Terpenoids and bibenzyls of 25 liverwort Frullania species

Twenty-five Frullania species (liverworts) were chemically investigated. Fourteen species produce allergy-inducing sesquiterpene lactones. Eighteen species contain bibenzyls. The sesquiterpene lactones and bibenzyls are obtained as the major components and they are valuable chemosystematic markers of Frullania species. On the basis of their chemical constituents, Frullania species can be divided into five chemotypes: sesquiterpene lactone-bibenzyl type; sesquiterpene lactone type; bibenzyl type; monoterpene type and cyclocolorenone type.     

Sesquiterpenoids as chemosystematic markers in the subtribe Hypochaeridinae (Lactuceae,Asteraceae)

Sesquiterpene lactones are well established as chemosystematic markers in the Asteraceae family. From the Lactuceae tribe of the Asteraceae family a large number of sesquiterpene lactones – mainly of the guaiane type – have been isolated. One of the 11 subtribes of the Lactuceae recognized by Bremer is the subtribe Hypochaeridinae, which encompasses 10 genera with approximately 170 species. The present communication summarizes the sesquiterpene derivatives reported from these 10 genera, points out, which constituents are characteristic for particular groups, and discusses the occurrence of these secondary metabolites in a chemosystematic context. To this end, each of the reported sesquiterpenoids reported for the Hypochaeridinae is classified into one of three main compound classes (MCCs; eudesmane-, germacrane-, guaiane-derivatives) and into one of a number of compound classes (CCs) within these principal groups. The distribution of sesquiterpenoids belonging to these particular classes of sesquiterpenoids generally follows the currently accepted generic limits. However, the genus Helminthoteca, which is included into Picris by many authors, possesses an array of compounds implying a closer relationship to the genus Hypochaeris than to the remainder of the genus Picris. Furthermore, Leontodon subgenus Oporinia shows closer similarity in secondary metabolite patterns to the genus Picris than to Leontodon subgenus Leontodon. On the other hand Leontodon subgenus Leontodon has more chemical characters in common with the genus Hedypnois than with Leontodon subgenus Oporinia. These findings are in-line with recent results of molecular analyses, which imply that current generic limits within the Hypochaeridinae might not reflect the phylogeny of the subtribe.     

Chemosystematics of section Palaeonarthex of the Genus Ferula

Ferula species of the section Palaeonarthex contains various sesquiterpenoids. While C-15 terpenoid coumarins of the iresan type are the most characteristic constituents of species in the subsection Foetidissimae, sesquiterpene lactones and C-10 terpenoid coumarns are found in the subsection Tumidae and esters of the sesquiterpene alcohols in the subsection Jaeschkaenae. The biogenetic relationships of the Ferula sesquiterpenoids and their chemosystematic value are discussed.     

Caffeic acid ester derivatives and flavonoids of genus Arnaldoa (Asteraceae,Barnadesioideae)

The phytochemical composition of Arnaldoa species is barely known. In this work, the occurrence of caffeic acid ester derivatives and flavonoids in A. argentea, A. macbrideana and A. weberbaueri was established by liquid chromatography associated to high-resolution mass spectrometry analyses and comparison with data from isolated compounds. The distribution of chlorogenic acids in the genus Arnaldoa is herein described for the first time. The metabolite profile of Arnaldoa species was compared to that of Tithonia diversifolia, a known and rich source of chlorogenic acids and sesquiterpene lactones. In addition to the mono- and dicaffeoyl quinic acids present in T. diversifolia, Arnaldoa species exhibited the mono- and dicaffeoyl tartaric acids. Furthermore, mass features correspondent to that of sesquiterpene lactones present in T. diversifolia were not observed in Arnaldoa species. The chemotaxonomic implications of caffeic acid ester derivatives and flavonoid glycosides, as well as the potential absence of sesquiterpene lactones in the genus Arnaldoa and subfamily Barnadesioideae are discussed.     

Sesquiterpene Lactones from Centaurea zuccariniana and Their Antimicrobial Activity

Twenty‐nine compounds were isolated from the aerial parts of the Greek plant C. zuccariniana DC. The structures of the isolated compounds were established by means of NMR‐ (¹H,¹H‐COSY, ¹H,¹³C‐HSQC, HMBC, NOESY, and ROESY) and mass‐spectral analyses. These compounds comprise 13 sesquiterpene lactones, 14 flavonoids, two lignans, and one simple lactone. Among the isolated sesquiterpene lactones, three are new, namely one heliangolide, (1E,4Z)‐15‐hydroxy‐8α‐O‐(4′‐acetoxy‐3′‐hydroxy‐2′‐methylidenebutanoyl)‐6βH,7αH‐germacra‐1,4,11(13)‐trien‐6,12‐olide; and two eudesmanolides, 8α‐(4′,5′‐diacetoxyangeloyl)sonchucarpolide and one unusual eudesmanolide with an oxygenated bridge linking C(1) and C(4), named zuccarinin. The main sesquiterpene lactones were malacitenolide, cnicin, and 4′‐O‐acetylcnicin. These results are in agreement with those obtained from the previously studied Greek Centaurea sp. belonging to the section Acrolophus (Cass .) DC.; this finding could be of chemotaxonomic significance for the genus Centaurea. The in vitro antimicrobial activities of the isolated new sesquiterpene lactones were against eight bacteria and eight fungal species. A 96‐well microbioassay procedure for fast and easy evaluation of antibacterial and antifungal activities was applied to compare these compounds with commercial antibiotic and fungicide standards, and with previously isolated analogous sesquiterpene lactones tested by the same bioassay. All of the compounds tested showed moderate antibacterial, but significant antifungal activities; the present results corroborate with previous data, indicating that these types of compounds exhibit low or moderate antibacterial, but potent antifungal activities. The unusual eudesmanolide zuccarinin proved to be the most potent among the present tested sesquiterpene lactones, as well as among all previously tested eudesmanolides isolated from Greek Centaurea sp.     

Metabolite profiling of sesquiterpene lactones from Lactuca species. Major latex components are novel oxalate and sulfate conjugates of lactucin and its derivatives

Wounding leaves or stems of Lactuca species releases a milky latex onto the plant surface. We have examined the constituents of latex from Lactuca sativa (lettuce) cv. Diana. The major components were shown to be novel 15-oxalyl and 8-sulfate conjugates of the guaianolide sesquiterpene lactones, lactucin, deoxylactucin, and lactucopicrin. The oxalates were unstable, reverting to the parent sesquiterpene lactone on hydrolysis. Oxalyl derivatives have been reported rarely from natural sources. The sulfates were stable and are the first reported sesquiterpene sulfates from plants. Unusual tannins based on 4-hydroxyphenylacetyl conjugates of glucose were also identified. Significant qualitative and quantitative variation was found in sesquiterpene lactone profiles in different lettuce varieties and in other Lactuca spp. The proportions of each conjugate in latex also changed depending on the stage of plant development. A similar profile was found in chicory, in which oxalyl conjugates were identified, but the 8-sulfate conjugates were notably absent. The presence of the constitutive sesquiterpene lactones was not correlated with resistance to pathogens but may have a significant bearing on the molecular basis of the bitter taste of lettuce and related species. The induced sesquiterpene lactone phytoalexin, lettucenin A, was found in the Lactuca spp. but not in chicory.     

Sesquiterpene lactones and systematics of the genus Artemisia

The sesquiterpene lactones isolated from species in the genus Artemisia have been reviewed in an attempt to better understand the phylogeny and systematics of the four sections (subgenera), Abrotanum, Absinthium, Dracunculus and Seriphidium, proposed by Besser in 1829. The absence of hair on the receptacle is the only morphological characteristic separating species of Abrotanum from the species of Absinthium. There are no chemical characteristics segregating the species in these two subgenera since both produce eudesmanolides and guaianolides that are identical or biosynthetically similar. This suggests that the two subgenera could be combined into one (Artemisia) as proposed by Poljakov. The subgenus Seriphidium is composed of two geographical groups, one in the Old World and the other in the New World. The Old World species almost exclusively produce sesquiterpene lactones in the eudesmanolide class whereas the New World species (section Tridentatae) produce eudesmanolides and guaianolides, many of the latter being identical or structurally related to the sesquiterpene lactones in New World Abrotanum species. The chemical data in conjunction with geographic distributions suggest that the subgenus Seriphidium is polyphyletic and that the section Tridentatae originated from Abrotanum. Consequently, the Tridentate should be recognized as a subgenus separate and distinct from the Old World Seriphidium. There was insufficient information from the subgenus Dracunculus for interpretation.     

Molecular and phytochemical systematics of the subtribe Hypochaeridinae (Asteraceae,Cichorieae)

The systematics of the Hypochaeridinae subtribe was re-evaluated based on a combination of published and new molecular data. Newly found clades were additionally characterized using published and new phytochemical data. In addition to flavonoids and sesquiterpene lactones, which had been reviewed recently as chemosystematic markers in the Cichorieae, we analysed the reported occurrences of caffeic acid derivatives and their potential as chemosystematic markers. Our molecular results required further changes in the systematics of the genus Leontodon. Based on previous molecular data, Leontodon s.l.—i.e. including sections Asterothrix, Leontodon, Thrincia, Kalbfussia, and Oporinia (Widder 1975)—had been split into the genera Leontodon s.str. (sections Asterothrix, Leontodon, and Thrincia) and Scorzoneroides (sections Kalbfussia and Oporinia). Instead of splitting Leontodon into even a higher number of segregate genera we propose to include Hedypnois into Leontodon s.str. and here into section Leontodon. Moreover, sections Asterothrix and Leontodon should be merged into a single section Leontodon. The newly defined genus Leontodon is characterised by the unique occurrence of hydroxyhypocretenolides. The monophyly of the genus Hypochaeris is neither supported nor contradicted and potentially comprises two separate molecular clades. The clade Hypochaeris I comprises the majority of the European and Mediterranean as well as all South American taxa of Hypochaeris s.l. while the clade Hypochaeris II encompasses only H. achyrophorus L., H. glabra L., H. laevigata Benth. & Hook.f., and H. radicata L.     

Chemotaxonomy of Gonospermum and related genera

Aerial parts of Gonospermum fruticosum collected at several locations in the Canary Islands afforded, in addition to known compounds, four sesquiterpene alcohols related to costol and a sesquiterpene lactone, whose structures were established on the basis of their spectroscopic data and chemical transformations. Except for Gonospermum species collected on the island of Tenerife, those collected on the island of El Hierro and, in a previous study those from La Gomera, contain sesquiterpene lactones that can be used as chemotaxonomic markers confirming the inclusion of Gonospermum, Lugoa, and species of Tanacetum endemic to the Canary Islands in a genus that does not support the monophyly of Gonosperminae.     

Variation of sesquiterpene lactone contents in Lactuca altaica natural populations from Armenia

In recent years we initiated extensive studies on the characterization of the population structure of wild Lactuca relatives (WLRs) originating from their center of origin and diversity in Southwest Asia. A comparative phytochemical study of nine sesquiterpene lactones in natural populations of the wild lettuce L. altaica Fisch. & C.A. Mey. (Asteraceae) was performed, based on 22 plants, representing seven original individual seed samples derived from three localities representing three regions in Armenia. The compounds were profiled and quantified in leaves and roots of the plants, grown in a controlled glasshouse. The contents of major sesquiterpene lactones, that including the following eight guaianolides: cichorioside B, lactucin, 11β,13-dihydrolactucin, crepidiaside B, 8-deoxylactucin, jacquinelin, lactucopicrin/11β,13-dihydrolactucopicrin, as well as the germacranolide glucoside – lactuside A, were estimated by HPLC/PDA. The L. altaica plants could be characterized by the occurrence of lactuside A in their roots, and the mixture of lactucopicrin/11β,13-dihydrolactucopicrin in both their roots and leaves by relatively high amounts, similarly to results obtained for three commercial cultivars of L. sativa. The total content of sesquiterpene lactones in the roots was significantly higher than that in the leaves. This study is likely the first report of detailed screening of L. altaica natural populations and individuals, even by low sample size, for any trait. Species within the primary lettuce gene pool, should be considered as an attractive source of germplasm in further research and improvement of cultivated lettuce, Lactuca sativa L. While using interspecific hybridization in order to elevate the sesquiterpene levels in cultivated lettuces, the lactones quality (profile) and quantity, as well as the cross-ability level of the wild Lactuca spp. with the crop and fertility of the obtained offspring should be considered.     

Further Amphoricarpolides from the Surface Extracts of Amphoricarpos Complex from Montenegro

Analysis of composition of sesquiterpene lactone fraction of leaf cuticular neutral lipids of Amphoricarpos complex from two different localities in north Montenegro, i.e., canyon of river Tara (A. autariatus ssp. autariatus) and mountain Zeletin (A. autariatus ssp. bertisceus) afforded sesquiterpene lactones with guaianolide skeletons (17 compounds), so called amphoricarpolides, typical for this genus. Nine of them, 9 – 17 , were new compounds, and their structures were elucidated by detailed analyses of IR, NMR, and MS data.     

The metabolic interactions between Paramecium bursaria Ehrbg. and Chlorella spec. in the Paramecium bursaria-symbiosis

In an organism (strain C 1/2 from Dr. P. R. Hayes, Leeds) regarded as a typical representative of the genus Flavobacterium, flexirubin-type pigments have been identified. The Flavobacterium pigments contain structural elements of both, the pigments of the genus Flexibacter and the pigments of the genus Cytophaga. As flexirubin-type pigments seem to have a rather restricted distribution among bacteria, and have formerly proved to be useful chemosystematic markers for the flexibacteria, this new observation may indicate that there is a relatively close phylogenetic relationship between this type of flavobacteria and the Cytophaga-Flexibacter group.     

Antiviral and antimicrobial activities of three sesquiterpene lactones from Centaurea solstitialis L. ssp. solstitialis

Three sesquiterpene lactones (centaurepensin=chlorohyssopifolin A, chlorojanerin and 13-acetyl solstitialin A) isolated from the aerial parts of Centaurea solstitialis L. ssp. solstitialis (Asteraceae) were investigated for antimicrobial and antiviral activities. For the antimicrobial activity assessment, both standard and isolated strains of Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, Staphylococcus aureus, Candida albicans and C. parapsilosis were employed by the microdilution method. Herpes simplex type-1, a DNA virus, and Parainfluenza, an RNA virus, were employed for the determination of the antiviral activity of these three sesquiterpene lactones using Vero cell lines. Ampicilline, ofloxocine, ketoconazole, fluconazole, acyclovir and oseltamivir were used as the reference drugs. 13-Acetyl solstitialin A displayed remarkable antibacterial activity against isolated strains of E. faecalis at 1 μg/ml concentration, which was close to the effective concentrations of ampicillin. The same compound also showed significant activity against the DNA virus, being as potent as the reference compound acyclovir at maximum and minimum concentrations of 16–<0.00006 μg/ml. This is the first report showing that 13-acetyl solstitialin A possesses significant antiviral activity.     

A new infrageneric classification and phylogenetic trends in the genusRhododendron (Ericaceae)

Recent studies have improved the infrageneric classification ofRhododendron, including my own investigations on flavonoids and anthocyanins as chemosystematic markers. From a synoptical comparison of morphological, anatomical and phytochemical characters a new system for the genus is proposed. Phylogenetic character progressions and relationships among subgenera, sections and subsections are discussed and illustrated. Key positions for subg.Candidastrum between chori subgenerumRhododendron andNomazalea, and for subg.Choniastrum between chori subgenerumHymenanthes andNomazalea are suggested.     

Sesquiterpene lactones and their precursors as chemosystematic markers in the tribe Cichorieae of the Asteraceae

This review summarizes all reports on sesquiterpene lactones and their immediate precursors from the Cichorieae (Lactuceae) tribe of the Asteraceae. A total of 360 compounds have been reported from this tribe. The reported substances belong to three classes of sesquiterpenoids: guaianolides (243 compounds), eudesmanolides (73 compounds), and germacranolides (44 compounds). Sources of these compounds encompass 139 taxa from 31 different genera. The distribution of these lactones within the tribe Cichorieae is discussed in a chemosystematic context. Moreover, some general ideas about the interpretation of chemosystematic data are discussed.     

New germacrolide- and heliangolide-type sesquiterpene lactones from Melampodium linearilobum

Chemical analysis of Melampodium linearilobum yielded, besides coumarin, seven germacrolide-type sesquiterpene lactones, linearilobin A to G and two heliangolides, linearilobin H and I. All new sesquiterpene lactones are oxygenated at C-14 and C-15 and differ by the number and types of ester moieties at C-8, C-14 and C-15. M. linearilobum represents the first species within the genus known to produce germacrolides and heliangolides instead of the more common melampolides.     

Evolutionary implications of herbivory onVernonia (Compositae)

A field insect feeding experiment was conducted with two species ofVernonia which produce the sesquiterpene lactone glaucolide-A, one species which does not contain this bitter compound, and two F₁ hybrid combinations. Also, naturalVernonia populations were observed over a two year period for their degree of herbivory. Contrary to the pattern observed in laboratory feeding preference tests,Vernonia flaccidifolia, the species lacking sesquiterpene lactones, was consistently fed upon less by insects than wereV. gigantea andV. glauca. Even though glaucolide-A appears to adequately protect some Vernonias against herbivores, especially mammals,Vernonia flaccidifolia has lost this compound. ApparentlyV. flaccidifolia has evolved an alternative defensive mechanism which is more effective against insects but less effective against mammalian herbivores.     

Variation of sesquiterpene lactones in Lactuca aculeata natural populations from Israel,Jordan and Turkey

A comparative phytochemical study of seven sesquiterpene lactones in natural populations of the wild lettuce Lactuca aculeata Boiss. (Asteraceae) was performed, based on 23 accessions derived from eight, two, and single localities from Israel, Jordan, and Turkey, respectively. The compounds were profiled and quantified in leaves and roots of the plants, grown from achenes (cypselas) in a greenhouse under controlled conditions, using reverse phase HPLC with on-line photodiode array detector. In the present study, L. aculeata was confirmed as a taxon strongly characterized by four dominant sesquiterpene lactones: 8-deoxylactucin, jacquinelin, crepidiaside B and lactuside A. An analysis of quantitative results of these four constituents led to the following conclusions: (i) the sesquiterpene lactone contents varied significantly, mainly within the populations; however, for two variables (crepidiaside B and lactuside A in root samples) the contents varied mostly between populations, (ii) these differences are likely to be genetically controlled since all accessions were grown under standardized glasshouse conditions. Accessions containing high levels of some sesquiterpene lactones were found in several populations. These traits should be conserved in situ and ex situ and utilized in further research and lettuce improvement.     

Neue melampolide und cis,cis-germacranolide aus vertretern der subtribus melampodiinae

The investigation of four South American species of the tribe Heliantheae afforded in addition to known compounds 14 new sesquiterpene lactones, mostly belonging to the melampolides, but four being further examples of cis,cis-germacranolides. The stereochemistry is established by intensive ¹H-NMR studies and some chemical transformations. Some of the new lactones were only obtainable as inseparable mixtures of 2-methylbutyric and isovaleric esters. Furthermore a new acetylenic aldehyde was isolated. The chemotaxonomic situation is discussed especially with regard to the position of the genus Smallanthus.