Iridoid glucosides in fouquieriaceae

From three Fouquieria sp. 12 iridoid glucosides were isolated and identified. Eight of these were structurally related to galioside (monotropein methylester), while four were hydroxy substitution products of deoxyloganin. In three cases the glucoside occurred together with the corresponding 10-O-acetate.     

Low rates of iridoid glycoside hydrolysis in two Longitarsus leaf beetles with different feeding specialization confer tolerance to iridoid glycoside containing host plants

Iridoid glycosides are plant defence compounds that are deterrent and/or toxic for unadapted herbivores but are readily sequestered by dietary specialists of different insect orders. Hydrolysis of iridoid glycosides by β‐glucosidase leads to protein denaturation. Insect digestive β‐glucosidases thus have the potential to mediate plant–insect interactions. In the present study, mechanisms associated with iridoid glycoside tolerance are investigated in two closely‐related leaf beetle species (Coleoptera: Chrysomelidae) that feed on iridoid glycoside containing host plants. The polyphagous Longitarsus luridus Scopoli does not sequester iridoid glycosides, whereas the specialist Longitarsus tabidus Fabricius sequesters these compounds from its host plants. To study whether the biochemical properties of their β‐glucosidases correspond to the differences in feeding specialization, the number of β‐glucosidase isoforms and their kinetic properties are compared between the two beetle species. To examine the impact of iridoid glycosides on the β‐glucosidase activity of the generalist, L. luridus beetles are kept on host plants with or without iridoid glycosides. Furthermore, β‐glucosidase activities of both species are examined using an artificial β‐glucosidase substrate and the iridoid glycoside aucubin present in their host plants. Both species have one or two β‐glucosidases with different substrate affinities. Interestingly, host plant use does not influence the specific β‐glucosidase activities of the generalist. Both species hydrolyse aucubin with a much lower affinity than the standard substrate. The neutral pH reduces the β‐glucosidase activity of the specialist beetles by approximately 60% relative to its pH optimum. These low rates of aucubin hydrolysis suggest that the ability to sequester iridoid glycosides has evolved as a key to potentially preventing iridoid glycoside hydrolysis by plant‐derived β‐glucosidases.     

Population differences in larval hostplant use in the checkerspot butterfly, Euphydryas chalcedona

Larvae from two populations of Euphydryas chalcedona Doubleday & Hewitson (Nymphalidae) were reared on their own hostplant and that of the other population, in both pre-diapause and post-diapause instars. One population, Chico, uses Penstemon breviflorus Lindl. (Scrophulariaceae), and the other, Echo Lake, uses P. newberryi Gray. Growth rate and survival were determined for pre-diapause and post-diapause larvae from both populations on both plant species; and digestive efficiencies were calculated during the prediapause instars. The results showed that larvae from the two populations differed in their responses to the two plant species. Pre-diapause larvae from Chico performed equally well on both plant species—survival and digestive indices were not significantly different for two Penstemon species. In contrast, pre-diapause larvae from Echo Lake performed significantly worse on the non-hostplant—growth and survival were significantly lower on the non-host, P. breviflorus. In addition, comparison of digestive efficiencies for the two plants showed that larvae from Echo Lake digested P. breviflorus better than P. newberryi, but were significantly less able to convert P. breviflorus to body mass. In the post-diapause instars, larvae from Chico grew faster on the host than on the non-host. Larvae from Echo Lake grew quite slowly on both plant species and significantly more of the Echo Lake larvae returned to diapause instead of completing development.

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Résumé Des chenilles de deux populations d'E. chalcedona ont été élevées sur leur propre plante-hôte et sur celle de l'autre population, aux stades avant et après diapause. Les deux populations s'alimentent sur différentes espèces de Penstemon (Scrophulariaceae), et une population—Echo Lake—est monophage sur P. newberry, tandis que l'autre—Chico—utilise d'abord P. breviflorus, mais les chenilles après diapause sont trouvées sur au moins deux autres espèces de plantes. Les taux de croissance et de survie ont été déterminés pour des chenilles avant et après diapause pour les deux populations sur les deux plantes; les efficacités digestives ont été calculées sur les chenilles avant diapause.Les résultats ont montré que les chenilles des deux populations différaient par leur degré de spécialisation digestive sur leur plante hôte normale: les chenilles de Chico ont utilisé aussi bien les deux plantes, tandis que celles d'Echo Lake le faisaient significativement moins bien sur la plante non-hôte, par suite de l'inaptitude à la digérer. Ainsi la population oligophage est alimentairement moins spécialisée et plus capable de se débrouiller avec une plante non-hôte. Après diapause, les chenilles de Chico s'alimentaient significativement mieux sur plante hôte que non-hôte, ce qui était le cas aussi pour la population monophage. Dans l'ensemble, les chenilles de la population monophage semblaient moins capables de se débrouiller dans des conditions défavorables ou moins avantageuses.

     

6β-Hydroxyipolamiide,an iridoid glucoside from Stachytarpheta mutabilis

A new iridoid glucoside has been isolated from Stachytarpheta mutabilis and assigned the structure and configuration of 6β-hydroxyipolamiide on the basis of ¹H NMR and ¹³C NMR evidence. The conversion of this compound into penta- acetyllamiol proved the above assignment.     

Variable chemical defence in the checkerspot butterfly Euphydryas gillettii (Lepidoptera: NymphaIidae)

Abstract.

• 1 Like other checkerspots, Euphydryas gillettii butterflies may contain the defensive chemicals, iridoid glycosides, which are sequestered from their hostplants during larval feeding.
• 2 We analysed the iridoid glycoside content of E.gillettii adults from two different populations, Warm Lake, Idaho, and Granite Creek, Wyoming, that have different patterns of hostplant use.
• 3 Gas chromatographic analysis of thirty butterflies from the Wyoming population showed that they contained a mean of 1.27 (±0.19 SE) % dry weight iridoid glycosides. Notably, 20% of these butterflies contained no detectable iridoid glycosides.
• 4 In contrast, nineteen butterflies from the Idaho population contained a mean of 3.89 (±0.38 SE) % dry weight iridoid glycosides, and all butterflies contained iridoid glycosides.
• 5 These results illustrate how the chemical defence of herbivorous insects varies according to differential use of potential hostplants.

     

2′-p-Hydroxybenzoyl mussaenosidic acid,a new iridoid glucoside from Vitex negundo.

Ethanolic extract of the leaves of Vitex negundo yielded a new iridoid named 2′-p-hydroxybenzoyl mussaenosidic acid. The structure was established on the basis of chemical and spectral data.     

Cynanchoside,a highly oxygenated iridoid glucoside from Macfadyena cynanchoides

The elucidation of the structure and stereochemistry of cynanchoside, a new highly oxygenated iridoid glucoside isolated from Macfadyena cynanchoides (Bignoniaceae), has been accomplished using mainly ¹H and ¹³C NMR spectral data and further confirmed by simple chemical transformations.     

Iridoid glycosides from Galium verum

From the aerial parts of Galium verum in flower, asperuloside and V₁ iridoid were isolated. From the mother liquor obtained on recrystallizatio     

Two new iridoid glucosides from Ixora chinensis

From leaves and twigs of Ixora chinensis, two new iridoid glucosides, ixoroside (1) and ixoside (7,8-dehydroforsythide) (2) along with known geniposidic acid (3) have been isolated and their structures have been established.