Acta Chim. Slov. 2002, 49, 805-813.
805
SYNTHESIS AND SELECTIVE CATALYTIC OXIDATION OF NEW DIMERIC
STEROIDS
Khaled Q. Shawakfeh, Ahmad M. Al-Ajlouni and Abdelatif Ibdah
Department of Applied Chemical Science, Jordan University of Science and Technology,
P. O. Box 3030, Irbid 22110, Jordan
Phone: 962-2-7201000; Fax: 962-2-7201014; E-mail: shawakfa@just.edu.jo
Received 03-04-2002
Abstract
New dimeric steroids were synthesized by reductive amination of the aldehyde of 3-oxopregn-4-ene-20ß-carboxaldehyde and the ketone of stigmasterol and cholesterol, with 1,3-diaminopropane, 1,4-diaminobutane and 1,6-diaminohexane using sodium triacetoxyborohydride. The catalytic oxidation of the double bond in these dimeric steroids by CH3ReO3/H2O2 system was carried out. In the case of stigmasterol dimer 6, only the internal double bond was oxidized.
Introduction
Dimeric and oligomeric steroids posses interesting micellular, detergent, and
liquid crystal properties.1 Steroidal dimers have been used as catalysts for different types of reactions and many lead to enhance pharmacological activity.2,3 For example, the dimeric steroids cephalostatins are among the most potent natural cytotoxins.4 This exceptional activity of cephalostatins spurred the interest in their synthesis as well as for their analogues as potential anti-tumor agents.5 It has been suggested that polyamine dimeric steroid binds to DNA due to the presence of two parts, one hydrophilic (positively charged nitrogen) and the other is hydrophobic steroid skeleton.6
The dimeric steroidal alkaloids ritterazines are closely related to cephalostatin.7 Seketsu and co-workers7 have examined the cytotoxicity of ritterazines (A-D) derivatives. Their studies showed that ritterazine A which contains the highest number of hydroxyl groups (five hydroxyl group) is the most potent. The activity decreases with decreasing the number of hydroxyl groups. The study showed that the presence of hydroxyl groups is important for the enhancement of the biological activity.8
Here we are presenting new dimeric steroids that were prepared by reductive amination using alkyl diamines and selective reducing agent. The oxidation of some of these dimers was carried out by catalytic system (MTO/ H2O2) 9-12 that led finally to the 1,2-diol products.
K. Q. Shawakfeh, A. M. Al-Ajlouni, A. Ibdah: Synthesis and selective catalytic oxidation of new…
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Results and Discussion
We   prepared   dimeric    steroids   using   3-oxopregn-4-ene-20ß-carboxaldehyde
(ketobisnoraldehde) (1) as starting material with 1,3-diaminopropane and 1,6-diaminohexane. Reductive amination of ketobisnoraldehyde (1) in the presence of 1,3-diaminopropane in dichoroethane (DCE) was carried out using NaBH(OAc)3 and gave the dimer 2 in 65% yield (Scheme 1). The choice of NaBH(OAc)3 as a reducing agent was crucial due to its selectivity in reducing imines intermediate.13 Following the same procedure, ketobisnoraldehyde dimer 3 was synthesized by reductive amination of ketobisnoraldehyde with 1,6-diaminohexane in 64% yield. The 1H-NMR data showed a singlet at 5.7 ppm characteristic for C4-H, and a multiplet at 2.3  and 2.6 ppm
characteristic for C22-H2 and C23-H2, respectively.
Scheme 1. Reductive amination of (1)
O
3:n=6
In order to study the structure activity relationships, new dimers were synthesized starting from cheap, readily available steroids such as stigmasterol and cholesterol. Starting from stigmasterol (4), and using a modified method of Parish,14 the desired ketone 5 was obtained in 82 % yield. Reductive amination of ketone 5 in the presence of 1,3-diaminopropane or 1,6-diaminohexane in DCE using NaBH(OAc)3, gave the dimers 6 and 7 in 60% and 53% yield, respectively (Scheme 2). The 1H-NMR data for compounds 6 and 7 showed a singlet at 5.3 ppm characteristics for the hydrogen on C6, and a multiplet at 4.9-5.1 ppm characteristic for C22-H and C23-H. In addition, a triplet at 2.7 ppm indicates the presence of a methylene unit attached to NH (C30). The 13C-NMR data proved the disappearance of the carbonyl peak and the presence of an sp3 carbon attached to NH (C3) at 54 ppm.
K. Q. Shawakfeh, A. M. Al-Ajlouni, A. Ibdah: Synthesis and selective catalytic oxidation of new…
Acta Chim. Slov. 2002, 49, 805-813.
807
Scheme 2. Synthesis of Dimers 6 , 7 from Stigmasterol
HO
O
Stigmasterol (4)
//,,
f^\
'NH(CH2)nHN
6 : n = 3
7 : n = 6
i) PCC, CaC03, CH2CI2 ; ii) H2N(CH2)nNH2, NaBH(OAc)3, DCE, AcOH
Starting from cholesterol 8, and using the same oxidation method, the desired product ß,?-unsaturated ketone 9 was obtained in 89 % yield.14 Reductive amination of the ketone 9 with 1,3-diaminopropane, 1,4-diaminobutane and 1,6-diaminohexane in DCE using NaBH(OAc)3, gave the dimers 10, 11 and 12 in 60% yield, (Scheme 3). The 1H-NMR data for compounds 10, 11 and 12 showed a singlet at 5.3ppm characteristics for the hydrogen on C6-H, and a multiplet at 3.2-2.7 ppm characteristics for the hydrogen on C3-H. The 13C-NMR spectral data were also in good agreements with their chemical shift regions.15-17
The conversion of the olefinic bond of some of these new steroidal diamine dimers was carried out by oxidation with H2O2/CH3ReO3 (MTO) followed by hydration to trans-1,2-diols which is expected to be biologically active polyoxygenated steroids.18
5
ii
K. Q. Shawakfeh, A. M. Al-Ajlouni, A. Ibdah: Synthesis and selective catalytic oxidation of new…
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Acta Chim. Slov. 2002, 49, 805-813.
Scheme 3. Synthesis of Dimers 10 , 11 and 12 from Cholesterol
HO
Cholesterol 8
/
O'
NH(CH2)nHN
10 11
n = 3 n = 4
12 : n = 6 i) PCC,  CaC03, CH2CI2 ; ii) H2N(CH2)nNH2, NaBH(OAc)3, DCE, AcOH
The double bond of cholesterol dimer 11 was oxidized by H2O2/MTO to diol 13 in 60% yield ( (Scheme 4). The 1H-NMR spectral data indicate the presence of a broad peak at 3.4ppm charectaristic for C6-H.19The double bond protons of 11 at 5.3 ppm disappeared indicating total conversion.
Under the same conditions used for cholesterol dimer 13, the stigmasterol dimer 6 was epoxidized and the dimer 14 was produced in 67% yield (Scheme 5). Only the internal double bond (C5-C6) was oxidized. The 1H-NMR spectrum showed a multiplet at 5.2-4.9 ppm characteristics of C22-H and C23-H, and triplet at 3.4ppm characteristic for C6-H. The 13C-NMR spectrum showed only two olefinic carbons at 129.5 and 137.8 ppm characteristic for C-23 and C-22, respectively. In addition, two peaks at 76 and 67.6 ppm characteristic for C-6 and C-5 that have the hydroxyl groups.
Conclusions
New dimeric steroids were synthesized starting from cheap and available steroids
such   as   3-oxopregn-4-ene-20ß-carboxaldehyde,   cholesterol   and   stigmasterol   by reductively amination in the presence of 1,3-diaminopropane, 1,4-diaminobutane and
9
K. Q. Shawakfeh, A. M. Al-Ajlouni, A. Ibdah: Synthesis and selective catalytic oxidation of new…
Acta Chim. Slov. 2002, 49, 805-813.
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1,6-diaminohexane using sodium triacetoxyborohydride. The catalytic oxidation using CH3ReO3/H2O2 of stigmasterone dimer was selectively epoxidized on the internal double bond. The final products were characterized as the 1,2-diols.
Scheme 4. Synthesis of Hydroxylated Steroid Dimer 13
^
OH
OH
"NH(CH2)4H
11
CH3ReO3 / H2O2 HClO4 , THF
NH(CH2)4HN' 13
OH
Scheme 5. Synthesis of Hydroxylated Steroid Dimer 14
^
-s/
-^\t
OH
OH
"NH(CH2)3H 6
^
CH3ReO3 / H2O2 HClO4 , THF
NH(CH2)3HN' 14
OH
Y
K. Q. Shawakfeh, A. M. Al-Ajlouni, A. Ibdah: Synthesis and selective catalytic oxidation of new…
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Acta Chim. Slov. 2002, 49, 805-813.
Experimental General
Melting points were determined on a Thomas-Hoover capillary melting point
apparatus and are uncorrected. IR spectra were recorded on a Nicolet-Impact 410 FT-IR spectrometer. 1H-NMR and 13C-NMR spectra were recorded using a 200 MHz or 300 MHz Brucker. Spectra were recorded in deuteriochloroform CDCl3 with chemical shift values in ppm relative to the solvent peak (7.26 ppm). All reductive amination reactions were carried out under nitrogen atmosphere. Cholesterol (95% from Acros) was recrystallized from acetone before use. The following chemicals were used as received: Stigmasterol (Aldrich), ketobisnoraldehyde (donated from Temple University).
General Procedure for Reductive Amination of Ketobisnoaldehyde with Diamines:
To a solution of ketobisnoaldehyde (350 mg, 1 mmol) in DCE (20 ml) diamines (1 mmol) was added, the mixture was stirred at r.t. under nitrogen for 24 hrs. Sodium triacetoxyborohydride (430 mg, 2 mmol) and glacial acetic acid (0.5 ml) was added. The reaction mixture was stirred for 72 hrs. The reaction was neutralized with 1N NaOH and the product was extracted with chloroform (4x40 ml). The organic layer was washed twice with brine (25 ml), dried over MgSO4, and filtered. The solvent was evaporated under vacuum to give a pale yellow solid that was recrystalized from EtOH.
Product 2 ( Diamine is 1,3-diaminopropane): Yield = 65%. M.p = 140-142 oC. IR (KBr): ? 3455, 2945, 1667 cm-1. 1H NMR: ? 5.7 (brs, 1H, C4), 2.3 (m, 2H, C22), 2.6 (m, 2H, C23), 1.21 (s, 3H, C19), 0.85 (s, 3H, C18). 13C-NMR: ? 199.4 (C3), 170.9 (C5), 123.8 (C4), 56.04 (C14), 55.8 (C17), 53.75 (C22), 39.35 (C23), 17.1 (C19), 12.1 (C18). Anal. calc. for: C47H74N2O2: C, 80.75; H, 10.67; N, 4.01. Found: C, 80.45; H, 10.47; N, 3.94.
Product 3 ( Diamine is 1,6-diaminohexane): Yield =64%. M.p = 175-176 oC. IR (KBr): ? 3414, 2940, 1673. 1H NMR: ? 5.7 (brs, 1H, C4), 2.8-3.0 (m, 4H, C22, C23), 2.5-2.7 (m, 2H, C2), 1.26 (s, 3H, C19), 0.85 (s, 3H, C18). 13C-NMR: ? 199 (C3), 170 (C5), 123 (C6), 54.5 (C22), 39 (C23), 17.8 (C19), 12.5 (C18). Anal. calc. for: C50H80N2O2: C, 81.02; H, 10.88; N, 3.78. Found: C, 80.56; H, 10.70; N, 3.68.
K. Q. Shawakfeh, A. M. Al-Ajlouni, A. Ibdah: Synthesis and selective catalytic oxidation of new…
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General Procedure for Reductive Amination of Ketone 5 with Diamines:
To a solution of 5 (410 mg, 1.0 mmol) in DCE (40 ml) was added diamines(1.0 mmol) and NaBH(OAc)3 (850 mg, 4.0 mmol) at r.t.. The mixture was stirred under argon for 48 hrs, then glacial acetic acid (1.0 ml) was added and the mixture stirred for 88 hrs. Work up procedure similar to 2 afforded a solid which was recrystalized from EtOH.
Product 6 ( Diamine is 1,3-diaminopropane): Yield = 60%. M.p = 170-172 C°; IR (KBr): ? 3450, 2956 cm-1. 1H NMR: ? 5.25 (brs, 1H, C6), 4.9-5.1(m, 2H, C22, C23), 3.1(b, 1H, C3), 2.6-2.9 (m, 2H, C30), 1.01 (s, 3H, C19), 0.82 (s, 3H, C18); 13C-NMR:? 146 (C5), 125 (C6), 138 (C22), 129 (C23), 56.0 (C14), 55.8 (C17), 54.5 (C3), 39.67 (C30), 19.1 (C19), 12.4 (C18). Anal. calc. for: C61H102N2: C, 84.85; H, 11.91; N, 3.24. Found: C, 84.78; H, 11.86; N, 3.21.
Product 7(Diamine is 1,6-diaminohexane): Yield = 53%. M.p = 120-123 oC; IR (KBr):? 3459, 2940 cm-1. 1H NMR: ? 5.3 (brs, 1H, C6), 4.9-5.1 (m, 2H, C22, C23), 2.6-2.9 (m, 2H, C30), 1.06 (s, 3H, C19), 0.77 (s, 3H, C18). 13C-NMR: ? 147 (C5), 123 (C6), 138 (C22), 129 (C23), 54.6 (C3), 39.3 (C30), 19.3 (C19), 12.1 (C18). Anal. Calcd. For: C64H108N2: C, 84.89; H, 12.02; N, 3.09. Found: C, 84.48; H, 11.96; N, 3.00.
General Procedure for Reductive Amination of the Ketone 9 with Diamines: To a solution of 9 (380 mg, 1.0 mmol) in DCE (40 mL) was added diamines (1.35 mmol) and NaBH(OAc)3 (439 mg, 2.0 mmol) at r.t. The mixture was stirred under argon for 40 hrs, then glacial HOAc (1.0 ml) was added and the mixture stirred for 36 hrs. Work up procedure similar to 2 afforded a yellow solid which was washed with ether.
Product 10 ( Diamine is 1,3-diaminopropane): Yield = 60%. M.p.= 178- 180 oC; IR (KBr): ? 3450, 2970 cm-1. 1H NMR: ? 5.25 (brs, 1H, C6), 2.7-2.4 (b, 3H, C3, C28), 1.10 (s, 3H, C19), 0.70 (s, 3H, C18); .13C-NMR:? 150 (C5), 116 (C6), 55.9 (C14), 54.6 (C17), 54.1 (C3), 39.5 (C28), 18.8 (C19), 11.9 (C18). Anal. calc. for: C57H98N2 : C, 84.37; H, 12.17 ; N, 3.45. Found: C, 84.18; H, 11.96; N, 3.27.
K. Q. Shawakfeh, A. M. Al-Ajlouni, A. Ibdah: Synthesis and selective catalytic oxidation of new…
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Product 11 ( Diamine is 1,4-diaminobutane): Yield = 60%. M.p= 174 -176 °C; IR (KBr): v 3465, 2976 cm"1. 'H NMR: 5 5.3 (brs, 1H, C6), 3.2 (b, 1H, C3), 2.7-2.9 (b, 2H, C28), 1.12 (s, 3H, C19), 0.73 (s, 3H, C18); .13C-NMR: 5 148 (C5), 120 (C6), 54.3 (C3), 39.5 (C28), 18.6 (C19), 11.8 (C18). Anal. Calcd. For: C58HiooN2: C, 84.40; H, 12.21; N, 3.39. Found: C, 84; H, 12.16; N, 3.10.
Product 12 ( Diamine is 1,6-diaminohexane): Yield = 60%. M.p= 134 -136 °C; IR (KBr): v 3459, 2980 cm"1. 'H NMR: 5 5.4 (brs, 1H, C6), 3.1-2.7 (b, 3H, C3, C28), 1.11 (s, 3H, C19), 0.71 (s, 3H, C18); .13C-NMR: 5 152 (C5), 114 (C6), 55.9 (C14), 54.9 (C17), 54.1 (C3), 39.3 (C28), 19.0 (C19), 12.1 (C18). Anal. Calcd. For: C6oHio4N2: C, 84.44; H, 12.28; N, 3.29. Found: C, 84.25; H, 12.09; N, 3.21.
General Procedure for Epoxidation with MTO/H2O2:
To a mixture of MTO (10 mg, 0.04 mmol), lmL 30% H202 and lmL HC104 (1.0 M) in 15 mL THF, steroid dimers (0.15 mmol) were added. The reaction mixture was stirred and protected from light for 24 h. The reaction mixture was neutralized with IN NaOH, and the product was extracted with chloroform. The organic layer was washed with brine. Dried over MgS04, and filtered. The solvent was evaporated under vacuum. The crude product was recrystalized from CHC13.
Product 13: Yield = 60%. M.p= 185-187 °C. IR (KBr): v 3489, 2970. ^NMR^ 3.4 (brs, 1H, C6), 2.8-3.2(brs, 3H, C3, C28), 1.1 (s, 3H, C19), 0.75 (s, 3H, C18). 13C-NMR: 5 75.1 (C6), 67.5 (C5), 54.5 (C3), 19.9 (C19), 13.1 (C18). Anal. calc. or: C58Hio4N204: C, 77.97; H, 11.73; N, 3.14. Found: C, 77.58; H, 11.66; N, 3.09.
Product 14: Yield = 67%. M.p= 199-201 °C. IR (KBr): v 3510, 2990. 'H NMR: 5 4.9-5.2 (m, 2H, C22, C23), 3.05-3.4 (brs, 2H, C3 and C6), 1.4-2.2 (m, 6H, C-31, 32, 35), 1.0 (s, 3H, C-19), 0.71 (s, 3H, C-18). 13C-NMR: 5 129.5 (C23), 137.8 (C22), 76.0 (C-6), 67.6 (C5), 55.7 (C3), 19.6 (C19), 12.8 (C18). Anal. calc. for: C6iHi06N2O4: C, 78.65; H, 11.47; N, 3.01. Found: C, 78.20; H, 11.37; N, 2.94.
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Acknowledgements
The authors thank the Deanship of Research at Jordan University of Science and Technology for financial support, Grant No. 108/99.
References and Notes
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Povzetek
Z reduktivnim aminiranjem smo sintetizirali nove dimerne steroide. S katalitsko oksidacijo z CH3ReO3/H2O2 smo oksidirali dvojno vez.
K. Q. Shawakfeh, A. M. Al-Ajlouni, A. Ibdah: Synthesis and selective catalytic oxidation of new…