Search results for "absolute configuration"
showing 10 items of 121 documents
Acid Rearrangment of Epoxy-germacranolides and Absolute Configuration of 1β,10α-Epoxy-salonitenolide
2010
The acid-catalyzed cyclization of mono epoxides of cnicin acetonide (3) was investigated. Several 6,12-eudesmanolides were obtained, and their stereochemistry established by extensive spectroscopic analyses. Chemical correlations also led to the assignment of the absolute configuration of 1β,10α-epoxy-salonitenolide (13), a previously isolated natural product. The cytotoxic activities of some compounds were determined against A549 and MCF-7 tumor cell lines. The esterified germacranolides 2–6 were selectively cytotoxic against the MCF-7 breast cancer cell line.
Neoclerodane Diterpenoids from Scutellaria pontica
1997
Seven novel neoclerodane diterpenoids, scupontins A-G, have been isolated from the Me2CO extract of the aerial parts of Scutellaria pontica (1-7), together with the known neoclerodanes scutalbin A and scutalpin M. Structures 1-7 were established by exhaustive NMR spectroscopic studies and chemical transformations. Scupontins A-D(1-4, respectively) and scupontins E (5)andF(6) possess unusual [(3¢S,3¢¢S)-3¢-[(3¢¢-acetoxybutyryl)oxy]butyryloxy and [(3¢S,3¢¢S,3¢¢¢S)- 3¢-[[3¢¢-[(3¢¢¢-hydroxybutyryl)oxy]butyryl]oxy]butyryl]oxy substituents, respectively, attached to the C-19 position of the neoclerodane framework. In the case of the 6R,7â-dibenzoate derivative 7 (scupontin G) its absolute config…
Correlation of the Extent of Fjord-Region Oxidation with DNA Binding and Mutagenicity of the Enantiomeric 11,12-Dihydrodiols of Dibenzo[a,l]pyrene
1996
Abstract In vitro studies on the hepatic biotransformation of the enantiomeric trans-11,12-dihydrodiols of dibenzo[a,l]pyrene (DB[a,l]P) using microsomal fractions of animals pretreated with Aroclor 1254 revealed that the formation of fjord-region dihydrodiol epoxides strongly depends on the absolute configuration of the substrate. Both the (-)-11R,12R- and the (+)-11S,12S-enantiomer are converted diastereoselectively to the (-)- and (+)-anti-dihydrodiol epoxide, respectively, by either rat or mouse liver microsomes. Fjord-region oxidation occurs to greatest extent on incubation of the (-)-11R,12R-dihydrodiol with preparations from rats. This finding is in line with the differences seen for…
Crystal structure of (1S,2R,4S)-1-[(morpholin-4-yl)methyl]-4-(prop-1-en-2-yl)cyclohexane-1,2-diol
2014
Besides intramolecular O—H⋯N hydrogen bonds, the crystal structure displays intermolecular O—H⋯O and C—H⋯O hydrogen bonds linking the molecules into undulating layers parallel to the (01) plane.
Perthamides C-F, potent human antipsoriatic cyclopeptides
2011
Abstract Two new cyclopeptides, perthamides E and F were isolated from the polar extracts of the sponge Theonella swinhoei . The new structures, featuring an unprecedented β-amino acid unit (AHMOA), were determined by interpretation of NMR and MS data. The absolute configuration of the AHMOA residue was proposed on the basis of quantum chemical calculation of NMR chemical shifts. Perthamides were proved to inhibit TNF-α and IL-8 release in primary human keratinocytes cells and therefore could represent potentially leads for the treatment of psoriasis.
High pressure liquid chromatography resolution of racemic mixtures of chiral tricarbonyl arene chromium(0) and cyclopentadienyl-titanium(IV) complexes
1998
Abstract Enantiomers of chiral tricarbonyl arene chromium(0) and cyclopentadienyl-titanium(IV) complexes have been separated by high pressure liquid chromatography employing a Chiralcel OD (Daicel) column, eluting with hexane/2-propanol mixtures. The capacity factors ( k ) and selectivity factors ( α ) concerning the separation of these compounds have been determined. The resolution of tricarbonyl( η 6 -methyl o -acetylbenzoate)chromium ( IV ), was carried out on semipreparative scale: a comparison of the CD spectra of the enantiomers IVa and IVb with that reported in the literature for a similar complex allowed to establish the absolute configuration [( 1R )] for the most retained enantiom…
Synthesis, Absolute Configuration, and Bacterial Mutagenicity of the 8 Stereoisomeric Vicinal Diol Epoxides at the Terminal Benzo Ring of Carcinogeni…
2011
The synthesis of the 8 possible stereoisomeric diol epoxides (DEs) at the terminal benzo ring of carcinogenic dibenz[a,h]anthracene (DBA) is reported. trans-3,4-Dihydroxy-3,4-dihydro-DBA (1) afforded the 4 bay region DEs: the enantiomeric pairs of the anti diastereomers (+)-3/(-)-3 and of the syn diastereomers (-)-4/(+)-4, respectively. trans-1,2-Dihydroxy-1,2-dihydro-DBA (2) served as precursor of the 4 reverse DEs: the enantiomeric pairs of the anti diastereomers (+)-5/(-)-5 and of the syn diastereomers (-)-6/(+)-6, respectively. The transformation of the olefinic double bond in the enantiomeric trans-dihydrodiols to epoxides was achieved by either (i) oxidation with m-chloroperoxybenzoic…
Individual stereoisomers of phosphinic dipeptide inhibitor of leucine aminopeptidase
2008
Abstract Individual stereoisomers of the phosphinic pseudodipeptide hPheψ[P(O)(OH)CH2]Phe were obtained by stereoselective liquid chromatographic separation as N- and C-terminally protected derivative on quinidine carbamate modified silica stationary phase. The stereoisomeric purity, exceeding 95% for each fraction, was determined before and after deprotection using two independent methods. The absolute configuration was rationally assigned by application of enantiomerically pure phosphinic acid substrates in the synthetic procedure and correlation with biological activity of the products. Substantial differences in inhibition of leucine aminopeptidase by the individual isomers revealed nov…
Synthesis of all 7αH-guaia-4,11-dien-3-one diastereomers from (+)-dihydrocarvone
2005
Abstract All four 7α H -guaia-4,11-dien-3-one diastereomers have been synthesized from the common intermediate 1α H ,10α-acetoxy-7α H -guaia-4,11-dien-3-one obtained from (+)-dihydrocarvone. The spectral features of the four diasteromers have been correlated and the structure and absolute configuration of 1β H ,10β H ,7α H -guaia-4,11-dien-3-one isolated from Pleocarphus revolutus has been confirmed.
Synthesis of (−)-auricularic acid and its C-4 epimer the absolute configuration of auricularic acid
1991
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).