Structure of a Neoclerodane Dilactone from Baccharis rhomboidalis

Abstract

1-Hydroxyneoclerodane-3,13-diene- 15,16;- 19,20-diolide, C2oH2605, Mr = 346.42, orthorhombic, P212121, a = 15-601 (4), b = 15.962 (4), c = 7-093 (2) A, V = 1766.3 A 3, Z= 4, Dx = 1.303 Mg m -3, a(Mo Ka) = 0"71069 A, /z = 0.09 mm-1, F(000) = 744, T = 293 K, final R = 0.064 for 1430 unique observed reflections with F > 3tr(F). The molecular structure of the title compound consists of two trans-fused six-membered rings with a butenolide ring fused to both, and possesses as substituents a secondary and tertiary methyl group at C(8) and C(9), respectively, a secondary hydroxyl group at C(1), and a side chain with an trJ3-unsaturated y-laetone group at C(9). The methyl and hydroxyl groups and C(19) are in cis-axial configuration in agreement with the molecular structure proposed previously on the basis of chemical and spectroscopic methods [San-Martin, Rovirosa, Labb6, Givovich, Mahfi & Castillo (1986). Phytochemistry, 25, 1393-1395]. All bond lengths and angles are within the expected ranges.