Synthesis and alkylation of indolo[3,2-b]carbazoles

Article abstract of DOI:10.1016/S0040-4020(03)00029-2

Double Fischer cyclisation was used to prepare indolo[3,2-b]carbazole and its 2,8-di-OMe, OH, Br and F-derivatives. N-monosubstituted derivatives of indolo[3,2-b]carbazole (methyl, hydroxymethyl, dimethylaminoethyl) were obtained starting from 5,11-di-Boc

Full text of DOI:10.1016/S0040-4020(03)00029-2

Tetrahedron 59 (2003) 1265–1275
Synthesis and alkylation of indolo[3,2-b]carbazoles
Larisa N. Yudinaa and Jan Bergmana,b
,
*
aDepartment of Organic Chemistry, Department of Biosciences, Karolinska Institute, Novum Research Park, Huddinge S-141 57, Sweden
¨ ¨
Sodertorn University College, SE-141 04 Huddinge, Sweden
b
Received 25 October 2002; revised 27 November 2002; accepted 19 December 2002
Abstract—Double Fischer cyclisation was used to prepare indolo[3,2-b]carbazole and its 2,8-di-OMe, OH, Br and F-derivatives.
N-monosubstituted derivatives of indolo[3,2-b]carbazole (methyl, hydroxymethyl, dimethylaminoethyl) were obtained starting from 5,11-di-
Boc-indolo[3,2-b]carbazole. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction and background
b]carbazole derivatives are produced, however, this strategy
only works for aromatic aldehydes or with sterically
hindered aliphatic aldehydes like iso-propanal.7 For pre-
parative purposes, compound 1a can be prepared by double
Fischer indolisation of the bis-phenylhydrazone of cyclo-
hexane-1,4-dione under conditions described by Robinson.8
Under slightly different conditions (HCl/EtOH) the yield of
1a is much lower and an array of other products, including
heterohelicenes,9 are formed. Compound 1a can also be
prepared by Suzuki coupling of 1,4-dibromo-3,6-dinitro-
benzene with phenylboronic acid and followed by reductive
cyclisation, induced by P(OEt)3.10
Indolo[3,2-b]carbazole1 (ICZ) 1a (Fig. 1) is a molecule of
considerable biological significance, since it is formed in
vivo after consumption of cruciferous vegetables such as
cabbage and Brussels sprouts.2 ICZ has a strong affinity to
the TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin, 2) receptor
(Ah-receptor), and recently it has been demonstrated that
6-formylindolo[3,2-b]carbazole3 (3a) has an extremely
strong affinity to the TCDD receptor, in fact even stronger
than the highly toxic dioxin TCDD itself.4 The TCDD
receptor is very important in the primary detoxification of
unpolar substances, as this receptor triggers the expression
of many enzymes (including cytochrome 1A1) involved in
this process. Furthermore, in certain animals, the develop-
ment of a proper liver and immune system are dependent on
a working receptor.5
In this paper, the preparation of ICZ and derivatives thereof
via double Fischer cyclisation of diarylhydrazones (4) has
been studied using several condensing agents. The preferred
synthetic route for preparation of 1a was found to be a
modification of Robinson’s method, e.g. (H2SO4 in AcOH).
Several phosphorus containing agents like PPA, PCl3 and
polyphosphoric acid trimethylsilylester (PPSE) gave not
only ICZ (i.e. the linear isomer), but also the angular isomer,
indolo[2,3-c]carbazole (5a), the structure of which was
confirmed by an independent synthesis.11 Furthermore,
several mono- and disubstituted N,N0-derivatives of 1a have
been prepared to enable determination of their activities.
Although indole-3-carbinol, indole and 3-formylindole
under acidic conditions all produce 1a,6 the low yields
obtained and the complex product pattern prohibits the use
of these simple approaches for synthetic purposes. In the
simple condensation of indole with aldehydes, indolo[3,2-
2. Results and discussion
In contrast with the numerous studies concerning the
affinities and activities of ICZ and particularly 6-formyl-
indolo[3,2-b]carbazole (3a) very little is known about their
metabolic fate.4,12,13 As certain carbazole derivatives are
hydroxylated in the benzene rings,14 a similar transform-
ation might also metabolise indolo[3,2-b]carbazole. One of
the most likely metabolites would be 2,8-dihydroxy-
indolo[3,2-b]carbazole (6). As a precursor for 6 we planned
Figure 1.
Keywords: indolo[3,2-b]carbazole; Ah-receptor; Fischer cyclisation.
*
Corresponding author. Tel.: þ46-8-6089204; e-mail: jabe@biosci.ki.se
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00029-2

1266
L. N. Yudina, J. Bergman / Tetrahedron 59 (2003) 1265–1275
Scheme 1.
to synthesise 2,8-dimethoxy- and 2,8-dibromoindolo[3,2-
b]carbazoles (1b,d).
swiftly from 10 to 708C, otherwise the yield of 1c
significally decreased. This ring closure experiment suffered
from variable reproducibility and other cyclisation media
such as AcOH/H2SO4, PPSE or TsOH/toluene did not
provide any improvements. The fluoroindolocarbazole 1c
was purified by refluxing in acetonitrile. Starting from the
bis-bromophenylhydrazone 4d, formation of 5,11-dibromo-
indolo[3,2-b]carbazole (1d) could only be effected in a
mixture of AcOH–H2SO4 (4:1) and progressed in 25%
yield. The crude bromoindolocarbazole 1d was protected
with Boc2O to 8d, a compound that was easily purified by
reflux in dioxane and filtration. The Boc-groups in 8d were
eliminated at 1958C/0.1 mm Hg during 5 h to produce 1d.
Yields for products of Fischer cyclisation of 4a–d presented
in Table 1.
The bishydrazones 4 were obtained in 50–60% yield by
condensation of p-methoxy, p-F- or p-Br-phenylhydrazines,
respectively, with cyclohexane-1,4-dione in EtOH in the
absence of acid and used immediately. For the synthesis of
1b PPSE15 was the only medium that yielded the desired
compound. The best results were obtained by adding the
freshly prepared powdered phenylhydrazone 4b portionwise
to PPSE at 100–1058C (Scheme 1).
The angular isomer 2,11-dimethoxyindolo[2,3-c]carbazole
(5b) and 6,7-dihydro-2,11-dimethoxy-indolo[2,3-c]carba-
zole (7b) were obtained as co-products. Attempts to use
Boc-protection to separate the residual mixture of products
were unsuccessful, since the retention values of the Boc-
protected products 8b–10b are very close. The Boc-
protected dihydro derivative 7b underwent dehydrogenation
readily to give 5b, especially in the presence of silica gel.
The angular isomer 5b is soluble in CH3CN and it was
isolated from the reaction mixture upon washing with
CH3CN, followed by column chromatography and sublima-
tion at 2158C. For the isolation of 1b, the remaining mixture
of 1b and 7b was refluxed with Pd/C in the presence of air,
resulting in a mixture consisting mainly of 1b, which was
N-Boc-protected and purified by column chromatography to
produce 8b in 20% yield (from 4b). Finally, 8b was
crystallised from 1,4-dioxane and deprotected at
2058C/0.1 mm Hg to produce 2,8-dimethoxyindolo[3,2-
b]carbazole (1b) in quantitative yield (from 8b). The
structures of 1b and 5b were established by NOEDIF
experiments. Thus, saturation of the singlet 6/12-H in 1b
produced a NOE enhancement of the signal 7/1-H on 16%,
which correlates to a proximity in space of the protons and
confirms the structure of the 3,2-b isomer. Analogous
experiments for 5b did not display any NOE enhancement
in the intensity of the signals.
It should be noted that double Fischer cyclisation to prepare
indolocarbazoles can be successfully performed under very
strong acidic conditions. Attempts to perform cyclisations
without isolation of the unstable intermediate 4 mainly gave
monocyclised products.
Due to the relatively low yield of 1b an alternative
synthesis, involving a cyclisation, catalyzed by Pd(OAc)2,
was attempted (Scheme 2). This technique has recently been
used for the synthesis of 6,12-dicarboethoxyindolo[3,2-
b]carbazole in high yield.7 However, cyclisation of the
diarylamine 12 with equimolar amount of Pd(OAc)2
resulted only in the formation of 2,11-dimethoxy
indolo[2,3-c]carbazole (5b), isolated in its Boc-protected
form 9b, identical with the previous sample obtained vide
supra.
Table 1. Yields of products from Fischer cyclisation of the phenylhy-
drazones 4
Hydrazones 4a–d
Yields of products (%)
1a–d
5a–d
7a–d
11a–d
2,8-Difluoroindolo[3,2-b]carbazole (1c) was obtained in
26–48% yield together with 3-amino-6-fluorocarbazole 11c
(20–60%) after intramolecular condensation of 4c in
polyphosphoric acid at 1908C. It is necessary to heat 4c
4a
4b
4c
4d
47
20
49
24
0
11
0
0
ca 15
0
0
16
0
21
0
0

L. N. Yudina, J. Bergman / Tetrahedron 59 (2003) 1265–1275
1267
Scheme 2. (a) PhH, reflux (13%); (b) Pd(OAc)2, AcOH, reflux; (c) Boc2O/DMAP, THF (10% for b and c).
We attempted to get the 2,8-dimethoxyindolocarbazole 1b
by exchanging the bromine atoms in 2,8-dibromo-
indolo[3,2-b]carbazole with methoxy groups. However,
heating 1d in DMF or DMA for 3 h with 5–10 eq. of
CH3ONa and 3–5 eq. of CuI did not provide more than 30%
of 1b. Harsher reaction conditions or prolonged reaction
times resulted in increased degradation of the
indolocarbazoles.
2,8-Dihydroxyindolo[3,2-b]carbazole 6 was obtained by
demethylation of 1b by 20 eq. BBr3 at 2788C to 218C
(Scheme 3). O-Protection with t-BuMe2SiCl in the presence
Figure 3.
of imidazole in DMF gave the quite soluble product 13,
which was purified by column chromatography. Deprotec-
tion of the TBDMS group was performed with n-Bu4NF to
give 6 in 70% yield starting from 1b.
equivalents of Me2NCH2CH2Cl used produced a mixture of
15a and b, which could be separated by column chroma-
tography. The ease of the preparation of this type of
compound and its good solubility (in e.g. CHCl3) should
assist the characterisation of ICZ and its derivatives. In
connection with the preparation of 15a, its lower and less
stable homologue 16, was readily obtained by reaction of 1a
with formaldehyde and dimethylamine in the presence of
acetic acid in hot N,N-dimethylacetamide. In the absence of
dimethylamine 5,11-dihydroxymethylindolo[3,2-b]carba-
zole (17) was readily prepared. We next wanted to develop
a method to selectively obtain unsymmetrical alkyl
derivatives of 1a, including 15b (Scheme 4).
Scheme 3. (a) BBr3 (20 eq.), CH2Cl2, 278!218C, 48 h; (b) t-BuMe2SiCl,
imidazole, DMF; (c) n-Bu4NF, THF (70% for a–c).
The key compound for this synthesis was 5-t-butyloxy-
carbonylindolo[3,2-b]carbazole (18). In the next step we
planned to introduce other substituents, such as methyl,
hydroxymethyl and 2-dimethylaminoethyl in the molecule
and then remove the Boc group. We obtained 5,11-di-t-
butyloxycarbonylindolo[3,2-b]carbazole (19)19 and
removed one protecting group with 4–5 eq. of n-BuLi
(depending on the scale) at 08C to form the monoprotected
derivative 18 in 72% yield. It was necessary to monitor the
reaction carefully by TLC to avoid the removal of both
protecting groups, but because of insolubility it is difficult to
check for the presence of ICZ by TLC. MonoBoc-ICZ 18
was purified by column chromatography and crystallised
from dioxane. The disubstituted unsymmetrical derivatives
20 and 21 were obtained by treatment of 5-t-butyloxy-
carbonylindolo[3,2-b]carbazole with MeI or ClCOOEt in
two phase systems in 86 and 84% yields, respectively.
N-Boc-deprotection of 20 was carried out at 2108C/
0.1 mm Hg to provide analytically pure crystals of
5-methylindolo[3,2-b]carbazole (22). 5-Ethoxycarbonyl-
indolo[3,2-b]carbazole (23) was obtained by treatment of
21 in TFA/CH2Cl2 and crystallised from CH3CN in 83%
yield. Attempts to use LiAlH4 for this purpose caused
selective elimination of COOEt to give 18. Finally
5-hydroxymethylindolo[3,2-b]carbazole (24) was obtained
in 90% yield by rapid reduction of 23 with LiAlH4 at 08C
and purified by column chromatography then suspending
the product in acetone and collecting the solid. Due to its
N-Alkylated derivatives of ICZ have attracted considerable
interest. They are readily obtained in high yields by treating
ICZ with dialkyl oxalates under basic conditions, a
methodology that has previously been used for alkylation
of indoles and carbazoles.16 Dialkylated derivatives of 1a,
e.g. 3b and c, have earlier been tested for high affinity as
TCDD-receptor ligands.17 In view of the high activity of
14a (Fig. 2) and the strong propensity of 14b to stabilise
triplex forms of synthetic DNA and RNA,18 it appeared to
be of considerable interest to synthesise related compounds
such as 15b (Fig. 3) in the ICZ series.
N,N-Dimethylaminoethylation of ICZ was performed with
commercial 2-dimethylamino-1-chloroethane·HCl in
DMSO with NaH as a base. When slightly more than
2 eq. of the alkylation reagent was used the dialkylated
product 15a was the sole product. Reducing the number of
Figure 2.

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L. N. Yudina, J. Bergman / Tetrahedron 59 (2003) 1265–1275
Scheme 4. (a) n-BuLi, THF, 08C, NH4Cl, 218C (72%); (b) H2CO, EtOH (88%); (c) i. NaOH, CH2Cl2, Bu4NHSO4 ii. ClCO2Et (84%); (d) NaOH, CH2Cl2,
Bu4NBr ii. MeI (86%); (e) 2008C/0.1 mm Hg (quant.); (f) 10% TFA/CH2Cl2 (83%); (g) LiAlH4, THF 08C (90%).
thermal instability, all attempts to crystallise 24 were
unsuccessful. While examining an alternative route to 24
5-Boc-11-hydroxymethylindolo[3,2-b]carbazole (25) was
obtained in 88% yield by treatment of 18 with an excess
of 37% formaldehyde. Despite several attempts to deprotect
25 to give 24, by using basic or acidic catalysis or reduced
pressure (at 1608C), no satisfactory results could be
obtained. It should be noted that compounds 20 and 21
could be easily obtained, directly without isolation of 18, by
treating the reaction mixture, obtained from the mono-
deprotection of 19, with ClCOOEt or MeI, but in this case
the purification of the target compounds from by-products
(5,11-diethoxycarbonyl- or 5,11-dimethylindolo[3,2-b]car-
bazoles) is troublesome.
conditions, at room temperature for 72 h in 1.5 M NaOMe to
give 15b in 73% yield.
In summary, the symmetrical 2,8-disubstituted OMe, F and
Br indolo[3,2-b]carbazoles have been synthesised by double
Fischer cyclisations. It was demonstrated that besides the
linear isomer, the angular isomer indolo[2,3-c]carbazole
was also produced during these cyclisations. Demethylation
of 2,8-dimethoxyindolo[3,2-b]carbazole with BBr3 gave
dihydroxy-ICZ in high yield. Several N-monosubstituted
indolo[3,2-b]carbazoles were prepared in moderate yields
starting from 5,11-di-BocICZ.
3. Experimental
The N-alkylation of 18 to introduce 2-dimethylaminoethyl
substituent was troublesome. Satisfactory results were only
obtained by treatment 18 with t-BuOK and freshly prepared
2-dimethylamino-1-chloroethane in DMF (Scheme 5).
Under these conditions 5-Boc-11-(2-dimethylaminoethyl)-
indolo[3,2-b]carbazole 26 was obtained in 60% yield. Boc-
deprotection of 26 took place only under strongly basic
3.1. General methods
1H and 13C NMR spectra were obtained on a Bruker DPX
300 (300 MHz) instrument. Chemical shifts are reported in
d, ppm and coupling constants (J) are given in Hz. IR
spectra were recorded on Perkin–Elmer 1600 FT-IR
Scheme 5. (a) t-BuOK, DMF, (CH3)2NCH2CH2Cl (60%); (b) 1.5N CH3ONa, 72 h (73%).

L. N. Yudina, J. Bergman / Tetrahedron 59 (2003) 1265–1275
1269
spectrophotometer using KBr films. Mass-spectra were
obtained by electron impact (EI) method on a SSQ 710
Finnigan spectrometer. High resolution mass spectra was
performed by Einor Nilsson, University of Lund, Sweden.
Melting points (uncorrected) were determined on a Bu¨chi
B-545 apparatus or a Reichert Kofler hot stage. Column
chromatography was carried out by using Merck Kieselgel
F254 or Aluminium oxide 90 (70–230 mesh). The
substances were developed with the van Urk reagent
(2% p-dimethylaminobenzaldehyde in EtOH–50% H2SO4,
1:1).
phenylhydrazine (2.34 g, 85%), mp 63–648C (lit.22
64–658C).
To
a solution of cyclohexane-1,4-dione (0.905 g,
8.08 mmol) in absolute EtOH (30 mL) was added freshly
prepared p-methoxyphenylhydrazine (2.03 g, 14.70 mmol)
in several portions. The reaction mixture was stirred for
20 min under light protection, then cooled in an ice bath.
The solid was collected, washed with cold EtOH (5 mL),
and dried in the same manner as p-methoxyhenylhydrazine
to give 4b (1.75 g, 68%) as a brown powder. Mp 1158C
(decomp.) The product stored at 2188C. MS EI m/z: 351
[M21]þ (100); IR (KBr) 3428, 1604, 1509, 1239, 1085,
1032, 824 cm21; 1H NMR (DMSO-d6) d 8.32 (2H, s, NH),
7.03 (4H, d, J¼9.0 Hz), 6.77 (4H, d, J¼9.0 Hz), 3.64 (6H, s,
OMe), 2.60 (4H, m, CH2), 2.53 (4H, m, CH2); 13C NMR
(DMSO-d6) d 152.13 (s), 146.41 (s), 140.72 (s), 114.15 (d),
113.44 (d), 55.14 (q), 29.30 (t), 25.72 (t).
3.1.1. Cyclohexane-1,4-dione bisphenylhydrazone (4a).
Cyclohexane-1,4-dione bisphenylhydrazone 4a was
obtained in accordance with Ref. 20 in 98% yield by
boiling
a mixture of cyclohexane-1,4-dione (5.6 g,
45 mmol) and phenylhydrazine (10.9 mL, 110 mmol) in
ethanol (90 mL) for 3 min in the presence of glacial acetic
acid (0.1 mL). Mp 1508C (lit.20 150–1518C).
3.1.4. Indolisation of cyclohexane-1,4-dione bis-(p-meth-
oxyphenyl)-hydrazone (4b) in PPSE. A mixture of P2O5
(4.97 g, 35 mmol) and (Me3Si)2O (11.90 mL, 56 mmol) in
CH2Cl2 (35 mL) was refluxed for 35 min, before the flask
was equipped with a distillation head and the solvent was
evaporated in vacuo. The temperature was quickly raised to
1608C, whereafter the heating was stopped. The mixture
was allowed to cool to 1078C and then compound 4b
(1.73 g, 4.92 mmol) was added in small portions to the
freshly prepared PPSE. The temperature of reaction mixture
was kept between 104 and 1128C for 5 min and then poured
into iced water. After 1 h a precipitate was slowly filtered
off, washed carefully with water, 0.5 M NaOH solution and
finally water to give a crude mixture of 1b,5b and 7b
(1.12 g). The mixture was suspended in CH3CN (30 mL),
refluxed for 5 min and filtered. The acetonitrile solution,
containing mainly 5b was purified by column chromato-
graphy (hexane–EtOAc 2:1) to give 5b (165 mg, 11% from
4b). Sublimation of this material at 213–2158C at
0.1 mm Hg for 24 h gave analytically pure 2,11-dimethoxy-
indolo[2,3-c]carbazole (5b) as a fine greenish powder. The
residue, which after washing with acetonitrile contained
mainly 1b and 7b, was refluxed for 12 h in diglyme in the
presence of 5% Pd/C (70 mg) and air. Once all of 7b had
degradated (as judged by TLC), the solid, containing Pd/C,
was filtered and washed with DMF and acetone. The
combined filtrate was evaporated in vacuo and the residue
was treated with Boc2O (1.52 g, 6.95 mmol) and DMAP
(0.193 g, 1.58 mmol) in THF (12 mL) for 4 h at room
temperature. The reaction mixture was diluted with CHCl3,
washed twice with water, dried (MgSO4), evaporated in
vacuo. The remaining residue was purified twice by column
chromatography (hexane–EtOAc 2.2:1) and then (hexane–
EtOAc 5:1) to give 5,11-di-t-butyloxycarbonyl-2,8-
dimethoxyindolo[3,2-b]carbazole (8b) (503 mg, 20%, calc.
for 4b). The product was crystallised from dioxane to give
slightly pinkish crystals. The substance 8b was deprotected
during 8 h at 2058C, 0.1 mm Hg to give a quantitative yield
of 2,8-dimethoxyindolo[3,2-b]carbazole (1b) as a fine
greenish powder.
3.1.2. Indolo[3,2-b]carbazole (1a) (a modification of
Robinson’s8 method). Compound 4a (8.80 g, 30 mmol)
was added portionwise to a mixture of AcOH and H2SO4
(1:4, 40 mL), cooled to 08C. After 5 min of stirring the
mixture was quickly heated to 50–558C, and thereafter, the
temperature was increased slowly. At 84–878C the mixture
changed colour from bright raspberry to grey-green and the
temperature jumped up to 1108C. The reaction mixture was
kept at this temperature for 10–15 min, then allowed to cool
and left overnight, before the mixture was diluted with
EtOH. After 1 h a greenish precipitate was collected,
washed carefully with water to neutral pH and dried to
give pure 1a (3.07 g, 40%). To increase the yield the first
100 mL of washings was combined with the mother liquid,
and the mixture was evaporated in vacuo to remove EtOH
and part of the AcOH. The rest was diluted with EtOH, and
the precipitate obtained (mainly containing 1a) was
collected and washed carefully with water, dried and finally
purified by reflux in DMF. The insoluble residue was
collected and dried at 1408C for 24 h to give further 1a
(0.53 g, total yield 47%). The filtrate after removing the
second precipitate was diluted with water and basified by
2 M NaOH to pH 9. The resulting fine precipitate was
collected, and washed carefully with water to give pure
3-aminocarbazole 11a (yield 16%). Mp 254–2558C (lit.21
2548C). IR (KBr) 3401, 3048, 1608, 1584, 1495, 1461,
1
1325, 1226, 1143, 860, 804, 743 cm21; H NMR (DMSO-
d6) d 10.76 (1H, NH), 7.91 (1H, d, J¼7.6 Hz), 7.41 (1H, d,
J¼8.2 Hz), 7.31 (1H, d, J¼2.3 Hz), 7.28 (1H, dd, J¼7.6,
7.4 Hz), 7.22 (1H, d, J¼8.0 Hz), 7.04 (1H, dd, J¼8.0,
7.4 Hz), 6.82 (1H, dd, J¼8.2, 2.3 Hz), 4.61 (2H, NH2); 13
C
NMR (DMSO-d6) d 141.13 (s), 140.15 (s), 132.76 (s),
124.72 (s), 123.00 (d), 122.15 (s), 119.70 (d), 117.36 (d),
115.14 (d), 111.06 (d), 110.61 (d), 103.77 (d).
3.1.3. Cyclohexane-1,4-dione bis-(p-methoxyphenyl)-
hydrazone (4b). A suspension of p-methoxyphenylhydra-
zine hydrochloride (3.5 g, 20 mmol) in water (50 mL) was
stirred rapidly for 10 min before 2 M NaOH (10 mL) was
added dropwise. p-Methoxyphenylhydrazine began to
precipitate during the addition and 2 min after completion
of addition, the precipitate was collected and dried under
vacuum on the filter wrapped in foil to give p-methoxy-
3.1.5. 2,8-Dimethoxyindolo[3,2-b]carbazole (1b). Mp
.4108C. Anal. calcd for C20H16N2O2: C, 75.93; H, 5.10;
N, 8.85. Found: C, 75.83; H, 4.97; N, 8.68. IR (KBr) 3401,

1270
L. N. Yudina, J. Bergman / Tetrahedron 59 (2003) 1265–1275
1522, 1489, 1467, 1279, 1216, 1204, 1157, 1031, 841, 818,
798, 607 cm21; 1H NMR (DMSO-d6) d 10.73 (2H, s, NH),
8.05 (2H, s, H-6/12), 7.75 (2H, d, J¼2.5 Hz, H-1/7), 7.34
(2H, d, J¼8.4 Hz, H-4/10), 7.00 (2H, dd, J¼8.4, 2.5 Hz,
H-3/9), 3.85 (6H, s, OMe); 13C NMR (DMSO-d6) d 152.39
(s), 136.06 (s), 136.62 (s), 122.93 (s), 122.83 (s), 114.52 (d),
111.05 (d), 103.31 (d), 100.47 (d), 55.67 (q).
precooled (2788C) suspension of 1b (171 mg, 0.54 mmol)
in dry CH2Cl2 (20 mL), a 1 M solution of BBr3 in
dichloromethane (21.64 mmol, 21.64 mL) was added
during 25 min under a stream of Ar. The reaction mixture
was stirred at 2788C for 10 h, and then during 9 h the
temperature was allowed to increase to 218C. The ambient
temperature was kept for 24 h before the mixture was cooled
to 08C, slowly quenched by addition of a saturated NH4Cl
solution (2 mL), then diluted with H2O (100 mL) and
neutralised with NaOH solution. The resulting dark
precipitate, mainly containing the hydroxyindolocarbazole
6, was collected and washed with water and CHCl3. To
increase the solubility, 6 was then O-protected by TBDMS.
Thus t-BuMe2SiCl (812 mg, 5.41 mmol) and imidazole
(368 mg, 5.41 mmol) were added to a suspension of the
precipitate in DMF (12 mL). After stirring at 218C for 2 h
the reaction was complete (as judged by TLC in hexane–
EtOAc 2:1). The reaction mixture was poured onto ice,
extracted with EtOAc, dried over MgSO4, evaporated and
then purified by flash chromatography (hexane–EtOAc 2:1)
to give 2,8-di(t-butyldimethylsilyloxy)indolo[3,2-b]carba-
zole (13) (212 mg, 76%) as a light yellow powder. Then a
solution of 13 (200 mg, 0.39 mmol) in THF (25 mL) was
treated with n-Bu4NF (1N solution in THF, 3.10 mL) at
room temperature. After 5 min of stirring the deprotection
was complete (TLC in hexane–EtOAc 2:1). The resulting
suspension was diluted with EtOAc (100 mL) and washed
with brine and then water. The combined organic solvents
were then evaporated in vacuo to give 7 (103 mg, 92% from
13) as a fine grey-greenish powder. Mp .4108C. HRMS
calcd for C18H12N2O2 288.0899, found 288.0923; IR (KBr)
1716, 1490, 1449, 1434, 1380, 1306, 1202, 1155,
3.1.6. 2,11-Dimethoxyindolo[2,3-c]carbazole (5b). Mp
231–2328C. Anal. calcd for C20H16N2O2: C, 75.93; H,
5.10; N, 8.85. Found: C, 76.11; H, 5.26; N, 8.65. IR (KBr)
3389, 3346, 1576, 1489, 1479, 1292, 1219, 1143, 1091,
1038, 789, 602 cm21; 1H NMR (DMSO-d6) d 11.24 (2H, s,
NH), 8.14 (2H, d, J¼2.2 Hz, H-1/12), 7.57 (2H, s, H-6/7),
7.50 (2H, d, J¼8.8 Hz, H-4/9), 7.08 (2H, dd, J¼8.8, 2.2 Hz,
H-3/10), 3.99 (6H, s, OMe); 13C NMR (DMSO-d6) d 152.37
(s), 134.99 (s), 134.31 (s), 122.02 (s), 115.07 (s), 133.88 (d),
111.84 (d), 110.47 (d), 104.28 (d), 55.25 (q).
3.1.7. 6,7-Dihydro-2,11-dimethoxy-indolo[2,3-c]carba-
zole (7b). The substance was identified by NMR in the
reaction mixture after cyclisation of 4b. 1H NMR (DMSO-
d6) d 10.81 (2H, s, NH), 7.22 (2H, d, J¼8.8 Hz, H-4/9), 7.05
(2H, d, J¼2 Hz, H-1/12), 6.69 (2H, dd, J¼8.7, 2.3 Hz,
H-3/10), 3.98 (4H, s, CH2), 3.78 (6H, s, OMe).
3.1.8. 5,11-Di-(t-butoxycarbonyl)-2,8-dimethoxy-
indolo[3,2-b]carbazole (8b). Undergoes Boc-deprotection
at temperature over 2208C; HRMS calcd for C30H32N2O6
516.2260, found 516.2263; IR (KBr) 1716, 1490, 1449,
1434, 1380, 1306, 1202, 1155, 1022 cm21 1H NMR
;
(CDCl3) d 8.91 (2H, bs, H-6/12), 8.15 (2H, d, J¼9.0 Hz,
H-4/10), 7.56 (2H, d, J¼2.9 Hz, H-1/7), 7.07 (2H, dd,
J¼9.0, 2.9 Hz, H-3/9), 3.96 (6H, s, OMe), 1.83 (18H, s,
2£Boc); 13C NMR (CDCl3) d 156.26 (s), 151.49 (s), 135.87
(s), 133.70 (s) 127.40 (s), 126.06 (s), 117.31 (d), 115.34 (d),
107.03 (d), 103.06 (d), 83.90 (s), 56.03 (q), 28.59 (q).
1022 cm21 1H NMR (DMSO-d6) d 10.50 (2H, s, NH-
;
5/11), 8.81 (2H, s, OH-2/8), 7.88 (2H, s, H-6/12), 7.46 (2H,
d, J¼2.2 Hz, H-1/7), 7.23 (2H, d, J¼8.6 Hz, H-4/10), 6.86
(2H, dd, J¼8.6, 2.2 Hz, H-3/9); 13C NMR (DMSO-d6) d
149.72 (s), 135.61 (s), 135.26 (s), 123.23 (s) 122.58 (s),
114.70 (d), 110.78 (d), 105.02 (d), 100.11 (d).
3.1.9. 5,8-Di-(t-butoxycarbonyl)-2,11-dimethoxy-
indolo[2,3-c]carbazole (9b). Mp 175–1768C. HRMS
calcd for C30H32N2O6 516.2260, found 516.2249; IR
(KBr) 2976, 1719, 1484, 1316, 1157, 1122, 1027, 814,
3.1.12. 2,8-Di(t-butyldimethylsilyloxy)indolo[3,2-b]car-
bazole (13). Mp 1948C (decomp.). HRMS calcd for
C30H40N2O2Si2 516.2628, found 516.2624; IR (KBr)
3391, 3102, 1586, 1461, 1396, 1325, 1195, 1155, 847,
1
757 cm21; H NMR (CDCl3) d 8.56 (2H, s, H-6/7), 8.36
1
(2H, d, J¼9.1 Hz, H-4/9), 8.19 (2H, d, J¼2.5 Hz, H-1/12),
7.15 (2H, dd, J¼9.1, 2.5 Hz, H-3/10), 4.01 (6H, s, OMe),
1.80 (18H, s, 2£Boc). 13C NMR (CDCl3) d 155.71 (s),
151.11 (s), 136.29 (s), 133.54 (s), 126.41 (s), 119.63 (s),
117.17 (d), 115.34 (d), 114.45 (d), 106.77 (d), 84.10 (s),
56.00 (q), 28.61 (q).
810, 598 cm21; H NMR (acetone-d6) d 9.86 (2H, s, NH-
5/11), 8.08 (2H, s, H-6/12), 7.64 (2H, d, J¼2.4 Hz, H-1/7),
7.35 (2H, d, J¼8.6 Hz, H-4/10), 6.96 (2H, dd, J¼8.6,
2.4 Hz, H-3/9), 1.05 (18H, s, t-Bu), 0.26 (12H, s, Me); 13C
NMR (acetone-d6) d 149.05 (s), 137.96 (s), 137.29 (s),
124.93 (s), 124.41 (s), 119.78 (d), 111.73 (d), 111.14 (d),
101.45 (d), 26.29 (q), 18.91 (s), 23.50 (q).
3.1.10. 5,8-Di-(t-butoxycarbonyl)-6,7-dihydro-2,11-
dimethoxyindolo[2,3-c]carbazole (10b). The sample of
10b was obtained by Boc-protection of the mixture 1b, 5b
and 7b (obtained after condensation of 4b) by excess of
Boc2O in the presence of DMAP, followed by separating by
preparative TLC (hexane–CH2Cl2 2:1; Rf(10b)¼0.22,
Rf(9b)¼0.15, Rf(8b)¼0.12). EI/MS (70 eV) (m/z): 518
3.1.13. Bis(p-methoxyphenyl)phenylenediamine (12). A
mixture of cyclohexane-1,4-dione (1.12 g, 10 mmol) and
p-methoxyaniline (2.46 g, 20 mmol) in benzene (60 mL)
was refluxed under Dean-Stark conditions. After 18 h the
p-methoxyaniline was consumed (TLC hexane–EtOAc,
2:1) to produce a complex mixture. The mixture was kept
for 24 h without treatment before 12 (Rf 0.65, bright brown
colour under van Urk reagent) crystallised from the reaction
mixture. Recrystallisation from EtOH gave 12 (410 mg,
13%) as a light brown powder. Mp 202–2038C (lit.23
199.58C). MS EI m/z: 320 [M]þ (100); IR (KBr) 3393, 2832,
1
[M]þ (100); H NMR (CDCl3) d 8.03 (2H, d, J¼9.0 Hz,
H-4/9), 7.00 (2H, d, J¼2.8 Hz, H-1/12), 6.94 (2H, dd,
J¼9.0, 3.0 Hz, H-3/10), 4.32 (4H, s, CH2), 3.90 (6H, s,
OMe), 1.76 (18H, s, Boc).
3.1.11. 2,8-Dihydroxyindolo[3,2-b]carbazole (6). To a
1514, 1498, 1239, 1028, 823, 810 cm21 1H NMR
;

L. N. Yudina, J. Bergman / Tetrahedron 59 (2003) 1265–1275
1271
(DMSO-d6) d 7.46 (2H, s, NH), 6.91 (4H, d, J¼8.9 Hz,
ArH), 6.87 (4H, s), 6.79 (4H, d, J¼8.9 Hz, ArH), 3.68 (6H,
s, OMe); 13C NMR (DMSO-d6) d 152.57 (s), 138.20 (s),
137.19 (s), 118.15 (d), 117.73 (d), 114.59 (d), 55.18 (q).
evaporated in vacuo and diluted with water. The solid was
collected, washed with water, and dried to give a crude
mixture (60 mg, more than three products according NMR).
The residual filtrate was basified with 2 M NaOH to pH 9.
The solid was collected and washed with water to give
3-amino-6-fluorocarbazole (11c) (125 mg, 21%). The crude
solid of 1c was suspended in CH3CN (50 mL), reflux for
10 min, collected and washed with hot acetonitrile to give
1c (435 mg, 49%) as a fine greenish solid.
3.1.14. Condensation of bis(p-methoxyphenyl)phenyl-
enediamine (12) in the presence Pd(OAc)2. Compound
12 (200 mg, 0.63 mmol) was dissolved in degassed AcOH
(10 mL) under an Ar flow at room temperature and
Pd(OAc)2 (317 mg, 1.38 mmol) was added to the solution
in one portion. The temperature was quickly raised to 1008C
and kept so for 5 h, whereupon 12 had been consumed (as
judged by TLC in hexane–EtOAc 2:1). Upon the com-
pletion of the reaction a palladium mirror was observed. The
solvent was evaporated and the residue was treated with
Boc2O (861 mg, 3.94 mmol) and DMAP (49.6 mg,
0.41 mmol) in THF (15 mL). After the usual work up the
mixture was purified by flash chromatography (hexane–
EtOAc 1:1) to give 9b (31 mg, 10%) as a single product.
Spectral data and melting point are in accordance with data,
described above for 9b.
3.1.17. 2,8-Difluoroindolo[3,2-b]carbazole (1c). Mp
.4108C. Anal. calcd for C18H10F2N2: C, 73.97; H, 3.45;
N, 9.58. Found: C, 74.10; H, 3.35; N, 9.47; IR (KBr) 3404,
2863, 2610, 2359, 1617, 1587, 1529, 1490, 1468, 1438,
1286, 1238, 1189, 1150, 1076, 1024, 915, 869, 847, 802,
589 cm21; 1H NMR (DMSO-d6) d 11.07 (2H, s, NH), 8.14
(2H, s, H-6/12), 8.05 (2H, dd, JH1–F¼9.4 Hz,
JH1–H3¼2.3 Hz, H-1/7), 7.42 (2H, dd, JH4–H3¼8.7 Hz,
JH4–F¼4.4 Hz, H-4/10), 7.22 (2H, td, JH3–H4¼8.8 Hz,
JH3–F¼9.3 Hz, JH3–H1¼2.5 Hz, H-3/9); 13C NMR
(DMSO-d6) d 0 155.89 (d, C-2,8, JC2–F¼229.95 Hz),
0
136.83 (d, C-1 , JC1 –F¼132.15 Hz), 122.97 (s), 122.91
3.1.15. Cyclohexane-1,4-dione bis-(p-fluorophenyl)-
hydrazone (4c). To a suspension of p-fluorophenylhydra-
zine hydrochloride (4.07 g, 25 mmol) in water (30 mL) was
added at room temperature a solution of NaOH (1.00 g,
25 mmol) in water (30 mL). After 15 min of stirring the
light yellow solution obtained was extracted with EtOAc
(3£100 mL). The combined organic fractions were dried
over Na2SO4 and evaporated in vacuo to give p-fluoro-
phenylhydrazine (2.91 g, 23.5 mmol, 94%). Mp 32–338C
(lit.24 348C).
(s), 122.89 (s), 113.14 (d, C-1 or C-3, JC1–F¼25.05 Hz),
111.16 (d, C-4/10, JC4–F¼8.92 Hz), 105.98 (d, C-3 or C-1,
JC3–F¼23.47 Hz), 101.13 (d, C-6/12).
3.1.18. 3-Amino-6-fluorocarbazole (11c). Mp 229–2308C
(decomp.). MS EI m/z: 201 [Mþ1]þ (100); IR (KBr) 3393,
1
1577, 1502, 1464, 1227, 1150, 868, 811, 585 cm21; H
NMR (DMSO-d6) d 10.72 (1H, s, NH), 7.69 (1H, dd,
JH5–F¼9.5 Hz, JH5–H7¼2.5 Hz, H-5), 7.33 (1H, dd,
JH8–H7¼8.8 Hz, JH8–F¼4.5 Hz, H-8), 7.20 (1H, d,
JH4–H2¼2.0 Hz, H-4), 7.18 (1H, d, JH1–H2¼8.5 Hz, H-1),
To a solution of cyclohexane-1,4-dione (1.34 g, 12 mmol)
in absolute EtOH (44 mL), the freshly obtained p-fluoro-
phenylhydrazine in absolute EtOH (12 mL) was added
dropwise. After 0.5 h a light yellow powder began to
precipitate. After stirring at 218C for 1 h 40 min the starting
material was consumed (TLC hexane–EtOAc 4:1) and the
reaction mixture was cooled to 08C. The solid was collected,
washed with cold EtOH (4 mL) and dried. Concentration of
the mother liquid gave an additional amount of solid 4c
(total amount 1.50 g, 46%). Mp 1278C (decomp.); MS EI
m/z: 327 [M21]þ (100); IR (KBr) 3445, 1611, 1509, 1247,
7.11 (1H, td, JH7–H8¼8.9 Hz, JH7–F¼9.4 Hz, JH7–H5¼
2.5 Hz, H-7), 6.78 (1H, dd, J¼8.5, 2.3 Hz H-2), 4.51 (2H,
bs, NH2); 13C NMR (DMSO-d6)
d
155.89 (s,
JC6–F¼230.0 Hz), 141.11 (s), 136.66 (s), 134.01 (s),
122.77 (s, JC–F¼4.1 Hz), 122.42 (s, JC–F¼9.4 Hz), 116.07
(d), 112.35 (d, JC–F¼25.2 Hz), 111.43 (d), 111.37 (d,
JC8–F¼8.9 Hz), 105.12 (d, JC–F¼23.0 Hz), 103.81 (d).
3.1.19. Cyclohexane-1,4-dione bis(p-bromophenyl)-
hydrazone (4d). To a solution of cyclohexane-1,4-dione
(2.464 g, 22.0 mmol) in absolute EtOH (40 mL) a solution
of p-bromophenylhydrazine hydrochloride (8.936 g,
40 mol) in absolute EtOH (50 mL) was added dropwise
during 10 min at rt. A solid soon started to precipitate. The
reaction mixture was kept at 408C for 1.5 h and then cooled.
The solid was collected and washed with cold EtOH
(10–15 mL) and dried to give 4d (4.360 g, 49%) as light
yellow solid. The substance was stored at 2188C. Mp 148–
1498C; MS EI m/z: 449 [M21]þ (100); IR (KBr) 3436,
1
1213, 1110, 1087, 826, 627 cm21; H NMR (DMSO-d6) d
8.60 (2H, s, NH), 7.03 (4H, m), 6.99 (4H, m), 2.60 (4H, m),
2.53 (4H, m); 13C NMR (DMSO-d6) d 145.34 (s,
JC–F¼315.0 Hz), 124.32 (s), 115.10 (d, JC–F¼22.0 Hz),
113.29 (d, JC–F¼7.3 Hz), 113.10 (s), 29.34 (t), 25.77 (t).
3.1.16. Indolisation of cyclohexane-1,4-dione bis-(p-
fluorophenyl)hydrazone (4c) in PPA. The p-fluoro-
phenylhydrazone 4c (1.00 g, 3.05 mmol) was mixed with
polyphosphoric acid (PPA) (12.5 g) at 08C. The mixture was
heated quickly to 808C and then more slowly (during
10–15 min) to 1858C. Between 60 and 808C the colour of
the mixture changed from dark brown-reddish to light
brown, and after 1508C it became greenish-yellow. The
mixture was kept at 185–1908C for 8–10 min, before it was
allowed to cool down over 2 h. The reaction mixture then
was diluted with 95% EtOH to 150 mL. A fine grey-
greenish solid, containing 1c, was slowly filtered off and
washed with water to pH 7, and dried. The filtrate was partly
1
2485, 1487, 1240, 1070, 1011, 830, 541 cm21; H NMR
(DMSO-d6) d 8.91 (2H, s), 7.29 (4H, d, J¼8.8 Hz), 7.02
(4H, d, J¼8.8 Hz), 2.67 (4H, m), 257 (4H, m); 13C NMR
(DMSO-d6) d 149.55 (s), 145.71 (s), 131.32 (d), 114.38 (d),
109.09 (s), 31.76 (t), 29.29 (t), 25.97 (t), 23.27 (t).
3.1.20. Indolisation of cyclohexane-1,4-dione bis-(p-
bromophenyl)hydrazone (4d). Compound 4d (4.350 g,
9.67 mmol) was suspended in a precooled (58C) mixture of
glacial acetic and sulfuric acids (4:1, 25 mL). The mixture
was heated quickly to 608C and thereafter the heating was

1272
L. N. Yudina, J. Bergman / Tetrahedron 59 (2003) 1265–1275
continued slowly to reflux. Above 808C the dark brown
solution transformed into a green-yellow suspension. The
mixture was kept at reflux for 3–5 min and then allowed to
cool to room temperature. After 1 h it was diluted with
EtOH (55 mL). The resulting suspension formed was kept
for 1 h, when the precipitate was collected, washed carefully
with water and dried to give 1d (1.05 g, 26%) as a fine
greenish-yellow powder. For purification the product was
Boc-protected with Boc2O (2.44 g, 11.16 mmol) and
DMAP (0.124 g, 1.01 mmol) in THF (30 mL) during 4 h.
The reaction mixture was diluted with CHCl3 (350 mL),
washed twice with water and evaporated. The solid was
suspended in acetonitrile (30 mL), refluxed during 5 min,
filtered off, washed with hot acetonitrile (8 mL) and dried to
give analytically pure 8d (1.42 g, 91%). Boc-indolocarba-
zole 8d was deprotected during 6 h at 2008C, 0.1 mm Hg to
give a quantitative yield of pure 1d as a fine greenish
powder.
(2H, s), 7.52 (2H, d, J¼8.2 Hz), 7.44 (2H, dd, J¼7.5,
7.3 Hz), 7.24 (2H, dd, J¼7.2, 8.2 Hz), 4.55 (4H, t,
J¼7.5 Hz, N–CH2), 2.78 (4H, t, J¼7.5 Hz, –CH2–
NMe2), 2.43 (12H, s, Me); 13C NMR (CDCl3) d 140.99
(s), 135.45 (s), 125.30 (d), 122.44 (s), 122.40 (s), 119.77 (d),
117.73 (d), 107.69 (d), 98.16 (d), 56.58 (t), 45.46 (q), 41.40
(t).
3.1.24. 5,11-Bis(dimethylaminomethyl)indolo[3,2-b]car-
bazole (16). To a precooled (08C) 40% water solution of
Me2NH (3.16 mL, 25 mmol), acetic acid (2.28 mL,
40 mmol) was added slowly, whilst maintaining a tempera-
ture below 58C, followed by 37% aqueous solution of H2CO
(1.50 mL, 20 mmol). The resulting mixture was stirred for
10 min at 08C and then added slowly under Ar flow to a
suspension of 1a (512 mg, 2 mmol) in DMA (15 mL) at
room temperature. The resulting suspension was heated to
908C and kept at this temperature for 10 min. The reaction
mixture was then cooled and the solvent was evaporated in
vacuo. Water (20 mL) was added to the residue and the
resulting solid was collected, washed with water and dried
to give 470 mg of 16 (64%) as a cream solid. HRMS calcd
for C24H26N4 370.2157, found 370.2174. Mp .2008C
(decomp.). IR (KBr) 1612, 1506, 1455, 1358, 1264, 1243,
3.1.21. 2,8-Dibromoindolo[3,2-b]carbazole (1d). Mp
.4108C. Anal. calcd for C18H10N2Br2: C, 52.21; H, 2.43;
N, 6.76; Br, 38.59. Found: C, 52.29; H, 2.36; N, 6.70; Br,
38.48. IR (KBr) 3394, 1468, 1446, 1285, 1235, 1178, 1054,
848, 811 cm21; 1H NMR (DMSO-d6): d 11.28 (2H, s, NH),
8.46 (2H, d, J¼1.7 Hz, H-1/7), 8.21 (2H, s, H-6/12), 7.49
(2H, dd, J¼8.5, 1.7 Hz, H-3/9), 7.41 (2H, d, J¼8.5 Hz,
H-4/10); 13C NMR (DMSO-d6) d 139.89 (s), 135.50 (s),
127.98 (d), 124.44 (s), 122.93 (d), 122.26 (s), 112.40 (d),
109.61 (s), 101.28 (d).
1
1150, 1040, 866, 734 cm21; H NMR (DMSO-d6) d 8.37
(2H, s), 8.26 (2H, d, J¼7.7 Hz), 7.66 (2H, d, J¼7.9 Hz),
7.44 (2H, dd, J¼7.5, 7.9 Hz), 7.20 (2H, dd, J¼7.5, 7.7 Hz),
5.05 (4H, s, CH2), 2.33 (12H, s, Me); 13C NMR (DMSO-d6)
d 141.94 (s), 136.45 (s), 125.67 (d), 122.49 (s), 122.24 (s),
120.16 (d), 118.42 (d), 109.75 (d), 100.08 (d), 65.36 (t),
42.72 (q).
3.1.22. 2,8-Dibromo-5,11-di-t-butyloxycarbonyl-
indolo[3,2-b]carbazole (8d). Undergoes Boc-deprotection
at temperatures above 2708C. HRMS calcd for
C28H26N2Br2O4 612.0259, found 612.0258; IR (KBr)
3418, 1719, 1465, 1431, 1373, 1338, 1305, 1155, 1028,
811, 765 cm21; 1H NMR (CDCl3): d 8.88 (2H, s), 8.18 (2H,
d, J¼2.0 Hz), 8.16 (2H, d, J¼8.8 Hz), 7.59 (2H, dd, J¼8.8,
2.0 Hz), 1.83 (18H, s, Boc); 13C NMR (CDCl3): d 151.12
(CO), 138.29 (s), 130.31 (d), 128.19 (s), 125.38 (s), 122.82
(d), 118.06 (2C, d and s), 116.47 (s), 107.32 (d), 84.82 (s),
28.67 (q).
3.1.25. 5,11-Bis(hydroxymethyl)indolo[3,2-b]carbazole
(17). To a suspension of 1a (512 mg, 2.00 mmol) in DMA
(17 mL), K2CO3 (828 mg, 6.00 mmol) and 37% aqueous
solution of H2CO (1.80 mL, 24 mmol) were added under Ar
flow. The mixture was quickly heated to 1108C and then
kept at the same temperature during 10 min. The hot
solution was filtered from unreacted 1a and the solvent was
evaporated in vacuo. Water (20 mL) was added to the
residue and the resulting solid was collected, washed with
water and dried to give 17 (525 mg, 83%) as a cream solid.
HRMS calcd for C20H16N2O2 316.1212, found 316.1196.
Mp .2508C (decomp.). IR (KBr) 3386, 1613, 1509, 1462,
3.1.23. 5,11-Bis(2-dimethylaminoethyl)indolo[3,2-b]car-
bazole (15a). A suspension of 1a (2.00 g, 8.0 mmol) in
DMSO (25 mL) was added dropwise to a suspension of NaH
(1.02 g, 95% in oil, 40.0 mmol) in DMSO (25 mL) under N2
flow. Then the reaction mixture was heated to 358C. After
0.5 h of stirring the hydrochloride of 2-dimethylamino-1-
chloroethane (2.53 g, 17.6 mol) in DMSO (20 mL) was
added dropwise. The mixture was stirred at the same
temperature under N2 flow until complete consumption of
1a had occurred. After 3 h the reaction mixture was poured
onto ice (700 mL). The fine yellow powder obtained was
collected, washed with water and dried to give pure 15a
(2.41 g). The filtrate was extracted with CH2Cl2
(3£100 mL). The collected organic phases were washed
with water, dried over Na2SO4, evaporated in vacuo and
dried under reduced pressure to give more of 15a (0.502 g,
total yield 92%). Mp 180–1818C; MS EI m/z: 398 [M]þ
(100), 384 [M2Meþ1]þ (80), 340 [M24Meþ2]þ (55), 295
[M2CH2CH2NMe222Me21]þ (60). IR (KBr) 3423, 2940,
2756, 1610, 1508, 1469, 1446, 1264, 1117, 1020, 833, 741,
546 cm21; 1H NMR (CDCl3) d 8.21 (2H, d, J¼7.6 Hz), 8.05
1
1431, 1272, 1227, 1122, 1075, 1008, 984, 748 cm21; H
NMR (DMSO-d6) d 8.39 (2H, s), 8.24 (2H, d, J¼7.6 Hz),
7.67 (2H, d, J¼8.0 Hz), 7.47 (2H, dd, J¼7.3, 8.0 Hz), 7.24
(2H, dd, J¼7.3, 7.6 Hz), 6.40 (2H, t, J¼6.9 Hz, OH), 5.89
(4H, d, J¼6.9 Hz, CH2); 13C NMR (DMSO-d6) d 140.89 (s),
135.44 (s), 125.64 (d), 122.81 (s), 122.47 (s), 120.08 (d),
118.75 (d), 109.55 (d), 99.96 (d), 65.50 (t).
3.1.26. 5-t-Butyloxycarbonylindolo[3,2-b]carbazole (18).
Compound 19 (3.77 g, 8.26 mmol) was dissolved in THF
(140 mL), cooled to 08C under Ar flow and then n-BuLi
(25 mL, 1.6 M in pentane, 40 mmol) was added in portions
during 40 min. The reaction was monitored by TLC
(hexane–EtOAc 5:1). When the starting material was
consumed the reaction mixture was quenched with saturated
NH4Cl (2 mL) and diluted with CHCl3 (350 mL). The
organic layer was washed with water (5£300 mL) to pH 7,
dried and evaporated in vacuo. The crude product was
suspended in acetone, filtered and washed with small

L. N. Yudina, J. Bergman / Tetrahedron 59 (2003) 1265–1275
1273
amounts of acetone to give 18 as a light coloured powder
(2.12 g, 72%). The analytically pure sample was obtained
by crystallisation from dioxane. HRMS calcd for
C23H20N2O2 356.1525, found 356.1519. At heating over
2508C to measure melting point undergoes Boc-deprotec-
tion. IR (KBr) 3416, 3385, 1723, 1442, 1358, 1311, 1157,
746 cm21; 1H NMR (DMSO-d6) d 11.34 (1H, s, NH), 8.94
(1H, s, H-6), 8.29 (1H, d, J¼7.1 Hz), 8.24 (1H, d,
J¼7.1 Hz), 8.17 (1H, s, H-11), 8.15 (1H, d, J¼7.7 Hz),
7.55 (2H, m), 7.41 (2H, m), 7.19 (1H, dd, J¼7.3, 7.5 Hz),
1.83 (9H, s, Boc); 13C NMR (DMSO-d6) d 150.69 (s),
141.17 (s), 138.50 (s), 136.96 (s), 131.99 (s), 127.11 (d),
126.02 (d), 125.78 (s), 124.51 (s), 123.04 (d), 122.91 (s),
122.67 (s), 120.15 (d), 119.99 (d), 118.50 (d), 115.90 (d),
110.97 (d), 106.61 (d), 100.99 (d), 83.74 (s), 27.97 (q).
127.18 (d), 126.05 (d), 125.88 (s), 124.57 (s), 123.23 (d),
122.92 (s), 122.62 (s), 120.23 (d), 120.15 (d), 118.48 (d),
115.91 (d), 110.96 (d), 106.65 (d), 101.09 (d), 63.03 (t),
14.33 (q).
3.1.29. 5-Hydroxymethylindolo[3,2-b]carbazole (24).
Compound 23 (40 mg, 0.12 mmol) was dissolved in THF
(5 mL) and cooled to 08C under Ar flow. LiAlH4 (46 mg,
12.2 mmol) was then added in several portions, after which,
the temperature was allowed to reach rt. After 15 min at rt
the reaction was completed, as judged by TLC (hexane–
EtOAc 2.5:1). The reaction mixture was quenched with a
solution of saturated NH4Cl (0.5 mL), diluted with EtOAc
(25 mL) and washed with water (4£30 mL). The organic
phase was dried over Na2SO4 and evaporated in vacuo. The
residue was purified by column flash chtomatography
(hexane–EtOAc 2.5:1) to give 24 (31 mg, 90%) as light
coloured plates. Mp 1288C (decomp.). HRMS calcd for
C19H14N2O 286.1106, found 286.1116; IR (KBr) 3399,
3.1.27. 5-t-Butyloxycarbonyl-11-ethyloxycarbonyl-
indolo[3,2-b]carbazole (21). To a vigorously stirred
suspension of 18 (356 mg, 1.00 mmol) in CH2Cl2
(12 mL), 50% aqueous solution of NaOH (1 mL), n-Bu4-
NHSO4 (67.8 mg, 0.20 mmol) and ClCOOEt (0.122 mL,
1.25 mmol) were all added. After 30 min of stirring the
reaction was complete (as judged by TLC in hexane–
EtOAc 5:1). The mixture was diluted with CH2Cl2 (25 mL)
and decanted. The NaOH layer was washed with CH2Cl2
(2£5 mL). The combined organic phases were carefully
washed with water to pH 7, dried over Na2SO4, evaporated
in vacuo and purified by flash chromatography on a short
column (hexane–EtOAc 5:1) to give 21 (180 mg, 84%).
This material was crystallised from CH3CN to give white
crystals. Mp 167–1688C (decomp.). Anal. calcd for
C26H24N2O4: C, 72.88; H, 5.65; N, 6.54. Found: C, 72.94;
H, 5.60; N, 6.61. IR (KBr) 3553, 3476, 3413, 1722, 1637,
1616, 1478, 1436, 1379, 1308, 1291, 1243, 1223, 1165,
1
1515, 1458, 1322, 1250, 1226, 989, 847, 745 cm21; H
NMR (DMSO-d6) d 11.09 (1H, s), 8.34 (1H, s), 8.23 (1H, d,
J¼7.7 Hz), 8.19 (1H, d, J¼8.0 Hz), 8.14 (1H, s), 7.64 (1H,
d, J¼8.2 Hz), 7.47 (2H, m), 7.39 (1H, dd, J¼8.2, 7.3 Hz),
7.19 (1H, dd, J¼7.7, 7.3 Hz), 7.15 (1H, dd, J¼7.3, 7.3 Hz),
6.36 (1H, t, J¼7.0 Hz, OH), 5.87 (2H, d, J¼7.0 Hz, CH2);
13C NMR (DMSO-d6) d 141.10 (s), 140.87 (s), 135.41 (s),
135.07 (s), 125.53 (2C, d), 122.78 (s), 122.61 (s), 122.58 (s),
122.50 (s), 120.21 (d), 120.07 (d), 118.55 (d), 117.83 (d),
110.60 (d), 109.40 (d), 100.64 (d), 99 (d), 65.47 (t).
3.1.30. 5-t-Butyloxycarbonyl-11-hydroxymethyl-
indolo[3,2-b]carbazole (25). To a solution of 18 (295 mg,
0.647 mmol) in 95% EtOH (45 mL) a 37% aqueous solution
of H2CO (0.96 mL, 12.94 mmol) was added, followed by
the slow addition of a solution of K2CO3 (357 mg,
2.59 mmol) in water (2 mL). The reaction mixture was
stirred at room temperature for 1.5 h, before it was
concentrated in vacuo to 6–7 mL. The residue was diluted
with water and extracted with EtOAc. The combined
organic extracts were washed with brine, dried over
Na2SO4, evaporated in vacuo and purified by column
chromatography with a gradient system from CHCl3–
hexane 2:1 to CHCl3. After chromatography some 18
(45 mg) was recovered and 25 was isolated (178 mg, 88%
yield based on recovered 18). Washing 25 with a hot
solution of 10% EtOH/n-heptane gave analytically pure 25
as a pinkish crystals. Mp 1708C (decomp.). Anal. calcd for
C24H22N2O3: C, 74.59; H, 5.74; N, 7.25. Found: C, 74.47;
H, 5.66; N, 7.16. IR (KBr) 3436, 2974, 1720, 1512, 1482,
1
1152, 1052, 759, 743, 620 cm21; H NMR (DMSO-d6) d
8.93 (1H, s), 8.91 (1H, s), 8.28 (3H, m), 8.21 (1H, d,
J¼8.2 Hz), 7.57 (2H, m), 7.45 (2H, m), 4.63 (2H, q,
J¼7.1 Hz, CH2), 1.79 (9H, s, Boc), 1.56 (3H, t, J¼7.1 Hz,
CH3); 13C NMR (CDCl3) d 152.83 (s), 151.50 (s), 139.48
(s), 139.25 (s), 135.60 (s), 135.21 (s), 127.46 (d), 127.42 (d),
126.72 (s), 126.48 (s), 126.16 (s), 126.13 (s), 123.51 (d),
123.27 (d), 119.92 (2C, d), 116.58 (d), 116.55 (d), 107.16
(d), 107.02 (d), 84.19 (s), 63.35 (t), 28.69 (q), 14.79 (q).
3.1.28. 5-Ethoxycarbonylindolo[3,2-b]carbazole (23). A
solution of 21 (270 mg, 0.63 mmol) in dry CH2Cl2 (26 mL)
was cooled to 08C under Ar flow, and then TFA (2.70 mL)
was added in portions. The reaction mixture was stirred for
15 min at 08C before the ice bath was removed and stirring
continued for 2.5 h to complete the reaction (TLC in
hexane–EtOAc 5:1). The reaction mixture was evaporated
and re-evaporated in vacuo with CH2Cl2. The residue was
crystallised from CH3CN to give 23 (171 mg, 83%) as
cream crystals. Mp 253–2548C. Anal. calcd for
C21H16N2O2: C, 76.71; H, 4.91; N, 8.53. Found: C, 76.56;
H, 4.89; N, 8.42. IR (KBr) 3477, 3411, 1731, 1638, 1616,
1
1448, 1379, 1311, 1226, 1155, 986, 763, 743 cm21; H
NMR (DMSO-d6) d 8.96 (1H, s), 8.44 (1H, s), 8.27 (2H, m),
8.20 (1H, d, J¼7.5 Hz), 7.70 (1H, d, J¼8.0 Hz), 7.51 (2H,
m), 7.44 (1H, dd, J¼7.5, 7.3 Hz), 7.26 (1H, dd, J¼7.1,
7.0 Hz), 6.47 (1H, t, J¼6.6 Hz, OH), 5.90 (2H, d, J¼6.6 Hz,
CH2), 1.79 (9H, s, Boc); 13C NMR (DMSO-d6) d 150.60 (s),
140.91 (s), 138.48 (s), 137.03 (s), 132.41 (s), 127.20 (d),
126.08 (d), 125.72 (s), 124.46 (s), 123.14 (d), 122.86 (s),
122.78 (s), 120.00 (2C, d), 119.34 (d), 115.93 (d), 109.93
(d), 106.59 (d), 100.33 (d), 83.85 (s), 65.52 (t), 27.91 (q).
1
1444, 1372, 1294, 1182, 1048, 750, 623 cm21; H NMR
(DMSO-d6) d 11.38 (1H, s, NH), 8.96 (1H, s, H-6), 8.29
(1H, d, J¼7.3 Hz), 8.27 (1H, d, J¼8.2 Hz), 8.21 (1H, d,
J¼8.0 Hz), 8.18 (1H, s, H-12), 7.52 (2H, m), 7.43 (2H, m),
7.19 (1H, dd, J¼7.3, 7.7 Hz), 4.62 (2H, q, J¼7.1 Hz, CH2),
1.56 (3H, t, J¼7.1 Hz, CH3); 13C NMR (DMSO-d6) d
151.99 (s), 141.14 (s), 138.35 (s), 137.03 (s), 131.81 (s),
3.1.31. 5-t-Butyloxycarbonyl-11-(2-dimethylaminoethyl)-
indolo[3,2-b]carbazole (26). To a solution of 18 (700 mg,
1.97 mmol) in DMF (24 mL) under Ar flow, was added

1274
L. N. Yudina, J. Bergman / Tetrahedron 59 (2003) 1265–1275
t-BuOK (551 mg, 4.82 mmol) during 5 min. The resulting
solution was stirred for 10 min at room temperature. Freshly
prepared 2-dimethylamino-1-chloroethane as a free base25
(ca 3 eq.) was then added, followed by KI (981 mg,
5.91 mmol). The reaction mixture was stirred at 218C for
1 h, before the temperature was increased to 508C, and
stirring was continued for 2.5 h further. The solvent was
evaporated in vacuo, and the residue was diluted with
CH2Cl2 (250 mL) and water (120 mL). The aqueous phase
was washed with CH2Cl2, the combined organic phases
were washed with water, dried, evaporated and purified by
gradient flash chromatography (CH2Cl2!CH2Cl2–MeOH
9:1) to give 26 (505 mg, 56%). Crystallisation from
acetonitrile gave 26 as brownish crystals. Mp 918C.
HRMS calcd for C27H29N3O2 427.2260, found 427.2260;
IR (KBr) 2971, 2765, 1718, 1510, 1443, 1368, 1308, 1226,
40 min the reaction was complete (as judged by TLC in
hexane–EtOAc 5:1) and the mixture was diluted with
CH2Cl2 (20 mL) and decanted. The basic layer was
extracted with CH2Cl2 (2£5 mL). The combined organic
extracts were carefully washed with water to pH 7, dried
over Na2SO4 and evaporated in vacuo. The product was
crystallised from CH3CN to give analytically pure pale
crystals (106 mg) of 20. Flash chromatography of the
evaporated mother liquid (hexane–EtOAc 4:1) gave an
additional quantity of 20 (43 mg, total yield 86%). Mp 164–
1658C. HRMS calcd for C24H22N2O2 370.1681, found
370.1697; IR (KBr) 3428, 2925, 1727, 1510, 1474, 1440,
1
1368, 1312, 1292, 1255, 1148, 829, 739, 682 cm21; H
NMR (DMSO-d6) d 8.97 (1H, s, H-6), 8.37 (1H, s, H-12),
8.30 (1H, d, J¼7.3 Hz), 8.25 (1H, d, J¼8.2 Hz), 8.20 (1H, d,
J¼7.7 Hz), 7.62 (1H, d, J¼8.2 Hz), 7.51 (2H, m), 7.43 (1H,
dd, J¼7.5, 7.0 Hz), 7.23 (1H, dd, J¼7.3, 7.7 Hz), 3.99 (3H,
s, Me), 1.79 (9H, s, Boc); 13C NMR (DMSO-d6) d 150.60
(s), 141.82 (s), 138.46 (s), 138.06 (s), 131.99 (s), 127.15 (d),
126.11 (d), 125.78 (s), 124.54 (s), 123.06 (d), 122.24 (s),
122.17 (s), 120.05 (d), 119.99 (d), 118.61 (d), 115.90 (d),
109.04 (d), 106.63 (d), 99.48 (d), 83.77 (s), 29.22 (q), 27.90
(q).
1
1153, 1044, 835, 740 cm21; H NMR (DMSO-d6) d 8.95
(1H, s), 8.37 (1H, s), 8.32 (1H, d, J¼7.5 Hz), 8.25 (1H, d,
J¼8.1 Hz), 8.19 (1H, d, J¼7.6 Hz), 7.61 (1H, d, J¼8.1 Hz),
7.52 (2H, m), 7.40 (1H, dd, J¼7.4, 7.4 Hz), 7.23 (1H, dd,
J¼7.4, 7.5 Hz), 4.58 (2H, t, J¼6.8 Hz, CH2), 2.70 (2H, t,
J¼6.8 Hz, CH2), 2.25 (6H, s, Me), 1.78 (9H, s, Boc); 13C
NMR (DMSO-d6) d 150.64 (s), 141.29 (s), 138.49 (s),
137.43 (s), 132.05 (s), 127.22 (d), 126.16 (d), 125.80 (s),
124.60 (s), 123.06 (d), 122.42 (s), 122.34 (s), 120.28
(d), 120.09 (d), 118.70 (d), 115.92 (d), 109.32 (d), 106.71
(d), 99.68 (d), 83.81 (s), 57.12 (t), 45.58 (q), 41.00 (t), 27.93
(q).
3.1.34. 5-Methylindolo[3,2-b]carbazole (22). Compound
20 was deprotected by sublimation at 2008C for 4 h in
quantitative yield to give the product 22 as greenish-yellow
crystals. Mp 309–3108C. Anal. calcd for C19H14N2: C,
84.42; H, 5.22; N, 10.36. Found: C, 84.34; H, 5.14; N, 10.42.
IR (KBr) 3400, 1613, 1514, 1477, 1450, 1447, 1429, 1321,
1282, 1265, 1240, 1104, 1002, 874, 745, 688, 565 cm21; 1H
NMR (DMSO-d6) d 11.07 (1H, s, NH), 8.25 (1H, s), 8.23
(1H, d), 8.21 (1H, d, J¼7.6 Hz), 8.16 (1H, s), 7.55 (1H, d,
J¼8.1 Hz), 7.46 (2H, m), 7.39 (1H, dd, J¼7.2, 7.8 Hz), 7.16
(2H, m), 3.95 (3H, s, Me); 13C NMR (DMSO-d6) d 141.74
(s), 141.06 (s), 136.27 (s), 135.07 (s), 125.58 (d), 125.49 (d),
122.63 (2C, s), 122.10 (s), 122.02 (s), 120.20 (d), 120.13 (d),
117.73 (2C, d), 110.60 (d), 108.50 (d), 100.72 (d), 98.88 (d),
29.16 (q).
3.1.32. 5-(2-Dimethylaminoethyl)indolo[3,2-b]carbazole
(15b). To a precooled (08C) solution of 26 (220 mg,
0.515 mmol) in MeOH (8 mL) under Ar flow, was added
freshly prepared 2 M solution of MeONa in methanol
(16 mL) during 30 min. After 10 min the cooling bath was
removed and the reaction mixture was stirred at 218C under
Ar for 72 h, after which time the starting material had been
consumed (as judged by TLC in CHCl3–MeOH, 9:1). The
solvent was evaporated, and the residue was partitioned in
CH2Cl2 and water. The water phase was extracted twice
with CH2Cl2. The combined organic phases were then
washed with water to pH 7, dried by Na2SO4, evaporated in
vacuo and suspended in acetone (3 mL). The light yellow
precipitate obtained was collected and washed with acetone
(2 mL) to give pure 15b (125 mg, 74%). Mp 225–2268C.
HRMS calcd for C22H21N3 327.1735, found 327.1722; IR
(KBr) 3406, 3046, 2919, 2826, 1614, 1516, 1470, 1447,
1325, 1234, 1163, 1033, 739 cm21; 1H NMR (DMSO-d6) d
11.09 (1H, s, NH), 8.27 (1H, s), 8.25 (1H, d, J¼7.5 Hz),
8.22 (1H, d, J¼7.0 Hz), 8.15 (1H, s), 7.54 (1H, d,
J¼8.1 Hz), 7.48 (1H, d, J¼8.0 Hz), 7.39 (2H, m), 7.15
(2H, m), 4.55 (2H, t, J¼6.9 Hz, CH2), 2.69 (2H, t,
J¼6.9 Hz, CH2), 2.26 (6H, s, Me); 13C NMR (DMSO-d6)
d 141.18 (s), 141.08 (s), 135.48 (s), 135.08 (s), 125.58 (d),
125.52 (d), 122.64 (s), 122.60 (s), 122.24 (s), 122.17 (s),
120.28 (d), 120.24 (d), 117.77 (d), 117.68 (d), 110.54 (d),
108.67 (d), 100.73 (d), 98.96 (d), 57.04 (t), 45.60 (q), 40.96
(t).
References
¨
1. Bergman, J.; Janosik, T.; Wahlstrom, N. Adv. Heterocycl.
Chem. 2001, 80, 1–71.
2. Bjeldanes, L.; Kim, J.; Grose, K.; Bartholomew, J.; Bradfield,
C. Proc. Natl Acad. Sci. USA 1991, 88, 9543–9547.
¨
3. Rannug, U.; Rannug, A.; Sjoberg, U.; Li, H.; Westerholm, R.;
Bergman, J. Chem. Biol. 1995, 2, 841–845.
4. Wei, Y.; Helleberg, H.; Rannug, U.; Rannug, A. Chem. Biol.
Interact. 1998, 110, 39–55.
5. Gonzalez, F. J.; Fernandez-Salguero, P.; Ward, J. M.
J. Toxicol. Sci. 1996, 21, 273–277.
6. Bergman, J. Tetrahedron 1970, 26, 3353–3355.
7. Tholander, J.; Bergman, J. Tetrahedron 1999, 55,
12577–12594.
8. Robinson, B. J. Chem. Soc., Perkin Trans. 1 1963,
3097–3099.
3.1.33. 5-t-Butyloxycarbonyl-11-methylindolo[3,2-b]car-
bazole (20). To a vigorously stirred suspension of 18
(168 mg, 0.47 mmol) in CH2Cl2 (7.5 mL), 50% aqueous
solution of NaOH (1 mL), n-Bu4NBr (30 mg, 94 mmol) and
MeI (0.18 mL, 2.82 mmol) were added. After stirring for 1 h
9. (a) Teuber, H.; Vogel, L. Chem. Ber. 1970, 103, 3302–3318.
(b) Teuber, H.; Vogel, L. Chem. Ber. 1970, 103, 3319–3342.
10. Kistenmacher, A.; Mu¨llen, K. J. Heterocycl. Chem. 1992, 29,
1237–1239.

L. N. Yudina, J. Bergman / Tetrahedron 59 (2003) 1265–1275
1275
`
¨
18. (a) Zegar, I.; Graslund, A.; Bergman, J.; Norden, B.; Eriksson,
11. Bergman, J.; Janosik, T.; Yudina, L.; Desarbre, E.; Lidgren,
G.; Venemaln, L. Tetrahedron 2000, 56, 1911–1916.
12. Wei, Y.-D.; Bergander, L.; Rannug, U.; Rannug, A. Arch.
Biochem. Biophys. 2000, 383, 99–107.
M. Chem. Biol. Interact. 1989, 72, 277–293. (b) Sehlstedt, U.;
¨
Aich, P.; Bergman, J.; Vallberg, H.; Norden, B.; Graslund, A.
J. Mol. Biol. 1998, 278, 31–56.
13. Chen, Y.-H.; Riby, J.; Srivastava, P.; Bartholomew, J.;
Denison, M.; Bjeldanes, L. J. Biol. Chem. 1995, 270,
22548–22555.
19. Tholander, J.; Bergman, J. Tetrahedron 1999, 55, 6243–6260.
20. Gardner, H.; Haynes, R.; Brandon, A. J. Org. Chem. 1957, 22,
1206–1210.
14. Formisyn, P.; Tran-Minh, C.; Bourgois, J. Fr. Lett. Appl.
Microbiol. 1994, 19, 244–246.
21. Fuerst, B. Chem. Ber. 1951, 84, 83–86.
22. Grandberg, I. I.; Bobrova, N. I. Chem. Heterocycl. Compd
1973, 9, 196–199.
15. Bergman, J.; Pelcman, B. J. Org. Chem. 1989, 54, 824–828.
16. Bergman, J.; Norrby, P.-O.; Sand, P. Tetrahedron 1990, 46,
6113–6124.
23. Mitchell, J.; Pausacker, K. H. J. Chem. Soc. 1954, 4502–4504.
24. Miles, P.; Suschitzky, H. Tetrahedron 1963, 19, 385–390.
25. Hickmott, P. W.; Wood, S.; Murray-Rust, J. Chem. Soc.,
Perkin Trans. 1 1985, 2033–2038.
17. Gillner, M.; Bergman, J.; Cambillau, C.; Alexandersson, M.;
¨
Fernstrom, B. Mol. Pharmacol. 1993, 44, 336–345.