Wolfgang Robien

Bufadienolides from Urginea maritima from Egypt

Forty-one bufadienolides were isolated from the bulbs of Urginea maritima agg. from Egypt; 26 of them are new natural compounds. Structure elucidation was performed by comparison with authentic substances or by means of 1H, 13C NMR and FAB mass spectroscopy. Sixteen of the glycosides derive from nine structurally new aglycones: 16 beta-hydroxy-scillarenin, 16 beta-O-acetyl- scillarenin, 12 beta-hydroxy-5 alpha-4,5-dihydro-scillirosidin, 16 beta- hydroxy-5 alpha-4,5-dihydro-scillirosidin, 16 beta-O-acetyl-5 alpha-4,5- dihydro-scillirosidin, 12 beta-hydroxy-scillirubrosidin, 16 beta-O-acetyl- scillirubrosidin, 9-hydroxy-scilliphaeosidine and 12 beta-hydroxy-desacetyl- scillirosidine.

Comprehensive parameter set for the prediction of the 13C-NMR chemical shifts of sp3-hybridized carbon atoms in organic compounds

Abstract A parameter set is described for prediction of the carbon-13 chemical shifts of sp3-hybridized carbon atoms based on a simple linear additivity relationship. It was tested against 88 692 known chemical shift values. Many of the previously reported parameters were amended and new parameters added. With this parameter set, the chemical shifts in 99.7% of the 88 692 cases can be estimated with an overall standard deviation of 5.6 ppm for the predicted values relative the the experimental ones. The additivity parameters reported here can be used per se or in connection with a recent computer program for the estimation of carbon-13 chemical shifts, which automatically selects and applies additivity rules appropriate for the individual carbon atoms of the chemical constitution entered.

Parameter set for the prediction of the 13C-NMR chemical shifts of sp2- and sp-hybridized carbon atoms in organic compounds

Abstract A parameter set was compiled for the prediction of the carbon-13 chemical shifts of sp 2 - and sp-hybridized carbon atoms based on simple linear additivity relationships. Extensive tests were done against 80 115 known chemical shifts. Many of the previously reported parameters are amended and new parameters are added. Statistical measures of the quality of the prediction are given in cases for which a representative set of examples was available. The parameter set together with previously published increments for sp 3 -hybridized carbon atoms could predict 97% of the 150 000 chemical shifts investigated, with a standard deviation of 5.5 ppm. The additivity rules reported can be used alone or in connection with a recently published computer program for the estimation of carbon-13 chemical shifts. This program automatically selects and applies the addivity rules appropriate to the individual carbon atoms of the chemical constitution entered.

Types of sesquiterpene-coumarin ethers from Achillea ochroleuca and Artemisia tripartita

Abstract In addition to known derivatives, four new sesquiterpene-coumarin ethers were isolated from the roots of Achillea ochroleuca and Artemisia tripartita and identified by 1 H and 13 C NMR spectroscopy, including lanthanide induced shifts. The new compounds are isofraxidin derived ethers which differ from the previously described derivatives by ring cleavage and methyl migration within the terpenoid unit. The chemosystematic importance of sesquiterpene-coumarin ether accumulation within the two genera is briefly discussed.

13C NMR and 1H lanthanide induced shifts of naturally occurring alkamides with cyclic amide moieties -amides from achilleafalcata

Abstract The 13C NMR spectra of 12 alkamides, especially of piperidides and piperideides isolated from different Achillea species were recorded. Assignments were based on systematic comparisons within the series of spectra and on selective 13C-{1H} decoupling experiments. Due to the dynamic behaviour of α, β-unsaturated 5- and 6-ring amides some carbon atoms of the cyclic amine moiety and the acid rest give rise to rather broad signals. Complementary information on the conformation of the amide bond and the geometry of the acid chain was obtained by means of 1h-lanthanide induced shifts (LIS). A re-investigation of the roots of Achillea falcata afforded in addition to known olefinic C10-carbonic acid amides a further new derivative of that series, 2E,4E, 8Z-deca-2,4,8-trienoic acid piperideide, together with three known acetylenic C11-carbonic acid amides, all derived from 2E,4E-undeca-2,4-diene-8,10-diynoic acid.

MCSS: a new algorithm for perception of maximal common substructures and its application to NMR spectral studies. 1. The algorithm

A new algorithm has been developed which can be used to deal with structure isomorphism, substructure searching, and Maximal Common Substructure (MCSS) detection. The algorithm described can perceive topological or colored maximal common substructures of two given structures, including structures which consist of two or more disconnected parts. The new strategies used in the algorithm are discussed in detail. The program was tested upon a set of carefully selected structure pairs and then on a database containing about 80 000 structures. The investigation revealed that the algorithm has high efficiency and flexibility. The MCSS algorithm has been implemented into the CSEARCH-NMR database system allowing automatic increment analysis and error detection.

Prenylated flavanones and flavanonols as chemical markers in Glycosmis species (Rutaceae).

Fifteen prenylated or geranylated flavanones and flavanonols were isolated from the leaf extracts of different Glycosmis species collected in Thailand and Malaysia. All structures were elucidated by spectroscopic methods, especially 1D and 2D NMR. Six compounds were described for the first time and two were only known so far as synthetic products. The chemotaxonomic significance of flavanoid accumulation within the genus Glycosmis is highlighted.

Ferrocene derivatives, part 6757Fe-NMR spectroscopy of ferrocenes

Abstract57Fe NMR-spectra of 28 mono and disubstituted ferrocenes with a natural abundance of57Fe have been measured relative to internal ferrocene. Most of the resonances appear at the high frequency side. The shielding influence of the various substituents is discussed qualitatively.57Fe shifts are very sensitive to ring tilting as occurring in [3]ferrocenophanes.Zusammenfassung57Fe-NMR-Signale von 28 mono- und disubstituierten Ferrocenen mit natürlicher Häufigkeit an57Fe wurden gegen Ferrocen als innerem Standard gemessen. Die meisten Resonanzen sind zu höherer Frequenz verschoben. Die57Fe-Verschiebung reagiert sehr empfindlich auf Ringneigung, wie an [3]Ferrocenophanen gezeigt wurde. Substituenteneinflüsse auf die Verschiebung werden qualitativ diskutiert.

Eudesmanolides from Achillea pratensis

Abstract From flower heads of Achillea pratensis five eudesmanolides were isolated by repeated column chromatography and HPLC. The compounds were identified as tauremisin, arglanin, 4-epi-arglanin, 4α-hydroperoxy-4α-dehydroxy-arglanin and santamarin.

13C-NMR spectra of santalol derivatives: a comparison of DFT-based calculations and database-oriented prediction techniques†

A systematic investigation of a series of santalol and epi‐santalol derivatives by means of ab initio and density functional theory (DFT) calculations together with database‐oriented prediction methods leads to a configurational reassignment within this compound class. The DFT calculations as well as the HOSE‐code and neural network‐based predictions allow deriving a general rule set for unambiguous assignment within this compound class. The methyl group in position 2′ serves as an indication for the configuration at this stereocenter allowing easy differentiation between santalol derivatives and their diastereomers belonging to the epi‐santalol series. Copyright