Synthesis of metabolites of the Ah receptor ligand 6-formylindolo[3,2-b] carbazole

Article abstract of DOI:10.1002/ejoc.200400087

Synthesis of the five mono- and di-hydroxylated metabolites of the aryl hydrocarbon receptor high affinity ligand 6-formylindolo[3,2-b]carbazole is described. The structures of the metabolites were unequivocally established as 2-hydroxy-, 8-hydroxy-, 2,10-dihydroxy-, 4,8-dihydroxy- and 2,8- dihydroxyindolo[3,2-b]carbazole-6-carboxaldehyde. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejoc.200400087

FULL PAPER
Synthesis of Metabolites of the Ah Receptor Ligand
6-Formylindolo[3,2-b]carbazole
Niklas Wahlström,[a,b] Ivan Romero,[a] and Jan Bergman*[a,b]
Keywords: Bis(indoles) / Acylations / Ah receptor / 6-Formylindolo[3,2-b]carbazole / Metabolite
Synthesis of the five mono- and di-hydroxylated metabolites
8-hydroxy-, 2,10-dihydroxy-, 4,8-dihydroxy- and 2,8-dihy-
of the aryl hydrocarbon receptor high affinity ligand 6-formy- droxyindolo[3,2-b]carbazole-6-carboxaldehyde.
lindolo[3,2-b]carbazole is described. The structures of the
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
metabolites were unequivocally established as 2-hydroxy-,
Germany, 2004)
Introduction
fractions separated contained two substances, the NMR
spectra displayed overlapping signals. Therefore, it was not
possible to determine the relative position (2 or 3) of the
hydroxy group in the A-ring (Figure 1) of these metabolites.
We embarked on the synthesis of the assigned metabolites
5aϪb and 5dϪf (Figure 2) with the objective of establishing
the substitution patterns of the hydroxylated metabolites,
and to determine the activity and toxicity of the pure prod-
ucts.
The aryl hydrocarbon (Ah) receptor is an intracellar pro-
tein present in all rodent cells examined to date.[1] In the
cell, the Ah receptor is involved in the primary detox-
ification of nonpolar substances, such as polyaromatic hy-
drocarbons, and xenobiotics like the highly toxic environ-
mental
pollutant
2,3,7,8-tetrachlorodibenzo-p-dioxin
(TCDD, 1). The Ah receptor triggers the expression of
many enzymes (including cytochrome P-4501A1) involved
in detoxification processes.[2] Natural ligands for this recep-
tor include di(indol-3-yl)methane (2) and indolo[3,2-b]car-
bazole (ICZ, 3),[3] which are transformation products from
the essential amino acid tryptophan. Irradiation of a tryp-
tophan solution in water gives two ICZ derivatives that have
been isolated[4] and structurally corroborated by indepen-
dent syntheses to be 6-formylindolo[3,2-b]carbazole (4a)[5]
and 6,12-diformylindolo[3,2-b]carbazole (4b).[5] The mono-
formylated ICZ derivative 4a exhibits the highest binding
affinity for the Ah receptor so far observed.[6] Further in-
vestigations of 4a showed that the Ah receptor expression
induced by 4a is both rapid and transient, which seems to
be a prerequisite for an endogenous ligand.[7] Additionally,
the Ah receptor activation of an endogenous ligand has
been suggested to be involved in the degradation of the li-
gand.[7]
Figure 1. Potent aryl hydrocarbon receptor ligands 1Ϫ4b
Recently, indolo[3,2-b]carbazole-6-carbaldehyde (4a) was
metabolized by incubation with an activated cytochrome P-
4501A1 system in vivo. The resulting metabolites were iso-
lated by HPLC and characterized using mass spectrometry
and NMR spectroscopy.[8] Since two of the three metabolite
Results and Discussion
In our first approach, the di(indolyl)methanes 6aϪg,[9]
were initially acylated using dichloroacetyl chloride and
pyridine in THF to give the corresponding acylated prod-
ucts (exemplified here by compound 7).[5,8] Ring closure
and hydrolysis of the dichloromethyl compound 7 produced
directly the desired aldehyde functionality. However, when
the di(indolyl)methanes 7 were substituted with more than
[a]
Unit for Organic Chemistry, CNT, Department of Biosciences
at NOVUM, Karolinska Institute, Novum Research Park,
141 57 Huddinge, Sweden
Fax: (internat.) ϩ46-8-6081501
E-mail: jabe@biosci.ki.se
[b]
Södertörn University College,
141 04 Huddinge, Sweden
Eur. J. Org. Chem. 2004, 2593Ϫ2602
DOI: 10.1002/ejoc.200400087
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2593

N. Wahlström, I. Romero, J. Bergman
FULL PAPER
While attempting to increase the solubility of the mixture
containing 10d by protection of the nitrogen atoms, we
noted the instability of the N,NЈ-diBoc derivative of 10d.
This sensitivity towards deprotection of the carbamate ad-
jacent to the formyl group was attributed to electron do-
nation by the methoxy group para to the nitrogen as well
as the driving force of formation of a hydrogen bond be-
tween the formyl group and the NH proton. As a conse-
quence of these difficulties, the first route was abandoned.
In order to overcome these problems, another route was
employed. The di(indolyl)methanes 6aϪg were acylated by
using ethyl oxalyl chloride/pyridine in THF to produce the
esters 9aϪg (Scheme 2, Table 2). Facile ring closure of
Figure 2. ICZs 5aϪf with atom numbering outlined and the (indol- 9aϪg was performed with methanesulfonic acid in 1,4-diox-
2-yl)(indol-3-yl)methanes 6aϪg
ane to produce ICZs 11aϪg in yields higher than 82%
(Scheme 2, Table 3). The esters 11aϪg were reduced with
one methoxy group the co-formation of a decarbonylated
lithium aluminum hydride to their corresponding alcohols,
by-product, 8, resulted in an inseparable mixture of ICZ
derivatives. As an example of this, the bis(indole) 7 was pre-
pared from 6e (Scheme 1). The ratio of products in the mix-
ture resulting from treatment of 7 with various acids under
the conditions outlined in Table 1 indicates that the extent
of decarbonylation increased (formation of 8) with higher
temperature and increasing acid strength. (Table 1).
which were subsequently dehydrogenated with 2,3-dichloro-
5,6-dicyanobenzoquinone (DDQ) to the aldehydes 10aϪf
(Scheme 2, Table 3). This series of operations prevented the
formation of the decarbonylated indolocarbazoles from
precursors containing the dichloro functionality (i.e.) 7. In
this fashion, indolo[3,2-b]carbazole-6-carboxaldehyde (4a)
could be obtained in 89% yield from ethyl indolo[3,2-b]car-
bazole-6-carboxylate (11a).
Demethylation of 10aϪf with excess boron tribromide in
Table 1. Result from acid induced cyclisation of 7
dichloromethane produced the crude hydroxylated indolo-
Entry
[h][a]
Catalyst
T [°C]
Ratio 10d:8[b] [c]
carbazoles 5aϪf. Before purification, the hydroxy groups
were protected as their silyl ethers using tert-butyldimeth-
ylsilyl chloride and imidazole in DMF to give 12aϪf
(Table 3) after silica gel column chromatography. Deprotec-
tion with tetrabutylammonium fluoride in THF produced
the hydroxylated metabolites 5aϪb and 5dϪf in pure form
(Scheme 2, Table 4). By comparison with spectroscopic data
reported previously,[8] we determined that the hydroxy
1
2
3
4
5
6
2  HCl
78
100
50
50
100
1:1
2:1
9:2
1:2
1:20
1.5
20
5.5
0.4
CH3SO3H
CH3SO3H
CF3SO3H
CF3SO3H
[a]
[b]
1
Reaction time.
Determined by H NMR after workup of
[c]
reaction. Yields were not determined.
Scheme 1. i. Pyridine, Cl2CHCOCl, THF ii. Ethanol/1,4-dioxane, 2  HCl or MeSO3H or CF3SO3H.
2594 www.eurjoc.org
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Eur. J. Org. Chem. 2004, 2593Ϫ2602

Synthesis of Metabolites of the Ah Receptor Ligand 6-Formylindolo[3,2-b]carbazole
FULL PAPER
Scheme 2. i. Pyridine, ClCOCO2Et, THF ii. MeSO3H, 1,4-dioxane iii. LiAlH4, THF iv. DDQ, 1,4-dioxane v. BBr3, CH2Cl2 vii. TBSCl,
imidazole, DMF vii. TBAF, THF viii. BBr3, CH2Cl2 ix. Heat
Table 2. Acylation products 9aϪf from di(indolyl)methanes 6aϪg
Table 4. Indolo[3,2-b]carbazoles 5aϪf, 13aϪc and 14aϪb
Compound
R1
R2
Yield [%]
Compound
R1
R2
R3
Yield [%]
9a
9b
9c
9d
9e
9f
H
H
5-OMe
H
5-OMe
5-OMe
7-OMe
H
88[a]
67
65
56
64
5a
5b
H
8-OH
H
8-OH
8-OH
10-OH
H
8-OH
H
2-OH
H
3-OH
2-OH
4-OH
2-OH
H
2-OH
2-OH
2-OH
2-OH
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
CO2H
CO2H
CO2H
H
95
96
77
77
98
84
93
95
93
100
97
5Ј-OMe
H
6Ј-OMe
5Ј-OMe
7Ј-OMe
5Ј-OMe
5c
5d
5e
71
63
5f
9g
13a
13b
13c
14a
14b
[a]
Synthesized previously in similar yield.[5]
8-OH
H
H
Table 3. Indolo[3,2-b]carbazoles 11aϪg, 10aϪf and 12aϪf
Compound
R1
R2
Yield [%]
hydroxy functionalities in the A and E-rings (Figure 1) of
compounds 10, 12 and 5, the solubilities were much im-
proved. On the other hand, compounds with only one
hydroxy functionality present had lower solubilities. The
methoxyindolocarbazole 10b and the metabolite 8-hydroxy-
indolo[3,2-b]carbazole-6-carboxaldehyde (5b) were even
more insoluble than indolo[3,2-b]carbazole-6-carboxal-
dehyde (4a). Several of the tetra- and penta-cyclic com-
pounds prepared co-crystallized with small amounts of 1,4-
dioxane or ethyl acetate. These solvents could not be re-
moved by conventional methods and the compounds were
purified by sublimation at high temperature and under high
vacuum. The ester 11a was hydrolyzed with 2  sodium
hydroxide in ethanol to give 13a (Scheme 2, Table 4). The
esters 11e and 11b were simultaneously demethylated and
hydrolyzed to give the acids 13bϪc (Scheme 2, Table 4). In
both cases, these acids were decarboxylated to give the
hydroxy indolocarbazoles 14aϪb in 97Ϫ100% yield.
11a
11b
11c
11d
11e
11f
11g
4a
10a
10b
10c
10d
10e
10f
12a
12b
12c
12d
12e
12f
H
H
H
2-OMe
H
3-OMe
2-OMe
4-OMe
2-OMe
H
2-OMe
H
3-OMe
2-OMe
4-OMe
2-OMe
2-OTBS
H
3-OTBS
2-OTBS
4-OTBS
2-OTBS
92[a]
90
88
89
95
86
82
89
87
82
62
93
78
82
70
44
45
44
41
72
8-OMe
H
8-OMe
8-OMe
10-OMe
H
H
8-OMe
H
8-OMe
8-OMe
10-OMe
H
8-OTBS
H
8-OTBS
8-OTBS
10-OTBS
[a]
Synthesized previously in 88% yield.[5]
Conclusions
group occupies the 2-position of the A-ring (Figure 1). The
considerable variation in the solubility of the different
In summary, we have synthesized the five primary metab-
metabolites influenced their workup strategies. With two olites 5aϪb and 5dϪf of the highly potent aryl hydrocarbon
Eur. J. Org. Chem. 2004, 2593Ϫ2602
www.eurjoc.org  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2595

N. Wahlström, I. Romero, J. Bergman
FULL PAPER
Procedure for the Preparation of 9a؊g: Ethyl oxalyl chloride
(12 mmol) was added dropwise during 10 min to a solution of di(in-
dolyl)methane (8 mmol) and pyridine (12 mmol) in THF (50 mL)
under argon at 0 °C. The temperature was then increased to 21 °C
and the mixture stirred for 4Ϫ8 h. EtOAc (150 mL) was added and
the mixture was washed with 2  HCl (50 mL), satd. NaHCO3
(60 mL), then water (50 mL) and finally brine (100 mL) before dry-
ing over Na2SO4. The solvents were concentrated to give a yellow
solid. The solid was suspended in CH2Cl2 (50 mL) and stirred until
homogeneous. The precipitate was collected, washed with CH2Cl2
and then dried to give 9 as a light yellowish solid. The solvent was
concentrated to give an additional small crop of 9.
receptor ligand indolo[3,2-b]carbazole-6-carboxaldehyde
(4a) and thus have determined unambiguously the substi-
tution pattern of their hydroxy groups. These results will
enable further studies on the affinity and toxicity of these
metabolites.
Experimental Section
General Remarks: NMR spectra were obtained with a Bruker Av-
ance 300 DPX spectrometer (Bruker, Newark, USA) operating at
300 MHz or a Jeol Eclipse ϩ500 FT NMR spectrometer (Jeol Ltd.,
Tokyo, Japan) operating at 500 MHz. Spectra were recorded in
[D6]acetone, [D6]DMSO or CDCl3, using the residual solvent as
internal standard at 300.1 or 500.2 MHz for 1H and 75.5 or
125.8 MHz for 13C at 298 K unless stated otherwise. Coupling con-
stants and chemical shifts are given in Hz and ppm, respectively.
IR spectra were recorded with a PerkinϪElmer FT-IR 1600 spec-
trophotometer. Melting points were determined using the capillary
method on a Büchi B-545 or on a Heizbank Kofler hotbench and
are uncorrected. Mass spectra were recorded using an LC/MS sys-
tem operating in the electrospray ionization (ESI) mode at 70 eV.
HRMS (FAB) experiments were performed by E. Nilsson, Kem-
icentrum, Lund, Sweden. Elemental analyses were performed by
H. Kolbe Microanalytisches Laboratorium, Mülheim an der Ruhr,
Germany. All reagents were of standard purity and used as received
from Lancaster, Aldrich, Biosynth or Merck. Solvents were puri-
fied by distillation or were of HPLC grade and used as received.
Dichloromethane was distilled from CaH2 and stored over acti-
vated molecular sieves prior to use. 1,4-Dioxane was stored over
sodium. THF was distilled from sodium/benzophenone. Chromato-
graphic separations were performed on silica gel 60 (230Ϫ400
mesh). Reactions were monitored by thin-layer chromatography, on
silica gel coated plates containing a fluorescent indicator.
Ethyl 2-(5-Methoxy-1H-indol-3-ylmethyl)-1H-indol-3-yl]-2-oxoacet-
ate (9b): An analytical sample was crystallized from MeCN. Yellow
crystals, M.p. 193.5Ϫ194.5 °C. IR (KBr) ϭ 3382, 3229, 1732, 1563,
1457, 1267, 1168, 1025, 756 cmϪ1
.
1H NMR (300.1 MHz;
[D6]DMSO): δ ϭ 12.21 (s, 1 H), 10.83 (s, 1 H), 7.78Ϫ7.75 (m, 1
H), 7.46Ϫ7.43 (m, 1 H), 7.28Ϫ7.18 (m, 3 H), 7.16 (d, J ϭ 2.3 Hz,
1 H), 7.00 (d, J ϭ 2.3 Hz, 1 H), 6.73 (dd, J ϭ 8.8, 2.4 Hz, 1 H),
4.47 (s, 2 H), 4.29 (q, J ϭ 7.1 Hz, 2 H), 3.70 (s, 3 H), 1.22 (t, J ϭ
7.1 Hz, 3 H) ppm. 13C NMR (75.5 MHz; [D6]DMSO): δ ϭ 181.5
(s), 166.1 (s), 153.1 (s), 150.9 (s), 135.4 (s), 131.3 (s), 127.0 (s), 126.1
(s), 124.5 (d), 122.9 (d), 122.4 (d), 119.3 (d), 122.2 (d), 112.1 (d),
111.2 (d), 109.6 (s), 107.6 (s), 100.1 (d), 61.6 (t), 55.2 (q), 23.6 (t),
13.7 (q) ppm. MS (ESI): m/z ϭ 377 [M ϩ 1]ϩ, 375 [M Ϫ 1]Ϫ.
C22H20N2O4 (376.4): calcd. C 70.20, H 5.36, N 7.44; found C 70.15,
H 5.31, N 7.41.
Ethyl 2-[5-Methoxy-2-(1H-indol-3-ylmethyl)-1H-indol-3-yl]-2-oxo-
acetate (9c): An analytical sample was crystallized from MeCN.
Yellow crystals, M.p. 191.0Ϫ193.5 °C. IR (KBr): ν˜ ϭ 3370, 3202,
1737, 1596, 1558, 1464, 1183, 1028, 748 cmϪ1
.
1H NMR
(500.2 MHz; [D6]DMSO): δ ϭ 12.00 (s, 1 H), 10.99 (s, 1 H), 7.43
(d, J ϭ 7.8 Hz, 1 H), 7.37 (d, J ϭ 8.2 Hz, 1 H), 7.34Ϫ7.31 (m, 2
H), 7.16 (d, J ϭ 1.8 Hz, 1 H), 7.07 (dd, J ϭ 7.8, 7.4 Hz, 1 H), 6.95
(dd, J ϭ 7.8, 6.9 Hz, 1 H), 6.83 (dd, J ϭ 8.7, 2.3 Hz, 1 H), 4.42 (s,
2 H), 4.23 (q, 2 H, 6.8 Hz), 3.76 (s, 3 H), 1.19 (t, J ϭ 6.8 Hz, 3 H)
ppm. 13C NMR (125.8 MHz; [D6]DMSO): δ ϭ 181.3 (s), 166.1 (s),
155.7 (s), 150.6 (s), 136.2 (s), 130.1 (s), 127.2 (s), 126.6 (s), 124.0
(d), 121.2 (d), 118.6 (d), 118.0 (d), 112.9 (d), 112.1 (d), 111.5 (d),
109.7 (s), 107.7 (s), 102.2 (d), 61.6 (t), 55.3 (q), 23.6 (t), 13.7 (q)
ppm. MS (ESI): m/z ϭ 377 [M ϩ 1]ϩ, 375 [M Ϫ 1]Ϫ. C22H20N2O4
(376.4): calcd. C 70.20, H 5.36, N7.44; found C 70.34, H 5.36,
N 7.39.
2,2-Dichloro-1-[5-methoxy-2-(5-methoxy-1H-indol-3-ylmethyl)-1H-
indol-3-yl]ethanone (7): Dichloroacetyl chloride (1.10 mL,
11.42 mmol) was added dropwise via syringe to a solution of
5-methoxy-2-(5-methoxy-1H-indol-3-ylmethyl)-1H-indole
(6e)
(2.80 g, 9.14 mmol) and pyridine (0.92 mL, 11.42 mmol) in THF
(50 mL) under argon at Ϫ10 °C. The resulting suspension was then
stirred at 21 °C for 5 h when a saturated aqueous solution of
NH4Cl (0.50 mL) was added. EtOAc (100 mL) and water (50 mL)
were added, and the organic phase was separated, washed with 2
 HCl (40 mL), saturated aq. NaHCO3 (40 mL), followed by water
(50 mL) and finally brine (2 ϫ 40 mL) before drying over Na2SO4.
Evaporation at 30 °C gave a white-greenish semi-solid that was
subjected to column chromatography (aluminum oxide) using a
gradient elution by EtOAc/hexane (40Ϫ100%). Fractions contain-
ing the product were concentrated, and evaporated at 30 °C with
Et2O/hexane to give the acylated bis(indole) 7 (3.47 g, 91%) as a
yellow solid. An analytical sample was crystallized from CH2Cl2/
hexane. M.p. 65 °C (dec.). IR (KBr): ν˜ ϭ 3320, 2934, 2830, 1632,
Ethyl 2-[6-Methoxy-2-(1H-indol-3-ylmethyl)-1H-indol-3-yl]-2-oxo-
acetate (9d): An analytical sample was crystallized from EtOAc.
Yellow crystals, M.p. 211.0Ϫ214.0 °C. IR (KBr): ν˜ ϭ 3389, 3339,
1726, 1601, 1459, 1267, 1164, 1027 cmϪ1 1H NMR (300.1 MHz;
.
[D6]DMSO): δ ϭ 12.14 (s, 1 H), 10.77 (s, 1 H), 7.79Ϫ7.75 (m, 1
H), 7.44Ϫ7.40 (m, 1 H), 7.31 (d, J ϭ 8.6 Hz, 1 H), 7.23Ϫ7.17 (m,
2 H), 7.03 (d, J ϭ 2.2 Hz, 1 H), 6.86 (d, J ϭ 2.2 Hz, 1 H), 6.62
(dd, J ϭ 8.6, 2.3 Hz, 1 H), 4.42 (s, 2 H), 4.28 (q, J ϭ 7.1 Hz, 2 H),
3.74 (s, 3 H), 1.20 (t, J ϭ 7.1 Hz, 3 H) ppm. 13C NMR (75.5 MHz;
[D6]DMSO): δ ϭ 182.4 (s), 166.9 (s), 156.5 (s), 151.7 (s), 137.8 (s),
136.2 (s), 127.1 (s), 123.8 (d), 123.5 (d), 123.3 (d), 122.0 (s), 120.3
(d), 119.6 (d), 113.1 (d), 110.6 (s), 109.7 (d), 108.5 (s), 95.5 (d), 62.5
(t), 56.0 (q), 24.5 (t), 14.6 (q) ppm. MS (ESI): m/z ϭ 375 [M Ϫ
1]Ϫ,377 [M ϩ 1]ϩ. C22H20N2O4 (376.4): calcd. C 70.20, H 5.36,
N7.44; found C 70.17, H 5.40, N 7.48.
1585, 1463, 1214, 1107, 1026, 800 cmϪ1 1H NMR (300.1 MHz;
.
[D6]acetone): δ ϭ 10.84 (br. s, 1 H), 10.09 (br. s, 1 H), 7.61 (d, J ϭ
2.3 Hz, 1 H), 7.34Ϫ7.24 (m, 4 H), 7.00 (d, J ϭ 2.4 Hz, 1 H),
6.83Ϫ6.76 (m, 2 H), 4.72 (s, 2 H), 3.87 (s, 3 H), 3.70 (s, 3 H) ppm.
13C NMR (75.5 MHz; [D6]acetone): δ ϭ 181.9 (s), 157.3 (s), 155.1
(s), 151.8 (s), 132.9 (s), 131.2 (s), 128.7 (s), 128.3 (s), 125.8 (d),
113.5 (d), 113.1 (d), 112.9 (d), 112.9 (d), 110.4 (s), 108.9 (s), 104.7 Ethyl 2-[5-Methoxy-2-(5-methoxy-1H-indol-3-ylmethyl)-1H-indol-3-
(d), 101.0 (d), 71.5 (d), 56.0 (q), 55.9 (q), 26.0 (t) ppm. HRMS
yl]-2-oxoacetate (9e): An analytical sample was crystallized from
EtOAc/MeCN as yellow crystals. M.p. 209Ϫ211 °C. IR (KBr) ϭ
(FAB) calcd. for C21H18Cl2N2O3 416.0694 [M]ϩ; found 416.0703.
2596
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2004, 2593Ϫ2602

Synthesis of Metabolites of the Ah Receptor Ligand 6-Formylindolo[3,2-b]carbazole
3372, 3198, 1734, 1625, 1591, 1557, 1472, 1375, 1278, 1217, 1029, 121.3 (s), 120.2 (s), 117.6 (d), 115.4 (d), 112.2 (d), 110.7 (d), 106.9
FULL PAPER
799 cmϪ1. 1H NMR (300.1 MHz; [D6]DMSO): δ ϭ 12.04 (s, 1 H),
(d), 105.0 (s), 103.3 (d), 60.8 (t), 55.6 (q), 14.5 (q) ppm. MS (ESI):
10.81 (s, 1 H), 7.33 (d, J ϭ 8.8 Hz, 1 H), 7.29 (d, J ϭ 2.3 Hz, 1 m/z ϭ 359 [M ϩ 1]ϩ , 357 [M Ϫ 1]Ϫ. C22H18N2O3 (358.4): calcd.
H), 7.25 (d, J ϭ 8.8 Hz, 1 H), 7.12 (d, J ϭ 2.3 Hz, 1 H), 6.96 (d, C 73.73, H 5.06, N 7.82; found C 73.81, H 4.95, N 7.76.
J ϭ 2.3 Hz, 1 H), 6.84 (dd, J ϭ 8.8, 2.4 Hz, 1 H), 6.72 (dd, J ϭ
Ethyl 8-Methoxyindolo[3,2-b]carbazole-6-carboxylate (11c): Yellow
8.7, 2.3 Hz, 1 H), 4.39 (s, 2 H), 4.25 (q, J ϭ 7.0 Hz, 2 H), 3.76 (s,
solid. (77%) This substance starts to decompose at 169.5 °C and
3 H), 3.69 (s, 3 H), 1.20 (t, J ϭ 7.0 Hz, 3 H) ppm. 13C NMR
finally melts at 187.0 °C. IR (KBr): ν˜ ϭ 3465, 3406, 1712, 1461,
(75.5 MHz; [D6]DMSO): δ ϭ 181.3 (s), 166.1 (s), 155.7 (s), 153.1
(s), 150.7 (s), 131.3 (s), 130.1 (s), 127.2 (s), 127.0 (s), 124.5 (d),
112.9 (d), 112.1 (d), 112.0 (d), 111.2 (d), 109.6 (s), 107.6 (s), 102.1
1
1303, 1215, 1171, 1143 cmϪ1. H NMR (300.1 MHz; [D6]DMSO):
δ ϭ 11.31 (s, 1 H), 10.91 (s, 1 H), 8.44 (s, 1 H), 8.27Ϫ8.24 (m, 2
H), 7.67 (d, J ϭ 8.0 Hz, 1 H), 7.47Ϫ7.41 (m, 2 H), 7.19 (dd, J ϭ
(d), 100.0 (d), 61.6 (t), 55.3 (q), 55.2 (q), 23.6 (t), 13.7 (q) ppm. MS
7.5, 7.4 Hz, 1 H), 7.12 (dd, J ϭ 8.8, 2.5 Hz, 1 H), 4.70 (q, J ϭ 7.1
(ESI): m/z ϭ 405 [M Ϫ 1]Ϫ , 407 [M ϩ 1]ϩ. C23H22N2O5 (406.4):
Hz, 2 H), 3.86 (s, 3 H), 1.53 (t, J ϭ 7.1 Hz, 3 H) ppm. 13C NMR
calcd. C 67.97, H 5.46, N 6.89; found C 67.96, H 5.40, N 6.79.
(75.5 MHz; [D6]DMSO): δ ϭ 167.2 (s), 151.9 (s), 141.2 (s), 136.7
Ethyl 2-[5-Methoxy-2-(7-methoxy-1H-indol-3-ylmethyl)-1H-indol-3-
yl]-2-oxoacetate (9f): Yellow crystals from MeCN. M.p. 143 °C 120.3 (d), 119.8 (s), 118.5 (d), 115.7 (d), 111.4 (d), 111.2 (d), 107.5
(dec.). IR (neat): ν˜ ϭ 3312, 3190, 1714, 1578, 1460, 1260, 1212, (d), 106.9 (d), 104.8 (s), 60.8 (t), 55.6 (q), 14.5 (q) ppm. MS (ESI):
(s), 135.9 (s), 135.6 (s), 126.2 (d), 123.3 (s), 121.6 (s), 121.4 (s),
1024 cmϪ1 1H NMR (300.1 MHz; [D6]acetone): δ ϭ 11.14 (s, 1 m/z ϭ 357 [M Ϫ 1]Ϫ, 359 [M ϩ 1]ϩ. HRMS (FAB) calcd. for
.
H), 9.98 (s, 1 H), 7.49 (d, J ϭ 8.1 Hz, 1 H), 7.28 (d, J ϭ 8.8 Hz, 1 C22H18N2O3 358.1317 [M]ϩ, found 358.1319.
H), 7.17 (d, J ϭ 2.1 Hz, 1 H), 7.15Ϫ7.10 (m, 2 H), 6.78Ϫ6.73 (m,
Ethyl 3-Methoxyindolo[3,2-b]carbazole-6-carboxylate (11d): Yellow
2 H), 4.59 (s, 2 H), 4.28 (q, J ϭ 7.1 Hz, 2 H), 3.87 (s, 3 H), 3.75
(s, 3 H), 1.24 (t, J ϭ 7.1 Hz, 3 H) ppm. 13C NMR (75.5 MHz;
[D6]DMSO): δ ϭ 181.2 (s), 166.1 (s), 155.7 (s), 150.7 (s), 146.2 (s),
130.1 (s), 128.2 (s), 127.2 (s), 126.3 (s), 123.6 (d), 119.2 (d), 113.0
(d), 112.1 (d), 110.9 (d), 110.1 (s), 107.6 (s), 102.1 (d), 101.7 (d),
61.6 (t), 55.3 (q), 55.1 (q), 23.7 (t), 13.7 (q) ppm. MS (ESI): m/z ϭ
405 [M Ϫ 1]Ϫ, 407 [M ϩ 1]ϩ. HRMS (FAB) calcd. for C23H22N2O5
406.1529 [M]ϩ, found 406.1533.
solid. M.p. 225Ϫ227 °C. IR (KBr): ν˜ ϭ 3459, 3400, 1717, 1619,
1514, 1308, 1247, 1205, 1155, 818, 745 cmϪ1 1H NMR
.
(300.1 MHz; [D6]DMSO): δ ϭ 11.45 (s, 1 H), 10.83 (s, 1 H), 8.71
(d, J ϭ 8.2 Hz, 1 H), 8.35 (s, 1 H), 8.13 (d, J ϭ 8.5 Hz, 1 H), 7.52
(d, J ϭ 8.0 Hz, 1 H), 7.41 (dd, J ϭ 7.7, 7.2 Hz, 1 H), 7.23 (d, J ϭ
1.9 Hz, 1 H), 7.13 (dd, J ϭ 7.6, 7.3 Hz, 1 H), 6.81 (dd, J ϭ 8.5,
2.0 Hz, 1 H), 4.68 (q, J ϭ 7.1 Hz, 2 H), 3.87 (s, 3 H), 1.52 (t, J ϭ
7.1 Hz, 3 H) ppm. 13C NMR (75.5 MHz; [D6]DMSO): δ ϭ 167.2
(s), 159.0 (s), 142.6 (s), 141.3 (s), 135.8 (s), 135.3 (s), 125.7 (d),
Ethyl 2-[7-Methoxy-2-(5-methoxy-1H-indol-3-ylmethyl)-1H-indol-3-
yl]-2-oxoacetate (9g): Yellow crystals from MeCN. M.p. 124.(d), 123.6 (s), 121.4 (s), 121.1 (d), 118.7 (s), 117.6 (d), 115.3 (s),
157.0Ϫ159.0 °C. IR (KBr): ν˜ ϭ 3356, 1719, 1619, 1579, 1458 cmϪ1
.
110.6 (d), 107.6 (d), 105.8 (d), 105.0 (s), 95.3 (d), 60.8 (t), 55.2 (q),
1H NMR (300.1 MHz; [D6]acetone): δ ϭ 11.11 (br. s, 1 H), 9.97 14.5 (q). MS (ESI): m/z ϭ 357 [M Ϫ 1]Ϫ . C22H18N2O3 (358.4):
(br. s, 1 H), 7.48 (d, J ϭ 8.0 Hz, 1 H), 7.27 (d, J ϭ 8.8 Hz, 1 H), calcd. C 73.73, H 5.06, N 7.82; found C 73.61, H 4.98, N 7.75.
7.17Ϫ7.10 (m, 3 H), 6.78Ϫ6.73 (m, 2 H), 4.59 (s, 2 H), 4.28 (q, J ϭ
Ethyl 2,8-Dimethoxyindolo[3,2-b]carbazole-6-carboxylate (11e): Yel-
7.1 Hz, 2 H), 3.87 (s, 3 H), 3.75 (s, 3 H), 1.25 (t, J ϭ 7.1 Hz, 3 H)
low solid. M.p. 70Ϫ75 °C dec. IR (KBr): ν˜ ϭ 3464, 3294, 1681,
ppm. 13C NMR (75.5 MHz; [D6]acetone): δ ϭ 182.2 (s), 166.7 (s),
1485, 1294, 1215, 1197, 1158, 803 cmϪ1 1H NMR (300.1 MHz;
.
154.4 (s), 150.0 (s), 146.6 (s), 132.2 (s), 128.7 (s), 128.0 (s), 125.9
(s), 124.8 (d), 123.5 (d), 112.9 (d), 112.4 (d), 112.2 (d), 111.3 (s),
109.6 (s), 104.0 (d), 100.6 (d), 61.7 (t), 55.3 (2 ϫ q), 24.0 (t), 13.7
(q) ppm. MS (ESI): m/z ϭ 407 [M Ϫ 1]Ϫ, 405 [M ϩ 1]ϩ. HRMS
(FAB) calcd. for C23H22N2O5 406.1529 [M]ϩ, found 406.1530.
[D6]acetone): δ ϭ 10.36 (s, 1 H), 10.34 (s, 1 H), 8.54 (d, J ϭ 2.5
Hz, 1 H), 8.47 (s, 1 H), 7.77 (d, J ϭ 2.5 Hz, 1 H), 7.56 (d, J ϭ 8.7
Hz, 1 H), 7.46 (d, J ϭ 8.8 Hz, 1 H), 7.14Ϫ7.07 (m, 2 H), 4.73 (q,
J ϭ 7.1 Hz, 2 H), 3.91 (s, 3 H), 3.91 (s, 3 H), 1.58 (t, J ϭ 7.1 Hz,
3 H) ppm. 13C NMR (75.5 MHz; [D6]acetone): δ ϭ 168.5 (s), 154.8
(s), 153.7 (s), 138.6 (s), 138.2 (s), 137.3 (s), 137.1 (s), 124.9 (s), 123.7
Procedure for the Preparation of 11a؊g: MeSO3H (2.0 mL) was
added dropwise to a solution of 9 (4.0 mmol) in 1,4-dioxane (s), 123.4 (s), 122.1 (s), 116.9 (d), 116.4 (d), 112.8 (d), 111.9 (d),
(100 mL) at 21 °C under nitrogen. The mixture was heated at reflux
for 1 hfollowed by cooling to 21 °C and addition of silica (10 g).
The solvents were evaporated and the remaining solid purified with
column chromatography on silica eluting with CHCl3/hexane
(gradient 0Ϫ100%) yielding the indolocarbazoles 11 as yellow
solids.
109.5 (d), 108.0 (d), 106.0 (d), 104.1 (s), 61.6 (t), 56.3 (q), 56.2 (q),
15.2 (q) ppm. MS (ESI): m/z ϭ 387 [M Ϫ 1] Ϫ. C23H20N2O4 (388.4):
calcd. C 71.12, H 5.19, N 7.21; found C 71.08, H 5.25, N 7.16.
Ethyl 4,8-Dimethoxyindolo[3,2-b]carbazole-6-carboxylate (11f): Elu-
ent 0Ϫ50% CHCl3/hexane. Yellow solid. M.p. 176.0Ϫ177.5 °C. IR
(KBr): ν˜ ϭ 3484, 3404, 1709, 1676, 1514, 1293, 1257, 1214, 1144,
1
Ethyl Indolo[3,2-b]carbazole-6-carboxylate (11a): (92%) Identical in
798 cmϪ1. H NMR (300.1 MHz; [D6]acetone): δ ϭ 10.40 (br. s, 1
all respects with a reference that was prepared in a yield of 88%.[5]
H), 9.97 (br. s, 1 H), 8.55 (br. s, 1 H), 8.44 (s, 1 H), 7.78 (d, J ϭ
7.7 Hz, 1 H), 7.47 (d, J ϭ 8.8 Hz, 1 H), 7.18Ϫ7.03 (m, 3 H), 4.76
(q, J ϭ 7.0 Hz, 2 H), 4.06 (s, 3 H), 3.93 (s, 3 H), 1.62 (t, J ϭ 7.0
Hz, 3 H) ppm. 13C NMR (75.5 MHz; [D6]acetone): δ ϭ 168.7 (s),
153.8 (s), 146.6 (s), 138.2 (s), 137.7 (s), 137.6 (s), 131.7 (s), 124.9
(s), 124.3 (s), 123.3 (s), 122.0 (s), 120.7 (d), 117.1 (d), 113.7 (d),
112.0 (d), 109.4 (d), 108.4 (d), 107.9 (d), 106.1 (s), 61.9 (t), 56.3 (q),
56.1 (q), 15.1 (q) ppm. MS (ESI): m/z ϭ 387 [M Ϫ 1]Ϫ, 389 [M ϩ
1]ϩ. C23H20N2O4 (388.4): calcd. C 71.12, H 5.19, N 7.21; found C
71.03, H 5.14, N 7.16.
Ethyl 2-Methoxyindolo[3,2-b]carbazole-6-carboxylate (11b): Yellow
solid. (90%) This substance starts to decompose around 70 °C and
finally melts between 159.5Ϫ160.5 °C. IR (KBr): ν˜ ϭ 3410, 1675,
1
1488, 1298, 1202, 1153 cmϪ1. H NMR (300.1 MHz; [D6]DMSO):
δ ϭ 11.51 (s, 1 H), 10.78 (s, 1 H), 8.76 (d, J ϭ 8.2 Hz, 1 H), 8.51
(s, 1 H), 7.88 (d, J ϭ 2.4 Hz, 1 H), 7.61 (d, J ϭ 8.7 Hz, 1 H), 7.56
(d, J ϭ 8.0 Hz, 1 H), 7.45 (dd, J ϭ 7.8, 7.2 Hz, 1 H), 7.16 (dd, J ϭ
7.7, 7.6 Hz, 1 H), 7.10 (dd, J ϭ 8.7, 2.5 Hz, 1 H), 4.69 (q, J ϭ 7.1
Hz, 2 H), 3.90 (s, 3 H), 1.53 (t, J ϭ 7.1 Hz, 3 H) ppm. 13C NMR
(75.5 MHz; [D6]DMSO): δ ϭ 167.2 (s), 153.1 (s), 141.7 (d), 136.4 Ethyl 2,10-Dimethoxyindolo[3,2-b]carbazole-6-carboxylate (11g):
(s), 135.9 (s), 134.8 (s), 126.1 (s), 124.9 (d), 123.4 (s), 122.0 (s), Yellow solid. M.p. 170.5Ϫ172.5 °C. IR (KBr): ν˜ ϭ 3456, 3347,
Eur. J. Org. Chem. 2004, 2593Ϫ2602
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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2597

N. Wahlström, I. Romero, J. Bergman
FULL PAPER
1714, 1487, 1255, 1205, 1148 cmϪ1. 1H NMR (300.1 MHz; [D6]ace-
7.3, 7.2 Hz, 1 H), 6.85 (dd, J ϭ 8.5, 2.2 Hz, 1 H), 3.86 (s, 3 H)
tone): δ ϭ 10.55 (s, 1 H), 10.37 (s, 1 H), 8.56 (s, 1 H), 8.52 (d, J ϭ ppm. 13C NMR (75.5 MHz; [D6]DMSO): δ ϭ 190.1 (d), 159.0 (s),
8.2 Hz, 1 H), 7.77 (d, J ϭ 2.3 Hz, 1 H), 7.57 (d, J ϭ 8.8 Hz, 1 H),
7.12Ϫ7.00 (m, 3 H), 4.70 (q, J ϭ 7.1 Hz, 2 H), 3.19 (s, 3 H), 3.92
143.1 (s), 141.3 (s), 135.5 (s), 134.8 (s), 126.0 (d), 124.3 (d), 123.6
(s), 121.2 (d), 121.1 (s), 120.2 (s), 118.7 (d), 115.0 (s), 112.2 (s),
(s, 3 H), 1.57 (t, J ϭ 7.1 Hz, 3 H) ppm. 13C NMR (75.5 MHz; 111.3 (d), 108.9 (d), 108.0 (d), 96.0 (d), 55,3 (q) ppm. MS (FIA):
[D6]acetone): δ ϭ 168.5 (s), 154.9 (s), 146.6 (s), 138.8 (s), 137.1 (s),
136.4 (s), 133.5 (s), 124.8 (s), 124.1 (s), 123.7 (s), 122.5 (s), 119.3
(d), 119.0 (d), 116.4 (d), 112.8 (d), 108.4 (d), 107.1 (d), 106.0 (s),
104.0 (d), 61.1 (t), 56.2 (q), 56.0 (q), 15.0 (q) ppm. MS (ESI):
m/z ϭ 387 [M Ϫ 1]Ϫ , 389 [M ϩ 1]ϩ. C23H20N2O4 (388.4): calcd.
C 71.12, H 5.19, N 7.21; found C 71.04, H 5.15, N 7.16.
m/z ϭ 313 [M Ϫ H]Ϫ. HRMS (FAB) calcd. for C20H14N2O2
314.1055 [M]ϩ, found 314.1051.
Representative Procedure for the Preparation of 10a, 10d and 10f:
Ethyl 2-methoxyindolo[3,2-b]carbazole-6-carboxylate (11b) (1.08 g,
3.00 mmol) dissolved in THF (40 mL) was added dropwise to a
suspension of LiAlH4 (1.37 g, 36.00 mmol) in THF (50 mL) below
Ϫ10 °C under argon. The reddish suspension was then stirred for
1 h at Ϫ10 °C, and then at 0 °C for 3.5 h. The cooling bath was
removed and a saturated aqueous solution of NH4Cl was added to
quench the excess LiAlH4. The suspension was diluted with EtOAc
(200 mL) and water (100 mL) and then the organic phases were
separated. The water phase was extracted with EtOAc (2 ϫ
100 mL) and the combined organic phases were washed with brine
Representative Procedure for the Preparation of 4a, 10b and 10c:
Ethyl
Indolo[3,2-b]carbazole-6-carboxylate
(11a)
(343 mg,
1.00 mmol) dissolved in THF (12 mL) was added dropwise to a
suspension of LiAlH4 (228 mg, 6.00 mmol) in THF (40 mL) below
Ϫ10 °C under argon. The reddish suspension was then stirred for
1 h at Ϫ10 °C, and then at 0 °C for 3.5 h. The cooling bath was
removed and a saturated aqueous solution of NH4Cl was added to
quench the excess LiAlH4. EtOAc (200 mL) and water (100 mL) (2 ϫ 100 mL) and finally dried with MgSO4. Evaporation of the
were then added to the suspension. The organic phases were sepa- solvents produced a yellow solid that was dissolved by gentle heat-
rated and the water phase extracted with EtOAc (2 ϫ 100 mL). ing in 1,4-dioxane (100 mL). DDQ (0.68 g, 3.00 mmol) dissolved in
The combined organic phases were then washed with brine (2 ϫ
1,4-dioxane (6 mL) was added dropwise during 15 minutes under
100 mL) and finally dried with MgSO4. Evaporation of the solvents
argon at 40 °C. After 15 h at 21 °C, 1  NaOH (100 mL) and
produced a yellow solid (290 mg) which was dissolved by gentle EtOAc (300 mL) were added. The organic phases were separated
heating in 1,4-dioxane (60 mL) under argon. A solution of DDQ
(227 mg, 1.00 mmol) in dioxane (3 mL) was added over 10 min.
The resulting suspension was stirred for 48 h to ensure complete
dehydrogenation. EtOAc (300 mL) and a saturated aqueous solu-
tion of NaHCO3 (100 mL) were added and the mixture stirred for
1 h. The precipitate formed was collected and washed with an ex-
cess of water and EtOAc. The yellow solid was dried at 240 °C
and 0.12 mbar to give 77 mg of 4a. The organic solvents from the
washings were separated and the aqueous phase extracted with
EtOAc (3 ϫ 100 mL). The combined organic extracts were washed
with water (100 mL) and brine (100 mL) and dried with MgSO4.
Evaporation of the solvents produced a further 163 mg of 4a.
and the aqueous phase extracted with EtOAc (2 ϫ 100 mL). The
combined organic phases were washed with water (100 mL), then
brine (2 ϫ 100 mL) and dried with MgSO4. The solvents were eva-
porated onto silica (5 g) and the residue subjected to gravity col-
umn chromatography (silica) with EtOAc as eluent to give indolo-
carbazole 10a (0.82 g, 87%) as an orange solid.
2-Methoxyindolo[3,2-b]carbazole-6-carboxaldehyde (10a): Orange
solid. M.p. 282.5Ϫ284.0 °C. IR (KBr): ν˜ ϭ 3391, 3375, 1657, 1487,
1
1463, 1215, 1086, 1031 cmϪ1. H NMR (300.1 MHz; [D6]DMSO):
δ ϭ 11.61 (s, 1 H), 11.56 (s, 1 H), 11.34 (s, 1 H), 8.60 (s, 1 H), 8.54
(d, J ϭ 8.1 Hz, 1 H), 7.89 (d, J ϭ 1.9 Hz, 1 H), 7.64 (d, J ϭ 8.7
Hz, 1 H), 7.59 (d, J ϭ 8.2 Hz, 1 H), 7.48 (dd, J ϭ 7.7, 7.3 Hz, 1
H), 7.19 (dd, J ϭ 7.6, 7.4 Hz, 1 H), 7.08 (dd, J ϭ 8.7, 2.2 Hz, 1
H), 3.89 (s, 3 H) ppm. 13C NMR (75.5 MHz; [D6]DMSO): δ ϭ
189.8 (d), 153.5 (s), 141.6 (s), 136.3 (s), 135.9 (s), 134.4 (s), 126.4
(d), 124.5 (d), 123.5 (s), 121.7 (s), 120.9 (s), 118.8 (d), 115.3 (d),
112.7 (d), 112.2 (s), 111.4 (d), 110.1 (d), 103.4 (d), 55.6 (q) ppm
(one carbon resonance not observed). MS (ESI): m/z ϭ 313 [M Ϫ
H]Ϫ. C20H14N2O2 (314.3): calcd. C 76.42, H 4.49, N 8.91; found C
76.52, H 4.37, N 8.92.
Indolo[3,2-b]carbazole-6-carboxaldehyde (4a): Spectral and physical
data were identical with a reference sample.[5]
8-Methoxyindolo[3,2-b]carbazole-6-carboxaldehyde (10b): The alde-
hyde 10b was prepared from 11c in a similar manner to that for 4a.
Yellow solid, M.p. 341.0Ϫ345.5 °C. IR (KBr): ν˜ ϭ 3462, 3383,
3351, 1659, 1484, 1458, 1213, 1088, 810, 752 cmϪ1 1H NMR
.
(500.2 MHz; [D6]DMSO): δ ϭ 11.73 (s, 1 H), 11.43 (s, 1 H), 11.33
(s, 1 H), 8.57 (s, 1 H), 8.28 (d, J ϭ 7.3 Hz, 1 H), 8.02 (d, J ϭ 2.3
Hz, 1 H), 7.73 (d, J ϭ 7.8 Hz, 1 H), 7.52 (d, J ϭ 8.7 Hz, 1 H),
2,8-Dimethoxyindolo[3,2-b]carbazole-6-carboxaldehyde (10d): The
7.44 (dd, J ϭ 7.8, 7.3 Hz, 1 H), 7.23 (dd, J ϭ 7.8, 7.3 Hz, 1 H), aldehyde 10d was prepared from 11e using the same procedure as
7.16 (dd, J ϭ 8.7, 2.3 Hz, 1 H), 3.91 (s, 3 H) ppm. 13C NMR
(125.8 MHz; [D6]DMSO): δ ϭ 190.0 (d), 152.9 (s), 141.6 (s), 136.7
(s), 135.4 (s), 126.2 (d), 123.3 (s), 121.4 (s), 121.3 (s), 121.0 (s),
for 10a. Orange-reddish solid. M.p. 312.0 °C (dec.). IR (neat): ν˜ ϭ
3388, 3355, 2992, 2834, 1654, 1620, 1484, 1296, 2307, 1082, 1027,
1
812, 797 cmϪ1. H NMR (500.2 MHz; [D6]DMSO): δ ϭ 11.56 (s,
120.3 (d), 119.2 (d), 116.6 (d), 112.2 (d), 112.0 (s), 112.0 (d), 110.1 1 H), 11.42 (s, 1 H), 11.31 (s, 1 H), 8.57 (s, 1 H), 7.99 (d, J ϭ 2.3
(d), 106.6 (d), 55.7 (q) ppm (one carbon resonance not observed). Hz, 1 H), 7.87 (d, J ϭ 2.2 Hz, 1 H), 7.63 (d, J ϭ 8.7 Hz, 1 H),
MS (FIA): m/z ϭ 315 [M ϩ H]ϩ. C20H14N2O2 (314.3): calcd. C 7.51 (d, J ϭ 8.7 Hz, 1 H), 7.15 (dd, J ϭ 8.7, 2.3 Hz, 1 H), 7.07
76.42, H 4.49, N 8.91; found C 76.34, H 4.44, N 8.85.
(dd, J ϭ 8.7, 2.2 Hz, 1 H), 3.91 (s, 3 H), 3.89 (s, 3 H) ppm. 13C
NMR (125.8 MHz; [D6]DMSO): δ ϭ 189.8 (d), 153.5 (s), 152.9 (s),
136.8 (s), 136.3 (s), 136.0 (s), 135.1 (s), 123.4 (s), 121.8 (s), 121.5
(s), 121.0 (s), 116.6 (d), 115.3 (d), 112.7 (d), 112.2 (d), 111.9 (s),
110.3 (d), 106.5 (d), 103.4 (d), 55.7 (q), 55.6 (q) ppm. MS (ESI):
m/z ϭ 345 [M ϩ 1]ϩ, 343 [M Ϫ 1]Ϫ. C21H16N2O3 (344.4): calcd. C
73.24, H 4.68, N 8.13; found C 73.20, H 4.61, N 8.15.
3-Methoxyindolo[3,2-b]carbazole-6-carboxaldehyde (10c): The alde-
hyde 10c was prepared from 11d in a similar manor as for 4a. Yel-
low solid. This sample gradually becomes darker and finally melts
between 374.0Ϫ379.0 °C. IR (KBr): ν˜ ϭ 3377, 1654, 1617, 1310,
1243, 745 cmϪ1. 1H NMR (300.1 MHz; [D6]DMSO): δ ϭ 11.61 (s,
1 H), 11.56 (s, 1 H), 11.33 (s, 1 H), 8.52 (d, J ϭ 8.1 Hz, 1 H), 8.46
(s, 1 H), 8.54 (d, J ϭ 8.5 Hz, 1 H), 7.58 (d, J ϭ 8.1 Hz, 1 H), 7.46 2,10-Dimethoxyindolo[3,2-b]carbazole-6-carboxaldehyde (10f): The
(dd, J ϭ 7.6, 7.3 Hz, 1 H), 7.30 (d, J ϭ 2.1 Hz, 1 H), 7.18 (dd, J ϭ aldehyde 10f was prepared from 11g using the same procedure as
2598
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 2593Ϫ2602

Synthesis of Metabolites of the Ah Receptor Ligand 6-Formylindolo[3,2-b]carbazole
FULL PAPER
for 10a. Red solid. M.p. 295.0Ϫ296.0 °C. IR (KBr): ν˜ ϭ 3429,
3206, 2993, 2832, 1646, 1617, 1595, 1559, 1486, 1249, 1217, 1070
phases were washed with brine (50 mL) and dried with MgSO4 and
the solvents evaporated to produce the crude indolocarbazole 12a
cmϪ1. 1H NMR (300.1 MHz; [D6]DMSO): δ ϭ 11.73 (s, 1 H), 11.57 as a yellow solid. This solid was dissolved in DMF (10 mL) under
(s, 1 H), 11.31 (s, 1 H), 8.55 (s, 1 H), 8.09 (d, J ϭ 7.8 Hz, 1 H), argon. Imidazole (249 mg, 3.66 mmol) and tert-butyldimethylsilyl
7.85 (d, J ϭ 2.3 Hz, 1 H), 7.64 (d, J ϭ 8.8 Hz, 1 H), 7.16Ϫ7.05 chloride (551 mg, 3.66 mmol) were added and the solution stirred
(m, 3 H), 4.04 (s, 3 H), 3.89 (s, 3 H) ppm. 13C NMR (75.5 MHz;
until the starting material disappeared (90 min) as judged from
[D6]DMSO): δ ϭ 189.8 (d), 153.5 (s), 145.8 (s), 136.3 (s), 135.9 (s), TLC. EtOAc (100 mL) and water (50 mL) were added and the or-
134.3 (s), 131.9 (s), 123.4 (s), 122.1 (s), 121.7 (s), 119.3 (d), 116.8 ganic phase separated. The aqueous phase was extracted with
(d), 115.4 (d), 112.8 (d), 111.9 (s), 110.6 (d), 106.5 (d), 103.2 (d), EtOAc (100 mL). The combined organic phases were washed with
55.6 (q), 55.4 (q) ppm (one carbon resonance not observed). MS
(ESI): m/z ϭ 345 [M ϩ 1]ϩ. HRMS (FAB) calcd. for C21H16N2O3
344.1161 [M]ϩ, found 344.1166.
water (50 mL) and brine (50 mL) and then dried with MgSO4.
Evaporation produced a semisolid that was subjected to column
chromatography with EtOAc/hexane (0Ϫ20%) as eluent. The silyl-
ated indolocarbazole 12a was obtained in 110 mg (72%) as an or-
ange-reddish solid.
4,8-Dimethoxyindolo[3,2-b]carbazole-6-carboxaldehyde (10e): Ethyl
4,8-Dimethoxyindolo[3,2-b]carbazole-6-carboxylate (11f) (405 mg,
1.04 mmol) dissolved in THF (10 mL) was added during 10 mi-
nutes to a suspension of LiAlH4 (490 mg, 12.51 mmol) in THF
(40 mL) at Ϫ10 °C under nitrogen, and then stirred for an ad-
ditional period of 4 h. The temperature was then raised to 21 °C
over 2 h. The cooling bath was then removed and a saturated aque-
ous solution of NH4Cl (2 mL) was carefully added. EtOAc
(200 mL) and water (100 mL) were added and the organic phases
were separated. The water phase was extracted with EtOAc (2 ϫ
75 mL). The combined organic phases were washed with brine (2
ϫ 100 mL) and then dried with MgSO4 and then evaporated to
give a yellow solid. This solid was dissolved in 1,4-dioxane (40 mL)
under nitrogen and warmed to 40 °C. DDQ (236 mg, 1.04 mmol)
dissolved in 1,4-dioxane (4 mL) was added over 15 minutes and the
reaction mixture stirred for 14 h at 21 °C. EtOAc (300 mL) and a
saturated aqueous solution of NaHCO3 (150 mL) were added. The
organic phase was separated, and the aqueous phase extracted with
EtOAc (3 ϫ 100 mL). The combined organic phases were washed
with water (2 ϫ 100 mL) and brine (2 ϫ 100 mL) and then dried
with MgSO4. As the solvents were reduced in volume, a red solid
precipitated. The solid was collected and washed with EtOAc and
then dried to give 130 mg of 10f. Another crop gave an additional
96 mg of 10f. Silica (3 g) was added to the filtrate and the solvents
were removed. Column chromatography (silica) with EtOAc as elu-
ent produced a further 55 mg of the yellow-reddish indolocarbazole
10f. The total yield of 10f was 281 mg (78%). M.p. 292.5Ϫ296.5
°C. IR (KBr): ν˜ ϭ 3435, 3409, 2923, 2852, 1655, 1605, 1487, 1259,
2-(tert-Butyldimethylsilyloxy)indolo[3,2-b]carbazole-6-carboxal-
dehyde (12a): Orange solid. M.p. 296.5Ϫ298.5 °C. IR (KBr): ν˜ ϭ
3433, 3234, 2955, 2929, 2857, 1649, 1618, 1597, 1464, 1264, 1085,
900 cmϪ1. 1H NMR (300.1 MHz; [D6]DMSO): δ ϭ 11.57 (s, 1 H),
11.56 (s, 1 H), 11.33 (s, 1 H), 8.60 (s, 1 H), 8.54 (d, J ϭ 8.1 Hz, 1
H), 7.75 (d, J ϭ 2.3 Hz, 1 H), 7.62Ϫ7.58 (m, 2 H), 7.48 (dd, J ϭ
7.5, 7.3 Hz, 1 H), 7.19 (dd, J ϭ 7.2, 7.1 Hz, 1 H), 6.98 (dd, J ϭ
8.6, 2.3 Hz, 1 H), 1.02 (s, 9 H), 0.25 (s, 6 H) ppm. 13C NMR
(75.5 MHz; [D6]DMSO): δ ϭ 189.8 (d), 148.4 (s), 141.6 (s), 136.7
(s), 136.0 (s), 134.4 (s), 126.4 (d), 124.5 (d), 123.3 (s), 122.0 (s),
121.8 (s), 120.9 (s), 119.4 (d), 118.8 (d), 112.5 (d), 112.1 (s), 111.4
(d), 110.4 (d), 110.3 (d), 25.7 (q), 18.0 (q), Ϫ4.4 (q) ppm. MS (ESI):
m/z ϭ 415 [M ϩ 1]ϩ, 413 [M Ϫ 1]Ϫ. C25H26N2O2Si (414.6): calcd.
C 72.43, H 6.32, N 6.76; found C 72.28, H 6.30, N 6.67.
3-(tert-Butyldimethylsilyloxy)indolo[3,2-b]carbazole-6-carboxal-
dehyde (12c): The silylated ICZ 12c was prepared from 10c using
the same procedure as for 12a. Orange solid. M.p. 318.5Ϫ323.0 °C.
IR (KBr): ν˜ ϭ 3424, 3387, 2954, 2928, 2857, 1650, 1622, 1248,
1
1152, 859 cmϪ1. H NMR (300.1 MHz; [D6]DMSO): δ ϭ 11.58 (s,
1 H), 11.56 (s, 1 H), 11.33 (s, 1 H), 8.51 (d, J ϭ 8.1 Hz, 1 H), 8.46
(s, 1 H), 8.12 (d, J ϭ 8.4 Hz, 1 H), 7.58 (d, J ϭ 8.1 Hz, 1 H), 7.46
(dd, J ϭ 8.0, 7.2 Hz, 1 H), 7.27 (d, J ϭ 2.1 Hz, 1 H), 7.19 (dd, J ϭ
7.9, 7.2 Hz, 1 H), 6.75 (dd, J ϭ 8.4, 2.1 Hz, 1 H), 1.00 (s, 9 H),
0.26 (s, 6 H) ppm. 13C NMR (75.5 MHz; [D6]DMSO): δ ϭ 190.0
(d), 154.5 (s), 143.0 (s), 141.3 (s), 135.5 (s), 134.8 (s), 126.1 (d),
124.3 (d), 123.5 (s), 121.1 (d), 121.0 (s), 120.5 (s), 118.8 (d), 115.7
(s), 112.7 (d), 112.2 (s), 111.4 (d), 109.0 (d), 102.7 (d), 25.6 (q), 18.0
(q), Ϫ4.4 (q) ppm. C25H26N2O2Si (414.6): calcd. C 72.43, H 6.32,
N 6.76; found C 72.29, H 6.26, N 6.67.
1211, 1073, 802 cmϪ1 1H NMR (300.1 MHz; [D6]DMSO): δ ϭ
.
11.45 (s, 1 H), 11.30 (s, 1 H), 10.95 (s, 1 H), 8.56 (s, 1 H), 8.23 (d,
J ϭ 2.4 Hz, 1 H), 7.90 (d, J ϭ 7.7 Hz, 1 H), 7.51 (d, J ϭ 8.8 Hz,
1 H), 7.24Ϫ7.10 (m, 3 H), 4.04 (s, 3 H), 3.90 (s, 3 H) ppm. 13C
NMR (75.5 MHz; [D6]DMSO): δ ϭ 190.9 (d), 152.7 (s), 145.3 (s),
136.9 (s), 136.4 (s), 135.8 (s), 130.5 (s), 123.5 (s), 122.7 (s), 121.1
(s), 120.9 (s), 120.3 (d), 116.8 (d), 113.1 (d), 112.2 (s), 112.0 (d),
110.3 (d), 107.5 (d), 106.9 (d), 55.7 (q), 55.6 (q) ppm. MS (ESI):
m/z ϭ 343 [M Ϫ 1]Ϫ. HRMS (FAB) calcd. for C21H16N2O3
344.1161 [M]ϩ, found 344.1164.
2,8-Bis(tert-butyldimethylsilyloxy)indolo[3,2-b]carbazole-6-carb-
oxaldehyde (12d): The silylated ICZ 12d was prepared from 10d
using the same procedure as for 12a. Red solid. M.p. 268 °C (dec.).
IR (neat): ν˜ ϭ 3430, 2954, 2928, 2856, 1647, 1595, 1471, 1259,
1191, 1079, 891, 778 cmϪ1 1H NMR (300.1 MHz; [D6]DMSO):
.
δ ϭ 11.57 (s, 1 H), 11.38 (s, 1 H), 11.20 (s, 1 H), 8.47 (s, 1 H), 7.99
(d, J ϭ 2.1 Hz, 1 H), 7.74 (d, J ϭ 2.3 Hz, 1 H), 7.58 (d, J ϭ 8.6
Hz, 1 H), 7.47 (d, J ϭ 8.7 Hz, 1 H), 7.05 (dd, J ϭ 8.7, 2.2 Hz, 1
H), 6.98 (dd, J ϭ 8.6, 2.3 Hz, 1 H), 1.02 (s, 9 H), 1.01 (s, 9 H),
0.25 (s, 6 H), 0.24 (s, 6 H) ppm. 13C NMR (75.5 MHz; [D6]DMSO):
δ ϭ 189.3 (d) 148.4 (s), 147.7 (s), 137.2 (s), 136.8 (s), 136.5 (s),
135.2 (s), 123.4 (s), 122.1 (s), 121.3 (s), 121.1 (s), 120.2 (d), 119.4
(d), 114.0 (d), 112.4 (d), 112.0 (s), 111.9 (d), 110.5 (s), 110.4 (d),
25.7 (q), 25.7 (q), 18.0 (s), 18.0 (s), Ϫ4.4 (2 ϫ q) ppm. MS (ESI):
m/z ϭ 545 [M ϩ 1]ϩ, 543 [M Ϫ 1]Ϫ. HRMS (FAB) calcd. for
C31H40N2O3Si2 [M]ϩ 544.2577, found 544.2592.
Representative Procedure for the Preparation of the Silylated Indolo-
carbazoles 12a, 12c؊f: BBr3 (1  in CH2Cl2, 3.66 mL, 10 equiv.)
was added during 25 minutes to a suspension of 2-methoxyin-
dolo[3,2-b]carbazole-6-carboxaldehyde (10a) (115 mg, 0.36 mmol)
in CH2Cl2 (50 mL) at Ϫ78 °C under argon. After addition was
complete, the temperature was slowly raised to 21 °C and the mix-
ture stirred for 12 h. The suspension was then cooled to 0 °C and
a saturated aqueous solution of NaHCO3 (5 mL) was added and
the resulting slurry stirred 1 h. The bulk of the dichloromethane
was evaporated and the precipitate dissolved in EtOAc (100 mL)
and water (50 mL). The organic layer was separated and the aque-
ous phase extracted with EtOAc (100 mL). The combined organic
4,8-Bis(tert-butyldimethylsilyloxy)indolo[3,2-b]carbazole-6-carb-
oxaldehyde (12e): The silylated ICZ 12e was prepared from 10e
Eur. J. Org. Chem. 2004, 2593Ϫ2602
www.eurjoc.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2599

N. Wahlström, I. Romero, J. Bergman
FULL PAPER
using the same procedure as for 12a. Orange solid. M.p.
209.0Ϫ211.5 °C. IR (neat): ν˜ ϭ 3420, 3387, 2952, 2928, 2856, 1653,
Representative Procedure for the Preparation of the Hydroxylated
Indolocarbazoles 5a؊e: Tetrabutylammonium fluoride (1  in THF,
1604, 1476, 1266, 1205, 893, 836, 777 cmϪ1. 1H NMR (300.1 MHz; 0.37 mL, 0.37 mmol) was added to a solution of 2-(tert-butyl-
[D6]acetone): δ ϭ 11.38 (s, 1 H), 10.63 (br. s, 1 H), 10.56 (br. s, 1
dimethylsilyloxy)indolo[3,2-b]carbazole-6-carboxaldehyde
(12a)
H), 8.56 (s, 1 H), 7.95 (d, J ϭ 2.3 Hz, 1 H), 7.87 (d, J ϭ 7.8 Hz, 1 (70 mg, 0.169 mmol) in THF (12 mL) at 0Ϫ2 °C under argon. After
H), 7.54 (d, J ϭ 8.7 Hz, 1 H), 7.19Ϫ7.12 (m, 2 H), 7.04 (dd, J ϭ
10Ϫ20 min the reaction was complete as judged by TLC. A buffer
7.7, 0.8 Hz, 1 H), 1.18 (s, 9 H), 1.08 (s, 9 H), 0.37 (s, 6 H), 0.31 (s,
solution (pH 7.4, 60 mL) was added and the resulting slurry stirred
6 H) ppm. 13C NMR (75.5 MHz; [D6]acetone): δ ϭ 191.0 (d), 149.9 for 30Ϫ60 min. A yellow-brownish solid was collected and washed
(s), 142.0 (s, 1 H), 138.6 (s), 137.3 (s), 136.5 (s), 134.6 (s), 125.1 (s),
with excess water before drying at reduced pressure. The dried solid
124.8 (s), 123.3 (s), 122.8 (s), 121.7 (d), 121.4 (d), 116.7 (d), 114.9 was boiled 3 times in hexane, each time carefully removing the sol-
(d), 114.8 (d), 113.5 (s), 113.0 (d), 111.1 (d), 26.3 (2 ϫ q), 19.0 (s), vents with a pipette. The insoluble indolocarbazole 5a was obtained
18.9 (s), Ϫ4.0 (q), Ϫ4.1 (q) ppm. MS (ESI): m/z ϭ 543 [M Ϫ 1]Ϫ,
545 [M ϩ 1]ϩ. HRMS (FAB) calcd. for C31H40N2O3Si2 [M]ϩ
544.2577, found 544.2570.
in 48 mg (95%) as a yellow-brownish solid.
In the spectroscopic data of the metabolites 5aϪb and 5dϪf, the
1H NMR spectra ([D6]acetone) is included for comparison with the
previous data.[8] Due to the low solubility of 5aϪb and 5dϪf, 13C
NMR spectra in [D6]acetone could not be recorded.
2,10-Bis(tert-butyldimethylsilyloxy)indolo[3,2-b]carbazole-6-carb-
oxaldehyde (12f): The silylated ICZ 12f was prepared from 10f
using the same procedure as for 12a. The red solid starts to decom-
pose at 210 °C and finally melts at 245.0 °C. IR (neat): ν˜ ϭ 3463, 2-Hydroxyindolo[3,2-b]carbazole-6-carboxaldehyde (5a): This or-
3425, 3375, 2950, 2923, 2850, 1655, 1619, 1461, 1267, 1251, 1100, ange solid starts to decompose at 341.5 °C and finally melts be-
891, 827, 778 cmϪ1. 1H NMR (300.1 MHz; [D6]acetone): δ ϭ 11.40 tween 351.0Ϫ354.5 °C. IR (KBr): ν˜ ϭ 3391, 3375, 1657, 1487, 1463,
(s, 1 H), 11.05 (br. s, 1 H), 10.28 (br. s, 1 H), 8.57 (s, 1 H), 8.08 (d,
1215, 1086, 1031 cmϪ1. 1H NMR (500.2 MHz; [D6]acetone, 294 K):
J ϭ 8.0 Hz, 1 H), 7.70Ϫ7.67 (m, 2 H), 7.13 (dd, J ϭ 7.9, 7.8 Hz, δ ϭ 11.43 (s, 1 H), 10.98 (br. s, 1 H), 10.65 (br. s, 1 H), 8.52 (3,
1 H), 7.07Ϫ7.03 (m, 2 H), 1.11 (s, 9 H), 1.06 (s, 9 H), 0.38 (s, 6 H),
0.28 (s, 6 H) ppm. 13C NMR (75.5 MHz; [D6]acetone): δ ϭ 190.6
(d), 150.3 (s), 142.7 (s), 138.0 (s), 137.6 (s), 135.8 (s), 135.8 (s),
1H), 8.49 (d, J ϭ 8.2 Hz, 1 H), 8.06 (s, 1 H), 7.65 (d, J ϭ 2.3 Hz,
1 H), 7.63 (d, J ϭ 8.7 Hz, 1 H), 7.62 (d, J ϭ 7.8 Hz, 1 H), 7.48
(ddd, J ϭ 7.8, 6.8, 0.9 Hz, 1 H), 7.24 (ddd, J ϭ 7.8, 6.8, 0.9 Hz, 1
1
124.8 (s), 124.4 (s), 124.3 (s), 123.6 (s), 120.8 (d), 120.7 (d), 118.4 H), 7.05 (dd, J ϭ 8.7, 2.3 Hz, 1 H) ppm. H NMR (300.1 MHz;
(d), 115.7 (d), 113.5 (s), 113.3 (d), 111.3 (d), 111.2 (d), 26.4 (q), [D6]DMSO): δ ϭ 11.53 (s, 1 H), 11.44 (s, 1 H), 11.32 (s, 1 H), 9.04
26.3 (q), 19.1 (s), 18.9 (s), Ϫ3.8 (q), Ϫ4.1 (q) ppm. MS (ESI): m/z (br. s, 1 H), 8.53 (d, J ϭ 7.8 Hz, 1 H), 8.47 (s, 1 H), 7.59Ϫ7.54 (m,
[M
ϩ
1]ϩ 545, [M
Ϫ
1]Ϫ 543. HRMS (FAB) calcd. for
3 H), 7.47 (dd, J ϭ 7.8, 7.3 Hz, 1 H), 7.18 (dd, J ϭ 7.8, 7.3 Hz, 1
H), 6.94 (dd, J ϭ 8.7, 1.8 Hz, 1 H) ppm. 13C NMR (75.5 MHz;
[D6]DMSO): δ ϭ 189.7 (d), 151.0 (s), 141.5 (s), 136.0 (s), 135.4 (s),
134.2 (s), 126.3 (d), 124.5 (d), 123.4 (s), 122.0 (s), 121.6 (s), 121.0
(s), 118.7 (d), 115.6 (d), 112.5 (d), 112.1 (s), 111.4 (d), 110.0 (d),
105.2 (d) ppm. MS EI(30 eV): m/z (%) ϭ 300 (41) [M]ϩ, 73 (97),
60 (100). HRMS (FAB) calcd. for C19H12N2O2 [M]ϩ 300.0899,
found 300.0910.
C31H40N2O3Si2 544.2577 [M]ϩ, found 544.2569.
8-(tert-Butyldimethylsilyloxy)indolo[3,2-b]carbazole-6-carboxal-
dehyde (12b): BBr3 (1  in CH2Cl2, 10 mL, 10.00 mmol) was added
over 30 minutes to a cooled (Ϫ78 °C) suspension of 8-methoxyin-
dolo[3,2-b]carbazole-6-carboxaldehyde (10b) (314 mg, 1.00 mmol)
in CH2Cl2 (80 mL). The temperature of the resulting suspension
was raised to 21 °C over 26 h, and after that time demethylation
was complete as judged by TLC (eluent 75% EtOAc/hexane). A
saturated aqueous solution of NaHCO3 (30 mL) was added and
the dichloromethane removed under reduced pressure. The precipi-
tate was filtered and washed with excess water and then dried at
60 °C and 0.01 mbar to give a red solid. The solid was suspended
in DMF (15 mL) under argon, followed by addition of imidazole
(410 mg, 6.00 mmol) and tert-butyldimethylsilyl chloride (754 mg,
5.00 mmol). The mixture was stirred for 48 h and then poured into
water (200 mL) and extracted with EtOAc (4 ϫ 50 mL). The com-
bined organic layers were washed with water (3 ϫ 50 mL) and brine
(50 mL) before drying over MgSO4. Evaporation produced the
crude product that was subjected to column chromatography on
silica with EtOAc/hexane (0Ϫ50%) as eluent. The silylated indolo-
carbazole 12b was obtained in 184 mg (44%) as an orange solid.
An analytical sample was recrystallized from toluene. M.p.
322.0Ϫ326.5 °C. IR (neat): ν˜ ϭ 3401, 3340, 2954, 2928, 2856, 1661,
8-Hydroxyindolo[3,2-b]carbazole-6-carboxaldehyde (5b): The hy-
droxyindolocarbazole 5b was prepared from 12b using the same
procedure as for 5a. Brick red solid. M.p. 371.0Ϫ373.5 °C. IR
(neat): ν˜ ϭ 3428, 3387, 3309, 1643, 1597, 1476, 1196, 1085, 819,
1
756 cmϪ1. H NMR (500.2 MHz; [D6] acetone, 294 K): δ ϭ 11.36
(s, 1 H), 11.17 (br. s, 1 H), 10.44 (br. s, 1 H), 8.56 (s, 1 H), 8.23 (d,
J ϭ 7.8 Hz, 1 H), 8.04 (s, 1 H), 7.88 (d, J ϭ 1.8 Hz, 1 H), 7.79 (d,
J ϭ 8.2 Hz, 1 H), 7.50Ϫ7.45 (m, 2 H), 7.25 (dd, J ϭ 7.4, 7.3 Hz,
1
1 H), 7.11 (dd, J ϭ 8.2, 1.8 Hz, 1 H) ppm. H NMR (500.2 MHz;
[D6]DMSO): δ ϭ 11.66 (s, 1 H, NH-5), 11.27 (s, 1 H, NH-11),
11.23 (s, 1 H, CHO-6), 9.03 (s, 1 H, OH-8), 8.53 (s, 1 H, CH-12),
8.27 (d, J ϭ 7.3 Hz, 1 H, CH-1), 7.83 (d, J ϭ 1.8 Hz, 1 H, CH-7),
7.73 (d, J ϭ 7.8 Hz, 1 H, CH-4), 7.44Ϫ7.41 (m, 2 H, CH-3 and
CH-10), 7.22 (dd, J ϭ 7.8, 7.3 Hz, 1 H, CH-2), 7.03 (dd, J ϭ 8.7,
2.3 Hz, 1 H, CH-9) ppm. 13C NMR (125.8 MHz; [D6]DMSO): δ ϭ
189.4 (d), 150.4 (s), 141.5 (s), 136.0 (s), 135.5 (s), 135.2 (s), 126.2
(d), 123.1 (s), 121.3 (2 ϫ s), 121.3 (s), 120.3 (d), 119.2 (d), 116.6
(d), 112.1 (s), 112.0 (d), 111.9 (d), 110.0 (d), 108.6 (d) ppm. MS
EI(70 eV): m/z (%) ϭ 300 (21) [M]ϩ, 272 (9), 242 (9), 87 (10), 74
(17), 73 (61), 64 (39), 63 (22), 61 (18), 60 (100). HRMS (FAB)
calcd. for C19H12N2O2 [M]ϩ 300.0899, found 300.0887.
1604, 1476, 1458, 1263, 1205, 894, 807, 775, 732 cmϪ1. H NMR
1
(300.1 MHz; [D6]DMSO): δ ϭ 11.76 (s, 1 H), 11.46 (s, 1 H), 11.23
(s, 1 H), 8.57 (s, 1 H), 8.28 (d, J ϭ 7.6 Hz, 1 H), 8.03 (d, J ϭ 2.2
Hz, 1 H), 7.72 (d, J ϭ 8.1 Hz, 1 H), 7.49Ϫ7.41 (m, 2 H), 7.23 (dd,
J ϭ 7.9, 7.1 Hz, 1 H), 7.06 (dd, J ϭ 8.7, 2.2 Hz, 1 H), 1.02 (s, 9
H), 0.26 (s, 6 H) ppm. 13C NMR (75.5 MHz; [D6]DMSO): δ ϭ
189.5 (d), 147.7 (s), 141.6 (s), 137.2 (s), 135.8 (s), 135.5 (s), 126.3 3-Hydroxyindole[3,2-b]carbazole-6-carboxaldehyde (5c): The hy-
(d), 123.4 (s), 121.4 (s), 121.3 (s), 121.2 (s), 121.0 (s), 120.4 (d),
120.3 (d), 119.2 (d), 114.1 (d), 111.9 (d), 111.9 (d), 110.0 (d), 25.8
droxyindolocarbazole 5c was prepared from 12c using the same
procedure as for 5a. Yellow solid. M.p. 380 °C (dec.). IR (KBr):
(q), 18.0 (s), Ϫ4.4 (q) ppm. C25H26N2O2Si (414.6): calcd. C 72.43, ν˜ ϭ 3377, 1654, 1617, 1310, 1243, 745 cmϪ1. 1H NMR (500.2 MHz;
H 6.32, N 6.76; found C 72.29, H 6.28, N 6.63.
[D6]acetone, 294 K): δ ϭ 11.42 (s, 1 H), 11.01 (s, 1 H), 10.62 (s, 1
2600
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 2593Ϫ2602

Synthesis of Metabolites of the Ah Receptor Ligand 6-Formylindolo[3,2-b]carbazole
FULL PAPER
H), 8.58 (s, 1 H), 8.45 (d, J ϭ 7.8 Hz, 1 H), 8.43 (s, 1 H), 8.02 (d, H), 7.95 (d, J ϭ 7.8 Hz, 1 H), 7.64Ϫ7.62 (m, 2 H), 7.08Ϫ7.05 (m,
J ϭ 8.2 Hz, 1 H), 7.60 (d, J ϭ 8.2 Hz, 1 H), 7.45 (dd, J ϭ 8.2, 6.9 2 H), 6.97 (d, J ϭ 7.3 Hz, 1 H) ppm. 1H NMR (300.1 MHz;
Hz, 1 H), 7.26 (d, J ϭ 2.3 Hz, 1 H), 7.22 (dd, J ϭ 7.4, 6.8 Hz, 1
H), 6.81 (dd, J ϭ 8.2, 2.3 Hz, 1 H) ppm. 13C NMR (125.8 MHz; (br. s, 1 H), 9.03 (s, 1 H), 8.41 (s, 1 H), 7.92 (d, J ϭ 7.9 Hz, 1 H),
[D6]acetone): δ ϭ 190.8 (d), 158.3 (s), 144.4 (s), 142.5 (s), 136.8 (s),
7.55Ϫ7.52 (m, 2 H), 7.01Ϫ6.88 (m, 3 H) ppm. 13C NMR
136.1 (s), 126.8 (d), 125.3 (s), 124.9 (d), 122.6 (s), 121.9 (d), 121.7 (75.5 MHz; [D6]DMSO): δ ϭ 189.7 (d), 151.0 (s), 143.2 (s), 135.9
[D6]DMSO): δ ϭ 11.40 (s, 1 H), 11.33 (s, 1 H), 11.27 (s, 1 H), 9.94
(s), 120.0 (d), 115.7 (s), 113.4 (s), 112.2 (d), 109.9 (d), 109.2 (d),
98.6 (d) ppm. HRMS (FAB) calcd. for C19H12N2O2 300.0899 [M]ϩ
found 300.0898.
(s), 135.4 (s), 134.2 (s), 131.9 (s), 123.1 (s), 122.3 (s), 122.2 (s), 121.9
(s), 119.4 (d), 115.5 (d), 115.2 (d), 112.6 (d), 111.8 (s), 110.3 (2 ϫ
d), 104.9 (d) ppm. MS (ESI): m/z ϭ 317 [M ϩ 1]ϩ, 315 [M Ϫ 1]Ϫ.
HRMS (FAB) calcd. for C19H12N2O3 316.0848 [M]ϩ, found
316.0849.
2,8-Dihydroxyindolo[3,2-b]carbazole-12-carboxaldehyde (5d): The
hydroxyindolocarbazole 5d was prepared from 12d using the same
procedure as for 5a. Red solid. M.p. 383.0Ϫ385.5 °C. IR (KBr):
Indolo[3,2-b]carbazole-6-carboxylic Acid (13a): The ester 11a
(920 mg, 2.80 mmol) was heated under nitrogen in a mixture of
EtOH (150 mL) and 2  NaOH (100 mL) at reflux for 12 h and
was then cooled to 21 °C. The bulk of the solvents were removed
until 10Ϫ15 mL remained. Water (200 mL) was added together
with ice and 2  HCl (250 mL). The precipitate formed was col-
lected and washed with excess of water before drying in vacuo to
give the acid 13a in 0.78 g (93%) as a yellow solid. This material
slowly lost the yellow color to a more grey-greenish color during
attempted melting point measurements, and no value could be re-
corded. IR (KBr): ν˜ ϭ 3404, 1653, 1616, 1512, 1459, 1436, 1322,
ν˜ ϭ 3429, 3315, 1640, 1594, 1475, 1189, 1079 cmϪ1 1H NMR
.
(500.2 MHz; [D6]acetone, 294 K): δ ϭ 11.32 (s, 1 H), 10.94 (br. s,
1 H), 10.36 (br. s, 1 H), 8.46 (s, 1 H), 8.05 (s, 1 H), 8.02 (s, 1 H),
7.86 (J ϭ 2.2 Hz, 1 H), 7.63 (d, J ϭ 2.3 Hz, 1 H), 7.61 (d, J ϭ 8.7
Hz, 1 H), 7.47 (d, J ϭ 8.7 Hz, 1 H), 7.10 (dd, J ϭ 8.7, 2.3 Hz, 1
1
H), 7.04 (dd, J ϭ 8.7, 2.2 Hz, 1 H) ppm. H NMR (300.1 MHz;
[D6]DMSO): δ ϭ 11.36 (s, 1 H), 11.87 (s, 2 H), 9.03 (s, 1 H), 9.00
(s, 1 H), 8.40 (s, 1 H), 7.80 (d, J ϭ 2.1 Hz, 1 H), 7.56 (d, J ϭ 2.2
Hz, 1 H), 7.52 (d, J ϭ 8.6 Hz, 1 H), 7.40 (d, J ϭ 8.7 Hz, 1 H),
7.01 (dd, J ϭ 8.7, 2.1 Hz, 1 H), 6.93 (dd, J ϭ 8.6, 2.2 Hz, 1 H)
ppm. 13C NMR (75.5 MHz; [D6]DMSO): δ ϭ 189.0 (d), 151.0 (s,
1 H), 150.4 (s), 136.0 (2 ϫ s), 135.4 (s), 135.0 (s), 123.2 (s), 122.0
(s), 121.4 (s), 121.2 (s), 116.5 (d), 115.4 (d), 112.4 (d), 111.9 (d),
111.9 (s), 110.1 (d), 108.5 (d), 105.2 (d) ppm. MS (ESI): m/z ϭ 317
[M Ϫ 1]Ϫ, 315 [M ϩ 1]ϩ. HRMS (FAB) calcd. for C19H12N2O3
316.0848 [M]ϩ found 316.0844.
1229, 741 cmϪ1 1H NMR (300.1 MHz; [D6]DMSO): δ ϭ 13.53
.
(br. s, 1 H), 11.46 (s, 1 H), 10.98 (s, 1 H), 8.93 (d, J ϭ 8.2 Hz, 1
H), 8.45 (s, 1 H), 8.25 (d, J ϭ 7.7 Hz, 1 H), 7.71 (d, J ϭ 8.1 Hz, 1
H), 7.52 (d, J ϭ 8.0 Hz, 1 H), 7.42 (dd, J ϭ 8.0, 7.2 Hz, 2 H),
7.20Ϫ7.10 (m, 2 H) ppm. 13C NMR (75.5 MHz; [D6]DMSO): δ ϭ
168.9 (s), 141.6 (s), 141.1 (s), 136.1 (s), 135.2 (s), 126.1 (d), 126.0
(d), 125.5 (d), 123.2 (s), 121.6 (s), 121.4 (s), 120.4 (s), 120.2 (d),
118.4 (d), 117.6 (d), 111.6 (d), 110.5 (d), 106.4 (d), 105.9 (s) ppm.
HRMS (FAB) calcd. for C19H12N2O2 300.0899 [M]ϩ found
300.0896.
4,8-Dihydroxyindolo[3,2-b]carbazole-6-carboxaldehyde (5e): The
hydroxyindolocarbazole 5e was prepared from 12e using the same
procedure as for 5a. Red solid. M.p. 393.0 °C (dec.). IR (neat): ν˜ ϭ
3384, 1630, 1593, 1462, 1273, 1185, 793 cmϪ1
.
1H NMR
(500.2 MHz; [D6]acetone, 294 K): δ ϭ 11.36 (s, 1 H), 10.76 (br. s,
1 H), 10.44 (br. s, 1 H), 9.01 (s, 1 H), 8.52 (s, 1 H), 8.06 (s, 1 H),
7.89 (d, J ϭ 2.3 Hz, 1 H), 7.74 (d, J ϭ 7.8 Hz, 1 H), 7.49 (d, J ϭ
8.7 Hz, 1 H), 7.13Ϫ7.09 (m, 2 H), 6.99 (d, J ϭ 7.8 Hz, 1 H) ppm.
1H NMR (300.1 MHz; [D6]DMSO): δ ϭ 11.28 (s, 1 H), 11.27 (s,
1 H), 11.23 (s, 1 H), 9.95 (br. s, 1 H), 9.03 (br. s, 1 H), 8.48 (s, 1
H), 7.83 (d, J ϭ 1.5 Hz, 1 H), 7.75 (d, J ϭ 7.7 Hz, 1 H), 7.42 (d,
J ϭ 8.7 Hz, 1 H), 7.11Ϫ7.01 (m, 2 H), 6.88 (d, J ϭ 7.7 Hz, 1 H)
ppm. 13C NMR (75.5 MHz; [D6]DMSO): δ ϭ 189.7 (d), 150.4 (s),
142.7 (s), 136.1 (s), 135.6 (s), 134.9 (s), 130.0 (s), 123.5 (s), 123.3
(s), 121.4 (s), 121.3 (s), 120.4 (d), 116.7 (d), 112.2 (s), 112.1 (d),
111.9 (d), 111.4 (d), 110.1 (d), 108.6 (d) ppm. MS (ESI): m/z ϭ 315
[M Ϫ 1]Ϫ, 317 [M ϩ 1]ϩ. HRMS (FAB) calcd. for C19H12N2O3
316.0848 [M]ϩ, found 316.0852.
Representative Procedure for the Preparation of 13b؊c: BBr3 (1 
in CH2Cl2, 4.63 mL, 4.63 mmol) was added dropwise to a solution
of 11e (92 mg, 0.23 mmol) in dry dichloromethane (20 mL) at Ϫ78
°C under argon. The cooling bath was then removed and the re-
sulting suspension stirred at 21 °C until reaction was complete as
judged by TLC (1Ϫ2 days). Ice/water (100 mL) was then added
and the mixture extracted with EtOAc (4 ϫ 75 mL). The combined
organic solvents were washed with water and dried with MgSO4.
The solvents were reduced together with 500 mg of silica gel. Col-
umn chromatography (silica) with EtOAc/hexane (50Ϫ100%) as
eluent produced the acid 13b in 75 mg (95%) as a yellow solid. This
material slowly changed from the yellow color to a more grey color
during attempted melting point measurements, and no value could
be recorded.
2,10-Dihydroxyindolo[3,2-b]carbazole-6-carboxaldehyde (5f): Tetra-
butylammonium fluoride (1  in THF, 1.83 mL, 1.83 mmol) was
added to a solution of 12f (166 mg, 0.30 mmol) in THF (5 mL) at
0Ϫ2 °C under argon. After 15 min the reaction was complete as
judged by TLC. A buffer solution (pH 7.4, 70 mL) was added and
the resulting slurry stirred for 30Ϫ60 min. The mixture was ex-
tracted with EtOAc (200 mL). The organic solvents were washed
with water (4 ϫ 50 mL) and brine (2 ϫ 50 mL) and dried with
MgSO4. Evaporation produced a red solid that was boiled 3 times
in hexane, each time carefully removing the solvent with a pipette.
Drying produced the indolocarbazole 5f in 73 mg (84%) as a dark-
reddish solid. This sample gradually becomes darker and darker
and no melting point could be recorded below 410 °C. IR (neat):
2,8-Dihydroxyindolo[3,2-b]carbazole-6-carboxylic Acid (13b): IR
(KBr): ν˜ ϭ 3413, 1678, 1477, 1320, 1212, 1187, 1161, 808 cmϪ1
.
1H NMR (300.1 MHz; [D6]DMSO): δ ϭ 13.30 (br. s, 1 H), 10.98
(s, 1 H), 10.54 (s, 1 H), 8.91 (s, 1 H), 8.76 (s, 1 H), 8.29 (d, J ϭ 2.2
Hz, 1 H), 8.23 (s, 1 H), 7.51 (d, J ϭ 2.2 Hz, 1 H), 7.47 (d, J ϭ 8.6
Hz, 1 H), 7.30 (d, J ϭ 8.6 Hz, 1 H), 6.95Ϫ6.88 (m, 2 H) ppm. 13C
NMR (75.5 MHz; [D6]DMSO): δ ϭ 168.8 (s), 150.3 (s), 149.1 (s),
136.6 (s), 136.0 (s), 135.6 (s), 135.1 (s), 123.0 (s), 122.2 (s), 122.1
(s), 120.3 (s), 115.8 (d), 115. 3 (d), 111.9 (d), 110.5 (d), 110.3 (d),
106.3 (d),105.3 (s), 104.9 (d) ppm. HRMS (FAB) calcd. for
C19H12N2O4 332.0797 [M]ϩ, found 332.0803.
2-Hydroxyindolo[3,2-b]carbazole-6-carboxylic Acid (13c): The ICZ
ν˜ ϭ 3383, 3341, 1634, 1619, 1561, 1329, 1196, 1098 cmϪ1. 1H NMR 13c was prepared from 11b using the same procedure as for 13b.
(500.2 MHz; [D6]acetone, 294 K): δ ϭ 11.39 (s, 1 H), 10.97 (br. s,
The eluent was EtOAc. This material slowly lost its yellow color to
1 H), 10.54 (br. s, 1 H), 8.93 (br. s, 1 H), 8.55 (s, 1 H), 8.07 (s, 1 a more grey color upon attempted melting point measurements,
Eur. J. Org. Chem. 2004, 2593Ϫ2602
www.eurjoc.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2601

N. Wahlström, I. Romero, J. Bergman
FULL PAPER
and no value could be recorded. IR (KBr): ν˜ ϭ 3460, 3405, 1678,
122.5 (s), 120.1 (d), 117.5 (d), 114.8 (d), 110.8 (d), 110.4 (d), 105.0
1656, 1485, 1432, 1298, 1216, 1155, 745 cmϪ1
.
1H NMR (d), 100.3 (d), 100.2 (d) ppm.
(300.1 MHz; [D6]DMSO): δ ϭ 13.42 (br. s, 1 H), 11.35 (s, 1 H),
10.64 (s, 1 H), 8.93Ϫ8.90 (m, 2 H), 8.31 (s, 1 H), 7.54 (d, J ϭ 2.2
Hz, 1 H), 7.51Ϫ7.48 (m, 2 H), 7.40 (t, J ϭ 7.1 Hz, 1 H), 7.10 (dd,
J ϭ 7.2, 7.1 Hz, 1 H), 6.92 (dd, J ϭ 8.6, 2.3 Hz, 1 H) ppm. 13C
NMR (75.5 MHz; [D6]DMSO): δ ϭ 168.9 (s), 150.4 (s), 141.6 (s),
136.9 (s), 135.1 (s), 134.7 (s), 125.8 (d), 125.5 (d), 123.2 (s), 122.2
(s), 121.5 (s), 120.4 (s), 117.5 (d), 115.5 (d), 112.0 (d), 110.5 (d),
106.4 (d), 105.4 (s), 105.0 (d) ppm. HRMS (FAB) calcd. for
C19H12N2O3 316.0848 [M]ϩ, found 316.0861.
Acknowledgments
We thank Dr. Tomasz Janosik for a constructive discussion during
the preparation of this manuscript and Dr. Marcus Ruda for help
with low resolution mass spectroscopic measurements.
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D. W. Nebert, A. L. Roe, M. Z. Dieter, W. A. Solis, Y. Yang,
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The isolated yields were almost quantitative.
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262, 15422Ϫ15427.
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J. Tholander, J. Bergman, Tetrahedron 1999, 55, 6243Ϫ6260.
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[6]
2-Hydroxyindolo[3,2-b]carbazole (14b): Greenish solid. M.p. Ͼ 410
°C. IR (KBr): ν˜ ϭ 3528, 3395, 1608, 1520, 1471, 1457, 1446, 1218,
[7]
1143, 845, 746 cmϪ1 1H NMR (300.1 MHz; [D6]DMSO): δ ϭ
.
10.91 (s, 1 H), 10.60 (s, 1 H), 8.83 (s, 1 H), 8.16 (d, J ϭ 8.0 Hz, 1
H), 8.02 (s, 1 H), 7.96 (s, 1 H), 7.49 (d, J ϭ 2.4 Hz, 1 H), 7.43 (d,
J ϭ 8.0 Hz, 1 H), 7.35 (t, J ϭ 7.0 Hz, 1 H), 7.25 (d, J ϭ 8.5 Hz,
1 H), 7.10 (dd, J ϭ 8.0, 7.8 Hz, 1 H), 6.88 (dd, J ϭ 8.5, 2.0 Hz, 1
H) ppm. 13C NMR (75.5 MHz; [D6]DMSO): δ ϭ 149.8 (s), 141.1
(s), 135.9 (s), 135.2 (s), 134.6 (s), 125.3 (d), 123.2 (s), 122.6 (2 ϫ s),
[8]
[9]
script accepted.
[10]
L. N. Yudina, J. Bergman, Tetrahedron 2003, 59, 1265Ϫ1275.
Received February 10, 2004
2602
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 2593Ϫ2602