Synthesis of 5,6-dihydropyrrolo[2,1-a]isoquinolines featuring an intramolecular radical-oxidative cyclization of polysubstituted pyrroles, and evaluation of their cytotoxic activity

Article abstract of DOI:10.1039/c004399k

A three-step protocol for the synthesis of 1,2,3,8,9-pentasubstituted-5,6- dihydropyrrolo[2,1-a]isoquinolines is described, using van LeuseN′s polysubstituted pyrrole construction followed by intramolecular radical-oxidative cyclization of the isoquinoline system. The cytotoxic activities of the dihydropyrroloisoquinolines were tested on six tumor cell lines. Preliminary structure-activity studies revealed the importance of the identity of the aromatic substituent at the C-2 position, particularly a phenyl, m-(amino) phenyl or m-(cyclohexylmethylpiperazinamide) phenyl substituent, for cytotoxic activity.

Full text of DOI:10.1039/c004399k

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Synthesis of 5,6-dihydropyrrolo[2,1-a]isoquinolines featuring an
intramolecular radical-oxidative cyclization of polysubstituted pyrroles, and
evaluation of their cytotoxic activity†
Paul E. Reyes-Gutie´rrez, Jose´ R. Camacho,‡ Ma. Teresa Ram´ırez-Apan, Yazmin M. Osornio§ and
Roberto Mart´ınez*
Received 17th March 2010, Accepted 17th June 2010
DOI: 10.1039/c004399k
A three-step protocol for the synthesis of 1,2,3,8,9-pentasubstituted-5,6-dihydropyrrolo[2,1-a]-
isoquinolines is described, using van Leusen’s polysubstituted pyrrole construction followed by
intramolecular radical-oxidative cyclization of the isoquinoline system. The cytotoxic activities of the
dihydropyrroloisoquinolines were tested on six tumor cell lines. Preliminary structure–activity studies
revealed the importance of the identity of the aromatic substituent at the C-2 position, particularly a
phenyl, m-(amino) phenyl or m-(cyclohexylmethylpiperazinamide) phenyl substituent, for cytotoxic
activity.
With the discovery of the biological activity of lamellarins,2j
several routes for the synthesis of the pyrrolo[2,1-a]isoquinoline
Introduction
skeleton have been described.2d,5 The majority of these routes
are based on pyrrole construction (ring C, 1) from 1- and/or
N-functionalized isoquinolines,6,7 and the remainder are based
on closure of the dihydroisoquinoline system AB (1) from
the respective pyrrole.8,9 Here, we report a new and straight-
forward three-step synthesis of 1,2,3,8,9-pentasubstituted-5,6-
dihydropyrrolo[2,1-a]isoquinolines 5 (Scheme 1), using readily
accessible starting materials, such as 1,2-disubstituted alkenes (9)
and p-toluenesulfonylmethylisocyanide (TosMIC) (10), featuring
a van Leusen’s polysubstituted pyrrole construction and the
formation of an aromatic sp2 C–C bond through an oxidative
free radical cyclization. The retrosynthesis for 5 is shown in
Scheme 1. Deconstruction of the dihydroisoquinoline system
The synthesis of pyrrolo[2,1-a]isoquinoline (1, Fig. 1) has re-
cently become an important goal after the discovery of this
tricyclic core in several alkaloids, including ( )-crispine A (2)1
and the lamellarin family (3),2 such as lamellarin D (4),3 which
exhibits significant cytotoxic activity. In addition, compounds
with a pyrroloisoquinoline frame (1) have been described as
having phosphodiesterase 10a (PDE 10a) inhibitory activity,4a,b
antineoplastic activity,4b–e and hypotensive, sympatholytic and
psychotropic properties,4f as well as being useful in the treatment
of diseases such as psoriasis.4g
Fig. 1 Alkaloids that contain a pyrrolo[2,1-a]isoquinoline core (1).
Instituto de Qu´ımica, Universidad Nacional Auto´noma de Me´xico, Circuito
Exterior, Ciudad Universitaria, Me´xico, D.F. 04510, Me´xico. E-mail:
robmar@servidor.unam.mx
† Electronic supplementary information (ESI) available: Further experi-
mental details and NMR spectra. CCDC reference numbers 770152. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c004399k
‡ Actual address: Departamento de Qu´ımica, Universidad Simo´n Bolivar,
Apartado 47206, Caracas 1080-A Venezuela.
§ Actual address: Organic Chemistry Institute, University of Zurich,
Winterthurerstrasse 190, 8057 Zurich, Switzerland.
Scheme
pyrrolo[2,1-a]isoquinolines 5.
1
Retrosynthesis of 1,2,3,8,9-pentasubstituted-5,6-dihydro-
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Table 1 Cyclization of the isoquinoline system (AB)
(AB, 5) via a radical-oxidative cyclization leads to precursor 6,
which, in principle, could be obtained through the N-alkylation
of the pyrrole 7 and the alkylating agent 8. Finally, the 2,3,4-
trisubstituted pyrrole 7 could be constructed using the van
Leusen’s synthesis of pyrroles, reaction of TosMIC (10) with a
Michael acceptor 9.10 We measured the cytotoxic activity of the
products in six cancer cell lines.
Entry
Product
R1
R2
Methoda
Yield (%)
Results and discussion
1
2
3
4
5
6
7
5a
5a
5a
5b
5c
5d
5e
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CN
H
H
H
a
b
c
c
c
c
c
40
53
70
80
85
90
75
Chemistry
Following our retrosynthetic strategy, we first obtained the alkenes
9b–e via the Heck reaction with a Pd(OAc)2 catalyst. The
compounds 9b–d were obtained exclusively as (E)-isomers with
moderate (9d, 65%) to good yields (9b, 97% and 9c, 80%).11 The 3-
phenylacrylonitrile (9e) was isolated as a mixture of E/Z isomers
(65 : 35, determined by 1H-NMR) with 88% yield. In parallel,
the commercially available TosMIC was alkylated under phase-
transfer conditions, as reported previously by van Leusen,12 to
afford the mono-alkylated TosMIC (10, R3 = Me) in 90% yield.
With the alkenes 9a–e and the Me-TosMIC in hand, our next
step was the synthesis of 7 (Scheme 2), following van Lausen’s
protocol, to obtain the 2,3,4-polysubstituted pyrroles.10 Pyrrole
7a was obtained from the commercially available ethylacrylate
in 85% yield,13 whereas the pyrroles 7b–e were prepared from
their respective above-described alkenes, 9b–e, with moderate
(7c–e 61–82% yields) to good yields (7b, 91%, Scheme 2). It is
noteworthy that the C-4 substituent in each pyrrole acted as an
electron withdrawing group (R1 = –CO2Et or –CN) in the general
van Leusen’s reaction mechanism. Having prepared the pyrroles
7a–e, our next step was their N-alkylation with 2-(2-bromo-4,5-
dimethoxyphenyl)ethyl p-toluenesulfonate (8, X = Br and Y =
OTs, 2.0 eq.), in the presence of NaH (2.5 eq.) in DMSO solvent,
to afford the N-alkyl-pyrroles 6a–e with moderate yields (60–87%,
Scheme 2). The elimination product from 8 was also observed. In
preliminary reactions, the 2-(2-bromo-4,5-dimethoxyphenyl)ethyl
bromide compound (8, X = Y = Br) was used as an alkylating agent,
but the elimination product was afforded as the major product. To
avoid the elimination product, Albericio8b previously reported N-
alkylation of the methyl pyrrole-2-carboxylate, using K2CO3 as the
base instead of a stronger base such as NaH. However, alkylation
was only carried out in the absence of methoxy groups on the aryl
moiety of 8.
C6H5
m-C6H4NH2
C4H3S
C6H5
a Method: (a) Pd(OAc)2 (0.33 eq.), PPh3 (0.33 eq.), nBu4NBr (0.1 eq.),
K2CO3 (2 eq.), DMF, 120◦ C, 12 h; (b) AIBN (0.3 eq.), nBu3SnH (1.2 eq.),
refluxing toluene, 2.0 h; and method (c) nBu3SnH (2.5 eq)/toluene (0.75
M), DLP (2.5 eq.), reflux, 7.0 h.
In preliminary reactions, the N-alkyl-pyrrole 6a was cy-
clized to the corresponding tetrasubstituted 5,6-dihydro-
pyrroloisoquinoline 5a using either palladium-catalyzed cycliza-
tion with a 40% yield (entry 1, Table 1)14 or using n-Bu3SnH–AIBN
conditions, after which the product 5a was isolated with 53%
yield (entry 2). Even though the yield of the tin-mediated radical
reaction was moderate (entry 2), intramolecular radical cyclization
has rarely been used to construct a pyrroloisoquinoline frame.15
With this strategy, our next challenge was to improve the yield of
the ring closure process by performing a free radical reaction.
Miranda16 previously reported an oxidative-radical cyclization
in enamide systems using a mixture of n-Bu3SnH and dilauroyl
peroxide (DLP) as the initiator, rather than AIBN, and the
oxidized products were obtained. The implementation of this
strategy afforded compound 5a with 70% yield instead of the
40% yield achieved using n-Bu3SnH–AIBN (entry 3, Table 1),
giving a 46% overall yield. In applying this optimization procedure,
the 5,6-dihydropyrroloisoquinoline 5b was obtained from the N-
alkylpyrrole 6b with 80% yield and 55% overall yield (entry
4),17a 6c was cyclized to the C-2 m-aniline pyrroloisoquinoline
5c with 85% yield and 60% overall yield (entry 5, 63% overall
yield previously reported),4a and the C-2 thiophene compound 5d
Scheme 2 Synthesis of the N-alkylated pyrroles 6a–e. Conditions: (i) NaH (2.0 eq.)/Et2O; 9a–e (1.0 eq.) and 10 (R3 = Me, 1.1 eq.)/Et2O–DMSO (2 : 1),
RT, 1.0 h; (ii) 8 (X = Br, Y = OTs, 2.0 eq.), NaH (2.5 eq.), DMSO, RT, 2.0 h. a These compounds were isolated and used as a cis–trans mixture (cis : trans,
65 : 35).
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Scheme 3 Synthesis of the pyrrolo[2,1-a]isoquinoline 16. Conditions: (i) DCC (1.1 eq.), CH2Cl2, 0◦ C, 30 min, then RT, 4.0 h. (ii) NaH (2.0 eq.)/Et2O;
13 (1.0 eq.) and 10 (R3 = Me, 1.1 eq.)/Et2O–DMSO (2 : 1), RT, 1.0 h; (iii) 8 (X = Br, Y = OTs, 2.0 eq.), NaH (2.5 eq.), DMSO, RT, 2.0 h; (iv) nBu3SnH
(2.5 eq.)/toluene (0.75 M), DLP (2.5 eq.), reflux, 7.0 h.
was isolated with 90% yield and 52% overall yield (entry 6, 42%
overall yield previously reported).17b Finally, pyrroloisoquinoline
5e, which contains the nitrile substituent at the C-1 position in
place of the ethyl ester (5b), was afforded with 75% yield and 28%
overall yield (entry 7).
Having demonstrated the viability of the intramolecular
radical-oxidative cyclization strategy, we next demonstrated the
scope of the methodology through the synthesis of the 5,6-
dihydropyrroloisoquinoline 16 (Scheme 3), which is an inhibitor
of PDE 10a.4b First, we prepared the alkene 11 by performing
a Heck reaction between 3-iodobenzoic acid and ethylacrylate,
with 66% yield.18 In parallel, the 1-(cyclohexylmethyl)piperazine
(12) was obtained with 62% yield from N-formylpiperazine19a
Fig. 2 ORTEP drawing of 16 (30% probability level). The cyclohexyl-
methyl group at the piperazine moiety is modeled as disordered over two
positions.
and (bromomethyl)cyclohexane, as previously reported by
Meanwell.19b The coupling reaction between 11 and N-alkyl
piperazine 12 (Scheme 3) was achieved in the presence of N,N¢-
dicyclohexylcarbodiimide (DCC) in CH2Cl2 at 0◦ C, to afford 13
with 93% yield. With the alkene 13 in hand, our next step was
the synthesis of the 2,3,4-trisubstituted-pyrrole 14, obtained with
84% yield through a mediated van Leusen’s reaction. Finally, N-
alkylation of 14 afforded the pyrroloisoquinoline precursor 15
(60% yield), which was radical-cyclized to 16 with 90% yield and
42% overall yield from 13 (Scheme 3, ref. 4b 36% overall yield).
The structure of the pyrroloisoquinoline 16 was confirmed by
crystallographic analysis (Fig. 2).
Biological activity
We evaluated the inhibitory activity of compounds 5a–e, 16, and
16·HCl20 toward the growth of PC-3 prostate cancer, U-251 central
nervous system cancer, K-562 leukemia, HCT-15 colon cancer,
MFC-7 breast cancer and SKUL-1 lung cancer cells (Table 2).
Compound 5a (R1 = CO2Et and R2 = H) moderately inhibited the
growth of two cancer cell lines, with IC50 values in the micromolar
range (U-251, IC50 = 33.43 4.500 mM; and K-562, IC50 = 48.11
0.600 mM) and did not show activity toward the SKLU-1 cancer
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Table 2 The IC50 values (mM) of compounds 5a–e, 16 and 16·HCl in the six cancer cell lines.a
Comp.
PC-3 (prostate)
U-251 (CNS)
K-562 (leukemia)
HCT-15 (colon)
MCF-7 (breast)
SKLU-1 (lung)
5a
68.17 5.300
18.15 0.600
21.2 1.200
8.47 0.230
>100
33.43 4.500
4.86 0.600
5.96 0.500
6.99 0.670
>100
48.11 0.600
76.78 7.300
2.5 0.800
4.07 0.490
>100
54.07 4.400
0.14 0.060
0.01 0.003b
0.59 0.050b
>100
68.51 4.70
25.2 2.000
1.3 0.100
7.41 0.090
>100
5.58 0.040
1.06 0.040
0.16 0.01 b
100
5b
0.59 0.005b
0.10 0.010b
2.13 0.030
>100
5c
5d
5e
16
0.16 0.010b
3.58 0.100
0.12 0.010 b
0.05 0.009b
0.16 0.020b
0.024 0.005 b
0.16 0.010b
1.15 0.050
0.59 0.020 b
0.02 0.010b
0.05 0.003b
0.13 0.005 b
0.02 0.001b
0.44 0.010b
0.15 0.009 b
16·HCl
CPTc
a Values are means of three experiments, (>100, not active). b IC50 values can be expressed in the nanomolar range (nM). c Camptothecin (CPT) was
purchased from Sigma-Aldrich Chemical Co.
cell line. Substitution of the R2 = H substituent at the C-2 position
with a benzene ring (compound 5b, R1 = CO2Et and R2 = C6H5)
produced an increase in the growth inhibitory activity in five cell
lines, U-251 (IC50 = 4.86 0.600 mM), HCT-15 (IC50 = 0.14 0.060
mM), and SKLU-1 (IC50 = 0.59 0.005 mM), with the exception of
K-562 (IC50 = 76.78 7.300 mM). In contrast to 5b, when the ethyl
ester substituent at the C-1 position was changed to a cyano group
(compound 5e, R1 = CN and R2 = C6H5), the resulting compound
did not inhibit proliferation of any of the six cancer cell lines
tested. Based on this last result, the ethyl ester substituent was
fixed at the C-1 position, and only the aromatic moiety at the C-2
position was modified (5c–d). In a previous report,4a compound 5c
(R1 = CO2Et and R2 = m-C6H4–NH2) was described as having PDE
10a inhibitory activity (IC50= 110 nM) and was assessed in vitro
on a MDA-MB-231 human breast carcinoma proliferation assay
(% inhibition at 10 mM = 93.0). Here, we evaluated the ability of
compound 5c to inhibit growth of six cancer cell lines. Surprisingly,
incorporation of the amine group at the meta position of the
benzene ring in 5c significantly increased the inhibitory activity
cyclohexylmethyl piperazinamide substituent in 16 played an
important role in the cytotoxic activity of compounds with IC50
values in the nanomolar range: U-251 (IC50 = 50 0.009 nM),
HCT-15 (IC50 = 20
0.010 nM), and SKLU-1 (IC50 = 20
0.001 nM). The inhibitory growth activity of the hydrochloric salt
16·HCl was evaluated, but the activity was not higher than that of
the neutral compound (16). It is noteworthy that even when the
activity of 16 was higher in three cell lines than the activity of the
m-amine compound 5c, the latter compound had the smallest IC50
value in the HCT-15 cell line (IC50 = 10.0 0.003 nM).
Nowadays, an important group of lamellarins are described
as inhibitors of topoisomerase I (Top I-DNA), including the
lamelarin D (4).2j,3d,21 With this idea, the cytotoxic activity of the
synthesized compounds 5a–e, 16 and 16·HCl was compared with
a commercially available inhibitor of Top I-DNA, camptothecin
(CPT).22 As is shown in Table 2, we observed that CPT was more
active than all the synthesized pyrrolo[2,1-a]isoquinolines in the
prostate PC-3 cell line (IC50 = 0.12 0.010 mM), CNS U-251 cell
line (IC50 = 0.024 0.005 mM) and breast MCF-7 cell line (IC50
0.16 0.010 mM). On the other hand, the synthesized compound
16 showed more activity in the leukemia K-562 cell line (IC50
=
relative to 5b: U-251 (IC50 = 5.96 0.500 mM), K-562 (IC50
=
2.5 0.800 mM), MCF-7 (IC50 = 1.3 0.100 mM), and SKLU-1
(IC50 = 0.10 0.010 mM). Furthermore, the IC50 of the HCT-
15 cell line was measured to be in the nanomolar range (10.0
0.003 nM). When the benzene ring was changed to a thiophene ring
(compound 5d, R1 = CO2Et and R2 = C4H3S), growth inhibition of
=
0.16 0.010 mM) and lung SKLU-1 cell line (IC50 = 0.02 0.001
mM) compared with the reference CPT (IC50 = 0.59 0.020 mM
and 0.15 0.009 mM, respectively). Finally, compound 5c showed
a higher activity than CPT (IC50 = 0.13 0.005 mM) in the colon
HCT-15 cell line (IC50 = 0.01 0.003 mM) and a similar activity in
the lung SKLU-1 cell line (IC50 = 0.10 0.010 mM).
three cell lines surpassed the inhibitory activity of 5b: PC-3 (IC50
=
8.47 0.230 mM), K-562 (IC50 = 4.07 0.490 mM), and MCF-7
(IC50 = 7.41 0.090 mM), but was not better than 5c in any cell
lines except the PC-3 prostate cell line. These preliminary results
demonstrated the positive effect of the ethyl ester substituent at the
C-1 position on the growth inhibitory activity of 5a–d, showing
better results than compounds containing a nitrile substituent
(5e). Additionally, the aromatic moiety at the C-2 position plays
an important role (5b–d), specifically when this substituent is a
benzene ring (5b–c), and the meta-substituted amine group (5c) is
even more significant.
In addition, we evaluated the activity of compound 16, which
has a cyclohexylmethyl piperazinamide substituent at the meta
position of the benzene. The piperazinamide moiety was shown
to have an important role in the biological activity of some
compounds, such as dihydroimidazo[4,5-b]quinolinones, which
have been reported to show blood platelet cAMP PDE inhibitory
activity and ADP-induced platelet aggregation.19a Furthermore,
the hydrochloric salt of 16 (16·HCl) was described as a PDE
10a inhibitor (IC50 = 410 nM).4b These reports suggest that the
Conclusion
In summary, a short and practical route to the C-1 and C-
2 functionalized 5,6-dihydropyrrolo[2,1-a]isoquinolines, involving
a van Leusen’s polysubstituted pyrrole construction and an in-
tramolecular radical-oxidative cyclization of the AB isoquinoline
system, is described. The expedient synthesis of a more complex
structure that contains the m-(cyclohexylmethylpiperazinamide)
phenyl substituent at the C-2 position of the pyrroloisoquinoline
frame (16) underscores the scope of the structural diversity of
this methodology. We evaluated the inhibitory activities of the
5,6-dihydropyrroloisoquinolines 5a–b, 16, and 16·HCl toward the
growth of six cancer cell lines. We demonstrated that the aromatic
moiety at the C-2 position has a significant influence on the
cytotoxic activity (5b–d), particularly if this moiety is a benzene
ring (5b–c) or, even more significantly, if this moiety is an amine
group, i.e. 5c, which showed the lowest IC50 value, in the nanomolar
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range (HCT-15 cell line). We also observed that a cyclohexylmethyl
piperazinamide substituent at the meta position of the benzene
ring in 16 increased the activity relative to the compound contain-
ing a simple benzene ring at the C-2 position (5b), with IC50 values
in the nanomolar range (HCT-15 and SKLU-1 cell lines). The cy-
totoxic activity of the synthesized compounds was compared with
the Top I-DNA inhibitor camptothecin (CPT). The compounds
16 and 5c were more active than CPT in the K-562, HCT-15
and SKLU-1 cell lines. In view of these preliminary structure–
activity relationship studies, we are currently continuing to
synthesize new 1,2,3,8,9-pentasubstituted-5,6-dihydropyrrolo[2,1-
a]isoquinolines, applying the synthetic methodology described
here toward development of novel anticancer agents.
47.6, 42.1, 34.9, 31.7, 26.7, 26.0, 14.3; IR (Film, cm-1) 3411, 3059,
2981, 2923, 2851, 2806, 2771, 1713, 1638, 1443; MS (EI) m/z 384
(M+, 15%), 301 (M+-83, 100%); Found: C, 71.90; H, 8.32; N,
7.32. Calc. for C23H32N2O3: C, 71.84; H, 8.39; N, 7.29%.
Experimental procedure for the pyrroles
A
solution of the alkene (2.6 mmol) and 1-(1-
isocyanoethylsulfonyl)-4-methylbenzene (10, 0.6 g, 2.9 mmol) in
Et2O–DMSO (2 : 1, 15 mL) was added dropwise to a suspension
of NaH (0.23 g, 5.7 mmol, 60% dispersion in mineral oil and
previously washed with dry hexane) in dry ether (5 mL). The
mixture was stirred at room temperature for 1.0 h, then H2O
(15 mL) was added dropwise and the product was extracted with
EtOAc (3 ¥ 30 mL). The organic layer was washed with H2O and
brine (3 ¥ 10 mL), and dried with Na2SO4, then evaporated in
vacuo. The residue was purified by flash column chromatography
on silica gel to furnish the respective pyrrole.
Experimental
General details
1H NMR spectra were recorded on Varian Gemini-200 MHz and
Eclipse 300 MHz JEOL spectrometers in deuterated chloroform
(CDCl3) solutions with internal standard TMS (0 ppm), or in
deuterated dimethyl sulfoxide (DMSO-d6). The chemical shifts
are reported in parts per million (d (ppm)). The peak patterns are
indicated as follows: s, singlet; d, doublet; t, triplet; q, quartet;
m, multiplet; br, broad. The coupling constants (J) are reported
in Hertz (Hz). 13C NMR spectra were recorded at 50 MHz and
75 MHz on the same instruments. Assignments of 13C spectra
were performed by distortionless enhancement by polarization
transfer (DEPT) experiments. IR spectra were collected on a FT-
IR Tensor 27 Bruker spectrometer. Mass spectra were recorded on
a JEOL JEM-AX505HA spectrometer by electronic impact (EI)
at 70 eV for low resolution. Elemental analysis was performed
on a CE-440 elemental analyzer (Exeter Analytical, Inc). X-Ray
crystallography was carried out on a Bruker Smart Apex CCD
diffractometer. Flash column chromatography was carried out on
silica gel 60 (230–400 mesh ASTM) from Macherey-Nagel GmbH
& Co.
Ethyl 5-methyl-1H-pyrrole-3-carboxylate (7a). From commer-
cially available ethylacrylate (0.28 mL, 2.6 mmol), purified by flash
column chromatogr◦aphy on silica gel, to furnish 0.34 g of 7a as a
white solid, m.p. 65 C (lit.ref. 13 70◦ C), yield 85%. TLC (hexane–
EtOAc–Et3N, 45 : 50 : 5 v/v): Rf 0.69, 1H-NMR (300 MHz, CDCl3)
d (ppm): 1.33 (t, J = 7.2 Hz, 3H), 2.23 (s, 3H), 4.26 (q, J = 7.2 Hz,
2H), 6.28–6.30 (m, 1H), 7.26–7.28 (m, 1H), 8.75 (brs, 1H, –NH);
13C-NMR (75 MHz, CDCl3) d (ppm): 165.5, 128.8, 122.5, 116.3,
106.9, 59.6, 14.4, 12.7; IR (KBr, cm-1) 3276, 3169, 2983, 2928,
2867, 2685, 2577, 1676, 1586, 1517, 1441; MS (EI) m/z 153 (M+,
80%), 108 (M+-45, 100%); Found: C, 62.76; H, 7.22; N, 9.22. Calc.
for C8H11NO2: C, 62.73; H, 7.24; N, 9.14%.
Ethyl 5-methyl-4-phenyl-1H-pyrrole-3-carboxylate (7b). From
ethyl cinnamate (9b, 0.45 g, 2.6 mmol), purified by flash column
chromatography on silica gel, to furnish 0.54 g of 7b as a
yellow solid, m.p. 136 ◦C, yield 91%. TLC (hexane–EtOAc–Et3N,
45 : 50 : 5 v/v): Rf 0.66, 1H-NMR (300 MHz, CDCl3) d (ppm): 1.17
(t, J = 7.2 Hz, 3H), 2.13 (s, 3H), 4.14 (q, J = 7.2 Hz, 2H), 7.23–
7.37 (m, 6H), 8.59 (brs, 1H, –NH); 13C-NMR (75 MHz, CDCl3) d
(ppm): 165.1, 135.2, 130.5, 127.4, 126.6, 126.1, 122.9, 122.1, 114.5,
59.3, 14.1, 11.4; IR (KBr, cm-1) 3277, 2986, 2942, 2896, 2819, 1952,
1884, 1811, 1682, 1606, 1518, 1494, 1447, 1409, 1383; MS (EI) m/z
229 (M+, 100%), 184 (M+-45, 90%); Found: C, 73.32; H, 6.63; N,
6.08. Calc. for C14H15NO2: C, 73.34; H, 6.59; N, 6.11%.
(E)-Ethyl 3-(3-(4-(cyclohexylmethyl)piperazine-1-carbonyl)-
phenyl)acrylate (13)
To
a
solution of (E)-3-(2-ethoxycarbonyl-vinyl)benzoic
acid (11, 1.0 g, 4.5 mmol) in CH2Cl2 (4.5 mL), 1-
(cyclohexylmethyl)piperazine (12, 0.83 g, 4.5 mmol) was
added and cooled to 0◦ C. N,N¢-Dicyclohexylcarbodiimide (1.0 g,
5 mmol) was then added, and the mixture was stirred for 30 min.
After that time, the reaction was warmed at room temperature
and stirred for an additional 4.0 h. The N,N¢-dicyclohexylurea
was eliminated by filtration and washed with CH2Cl2. The solvent
was evaporated in vacuo, and the residue was purified by flash
column chromatography on silica gel, TLC (EtOAc–Et3N, 80 : 20
v/v): Rf 0.71, to furnish 13 (1.97 g) as a brown solid, m.p. 58 ◦C,
Ethyl
4-(3-aminophenyl)-5-methyl-1H-pyrrole-3-carboxylate
(7c). From (E)-ethyl 3-(3-aminophenyl)acrylate (9c, 0.50 g,
2.6 mmol), purified by flash column chromatography on silica
gel, to furnish 0.51 g of 7c as a white solid, m.p. 48 ◦C, yield 80%.
TLC (hexane–EtOAc–Et3N, 45 : 50 : 5 v/v): Rf 0.28; 1H-NMR
(300 MHz, CDCl3) d (ppm): 1.19 (t, J = 7.2 Hz, 3H), 2.14 (s, 3H),
3.61 (brs, 2H, –NH2), 4.15 (q, J = 7.2 Hz, 2H), 6.59–6.72 (m, 3H),
7.13 (t, J = 8.1 Hz, 1H), 7.30–7.31 (m, 1H), 8.47 (brs, 1H, –NH);
13C-NMR (75 MHz, CDCl3) d (ppm): 165.0, 145.5, 136.2, 128.3,
126.5, 122.7, 122.2, 121.2, 117.6, 114.6, 113.3, 59.3, 14.2, 11.5;
IR (KBr, cm-1) 3459, 3369, 3288, 2983, 2942, 2900, 1684, 1615,
1519, 1491, 1464, 1409, 1382; MS (EI) m/z 244 (M+, 100%), 198
(M+ -46, 100%); Found: C, 68.92; H, 6.76; N, 11.39. Calc. for
C14H16N2O2: C, 68.83; H, 6.60; N, 11.47%.
1
yield 93%. H-NMR (200 MHz, CDCl3) d (ppm): 0.79–0.95 (m,
2H), 1.11–1.25 (m, 3H), 1.34 (t, J = 7.2, 3H), 1.45–1.80 (m, 6H),
2.17 (d, J = 7.2 Hz, 2H), 2.36 (brs, 2H), 2.47 (brs, 2H), 3.42 (brs,
2H), 3.80 (brs, 2H), 4.27 (q, J = 7.0 Hz, 2H), 6.46 (d, J = 16.0 Hz,
1H), 7.40–7.43 (m, 2H), 7.55–7.57 (m, 2H), 7.67 (d, J = 16.0 Hz,
1H); 13C-NMR (50 MHz, CDCl3) d (ppm): 169.4, 166.7, 143.5,
136.7, 134.8, 129.0, 128.6, 126.5, 119.4, 65.3, 60.6, 53.9, 53.2,
4378 | Org. Biomol. Chem., 2010, 8, 4374–4382
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1
Ethyl 5-methyl-4-(thiophen-2-yl)-1H-pyrrole-3-carboxylate (7d).
From (E)-ethyl 3-(thiophen-3-yl)acrylate (9d, 0.47 g, 2.6 mmol),
purified by flash column chromatography on silica gel, to furnish
0.50 g of 7d as yellow solid mp 108 ◦C, yield 82%. TLC (hexane–
EtOAc–Et3N, 45 : 50 : 5 v/v): Rf 0.64; 1H-NMR (300 MHz, CDCl3)
d (ppm): 1.22 (t, J = 7.2 Hz, 3H), 2.21 (s, 3H), 4.18 (q, J = 7.2 Hz,
2H), 6.98–7.05 (m, 2H), 7.27–7.31 (m, 2H), 8.60 (brs, 1H, –NH);
13C-NMR (75 MHz, CDCl3) d (ppm): 164.8, 136.0, 128.4, 127.2,
126.4, 124.7, 123.0, 115.3, 114.3, 59.5, 14.2, 11.7; IR (KBr, cm-1)
3259, 3139, 2984, 2927, 2866, 1674, 1578, 1506, 1468, 1410, 1329;
MS (EI) m/z 235 (M+, 100%), 190 (M+-45, 80%); Found: C, 61.28;
H, 5.60;N, 5.93. Calc. for C12H13NO2S:C, 61.25;H, 5.57;N, 5.95%.
Et3N, 60 : 30 : 10 v/v): Rf 0.52; H-NMR (300 MHz, CDCl3) d
(ppm): 1.31 (t, J = 7.2 Hz, 3H), 2.0 (s, 3H), 3.04 (t, J = 6.9 Hz,
2H), 3.69 (s, 3H), 3.85 (s, 3H), 4.01 (t, J = 6.9 Hz, 2H), 4.24 (q,
J = 6.9 Hz, 2H), 6.23–6.24 (m, 1H), 6.27 (s, 1H), 7.01 (s, 1H),
7.19 (d, J = 1.8 Hz, 1H); 13C-NMR (75 MHz, CDCl3) d (ppm):
164.9, 148.6, 148.4, 129.9, 128.8, 125.3, 115.4, 114.9, 113.9, 113.4,
107.9, 59.4, 56.1, 55.9, 46.6, 37.9, 14.5, 11.6; IR (Film, cm-1) 3596,
3522, 3128, 3080, 2975, 2938, 2846, 1702, 1603, 1569, 1507, 1460,
1447, 1382; MS (EI) m/z 350 (M+-45, 5%), 352 ([M++2]-45, 5%),
316 (M+-79, 100%); Found: C, 54.60; H, 5.57; N, 3.55. Calc. for
C18H22BrNO4: C, 54.56; H, 5.60; N, 3.53%.
Ethyl 1-(2-bromo-4,5-dimethoxyphenethyl)-5-methyl-4-phenyl-
1H-pyrrole-3-carboxylate (6b). From 7b (0.52 g, 2.3 mmol),
purified by flash column chromatography on silica gel, to furnish
0.8 g of 6b as a white solid, m.p. 128 ◦C, yield 75%. TLC (hexane–
EtOAc–Et3N, 60 : 30 : 10 v/v): Rf 0.52; 1H-NMR (300 MHz,
CDCl3) d (ppm): 1.14 (t, J = 7.2 Hz, 3H), 1.92 (s, 3H), 3.1 (t,
J = 7.2 Hz, 2H), 3.72 (s, 3H), 3.86 (s, 3H), 4.07 (t, J = 6.9 Hz, 2H),
4.11 (q, J = 7.2 Hz, 2H), 6.33 (s, 1H), 7.02 (s, 1H), 7.2–7.28 (m, 3H),
7.29–7.36 (m, 3H); 13C-NMR (75 MHz, CDCl3) d (ppm): 164.6,
149.2, 149.0, 135.8, 130.6, 129.1, 127.7, 127.4, 126.1, 125.8, 123.4,
116.3, 114.2, 59.1, 56.4, 56.2, 47.0, 37.8, 14.1, 9.9; IR (KBr, cm-1)
3134, 3046, 3013, 2981, 2958, 2932, 2907, 2865, 2838, 2603, 1954,
1895, 1814, 1761, 1679, 1603, 1533, 1509, 1458, 1439, 1385; MS
(EI) m/z 471 (M+, 2%), 473 (M+ +2, 2%), 426 (M+ -45, 5%), 428
([M+ +2]-45, 5%), 392 (M+-79, 100%); Found: C, 61.14; H, 5.63;
N, 2.90. Calc. for C24H26BrNO4: C, 61.02; H, 5.55; N, 2.97%.
5-Methyl-4-phenyl-1H-pyrrole-3-carbonitrile
(7e). From
(E)/(Z)-3-phenylacrylonitrile (9e, 65 : 35, 0.34 g, 2.6 mmol),
purified by flash column chromatography on silica gel, to
furnish 0.29 g of 7e as a white solid, m.p. 142 ◦C, yield 61%.
TLC (hexane–EtOAc–Et3N, 45 : 50 : 5 v/v): Rf 0.53; 1H-NMR
(300 MHz, CDCl3) d (ppm): 2.28 (s, 3H), 7.17–7.18 (d, J = 3.0 Hz,
1H), 7.25–7.34 (m, 1H), 7.38–7.42 (m, 4H), 8.74 (brs, 1H, –NH);
13C-NMR (75 MHz, CDCl3) d (ppm): 133.1, 128.7, 128.5, 126.8,
125.9, 124.7, 123.1, 117.2, 92.9, 11.7; IR (KBr, cm-1) 3301, 3141,
3051, 2925, 2856, 2219, 1603, 1584, 1519, 1496, 1455; MS (EI)
m/z 182 (M+, 100%); Found: C, 79.02; H, 5.60; N, 15.39. Calc.
for C12H10N2: C, 79.10; H, 5.53; N, 15.37%.
Ethyl 4-(3-(4-(cyclohexylmethyl)piperazine-1-carbonyl)phenyl)-
5-methyl-1H-pyrrole-3-carboxylate (14). From (E)-ethyl 3-(3-
(4-(cyclohexylmethyl)piperazine-1-carbonyl)phenyl)acrylate (13,
1.0 g, 2.6 mmol), purified by flash column chromatography◦on
silica gel, to furnish 0.96 g of 14 as a yellow solid, m.p. 137 C,
yield 84%. TLC (hexane–EtOAc–Et3N, 45 : 50 : 5 v/v): Rf 0.28;
1H-NMR (200 MHz, CDCl3) d (ppm): 0.83–0.94 (m, 2H), 1.12–
1.23 (m, 6H), 1.42–1.49 (m, 1H), 1.68–1.80 (m, 5H), 2.04 (s, 3H),
2.14 (d, J = 7.2 Hz, 2H), 2.35 (brs, 2H), 2.45 (brs, 2H), 3.53 (brs,
2H), 3.77 (brs, 2H), 4.12 (q, J = 7.2 Hz, 2H), 7.27–7.40 (m, 5H),
9.3 (brs, 1H, –NH); 13C-NMR (50 MHz, CDCl3) d (ppm): 170.8,
164.8, 135.4, 134.8, 131.7, 129.1, 127.7, 127.0, 124.9, 123.1, 121.2,
114.0, 65.5, 59.2, 54.2, 53.4, 47.8, 42.2, 34.9, 31.8, 26.7, 26.0, 14.3,
14.2, 11.3, 11.2; IR (KBr, cm-1) 3411, 3181, 3123, 2922, 2014,
1899, 1710, 1600, 1519, 1491, 1451; MS (EI) m/z 437 (M+, 10%),
354 (M+-83, 100%); Found: C, 71.26; H, 8.19; N, 9.57. Calc. for
C26H35N3O3: C, 71.37; H, 8.06; N, 9.60%.
Ethyl 4-(3-aminophenyl)-1-(2-bromo-4,5-dimethoxyphenethyl)-
5-methyl-1H-pyrrole-3-carboxylate (6c). From 7c (0.56 g,
2.3 mmol), purified by flash column chromatography on silica
gel, to furnish 0.97 g of 6c as a yellow solid, m.p. 54 ◦C, yield 87%.
1
TLC (hexane–EtOAc–Et3N, 40 : 50 : 10 v/v): Rf 0.26; H-NMR
(300 MHz, CDCl3) d (ppm): 1.16 (t, J = 7.2 Hz, 3H), 1.93 (s, 3H),
3.09 (t, J = 7.2 Hz, 2H), 3.61 (brs, 1H, –NH2), 3.72 (s, 3H), 3.86
(s, 3H), 4.05 (t, J = 6.9 Hz, 2H), 4.12 (q, J = 6.9 Hz, 2H), 6.34 (s,
1H), 6.55–6.64 (m, 3H), 7.02 (s, 1H), 7.12 (t, J = 7.8 Hz, 1H), 7.26
(s, 2H); 13C-NMR (75 MHz, CDCl3) d (ppm): 164.7, 148.7, 148.5,
145.5, 136.6, 128.8, 128.3, 127.8, 125.7, 121.3, 117.7, 115.4, 114.0,
113.4, 113.3, 59.2, 56.2, 56.0, 46.9, 37.9, 14.2, 10.0; IR (KBr, cm-1)
3454, 3367, 3233, 3128, 2974, 2938, 2844, 1705, 1607, 1508, 1451,
1382; MS (EI) m/z 407 (M+-79, 5%), 30 (M+-456, 100%); Found:
C, 59.24; H, 5.62; N, 5.72. Calc. for C24H27BrN2O4: C, 59.14; H,
5.58; N, 5.75%.
Experimental procedure for the N-alkylpyrroles
NaH (0.2 g, 5.7 mmol, 60% dispersion in mineral oil and previously
washed with dry hexane) was added portionwise to a solution
of the pyrrole (2.3 mmol) and 2-bromo-4,5-dimethoxyphenethyl
4-methylbenzenesulfonate (8, 1.9 g, 4.5 mmol) in dry dimethyl
sulfoxide (10 mL). The mixture was stirred at room temperature
for 2.0 h, and EtOAc (20 mL) was added followed by washing
with H2O and brine (3 ¥ 10 mL). The organic layer was dried
with Na2SO4 and evaporated in vacuo. The residue was purified by
flash column chromatography on silica gel to furnish the respective
N-alkylpyrrole.
Ethyl
1-(2-bromo-4,5-dimethoxyphenethyl)-5-methyl-4-(thio-
phen-2-yl)-1H-pyrrole-3-carboxylate (6d). From 7d (0.54 g,
2.3 mmol), purified by flash column chromatography on silica gel,
to furnish 0.77 g of 6d as a yellow oil, yield 70%. TLC (hexane–
EtOAc–Et3N, 60 : 30 : 10 v/v): Rf 0.35; 1H-NMR (300 MHz,
CDCl3) d (ppm): 1.18 (t, J = 7.2 Hz, 3H), 1.97 (s, 3H), 3.08 (t, J =
7.2 Hz, 2H), 3.72 (s, 3H), 3.85 (s, 3H), 4.06 (t, J = 6.9 Hz, 2H),
4.14 (q, J = 7.2 Hz, 2H), 6.3 (s, 1H), 6.87 (dd, J= 3.3 y 0.9 Hz,
1H), 6.99–7.02 (m, 2H), 7.24–7.27 (m, 2H); 13C-NMR (75 MHz,
CDCl3) d (ppm): 164.3, 148.8, 148.6, 136.4, 129.7, 128.7, 127.3,
126.3, 125.9, 124.8, 115.6, 114.9, 114.4, 114.0, 113.4, 59.3, 56.2,
56.0, 47.1, 37.8, 14.2, 10.0; IR (Film, cm-1) 3127, 3072, 2976,
2936, 2843, 1709, 1602, 1534, 1508, 1461, 1443; MS (EI) m/z
Ethyl
1-(2-bromo-4,5-dimethoxyphenethyl)-5-methyl-1H-
pyrrole-3-carboxylate (6a). From 7a (0.35 g, 2.3 mmol), purified
by flash column chromatography on silica gel, to furnish. 0.7 g of
6a as a yellow solid, m.p. 48 ◦C, yield 77%. TLC (hexane–EtOAc–
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398 (M+-79, 100%); Found: C, 55.18; H, 5.17; N, 2.95. Calc. for
C22H24BrNO4S: C, 55.23; H, 5.06; N, 2.93%.
59.5, 56.1, 55.9, 41.0, 29.3, 14.5, 11.9; IR (KBr, cm-1) 3432, 3107,
3013, 2977, 2935, 2843, 2677, 1685, 1609, 1581, 1529, 1468; MS
(EI) m/z 315 (M+, 100%); Found: C, 68.50; H, 6.75; N, 4.47. Calc.
for C18H21NO4: C, 68.55; H, 6.71; N, 4.44%.
1-(2-Bromo-4,5-dimethoxyphenethyl)-5-methyl-4-phenyl-1H-
pyrrole-3-carbonitrile (6e). From 7e (0.42 g, 2.3 mmol), purified
by flash column chromatography on silica gel, to furnish 0.58 g of
6e as a yellow solid, m.p. 160 ◦C, yield 60%. TLC (hexane–EtOAc–
Method b). A solution of N-alkylpyrrole 6a (0.59 g, 1.5 mmol)
and AIBN (0.07 g, 0.45 mmol) in degassed dry toluene (10 mL)
was heated at refluxing temperature, and n-Bu3SnH (0.48 mL,
1.8 mmol) was added dropwise. The reaction was stirred for 2 h.
After that time, the reaction was cooled to room temperature,
the solvent was removed under reduced pressure, and the crude
residue was purified by flash column chromatography on silica gel.
Hexane was first added to remove the n-Bu3SnBr, then hexane–
EtOAc–Et3N (70 : 25 : 5 to 50 : 45 : 5) was added to furnish the
pyrroloisoquinoline 5a (0.25 g), with a 53% yield.
1
Et3N, 60 : 30 : 10 v/v): Rf 0.35; H-NMR (300 MHz, CDCl3) d
(ppm): 2.06 (s, 3H), 3.08 (t, J = 6.9 Hz, 2H), 3.7 (s, 3H), 3.86 (s,
3H), 4.09 (t, J = 6.9 Hz, 2H), 6.3 (s, 1H), 7.02 (s, 1H), 7.08 (s, 1H),
7.26–7.43 (m, 5H); 13C-NMR (75 MHz, CDCl3) d (ppm): 148.9,
148.6, 133.4, 128.9, 128.5, 128.3, 127.3, 127.0, 126.8, 124.2, 116.7,
115.6, 114.1, 113.4, 92.1, 56.2, 56.0, 47.2, 37.7, 10.1; IR (KBr, cm-1)
3125, 3080, 3058, 2994, 2959, 2936, 2908, 2838, 2215, 1736, 1604,
1506, 1461, 1440, 1390, 1347; MS (EI) m/z 345 (M+-79, 100%);
Found: C, 62.10; H, 5.00; N, 6.58. Calc. for C22H21BrN2O2: C,
62.13; H, 4.98; N, 6.59%.
Method c). To a refluxing solution of the N-alkylpyrrole 6a
(0.59 g, 1.5 mmol) in degassed dry toluene (10 mL), a solution
of n-Bu3SnH (1.0 mL, 3.7 mmol) in toluene (5 mL) was added
dropwise (syringe pump) over 7 h. During that time, solid dilauroyl
peroxide (DLP) was added portionwise (1.49 g, 3.7 mmol, 0.11
g/30 min). The solvent was removed under reduced pressure and
the crude residue was purified by flash column chromatography
on silica gel. Hexane was first added to remove the n-Bu3SnBr,
then hexane–EtOAc–Et3N (70 : 25 : 5 to 50 : 45 : 5) was added to
furnish the desired pyrroloisoquinoline 5a (0.33 g), with a 70%
yield.
Ethyl 1-(2-bromo-4,5-dimethoxyphenethyl)-4-(3-(4-(cyclohexyl-
methyl)piperazine-1-carbonyl)-5-methyl-1H-pyrrole-3-carboxylate
(15). From 14 (1.0 g, 2.3 mmol), purified by flash column
chromatography on silica gel, to furnish 0.94 g of 15 as a white
solid, m.p. 158 ◦C, yield 60%. TLC (hexane–EtOAc–Et3N,
1
60 : 30 : 10 v/v): Rf 0.26; H-NMR (300 MHz, CDCl3) d (ppm):
0.81–0.92 (m, 2H), 1.13–1.28 (m, 6H), 1.38–1.48 (m, 1H),
1.69–1.79 (m, 5H), 1.96 (s, 3H), 2.14 (d, J = 6.9 Hz, 2H), 2.34
(brs, 2H), 2.45 (brs, 2H), 3.08 (t, J = 7.2 Hz, 2H), 3.53 (brs, 2H),
3.73 (s, 3H), 3.77 (brs, 2H), 3.87 (s, 3H), 4.07 (t, J = 7.2 Hz, 2H),
4.12 (q, J = 7.2 Hz, 2H), 6.37 (s, 1H), 7.03 (s, 1H), 7.25–7.41 (m,
5H); 13C-NMR (75 MHz, CDCl3) d (ppm): 170.5, 164.3, 148.9,
148.6, 135.5, 135.1, 131.6, 129.3, 128.8, 128.0, 127.7, 126.0, 125.1,
122.5, 115.8, 114.1, 113.6, 113.2, 65.5, 59.1, 56.2, 56.0, 54.0, 47.8,
47.0, 45.8, 42.2, 37.8, 35.0, 31.8, 26.7, 26.1, 14.3, 14.2, 9.9; IR
(KBr, cm-1) 3121, 3054, 2979, 2921, 2845, 2804, 2767, 1704, 1624,
1509, 1445, 1405; MS (EI) m/z 679 (M+, 10%), 681 (M++2, 10%),
596 (M+-83, 100%); Found: C, 63.54; H, 6.83; N, 6.10. Calc. for
C36H46BrN3O5: C, 63.52; H, 6.81; N, 6.17%.
Ethyl 8,9-dimethoxy-3-metyl-2-phenyl-5,6-dihydropyrrolo[2,1-
a]isoquinoline-1-carboxylate (5b). From the N-alkylpyrrole 6b
(0.71 g, 1.5 mmol), purified by flash column chromatography on
silica gel, to furnish 0.47 g (yield 80%) of 5b as a white solid, m.p.
170◦ C (lit.ref. 17a 167–168◦ C), following the method c described
1
above. TLC (hexane–AcOEt:Et3N, 50 : 45 : 5 v/v): Rf 0.54; H-
NMR (300 MHz, CDCl3) d (ppm): 0.80 (t, J = 7.2 Hz, 3H), 2.09
(s, 3H), 2.92 (t, J = 6.9 Hz, 2H), 3.82 (s, 3H), 3.84 (s, 3H), 3.84 (t,
2H), 3.94 (q, J = 7.2 Hz, 2H), 6.63 (s, 1H), 7.16–7.31 (m, 5H), 7.9
(s, 1H); 13C-NMR (75 MHz, CDCl3) d (ppm): 167.0, 148.3, 148.2,
136.8, 130.8, 130.1, 127.6, 125.9, 125.5, 125.2, 123.9, 121.8, 111.3,
111.0, 59.7, 56.1, 41.2, 29.2, 13.6, 10.1, 1.0; IR (KBr, cm-1) 3093,
3048, 2985, 2958, 2904, 2873, 2833, 2049, 1957, 1895, 1835, 1765,
1691, 1604, 1533, 1498, 1459, 1389; MS (EI) m/z 391 (M+, 100%);
Found: C, 73.66; H, 6.45; N, 3.58. Calc. for C24H25NO4: C, 73.64;
H, 6.44; N, 3.58%.
Experimental procedure for the 5,6-dihydropyrrolo[2,1-a]-
isoquinolines
Ethyl 8,9-dimethoxy-3-metyl-5,6-dihydropyrrolo[2,1-a]isoquino-
line-1-carboxylate (5a).
Method a). To a solution of N-alkylpyrrole 6a (0.67 g,
1.7 mmol) in dry DMF (10 mL) was added Pd(OAc)2 (0.125 g,
0.33 mmol), PPh3 (0.089 g, 0.33 eq.), n-Bu4NBr (0.55 g, 1.7 mmol),
and K2CO3 (0.47 g, 3.4 mmol). The resulting suspension was
stirred for 12 h at 120 ◦C. Subsequently, the reaction was cooled
to room temperature, and H2O was added. The solution was
extracted with EtOAc (3 ¥ 10 mL). The organic layer was washed
with H2O and brine (3 ¥ 10 mL), dried with Na2SO4, and then
evaporated in vacuo. The residue was purified by flash column
chromatography on silica gel, to furnish the pyrroloisoquinoline
5a (0.21 g) as a white solid, m.p. 130◦ C, yield 40%. TLC (hexane–
AcOEt–Et3N, 50 : 45 : 5 v/v): Rf 0.54; 1H-NMR (300 MHz,
CDCl3) d (ppm): 1.35 (t, J = 7.2 Hz, 3H), 2.23 (d, J = 0.9 Hz,
3H), 2.94 (t, J = 6.6 Hz, 2H), 3.87 (t, J = 6.9 Hz, 2H), 3.90 (s, 3H),
3.96 (s, 3H), 4.29 (q, J = 7.2 Hz, 2H), 6.43 (d, J = 0.9 Hz, 1H), 6.70
(s, 1H), 8.44 (s, 1H) 13C-NMR (75 MHz, CDCl3) d (ppm): 165.5,
148.0, 147.6, 132.9, 127.2, 125.2, 121.6, 111.5, 110.4, 110.3, 110.0,
Ethyl 2-(3-aminophenyl)-8,9-dimethoxy-3-methyl-5,6-dihydro-
pyrrolo[2,1-a]isoquinoline-1-carboxylate (5c). From the N-
alkylpyrrole 6c (0.73 g, 1.5 mmol), purified by flash column
chromatography on silica gel, to furnish 0.52 g (yield 85%) of 5c
as a yellow solid, m.p. 168 ◦C (lit.ref. 4a 170–172 ◦C), following the
method c described above. TLC (hexane–AcOEt:Et3N, 50 : 45 : 5
v/v): Rf 0.25; 1H-NMR (300 MHz, CDCl3) d (ppm): 0.96 (t, J =
7.2 Hz, 3H), 2.18 (s, 3H), 2.98 (t, J = 6.6 Hz, 2H), 3.46 (brs, 2H,
–NH2), 3.90 (s, 3H), 3.91 (s, 3H, overlapping a triplet, 2H), 4.05 (q,
J = 7.2 Hz, 2H), 6.6–6.71 (m, 4H), 7.1–7.15 (m, 1H), 7.95 (s, 1H);
13C-NMR (75 MHz, CDCl3) d (ppm): 167.2, 147.9, 147.7, 145.7,
137.5, 130.4, 128.5, 125.4, 125.1, 123.6, 121.4, 120.7, 116.9, 112.9,
110.6, 110.2, 59.9, 56.0, 55.9, 41.1, 29.1, 13.7, 10.3; IR (KBr, cm-1)
3455, 3369, 3232, 2933, 2842, 1691, 1608, 1531, 1494, 1467; MS
(EI) m/z 406 (M+, 100%); Found: C, 70.97; H, 6.48; N, 6.87. Calc.
for C24H26N2O4: C, 70.92; H, 6.45; N, 6.89%.
4380 | Org. Biomol. Chem., 2010, 8, 4374–4382
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Ethyl
8,9-dimethoxy-3-methyl-2-(thiophen-2-yl)-5,6-dihydro-
Smart Apex CCD diffractometer with area detector (graphite
˚
pyrrolo[2,1-a]isoquinoline-1-carboxylate (5d). From the N-
alkylpyrrole 6d (0.72 g, 1.5 mmol), purified by flash column
chromatography on silica gel, to furnish 0.54 g (yield 90%)
of 5d as a yellow solid, m.p. 114 ◦C, following the method c
described above. TLC (hexane–AcOEt–Et3N, 50 : 45 : 5 v/v): Rf
monochromator, l = 0.71073 A◦) with a resolution of (sin q/l)max
=
-1
˚
0.83 A at a temperature of 21 C. The reflections were corrected
for absorption and scaled on the basis of multiple measured reflec-
tions using an empirical method. (0.9832–0.9566 correction range)
5912 reflections were unique (Rint = 0.0581). The structure was
solved using Direct Methods (program SHELXS-97) and refined
with SHELXL-97 against F2 from all reflections. Non hydrogen
atoms were refined with anisotropic displacement parameters.
All hydrogen atoms were located in difference Fourier maps.
Methyl and phenyl hydrogen atoms were refined with a riding
model; all other hydrogen atoms were refined freely with isotropic
displacement parameters. 171 parameters were refined with no
restraints. R1/wR2[I > 2s(I)]: 0.0658/0.1377. R1/wR2[all refl.]:
0.1118/0.1587, S = 0.917. The maximum residual electron density
1
0.51; H-NMR (300 MHz, CDCl3) d (ppm): 1.01 (t, J = 7.2 Hz,
3H), 2.22 (s, 3H), 2.98 (t, J = 6.6 Hz, 2H), 3.90 (s, 3H), 3.91 (s,
3H), 3.92 (t, J = 6.6 Hz, 2H), 4.90 (q, J = 7.2 Hz, 2H), 6.71 (s,
1H), 6.89 (dd, J= 3.6 y 1.2 Hz, 1H), 7.04 (dd, J= 5.1 y 3.3 Hz, 1H),
7.28 (dd, J= 5.4 y 1.2 Hz, 1H), 7.92 (s, 1H); 13C-NMR (75 MHz,
CDCl3) d (ppm): 166.7, 148.1, 147.8, 137.5, 130.8, 127.4, 126.6,
126.5, 125.1, 124.6, 121.2, 115.3, 111.1, 110.6, 110.3, 60.1, 56.0,
55.9, 41.3, 29.1, 13.7, 10.4; IR (KBr, cm-1) 3096, 2979, 2921,
2874, 2850, 1691, 1609, 1584, 1541, 1518, 1458, 1388; MS (EI)
m/z 397 (M+, 100%); Found: C, 66.46; H, 5.80; N, 3.48. Calc. for
C22H23NO4S: C, 66.48; H, 5.83; N, 3.52%.
-3
˚
peak had a height of 0.230 and -0.143 A .
8,9-Dimethoxy-3-methyl-2-phenyl-5,6-dihydropyrrolo[2,1-a]iso-
quinolne-1-carbonitrile (5e). From the N-alkylpyrrole 6e (0.64 g,
1.5 mmol), purified by flash column chromatography on silica gel,
Cell lines and culture medium
The compounds were screened in vitro against six human cancer
cell lines: HCT-15 (human colorectal adenocarcinoma), MCF-
7 (human mammary adenocarcinoma), K-562 (human chronic
myelogenous leukemia), U-251 (human glioblastoma), PC-3
(human prostatic adenocarcinoma), and SKLU-1 (human lung
adenocarcinoma) cell lines, supplied by the National Cancer
Institute (NCI, USA). The human tumor cytotoxicities were
determined following protocols established by the NCI.23 The cell
lines were cultured in RPMI-1640 medium supplemented with
10% fetal bovine serum, 2 mM L-glutamine, 10000 units/mL
penicillin G sodium, 10000 mg mL-1 streptomycin sulfate, 25
mg mL-1 amphotericin B (Gibco), and 1% non-essential amino
acids (Gibco). Cells were maintained at 37◦ C in a humidified
atmosphere with 5% CO2. The viability of the cells used in the
experiments exceeded 95%, as determined with a trypan blue assay.
◦
to furnish 0.39 g (yield 75%) of 5e as a white solid, m.p. 233 C,
following the method c described above. TLC (hexane–AcOEt–
Et3N, 50 : 45 : 5 v/v): Rf 0.34; 1H-NMR (300 MHz, CDCl3) d
(ppm): 2.29 (s, 3H), 3.04 (t, J = 6.6 Hz, 2H), 3.91 (s, 3H), 3.96 (s,
3H), 3.98 (t, J = 6.6 Hz, 2H), 6.74 (s, 1H), 7.27–7.44 (m, 5H), 7.82
(s, 1H); 13C-NMR (75 MHz, CDCl3) d (ppm): 148.8, 148.5, 135.2,
133.3, 129.1, 128.5, 126.8, 125.7, 124.6, 124.0, 119.9, 118.4, 110.9,
106.9, 86.2, 56.1, 56.0, 41.2, 28.4, 10.3; IR (KBr, cm-1) 3047, 2998,
2945, 2908, 2839, 2206, 1734, 1606, 1536, 1498, 1481, 1454, 1436;
MS (EI) m/z 344 (M+, 100%); Found: C, 76.69; H, 5.88; N, 8.10.
Calc. for C22H20N2O2: C, 76.72; H, 5.85; N, 8.13%.
Ethyl 2-(3-(4-(cyclohexylmethyl)piperazine-1-carbonyl)phenyl)-
8,9-dimethoxy-3-methyl-5,6-dihydropyrrolo[2,1-a]isoquinoline-1-
carboxylate (16). From the N-alkylpyrrole 15 (1.0 g, 1.5 mmol),
purified by flash column chromatography on silica gel, to furnish
0.81 g (yield 90%) of 16 as a white solid, m.p. 160 ◦C, following the
method c described above. TLC (hexane–AcOEt–Et3N, 50 : 45 : 5
Cytotoxicity assay. Cytotoxicity, after treatment of the tumor
cells with the test compounds, was determined using the protein
binding dye, sulforhodamine B (SRB), in a microculture assay
to measure cell viability and cell growth.23 The cells were removed
from the tissue culture flasks by treatment with trypsin and diluted
with fresh media. Of the cell suspension, 100 mL, containing 5000
or 7500 cells per well, were pipetted into 96 well microtiter plates
(Costar), and the material was incubated at 37◦ C for 24 h in a
5% CO2 atmosphere. Subsequently, a 100 mL aliquot of the test
compounds in solution, obtained by dilution of the stocks, was
added to each well. The cultures were exposed for 48 h to the
drug at concentrations ranging from 1 ¥ 10-3 to 10 mM. After
the incubation period, cells were fixed to the plastic substratum
by the addition of 50 mL cold 50% aqueous trichloroacetic acid.
The plates were incubated at 4◦ C for 1 h, washed with tap H2O,
and air-dried. The trichloroacetic acid-fixed cells were stained by
the addition of 0.4% SRB. Free SRB solution was then removed
by washing with 1% aqueous acetic acid. The plates were then
air-dried, and the bound dye was solubilized by the addition of
10 mM unbuffered Tris base (100 mL). The plates were placed on
a shaker for 5 min, and the absorption was determined at 515 nm
using an ELISA plates reader (Bio-Tex Instruments).
1
v/v): Rf 0.28; H-NMR (300 MHz, CDCl3) d (ppm): 0.85–0.95
(m, 2H), 0.92 (t, J = 6.9 Hz, 3H), 1.13–1.28 (m, 3H), 1.44–1.50 (m,
1H), 1.68–1.79 (m, 5H), 2.14–2.15 (m, 5H), 2.36 (brs, 2H), 2.44
(brs, 2H), 2.99 (t, J = 6.6 Hz, 2H), 3.5 (brs, 2H), 3.79 (brs, 2H),
3.90 (s, 3H), 3.92 (s, 3H), 3.92 (t, 2H), 4.03 (q, J = 7.2 Hz, 2H),
6.73 (s, 1H), 7.29–7.42 (m, 4H), 7.97 (s, 1H); 13C-NMR (75 MHz,
CDCl3) d (ppm): 170.3, 166.5, 148.2, 147.8, 136.8, 135.4, 131.3,
131.1, 128.5, 127.8, 125.7, 125.3, 124.8, 122.9, 121.2, 110.7 (2C),
65.4, 59.7, 56.0, 55.9, 53.6, 47.6, 42.1, 41.2, 34.9, 31.8, 29.1, 26.7,
26.0, 13.7, 10.2; IR (KBr, cm-1) 3102, 2980, 2929, 2849, 2808, 2770,
1737, 1691, 1618, 1578, 1528, 1467, 1441; MS (EI) m/z 599 (M+,
80%), 516 (M+-83, 100%); Found: C, 72.02; H, 7.53; N, 7.00. Calc.
for C36H45N3O5: C, 72.09; H, 7.56; N, 7.01%.
Crystallographic data
Crystal structure analysis of 16 (solved by R. A. Toscano):
C36H45N3O5, FW = 599.75, colorless, 0.428 ¥ 0.162 ¥ 0.162 mm3,
˚
monoclinic, P◦2l/n, a = 10.400(1), b = 11.217(1), c = 27.800(2) A,
3
-3
˚
b = 96.122(1) , V = 3224.6(5) A , Z = 4, Dx = 1.235 Mg m ,
m = 0.082 mm-1, 26547 reflections were measured on a Bruker
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139, 69161j); (c) W. K. Anderson, A. R. Heider, R. Natarajan and
J. A. Yucht, J. Med. Chem., 1988, 31, 2097; (d) D. Pla, A. Marchal,
C. A. Olsen, A. Francesch, C. Cuevas, F. Albericio and M. Alvarez,
J. Med. Chem., 2006, 49, 3257; (e) W. K. Anderson, H. L. McPeterson
Jr., J. S. New and A. C. Rick, J. Med. Chem., 1984, 27, 1321; (f) M. T.
Niewohner, et al. GB 1,153,670 (Chem. Abstr., 1969, 71, 81215q); (g) C.
Rossi, WO 98/55118 (Chem. Abstr., 1999, 130, 57206d).
5 O. Barun, S. Chakrabarti, H. Ila and H. Junjappa, J. Org. Chem., 2001,
66, 4457.
6 (a) S. Espenlaub, H. Gerster and G. Maas, Arkivoc, 2007, iii, 114;
(b) N. N. Polygalova, A. G. Mikhailovskii, E. V. Vikhareva and M. I.
Vakhrin, Chem. Heterocycl. Compd., 2007, 43, 900; (c) B.-X. Zhao, Y.
Yu and S. Eguchi, Tetrahedron, 1996, 52, 12049; (d) T. A. Abdallah
and K. M. Dawood, Tetrahedron, 2008, 64, 7890; (e) M. Nyerges and
L. To˝ke, Tetrahedron Lett., 2005, 46, 7531; (f) R. Grigg, P. Myers, A.
Somasunderam and V. Sridharan, Tetrahedron, 1992, 48, 9735.
7 See references 1, 2b, 2d–e, 4a–b and 5.
Acknowledgements
´
Financial support from the DGAPA, UNAM (project PAPIIT-
IN213407) is gratefully acknowledged. We also thank R. Patin˜o,
A. Pen˜a, E. Huerta and E. Garc´ıa-Rios, L. Velasco, and J. Pe´rez for
technical support and Dr A. Toscano for X-ray crystallography.
During the experimentation process Paul E. Reyes-Gutie´rrez was
a CONACyT Graduate Scholarship holder and Jose´ R. Camacho
participated on the Movilidad Red de Macrouniversidades pro-
gram, DID-USB, FONACIT-S3-2009000393.
Notes and references
1 (a) I. Coldham, S. Jana, L. Watson and N. G. Martin, Org. Biomol.
Chem., 2009, 7, 1674; (b) F. Xu, B. Simmons, R. A. Reamer, E. Corley,
J. Murry and D. Tschaen, J. Org. Chem., 2008, 73, 312; (c) K. R. Bailey,
A. J. Ellis, R. Reiss, T. J. Snape and N. J. Turner, Chem. Commun.,
2007, 3640; (d) F. D. King, Tetrahedron, 2007, 63, 2053; (e) N. Meyer
and T. Opatz, Eur. J. Org. Chem., 2006, 3997; (f) H.-J. Kno¨lker and
S. Agarwal, Tetrahedron Lett., 2005, 46, 1173; (g) Q. Zhang, G. Tu, Y.
Zhao and T. Cheng, Tetrahedron, 2002, 58, 6795.
8 (a) C. Blaszykowski, E. Aktoudianakis, D. Alberico, C. Bressy, D. G.
Hulcoop, F. Jafarpour, A. Joushaghani, B. Laleu and M. Lautens,
J. Org. Chem., 2008, 73, 1888; (b) C. A. Olsen, N. Perera, F. Albericio
´
and M. Alvarez, Tetrahedron Lett., 2005, 46, 2041.
9 See references 2f and 3a–b.
10 A. M. van Leusen, H. Siderius, B. E. Hoogenboom and D. van Leusen,
Tetrahedron Lett., 1972, 13, 5337.
2 Synthesis: (a) J. S. Yadav, K. U. Gayathri, B. V. S. Reddy and A. R.
Prasad, Synlett, 2009, 43; (b) J. C. Liermann and T. Opatz, J. Org.
Chem., 2008, 73, 4526; (c) L. C. Axford, K. E. Holden, K. Hasse,
M. G. Banwell, W. Steglich, J. Wagler and A. C. Willis, Aust. J. Chem.,
2008, 61, 80; (d) P. Ploypradith, T. Petchmanee, P. Sahakitpichan,
N. D. Litvinas and S. Ruchirawat, J. Org. Chem., 2006, 71, 9440; (e) P.
Ploypradith, R. K. Kagan and S. Ruchirawat, J. Org. Chem., 2005, 70,
5119; (f) S. T. Handy, Y. Zhang and H. Bregman, J. Org. Chem., 2004,
11 (a) Y. Li, Z. Li, F. Li, Q. Wang and F. Tao, Tetrahedron Lett., 2005, 46,
6159; (b) J. P. Genet, E. Blart and M. Savignac, Synlett, 1992, 715.
12 A. M. van Leusen, R. J. Bouma and O. Possel, Tetrahedron Lett., 1975,
16, 3487.
13 M. Cox, R. H. Prager and D. M. Riessen, Arkivoc, 2001, vii,
88.
14 J. B. Bremner and W. Sengpracha, Tetrahedron, 2005, 61, 5489.
15 R. Mart´ınez, M. Menez-Arzate and M. T. Ram´ırez-Apan, Bioorg. Med.
Chem., 2009, 17, 1849.
´
69, 2362; (g) P. Cironi, C. Cuevas, F. Albericio and M. A. Alvarez,
Tetrahedron, 2004, 60, 8669. Biological activity: (h) M. Chittchang, P.
Batsomboon, S. Ruchirawat and P. Ploypradith, Chem. Med. Chem.,
2009, 4, 457; (i) D. Baunbaek, N. Trinker, Y. Ferandin, O. Lozach, P.
Ploypradith, S. Rucirawat, F. Ishibashi, M. Iwao and L. Meijer, Mar.
Drugs, 2008, 6, 514; (j) H. Fan, J. Peng, M. T. Hamann and J.-F. Hu,
Chem. Rev., 2008, 108, 264; (k) C. Tardy, M. Facompre´, W. Laine, B.
Baldeyrou, D. Garc´ıa-Gravalos, A. Francesch, C. Mateo, A. Pastor,
J. A. Jime´nez, I. Manzanares, C. Cuevas and C. Bailly, Bioorg. Med.
Chem., 2004, 12, 1697; (l) C. Bailly, Curr. Med. Chem.: Anti-Cancer
Agents, 2004, 4, 363; (m) F. Ishibashi, S. Tanabe, T. Oda and M. Iwao,
J. Nat. Prod., 2002, 65, 500.
16 M. A. Guerrero, R. Cruz-Almanza and L. D. Miranda, Tetrahedron,
2003, 59, 4953.
17 (a) H. Meyer, Liebigs Ann. Chem., 1981, 1534; (b) U. Niewohner, et al.
WO 03/14116 (Chem. Abstr., 2003, 138, 187651w).
18 S. H. Reich, T. Johnson, M. B. Wallace, S. E. Kephart, S. A. Fuhrman,
S. T. Worland, D. A. Matthews, T. F. Hendrickson, F. Chan, J. Meador,
R. A. Ferre, E. L. Brown, D. M. DeLisle, A. K. Patick, S. L. Binford
and C. E. Ford, J. Med. Chem., 2000, 43, 1670.
19 (a) B. W. Horrom, M. Freifelder and G. R. Stone, J. Am. Chem. Soc.,
1955, 77, 753; (b) N. A. Meanwell, R. D. Dennis, H. R. Roth, M. J.
Rosenfeld, E. C. R. Smith, J. J. K. Wright, J. O. Buchanan, C. L.
Brassard, M. Gamberdella, E. Gillespie, S. M. Seiler, G. B. Zavoico
and J. S. Fleming, J. Med. Chem., 1992, 35, 2688.
20 To an ether-solution of 16, was added some drops of HCl (36.46%) and
the resulting precipitate (16·HCl) was filtrated and washed with ether.
21 E. Marco, W. Laine, C. Tardy, A. Lansiaux, M. Iwao, F. Ishibashi, C.
Bailly and F. Gago, J. Med. Chem., 2005, 48, 3796.
22 H. Ulukan and P. W. Swaan, Drugs, 2002, 62, 2039.
23 P. Skehan, R. Storeng, D. Scudiero, A. Monks, J. McMahon, D. Vistica,
J. T. Warren, H. Bokesch, S. Kenney and M. R. Boyd, J. Natl. Cancer
Inst., 1990, 82, 1107.
3 Synthesis: (a) N. Fujikawa, T. Ohta, T. Yamaguchi, T. Fukuda, F.
Ishibashi and M. Iwao, Tetrahedron, 2006, 62, 594; (b) D. Pla, A.
´
Marchal, C. A. Olsen, F. Albericio and M. Alvarez, J. Org. Chem.,
2005, 70, 8231. Biological activity: (c) J. Kluza, M.-A. Gallego, A.
Loyens, J.-C. Beauvillain, J.-M. Ferna´ndez Sousa-Faro, C. Cuevas, P.
Marchetti and C. Bailly, Cancer Res., 2006, 66, 3177; (d) M. Facompre´,
C. Tardy, C. Bal-Mahieu, P. Colson, I. Manzanares, C. Cuevas and C.
Bailly, Cancer Res., 2003, 63, 7392.
4 (a) U. Niewohner, et al. WO 02/48144 (Chem. Abstr., 2002, 137,
47106b); (b) C. Zhang, et al. WO 03/051877 (Chem. Abstr., 2003,
4382 | Org. Biomol. Chem., 2010, 8, 4374–4382
This journal is
The Royal Society of Chemistry 2010
©