A semiempirical molecular orbital and dynamic NMR study of conformational isomerism in angiotensin-converting enzyme inhibitors

The conformational isomerism in a series of molecules related to inhibitors of the angiotensinconverting enzyme (ACE) is investigated using the semiempirical quantum mechanical molecular orbital model, AM1, and dynamic NMR spectroscopy. The theoretical method is tested by the prediction of relative barriers to rotation about amide C-N and acylhydrazine N-N bonds, and of the trans: cis ratio for a series of model compounds. The conformational energetics of captopril and a series of acylhydrazines are predicted and used to interpret the dynamic NMR spectra of these molecules, presented herein. © 1991.