Chiral Silylation Reagents: Determining Configuration via NMR-Spectroscopic Coanalysis

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showed that when these two variables were controlled, the kidney was still able to increase sodium excretion in response to a salt load. Several lines of evidence argued for a small-molecule signal as a definitive modulator of sodium excretion by the kidney. However, the chemical nature of the suspected natriuretic agent remained unknown. Here we report the identification and natriuretic activity of two closely related small molecules isolated from human urine, xanthurenic acid 8-O-␤-D-glucoside and xanthurenic acid 8-O-sulfate. The two compounds were partially purified by activity-guided fractionation and subsequently identified by using NMR spectroscopic analyses of enriched active fractions. Both compounds caused substantial and sustained (1-to 2-h) natriuresis in rats and no or minimal concomitant potassium excretion. We believe these compounds constitute a class of kidney hormones that also could influence sodium transport in nonkidney tissues given that these tryptophan metabolites presumably represent evolutionarily old structures.diuresis ͉ kidney ͉ nonpeptidic ͉ sodium homeostasis ͉ NMR spectroscopy

Section: Resultssupporting

confidence: 65%

Section: Resultsmentioning

confidence: 99%

Identification of xanthurenic acid 8- O -β- d -glucoside and xanthurenic acid 8- O -sulfate as human natriuretic hormones

Cain¹,

Schroeder

Shankel³

et al. 2007

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“…In combination with the results from UV and infrared spectroscopic analysis, these data indicated that 3-hydroxyphenylalanine, commonly known as mtyrosine, is the major component of the active fraction isolated from the root exudates. This structural assignment was confirmed via an NMR-spectroscopic mixing experiment, whereby a small amount of synthetic m-tyrosine was added to the isolated active fraction (7). Finally, the absolute configuration of the isolated m-tyrosine was determined to be L by NMRspectroscopic comparison of its (S)-methoxytrifluoromethylphenylacetic acid [(S)-MTPA] derivative with the (R)-and (S)-MTPA derivatives of synthetic m-tyrosine (8).…”

Section: Resultsmentioning

confidence: 92%

Grass roots chemistry: meta -Tyrosine, an herbicidal nonprotein amino acid

Bertin

Weston²,

Huang

et al. 2007

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172

185

Fine fescue grasses displace neighboring plants by depositing large quantities of an aqueous phytotoxic root exudate in the soil rhizosphere. Via activity-guided fractionation, we have isolated and identified the nonprotein amino acid m-tyrosine as the major active component. m-Tyrosine is significantly more phytotoxic than its structural isomers o-and p-tyrosine. We show that mtyrosine exposure results in growth inhibition for a wide range of plant species and propose that the release of this nonprotein amino acid interferes with root development of competing plants. Acid hydrolysis of total root protein from Arabidopsis thaliana showed incorporation of m-tyrosine, suggesting this as a possible mechanism of phytotoxicity. m-Tyrosine inhibition of A. thaliana root growth is counteracted by exogenous addition of protein amino acids, with phenylalanine having the most significant effect. The discovery of m-tyrosine, as well as a further understanding of its mode(s) of action, could lead to the development of biorational approaches to weed control.allelopathy ͉ festuca ͉ rhizosphere ͉ root ecology ͉ Arabidopsis R oot exudation of small molecules plays a major role in plant ecosystems and is often associated with the development of competitive advantage through allelopathy (1, 2). Juglone, a highly phytotoxic naphthoquinone produced by black walnut (Juglans nigra L.), and sorgoleone, a substituted quinone from sorghum (Sorghum spp.), are two classic examples of potently active allelochemicals deposited via the plant's living root system ( Fig. 1) (3). Elucidation of the structures and mode of action of previously unknown root-derived phytotoxins could lead to new biorational approaches to weed control.Because of their stress tolerance and disease resistance, fescue (Festuca spp.) grasses are commonly used in landscape, roadside, and pasture settings, as well as for conservation purposes (4, 5). The unusual ability of many fine leaf fescue species to outcompete other plants is well known, and previous investigations suggested that fescue root exudates have phytotoxic properties (4). Here, we report the isolation, identification, and biological activity of m-tyrosine, a potent, structurally unusual broadspectrum phytotoxin exuded by the roots of some fine leaf fescue grasses. Results and DiscussionIn an initial field evaluation of 80 fine fescue cultivars, 8 cultivars with strong weed suppressive potential were identified and their allelopathic potential in laboratory settings was confirmed (4). Based on both field and laboratory results, we selected ''Intrigue,'' a common Chewing's fescue cultivar (Festuca rubra L. ssp. commutata), for further studies.To identify the allelopathic compound(s) contained in Intrigue root exudates, we developed an activity-guided separation scheme based on the inhibition of lettuce (Lactuca sativa L.) radicle elongation in a filter paper-based assay. By using this assay, we compared the phytotoxicity of root surface washes (hexanes, dichloromethane, methanol, and water) prepared from 2-w...

“…3) and pinoresinol in a ratio of Ϸ96:4. For the determination of the absolute configuration of the pinoresinol, we used our recently introduced chiral silylation reagents, which showed the caterpillars' compound to be (Ϫ)-pinoresinol of 94% enantiomeric purity (13,14).…”

Section: Resultsmentioning

confidence: 99%

“…In addition, small samples of the residue were analyzed by using combinations of gas chromatography and electron-impact ionization MS as well as HPLC and electrospray-ionization MS. For additional NMR spectroscopic and MS analyses, the extract was subjected to column chromatography on silica with a 1:1 mixture of ethyl acetate and hexane as solvent, which produced 0.05 mg of pure pinoresinol. For determination of its absolute configuration, we used our recently described chiral silylation reagents (12,13).…”

Section: Methodsmentioning

confidence: 99%

Pinoresinol: A lignol of plant origin serving for defense in a caterpillar

Schroeder

Campo

Grant

et al. 2006

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Pinoresinol, a lignan of wide distribution in plants, is found to occur as a minor component in the defensive secretion produced by glandular hairs of caterpillars of the cabbage butterfly, Pieris rapae. The compound or a derivative is appropriated by the larva from its normal food plant (the cabbage, Brassica oleracea). Pinoresinol was shown to be absent from the secretion if the larva was given a cabbage-free diet but present in the effluent if that diet was supplemented with pinoresinol. Pinoresinol is shown to be a feeding deterrent to ants (Formica exsectoides), indicating that it can complement the defensive action of the primary components of the secretion, a set of previously reported lipids called mayolenes. In the test with F. exsectoides, pinoresinol proved to be more potent than concomitantly tested mayolene-16.ignans comprise a large class of secondary metabolites in vascular plants. Derived from the three phenyl-propanoid precursors, p-coumaryl alcohol (1 in Fig. 1), coniferyl alcohol (2 in Fig. 1) and sinapyl alcohol (3 in Fig. 1), they fulfill important physiological functions in plants (1) and are of considerable pharmaceutical interest (2). For example, podophyllotoxin (4 in Fig. 1) derivatives are used extensively in anticancer treatments and have been shown recently to possess antiviral properties as well (3). Pinoresinol (5 in Fig. 1) is one of the structurally simplest lignans, being a dimer of coniferyl alcohol, and its frequent presence in woody or fibrous plants should come as no surprise [the Beilstein database (MDL Information Systems, San Leandro, CA) revealed 46 and 8 references, respectively, for the isolation of (ϩ)-pinoresinol and (Ϫ)-pinoresinol from plants] (4). Virtually any plant capable of producing lignin can be presumed to have the enzymes necessary to link two units of coniferyl alcohol (2 in Fig. 1) in a fashion leading to the bicyclic ring core of pinoresinol (5 in Fig. 1).The amount of pinoresinol produced by plants varies widely. Particularly high concentrations of pinoresinol have been found in young foliage, for example of Forsythia spp., as well as in the reproductive organs and seeds of many plants (5). The compound is therefore generally presumed to be a defensive agent, as is suggested also by its antihelminthic and antifungal activity (6-9). Animals are not known to produce pinoresinol or other dimeric lignols, nor have they been shown to acquire such compounds from plants. We here report the presence of pinoresinol in the defensive secretion of a caterpillar, the larva of Pieris rapae, the cabbage butterfly, one of the world's most familiar lepidopterans (10). We had earlier reported on the composition of this secretion, produced as droplets by glandular hairs on the back and flanks of the larva (11) (Fig. 2). We had noted the fluid to contain a series of structurally labile linolenic acid derivatives, the mayolenes (6 in Fig. 3), which we demonstrated to be protective against ants (Crematogaster lineolata) (11). We have found pinoresinol itself to also be dete...