Crystal structure of salograviolide A, a guaiane-type sesquiterpene lactone

Authors:

• Urszula Rychlewska,
• Beata Szczepańska,
• Włodzimierz M. Daniewski,
• Gerard Nowak

Abstract

A new naturally occurring sesquiterpene lactone, 3 β-acetoxy-8 α, 9 β-dihydroxy-1 αH, 5 αH, 6 βH, 7 αH-guaian-4(15), 10(14), 11(13)-trien-6,12-olide (Scheme 1) has been structurally characterized by X-ray diffraction methods. The compound crystallizes in the monoclinic space group P2₁ with two molecules in the unit cell of dimensions a=8.485(2), b=7.398(1), c=12.919(3) Å, β=98.17(3)°. The structure has been refined to a final value of R of 0.039 for 2091 observed reflections. The molecule possesses a polyunsaturated guaianolide system which contains a twist chair exomethylenecycloheptane moiety, cis-fused with the exomethylene-cyclopentane [at C(1) and C(5)] and trans-annelated with the α-exomethylene-γ-lactone at C(6) and C(7). The acetoxy substituent at C(3) is β-oriented and trans to the C(8) hydroxyl which, in turn, is trans to the neighboring C(9) hydroxyl. Substitution at C(9) is unprecedented among guaianolides isolated from Centaureinae subtribe. © 1992 Plenum Publishing Corporation.