Crystal and molecular structure and absolute configuration of Withaperuvin E:: a C28 steroidal lactone

The withanolide Withaperuvin E, C28H36O8, has been obtained from the air dried roots of Physalis peruviana and purified by silica gel chromatography. This compound exhibits significant antineo plastic activity. Prismatic pale yellow crystals were obtained from a methanol/acetone solution. The compound crystallizes together with a partially occupied [40(1)%] acetic acid molecule, in space group P2(1)2(1)2(1), Z = 4, D-c = 1.242 g cm(-3), with unit, cell parameters a = 11.431(3), b = 14.104(1), c = 17.387(5) Angstrom, V = 2803.2(11)Angstrom(3), and mu(CuK alpha) = 0.072mm(-1). Through the X-ray analysis the molecule was found to be comprised of a steroidal skeleton with a beta-oriented oxygen bridging atoms C(5) and C(6) in ring B. Steroid ring conformations are: A sofa; B sofa; C chair; D intermediate half-chair/sofa; the lactone ring E has a sofa conformation. All rings of the steroid skeleton are trans connected. The absolute configuration of the Withaperuvin E skeleton corresponds to that of naturally occurring steroids, C(18) and C(19) both being beta-oriented. The partially occupied acetic acid molecule forms a hydrogen bond to the steroid molecule. Hydrogen bonding also occurs between OH(14) and a symmetry related oxygen O(20) of the steroid.