Caloxanthone C: a pyran­oxanthone from the stem bark of Calophyllum soulattri

Gwendoline Cheng Lian Ee; Siau Hui Mah; Huey Chong Kwong; Soek Sin Teh; Mohamed Ibrahim Mohamed Tahir; Sidik Silong

doi:10.1107/S1600536811036294

. 2011 Sep 14;67(Pt 10):o2607–o2608. doi: 10.1107/S1600536811036294

Caloxanthone C: a pyranoxanthone from the stem bark of Calophyllum soulattri

Gwendoline Cheng Lian Ee ^a,^*, Siau Hui Mah ^a, Huey Chong Kwong ^a, Soek Sin Teh ^a, Mohamed Ibrahim Mohamed Tahir ^a, Sidik Silong ^a

PMCID: PMC3201296 PMID: 22064829

Abstract

The title compound [systematic name: 5,10-dihydroxy-2,2-dimethyl-12-(2-methylbut-3-en-2-yl)pyrano[3,2-b]xanthen-6(2H)-one], C₂₃H₂₂O₅, isolated from the stem bark of Calophyllum soulattri, consists of four six-membered rings and a 2-methylbut-3-en-2-yl side chain. The tricyclic xanthone ring system is almost planar [maximum deviation = 0.093 (2) Å], whereas the pyranoid ring is in a distorted boat conformation. The 2-methylbut-3-en-2-yl side chain is in a synperiplanar conformation. There are two intramolecular O—H⋯O hydrogen bonds. In the crystal, molecules are linked by C—H⋯O interactions, forming a zigzag chain propagating in [010].

Related literature

For related structures, see: Ee et al. (2010 ▶); Fun et al. (2006 ▶); Doriguetto et al. (2001 ▶); Boonnak et al. (2007 ▶); Ndjakou et al. (2007 ▶). For the biological activity of Calophyllum species, see: Dharmaratne et al. (1999 ▶, 2009 ▶); Zou et al. (2005 ▶); Ito et al. (1999 ▶, 2002 ▶); Ee et al. (2004 ▶). For standard bond lengths, see Allen et al. (1987 ▶).

Experimental

Crystal data

C₂₃H₂₂O₅
M _r = 378.42
Monoclinic,
a = 6.7013 (3) Å
b = 15.8951 (7) Å
c = 17.3891 (7) Å
β = 93.181 (4)°
V = 1849.39 (14) Å³
Z = 4
Cu Kα radiation
μ = 0.78 mm⁻¹
T = 150 K
0.34 × 0.15 × 0.07 mm

Data collection

Oxford Diffraction Gemini diffractometer
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2006 ▶) T _min = 0.890, T _max = 0.947
10133 measured reflections
3503 independent reflections
3048 reflections with I > 2σ(I)
R _int = 0.023

Refinement

R[F ² > 2σ(F ²)] = 0.056
wR(F ²) = 0.170
S = 1.00
3488 reflections
254 parameters
H-atom parameters constrained
Δρ_max = 0.34 e Å⁻³
Δρ_min = −0.34 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2006 ▶); cell refinement: CrysAlis RED (Oxford Diffraction, 2006 ▶); data reduction: CrysAlis RED; program(s) used to solve structure: SIR92 (Altomare et al., 1994 ▶); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003 ▶); molecular graphics: Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: CRYSTALS.

Supplementary Material

Crystal structure: contains datablock(s) I. DOI: 10.1107/S1600536811036294/su2302sup1.cif

e-67-o2607-sup1.cif^{(23.4KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811036294/su2302Isup2.hkl

e-67-o2607-Isup2.hkl^{(219.7KB, hkl)}

Supplementary material file. DOI: 10.1107/S1600536811036294/su2302Isup3.cml

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
O16—H16⋯O5	0.83	1.79	2.570 (2)	155
O28—H28⋯O1	0.81	2.25	2.690 (2)	115
C12—H12⋯O5ⁱ	0.94	2.51	3.441 (3)	168

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Symmetry code: (i) Inline graphic .

Acknowledgments

The authors are grateful to the Ministry of Science, Technology and Innovation (MOSTI) for a grant from the e-science fund.

supplementary crystallographic information

Comment

Calophyllum species are native to tropical areas, mainly in Asia, Australia, Africa and Polynesia. This genus is well known for various bioactivities due to the existence of a variety of secondary metabolites such as xanthones (Dharmaratne et al., 1999), coumarins (Ee et al., 2004) and flavanoids (Ito et al., 1999). Xanthones are known to have various biological activities such as, antifungal (Dharmaratne et al., 1999), anti-oxidant (Dharmaratne et al., 2009), anti-inflammatory (Zou et al., 2005) and anti-cancer (Ito et al., 2002). We present here the crystal structure of Caloxanthone C, isolated from the stem bark of Calophyllum soulattri.

The molecular structure of the title compound is illustrated in Fig. 1. The bond distances are in the normal range (Allen et al., 1987) and together with the bond angles are comparable to those reported for other pyranoxanthone structures (Ee et al. 2010; Fun et al. 2006; Doriguetto et al. 2001), and other closely related structures (Boonnak et al., 2007; Ndjakou et al. 2007).

The title molecule has a xanthone skeleton, which is essentially planar [maximum deviation 0.093 (2) Å for atom C14] with two intramolecular O-H···O hydrogen bonds (Fig. 1 & Table 1). Rings A (C2,C3,C24-C27), B (O1,C2-C4,C6,C7) and C (C6-C9,C14,C15) are practically coplanar, including atoms O28, O5, and O16, that are linked to them; the latter deviate from the individual mean planes by 0.009 (2) Å, 0.016 (2) Å, and 0.056 (2) Å, for O28 from ring A, O5 from ring B and O16 from ring C, respectively. Rings A and B nearly lie in the same plane, as they form a dihedral angle of only 0.46 (9)°, while rings B and C are inclined to one another by 4.25 (9)°. The mean planes of rings A and C, which intersect on a line approximately through the middle of ring B, are inclined to one another by 4.62 (10)°. The same dihedral angle is 7.78 (9) ° in the trihydroxy derivative of the title compound, reported on by (Fun et al., 2006), and 7.75 (7) ° for a similar pyranoxanthone structure (12-Acetyl-6-hydroxy-3,3,9,9-tetramethylfuro[3,4-b]pyrano[3,2-h]xanthene-7,11(3H,9H)-dione ) reported on by (Ee et al., 2010).

The mean torsional angle of ring D (C9,O10,C11-C14) is 21.08 (13)° and it adopts a conformation half way between an envelope and a half boat. This conformation is probably caused by the constraint of the C12═C13 double bond which results in considerable pucking of ring D, happening at C11. This conformation is similar to that observed in other pyranoxanthone structures, such as 12-Acetyl-6-hydroxy-3,3,9,9-tetramethylfuro[3,4-b]pyrano[3,2-h]xanthene-7,11(3H,9H)-dione (Ee et al., 2010) and 12-(1,1-Dimethyl-2-propenyl)-5,9,10-trihydroxy-2,2-dimethyl-2H,6H-pyrano[3,2-b]xanthen-6-one (Fun et al., 2006).

The orientation of the 2-methylbut-3-en-2-yl (C19—C23) side chain with respect to the benzene ring C is indicated by the torsion angle of C7—C8—C19—C20 = 27.6 (3)° [compared to 28.8 (3) ° in (Fun et al., 2006)], indicating a synperiplanar conformation.

In the crystal, there is an intermolecular C—H···O hydrogen bond (Table 1, Fig. 2) the leads to the fomation of a zigzag chain propagating in [010].

Experimental

The stem bark of Calophyllum soulattri was collected from the Sri Aman district in Sarawak, Malaysia. Approximately 1 kg of air-dried stem bark of Calophyllum soulattri was ground into a fine powder and extracted successively in a Soxhlet apparatus with n-hexane, dichloromethane, ethyl acetate and methanol for 72 h. The extracts were evaporated to dryness under vacuum to give 15.3 g of dichloromethane extract, which was subjected to column chromatography, over silica gel, several times. Stepwise gradient systems using n-hexane, dichloromethane, ethyl acetate and methanol and eluting through the columns resulted in separation and purification of the extract. Caloxanthone C, a yellowish crystal with the melting point of 210–212 °C was isolated. Single crystals, suitable for X-ray diffraction analysis, were prepared by the slow evaporation and diffusion of diethyl ether into a solution of Caloxanthone C in chloroform at room temperature.