CRYSTAL AND MOLECULAR-STRUCTURES OF THE 3-BETA-ACETOXY AND 3-BETA-BENZOXY DERIVATIVES OF ALPHA-AMYRIN

Crystals of the 3β-acetoxy derivative of α-amyrin are monoclinic, space group P21 with a = 8.021(1), b = 11.474(1), c = 15.564(2) Å, and β = 100.496(3) °. Crystals of the 3β-benzoxy derivative are orthorhombic, space group P212121, with a = 6.752(1), b = 12.974(1), and c = 36.664(3) Å. Both structures have been solved by direct methods and refined by full-matrix least-squares, using data collected on an automated four-circle diffractometer. The final residuals for the acetoxy and benzoxy structures are 0.055 (2274 significant independent reflections) and 0.152 (1220 significant independent reflections) respectively. The geometry of the α-amyrin skeleton in both structures is similar to that found in other triterpene structures containing a system of five condensed six-membered rings. Ring C has a C(8)β-sofa conformation due to the presence of the double bond at C(12)-C(13) whereas in the remaining rings the chair conformation predominates. © 1980 Plenum Publishing Corporation.