Crystal and MolecularStructure of Parthenolide [4,5-€poxygermacra-I (1 0),11(13)-dien-12,6-olactone] By Andrew Quick and Donald Rogers," Chemical Crystallography Laboratory, Imperial College, London
SW7 2AYThe crystal structure of the title compound has been determined from single-crystal X-ray data by direct methods.Crystals are orthorhombic, a = 7 1.929(1), b = 12.267(2), c = 18.761 (2) 8, space group P212121, Z = 8, i.e. two independent niolecules per asymmetric unit. Full-matrix least-squares refinement based on 2 330 independent reflections has reached R 0.047. Thedouble bond C(l)-C(lO) and the equivalent double bond C(4)-C(5) are both rrans, both methyl groups are @, and the ten-membered ring has a conformation typical of several germacranolides.THE sesquiterpenic lactone, parthenolide, isolated from Chrysanthemum 9arthenizm (L) , was originally assigned the structure (I).l The same compound was isolated from the trunk bark of Michelia chaqbaca and its structure revised to (11) 2 from a study of its n.m.r. spectrum and chemical reactions. The absolute configuration of the molecule has been determined and it was shown that parthenolide can be represented by the stereoformula (111) .3The present crystal structure, part of a series of studies of ten-membered ring compounds, was undertaken to show the conformation of the epoxide ring and also the orientation of the methyls at C(4) and C(10). E SPERIMENTAL The crystals were colourless plates. Crystal Data.-C,,H,,O,, n/I = 248.3, Orthorhombic. a = 11.929(1), b = 12.267(2), c = 18.761(2) A, U = 2 745.4 A3, t Reprints are not available.