Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1260331201pmid: N/A

Agrawal, Pawan K.; Jain, Dharam C.; Pathak, Ashish K.

doi: 10.1002/mrc.1260331202pmid: N/A

The 13C NMR chemical shifts of 126 Steroidal sapogenins published between 1983 and 1993 are listed and critical spectral features and advances made in the NMR characterization of these compounds are discussed as a guide for the identification of the parent skeleton and the determination of substitution patterns. The NMR spectroscopic methods applicable to deduce the complete structure of the oligosaccharide moiety and its linkage to the sapogenin residue are also presented to elucidate the structure of steroidal saponins.

Licoccia, Silvia; Paci, Maurizio; Paolesse, Roberto

doi: 10.1002/mrc.1260331203pmid: N/A

The synthesis and characterization of hexacoordinated ruthenium complexes of etioporphyrin I (EP) of general formula [(EP)RuL2] (L = teriary phosphine) and of the pentacoordinated complex [(EP)Ru(PPh3)] are reported. The multiplicity observed in the 1H NMR spectra of complexes is discussed on the basis of the steric interactions between the axial ligands and the macrocycle.

Günther, Ulrich L.; Sudmeier, James L.; Coutts, Simon J.; Snow, Roger J.; Barton, Randall W.; Bachovchin, William W.

doi: 10.1002/mrc.1260331204pmid: N/A

L‐Val‐L‐boroPro, a potent DP IV (CD26) inhibitor, and its non‐inhibitory diastereomer L‐Val‐D‐boroPro, were studied by 1D 1H and 11H NMR and by 2D 1H NMR methods in aqueous solution. Complete 1D 1H NMR fine structures were computer analyzed to obtain the 1H chemical shifts and spin‐coupling constants. Dihedral angles were derived from coupling constants on the basis of the Altona equation (i.e. an improved Karplus equation). The structures and populations of proline ring conformations were determined with the aid of pseudo‐rotation analysis. Good agreement between the distances derived from NOESY data and dihedral angle‐constrained force‐field calculations was obtained. Structural analysis allowed the identification of the absolute stereochemistry of the α‐carbon of the proline residue, and showed that the active inhibitor is the diastereomer which is homochiral with L‐proline. L‐Val‐L‐boroPro exists largely in a single conformer, in contrast to L‐Val‐D‐boroPro, which adopts two proline conformations in a 2:1 ratio. Analysis of 1H and 11H NMR spectra proves that inactivation of the inhibitor at physiological pH results from a cyclization reaction in which the free N‐terminal nitrogen atom forms a covalent bond with the B atom.

Olagnon‐Bourgeot, Sabine; Chastrette, Francine; Wilhelm, Didier

doi: 10.1002/mrc.1260331205pmid: N/A

31P chemical shift‐structure correlations were established from methyl and ethyl esters of simple phosphonocarboxylic acids. The influence of solvent, acidity, function and neighbourhood of phosphorus was studied. The correlations could be extended and led to the identification of esters obtained when a series of phosphonocarboxylic acids were reacted with alcohols—reactions which were designed as models of cellulose cross‐linking by these acids.

Barberis, Claude; Campredon, Myléne; Lokshin, Vladimir; Giusti, Gérard; Faure, Robert

doi: 10.1002/mrc.1260331206pmid: N/A

The total assignment of the 1H and 13C NMR spectra of four fluoro‐substituted chromenes was deduced from the concerted application of homonuclear correlation (COSY), 1H‐detected one‐bond heteronuclear multiple quantum coherence (HMQC) and long‐range (two and three bonds) heteronuclear multiple bond connectivity (HMBC) experiments.

Sveshnikov, Nikolay N.; Sipyagin, Alexey M.; Dobrokhotova, Olga V.

doi: 10.1002/mrc.1260331207pmid: N/A

A 13C NMR study of a series of novel 2,4‐thio‐substituted 5‐trifluoromethylpoly‐chloropyridines was carried out. The carbon chemical shifts and external long‐range 13C, 19F NMR coupling constants between the pyridine ring carbons and the trifluoromethyl group are reported.

Roy, René; Tropper, François D.; Williams, Antony J.

doi: 10.1002/mrc.1260331208pmid: N/A

The additive behaviour generally observed for the substituent‐induced chemical shifts (SCS) for disubstituted benzenes was examined for a series of aryl 2‐N‐acetamido‐2‐deoxy‐β‐D‐glucopyranosides having a wide range of para substituents with varying possible electronic contributions. The SCS values associated with non‐acetylated and peracetylated glucoside rings in para‐substituted aryl 2‐N‐acetamido‐2‐deoxy‐β‐D‐glucopyranosides were calculated. The additive nature of SCS analysis for para‐substituted systems was shown to hold for the meta and para positions but the very small change in chemical shifts for the ortho positions precluded attempts at analysis of these data. The observation of a good correlation for the ipso carbons for the acetylated compounds compared with a poor correlation for the same site in the non‐acetylated compounds is not well understood.

Ludwig, M.; Öhrström, L.; Steinborn, D.

doi: 10.1002/mrc.1260331209pmid: N/A

The 103Rh NMR chemical shifts of rhodoximes [Rh(dmgH)2(PPh3)X] (1) and organorhodoximes [Rh(dmgH)2(L)R] (2, L = PPh3; 3, L = PMe3; 4, L = P(OPh)3; 5, L = SMe2; 6, L = py) were measured with a wide range of anionic ligands X, organo groups R and axial ligands L. The chemical shifts δ(103Rh) in the halide complexes 1 show the ‘normal halogen dependence’ (Cl > Br > I). δ(103Rh) in 2–6 depends on the axial base L in the order py > SMe2 > PPh3 > P(OPh)3 ≈︁ PMe3 and in 2 on the organo group R in the order Et ≈︁ Me < nPr < CH2Ph ≈︁ CH2OMe < CH2Br < CH2Cl < iPr < Cy < CHCH2 < CH2SiMe3 < tBu < cis‐CHCHPh ≈︁ cis‐CHCHPr < Ph ≈︁ CCPh < CPrCH2. The coupling constants 1J(103Rh,31P) in 2 reflect the (NMR) trans influence of R. There is a strong correspondence between the NMR trans influence and the structural trans influence, as indicated by the bond lengths d(Rh—P).

Rao, H. Surya Prakash; Reddy, K. Subba

doi: 10.1002/mrc.1260331210pmid: N/A

Carbon‐13 NMR signal assignments of some bicyclo[4.3.0]nonan‐4‐ones (hydrindanones) and bicyclo[4.4.0]decal‐4‐ones are reported.