摘要:

Abstract1H and13C NMR parameters of methotrexate in [2H6]dimethyl sulphoxide were obtained and analysed in terms of a ‘preferred’ conformation. The effective correlation time of the anisotropic motion of the pteridinylbenzoyl moiety was evaluated asca. 10 ns at 300 K. The1H1H and13C1H distances obtained were used to construct the molecular structure in s

ISSN:0749-1581    

DOI:10.1002/mrc.1260310502

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe31P CP/MAS NMR spectrum ofcis‐[PtCl2(PPh2nPr)(BzS{O}Bz)] was found to exhibit two central resonances with appropriate couplings to195Pt, despite the fact that a single‐crystal x‐ray diffraction study indicated that the complex crystallized in the monoclinic space groupP21/nwithZ= 4, i.e. that there is only a single crystallographically unique phosphorus atom. The possibility that the 21screw axis was absent (i.e. that the space group was actuallyPn) was examined by a reinvestigation of the original x‐ray data, but no definitive evidence for the alternative space group could be obtained. An examination of a bulk sample ofcis‐ [PtCl2(PPh2nPr)(BzS{O}Bz)] by x‐ray powder diffraction and comparison of the results with data from the single‐crystal x‐ray diffraction experiment revealed that the crystal selected for diffraction studies was a different polymorph from the bulk of the sample which was used for the31P CP/MAS NMR measurements. X‐ray powder diffraction is thus shown to provide a valuable bridge between solid‐state CP/MAS NMR measurements and single‐crystal x

ISSN:0749-1581    

DOI:10.1002/mrc.1260310503

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractAn investigation of bis(diphenylphosphino)methane dioxide (dppm dioxide),cis‐[PtCl2(PPh3)2]cis‐[PtCl2{P(p‐C6H4Cl)3}2] andcis‐[PtBr2(PPh3)2] by solid‐state CP/MAS31P NMR spectroscopy, x‐ray powder diffraction and1H,13C{1H} and31P{1H} solution NMR methods illustrates the sensitivity of the appearance of solid‐state NMR spectra to solvation effects in crystalline solids. The presence or absence of solvent of crystallization and the slow loss of solvent of crystallization from a sample over time are clearly manifested in the solid‐state NMR spectra as the local site symmetry in the solid is changed. These effects have led workers to report different data for a given compound when, in fact, different types of solvates we

ISSN:0749-1581    

DOI:10.1002/mrc.1260310504

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractA re‐analysis of previously published13C NMR data on C‐7‐substituted 6α,14α‐endo‐ethanotetrahydrothebaines shows that the13C chemical shift of C‐18 in these medicinally important compounds can be used as an indicator of C‐7 stereochemistry, this being due to a steric gamma effect between C‐18 and C‐7 substituents in an α orientation. In seven examples of α‐isomers the C‐18 chemical shift ranges from δ17.02 to δ18.42 (average δ17.72), whereas in four examples of β‐isomers the C‐18 chemical shift ranges from δ22.09 to δ24.00 (average δ22.73‐23.40). Since suitable etheno compounds can be chemically reduced to ethano compounds, C‐7 stereochemistry in such 6α,14α‐endo

ISSN:0749-1581    

DOI:10.1002/mrc.1260310505

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

Abstract15N,14N,13C and1H NMR data were used for the structural analysis of seven 1,2,3,4‐thiatriazoles with various exocyclic groups. Measurements at various temperatures were carried out in order to study the behaviour of exocyclic groups. Some15N‐labelled compounds were prepared to assist in the interpretation of the15N NMR spectra. The results suggest that the investigated compounds exist in the cyclic structure. Three of the investigated compounds have not been previously synthesi

ISSN:0749-1581    

DOI:10.1002/mrc.1260310506

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe barriers to rotation about the C(O)N bond for 13 α‐alkyl‐ and α‐halo‐substitutedN‐theyl‐N‐methylamides were determined by1H NMR spectroscopy at coalescence temperature. Plots of Gibbs free energy (ΔG°) and Gibbs energy of activation (ΔG‡) values against Charton's electronic and steric parameters of the α‐carbonyl groups allows the conclusion that both the isomeric preference and the barrier to rotation about the C(O)N bond of theN‐ethyl‐N‐methylamides depend mainly on the ster

ISSN:0749-1581    

DOI:10.1002/mrc.1260310507

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe structural features of the inclusion complexes of cyclodextrins (CDs) with the chiral cognition activator drug (±)9‐[(phenylmethyl)amino]‐1,2,3,4‐tetrahydroacridin‐1‐ol maleate (suronacrine maleate, HP‐128) were studied using both high‐resolution1H NMR spectroscopy and molecular modelling methods. The partial inclusion of the guest from the secondary hydroxyl side of α‐CD was demonstrated in aqueous solution, in addition to a higher degree of penetration into the cavity of β‐CD from the same side. NMR‐ROESY experiments allowed the unambiguous location of the benzylic ring of the guest inside the β‐CD cavity. The formation of diastereoisomeric pairs was demonstrated by the duplication of the benzylic proton signals. Molecular mechanics calculations were used to complement the NMR analysis. Molecular modelling procedures (MacroModel interactive computer program) allowed the prediction of the most stable structures of the complexes, and showed that specific site interactions, provided by hydrogen bond formation, are capable of differentiating the diastereoisomeric intramolecular inclusion complexes according to availa

ISSN:0749-1581    

DOI:10.1002/mrc.1260310508

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractNMR data (13C,15N,17O) for the three ring atoms of various oxaziridines are compared. Their significance for the prediction of the enantioselectivity of the oxidation of sulphides by chiral oxaziridines is discussed.

ISSN:0749-1581    

DOI:10.1002/mrc.1260310509

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe synthesis of five substituted anthraquinones related to anthracyclines is described. One‐electron reduction of these compounds yields the corresponding semiquinones, which were characterized by EPR, ENDOR and TRIPLE resonance spectroscopy. The data indicate a rapid conformational interconversion of the cyclohexene moiety (ring A in the anthracyclines). The low‐temperature structures could be assigned to half‐chair conformers whose splitting constants and torsion angles were obtained by simple calculations. Introduction of substituents in the 4‐position, disturbing the symmetry of the anthraquinone, results in remarkable changes in the spin density distribution, in contrast to published results. A reinterpretation and assignment of known anthraquinone radicals is pr

ISSN:0749-1581    

DOI:10.1002/mrc.1260310510

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractHigh‐field NMR experiments, including the 2D INADEQUATE technique coupled with a computerized spectral analysis, were used to determine the full structure of a new saponin extracted from a plant (Alphitonia zizyphoides) found in the Samoan rain forests. The saponin, which shows significant pharmacological activity, consists of an aglycone framework of six rings (three saturated six‐membered rings, two oxygen‐containing five‐membered rings and a five‐membered carbon ring) to which are attached four sugar units and a six‐carbon side‐chain. The INADEQUATE experiment, which was carried out on 60 mg of sample, provided absolute confirmation of the assignments for 35 of the possible 53 CC bonds from the13C–1

ISSN:0749-1581    

DOI:10.1002/mrc.1260310511

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY