RESUMEN
Acetyl 29-methyl-29-methylidene-D:C-friedoolean-8-en-3beta-o1 (2), derived from bryonolic acid (D:C-friedoolean-8-en-3beta-ol-29-oic acid) (1), was crystallographically analyzed. Rings A-E of 2 adopted chair, half-chair, half-chair, boat (with bow and stern at C-13 and C-16), boat (with bow and stem at C-19 and C-22) conformations, respectively. Good agreement was found between the structures from X-ray crystallography and that from MM2 calculations.
RESUMEN
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 (D:C-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 0:100-32:68 for the "trigonal" type and 48:52-100:0 for the "tetrahedral." The reliability of the results is discussed.
