Synthesis an crystal structure of 3beta-p-bromobenzoyloxy-14alpha, 15alpha-epoxy-5alpha-cholest-7-ene

The chemical synthesis of 3beta-bromobenzoyloxy-14alpha, 15alpha-epoxy-5alpha-cholest-7-ene is described. Single crystal structral analysis was employed to unambiguously determine the location and absolute configuration of the epoxide moiety in the 3beta-p-bromobenzoyloxy-14alpha, 15alpha-epoxy-5alpha-cholest-7-ene. The space group of the crystal was P1, with unit cell parameters: a=10.873 A, b=13.841 A, c=11.037 A, alpha=75.19 degrees, beta=78.79 degrees, gamma=101.57 degrees, and two molecules per unit cell. Intitial phases were derived from the two bromine atoms. Least squares refinements on all non-hydrogen atoms were carried out to a final unweighted R value of 0.10 and weighted R value of 0.04. The epoxide ring was located at the 14, 15 position and was found to extend to the alpha side of the molecule. Molecular measurements for asymmetry parameters of the sterol nuceus indicate that ring A has a symmetrical chair conformation and ring B has a half chair conformation due to the double bond at C(7). Ring C has a fairly distorted chair conformation due to the trigonal C(8) on one sie and the almost planar 5-membered ring on the other. Ring D has the 17alpha-envelope conformation.