The sensitivity of the cis/trans-isomerization of enalapril and enalaprilat to solvent conditions.

The cis- and trans-isomers of enalapril and enalaprilat can be resolved by HPLC and by capillary electrophoresis. The isomeric content of enalapril is perturbed by the ionization of both its carboxyl and amine groups, while the isomeric content of enalaprilat is only perturbed by the ionization of its amine group. Increasing the hydrophobicity of the analyte solvent, as reflected in its molar polarization, increases the Z (cis) content of enalapril and markedly decreases the kinetics for isomerization.

Analysis of the isomeric composition of the proline peptide bond in an angiotensin-converting enzyme inhibitor using capillary electrophoresis.

The cis and trans isomeric composition of a proline peptide bond can be determined by routine free-solution capillary electrophoresis measurements provided that one isomeric form is preferentially stabilized by a dissociable ionic group. This capability is illustrated using the angiotensin converting enzyme (ACE) inhibitor (S)-1-N-[1-(ethoxycarbonyl)-3-phenylpropyl]-L-ala-L-pro, which has the trade name enalapril. Electropherograms indicate that the two isomeric forms of enalapril can be separated with baseline resolution at 15 degrees C using capillary buffers having pH values in the dissociation ranges of the enalapril carboxyl group, pK(cis) and pK(trans) of 2.

Nonaromatic hydroxylation of bupivacaine during continuous epidural infusion in man.

Less than 11% of the dose of bupivacaine could be accounted for in urine from 10 patients receiving continuous epidural infusions. HPLC analysis of metabolites confirmed (S)-bupivacaine was more extensively metabolised than (R)-bupivacaine, and dealkylation was the predominant metabolic pathway although co-elution of metabolites made quantitation difficult. The percentage of (S)-2',6'-pipecoloxylidide and co-eluting metabolites excreted relative to (R)-2',6'-pipecoloxylidide from three patients was 0.

Isocratic liquid chromatographic assay for monitoring the degradation of luteinizing hormone releasing hormone by extracts from the gastrointestinal tract of possums.

A simple HPLC method to separate human luteinizing hormone releasing hormone (LHRH) from its metabolites using an isocratic elution is described. Intact LHRH and five metabolites were separated in 11.4 min.

Quantitative capillary electrophoresis assay for the proteolytic stability of luteinizing hormone-releasing hormones.

A rapid and simple capillary electrophoresis (CE) assay for measuring the stability of luteinizing hormone-releasing hormone (LHRH) analogues in the presence of intestinal enzymes has been developed and validated. Buffer pH and sample stacking were important factors in controlling resolution and reproducibility. The CE assay for human (h) and salmon LHRH analogues between 0.