Synthesis of N-alkyl substituted bioactive indolocarbazoles related to G?6976

Article abstract of DOI:10.1016/j.tet.2006.05.049

The syntheses of new nitrile and amide analogues of 7-keto G?6976 are described. The amide analogue 22 was formed via the condensation with a new functionalized indoleacetic acid derivative 25 to overcome the solubility problem during the coupling reaction.

Full text of DOI:10.1016/j.tet.2006.05.049

Tetrahedron 62 (2006) 7838–7845
Synthesis of N-alkyl substituted bioactive indolocarbazoles
€
related to Go6976
Sudipta Roy,a Alan Eastmanb and Gordon W. Gribblea,
*
aDepartment of Chemistry, Dartmouth College, Hanover, NH 03755, USA
bDepartment of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, NH 03755, USA
Received 17 March 2006; revised 17 May 2006; accepted 19 May 2006
Available online 19 June 2006
€
Abstract—The syntheses of new nitrile and amide analogues of 7-keto Go6976 are described. The amide analogue 22 was formed via the
condensation with a new functionalized indoleacetic acid derivative 25 to overcome the solubility problem during the coupling reaction.
Ó 2006 Elsevier Ltd. All rights reserved.
H3C
O
N
1. Introduction
O
O
CH3
N
CH3
N
H3C
O
N
4
Cell cycle checkpoints are activated in response to DNA
damage thereby delaying cell cycle progression in order to
provide more time for DNA repair. Cell cycle arrest in G1
or S phase prevents replication of damaged DNA, while
arrest in G2 prevents damaged chromosomes from being seg-
regated in mitosis; thus preventing the propagation of genetic
abnormalities. Inhibition of the G2 checkpoint has attracted
widespread interest because most cancer cells have an inop-
erative G1 checkpoint. The activity of the G1 checkpoint is
dependent on the p53 tumor suppressor protein, which is
deleted or mutated in more than 50% of all cancers. Although
cells with defective p53 are unable to activate the G1 check-
point in response to DNA damage, they retain the ability to
arrest in S and G2. This provides the cells with an opportunity
to repair their DNA and thereby survive and grow. The S and
G2 checkpoints are regulated by various kinases among
which checkpoint kinase 1 (Chk1) plays a major role. Inhib-
itors of Chk1 preferentially abrogate cell cycle arrest in p53-
defective cells and selectively sensitize cancer cells with
mutated p53 to killing by DNA-damaging agents. Therefore,
combining a Chk1 inhibitor with a DNA-damaging agent
should selectively drive p53-defective cells into a premature
and lethal mitosis.1
N
N
N
CH3
O
N
CH3
Pentoxifylline (2)
Caffeine (1)
Figure 1.
However, caffeine cannot be used to inhibit this pathway in
human beings as the doses required cause central nervous
system and cardiac toxicities.
UCN-01 (3), one member of the indolocarbazole family,3
generated considerable interest in our laboratory when it
was found to be a potent inhibitor of DNA damage-induced
S and G2 cell cycle checkpoints, which led to increased kill-
ing of tumor cells (Fig. 2).4 Although UCN-01 is well recog-
nized as a protein kinase C inhibitor,5 this checkpoint
inhibition was attributed to its ability to inhibit Chk1.6 Un-
fortunately, UCN-01 binds avidly to human serum proteins
thereby compromising its potential therapeutic activity.7
Subsequent research identified other Chk1 inhibitors such
as staurosporine (4),2 granulatimide (5), and isogranulat-
imide (6),8 but their nonselectivity and/or their weak inhibi-
tory activity justifies the search for new selective Chk1
inhibitors. Accordingly, we initiated a synthetic program
to develop novel analogues rationally designed to overcome
the obstacles observed with the other analogues and with
improved therapeutic potential.
Several small molecules that inhibit checkpoint proteins have
been described in the literature, the first of which were the
purine alkaloids caffeine (1) and pentoxifylline (2), which
inhibit two upstream kinases, ATM and ATR (Fig. 1).2
Initially, a K252a (7) analogue, ICP-1 (8), was synthesized
and tested, and was found to overcome the problem of pro-
tein binding but it has considerably reduced potency
(Fig. 3).9
€
Keywords: Indolocarbazoles; Bisindolylmaleimide; Go6976; UCN-01;
Checkpoint inhibitors.
* Corresponding author. Tel.: +1 603 646 3118; fax: +1 603 646 3946;
e-mail: ggribble@dartmouth.edu
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.05.049

S. Roy et al. / Tetrahedron 62 (2006) 7838–7845
7839
H
N
H
N
O
HO
O
H
H
N
H
N
O
O
O
O
N
N
N
N
NH
O
O
N
H3C
H3C
H
N
N
H
N
H
N
H3CO
H3CO
NHCH3
NHCH3
UCN-01 (3)
Staurosporine (4)
Granulatimide (5)
Isogranulatimide (6)
Figure 2.
H
N
H
N
H
N
O
O
O
H
O
O
N
O
O
N
N
N
N
N
CH3
N
O
O
N
CH3
N
H3C
H3CO2C
H3C
CN
H3CO2C
OH
OH
CN
ICP-109 (12)
K252a (7)
ICP-1 (8)
ICP-106 (11)
Figure 3.
Figure 5.
€
More recently, we found that Go6976 (9) is a very potent
checkpoint inhibitor even in the presence of human serum,10
and this has also been attributed to the inhibition of Chk1
indole-1-butanenitrile (14), respectively. Compound 13 was
obtained in 51% yield and compound 14 was obtained in
60% yield (Scheme 1). Similar N-alkylation of indole-3-ace-
tic acid using methyl iodide in the presence of excess NaH
gave 1-methylindole-3-acetic acid (17) in 94% yield.
Indole-1-acetonitrile (13) was then treated with oxalyl chlo-
ride in dichloromethane to furnish the glyoxylyl chloride 15,
which was immediately treated with 1-methylindole-3-
acetic acid (17) in the presence of triethylamine to produce
anhydride 18 in 40% yield in two steps from 13.13 Similarly,
indole-1-butanenitrile (14) furnished 19 in 45% yield via the
intermediate glyoxylyl chloride 16. Due to the potentially la-
bile nitrile functionality, ammonia was generated in situ from
1,1,1,3,3,3-hexamethyldisilazane (HMDS) and methanol
and these conditions were used to convert anhydrides 18
and 19 to imides 20 and 21, respectively, at rt.14 During our
synthesis of ICP-103 (10), we found that the final oxidative
cyclization was quite challenging for the bisindolylmale-
imide with substituents present on both N-12 and
N-13.12,15,16 However, heating bisindolylmaleimide 20 and
21 in DMF in the presence of palladium(II) trifluoroacetate
gave the target compounds 11 and 12 in 8 and 50% yields,
respectively. The lower yield of 11 may be a consequence
of the strong inductive electron withdrawing effect of the cy-
ano group that retards the (electrophilic) oxidative addition
of Pd(II) to bisindolylmaleimide 20.
(Fig. 4).11 Additionally, Go6976 abrogated S and G2 arrest
€
at a concentration substantially lower than that required to
inhibit PKC. Interestingly, UCN-01 (3) did not demonstrate
this selectivity for checkpoint inhibition. As a consequence,
we have begun a structure–activity study of analogues of
Go6976 (9). During our screening to identify novel inhibitors
of Chk1 related to Go6976, we found that ICP-103 (10) is
€
€
also a potent checkpoint inhibitor.12 Therefore, we have
focused our investigation on this class of molecules as poten-
tial inhibitors of Chk1. Our initial objectivewas to investigate
the effect of the nitrile chain-length on Chk1 activity, and we
now report our results.
H
N
H
N
O
O
O
N
N
N
N
CH3
CH3
CN
Gö6976 (9)
CN
ICP-103 (10)
Figure 4.
In work to be reported separately, we find that ICP-106 (11)
and ICP-109 (12) are less potent than ICP-103 (10) at abro-
gating DNA damage-induced cell cycle arrest. In an assay
using flow cytometry analysis,10 ICP-106 and ICP-109 were
found to abrogate S phase arrest at 3 mM and 10 mM, respec-
tively, whereas ICP-103 (10) was effective at 100 nM. These
2. Results and discussion
In the course of our structure–activity relationship studies on
ICP-103 analogues, we have synthesized and tested two new
nitrile homologues, ICP-106 (11) and ICP-109 (12) (Fig. 5).
€
values can be compared to the efficacy of Go6976 (9) of
30 nM in the same assay.10 For drugs to be used in patients,
it is also essential that they do not elicit undesirable toxici-
ties. In this regard, the breast cancer MDA-MB-231 cell
line was used in an assay of growth inhibition. Cells were
Thus, for the synthesis of 11 and 12, we alkylated the indole
nitrogen with bromoacetonitrile and 4-bromobutyronitrile in
the presence of NaH to furnish indole-1-acetonitrile (13) and

7840
S. Roy et al. / Tetrahedron 62 (2006) 7838–7845
O
OH
O
O
N
CH3
Cl
(17)
i) NaH, DMF
Br CN
(COCl)2
CH2Cl2
Et3N, CH2Cl2
ii)
N
H
N
N
n
n
n
NC
NC
13 (n=1, 51%)
14 (n=3, 60%)
15 (n=1)
16 (n=3)
H
H
N
O
N
O
O
O
O
O
O
Pd(O2CCF3)2
DMF, ∆
HMDS, MeOH
DMF
N
N
CH3
N
CH3
N
N
CH3
N
n
n
n
NC
NC
NC
18 (n=1, 40%)
19 (n=3, 45%)
20 (n=1, 93%)
21 (n=3, 94%)
11 (n=1, 8%)
12 (n=3, 50%)
Scheme 1.
incubated with the compounds for 24 h, and the cell number
assessed after 7 days. The concentration that inhibited 50%
€
of growth was: Go6976, 6 mM; ICP-103, 2.5 mM; ICP-106,
>10 mM; ICP-109, 2 mM. Accordingly, the concentrations
Use of more polar solvents, such as 1,2-dichloroethane,
THF, and DMF, also failed to furnish the desired coupling
product 24.
that inhibit growth do not correlate with those that overcome
€
cell cycle arrest, and Go6976 and ICP-103 are clearly active
as checkpoint inhibitors at noncytotoxic concentrations.
KOH,
CH2=CH-CONH2
dioxane
N
H
N
CH2CH2CONH2
From this activity data for the nitrile analogues 10, 11, and
12, it was found that two methylene groups provide maxi-
mum activity. Therefore, we attempted to synthesize a novel
amide analogue of ICP-103, ICP-112 (22), bearing the same
number of carbons in the amide arm (Fig. 6). We wanted to
further explore the SAR by replacing the nitrile with an
amide.
23 (40%)
O
O
O
i) (COCl)2, CH2Cl2
ii)
O
N
N
O
OH
CH3
N
CH3
NH2
(17)
H
N
24
O
O
Et3N, CH2Cl2
Scheme 2.
N
CH3
N
O
To possibly circumvent this solubility issue in the coupling
reaction, we decided to attach the amide-chain on the
indole-3-acetic acid fragment. Although there does not
appear to be literature precedent for these compounds, we
were able to synthesize 1-(2-carbamoyl-ethyl)indole-3-
acetic acid (25) from indole-3-acetic acid in one step, using
3-chloropropionamide as an alkylating agent in the presence
of excess NaH (51% yield) (Scheme 3).
NH2
ICP-112 (22)
Figure 6.
For the synthesis of ICP-112 (22), we initially proceeded
through the same route that we used for the nitrile com-
pounds. For this purpose, indole-1-propionamide (23) was
synthesized from indole and acrylamide in the presence of
KOH in 40% yield (Scheme 2). We then treated 23 with
oxalyl chloride to prepare the corresponding glyoxylyl chloride
that was to be coupled with 1-methylindole-3-acetic acid (17)
in the presence of triethylamine. To our surprise, the desired
anhydride 24 was not formed. The coupling reaction failed
probably due to the highly insoluble nature of the glyoxylyl
chloride intermediate bearing the polar amide functionality.
HOOC
HOOC
i) NaH, DMF
ii) ClCH2CH2CONH2
N
N
H
NH2
O
25 (51%)
Scheme 3.

S. Roy et al. / Tetrahedron 62 (2006) 7838–7845
7841
O
O
Cl
(COCl)2
CH2Cl2
i) KOH, acetone
ii) CH3I
25
Et3N, CH2Cl2
N
H
N
N
CH3
CH3
27
26 (90%)
H
H
N
N
O
O
O
O
O
O
O
Pd(O2CCF3)2
HMDS, MeOH
DMF
DMF, ∆
N
O
N
CH3
N
CH3
N
N
CH3
N
O
NH2
O
NH2
NH2
22 (30%)
28 (31% in two steps)
29 (96%)
Scheme 4.
Compound 25 was treated with 1-methylindole-3-glyoxylyl
chloride (27), derived from the reaction between 1-methyl-
indole (26) and oxalyl chloride, to form the desired anhy-
dride 28 in 31% yield over the two steps (Scheme 4).
Anhydride 28 was treated with HMDS and methanol to
give imide 29 in 96% yield. Heating 29 in DMF with palla-
dium(II) trifluoroacetate afforded the target compound
ICP-112 (22) in 30% yield. An alternative oxidative cycliza-
tion of 29 using ultraviolet light in the presence of a catalytic
amount of iodine in THF:acetonitrile (1:1) yielded 22 only in
5% yield.17
a solvent purification system; anhydrous DMF and Et3N
were purchased from Aldrich.
4.1.1. 1H-Indole-1-acetonitrile (13). Toa stirred suspension
of NaH (600 mg, 15 mmol, 60% dispersion in mineral oil) in
DMF (35 mL) at 0 ꢀC was added dropwise a solution of
indole (1.17 g, 10 mmol) in DMF (15 mL). After stirring
the mixture for 30 min at 0 ꢀC, a solution of bromoaceto-
nitrile (1.1 mL, 15 mmol) in DMF (15 mL) was added drop-
wise. The mixture was allowed to slowly reach rt and
continued to stir overnight. The mixture was poured into
cold water (100 mL) and extracted with ether (3ꢁ50 mL).
Thecombined organicextracts were dried (Na2SO4) and con-
centrated in vacuo. The residue was purified by column chro-
matography on silica gel (3:1 hexane:ethyl acetate) to give
the desired product (796 mg, 51%) as a colorless oil, which
solidified after prolonged drying: mp 75–77 ꢀC (lit.18 74–
75 ꢀC); IR (thin film) 3097, 2978, 2941, 2252, 1611, 1462,
1317 cmꢂ1; 1H NMR (CDCl3): d 7.75–7.71 (m, 1H), 7.44–
7.35 (m, 2H), 7.31–7.25 (m, 1H), 7.13 (d, 1H, J¼3.4 Hz),
6.67 (dd, 1H, J¼3.2 Hz, 0.7 Hz), 4.99 (m, 2H); 13C NMR
(CDCl3): d 129.1, 127.3, 123.1, 121.7, 121.0, 114.6, 109.0,
104.3, 34.4.
The new indolocarbazole ICP-112 (22) abrogated S phase
arrest at 1–3 mM. This value should be compared to the
100 nM efficacy observed with the nitrile analogue, ICP-103
(10). Accordingly, it appears that the nitrile is the preferred
structure for further study. Our detailed biological activity
data will be reported separately.
3. Conclusion
In summary, we have explored one aspect of the structure–
€
activity relationships (SARs) of Go6976 and discovered
that a three-carbon nitrile chain seems essential for optimal
activity. Also, we find that a nitrile is the more desirable
functionality than an amide for activity. Work is in progress
in our laboratory with other nitrogen-bearing functionalities
and these will be reported in due course.
4.1.2. 1H-Indole-1-butanenitrile (14). To a stirred suspen-
sion of NaH (600 mg, 15 mmol, 60% dispersion in mineral
oil) in DMF (35 mL) at 0 ꢀC was added dropwise a solution
of indole (1.17 g, 10 mmol) in DMF (15 mL). After stirring
the mixture for 30 min at 0 ꢀC, a solution of bromobutyro-
nitrile (1.6 mL, 15 mmol) in DMF (15 mL) was added
dropwise. The mixture was allowed to slowly reach rt and
continued to stir overnight. The mixture was poured into
cold water (100 mL) and extracted with ethyl acetate
(3ꢁ50 mL). The combined organic extracts were dried
(Na2SO4) and concentrated in vacuo. The residue was puri-
fied by column chromatography on silica gel (2:1 hexane:
ethyl acetate) to give the desired product (1.1 g, 60%) as a
colorless oil:19 IR (thin film) 3051, 2939, 2246, 1610,
4. Experimental
4.1. General experimental procedures
Melting points were determined with a Mel-Temp Labora-
tory Device apparatus and are uncorrected. IR spectra were
recorded on a Perkin–Elmer 600 series FTIR spectrophoto-
1
1
meter. H and 13C NMR spectra were recorded on either
1512, 1463, 1314 cmꢂ1; H NMR (CDCl3): d 7.77–7.74
a Varian XL-300 or 500 Fourier-transform NMR spectro-
meter. Both low- and high-resolution mass spectra were
carried out at the Mass Spectrometry Laboratory, School of
Chemical Sciences, University of Illinois at Urbana
Champaign. Anhydrous THF and CH2Cl2 were prepared by
(m, 1H), 7.45–7.42 (m, 1H), 7.37–7.31 (m, 1H), 7.27–7.22
(m, 1H), 7.17 (d, 1H, J¼3.2 Hz), 6.63 (dd, 1H, J¼3.2 Hz,
0.7 Hz), 4.35–4.31 (m, 2H), 2.27–2.18 (m, 4H); 13C NMR
(CDCl3): d 135.8, 128.8, 127.8, 122.0, 121.3, 119.8, 118.9,
109.2, 102.1, 44.4, 26.0, 14.6.

7842
S. Roy et al. / Tetrahedron 62 (2006) 7838–7845
4.1.3. 1-Methyl-1H-indole-3-acetic acid (17). To a stirred
suspension of NaH (6.0 g, 150 mmol, 60% dispersion in min-
eral oil) in THF (125 mL) at 0 ꢀC was added a solution of in-
dole-3-acetic acid (5.25 g, 30 mmol) in THF (50 mL). After
stirring the mixture for 30 min at 0 ꢀC, a solution of methyl
iodide (14.2 g, 100 mmol) in THF (50 mL) was added drop-
wise. The mixture was allowed to slowly reach rt and contin-
ued to stir for 16 h. The reaction mixture was then cooled to
0 ꢀC and excess hydride was carefully destroyed by slow
addition of MeOH (5 mL) with vigorous stirring followed
by cold water until a clear yellow solution resulted. Ether
(100 mL) was added. The aqueous phasewas separated, acid-
ified with 6 N HCl, and extracted with dichloromethane
(3ꢁ100 mL). The combined dichloromethane extracts were
dried (Na2SO4) and concentrated to about 40–50 mL. Pet
ether was then added slowly until a brownish colored solid
completely precipitated out. The crude solid was recrystal-
lized from ethanol to give the desired product (5.33 g,
94%) as a pale brown solid: mp 127–128 ꢀC (lit.20 127–
129 ꢀC); IR (thin film) 3059, 2933, 1699, 1617,
1474 cmꢂ1; 1H NMR (CDCl3): d 7.64–7.62 (m, 1H), 7.34–
7.26 (m, 2H), 7.19–7.15 (m, 1H), 7.07 (s, 1H), 3.83 (s, 2H),
3.78 (s, 3H); 13C NMR (CDCl3): d 178.8, 137.0, 128.1,
127.7, 122.0, 119.5, 119.1, 109.5, 106.2, 32.9, 31.2.
acid (851 mg, 4.5 mmol) and triethylamine (911 mg,
9 mmol) in dichloromethane (15 mL). The mixture was
stirred overnight at rt and the solvent was removed in vacuo.
The residue was purified by column chromatography on
silica gel (97:3 dichloromethane:methanol) to give the
desired product (829 mg, 45%) as a red solid: mp 89–91 ꢀC
(dec); IR (thin film) 3052, 2941, 2247, 1816, 1750, 1628,
1
1529, 1255 cmꢂ1; H NMR (DMSO-d6): d 7.98 (s, 1H),
7.80 (s, 1H), 7.56 (d, 1H, J¼8.3 Hz), 7.49 (d, 1H,
J¼8.1 Hz), 7.15–7.09 (m, 2H), 7.05 (d, 1H, J¼7.8 Hz),
6.83 (t, 1H, J¼7.6 Hz), 6.74–6.70 (m, 2H), 4.30 (t, 2H,
J¼6.8 Hz), 3.87 (s, 3H), 2.41 (t, 2H, J¼7.3 Hz), 2.02 (qn,
2H, J¼7.1 Hz); 13C NMR (DMSO-d6): d 166.5, 166.3,
136.9, 135.9, 134.6, 132.8, 128.5, 126.8, 125.7, 124.9,
122.5, 122.3, 121.7, 121.5, 120.3, 120.2, 120.0, 110.7,
110.5, 104.7, 103.9, 44.7, 33.1, 25.6, 13.8; LRMS (EI): m/z
409 (M+), 380, 355, 203, 144 (100%), 62; HRMS (EI) calcd
for C25H19N3O3: 409.1426, found: 409.1424.
4.1.6. 3-[2,5-Dihydro-4-(1-methyl-1H-indol-3-yl)-2,5-
dioxo-1H-pyrrol-3-yl]-1H-indole-1-acetonitrile (20). To
a stirred solution of anhydride 18 (381 mg, 1 mmol) in
DMF (4 mL) was added 1,1,1,3,3,3-hexamethyldisilazane
(1.61 g, 10 mmol) followed by methanol (0.16 g, 5 mmol).
The tightly closed reaction mixture was stirred for 24 h at
rt. The mixture was then poured into water (25 mL) and ex-
tracted with ethyl acetate (3ꢁ50 mL). The combined organic
extracts were washed with water (50 mL). The separated or-
ganic phase was dried (MgSO4) and concentrated in vacuo.
The residue was purified by column chromatography on sil-
ica gel (93:7 dichloromethane:methanol) to give the desired
product (354 mg, 93%) as an orange-red solid: mp 278–
4.1.4. 3-[2,5-Dihydro-4-(1-methyl-1H-indol-3-yl)-2,5-di-
oxo-3-furanyl]-1H-indole-1-acetonitrile (18). To a stirred
solution of indole-1-acetonitrile (683 mg, 4.37 mmol) in
dichloromethane (45 mL) at 0 ꢀC was added dropwise oxalyl
chloride (594 mg, 4.68 mmol). The mixture was stirred at
0 ꢀC for 2 h and again oxalyl chloride (0.5 mL) was added.
The mixture was further stirred at 0 ꢀC for 3 h and allowed
to slowly reach rt and continued to stir for 8 h. Oxalyl chlo-
ride (1 mL) was again added and stirred for 1 h at rt. The sol-
vent was removed in vacuo. The residue was redissolved in
dichloromethane (60 mL) and added dropwise to a stirred
solution of 1-methylindole-3-acetic acid (827 mg, 4.37 mmol)
and triethylamine (885 mg, 8.74 mmol) in dichloromethane
(15 mL). The mixture was stirred overnight and concentrated
in vacuo. The residue was purified by column chromato-
graphy on silica gel (97:3 dichloromethane:methanol) to
give the desired product (666 mg, 40%) as an orange-red
solid: mp 231–233 ꢀC; IR (thin film) 3119, 1816, 1750,
280 ꢀC; IR (thin film) 3311, 1692, 1628, 1532, 1329 cmꢂ1
;
1H NMR (DMSO-d6): d 11.02 (s, 1H), 7.91 (s, 1H), 7.83 (s,
1H), 7.58 (d, 1H, J¼8.4 Hz), 7.42 (d, 1H, J¼8.4 Hz), 7.15
(t, 1H, J¼7.7 Hz), 7.07–7.01 (m, 1H), 6.92 (d, 1H, J¼
7.7 Hz), 6.78 (t, 1H, J¼7.5 Hz), 6.68–6.60 (m, 2H), 5.63 (s,
2H), 3.86 (s, 3H); 13C NMR (DMSO-d6): d 172.8, 172.7,
136.6, 135.4, 133.6, 131.3, 129.2, 126.5, 125.6, 125.4,
122.6, 121.8, 121.4, 121.0, 120.5, 119.7, 116.2, 110.2,
110.0, 107.0, 104.4, 34.1, 32.9; LRMS (EI): m/z 380 (M+,
100%), 340, 297, 269, 176, 135, 121, 62; HRMS (EI) calcd
for C23H16N4O2: 380.1273, found: 380.1272.
1
1629, 1531, 1255 cmꢂ1; H NMR (DMSO-d6): d 8.04 (s,
1H), 7.92 (s, 1H), 7.63 (d, 1H, J¼8.3 Hz), 7.49 (d, 1H,
J¼8.3 Hz), 7.24–7.19 (m, 1H), 7.13–7.08 (m, 1H), 7.01 (d,
1H, J¼7.8 Hz), 6.89–6.84 (m, 1H), 6.74–6.66 (m, 2H),
5.66 (s, 2H), 3.89 (s, 3H); 13C NMR (DMSO-d6): d 166.4,
166.3, 136.9, 135.6, 135.0, 132.3, 130.1, 126.0, 125.7,
125.1, 123.2, 122.4, 121.7, 121.4, 121.0, 120.4, 116.1,
110.7, 110.4, 106.2, 103.9, 34.2, 33.2; LRMS (EI): m/z 381
(M+), 223, 203, 168, 156, 144, 141, 116, 91, 77, 62
(100%); HRMS (EI) calcd for C23H15N3O3: 381.1113,
found: 381.1108.
4.1.7. 3-[2,5-Dihydro-4-(1-methyl-1H-indol-3-yl)-2,5-
dioxo-1H-pyrrol-3-yl]-1H-indole-1-butanenitrile (21).
To a stirred solution of anhydride 19 (409 mg, 1 mmol) in
DMF (4 mL) was added 1,1,1,3,3,3-hexamethyldisilazane
(1.61 g, 10 mmol) followed by methanol (0.16 g, 5 mmol).
The tightly closed reaction mixture was stirred for 24 h at
rt. The mixture was then poured into water (25 mL) and ex-
tracted with ethyl acetate (3ꢁ50 mL). The combined organic
extracts were washed with water (50 mL). The separated or-
ganic phase was dried (MgSO4) and concentrated in vacuo.
The residue was purified by column chromatography on
silica gel (93:7 dichloromethane:methanol) to give the
desired product (384 mg, 94%) as a red solid: mp 249–
251 ꢀC; IR (thin film) 3281, 2246, 1756, 1704, 1610, 1532,
1334 cmꢂ1; 1H NMR (DMSO-d6): d 10.95 (s, 1H), 7.86 (s,
1H), 7.68 (s, 1H), 7.50 (d, 1H, J¼8.4 Hz), 7.43 (d, 1H,
J¼8.4 Hz), 7.10–6.98 (m, 3H), 6.75 (t, 1H, J¼7.7 Hz),
6.68–6.61 (m, 2H), 4.27 (t, 2H, J¼6.8 Hz), 3.85 (s, 3H),
2.38 (t, 2H, J¼7.3 Hz), 2.01 (qn, 2H, J¼7.0 Hz); 13C NMR
4.1.5. 3-[2,5-Dihydro-4-(1-methyl-1H-indol-3-yl)-2,5-di-
oxo-3-furanyl]-1H-indole-1 butanenitrile (19). To a stirred
solution of indole-1-butyronitrile (829 mg, 4.5 mmol) in di-
chloromethane (45 mL) at 0 ꢀC was added dropwise oxalyl
chloride (600 mg, 4.73 mmol). After stirring the mixture
for 1 h at 0 ꢀC, the solvent was removed invacuo. The residue
was redissolved in dichloromethane (45 mL) and added
dropwise to a stirred solution of 1-methylindole-3-acetic

S. Roy et al. / Tetrahedron 62 (2006) 7838–7845
7843
(DMSO-d6): d 172.9, 172.8, 136.6, 135.7, 133.3, 131.6,
128.0, 126.6, 126.1, 125.4, 121.9, 121.7, 121.4, 121.1,
119.9, 119.7, 119.5, 110.2, 110.0, 105.5, 104.4, 44.4, 32.9,
25.6, 13.7; LRMS (EI): m/z 408 (M+, 100%), 380, 354,
297, 283, 269, 204, 142, 121, 62; HRMS (EI) calcd for
C25H20N4O2: 408.1586, found: 408.1595.
give the desired product (1.88 g, 40%) as a white solid: mp
101–102 ꢀC (lit.21 90–92 ꢀC); IR (thin film) 3446, 3358,
3190, 1668, 1611, 1462, 1402, 1314 cmꢂ1 1H NMR
;
(DMSO-d6): d 7.54–7.53 (m, 1H), 7.49–7.48 (m, 1H), 7.39
(s, 1H), 7.31 (d, 1H, J¼3.2 Hz), 7.15–7.11 (m, 1H), 7.03–
7.00 (m, 1H), 6.92 (s, 1H), 6.41–6.40 (m, 1H), 4.39 (t, 2H,
J¼6.9 Hz), 2.57 (t, 2H, J¼6.8 Hz); 13C NMR (DMSO-d6):
d 171.9, 135.5, 128.6, 128.1, 121.0, 120.4, 119.0, 109.8,
100.5, 41.8, 35.8.
4.1.8. 5,6,7,13-Tetrahydro-13-methyl-5,7-dioxo-12H-
indolo[2,3-a]pyrrolo[3,4-c]carbazole-12-acetonitrile (11).
A mixture of maleimide 20 (19 mg, 0.05 mmol) and palla-
dium(II) trifluoroacetate (83 mg, 0.25 mmol) in DMF
(3 mL) was heated at 90 ꢀC for 9 h. The reaction mixture
was then cooled, diluted with ethyl acetate (25 mL), and
washed with 0.5 N HCl (50 mL). The organic phase was
dried (Na2SO4) and filtered through Hyflo. The filtrate was
concentrated invacuo and the residue was purified by column
chromatography on silica gel (97:3 dichloromethane:metha-
nol) to give the desired product (1.5 mg, 8%) as a fluorescent
yellow solid: mp >250 ꢀC (dec); IR (thin film) 3201, 2919,
4.1.11. (2-Carbamoyl-ethyl)-1H-indole-3-acetic acid (25).
To a stirred suspension of NaH (1 g, 25 mmol, 60% disper-
sion in mineral oil) in DMF (10 mL) at 0 ꢀC was added drop-
wise a solution of indole-3-acetic acid (1.7 g, 10 mmol) in
DMF (10 mL). After the addition, the solution was allowed
to warm to rt and stirred for 1 h. It was then cooled to 0 ꢀC
and a solution of 3-chloropropionamide (1.2 g, 11 mmol)
was added dropwise. The solution was allowed to warm to
rt and stirred for 8 h. It was then stirred at 70 ꢀC for 17 h
and 90 ꢀC for 2 h. The mixture was cooled to rt and the sol-
vent was evaporated. Ether (50 mL) was slowly added to
the oily-residue and excess sodium hydride was destroyed
by the dropwise addition of water. The solution was acidified
with 1 N HCl (50 mL) and extracted with ethyl acetate
(2ꢁ100 mL). The combined organic phase was washed
with water (100 mL) and dried (Na2SO4). Solventwas evapo-
rated and the residue was purified by column chromato-
graphy on silica gel (90:10 dichloromethane:methanol) to
yield the desired product (1.25 g, 51%) as a yellowish oil,
which solidified upon extensive drying: mp 141–143 ꢀC; IR
1
2615, 2282, 1696 cmꢂ1; H NMR (DMSO-d6): d 11.26 (s,
1H), 9.14–9.11 (m, 2H), 7.95 (d, 1H, J¼8.1 Hz), 7.82 (d,
1H, J¼8.6 Hz), 7.75–7.68 (m, 2H), 7.53 (t, 1H, J¼7.4 Hz),
7.45 (t, 1H, J¼7.7 Hz), 5.87 (s, 2H), 4.29 (s, 3H); 13C
NMR (DMSO-d6): d 171.2, 170.5, 144.4, 144.3, 132.8,
128.3, 123.4, 122.3, 121.4, 120.3, 119.7, 118.9, 116.3,
112.7, 111.4, 38.5, 35.6; LRMS (EI): m/z 378 (M+), 272,
239, 229, 213, 161, 149 (100%), 133, 119, 109, 104, 95,
91, 83, 78, 69, 62; HRMS (EI) calcd for C23H14N4O2:
378.1117, found: 378.1119.
1
4.1.9. 5,6,7,13-Tetrahydro-13-methyl-5,7-dioxo-12H-
indolo[2,3-a]pyrrolo[3,4-c]carbazole-12-butanenitrile
(12). A mixture of maleimide 21 (20 mg, 0.05 mmol) and
palladium(II) trifluoroacetate (83 mg, 0.25 mmol) in DMF
(3 mL) was heated at 90 ꢀC for 2 h. The reaction mixture
was then cooled, diluted with ethyl acetate (25 mL), and
washed with 0.5 N HCl (50 mL). The organic phase was
dried (Na2SO4) and filtered through Hyflo. The filtrate was
concentrated invacuo and the residue was purified by column
chromatography on silica gel (97:3 dichloromethane:metha-
nol) to give the desired product (10 mg, 50%) as a fluorescent
yellow solid: mp >200 ꢀC (dec); IR (thin film) 3201, 2245,
(thin film) 3333, 2359, 1660 cmꢂ1; H NMR (DMSO-d6):
d 12.22 (br s, 1H), 7.50 (d, 1H, J¼7.6 Hz), 7.45 (d, 1H,
J¼8.2 Hz), 7.40 (br s, 1H), 7.22 (s, 1H), 7.15–7.12 (m,
1H), 7.02 (t, 1H, J¼7.5 Hz), 6.91 (br s, 1H), 4.34 (t, 2H,
J¼6.7 Hz), 3.62 (s, 2H), 2.55 (t, 2H, J¼6.9 Hz); 13C NMR
(DMSO-d6): d 173.0, 171.9, 135.7, 127.6, 127.2, 121.2,
118.9, 118.6, 109.7, 107.2, 41.6, 35.8, 30.9; LRMS (EI):
m/z 246 (M+), 201 (100%), 130, 115; HRMS (EI) calcd for
C13H14N2O3: 246.1004, found: 246.1003.
4.1.12. 1-Methyl-1H-indole (26). To a stirred solution of
indole (4.68 g, 40 mmol) in acetone (120 mL) at 0 ꢀC was
added freshly powdered potassium hydroxide (11.22 g,
200 mmol). After stirring the mixture for 30 min at 0 ꢀC,
methyl iodide (11.35 g, 80 mmol) was added dropwise with
vigorous stirring. The mixture was allowed to slowly reach
rt and continued to stir for 18 h. The mixture was filtered to
remove the insoluble materials and concentrated in vacuo.
The residue was distilled at a reduced pressure (bp 123–
125 ꢀC/22–25 Torr) to give the desired product (4.72 g,
1748, 1710, 1695, 1317 cmꢂ1 1H NMR (DMSO-d6):
;
d 11.14 (s, 1H), 9.14 (d, 1H, J¼7.8 Hz), 9.11 (d, 1H, J¼
7.8 Hz), 7.89 (d, 1H, J¼8.3 Hz), 7.77 (d, 1H, J¼8.3 Hz),
7.67–7.63 (m, 2H), 7.44–7.40 (m, 2H), 4.86 (t, 2H, J¼
7.6 Hz), 4.24 (s, 3H), 2.26 (t, 2H, J¼7.1 Hz), 1.85 (qn, 2H,
J¼7.3 Hz); 13C NMR (DMSO-d6): d 171.5, 171.4, 145.5,
144.1, 133.8, 132.5, 128.3, 128.1, 125.5, 125.2, 123.6, 122.5,
122.1, 121.8, 121.7, 120.8, 120.5, 120.1, 119.4, 112.9, 112.0,
47.6, 37.4, 24.6, 14.3; LRMS (EI): m/z 406 (M+), 378, 338,
239, 211, 161, 149, 133, 130, 119, 109, 104, 97, 91, 83, 77,
71, 69, 62 (100%); HRMS (EI) calcd for C25H18N4O2:
406.1430, found: 406.1436.
1
90%) as a colorless oil: (lit.22 bp 118–120 ꢀC/20 Torr); H
NMR (CDCl3): d 7.86–7.83 (m, 1H), 7.49–7.39 (m, 2H),
7.35–7.29 (m, 1H), 7.17 (d, 1H, J¼3.2 Hz), 6.69–6.67 (m,
1H), 3.86 (s, 3H); 13C NMR (CDCl3): d 136.8, 128.9,
128.6, 121.6, 120.9, 119.3, 109.3, 100.9, 32.8.
4.1.10. 1H-Indole-1-propanamide (23). To a stirred solu-
tion of indole (2.93 g, 25 mmol) in dioxane (75 ml) at 0 ꢀC
was added acrylamide (2.67 g, 37.5 mmol) and freshly pow-
dered KOH (1.4 g, 25 mmol). The reaction mixture was
slowly allowed to come to rt and stirred for 24 h. The solution
was filtered to remove the insoluble materials and the solvent
was removed in vacuo. The residue was purified with column
chromatography on silica gel (15:1 chloroform:methanol) to
4.1.13. 3-[2,5-Dihydro-4-(1-methyl-1H-indol-3-yl)-
2,5-dioxo-3-furanyl]-1H-indole-1-propanamide (28). To
a stirred solution of 1-methylindole (656 mg, 5 mmol) in
dichloromethane (50 mL) at 0 ꢀC was added dropwise oxalyl
chloride (635 mg, 5 mmol). After stirring the mixture for 1 h
at 0 ꢀC, the solvent was removed in vacuo. The residue was
redissolved in dichloromethane (50 mL) and added dropwise

7844
S. Roy et al. / Tetrahedron 62 (2006) 7838–7845
to a stirred solution of 25 (1.23 g, 5 mmol) and triethylamine
(1.01 g, 10 mmol) in dichloromethane (20 mL). The mixture
was stirred overnight at rt and the solvent was removed in
vacuo. The residue was purified by column chromatography
on silica gel (90:10 dichloromethane:methanol) to give the
desired product (640 mg, 31%) as a red solid: mp 218–
220 ꢀC; IR (thin film) 3194, 1816, 1749, 1673, 1612, 1529,
33.7; LRMS (ESI): m/z 411 [M+H]+; HRMS (ESI) calcd
for C24H19N4O3 [M+H]: 411.1457, found: 411.1448.
Acknowledgements
This investigation was supported in part by the donors of
the Petroleum Research Fund (PRF), administered by the
American Chemical Society, the National Institutes of
Health (CA 82220), and Wyeth.
1
1257 cmꢂ1; H NMR (DMSO-d6): d 7.96 (s, 1H), 7.83 (s,
1H), 7.55 (d, 1H, J¼8.2 Hz), 7.48 (d, 1H, J¼8.2 Hz), 7.42
(br s, 1H), 7.12–7.07 (m, 2H), 6.96 (br s, 1H), 6.91–6.88 (m,
1H), 6.76–6.69 (m, 3H), 4.46 (t, 2H, J¼6.7 Hz), 3.89 (s,
3H), 2.58 (t, 2H, J¼6.7 Hz); 13C NMR (DMSO-d6): d 171.6,
166.5, 166.4, 136.7, 135.7, 134.4, 133.2, 127.9, 126.9,
125.7, 125.3, 122.3, 122.2, 121.5, 121.4, 120.3, 120.1,
110.6, 110.5, 104.4, 104.1, 42.4, 35.4, 33.1; LRMS (EI):
m/z 413 (M+), 260, 201 (100%), 158, 130, 72; HRMS (EI)
calcd for C24H19N3O4: 413.1376, found: 413.1368.
References and notes
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4.1.14. 3-[2,5-Dihydro-4-(1-methyl-1H-indol-3-yl)-2,5-
dioxo-1H-pyrrol-3-yl]-1H-indole-1-propanamide (29).
To a stirred solution of anhydride 28 (265 mg, 0.64 mmol)
in DMF (3 mL) was added a 1,1,1,3,3,3-hexamethyldisila-
zane (1.03 g, 6.4 mmol) followed by methanol (102 mg,
3.2 mmol). The tightly closed mixture was stirred for 30 h
at rt. The mixture was then poured into water (25 mL) and ex-
tracted with ethyl acetate (3ꢁ50 mL). The combined organic
extracts were washed with water (50 mL). The separated
organic phase was dried (MgSO4) and concentrated in vacuo.
The residue was purified by column chromatography on sil-
ica gel (90:10 dichloromethane:methanol) to give the desired
product (253 mg, 96%) as a red solid: mp >230 ꢀC (dec); IR
(thin film) 3189, 3044, 1750, 1701, 1661, 1606, 1530,
1336 cmꢂ1; 1H NMR (DMSO-d6): d 10.94 (s, 1H), 7.84 (s,
1H), 7.73 (s, 1H), 7.50 (d, 1H, J¼8.2 Hz), 7.42–7.40 (m, 2H),
7.04–7.01 (m, 2H), 6.96 (br s, 1H), 6.82 (d, 1H, J¼7.9 Hz),
6.67–6.63 (m, 3H), 4.44 (t, 2H, J¼6.7 Hz), 3.85 (s, 3H),
2.58 (t, 2H, J¼6.7 Hz); 13C NMR (DMSO-d6): d 173.0,
172.9, 171.8, 136.5, 135.5, 133.1, 132.0, 127.6, 126.7,
126.2, 125.8, 121.8, 121.7, 121.2, 121.1, 119.8, 119.6,
110.3, 110.1, 105.1, 104.7, 42.3, 35.6, 33.0; LRMS (ESI):
m/z 413 [M+H]+; HRMS (ESI) calcd for C24H21N4O3
[M+H]: 413.1614, found: 413.1596.
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dolo[2,3-a]pyrrolo[3,4-c]carbazole-12-propanamide
(22). A mixture of maleimide 29 (21 mg, 0.05 mmol) and
palladium(II) trifluoroacetate (83 mg, 0.25 mmol) in DMF
(3 mL) was heated at 90 ꢀC for 2 h. The reaction mixture
was then cooled, diluted with ethyl acetate (25 mL), and
washed with 0.5 N HCl (50 mL). The organic phase was
dried (Na2SO4) and filtered through Hyflo. The filtrate was
concentrated invacuo and the residue was purified by column
chromatography on silica gel (90:10 dichloromethane:
methanol) to give the desired product (6 mg, 30%) as a fluo-
rescent yellow solid: mp >250 ꢀC (dec); IR (thin film) 2921,
2853, 1715, 1645, 1254 cmꢂ1; 1H NMR (DMSO-d6): d 11.14
(s, 1H), 9.14 (t, 2H, J¼8.2 Hz), 7.91 (d, 1H, J¼
8.2 Hz), 7.82 (d, 1H, J¼8.2 Hz), 7.68–7.63 (m, 2H), 7.45–
7.41 (m, 2H), 7.24 (s, 1H), 6.80 (s, 1H), 5.01 (t, 2H,
J¼7.6 Hz), 4.26 (s, 3H), 2.41 (t, 2H, J¼7.6 Hz); 13C NMR
(DMSO-d6): d 171.3, 170.8, 170.7, 144.7, 143.6, 133.2,
131.9, 127.6, 127.4, 124.7, 124.5, 122.9, 121.8, 121.3,
121.1, 120.8, 120.0, 119.4, 118.6, 112.3, 111.3, 44.7, 36.8,
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