Conformation of Bryonolic Acid and Its Derivatives in CDCl3 Solution by 1H NMR and 13C NMR Spectroscopy

Article abstract of DOI:10.1002/mrc.1260251004

Comparison of the 1H and 13C chemical shift data of bryonolic acid (D:C-friedoolean-8-en-3β-ol-29-oic acid) and its derivatives (13 species) revealed that the conformational features of these compounds in CDCl3 solution depend on whether the functional groups at C-29 are trigonal, such as COOCH3, or tetrahedral, such as CH2OH.In order to study the conformational features of these two groups of compounds, vicinal coupling constants between the protons on the E rings of the methyl ester of D:C-friedoolean-8-en-29-oic acid, D:C-fridoolean-8-en-29-ol and its acetate were measured.Comparison of the results with the steric geometries to be expected from the molecular mechanics calculation for the E-ring moieties of these derivatives in the S form (D-E rings: boat-boat form) and the F form (D-E rings: chair-chair form) led to the conclusion that the compounds having a trigonal functional group at C-29 mainly adopt the S form, and those having a tetrahedral functional group at C-29 are present as mixtures of the S and F form in equilibrium in the solutions.KEY WORDS - Conformation D:C-friedoolean-8-enes Molecular mechanics calculation 1H and 13C NMR