The Crystal Structures of the α- and β-Diastereomers of 4,5-Epoxy-cholestan-3-one

Article abstract of DOI:10.1007/s10870-016-0639-x

The α and β-diastereomers of 4,5-epoxy-cholestan-3-one were obtained by epoxidation of cholest-4-en-3-one with H₂O₂ in basic media. The α-diastereomer 2a shows a monoclinic crystal system with dimension of cell unit: a = 11.6088(15), b = 6.3272(8), c = 16.164(2) ?; β = 94.040(11)° and trans A/B, B/C and C/D ring junctions and the β-diastereomer 2b has a orthorhombic crystal system with dimension of cell unit: a = 9.0542(4), b = 10.6737(5), c = 24.9723(9) ? and cis A/B, trans B/C and trans C/D rings junctions.

Full text of DOI:10.1007/s10870-016-0639-x

J Chem Crystallogr (2016) 46:155–161
DOI 10.1007/s10870-016-0639-x
ORIGINAL PAPER
The Crystal Structures of the a- and b-Diastereomers of
4,5-Epoxy-cholestan-3-one
1
1
•
Carlos Alarcon-Manjarrez Katherine Vargas-Romero1 Thelma L. Gonzalez-Cruz
•
•
´
Marcos Flores-Alamo Martın A. Iglesias-Arteaga
´
1
1
´
•
´
Received: 7 August 2015 / Accepted: 14 February 2016 / Published online: 23 February 2016
Ó Springer Science+Business Media New York 2016
Abstract The a and b-diastereomers of 4,5-epoxy-c-
holestan-3-one were obtained by epoxidation of cholest-4-
en-3-one with H2O2 in basic media. The a-diastereomer 2a
shows a monoclinic crystal system with dimension of cell
˚
unit: a = 11.6088(15), b = 6.3272(8), c = 16.164(2) A;
b = 94.040(11)° and trans A/B, B/C and C/D ring junc-
tions and the b-diastereomer 2b has a orthorhombic crystal
system with dimension of cell unit: a = 9.0542(4),
˚
b = 10.6737(5), c = 24.9723(9) A and cis A/B, trans B/C
and trans C/D rings junctions.
Graphical Abstract The crystal structures of 4,5-epoxy-
5a-cholestan-3-one (2a) and 4,5-epoxy-5b-cholestan-3-one
(2b) are described.
Keywords 4,5-Epoxy-5a-cholestan-3-one Á 4,5-Epoxy-
5b-cholestan-3-one Á Synthesis Á Crystal structures
Introduction
Steroids bearing the 4,5-epoxy-3-oxo moiety are of special
utility as synthetic precursors of a wide variety of poly-
functional derivatives [1–6]. As a part of our program on
the synthesis of potentially bioactive steroids, we have
become interested on the unambiguous structural charac-
terization of different 4,5-epoxy-3-oxo steroids that are
being employed as starting materials in different synthetic
protocols. Herein we report on the crystal structures of the
a and b diastereomers of 4,5-epoxy-cholestan-3-one.
´
& Martın A. Iglesias-Arteaga
martin.iglesias@unam.mx
1
´
Facultad de Quımica, Universidad Nacional Autonoma de
Mexico, Ciudad Universitaria, 04510 Mexico, D.F., Mexico
´
´
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J Chem Crystallogr (2016) 46:155–161
36.7 C-10, 21.4 C-11, 39.7 C-12, 42.5 C-13, 55.6 C-14,
23.8 C-15, 28.2 C-16, 56.2 C-17, 12.0 C-18, 16.5 C-19,
35.8 C-20, 18.7 C-21, 36.1 C-22, 24.2 C-23, 39.5 C-24,
28.0 C-25, 22.8 C-26, 22.6 C-27.
Experimental
Reactions were monitored by TLC on ALUGRAMÒ SIL
G/UV254 plates from MACHEREY-NAGEL. Chromato-
graphic plates were sprayed with a 1 % solution of vanillin
in 50 % HClO4 and heated until color developed. Melting
points were measured on a Melt-Temp II apparatus. NMR
spectra were recorded in CDCl3 solutions in a Varian
INOVA 400 spectrometer using the solvent signal as ref-
erences. NMR signals assignments were carried out with
the aid of a combination of 1D and 2D NMR techniques
4,5-Epoxy-5b-cholestan-3-one (2b)
Mp. 118–119 °C (from hexane–ethyl acetate) 118–119 °C
[5]. 1H NMR (400 MHz, CDCl3) d 2.96 (s, 1H, H-4a), 2.28
(ddd, J = 19.4, 5.9, 2.2 Hz, 1H, H-2a), 2.14 (dd, J = 13.4,
6.5 Hz, 1H, H-2b), 1.14 (s, 3H, H-19), 0.89 (d, J = 6.5 Hz,
3H, H-21), 0.86 (d, J = 1.8 Hz, 3H, H-26), 0.85 (d,
J = 1.8 Hz, 3H, H-27), 0.68 (s, 3H, H-18). 13C NMR
(100.52 MHz) d ppm: 26.1C-1, 32.6 C-2, 206.9 C-3, 62.7
C-4, 70.5 C-5, 29.9 C-6, 30.4 C-7, 35.0 C-8, 46.4 C-9, 37.2
C-10, 21.5 C-11, 39.4 C-12, 42.6 C-13, 55.8 C-14, 23.8
C-15, 28.1 C-16, 56.1 C-17, 12.0 C-18, 19.0 C-19, 35.7
C-20, 18.6 C-21, 36.1 C-22, 24.2 C-23, 39.5 C-24, 28.0
C-25, 22.8 C-26, 22.5 C-27.
1
that included H, 13C, COSY, Nuclear Overhauser Effect
Spectroscopy (NOESY), Heteronuclear Single Quantum
Correlation (HSQC) and Heteronuclear Multiple Bond
Correlation (HMBC). All 2D NMR spectra were recorded
using the standard pulse sequences and parameters rec-
ommended by the manufacturer and were processed
employing the MestreNova NMR processing program (see
http://mestrelab.com/).
4,5-epoxy-5a-cholestan-3-one (2a) and 4,5-epoxy-5b-
cholestan-3-one (2b) Methanol (100 mL) 10 % p/v NaOH
solution (5.6 mL) and 30 % H2O2 (11.2 mL) were added in
this order to a solution of the a,b-unsaturated ketone 1
(7.28 g, 20 mmol) in CH2Cl2 (100 mL) and the resulting
mixture was stirred for 72 h at room temperature. The
mixture was neutralized with 10 % aqueous acetic acid
solution, 10 % aqueous Na2SO3 solution (40 mL) was
added and the resulting mixture was stirred for 20 min.
Evaporation of the organic solvent under vacuum (cau-
tion!! abundant spume is produced) produced a solid that
was filtered off and washed with water to afford the mix-
ture of the epoxides 2a and 2b (4.89 g). The mother liquor
where extracted with ethyl acetate (3 9 150 mL) and the
organic layer was washed with water (3 9 150 mL), brine
(100 mL) dried (anh,. Na2SO4 and evaporated to afford and
additional amount (0.96 g) of the mixture of the epoxides
2a and 2b. Total yield 5.85 g (73 %). Recrystallization
from hexane/ethyl acetate 9/1 afforded an analytical sam-
ple of the epoxide 2b while chromatographic separation
employing hexane/ethyl acetate 9/1 as eluent followed by
crystallization from hexane, afforded the analytical sample
of 2a.
X-ray Crystallography
Suitable single crystals of compounds 2a and 2b respec-
tively obtained by slow evaporation of hexane and hex-
ane/ethyl acetate solutions, were mounted on a glass fiber
in the goniometer head with a crystal-to-detector distance
of 55.00 mm and crystallographic data were collected at
130 K with an Oxford Diffraction Gemini ‘‘A’’ diffrac-
˚
tometer (kMoKa = 0.71073 A, monochromator: graphite)
with a CCD area detector. The collected data set con-
sisted of 5 runs of 417 frames of intensity (1° in x) for 2a
and 3 runs of 165 frames of intensity (1° in x) for 2b.
The double pass method of scanning was used to exclude
any noise. The collected frames were integrated by using
an orientation matrix determined from the narrow frame
scans.
CrysAlisPro and CrysAlis RED software packages [7]
were used for data collection and integration. Analysis of
the integrated data did not reveal any decay. Final cell
parameters were determined by a global refinement of 2229
(3.458° \ h \ 30.142°) and 3906 (3.781° \ h \ 29.299°)
reflections for 2a and 2b respectively. Collected data were
corrected for absorption effects by analytical numeric
absorption [8] using a multifaceted crystal model based on
expressions upon the Laue symmetry with equivalent
reflections. Structure solution and refinement were carried
with the programs SHELXS-2014 and SHELXL-2014
respectively [9]. WinGX v2014.1 software [10] was used to
prepare material for publication.
4,5-Epoxy-5a-cholestan-3-one (2a)
Mp. 118 °C (from hexane–ethyl acetate) 123–124 °C [5].
1H NMR (400 MHz, CDCl3) d ppm: 3.03 (s, 1H, H-4b),
2.39 (ddd, J = 19.6, 7.2, 1.2 Hz, 1H, H-2a), 2.24 (dd,
J = 7.2, 4.3 Hz, 1H, H-2b), 1.05 (s, 3H H-19), 0.91 (d,
J = 6.5 Hz, 3H, H-21), 0.87 (d, J = 1.9 Hz, 3H, H-26),
0.86 (d, J = 1.9 Hz, 3H, H-27), 0.69 (s, 3H, H-18). 13C
NMR (100.52 MHz) d ppm: 29.1 C-1, 33.1 C-2, 207.2 C-3,
62.9 C-4, 70.3 C-5, 29.8 C-6, 29.0 C-7, 35.4 C-8, 50.7 C-9,
Full-matrix least-squares refinement was carried out by
minimizing (Fo2 - Fc2)2. All nonhydrogen atoms were
anisotropically refined. Hydrogen atoms attached to
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J Chem Crystallogr (2016) 46:155–161
157
Table 1 Crystal data and structure refinement for 2a and 2b compounds
Identification code
2a
2b
Empirical formula
CCDC deposition Number
Formula weight
Temperature
C27 H44 O2
1417471
400.62
C27 H44 O2
1417470
400.62
130(2) K
130(2) K
˚
0.71073 A
˚
0.71073 A
Wavelength
Crystal system
Monoclinic
P 21
Orthorhombic
P 21 21 21
Space group
˚
a = 11.6058(14) A
˚
a = 9.0542(4) A
Unit cell dimensions
˚
b = 6.3296(8) A
˚
b = 10.6737(5) A
˚
c = 16.1643(17) A
˚
c = 24.9723(9) A
b = 94.008(10)°
1184.5(2) A
3
˚
3
˚
2413.37(18) A
Volume
Z
2
4
Density (calculated)
Absorption coefficient
F(000)
1.123 mg/m3
0.068 mm-1
1.103 mg/m3
0.067 mm-1
444
0.30 9 0.14 9 0.09 mm3
888
0.27 9 0.34 9 0.53 mm3
Crystal size
Theta range for data collection
Index ranges
3.458–30.142°
-14 B h B 14, -8 B k B 8, -20 B l B22
3.781–29.299°
-12 B h B 11, -8 B k B 13, -33 B l B 34
Reflections collected
Independent reflections
Completeness to theta = 25.242°
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I [ 2sigma(I)]
R indices (all data)
Absolute structure parameter
Extinction coefficient
Largest diff. peak and hole
12,993
10,466
5364 [R(int) = 0.0647]
5347 [R(int) = 0.0330]
99.7 %
Full-matrix least-squares on F2
99.6 %
Full-matrix least-squares on F2
5364/586/396
5347/42/264
1.023
1.018
R1 = 0.0582, wR2 = 0.1108
R1 = 0.0472, wR2 = 0.0994
R1 = 0.1092, wR2 = 0.1488
R1 = 0.0581, wR2 = 0.1080
0.4(10)
n/a
1.2(7)
n/a
-3
-3
˚
0.169 and -0.213 e A
˚
0.216 and -0.265 e A
22
24
27
18
20
25
23
12
26
11
17
13
14
19
16
1
9
2
15
10
8
3
i
5
7
+
6
O
O
O
4
O
O
1
2a
2b
i) H2O2, NaOH, CH3OH/CH2Cl2
Scheme 1 Synthesis of the diastereomeric epoxides 2a and 2b
123

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J Chem Crystallogr (2016) 46:155–161
Fig. 1 ORTEP drawing of the asymmetric unit of 2a with the thermal ellipsoids drawn at the 50 % of probability
˚
Table 2 Selected bond lengths [A] and angles [°] for 2a and 2b
carbons were placed in geometrically idealized positions
and refined as riding on their parent atoms, with C–
2a
2b
˚
H = 0.97–1.00 A with Uiso (H) = 1.2Ueq(C) for methy-
˚
Distance (A)
˚
Distance (A)
Bond
Bond
lene and methyne groups, and Uiso (H) = 1.5 Ueq(C) for
methyl groups.
C-1a–C-10a
C-1a–C-2a
C-2a–C-3
1.48(3)
C-1–C-2
1.524(4)
1.533(3)
1.502(3)
1.215(3)
1.491(3)
1.461(2)
1.481(3)
1.449(2)
1.527(3)
1.540(3)
1.534(3)
1.559(3)
1.545(3)
1.533(3)
1.532(3)
1.553(9)
1.51(3)
C-1–C-10
C-2–C-3
In the crystal structure almost all atoms of 2a show
disorder over two sites with occupancies 0.65:0.35, while
in 2b C-26 and C-27 shows disorder over two sites with
occupancies 0.54:0.46. Crystal data and experimental
details of the structure determination are listed in Table 1.
The absolute configuration of the title compounds can be
assumed without risk, as that known for the starting
material considering that the synthetic transformations
carried out do not affect the absolute configuration of the
chiral centres in the naturally occurring steroid framework.
1.57(2)
C-3–O-1
1.225(4)
1.468(6)
1.458(4)
1.477(5)
1.458(4)
1.584(9)
1.473(12)
1.525(5)
1.477(13)
1.500(17)
1.50(3)
C-3–O-1
C-3–C-4
C-3–C-4
C-4–O-2
C-4–O-2
C-4–C-5
C-4–C-5
C-5–O-2
C-5–O-2
C-5–C-10a
C10a–C-19
C-13–C-18
C-16a–C-17
C-17–C-20a
C-20a–C-21a
C-24a–C-25a
C-25a–C-26a
C-5–C-10
C-10–C-19
C-13–C-18
C-16–C-17
C-17–C-20
C-20–C-21
C-24–C-25
C-25–C-26a
Results and Discussion
1.532(12)
1.502(15)
Treatment of a methanol/CH2Cl2 solution of the a,b-unsat-
urated ketone 1 with H2O2 and NaOH afforded 73 % yield of
a mixture of the diasteromeric epoxides 2a and 2b that were
separated by fractional crystallization from hexane/ethyl
acetate and column chromatography (Scheme 1).
Bond
Angle (°) Bond
Angle (°)
C10a–C1a–C2a
C-1a–C-2a–C-3
O-1–C-3–C-4
O-1–C-3–C-2a
O-2–C-4–C-3
O-2–C-4–C-5
C-3–C-4–C-5
115.2(17) C-2–C-1–C-10
110.4(15) C-3–C-2–C-1
114.8(2)
114.0(2)
In compound 2a (see Fig. 1) the A/B, B/C and C/D rings
junctions are trans and the steroid skeleton bears b-ori-
ented the C-18 and C-19 methyl groups attached to C-10
and C-13 respectively. Almost all carbon atoms are dis-
ordered over two sites with occupancies 0.65:0.35. Selec-
ted bond lengths and angles for the higher occupancy are
presented in Table 2.
120.3(4)
122.0(8)
115.0(3)
59.6(2)
O-1–C-3–C-4
O-1–C-3–C-2
O-2–C-4–C-5
O-2–C-4–C-3
C-5–C-4–C-3
C-20–C-17–C-16
C-23–C-24–C-25
119.9(2)
122.5(2)
59.02(12)
115.58(18)
121.83(19)
112.58(16)
114.35(19)
120.7(3)
112.0(9)
C-16a–C-17–C-20a
C-22a–C-24a–C-25a 114.1(9)
A comparison of the positions of the atoms with higher
occupancy in the ring A of 2a with the equivalent fragment
C-26a–C-25a–C-27a 105.9(10) C-27a–C-25–C-26a 113.3(3)
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J Chem Crystallogr (2016) 46:155–161
159
Fig. 2 Crystal array of 2a, view
along the a axis and with
perspective to the plane formed
by b–c axes emphasizing the
C(7) motif
Fig. 3 Crystal structure of 2b with the thermal ellipsoids drawn at 50 % of probability
123

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J Chem Crystallogr (2016) 46:155–161
Table 3 Least-square overlay
analysis of the rings, performed
by each pair of molecules 2b
and 2b0
(11)° and DCs(C-7) = 12.7(8)° and the average magnitude
of the torsion angles is 57.0(4)°.
Ring C also assumes a slightly distorted chair confor-
Rings
2b versus 2b0
A
B
C
D
0.0389
0.0189
0.0138
0.0156
˚
mation [puckering parameters Q = 0.602(18) A, h =
11.9(17) and / = 288(8)° if the calculation starts from C-8
to C-14 and proceeds in clockwise direction]. The five-
membered D ring shows a twisted conformation on C-13–
2
˚
C-14 [puckering parameters q = 0.43(1) A and u2 =
(C-1–C-2, C-2–C-3, C-3–C-4 and C-4–C-5) of the starting
material cholest-4-en-3-one (1) [11] shows differences in
the bond lengths and torsion angles that may be attributed
to the disorder over two sites on the crystal structure of 2a
that lacks the double bond present in the staring material
(1), and the distortion exerted by epoxy moiety (rms
195.5(19)°]. Asymmetry parameters [14] are: D = 713.8,
sm = 45.5(8), DCs(C-13) = 14.9(12) and DC2(C-13,
C-14) = 4.0(12)°.
In the crystal structure there is one interaction C–HÁÁÁO
of hydrogen bond type. Each molecule features one inter-
˚
action C-19–H-19bÁÁÁO-2 (2.42 A) to its neighbor related
˚
deviation of fitted atoms = 0.0604 A in 2a vs rms devia-
˚
tion of fitted atoms = 0.0316 A in 1). The A ring of 2a
by the symmetry operation -x, -1/2 ? y, -z: forming the
C11(7) motif [15]. This intermolecular interaction is
observed along the b-c plane and leads to infinite laminar
array in the supramolecular network (see Fig. 2).
assumes a distorted half-chair conformation [puckering
˚
parameters: [12] Q = 0.51(2) A, h = 56.7(19), u =
349.8(18)°, if the calculation starts from C-1 to C-10 and
proceeds in counterclockwise direction]. Asymmetry
parameters [13] are: DC2(C-2–C-3) = 64.1(19), DC2(C-
3–C-4) = 24(2), DC2(C-4–C-5) = 40.6(16), DCs(C-3) =
41.3(16) and DCs(C-5) = 49.3(14)°.
For 2b, the asymmetric unit consist of one unit of 4,5-
epoxy-5b-cholestan-3-one with C-26 and C-27 disordered
over two sites with occupancies 0.54:0.46. Selected bond
lengths and angles for the higher occupancy are presented
in Table 2. Compound 2b has cis A/B and trans B/C and
C/D rings junctions. The steroid skeleton bears the b-ori-
ented C-18 and C-19 methyl groups attached to C-10 and
C-13 respectively (Fig. 3). The bond lengths C-1–C-2,
C-2–C-3 and the nearly planar grouping C-2, C-3, C-4,
C-5, O-1 are similar to those of the starting material 1 (rms
B ring assumes a slightly distorted chair conformation
˚
[puckering parameters Q = 0.617(12) A, h = 12.5(10),
u = 208(5)°, if the calculation starts from C-5 to C-10 and
proceeds in counterclockwise direction]. Rotational sym-
metry is dominant; a pseudo-C2 axis bisects the C-6–C-7
bond. Asymmetry parameters are: DC2(C-6–C-7) = 15.3
˚
deviation of fitted atoms = 0.0371 A for 2b versus rms
Fig. 4 Crystal array of 2b; view along the axis b; with perspective to the plane formed by a and c axes emphasizing the R22(9) and R22(12) motifs
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J Chem Crystallogr (2016) 46:155–161
161
˚
˚
deviation of fitted atoms = 0.0316 A in 1). However, there
are differences in the torsion angles C-1–C-2–C-3–C-4 and
C-2–C-3–C-4–C-5 attributed to the distorting effect of
epoxide moiety in compound 2b, that lacks the C-4–C-5
double bond present in the cholest-4-en-3-one (1).
In order to establish differences between 2b and the
previously reported data for this compound (2b0), that was
collected at room temperature [16], a least-squares overlay
analysis of the structures by pairs was performed with the
Mercury program [17] (Table 3). The obtained data evi-
dence small differences in the A ring with a rms 0.0389 and
in the C-23–C-24–C-25–C-26 torsion angle with 171.30 for
2b and 163.85° for 2b0.
1 2.70, C-7–H-7bÁÁÁO2 2.69 A and C-19–H-19aÁÁÁO1
˚
2.63 A). These intermolecular interactions with symmetry
operations 1/2 ? x, 3/2 - y, -z and -1/2 ? x, 3/2 - y,
-z show R22(9) and R22(12) motifs and lead to infinite
laminar array along the a–c plane.
Acknowledgments The authors acknowledge the financial support
provided by Direccio´n General de Asuntos del Personal Acade´mico
(Project DGAPA-IN211714) and the Faculty of Chemistry (PAIP-
5000-9063). Thanks are due to CONACYT-Mexico for the scholar-
ship granted to C.A.M. We want to express our gratitude to Rosa I.
del Villar Morales (USAI-UNAM) for recording NMR spectra and to
Dr. Carlos Cobas from Mestrelab for assistance with the MestreNova
NMR processing program.
In compound 2b, the A ring assumes a twisted confor-
mation on C-1–C-2 [puckering parameters: Q =
˚
0.458(2) A, h = 122.9(3), u = 169.0(3)°, if the calcula-
References
tion starts from C-1 to C-10 and proceeds in counter-
clockwise direction. Asymmetry parameters are: DC2(C-2–
C-3) = 55.1(3), DC2(C-3–C-4) = 19.8(3), DC2(C-4–C-5) =
35.4(3), DCs(C-3) = 35.2(2) and DCs(C-5) = 42.6(2)°.
The B ring assumes a perfect chair conformation [puck-
1. Uyanic C, Malay A, Ayna AS, Hanson JR, Hitchcock PB (2005)
Steroids 70:71–75
2. Boar RB, Jones SL, Patel AC (1982) J Chem Soc Perkin Trans
1:513–516
3. Back TG, Chau JH-L, Codding PW, Gladstone PL, Jones DH,
Morzycki JW, Roszak AW (1992) J Org Chem 57:4110–4121
4. Neeman M, O’Grodnick JS (1972) Tetrahedron Lett 13:783–786
5. Nickon A, Mendelson WL (1965) J Am Chem Soc 87:3921–3928
6. Jennings BR, Bengtson JM (1978) Steroids 31:49–67
7. Agilent (2013). CrysAlis-PRO and CrysAlis-RED. Agilent
Technologies, Yarnton
˚
ering parameters Q = 0.577(2) A, h = 2.3(2), u = 327(6)°,
if the calculation starts from C-5 to C-10 and proceeds in
counterclockwise direction. Rotational symmetry is domi-
nant; a pseudo-C2 axis bisects the C-6–C-7 bond. Asym-
metry parameters are: DC2(C-6–C-7) = 4.4(2)° and DCs(C-
7) = 3.5(2)° and the average magnitude of the torsion angles
is 56.2(8)°.
8. Clark RC, Reid JS (1995) Acta Cryst A51:887–897
9. Sheldrick GM (2015) Acta Cryst C71:3–8
10. Farrugia LJ (2012) J Appl Crystallogr 45:849–854
11. Sheldrick GM, Oeser E (1976) Acta Cryst B32:1984–1987
12. Cremer D, Pople JA (1975) J Am Chem Soc 97:1354–1358
13. Duax WL, Weeks CM, Rohrer DC (1976) In: Eliel EL, Allinger
N (eds) Topics in Stereochemistry, vol 2. Wiley, New York,
pp 271–283
Ring C also assumes a chair conformation [puckering
˚
parameters Q = 0.582(2) A, h = 4.8(2) and / = 272(2)°
if the calculation starts from C-8 to C-14 and proceeds in
clockwise direction].
The five-membered D ring shows a twisted conforma-
2
tion on C-13–C-14 [puckering parameters q = 0.450(2) A
14. Altona C, Geise HJ, Romers C (1968) Tetrahedron 24:13–32
15. Etter MC (1990) Acc Chem Res 23:120–126
16. Russell JC, Nassimbeni LR, Cragg GLM (1977) Acta Crystallogr
Sect B Struct Crystallogr Cryst Chem 33:2128–2131
17. Macrae CF, Edgington PR, McCabe P, Pidcock E, Shields GP,
Taylor R, Towler M, van De Streek J (2006) J App Cryst
39:453–457
˚
and u2 = 194.1(3)°]. Asymmetry parameters are: D =
713.8, sm = 45.8(1), DCs(C-13) = 14.5(2) and DC2(C-13,
C-14) = 4.2(2)°.
The crystal structure of 2b (Fig. 4) shows three inter-
molecular contacts of hydrogen bond type (C-14–H-14ÁÁÁO-
123