Heteroarotinoids: Crystal and molecular structure analysis of the methyl (Z)- and methyl (E) -4-[2-(4,4-Dimethylchroman-6-yl)-1-Propenyl]benzoate

Crystal structure determinations and MM2P molecular mechanics force-field and AM1 molecular orbital calculations were performed on methyl(E)- and methyl(Z)-4-[2-(4,4-dimethylchroman-6-yl)-1-pro-penyl]-benzoate (1). The calculated molecular structures are in good agreement with the observed crystallographic conformations which show that both isomers have a twist-sofa oxo ring conformation and nearly perpendicular aromatic ring systems (87.7(4)° and 60.5(5)° for (E)-1 and (Z)-1, respectively). Full relaxation MM2P conformational energy profiles for the rotation about the propenyl bridge indicate that the maximum energy barrier is less than 3.5 kcal/mol for both isomers. The AM1 results indicate an (E)/(Z) preference of 1.05 kcal/mol in favor of (E)-1, in agreement with experimental evidence. This report is also the first description of the isolation and total structural characterization of (Z)-1 in this family of heteroarotinoids. Biologic analysis of (E)-1 and (Z)-1 was performed using the ornithine decarboxylase assay and demonstrated that (E)-1 was the more active by nearly a factor of 2.