Relative population of S-form and F-form conformers of bryonolic acid and its derivatives in equilibrium in CdCl3 solutions.

ABSTRACT

Relative populations of S-form (D-E rings boat-boat form) and F-form (D-E rings chair-chair form) conformers, in equilibrium in CDCl3 solutions, of 20 derivatives (2-21) of bryonolic acid (DC-friedoolean-8-en-3beta-ol-29-oic acid) (1) were calculated from NMR spectral data (J-values and chemical shifts), with the aid of molecular mechanic calculation using a MM2/CONFLEX program system. The principal deciding factor of the population ratio was found to be whether the functionality at C-29 is trigonal or tetrahedral; the S-form F-form was 0100-3268 for the "trigonal" type and 4852-1000 for the "tetrahedral." The reliability of the results is discussed.