Synthesis and evaluation as potential anticancer agents of novel tetracyclic indenoquinoline derivatives

Article abstract of DOI:10.1016/j.bmc.2012.12.026

We report the synthesis and evaluation as potential anticancer agents of a series of tetracyclic indenoquinolines. The compounds, which are obtained through the photoisomerization of Diels-Alder adducts formed between purpurogallin derivatives and nitrosobenzene, have in vitro antiproliferative activities in the μM to nM range against breast (MCF-7), lung epithelial (A-549), and cervical (HeLa) adenocarcinoma cells. The cytotoxicities of several of the novel tetracycles are comparable to or better than that of camptothecin. A strong correlation between the activity of the compounds and their aromaticity and planarity was observed, suggesting a mode of action similar to that of topoisomerase poisons.

Full text of DOI:10.1016/j.bmc.2012.12.026

Bioorganic & Medicinal Chemistry 21 (2013) 1143–1149
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and evaluation as potential anticancer agents of novel
tetracyclic indenoquinoline derivatives
Shubhashis Chakrabarty a, Michael S. Croft a, Melissa G. Marko b, Guillermo Moyna a,c,
⇑
a Department of Chemistry & Biochemistry, University of the Sciences in Philadelphia, 600 South Forty-Third Street, Philadelphia, PA 19104, USA
b Department of Biological Sciences, University of the Sciences in Philadelphia, 600 South Forty-Third Street, Philadelphia, PA 19104, USA
c Departamento de Química del Litoral, Polo Agroalimentario y Agroindustrial, Universidad de la República, Ruta 3 Km 363, Paysandú 60000, Uruguay
a r t i c l e i n f o
a b s t r a c t
Article history:
We report the synthesis and evaluation as potential anticancer agents of a series of tetracyclic indeno-
quinolines. The compounds, which are obtained through the photoisomerization of Diels–Alder adducts
formed between purpurogallin derivatives and nitrosobenzene, have in vitro antiproliferative activities in
Received 15 November 2012
Revised 17 December 2012
Accepted 25 December 2012
Available online 3 January 2013
the lM to nM range against breast (MCF-7), lung epithelial (A-549), and cervical (HeLa) adenocarcinoma
cells. The cytotoxicities of several of the novel tetracycles are comparable to or better than that of
camptothecin. A strong correlation between the activity of the compounds and their aromaticity and
planarity was observed, suggesting a mode of action similar to that of topoisomerase poisons.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Anticancer activity
Indenoquinolines
Photoisomerization
Topoisomerase
1. Introduction
overall structure of this system resembles that of known topoI
poisons. Furthermore, the tetracycle could be easily aromatized
Given their central role in DNA replication, topoisomerases I
and II (topoI and topoII) are well-established chemotherapeutic
targets.1–9 Indeed, inhibitors of these enzymes are employed for
the treatment of a number of ailments, ranging from bacterial
infections to various cancers. Tetracyclines such as camptothecin,
an indolizinoquinoline, and doxorubicin, an anthracycline, are
representative topoI and topoII poisons, respectively.10,11 Two
water-soluble derivatives of the former, topotecan and irinotecan,
have received FDA approval for the treatment of ovarian, cervical,
lung, and colon cancer. As with other antineoplastic drugs, toxicity
and the emergence of multidrug resistance through induction of
ATP-dependent P-glycoproteins and other efflux pumps limits
the clinical efficacy of these molecules.12 Thus, there have been
important efforts to design inhibitors that can overcome these
limitations. This is nicely illustrated by the work on indenoisoquin-
olines, molecules that display a mode of action similar to campto-
thecin and its analogs but have better chemical stability, form
longer-lived complexes with topoI, and are not the substrates of
efflux pumps.13–15
to attain the planarity which is believed to be critical in this type
of inhibitors.7,8,10,17 We therefore set out to prepare a series of
compounds based on derivatives of this molecular framework
and evaluate their antiproliferative activity, and our results are
summarized in this report. As described herein, the in vitro cyto-
toxicity of several of the novel indenoquinolines against breast,
lung, and cervical cancer cells is comparable to or better than that
of camptothecin in the same assays.
2. Results and discussion
2.1. Chemistry
Based on a strategy employed in earlier exploratory structure–
activity relationship (SAR) studies,18–21 we prepared a preliminary
set of trimethylpurpurogallin derivatives with varying ether sub-
stituents at the C-1 position employing standard Williamson ether-
ification conditions (compounds 2a–j, Scheme 2). As shown in our
previous work, this abridged library of alkyl and aryl derivatives is
straightforward to synthesize and leads to compounds with a rep-
resentative range of molecular sizes and physicochemical proper-
ties.18–21 Ethers 2a–j were then cleanly transformed into Diels–
Alder adducts 3a–j by treatment with nitrosobenzene following
the conditions detailed in Scheme 2. Irradiation of benzene solu-
tions of these bridged oxazines in a soda lime glass reactor afforded
the fused tetracyclic framework (compounds 4a–j, Scheme 3). A
Our group recently reported the preparation of a new tetrahydr-
oindenoquinoline scaffold through photoisomerization of Diels–Al-
der adducts formed between purpurogallin derivatives and
nitrosobenzene (Scheme 1).16 While it bears four sp3 centers, the
⇑
Corresponding author. Tel./fax: +598 4722 7950.
E-mail address: gmoyna@fq.edu.uy (G. Moyna).
0968-0896/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2012.12.026

1144
S. Chakrabarty et al. / Bioorg. Med. Chem. 21 (2013) 1143–1149
Table 1
O
RO
O
RO
OMe
Growth inhibitory activity of compounds 4a–j
MeO
MeO
MeO
MeO
H
CO2Me
hν
Compound
GI50 (lM)
O
MCF-7
A-549
HeLa
N
4a
4b
4c
4d
4e
4f
4g
4h
7.500
27.00
12.00
29.00
30.00
31.00
27.00
20.00
17.00
25.00
0.002
12.50
20.00
20.10
9.900
15.50
11.00
23.00
13.00
25.00
9.500
0.007
13.00
8.000
8.000
24.00
20.50
10.50
5.100
11.00
20.00
9.500
0.050
H
HN
Scheme 1. Photoisomerization of benzotropolone Diels–Alder adducts.
O
O
HO
RO
1
4i
4j
OMe
OMe
9
MeO
MeO
MeO
MeO
9a
8
Camptothecin
a or b
2
7
3
4a
6
4
5
1
2a-j
dicyano-1,4-benzoquinone (DDQ) in refluxing benzene (Scheme 3).
As anticipated, the reaction proceeded smoothly and its success
could be conveniently confirmed by the lack of the NMR signals
corresponding to the 4b, 5, 10, and 10a protons in the final
products.
O
a - R = Me
b - R = Et
c - R = n-Pr
d - R = n-Bu
e - R = Allyl
f - R = Bn
RO
OMe
MeO
MeO
c
O
N
g - R = pF-Bn
h - R = oF-Bn
i - R = pCl-Bn
2.2. Biology
j - R = pOMe-Bn
The cytotoxic activity of the novel indenoquinolines and their
tetrahydroindenoquinoline precursors was evaluated against
breast (MCF-7), lung epithelial (A-549), and cervical (HeLa) adeno-
carcinoma cells. The 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltet-
razolium bromide (MTT) colorimetric assay,23 which measures the
reduction of the tetrazolium bromide salt into a formazan dye by
mitochondrial dehydrogenases in treated versus untreated cells,
was employed. The results are summarized in Tables 1 and 2. For
compounds 4a–j, GI50 values were all in the micromolar range.
While there is no clear correlation between cytotoxicity and the
size or nature of the substituent on the C-1 carbon, tetrahydroinde-
noquinolines bearing aromatic ethers are, on average, more active
than aliphatic derivatives. Regardless, compounds in this series are
100- to 15000-fold less active than camptothecin in the MTT assay.
On the other hand, indenoquinolines 5a–j displayed submi-
cromolar to nanomolar GI50 values against the three cell lines stud-
ied. Compounds 5a, 5f, 5g, 5h, 5i, and 5j showed cytotoxicities
comparable to that of camptothecin against MCF-7 cells. Ethers
5b, 5f, 5g, 5h, and 5i were comparable to, and 5a and 5j were better
3a-j
Scheme 2. Reagents and conditions: (a) (CH3)2SO4, NaOH, H2O, rt (2a); (b) R–X,
NaOH, DMSO, rt (2b–j); (c) Ph–N@O, benzene, rt.
detailed study of this reaction has revealed that the photoisomer-
ization involves both the b,c-unsaturated ketone and –N–O– moi-
eties present in the substrates, proceeds through the formation of
allyl, aroyl, and
stereoselective.16
a-carbonyl radical intermediates, and is highly
It is worth noting that while the yields of the phototransforma-
tions are moderate, the only impurities found in the crude irradia-
tion mixtures are the starting materials, adducts 3a–j, and their
retro Diels–Alder decomposition products, ethers 2a–j.18,22 Indeed,
conversion yields ranging from 60 to 75% are observed for this step
if the recovered starting materials are taken into account.
The tetrahydroindenoquinolines were then converted into aro-
matic indenoquinolines 5a–j by oxidation with 2,3-dichloro-5,6-
O
RO
RO
O
OMe
1
MeO
MeO
MeO
11a
11
H
10
CO2Me
a
2
10a
O
9a
9
4a
3
4b
N
MeO
4
H
HN
8
5a
5
6
7
4a-j
3a-j
a - R = Me
b - R = Et
c - R = n-Pr
d - R = n-Bu
e - R = Allyl
f - R = Bn
RO
O
N
MeO
CO2Me
b
MeO
g - R = pF-Bn
h - R = oF-Bn
i - R = pCl-Bn
j - R = pOMe-Bn
5a-j
Scheme 3. Reagents and conditions: (a) h
m
, benzene, 5 °C; (b) DDQ, benzene, reflux.

S. Chakrabarty et al. / Bioorg. Med. Chem. 21 (2013) 1143–1149
1145
Table 2
Nicolet Avatar 370 DTGS FT-IR spectrophotometer. NMR experi-
ments were performed on Bruker AVANCE and AVANCE-III 400
spectrometers operating at 1H and 13C frequencies of 400.13 and
100.61 MHz, respectively, using CDCl3 as solvent. Chemical shifts
(d) are in ppm relative to the residual solvent signal (7.28 and
77.0 ppm for 1H and 13C, respectively), and coupling constants
(J) are reported in Hz. HR-MS spectra were recorded on a Thermo
Scientific Exactive Orbitrap mass spectrometer equipped with an
atmospheric solids analysis probe (ASAP).25
Growth inhibitory activity of compounds 5a–j
Compound
GI50 (lM)
MCF-7
A-549
HeLa
5a
5b
5c
5d
5e
5f
5g
5h
0.002
0.020
0.010
0.020
0.040
0.005
0.008
0.008
0.006
0.007
0.002
0.005
0.010
0.110
0.098
0.025
0.008
0.008
0.010
0.010
0.006
0.007
0.110
0.050
0.100
0.100
0.200
0.010
0.020
0.011
0.009
0.006
0.050
4.1.1. 1-Allyl-2,3,8-trimethylpurpurogallin (2e)
Obtained from 1 and allyl chloride as a pale yellow oil in 68%
yield following the procedure used for the preparation of ethers
2b–d and 2f–j.19,20 IR (NaCl film, cmꢀ1): 2934, 2837, 1649, 1623,
1575, 1489, 1351, 1213, 1145, 1102. 1H NMR: d 6.88 (br d,
J = 11.7, 1H), 6.74 (br s, 1H), 6.49 (dd, J = 11.7, J = 8.7, 1H), 6.21
(ddt, J = 17.2, J = 10.3, J = 6.0, 1H), 6.13 (br d, J = 8.7, 1H), 5.39
(ddt, J = 17.2, J = 1.7, J = 1.6, 1H), 5.22 (ddt, J = 10.3, J = 1.7, J = 1.1,
1H), 4.70 (ddd, J = 6.0, J = 1.6, J = 1.1, 2H), 3.96 (s, 3H), 3.92
(s, 3H), 3.81 (s, 3H). 13C NMR: d 185.0, 159.2, 155.5, 152.1, 144.0,
134.7, 133.1, 129.2, 126.3, 123.7, 118.3, 107.2, 105.2, 76.5, 61.4,
56.4, 56.3. HR-MS (ASAP): m/z calcd for C17H19O5 ([M+H]+):
303.1227, found: 303.1220.
5i
5j
Camptothecin
than the control in the A-549 assay. With the exception of 5c, 5d,
and 5e, the compounds in this series were more active than
camptothecin against HeLa cells. When compared to the data pre-
sented earlier for tetrahydroindenoquinolines 4a–j, these results
indicate a strong correlation between cytotoxicity and the aroma-
ticity of the tetracyclic system. It is also worth noting that except
methyl derivative 5a, which was the most active compound in
the MCF-7 and A-549 assays, aromatic ethers are more cytotoxic
than aliphatic ones. This trend was also observed with 4a–j (vide
supra), and is likely related to variations in membrane permeabil-
ity among the compounds in both series.
4.1.2. General procedure for the preparation of Diels–Alder
adducts 3a–j
A solution of the desired trimethylpurpurogallin derivative
(500 mg) and nitrosobenzene (1.5 equiv.) in benzene (20 mL) was
protected from light and stirred at room temperature under nitro-
gen for 48 h. The solvent was then removed at room temperature
under reduced pressure. The resulting solids were triturated with
ether to remove unreacted dienophile, yielding the desired adducts
which were used in the following step without further purification.
3. Conclusions
In summary, we have described the synthesis of a series of
novel tetrahydroindenoquinolines and indenoquinolines and their
evaluation as potential anticancer agents. The strategy employed
to prepare these compounds is straightforward and takes advan-
tage of the photoisomerization of readily available precursors. As
evidenced by the results of the growth inhibition assays, the
in vitro antiproliferative activity of the tetracycles is strongly
associated with their aromatic character and planar structure.
Furthermore, their structural similarities with camptothecin
suggest that indenoquinolines 5a–j and this drug have a common
or closely related pharmacophore. If this is indeed the case, these
compounds would represent a new class of topoI inhibitors with
distinctive pharmacological properties. For example, the lack of
an hydrolyzable lactone ring could make these molecules resistant
to inactivation at physiological pH.7,8,14
4.1.2.1. 1,2-Dihydro-4,6,7,8-tetramethoxy-2-phenyl-1,4-etheno-
3,2-benzoxazepin-5(4H)-one (3a).
Obtained from 2a in 79%
yield. Mp: 112–113 °C. IR (KBr disc, cmꢀ1): 3057, 2997, 2945,
2838, 1698, 1584, 1487, 1329, 1132, 1100. 1H NMR: d 7.31
(AA0MM0X, 2H), 7.18 (AA0MM0X, 2H), 7.03 (tt, J = 7.3, J = 1.1, 1H),
6.72 (br s, 1H), 6.65 (dd, J = 9.3, J = 6.7, 1H), 6.22 (dd, J = 9.3,
J = 0.9, 1H), 5.28 (br dd, J = 6.7, J = 0.9, 1H), 3.97 (s, 3H), 3.94
(s, 3H), 3.89 (s, 3H), 3.72 (s, 3H). 13C NMR: d 190.2, 157.9, 156.7,
150.8, 144.1, 136.6, 135.8, 129.3, 127.7, 123.4, 120.4, 118.3,
109.3, 102.7, 69.5, 62.2, 61.5, 56.6, 53.4. HR-MS (ASAP): m/z calcd
for C21H22NO6 ([M+H]+): 384.1447, found: 384.1499.
Additional studies will be required to determine the mode of
action of these tetracycles.24 Similarly, and based on the prelimin-
ary results obtained for C-1 ethers presented here, further SAR
studies will be carried out. In particular, our efforts will focus on
the preparation of ester and amide derivatives of the C-10 carboxyl
group. Results from these ongoing investigations will be reported
in due course.
4.1.2.2. 1,2-Dihydro-6-ethoxy-4,7,8-trimethoxy-2-phenyl-1,4-
etheno-3,2-benzoxazepin-5(4H)-one (3b).
Obtained from
2b in 81% yield. Mp: 123–124 °C. IR (KBr disc, cmꢀ1): 3054, 2973,
2940, 2841, 1704, 1586, 1493, 1325, 1143, 1107. 1H NMR: d 7.31
(AA0MM0X, 2H), 7.18 (AA0MM0X, 2H), 7.03 (tt, J = 7.3, J = 1.1, 1H),
6.72 (br s (1H), 6.66 (dd, J = 9.3, J = 6.7, 1H), 6.21 (dd, J = 9.3,
J = 0.9, 1H), 5.30 (br dd, J = 6.7, J = 0.9, 1H), 4.12 (dq, J = 8.9,
J = 7.0, 1H), 4.08 (dq, J = 8.9, J = 7.0, 1H), 3.96 (s, 3H), 3.88 (s, 3H),
3.71 (s, 3H), 1.47 (t, J = 7.0, 3H). 13C NMR: d 190.0, 157.0, 156.6,
150.8, 144.3, 136.7, 135.7, 129.3, 127.8, 123.4, 120.6, 118.3,
109.1, 102.7, 71.0, 69.6, 61.4, 56.6, 53.3, 16.0. HR-MS (ASAP): m/z
calcd for C22H24NO6 ([M+H]+): 398.1598, found: 398.1590.
4. Experimental section
4.1. Chemistry
The preparation of trimethylpurpurogallin (1) and its ethers
derivatives 2a–d and 2f–j is reported elsewhere.19,20 Irradiations
were carried out with a 450 W photochemical reaction assembly
(Ace Glass Inc., model 7861-245) fitted with a custom-made soda
lime glass vessel. Melting points were determined on a Thomas–
Hoover capillary melting point apparatus and are uncorrected.
Flash column chromatography was carried out using 230–450
mesh silica gel. IR spectra were recorded on a Thermo Electron
4.1.2.3. 1,2-Dihydro-4,7,8-trimethoxy-2-phenyl-6-propoxy-1,4-
etheno-3,2-benzoxazepin-5(4H)-one (3c).
Obtained from
2c in 69% yield. Mp: 98–100 °C. IR (KBr disc, cmꢀ1): 3069, 2978,
2945, 2845, 1696, 1589, 1491, 1324, 1141, 1112. 1H NMR: d 7.31
(AA0MM0X, 2H), 7.18 (AA0MM0X, 2H), 7.03 (tt, J = 7.3, J = 1.1, 1H),
6.71 (br s, 1H), 6.66 (dd, J = 9.3, J = 6.7, 1H), 6.21 (dd, J = 9.3,
J = 0.9, 1H), 5.30 (br dd, J = 6.7, J = 0.9, 1H), 4.04 (dt, J = 8.6, J = 6.7,

1146
S. Chakrabarty et al. / Bioorg. Med. Chem. 21 (2013) 1143–1149
1H), 3.96 (s, 3H), 3.94 (dt, J = 8.6, J = 6.8, 1H), 3.87 (s, 3H), 3.71
(s, 3H), 1.89 (qdd, J = 7.4, J = 6.8, J = 6.7, 2H), 1.06 (t, J = 7.4, 3H).
13C NMR: d 190.0, 157.3, 156.7, 150.8, 144.2, 136.7, 135.7, 129.3,
127.8, 123.4, 120.6, 118.4, 109.1, 102.7, 76.9, 69.6, 61.5, 56.6,
4.1.2.8. 1,2-Dihydro-6-o-fluorobenzyloxy-4,7,8-trimethoxy-2-
phenyl-1,4-etheno-3,2-benzoxazepin-5(4H)-one
(3h).
Obtained from 2h in 81% yield. Mp: 105–106 °C. IR (KBr
disc, cmꢀ1): 3064, 2994, 2945, 2840, 1691, 1586, 1490, 1324, 1137,
4
53.3, 23.8, 10.9. HR-MS (ASAP): m/z calcd for
C23H26NO6
1107. 1H NMR: d 7.84 (ddd, JHF = 7.5, J = 7.5, J = 1.8, 1H), 7.32
([M+H]+): 412.1760, found: 412.1760.
(dddd, J = 8.2, J = 7.5, JHF = 5.4, J = 1.8, 1H), 7.31 (AA0MM0X, 2H),
4
7.21 (ddd, J = 8.2, J = 7.5, J = 1.2, 1H), 7.18 (AA0MM0X, 2H), 7.08
3
4.1.2.4. 1,2-Dihydro-6-butoxy-4,7,8-trimethoxy-2-phenyl-1,4-
etheno-3,2-benzoxazepin-5(4H)-one (3d). Obtained from
(ddd, JHF = 9.6, J = 8.2, J = 1.2, 1H), 7.03 (tt, J = 7.3, J = 1.1, 1H),
6.76 (br s, 1H), 6.69 (dd, J = 9.2, J = 6.7, 1H), 6.23 (dd, J = 9.2,
J = 0.7, 1H), 5.32 (br dd, J = 6.7, J = 0.7, 1H), 5.20 (ABX, J = 10.5,
2d in 87% yield. Mp: 78–79 °C. IR (KBr disc, cmꢀ1): 3063, 2959,
2942, 2872, 1696, 1585, 1489, 1322, 1138, 1105. 1H NMR: d 7.31
(AA0MM0X, 2H), 7.18 (AA0MM0X, 2H), 7.03 (tt, J = 7.3, J = 1.1, 1H),
6.71 (br s, 1H), 6.66 (dd, J = 9.3, J = 6.7, 1H), 6.22 (dd, J = 9.3,
J = 0.8, 1H), 5.29 (br dd, J = 6.7, J = 0.8, 1H), 4.07 (dt, J = 8.8, J = 6.7,
1H), 3.98 (dt, J = 8.8, J = 6.7, 1H), 3.96 (s, 3H), 3.87 (s, 3H), 3.71
(s, 3H), 1.86 (tt, J = 7.0, J = 6.7, 1H), 1.53 (tq, J = 7.4, J = 7.0, 2H),
1.00 (t, J = 7.4, 3H). 13C NMR: d 190.0, 157.3, 156.7, 150.8, 144.2,
136.6, 135.7, 129.3, 127.8, 123.4, 120.6, 118.4, 109.0, 102.7, 75.1,
69.7, 61.5, 56.6, 53.3, 32.6, 19.5, 14.3. HR-MS (ASAP): m/z calcd
for C24H28NO6 ([M+H]+): 426.1911, found: 426.1909.
4
4JHF = 1.0, 1H), 5.16 (ABX, J = 10.5, JHF = 1.0, 1H), 3.98 (s, 3H),
3.87 (s, 3H), 3.69 (s, 3H). 13C NMR:
d
190.1, 161.2
1
(d, JCF = 248.0), 156.8, 156.3, 150.7, 144.4, 136.7, 135.7, 131.8 (d,
3
2
3JCF = 4.1), 130.2 (d, JCF = 8.1), 129.3, 127.8, 124.9 (d, JCF = 14.5),
4
2
124.5 (d, JCF = 3.6), 123.5, 120.8, 118.4, 115.5 (d, JCF = 21.5),
4
109.6, 102.7, 69.7, 69.6 (d, JCF = 4.3), 61.1, 56.6, 53.3. HR-MS
(ASAP): m/z calcd for C27H25FNO6 ([M+H]+): 478.1666, found:
478.1674.
4.1.2.9. 1,2-Dihydro-6-p-chlorobenzyloxy-4,7,8-trimethoxy-2-
phenyl-1,4-etheno-3,2-benzoxazepin-5(4H)-one
4.1.2.5. 1,2-Dihydro-6-allyloxy-4,7,8-trimethoxy-2-phenyl-1,4-
(3i).
Obtained from 2i in 78% yield. Mp: 82–84 °C. IR (KBr disc,
etheno-3,2-benzoxazepin-5(4H)-one (3e).
Obtained from
cmꢀ1): 3059, 2981, 2937, 2842, 1696, 1584, 1491, 1321, 1142,
2e in 38% yield. Mp: 91–92 °C. IR (KBr disc, cmꢀ1): 3053, 2989,
2941, 2842, 1702, 1586, 1493, 1323, 1142, 1105. 1H NMR: d 7.31
(AA0MM0X, 2H), 7.18 (AA0MM0X, 2H), 7.03 (tt, J = 7.3, J = 1.1, 1H),
6.73 (br s, 1H), 6.66 (dd, J = 9.3, J = 6.7, 1H), 6.22 (dd, J = 9.3,
J = 0.8, 1H), 6.22 (ddt, J = 17.2, J = 10.3, J = 6.1, 1H), 5.42 (ddt,
J = 17.2, J = 1.7, J = 1.5, 1H), 5.30 (br dd, J = 6.7, J = 0.8, 1H), 5.26
(ddt, J = 10.3, J = 1.7, J = 1.1, 1H), 4.63 (dddd, J = 11.5, J = 6.1,
J = 1.5, J = 1.1, 1H), 4.53 (dddd, J = 11.5, J = 6.1, J = 1.5, J = 1.1, 1H),
3.97 (s, 3H), 3.88 (s, 3H), 3.71 (s, 3H). 13C NMR: d 190.1, 156.6,
156.5, 150.8, 144.2, 136.6, 135.7, 134.5, 129.3, 127.8, 123.5,
120.8, 118.6, 118.4, 109.3, 102.7, 75.9, 69.7, 61.5, 56.6, 53.3. HR-MS
(ASAP): m/z calcd for C23H24NO6 ([M+H]+): 410.1598, found:
410.1594.
1108. H NMR: d 7.59 (AA0XX0, 2H), 7.38 (AA0XX0, 2H), 7.31
1
(AA0MM0X, 2H), 7.17 (AA0MM0X, 2H), 7.03 (tt, J = 7.3, J = 1.1, 1H),
6.75 (br s, 1H), 6.71 (dd, J = 9.3, J = 6.8, 1H), 6.23 (dd, J = 9.3,
J = 0.9, 1H), 5.31 (br dd, J = 6.8, J = 0.9, 1H), 5.11 (AB, J = 10.0, 1H),
4.96 (AB, J = 10.0, 1H), 3.98 (s, 3H), 3.85 (s, 3H), 3.68 (s, 3H).
13C NMR: d 190.1, 156.8, 156.3, 150.7, 144.3, 136.9, 136.2, 135.9,
134.3, 130.7, 129.3, 128.9, 127.7, 123.5, 120.8, 118.4, 109.6,
102.7, 75.5, 69.6, 66.3, 61.6, 56.6, 53.3. HR-MS (ASAP): m/z calcd
for C27H25ClNO6 ([M+H]+): 494.1370, found: 494.1377.
4.1.2.10. 1,2-Dihydro-4,7,8-trimethoxy-6-p-methoxybenzyloxy-
2-phenyl-1,4-etheno-3,2-benzoxazepin-5(4H)-one
(3j).
Obtained from 2j in 86% yield. Mp: 122–123 °C. IR (KBr
disc, cmꢀ1): 3078, 3006, 2944, 2839, 1685, 1587, 1487, 1317,
1
1132, 1106. H NMR: d 7.60 (AA0XX0, 2H), 7.31 (AA0MM0X, 2H),
4.1.2.6.
1,2-Dihydro-6-benzyloxy-4,7,8-trimethoxy-2-phenyl-
(3f). Obtained
7.17 (AA0MM0X, 2H), 7.03 (tt, J = 7.3, J = 1.1, 1H), 6.94 (AA0XX0,
2H), 6.73 (br s, 1H), 6.69 (dd, J = 9.3, J = 6.7, 1H), 6.23 (dd, J = 9.3,
J = 0.9, 1H), 5.30 (br dd, J = 6.7, J = 0.9), 5.08 (AB, J = 9.4, 1H), 4.95
(AB, J = 9.4, 1H), 3.97 (s, 3H), 3.87 (s, 3H), 3.84 (s, 3H), 3.69
(s, 3H). 13C NMR: d 190.2, 160.0, 156.7, 156.5, 150.8, 144.5,
136.8, 135.7, 131.2, 129.9, 129.3, 123.5, 121.0, 118.4, 114.2,
109.5, 102.7, 76.2, 69.7, 61.5, 56.6, 55.7, 53.3. HR-MS (ASAP): m/z
calcd for C28H28NO7 ([M+H]+): 490.1866, found: 490.1866.
1,4-etheno-3,2-benzoxazepin-5(4H)-one
from 2f in 89% yield. Mp: 116–117 °C. IR (KBr disc, cmꢀ1): 3077,
3034, 2944, 2844, 1684, 1584, 1487, 1320, 1135, 1106. 1H NMR:
d 7.67 (AA0MM0X, 2H), 7.42 (AA0MM0X, 2H), 7.35 (tt, J = 7.2,
J = 1.4, 1H), 7.31 (AA0MM0X, 2H), 7.18 (AA0MM0X, 2H), 7.03
(tt, J = 7.3, J = 1.2, 1H), 6.75 (br s, 1H), 6.69 (dd, J = 9.2, J = 6.7,
1H), 6.23 (dd, J = 9.2, J = 0.9, 1H), 5.31 (br dd, J = 6.7, J = 0.9, 1H),
5.16 (AB, J = 9.8, 1H), 5.01 (AB, J = 9.8, 1H), 3.97 (s, 3H), 3.87 (s, 3H),
3.69 (s, 3H). 13C NMR: d 190.2, 156.8, 156.5, 150.8, 144.4, 137.7,
136.8, 135.8, 129.4, 129.3, 128.8, 128.5, 127.8, 123.5, 120.9, 118.4,
109.5, 102.8, 76.5, 69.7, 61.6, 56.6, 53.3. HR-MS (ASAP): m/z calcd
for C27H26NO6 ([M+H]+): 460.1760, found: 460.1765.
4.1.3. General procedure for the preparation of
tetrahydroindenoquinolines 4a–j
A solution of the appropriate Diels–Alder adduct (200 mg) in
benzene (200 mL) was irradiated at 5 °C for 8–12 h. The solvent
was then removed under vacuum, and the crude product was puri-
fied by column chromatography using hexanes–EtOAc (1:1) as
eluting solvent to yield the desired products.
4.1.2.7. 1,2-Dihydro-6-p-fluorobenzyloxy-4,7,8-trimethoxy-2-
phenyl-1,4-etheno-3,2-benzoxazepin-5(4H)-one
(3g).
Obtained from 2g in 79% yield. Mp: 130–131 °C. IR (KBr
disc, cmꢀ1): 3077, 3003, 2947, 2838, 1685, 1585, 1488, 1322, 1136,
4.1.3.1. Methyl 1,2,3-trimethoxy-11-oxo-5,10,10a,11-tetrahydro-
1
4
1108. H NMR: d 7.64 (AA0MM0X, JHF = 5.5, 2H), 7.31 (AA0MM0X,
4bH-indeno[1,2-b]quinoline-10-carboxylate (4a).
Obtained
3
from 3a in 35% yield. Mp: 187–188 °C (lit.16 193.3–194.5 °C). IR
(KBr disc, cmꢀ1): 2944, 2839, 1734, 1700, 1591, 1482, 1343, 1253,
1197, 1144. 1H NMR: d 7.37 (dd, J = 7.7, J = 1.5, 1H), 7.17 (ddd,
J = 7.8, J = 7.7, J = 1.5, 1H), 6.89 (d, J = 0.8, 1H), 6.89 (ddd, J = 7.7,
J = 7.7, J = 1.1, 1H), 6.79 (dd, J = 7.8, J = 1.1, 1H), 4.83 (dd, J = 8.2,
J = 0.8, 1H), 4.42 (d, J = 7.5, 1H), 4.33 (br s, 1H), 4.08 (s, 3H), 4.01
(s, 3H), 3.89 (s, 3H), 3.48 (s, 3H), 3.34 (dd, J = 8.2, J = 7.5, 1H).
13C NMR: d 200.8, 171.2, 160.3, 152.2, 151.7, 145.6, 142.2, 129.8,
129.1, 123.5, 123.3, 120.9, 116.7, 102.6, 62.5, 61.8, 56.8, 54.6, 52.5,
2H), 7.17 (AA0MM0X, 2H), 7.09 (AA0MM0X, JHF = 8.8, 2H), 7.03
(tt, J = 7.3, J = 1.1, 1H), 6.75 (br s, 1H), 6.70 (dd, J = 9.3, J = 6.7,
1H), 6.23 (dd, J = 9.3, J = 0.9, 1H), 5.31 (br dd, J = 6.7, J = 0.9, 1H),
5.10 (AB, J = 9.7, 1H), 4.96 (AB, J = 9.7, 1H), 3.97 (s, 3H), 3.85
1
(s, 3H), 3.69 (s, 3H). 13C NMR: d 190.2, 163.1 (d, JCF = 246.2),
4
156.8, 156.3, 150.7, 144.4, 136.9, 135.9, 133.5 (d, JCF = 3.3), 131.4
3
(d, JCF = 8.3), 129.3, 127.7, 123.5, 120.8, 118.4, 115.6 (d,
2JCF = 21.3), 109.6, 102.7, 75.6, 69.6, 61.6, 56.6, 53.3. HR-MS (ASAP):
m/z calcd for C27H25FNO6 ([M+H]+): 478.1666, found: 478.1671.

S. Chakrabarty et al. / Bioorg. Med. Chem. 21 (2013) 1143–1149
1147
50.9, 45.7. HR-MS (ASAP): m/z calcd for C21H22NO6 ([M+H]+):
(ASAP): m/z calcd for
C
23H24NO6 ([M+H]+): 410.1958, found:
384.1447, found: 384.1432.
410.1954.
4.1.3.6. Methyl 1-benzyloxy-2,3-dimethoxy-11-oxo-5,10,10a,11-tetra-
hydro-4bH-indeno[1,2-b]quinoline-10-carboxylate (4f). Obtained
4.1.3.2. Methyl 1-ethoxy-2,3-dimethoxy-11-oxo-5,10,10a,11-tetrahy-
dro-4bH-indeno[1,2-b]quinoline-10-carboxylate (4b).
Obtained
from 3f in 30% yield. Mp: 157–158 °C. IR (KBr disc, cmꢀ1): 2947,
2846, 1735, 1701, 1591, 1482, 1341, 1251, 1195, 1146. 1H NMR:
d 7.58 (AA0MM0X, 2H), 7.40 (dd, J = 7.5, J = 1.5, 1H), 7.39 (AA0MM0X,
2H), 7.33 (tt, J = 7.3, J = 1.3, 1H), 7.19 (ddd, J = 7.8, J = 7.5, J = 1.5,
1H), 6.91 (ddd, J = 7.5, J = 7.5, J = 1.2, 1H), 6.90 (d, J = 0.8, 1H),
6.80 (dd, J = 7.8, J = 1.2, 1H), 5.33 (AB, J = 11.3, 1H), 5.25 (AB,
J = 11.3, 1H), 4.85 (dd, J = 8.2, J = 0.8, 1H), 4.46 (d, J = 7.5, 1H),
4.31 (br s, 1H), 4.01 (s, 3H), 3.80 (s, 3H), 3.50 (s, 3H), 3.37 (dd,
J = 8.2, J = 7.5, 1H). 13C NMR: d 200.8, 171.2, 160.3, 152.0, 150.5,
145.6, 142.7, 137.8, 129.8, 129.1, 129.0, 128.8, 128.7, 128.4,
124.0, 123.4, 121.0, 116.7, 76.8, 61.7, 56.8, 54.7, 52.6, 50.9, 45.8.
HR-MS (ASAP): m/z calcd for C27H26NO6 ([M+H]+): 460.1760,
found: 460.1749.
from 3b in 40% yield. Mp: 109–111 °C. IR (KBr disc, cmꢀ1):
2944, 2867, 1730, 1685, 1593, 1484, 1340, 1250, 1194, 1146. 1H
NMR: d 7.38 (dd, J = 7.5, J = 1.5, 1H), 7.18 (ddd, J = 7.7, J = 7.6,
J = 1.5, 1H), 6.89 (ddd, J = 7.6, J = 7.5, J = 1.2, 1H), 6.88 (d, J = 0.7,
1H), 6.79 (dd, J = 7.7, J = 1.2, 1H), 4.83 (dd, J = 8.2, J = 0.7, 1H),
4.42 (d, J = 7.5, 1H), 4.32 (dq, J = 9.6, J = 7.0, 1H), 4.29 (br s, 1H),
4.28 (dq, J = 9.6, J = 7.0, 1H), 4.02 (s, 3H), 3.91 (s, 3H), 3.48
(s, 3H), 3.33 (dd, J = 8.2, J = 7.5, 1H), 1.44 (t, J = 7.0, 3H).
13C NMR: d 200.8, 171.2, 160.2, 152.0, 150.7, 145.6, 142.8,
129.8, 129.1, 128.7, 123.4, 121.0, 116.7, 102.6, 71.1 61.7, 56.8,
54.6, 52.5, 50.9, 45.8, 16.0. HR-MS (ASAP): m/z calcd for
C
22H24NO6 ([M+H]+): 398.1598, found: 398.1595.
4.1.3.3. Methyl 2,3-dimethoxy-11-oxo-1-propoxy-5,10,10a,11-tetrahy-
dro-4bH-indeno[1,2-b]quinoline-10-carboxylate (4c). Obtained
4.1.3.7. Methyl 1-p-fluorobenzyloxy-2,3-dimethoxy-11-oxo-
5,10,10a,11-tetrahydro-4bH-indeno[1,2-b]quinoline-10-carbox-
from 3c in 39% yield. Mp: 162–163 °C. IR (KBr disc, cmꢀ1):
2958, 2928, 2858, 1735, 1716, 1580, 1472, 1341, 1270, 1197,
1141. 1H NMR: d 7.37 (dd, J = 7.5, J = 1.5, 1H), 7.17 (ddd, J = 7.8,
J = 7.5, J = 1.5, 1H), 6.89 (ddd, J = 7.5, J = 7.5, J = 1.2, 1H), 6.88
(d, J = 0.8, 1H), 6.79 (dd, J = 7.8, J = 1.2, 1H), 4.83 (dd, J = 8.2,
J = 0.8, 1H), 4.42 (d, J = 7.6, 1H), 4.32 (br s, 1H), 4.21 (dt, J = 9.6,
J = 6.8, 1H), 4.18 (dt, J = 9.6, J = 6.8, 1H), 4.01 (s, 3H), 3.89
(s, 3H), 3.48 (s, 3H), 3.33 (dd, J = 8.2, J = 7.6, 1H), 1.84
(qt, J = 7.4, J = 6.8, 2H), 1.05 (t, J = 7.4, 3H). 13C NMR: d 200.8,
171.2, 160.3, 152.1, 151.1, 145.6, 142.6, 129.8, 129.1, 123.9,
123.3, 120.9, 116.7, 102.5, 77.0, 61.7, 56.8, 54.6, 52.5, 50.9,
ylate (4g).
Obtained from 3g in 36% yield. Mp: 108–110 °C. IR
(KBr disc, cmꢀ1): 2946, 2929, 2848, 1375, 1701, 1591, 1483, 1337,
1
4
1256, 1195, 1146. H NMR: d 7.55 (AA0MM0X, JHF = 5.5, 2H), 7.41
(dd, J = 7.5, J = 1.5, 1H), 7.19 (ddd, J = 7.8, J = 7.5, J = 1.5, 1H), 7.04
3
(AA0MM0X, JHF = 8.8, 2H), 6.91 (ddd, J = 7.5, J = 7.5, J = 1.2, 1H),
6.90 (d, J = 0.8, 1H), 6.80 (dd, J = 7.8, J = 1.2, 1H), 5.28 (AB, J = 11.2,
1H), 5.22 (AB, J = 11.2, 1H), 4.85 (dd, J = 8.2, J = 0.8, 1H), 4.45
(d, J = 7.5, 1H), 4.33 (br s, 1H), 4.01 (s, 3H), 3.81 (s, 3H), 3.50
(s, 3H), 3.37 (dd, J = 8.2, J = 7.5, 1H). 13C NMR: d 200.9, 171.3,
1
163.0 (d, JCF = 245.8), 160.3, 152.1, 150.2, 145.6, 142.8, 133.6
4
3
(d, JCF = 3.1), 131.0 (d, JCF = 8.3), 129.8, 129.1, 124.0, 123.4,
45.7, 23.8, 10.8. HR-MS (ASAP): m/z calcd for
C23H26NO6
2
([M+H]+): 412.1760, found: 412.1751.
121.1, 116.7, 115.5 (d, JCF = 21.5), 102.9, 75.9, 61.7, 56.8, 54.7,
52.6, 50.9, 45.8. HR-MS (ASAP): m/z calcd for
C27H25FNO6
([M+H]+): 478.1666, found: 478.1672.
4.1.3.4. Methyl 1-butoxy-2,3-dimethoxy-11-oxo-5,10,10a,11-tetrahy-
dro-4bH-indeno[1,2-b]quinoline-10-carboxylate (4d). Obtained
from 3d in 25% yield. Mp: 171–172 °C. IR (KBr disc, cmꢀ1):
2955, 2864, 1730, 1690, 1591, 1481, 1340, 1248, 1194, 1145.
1H NMR: d 7.38 (dd, J = 7.5, J = 1.5, 1H), 7.18 (ddd, J = 7.8,
J = 7.5, J = 1.5, 1H), 6.89 (ddd, J = 7.5, J = 7.5, J = 1.2, 1H), 6.88
(d, J = 0.8, 1H), 6.79 (dd, J = 7.8, J = 1.2, 1H), 4.83 (dd, J = 8.2,
J = 0.8, 1H), 4.43 (d, J = 7.6, 1H), 4.28 (br s, 1H), 4.26 (dt, J = 9.6,
J = 6.7, 1H), 4.22 (dt, J = 9.6, J = 6.7, 1H), 4.02 (s, 3H), 3.90
(s, 3H), 3.48 (s, 3H), 3.33 (dd, J = 8.2, J = 7.6, 1H), 1.80
(tt, J = 7.0, J = 6.7, 2H), 1.52 (tq, J = 7.4, J = 7.0, 2H), 0.97
(t, J = 7.4, 3H). 13C NMR: d 200.8, 171.2, 160.2, 152.0, 151.2,
145.6, 142.6, 129.8, 129.1, 124.0 123.4, 121.0, 116.7, 102.5,
75.2, 61.7, 56.8, 54.6, 52.5, 50.8, 45.8, 32.6, 19.4, 14.3. HR-MS
(ASAP): m/z calcd for C24H28NO6 ([M+H]+): 426.1911, found:
426.1895.
4.1.3.8. Methyl 1-o-fluorobenzyloxy-2,3-dimethoxy-11-oxo-
5,10,10a,11-tetrahydro-4bH-indeno[1,2-b]quinoline-10-carbox-
ylate (4h).
Obtained from 3h in 32% yield. Mp: 150–151 °C. IR
(KBr disc, cmꢀ1): 2955, 2930, 2855, 1731, 1703, 1590, 1465, 1341,
1270, 1195, 1145. 1H NMR: d 7.73 (ddd, JHF = 7.5, J = 7.5, J = 1.8,
4
1H), 7.40 (dd, J = 7.6, J = 1.5, 1H), 7.30 (dddd, J = 8.2, J = 7.5,
4JHF = 5.4, J = 1.8, 1H), 7.19 (ddd, J = 7.8, J = 7.5, J = 1.5, 1H), 7.16
3
(ddd, J = 7.5, J = 7.5, J = 1.2, 1H), 7.06 (ddd, JHF = 9.8, J = 8.2,
J = 1.2, 1H), 6.91 (ddd, J = 7.6, J = 7.5, J = 1.2, 1H), 6.90 (d, J = 0.8,
4
1H), 6.81 (dd, J = 7.8, J = 1.2, 1H), 5.42 (ABX, J = 11.9, JHF = 1.2,
4
1H), 5.33 (ABX, J = 11.9, JHF = 1.2, 1H), 4.86 (dd, J = 8.2, J = 0.8,
1H), 4.46 (d, J = 7.5), 4.31 (br s, 1H), 4.01 (s, 3H), 3.83 (s, 3H),
3.50 (s 3H), 3.37 (dd, J = 8.2, J = 7.5, 1H). 13C NMR: d 200.8, 171.2,
1
160.3, 161.2 (d, JCF = 247.7), 152.0, 150.2, 145.6, 142.8, 131.5
3
3
(d, JCF = 4.2), 130.1 (d, JCF = 8.2), 129.8, 129.1, 125.0 (d,
2JCF = 14.7), 124.5 (d, JCF = 3.6), 123.9, 123.4, 121.0, 116.7, 115.4
4
4.1.3.5.
11-tetrahydro-4bH-indeno[1,2-b]quinoline-10-carboxylate
(4e). Obtained from 3e in 27% yield. Mp: 135–137 °C. IR (KBr
Methyl
1-allyloxy-2,3-dimethoxy-11-oxo-5,10,10a,
2
4
(d, JCF = 21.3), 102.9, 70.2 (d, JCF = 4.2), 61.8, 56.8, 54.7, 52.6,
50.9, 45.8. HR-MS (ASAP): m/z calcd for C27H25FNO6 ([M+H]+):
478.1666, found: 478.1658.
disc, cmꢀ1): 2947, 2847, 1735, 1700, 1592, 1483, 1341, 1250, 1195,
1146. 1H NMR: d 7.39 (dd, J = 7.5, J = 1.5, 1H), 7.18 (ddd, J = 7.8,
J = 7.7, J = 1.5, 1H), 6.90 (ddd, J = 7.7, J = 7.5, J = 1.1, 1H), 6.89 (d,
J = 0.8, 1H), 6.79 (dd, J = 7.8, J = 1.1, 1H), 6.14 (ddt, J = 17.2, J = 10.4,
J = 6.1, 1H), 5.40 (ddt, J = 17.2, J = 1.7, J = 1.5, 1H), 5.21 (ddt, J = 10.4,
J = 1.7, J = 1.1, 1H), 4.84 (dd, J = 8.2, J = 0.8, 1H), 4.83 (dddd, J = 12.4,
J = 6.1, J = 1.5, J = 1.1, 1H), 4.75 (dddd, J = 12.4, J = 6.1, J = 1.5, J = 1.1,
1H), 4.43 (d, J = 7.6, 1H), 4.28 (br s, 1H), 4.02 (s, 3H), 3.90 (s, 3H),
3.49 (s, 3H), 3.34 (dd, J = 8.2, J = 7.6, 1H). 13C NMR: d 200.8, 171.2,
160.2, 152.0, 150.3, 145.6, 142.7, 134.4, 129.8, 129.1, 123.9, 123.4,
121.0, 118.6, 116.7, 102.7, 75.9, 61.8, 56.8, 54.6, 52.6, 50.9. HR-MS
4.1.3.9. Methyl 1-p-chlorobenzyloxy-2,3-dimethoxy-11-oxo-
5,10,10a,11-tetrahydro-4bH-indeno[1,2-b]quinoline-10-carbox-
ylate (4i).
Obtained from 3i in 27% yield. Mp: 145–147 °C. IR
(KBr disc, cmꢀ1): 2952, 2926, 2874, 1735, 1701, 1592, 1481, 1341,
1
1252, 1195, 1146. H NMR: d 7.51 (AA0XX0, 2H), 7.41 (dd, J = 7.6,
J = 1.5, 1H), 7.19 (ddd, J = 7.8, J = 7.5, J = 1.5, 1H), 7.33 (AA0XX0,
2H), 6.91 (ddd, J = 7.6, J = 7.5, J = 1.2, 1H), 6.89 (d, J = 0.8, 1H),
6.80 (dd, J = 7.8, J = 1.2, 1H), 5.29 (AB, J = 11.4, 1H), 5.23 (AB,
J = 11.4, 1H), 4.85 (dd, J = 8.2, J = 0.8, 1H), 4.44 (d, J = 7.4, 1H),

1148
S. Chakrabarty et al. / Bioorg. Med. Chem. 21 (2013) 1143–1149
4.30 (br s, 1H), 4.02 (s, 3H), 3.81 (s, 3H), 3.50 (s, 3H), 3.37 (dd,
J = 8.2, J = 7.4, 1H). 13C NMR: d 200.9, 171.3, 160.4, 152.1, 150.2,
145.5, 142.7, 136.3, 134.2, 130.4, 129.8, 129.1, 128.9, 123.9,
123.4, 121.1, 116.8, 103.0, 75.8, 61.7, 56.8, 54.7, 52.6, 50.9, 45.8.
HR-MS (ASAP): m/z calcd for C27H25ClNO6 ([M+H]+): 494.1370,
found: 494.1361.
(ddd, J = 8.4, J = 7.1, J = 1.5, 1H), 7.57 (ddd, J = 8.2, J = 7.1, J = 1.3,
1H), 7.44 (s, 1H), 4.29 (t, J = 6.7, 2H), 4.17 (s, 3H), 4.10 (s, 3H),
3.94 (s, 3H), 1.89 (qt, J = 7.4, J = 6.7, 2H), 1.09 (t, J = 7.4, 3H).
13C NMR: d 185.9, 166.5, 160.8, 160.7, 152.9, 150.7, 145.5, 141.3,
135.8, 132.4, 130.3, 128.2, 127.3, 124.1, 124.0, 123.1, 100.9, 77.2,
61.8, 57.2, 53.6, 23.9, 10.8. HR-MS (ASAP): m/z calcd for
C
23H22NO6 ([M+H]+): 408.1442, found: 408.1461.
4.1.3.10. Methyl 2,3-dimethoxy-1-p-methoxybenzyloxy-11-oxo-
5,10,10a,11-tetrahydro-4bH-indeno[1,2-b]quinoline-10-carbox-
4.1.4.4. Methyl 1-butoxy-2,3-dimethoxy-11-oxo-11H-indeno[1,
2-b]quinoline-10-carboxylate (5d). Obtained from 4d in 49%
ylate (4j).
Obtained from 3j in 28% yield. Mp: 114–115 °C. IR
yield. Mp: 179–181 °C. IR (KBr disc, cmꢀ1): 2953, 2926, 2849, 1726,
1697, 1616, 1578, 1465, 1350, 1238, 1139. 1H NMR: d 8.13 (ddd,
J = 8.4, J = 1.2, J = 0.6, 1H), 7.82 (ddd, J = 8.2, J = 1.5, J = 0.6, 1H),
7.79 (ddd, J = 8.4, J = 7.1, J = 1.5, 1H), 7.58 (ddd, J = 8.2, J = 7.1,
J = 1.2, 1H), 4.33 (t, J = 6.7, 2H), 4.17 (s, 3H), 4.11 (s, 3H), 3.94
(s, 3H), 1.85 (tt, J = 7.0, J = 6.7, 2H), 1.56 (qt, J = 7.4, J = 7.0, 2H)
1.01 (t, J = 7.4, 3H). 13C NMR: d 185.9, 166.6, 160.8, 152.9, 150.7,
145.5, 141.3, 135.8, 132.4, 130.3, 128.2, 127.3, 124.1, 124.0,
123.1, 100.9, 75.4, 61.8, 57.2, 53.7, 32.7, 19.4, 14.3. HR-MS (ASAP):
m/z calcd for C24H24NO6 ([M+H]+): 422.1598, found: 422.1582.
(KBr disc, cmꢀ1): 2961, 2931, 2870, 1735, 1701, 1590, 1481, 1326,
1
1249, 1174, 1144. H NMR: d 7.50 (AA0XX0, 2H), 7.41 (dd, J = 7.6,
J = 1.5, 1H), 7.19 (ddd, J = 7.8, J = 7.5, J = 1.5, 1H), 6.91 (ddd,
J = 7.6, J = 7.5, J = 1.2, 1H), 6.89 (AA0XX0, 2H), 6.89 (d, J = 0.8, 1H),
6.80 (dd, J = 7.8, J = 1.2, 1H), 5.25 (AB, J = 10.9, 1H), 5.19 (AB,
J = 10.9, 1H), 4.85 (dd, J = 8.2, J = 0.8, 1H), 4.45 (d, J = 7.5, 1H),
4.29 (br s, 1H), 4.01 (s, 3H), 3.82 (s, 3H), 3.80 (s, 3H), 3.50 (s, 3H),
3.36 (dd, J = 8.2, J = 7.5, 1H). 13C NMR: d 200.8, 171.3, 160.3,
159.9, 152.0, 150.4, 145.5, 142.9, 130.8, 130.0, 129.8, 129.1,
124.1, 123.4, 121.1, 116.8, 114.1, 102.8, 76.5, 61.7, 56.8, 55.6,
54.7, 52.6, 50.9, 45.8. HR-MS (ASAP): m/z calcd for C28H28NO7
([M+H]+): 490.1866, found: 490.1859.
4.1.4.5. Methyl 1-allyloxy-2,3-dimethoxy-11-oxo-11H-indeno[1,
2-b]quinoline-10-carboxylate (5e).
Obtained from 4e in 65%
yield. Mp: 186–187 °C. IR (KBr disc, cmꢀ1): 2961, 2932, 2867, 1725,
1696, 1617, 1578, 1465. 1349, 1239, 1139. 1H NMR: d 8.13 (ddd,
J = 8.4, J = 1.2, J = 0.7, 1H), 7.82 (ddd, J = 8.2, J = 1.5, J = 0.7, 1H),
7.80 (ddd, J = 8.4, J = 7.1, J = 1.5, 1H), 7.58 (ddd, J = 8.2, J = 7.1,
J = 1.2, 1H), 7.45 (s, 1H), 6.16 (ddt, J = 17.2, J = 10.4, J = 5.9, 1H),
5.45 (ddt, J = 17.2, J = 1.7, J = 1.5, 1H), 5.27 (ddt, J = 10.4, J = 1.7,
J = 1.2, 1H), 4.88 (ddd, J = 5.9, J = 1.5, J = 1.2, 2H), 4.17 (s, 3H), 4.11
(s, 3H), 3.95 (s, 3H). 13C NMR: d 185.9, 166.5, 160.8, 160.7, 152.1,
150.6, 145.5, 141.2, 135.9, 134.1, 132.5, 130.3, 128.2, 127.3,
124.1, 124.0, 123.1, 118.9, 101.2, 75.9, 66.3, 61.9, 57.2, 53.7. HR-MS
(ASAP): m/z calcd for C23H20NO6 ([M+H]+): 406.1285, found:
406.1285.
4.1.4. General procedure for the preparation of
indenoquinolines 5a–j
A
solution of the appropriate tetrahydroindenoquinoline
(50 mg) and DDQ (1.5 equiv.) in benzene (25 mL) was heated to
reflux until no starting materials were detectable by TLC (2–4 h).
The reaction mixture was then allowed to cool to room tempera-
ture, and washed with 1 M Na2SO3 (3 ꢁ 10 mL) and water
(3 ꢁ 10 mL). The aqueous phase was extracted with ethyl acetate
(3 ꢁ 10 mL), and the combined organic layers dried with MgSO4
and concentrated under reduced pressure. The resulting crude
products were purified by column chromatography using
hexanes–EtOAc (2:1–1:1) as eluting solvent.
4.1.4.6. Methyl 1-benzyloxy-2,3-dimethoxy-11-oxo-11H-indeno
4.1.4.1. Methyl 1,2,3-trimethoxy-11-oxo-11H-indeno[1,2-b]qui-
[1,2-b]quinoline-10-carboxylate (5f).
Obtained from 4f in
77% yield. Mp: 201–203 °C. IR (KBr disc, cmꢀ1): 2929, 2850,
1731, 1701, 1624, 1576, 1472, 1351, 1254, 1143. 1H NMR: d 8.12
(ddd, J = 8.4, J = 1.2, J = 0.6, 1H), 7.82 (ddd, J = 8.2, J = 1.5, J = 0.6,
1H), 7.79 (ddd, J = 8.4, J = 7.0, J = 1.5, 1H), 7.60 (AA0MM0X, 2H,
2H), 7.57 (ddd, J = 8.2, J = 7.0, J = 1.2, 1H), 7.44 (s, 1H), 7.40
(AA0MM0X, 2H, 2H), 7.34 (tt, J = 7.3, J = 1.4, 1H). 13C NMR: d 185.9,
166.6, 160.8, 160.7, 152.2, 150.7, 145.5, 141.4, 137.4, 135.9,
132.4, 130.3, 128.9, 128.8, 128.6, 128.2, 127.3, 124.1, 124.0,
123.1, 101.2, 76.8, 61.9, 57.2, 53.7. HR-MS (ASAP): m/z calcd for
noline-10-carboxylate (5a).
Obtained from 4a in 81% yield.
Mp: 198–199 °C. IR (KBr disc, cmꢀ1): 2935, 2846, 1726, 1700,
1616, 1578, 1468, 1348, 1244, 1138. 1H NMR: d 8.11 (ddd, J = 8.4,
J = 1.2, J = 0.6, 1H), 7.81 (ddd, J = 8.2, J = 1.5, J = 0.6, 1H), 7.78 (ddd,
J = 8.4, J = 7.1, J = 1.5, 1H), 7.57 (ddd, J = 8.2, J = 7.1, J = 1.2, 1H),
7.43 (s, 1H), 4.16 (s, 3H), 4.16 (s, 3H), 4.10 (s, 3H), 3.94 (s, 3H).
13C NMR: d 186.0, 166.5, 160.9, 160.7, 153.5, 150.7, 145.0, 141.3,
135.9, 132.5, 130.3, 128.2, 127.3, 124.1, 124.0, 122.6, 101.0, 62.6,
61.0, 57.2, 53.7. HR-MS (ASAP): m/z calcd for
C21H18NO6
([M+H]+): 380.1129, found: 380.1133.
C
27H22NO6 ([M+H]+): 456.1442, found: 456.1459.
4.1.4.7. Methyl 1-p-flurorobenzyl-2,3-dimethoxy-11-oxo-11H-
4.1.4.2. Methyl 1-ethoxy-2,3-dimethoxy-11-oxo-11H-indeno[1,
2-b]quinoline-10-carboxylate (5b). Obtained from 4b in 62%
indeno[1,2-b]quinoline-10-carboxylate (5g).
Obtained from
4g in 50% yield. Mp: 171–173 °C. IR (KBr disc, cmꢀ1): 2946, 2850,
1722, 1696, 1614, 1576, 1465, 1350, 1238, 1137. 1H NMR: d 8.11
(ddd, J = 8.4, J = 1.2, J = 0.6, 1H), 7.82 (ddd, J = 8.2, J = 1.5, J = 0.6,
1H), 7.78 (ddd, J = 8.4, J = 7.0, J = 1.5, 1H), 7.58 (AA0MM0X,
4JHF = 5.4, 2H), 7.57 (ddd, J = 8.2, J = 7.0, J = 1.2, 1H), 7.44 (s, 1H),
yield. Mp: 170–172 °C. IR (KBr disc, cmꢀ1): 2971, 2933, 2829, 1724,
1696, 1617, 1579, 1485, 1349, 1242, 1139. 1H NMR: d 8.12 (ddd,
J = 8.4, J = 1.2, J = 0.6, 1H), 7.81 (ddd, J = 8.2, J = 1.4, J = 0.6, 1H),
7.79 (ddd, J = 8.4, J = 7.0, J = 1.4, 1H), 7.57 (ddd, J = 8.2, J = 7.0,
J = 1.2, 1H), 7.43 (s, 1H), 4.40 (q, J = 7.0, 2H), 4.17 (s, 3H), 4.10
(s, 3H), 3.95 (s, 3H), 1.49 (t, J = 7.0, 3H). 13C NMR: d 186.0, 166.5,
160.8, 160.7, 152.5, 150.7, 145.6, 141.3, 135.8, 132.4, 130.3,
128.2, 127.3, 124.1, 124.0, 123.2, 101.0, 71.2, 61.8, 57.2, 53.6,
3
7.08 (AA0MM0X, JHF = 8.8, 2H), 5.33 (s, 2H), 4.18 (s, 3H), 4.09
(s, 3H), 3.88 (s, 3H). 13C NMR:
d
186.0, 166.5, 163.1 (d,
1JCF = 246.4), 160.9, 160.7, 151.9, 150.7, 145.5, 141.4, 135.9, 133.2
4
3
16.2. HR-MS (ASAP): m/z calcd for
C
22H20NO6 ([M+H]+):
(d, JCF = 3.2), 132.5, 130.8 (d, JCF = 8.2), 130.4, 128.2, 127.3,
2
124.1, 123.9, 123.1, 115.7 (d, JCF = 21.4), 101.3, 75.9, 61.8, 57.2,
394.1285, found: 394.1282.
53.7. HR-MS (ASAP): m/z calcd for
C
27H21FNO6 ([M+H]+):
474.1347, found: 474.1364.
4.1.4.3. Methyl 2,3-dimethoxy-11-oxo-1-propoxy-11H-indeno[1,
2-b]quinoline-10-carboxylate (5c).
Obtained from 4c in 71%
yield. Mp: 190–191 °C. IR (KBr disc, cmꢀ1): 2958, 2874, 1726, 1696,
1619, 1578, 1465, 1350, 1237, 1138. 1H NMR: d 8.11 (ddd, J = 8.4,
J = 1.3, J = 0.6, 1H), 7.82 (ddd, J = 8.2, J = 1.5, J = 0.6, 1H), 7.79
4.1.4.8. Methyl 1-o-flurorobenzyl-2,3-dimethoxy-11-oxo-11H-
indeno[1,2-b]quinoline-10-carboxylate (5h). Obtained from
4h in 62% yield. Mp: 232–234 °C. IR (KBr disc, cmꢀ1): 2930, 2824,

S. Chakrabarty et al. / Bioorg. Med. Chem. 21 (2013) 1143–1149
1149
1731, 1700, 1623, 1578, 1474, 1351, 1231, 1151. 1H NMR: d 8.13
(ddd, J = 8.5, J = 1.2, J = 0.7, 1H), 7.83 (ddd, J = 8.2, J = 1.5, J = 0.7,
1H), 7.80 (ddd, J = 8.5, J = 7.1, J = 1.5, 1H), 7.76 (ddd, JHF = 7.5,
cells were incubated for an additional 48 h in the same conditions
as described before. 20 ml of MTT assay solution (Sigma–Aldrich,
St. Louis, MO) were then added to each well and the plate was
incubated for an additional 4 h. The resulting formazan crystals
were dissolved in 150 mL DMSO, and the absorbance of the result-
ing solution was measured at 570 nm in a SpectraMaxÒ Plus384
microplate reader (Molecular Devices, Sunnyvale, CA). The%
4
J = 7.5, J = 1.8, 1H), 7.58 (ddd, J = 8.2, J = 7.1, J = 1.2, 1H), 7.46 (s,
4
1H), 7.34 (dddd, J = 8.2, J = 7.5, JHF = 5.4, J = 1.8, 1H), 7.21 (ddd,
3
J = 7.5, J = 7.5, J = 1.2, 1H), 7.08 (ddd, JHF = 9.6, J = 8.2, J = 1.2, 1H),
5.47 (br s, 2H), 4.18 (s, 3H), 4.10 (s, 3H), 3.88 (s, 3H). 13C NMR: d
1
185.9, 166.5, 161.2 (d, JCF = 247.6), 160.9, 160.7, 151.9, 150.7,
growth inhibition (GI%) was calculated as GI% = [(1 ꢀ At)
/
3
145.5, 141.3, 135.9, 132.5, 131.3 (d, JCF = 3.9), 130.4 (d,
Aut] ꢁ 100, where At and Aut are the absorbance in treated and un-
treated cultures, respectively. The GI50 was determined by interpo-
lation from the dose response curves.
2
3JCF = 8.1), 130.3, 128.2, 127.3, 124.7 (d, JCF = 14.9), 124.6 (d,
2
4JCF = 3.8), 124.1, 124.0, 123.0, 115.6 (d, JCF = 21.3), 101.3, 70.3
3
(d, JCF = 4.2), 61.9, 57.2, 53.7. HR-MS (ASAP): m/z calcd for
C
27H21FNO6 ([M+H]+): 474.1347, found: 474.1364.
Acknowledgments
4.1.4.9. Methyl 1-p-chlorobenzyl-2,3-dimethoxy-11-oxo-11H-
indeno[1,2-b]quinoline-10-carboxylate (5i). Obtained from
Financial support from the National Science Foundation (DUE-
9952264), the Pennsylvania Department of Community and Eco-
nomic Development (KIZK-C000048830), and Norquay Technology
Inc. is acknowledged. We also wish to thank Mr. Jaime Franco for
technical assistance.
4i in 81% yield. Mp: 184–186 °C. IR (KBr disc, cmꢀ1): 2925, 2849,
1723, 1696, 1618, 1576, 1465, 1350, 1242, 1140. 1H NMR: d 8.11
(ddd, J = 8.4, J = 1.2, J = 0.7, 1H), 7.82 (ddd, J = 8.2, J = 1.5, J = 0.7,
1H), 7.79 (ddd, J = 8.4, J = 7.0, J = 1.5, 1H), 7.57 (ddd, J = 8.2, J = 7.0,
J = 1.2, 1H), 7.55 (AA0XX0, 2H), 7.44 (s, 1H), 7.37 (AA0XX0, 2H), 5.34
(br s, 2H), 4.18 (s, 3H), 4.10 (s, 3H), 3.88 (s, 3H). 13C NMR: d
186.0, 166.5, 160.9, 160.6, 151.9, 150.7, 145.4, 141.4, 136.0,
135.9, 134.4, 132.5, 130.7, 130.4, 130.1, 129.0, 128.3, 127.3,
124.1, 123.9, 123.0, 114.2, 101.3, 75.8, 61.9, 57.2, 53.7. HR-MS
(ASAP): m/z calcd for C27H21ClNO6 ([M+H]+): 490.1052, found:
490.1066.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmc.2012.12.026.
References and notes
1. Liu, L. F. Annu. Rev. Biochem. 1989, 58, 351.
2. Cummings, J.; Smyth, J. F. Ann. Oncol. 1993, 4, 533.
3. Sinha, B. K. Drugs 1995, 49, 11.
4. Froelich-Ammon, S. J.; Osheroff, N. J. Biol. Chem. 1995, 270, 21429.
5. Wang, J. C. Annu. Rev. Biochem. 1996, 65, 635.
6. Hande, K. R. Update Cancer Ther. 2006, 1, 3.
7. Pommier, Y. Nat. Rev. Cancer 2006, 6, 789.
4.1.4.10. Methyl 2,3-dimethoxy-1-p-methoxybenzyloxy-11-oxo-
11H-indeno[1,2-b]quinoline-10-carboxylate (5j).
Obtained
from 4j in 71% yield. Mp: 169–171 °C. IR (KBr disc, cmꢀ1): 2929,
2847, 1727, 1696, 1617, 1580, 1464, 1350, 1244, 1141. 1H NMR:
d 8.13 (ddd, J = 8.4, J = 1.2, J = 0.6, 1H), 7.83 (ddd, J = 8.2, J = 1.4,
J = 0.6, 1H), 7.79 (ddd, J = 8.4, J = 7.0, J = 1.4, 1H), 7.58 (ddd, J = 8.2,
J = 7.0, J = 1.2, 1H), 7.52 (AA0XX0, 2H), 7.44 (s, 1H), 6.92 (AA0XX0,
2H), 5.33 (br s, 2H), 4.19 (s, 3H), 4.10 (s, 3H), 3.88 (s, 3H), 3.83 (s,
3H). 13C NMR: d 185.9, 166.6, 160.8 (2), 160.0, 152.1, 150.7,
145.7, 141.3, 135.9, 132.4, 130.7, 130.3, 129.6, 128.2, 127.3,
124.1, 124.0, 123.3, 114.2, 101.2, 76.6, 61.8, 57.2, 55.7, 53.7. HR-
MS (ASAP): m/z calcd for C28H24NO7 ([M+H]+): 486.1547, found:
486.1566.
8. Pommier, Y. Chem. Rev. 2009, 109, 2894.
9. Pommier, Y.; Leo, E.; Zhang, H.; Marchand, C. Chem. Biol. 2010, 17, 421.
10. Ulukan, H.; Swaan, P. W. Drugs 2002, 62, 2039.
11. Hortobágyi, G. Drugs 1997, 54, 1.
12. Gottesman, M. M.; Fojo, T.; Bates, S. E. Nature 2002, 2, 48.
13. Strumberg, D.; Pommier, Y.; Paull, K.; Jayaraman, M.; Nagafuji, P.; Cushman, M.
J. Med. Chem. 1999, 42, 446.
14. Pommier, Y.; Cushman, M. Mol. Cancer Ther. 2009, 8, 1008.
15. Beretta, G. L.; Zuco, V.; Perego, P.; Zaffaroni, N. Curr. Med. Chem. 2012, 19, 1238.
16. Tabarez, C.; Waterman, C.; Rapp, A. L.; Moyna, P.; Moyna, G. Tetrahedron Lett.
2009, 50, 7128.
17. Jaxel, C.; Capranico, G.; Kerrigan, D.; Kohn, K. W.; Pommier, Y. J. Biol. Chem.
1991, 266, 20418.
18. Ren, H.; Grady, S.; Gamenara, D.; Heinzen, H.; Moyna, P.; Croft, S. L.; Kendrick,
H.; Yardley, V.; Moyna, G. Bioorg. Med. Chem. Lett. 2001, 11, 1851.
19. Ren, H.; Grady, S.; Banghart, M.; Moulthrop, J. S.; Kendrick, H.; Yardley, V.;
Croft, S. L.; Moyna, G. Eur. J. Med. Chem. 2003, 38, 949.
20. Khrizman, A.; Moulthrop, J. S.; Little, S.; Wharton, H.; Yardley, V.; Moyna, G.
Bioorg. Med. Chem. Lett. 2007, 17, 4183.
21. Khrizman, A.; Slack, R. D.; Remsing, R. C.; Little, S.; Yardley, V.; Moyna, G. Arch.
Pharm. 2007, 340, 569.
22. Gamenara, D.; Días, E.; Tancredi, N.; Heinzen, H.; Moyna, P.; Forbes, E. J. J. Braz.
Chem. Soc. 2001, 12, 489.
4.2. Biology
4.2.1. MTT cell proliferation assays
MCF-7, A-549, and HeLa cells were plated in 96-well plates at a
density of 5000 (HeLa) and 10000 (MCF-7 and A-549) cells/well, in
EMEM (MCF-7) or DMEM (A-549 and HeLa) media supplemented
with 10% FBS and 2 mM L-glutamine (100 mL/well). Cells were
incubated for 24 h at 37 °C in presence of 5% CO2. After 24 h, cells
were treated with different concentrations of drugs (0.001–
100 mM), 0.1% DMSO (vehicle control), and 1 mM H2O2 (positive
control). Untreated wells were used as negative controls. Treated
23. Mosmann, T. J. Immunol. Methods 1983, 65, 55.
24. Dexheimer, T. S.; Pommier, Y. Nature 2008, 3, 1736.
25. McEwen, C. N.; McKay, R. G.; Larsen, B. S. Anal. Chem. 2005, 77, 7826.