STEREOCHEMICAL STUDY OF A 13-BETA,28-EPOXYOLEANANE

The stereochemistry of 3 beta-acetoxy-12 alpha-bromo-13 beta,28-epoxyo leanan-16 alpha-ol (2b) has been examined by n.m.r. methods and establ ished by an X-ray crystallographic examination. Steric hindrance of th e 16 alpha-hydroxy group is shown not to be as great as previously rep orted. The bromo epoxide (2b), C32H51BrO4, M 579.66, crystallized in t he orthorhombic space group P2(1)2(1)2(1) with a 16.118(2), b 16.615(3 ), c 11.024(7) Angstrom, V 2952(1) Angstrom(3), D-c(Z = 4) 1.304 g cm( -3), N = N(unique) = 1954, N-o 1731 [I > 2.5 sigma(I)], N-var = 335, c onventional R 0.039, R-w 0.038.