From biomass to medicines. A simple synthesis of indolo[3,2-c]quinolines, antimalarial alkaloid isocryptolepine, and its derivatives

Article abstract of DOI:10.1039/c2ob25836f

Indolo[3,2-c]quinolines are pharmacologically attractive class of heterocyclic compounds. The method of their synthesis, based on transformation of furfural, which is a large-scale product of treatment of biomass including agricultural and forestry wastes, has been developed. This method was utilized for the total synthesis of antimalarial alkaloid isocryptolepine and its derivatives.

Full text of DOI:10.1039/c2ob25836f

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From biomass to medicines. A simple synthesis of indolo[3,2-
c]quinolines, antimalarial alkaloid isocryptolepine, and its derivatives†
Maxim G. Uchuskin,a Arkady S. Pilipenko,a Olga V. Serdyuk,b Igor V. Trushkov,c,d and Alexander V.
Butin*a,e
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
Indolo[3,2-c]quinolines are pharmacologically attractive class
of heterocyclic compounds. The method of their synthesis,
based on transformation of furfural, which is a large-scale
10 product of treatment of biomass including agricultural and
forestry wastes, has been developed. This method was utilized
for the total synthesis of antimalarial alkaloid isocryptolepine
and its derivatives.
A sustainable conversion of biomass into drugs, chemicals,
15 biofuels, and various materials is one of the most challenging
tasks for the modern chemistry and industry.1,2 Promising
ways to solve this problem are depolymerization and
fermentation of biopolymers affording molecules which can
be either directly used or easily transformed into other
20 valuable products. Thus, the current world production of
furfural from agricultural and forestry wastes is 280 000
tonnes per year.3 It is mainly employed as an intermediate for
furan, tetrahydrofuran, and furfuryl alcohol production,2a as
well as in fine organic synthesis.
Scheme 1 Synthesis of 3ꢀ(2ꢀacylvinyl)ꢀ2ꢀarylindoles 4
Herein, we describe the utilization of this new method of
55 indoles synthesis for preparation of indolo[3,2ꢀc]quinolines 57
(Scheme 2) which attract attention due to their ability to form
strong complexes with DNA,8 antimalarial activity,9
antiproliferative properties,10 etc.8b,11 We supposed that
indoles 4 can be suitable precursors of 5 if they have a latent
60 amino group in the orthoꢀposition of 2ꢀaryl substituent. The
liberation of amine functionality should allow for easy
pyridine ring formation through Michael addition to α,βꢀenone
moiety affording the corresponding tetracyclic compounds.12
In one’s turn, such indoles can be synthesized from 2ꢀ
65 furylanilines 3 and the corresponding aldehydes 6.
25 For a long time, we are dealing with the development of
procedures for transformations of furfural into diverse furan
derivatives and
a
broad variety of other heterocycles.4
Recently, we have discovered a simple route from furfural (1)
to 3ꢀ(2ꢀacylvinyl)ꢀ2ꢀ(hetero)arylindoles 4, the key step of
30 which is unusual furanꢀtoꢀindole recyclization (Scheme 1).5
This transformation is based on the acidꢀinduced reaction of
2ꢀfurylanilines 36 with (hetero)aromatic aldehydes followed
by attack of the formed iminium ion onto the C(2) atom of the
furan ring.
O
X
X
_____________________________________________________________________________________________
N
N
35
a Research Institute of Heterocyclic Compounds Chemistry, Kuban State
Technological University, Moskovskaya st. 2, Krasnodar, 350072,
Russian Federation
N
N
H
H
R
R
5
4
b Department of Chemistry, Southern Federal University, Zorge 7,
40 Rostov-on-Don, 344090, Russian Federation
c Department of Chemistry, M.V. Lomonosov Moscow State University,
Leninskie Gory 1-3, Moscow 119991, Russian Federation
d Laboratory of Chemical Synthesis, Federal Research Center of
Pediatric Hematology, Oncology and Immunology, Samora Mashel 1,
45 Moscow, 117198, Russian Federation
N
X
O
OHC
+
R
NH2
3
6
e Perm State University, Bukireva 15, Perm, 614990, Russian Federation.
Fax: (+7) 342-2371480; E-mail: alexander_butin@mail.ru
† Electronic Supplementary Information (ESI) available: Experimental
Scheme 2 Retrosynthetic scheme for indolo[3,2ꢀc]quinolines 5
1
procedures, characterization data and copies of H and 13C NMR spectra
We selected 2ꢀnitrobenzaldehydes as starting aldehydes since:
70 1) a broad range of substituted 2ꢀnitrobenzaldehydes is
50 for all new compounds. See DOI: 10.1039/b000000x/
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 | 1

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commercially available or can be easily synthesized that
allows for preparation of a library of indolo[3,2ꢀc]quinolines;
aromatization is not unprecedented process.13 The similar
nitromethane, malonitrile, and dimethyl malonate eliminations
2) the reduction of nitroarenes to anilines is the simple and 40 during Fe/AcOHꢀmediated reductive cyclizations of nitro
environmentꢀfriendly process.
derivatives to quinolines were also recently reported.14
5
To our delight, 2ꢀnitrobenzaldehydes 6a-g afford the
corresponding 2ꢀ(2ꢀnitrophenyl)indoles 4a-k in reaction with
2ꢀfurylanilines 3a-c (Table 1). However, the nitro group in the
With the optimized conditions in hand, we performed this
reductive cyclizations for a series of 2ꢀ(2ꢀnitrophenyl)indoles
4a-k synthesized above. The results demonstrated that the
orthoꢀposition of aromatic aldehydes was found to decrease 45 reaction has a general character; electronꢀdonating alkyl and
the product yields in this furanꢀtoꢀindole transformation. We
alkoxy groups as well as electronꢀwithdrawing halide
substituents have no significant effect on the yields of
indolo[3,2ꢀc]quinolines (Table 2).
10 believe it is a result of combination of unfavourable steric and
electronic effects of orthoꢀnitroꢀgroup rendering the iminium
ion attack onto the furan ring. Substituents in orthoꢀ
Methylation of 5a is known15 to afford alkaloid
nitrobenzaldehydes and 2ꢀfurylanilines have no significant 50 isocryptolepine (7a)16 which was isolated in 1995 from the
influence on yields of indoles 4. Despite the moderate yields
15 of the isolated products (54ꢀ67%), this reaction is very
convenient from a preparative point of view. The formed 2ꢀ(2ꢀ
nitrophenyl)indoles are precipitated from reaction mixture and
can be used in further transformations without additional
purification.
West African plant Cryptolepis sanguinolenta17 and
demonstrated to have a significant antiprotozoal activity.18
Table 2 Reductive cyclization of 2ꢀ(2ꢀnitrophenyl)indoles 4 to
indolo[3,2ꢀc]quinolines 5
20 Table 1 Synthesis of 3ꢀ(2ꢀacetylvinyl)ꢀ2ꢀ(2ꢀnitrophenyl)indoles 4
55
Entry
1
2
3
4
5
6
7
8
Substrate
4a
4b
4c
4d
4e
4f
4g
4h
X
H
H
H
Cl
R1
H
OMe
OMe
H
OMe
OCH2O
H
R2
H
H
OMe
H
OMe
Product
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
Yield of 5, %a
86
74
79
75
77
72
73
70
78
79
76
Cl
Cl
Me
Me
Me
Me
Me
H
OCH2CH2O
OMe OMe
Cl
Br
9
10
11
4i
4j
4k
Entry
1
2
3
4
5
6
7
8
Substrate
3a/6a
3a/6b
3a/6c
3b/6a
3b/6c
3b/6d
3c/6a
3c/6e
3c/6c
3c/6f
X
H
H
H
Cl
R2
H
OMe
OMe
H
OMe
OCH2O
H
R3
H
H
OMe
H
OMe
Product
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
Yield of 4, %a
H
58
56
59
67
58
59
65
56
57
54
55
H
a Isolated yield
Cl
Cl
Being structural analogue of chloroquine and related drugs
Me
Me
Me
Me
Me
H
60 used for treatment of malaria, which is one of the most serious
parasitic diseases in the world being fatal for 655 000 people
in 2010,19 isocryptolepine can be considered as a good lead
compound for the development of new medication with the
antiplasmodial activity.
OCH2CH2O
OMe
H
9
10
11
OMe
Cl
Br
3c/6g
H
a Isolated yield
65 Therefore, we studied the methylation of the synthesized
indolo[3,2ꢀc]quinolines 5 to demonstrate that the developed
approach can be utilized for preparation of series of
substituted isocryptolepines allowing for structure–activity
relationship study and determination of derivatives with good
70 therapeutical properties.
We examined a number of reported procedures for the
methylation of 11Hꢀindolo[3,2ꢀc]quinolines 516a,c,e,20 using
unsubstituted 5a as a model substrate. The best result was
obtained when 5a was heated with methyl iodide in
75 nitrobenzene according to KermackꢀStorey procedure.21 This
reaction finished the total synthesis of isocryptolepine 7a
from furfural in six steps. Under the same conditions
isocryptolepine derivatives 7b-f were obtained in 74ꢀ86%
yields (Table 3).
Then, we studied the reductive cyclization of 3ꢀ(2ꢀ
25 acetylvinyl)ꢀ2ꢀ(2ꢀnitrophenyl)indole 4a. We have found that
the utilization of Zn/NaOH or Raney nickel leads to a
complex mixture of products. Heating of 4a with Zn/AcOH or
SnCl2 was also shown to be ineffective. However, the
treatment of 4a with Fe in AcOH under reflux for 5 min
30 afforded directly 11Hꢀindolo[3,2ꢀc]quinoline (5a). The
formation of 5 can be explained by mechanism including the
reduction of nitro group with formation of the corresponding
aniline A, the intramolecular Michael addition leading to 6ꢀ
acetonylꢀ5,6ꢀdihydroꢀ11Hꢀindolo[3,2ꢀc]quinoline B and the
35 aromatization of B by acetone elimination (Scheme 3). The
last step seems to be quite unusual, however, ketones
elimination from dihydroarenes leading to substrate
2
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Table 3 Synthesis of isocryptolepine 7a and its derivatives 7b-f
4
(a) A. S. Pilipenko, V. V. Mel’chin, I. V. Trushkov, D. A. Cheshkov
and A. V. Butin, Tetrahedron, 2012, 68, 619ꢀ627; (b) T. A. Nevolina,
V. A. Shcherbinin, O. V. Serdyuk and A. V. Butin, Synthesis, 2011,
3547ꢀ3551; (c) A. V. Butin, F. A. Tsiunchik, O. N. Kostyukova, M.
G. Uchuskin and I. V. Trushkov, Synthesis, 2011, 2629ꢀ2638; (d) A.
V. Butin, T. A. Nevolina, V. A. Shcherbinin, I. V. Trushkov, D. A.
Cheshkov and G. D. Krapivin, Org. Biomol. Chem., 2010, 8, 3316ꢀ
3327; (e) A. V. Butin, V. T. Abaev, V. V. Mel’chin, A. S. Dmitriev,
A. S. Pilipenko and A. S. Shashkov, Synthesis, 2008, 1798ꢀ1804; (f)
A. V. Butin, A. S. Dmitriev, M. G. Uchuskin, V. T. Abaev and I. V.
Trushkov, Synth. Commun., 2008, 38, 1569ꢀ1578; (g) A. S. Dmitriev,
V. T. Abaev, W. Bender and A. V. Butin, Tetrahedron, 2007, 63,
9437ꢀ9447.
50
55
60
65
70
75
80
85
90
95
100
Entry
Substrate
X
H
H
R2
H
OMe
OMe
H
R3
H
OMe
OMe
H
Product
7a
7b
7c
7d
Yield of 7, %a
1
2
3
4
5
6
5a
5c
5e
5g
5i
86
75
74
85
82
77
Cl
Me
Me
Me
5
6
7
A. V. Butin, M. G. Uchuskin, A. S. Pilipenko, F. A. Tsiunchik, D. A.
Cheshkov and I. V. Trushkov, Eur. J. Org. Chem., 2010, 920ꢀ926.
A. V. Butin, F. A. Tsiunchik, V. T. Abaev and V. E. Zavodnik,
Synlett, 2008, 1145ꢀ1148.
For some recent syntheses of 5, see: (a) L. K. Filak, G. Muehlgassner,
F. Bacher, A. Roller, M. Galanski, M. A. Jakupec, B. K. Keppler and
V. B. Arion, Organometallics, 2011, 30, 273ꢀ283; (b) G. Desimoni,
G. Faita, M. Mella, M. Toscanini and M. Boiocchi, Eur. J. Org.
Chem., 2009, 2627ꢀ2634; (c) P. K. Agarwal, D. Sawant, S. Sharma
and B. Kundu, Eur. J. Org. Chem., 2009, 292ꢀ303; (d) A. Beauchard,
H. Chabane, S. Sinbandhit, P. Guenot, V. Thiery and T. Besson,
Tetrahedron, 2006, 62, 1895ꢀ1903.
(a) E.ꢀS. Ibrahim, A. M. Montgomerie, A. H. Sneddon, G. R. Proctor
and B. Green, Eur. J. Med. Chem., 1988, 23, 183ꢀ188; (b) V. E.
Marquez, J. W. Cranston, R. W. Ruddon, L. B. Kier and J. H.
Burckhalter, J. Med. Chem., 1972, 15, 36ꢀ39.
(a) M.ꢀL. Go, T.ꢀL. Ngiam, A. L.ꢀC. Tan, K. Kuaha and P. Wilariat,
Eur. J. Pharm. Sci., 1998, 6, 19ꢀ26; (b) H. L. Koh, M. L. Go, T. L.
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394.
OMe
H
OMe
Br
7e
7f
5k
a Isolated yield
5
The selection of substituted indolo[3,2ꢀc]quinolines for this
transformation was performed according to the known data
that halide introduction increases antiplasmodial activity of
the related 4ꢀaminoquinolines and methoxy groups are often
10 important for good bioavailability of the potent drug.
Moreover, these substituents allow for easy modification of
synthesized compounds. A broad variety of isocryptolepines
containing many other substituents can be also obtained by
this reaction sequence directly.
8
9
15 In conclusion, we developed
a
simple method for
transformation of furfural, the largeꢀscale product of
processing of agricultural and forestry wastes, into indolo[3,2ꢀ
c]quinolines and isocryptolepines, which are potent
pharmacologically active compounds. This method is based
20 on the utilization of cheap reagents as well as
environmentallyꢀ and industryꢀfriendly reaction conditions.
On the contrary to the previously reported approaches, our
method allows for preparation of various 9ꢀsubstituted
indolo[3,2ꢀc]quinoline and isocryptolepine derivatives. It
25 expands significantly opportunities for synthesis of libraries
of these two classes of heterocyclic compounds as a part of a
program for development of new drugs for treatment of
malaria. The study of antiplasmodial activity of the
synthesized compounds is currently under investigation.
10 (a) C.ꢀM. Lu, Y.ꢀL. Chen, H.ꢀL. Chen, C.ꢀA. Chen, P.ꢀJ. Lu, C.ꢀN.
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30 Acknowledgements
We thank the Russian Foundation of Basic Research (Project
10ꢀ03ꢀ00254ꢀа) and Ministry of Education of the Perm Krai
for financial support of this work.
Notes and references
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From biomass to medicines. A simple synthesis of indolo[3,2-c]quinolines,
antimalarial alkaloid isocryptolepine, and its derivatives
Maxim G. Uchuskin, Arkady S. Pilipenko, Olga V. Serdyuk, Igor V. Trushkov, Alexander V. Butin
An approach to indolo[3,2-c]quinolines, alkaloid isocryptolepine and its derivatives from furfural is described.