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.     

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 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.     

Relationships and evolution of Hydrangeaceae based on RBCl sequence data

Phylogenetic analyses of rbcL sequences were used to address both systematic and evolutionary questions posed by the angiosperm family Hydrangeaceae. Our analyses suggest the presence of a monophyletic Hydrangeaceae most closely allied with Loasaceae, a finding in agreement with other molecular as well as morphological analyses. Molecular data indicate that Hydrangeaceae comprise Decumaria, Pileostegia, Schizophragma, Hydrangea, Dichroa, Broussaisia, Platycrater, Cardiandra, Deinanthe, Carpenteria, Philadelphus, Deutzia, Fendlerella, Whipplea, Fendlera, Jamesia, and the enigmatic Kirengeshoma. A particularly close relationship of Kirengeshoma and Deutzia is indicated. Analysis of rbcL sequences suggests that Fendlera and Jamesia are sister to the remainder of the family, lending support to the hypothesis that at least some Carpenterieae are basal in the family and that Hydrangeaceae may have originated in xeric habitats. If this phylogenetic placement of Jamesia and Fendlera is correct, the rbcL trees also suggest that the level of epigyny has decreased in these genera, as well as in the Fendlerella- Whipplea clade and Carpenteria when compared to the outgroup taxa, which are wholly epigynous. Furthermore, the rbcL trees support proposed evolutionary trends in wood anatomy, suggesting, for example, that upland tropical taxa have evolved longer vessel elements with more numerous bars on scalariform perforation plates. The xerophytic basal members of Hydrangeaceae, like the closely related Loasaceae, have short, narrow vessel elements with scalariform perforation plates bearing few bars. Following Jamesia and Fendlera, the remaining hydrangeoids are divided into two large subclades that closely parallel the traditional division of the family into Philadelpheae and Hydrangeae. Both rbcL sequences and morphological data suggest close relationships between: 1) Fendlerella and Whipplea; 2) Decumaria, Pileostegia, and Schizophragma; 3) Carpenteria and Philadelphus; 4) Deinanthe and Cardiandra; 5) Dichroa, Broussaisia, and Hydrangea macrophylla. Molecular and morphological data also concur in demonstrating that the large genus Hydrangea is not a monophyletic assemblage.     

Iridoid glucosides in Plantago alpina and P. Altissima

Two species of Plantago, namely P. Alpina and P. altissima were investigated. From the former, nine iridoid glucosides and verbascoside were isolated. Together with the known iridoids gardoside, geniposidic acid, 8-epi-loganic acid, mussaenosidic acid, aucubin, monomelittoside and melittoside, two new glucosides were found: 10-O-acetylgeniposidic acid and alpinoside, another compound with a 10-O-acetyl group. From P. altissima verbascoside and isoverbascoside were isolated together with the known iridoids gardoside, 8-epi-loganic acid, catalpol, aucubin, and hookerioside as well as the new compound desacetylhookerioside.     

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.     

Phytochemistry and the systematics and ecology of Loasaceae and Gronoviaceae (Loasales)

A screening for iridoid compounds of 78 of 315 species from all major groups in Gronoviaceae and Loasaceae has been carried out. The results were compared to the systematic concepts in the family and distribution and ecology of the taxa. Iridoids are present in at least some species of all genera screened. Some simple, monomeric compounds (e.g., loganin, sweroside) are found in all major groups of the two families and represent the basic iridoid inventory. Other compounds are restricted to certain taxonomic groups: nine-carbon iridoids (e.g., deutzioside) are restricted to Mentzelia (Loasaceae subfam. Mentzelioideae), hetero-oligomeric iridoids (e.g., tricoloroside methyl ester, acerifolioside) are restricted to two small groups in Loasa (Loasa ser. Macrospermae and ser. Floribundae, Loasaceae subfam. Loasoideae), and oleosides (e.g., 10-hydroxyoleoside dimethyl ester) are restricted to the large genus Caiophora sensu Weigend). The distribution of certain iridoid compounds thus confirms some of the generic limits. Iridoid phytochemistry does not correlate with systematic entities above the generic level nor does it in any way correlate with the morphological evolution of taxa. Conversely, the amount and complexity of iridoid compounds present in taxa correlate positively with the aridity of their habitat and the extent of mammalian herbivore pressure.     

Chemotaxonomy of the Oleaceae: iridoids as taxonomic markers

The distribution and biosynthesis of iridoid glucosides in the Oleaceae is reviewed and five distinct biosynthetic pathways to iridoids have been identified in the family, deoxyloganic acid apparently being a common intermediate. Likewise, the distributions of caffeoyl phenylethanoid glycosides (CPGs), i.e. verbascoside and its analogues, as well as cornoside are listed. Iridoid glucoside data exist for 17 genera of Oleaceae and the occurrence of iridoids from the different biosynthetic pathways correlate extremely well with the phylogenetic classification inferred from recent chloroplast DNA sequence data. Thus the tribe Fontanesieae (Fontanesia) contains "normal" secoiridoids, Forsythieae (Abeliophyllum, Forsythia) contains cornoside and/or iridoids from the forsythide pathway, Myxopyreae (Myxopyrum, Nyctanthes) have iridoids from the myxopyroside pathway, and finally, the two tribes Jasmineae and Oleeae (the remaining genera) both contain iridoids from the oleoside pathway. Within Jasmineae, one group of Jasminum sp. is characterized by the presence of jasminin or similar compounds, while another group of Jasminum species and Menodora display derivatives of 10-hydroxyoleoside, compounds not present in the other group. CPGs are reported from about half of the species investigated. With regard to taxonomy at the order level, the chemical data might support a position within or close to Lamiales due to the common presence of CPGs, the iridoids being of less significance since they are of a type that are barely found elsewhere.     

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.     

Two new acylated drimane-type sesquiterpene glucosides from Petrorhagia saxifraga

Two new acylated drimane sesquiterpenoid glucosides, saxifragoside A and B, have been isolated from the methanol extract of Petrorhagia saxifraga, a perennial herbaceous plant typical of the Mediterranean vegetation. The structures of these compounds have been elucidated on the basis of extensive 2D NMR spectroscopic analyses, including COSY, TOCSY, NOESY, HSQC, CIGAR-HMBC, H2BC and HSQC-TOCSY, along with Q-TOF HRMS² analysis. As drimane glucosides have already been reported in other plants of Petrorhagia genus, they could represent a useful chemotaxonomic marker for this genus.     

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.     

Benzoxazinoids and iridoid glucosides from four Lamium species

A new class of compounds for the plant family Lamiaceae, benzoxazinoids, was found in Lamium galeobdolon. From the aerial parts of the species were isolated the new 2-O-beta-D-glucopyranosyl-6-hydroxy-2H-1,4-benzoxazin-3(4H)-one (6-hydroxy blepharin) together with four known benzoxazinoids, DHBOA-Glc, blepharin, DIBOA, DIBOA-Glc, as well as harpagide, 8-O-acetyl-harpagide and salidroside. Eight known iridoid glucosides, 24-epi-pterosterone and verbascoside were isolated from Lamium amplexicaule, L. purpureum and L. garganicum. The iridoids, 5-deoxylamiol and sesamoside, as well as the phytoecdysone, 24-epi-pterosterone, were found for the first time for the genus Lamium. The phytochemical data are discussed from a systematic and evolutionary point of view.     

LC–ESI-MS analysis of iridoid glucosides in Lamium species

An LC–ESI-MS analysis was performed to determine the iridoid composition of Lamium album, Lamium amplexicaule, Lamium garganicum, Lamium maculatum, and Lamium purpureum. Nine iridoids known to occur in these species, lamalbid, sesamoside, lamiol, 5-deoxylamiol, shanzhiside methyl ester, caryoptoside, penstemoside, lamioside, and barlerin, could be detected. Confident identification of the individual compounds was achieved by a combination of HPLC retention times, both positive and negative ionization modes in MS and the presence of cluster and fragment ions. Iridoid glucosides new to four of the studied species were reported here for the first time. In most cases, the observed iridoid profiles were consistent and only small intraspecific variations were detected. Some chemosystematic implications from the observed iridoid composition were discussed.     

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.     

Chemical Traits of Hemiparasitism in Odontites luteus

The study of the monoterpene glycosides content of Odontites luteus has shown the presence of a total of fifteen iridoid glucosides. The presence of compounds 1  –  5 and 7  –  10 is perfectly on‐line with both the biogenetic pathway for iridoids biosynthesis in Lamiales and the current botanical classification of the species. On the other side, the presence of compounds like agnuside ( 6 ), adoxosidic acid ( 11 ), monotropein ( 12 ), 6,7‐dihydromonotropein ( 13 ), methyl oleoside ( 14 ) and methyl glucooleoside ( 15 ) is of high interest because, first of all, they have never been reported before in Lamiales. In second instance, the majority of the last compounds are formally derived from a different biogenetic pathway which involves deoxyloganic acid/loganin and led to the formation of decarboxylated iridoid showing the 8β‐configuration. Furthermore, a second abnormality was found during our study and this regards compounds 14 and 15 which are seco‐iriodids and thus not typical for this family. The presence of these unusual compounds, biogenetically not related to species belonging to Lamiales, is a clear evidence of the metabolites transfer from the hosts. In fact, the collection area is also populated by species belonging to Oleaceae and Ericaceae which could be the possible hosts since the biosynthesis of seco‐iridoids and or iridoids related to deoxyloganic acid/loganin pathway, with the 8β‐configuration, is well documented in these species.     

Iridoids and phenylethanoids in Lagotis integrifolia and Wulfeniopsis amherstiana (Plantaginaceae)

In a chemosystematic investigation of Wulfeniopsis amherstiana we have isolated four common iridoid glucosides as well as the esters 3″- and 4″-Cinnamoyl 6-O-rhamnopyranosylcatalpol. Furthermore the plant contained mannitol, arbutin, and four caffeoyl phenylethanoid glucosides, namely plantamajoside, aragoside and two new acetyl derivatives of the latter, named amherstianoside A and B. From Lagotis integrifolia we have obtained mannitol and three common iridoid glucosides together with the 8,9-unsaturated iridoids arborescosidic acid and anagalloside. The results show that the genus Wulfeniopsis is chemically different from Wulfenia and that it is closer related to Veronicastrum.     

Iridoid patterns in Galium L. and some phylogenetic considerations

From 19 species of Galium, members of 6 European sections of the genus, 24 compounds were isolated, namely 16 iridoid glucosides, 2 secoiridoid glucosides and 6 triterpene saponins (the later found only in G. rivale (Sibth. & Sm. Griseb.) The iridoid content was analyzed by thin layer chromatography - densitometry. An effort was made to clarify interspecies relationships, based on the obtained results and previous data. Generally, a nearly uniform iridoid pattern in the studied species was observed. Nevertheless, some distinctions gave reason the following chemical characters to be treated as taxonomic markers: iridoids, secogalioside (characteristic of G. mollugo group), iridoids V1 and V2 (G. humifusum Bieb. and G. verum L.), 6-acetylscandoside (G. incurvum group and G. verum) and the triterpene saponins, rivalioside A and rivalioside C (characteristic of G. rivale). The studied species regarding to the iridoids could be attributed to three lines of evolutionary differentiation. One line is leading to the differentiation of G. rivale. It contains specific triterpenoids as well as iridoid acids, which show parallel development of both glyceraldehyde 3-phosphate/pyruvate and mevalonate biosynthetic routes in this species. A second line includes G. mollugo and G. incurvum species groups and the species G. humifusum and G. verum. Variety of iridoid esters, hydroxy and carboxy derivatives of iridoids and secoiridoids characterised this line. Third line comprises the remaining studied species, members of different sections and species groups. They posses a nearly identical iridoid pattern, which suggests a convergent evolution regarding to the iridoids.     

Iridoid glucosides from the stems of three bioactive Brazilian Faramea species (Rubiaceae)

In this paper our previous chemical study of the anti-dengue active species Faramea bahiensis, Faramea hyacinthina and Faramea truncata (synonym of Faramea caudata) (Rubiaceae) is complemented by isolating from their stems, through a combination of silica gel and Sephadex LH-20 column chromatography and reversed-phase solid-phase extraction, the known iridoid glucosides monotropein (1), monotropein methyl ester (2) and 10-deacetylasperulosidic acid (3). The structures were established by HPLC-DAD-MS/MS analysis, NMR spectroscopy and comparison with literature data. This is the first report on the occurrence of these compounds in the genus Faramea Aubl. This work contributes to expand the knowledge of the chemical diversity of this botanical genus, of which a limited number of identified compounds have been reported.     

9-hydroxy substituted iridoids from Gelsemium sempervirens

Two chemotypes of Gelsemium sempervirens were investigated. One, cultivated in Copenhagen, contained six iridoids in appreciable amounts, namely gelsemide, gelsemide 7-glucoside, gelsemiol, gelsemiol 1- and 3-glucoside, and 9-hydroxysemperoside. The other sample, collected in the wild in North Carolina, U.S.A., contained semperoside and the known brasoside as well as the coumarin glycoside fabiatrin. The two iridoids were found only in trace amounts in the cultivated specimen. The structures of the seven new iridoids were established mainly by spectroscopic methods and that of gelsemide was confirmed by X-ray analysis. Two new structural features were noted: three of the compounds carried a hydroxyl group at the 9-position, while two contained the glucosyl moiety at C-3. All iridoids were lactones of the asperuloside type with or without a 3,4-double bond.     

Early development of androecia in polystemonous Hydrangeaceae

Polystemonous androecia are diverse in both number and position of stamens. This investigation of polystemonous Hydrangeaceae uses developmental data to characterize (1) the range of developmental variations that account for the diverse androecial patterns and (2) how the expressions of polystemony among Hydrangeaceae compare to those found generally among other angiosperms and especially in their sister family, the Loasaceae, some of which have particularly complex androecia. All polystemonous Hydrangeaceae share the common element of stamen clusters in antesepalous positions. In each of these taxa, the first stamens are initiated opposite the medians of the sepals. Subsequently, stamens form laterally on the flanks of the initial antesepalous stamens, giving rise to the clusters designated as antesepalous triplets. The simplest elaborations based on those common initial developmental steps include (1) adding additional lateral flanking stamens and (2) adding a single stamen in each antepetalous position between adjacent antesepalous groups. More complex elaborations are characteristic of (1) Carpenteria and Philadelphus, which form common primordia at the beginning of androecial development and, subsequently, have stamen primordia form on them, and (2) Deinanthe, which has an elongate hypanthial region on which numerous whorls of stamens are initiated. Carpenteria is unique among Hydrangeaceae in having groups of stamens that are initiated centrifugally in antepetalous positions, and this is similar to complex elements found among some Loasaceae. Generally, the polystemony of Hydrangeaceae that is based in the formation of antesepalous triplets is very similar to that found to evolve in parallel among various clades of rosids and asterids.