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Synthesis of model compounds derived from natural clerodane insect antifeedants

Insect antifeedants are compounds with the ability to reduce or inhibit insect feeding without directly killing the insect. Such compounds offer a number of properties that are highly desirable in environmentally friendly crop protection agents. Although the principle of insect control using antifeedants has been shown to work under field conditions, practical application of these compounds has until now been limited to a few examples, mainly consisting of extracts of the Neem tree containing the highly potent tetranortriterpene azadirachtin.One of the factors hampering the introduction of insect antifeedants in crop protection is the limited availability of many of these compounds, which prevents their widespread application at low cost. In efforts to solve these availability problems, synthetic approaches might provide an alternative to the isolation of antifeedants from natural sources. Since the total synthesis of natural insect antifeedants usually is too long and complex for this purpose, a more practical approach would be to develop simplified analogues, which have retained as much of the desired biological properties as possible. Apart from being potential crop protection agents themselves, such analogues may also serve as model compounds to investigate structure-activity relationships and thus to provide a basis for the design of more potent synthetic insect antifeedants.The class of neo -clerodane diterpenes has attracted considerable attention as a source of natural insect antifeedants. In the present thesis, neo -clerodane diterpenes as clerodin, ajugarin I and teucjaponin B were chosen as starting points in a search for potentially active model compounds. From the literature it is known that both halves of these molecules ( i.e. the decalin-fragment and the C-9 sidechain) are involved in the bioactivity of these diterpenes. Both parts separately also display antifeedant activity, but these fragments are much less potent than their parent compounds and are therefore unsuitable candidates for practical application. However, model compounds that consist of structural features from both halves soon become complicated themselves and were therefore considered to be an unpractical approach towards simplified bioactive analogues. Instead, we decided to focus our attention upon the C-9 sidechains of these molecules and to investigate the possibility to optimize the activity of such fragments.In the search for modifications that could enhance the activity of clerodane fragments, we were struck by the structural resemblance between the furo[2,3b]furan sidechain of clerodin and the furo[2,3b]pyran substructure present in azadirachtin. In view of this similarity, it was hypothesized that the introduction of structural features from azadirachtins furo[2,3b]pyran substructure into clerodane C-9 sidechain fragments might increase the antifeedant activity of these model compounds. Especially the C-20 hydroxy group present in the furo[2,3b]pyran substructure was seen as an interesting candidate for such a strategy.To examine this hypothesis, we synthesized several series of model compounds (furo[2,3b]pyrans, furo[2,3b]furans, 3-alkyl-but-2-enolides and -butanolides, 4-furano-2-spirolactones) with and without an extra hydroxy group at the corresponding position. These model compounds were tested in insect antifeedancy bioassays, using various insect species. Against larvae of the large cabbage white butterfly ( Pieris brassicae ) several of the test compounds displayed statistically significant antifeedant activity, though none of the compounds was found to be highly active. For the test series of furo[2,3b]furan analogues, the presence of a C-3a hydroxy group did not generally increase the activity of the test compounds, although this feature was present in the most potent compound within this series. Similarly, in the 3-alkyl-butyrolactone series the 3-hydroxy-butanolides were about equally active as the corresponding butenolides. For larvae of the Colorado potato beetle ( Leptinotarsa decemlineata ) and for nymphs of the green peach-potato aphid ( Myzus persicae ), none of the compounds tested showed statistically significant antifeedant activity.</p

Evaluation of Claviceps purpurea isolates on wheat reveals complex virulence and host susceptibility relationships

Ergot of cereals, caused by Claviceps purpurea, results in yield loss and downgrading of infested grain because of toxic alkaloids in the sclerotia. Resistant wheat genotypes are known, but their effectiveness against different C. purpurea isolates over geographic regions has not been studied. The objective of this study was to examine the pathogenic variability among isolates of C. purpurea on wheat lines differing in resistance. Under controlled environmental conditions, 41 single spore isolates of C. purpurea were obtained from Canadian and UK collections and inoculated onto a set of wheat genotypes composed of durum wheat lines ‘Melita’, ‘Kyle’ and 9260B-173A, and hexaploid spring wheat lines ‘Cadillac’, ‘Vista’, ‘Kenya Farmer’, ‘Lee’ and HY630. Honeydew production and weight of sclerotia produced per spike were assessed. There were significant differences among the wheat genotypes for overall reactions to the pathogen isolates, and among pathogen isolates for geographic origin and host origin. Twenty virulence phenotypes were identified using the honeydew production data, and 23 virulence phenotypes identified using the sclerotial weight data from the 41 isolates. The existence of different virulence phenotypes indicates that variability in virulence exists in populations of C. purpurea, and knowledge of virulence phenotypes is necessary to effectively breed for resistant commercial lines

Quantifying precision and accuracy of measurements of dissolved inorganic carbon stable isotopic composition using continuous-flow isotope-ratio mass spectrometry

RATIONALE: We describe an analytical procedure that allows sample collection and measurement of carbon isotopic composition (δ13CV-PDB value) and dissolved inorganic carbon concentration, [DIC], in aqueous samples without further manipulation post field collection. By comparing outputs from two different mass spectrometers, we quantify with the statistical rigour uncertainty associated with the estimation of an unknown measurement. This is rarely undertaken, but it is needed to understand the significance of field data and to interpret quality assurance exercises.&lt;p&gt;&lt;/p&gt; METHODS: Immediate acidification of field samples during collection in evacuated, pre-acidified vials removed the need for toxic chemicals to inhibit continued bacterial activity that might compromise isotopic and concentration measurements. Aqueous standards mimicked the sample matrix and avoided headspace fractionation corrections. Samples were analysed using continuous-flow isotope-ratio mass spectrometry, but for low DIC concentration the mass spectrometer response could be non-linear. This had to be corrected for.&lt;p&gt;&lt;/p&gt; RESULTS: Mass spectrometer non-linearity exists. Rather than estimating precision as the repeat analysis of an internal standard, we have adopted inverse linear calibrations to quantify the precision and 95% confidence intervals (CI) of the δ13CDIC values. The response for [DIC] estimation was always linear. For 0.05–0.5 mM DIC internal standards, however, changes in mass spectrometer linearity resulted in estimations of the precision in the δ13CVPDB value of an unknown ranging from ± 0.44‰ to ± 1.33‰ (mean values) and a mean 95% CI half-width of ±1.1–3.1‰.&lt;p&gt;&lt;/p&gt; CONCLUSIONS: Mass spectrometer non-linearity should be considered in estimating uncertainty in measurement. Similarly, statistically robust estimates of precision and accuracy should also be adopted. Such estimations do not inhibit research advances: our consideration of small-scale spatial variability at two points on a small order river system demonstrates field data ranges larger than the precision and uncertainties. However, without such statistical quantification, exercises such as inter-lab calibrations are less meaningful.&lt;p&gt;&lt;/p&gt

Optimizing seeding rates and plant densities for Camelina sativa

Non-Peer ReviewedCamelina is a relatively new oilseed crop to western Canada. Currently there is little research available for camelina seeding rates in western Canada. A field study was conducted in 2007 and 2008 for 9 site years at locations in western Canada to determine the effect of seeding rate on various agronomic aspects of camelina like yield, days to maturity, lodging, and plant height. The seeding rates used were 12, 25, 50, 100, 200, 400, 800, and 1600 seeds m-2. Camelina exhibited a plastic yield response to seeding rate. Maximum yield was reached at 450-500 seeds m-2. Small yield increases were seen with seeding rates greater than 100 seeds m-2. Days to maturity decreased by up to seven days as seeding rate increased. The optimum seeding rate was approximately 500 seeds m-2 because of the positive effect on maturity, plant height, and yield. 500 seeds m-2 would supply enough seeds to produce an acceptable plant density under poor seeding conditions to help prevent crop failure due to poor emergence or seedling mortality

Synthesis of perhydrofuro[2,3-b]furans from isopentenyl alcohol through carbonyl-ene and wacker-type reactions

A range of 2-substituted perhydrofuro[2,3-b]furans have been synthesized in a stereoselective manner through a sequence involving the Lewis-acid catalyzed carbonyl-ene reaction of a protected isopentenyl alcohol with a variety of enophiles, deprotection of the corresponding monoprotected diols, and palladium-catalyzed intramolecular acetalization under Wacker-type reaction conditions.This work was generously supported by the Spanish Ministerio de Ciencia e Innovación (MICINN), grant number CTQ2007-65218 and Consolider Ingenio 2010, grant number CSD2007-00006, the Generalitat Valenciana (GV; PROMETEO/2009/039), and Fondos Europeos para el Desarrollo Regional (FEDER). D. S. thanks the Vicerrectorado de Investigación, Desarrollo e Innovación of the Universidad de Alicante for a predoctoral grant. M. R.-F. thanks the ISO of the Universidad de Alicante for a postdoctoral grant

Identification of main effect and epistatic quantitative trait loci for morphological and yield-related traits in peanut (Arachis hypogaea L.)

An effort was made in the present study to identify the main effect and epistatic quantitative trait locus (QTL) for the morphological and yield-related traits in peanut. A recombinant inbred line (RIL) population derived from TAG 24 × GPBD 4 was phenotyped in seven environments at two locations. QTL analysis with available genetic map identified 62 main-effect QTLs (M-QTLs) for ten morphological and yield-related traits with the phenotypic variance explained (PVE) of 3.84–15.06%. Six major QTLs (PVE > 10%) were detected for PLHT, PPP, YPP, and SLNG. Stable M-QTLs appearing in at least two environments were detected for PLHT, LLN, YPP, YKGH, and HSW. Five M-QTLs governed two traits each, and 16 genomic regions showed co-localization of two to four M-QTLs. Intriguingly, a major QTL reported to be linked to rust resistance showed pleiotropic effect for yield-attributing traits like YPP (15.06%, PVE) and SLNG (13.40%, PVE). Of the 24 epistatic interactions identified across the traits, five interactions involved six M-QTLs. Three interactions were additive × additive and remaining two involved QTL × environment (QE) interactions. Only one major M-QTL governing PLHT showed epistatic interaction. Overall, this study identified the major M-QTLs for the important productivity traits and also described the lack of epistatic interactions for majority of them so that they can be conveniently employed in peanut breeding