Stability and conformation of methyl urocanates and their N-methyl derivatives. Analysis by molecular mechanics (MM2) and semi-empirical computations (PM3)

1994 ◽  
Vol 91 ◽  
pp. 1658-1681
Author(s):  
G Robinet ◽  
C Routaboul-Perrot ◽  
M Rivière ◽  
J Devillers
Keyword(s):  
Molecular Mechanics ◽  
Methyl Derivatives ◽  
Semi Empirical

Theoretical studies of model compounds of lathyrane-type diterpenes

2004 ◽  
Vol 82 (1) ◽  
pp. 11-18 ◽  
Author(s):  
Yukimasa Terada ◽  
Tomoo Matsuura ◽  
Yukari Mori ◽  
Shosuke Yamamura
Keyword(s):  
Ab Initio ◽  
Molecular Mechanics ◽  
Molecular Orbital ◽  
Theoretical Calculations ◽  
Membered Ring ◽  
Orbital Method ◽  
Methyl Groups ◽  
Molecular Orbital Method ◽  
Stable Conformation ◽  
Semi Empirical

The conformation of the 11-membered ring of the lathyrane skeleton has been investigated using NMR spectra and theoretical calculations. Some other skeletons, such as jatrophane, jatrapholane, and tigliane, seem to be derived from this framework, and the conformation is important in connection with the configuration of the resultant diterpenes. The conformation of lathyrane is principally defined by the orientation of the two methyl groups; namely, the methyl groups on C1 and C6 directed above or below the ring plane. Theoretical calculations revealed that the predominant conformation is altered depending on the oxygen functional groups on the ring. As far as the bond lengths, bond angles, and dihedral angles are concerned, all calculation methods afforded reasonable results. In contrast, as regards conformational stability, only the ab initio molecular orbital method (RHF/6-31G*) predicted the most stable conformation, consistent with NOE experiments. On the other hand, the stable conformations predicted by the ab initio method (RHF/STO-3G), the semi-empirical molecular orbital method (MOPAC(PM3)), and the molecular mechanics calculations (MM3) did not necessarily agree with the conformers suggested by the NOE experiments.Key words: ab initio MO, semi-empirical MO, molecular mechanics, 11-membered ring conformation, NOE.

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