Synthesis and some transformations of derivatives of pyrido-[3,2-b]indole (δ-carboline)

Article abstract of DOI:10.1023/A:1012743802689

The reactions of 2-dimethyliminomethyl-3-(p-nitrophenyl)aminoindole chloride with compounds with an active methylene center have been studied. A series of derivatives of δ-carboline have been synthesized. By the reaction of 3-ethoxycarbonyl-2-methyl-l-p-nitrophenylpyrido[3,2-b]indolinium chloride with the diethyl acetal of DMF the corresponding 2-dimethylaminovinyl derivative was synthesized which was converted into 5-p-nitrophenyl-1-oxo-1,10-dihydropyrano [3′,4′:5,6]pyrido[3,2-b]indol-5-ium chloride in the presence of acid.

Full text of DOI:10.1023/A:1012743802689

Chemistry of Heterocyclic Compounds, Vol. 37, No. 8, 2001
SYNTHESIS AND SOME
TRANSFORMATIONS OF
DERIVATIVES OF PYRIDO-
b
[3,2- ]INDOLE ( -CARBOLINE)
δ
S. Yu. Ryabova, L. M. Alekseeva, and V. G. Granik
The reactions of 2-dimethyliminomethyl-3-(p-nitrophenyl)aminoindole chloride with compounds with an
active methylene center have been studied. A series of derivatives of -carboline have been synthesized.
δ
By the reaction of 3-ethoxycarbonyl-2-methyl-1-p-nitrophenylpyrido[3,2-b]indolinium chloride with the
diethyl acetal of DMF the corresponding 2-dimethylaminovinyl derivative was synthesized which was
converted into 5-p-nitrophenyl-1-oxo-1,10-dihydropyrano[3',4':5,6]pyrido[3,2-b]indol-5-ium chloride
in the presence of acid.
Keywords: indole, carboline, pyranopyridoindole, pyridoindolinium, pyridoindole.
Previously we have synthesized the corresponding 2-formyl derivative (2) by Wilsmeier formylation of
3-(p-nitrophenyl)aminoindole (1). Compound 2 is a suitable starting material for the synthesis of various
substituted -carbolines [2, 4]. It is known [5] that the basic intermediate in the synthesis of aldehydes by the
δ
Wilsmeier reaction is an immonium salt of type 3. We did not isolate 3 but it was established that, in contrast to
aldehyde 2, it is capable of cyclizing to give derivatives of indolo[3,2-b]quinoline [1]. In other words the
immonium salt, because of the positive charge, is a more reactive synthon in reactions with electron-excess
centers than the corresponding formyl derivative. From this it appeared interesting to study the reactions of
immonium salt 3 with a series of carbanions and to compare the results with data previously obtained about the
reactions of aldehyde 2 with the same active methylene compounds. Salt 3 was isolated from the reaction
mixture and, without special purification*, was used in reactions with compounds containing active methylene
units in the presence of triethylamine. It appeared that reactions of salt 3 with malonodinitrile (4a),
cyanacetamide (4b), and ethyl cyanoacetate (4c) occurred considerably more readily than the reactions of
aldehyde 2 with the same compounds. Reactions with the immonium salt occurred even at room temperature and
did not require prolonged heating as in the case of aldehyde 2. Derivatives of indolylacrylic acid 5a-c were
isolated in high yield from condensation of salt 3 with compounds 4a-c.
_______
* As was to be expected, salt 3 is readily hydrolyzed with water to give aldehyde 2. On the chromatogram on
Silufol a small spot of aldehyde 2 was observed in addition to a spot of the salt at the starting point. The FAB
mass spectrum has m/z 309 [M+H]+; the compound does not have a melting point and, unlike aldehyde 2 which
has mp 237-238°C, decomposes at >200°C.
__________________________________________________________________________________________
State Scientific Center RF "NIOPIK", Moscow 103787, Russia; e-mail: makar-cl@ropnet.ru. Translated
from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, 1086-1094, August, 2001. Original article submitted
September 14, 1999.
0009-3122/01/3708-0997$25.00©2001 Plenum Publishing Corporation
997

H
N
H
N
H
N
Ar
Ar
Ar
POCl3/DMF
H2O
_
N
H
2
CHO
N
H
N
H
Cl
+
1
N
Me
Me
3
(Ar = p-NO2-C6H4 throughout)
With cyanacetamide 4b and ethyl cyanoacetate 4c the same products are obtained at higher temperature,
but with malonodinitrile 4a under these conditions only a derivative of -carboline – 1H-2-amino-3-cyano-1-p-
δ
nitrophenylpyrido[3,2-b]indole (6) – was obtained.
Ar
N
R
H
N
H2C
4a–c
NH2
CN
Ar
CN
3
R
N
H
N
CN
6
5a–c
4, 5 a R = CN, b R = CONH2, c R = COOEt
Compound 5a, which is undoubtedly formed initially, cyclizes on heating so rapidly that it could not be
isolated. It is probable that the different reactivity of compounds 5a-c with respect to cyclization is a result of
steric factors. The bulky substituents in 5b,c lead to a partial deflection of the vinyl fragment from the indole
ring plane which inhibits cyclization, whereas the two "rod-like" cyano groups in compound 5a make possible a
configuration favorable for closing the pyridine ring.
The next step in this work was the reaction of ethyl acetoacetate with the immonium salt 3 and the
aldehyde 2. Two substances were formed when 3 was boiled in propanol-2 with ethyl acetoacetate. The
principal product was 3-ethoxycarbonyl-2-methyl-1-p-nitrophenyl-5H-pyrido[3,2-b]indolinium chloride (7A) in
a yield of 39% (dimethylamine evolved during the reaction). The formation of the tricycle 7A evidently occurs
as follows:
H
O
O
N
Ar
NMe2
COMe
COOEt
3
+
HCl
+
Me
Me
O
–H2O
N
H
H
H
Ar
Ar
N
N
Me
Me
COOEt
.
–Me NH
HCl
Ar
2
N
COOEt
NMe2
N
7
H
H
KOH
+
N
Me
_
.
Me2NH
HCl
–Me2NH
Cl
N
COOEt
H
7A
In other words, stabilization of 7A as a result of aromatization is so great that the tricycle 7 is a stronger
base than dimethylamine. Only treatment of salt 7A with alkali makes possible the formation of the base 7. The
minor product, isolated from this reaction in 7% yield, was 3-carboxy-1-[3-(p-nitrophenyl)aminoindolyl-2]-2-[1-
p-nitrophenyl)pyrido[3,2-b]indolyl-2]ethylene (8).
998

ArHN
ArHN
Ar
N
Ar
N
H
H
+
N
H
N
H
H
H
_
N
H
COO
N
8
COOH
8A
The condensation of salt 3 with ethyl acetoacetate in the presence of triethylamine occurs more
unambiguously. In this case the only product isolated was the chloride of 7A, while the product of its further
.
condensation (8
8A) was observed in only trace amounts by TLC. In other words, the presence of large
amounts of base (without triethylamine the process is catalyzed only as a result of the diethylamine formed,
which produces a very small rate of condensation in the initial reaction) leads to considerable acceleration of the
formation of the tricycle 7, complete consumption of the starting material 3, and a sharply deceleration of the
secondary condensation to the bisheterylethylene derivative 8.
The structure of compound 8 follows from the 1H NMR spectrum (see Experimental) in which there is
a strongly broadened COOH signal at 12 ppm. The chemical shifts of the protons of the benzene ring of the
tricyclic part of the molecule are found between the signals observed in the 1H NMR spectra of compounds 7A
.
and 7 (salt and base) which supports the proposal that the equilibrium 8
8A occurs in solution. At the same
time the absence of COOH absorption in the IR spectrum of this compound suggests that in the solid state it
exists primarily as the zwitterion 8A. Compound 8 is evidently formed by reaction of the tricycle 7 with the
initial immonium salt 3 or with the aldehyde 2 formed in the reaction mixture as a result of hydrolysis of 3 with
water in the solvent. Hydrolysis of ethoxycarbonyl groups occurs very easily because of water formed during
the condensation reaction. The driving force for such easy saponification is probably also stabilization achieved
.
by the aromatic indole ring (8A). The structure of 8
8A was confirmed by an independent synthesis –
condensation of aldehyde 2 with tricycle 7 gave this compound in 92% yield.
It is interesting that the condensation of aldehyde 2 with ethyl acetoacetate depends on the solvent used.
The sole product on boiling in propanol-2 was the disubstituted ethylene 8, while the -carboline 7 was isolated
δ
in 40% yield on boiling in pyridine.
NHAr
CHO
i-PrOH
8
7
ethyl
8
+
acetoacetate
7
Py
N
H
2
When the reaction of immonium salt 3 with ethyl acetoacetate was carried out at room temperature in
the presence of triethylamine, a mixture of 7 and 7A was formed, from which compound 7 was isolated in 30%
yield (see Experimental). Under these condensation conditions, an intermediate vinyl containing compound with
M+ 393 occurred as an impurity in 7 (for 7 M+ = 375). Considering the low yield of compound 7 (30%) the
mother liquor after removal of the precipitate was kept at 20°C for 1 week; stepwise formation of a yellowish
compound was observed which was ascribed structure 9.
Ar
N
OH
Me
ethyl
acetoacetate
3
COOEt
N
H
O
OEt
3'
H
H
1'
2'
OH
9
999

TABLE 1. Characteristics of the Compounds Synthesized
Found, %
——————
Com-
Empirical
formula
Mass spectrum,
mp, °С,
Yield, %
(method)
Calculated, %
IR spectrum, ν, cm-1
pound
m/z
recrystallization solvent
C
H
N
Cl
C21H18ClN3O4
C21H17N3O4
375
375
61.64
61.24
4.59
4.41
10.20
10.20
8.40
8.61
3420, 2700-2500, 1720,
1630, 1610, 1590
1710, 1695, 1610, 1590
252-254 dec.
39 (А)
7A
7
i-PrOH–МеОН, 2 : 1
67 (B)
66.94
4.50
11.05
236-270 dec.
53 (А)
40 (B)
30 (C)
67.19
4.57
11.20
C34H22N6O6·H2O
610
64.44
64.96
4.04
3.85
12.98
13.37
3640-3600, 3460, 3380,
1620, 1590
248 dec.
92 (А)
92 (B)
7 (C)
8
C27H29N3O8
523
430
430
357
61.89
61.94
5.78
5.58
7.90
8.03
3460, 3350, 3300, 1730,
1710, 1595, 1580
1710, 1620
220-221
32
59
13
55
9
МеОН
C24H22N4O4
66.88
5.06
12.7
200-220 dec.
10
10A
11
66.97
5.15
13.02
i-PrOH
C24H23ClN4O4
C20H12ClN3O4·H2O
61.79
61.74
4.86
4.97
11.96
7.68
7.59
2700-2620, 1715, 1620
>200 dec.
12.00
i-PrOH
58.50
3.25
10.23
10.21
3360, 3600, 3420-3300,
1740, 1635, 1600
>350
58.33
3.64
МеОН

TABLE 2. 1H NMR Spectra of the Compounds Synthesized, δ, ppm, J (Hz)
3-COOC2H5
Com-
4-H
s
6-H
m
7-H
m
8-H
m
9-H
m
C6H4–NO2
2-CH3
s
J = 7.2
Other signals
pound
A2B2-system
t
q
9.2
8.91
8.61
7.9
7.63
7.73
7.7
7.35
7.58
7.1
6.7
7.16
6.1
6.08
5.97
8.2; 8.8
8.1; 8.7
8.10; 7.51
2.75
2.7
1.42
1.41
4.5
4.4
13.6 (br. s, 5-NH)
7A
7
8
7.14, 7.32 (two d, vinyl protons, J = 16.4);
9.03 (br. s, NH–C6H4NO2);
11.65 (br. s, NH-indole);
12.00 (br. s, COOH);
6.5, 7.94 (A2B2-system, C6H4NO2);
6.94-7.33 (m, arom., protons of the benzene ring
of indole)
8.57
8.79
7.48
7.71
7.2
6.61
7.00
6.0
7.96; 8.64
8.10; 8.70
1.32
1.34
4.34
4.39
2.72 (s, N(CH3)2 );
10
4.59, 6.62 (two d, vinyl protons, J = 12.4)
7.54
6.00
2.82 (s, N(CH3)2); 4.59, 7.00 (two d, vinyl protons);
10A
12.9 (br. s, 5-NH, J = 12.4)
11-H
9.52
9-H
7.94
8-H
7.85
7-H
7.19
6-H
6.38
C6H4NO2
8.2; 8.8
3-H
4-H
8.07
6.68
13.65 (br. s, 10-NH)
11
J = 6.5
J = 6.5

Elemental analysis data and the mass spectrum (which included a molecular ion peak at M+ 523, which
corresponds to the molecular mass of this compound) were in complete agreement with the proposed structure.
1
Most of the signals in the H NMR spectrum were doubled which may be connected with the presence of
geometric isomers or the presence of a mixture of diastereomers. Nevertheless, the 1H NMR spectrum does not
1
disagree with the proposed structure. H NMR spectrum of compound 9 (DMSO-d6), , ppm, J (Hz): 0.81 and
δ
0.87 (t, J = 7.2) and 3.80 (br. m) two COOEt; 1.27 (3H, s, 2-CH3); 2.60 (2H, AB-system, Jgem = 14, 3'-CH2); 3.45
(1H, d, J = 12, 3-H); 4.10 (1H, d, J = 12, 1'-H); 4.27 (1H, t, J = 12, 4-H); 5.1 (1H, s, 2-OH); 6.60 and 8.00 (4H,
A2B2 system, C6H4-NO2); 6.8-7.4 (4H, m, 6-H, 7-H, 8-H, 9-H); 11.2 (1H, br. s, NH). The mechanism for the
formation of this compound is not completely clear and requires further study.
The presence of the ortho-positioned ethoxycarbonyl and methyl groups in the pyridine ring of
compound 7 and the ready condensation of aldehyde 2 with the 2-methyl group suggested to us the use of the
acetal of DMF in reactions to form vinyl derivatives because this compound is known [6] to condense with acid
methyl and methylene groups. The reaction of the acetal of DMF with the tricycle 7A was carried with constant
monitoring by TLC. When the reagents (7A, acetal) were mixed formation of the basic -carboline 7 was
δ
observed, which dissolved in the excess of acetal on heating. After maintaining the solution for 2 h even at room
temperature both the -carboline 7A and compound 7 were completely absent according to TLC. After working
δ
up the reaction mixture two compounds were isolated: the 2-vinyl derivative 10 and its hydrochloride 10A in 42
and 13% yield respectively.
So in this case we observed stabilization of the protonated form on account of aromatization of the
derivative of 1H- -carboline 10A despite the fact that the reaction was carried out with an excess of acetal
δ
which ought to facilitate transformation of the hydrochloride into the base.
_
Ar
N
Ar
N
Cl
+
NMe2
NMe2
(EtO)2CHNMe2
7A
+
N
COOEt
N
H
COOEt
10
10A
HCl
_
Ar
N
Cl
6
9
4
+
5
7
8
3
O 2
N
1
H 10
11
O
11
On treating a solution of the 2-vinyl derivative of -carboline 10 in propanol-2 with hydrogen chloride
δ
in order to obtain the hydrochloride 10A, closure of the pyran ring occurred to give the new tetracyclic
derivative, pyrano[3',4':5,6]pyrido[3,2-b]indolium chloride (11).
EXPERIMENTAL
IR spectra of nujol mulls were recorded with a Perkin-Elmer 457 instrument. Mass spectra were
1
recorded by direct injection into the ion source of a Varian MAT-112 (70 eV) machine. H NMR spectra of
DMSO-d6 solutions with TMS as internal standard were recorded with a UNITY plus 400 (400 MHz)
spectrometer. The course of reactions and the purity of products were monitored by TLC on Silufol UV-254
1002

plates with 10:1 chloroform–methanol and 5:3:1 ethyl acetate–propanol-2–ammonia systems as eluents. The
physicochemical properties and yields of all new compounds are presented in Table 1 and the 1H NMR spectra
are cited in Table 2.
2-Dimethyliminomethyl-3-(p-nitrophenyl)aminoindole Chloride (Immonium Salt, 3). A solution of
3-(p-nitrophenyl)aminoindole 1 (20.05 g, 79 mmol) in DMF (21.5 ml) was added dropwise at 15-20°C to the
Wilsmeier complex prepared in the usual way from DMF (48 ml) and POCl3 (21.5 ml). The mixture was kept at
20°C for 20 h. The precipitate was filtered, washed with DMF and chloroform to give the immonium salt 3
(18.3 g, 67%). C17H17ClN4O2; mp >200°C (dec.).
-Cyano- [3-(p-nitrophenyl)aminoindolyl-2]acrylonitrile (5a). A mixture of the immonium salt 3
α
α
(0.7 g, 2 mmol), malonodinitrile (0.22 g, 3.4 mmol), propanol-2 (20 ml), and triethylamine (0.28 ml, 2 mmol)
was stirred for 1.5 h at 20°C. The precipitate was filtered off and washed with propanol-2 to give nitrile 5a
(0.66 g, 99%); mp 226-227°C. The IR and 1H NMR spectra were identical with a sample obtained by method [3].
1H-2-Amino-3-cyano-1-(p-nitrophenyl)pyrido[3,2-b]indole (6). A mixture of the immonium salt 3
(0.7 g, 2 mmol), malonodinitrile (0.22 g, 3.4 mmol), propanol-2 (20 ml), and triethylamine (0.28 ml, 2 mmol)
were boiled for 1 h. The mixture was cooled, the precipitate was filtered off and washed with propanol-2 to give
1
the pyridoindole (0.57 g, 85%), the IR and H NMR spectra of which were identical to those of the same
substance prepared by method [3].
-Cyano-β-[3-(
p-nitrophenyl)aminoindolyl-2]acrylamide (5b). A mixture of the immonium salt 3
α
(0.7 g, 2 mmol), cyanacetamide (0.21 g, 2.5 mmol), propanol-2 (20 ml), and triethylamine (0.28 ml, 2 mmol)
was boiled for 1 h. The mixture was cooled, the precipitate was filtered off, washed with propanol-2 to give
amide 5b (0.64 g, 92%), the IR and 1H NMR spectra were identical to a sample made by method [3].
-Cyano-β-[3-(
Ethyl
p-nitrophenyl)aminoindolyl-2]acrylate (5c). A mixture of immonium salt 3 (0.7 g,
α
2 mmol), ethyl cyanoacetate (0.55 ml, 7.5 mmol), propanol-2 (20 ml), and triethylamine (0.28 ml, 2 mmol) was
stirred for 2 h, 20°C or boiled for 1 h (then cooled). The precipitate was filtered off and washed with propanol-2
to give ester 5c (0.74 g, 98%), the IR and 1H NMR spectra were identical to a sample made by method [3].
3-Ethoxycarbonyl-2-methyl-1-p-nitrophenyl-5H-pyrido[3,2-b]indolinium Chloride (7A). A. Ethyl
acetoacetate (2.9 ml, 22.8 mmol) was added to a suspension of immonium salt 3 (2 g, 5.8 mmol) in propanol-2
(58 ml) and heated to boiling with stirring. The solution formed was boiled for 5 h. A precipitate began to form
3 h from the beginning of boiling. The reaction mixture was held at 20°C for 16 h. The precipitate was filtered
off and washed with propanol-2 to give a mixture of chloride 7A and the -carboline 8 (1.66 g). Water (60 ml)
δ
was added, the mixture was heated to boiling, and the insoluble deep cherry red residue was filtered off (0.26 g,
disubstituted ethylene derivative 8, Table 1, method C). The aqueous mother liquor was evaporated to dryness
in vacuum to give the chloride 7A (0.9 g).
B. Ethyl acetoacetate (2.9 ml, 22.8 mmol) and triethylamine (0.8 ml, 5.8 mmol) were added to a
suspension of immonium salt 3 (2 g, 5.8 mmol) in propanol-2 (58 ml), the mixture was boiled for 5 h, and
allowed to stand at 20°C for 16 h. The precipitate was filtered off and washed with propanol-2 to give chloride
7A (1.6 g). No depression was obtained when a mixed melting point was taken with a sample made by
method A.
1H-3-Ethoxycarbonyl-2-methyl-1-(p-nitrophenyl)pyrido[3,2-b]indole (7). A. The compound was
made from the immonium salt 3 (2 g, 5.8 mmol) analogously to the synthesis of 7A by method A. After
separation of the disubstituted ethylene derivative 8, the mother liquor was cooled and made basic with 1M
potassium hydroxide. The precipitate was filtered off, and washed with water, propanol-2, and ether to give the
-carboline 7 (1.15 g).
δ
B. Ethyl acetoacetate (0.5 ml, 4 mmol) was added to a solution of 2-formylindole 2 [1] (0.28 g, 1 mmol)
in pyridine (5 ml), the mixture was boiled for 20 min, cooled, the precipitate was filtered off, and washed with
pyridine, propanol-2, and ether to give -carboline 7 (0.15 g). A mixed melting point with a sample made by
δ
method A did not give a depression of the melting point.
1003

C. A mixture of immonium salt 3 (0.7 g, 2 mmol), ethyl acetoacetate (1 ml, 8 mmol), propanol-2 (20 ml)
and triethylamine (0.28 ml, 2 mmol) was stirred for 8 h at 20°C and then kept for 16 h at 20°C. The precipitate
was filtered off and washed with propanol-2 to give a mixture of the chloride 7A and the base 7 (0.43 g) which
was heated to boiling in water (30 ml). The insoluble base was filtered off, washed with water and propanol-2 to
give the -carboline 7 (0.13 g). The aqueous mother liquor was made basic with 1 M potassium hydroxide to
δ
give more -carboline 7 (0.16 g, overall yield 0.29 g). A mixed melting point with a sample made by method A
δ
did not give a depression of the melting point.
2-[3-Carboxy-1-(p-nitrophenyl)pyrido[3,2-b]indolyl-2]-1-[3-(p-nitrophenyl)aminoindolyl-2]ethylene
(8). A. A mixture of 2-formylindole 2 [1] (1.4 g, 5 mmol), ethyl acetoacetate (2.5 ml, 19.7 mmol), and
triethylamine (0.7 ml, 5 mmol) in propanol-2 (50 ml) was boiled for 4 h, then kept at 20°C for 16 h. The
precipitate was filtered off and washed with propanol-2 to give the disubstituted ethylene 8 (1.4 g).
B. A mixture of -carboline 7 (0.2 g, 0.53 mmol), 2-formylindole 2 [1] (0.15 g, 0.53 mmol), and
δ
triethylamine (0.1 ml, 0.72 mmol) was boiled for 1.5 h. The mixture was cooled, the precipitate was filtered off
and washed with propanol-2 and ether to give compound 8 (0.3 g). A mixed melting point with a sample made
by method A did not give a depression of the melting point.
C. As described in the synthesis of chloride 7A.
1H-3-Ethoxycarbonyl-2-hydroxy-4-(2-hydroxy-3-ethoxycarbonylpropen-2-yl)-2-methyl-1-(p-
nitrophenyl)-2,3,4,5-tetrahydropyrido[3,2-b]indole (9). The isopropanol mother liquor after the removal of
the precipitate of a mixture of the -carbolines 7 and 7A, obtained by method C, was stirred for 7-8 days at
δ
20°C. The precipitate was filtered off and washed with propanol-2 and ether to give tetrahydrocarboline 9 (0.34 g).
1H-2- -Dimethylaminovinyl-3-ethoxycarbonyl-1-(p-nitrophenyl)pyrido[3,2-b]indole (10). A suspension
β
of the chloride of -carboline 7A (0.4 g, 1.0 mmol) and the diethyl acetal of dimethyl formamide (4 ml) was
δ
heated to solution and then stirred for 2 h at 20°C. The acetal was distilled off in vacuum. The oily residue was
stirred with propanol-2 and cooled. The residue was filtered off and washed with propanol-2 and ether to give
the -carboline 10 (0.18 g).
δ
2-β-Dimethylaminovinyl-3-ethoxycarbonyl-1-(
p-nitrophenyl)-5H-pyrido[3,2-b]indolinium Chloride
(10A). The mother liquor left after separation of -carboline 10 was evaporated and the residue was stirred with
δ
ether containing a few drops of propanol-2 and cooled. The residue was filtered and washed with ether to give
the chloride 10A (0.06 g).
5-(p-Nitrophenyl)-1-oxo-1,10-dihydropyrano[3',4':5,6]pyrido[3,2-b]indolinium Chloride (11). A
few drops of methanolic HCl were added to a solution of carboline 10 (0.5 g, 1.2 mmol) in propanol-2 to give a
pH 2-3. The solution was kept at 20°C for 3 weeks. The precipitate was filtered off and washed with propanol-2
to give the tetracycle 11 (0.25 g).
This work was carried with financial support of RFFI, grant No. 97-03-33066.
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2.
3.
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1004