursor tryptophan and the non-volatile nature of the aglycones formed upon enzymic hydrolysis in damaged tissues are proposed as properties of indole glucosinolates that contribute to this possible adaptive advantage.

Biosynthesis of costunolide, dihydrocostunolide, and leucodin. Demonstration of cytochrome P450-catalyzed formation of the lactone ring present in sesquiterpene lactones of chicory

Chicory (Cichorium intybus) is known to contain guaianolides, eudesmanolides, and germacranolides. These sesquiterpene lactones are postulated to originate from a common germacranolide, namely (+)-costunolide. Whereas a pathway for the formation of germacra-1(10),4,11(13)-trien-12-oic acid from farnesyl diphosphate had previously been established, we now report the isolation of an enzyme activity from chicory roots that converts the germacrene acid into (+)-costunolide. This (+)-costunolide synthase catalyzes the last step in the formation of the lactone ring present in sesquiterpene lactones and is dependent on NADPH and molecular oxygen. Incubation of the germacrene acid in the presence of18O2 resulted in the incorporation of one atom of 18O into (+)-costunolide. The label was situated at the ring oxygen atom. Hence, formation of the lactone ring most likely occurs via C6-hydroxylation of the germacrene acid and subsequent attack of this hydroxyl group at the C12-atom of the carboxyl group. Blue light-reversible CO inhibition and experiments with cytochrome P450 inhibitors demonstrated that the (+)-costunolide synthase is a cytochrome P450 enzyme. In addition, enzymatic conversion of (+)-costunolide into 11(S),13-dihydrocostunolide and leucodin, a guaianolide, was detected. The first-mentioned reaction involves an enoate reductase, whereas the formation of leucodin from (+)-costunolide probably involves more than one enzyme, including a cytochrome P450 enzyme.

Insect antifeedant activity of clerodane diterpenes and related model compounds

A comprehensive compilation of all test results on the insect antifeedant activity of clerodane diterpenes and related model compounds is reported. To increase the compatibility of data from different sources, some of the results reported in the literature have been converted into a standardized form. The compounds were sorted into groups according to the different types of sidechain attached to C-9. Despite the wealth of information, collected in 15 tables, it remains difficult to assign importance to separate structural elements in relation to the observed antifeedant activity. A detailed analysis of the structure-activity relationships could not be presented, but some interesting trends can be distinguished based on the structures of the strongest antifeedants. The compilation covers the literature up to December 2001.

High-performance liquid chromatographic method for the analysis of anthraquinone glycosides and aglycones in madder root (Rubia tinctorum L.).

A HPLC method has been developed for the simultaneous characterisation of anthraquinone glycosides and aglycones in extracts of Rubia tinctorum L. The anthraquinones are separated on an end-capped C18-RP column with a water–acetonitrile gradient as eluent and measured with UV detection at 250 nm. With this method the glycosides lucidin primeveroside and ruberythric acid and the aglycones lucidin, alizarin, purpurin, quinizarin and 2,6-dihydroxyanthraquinone can be analysed. Lucidin which is not commercially available was synthesised starting from resorcinol and phthalic anhydride. The glycosides ruberythric acid and lucidin primeveroside are commercially available as a mixture and were separated by droplet counter-current chromatography in ascending flow with chloroform–methanol–water as eluents prior to their use as standards.

Germacrenes from fresh costus roots

Four germacrenes, previously shown to be intermediates in sesquiterpene lactone biosynthesis, were isolated from fresh costus roots (Saussurea lappa). The structures of (+)-germacrene A, germacra-1(10),4,11(13)-trien-12-ol, germacra-1(10),4,11(13)-trien-12-al, and germacra-1(10),4,11(13)-trien-12-oic acid were deduced by a combination of spectral data and chemical transformations. Heating of these compounds yields (-)-beta-elemene, (-)-elema-1,3,11(13)-trien-12-ol, (-)-elema-1,3,11(13)-trien-12-al, and elema-1,3,11(13)-trien-12-oic acid respectively, in addition to small amounts of their diastereomers. Acid induced cyclisation of the germacrenes yields selinene, costol, costal, and costic acid respectively. It is highly probable that the elemenes reported in literature for costus root oil are artefacts.

The synthesis of mono- and dihydroxy aromadendrane sesquiterpenes, starting from natural (+)-aromadendrene-III

Abstract The monoalcohols (−)-globulol ( 2 ), (−)-epiglobulol ( 3 ), (−)-ledol ( 4 ), and (+)-viridiflorol ( 5 ) were synthesized from (+)-aromadendrene ( 1 ). The cis-fused alloaromandedrone ( 14 ), the key intermediate used in the synthesis of 4 and 5 , was obtained from the trans-fused apoaromadendrone ( 13 ) via a selective protonation of the thermodynamic enol trimethylsilylether 15 . After hydroxylation of the tertiary C11 of 13 with RuO 4 , (+)-spathulenol ( 6 ), (−)-allospathulenol ( 7 ), and the aromadendrane diols 8 – 11 could be prepared. Compounds 2 – 11 were tested for antifungal properties, but their activity was only moderate.

The synthesis of Ambrox®-like compounds starting from (+)-larixol

Abstract The oxidation of the (3-hydroxy-3-methyl-4-pentenyl)-side chain at C(9) of some labdanic diterpenoids with potassium permanganate was investigated. Triols, ketones, or cyclic enol ethers are the main reaction products, strongly influenced by the substituent at C(8). Further degradation of the methyl ketones by the Baeyer–Villiger reaction and modification of the exocyclic 8(17) double bond lead to suitable intermediates, which have been transformed into Ambrox®-like compounds. Synthetic routes using palladium catalyzed elimination or isomerization of allylic acetates, followed by ozonolysis have been developed as well for shortening of the side chain of (+)-larixol. Products from both routes have been cyclized to 6α-hydroxy Ambrox®. This compound was used as the key intermediate for the synthesis of several other Ambrox®-like compounds of which some showed pleasant odour properties.

The conversion of (-)- and (+)-dihydrocarvone into chiral intermediates for the synthesis of (-)-polygodial, (-)-warburganal and (-)-muzigadial.

Abstract (−)-Dihydrocarvone was converted into (−)-(4aR, 8aR)-3,4,4a,5,6,7,8,8a-octahydro-4a, 8,8-trimethylnaphthalene-2(H)-one (1) via an efficient route in which a Wolff-Kishner reduction, accompanied with a double bond isomerisation brought on a major simplification. Ketone 1 is a suitable intermediate for the syntheses of the insectantifeedants (−)-polygodial and (−)-warburganal. (+)-Dihydrocarvone was converted into (+)-(4aR, 7S, 8aR)-4a,7-dimethyl-8-methylene-3, 4,4a,5,6,7,8,8a-octahydronaphthalene-2(1H)-one (2), an intermediate ketone for the synthesis of (−)-muzigadial.

Colony formation in Scenedesmus: a literature overview and further steps towards the chemical characterisation of the Daphnia kairomone

Semiochemicals play an important role in interactions between living organisms in aquatic environments. Although the presence of chemical cues is confirmed in more and more systems, the chemical structures remain predominantly elusive. To create more accurate prey–predator interaction models and to advance the research on chemical communication, it is essential to identify these compounds. A literature overview of cues involving Daphnia (either as producer or receiver) is given and the progress towards their isolation and structure elucidation is described. Most of the research so far has concentrated on the elucidation of kairomones produced by predators of Daphnia (especially Chaoborus and several species of fish). Although some progress has been made, these cues have not been isolated and identified yet. Additionally new results on the isolation and identification of the kairomone responsible for the colony formation in Scenedesmus using differential diagnosis and bioassay-directed fractionation of Daphnia exudates are presented. The importance of suitable and well performing bioassays herein cannot be underestimated. Some preliminary results with solid-phase extraction with C18 proved to be reproducible for extracting the active compound from Daphnia water, although it was not possible to get the biological activity into a single fraction. The cue was not extractable with an anion exchanger (SAX). Subjecting the extract to HPLC led to one active fraction.