Redetermined structure, inter­molecular inter­actions and absolute configuration of royleanone

Hoong-Kun Fun; Suchada Chantrapromma; Abdul Wahab Salae; Ibrahim Abdul Razak; Chatchanok Karalai

doi:10.1107/S1600536811011457

. 2011 Apr 7;67(Pt 5):o1032–o1033. doi: 10.1107/S1600536811011457

Redetermined structure, intermolecular interactions and absolute configuration of royleanone

Hoong-Kun Fun ^a,^*,^‡, Suchada Chantrapromma ^b,^§, Abdul Wahab Salae ^a,^¶, Ibrahim Abdul Razak ^a, Chatchanok Karalai ^b

PMCID: PMC3089143 PMID: 21754362

Abstract

The structure of the title diterpenoid, C₂₀H₂₈O₃, {systematic name: (4bS,8aS)-3-hydroxy-2-isopropyl-4b,8,8-trimethyl-4b,5,6,7,8,8a,9,10-octahydrophenanthrene-1,4-dione} is confirmed [Eugster et al. (1993 ▶). Private communication (refcode HACGUN). CCDC, Union Road, Cambridge] and its packing is now described. Its absolute structure was established by refinement against data collected with Cu radiation: the two stereogenic centres both have S configurations. One cyclohexane ring adopts a chair conformation whereas the other cyclohexane ring is in a half-chair conformation and the benzoquinone ring is slightly twisted. An intramolecular O—H⋯O hydrogen bond generates an S(5) ring motif. In the crystal, molecules are linked into chains along [010] by O—H⋯O hydrogen bonds and weak C—H⋯O interactions. The packing also features C⋯O [3.131 (3) Å] short contacts.

Related literature

For the previous determination of the title structure, see: Eugster et al. (1993 ▶). For ring conformations, see: Cremer & Pople (1975 ▶). For bond-length data, see: Allen et al. (1987 ▶). For background to Verbenaceae plants and the bioactivity of diterpenoids, see: Bunluepuech & Tewtrakul (2009 ▶); Edwards et al. (1962 ▶); Kabouche et al. (2007 ▶); Suresh et al. (2011 ▶); Slamenová et al. (2004 ▶); Tezuka et al. (1998 ▶). For a related structure, see: Razak et al. (2010 ▶). For hydrogen-bond motifs, see: Bernstein et al. (1995) ▶. For the stability of the temperature controller used in the data collection, see Cosier & Glazer, (1986 ▶).

Experimental

Crystal data

C₂₀H₂₈O₃
M _r = 316.42
Monoclinic,
a = 10.2247 (2) Å
b = 7.6353 (1) Å
c = 10.7292 (2) Å
β = 97.992 (1)°
V = 829.48 (2) Å³
Z = 2
Cu Kα radiation
μ = 0.66 mm⁻¹
T = 100 K
0.52 × 0.31 × 0.15 mm

Data collection

Bruker APEX DUO CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2009 ▶) T _min = 0.726, T _max = 0.909
5901 measured reflections
2390 independent reflections
2375 reflections with I > 2σ(I)
R _int = 0.021

Refinement

R[F ² > 2σ(F ²)] = 0.036
wR(F ²) = 0.098
S = 1.06
2390 reflections
217 parameters
1 restraint
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.35 e Å⁻³
Δρ_min = −0.20 e Å⁻³
Absolute structure: Flack (1983 ▶) 699 Friedel pairs
Flack parameter: 0.11 (19)

Data collection: APEX2 (Bruker, 2009) ▶; cell refinement: SAINT (Bruker, 2009) ▶; data reduction: SAINT ▶; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL (Sheldrick, 2008 ▶) and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811011457/hb5812sup1.cif

e-67-o1032-sup1.cif^{(22.6KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811011457/hb5812Isup2.hkl

e-67-o1032-Isup2.hkl^{(117.4KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H1O2⋯O1	0.88 (4)	2.05 (3)	2.5977 (18)	119 (3)
O2—H1O2⋯O3ⁱ	0.88 (4)	2.35 (4)	3.1079 (19)	145 (3)
C1—H1A⋯O1	0.97	2.38	2.993 (2)	120
C7—H7A⋯O1ⁱⁱ	0.97	2.51	3.131 (3)	122
C17—H17B⋯O2	0.96	2.49	3.071 (2)	119
C20—H20A⋯O1	0.96	2.47	3.125 (2)	125

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Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

AWS thanks Universiti Sains Malaysia for the PhD student visiting fellowship. SC thanks the Prince of Songkla University for generous support. The authors thank Universiti Sains Malaysia for the Research University Grant No.1001/PFIZIK/811151.

supplementary crystallographic information

Comment

The extracts of Verbenaceae plants have been found to possess anti-HIV-1 integrase activity (Bunluepuech & Tewtrakul, 2009) and cytotoxicity (Suresh et al., 2011). During the course of our study of chemical constituents and bioactive compounds from Premna obtusifolia (Verbenaceae), the title diterpenoid (I), which is known as royleanone (Edwards et al., 1962; Tezuka et al., 1998) was isolated from the roots of this plant. Compound (I) was reported to show significant biological properties such as antioxidant (Kabouche et al., 2007) and cytotoxic activities (Slame˘nová et al., 2004). The absolute configuration of (I) was determined by making use of the anomalous scattering of Cu KαX-radiation with the Flack parameter being refined to 0.11 (19). We herein report the crystal structure of (I).

The molecule of (I) has three fused six membered rings (Fig. 1). The two cyclohexane rings are trans fused. One cyclohexane ring (C1–C5/C10) is in a standard chair conformation whereas the other (C5–C10) is in half chair conformation, with the C5 and C6 atoms having the deviation of 0.396 (2) and -0.323 (2) Å, respectively from the plane through C7–C10 atoms and the puckering parameters Q = 0.563 (2) Å, θ = 55.20 (19)° and φ = 16.1 (2)° (Cremer & Pople, 1975). The benzoquinone ring (C8–C9/C11–C14/O1/O3) is slightly twisted with the maximum deviations of -0.091 (1) and 0.055 (2) Å for atoms C9 and C13, respectively, and with the puckering parameters Q = 0.1474 (19) Å, θ = 72.9 (7)° and φ = 86.8 (8)° (Cremer & Pople, 1975). The O1, O2 and O3 atoms lie close to the mean plane of the C8–C9/C11–C14 ring with the r.m.s. of 0.0870 (1) Å. The bond angles around C8, C9, C12 and C13 are indicative of sp² hybridization for these atoms. The orientation of the propanyl group is described by the torsion angles C12–C13–C15–C16 = -69.8 (2) and C12–C13–C15–C17 = 54.2 (2) °. Intramolecular O2—H1O2···O1 hydrogen bond (Table 1) generate S(5) ring motif (Fig. 1) (Bernstein et al., 1995). The bond distances and angles in (I) are within normal ranges (Allen et al., 1987) and comparable with a related structure (Razak et al., 2010). The absolute configuration at atoms C1 and C5 or positions 4b and 8a of royleanone are both S, which agrees with the previous stereochemistry of royleanone (Kabouche et al., 2007; Slame˘nová et al., 2004; Tezuka et al., 1998). The S,S configurations are also consistent with those in a related structure (Razak et al., 2010).

In the crystal of (I) (Fig. 2), the molecules are linked into chains along the [0 1 0] through O2—H1O2···O3 hydrogen bond and C7—H7A···O1 weak interaction (Fig. 2 and Table 1). The crystal is stabilized by these interactions together with C···O[3.131 (3) Å] short contacts.

Experimental

The air-dried roots of premna obtusifolia (4.5 kg) were extracted with hexane (2 × 20 l) at room temperature. The combined extracts were concentrated under reduced pressure to give a dark yellow extract (40.0 g) which was subjected to quick column chromatography (QCC) over silica gel using solvents of increasing polarity from n-hexane to EtOAc to afford 7 fractions (F1-F7). Fraction F2 was further purified by quick column chromatography using hexane, yielding the title compound (6.1 mg). Yellow blocks were recrystallized from CH₂Cl₂ by the slow evaporation of the solvent at room temperature after several days, M.p 451-453 K.