17-Acetoxymulinic acid

Abstract

The title compound, [systematic name: 5a-acet­oxy­methyl-3-isopropyl-8-methyl-1,2,3,3a,4,5,5a,6,7,10,10a,10b-dodeca­hydro-7,10-endo-epidi­oxy­cyclo­hepta­[e]indene-3a-carb­oxy­lic acid], C22H32O6 (I), is closely related to methyl 5a-acet­oxy­methyl-3-isopropyl-8-methyl-1,2,3,3a,4,5,5a,6,7,10,10a,10b-dodeca­hydro-7,10-endo-epidi­oxy­cyclo­hepta­[e]indene-3a-carboxyl­ate, (II) [Brito et al., (2008 ▶). Acta Cryst. E64, o1209]. There are two mol­ecules in the asymmetric unit, which are linked by two strong intra­molecular 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 acet­oxy­methyl fragments in both mol­ecules 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)

Absolute Configuration of Mulinolic Acid

“…Recrystallization de mulinolic acid from ethyl acetate a room temperature yielded white crystals, which were suitable for X-ray diffraction analysis. The spectroscopic data showed resemblance with those similar mulinane structures reported in the literature [4][5][6][7][8][9][10][11] . The relative stereochemistry of mulinolic acid was assigned based on careful analysis of the ROESY experiment 6 , and in this work we have assigned the absolute configuration of this diterpene using X-ray crystal analysis.…”

“…The relative stereochemistry of the title compound was assigned by spectroscopic data and by chemical transformations 3 . In this paper we report the absolute configuration of the title compound which has been determined from the refinement of the Flack parameter 15 , x = 0.05 (11), which indicate that the correct configuration had been assigned against 925, CuKα Bijvoet pairs. On this basis the absolute configuration was assigned as C3R, C5S, C8S, C9S, C10S and C13R.…”

“…The absolute configuration of the title compound which has been determined from the refinement of the Flack parameter 15 , x = 0.05 (11), indicated that correct configuration had been assigned, against 925, CuKα Bijvoet pairs.…”