17-Acet­oxy­mulinic acid

THE TITLE COMPOUND, [SYSTEMATIC NAME: 5a-acet-oxy-methyl-3-isopropyl-8-methyl-1,2,3,3a,4,5,5a,6,7,10,10a,10b-dodeca-hydro-7,10-endo-epidi-oxy-cyclo-hepta-[e]indene-3a-carb-oxy-lic acid], C(22)H(32)O(6) (I), is closely related to methyl 5a-acet-oxy-methyl-3-isopropyl-8-methyl-1,2,3,3a,4,5,5a,6,7,10,10a,10b-dodeca-hydro-7,10-endo-epidi-oxy-cyclo-hepta-[e]indene-3a-carboxyl-ate, (II) [Brito et al., (2008 ▶). Acta Cryst. E64, o1209]. There are two mol-ecules in the asymmetric unit, which are linked by two strong intra-molecular O-H⋯O hydrogen bonds with graph-set motif R(2) (2)(8). In both (I) and (II), the conformation of the three fused rings are almost identical. The five-membered ring has an envelope conformation, the six-membered ring has a chair conformation and the seven-membered ring has a boat conformation. The most obvious differences between the two compounds is the observed disorder of the acet-oxy-methyl fragments in both mol-ecules of the asymmetric unit of (I). This disorder is not observed in (II). The crystal structure and the molecular conformation is stabilized by intermolecular C-H⋯O hydrogen bonds. The ability to form hydrogen bonds is different in the two compounds. The crystal studied was a non-merohedral twin, the ratio of the twin components being 0.28 (1):0.72 (1).