X-Ray determination of the structure of podolide, an antileukemic norditerpene dilactone
The crystal structure of podolide, (I), C19H22O5, an antileukemic norditerpene dilactone isolated from Podocarpus gracilior, has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P21, with a= 12.165(3), b= 7.771(1), c= 9.708(4)Å, β= 113.76(3)°, and Z= 2. The structure was solved by direct methods and refined by least-squares methods to R0.045 for 1 975 independent reflections measured by counter diffractometry. The molecule has a double bond at C(2)–C(3), an epoxide α at C(7)–C(8), and an isopropyl substituent α at C(14). Rings A and B have slightly distorted 1,2-diplanar conformations, the pyran ring C has a near 1,3-diplanar conformation, while the γ-lactone is a C(5) envelope.