Search results for "ASTER"

On the Occurrence of Caffeoyltartronic Acid and Other Phenolics in Chondrilla juncea

1993

Abstract Caffeoyltartronic acid and other eleven phenolic com pounds were identified in the MeOH extract of Chondrilla juncea: the flavonoids luteolin, luteolin-7-glucoside, luteolin-7-galactosylglucuronide and quercetin-3-galactoside; the phenolic acids protocatechuic, caffeic, chlorogenic, isochlorogenic and isoferulic and the coumarins cichoriin and aesculetin. The taxonomic im plications of these com pounds have been discussed.

Distribution of Δ5-olefinic acids in the triacylglycerols fromPinus koraiensisandPinus pinasterseed oils

1996

Purified triacylglycerols (TAG) fromPinus koraiensis andP. pinaster seed oils, which are interesting and commercially available sources of Δ5-olefinic acids (i.e.,cis-5,cis-9,cis-12 18:3 andcis-5,cis-11,cis-14 20:3 acids) were fractionated by reversed-phase high-performance liquid chromatography, and each fraction was examined by capillary gas-liquid chromatography for its fatty acid composition. A structure could be assigned to more than 92% of TAG from both oils. In both instances, ca. 48% of the TAG were shown to contain at least one δ5-olefinic acid. In the great majority of TAG, our data showed that there is only one molecule of δ5-olefinic acid per molecule of TAG. This is compatible …

Capping α-Cyclodextrin with Cyclotriveratrylene by Triple Disulfide-Bridge Formation

2013

Disulfide-bond formation is an expeditious coupling reaction to make macropolycyclic symmetrical receptors. It is used here for the preparation of unsymmetrical cavitands based on α-cyclodextrin (α-CDX) and cyclotriveratrylene (CTV) analogues. Accordingly, diastereomeric hemicryptophanes 2a and 2b were obtained in 11 % isolated yield by the iodine oxidation of a 1:1 mixture of racemic cyclotrithiophenolene (3) and the C3-symmetric trithiol derivative of permethylated α-cyclodextrin (PM α-CDX) 4. Remarkably, the target hemicryptophanes were obtained in a 5:3 diastereomeric ratio. The reaction produced mainly (34 %) a singly disulfide-bridged PM α-CDX dimer 7, however no traces of triply disu…

Immobilized Chiral ortho-Metalated Dirhodium(II) Compounds as Catalysts in the Asymmetric Cyclopropanation of Styrene with Ethyl Diazoacetate

2007

Immobilization of ortho-metalated dirhodium(II) compounds has been achieved by a carboxylate interchange reaction between (M)-Rh2(l-protos)2[(p-XC6H3)P(p-XC6H4)2]2 diastereoisomers and carboxyethylpolystyrene polymer (PS-C6H4(CH2)2CO2H). The immobilized chiral catalysts have been tested in the standard reaction of asymmetric cyclopropanation of styrene with ethyl diazoacetate, giving higher yields than homogeneous chiral trifluoroacetate derivatives, but their diastereo- and enantioselectivities were lower. Some of the immobilized catalysts have proved to be very robust. The catalytic behavior of (M)-Rh2(O2C(CH2)2C6H5)2[(p-XC6H3)P(p-XC6H5)2]2 compounds has been studied as a model for the im…

Stereoselective Total Synthesis of the Diastereomeric Tricyclic Alkaloids Tetraponerine-7 and Tetraponerine-8 Using O-Pivalo­ylated d-Arabinopyranosy…

2015

Based on a diastereoselective domino Mannich–Michael reaction cascade of 2- N -[( S )-3-{(benzyloxycarbonyl)[4-( tert -butyldiphenylsiloxy)butyl]amino}octylidene]-2,3,4-tri- O -pivaloyl-α- d -arabinopyranosylamine with the Danishefsky diene, the major component of the neurotoxic venom of the New Guinean ant Tetraponera punctulata , tetraponerine-8, and its diastereomer tetraponerine-7 were synthesized in pure form. While the Mannich reaction of the arabinosyl imine of the required ( S )-configured β-aminoaldehyde gave the 2-substituted piperidinone precursor of tetraponerine-8 with excellent diastereoselectivity, the analogous Mannich reaction of the ( R )-configured β-aminoaldehyde afforde…

Asymmetrische Hetero-Diels-Alder-Reaktionen in wäßriger Lösung unter Verwendung von Aminosäureestern als chiralen Auxiliaren

1989

(R)- und (S)-Aminosaure-methylester-hydrochloride bilden mit Formaldehyd in THF/Wasser-Gemischen Iminium-Ionen, die als elektronenarme Dienophile mit Cyclopentadien, 1,3-Cyclohexadien und Alkyl-substituierten Butadienen bereits bei 0°C Hetero-Diels-Alder-Reaktionen eingehen. Die Cycloaddukte werden mit hohen Ausbeuten im Multigrammasstab und mit Diastereomerenverhaltnissen (bis zu 93:7) gebildet, die mit anderen chiralen Aminen bisher nicht erreicht werden konnten. Mit Hilfe von NOE-Experimenten werden die absoluten Konfigurationen der Hauptdiastereomeren zugeordnet. Aus den Phenylglycin- und den Serin-Derivaten konnen die chiralen Hilfsgruppen mittels hydrogenolytischer Methoden bzw. unter…

Diastereomeric Differentiation in the Quenching of Excited States by Hydrogen Donors

2003

Synthesis of Optically Active N-(4-Hydroxynon-2-enyl)pyrrolidines: Key Building Blocks in the Total Synthesis of Streptomyces coelicolor Butanolide 5…

2021

AbstractStarting from 5-methylhexanal and (S)-configured N-propargylprolinol ethers, coupling delivered N-(4-hydroxynon-2-ynyl)prolinol derivatives as mixtures of C4 diastereomers. Resolution of the epimers succeeded after introduction of an (R)-mandelic ester derivative and subsequent HPLC separation. Alternatively, suitable oxidation gave the corresponding alkynyl ketone. Midland reagent controlled diastereoselective reduction afforded a defined configured propargyl alcohol with high selectivity. LiAlH4 reduction and Mosher analyses of the allyl alcohols enabled structure elucidation. The suitably protected products are used as key intermediates in enantioselective Streptomyces γ-butyrola…

Cytotoxicity of an unprecedented brominated oleanolide and a new furoceramide from the Cameroonian spice, Echinops giganteus

2016

A preliminary study on Echinops giganteus (Asteraceae) showed that the methanolic extract has interesting cytotoxicities against a panel of cancer cell lines. From this extract, a lignan, a flavonoid and a polyacetylenic thiophene identified were three times less cytotoxic than the extract. In the search of the metabolites responsible for the bioactivity, a new harvested E. giganteus was subjected to a phytochemical study using chromatographic methods. In the course of the work, two new compounds: a brominated oleanolide (1) and a tetrahydrofurano-ceramide (2) were obtained along with β-amyrin acetate (3), 2-(penta-1,3-diynyl)-5-(4-hydroxybut-1-ynyl)-thiophene (4), 2-(penta-1,3-diynyl)-5-(3…

Tandem asymmetric Michael reaction-intramolecular Michael addition. An easy entry to chiral fluorinated 1,4-dihydropyridines.

2010

A novel one-pot tandem asymmetric Hantzsch-type process has been employed to generate fluorinated 1,4-dihydropyridines (1,4-DHPs) as single diastereoisomers. It involves the condensation of (R)-(+)-allyl p-tolyl sulfoxide, fluorinated nitriles, and alkyl propiolates, giving access to a new family of enantiomerically pure fluorine-containing 1,4-DHPs.