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Semiempirical studies of ring twisting in cis ‐stilbene and related biomolecules
Author(s) -
Monaco Regina R.,
Gardiner William C.,
Kirschner Stephen
Publication year - 1999
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1999)71:1<57::aid-qua6>3.0.co;2-i
Subject(s) - dihedral angle , chemistry , steric effects , mndo , ring (chemistry) , computational chemistry , crystallography , stereochemistry , molecule , organic chemistry , hydrogen bond
The geometric and energetic predictions of the MNDO, AM1, and SAM1 models as they describe rotation of the dihedral angle between the plane of one of the phenyl rings and the plane of the olefin core of cis ‐stilbene ( cis ‐1,2‐diphenylethylene) were tested for a variety of constraints. All three models predict that distortions away from the stable structure fixed by a compromise between π‐electron and steric repulsions lead to small (at most 1–2 kcal/mol) strain energies and geometry relaxations. Extensive peripheral substitution on the phenyl rings present in a prototype natural product having the cis ‐stilbene structure, Combretastatin A‐4 (3,4,5‐trimethoxy‐3′‐hydroxy‐4′‐methoxy‐(Z)‐stilbene), distorted the shapes of the cis ‐stilbene barriers to conformation change only minimally. It is concluded that natural products having the cis ‐stilbene structure should be expected to interact with other biomolecules as if the phenyl twists are barrier free. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 57–62, 1999