Triterpenoide. XIV. [2,3-<i>d</i>]Isoxazoltriterpenderivate
作者:A. Gzella、E. Linkowska、L. Zaprutko、U. Wrzeciono
DOI:10.1107/s010827019900013x
日期:1999.6.15
The X-ray crystal structure analyses of two triterpene isoxazoles, namely olean-2,12-dieno[2,3-d]isoxazol-28-oic acid methyl ester methyl isoxazolo[4,5-b]olean-2,12-dien-28-oate, C32H47NO3, (2a)} and 19 beta,28-epoxy-18 alpha-olean-2-eno[2,3-d]isoxazole 19 beta,28-epoxy-isoxazolo[4,5-b]-18 alpha-olean-2-ene, C31H47NO2, (4a)} are described. These compounds were obtained by treatment of 2-formyl- or 2-hydroxymethylene derivatives of 3-oxoolean-12-en-28-oic methyl ester, (la) and (Ib), and 19 beta,28-epoxy-18H alpha-oleanan-3-one, (3a) and (3b), with hydroxylamine hydrochloride according to the method described by Govardhan, Reddy, Ramaiah & Rao [J. Indian Chem. Sac. (1983), pp. 858-860] for the synthesis of ring-A-fused triterpene [3,2-c]isoxazoles. The structures of the obtained [2,3-d]isoxazoles, (2a) and (4a), were confirmed by the comparison of the bond lengths and bond angles found for the isoxazole rings of compounds (2a) and (4a) with the corresponding data given in the literature. The isoxazole rings in both compounds are planar. Ring A in (2a) and (4a) has a conformation between the half-chair and sofa form. Rings B, D and E in (2a), and B, C, D and E in (4a) have the chair conformation. Ring C in (2a) has a distorted sofa form. In (2a), the rings A/B, B/C and C/D are trans-fused and the rings D/E cis-fused, In (4a), the A/B, B/C, C/D and D/E ring junctions are trans. The axial O2 and C28 atoms in (4a) are beta oriented and form, together with the C17, C18 and C19 atoms, the five-membered ring F, which has an envelope conformation.