Redetermination and absolute configuration of 7α-hy­droxy­royleanone

The title compound [systematic name: 7α,12-dihy­droxy-8,12-abietadiene,11,14-dione or (4bS,8aS,10R)-3,10-dihy­droxy-2-isopropyl-4b,8,8-trimethyl-1,4,4b,5,6,7,8,8a,9,10-deca­hydro­phenanthrene-1,4-dione], C(20)H(28)O(4), is an abietane diterpen­oid, which was isolated from the roots of Premna obtusifolia (Verbenaceae). Its crystal structure has been reported previously [Chen et al. (2000 ▶). Jiegou Huaxue, 19, 122–125], but the absolute configuration could not be determined using data collected with Mo radiation. This redetermination using Cu radiation shows the the absolute configurations of the stereogenic centres at positions 4b, 8a and 10 to be S, S and R, respectively. Two intra­molecular O—H⋯O hydrogen bonds [one generating an S(5) ring and one generating an S(6) ring] and a number of short C—H⋯O contacts occur. In the crystal, mol­ecules are linked into infinite chains propagating in [100] by O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions.