Synthesis of new di- and triamine diosgenin dimers

Article abstract of DOI:10.1016/j.tet.2009.11.037

In this study, a high yield synthesis of symmetrical steroidal polyamine dimers was achieved by the dimerization of (25R)-3β-acetoxyfurost-5-en-26-al via several di- and triamine linkers under mild conditions. To ensure the dimerization via E-E ring, the hydroxyl group in diosgenin was protected by an acetyl group. The important step is opening the spiroketal moiety using NaCNBH₃/AcOH to furnish the primary alcohol at C-26, followed by oxidation using PCC/CH₂Cl₂ to synthesize the desired aldehyde. Finally, reductive amination with diaminopropane, diaminobutane, diaminohexane, and spermidine using Na(OAc)₃BH as reducing agent, afforded the required four dimers.

Full text of DOI:10.1016/j.tet.2009.11.037

Tetrahedron 66 (2010) 1420–1423
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of new di- and triamine diosgenin dimers
*
Khaled Q. Shawakfeh , Naim H. Al-Said, Eman K. Abboushi
Department of Applied Chemical Sciences, Jordan University of Science and Technology, PO Box 3030, Irbid 22110, Jordan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 June 2009
Received in revised form 20 October 2009
Accepted 5 November 2009
Available online 10 November 2009
In this study, a high yield synthesis of symmetrical steroidal polyamine dimers was achieved by the
dimerization of (25R)-3b-acetoxyfurost-5-en-26-al via several di- and triamine linkers under mild
conditions. To ensure the dimerization via E-E ring, the hydroxyl group in diosgenin was protected by an
acetyl group. The important step is opening the spiroketal moiety using NaCNBH3/AcOH to furnish the
primary alcohol at C-26, followed by oxidation using PCC/CH2Cl2 to synthesize the desired aldehyde.
Finally, reductive amination with diaminopropane, diaminobutane, diaminohexane, and spermidine
using Na(OAc)3BH as reducing agent, afforded the required four dimers.
Keywords:
Dimer
Ó 2009 Published by Elsevier Ltd.
Aldehyde
Diamine
Reductive
Amination
Spacer
1. Introduction
human sex hormones and can be used for developing muscle mass
and strength.7
Most DNA-major and minor groove binding molecules possess
cationic functional groups, size and shape complementarities to
one of the grooves, an aromatic ring system, or combination of
these. Steroidal diamines are cationic molecules that have a typical
small size aliphatic moiety.1 The cation type, regiochemical distri-
bution of the ammonium groups, and steroid hydrophobicity may
also contribute to the strength and type of steroid–DNA in-
teractions.2 The binding of spermine and spermidine to DNA is
preferentially to the GC-rich major groove and to the AT-rich minor
groove regions,3,4 while hydrophobicity of the steroid surface is
important for minor groove recognition and binding. DNA con-
densation is dependent upon hydrophobicity and distance between
positive charges, as well as the total number of charges.5 The in-
teraction between DNA and steroidal di- or polyamine leads to
increase in DNA stability, DNA/RNA discrimination and sequence-
selectivity.6 One of the major sources of steroidal intermediates for
the synthesis of steroid hormones and pharmaceutical analogues is
Diosgenin that has been reported to have tremendous medical
applications. Recently, it has been used to minimize post-meno-
pausal symptoms and has been processed and given to patients to
relieve arthritis, asthma, eczema, regulate metabolism, and control
fertility. It also provides the steroid building blocks for developing
In searching for dimeric steroids using diosgenin, few examples
were found. The first one is the dimer that was synthesized as
a component of artificial lipid bilayer membranes to control their
fluidity, and to increase the membranes stability and life time
leading to improve their quality by working as a bilayer binder.8
The dimer was synthesized from diosgenin in 4 steps and 16%
overall yield.9 Moreover, we successfully achieved synthesis of bis-
diosgenin pyrazine dimers that represent examples of new ceph-
alostatin analogs.10 This inspired us to synthesize new dimeric
steroids from diosgenin with diamine and triamine as linkers to
improve the biological action of these dimers compared with
others, which have carbon chains as linkers. These dimers were
expected to mimic nature or form a bimolecular sheet for appli-
cation in the fields of biomimetic and molecular recognition
chemistry. In addition, it is expected that their interaction ability
with DNA will lead to increase in DNA stability, sequence-selec-
tivity, DNA/RNA discrimination, and hypochromicity of oligonu-
cleotide duplex.
2. Results and discussions
In the present research, we present the synthesis of four dimeric
steroids as di- or tri-amino diosgenin dimers. The desired dimers
consist of di- or triamine binding two steroid nucleuses via E-E ring
linkage type. The dimerization step was achieved through re-
ductive amination reaction between di- or triamine and aldehyde
functionality at the steroid E-ring. This functionality obtained from
* Corresponding author. Tel.: þ962 795886160.
E-mail address: shawakfa@just.edu.jo (K.Q. Shawakfeh).
0040-4020/$ – see front matter Ó 2009 Published by Elsevier Ltd.
doi:10.1016/j.tet.2009.11.037

K.Q. Shawakfeh et al. / Tetrahedron 66 (2010) 1420–1423
1421
the oxidation of the hydroxyl group on C-26, which was the product
of an F-ring opening reaction of diosgenin acetate 2. The diosgenin
acetate 2 was prepared via esterification reaction of the hydroxyl
group at C-3 of diosgenin 1 (Scheme 1). The hydroxyl group in
diosgenin 1 was reacted with Ac2O to furnish in high yield dio-
sgenin acetate 2.11 The choice for this group depends on the fact
that this group is easy to be removed, and it would not be affected
by the chemical transformation in the following steps. The 1H NMR
spectrum confirmed the presence of the acetoxy group at C-3.
showed a peak at 3.3 ppm (m) for the C-22 proton, which con-
firmed F-ring opening. In the 13C NMR spectrum, the disappearance
of the peak at 109.3 ppm and the appearance of a peak at 90.3 ppm
for C-22, further confirmed the fission of the spiroketal moiety.
These data were in excellent agreement with the literature values.11
The next step was to produce the aldehyde functionality from
the alcohol 3. Several oxidizing agents could accomplish this goal.
However, the most common one is PCC/CH2Cl2 in the presence of
CaCO3, where CaCO3 was added to moderate the acidic character of
PCC. This reagent oxidized the primary alcohol without affecting
the acetate group, and it gave compound 4 with an excellent yield.
The disappearance of the alcohol peak at 3487 cmꢀ1 and the ap-
pearance of two peaks for the C-H of the aldehyde functionality,
and a peak at 1760 cmꢀ1 for C]O stretching. The elemental analysis
and the mass (ESI) data were in excellent agreement with the
proposed structure for compound 4.
O
O
H
H
O
H
O
H
H
H
a
H
H
H
H
95%
HO
AcO
2
1
83%
b
The final step is the dimerization of the steroidal aldehyde 4
with di- and triamine. This step was achieved using nucleophilic
addition of amine followed by reduction of the imine with NaB-
H(OAc)3 under N2 gas in dichloroethane (DCE).15,16,17
H
O
H
O
H
H
O
OH
H
H
c
H
H
H
H
H
H
H
Having the aldehyde 4 in hand, the first dimer 5 was prepared
from reductive amination of aldehyde 4 with 1,3-diaminopropane
(Scheme 2). The 1H NMR spectrum showed the presence of peaks at
2.3–2.6 ppm (m) for the 1,3-diaminopropane methylenes protons
that are next to nitrogen and for C-26 protons, in addition, the
disappearance of the aldehyde proton at 9.7 ppm confirmed the
structure of dimer 5. In the 13C NMR spectrum, the disappearance of
the aldehyde peak at 205.3 ppm, and the appearance of a peak at
50.0 ppm for the C–N carbon, also gives a good indication of the
structure. The ESI-MS spectrum of dimer 5 showed a molecular ion
peak (MþH) at m/z 955.9, which also confirmed the structure of
dimer 5. The elemental analysis data were in good agreement with
the above results and also proved the proposed structure of 5.
In order to have several dimers with different length spacers to
study the structure–activity relationship, two dimers 6 and 7 were
prepared in good yields by reductive amination of aldehyde 4 with
1,4-diaminobutane (putrescine) and 1,6-diaminohexane, re-
spectively (Scheme 2).
60%
AcO
AcO
3
4
Reagents and Conditions: a: Ac2O, E3N, DMAP, CH2Cl2, 24 h. b: NaBH3CN,
AcOH, 48 h. c: PCC, CaCO3, Silica, CH2Cl2, 12h.
Scheme 1. Synthesis of (25R)-3b-acetoxyfurost-5-en-26-al (4).
Next, F-ring opening in diosgenin acetate 2 produced the re-
quired hyroxylated steroid. Several reagents have been reported to
open the F-ring where Ac2O/BF312 and ZnCl2/Ac2O13 favored E-ring
cleavage and Zn/HCl, which gave a triol product.14 Moreover,
LiAlH4/AlCl3 reductively opened the F-ring with loss of the pro-
tecting group at the A-ring to furnish a triol derivative.9 Our
objective was to have only one hydroxyl group at the alkyl chain
without opening the E-ring, and without losing the acetate pro-
tecting group. This objective was achieved by implementing the
methodology reported by Winterfeldt.11 Therefore, selective F-ring
opening was conducted using NaBH3CN in acetic acid to furnish 3 in
good yield after chromatographic separation.
The FTIR for dimer 6 showed a peak at 3300 cmꢀ1 for the amino
groups, while the 1H NMR spectrum exhibited peaks at 2.3–
2.8 ppm for the 1,4-diaminobutane methylenes protons that are
The FTIR spectrum of compound 3 showed a broad peak at
3487 cmꢀ1 characteristic of an alcohol group. The 1H NMR spectra
H
H
N
H
N (CH2)n
H
O
H
O
H
H
5: n = 3, 71%
6: n = 4, 59%
7: n = 6, 86%
H
H
H
H
H
AcO
OAc
a: 59-86%
4
b: 86%
H
H
N
H
N
H
N
H
O
H
O
H
H
H
H
H
H
H
8
OAc
AcO
Reagents and Conditions: a: 1) 1 equiv of 4 in DCE, AcOH, 1 equiv. of diamine;
2) AcOH, NaBH(OAc)3, 4 days. b: 1) 1 equiv of 4 in DCE, AcOH, 0.5 equiv. of spermidine;
2) AcOH, NaBH(OAc)3, 4 days.
Scheme 2. Synthesis of dimers 5, 6, 7 and 8.

1422
K.Q. Shawakfeh et al. / Tetrahedron 66 (2010) 1420–1423
next to nitrogen, and for the C-26 protons. The ESI-MS spectrum,
showed a molecular ion peak (MþH) at m/z 972.1, which proved the
molecular weight for dimer 6. Dimer 7 showed no differences in its
FTIR spectrum from that of dimer 6, however, the 1H NMR spectrum
showed peaks at 2.3–2.7 ppm for the 1,6-diaminohexane methy-
lene protons that are next to nitrogen and for the C-26 protons. In
addition, the ESI-MS spectrum, showed a molecular ion peak
(MþH) at m/z 999.3, which confirmed the presence of dimer 7.
Polyamines such as spermidine is widely distributed in nature
and display a variety of important biological activities such as
protecting DNA against thermal or X-ray induced denaturation,
methylation, enzymatic degradation, breakage, and radiation
damage.18 Therefore, we reductively aminated the aldehyde 4 with
spermidine and synthesized dimer 8 in 86% yield. The 1H NMR
spectrum of dimer 8 exhibited peaks at 2.3–3.1 ppm for the 1,8-
diamino-4-azaoctane methylenes protons that are next to nitro-
gen and for the C-26 protons. In the ESI-MS spectrum, the
molecular ion peak appear at m/z 1026.7, which confirmed the
presence of dimer 8.
2.0 mL of glacial AcOH was added, and the mixture was stirred
under nitrogen at room temperature for 1 h. 1,3-Diaminopropane
(0.078 g, 1.05 mmol) was added and stirred under nitrogen at room
temperature for 48 h. Na(OAc)3BH (0.28 g, 1.3 mmol), then glacial
AcOH (0.5 mL) were added and the reaction mixture was stirred
under nitrogen for 48 h. The reaction was neutralized with 1 N
NaOH and the product was extracted with CHCl3 (2ꢂ20.0 mL). The
organic layer was washed twice with brine (20 mL), dried over
anhydrous Na2SO4, and filtered. The solvent was removed under
vacuum to yield a yellow oil, which was washed with ether then
evaporating under vacuum, to give yellow solid, the solid was pu-
rified by preparative TLC (5% ammonia solution/ethanol) to furnish
5 (pale yellow solid, 0.48 g, 71%); mp 71–74 ꢁC. FTIR (KBr), nmax
3459, 2956, 2334, 1734, 1561, 1450, 1377, 1252, 1040 cmꢀ1. 1H NMR
(CDCl3, 400 MHz) selected signals d: 2.0 (s, 3H, AcO), 2.3–2.6 (m, 4H,
methylenes next to nitrogen), 3.3 (m, 1H, C-22), 4.3 (m, 1H, C-16),
4.6 (m, 1H, C-3), 5.4 (d, J¼4.5 Hz, 1H, C-6). 13C NMR (CDCl3,
100 MHz) selected signals d: 21.5 (CH3COO), 50.0 (C–N), 73.9 (C-3),
83.2 (C-16), 90.5 (C-22), 122.4 (C-6), 139.7 (C-5), 170.6 (CH3COO).
M.wt calcd for C61H98N2O6: 955.4 g/mol. Found MS (ESI), m/z (rel-
ative intensity): 955.9 (Mþ, 39), 557.5 (C35O3N2H5þ9,100). Anal. Calcd
for C61H98N2O6: C, 76.68; H, 10.34; N, 2.93. Found: C, 75.48; H, 9.71;
N, 3.38.
3. Conclusion
In order to mimic a bimolecular sheet for application in the
fields of biomimetic and molecular recognition chemistry, four new
symmetrical steroidal polyamine dimers were designed and syn-
thesized. These dimers were achieved by the dimerization of (25R)-
4.2.2. Synthesis of 1,4-bis((22b,25R)-3b-acetoxyfurost-5-en-26-amino)-
butane, 6. Pure dimer 6 (pale yellow solid, 0.40 g, 59%) was pre-
pared utilizing the general procedure, through the reaction of 4
(0.3 g, 0.7 mmol), 1,4-diaminobutane (0.09 g, 1.05 mmol) and
Na(OAc)3BH (0.28 g, 1.3 mmol); mp 95–98 ꢁC (Decomposition).
3b-acetoxyfurost-5-en-26-al via four di- and triamine linkers under
mild conditions and in relatively high yield.
4. Experimental
FTIR (KBr) nmax
:
3377, 2943, 2358, 1662, 1598, 1449, 1235,
: 2.0 (s, 3H, AcO), 2.3–
1053 cmꢀ1. 1H NMR (ppm) selected signals
d
4.1. General remarks
2.9 (m, 4H, methylenes next to nitrogen), 3.3 (m, 1H, C-22), 4.3 (m,
1H, C-16), 4.6 (m, 1H, C-3), 5.4 (br s, 1H, C-6). 13C NMR (ppm) se-
Melting points (mp) were determined on electrothermal digital
melting point apparatus. Materials and reagents were obtained
from commercial sources and were used without further purifica-
tion. FTIR spectra were recorded on a Nicolet-Impact 410 spectro-
photometer. Both 1H and 13C NMR spectra were recorded on Bruker
lected signals d: 21.3 (CH3COO), 50.0 (C–N), 73.8 (C-3), 83.3 (C-16),
90.2 (C-22), 122.1 (C-6), 139.7 (C-5), 170.5 (CH3COO). M.wt calcd for
C62H100N2O6: 968.8 g/mol. Found MS (ESI), m/z (relative intensity):
972.1 (Mþþ2, 100), 660.9 (81), 611.9 (C39H68N2Oþ3 , 33).
DPX-400 instruments. The chemical shifts (
d
) are reported in parts
4.2.3. Synthesis of 1,6-bis((22b,25R)-3b-acetoxyfurost-5-en-26-amino)-
per million relative to TMS used as an internal standard. Mass
spectra (MS) were obtained from a LC-MSD-Trap_00125 spec-
trometer with ESI ion source type. Reactions were monitored by
thin layer chromatography (Silica gel 60 F254). Solvents were
purified according to the standard.
hexane, 7. Pure dimer 7 (pale yellow solid, 0.60 g, 86%) was pre-
pared utilizing the general procedure, through the reaction of 4
(0.3 g, 0.7 mmol), 1,6-diaminohexane (0.12 g, 1.05 mmol) and
Na(OAc)3BH (0.28 g, 1.3 mmol); mp 67 ꢁC (Decomposition). FTIR
(KBr), nmax 3467, 2942, 2367, 1747, 1572, 1424, 1243, 1024 cmꢀ1. 1H
NMR (CDCl3, 400 MHz) selected signals d: 2.0(s, 3H, AcO), 2.2–2.7
4.1.1. Synthesis of (22
b
,25R)-3
b
-acetoxyfurost-5-en-26-al, 4. PCC
(m, 4H, methylenes next to nitrogen), 3.3 (m, 1H, C-22), 4.3 (dt,
(0.7 g, 3.0 mmol) was added to a mixture of powdered CaCO3 (1.3 g,
3.0 mmol), silica (1.0 g), and 3 (2.5 g, 5.5 mmol) in CH2Cl2 (50.0 mL)
at room temperature. The reaction mixture was stirred for 12 h at
room temperature. Then, the reaction mixture was diluted with
diethyl ether (50.0 mL) and poured through a short column of
Florisil. The solvent was removed under vacuum. Then the residue
was purified by column chromatography (10% ethyl acetate/hex-
ane) to give pure product 4 (white solid,1.5 g, 60%); mp 122–125 ꢁC.
FTIR (KBr), nmax 2947, 2893, 2832, 2717,1736,1534,1463,1380,1243,
J¼13.0, 7.5 Hz, 1H, C-16), 4.6 (m, 1H, C-3), 5.3 (d, J¼4.3 Hz, 1H, C-6).
13C NMR (CDCl3, 100 MHz) selected signals
d: 21.4(CH3COO), 50.0
(C–N), 73.8 (C-3), 83.1 (C-16), 90.4 (C-22), 122.3 (C-6), 139.6 (C-5),
170.5 (CH3COO). M.wt calcd for C64H104N2O6: 997.5 g/mol. Found
MS, m/z (relative intensity): 999.3 (Mþþ1, 32). Anal. Calcd for
C64H104N2O6: C, 77.06; H, 10.51; N, 2.81. Found: C, 76.70; H, 10.09;
N, 2.49.
4.2.4. Synthesisof 1,8-bis((22b,25R)-3b-acetoxyfurost-5-en-26-amino)-
1035 cmꢀ1. 1H NMR (CDCl3, 400 MHz) selected signals
d: 2.0 (s, 3H,
4-azaoctane, 8. Pure dimer 8 (pale yellow solid, 0.62 g, 86%) was
prepared utilizing the general procedure, through the reaction of 4
(0.3 g, 0.7 mmol), 1,8-diamino-4-azaoctane (0.15 g, 1.05 mmol) and
Na(OAc)3BH (0.28 g, 1.3 mmol); mp 227–230 ꢁC (Decomposition).
AcO), 3.3 (m, 1H, C-22), 4.3 (m, 1H, C-16), 4.6 (m, 1H, C-3), 5.3 (d,
J¼5.3 Hz, 1H, C-6), 9.7 (d, J¼2.0 Hz, 1H, C-26). 13C NMR (CDCl3,
100 MHz) selected signals d: 21.4 (CH3COO), 73.9 (C-3), 83.3 (C-16),
89.7 (C-22), 122.4 (C-6), 139.7 (C-5), 170.6 (CH3COO), 205.3 (C-26).
Anal. Calcd for C29H44O4: C, 76.27; H, 9.71. Found: C, 75.89; H, 9.53.
FTIR (KBr), nmax 3480, 2954, 2356, 1737, 1574, 1444, 1248, 1139 cmꢀ1
.
1H NMR (CDCl3, 400 MHz) selected signals
d: 2.0 (s, 3H, AcO), 2.3–
3.0 (m, methylenes next to nitrogen), 3.3 (m, 1H, C-22), 4.3 (m, 1H,
4.2. General procedure for the dimerization step
C-16), 4.6 (m, 1H, C-3), 5.4 (d, J¼4.5 Hz, 1H, C-6). 13C NMR (CDCl3,
100 MHz) selected signals d: 21.6 (CH3COO), 50.3 (C–N), 74.4 (C-3),
4.2.1. Synthesis of 1,3-bis((22
propane, 5. To a solution of 4 (0.3 g, 0.7 mmol) in DCE (10.0 mL),
b
,25R)-3
b
-acetoxyfurost-5-en-26-amino)-
83.5 (C-16), 90.2 (C-22), 123.4 (C-6), 139.9 (C-5), 171.3 (CH3COO).
M.wt calcd for C65H107N3O6: 1026.6 g/mol. Found MS, m/z (relative

K.Q. Shawakfeh et al. / Tetrahedron 66 (2010) 1420–1423
1423
intensity): 1026.7 (Mþ, 19), 630.0 (C39H68N3Oþ3 , 64), 689.5
(C36H63N3Oþ3 , 100). Anal. Calcd for C65H107N3O6: C, 76.05; H, 10.51;
N, 4.09. Found: C, 76.37; H, 9.98; N, 3.91.
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