X-Ray determination of the structure of podolide, an antileukemic norditerpene dilactone

Abstract
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.

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