Validation of quantitative NMR.

9 – Nuclear Magnetic Resonance Analysis Using Chiral Shift Reagents

The pharmacological and therapeutic action of penicillamine are very largely explained by its ability to chelate metal ions and take part in oxidation-reduction reactions, sulfhydryldisulfide interchange, and nucleophilic addition. Effects of penicillamine on particular enzymes are explained by its chemical properties. Possible interactions with amino acids, tissue proteins, food constituents, and intermediates in the metabolism and biosynthesis of sulfur containing amino acids are discussed.

Chemical basis for pharmacological and therapeutic actions of penicillamine.

Epimerization at C‐2 of 2‐substituted thiazolidine‐4‐carboxylic acids

TLC and HPLC methods were developed for indirect chiral separation of penicillamine (3,3-dimethylcysteine) enantiomers after derivatization with Marfey's reagent (FDNP-Ala-NH(2)) and two of its structural variants, FDNP-Phe-NH(2) and FDNP-Val-NH(2). The binary mobile phase of phenol-water (3:1 v/v) and solvent combinations of acetonitrile and triethylamine phosphate buffer were found to give the best separation in normal and reversed-phase TLC, respectively. The diastereomers were also resolved on a reversed-phase C18 HPLC column with gradient elution of acetonitrile and 0.01 m trifluoroacetic acid. The results due to these three reagents were compared. The method was successful for checking the enantiomeric impurity of l-penicillamine in d-penicillamine and to check the enantiomeric purity of pharmaceutical formulations of d-penicillamine. The method was validated for linearity, repeatability, limit of detection and limit of quantification.

Indirect resolution of enantiomers of penicillamine by TLC and HPLC using Marfey's reagent and its variants

An NMR method is described for assaying the enantiomer composition of the pharmacologically active material penicillamine (1), using tris-(3-heptafluorobutyryl-d-camphorato)europium. The L enantiomer can be detected at levels of 0·4 to 0·5% in DL mixtures. Problems due to the insolubility of penicillamine in nonpolar solvents can be overcome by a two step derivatisation procedure.

NMR determination of the enantiomer composition of penicillamine using an optically active europium shift reagent

Highly specific proton line-broadening and paramagnetic 13C shifts observed for N-butyl-N(4-methyloxazol-2-yl)-2-methylpropionamide in the presence of fluorinated lanthanide shift reagents, are absent when non-fluorinated reagents are used. This unusual behaviour is rationalized in terms of possible chelation of the N-butyl-N(4-methyloxazol-2-yl)-2-methylpropionamide to the lanthanide reagent, causing transfer of the unpaired electron into the heterocyclic ring.

Lanthanide shift reagents. IX. Proton and carbon magnetic resonance study of specific contact interactions of a bifunctional oxazole amide with fluorinated lanthanide shift reagents

Roger G. Harrison

Papers

NMR determination of the enantiomer composition of penicillamine using an optically active europium shift reagent

Lanthanide shift reagents. IX. Proton and carbon magnetic resonance study of specific contact interactions of a bifunctional oxazole amide with fluorinated lanthanide shift reagents