Alpinumisoflavone

Jerry Joe Ebow Kingsley Harrison; Youhei Tabuchi; Hiroyuki Ishida; Robert Kingsford-Adaboh

doi:10.1107/S1600536808006867

. 2008 Mar 14;64(Pt 4):o713. doi: 10.1107/S1600536808006867

Alpinumisoflavone

Jerry Joe Ebow Kingsley Harrison ^a, Youhei Tabuchi ^b, Hiroyuki Ishida ^b, Robert Kingsford-Adaboh ^a,^*

PMCID: PMC2960904 PMID: 21202104

Abstract

The title compound, C₂₀H₁₆O₅, {systematic name: 5-hydroxy-7-(4-hydroxyphenyl)-2,2-dimethyl-2H,6H-benzo[1,2-b:5,4-b′]dipyran-6-one}, was obtained by demethylation of the biologically active related compound, 4-O-methylalpinumisoflavone. The molecular structure of the title compound is characterized by a fused tricyclic system that contains an approximately planar benzopyrone ring fragment. The six membered pyran ring adopts a half-chair conformation. Both ring systems show an out-of-plane twist. The dihedral angle between the mean plane of the benzopyrone system and the benzene ring is 54.29 (3)°. The molecules are linked by O—H⋯O hydrogen bonds, forming a molecular tape running along the b axis.

Related literature

For related compounds, see: Kingsford-Adaboh et al. (2001 ▶, 2006 ▶). For ring puckering analysis, see: Cremer & Pople (1975 ▶).

Experimental

Crystal data

C₂₀H₁₆O₅
M _r = 336.34
Monoclinic,
a = 13.8333 (3) Å
b = 5.92699 (17) Å
c = 19.8352 (4) Å
β = 99.6806 (7)°
V = 1603.13 (7) Å³
Z = 4
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 93 (2) K
0.53 × 0.45 × 0.43 mm

Data collection

Rigaku R-AXIS RAPIDII diffractometer
Absorption correction: multi-scan (ABSCOR; Higashi, 1995 ▶) T _min = 0.771, T _max = 0.958
30574 measured reflections
4676 independent reflections
4296 reflections with I > 2σ(I)
R _int = 0.036

Refinement

R[F ² > 2σ(F ²)] = 0.042
wR(F ²) = 0.123
S = 1.04
4676 reflections
237 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.51 e Å⁻³
Δρ_min = −0.26 e Å⁻³

Data collection: PROCESS-AUTO (Rigaku/MSC, 2004 ▶); cell refinement: PROCESS-AUTO ; data reduction: CrystalStructure (Rigaku/MSC, 2004 ▶); 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: CrystalStructure and PLATON (Spek, 2003 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808006867/fb2087sup1.cif

e-64-0o713-sup1.cif^{(20.7KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808006867/fb2087Isup2.hkl

e-64-0o713-Isup2.hkl^{(229.1KB, 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—H2O⋯O3	0.92 (2)	1.76 (2)	2.6023 (10)	152.2 (17)
O5—H5O⋯O3ⁱ	0.871 (18)	1.943 (18)	2.7823 (10)	161.4 (17)

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Symmetry code: (i) Inline graphic .

Acknowledgments

This work was supported by the Japanese Society for the Promotion of Science (JSPS) Research Program and RK-A thanks the JSPS for the postdoctoral fellowship awarded.

supplementary crystallographic information

Comment

The 4-O-methylalpinumisoflavone, O,O-dimethylalpinumisoflavone and 5-O-methyl-4-O-(3-methylbut-2-en-1-yl)alpinumisoflavone are some of the solvent-extracted compounds from the rootbark and seeds of Milletia thonningii whose crystal structures have been studied for obtaining fundamental information on their chemical and biological properties (Kingsford-Adaboh et al., 2001, 2006). These compounds have shown considerable brine shrimp lethality (Kingsford-Adaboh et al., 2006).

In the present work, single crystals of alpinumisoflavone suitable for X-ray diffraction were obtained by demethylation of 4-O-methylalpinumisoflavone using cold BCl₃. The crystals isolated from the crude extract were usually of poor quality. Therefore we decided to modify 4-O-methylalpinumisoflavone chemically by demethylation (Scheme 2) hoping that a new compound would yield crystals of a better quality. This turned to be true. The molecular structure of the title compound differs from 4-O-methylalpinumisoflavone only in the replacement of the methoxy group by the hydroxyl on the benzene ring D.

The molecular structure of the title compound is characterized by a tricyclic fused ring system, A/B/C, and a benzene ring D (Fig. 1). The benzopyrone ring fragment, B/C, is planar and it is twisted out of plane with respect to the benzene ring D. The outer six-membered ring A is deformed into a half-chair conformation, with Cremer & Pople (1975) parameters q₂, q₃ and φ₂ of 0.2342 (9), -0.1148 (9) Å and 220.4 (2)°, respectively.

The presence of the hydroxyl group proximal to the keto group on the ring C permits the formation of a relatively stronger intramolecular O—H···O hydrogen bond (Table 1). This distance is comparable to the intramolecular contact distance equal to 1.724 (17) Å in 4-O-methylalpinumisoflavone which is the closest related compound in the studied series (Kingsford-Adaboh et al., 2001, 2006). The corresponding distances observed in other members of the series are longer (ca 2.3 Å; Kingsford-Adaboh et al., 2006).

The observed intramolecular contact is affected by the coplanar arrangement between the hydroxyl and the carbonyl groups in the pertinent part of the molecule. This is demonstrated by the observed torsion angle C9—C8—C7—O2 = -1.19 (13)° in the title structure. The largest deviation from the coplanarity in the series is observed in O,O-dimethylalpinumisoflavone with the corresponding angle equal to -12.83 (18)° (Kingsford-Adaboh et al., 2001). The intermolecular O—H···O hydrogen bond (Table 1), where the terminal OH group of the benzene ring D serves as a proton donor to the carbonyl oxygen atom, is observed to play an important role in the molecular bonding in the crystal structure (Tab. 1, Fig. 2).

Experimental

Alpinumisoflavone was obtained from the demethylation of 4-O-methylalpinumisoflavone. Solvent extraction of 4-O-methylalpinumisoflavone from the pulverized root bark of Milletia thonningii followed similar procedure as described in our earlier work (Kingsford-Adaboh et al., 2001). A cold solution of BCl₃ in chloroform (-78 °C) was added slowly to about 15 ml of a chloroform solution of 4-O-methylalpinumisoflavone (200 mg, 0.571 mmol) cooled to -78 °C using dry ice and acetone mixture. The solution was stirred for about 10 min under argon atmosphere. 30 ml of water was added slowly and the resulting yellowish mixture was extracted with chloroform three times. The combined extracts were washed with water twice and then dried over anhydrous sodium sulphate. After evaporation of the solvent under vacuum, the residue was chromatographed on a silica gel using petroleum ether and ethylacetate mixture in the ratio of between 8/1 and 5/1 as the mobile phase. The product was recrystallized from acetonitrile. The demethylation yield (159.6 mg about 80%, m.p. 486 K). The product was confirmed by ¹³C NMR spectra of both the reactants and the product.)