Chemotaxonomy of Plantago. Iridoid glucosides and caffeoyl phenylethanoid glycosides

Data for 34 species of Plantago (Plantaginaceae), including subgen. Littorella (= Littorella uniflora), have been collected with regard to their content of iridoid glucosides and caffeoyl phenylethanoid glycosides (CPGs). In the present work, 21 species were investigated for the first time and many known compounds were found together with three new iridoid glucosides. Of these, arborescoside and arborescosidic acid, both of the uncommon type with an 8,9-double bond, were present in several species, while 6-deoxymelittoside was found only in P. subulata. The known compounds deoxyloganic acid, caryoptoside and rehmannioside D were isolated from the genus for the first time. The earlier reported occurrence of sorbitol in the family was confirmed, and this compound was shown by NMR spectroscopy to be the main sugar in the three species investigated for this. The combined data show that CPGs are present in all species investigated. With regard to the iridoids, the distribution patterns showed a good correlation with the classification of Rahn. Thus, aucubin is typical for the whole genus, while bartsioside and catalpol as well as 5-substituted iridoids are each characteristic for a subgenus in the family. Finally, the close relationship between Plantago and Veronica suggested by chloroplast DNA sequence analysis. could be corroborated by the common occurrence of the rare 8,9-unsaturated iridoids in these two genera.     

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.     

Iridoid glucosides in Avicennia officinalis

The new iridoids avicennioside and 7-cinnamoyl-8-epiloganic acid, as well as the known compounds geniposidic acid and 2′-cinnamoyl-mussaenosidic acid, have been isolated from the leaves of Avicennia officinalis. In the plant the acids are accumulated as salts. The taxonomic significance of these findings is discussed.     

Iridoid glucosides from Melampyrum

Melampyrum arvense and M. cristatum contain, besides aucubin, 8-epiloganin and melampyroside, a new natural iridoid glucoside: gardoside methyl ester. In addition, M. arvense contains mussaenoside and M. cristatum mussaenosidic acid, another novel iridoid glucoside.     

Iridoid glucosides from clerodendrum incisum

8-O-Foliamenthoyleuphroside and 2′-O,8-O-difoliamenthoyleuphroside, new foliamenthic acid esters of euphroside, and the known iridoid euphroside have been isolated from the leaves and twigs of Clerodendrum incisum. From the roots of the same plant the known iridoid plantarenaloside has been isolated. The taxonomic significance of these findings is discussed.     

Iridoid glucosides of Linaria clementei

From an acetone extract of the whole plant of Linaria clementei, besides antirride and antirrinoside, the new iridoid glucosides 6-senecioyl- and 6-angeloylantirrinoside were isolated.     

Iridoid glucosides from Strychnos nux-vomica

From seeds of Strychnos nux-vomica three iridoids, 6'-O-acetylloganic acid, 4'-O-acetylloganic acid and 3'-O-acetylloganic acid were isolated together with two known iridoid glucosides, loganic acid and 7-O-acetylloganic acid. The structures of the compounds were established by ESI-MS and by 1D and 2D NMR spectroscopic methods.     

Iridoid glucosides from Parentucellia Viscosa

From Parentucellia viscosa a new glucosidic iridoid, gardoside methyl ester, was isolated along with bartioside, aucubin, melampyroside, shanzhiside methyl ester and 8-epiloganin. The structure of the new glucoside was confirmed by its chemical conversion into 8-epiloganin.     

Iridoid glucosides from Thunbergia laurifolia

Two iridoid glucosides, 8-epi-grandifloric acid and 3′-O-β-glucopyranosyl-stilbericoside, were isolated from the aerial part of Thunbergia laurifolia along with seven known compounds, benzyl β-glucopyranoside, benzyl β-(2′-O-β-glucopyranosyl) glucopyranoside, grandifloric acid, (E)-2-hexenyl β-glucopyranoside, hexanol β-glucopyranoside, 6-C-glucopyranosylapigenin and 6,8-di-C-glucopyranosylapigenin. Strucural elucidation was based on the analyses of spectroscopic data.     

Iridoid glucosides from Satureja Vulgaris

Satureja vulgaris was shown to contain two new iridoid glucosides, 5-deoxylamiol and 4-methylantirrhinoside, as well as the known iridoid glucosides lamiol and 5-deoxylamioside. The structures of the new glucosides were established by spectroscopic studies and chemical evidence.     

Iridoid glucosides from Barleria lupulina

From the aerial part of Barleria lupulina, 8-O-acetyl-6-O-trans-p-coumaroylshanzhiside, saletpangponosides A-C and 8-O-acetylmussaenoside were isolated together with 13 known compounds. The structural elucidations were based on analyses of physical and spectroscopic data.     

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.     

Iridoid glucosides of Odontites verna

Five iridoids have been identified in the whole plant of Odontites verna.     

Iridoid glucosides from Veronica pectinata var. glandulosa

A new highly oxygenated iridoid glucoside, urphoside B (1) was isolated from the Veronica pectinata var. glandulosa together with seven known iridoid glucosides, aucubin, catalpol, veronicoside, catalposide, verproside, amphicoside and 6-O-veratroyl catalpol. The planar as well as the stereo structures of the isolated compounds were determined by means of extensive 1D- and 2D-NMR spectroscopy and confirmed by HR-Mass.     

Iridoid glucosides in Avicennia marina

2′-Cinnamoyl-mussaenoside, 10-O-(5-phenyl-2,4-pentadienoyl)-geniposide, 7-O-(5-phenyl-2,4-pentadienoyl)-8-epiloganin, and the known iridoids geniposide and mussaenoside have been isolated from a methylated extract of the leaves of Avicennia marina. Evidence is presented that the iridoids occur as the free acids in the plant. The taxonomic significance of these findings is discussed.     

Iridoid glucosides from Pedicularis

Pedicularis palustris contains the iridoid glucosides aucubin and gardoside methyl ester, and five hydroxy derivatives of 8-epi-deoxyloganin, together with boschnaloside and three hydroxy derivatives of boschnaloside. From P. silvatica, plantarenaloside, 8-epiloganin and euphroside have been isolated. Euphroside is also present in P. lapponica, in addition to aucubin and mussaenoside. Chemical evidence for the structure of euphroside is presented. Pedicularioside is shown to be identical with penstemoside, and the former name is thus redundant.     

Iridoid patterns of genus Plantago L. and their systematic significance

The distribution of 14 iridoid glucosides in 14 Plantago L. species (44 samples corresponding to 18 taxa) was shown. P. tenuiflora and P. gentianoides were studied for iridoids for the first time. The iridoid patterns showed a good correlation with morphological and other chemical features of the representatives of genus Plantago. The studied species are grouped together according to the iridoid patterns: species containing mainly aucubin (P. major, P. cornuti, P. gentianoides); species containing aucubin and aucubin derivatives (P. subulata, P. media); species containing aucubin and catalpol (P. lanceolata, P. altissima, P. argentea, P. lagopus, P. atrata); species containing aucubin and plantarenaloside (P. afra, P. scabra).     

Iridoid glucosides from Phlomis tuberosa L. and Phlomis herba-ventis L

A new iridoid glucoside, 5-desoxysesamoside, was isolated from Phlomis tuberosa L. (Lamiaceae) together with three known iridoid glucosides sesamoside, shanziside methyl ester and lamalbid. Lamiide was found in P. herba-ventis ssp. pungens in high concentrations.