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Acta Cryst. (2009). E65, o753    [ doi:10.1107/S1600536809008253 ]

(1S*,2R*,4aS*,6aS*,6bR*,10S*,12aR*,14aS*)-10-Hydroxy-1,2,6a,6b,9,9,12a-heptamethylperhydropicene-4a,14a-carbolactone

D.-W. Ou-yang, J.-P. Gao, Q.-S. Li and J.-P. Guo

Abstract top

The title compound, C30H48O3, was extracted from the plant Dracocephalum rupestre Hance. The molecule contains five fused cyclohexane rings and one five-membered lactone ring. Intermolecular O-H...O hydrogen bonds between the hydroxyl and carbonyl groups link the molecules into chains along [010]. The absolute structure has not been determined.

Comment top

The title compound is extracted from the plant Dracocephalum rupestre Hance (Jiangsu College of New Medicine, 1977) with ethanol. The compound (Katai et al., 1983) was successfully crystallized from methanol. There are five six-membered rings and one five-membered ring in the molecule. The six-membered rings are composed of sp3-hybridised C and the five-membered ring is a lactone in which C28 is sp2 hybridised. The bond distances between C28 and O are 1.349 (3) [O1—C28] and 1.218 (4) Å [O2—C28]. The O2—C28 bond length of 1.216 (5) Å is a typical C=O double bond.

Related literature top

For related literature concerning the title compound and the plant Dracocephalum rupestre Hance, see: Jiangsu College of New Medicine (1977); Katai et al. (1983).

Experimental top

The dry aerial part of the plant (5.3 kg) was extracted with 95% ethanol 3 times under reflux. The ethanol extract was diluted with a large amount of water,and then extracted with petroleum ether, chloroform, EtOAc and n-butanol. The chloroform fraction (70 g) was subjected to Si gel column (1.5 kg,200–300 mesh) chromatography eluting with a gradient (petroleum ether-EtOAc, 99:1, 98:2, 97:3, 95:5, 9:1, 8:2,7:3, 1:1, v/v) to obtain 8 fractions (F1—F8). Fraction F3 (19.4 g) was separated by Si gel column (500 g, 200–300 mesh) chromatography eluting with a gradient (chloroform-methanol, 99:1, 98:2, 97:3, 95:5, 9:1,8:2,7:3, 1:1, v/v) to yield four portions. Subfraction 1 was subsequently subjected to Si gel column chromatography eluting with chloroform-methanol (10:1), and recrystallized from methanol, to obtain the title compound (25 mg).

Refinement top

H atoms were placed geometrically and allowed to ride with Uiso(H) = 1.2 or 1.5Ueq(C/O). In the absence of significant anomalous scattering, Friedel pairs were merged as equivalent data, and the absolute structure has not been determined.

Computing details top

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Molecular structure showing displacement ellipsoids at 50% probabilty for non-H atoms.
(1S*,2R*,4aS*,6aS*,6bR*,10S*, 12aR*,14aS*)-10-Hydroxy-1,2,6a,6b,9,9,12a- heptamethylperhydropicene-4a,14a-carbolactone top
Crystal data top
C30H48O3F(000) = 504
Mr = 456.68Dx = 1.150 Mg m−3
Monoclinic, P21Melting point: 519 K
Hall symbol: P 2ybMo Kα radiation, λ = 0.71073 Å
a = 8.156 (3) ÅCell parameters from 2717 reflections
b = 12.005 (5) Åθ = 2.3–26.2°
c = 13.475 (5) ŵ = 0.07 mm−1
β = 90.520 (7)°T = 293 K
V = 1319.3 (9) Å3Block, colourless
Z = 20.60 × 0.50 × 0.30 mm
Data collection top
Bruker SMART CCD
diffractometer		2428 independent reflections
Radiation source: fine-focus sealed tube2052 reflections with I > 2σ(I)
graphiteRint = 0.032
ω scansθmax = 25.0°, θmin = 1.5°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		h = −9→7
Tmin = 0.958, Tmax = 0.979k = −14→14
5150 measured reflectionsl = −13→16
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.052Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.142H-atom parameters constrained
S = 1.03 w = 1/[σ2(Fo2) + (0.0816P)2 + 0.1773P]
where P = (Fo2 + 2Fc2)/3
2428 reflections(Δ/σ)max < 0.001
299 parametersΔρmax = 0.24 e Å−3
1 restraintΔρmin = −0.24 e Å−3
Crystal data top
C30H48O3V = 1319.3 (9) Å3
Mr = 456.68Z = 2
Monoclinic, P21Mo Kα radiation
a = 8.156 (3) ŵ = 0.07 mm−1
b = 12.005 (5) ÅT = 293 K
c = 13.475 (5) Å0.60 × 0.50 × 0.30 mm
β = 90.520 (7)°
Data collection top
Bruker SMART CCD
diffractometer		2428 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		2052 reflections with I > 2σ(I)
Tmin = 0.958, Tmax = 0.979Rint = 0.032
5150 measured reflectionsθmax = 25.0°
Refinement top
R[F2 > 2σ(F2)] = 0.052H-atom parameters constrained
wR(F2) = 0.142Δρmax = 0.24 e Å−3
S = 1.03Δρmin = −0.24 e Å−3
2428 reflectionsAbsolute structure: ?
299 parametersFlack parameter: ?
1 restraintRogers parameter: ?
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
xyzUiso*/Ueq
O1−0.1317 (3)0.74752 (19)0.69165 (16)0.0521 (6)
O2−0.1163 (4)0.6395 (2)0.5579 (2)0.0776 (9)
O30.2976 (4)0.9857 (3)1.2991 (2)0.0794 (9)
H3A0.24591.02761.33530.119*
C1−0.0162 (4)0.9125 (4)1.1007 (3)0.0566 (9)
H1A−0.04760.98701.08010.068*
H1B−0.11540.86811.10510.068*
C20.0658 (5)0.9185 (4)1.2036 (3)0.0654 (10)
H2A−0.00950.95291.24970.078*
H2B0.08790.84351.22680.078*
C30.2236 (5)0.9837 (3)1.2033 (3)0.0592 (9)
H3B0.19691.06061.18520.071*
C40.3498 (4)0.9406 (3)1.1284 (3)0.0543 (8)
C50.2606 (4)0.9273 (3)1.0255 (2)0.0464 (8)
H5A0.22931.00341.00720.056*
C60.3736 (4)0.8899 (4)0.9416 (3)0.0590 (9)
H6A0.47760.92870.94720.071*
H6B0.39460.81070.94750.071*
C70.2955 (4)0.9145 (4)0.8405 (3)0.0583 (9)
H7A0.36900.88880.78910.070*
H7B0.28380.99450.83320.070*
C80.1261 (4)0.8596 (3)0.8242 (2)0.0466 (8)
C90.0174 (3)0.8830 (3)0.9165 (2)0.0432 (7)
H9A−0.00320.96340.91470.052*
C100.0967 (4)0.8611 (3)1.0212 (2)0.0457 (7)
C11−0.1523 (4)0.8290 (3)0.9008 (2)0.0510 (8)
H11A−0.13930.74920.89300.061*
H11B−0.21900.84210.95890.061*
C12−0.2392 (4)0.8762 (3)0.8096 (2)0.0527 (8)
H12A−0.34150.83630.79980.063*
H12B−0.26600.95360.82220.063*
C13−0.1418 (4)0.8697 (3)0.7150 (2)0.0439 (7)
C140.0382 (4)0.9125 (3)0.7273 (2)0.0430 (7)
C150.1341 (4)0.8817 (4)0.6322 (2)0.0550 (9)
H15A0.23030.92890.62840.066*
H15B0.17180.80530.63820.066*
C160.0360 (4)0.8931 (3)0.5351 (2)0.0532 (9)
H16A0.09520.85590.48250.064*
H16B0.02820.97140.51790.064*
C17−0.1378 (4)0.8442 (3)0.5403 (2)0.0477 (8)
C18−0.2370 (4)0.9073 (3)0.6187 (2)0.0445 (7)
H18A−0.34170.86750.62160.053*
C19−0.2835 (4)1.0265 (3)0.5865 (2)0.0496 (8)
H19A−0.18251.06940.57740.059*
C20−0.3750 (4)1.0192 (3)0.4849 (2)0.0530 (8)
H20A−0.47610.97670.49490.064*
C21−0.2730 (5)0.9578 (4)0.4078 (3)0.0577 (9)
H21A−0.17451.00050.39490.069*
H21B−0.33530.95330.34620.069*
C22−0.2241 (5)0.8403 (3)0.4399 (3)0.0592 (9)
H22A−0.32100.79390.44410.071*
H22B−0.15160.80800.39100.071*
C230.4318 (5)0.8333 (4)1.1653 (3)0.0712 (11)
H23A0.48470.84711.22810.107*
H23B0.51180.80941.11810.107*
H23C0.35040.77631.17300.107*
C240.4838 (5)1.0301 (4)1.1204 (3)0.0748 (12)
H24A0.53861.03811.18330.112*
H24B0.43481.09981.10180.112*
H24C0.56161.00831.07100.112*
C250.1145 (5)0.7347 (3)1.0452 (3)0.0612 (9)
H25A0.11140.72391.11570.092*
H25B0.21710.70801.02020.092*
H25C0.02610.69441.01440.092*
C260.1588 (5)0.7321 (3)0.8123 (3)0.0622 (10)
H26A0.23800.70850.86110.093*
H26B0.20020.71760.74710.093*
H26C0.05840.69180.82140.093*
C270.0327 (4)1.0412 (3)0.7341 (3)0.0542 (8)
H27A−0.01921.07080.67550.081*
H27B0.14231.06980.73950.081*
H27C−0.02861.06290.79140.081*
C28−0.1268 (4)0.7329 (3)0.5923 (3)0.0546 (8)
C29−0.3888 (5)1.0861 (4)0.6629 (3)0.0715 (11)
H29A−0.33041.09000.72500.107*
H29B−0.48921.04560.67180.107*
H29C−0.41321.16000.64010.107*
C30−0.4225 (5)1.1339 (4)0.4454 (3)0.0727 (11)
H30A−0.47881.12580.38300.109*
H30B−0.32541.17780.43630.109*
H30C−0.49301.17020.49190.109*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0634 (14)0.0347 (12)0.0582 (13)−0.0028 (11)0.0101 (10)0.0014 (10)
O20.115 (2)0.0379 (14)0.0798 (18)0.0061 (15)0.0098 (16)−0.0079 (13)
O30.088 (2)0.084 (2)0.0662 (16)0.0096 (17)−0.0086 (15)−0.0169 (15)
C10.0500 (19)0.064 (2)0.056 (2)−0.0025 (17)0.0118 (15)−0.0011 (17)
C20.067 (2)0.072 (3)0.057 (2)0.002 (2)0.0129 (18)−0.0041 (18)
C30.066 (2)0.051 (2)0.060 (2)0.0044 (18)−0.0036 (17)−0.0040 (16)
C40.0513 (19)0.049 (2)0.063 (2)0.0008 (16)−0.0003 (16)0.0036 (16)
C50.0414 (16)0.0422 (18)0.0556 (19)0.0017 (14)0.0075 (14)0.0048 (14)
C60.0375 (16)0.072 (3)0.068 (2)0.0045 (17)0.0072 (15)0.0029 (19)
C70.0363 (16)0.079 (3)0.060 (2)0.0016 (17)0.0129 (14)0.0043 (18)
C80.0405 (16)0.0441 (18)0.0554 (18)0.0041 (14)0.0097 (14)−0.0002 (14)
C90.0378 (15)0.0371 (17)0.0548 (18)−0.0002 (13)0.0093 (13)0.0008 (14)
C100.0448 (16)0.0393 (17)0.0534 (18)−0.0012 (14)0.0095 (13)0.0012 (14)
C110.0457 (17)0.057 (2)0.0503 (18)−0.0076 (16)0.0087 (14)0.0028 (15)
C120.0392 (16)0.059 (2)0.060 (2)−0.0053 (16)0.0118 (14)−0.0015 (17)
C130.0466 (16)0.0351 (16)0.0503 (17)−0.0012 (13)0.0116 (13)−0.0015 (13)
C140.0369 (15)0.0408 (17)0.0514 (18)0.0015 (13)0.0093 (13)−0.0015 (13)
C150.0449 (17)0.063 (2)0.058 (2)0.0042 (17)0.0160 (15)0.0022 (17)
C160.0548 (19)0.053 (2)0.052 (2)−0.0003 (16)0.0198 (15)0.0009 (16)
C170.0532 (18)0.0382 (17)0.0520 (18)−0.0007 (14)0.0071 (15)−0.0029 (14)
C180.0388 (15)0.0405 (17)0.0544 (19)−0.0043 (13)0.0078 (14)−0.0005 (14)
C190.0439 (17)0.0424 (18)0.062 (2)0.0007 (15)0.0053 (14)−0.0021 (15)
C200.0451 (17)0.053 (2)0.061 (2)−0.0043 (16)0.0036 (14)0.0053 (16)
C210.057 (2)0.065 (2)0.0516 (18)−0.0027 (18)0.0019 (15)0.0040 (17)
C220.069 (2)0.054 (2)0.055 (2)−0.0101 (18)0.0092 (17)−0.0098 (17)
C230.075 (3)0.063 (3)0.075 (3)0.014 (2)−0.010 (2)0.003 (2)
C240.072 (3)0.071 (3)0.081 (3)−0.019 (2)−0.011 (2)0.002 (2)
C250.074 (2)0.0439 (19)0.065 (2)−0.0057 (19)−0.0016 (17)0.0081 (17)
C260.072 (2)0.057 (2)0.058 (2)0.025 (2)0.0082 (17)−0.0017 (18)
C270.0536 (19)0.0434 (19)0.066 (2)−0.0041 (15)−0.0010 (16)0.0010 (16)
C280.064 (2)0.0377 (18)0.062 (2)0.0028 (16)0.0095 (16)−0.0004 (16)
C290.078 (3)0.066 (3)0.070 (2)0.029 (2)0.002 (2)−0.006 (2)
C300.075 (3)0.067 (3)0.075 (2)0.012 (2)−0.003 (2)0.011 (2)
Geometric parameters (Å, °) top
O1—C281.351 (4)C15—C161.534 (5)
O1—C131.502 (4)C15—H15A0.970
O2—C281.216 (5)C15—H15B0.970
O3—C31.421 (4)C16—C171.537 (5)
O3—H3A0.820C16—H16A0.970
C1—C21.536 (5)C16—H16B0.970
C1—C101.547 (4)C17—C281.511 (5)
C1—H1A0.970C17—C221.520 (5)
C1—H1B0.970C17—C181.536 (4)
C2—C31.506 (5)C18—C191.542 (5)
C2—H2A0.970C18—H18A0.980
C2—H2B0.970C19—C291.525 (5)
C3—C41.537 (5)C19—C201.555 (5)
C3—H3B0.980C19—H19A0.980
C4—C231.533 (5)C20—C301.525 (6)
C4—C241.537 (5)C20—C211.527 (5)
C4—C51.568 (5)C20—H20A0.980
C5—C61.532 (4)C21—C221.527 (6)
C5—C101.556 (4)C21—H21A0.970
C5—H5A0.980C21—H21B0.970
C6—C71.528 (5)C22—H22A0.970
C6—H6A0.970C22—H22B0.970
C6—H6B0.970C23—H23A0.960
C7—C81.545 (5)C23—H23B0.960
C7—H7A0.970C23—H23C0.960
C7—H7B0.970C24—H24A0.960
C8—C91.559 (4)C24—H24B0.960
C8—C261.562 (5)C24—H24C0.960
C8—C141.614 (4)C25—H25A0.960
C9—C111.541 (4)C25—H25B0.960
C9—C101.569 (4)C25—H25C0.960
C9—H9A0.980C26—H26A0.960
C10—C251.558 (5)C26—H26B0.960
C11—C121.522 (5)C26—H26C0.960
C11—H11A0.970C27—H27A0.960
C11—H11B0.970C27—H27B0.960
C12—C131.510 (4)C27—H27C0.960
C12—H12A0.970C29—H29A0.960
C12—H12B0.970C29—H29B0.960
C13—C141.563 (4)C29—H29C0.960
C13—C181.573 (4)C30—H30A0.960
C14—C271.549 (5)C30—H30B0.960
C14—C151.552 (4)C30—H30C0.960
C28—O1—C13109.7 (2)C14—C15—H15B108.6
C3—O3—H3A109.5H15A—C15—H15B107.5
C2—C1—C10112.7 (3)C15—C16—C17113.6 (3)
C2—C1—H1A109.0C15—C16—H16A108.8
C10—C1—H1A109.0C17—C16—H16A108.8
C2—C1—H1B109.0C15—C16—H16B108.8
C10—C1—H1B109.0C17—C16—H16B108.8
H1A—C1—H1B107.8H16A—C16—H16B107.7
C3—C2—C1112.8 (3)C28—C17—C22114.3 (3)
C3—C2—H2A109.0C28—C17—C1898.5 (3)
C1—C2—H2A109.0C22—C17—C18112.6 (3)
C3—C2—H2B109.0C28—C17—C16107.9 (3)
C1—C2—H2B109.0C22—C17—C16113.0 (3)
H2A—C2—H2B107.8C18—C17—C16109.5 (3)
O3—C3—C2111.3 (3)C17—C18—C19113.2 (3)
O3—C3—C4108.7 (3)C17—C18—C1399.6 (2)
C2—C3—C4113.9 (3)C19—C18—C13128.1 (3)
O3—C3—H3B107.6C17—C18—H18A104.6
C2—C3—H3B107.6C19—C18—H18A104.6
C4—C3—H3B107.6C13—C18—H18A104.6
C23—C4—C24107.6 (3)C29—C19—C18112.5 (3)
C23—C4—C3111.2 (3)C29—C19—C20110.6 (3)
C24—C4—C3107.0 (3)C18—C19—C20108.1 (3)
C23—C4—C5113.5 (3)C29—C19—H19A108.5
C24—C4—C5109.5 (3)C18—C19—H19A108.5
C3—C4—C5107.9 (3)C20—C19—H19A108.5
C6—C5—C10110.2 (3)C30—C20—C21109.6 (3)
C6—C5—C4113.9 (3)C30—C20—C19112.0 (3)
C10—C5—C4118.4 (3)C21—C20—C19111.5 (3)
C6—C5—H5A104.2C30—C20—H20A107.9
C10—C5—H5A104.2C21—C20—H20A107.9
C4—C5—H5A104.2C19—C20—H20A107.9
C7—C6—C5110.7 (3)C20—C21—C22113.3 (3)
C7—C6—H6A109.5C20—C21—H21A108.9
C5—C6—H6A109.5C22—C21—H21A108.9
C7—C6—H6B109.5C20—C21—H21B108.9
C5—C6—H6B109.5C22—C21—H21B108.9
H6A—C6—H6B108.1H21A—C21—H21B107.7
C6—C7—C8114.2 (3)C17—C22—C21110.0 (3)
C6—C7—H7A108.7C17—C22—H22A109.7
C8—C7—H7A108.7C21—C22—H22A109.7
C6—C7—H7B108.7C17—C22—H22B109.7
C8—C7—H7B108.7C21—C22—H22B109.7
H7A—C7—H7B107.6H22A—C22—H22B108.2
C7—C8—C9108.9 (3)C4—C23—H23A109.5
C7—C8—C26106.2 (3)C4—C23—H23B109.5
C9—C8—C26110.9 (3)H23A—C23—H23B109.5
C7—C8—C14109.7 (3)C4—C23—H23C109.5
C9—C8—C14108.8 (2)H23A—C23—H23C109.5
C26—C8—C14112.2 (3)H23B—C23—H23C109.5
C11—C9—C8109.3 (3)C4—C24—H24A109.5
C11—C9—C10114.6 (3)C4—C24—H24B109.5
C8—C9—C10117.0 (2)H24A—C24—H24B109.5
C11—C9—H9A104.9C4—C24—H24C109.5
C8—C9—H9A104.9H24A—C24—H24C109.5
C10—C9—H9A104.9H24B—C24—H24C109.5
C1—C10—C5106.7 (3)C10—C25—H25A109.5
C1—C10—C25107.4 (3)C10—C25—H25B109.5
C5—C10—C25114.3 (3)H25A—C25—H25B109.5
C1—C10—C9108.2 (3)C10—C25—H25C109.5
C5—C10—C9107.1 (2)H25A—C25—H25C109.5
C25—C10—C9112.7 (3)H25B—C25—H25C109.5
C12—C11—C9111.4 (3)C8—C26—H26A109.5
C12—C11—H11A109.3C8—C26—H26B109.5
C9—C11—H11A109.3H26A—C26—H26B109.5
C12—C11—H11B109.3C8—C26—H26C109.5
C9—C11—H11B109.3H26A—C26—H26C109.5
H11A—C11—H11B108.0H26B—C26—H26C109.5
C13—C12—C11114.7 (3)C14—C27—H27A109.5
C13—C12—H12A108.6C14—C27—H27B109.5
C11—C12—H12A108.6H27A—C27—H27B109.5
C13—C12—H12B108.6C14—C27—H27C109.5
C11—C12—H12B108.6H27A—C27—H27C109.5
H12A—C12—H12B107.6H27B—C27—H27C109.5
O1—C13—C12104.9 (3)O2—C28—O1120.0 (3)
O1—C13—C14106.9 (2)O2—C28—C17130.0 (3)
C12—C13—C14113.2 (3)O1—C28—C17110.0 (3)
O1—C13—C1897.8 (2)C19—C29—H29A109.5
C12—C13—C18115.0 (3)C19—C29—H29B109.5
C14—C13—C18116.7 (2)H29A—C29—H29B109.5
C27—C14—C15107.5 (3)C19—C29—H29C109.5
C27—C14—C13107.8 (3)H29A—C29—H29C109.5
C15—C14—C13108.3 (3)H29B—C29—H29C109.5
C27—C14—C8111.0 (3)C20—C30—H30A109.5
C15—C14—C8110.5 (3)C20—C30—H30B109.5
C13—C14—C8111.5 (2)H30A—C30—H30B109.5
C16—C15—C14114.9 (3)C20—C30—H30C109.5
C16—C15—H15A108.6H30A—C30—H30C109.5
C14—C15—H15A108.6H30B—C30—H30C109.5
C16—C15—H15B108.6
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O3—H3A···O2i0.822.243.059 (4)176
Symmetry codes: (i) −x, y+1/2, −z+2.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O3—H3A···O2i0.822.243.059 (4)176
Symmetry codes: (i) −x, y+1/2, −z+2.
Acknowledgements top

Financial support from Science and Technology Commission of Taiyuan (2006), and from the Undergraduate Innovation Item of Shanxi Medical University (No. 200448) is gratefully acknowledged.

references
References top

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Jiangsu College of New Medicine (1977). A Dictionary of the Traditional Chinese Medicines, p. 549. Shanghai: Shanghai Science and Technology Press.

Katai, M., Terai, T. & Meguri, H. (1983). Chem. Pharm. Bull. 31, 1567–1571.

Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.