Crystal structure of 6,7-dehydroroyleanone isolated from Taxodium distichum (L.) Rich.

The crystal structure features two O—H⋯O hydrogen bonds, forming chains along the [010] direction.


Chemical context
Taxodium distichum (L.) Rich. is a tree native to North America that can grow to 25 m in height (Ogunwande et al., 2007). Its leaves and seeds are used for the treatment of malaria and liver disease (Kupchan et al., 1968). Previous studies revealed that it contains multiple compounds such as diterpenes (Kusumoto et al., 2010), flavonoids (Zaghloul et al., 2008), proanthocyanidins (Stafford & Lester, 1986), lignins (Logan & Thomas, 1985), sterols and fatty acids (Geiger & de Groot-Pfleiderer, 1979). A detailed phytochemical investigation of a petroleum ether extract of the seeds of Taxodium distichum (L.) Rich. led to the isolation of the title compound 6,7-dehydroroyleanone. Herein we present the crystal structure of 6,7-dehydroroyleanone, which was undertaken in order to establish unambiguously the stereochemical features of this natural compound.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The title compound belongs to the class of abietanetype diterpenes and the structure contains two ketone groups at C14 and C17 and three double bonds located between atoms C10 and C11, C12 and C13, C15 and C16. The torsion angles C17-C12-C13-C1 [176.8 (2)

Database survey
A search of the Cambridge Structural Database (CSD, Version 5.27, last update Feb 2017;Groom et al., 2016) yielded the compound royleanone (HACGUN01; Fun et al., 2011), which has a similar structure to the title compound but without the double bond between C10 and C11.

Figure 2
Part of the crystal structure of the title compound, with hydrogen bonds (see Table 1) shown as dashed lines.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. C-bound H atoms were positioned with idealized geometry and refined isotropically using a riding model with C-H = 0.94-0.99 Å and U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for all others. The OH hydrogen atom was refined freely with U iso (H) = 1.5U eq (O).

sup-1
Acta Cryst. Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.