3-Hy­droxy-8-oxo-3-nor-methyl­chamigrane-2,7-peroxide

Liu, D.

doi:10.1107/S1600536810024517

organic compounds

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ISSN: 2056-9890

Volume 66| Part 7| July 2010| Page o1875

doi:10.1107/S1600536810024517

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3-Hydroxy-8-oxo-3-nor-methylchamigrane-2,7-peroxide

Dongze Liu ^a ^*

^aSouth China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, People's Republic of China
^*Correspondence e-mail: dongzeliu@scsio.ac.cn

(Received 1 June 2010; accepted 23 June 2010; online 30 June 2010)

In the title compound, C₁₄H₂₂O₄ (systematic name: 9-hydroxy-1,5,5-trimethyl-1,8-epidioxyspiro[5.5]decan-2-one), which was isolated from the fermentation broth of Steccherinum ochraceum, the two six-membered rings adopt chair conformations and are bridged by a peroxide group. The hydroxy H atom forms a three-centre cyclic intermolecular O—H⋯(O,O′) hydrogen-bonding interaction with a peroxide and a carbonyl O-atom acceptor, forming [100] chains.

Related literature

For similar structures, see Miyashita et al. (1998 ).

Experimental

Crystal data

C₁₄H₂₂O₄
M_r = 254.32
Orthorhombic, P 2₁ 2₁ 2₁
a = 7.3138 (4) Å
b = 12.4206 (7) Å
c = 13.9408 (8) Å
V = 1266.41 (12) Å³
Z = 4
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 173 K
0.42 × 0.38 × 0.35 mm

Data collection

Bruker SMART 1000 CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ) T_min = 0.961, T_max = 0.967
6456 measured reflections
1602 independent reflections
1471 reflections with I > 2σ(I)
R_int = 0.021

Refinement

R[F² > 2σ(F²)] = 0.037
wR(F²) = 0.103
S = 1.08
1602 reflections
167 parameters
H-atom parameters constrained
Δρ_max = 0.30 e Å⁻³
Δρ_min = −0.17 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H2A⋯O1ⁱ	0.84	2.51	3.112 (2)	130
O2—H2A⋯O4ⁱ	0.84	2.17	2.943 (2)	154
Symmetry code: (i) $[x-{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]$ .

Data collection: SMART (Bruker, 2001 ); cell refinement: SAINT-Plus (Bruker, 2003 ); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536810024517/zs2044sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536810024517/zs2044Isup2.hkl

checkCIF report

Comment top

Mushrooms have proved to be a rich source of secondary metabolites with unusual structures as well as interesting biological activities. As a continuation of our study characterizing bioactive metabolites from higher fungi in China, a new norsesquiterpene peroxide, 3-hydroxy-8-oxo-3-nor-methylchamigrane-2,7-peroxide, C₁₄H₂₂O₄ (I) was isolated from the fermentation broth of Steccherinum ochraceum. The six-membered C1–C2–C3–C4–C5–C6 and C1–C2–O(1)–O(2)–C7–C6 rings both adopt chair conformations and are bridged by the peroxide group (Fig. 1). The absolute configuration was not determined for the four chiral centres in this compound and the structures of no other compounds with a similar peroxide-bridged cage system are present in the CSD. The hydroxyl H in (I) gives a three-centre cyclic intermolecular O–H···O,O' hydrogen-bonding interaction with both a peroxide and a carbonyl O acceptor, (Table 1) giving one-dimensional chains which extend down the a direction of the unit cell.

Related literature top

For similar structures, see Miyashita et al. (1998).

Experimental top

S. ochraceum was collected from the Ailao Mountain of Yunnan Province, China. The strain was cultured in a liquid medium composed of potato (200 g), glucose (20 g), KH₂PO₄ (3 g), MgSO₄ (1.5 g), citric acid (0.1 g), and thiamin hydrochloride (10 mg) in 1 L of deionized water. The fungus was grown in reagent bottles (500 mL; media of 300 mL). The pH was adjusted to 6.5 before autoclaving. Fermentation was carried out on a shaker at 22° C and 150 RPM for 25 days. The culture broth (20 L) was filtered to remove the mycelium. The filtrate was then successively extracted twice with ethyl acetate, and the crude extract (3.5 g) was chromatographed on a silica gel column using a CHCl₃/MeOH gradient. Several fractions of increasing polarity were collected. Fraction II (850 mg) eluted with CHCl₃/MeOH (100:1, v/v) was subjected to column chromatography over silica gel and Sephadex LH-20, using a petroleum ether/ethyl acetate (8:1, v/v) and CHCl₃/MeOH (1:1, v/v) eluents respectively, and further purified by repeated recrystallization from MeOH to yield (I) (150 mg). Single crystals were obtained by slow evaporation of a MeOH solution.

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SAINT-Plus (Bruker, 2003); data reduction: SAINT-Plus (Bruker, 2003); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top

Fig. 1. Molecular configuration and atom numbering scheme for (I), with displacement ellipsoids for non-H atoms drawn at the 50% probability level.

9-hydroxy-1,5,5-trimethyl-1,8-epidioxyspiro[5.5]decan-2-one top

Crystal data top

C₁₄H₂₂O₄	F(000) = 552
M_r = 254.32	D_x = 1.334 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 4034 reflections
a = 7.3138 (4) Å	θ = 2.8–27.0°
b = 12.4206 (7) Å	µ = 0.10 mm⁻¹
c = 13.9408 (8) Å	T = 173 K
V = 1266.41 (12) Å³	Block, colorless
Z = 4	0.42 × 0.38 × 0.35 mm

Data collection top

Bruker SMART 1000 CCD diffractometer	1602 independent reflections
Radiation source: fine-focus sealed tube	1471 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.021
ω scans	θ_max = 27.0°, θ_min = 2.2°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −5→9
T_min = 0.961, T_max = 0.967	k = −15→15
6456 measured reflections	l = −17→13

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.103	H-atom parameters constrained
S = 1.08	w = 1/[σ²(F_o²) + (0.0611P)² + 0.2837P] where P = (F_o² + 2F_c²)/3
1602 reflections	(Δ/σ)_max < 0.001
167 parameters	Δρ_max = 0.30 e Å⁻³
0 restraints	Δρ_min = −0.17 e Å⁻³

Crystal data top

C₁₄H₂₂O₄	V = 1266.41 (12) Å³
M_r = 254.32	Z = 4
Orthorhombic, P2₁2₁2₁	Mo Kα radiation
a = 7.3138 (4) Å	µ = 0.10 mm⁻¹
b = 12.4206 (7) Å	T = 173 K
c = 13.9408 (8) Å	0.42 × 0.38 × 0.35 mm

Data collection top

Bruker SMART 1000 CCD diffractometer	1602 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	1471 reflections with I > 2σ(I)
T_min = 0.961, T_max = 0.967	R_int = 0.021
6456 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.037	0 restraints
wR(F²) = 0.103	H-atom parameters constrained
S = 1.08	Δρ_max = 0.30 e Å⁻³
1602 reflections	Δρ_min = −0.17 e Å⁻³
167 parameters

Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
C1	0.4858 (3)	0.29411 (15)	0.68490 (13)	0.0218 (4)
H1A	0.5496	0.2309	0.7124	0.026*
H1B	0.3532	0.2857	0.6971	0.026*
C2	0.5204 (3)	0.29930 (15)	0.57779 (13)	0.0225 (4)
H2	0.4747	0.2304	0.5495	0.027*
C3	0.4112 (3)	0.39043 (16)	0.53239 (13)	0.0247 (4)
H3	0.2786	0.3719	0.5380	0.030*
C4	0.4405 (3)	0.49914 (16)	0.58127 (15)	0.0296 (5)
H4A	0.3429	0.5494	0.5608	0.036*
H4B	0.5591	0.5295	0.5602	0.036*
C5	0.4393 (3)	0.49050 (15)	0.69173 (14)	0.0259 (4)
H5A	0.3114	0.4812	0.7134	0.031*
H5B	0.4846	0.5593	0.7187	0.031*
C6	0.5554 (2)	0.39771 (14)	0.73338 (13)	0.0183 (4)
C7	0.7632 (3)	0.40990 (16)	0.70409 (13)	0.0229 (4)
C8	0.8819 (3)	0.32554 (18)	0.75389 (15)	0.0280 (4)
C9	0.8623 (3)	0.3215 (2)	0.86128 (15)	0.0334 (5)
H9A	0.9072	0.3896	0.8897	0.040*
H9B	0.9367	0.2617	0.8873	0.040*
C10	0.6617 (3)	0.30478 (17)	0.88798 (14)	0.0285 (4)
H10A	0.6507	0.3054	0.9588	0.034*
H10B	0.6229	0.2328	0.8653	0.034*
C11	0.5305 (3)	0.38957 (16)	0.84637 (14)	0.0221 (4)
C12	0.3354 (3)	0.3526 (2)	0.87222 (16)	0.0331 (5)
H12A	0.3233	0.3480	0.9421	0.050*
H12B	0.3122	0.2817	0.8438	0.050*
H12C	0.2467	0.4046	0.8472	0.050*
C13	0.5579 (3)	0.49723 (17)	0.89893 (14)	0.0312 (5)
H13A	0.6821	0.5238	0.8871	0.047*
H13B	0.5401	0.4866	0.9679	0.047*
H13C	0.4691	0.5499	0.8752	0.047*
C14	0.8524 (3)	0.52104 (18)	0.72087 (16)	0.0341 (5)
H14A	0.7730	0.5775	0.6949	0.051*
H14B	0.9713	0.5235	0.6885	0.051*
H14C	0.8695	0.5326	0.7898	0.051*
O1	0.7133 (2)	0.30323 (12)	0.56148 (10)	0.0295 (4)
O2	0.4515 (2)	0.40426 (12)	0.43304 (10)	0.0333 (4)
H2A	0.4353	0.3457	0.4041	0.050*
O3	0.7841 (2)	0.40379 (13)	0.60137 (10)	0.0298 (3)
O4	0.9872 (2)	0.26855 (15)	0.71020 (12)	0.0423 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0262 (9)	0.0173 (8)	0.0219 (9)	−0.0021 (8)	−0.0017 (7)	−0.0004 (7)
C2	0.0273 (9)	0.0180 (8)	0.0222 (9)	−0.0018 (8)	−0.0007 (8)	−0.0047 (7)
C3	0.0310 (10)	0.0245 (9)	0.0187 (8)	−0.0002 (8)	−0.0046 (8)	−0.0016 (7)
C4	0.0439 (12)	0.0208 (9)	0.0242 (9)	0.0050 (9)	−0.0104 (9)	−0.0004 (8)
C5	0.0338 (10)	0.0211 (9)	0.0229 (9)	0.0069 (9)	−0.0053 (8)	−0.0041 (8)
C6	0.0198 (8)	0.0179 (8)	0.0174 (8)	−0.0001 (7)	0.0005 (7)	−0.0018 (7)
C7	0.0234 (9)	0.0278 (9)	0.0174 (8)	−0.0029 (8)	−0.0002 (7)	−0.0005 (8)
C8	0.0204 (9)	0.0350 (10)	0.0284 (10)	0.0006 (9)	−0.0018 (8)	−0.0055 (9)
C9	0.0306 (11)	0.0433 (12)	0.0264 (10)	0.0114 (10)	−0.0051 (9)	0.0013 (10)
C10	0.0342 (11)	0.0295 (10)	0.0217 (9)	0.0024 (9)	0.0005 (8)	0.0035 (8)
C11	0.0228 (9)	0.0254 (9)	0.0182 (8)	0.0007 (8)	0.0011 (7)	−0.0024 (8)
C12	0.0274 (10)	0.0467 (13)	0.0251 (10)	−0.0053 (10)	0.0068 (8)	−0.0040 (9)
C13	0.0389 (12)	0.0318 (10)	0.0228 (9)	0.0023 (10)	−0.0015 (9)	−0.0080 (8)
C14	0.0363 (11)	0.0364 (11)	0.0297 (10)	−0.0155 (10)	0.0007 (9)	0.0004 (9)
O1	0.0286 (7)	0.0345 (8)	0.0253 (7)	0.0029 (6)	0.0013 (6)	−0.0095 (6)
O2	0.0511 (10)	0.0305 (7)	0.0184 (6)	−0.0015 (8)	−0.0050 (7)	−0.0015 (6)
O3	0.0307 (7)	0.0378 (8)	0.0208 (7)	−0.0093 (7)	0.0037 (6)	−0.0027 (6)
O4	0.0329 (8)	0.0555 (10)	0.0386 (9)	0.0160 (8)	−0.0052 (7)	−0.0158 (8)

Geometric parameters (Å, º) top

C1—C2	1.516 (3)	C8—O4	1.211 (3)
C1—C6	1.540 (2)	C8—C9	1.505 (3)
C1—H1A	0.9900	C9—C10	1.528 (3)
C1—H1B	0.9900	C9—H9A	0.9900
C2—O1	1.430 (2)	C9—H9B	0.9900
C2—C3	1.523 (3)	C10—C11	1.538 (3)
C2—H2	1.0000	C10—H10A	0.9900
C3—O2	1.426 (2)	C10—H10B	0.9900
C3—C4	1.528 (3)	C11—C13	1.538 (3)
C3—H3	1.0000	C11—C12	1.542 (3)
C4—C5	1.544 (3)	C12—H12A	0.9800
C4—H4A	0.9900	C12—H12B	0.9800
C4—H4B	0.9900	C12—H12C	0.9800
C5—C6	1.545 (3)	C13—H13A	0.9800
C5—H5A	0.9900	C13—H13B	0.9800
C5—H5B	0.9900	C13—H13C	0.9800
C6—C7	1.581 (3)	C14—H14A	0.9800
C6—C11	1.589 (2)	C14—H14B	0.9800
C7—O3	1.442 (2)	C14—H14C	0.9800
C7—C8	1.527 (3)	O1—O3	1.462 (2)
C7—C14	1.545 (3)	O2—H2A	0.8400

C2—C1—C6	109.98 (15)	O4—C8—C9	122.8 (2)
C2—C1—H1A	109.7	O4—C8—C7	122.27 (19)
C6—C1—H1A	109.7	C9—C8—C7	114.91 (18)
C2—C1—H1B	109.7	C8—C9—C10	109.78 (18)
C6—C1—H1B	109.7	C8—C9—H9A	109.7
H1A—C1—H1B	108.2	C10—C9—H9A	109.7
O1—C2—C1	108.82 (16)	C8—C9—H9B	109.7
O1—C2—C3	115.22 (17)	C10—C9—H9B	109.7
C1—C2—C3	110.70 (16)	H9A—C9—H9B	108.2
O1—C2—H2	107.3	C9—C10—C11	114.46 (17)
C1—C2—H2	107.3	C9—C10—H10A	108.6
C3—C2—H2	107.3	C11—C10—H10A	108.6
O2—C3—C2	112.61 (17)	C9—C10—H10B	108.6
O2—C3—C4	107.32 (16)	C11—C10—H10B	108.6
C2—C3—C4	113.44 (16)	H10A—C10—H10B	107.6
O2—C3—H3	107.7	C13—C11—C10	109.54 (16)
C2—C3—H3	107.7	C13—C11—C12	105.55 (17)
C4—C3—H3	107.7	C10—C11—C12	106.57 (17)
C3—C4—C5	112.51 (16)	C13—C11—C6	113.71 (16)
C3—C4—H4A	109.1	C10—C11—C6	110.25 (15)
C5—C4—H4A	109.1	C12—C11—C6	110.88 (16)
C3—C4—H4B	109.1	C11—C12—H12A	109.5
C5—C4—H4B	109.1	C11—C12—H12B	109.5
H4A—C4—H4B	107.8	H12A—C12—H12B	109.5
C4—C5—C6	115.08 (16)	C11—C12—H12C	109.5
C4—C5—H5A	108.5	H12A—C12—H12C	109.5
C6—C5—H5A	108.5	H12B—C12—H12C	109.5
C4—C5—H5B	108.5	C11—C13—H13A	109.5
C6—C5—H5B	108.5	C11—C13—H13B	109.5
H5A—C5—H5B	107.5	H13A—C13—H13B	109.5
C1—C6—C5	106.09 (15)	C11—C13—H13C	109.5
C1—C6—C7	106.51 (15)	H13A—C13—H13C	109.5
C5—C6—C7	111.08 (16)	H13B—C13—H13C	109.5
C1—C6—C11	110.13 (15)	C7—C14—H14A	109.5
C5—C6—C11	110.94 (15)	C7—C14—H14B	109.5
C7—C6—C11	111.84 (15)	H14A—C14—H14B	109.5
O3—C7—C8	110.81 (16)	C7—C14—H14C	109.5
O3—C7—C14	98.79 (15)	H14A—C14—H14C	109.5
C8—C7—C14	107.71 (16)	H14B—C14—H14C	109.5
O3—C7—C6	110.67 (15)	C2—O1—O3	108.54 (14)
C8—C7—C6	111.29 (16)	C3—O2—H2A	109.5
C14—C7—C6	116.91 (17)	C7—O3—O1	112.66 (14)

C6—C1—C2—O1	63.6 (2)	C6—C7—C8—O4	128.6 (2)
C6—C1—C2—C3	−63.9 (2)	O3—C7—C8—C9	−176.93 (18)
O1—C2—C3—O2	50.9 (2)	C14—C7—C8—C9	76.0 (2)
C1—C2—C3—O2	174.94 (16)	C6—C7—C8—C9	−53.3 (2)
O1—C2—C3—C4	−71.2 (2)	O4—C8—C9—C10	−126.6 (2)
C1—C2—C3—C4	52.8 (2)	C7—C8—C9—C10	55.4 (3)
O2—C3—C4—C5	−168.47 (18)	C8—C9—C10—C11	−56.0 (3)
C2—C3—C4—C5	−43.4 (3)	C9—C10—C11—C13	−72.0 (2)
C3—C4—C5—C6	46.4 (3)	C9—C10—C11—C12	174.30 (18)
C2—C1—C6—C5	63.35 (19)	C9—C10—C11—C6	53.9 (2)
C2—C1—C6—C7	−55.08 (19)	C1—C6—C11—C13	−167.83 (16)
C2—C1—C6—C11	−176.53 (15)	C5—C6—C11—C13	−50.7 (2)
C4—C5—C6—C1	−55.3 (2)	C7—C6—C11—C13	73.9 (2)
C4—C5—C6—C7	60.0 (2)	C1—C6—C11—C10	68.7 (2)
C4—C5—C6—C11	−174.90 (17)	C5—C6—C11—C10	−174.15 (16)
C1—C6—C7—O3	52.6 (2)	C7—C6—C11—C10	−49.5 (2)
C5—C6—C7—O3	−62.5 (2)	C1—C6—C11—C12	−49.1 (2)
C11—C6—C7—O3	172.94 (15)	C5—C6—C11—C12	68.1 (2)
C1—C6—C7—C8	−71.10 (18)	C7—C6—C11—C12	−167.31 (16)
C5—C6—C7—C8	173.81 (15)	C1—C2—O1—O3	−64.81 (18)
C11—C6—C7—C8	49.3 (2)	C3—C2—O1—O3	60.17 (19)
C1—C6—C7—C14	164.57 (16)	C8—C7—O3—O1	66.13 (19)
C5—C6—C7—C14	49.5 (2)	C14—C7—O3—O1	178.97 (15)
C11—C6—C7—C14	−75.1 (2)	C6—C7—O3—O1	−57.8 (2)
O3—C7—C8—O4	5.0 (3)	C2—O1—O3—C7	64.05 (18)
C14—C7—C8—O4	−102.0 (2)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2A···O1ⁱ	0.84	2.51	3.112 (2)	130
O2—H2A···O4ⁱ	0.84	2.17	2.943 (2)	154
C2—H2···O1ⁱ	1.00	2.49	3.231 (2)	130

Symmetry code: (i) x−1/2, −y+1/2, −z+1.

Experimental details

Crystal data
Chemical formula	C₁₄H₂₂O₄
M_r	254.32
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	173
a, b, c (Å)	7.3138 (4), 12.4206 (7), 13.9408 (8)
V (Å³)	1266.41 (12)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.10
Crystal size (mm)	0.42 × 0.38 × 0.35

Data collection
Diffractometer	Bruker SMART 1000 CCD diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 1996)
T_min, T_max	0.961, 0.967
No. of measured, independent and observed [I > 2σ(I)] reflections	6456, 1602, 1471
R_int	0.021
(sin θ/λ)_max (Å⁻¹)	0.639

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.037, 0.103, 1.08
No. of reflections	1602
No. of parameters	167
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.30, −0.17

Computer programs: SMART (Bruker, 2001), SAINT-Plus (Bruker, 2003), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2A···O1ⁱ	0.84	2.51	3.112 (2)	130
O2—H2A···O4ⁱ	0.84	2.17	2.943 (2)	154

Symmetry code: (i) x−1/2, −y+1/2, −z+1.

Acknowledgements

This Project was supported by China Postdoctoral Science Foundation (5350209-7-1).

References

Bruker (2001). SMART. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (2003). SAINT-Plus. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Miyashita, K. Tanaka, A. Shintaku, H. & Iwata, C. (1998). Tetrahedron, 8, 1395–1406. Web of Science CrossRef Google Scholar
Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar