Ranunculin

Michael Benn; Lois Jean Yelland; Masood Parvez

doi:10.1107/S1600536810034847

. 2010 Sep 4;66(Pt 10):o2503. doi: 10.1107/S1600536810034847

Ranunculin

Michael Benn ^a, Lois Jean Yelland ^a, Masood Parvez ^a,^*

PMCID: PMC2983359 PMID: 21587499

Abstract

In the title molecule {systematic name: (5S)-5-[(β-d-glucopyranosyloxy)methyl]furan-2(5H)-one}, C₁₁H₁₆O₈, the five-membered ring is essentially planar, the maximum deviation being 0.0151 (13) Å for the O atom. The six-membered ring adopts a chair conformation with puckering parameters Q = 0.581 (2) Å, θ = 9.0 (2)° and ϕ = 39.7 (13)°, and with all of the substituents of the glucoside unit having normal equatorial orientations. The crystal structure is stabilized by extensive O—H⋯O and C—H⋯O hydrogen bonding, resulting in a three-dimensional network.

Related literature

For background to ranunculin, see: Hill & van Heyningen (1951 ▶); Bai et al. (1996 ▶); Benn & Yelland (1968 ▶); Boll (1968 ▶); Camps et al. (1982 ▶); Fang et al. (1989 ▶). For chemical and spectrometric data for closely related, simple butenolides, see: Perry et al. (1996 ▶). For comparison bond distances, see: Allen et al. (1987 ▶). For puckering parameters, see: Cremer & Pople (1975 ▶).

Experimental

Crystal data

C₁₁H₁₆O₈
M _r = 276.24
Monoclinic,
a = 5.7944 (4) Å
b = 6.9359 (3) Å
c = 15.0491 (10) Å
β = 97.895 (2)°
V = 599.08 (6) Å³
Z = 2
Mo Kα radiation
μ = 0.13 mm⁻¹
T = 173 K
0.30 × 0.24 × 0.02 mm

Data collection

Nonius KappaCCD diffractometer with APEXII CCD
Absorption correction: multi-scan (SORTAV; Blessing, 1997 ▶) T _min = 0.961, T _max = 0.997
1926 measured reflections
1133 independent reflections
1112 reflections with I > 2σ(I)
R _int = 0.018

Refinement

R[F ² > 2σ(F ²)] = 0.026
wR(F ²) = 0.069
S = 1.04
1133 reflections
184 parameters
1 restraint
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.18 e Å⁻³
Δρ_min = −0.16 e Å⁻³

Data collection: COLLECT (Hooft, 1998 ▶); cell refinement: DENZO (Otwinowski & Minor, 1997 ▶); data reduction: SCALEPACK (Otwinowski & Minor, 1997 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810034847/fl2315sup1.cif

e-66-o2503-sup1.cif^{(19.1KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810034847/fl2315Isup2.hkl

e-66-o2503-Isup2.hkl^{(54.9KB, 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
O5—H5O⋯O8ⁱ	0.86 (3)	2.17 (3)	2.910 (2)	144 (3)
O6—H6O⋯O5ⁱⁱ	0.92 (3)	1.94 (3)	2.824 (2)	162 (3)
O7—H7O⋯O6ⁱⁱ	0.84 (3)	1.84 (3)	2.668 (2)	173 (3)
O8—H8O⋯O2ⁱⁱⁱ	0.88 (3)	1.96 (3)	2.830 (2)	167 (3)
O6—H6O⋯O7	0.92 (3)	2.56 (3)	2.894 (2)	102 (2)

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

supplementary crystallographic information

Comment

Ranunculin (I) is the glycosidic precursor of the vesicant protoanemonin present in numerous species of Rannunculaceae and is especially associated with the burning sensation on chewing leaves of buttercup plants. It was first obtained in crystalline form by Hill and van Heyningen (1951) who established its gross structure and showed that it undergoes enzymatic cleavage by β-glucosidase to yield the aglucone, which underwent easy dehydration to protoanemonin. These processes were shown to occur readily under autolytic conditions (Bai et al., 1996). The S-stereochemistry of the dihydrofuranone ring was deduced by Benn and Yelland (1968), and Boll (1968), as shown in the schematic diagram, and later confirmed by synthesis (Camps et al., 1982; Fang et al., 1989). Our sample of (I) was a natural product, and as such had been biosynthesised in the plant (and not made in a laboratory). The only stereoisomer which occurs naturally is the D-isomer, and both that and the anomeric configuration of the glycoosidic bond in (I) were established by cleavage of the glycoside by β-D-glucosidases. The X-ray structure reported here provides the simplest unequivocal proof of that stereochemistry since the chirality follows from that of the D-glucopyranosyl moiety.

The molecular structure of (I) is presented in Fig. 1. The five membered ring, O1/C2—C5, is essentially planar with the maximum deviation of any atom being 0.0151 (13) Å for O1. The six-membered ring adopts a chair conformation with puckering parameters (Cremer & Pople, 1975): Q = 0.581 (2) Å, θ = 9.0 (2)° and φ = 39.7 (13)°, with all of the substituents of the glucoside unit having normal equatorial orientations. The 5-membered ring folds back away from the six-membered ring as reflected by the torsion angle C6—O3—C1—C5 -162.86 (17)°. The bond distances and angles are as expected (Allen, 2002). The structure is stabilized by extensive O—H···O and C—H···O hydrogen bonding resulting in a three diemsional network (Table 1 & Fig. 2).

There are two other, closely related, simple butenolides known, though their structures rest on chemical and spectrometric data, i.e., without X-ray crystallographic support. They are the (5R,6R) and (5S,6R) steeroisomers of 5-([1-β-D-glucopyranosyloxy]ethyl)-2(5H)-furanone (Perry et al., 1996); the glycosidic precursor of (Z)-5-ethylidene-2(5H)-furanone, a homologue of protoanemonin in Halocarpus biformis juvenile foliage.

Experimental

The details of the isolation, and some of the physical properties, of our sample of (I) have been reported previously (Benn & Yelland 1968). Suitable crystals of the title compound for X-ray study were grown from a solution in aqueous ethanol (ca 1:20) in the form of plates.