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Chemical Evidence (chemical + evidence)

Distribution by Scientific Domains

Chemistry	73%
Life Sciences	20%

Selected Abstracts

Hydrogen Atom Transfer Experiments Provide Chemical Evidence for the Conformational Differences between C - and O -Disaccharides

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2010
Elisa I. León
Abstract The glycopyran-6- O -yl radical promoted hydrogen atom transfer reaction (HAT) between the two pyranose units of ,- D -Manp -(1,4)-,- D -Glcp and ,- D -Manp -(1,4a)-4a-carba-,- D -Glcp disaccharides provides supporting chemical evidence for the conformational differences between O - and C -glycosyl compounds. In the O -disaccharide the 6-alkoxyl radical, generated under oxidative or reductive conditions, abstracts exclusively the hydrogen at C-5, via a completely regioselective 1,8-HAT reaction. This may be attributable to the conformational restriction of the glycosidic and aglyconic bonds due principally to steric and stereoelectronic effects. On the contrary, very little regioselectivity is observed in the homologous C -disaccharide and a mixture of compounds generated by 1,5-, 1,6-, and 1,8-HAT processes where the abstraction occurs at hydrogen atoms positioned at C-4a, C-1,, and C-5,, respectively, has been obtained. This study has been extended to simpler O - and C -glycosides, where the aglycon was a straight n -alkyl alcohol tether of five atoms; in general, all of the results obtained are shown to be consistent with a major conformational flexibility of the C -glycosidic bond. [source]

Host plant adaptations in myrtaceous-feeding Pergid sawflies: essential oils and the morphology and behaviour of Pergagrapta larvae (Hymenoptera, Symphyta, Pergidae)

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2000
S. SCHMIDT
Australian pergine sawflies typically feed on eucalypts and other closely-related Myrtaceae, which are known for their high content of essential oils. We describe a novel morphological adaptation of the inner mandibular surface of larval stage Pergagrapta species, which feed on leaves of Melaleuca quinquenervia (Myrtaceae). This ,scopa mandibularis' forms an extensive mesh of setaceous papillae on what is usually the grinding surface of the mandible. Behavioural, chemical and morphological investigations of the sawfly- Melaleuca system suggest that the scopa may function in the physical separation of toxic leaf oils from the diet. The oils are stored in a pharyngeal diverticulum from where they are ejected under two circumstances. Oil from the diverticulum is voided prior to feeding and/or during feeding at night, which indicates a mechanism to eliminate host-associated oils. Larvae rest in close aggregations during the day, when they retain a full diverticulum, but the oils may be emitted for defensive purposes when larvae are disturbed. Chemical evidence suggests that 1,8-cineole, the major component in the M. quinquenervia leaves, is selectively metabolized to a more soluble hydroxycineole. We postulate that the separation and regurgitation of oils is not only a defence mechanism against predators, as usually stated, but also a mechanism by which pergid larvae eliminate oils from their diet, to reduce the toxicity of their food plants. [source]

Hydrogen Atom Transfer Experiments Provide Chemical Evidence for the Conformational Differences between C - and O -Disaccharides

Geostatistical and multi-elemental analysis of soils to interpret land-use history in the Hebrides, Scotland

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2007
J.A. Entwistle
In the absence of documentary evidence about settlement form and agricultural practice in northwest Scotland before the mid-18th century, a geoarchaeological approach to reconstructing medieval land use and settlement form is presented here. This study applies multielemental analysis to soils previously collected from a settlement site in the Hebrides and highlights the importance of a detailed knowledge of the local soil environment and the cultural context. Geostatistical methods were used to analyze the spatial variability and distribution of a range of soil properties typically associated with geoarchaeological investigations. Semivariograms were produced to determine the spatial dependence of soil properties, and ordinary kriging was undertaken to produce prediction maps of the spatial distribution of these soil properties and enable interpolation over nonsampled locations in an attempt to more fully elucidate former land-use activity and settlement patterns. The importance of identifying the spatial covariance of elements and the need for several lines of physical and chemical evidence is highlighted. For many townships in the Hebrides, whose precise location and layout prior to extensive land reorganization in the late 18th,early 19th century is not recoverable through plans, multi-elemental analysis of soils can offer a valuable prospective and diagnostic tool. © 2007 Wiley Periodicals, Inc. [source]

Study on the Constituents of Roots of Aceriphyllum rossii

HELVETICA CHIMICA ACTA, Issue 9 2010
Le Thi Kim Van
Abstract A new stereoisomer of a tetrahydrofuranoid lignan, acerifuranoid A (1), and two new oleanane-type triterpenoids, aceriphyllic acids J and K (2 and 3), were isolated from the roots of Aceriphyllum rossii. Their structures were elucidated on the basis of spectroscopic analyses and chemical evidence. These isolated compounds exhibited weak cytotoxic activity against various cancer cell lines with IC50>150,,M. [source]

Triterpenoid Ester Saponins from Dipteronia dyeriana

HELVETICA CHIMICA ACTA, Issue 9 2008
Rong Guo
Abstract The phytochemical investigation of Dipteronia dyeriana (Aceraceae) resulted in the isolation and identification of five new triterpenoid ester saponins, dipterosides A,E (1,5). Their structures were elucidated by spectroscopic methods and chemical evidence. The inhibitory activities of these compounds against human leukemia K562 and human hepatoma HepG2 cells were also evaluated. [source]

Withanolides from Withania adpressa

HELVETICA CHIMICA ACTA, Issue 2 2007
Hasna Abdeljebbar, Lalla
Abstract From the leaves of Withania adpressa, a plant endemic to Sahara of Morocco and Algeria, the novel steroidal lactone (22R)-14,,15,,17,,20, -tetrahydroxy-1-oxowitha-2,5,24-trien-26,22-olide (=,(15S,17S)-14,15,17,20-tetrahydroxy-22,26-epoxyergosta-2,5,24-triene-1,26-dione; 1), was isolated, along with three known compounds, withanolides F (2), J (3), and oleanolic acid. Their structures were mainly solved by in-depth 1D- and 2D-NMR (including ADEQUATE) experiments, as well as by HR-MS analyses and chemical evidence. [source]

A New Ketone and a Known Anticancer Triterpenoid from the Leaves of Onosma limitaneum

HELVETICA CHIMICA ACTA, Issue 2 2005
Uddin Ahmad, Viqar
A new ketone, onosmone (1), and a known anticancer triterpenoid, bauerenone, besides , -sitosterol glycoside were isolated for the first time from the CHCl3 extract of the leaves of Onosma limitaneum. The structures of these compounds were established on the basis of spectral and chemical evidence. [source]

Novel Polyoxygenated Spirostanol Glycosides from the Rhizomes of Helleborus orientalis

HELVETICA CHIMICA ACTA, Issue 2 2003
Yoshihiro Mimaki
The two new polyoxygenated spirostanol bisdesmosides 1 and 2 and the new trisdesmoside 3, named hellebosaponin A (1), B (2), and C (3), respectively, were isolated from the MeOH extract of the rhizomes of Helleborus orientalis. The structures of the new compounds were elucidated as (1,,3,,23S,24S)-21-(acetyloxy)-24-[(, - D -fucopyranosyl)oxy]-3,23-dihydroxyspirosta-5,25(27)-dien-1-yl O-, - D -apiofuranosyl-(1,3)- O -(4- O -acetyl- , - L -rhamnopyranosyl)-(1,2)- O -[, - D -xylopyranosyl-(1,3)]- , - L -arabinopyranoside (1), (1,,3,,23S,24S)- 21-(acetyloxy)-24-{[O - , - D -glucopyranosyl-(1,4)- , - D -fucopyranosyl]oxy}-3,23-dihydroxyspirosta-5,25(27)-dien-1-yl O - , - D -apiofuranosyl-(1,3)- O -(4- O -acetyl- , - L -rhamnopyranosyl)-(1,2)- O -[, - D -xylopyranosyl-(1,3)]- , - L -arabinopyranoside (2), and (1,,3,,23S,24S)-24-[(, - D -fucopyranosyl)oxy]-21-{[O - , - D -glucopyranosyl-(1,2)- , - D -galactopyranosyl]oxy}-3,23-dihydroxyspirosta-5,25(27)-dien-1-yl O - , - D -apiofuranosyl-(1,3)- O -(4- O -acetyl- , - L -rhamnopyranosyl)-(1,2)- O -[, - D -xylopyranosyl-(1,3)]- , - L -arabinopyranoside (3), respectively, on the basis of detailed spectroscopic studies and chemical evidence. [source]

Balance of xanthophylls molecular and protonated molecular ions in electrospray ionization

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2005
Thais Guaratini
Abstract This paper reports the chemical evidence of the balance between radical molecular ions and protonatedmolecules of xanthophylls (an oxygen-containing carotenoid) with a conjugated ,-system (polyene) and oxygen as a heteroatom in ESI and HRESI mass spectrometry. The ionization energy of neutral xanthophylls was calculated by semi-empirical methods. The results were compared with those previously published for carotenoids and retinoids, which have also been shown in ESI-MS to form M+, and [M + H]+, respectively. This study demonstrates, for the first time, the correlation of an extended conjugation and the presence of oxygen in the formation and balance of M+, or [M + H]+ for the carotenoids, neoxanthin, lutein, violaxanthin and zeaxanthin. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Characterization of two minor saponins from Cordia piauhiensis by 1H and 13C NMR spectroscopy

MAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2005
Renata P. Santos
Abstract A careful NMR analysis with full assignment of the 1H and 13C spectral data for two minor saponins isolated from stems of Cordia piauhiensis is reported. These saponins were isolated by high-performance liquid chromatography and characterized as 3,- O -[,- L -rhamnopyranosyl-(1 , 2)-,- D -glucopyranosyl]pomolic acid 28- O -[,- D -glucopyanosyl-(1 , 6)-,- D -glucopyranosyl] ester (1) and 3,- O -[,- L -rhamnopyranosyl-(1 , 2)-,- D -glucopyranosyl]oleanolic acid 28- O -[,- D -xylopyranosyl-(1 , 2)-,- D -glucopyanosyl-(1 , 6)-,- D -glucopyranosyl] ester (2). Their structures were established using a combination of 1D and 2D (1H, 1H-COSY, TOCSY, NOESY, gs -HMQC and gs -HMBC) NMR techniques, electrospray ionization mass spectrometry and chemical evidence. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Natural hybridization between Senecio jacobaea and Senecio aquaticus: molecular and chemical evidence

MOLECULAR ECOLOGY, Issue 8 2004
HEATHER KIRK
Abstract Hybridization is known to be involved in a number of evolutionary processes, including species formation, and the generation of novel defence characteristics in plants. The genus Senecio of the Asteraceae family is highly speciose and has historically demonstrated significant levels of interspecific hybridization. The evolution of novel chemical defence characteristics may have contributed to the success of Senecio hybrids. Chemical defence against pathogens and herbivores has been studied extensively in the model species Senecio jacobaea, which is thought to hybridize in nature with Senecio aquaticus. Here, we use amplified fragment length polymorphisms (AFLPs) and pyrrolizidine alkaloid (PA) composition to confirm that natural hybridization occurs between S. jacobaea and the closely related species S. aquaticus. AFLPs are also used to estimate the ancestry of hybrids. We also demonstrate that even highly back-crossed hybrids can possess a unique mixture of defence chemicals specific to each of the parental species. This hybrid system may therefore prove to be useful in further studies of the role of hybridization in the evolution of plant defence and resistance. [source]

Linkage disequilibrium and natural selection for mimicry in the Batesian mimic Hypolimnas misippus (L.) (Lepidoptera: Nymphalidae) in the Afrotropics

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010
IAN J. GORDON
On two occasions, on opposite sides of the African continent (Cape Coast, Ghana, and Dar es Salaam, Tanzania), high adult population densities in the polymorphic butterfly Hypolimnas misippus (a presumed mimic of Danaus chrysippus) were followed by linkage disequilibrium in combinations of fore- and hindwing colour patterns. On both occasions, disequilibrium was caused by significant changes in morph frequencies favouring rarer and more mimetic forms. Recaptures were too few for analysis at Dar, although the changes there took place within a single generation and must have been the result of differential survival. Recapture rate data and survival rate estimates at Cape Coast support the hypothesis that selective predation was responsible, as does the observation of synchronous linkage disequilibrium at Dar in the model D. chrysippus, indicating parasitic mimicry. There was clear selection for the perfection of mimicry for forewings at Dar and for hindwings at Cape Coast. Disequilibrium is also reported for two other sites, Legon (Ghana) and Boksburg (South Africa) and, in all four sites, it was associated with an increase in the most mimetic forms. New chemical evidence is presented to support the contention that D. chrysippus is a defended model. Although all the evidence leads to the conclusion that H. misippus is a Batesian mimic of D. chrysippus, many questions remain, particularly with regard to the identity of predators, the episodic nature of selective predation events, and their apparent lack of lasting and significant impact on overall gene frequencies. We conclude that H. misippus presents both challenges and opportunities for studies on mimicry, and we suggest that linkage disequilibrium can be a useful generic indicator for Gestalt predation on polymorphic prey. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 180,194. [source]

A C-terminal disulfide bond in the copper-containing amine oxidase from pea seedlings violates the twofold symmetry of the molecular dimer

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 12 2006
Anthony P. Duff
The structure of a newly crystallized form of the copper-dependent amine oxidase from pea seedlings has been refined at a resolution of 2.2,Å to a final R factor of 0.181. The structure (form II) was originally discovered during a study of xenon binding to copper-dependent amine oxidases as a probe for dioxygen-binding sites [Duff et al. (2004), J. Mol. Biol.344, 599,607]. The form II crystals belong to space group P21, with two dimers in the asymmetric unit. The overall structure is very similar to the crystals of form I in space group P212121 with a dimer in the asymmetric unit [Kumar et al. (1996), Structure, 4, 943,955]. In form I the last three residues (644,647) observable in the two subunits were apparently splayed apart. It was noted that the absence of a disulfide bond between the Cys647 residues of the two subunits was inconsistent with chemical evidence for the absence of free sulfhydryl groups. In both of the crystallographically independent dimers of form II the two subunits are clearly joined by a disulfide bridge between the C-terminal cysteine residues. This is only possible if the two polypeptide chains in the dimer adopt different conformations near the C-terminus so that the twofold symmetry is lost. A proline residue (645) two residues before the cysteine has a cis conformation in one chain and a trans conformation in the other. As a result, the disulfide bond lies more than 5,Å from the twofold axis. The loss of local twofold symmetry in form II can be explained by intermolecular contacts, which provide an asymmetric environment. [source]

Two New Lignans from Taxus yunnanensis,

CHINESE JOURNAL OF CHEMISTRY, Issue 7 2003
Sheng-Hong Li
Abstract The phytochemical investigation on the ethanolic extracts of the barks of Taxus yunnanensis (Taxaceae) led to the isolation of two new neo -lignans, named taxuyunins A (1) and B (2), a-long with the known diterpenolignan, brevitaxin (3). Their structures were elucidated on the basis of spectroscopic and chemical evidences. Compound 1 is a neo -lignan xyloside while compound 2 belongs to the rare neo -lignan possessing a ramified C3side chain. [source]