Search results for "Absolute configuration"
showing 10 items of 121 documents
Assignment of the Absolute Configuration and Total Synthesis of (+)-Caripyrin
2014
The antifungal secondary metabolite (+)-caripyrin was studied by vibrational circular dichroism spectroscopy. Analysis of the recorded data, with the Boltzmann weighted-average of the spectra calculated at the B3LYP/6-311G(d,p) level of theory for all relevant conformers, unequivocally proved the (R,R)-configuration for the dextrorotatory natural product. Based on this finding, a short enantioselective synthesis of (+)-caripyrin was developed.
Crystal structures and absolute configurations of dexmedetomidine and its tosyl derivative
1993
Abstract X-ray diffraction data were used to determine the absolute configuration of dexmedetomidine, a new member of a class of drugs with 4-arylalkyl-1H-imidazole structure. When the anomalous effect of the parent compound proved to be too small for determination of the absolute configuration the tosyl derivative, with the same configuration, was synthesised and used as a reference. Stability of the stereogenic center was verified by HPLC technique. The absolute configuration of the compounds is S. Complete crystal structures are reported for both compounds. Co radiation was used for measurements.
Studium zum Vorgang der Wasserstoffübertragung, 50. Elektroreduktion und phasentransferkatalysierte Borhydrid-reduktion prochiraler Ketone
1978
Prochirale Carbonylverbindungen wurden in die entsprechenden sekundaren Alkohole ubergefuhrt a) durch Elektroreduktion und b) mit NaBH4, in beiden Fallen mit den gleichen Ephedriniumsalzen, und zwar fur a) als optisch aktive Leitsalze und fur b) als optisch aktive Phasentransfer-Katalysatoren. Es wurden bei der Elektroreduktion und bei der Phasentransfer-Katalyse die Ausbeuten an Carbinol (und Pinakol)3), die optische Ausbeute und die absolute Konfiguration des bevorzugt gebildeten Enantiomeren bestimmt. In der uberwiegenden Mehrzahl der untersuchten Beispiele besitzen die unter Mitwirkung optisch aktiver Ephedriniumsalze nach beiden Methoden erhaltenen Uberschusenantiomeren die entgegenges…
ChemInform Abstract: Synthesis of (-)-Auricularic Acid and its C-4 Epimer. The Absolute Configuration of Auricularic Acid.
2010
Abstract A synthesis of (−)-auricularic acid (2a) starting from methyl (+)-13-oxo- podocarp-8(14)-en-19-oate (3a) and a synthesis of its C-4 epimer (2b) starting from methyl (+)-13-oxopodocarp-8(14)-en-18-oate (3b) are described. The absolute configuration of natural auricularic acid is stablished as (4R, 5S, 8S, 9R, 10S, 14S).
Resolution and Determination of the Absolute Configuration of a Twisted Bis-Lactam Analogue of Tröger's Base: A Comparative Spectroscopic and Computa…
2015
The first reported twisted bis-lactam, a racemic Tröger's base (TB) analogue (2), was resolved into its enantiomers on a chiral stationary phase HPLC column. The absolute configuration of (+)-2 was determined to be (R,R)-2 by comparing experimental and calculated vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectra. The absolute configuration of (-)-2 was determined by comparing experimental and calculated electronic circular dichroism (ECD) spectra. The corresponding theoretical spectra were calculated using the lowest energy conformation of (R,R)-2 and (S,S)-2 at the B3LYP/6-31G(d,p) level of theory. The absolute configuration of (+)-2 was also determined t…
Analytical chemistry on many-center chiral compounds based on vibrational circular dichroism: Absolute configuration assignments and determination of…
2019
The absolute configuration of a chiral molecule is key to its biological activity. Being able to find out what this configuration is, is thus crucial for a wide range of applications. The difficulties associated with such a determination steeply rise as the number of chiral centers in a given compound becomes larger. Concurrently, it becomes increasingly more challenging to determine the levels and identity of potential stereochemical contaminants in a given sample with one and the same technique, leading in practice to extensive and laborious efforts employing multiple analytical techniques. Here, experimental and theoretical studies based on Vibrational Circular Dichroism (VCD) are presen…
Targeted solid phase fermentation of the soil dwelling fungus Gymnascella dankaliensis yields new brominated tyrosine-derived alkaloids
2016
Seven new brominated tyrosine-derived alkaloids, gymnastatins T–Y (1–6) and dankastatin D (7), together with three known likewise brominated analogues gymnastatins I–K (8–10) were isolated from the soil fungus Gymnascella dankaliensis through fermentation on solid rice medium following addition of NaBr. None of these compounds were detected when the fungus was cultured on rice that either lacked NaBr or that contained NaCl instead, indicating a remarkable plasticity of the fungal secondary metabolism. All structures were elucidated on the basis of one and two dimensional NMR spectroscopic analyses and MS data. The absolute configuration of the new gymnastatin T (1) was determined by X-ray c…
Xanthones and sesquiterpene derivatives from a marine-derived fungus Scopulariopsis sp.
2016
Abstract Two new xanthone derivatives, 12-dimethoxypinselin ( 1 ) and 12- O -acetyl-AGI-B4 ( 2 ), as well as two new phenolic bisabolane-type sesquiterpenes, 11,12-dihydroxysydonic acid ( 15 ) and 1-hydroxyboivinianic acid ( 16 ), together with one new alkaloid, scopulamide ( 21 ) and one new α-pyrone derivative, scopupyrone ( 26 ), in addition to twenty-three known compounds ( 3 – 14 , 17 – 20 , 22 – 25 , 27 – 29 ) were isolated from solid rice cultures of the marine-derived fungus Scopulariopsis sp. obtained from the Red Sea hard coral Stylophora sp. All compounds were unambiguously identified through extensive NMR spectroscopic analyses, and by comparison with the literature. Marfey's re…
Secondary metabolites of the lichen-associated fungus Apiospora montagnei
2017
Abstract The endolichenic fungus Apiospora montagnei isolated from the lichen Cladonia sp. was cultured on solid rice medium, yielding the new diterpenoid libertellenone L (1), the new pyridine alkaloid, 23-O-acetyl-N-hydroxyapiosporamide (2) and the new xanthone derivative 8-hydroxy-3-hydroxymethyl-9-oxo-9H-xanthene-1-carboxylic acid methyl ether (3) together with 19 known compounds (4–22). The structures of the new compounds were elucidated by 1D and 2D NMR spectra as well as by HRESIMS data. The absolute configuration of the new 6,7-seco-libertellenone derivative 1 was determined by single-crystal X-ray diffraction. Four additional known compounds 23–26 were isolated when NaCl or NH4Cl w…
New oxygenated eudesmanolides from artemisia herba-alba
1990
Abstract The aerial parts of Artemisia herba-alba Asso subsp.valentina Lam. (Asteraceae) yielded the new eudesmanolides 1-11 and the new sesquiterpene-monoterpene adducts 12-13. The absolute configuration of compound 6 was confirmed with the aid of X-ray diffraction analysis. Some aspects of the thermal and photochemical reactivity of 2,4-cyclohexadienones are discussed.