Structures of three pseudoguaianolides: parthenin, hymenolin (11β,13-dihydroparthenin) and bipinnatin

Abstract

Parthenin, C 1 5 H 1 8 0 4 , M r = 2623, tetragonal, P41, a = 6 8 6 2 ( 1 ) , c = 2 8 . 6 8 1 ( 8 ) / k , V= 1350.5 (8)/~3, Z = 4, Dx 1-290 g cm -3, A(Cu Ka) = 1.54184 A, /z = 7.25 cm-1, F(000) = 560, T = 298K, R = 0 0 3 6 for 1316 observations with I > 1 o'(/). Hymenolin (11/3,13-dihydroparthenin), C15H2004, Mr = 2643, monoclinic, P21, a = 6.495 (1), b = 28.380 (6), c = 7.587 (1) A, /3 = 102.90 (1) °, V = 1363.2 (7) A 3, Z = 4, Dx = 1.288 g cm -3, A(Mo Ka) = 0.71073/~, /z = 086 c m 1, F(000) = 568, T = 297 K, R = 0.060 for 1757 observations with I>0 .5 t r ( / ) . Bipinnatin, C15H2oO4, M r = 2643, orthorhombic, P212121, a = 9.231 (1), b = 9.713 (2), c = 15.453 (2) A, V = 1385.5 (6) A 3, Z = 4, Dx = 1.267 g c m -3, /.t,(Cu Ka) = 7.07 cm-1, F(000) = 568, T = 299 K, R = 0.058 for 1145 observations with 1>3o-(/) . The sevenmembered ring of parthenin has a chair conformation with a pseudo mirror passing through C10, and asymmetry parameter ACs=4.30. The cyclopentenone and lactone tings both have envelope conformations with C5 at the flap, ACs = 5-2 ° and C7 at the flap, ACs = 0-7 °, respectively. Molecules are linked in 0108-2701/89/122006-05503.00 chains along the symmetry axis by hydrogen bonds involving the hydroxyl group and lactone carbonyl, O...O distance 2.805 (5)A. The crystal structure of hymenolin contains two independent molecules. In both, the five-membered rings are in conformations closely resembling those of parthenin. The sevenmembered ring of one molecule has a twist-chair conformation with C10 lying on the pseudo diad, and asymmetry parameter ACE = 39 °, while the other molecule has an asymmetric seven-membered ring. Molecules are linked in chains of alternating molecule types, by hydrogen bonds involving hydroxy groups and lactone carbonyl O atoms. O...O distances are 2.855 (5) and 2-878 (5)/~. Hymenolin was isolated from Hymenoclea salsola T. and G. with unresolved stereochemistry at C l l [Toribio & Geissman (1968). Phytochemistry, 7, 1623-1630]. The seven-membered ring of bipinnatin also has two conformations in the crystal, but both exist at the same site as a ca 70-30% disorder of atoms C8 and C9. The seven-membered ring of the major conformer has the parthenin conformation, with ACs = 6.1 ° , while the minor conformer has the twist-chair © 1989 International Union of Crystallography F R A N K R. F R O N C Z E K et al. 2007 conformation of hymenolin, with ACE = 31 °. The cyclopentanone ring has the envelope conformation with C2 at the flap and ACs = 1.3 °, while the lactone ring has the half-chair conformation with C 12 on the pseudo diad, and ACE = 27 °. Molecules are linked in chains along the b direction by hydrogen bonds involving the hydroxy group and the lactone carbonyl, with O.-.O distance 2.774 (7) A. Experimental. Parthenin (I): crystal size 0.28 x 0.40 × 0 .52mm, space group determination by Laue symmetery 4/m, systematic absence 00l with l~4n and presumption of absolute configuration as determined for bromoambrosin (Emerson, Herz, Caughlan & Witters, 1966), cell dimensions for setting angles of 25 reflections 70 > 20 > 66 °, data collection on Enraf-Nonius CAD-4 diffractometer, graphite monochromator , CuKa radiation, 0 -20 scans designed to yield l=50 t r ( / ) , scan rates 0.20-5.0 ° minl . Data having 4 or(/). Non-H atoms anisotropic; H atoms from difference maps, fixed contributions, B = 5.0/~2. Secondary-extinction coefficient 4.4 (3) × 10 -6 . Final R = 0 . 0 3 6 , wR=0-037, s = 1.230 for 172 variables. Max. shift 0.01tr in final cycle, max. residual density 0.10, min. 0.13 e A 3.