Søren Rosendal Jensen

Gentianaceae: Chemotaxonomy and pharmacology of Gentianaceae

The occurrence of taxonomically informative types of compounds in the family Gentianaceae, namely iridoids, xanthones, mangiferin, and Cglucoflavones, has been recorded. The properties, biosynthesis, and distribution of each group of compounds are described. The iridoids (mainly secoiridoid glucosides) appear to be present in all species investigated, with a predominance of swertiamarin and/or gentiopicroside; c. 90 different compounds have been reported from 127 species in 24 genera. Xanthones are not universally present in Gentianaceae, but about 100 different compounds have been reported from 121 species in 21 genera. A coherent theory for the biosynthesis of xanthones, based partly on published biosynthetic results and partly on biosynthetic reasoning, is postulated and used to group the compounds into biosynthetic categories. Arranging the genera according to the xanthones present gives rise to four groups. Group 1 (Anthocleista, Blackstonia, Gentianopsis, Macrocarpaea, and Orphium) includes the taxa containing only few and biosynthetically primitive xanthones. Group 2 (Comastoma, Gentiana, Gentianella, Lomatogonium, Swertia, and, tentatively, Tripterospermum) contains xanthones with an intermediate degree of biosynthetic advancement. Group 3 (Frasera, Halenia, and Veratrilla) has the most advanced compounds, with the xanthones found in group 2 being the biosynthetic precursors. Group 4 (Canscora, Centaurium, Chironia, Eustoma, Hoppea, Ixanthus, and, with some reservation, Schultesia) contains another set of biosynthetically advanced compounds. A comparison of the above groups with strict consensus trees based on molecular data (trnL intron and matK sequences) and the new classification proposed by Struwe et al. (2002)

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.

Biosynthesis of secoiridoid glucosides in Oleaceae

Abstract The biosynthesis of the oleoside-type of glucosides (oleosides) has been investigated in two species of Oleaceae, namely Fraxinus excelsior and Syringa josikaea . Deuterated analogues of deoxyloganic acid, 8-epi-deoxyloganic acid, 7-epi-loganic acid and loganic acid were prepared. On administration of the above compounds high incorporations of deoxyloganic acid as well as of loganic acid and its 7-epimer were obtained, strongly implying that 7-ketologanic acid is an intermediate in the biosynthesis of oleosides. The incorporations were measured by 2 H NMR in several isolated secoiridoids all belonging to the oleosides. In addition, the content of acidic iridoids (both carbocyclic and seco-type) in two additional species of Oleaceae, namely Ligustrum ovalifolium and Phillyrea latifolia , were examined. Based on these results, a plausible biosynthetic route from deoxyloganic acid, 7-epi-loganic acid, 7-ketologanic acid, 8-epi-kingisidic acid, oleoside 11-methyl ester, 7-β-1- d -glucopyranosyl 11-methyl oleoside and ligstroside to oleuropein can now be presented.

NOVEL BIS-IRIDOID GLUCOSIDES FROM DIPSACUS SYLVESTRIS

Abstract In addition to the known iridoid glucosides loganin, sweroside and cantleyoside, Dipsacus sylvestris has provided 4 novel bis -iridoid glucosides named sylvestrosides I–IV, composed of swerosidic acid, secologanic acid, loganin and loganin aglucone. Sylvestroside I, II and III have been fully characterized by chemical conversions and by 13 C NMR spectroscopy. A probable formula for sylvestroside IV is presented.

Iridoid glucosides from Melampyrum

Abstract 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.

Excelsioside, a secoiridoid glucoside from Fraxinus excelsior

Abstract A new secoiridoid named excelsioside has been isolated from the leaves of Fraxinus excelsior along with several known secoirioids and verbascoside. The compounds were identified by NMR, and the structure of excelsioside was finally assigned on the basis of a long-range selective proton decoupling (LSPD) 13 C NMR experiment.

The distribution of iridoids in Bignoniaceae

The distribution of iridoids among the tribes of Bignoniaceae is shown. In the present work, 18 species from the tribes Bignonieae and Tecomeae as well as one from Eccremocarpeae have been investigated. These data combined with those obtained through a literature review were analysed and showed that iridoids occur predominantly in the tribe Tecomeae. In this tribe, a chemical distintion between the genera Tabebuia and Tecoma was observed: The iridoids in Tabebuia are decarboxylated whereas in Tecoma they are C-4 formylated. The species from Bignonieae are poorly investigated and only few reports have been published, however, the iridoids found are mainly C-4 carboxylated. The only exception, Dolichandra cynanchoides (=Macfadyena cynanchoides), with decarboxylated iridoids, is also morphologically abnormal in Bignonieae.

Iridoid mono- and di-glycosides in Mentzelia

Abstract 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 . 13 C and 1 H 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.

Sequestration of Glucosinolates and Iridoid Glucosides in Sawfly Species of the Genus Athalia and Their Role in Defense Against Ants

In this study, the larval sequestration abilities and defense effectiveness of four sawfly species of the genus Athalia (Hymenoptera: Tenthredinidae) that feed as larvae either on members of the Brassicaceae or Plantaginaceae were investigated. Brassicaceae are characterized by glucosinolates (GLSs), whereas Plantaginaceae contain iridoid glucosides (IGs) as characteristic secondary compounds. Athalia rosae and A. liberta feed on members of the Brassicaceae. Larvae of A. rosae sequester aromatic and aliphatic GLSs of Sinapis alba in their hemolymph, as shown previously, but no indolic GLSs; A. liberta larvae with a narrower host range sequester aliphatic as well as indolic GLSs from their host plant Alliaria petiolata. Larvae of A. circularis and A. cordata are specialized on members of the Plantaginaceae. Athalia circularis utilizes mainly Veronica beccabunga as host plant, whereas A. cordata feeds additionally on Plantago lanceolata. Both sawfly species sequester the IGs aucubin and catalpol. In V. beccabunga, catalpol esters and carboxylated IGs also occur. The high catalpol concentrations in hemolymph of A. circularis can only be explained by a metabolization of catalpol esters and subsequent uptake of the resulting catalpol. The carboxylated IGs of the plant are excreted. The IG-sequestering sawfly species are able to accumulate much higher glucoside concentrations in their hemolymph than the GLS-sequestering species, and the concentration of IGs in hemolymph increases constantly during larval development. The defensive effectiveness of hemolymph that contains GLSs or IGs and of the respective glucosides was tested in feeding-bioassays against a potential predator, the ant Myrmica rubra (Hymenoptera: Formicidae). Hemolymph of IG-sequestering cryptic A. cordata larvae has a higher deterrence potential than hemolymph of the GLS-sequestering conspicuous A. rosae larvae. The results show that glucoside sequestration is widespread in the genus Athalia, but that the specific glucoside uptake can result in different defense effectiveness against a predator species.

Caffeoyl phenylethanoid glycosides in Sanango racemosum and in the gesneriaceae

Abstract An investigation of Sanango racemosum for systematically useful glycosides has been performed. No iridoids could be detected, but reverse phase chromatography provided the caffeoyl phenylethanoid glycosides (CPGs) calceolarioside C and conandroside together with the new 2-(3,4-dihydroxyphenyl)ethyl 3-caffeoyl-β-allopyranoside which has been named sanangoside. The genus Sanago has previously been considered a member of Buddlejaceae, but recent work has shown that this is improbable. The presence of CPGs in S. racemosum combined with the lack of iridoid glucosides suggested a possible relationship with the Gesneriaceae. A survey of 20 species within this family showed that sanangoside was present in four species of subfamily Gesnerioideae and that all the investigated plants in the family contained CPGs, while no iridoids could be detected. The European genera Ramonda and Haberlea were characteristic by containing only the CPG-analogue myconoside, a dihydrocaffeoyl ester.