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1 H NMR and molecular mechanics studies of epimeric ethyl esters of 20( R, S )‐hydroxy‐23‐norcholanoic acids
Author(s) -
Maier M. S.,
Seldes A. M.,
Gros E. G.
Publication year - 1991
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260290208
Subject(s) - chemistry , epimer , pyridine , molecular mechanics , chemical shift , solvent , proton nmr , proton , stereochemistry , computational chemistry , nmr spectra database , medicinal chemistry , spectral line , organic chemistry , molecular dynamics , physics , quantum mechanics , astronomy
Proton chemical shifts for the C‐18, C‐21, CO 2 CH 2 CH 3 and CO 2 CH 2 CH 3 protons of epimeric ethyl esters of 20( R , S )‐hydroxy‐23‐norcholanoic acids were measured in deuteriochloroform and pyridine‐ d 5 . The observed solvent shifts due to specific OH—pyridine hydrogen‐bonded complexes allowed the quantification of the epimeric mixtures by analysis of the pyridine‐ d 5 1 H NMR spectra. The main features of the pyridine‐induced shifts are rationalized in terms of the preferred conformations for the 20 R ‐ and 20 S ‐epimers, which are predicted by molecular mechanics calculations.