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Nuclear magnetic resonance of psychotherapeutic agents. IV —conformational analysis of 2,3‐dihydro‐1 H ‐1,4‐benzodiazepines
Author(s) -
Romeo G.,
Aversa M. C.,
Giannetto P.,
Ficarra P.,
Vigorita M. G.
Publication year - 1981
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270150109
Subject(s) - conformational isomerism , lanthanide , chemistry , lone pair , steric effects , substituent , imine , ring (chemistry) , crystallography , population , electron paramagnetic resonance , stereochemistry , delocalized electron , molecule , nuclear magnetic resonance , organic chemistry , ion , physics , demography , sociology , catalysis
The lanthanide shift reagent (LSR)/ 1 H NMR study of some 7‐chloro‐5‐phenyl‐2,3‐dihydro‐1 H ‐1, 4‐benzodiazepines shows that these compounds exist in CDCI 3 solution as two pseudo‐boat conformers, rapidly interconverting at room temperature. Computer simulated lanthanide induced shifts (LIS) are consistent with LSR complexation by the imine nitrogen atom. The lanthanide shifts the conformational equilibrium towards conformer (a), with a pseudoequatorial 1‐substituent: this effect may be the result of the greater basicity of 4‐N when the 1‐N lone pair is pseudoaxially directed, thus permitting an extended electron delocalization from 1‐ to 4‐N through the fused benzene ring. The detection of H‐9/1‐Me through space spin‐spin coupling in medazepam (7‐chloro‐1‐methyl‐5‐phenyl‐2,3‐dihydro‐1 H ‐1,4‐benzodiazepine) supports the observed higher availability of conformer (a) to LSR. A LIS computer calculation to predict the population ratio results in reasonable agreement with the conformational changes based on the response of 3 J (HH) to lanthanide addition. The electronic and steric effects which determine the greater stability of conformer (a) may be effective in the drug‐receptor interaction.