A Novel Synthesis Towards Ellipticine and Its Derivatives. Synthesis of a New Precursor Compound

Article abstract of DOI:10.1081/SCC-120027282

The synthesis of a new precursor comppund 3, which may be important for the synthesis of ellipticine and its derivatives, was described. Many new intermediates 5-10 have also been synthesized.

Full text of DOI:10.1081/SCC-120027282

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A Novel Synthesis Towards Ellipticine and Its
Derivatives. Synthesis of a New Precursor Compound
Y. Ergün a , S. Patir b & G. Okay a
a Faculty of Science, Department of Chemistry, Hacettepe University, 06532,
Beytepe‐Ankara, Turkey
b Faculty of Education, Department of Science, Hacettepe University, Beytepe‐Ankara,
Turkey
Version of record first published: 16 Aug 2006.
To cite this article: Y. Ergün , S. Patir & G. Okay (2004): A Novel Synthesis Towards Ellipticine and Its Derivatives.
Synthesis of a New Precursor Compound, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 34:3, 435-442
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 3, pp. 435–442, 2004
A Novel Synthesis Towards Ellipticine
and Its Derivatives. Synthesis of a
New Precursor Compound
Y. Ergu¨n,1 S. Patir,2 and G. Okay1,
*
1Faculty of Science, Department of Chemistry, Hacettepe University,
Beytepe-Ankara, Turkey
2Faculty of Education, Department of Science, Hacettepe University,
Beytepe-Ankara, Turkey
ABSTRACT
The synthesis of a new precursor compound 3, which may be important
for the synthesis of ellipticine and its derivatives, was described. Many
new intermediates 5–10 have also been synthesized.
Key Words: Ellipticine; Synthesis; Olivacine; Ochrasia elliptica.
Ellipticine 1 and olivacine 2 are two naturally occuring 6H-pyrido[4,3-
b]carbazole alkaloids isolated from the leaves of Ochrasia elliptica Labill.[1]
*
Correspondence: G. Okay, Faculty of Science, Department of Chemistry, Hacettepe
University, 06532 Beytepe-Ankara, Turkey.
435
DOI: 10.1081/SCC-120027282
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Ergu¨n, Patir, and Okay
Ellipticine and its derivatives possess antitumor activities and have been
used in clinical trials.[2,3] Since the isolation of these two alkaloids many
synthetic routes to the 6H-pyrido[4,3-b]carbazole framework have been
reported.[4–7]
Ellipticine and derivatives have a tetracyclic structure. Synthetic
strategies leading to ellipticine are classified according to the construction
of the last ring as B, C, D, and B þ C types.[8,9]
We developed a new method for the synthesis of ellipticine precursors
by the construction of the ring D. The known methods of synthesis of the ring
D employ the intramolecular aromatic electrophilic substitution reaction.[10,11]
In the present work we constructed the ring D via intramolecular aldol
condensation and obtained compound 3 which may be an useful precursor
for the synthesis of ellipticine derivatives. Our approach is depicted in the
Sch. 1.
The starting tetrahydrocarbazole 5 was obtained by Fisher-indole
synthesis from ethyl-4-oxo-cyclohexanecarboxylate and phenylhydrazine.[12]
Compound 5 was selectively oxidized at position 1 with periodic acid in
methanol-water (1 : 1) at 08C to yield the 1-oxo-tetrahydrocarbazole
derivative 6.[13] The hydrolysis of the compound 6 with sodium hydroxide
(30%) in methanol-water gave the 1-oxo-tetrahydrocarbazole carboxylic acid
7,[14] which was converted into amide 10 by using ethyl chloroformate,
triethyl amine and aminoacetaldehyde dimethylacetal.[15] Compound 10 can
also be produced in an alternative way. Compound 5 was refluxed with sodium
hydroxide (30%) in methanol-water to afford tetrahydrocarbazole carboxylic
acid 8,[16] which was converted to tetrahydrocarbazole amide 9 with ethyl
chloroformate, triethyl amine and aminoacetaldehyde dimethylacetal.[17]
Oxidation of the tetrahydrocarbazole amide 9 at position 1 with periodic acid
in methanol-water (1 : 1) yielded compound 10, but the yield of this route was
low.[18] Treatment of compound 10 with boron tribromide in dichloromethane

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Novel Synthesis Towards Ellipticine
437
.
Scheme 1. Reagent and conditions: (i) PhNHNH2 HCl, EtOH, reflux, 6 h, 75%;
(ii) periodic acid, MeOH–H2O, 6 h, 60%; (iii) NaOH (30%), MeOH–H2O, reflux, 1 h,
95%; (iv) ClCO2C2H5, (C2H5)3N, 08C, 2 h, then aminoacetaldehyde dimethylacetal,
12 h, 68%; (v) NaOH (30%), MeOH–H2O, reflux, 1 h, 96%; (vi) ClCO2C2H5,
(C2H5)3N, 08C, 2 h, then aminoacetaldehyde dimethylacetal, 12 h, 65%; (vii) periodic
acid, MeOH–H2O, 6 h, 45%; (viii) BBr3, CH2Cl2, 2788C, stirred, 2 h, 65%; and (ix)
NaH, THF, 5 h, 55%.
at 2788C afforded unstable aldehyde 11[19] which without isolation was
immediately treated with sodium hydride in anhydrous tetrahydrofuran under
nitrogen atmosphere to form the tetracyclic compound 3 as a 1 : 1 mixture of
the epimeric alcohols.

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Ergu¨n, Patir, and Okay
EXPERIMENTAL
All melting points were measured in sealed tubes using an electrothermal
digital melting point apparatus (Gallenkamp) and are uncorrected. Infrared
1
spectra were recorded on Hitachi 270-30 infrared spectrometer. H NMR
spectra were obtained on a high resolution fourier transform Bruker WH-400
NMR spectrometer with tetramethylsilane as an internal stantard. Mass
spectra were recorded on a Micromass UK Platform II LC-MS spectrometer.
Column chromatography was carried out by using 70-230 mesh silica gel
(0.063–0.2 mm, Merck).
Ethyl-1,2,3,4-tetrahydrocarbazole-3-carboxylate (5). A stirred mix-
ture of ethyl-4-oxo-cyclohexanecarboxylate (25 g, 147 mmol) and phenyl-
hydrazine hydrochloride (22.5 g, 155 mmol) in absolute ethanol (250 mL)
was refluxed under nitrogen for 6 h. After cooling to room temperature and
removed the solvent, the residue was dissolved in chloroform and washed
with hydrochloric acid (50 mL, 10%), and then with sodium carbonate
(50 mL, 10%). The organic layer was dried with anhydrous magnesium
sulfate and the solvent was evaporated under reduced pressure. The residue
was chromatographed on silica gel with ethyl acetate as eluent. After the
solvent was evaporated the product was crystallized from methanol to
afford 5 (26.8 g, 75%) as a yellow solid. m.p.: 97–988C. IR nmax
(KBr) cm21: 3360 (NH), 2921 (CH), 1710 (C55O, ester). 1H NMR
(CDCl3, 400 MHz) d: 1.22 (t, 3H, J ¼ 7.1 Hz, OCH2CH3), 1.79–1.95 (m,
1H, CH), 2.12–2.26 (m, 1H, CH), 2.66–2.85 (m, 4H, 2 Â CH2), 2.96–
3.02 (m, 1H, CH), 4.10 (q, 2H, J ¼ 7.1 Hz, OCH2CH3), 6.92 (t, 1H,
J ¼ 7.9 Hz, ArH), 6.99 (t, 1H, J ¼ 8.0 Hz, ArH), 7.24 (d, 1H, J ¼ 7.9 Hz,
ArH), 7.35 (d, 1H, J ¼ 7.7 Hz, ArH), 10.70 (s, 1H, NH). MS m/z (rel.int.):
243 (31) [M]þ, 198 (3) [M-C2H5O]þ, 166 (100) [M-C3H9O]þ. Anal.
Calcd. for C15H17NO2: C, 74.07; H, 6.99; N, 5.76. Found: C, 74.22; H,
6.71; N, 5.82.
Ethyl-1-oxo-1,2,3,4-tetrahydrocarbazole-3-carboxylate (6). To a solu-
tion of periodic acid (9.35 g, 41 mmol) in methanol water (1 : 1, 100 mL) was
added dropwise compound 5 (5 g, 20.5 mmol) in methanol (25 mL) at 08C.
The reaction mixture was stirred for 1 h at 08C, then stirring was continued for
one more hour at room temperature. The solvent was evaporated then the
residue was dissolved in chloroform and washed first with sodium carbonate
(50 mL, 10%) and then with sodium bisulfite (50 mL, 10%). The organic layer
was dried over anhydrous magnesium sulfate and the solvent was evaporated.
The residue was chromotographed on silica gel using ethyl acetate and
crystallized from ether to yield compound 6 (3.17 g, 67%). mp: 137–1398C.
IR nmax (KBr) cm21: 3266 (NH), 2942 (CH), 1724 (C55O, ester), 1645
(C55O). 1H NMR (CDCl3, 400 MHz) d: 1.11 (t, 3H, J ¼ 7.13 Hz, OCH2CH3),

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Novel Synthesis Towards Ellipticine
439
2.76–2.78 (m, 2H, CH2), 3.04–3.11 (m, 1H, CH), 3.14–3.25 (m, 2H, CH2),
4.00–4.07 (q, 2H, J ¼ 7.1 Hz, OCH2CH3), 7.00 (t, 1H, J ¼ 8.0 Hz, ArH), 7.20
(t, 1H, J ¼ 8.0 Hz, ArH), 7.27 (d, 1H, J ¼ 8.4 Hz, ArH), 7.51 (d, 1H,
J ¼ 8.1 Hz, ArH), 9.02 (s, 1H, NH). MS m/z (rel.int.): 257 (100) [M]þ, 212
(24) [M-C2H5O]þ, 183 (100) [M-C3H6O2]þ, 167 (56) [M-C3H6O3]þ. Anal.
Calcd. for C15H15NO3: C, 70.04; H, 5.83; N, 5.45. Found: C, 70.12; H, 5.97;
N, 5.27.
1-Oxo-1,2,3,4-tetrahydrocarbazole-3-carboxylic acid (7). A solution
of the compound 6 (2.5 g, 9.70 mmol) and sodium hydroxide solution in
methanol-water (20 mL, 30%) was refluxed for 1 h. The solvent was removed
under reduced pressure and the residue was diluted with water and acidified
with hydrochloric acid. The solution was extracted with ethyl acetate. The
organic layer was dried over anhydrous magnesium sulfate and the solvent
was evaporated. The residue was crystallized from dichloromethane-
cyclohexane to yield
7 (2.17 g, 95%). mp: 203–2048C. IR nmax
1
(KBr) cm21: 3272 (NH), 2947 (CH), 1736 (C55O, acid), 1643 (C55O). H
NMR (DMSO-d6, 400 MHz) d: 2.76–2.79 (m, 2H, CH2), 3.12–3.20 (m, 1H,
CH), 3.25–3.32 (m, 2H, CH2), 7.02 (t, 1H, J ¼ 7.3 Hz, ArH), 7.22 (t, 1H,
J ¼ 7.2 Hz, ArH), 7.36 (d, 1H, J ¼ 8.1 Hz, ArH), 7.55 (d, 1H,
J ¼ 8.1 Hz, ArH), 11.24 (s, 1H, NH), 13.63 (s, 1H, OH). MS m/z (rel.int.):
229 (2) [M]þ, 212 (2) [M-HO]þ, 183 (45) [M-CH2O2]þ, 167 (4) [M-CH2O3]þ.
Anal. Calcd. for C13H11NO3: C, 68.12; H, 4.80; N, 6.11. Found: C, 68.86;
H, 4.49; N, 6.04.
1,2,3,4-Tetrahydrocarbazole-3-carboxylic acid (8). A solution of the
compound 5 (2.5 g, 10.29 mmol) in sodium hydroxide solution in methanol-
water (1 : 1) (20 mL, 30%) was refluxed for 1 h. The solvent was removed
under reduced pressure and the residue was diluted with water and acidified
with hydrochloric acid. The solution was extracted with ethyl acetate. The
organic layer was dried over anhydrous magnesium sulfate and the solvent
was evaporated. The residue was crystallized from dichloromethane-cyclo-
hexane (1 : 1) to yield compound 8 (2.12 g, 96%). mp: 199–2008C. IR nmax
(KBr) cm21: 3386 (NH), 2928 (CH), 1729 (C55O, acid). 1H NMR (DMSO-d6,
400 MHz) d: 1.83–1.90 (m, 1H, CH), 2.16–2.28 (m, 1H, CH), 2.67–2.80
(m, 4H, 2 Â CH2), 2.87–2.95 (m, 1H, CH), 6.91 (t, 1H, J ¼ 7.5 Hz, ArH),
6.98 (t, 1H, J ¼ 7.8 Hz, ArH), 7.23 (d, 1H, J ¼ 7.9 Hz, ArH), 7.35 (d, 1H,
J ¼ 7.7 Hz, ArH), 10.68 (s, 1H, NH), 12.27 (s, 1H, OH). MS m/z (rel.int.):
215 (67) [M]þ, 167 (100) [M-CH4O2]þ, 142 (100) [M-C3H5O2]þ. Anal.
Calcd. for C13H13NO2: C, 72.56; H, 6.05; N, 6.51. Found: C, 71.92; H, 6.22;
N, 6.47.
(N-(2,2-dimethoxyethyl)-1,2,3,4-tetrahydrocarbazole-3-carboxamide
(9). To a solution of ethyl chloroformate (1.09 g, 10 mmol) in dichloromethane
(60 mL) at 08C was added dropwise a solution of acid 8 (2.15 g, 10 mmol)

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Ergu¨n, Patir, and Okay
followed by triethyl amine (3.10 g, 30.69 mmol) in dichloromethane (5 mL).
The solution was stirred for 2 hours at 08C and aminoacetaldehyde
dimethylacetal (1.05 g, 10 mmol) was added. After 12 hours at room tempera-
ture, the mixture diluted with ethyl acetate and washed first with hydrochloric
acid (50 mL, 10%) and then with sodium carbonate (50 mL, 10%) solutions.
The organic layer was dried with anhydrous magnesium sulfate and the
solvent was evaporated under reduced pressure. The residue was chromato-
graphed on silica gel using ethyl acetate and crystallized from diethyl ether to
yield amide 9 (1.96 g, 65%). mp: 177–1788C. IR nmax (KBr) cm21: 3320
(NH), 3295(NH), 2934 (CH), 1623 (C55O, amide). 1H NMR (CDCl3,
400 MHz) d: 2.08–2.18 (m, 1H, CH), 2.20–2.27 (m, 1H, CH), 2.62–2.69 (m,
1H, CH), 2.81–2.89 (m, 2H, CH2), 2.90–2.96 (dd, 1H, J ¼ 15.4, 9.5 Hz, CH),
2.99–3.05 (dd, 1H, J ¼ 15.4, 5.5 Hz, CH), 3.40 (s, 3H, OCH3), 3.41 (s, 3H,
OCH3), 3.44–3.49 (t, 2H, J ¼ 5.4 Hz, NHCH2CH(OCH3)2), 4.42 (t, 1H,
J ¼ 5.3 Hz, CH(OCH3)2), 5.86 (s, 1H, NH), 7.08–7.18 (m, 2H, 2 Â ArH),
7.29 (d, 1H, J ¼ 7.7 Hz, ArH), 7.47 (d, 1H, J ¼ 7.6 Hz, ArH), 7.86 (s, 1H,
NH). MS m/z (rel.int.): 302 (65) [M]þ, 270 (97) [M-CH4O]þ, 198 (8)
[M-C4H10NO2]þ, 171 (68) [M-C5H9NO3]þ, 167 (100) [M-C5H13NO3]þ.
Anal. Calcd. for C17H22N2O3: C, 67.55; H, 7.28; N, 9.27. Found: C, 68.02;
H, 7.35; N, 8.92.
[N-(2,2-dimethoxyethyl)]-1-oxo-1,2,3,4-tetrahydrocarbazole-3-car-
boxyamide (10). Method I. To a solution of ethyl chloroformate (2.18 g,
20 mmol) in dichloromethane (50 mL) at 08C was added dropwise a
solution of acid 7 (4.58 g, 20 mmol) followed by triethyl amine (6 g,
59.4 mmol) in dichloromethane (30 mL). The solution was stirred for 2
hours at 08C and aminoacetaldehyde dimethylacetal (2.10 g, 20 mmol) was
added. After 12 hours at room temperature, the mixture was diluted with
ethyl acetate and washed with hydrochloric acid (50 mL, 10%) and with
sodium carbonate (50 mL, 10%). The organic layer was dried with anhydrous
magnesium sulfate and the solvent was evaporated under reduced pressure.
The residue was chromatographed on silica gel using ethyl acetate and
the obtained amide 10 was crystallized from diethyl ether. Yield 4.29 g
(68%).
Method II. To a solution of periodic acid (3.77 g, 16.55 mmol) in
methanol water (1 : 1) (100 mL) was added dropwise compound 9 (2.5 g,
8.28 mmol) in methanol (25 mL) at 08C. The reaction mixture was stirred for
1 h at 08C, then stirring was continued for one hour at room temperature. The
solvent was evaporated then the residue was dissolved in chloroform (60 mL)
and washed with sodium carbonate (50 mL, 10%) and with sodium bisulfite
(50 mL, 10%). The organic layer was dried over anhydrous magnesium sulfate
and the solvent was evaporated. The residue was chromotographed on silica
gel using ethyl acetate and crystallized from diethyl ether to yield compound

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441
10 (1.78 g, 45%). mp: 189–1918C. IR nmax (KBr) cm21: 3300 (NH), 3267
(NH), 2934 (CH), 1665 (C55O), 1652 (C55O, amide). H NMR (CDCl3,
1
400 MHz) d: 2.43–2.52 (m, 1H, CH), 2.57–2.62 (dd, 1H, J ¼ 16.6 and 3.8 Hz,
CH), 2.80–2.87 (dd, 1H, J ¼ 16.6 and 11.9 Hz, CH), 3.08–3.21 (m, 2H, CH2),
3.23–3.28 (t, 2H, J ¼ 5.6 Hz, NHCH2CH(OCH3)2), 3.29 (s, 3H, OCH3), 3.30
(s, 3H, OCH3), 4.33 (t, 1H, J ¼ 5.5 Hz, CH(OCH3)2), 7.00 (t, 1H, J ¼ 7.7 Hz,
ArH), 7.21 (t, 1H, J ¼ 7.9 Hz, ArH), 7.35 (d, 1H, J ¼ 8.4 Hz, ArH), 7.51
(d, 1H, J ¼ 8.1 Hz, ArH), 7.70 (t, 1H, J ¼ 5.7 Hz, amide-NH), 11.19 (s, 1H,
NH). MS m/z (rel.int.): 316 (2) [M]þ, 284 (20) [M-CH4O]þ, 253 (6)
[M-C2H7O2]þ, 183 (100) [M-C5H11NO3]þ, 167 (4) [M-C5H11NO4]þ. Anal.
Calcd for C17H20N2O4: C, 64.55; H, 6.33; N, 8.86. Found: C, 63.98; H, 6.51;
N, 8.95.
1,5-Dioxo-4-hydroxy-1,2,3,4,4a,5,11,11a-octahydro-6H-pyrido[4,3-b]
carbazole (3). To a stirred solution of compound 10 (1.5 g, 4.75 mmol) in
dichloromethane (25 mL) under nitrogen at 2788C was added via syringe
boron tribromide (3.57 g, 14.25 mmol) in chloroform (10 mL). After 1 h at
2788C, the reaction mixture was allowed to warm to room temperature over
2 h. Then the reaction mixture was poured slowly into ice-water mixture and
extracted with chloroform. The organic phase was washed with sodium
carbonate (25 mL, 10%) and dried with anhydrous magnesium sulfate. The
solvent was evaporated and the residue was chromatographed on silica gel
using ethyl acetate to yield product 11 (oil, 0.83 g, 65%). Compound 11 (2 g,
7.40 mmol) was immediately treated with sodium hydride (0.89 g,
22.2 mmol; 60% dispersion in oil) in anhydrous tetrahydrofuran (25 mL)
and the mixture was stirred under nitrogen atmosphere at 508C for 5 h. Then
the mixture was cooled in an ice bath and hydrochloric acid (10 mL, 10%)
was added slowly. After extraction with chloroform, the organic layer was
washed with sodium carbonate (10 mL, 5%), dried with anhydrous mag-
nesium sulfate and the solvent was evaporated. Purification of the residue by
column chromatography using silica gel and ethyl acetate-methanol (1 : 1)
yielded compound 3 (1.1 g, 55%) as a mixture of epimeric alcohols. mp:
218–2198C. IR nmax (KBr) cm21: 3500 (OH), 3380 (NH), 3265(NH), 2945
1
(CH), 1660 (C55O), 1625 (C55O, amide). H NMR (CDCl3, 400 MHz) d:
2.35–2.42 (m, 1H, CH), 2.46–2.52 (m, 1H, CH), 2.55–2.62 (m, 1H, CH),
2.70–2.82 (m, 1H, CH), 3.05 (bs, 1H, OH), 3.10-3.20 (m, 1H, CH), 3.47-
3.55 (t, 2H, J ¼ 5.3 Hz, NHCH2CH), 5.95 (bs, 1H, NH), 7.18 (t, 1H,
J ¼ 7.1 Hz, ArH), 7.40-7.45 (m, 2H, 2 Â ArH), 7.64 (d, 1H, J ¼ 8.1 Hz,
ArH), 9.15 (s, 1H, NH). MS m/z (rel.int.): 271 (3) [M þ 1]þ, 270 (5) [M]þ,
252 (4) [M-H2O]þ, 183 (13) [M-C3H5NO2]þ, 167 (73) [M-C3H5NO3]þ, 115
(49) [M-C7H9NO3]þ. Anal. Calcd. for C15H14N2O3: C, 66.67; H, 5.19;
N, 10.37. Found: C, 67.02; H, 4.96; N, 10.25.

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Ergu¨n, Patir, and Okay
ACKNOWLEDGMENT
The authors wish to express their gratitute to The Scientific and Technical
Research Council of Turkey (TUBITAK Grant No: 2024) for financial
support.
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Received in Poland June 27, 2003

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