Rauniticine-allo-oxindole B methanol monosolvate

Fatimah Salim; Rohaya Ahmad; Nor Hadiani Ismail; Hazrina Hazni; Seik Weng Ng

doi:10.1107/S1600536811016710

. 2011 May 7;67(Pt 6):o1345. doi: 10.1107/S1600536811016710

Rauniticine-allo-oxindole B methanol monosolvate

Fatimah Salim ^a, Rohaya Ahmad ^a, Nor Hadiani Ismail ^a, Hazrina Hazni ^b, Seik Weng Ng ^b,^*

PMCID: PMC3120594 PMID: 21754740

Abstract

The title pentacyclic oxindole alkadoid, isolated from Uncaria longiflora, crystallizes as a methanol solvate, C₂₀H₂₂N₂O₄·CH₄O. The five-membered ring comprising the indole fused ring is nearly planar [maximum atomic deviation = 0.031 (2) Å], whereas the five-membered ring having alphatic C atoms adopts an envelope shape (with the tertiary N atom representing the flap). The six-membered ring that shares an N atom with the envelope-shaped ring adopts a chair shape; the six-membered ring having an O atom is sofa-shaped. The carboxylic acid group acts as a hydrogen-bond donor to a methanol molecule; this, in turn, acts as a hydrogen-bond donor to the double-bond carboxyl O atom of an adjacent molecule, generating a chain. Adjacent chains are linked by N—H⋯O hydrogen bonds, forming a layer motif.

Related literature

For the spectroscopic identification of rauniticine-allo-oxindole B, see: Seki et al. (1993 ▶).

Experimental

Crystal data

C₂₀H₂₂N₂O₄·CH₄O
M _r = 386.44
Monoclinic,
a = 9.2330 (3) Å
b = 7.2110 (2) Å
c = 14.7678 (4) Å
β = 99.313 (3)°
V = 970.27 (5) Å³
Z = 2
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 100 K
0.20 × 0.10 × 0.05 mm

Data collection

Agilent SuperNova Dual diffractometer with an Atlas detector
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2010 ▶) T _min = 0.981, T _max = 0.995
9109 measured reflections
2381 independent reflections
2181 reflections with I > 2σ(I)
R _int = 0.039

Refinement

R[F ² > 2σ(F ²)] = 0.037
wR(F ²) = 0.093
S = 1.05
2381 reflections
266 parameters
4 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.21 e Å⁻³
Δρ_min = −0.19 e Å⁻³

Data collection: CrysAlis PRO (Agilent, 2010 ▶); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: X-SEED (Barbour, 2001 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811016710/xu5205sup1.cif

e-67-o1345-sup1.cif^{(21.9KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811016710/xu5205Isup2.hkl

e-67-o1345-Isup2.hkl^{(117KB, 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
O1—H1⋯O5	0.84 (3)	1.83 (3)	2.662 (3)	173 (4)
O5—H5⋯O2ⁱ	0.84 (3)	1.91 (3)	2.728 (2)	165 (4)
N2—H2⋯O4ⁱⁱ	0.88 (3)	1.97 (3)	2.805 (3)	158 (3)

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

Acknowledgments

We thank the University of Malaya for supporting this study.

supplementary crystallographic information

Comment

The genus Uncaria is a source of diverse bioactive compounds, and parts of the plant are use for medicinal purposes. The structure of rauniticine-allo-oxindole B was previously elucidated by NMR spectroscopy in on study on heteroyohimbine-type oxindole alkaloids (Seki et al., 1993). The assignment is confirmed in the present study on the methanol-solvated compound (Scheme I) isolated from Uncaria longiflora. The pentacyclic oxindole alkadoid, C₂₀H₂₂N₂O₄, features a five-membered ring that adopts the shape of an envelope (with the tertiary N atom representing the flap). The six-membered ring that shares an N atom with the envelope-shaped ring adopts the shape of a chair; the six-membered ring having an O atom is sofa-shaped (Fig. 1). The carboxylic acid portion of the molecule is hydrogen-bond donor to a methanol molecule; this, in turn, is hydrogen-bond donor to the double-bond carboxyl O atom of an adjacent molecule to generate a chain. Adjacent chains are linked by an N–H···O hydrogen bond to form a layer motif (Table 1, Fig. 2).

Experimental

Uncaria longiflora plant material was collected from Hutan Simpan Bangi, Selangor, Malaysia, and specimens were deposited at Taman Botani Putrajaya, Malaysia. Dried and ground stems were extracted with methanol for 72 h to give 25 g of crude extract. This was acidified with 5% hydrochloric acid, and non-alkaloidal material was removed followed with basification with 37% ammonium hydroxide to release the alkaloid. The alkaloid was extracted into chloroform to give 2.25 g of a crude alkaloid fraction. The fraction was dissolved in methanol and subjected to radial chromatography (4 mm thickness silica-gel plate) with dichloromethane:ethyl acetate followed by ethyl acetate:methanol with a gradual increase of solvent polarity. Rauniticine-allo-oxindole B was separated and purified by repeated preparative thin layer chromatography using chloroform:methanol (120:5). The polar fraction afforded colorless crystals when the solvent was allowed to evaporate (53 mg).