Acanthoic acid

Sunisa Suwancharoen; Wantanee Tommeurd; Chuttree Phurat; Nongnuj Muangsin; Surachai Pornpakakul

doi:10.1107/S1600536810019483

. 2010 Jun 5;66(Pt 7):o1531. doi: 10.1107/S1600536810019483

Acanthoic acid

Sunisa Suwancharoen ^a, Wantanee Tommeurd ^a, Chuttree Phurat ^a, Nongnuj Muangsin ^a, Surachai Pornpakakul ^a,^*

PMCID: PMC3006772 PMID: 21587780

Abstract

The title compound [systematic name: (1R,4aR,7S,8aS,10aS)-1,4a,7-trimethyl-7-vinyl-1,2,3,4,4a,6,7,8,8a,9,10,10a-dodecahydrophenanthrene-1-carboxylic acid], C₂₀H₃₀O₂, is a pimarane-type diterpene extracted from Croton oblongifolius. There are two independent molecules in the asymmetric unit. In both of these, the six-membered rings A, B and C adopt chair, boat and half-chair conformations, respectively. Rings A and B are trans-fused. The two molecules in the asymmetric unit form O—H⋯O hydrogen-bonded R ₂ ²(8) dimers. The absolute configuration was assigned on the basis of the published literature on analogous structures.

Related literature

For background to the structure of acanthoic acid, see: Kim et al. (1998 ▶); Ling et al. (2001 ▶); Suh et al. (2001 ▶). For the related absolute configuration, see: Ling et al. (2000 ▶). For puckering parameters, see: Cremer & Pople (1975 ▶).

Experimental

Crystal data

C₂₀H₃₀O₂
M _r = 302.44
Tetragonal,
a = 12.8697 (16) Å
c = 21.768 (2) Å
V = 3605.5 (7) Å³
Z = 8
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 100 K
0.40 × 0.20 × 0.02 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
21616 measured reflections
4824 independent reflections
3830 reflections with I > 2σ(I)
R _int = 0.050

Refinement

R[F ² > 2σ(F ²)] = 0.056
wR(F ²) = 0.158
S = 1.02
4824 reflections
405 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.37 e Å⁻³
Δρ_min = −0.29 e Å⁻³

Data collection: APEX2 (Bruker, 2008 ▶); cell refinement: SAINT (Bruker, 2008 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810019483/fj2300sup1.cif

e-66-o1531-sup1.cif^{(31.6KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810019483/fj2300Isup2.hkl

e-66-o1531-Isup2.hkl^{(231.5KB, 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′—H2′⋯O1	0.82	1.87	2.687 (3)	177
O2—H2⋯O1′	0.82	1.83	2.649 (3)	175

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Acknowledgments

This research was supported by a grant under the program Strategic Scholarships for Frontier Research Network for the PhD Program Thai Doctoral degree from the Office of the Higher Education Commission, Thailand, the 90^th Anniversary of Chulalongkorn University Fund (Ratchadaphiseksomphot Endowment Fund), the Department of Chemistry, Faculty of Science, Chulalongkorn University, and the National Center of Excellence for Petroleum, Petrochemicals, and Advanced materials are also gratefully acknowledged. Finally, we thank the Research Funds from the Faculty of Science (A1B1), the Thai Government Stimulus Package 2 (TKK2555) under the Project for Establishment of Comprehensive Center for Innovative Food, Health Products and Agriculture for their support of X-ray crystallography analysis by supporting the X-ray analysis fund.

supplementary crystallographic information

Comment

Acanthoic acid is a pimarane-type diterpene. It was first isolated from root bark of Acanthopanax koreanum Nakai (Araliaceae) (Kim et al., 1998) which has been used for treatment of neuralgia, hypertension, rheumatism and diabetes (Ling et al., 2001). This natural product exhibits anti-inflammatory activity (Suh et al., 2001). In this work, acanthoic acid was isolated in high yield from stem bark of Croton oblongifolius from Ratchaburi Province, Thailand.

There are two independent molecules in the asymmetric unit. In both independent molecules, the six memberred rings A, B and C adopts a chair, boat and half-chair conformations, respectively with the puckering parameters: Q = 0.546 Å, θ = 179.5° and φ = -107.0° for A, Q = 0.766 Å, θ = 89.9° and φ = -73.3° for B and Q = 0.493 Å, θ = 128.4° and φ = 35.2° for C. Rings A/B is trans-fused. The ethylene group substituted at C13 is in an equatorial position. The two molecules in the asymmetric unit form O—H···O hydrogen-bonded R₂²(8) dimers. The absolute configuration was assigned by comparison with the crystal structure of p-bromobenzoate ester-acanthoic derivative (Ling et al., 2000).

Experimental

Dried powder of stem bark of Croton oblongifolius Roxb. (5.23 kg) from Ratchaburi province was extracted with hexane (4Lx5). The hexane crude extract was obtained as viscous yellow brown oil. This crude extract was purified by quick column chromatography on silica gel using a mixture of hexane and ethyl acetate (100:0-0:100). Fractions with similar components were combined according to TLC profile. The combined fraction eluted with a 7:3 mixture of hexane and ethyl acetate was crystallized in hexane and ethyl acetate to give colourless crystals (5.5% yield).

mp. 140-142^oC; [a]²⁵_D -36.1 (c = 0.42, benzene); ¹H-NMR (400 MHz, CDCl₃) d 5.81 (dd, 1H, J=10.6, 17.4 Hz, H-15), 5.39 (m, 1H, H-11), 4.93 (dd, 1H, J=1.2, 17.4 Hz, H-16 trans), 4.86 (dd, 1H, J=1.2, 10.6 Hz, H-16 cis), 2.31 (m, 1H, H-8), 2.21 (m, 1H, H-2 b), 2.15 (m, 1H, H-3a), 2.01 (m, 1H, H-12a), 1.93 (m, 1H, H-2a), 1.89 (m, 1H, H-6 b), 1.81 (m, 1H, H-1a), 1.77 (m, 1H, H-12 b), 1.73 (m, 1H, H-7a), 1.66 (dd, 1H, J=6.2, 13.0 Hz, H-5), 1.48 (m, 1H, H-6a), 1.45 (m, 1H, H-14a), 1.28 (m, 1H, H-1 b), 1.25 (s, 3H, H-18), 1.21 (m, 1H, H-7 b), 1.05 (m, 1H, H-3 b), 1.03 (m, 1H, H-14 b), 0.99 (s, 3H, H-20), 0.96 (s, 3H, H-17); ¹³C NMR (100 MHz, CDCl₃) d 184.60 (C-19), 150.23 (C-15), 149.85 (C-9), 116.59 (C-11), 109.16 (C-16), 47.99 (C-5), 44.21 (C-4), 41.92 (C-1), 41.80 (C-14), 38.43 (C-10), 38.08 (C-3), 37.47 (C-12), 34.86 (C-13), 28.67 (C-8), 28.56 (C-18), 27.76 (C-7), 22.40 (C-20), 22.17 (C-17), 20.34 (C-6), 18.91 (C-2)