The crystal structure of a new diterpene lactone—chilobolide A

Chilobolide A, C₂₂H₃₀O₅, M.W. = 374,5, orthorhombic, space group P 2,2,2₁, a = 8.753 (2), b = 8.887 (3), c = 54.247 (14) Å, V = 4220(2) ų, Z = 8, D_x = 1.17 g·cm^?3, F(000) = 1616 e at room temperature. The structure was solved by direct methods with diffractometer data measured with Cu Kα radiation, and block-full-matrix least-squares refinement converged at R = 0.064 for 1805 observed reflections. Both molecules in an asymmetric unit have similar conformation. The molecular skeleton is bicyclic system, in which an envelope form γ-lactone ring is cis-fused to a cyclotridecadiene ring, the latter ring is in ?+?+?++++?+??] asymmetric conformation; the methyl groups attached to 4-C and 13-C are situated on E-type double bond, the acetyl group is in equatorial orientation at 10-C and the acetoxy group is in axial at 9-C.