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 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 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.     

头花马先蒿和管花马先蒿的化学成分

从头花马先蒿全草中发现13个化合物,经波谱分析鉴定为：（±）-松脂素（1）、金合欢素（2）、木犀草素（3）、7．去氧栀子新苷（4）、yuheinoside（5）、euphroside（6）、mussaenosidic acid（7）、莫桑苷（8）、桃叶珊瑚苷（9）、角胡麻苷（10）、异角胡麻苷（11）、贞桐苷A（12）和开德苷元（13）。从管花马先蒿全草中发现4个化合物,经鉴定为：（＋）．dehydrovomifoliol（14）、催吐萝芙木醇（15）、ω-hydroxypropioguaiacone（16）和3-hydroxy-1-（4-hydroxy-3,5-dimethoxyphenyl）-1-propanone（17）。所有化合物均为首次在该种中发现。     

Microorganisms and nematodes increase levels of secondary metabolites in roots and root exudates of Plantago lanceolata

Plant secondary metabolites play an important role in constitutive and inducible direct defense of plants against their natural enemies. While induction of defense by aboveground pathogens and herbivores is well-studied, induction by belowground organisms is less explored. Here, we examine whether soil microorganisms and nematodes can induce changes in levels of the secondary metabolites aucubin and catalpol (iridoid glycosides, IG) in roots and root exudates of two full-sib families of Plantago lanceolata originating from lines selected for low and high constitutive levels of IG in leaves. Addition of soil microorganisms enhanced the shoot and root biomass, and the concentration of aucubin in roots of both Plantago lines without affecting IG levels in the rhizosphere. By contrast, nematode addition tended to reduce the root biomass and enhanced the stalk biomass, and increased the levels of aucubin and catalpol in root exudates of both Plantago lines, without affecting root IG concentrations. The Plantago lines did not differ in constitutive levels of aucubin and total IG in roots, while the concentration of catalpol was slightly higher in roots of plants originally selected for low constitutive levels of IG in leaves. Root exudates of “high IG line” plants contained significantly higher levels of aucubin, which might be explained by their higher root biomass. We conclude that soil microorganisms can induce an increase of aucubin concentrations in the roots, whereas nematodes (probably plant feeders) lead to an enhancement of aucubin and catalpol levels in root exudates of P. lanceolata. A potential involvement of secondary metabolites in belowground interactions between plants and soil organisms is discussed.     

Iridoid glucosides as sources of cyclopentanoid 1,5-dialdehydes: Conversion of aucubigenin to aucommial and eucommiol

Aucubigenin, which exists only in the closed hemiacetal form, has been transformed into a stable conjugated 1,5-dialdehyde form, ‘eucommialrs, by a base-catalysed Δ⁷ → Δ⁸ double-bond shift. Further reduction of eucommial leads to eucommiol, which co-occurs with aucubin in the autumn in Eucommia ulmoides and Aucuba japonica. The successful transformation of aucubin to eucommiol seems to support an in vivo relationship between these compounds.     

Chemical markers in Veronica sect. Hebe. III

In a continued chemosystematic investigation of the water-soluble compounds in Veronica sect. Hebe, we have investigated two more of the species formerly classified as Parahebe. Both species contained mannitol in considerable amounts and in addition some glucosides of iridoid acids. Veronica cheesemanii was characterised by aucubin and its esters: 2′-O-benzoylaucubin and an aucubin diester named cheesemanioside. The main iridoid compounds in Veronica hookeriana were catalpol and its ester verminoside, but this species also contained the sugar ester methyl 1-O-benzoyl-3-α-glucuronosylglycerol and a caffeoyl phenylethanoid glycoside (CPG) named parahebeoside, a 2′-O-β-xylopyranosyl derivative of the known plantamajoside. The results show that the studied species of the former genus Parahebe are very different with regard to their chemical content. This is in agreement with the DNA sequence data and implies the genus was polyphyletic as previously circumscribed.     

8-Epiloganin,an iridoid glucoside from Odontites verna

Odontites verna subsp. serotina contains besides odontoside, aucubin, mussaenoside, shanzhiside methyl ester and catalpol, a new iridoid glucoside, 8-epiloganin.     

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).     

Biosynthesis of the iridoids aucubin antirrinoside from 8-epi-deoxyloganic acid

²H NMR spectroscopy shows that 8-epi-deoxy[6,7,8,10-²H₄]loganic acid is efficiently incorporated into aucubin in Plantago major and Scrophularia racemosa, and into antirrinoside in Antirrhinum majus. Deoxyloganic acid produced no observable incorporation in these species.     

Plant community diversity influences allocation to direct chemical defence in Plantago lanceolata

Background

Forecasting the consequences of accelerating rates of changes in biodiversity for ecosystem functioning requires a mechanistic understanding of the relationships between the structure of biological communities and variation in plant functional characteristics. So far, experimental data of how plant species diversity influences the investment of individual plants in direct chemical defences against herbivores and pathogens is lacking.

Methodology/Principal Findings

We used Plantago lanceolata as a model species in experimental grasslands differing in species richness and composition (Jena Experiment) to investigate foliar concentrations of the iridoid glycosides (IG), catalpol and its biosynthetic precursor aucubin. Total IG and aucubin concentrations decreased, while catalpol concentrations increased with increasing plant diversity in terms of species or functional group richness. Negative plant diversity effects on total IG and aucubin concentrations correlated with increasing specific leaf area of P. lanceolata, suggesting that greater allocation to light acquisition reduced the investment into these carbon-based defence components. In contrast, increasing leaf nitrogen concentrations best explained increasing concentrations of the biosynthetically more advanced IG, catalpol. Observed levels of leaf damage explained a significant proportion of variation in total IG and aucubin concentrations, but did not account for variance in catalpol concentrations.

Conclusions/Significance

Our results clearly show that plants growing in communities of varying species richness and composition differ in their defensive chemistry, which may modulate plant susceptibility to enemy attack and consequently their interactions with higher trophic level organisms.     

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.     

Structure-dependent reactivity of oxyfunctionalized acetophenones in the photooxidation of DNA: base oxidation and strand breaks through photolytic radical formation (spin trapping, EPR spectroscopy, transient kinetics) versus photosensitization (electron transfer, hydrogen-atom abstraction)

The photooxidative damage of DNA, specifically guanine oxidation and strand-break formation, by sidechain-oxyfunctionalized acetophenones (hydroxy, methoxy, tert-butoxy and acetoxy derivatives), has been examined. The involvement of triplet-excited ketones and their reactivity towards DNA has been determined by time-resolved laser-flash spectroscopy. The generation of carbon-centered radical species upon Norrish-type I cleavage has been assessed by spin-trapping experiments with 5,5-dimethyl-1-pyrroline N-oxide, coupled with electron paramagnetic resonance spectroscopy. The observed DNA-base oxidation and strand-break formation is discussed in terms of the peroxyl radicals derived from the triplet-excited ketones by α cleavage and molecular oxygen trapping, as well as direct interaction of the excited states by electron transfer and hydrogen-atom abstraction. It is concluded that acetophenone derivatives, which produce radicals upon photolysis, in particular the hydroxy (AP-OH) and tert-butoxy (AP-O^tBu) derivatives, are more effective in oxidizing DNA.     

N-acetyl-(L-Ala) 3 -p-nitroanilide as a new chromogenic substrate for elastase

The introduction of a useful new chromogenic substrate for the determination of elastase (EC 3.4.4.7) activity is described. N-acetyl-L-Ala-L-Ala-L-Ala-$\text{p}$-nitroanilide (AcAla₃NA) is a new specific elastase substrate whose hydrolysis can be followed spectrophotometrically at 410 nm in a wide pH range. Its rate of hydrolysis by α-chymotrypsin (EC 3.4.4.5) and trypsin (EC 3.4.4.4.) is 0.02% and 0.001% respectively compared to its rate of hydrolysis by elastase. As little as 0.1 μg elastase/ml can be satisfactorily determined. At pH 8, K_m = 0.88 mM and k_cat = 11.9 sec^?1.     

Mechaism of Arthrobacter sialophilus neuraminidase: The binding of substrates and transition-state analogs

2-Deoxy-2,3-dehydro-N-acetylneuraminic acid and its methyl ester are competitive inhibitors of Arthrobacter sialophilus neuraminidase with K_i = 1.4 × 10^?6$\text{M}$ and 4.8 × 10^?5$\text{M}$, respectively. The K_m for the substrate, N-acetylneuraminlactose, is 1.0 × 10^?3$\text{M}$. These data, taken together with the conformation of these compounds, indicate that these compounds are transition-state analogs of the enzyme. These results also suggest that the substrate upon binding to neuraminidase is distorted to a conformation approaching that of a half-chair.     

6-O-α-Sinuatosylaucubin from Verbascum sinuatum

From Verbascum sinuatum, besides aucubin, harpagide, 6-O-β-d-xylopyranosylaucubin and sinuatol (6-O- α-l-rhamnopyranosylaucubin), a new iridoid glycoside, sinuatoside, has been isolated and its structure elucidated as 6-O-(3-O-β-d-xylopyranosyl)α-d-galactopyranosyl aucubin on the basis of spectral data and chemical modifications. For the new disaccharide unit of the latter compound the name sinuatose is proposed.     

Slow decomposition of very fine roots and some factors controlling the process: a 4-year experiment in four temperate tree species

Background and aims

Nitrate leaching from intensively cropped soils represents a huge environmental problem. In order to diversify the range of nitrogen management strategies, this investigation is focused on the effects of ribwort plantain, Plantago lanceolata L., and its allelochemicals on soil N mineralization.

Methods

High-performance liquid chromatography was used in this study for phytochemical analysis of the major allelochemicals aucubin, catalpol, and verbascoside. Soil incubation experiments demonstrated a significant suppression of soil N mineralization caused by the incorporation of the iridoid glycoside (IG) aucubin, leaf material of two varieties (P. lanceolata cv. Libor and cv. Arterner), and an aqueous extract of P. lanceolata leaves.

Results

Throughout the growing season, the two varieties conspicuously differed in aucubin and verbascoside contents as well as in leaf dry weight. In soil incubation experiments, incorporated leaf material of both varieties affected long-term low soil nitrate concentrations. Experimental aucubin application resulted in an inhibitory effect on soil N mineralization. This was not true for the IG catalpol. Furthermore, we observed a negative relationship between IG concentrations and inorganic soil nitrogen concentrations when the soil was incubated with aqueous P. lanceolata leaf extract of different concentrations.

Conclusion

This study enforced the hypothesis that allelochemicals of P. lanceolata have an active role in a suppression effect on soil N mineralization. Further research may be necessary to investigate the specific effects of P. lanceolata allelochemicals on the nitrogen cycle.     

Proton NMR study of coordinated imidazoles in low-spin ferric heme complexes. Assignment of single proton histidine resonance in hemoproteins

The proton signals for the coordinated axial imidazoles in a series of low-spin ferric bis-imidazole complexes with natural porphyrin derivatives have been located and assigned. The methyl signals of several methyl-substituted imidazoles have also been resolved for the mixed ligand complexes of imidazole and cyanide ion. The imidazole spectra for the bis complexes are essentially the same as those reported earlier for synthetic porphyrins, with the hyperfine shifts exhibiting comparable contributions from the dipolar and contract interactions. The contact contribution reflects spin transfer into a vacant imidazole π orbital. The spectra of both the mono- and bis-imidazole complex concur in predicting that only the 2-H and 5CH₂ signals of an axial histidine are likely to resonate clearly outside the diamagnetic 0 to ?10 ppm from TMS region in hemoproteins. However, both the 2-H and 4-H imidazole peaks are found to be too broad to detect in a hemoprotein. Hence, it is suggested that the pair of non-heme, single proton resonances in low-spin met-myoglobin cyanides arise from the non-equivalent methylene protons at the 5-position of the histidyl imidazole. Both the resonance positions and relative linewidths in the model compounds are consistent with the data for this pair of protons in myoglobins. The possible interpretations of the average downfield bias of these signals as well as the magnitude of their spacing, are discussed in terms of the conformation of the proximal histidine relative to the heme group.     

Neue labdan-derivate aus Aristeguietia buddleaefolia

The aerial parts of Aristeguietia buddleaefolia afforded, in addition to known compounds, three new diterpenes, all being 12, 13-E-abienol derivatives. A further diterpene turned out to be jhanidiol-18-O-acetate, isolated earlier from an Ageratina species. Furthermore two derivatives of hydroxy dihydroconiferyl alcohol are present. The structures were elucidated by spectroscopic methods and by some chemical transformations.     

Eucommia ulmoides Oliver Extract,Aucubin, and Geniposide Enhance Lysosomal Activity to Regulate ER Stress and Hepatic Lipid Accumulation

Eucommia ulmoides Oliver is a natural product widely used as a dietary supplement and medicinal plant. Here, we examined the potential regulatory effects of Eucommia ulmoides Oliver extracts (EUE) on hepatic dyslipidemia and its related mechanisms by in vitro and in vivo studies. EUE and its two active constituents, aucubin and geniposide, inhibited palmitate-induced endoplasmic reticulum (ER) stress, reducing hepatic lipid accumulation through secretion of apolipoprotein B and associated triglycerides and cholesterol in human HepG2 hepatocytes. To determine how EUE diminishes the ER stress response, lysosomal and proteasomal protein degradation activities were analyzed. Although proteasomal activity was not affected, lysosomal enzyme activities including V-ATPase were significantly increased by EUE as well as aucubin and geniposide in HepG2 cells. Treatment with the V-ATPase inhibitor, bafilomycin, reversed the inhibition of ER stress, secretion of apolipoprotein B, and hepatic lipid accumulation induced by EUE or its component, aucubin or geniposide. In addition, EUE was determined to regulate hepatic dyslipidemia by enhancing lysosomal activity and to regulate ER stress in rats fed a high-fat diet. Together, these results suggest that EUE and its active components enhance lysosomal activity, resulting in decreased ER stress and hepatic dyslipidemia.