The crystal structure of diosgenin acetate and its 23-oxygenated derivatives

Article abstract of DOI:10.1007/s10870-013-0404-3

The crystal structures of diosgenin acetate (1), 23-ketodiosgenin acetate (2), (23R)-23-hydroxydiosgenin 3-monoacetate (3) and (23S)-23-hydroxydiosgenin 3-monoacetate (4) are described. Compounds 1, 2 and 3 crystallized as a monoclinic system with a space group P2₁; while compound 4, crystallized as orthorhombic systems with space group P2₁2 ₁2₁. The effects of the side chain modifications on the puckering parameters are presented and discussed. Graphical Abstract: The crystal structures and NMR characterization of diosgenin acetate and its three 23-oxigenated derivatives are described. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10870-013-0404-3

J Chem Crystallogr (2013) 43:187–196
DOI 10.1007/s10870-013-0404-3
ORIGINAL PAPER
The Crystal Structure of Diosgenin Acetate and Its 23-Oxygenated
Derivatives
•
Anielka Rosado-Abon Nuria Esturau-Escofet
•
´
Marcos Flores-Alamo Rafael Moreno-Esparza
•
•
´
Martın A. Iglesias-Arteaga
Received: 23 August 2012 / Accepted: 25 February 2013 / Published online: 17 March 2013
Ó Springer Science+Business Media New York 2013
Abstract The crystal structures of diosgenin acetate (1),
23-ketodiosgenin acetate (2), (23R)-23-hydroxydiosgenin
3-monoacetate (3) and (23S)-23-hydroxydiosgenin 3-mono-
acetate(4) aredescribed.Compounds1, 2 and3 crystallizedas
a monoclinic system with a space group P21; while compound
4, crystallized as orthorhombic systems with space group
P212121. The effects of the side chain modifications on the
puckering parameters are presented and discussed.
As a part of our project in the synthesis of structurally
modified steroid sapogenins we have became interested on
the synthesis and detailed characterization of several
members of this family of compounds bearing unnatural
substitution patterns the steroid framework [19–21] or the
side chain, [22, 23] that are serving as staring materials for
the synthesis of potentially bioactive steroids. Herein we
report on the crystal structure of diosgenin acetate,
23-oxodiosgenin acetate and both, the 23S and 23R epimers
of 23-hydroxydiosgenin 3-monoacetate.
Keywords Steroids Á Spirostane Á 23-Oxospirostane Á
23-Hydroxyspirostanes X-ray structure Á Puckering
parameters Á Ring conformation
Experimental
Introduction
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 equipment and
are uncorrected. Mass spectra were registered in a Thermo-
Electron spectrometer model DFS (Double Focus Sector).
NMR spectra were recorded in CDCl3 solution in a Varian
INOVA 400 spectrometer using the solvent signal
Steroid sapogenins are wide spread in the nature. Several
members of this family of compounds have served as
starting materials for the synthesis of a great variety of
bioactive steroids that includes sexual and adrenocortical
hormones [1], ecdysteroids [2], brasinossteroids analogues
[3–5], and cytotoxic steroids [6–12] amongst many others.
In addition to their usefulness as starting materials,
steroid sapogenins have been subject of intensive research
due to the fact that several members of the family have
showed biological activity [13–18].
1
7.26 ppm for H and 77.00 ppm for 13C as references.
(25R)-Spiros-5-en-3b-ol Acetate Namely Diosgenin
Acetate (1b)
Diosgenin (1a) (3 g, 7.24 mmol) was refluxed for 3 h in
acetic anhydride (15 ml) and the mixture is allowed to
reach room temperature before pouring into ice water
(200 ml). The resulting mixture is stirred overnight, the
produced solid was filtered off, washed with abundant
water and dried in the air. Recrystallization from acetone/
water afforded 2.5 g (5.48 mmol, 76 %) of diosgenin
´
A. Rosado-Abon Á N. Esturau-Escofet Á M. Flores-Alamo Á
R. Moreno-Esparza (&) Á M. A. Iglesias-Arteaga (&)
´
Facultad de Quımica, Universidad Nacional Autonoma de
Mexico, Ciudad Universitaria, 04510 Mexico, DF, Mexico
´
´
e-mail: moresp@servidor.unam.mx
M. A. Iglesias-Arteaga
e-mail: martin.iglesias@unam.mx
123

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J Chem Crystallogr (2013) 43:187–196
acetate (1b). mp 195 °C (from acetone/water) Lit. [24]
195–196 °C. RMN H (400 MHz, CDCl3) d ppm 5.36 (d,
additional amount of NaBH4 (18 mg) was added and the
solution stirred for 1 additional hour before addition of
acetone (2 ml). The solvents were evaporated and the solid
residue was dissolved in ethyl acetate (50 ml) and washed
with H2O (4 9 15 ml), saturated aqueous NaCl (3 9 15 ml)
solution, dried (anh. Na2SO4) and evaporated to afford the
mixture of the epimeric 23R and 23S-hydroxy-diosgenin
acetates that were separated in a chromatographic column
employing 8:1 hexane/ethyl acetate mixture to afford the
pure 23-hydroxyspirostanes.
1
J 5.1 Hz, 1H, H-6), 4.58 (m, 1H, H-16, H-3), 4.40 (m, 1H,
H-16, H-16), 3.46 (ddd J 10.9, 4.3, 1.3, H-26 eq.), 3.36 (dd
J 10.9,10.9 H-26ax.), 2.01 (s, 3H, CH3–COO-3), 1.02 (s,
3H, CH3-19), 0.96 (d, J 6.3, 3H, CH3-21), 0.78 (s, 3H,
CH3-18), 0.78 (d J 6.1 CH3-27). RMN 13C (100 MHz)
d ppm 36.9 C-1, 27.7 C-2, 73.8 C-3, 38.1 C-4, 139.6 C-5,
122.3 C-6, 32.0 C-7, 31.4 C-8, 49.9 C-9, 36.7 C-10, 20.8
C-11, 39.5 C-12, 40.2 C-13, 56.4 C-14, 31.8 C-15, 80.8
C-16, 62.2 C-17, 16.3 C-18, 19.3 C-19, 41.6 C-20, 14.5
C-21, 109.2 C-22, 31.4 C-23, 28.8 C-24, 30.3 C-25, 66.8
C-26, 17.1 C-27, 170.4 CH3–COO-3, 21.4 CH3–COO-3.
(23R,25R)-Spirost-5-en-3b,23-Diol 3 Monoacetate (3)
Yield 27.2 mg (0.058 mmol, 5 %) of the 23R epimer (3) mp
240–242 °C (from acetone/H2O) 1H NMR (400 MHz,
CDCl3) d ppm 5.37 (d, J 5.1 Hz, 1H, H-6), 4.60 (tdd, J 10.3,
6.1, 4.2 Hz, 1H, H-3), 4.47 (td, J 7.8, 5.7 Hz, 1H, H-16), 3.60
(m, 1H, H-23), 3.50 (ddd, J 10.8, 5.1, 1.4 Hz, 1H, H-26ec),
3.43 (dd, J 11.2 Hz, 1H, H-26ax), 2.31 (dd, J 9.0, 3.7 Hz, 2H,
H-4), 2.25 (td, J 12.7, 6.9 Hz, 1H, H-20), 2.03 (s, 3H,
CH3COO-3), 1.11 (d, J 7.0 Hz, 3H, CH3-21), 1.03 (s, 3H,
CH3-19), 0.80 (s, 3H, H-18), 0.80 (d, J 6.7 Hz, 3H, H-27). 13C
NMR (100 MHz) d ppm 37.0 C-1, 27.7 C-2, 73.9 C-3, 38.1
C-4, 139.7 C-5, 122.3 C-6, 32.1 C-7, 31.5 C-8, 50.0 C-9, 36.7
C-10, 20.7 C-11, 39.4 C-12, 40.7 C-13, 56.5 C-14, 32.0 C-15,
81.3 C-16, 64.0 C-17, 16.8 C-18, 19.3 C-19, 40.6 C-20, 16.1
C-21, 108.4C-22, 70.8C-23, 36.3C-24, 24.2C-25, 66.3C-26,
16.8 C-27, 170.5 CH3COO-3, 21.4 CH3COO-3. HRMS (EI,
70 eV): observed 472.3183, required for C29H44O5 472.3183.
(25R)-3b-Acetoxyspiros-5-en-23-one (2)
NaNO2 (0.5256 g) was slowly added (45 min) to a solution of
diosgenin acetate (1b) (3 g, 6.57 mmol) and BF3ÁEt2O
(2.69 ml) in acetic acid (75 ml). After conclusion of the addi-
tion, the addition of BF3ÁEt2O (2.69 ml) and NaNO2 (0.5256 g
in 45 min.) were repeated and the resulting mixture was stirred
for 1 h and poured into ice/water. The produces solid was fil-
tered, washed with abundant water, dissolved in ethyl acetate
(200 ml) and the organic solution washed with 5 % aqueous
solution of Na2CO3 (2 9 50 ml), H2O (1 9 50 ml), NaCl
(1 9 50 ml), dried (anh. Na2SO4) and evaporated. The result-
ing syrup was dissolved in the smallest amount of 1/1 benzene/
hexane solution left to stand overnight in a chromatographic
column packed with Al2O3 (Brockman activity III). Elution
with 10/1 hexane/ethyl acetate mixture afforded 1.093
(2.32 mmol, 35 %) of 23-oxodiosgenin acetate (2). mp 190–
192 °C (from ethyl acetate/hexane). Lit. [25] 191–192.5 °C
(23S,25R)-Spirost-5-en-3b,23-Diol 3 Monoacetate (4)
Yield 0.4517 g, (0.96 mmol, 80 %) mp 166–168 °C (from
1
RMN H (400 MHz, CDCl3) d ppm 5.35 (d, J 5.1 Hz, 1H,
1
H-6), 4.64–4.54 (m, 2H, H-16, H-3), 3.78 (t, J 11.3 Hz, 1H,
H-26ax), 3.58 (ddd, J 11.2, 4.6, 1.4 Hz, 1H, H-26ec), 2.87 (dd,
J 13.7, 6.9 Hz, 1H, H-20), 2.49–2.38 (m, 2H, H-24), 2.36–2.21
(m, 3H, H-4, H-25), 2.02 (s, 3H, CH3–COO-3), 1.02 (s, 3H,
CH3-19), 0.93 (d, J 7.1 Hz, 3H, CH3-21), 0.93 (d, J 6.5 Hz, 3H,
CH3-27), 0.78 (s, 3H, CH3-18). RMN 13C (100 MHz) d ppm
36.9 C-1, 27.7 C-2, 73.8 C-3, 38.1 C-4, 139.8 C-5, 122.2 C-6,
32.0 C-7, 31.4 C-8, 49.9 C-9, 36.7 C-10, 20.7 C-11, 39.5 C-12,
40.7 C-13, 56.5 C-14, 31.8 C-15, 83.3 C-16, 61.7 C-17, 16.0
C-18, 19.3 C-19, 34.8 C-20, 14.4 C-21, 109.8 C-22, 201.8 C-23,
45.3 C-24, 35.8 C-25, 65.6 C-26, 17.1 C-27, 170.5 CH3-COO-
3, 21.4 CH3-COO-3. * interchangeable.
methanol) H NMR (400 MHz, CDCl3) d ppm 5.36 (d,
J 5.2 Hz, 1H, H-6), 4.59 (tdd, J 10.4, 6.2, 4.2 Hz, 1H, H-3),
4.46 (dt, J 8.9, 7.2 Hz, 1H, H-16), 3.50–3.42 (m, 1H, H-23),
3.40 (ddd, J 10.8, 4.7, 2.0 Hz, 1H, H-26ec), 3.24 (dd, J 11.1,
11.1 Hz, 1H, H-26ax), 2.58–2.49 (m, 1H, H-20), 2.02 (s, 3H,
CH3COO-3), 1.02 (s, 3H, CH3-19), 0.94 (d, J 7.0 Hz, 3H,
CH3-21), 0.82 (s, 1H, H-18), 0.81 (d, J 6.7 Hz, 3H, H-27).
13C NMR (100 MHz) d ppm 36.9 C-1, 27.7 C-2, 73.8 C-3,
38.1 C-4, 139.7 C-5, 122.2 C-6, 32.0 C-7, 31.2 C-8, 49.9 C-9,
36.7 C-10, 20.7 C-11, 39.8 C-12, 40.7 C-13, 56.3 C-14, 31.8
C-15, 81.5 C-16, 61.5 C-17, 16.4 C-18, 19.3 C-19, 35.5 C-20,
14.1 C-21, 110.6 C-22, 67.0 C-23, 38.5 C-24, 30.8 C-25, 65.9
C-26, 16.6 C-27, 170.5 CH3COO-3, 21.4 CH3COO-3. Ele-
mental analysis: observed C 73.54 % H 9.30 %, required
for C29H44O5 C 73.69 % H 9.38 %.
(23R,25R)-Spirost-5-en-3b,23-Diol 3-Monoacetate (3)
and (23S,25R)-Spirost-5-en-3b,23-Diol 3-Monoacetate
(4)
Crystallography
NaBH4 (180 mg) was slowly added to a cold (10 °C)
solution of 23-oxodiosgenin acetate (561.7 mg, 1.2 mmol)
in methanol (21 ml) and the mixture was stirred for 3 h. An
X-ray diffraction measurements were performed at 100 K
on an Oxford Diffraction Atlas (Gemini) diffractometer
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J Chem Crystallogr (2013) 43:187–196
189
˚
with Mo Ka radiation k = 0.71073 A. Data collection
routine and data reduction were carried out with the Cry-
sAlisPro, Oxford Diffraction Ltd. Oxford Diffraction [26].
The structures of all molecules were solved using SIR2004
[27] and refined using SHELXL-97 [28]. All non-hydrogen
atoms were refined anisotropically and the hydrogen atoms
were found in difference Fourier maps, placed at geomet-
rically calculated positions and refined using the riding
model. The obtained bond lengths and angles of each
compound are normal and are available from the electronic
supporting information (CIF file) for the structure. Crys-
tallographic data have been deposited with the Cambridge
Crystallographic Data Center as supplementary material
numbers CCDC 897411 (1), CCDC 897414 (2), CCDC
897413 (3) and CCDC 897412 (4). Copies of the data can be
obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK. E-mail: deposit@ccdc.
cam.ac.uk.
Suitable crystals for X-ray diffraction studies were
obtained by slow evaporation at room temperature as fol-
lows: (25R)-spirost-5-en-3b-ol acetate (1) from acetone;
(25R)-3b-acetoxyspirost-5-en-23-one (2) from 10:1 hex-
ane/ethyl acetate mixture; (23R,25R)-spirost-5-en-3b,
23-diol 3-monoacetate (3) and (23R,25R)-spirost-5-en-
Table 1 Crystal data and structure refinement for 1, 2, 3 and 4
(1)
(2)
(3)
(4)
Formula
Fw
C29 H44 O4
456.64
C29 H42 O5
470.63
C29 H44 O5
472.64
C29 H44 O5
472.64
T (K)
100(2)
100(2)
100(2)
100(2)
˚
Wavelength (A)
Crystal system
Space group
0.71073
0.71073
0.71073
0.71073
Monoclinic
P 21
Monoclinic
P 21
Monoclinic
P 21
Orthorhombic
P 21 21 21
a = 8.3914(1)
b = 9.3208(1)
c = 32.9697(4)
˚
a (A)
14.4400(2)
6.1615(1)
14.6847(2)
100.846(1)
1,283.20(3)
2
14.3562(2)
6.2641(1)
14.5501(2)
99.677(2)
1,289.85(3)
2
a = 14.4364(3)
b = 6.1202(1)
c = 14.6243(3)
99.521(2)
1,274.31(4)
2
˚
b (A)
˚
c (A)
b (°)
˚
V (A3)
2,578.71(5)
Z
4
q calcd (Mg/m3)
1.182
1.212
1.232
1.217
l (mm-1
)
0.077
0.081
0.082
0.081
F(000)
Crystal size (mm3)
500
512
516
1032
0.41 9 0.17 9 0.11
3.40 to 26.06
0.56 9 0.19 9 0.03
3.39 to 26.10
0.43 9 0.36 9 0.16
3.39 to 26.11
0.54 9 0.53 9 0.36
3.46 to 26.15
Theta range for data
collection (°)
Index ranges
-17 B h B 17,
-7 B k B 7,
-18 B l B 18
-17 B h B 17,
-7 B k B 7,
-17 B l B 18
-17 B h B 17,
-7 B k B 7,
-17 B l B 18
-10 B h B 10,
-11 B k B 11,
-40 B l B 40
Reflections collected
37,549
38,588
19,161
72,348
Independent reflections
5,067
2,805
2,776
2,946
[R(int) = 0.0256]
99.7 %
[R(int) = 0.0414]
99.6 %
[R(int) = 0.0220]
99.4 %
[R(int) = 0.0352]
99.2 %
Completeness to
theta = 26.06°
Refinement method
Full-matrix least-squares Full-matrix least-squares Full-matrix least-squares Full-matrix least-squares
on F2
5,067/1/303
1.061
on F2
2,805/1/312
1.041
on F2
2,776/1/312
1.029
on F2
2,946/0/310
1.093
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices
[I [ 2sigma(I)]
R indices (all data)
R1 = 0.0301,
wR2 = 0.0806
R1 = 0.0323,
wR2 = 0.0848
R1 = 0.0334,
wR2 = 0.0901
R1 = 0.0364,
wR2 = 0.0939
R1 = 0.0310,
wR2 = 0.0810
R1 = 0.0336,
wR2 = 0.0856
R1 = 0.0345,
wR2 = 0.0909
R1 = 0.0366,
wR2 = 0.0941
Largest diff. peak and hole
-3
0.343 and -0.163
0.496 and -0.238
0.469 and -0.241
0.303 and -0.307
˚
(e.A
)
123

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J Chem Crystallogr (2013) 43:187–196
25
21
O
O
26
27
20
22
18
23
12
17
24
O
O
11
13
19
O
1
16
9
14
2
15
10
8
ii
4
7
3
5
AcO
i
AcO
6
23-oxodiosgenin acetate(2)
R= H, diosgenin (1a)
R= Ac, diosgenin acetate (1b)
OH
O
iii
O
S
R
OH
O
O
+
AcO
AcO
(23S)-23-hydroxydiosgenin 3-monoacetate (4)
(23R)-23-hydroxydiosgenin 3-monoacetate (3)
i) Ac2O/pyridin; ii a) NaNO2/ BF3.Et2O/ AcOH; b) Al2O3; iii) NaBH4/ MeOH
Scheme 1 Synthesis of 23-oxygenated derivatives of diosgenin acetate
3b,23-diol 3-monoacetate (4) from 8:1 hexane/ethyl acetate
mixture. Compounds 1, 2 and 3 crystallized as a mono-
clinic system with a space group P21; while compound 4,
crystallized as orthorhombic systems with space group
P212121. Table 1 summarizes all the crystallographic data
of the four structures.
Fig. 1 Crystal structure and
unit cell of diosgenin acetate (1)
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J Chem Crystallogr (2013) 43:187–196
191
Fig. 2 Crystal structure and
unit cell of 23-oxodiosgenin
acetate (2)
Results and Discussion
signals of the carbynolic C-23 at 70.8 and 67.0 ppm
respectively. Overlapping of the H-23 signals of the 23
hydroxy derivative hinder the determination of the config-
uration at C-23 by observation of the splitting pattern.
Nevertheless observation of the shielding effect of the
hydroxyl attached to C-23 allowed the determination of its
axial or equatorial orientation and consequently the corre-
sponding configuration at C-23. In the alcohol 3 the observed
upfield shift of the signal of C-25 respect to that of diosgenin
acetate (1) suggests a 1,3 diaxial interaction between the
hydroxyl at C-23 and H-25, indicating the R-configuration at
C-23. In the case of the alcohol 4 the upfield shift of the signal
of C-20 respect to that of diosgenin acetate can be attributed
to a d-syn interaction between the hydroxyl group attached to
C-23 and H-20, that indicates its equatorial orientation and
consequently the S configuration at C-23. Crystallographic
studies corroborated the assigned configuration for both
alcohols 3 and 4.
Synthesis and NMR Characterization
Acetylation of diosgenin following the standard Ac2O/
pyridine procedure
Treatment of diosgenin acetate (1b) with NaNO2 and
BF3ÁEt2O in acetic acid followed by hydrolysis in alumina
afforded 23-oxodiosgenin acetate (2) which was reduced
with NaBH4 in methanol to afford a mixture of the 23R-and
23S-hydroxydiosgenin 3-monoacetates 3 and 4 (Scheme 1).
The observed 1H and 13C NMR signals are in agreement
with our previously described data from compounds with
similar functionality in the F-ring [29]. In particular the
presence of the carbonyl function at C-23 in compound 2 can
be corroborated by the new functional signal at 201.8 ppm.
The 23-hydroxyspirostanes 3 and 4 are characterized by the
123

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J Chem Crystallogr (2013) 43:187–196
Crystallographic Studies
conformation in compounds 1, 2 and 3, while in compound
4 assumes an envelope on C(14) conformation. Finally in
compounds 1, 2 and 3, the E ring adopts an envelope on
O(3) exo conformation but in compound 4 changes to an
envelope on C(22) endo.
Each one of the studied compounds crystallizes as an iso-
lated molecule, all studied compounds contain the steroid
ABCD fused ring framework with axial methyl groups
attached to C(10) and C(13). The A/B, B/C and C/D ring
junctions are trans, whereas the cyclopentane ring D is cis-
fused to the tetrahydrofuran ring E, which is in agreement
with other steroids as indicated by the torsion angles shown
in the CIF file. Then, these five fused rings A [C(1)–C(5)/
C(10)], B[C(5)–C(10)], C[C(8)/C(9)/C(11)–C(14)], D, E
[O(3)/C(16)/C(17)/C(20)/C(22)] are attached to F [O(4)/
C(22)–C(26)] at C(22) which is shared by both rings D and
E. The six-membered rings A, C and F present chair con-
formations, while B presents a half chair conformation due
to the presence of the sp2 bond C(5)–C(6) for all the
studied compounds, however, in the case of the five-
membered rings, ring D adopts a twisted on C(13)–C(14)
In compounds 1, 2 and 3, the equatorial acetoxy group
bonded to C(3) is arranged in such a way that the carbonyl
O atom is close to eclipse the axial H atom attached to C(3)
and does not disturb Ring A, this arrangement can be
explained in terms of the intramolecular bond O(2)ÁÁÁH–
˚
˚
˚
C(3): 2.247(2) A for 1, 2.256(2) A for 2 and 2.245(2) A for
3. In the case of 4, the carbonyl O atom does not eclipse the
axial H atom due to intermolecular interactions with other
molecules.
In the absence of significant anomalous scattering
effects, the absolute structure was assigned based on the
crystal structure of the starting material (1), of which C(25)
has a R-configuration with an equatorially group C(27). In
Fig. 3 Crystal structure and
unit cell of (23R)-23-
hydroxydiosgenin
3-monoacetate (3)
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J Chem Crystallogr (2013) 43:187–196
193
Fig. 4 Crystal structure and
unit cell of (23S)-23-hydroxy
diosgenin 3-monoacetate (4)
Table 2 Puckering descriptors obtained using the PLATON program
Table 3 Least-squares overlay analysis of the rings, performed by
each pair of structures
1
2
3
4
(1–2)
(1–3)
(1–4)
Ring A C-form
Ring B H-form
Ring C C-form
Ring D Twisted on
C-form
C-form
C-form
H-form
C-form
Envelope
Ring A
Ring B
Ring C
Ring D
Ring E
Ring F
All Rings
0.00431
0.00334
0.00356
0.00449
0.01010
0.02840
0.04480
0.00770
0.00232
0.00404
0.00592
0.00709
0.01130
0.05260
0.00764
0.02260
0.02590
0.08910
0.10600
0.01620
0.54000
H-form
H-form
C-Form
Twisted on
C-form
Twisted on
C(13)–C(14) C(13)–C(14) C(13)–C(14) on C(14)
Ring E Envelope
O(3)-exo
Envelope
O(3)-exo
C-form
Envelope
O(3)-exo
C-form
Envelope
C(22) endo
C-form
Ring F C-form
The ORTEP plot of each crystal structure, were made
with the ORTEP 3 for windows program [31] and are
presented in Figs. 1, 2, 3 and 4, with the ellipsoid drawn at
the 50 % of probability. The unit cells, were plotted using
Mercury program [32]. The molecules in the unit cell of
compounds 1 to 3 show no classic hydrogen bonds and they
are linked via C–HÁÁÁO hydrogen bonds, while the mole-
cules of compound 4 presents one classic hydrogen bond,
but is also linked through C–HÁÁÁO bonds.
this way, the absolute structure of each compound is
established with the help of PLATON [30] as: C(3): S,
C(8): S, C(9): S, C(10): R, C(13): S, C(14): S. C(16): S,
C(17): R, C(20): S, C(22): R and C(25): R; for (1), while
for (2) every center have the same configuration but C(22):
S, on the other hand, differences arise in lateral chain, due
to the presence of the hydroxyl in C(23), R; for (3) and
C(23): S, for (4).
123

194
J Chem Crystallogr (2013) 43:187–196
Table 4 Relevant torsion angles for rings E and F of compounds 1–4
1
2
3
4
C(16)–C(17)–C(20)–C(21)
C(16)–C(17)–C(20)–C(22)
C(17)–C(20)–C(22)–O(4)
C(17)–C(20)–C(22)–C(23)
C(17)–C(16)–O(3)–C(22)
C(17)–C(20)–C(22)–O(3)
C(20)–C(22)–C(23)–C(24)
C(20)–C(22)–O(3)–C(16)
C(20)–C(22)–O(4)–C(26)
C(21)–C(20)–C(22)–O(3)
C(21)–C(20)–C(22)–O(4)
C(21)–C(20)–C(22)–C(23)
C(22)–C(23)–C(24)–C(25)
C(23)–C(24)–C(25)–C(26)
C(23)–C(24)–C(25)–C(27)
C(23)–C(22)–O(4)–C(26)
C(23)–C(22)–O(3)–C(16)
C(24)–C(25)–C(26)–O(4)
C(25)–C(26)–O(4)–C(22)
C(27)–C(25)–C(26)–O(4)
O(4)–C(22)–O(3)–C(16)
O(3)–C(16)–C(17)–C(20)
O(3)–C(22)–O(4)–C(26)
O(3)–C(22)–C(23)–C(24)
O(4)–C(22)–C(23)–C(24)
O(3)–C(22)–C(23)–O(5)
O(4)–C(22)–C(23)–O(5)
C(20)–C(22)–C(23)–O(5)
O(5)–C(23)–C(24)–C(25)
123.22(11)
-2.30(12)
95.64(10)
123.29(15)
-2.10(18)
99.29(16)
124.37(16)
-1.54(19)
97.02(17)
145.17(17)
19.70(18)
80.61(18)
-155.52(16)
-27.76(18)
-37.32(18)
-179.50(16)
41.15(18)
-171.78(16)
-163.05(17)
-45.1(2)
-140.55(10)
-40.09(11)
-21.41(12)
-175.98(11)
38.85(11)
-139.63(15)
-38.33(16)
-21.10(18)
-179.24(16)
37.66(17)
-173.78(15)
-146.01(16)
-25.6(2)
-136.24(18)
-38.64(17)
-21.31(19)
-179.04(18)
37.96(18)
-174.90(15)
-146.14(17)
-27.8(2)
-176.62(10)
-146.33(10)
-29.28(14)
94.52(13)
95.5(2)
98.9(2)
78.8(2)
52.49(15)
52.2(2)
53.2(3)
54.4(2)
-52.85(15)
-175.82(12)
57.57(13)
-49.7(2)
-54.2(2)
-52.9(2)
-172.82(18)
60.55(18)
161.23(14)
55.88(19)
-63.71(18)
179.69(16)
-82.55(16)
23.76(15)
-55.65(19)
62.3(2)
-176.33(19)
56.4(2)
-175.30(18)
60.3(2)
161.66(9)
160.19(14)
57.0(2)
165.59(14)
55.6(2)
57.06(14)
-60.48(13)
178.84(11)
-77.07(11)
24.80(11)
-58.86(19)
179.40(16)
-79.40(17)
23.42(18)
-59.4(2)
-61.0(2)
179.47(17)
-74.48(18)
3.44(17)
-62.32(12)
66.71(13)
-58.0(2)
65.3(2)
63.75(19)
-56.8(2)
-53.76(14)
-56.3(2)
-53.9(3)
-121.6(2)
119.8(2)
-172.46(16)
68.3(2)
-61.2(2)
178.18(16)
55.5(2)
-3.1(3)
-56.8(2)
-123.8(2)
-67.4(3)
179.17(17)
˚
˚
The molecules in the unit cell of 1, 2 and 3, show no classic
hydrogen bonds and all are linked via short contacts at
C(18):2.623(4) A, O(2)ÁÁÁH–C(15):2.666(4) AandO(1)ÁÁÁH–
˚
C(19):2.73(4) A. A view of the cell packing of compound 4 is
shown in the bottom of Fig. 4.
˚
C–HÁÁÁO hydrogen bonds, in O(2)ÁÁÁH–C(29): 2.548(3) A,
˚
˚
O(3)ÁÁÁH–C(29): 2.775(4) A and O(4)ÁÁÁH–C(24):2.775(4) A
Puckering parameters for compounds 1, 2, 3 and 4 were
calculated as described by Cremer and Pople [33]. In all
cases the calculation starts from C(1) to C(10) and pro-
ceeding in a counterclockwise direction for ring A, C(5) to
C(10) and proceeds in a counterclockwise direction for ring
B, from C(8) to C(14) and proceeds in a clockwise direc-
tion for ring C, for Ring D the calculation starts from C(13)
to C(17) and proceeds in a clockwise direction, while Ring
E the calculation follow this order; O(3), C(22), C(20),
C(17), C(16). Finally in ring F starts from O(4) to C(26)
and proceeds in a clockwise direction.
˚
for compound 1. In O(2)ÁÁÁH–C(29): 2.545(2) A, O(5)ÁÁÁH–
˚
˚
C(17): 2.784(4) A, O(5)ÁÁÁH–C(21):2.523 (4) A and O(3)
˚
˚
ÁÁÁH–C(29):2.725(4) A for 2. In O(2)ÁÁÁH–C(29): 2.553(3) A,
˚
˚
O(3)ÁÁÁH–C(29): 2.733(2) A and O(5)ÁÁÁH–C(21):2.800 (4) A
for 3. The packing of the crystals in these compounds is
assumed to be dictated by van der Waals interactions and
intermolecular C–HÁÁÁO hydrogen bonds and differences
between the packing diagrams are due to the way the mole-
cules chain one to the other, inside the crystal. In the bottom of
Figs. 1, 2 and 3 the view of the cell packing of compounds 1, 2
and 3 are shown, were less symmetrical arrangement than in 4
canbeobserved. Toconclude, for4 thereare fourmoleculesin
the unit cell all linked by both classical and non-classical
Table 2 shows the puckering descriptors as defined by
Cremer and Pople [33] and calculated using the PLATON
program [30]. The minor differences observed amongst
rings A to C across all compounds may be attributed to the
˚
hydrogen bonds in In O(2)ÁÁÁH–O(5): 2.128(2) A, O(2)ÁÁÁH–
123

J Chem Crystallogr (2013) 43:187–196
195
support via Project IN221911-3 and CONACyT for the scholarship
Granted to A.R-A. Thanks are due to Georgina Duarte Lisci and
different intermolecular interactions that are, of course,
influenced by the changes introduced in the side chain.
On the other hand, when rings D and E are compared, it
is clear, as expected, that the modifications introduced in
the side chain produce some interesting conformational
changes in the steroid framework. These changes consid-
erably differentiate compounds 1, 2 and 3 from 4.
When ring D is compared, a change from the twisted on
C(13)–C(14) conformation on 1, 2 and 3 to envelope on
C(14) on 4 is observed, something equivalent occurs when
comparing ring E, where there are conformation changes
from envelope O(3)-exo for 1, 2 and 3 to envelope C(22)
endo for 4, making the overlay of ring F of compound
between these rings very bad and also indicating important
conformational changes associated to the conversion.
In order to assess quantitative differences among all the
compounds, a least-squares overlay analysis is performed
(1 vs. 2, 1 vs. 3 and 1 vs. 4). Table 3 shows the results of
least-squares overlay analysis obtained with Mercury pro-
gram [32].
´
Margarita Guzman Villanueva (USAI-UNAM) for registering Mass
spectra. We want to express our gratitude to Dr. Carlos Cobas from
MestrelabÒ for assistance with the MestreNova NMR processing
program.
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