STRUCTURE OF XINDONGNIN-B

ent-3beta,7beta,11beta-Trihydroxy-15-oxokaur-16-en-6alpha-yl acetate, C22H3206, M(r) = 392.50, orthorhombic, P2(1)2(1)2(1), a = 6.739 (5), b = 16.963 (6), c 17.094 (6) angstrom, V = 1954.0 (3) angstrom3, Z = 4, D(x) = 1.334 g cm-3, lambda(Cu Kalpha) = 1.5410 angstrom, mu = 7.431 cm-1, F(000) = 848, room temperature, final R = 0.039 for 1055 observed reflections. The structure is composed of discrete molecules held together by hydrogen bonding. Each molecule contains three cyclohexane rings (A, B, C) in chair conformations, with the rings connected trans to each other. One five-membered ring is bridged by two C atoms to form an alpha-methylenecyclopentanone ring (D) with two unsaturated side groups. The five-membered ring has an envelope configuration with a C atom at the flap. This arrangement plays a key role in the anti-neoplastic activity of the compound.