(+)-Jaborol, a B-secowithanolide from Jaborosa magellanica

Abstract

C28H3606, Mr=46859, monoclinic, P2, a=6.919(3), b=17.042, c=10.267(3)A, fl= 93.39 (3) °, v= 1209 (2) A s, z= 2, Dx= 1-288 Mg m -3, 2(Mo Ka) = 0.71073 A, /~ = 0-083 mm -~, F(000) = 504, T= 293 (1) K, R = 0-033 for 2032 observed reflections with I> 300(/). The average bond distances are C(sp3)-C(sp 3) 1.534 (3), C(sp3)-C(sp 2) 1.498 (3), C(spZ)-C(sp 2) 1.481 (3), C=C 1.336 (3), C-C (aromatic) 1.388 (3), C(sp3)-O 1.445 (2), C(sp2)-O 1.342 (3) and C=O 1.221 (2) A. Ring A is essentially planar, the tetrahydrofuranoid ring B has a C(7)-envelope conformation while ring C has a twist-boat and ring D a C(13)-envelope conformation. The lactonic ring E is in a half-chair conformation. Atoms C(18) and 0(4) are/3, and the lactone moiety is a oriented. An hydroxy group is H-bonded to a ketonic O atom (O(61) ...H(O1) 1.96A). Introduction. Our continuing investigations on the withanolides found in Jaborosa magellanica (Griseb.) Drisen (Solanaceae) (Parvez, Fajardo & Shamma, 1988), has led to an usual withanolide, (+)-jaborol, in which the original steroidal ring B has suffered in vivo oxidative cleavage with formation of a phenolic ring A. Chemical and spectroscopic studies led to the proposal of structure (1) for jaborol (Fajardo, Freyer, Minard & Shamma, 1987). The crystal structure of (1) was determined in order to ascertain its conformation and molecular geometry. The absolute configuration was not established by the anomalous-dispersion method. However, the configuration indicated in (1) is derived from the fact that naturally occurring steroidal derivatives generally incorporate a C(18) methyl group which lies above the mean plane of the molecule.