The furan­osteroid viridiol

Pierre F Andersson; Anders Broberg; Daniel Lundberg

doi:10.1107/S1600536813005606

. 2013 Mar 2;69(Pt 4):o467–o468. doi: 10.1107/S1600536813005606

The furanosteroid viridiol

Pierre F Andersson ^a, Anders Broberg ^a, Daniel Lundberg ^a,^*

PMCID: PMC3629508 PMID: 23634026

Abstract

The asymmetric unit of the title compound, C₂₀H₁₈O₆ (systematic name: 1β,3β-dihydroxy-2β-methoxyfuro[4′,3′,2′:4,5,6]-18-norandrosta-8,11,13-triene-7,17-dione), a dihydro derivative of the fungal steroid viridin, contains two molecules with similar conformations. The rings bearing the hydroxy groups adopt boat conformations. The absolute structure was assigned based on the known chirality of a precursor compound. In the crystal, molecules are linked by O—H⋯O hydrogen bonds, generating a three-dimensional network and weak C—H⋯O interactions consolidate the packing.

Related literature

For background to fungal metabolites, see: Brian & McGowan (1945 ▶); Moffatt et al. (1969 ▶); Jones & Hancock (1987 ▶); Hanson (1995 ▶); Cross et al. (1995 ▶); Przybyl (2002 ▶); Smith et al. (2009 ▶); Andersson et al. (2010 ▶); Queloz et al. (2011 ▶); Andersson (2012 ▶); Andersson et al. (2012 ▶, 2013 ▶). For related structures, see: Neidle et al. (1972 ▶); Lang et al. (2009 ▶). For other characterization methods, see: Brian et al. (1957 ▶); Aldridge et al. (1975 ▶); Blight & Grove (1986 ▶). For background to the assignment of the absolute structure of the title compound, see: MacMillan et al. (1972 ▶); Harrison (1990 ▶); Dewick (2002 ▶); Wipf & Kerekes (2003 ▶); Flack & Bernardinelli (2000 ▶).

Experimental

Crystal data

C₂₀H₁₈O₆
M _r = 354.34
Orthorhombic,
a = 6.8285 (2) Å
b = 20.1939 (6) Å
c = 22.4344 (6) Å
V = 3093.57 (15) Å³
Z = 8
Mo Kα radiation
μ = 0.11 mm⁻¹
T = 93 K
0.3 × 0.25 × 0.2 mm

Data collection

Oxford Diffraction XcaliburIII Sapphire-3 CCD diffractometer
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2007 ▶) T _min = 0.891, T _max = 1.000
26916 measured reflections
4874 independent reflections
3294 reflections with I > 2σ(I)
R _int = 0.085

Refinement

R[F ² > 2σ(F ²)] = 0.049
wR(F ²) = 0.089
S = 0.91
4874 reflections
485 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.33 e Å⁻³
Δρ_min = −0.25 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2007 ▶); cell refinement: CrysAlis RED (Oxford Diffraction, 2007 ▶); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXD (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: SHELXL (Sheldrick, 2008 ▶); software used to prepare material for publication: DIAMOND (Brandenburg, 2001 ▶).

Supplementary Material

Click here for additional data file.^{(38.2KB, cif)}

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536813005606/hb7028sup1.cif

e-69-0o467-sup1.cif^{(38.2KB, cif)}

Click here for additional data file.^{(238.8KB, hkl)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536813005606/hb7028Isup2.hkl

e-69-0o467-Isup2.hkl^{(238.8KB, hkl)}

Click here for additional data file.^{(6.9KB, cml)}

Supplementary material file. DOI: 10.1107/S1600536813005606/hb7028Isup3.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
O19A—H19A⋯O19B ⁱ	0.85 (3)	2.08 (3)	2.886 (3)	160 (3)
O19B—H19B⋯O20A ⁱⁱ	0.83 (3)	2.30 (3)	3.002 (3)	143 (3)
O20A—H20A⋯O25B ⁱⁱⁱ	0.91 (3)	1.85 (3)	2.717 (3)	160 (3)
O20B—H20B⋯O24A ^iv	0.81 (3)	2.05 (3)	2.842 (3)	166 (3)
C2A—H2A⋯O23B ^v	1.00	2.45	3.325 (3)	146
C2B—H2B⋯O23A	1.00	2.38	3.295 (3)	151
C11A—H11A⋯O19A	0.95	2.43	3.084 (3)	126
C11B—H11B⋯O19B	0.95	2.58	3.230 (3)	126
C18A—H18A⋯O20A	0.98	2.38	3.227 (3)	145
C18B—H18D⋯O20B	0.98	2.39	3.241 (4)	145
C21A—H21A⋯O24A ^vi	0.95	2.37	3.282 (3)	162
C21B—H21B⋯O24B ^vii	0.95	2.25	3.180 (3)	167

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) .

Acknowledgments

We are grateful to Dr Lars Eriksson for skillful technical assistance and fruitful discussions. The isolate Ö3 from which the viridiol was obtained was from a study which was, in part, supported by the Swedish research council FORMAS grant No. 2010–1344.

supplementary crystallographic information

Comment

The disease known as dieback of ash on European ash (Fraxinus excelsior) was first observed in Poland in 1995, but has spread rapidly over most of the European subcontinent (Przybyl, 2002). During studies of the secondary metabolite production of the fungus Hymenoscyphus pseudoalbidus, the pathogen responsible for dieback of ash (Queloz et al., 2011), a number of steroidal compounds have been isolated (Andersson et al., 2010; Andersson et al. 2013; Andersson et al. 2012). These compounds belong to a family of fungal steroids (Hanson, 1995), of which some have been shown to have interesting bioactivities (Cross et al. 1995; Smith et al. 2009; Andersson 2012).

The first reported compound of this family was viridin (Brian & McGowan, 1945), with its crystal structure published nearly 30 years later (Neidle et al., 1972). The absolute structures of a few other members have been reported through successful osmylation (Lang et al. 2009). Other members of the same family have also been characterized through other methods than crystallography, including wortmannin (Brian et al., 1957), demethoxyviridin and demethoxyviridiol (Aldridge et al., 1975), and virone and wortmannolone (Blight & Grove, 1986). The phytotoxin viridiol (Moffatt et al., 1969), which has also been suggested to be part of the pathogenicity of H. pseudoalbidus (Andersson et al. 2010), can be produced in Gliocladium virens from viridin (Jones & Hancock, 1987). The previously reported absolute configuration of these compounds are based on the evidence of their steroidal origin i. e. the configuration of the C10 carbon is based on lanosterol (Dewick, 2002; Harrison, 1990). Here, we present the crystal structure of viridiol (I) confirming the previously presented structure, both relative and absolute (MacMillan et al., 1972; Moffatt et al., 1969; Wipf & Kerekes, 2003) (Scheme 1, Fig. 1)

Compound (I) crystallizes in the orthorhombic space group P2₁2₁2₁ (No. 19), with two crystallographically independent viridiol molecules with a total of eight in the unit cell. (Fig. 2) The nearly flat furanosteroid skeleton lies in the bc plane, with the A ring and its methoxy group bending away from the plane (Fig. 1). In the crystal, O—H···O and C—H···O interactions link the molecules (Table 1, Fig. 3).

Experimental

The viridiol containing fraction from a previous study (Andersson et al., 2013) was subjected to rotatory evaporation, which lead to crystal formation. The crystals, too small for crystallography, were harvested by filtration and dried (approx. 3 mg). The crystals were subsequently dissolved in 80 °C toluene (4 ml) in a 5 ml test tube. The solution was left at room temperature and the toluene was evaporated slowly by a gentle stream of nitrogen gas. Large enough crystals formed at the bottom of the test tube after stepwise precipitation of impurities on the inner test tube wall. A colourless block was mounted on a glass capillary and a data set was measured under cold conditions (93 K).