Crystal and molecular structure of a bis-p-bromobenzoate derivative of cyclograndisolide [3α-methoxy-9,19-cyclo-9β-lanost-24-en-27,23(R)-olide]

Abstract

Crystals of a bis-p-bromobenzoate derivative of cyclograndisolide, C₄₅H₆₀Br₂O₅, are orthorhombic, a= 6·635(1), b= 20·919(3), c= 30·530(5)Å, Z= 4, space group P2₁2₁2₁. The structure was determined with Cu-K_α diffractometer data by Patterson, electron-density, and least-squares methods, the final R being 0·096 for 1518 observed reflexions. The absolute configuration was determined by the anomalous dispersion method. The presence of a 9,19-cyclopropane system is confirmed, and the chemically assigned stereochemistry is upheld. The Ä ring of the triterpene nucleus is in the chair form, but the presence of the cyclopropane, and of a trans-fused five-membered ring D produces large distortions in rings B and C. There is a short intermolecular Br … Br distance of 3·57 Å.