Iridoid glucosides in Griselinia, Aralidium and Toricellia

From three of five investigated species of Griselinia a new iridoid glucoside, griselinoside, was isolated. It was found to be present also in foliage of Aralidium pinnatifidum and Toricellia angulata, accompanied in the former by aralidioside another novel iridoid glucoside. The structures and absolute configurations of the two iridoids were elucidated by NMR spectroscopy and chemical conversions. From G. littoralis and T. angulata the glucosides magnolioside and syringoside respectively were isolated. ¹³C NMR spectra are given for thirteen iridoid derivatives.     

Iridoid allosides from Viburnum opulus

Arbutin and four novel iridoid glycoside esters, named opulus iridoids I–IV, have been isolated from foliage of Viburnum opulus (Caprifoliaceae). Each opulus iridoid constitutes an inseparable mixture of two compounds, differing by containing either 2-methyl- or 3-methylbutyric acid in ester linkage at the 1-OH-group in an iridoid glycoside. In all glycosides 2′,3′-di-O-acetyl-β-D-allopyranose is linked through a glycosidic bond to C-11 in the iridoid aglycone. The opulus iridoids differ by the degree of acetylation of the aglycone and by the attachment, in III and IV, of a β-D-xylopyranosyl group at C-4 of the allose moiety. The structures have been elucidated by ¹H and ¹³C-NMR spectroscopy and by cleavage of the glycosidic linkage with boron trifluoride etherate in acetic anhydride, yielding the acetates of the cyclized aglycone and of the appropriate mono- or disaccharide. This is the second report of an iridoid attached to a sugar other than glucose and the second time allose has been encountered in higher plants. The systematic position of Viburnum is briefly discussed.     

Veronica: Iridoids and cornoside as chemosystematic markers

The iridoid glucoside, ajugol, and the phenylethanoid glucoside, cornoside, have been isolated from species of Veronica (Plantaginaceae) for the first time. The presence of these compounds has been screened in 18 plant accessions belonging to 15 species of Veronica (Plantaginaceae), by isolation or NMR spectroscopy of crude extracts. In addition, the distribution of iridoids in the genus has been reviewed, using mainly the published data of isolated compounds. Using the recent expansion and reclassification of the genus based on DNA-sequence results as the model, we find that the genus is rather homogeneous with regard to the distribution of iridoid glucosides, aucubin and/or catalpol as well as 6-O-esters of catalpol being universally present in 10 of the 12 subgenera for which data exist. Only the two subgenera Pocilla and Chamaedrys deviate from this pattern. Pocilla is heterogeneous; in this subgenus, species in subsect. Agrestes contain the standard iridoid garniture, while species in subsect. Biloba do not contain the 6-O-esters of catalpol, but ajugol instead. Veronica intercedens (subsect. Subracemosae) differs from the remainder of the subgenus in only containing 5-hydroxylated iridoids (melittoside and globularifolin) and is so far the only species within the genus in which such compounds have been detected. These chemical differences are clearly reflected in the DNA-based phylogram of the subgenus. Subg. Chamaedrys appears homogeneous in lacking iridoids or only containing these in small amounts, but instead half of the investigated species contained the phenylethanoid glucoside cornoside. The distribution of this compound in angiosperms is reviewed; cornoside often substitutes iridoid glucosides in plants where these are expected to be present. The chemical results of Veronica fit in very well with the phylogenetic implications of the DNA-sequence results.     

Iridoid glucosides as taxonomic markers in the genera Lantana,Lippia, Aloysia and Phyla

Nine species of Lantana, Lippia, Aloysia and Phyla have been examined for iridoids. Six of the species contain iridoid glucosides including pulchelloside I, mussaenoside, lamiide, durantoside I, geniposide and theviridoside as well as the sodium salts of geniposidic acid and theveside. A quinol glucoside, cornoside, has been isolated from Phyla nodiflora. The distribution of iridoids and cornoside shows a good correlation with the classification proposed by El-Gazzar and Watson.     

Iridoid aglycones from Deutzia scabra

Scabrogenin and deutziogenin, the stable aglycones of known iridoid glucosides scabroside and deutzioside, have been isolated from Deutzia scabra. Their structures and mutarotational equilibria were investigated by detailed analysis of ¹H NMR and ¹³C NMR data.     

Trans-fused Iridoid GlycosidEs from Penstemon Mucronatus

Two new trans-fused iridoid glycosides (5αH)-6α-8-epidihydrocornin and (5αH)-6α-8-hydroxy-8-epiloganin, were isolated from Penstemon mucronatus, along with cornin, penstemoside and three hastatosides. The trans-fused iridoids are only the second and third known among over 900 described cis-fused iridoid glycosides. Two pairs of iridoids, identical except for the stereochemistry at C-8, were found. Structures were determined by spectroscopic methods.     

Feretoside et gardenoside du Feretia apodanthera: rmn du carbone 13 en série iridoide

The ¹³C NMR spectra of some iridoids of known structure are analysed. The data obtained have been applied to the determination of structure of feretoside and the identification of gardenoside, both isolated from the stem bark of Feretia apodanthera.     

A new phenylethanoid triglycoside in Veronica beccabunga L

Besides the expected iridoid glucosides aucubin and catalpol as well as three known esters of the latter, Veronica beccabunga (brooklime) was shown to contain five carboxylated iridoid glucosides, namely gardoside, mussaenosidic acid, 8-epiloganic acid, arborescosidic acid and alpinoside. In addition to these compounds, the plant contained salidroside and a previously unknown caffeoyl phenylethanoid glycoside (CPG) which we have named chionoside J. The structure was elucidated mainly by 1D and 2D NMR spectroscopy to be 2″-(β-glucopyranosyl)-plantamajoside. The distribution of plantamajoside and its derivatives as well as that of carbocyclic iridoids with an 8,9-double bond is briefly discussed, and it is noted that such compounds are mainly confined to the tribe Veroniceae of the Plantaginaceae.     

Iridoid glucosides from Viburnum tinus

Five new iridoid glucosides, named viburtinosides I-V, together with suspensolide F, were isolated from leaves and branches of Viburnum tinus. All the iridoids contain a β-d-glucopyranosyl moiety linked to the oxymethylene at C-11 and an isovaleroyl at position 1, but differ for other acylating groups. The structures have been elucidated mainly by spectroscopic means.     

5-deoxystansioside,an iridoid glucoside from Tecoma stans

In addition to plantarenaloside and stansioside, a new iridoid glucoside with a formyl group at C-4 has been isolated from Tecoma stans. The new glucoside was shown to be 5-deoxystansioside by ¹³C NMR and ¹H NMR spectroscopy.     

5,7-Bisdeoxycynanchoside,an iridoid glucoside from Macfadyena cynanchoides

A new iridoid glucoside from Macfadyena cynanchoides leaves has been identified by spectral (¹H and ¹³C NMR) and chemical procedures as 5,7     

Three new iridoid glycosides isolated from the traditional herb Siphonostegia chinensis with NF-κB inhibitory activity

Siphonoids A–C (1–3), among which siphonoids A-B (1–2) are rare (E)-p-coumaroyl iridoids, were isolated from Siphonostegia chinensis along with ten known iridoids (4–13) and four lignans (14–17). The structures of the compounds were established by 1D- and 2D-NMR spectroscopy and mass spectrometry. Most of the iridoids isolated from S. chinensis were found to possess (E)-p-coumaroyl iridoid subtype skeletons. Hence, this type of iridoid could be regarded as a chemotaxonomic marker of S. chinensis. The inhibition activities for the NF-κB pathway of iridoids (1–6) were detected. The present results showed that compounds 1–2 and 4–6 processed moderate activity towards the inhibition of NF-κB.     

Structure and configuration of unedide,an iridoid glucoside from Arbutus unedo

Unedide, a novel iridoid glucoside isolated from Arbutus unedo (Ericaceae), has been established to be 6,7-dihydro-6β-hydroxymonotropein by detailed analysis of ¹H and ¹³ C NMR spectral data.     

Iridoid glycosides in the butterfly Euphydryas cynthia (lepidoptera,nymphalidae)

Larvae and pupae of the alpine butterfly Euphydryas cynthia contain three iridoid glucosides: two of them, aucubin and catalpol, are very common in the Plantaginaceae, but the third, 6-O-glucopyranosylaucubin, has hitherto only been isolated from Odontites verna and Verbascum sinuatum (Scrophulariaceae). The amounts of the three iridoids found in the insects were 0.53, 0.31 and 1.48 % dry wt, respectively. Preliminary feeding experiments with an insectivorous bird indicated some unpalatability in the insect, which probably stems from the iridoid content.     

Four iridoids from Randia canthioides

Four new iridoids, 10-dehydrogardenoside, dimeric 10-dehydrogardenoside, randioside and deacetylasperulosidic acid methyl ester aglycone, have been isolated together with three known iridoid glucosides, gardenoside, deacetylasperulosidic acid methyl ester and scandoside methyl ester, from Randia canthioides. It is conceivable that dimeric 10-dehydrogardenoside could be an artefact formed during the isolation process.     

Rare noriridoids from the roots of Andrographis paniculata

The rare noriridoids, Andrographidoids A–E (1–5), along with a known iridoid curvifloruside F (6), were isolated from roots of Andrographis paniculata. All noriridoids were aglycones and 1–4 had (semi-) acetal structures located at C-3 but not at C-1. Their structures were established by a series of 1D and 2D NMR analyses. The antibacterial activity of these iridoids was also assessed using the microtitre plate broth dilution method.     

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.     

Iridoid mono- and di-glycosides in Mentzelia

Eight species of Mentzelia (Loasaceae) have been investigated for iridoid glycosides. In addition to the known glucosides deutzioside, decaloside, mongolioside, loganin and sweroside, several novel compounds have been isolated and characterized by chemical and spectroscopic means. 6′-O-Acetyl deutzioside was found in a single species, while the diglycosidic compounds glucosyl-decaloside, allosyl-decaloside and quinovosyl-decaloside were each isolated from one or more species. In addition, a novel compound, epoxydecaloside (= 11-hydroxy-deutzioside), together with glucosyl-epoxydecaloside, allosyl-epoxydecaloside and mentzelosyl-epoxydecaloside are described. The last compound contains a 4-deoxy-α-l-erythro-pentopyranosyl moiety, whose parent sugar, named mentzelose, has not been encountered so far in nature. A non-glycosidic iridoid, mentzetriol, has been characterized solely by spectroscopic means and a structure is proposed. The secoiridoid secoxyloganin has been found for the first time in a plant source, and the coumarin glucoside scopolin has been isolated from two species of Mentzelia. ¹³C and ¹H NMR spectra of several iridoid compounds are presented. The biosynthesis of the compounds is considered and the systematic position of Loasaceae discussed concluding in a possible derivation from Cornalean ancestors.     

Iridoids in Hydrangeaceae

The content of glycosides in Kirengeshoma palmata and Jamesia americana (Hydrangeaceae) have been investigated. The former contains loganin and secoiridoids, including the alkaloid demethylalangiside. The latter contains no iridoids, but the known glucosides arbutin, picein and prunasin. In order to futher investigate the chemotaxonomy of the family Hydrangeaceae, the distribution of the iridoid and secoiridoid glucosides as well as the known biosynthetic pathways to these compounds have been reviewed. However, only a few genera of the family has been investigated. Loganin, secologanin, and derivatives of these are common. The genus Deutzia is characteristic in containing more structurally simple iridoids in which C-10 has been lost during biosynthesis. Such compounds have so far only been reported from the genus Mentzelia (Loasaceae). The taxonomic relationships between Hydrangeaceae and the closely related Cornaceae and Loasaceae is discussed and found to agree well with recent DNA sequence results.     

A 7-Deoxyloganetic Acid Glucosyltransferase Contributes a Key Step in Secologanin Biosynthesis in Madagascar Periwinkle

Iridoids form a broad and versatile class of biologically active molecules found in thousands of plant species. In addition to the many hundreds of iridoids occurring in plants, some iridoids, such as secologanin, serve as key building blocks in the biosynthesis of thousands of monoterpene indole alkaloids (MIAs) and many quinoline alkaloids. This study describes the molecular cloning and functional characterization of three iridoid glucosyltransfeases (UDP-SUGAR GLYCOSYLTRANSFERASE6 [UGT6], UGT7, and UGT8) from Madagascar periwinkle (Catharanthus roseus) with remarkably different catalytic efficiencies. Biochemical analyses reveal that UGT8 possessed a high catalytic efficiency toward its exclusive iridoid substrate, 7-deoxyloganetic acid, making it better suited for the biosynthesis of iridoids in periwinkle than the other two iridoid glucosyltransfeases. The role of UGT8 in the fourth to last step in secologanin biosynthesis was confirmed by virus-induced gene silencing in periwinkle plants, which reduced expression of this gene and resulted in a large decline in secologanin and MIA accumulation within silenced plants. Localization studies of UGT8 using a carborundum abrasion method for RNA extraction show that its expression occurs preferentially within periwinkle leaves rather than in epidermal cells, and in situ hybridization studies confirm that UGT8 is preferentially expressed in internal phloem associated parenchyma cells of periwinkle species.