Absolute configuration of xerophenone A

Abstract

The title compound, C33H42O5, known as xerophenone A {systematic name: (1R,3R,4R,6S,8E,10R)-10-hydroxy-8-[hydroxy(phenyl)methylene]-4-methyl-1,6-bis(3-methylbut-2-en-1-yl)-3-(3-methylbut-3-en-1-yl)-11-oxatricyclo[4.3.1.14,10]undecane-7,9-dione} is a naturally occurring rearranged benzophenone compound which was isolated from the twigs of Garcinia propinqua. The absolute configuration was determined by refining the Flack parameter to 0.18 (16). The absolute configurations at positions 1, 3, 4, 6 and 10 of the xerophenone A are R, R, R, S and R. In the molecule, the cyclohexane-1,3-dione, tetrahydro-2H-pyran and tetrahydrofuran rings adopt twisted boat, standard chair and envelope conformations, respectively. The 3-methylbut-3-en-1-yl substituent is disordered over two sets of sites in a 0.771 (11):0.229 (11) ratio. An intramolecular O—H...O hydrogen bond generates an S(6) ring motif. In the crystal, molecules are linked by O—H...O and weak C—H...O interactions into a chain along the a axis. A very weak C—H...π interaction and C...O short contact [2.989 (2) Å] are also present.