NMR Signal Assignments (nmr + signal_assignment)

Distribution by Scientific Domains

Selected Abstracts

DFT-GIAO1H NMR chemical shifts prediction for the spectral assignment and conformational analysis of the anticholinergic drugs (,)-scopolamine and (,)-hyoscyamine

Marcelo A. Muoz
Abstract The relatively large chemical shift differences observed in the 1H NMR spectra of the anticholinergic drugs (,)-scopolamine 1 and (,)-hyoscyamine 2 measured in CDCl3 are explained using a combination of systematic/molecular mechanics force field (MMFF) conformational searches and gas-phase density functional theory (DFT) single point calculations, geometry optimizations and chemical shift calculations within the gauge including/invariant atomic orbital (GIAO) approximation. These calculations show that both molecules prefer a compact conformation in which the phenyl ring of the tropic ester is positioned under the tropane bicycle, clearly suggesting that the chemical shift differences are produced by the anisotropic effect of the aromatic ring. As the calculations fairly well predict these experimental differences, diastereotopic NMR signal assignments for the two studied molecules are proposed. In addition, a cursory inspection of the published 1H and 13C NMR spectra of different forms of 1 and 2 in solution reveals that most of them show these diastereotopic chemical shift differences, strongly suggesting a preference for the compact conformation quite independent of the organic or aqueous nature of the solvent. Copyright 2010 John Wiley & Sons, Ltd. [source]

13C and 1H NMR signal assignments of some new synthetic dehydroabietic acid derivatives

Marinaldo S. de Carvalho
Abstract The 1H and 13C NMR signal assignments of a series of new synthetic derivatives of dehydroabietic acid are presented. Copyright 2008 John Wiley & Sons, Ltd. [source]

1H and 13C NMR signal assignments of Paecilin A and B, two new chromone derivatives from mangrove endophytic fungus Paecilomyces sp. (tree 1,7)

Zhiyong Guo
Abstract Two new natural products, named paecilin A (1) and B (2), together with two known compounds secalonic acid D (3) and (11)-cytochalasa-6(12),13-diene-1,21-dione-16,18-dimethyl-7-hydroxy-l0-phenyl-(7S*,13E,16S*,18S*) (4), were isolated from the mangrove endophytic fungus, Paecilomyces sp. (tree 1,7) from the South China Sea. 1D and 2D NMR experiments including COSY, HMQC, and HMBC were used for the determination of their structures. In our cytotoxicity assays, secalonic D (3) showed cytotoxicity toward KB cells with IC50 < 1 g ml,1 and inhibiting human topoisomerase I with IC50 at 0.16 mol ml,1. 1, 2, and 4 showed no activity to KB cells. Copyright 2007 John Wiley & Sons, Ltd. [source]

Complete NMR signal assignments of flavonol derivatives

Hojung Kim
Abstract Common substitution positions of flavonols are at C-5 and C-7; 6-substituted flavonol derivatives are rarely found in natural sources. Here, we report complete assignments of 1H and 13C chemical shifts of eight flavonol derivatives including four 6-substituted flavonols. Copyright 2005 John Wiley & Sons, Ltd. [source]

Hexamer oligonucleotide topology and assembly under solution phase NMR and theoretical modeling scrutiny

BIOPOLYMERS, Issue 12 2010
Maxim P. Evstigneev
Abstract The entire family of noncomplementary hexamer oligodeoxyribonucleotides d(GCXYGC) (X and Y = A, G, C, or T) were assessed for topological indicators and equilibrium thermodynamics using a priori molecular modeling and solution phase NMR spectroscopy. Feasible modeled hairpin structures formed a basis from which solution structure and equilibria for each oligonucleotide were considered. 1H and 31P variable temperature-dependent (VT) and concentration-dependent NMR data, NMR signal assignments, and diffusion parameters led to d(GCGAGC) and d(GCGGGC) being understood as exceptions within the family in terms of self-association and topological character. A mean diffusion coefficient D298 K = (2.0 0.07) 10,10 m2 s,1 was evaluated across all hexamers except for d(GCGAGC) (D298 K = 1.7 10,10 m2 s,1) and d(GCGGGC) (D298 K = 1.2 10,10 m2 s,1). Melting under VT analysis (Tm = 323 K) combined with supporting NMR evidence confirmed d(GCGAGC) as the shortest tandem sheared GA mismatched duplex. Diffusion measurements were used to conclude that d(GCGGGC) preferentially exists as the shortest stable quadruplex structure. Thermodynamic analysis of all data led to the assertion that, with the exception of XY = GA and GG, the remaining noncomplementary oligonucleotides adopt equilibria between monomer and duplex, contributed largely by monomer random-coil forms. Contrastingly, d(GCGAGC) showed preference for tandem sheared GA mismatch duplex formation with an association constant K = 3.9 105M,1. No direct evidence was acquired for hairpin formation in any instance although its potential existence is considered possible for d(GCGAGC) on the basis of molecular modeling studies. 2010 Wiley Periodicals, Inc. Biopolymers 93: 1023,1038, 2010. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]