Circular dichroism and carbon-13 nuclear magnetic resonance spectra of (S)-5-alkyl-5-(2'-pentyl)-2-thiobarbituric acids.

The circular dichroism (CD) and carbon-13 nuclear magnetic resonance (13C NMR) spectra of (S)-5-(2'-pentyl)-2-thiobarbituric acid and several (S)-5-alkyl-5-(2'-pentyl)-2-thiobarbituric acids were obtained. The results were compared to CD and 13C NMR spectral data obtained from (S)-5-(2'-pentyl)bartituric acid and (S)-5-alkyl-5-(2'-pentyl)barbituric acids.

Solution conformations of barbituric acid derivatives: a 3J(13C,1H) NMR study.

The conformations of the 5-alkyl chains of 5,5-dialkylbarbituric acid derivatives in polar and nonpolar media were determined from the magnitudes of the vicinal heteronuclear coupling constants between the alpha-alkyl hydrogens and the carbonyl carbons. The experimental 3J values have been compared to theoretical values, and the conformational populations of the alkyl side chains with respect to the trioxopyrimidine ring have been determined. The results show that all these compounds have a very low barrier to rotation for both butyl and ethyl side chains. The barbiturates that do not have a 1'-methyl group in the butyl side chain, butobarbital and amobarbital, have no preferred conformation for either the butyl or ethyl side chains. However, the compounds with a 1'-methyl group, pentobarbital and alpha-methylamobarbital, exhibit preferred conformation for both alkyl chains. The significance of these results to the relationship between conformations and pharmacological activity is discussed.

Crystal, solution, and molecular modeling structural properties and muscarinic antagonist activity of azaprophen.

The structure of azaprophen, which was originally assigned by 1H NMR analysis, was confirmed by X-ray crystallography. A comparison of 13C NMR isotropic chemical shift data for azaprophen in the solid state and in CDCl3 and DMSO-d6 solution was used to correlate solution and solid-state conformation as determined by the X-ray data. The data suggested that the solid-state and solution conformation of azaprophen were similar. The observed solid-state structure was also compared to low-energy conformations identified by molecular-mechanics calculations. A comparison of azaprophen and atropine radioligand binding in guinea pig ileum, rat heart, rat brain, and in CHO cells expressing transfected m1 and m3 receptors was conducted. Azaprophen is more active than atropine in all preparations except the m3 receptor expressed in CHO cells. However, like atropine, it does not provide major discrimination among the muscarinic receptor subtypes.

Carbon-13 nuclear magnetic resonance study of the alpha- and beta- isomers of methadol and acetylmethadol hydrochlorides.

The 13C-NMR spectra reported in these studies give direct evidence for the presence of two contributing conformers for alpha-methadol hydrochloride, alpha-acetylmethadol hydrochloride and beta-acetylmethadol hydrochloride. Indirect evidence is also available for the presence of more than one conformer for beta-methadol hydrochloride. However, in order to be more descriptive about the structures of the conformers, it is necessary to obtain 13C-NMR spectra that have a higher degree of resolution than is available from our present NMR system. Such systems are available, and plans are currently in progress to obtain 13C-NMR spectra or these compounds at high enough magnetic fields and low enough temperatures to give us the necessary data.