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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, USAb Department of Biological Sciences, University of the Sciences in Philadelphia, 600 South Forty-Third Street, Philadelphia, PA 19104, USAc 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

Article history:

Received 15 November 2012

Revised 17 December 2012

Accepted 25 December 2012

Available online 3 January 2013

Keywords:

Anticancer activity

Indenoquinolines

Photoisomerization

Topoisomerase

a b s t r a c t

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

thelM 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.

2012 Elsevier Ltd. All rights reserved.

1. Introduction

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 theselimitations. 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

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

overall structure of this system resembles that of known topoI

poisons. Furthermore, the tetracycle could be easily aromatizedto 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

0968-0896/$ - see front matter 2012 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.bmc.2012.12.026

⇑ Corresponding author. Tel./fax: +598 4722 7950.

E-mail address: [email protected] (G. Moyna).

Bioorganic & Medicinal Chemistry 21 (2013) 1143–1149

Contents lists available at SciVerse ScienceDirect

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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 exceptmethyl 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.

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, thein 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

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 carboxylgroup. Results from these ongoing investigations will be reported

in due course.

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 230–450mesh silica gel. IR spectra were recorded on a Thermo Electron

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

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, cm1): 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.

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.

4.1.2.1. 1,2-Dihydro-4,6,7,8-tetramethoxy-2-phenyl-1,4-etheno-

3,2-benzoxazepin-5(4 H )-one (3a). Obtained from 2a in 79%

yield. Mp: 112–113 C. IR (KBr disc, cm1): 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.

4.1.2.2. 1,2-Dihydro-6-ethoxy-4,7,8-trimethoxy-2-phenyl-1,4-

etheno-3,2-benzoxazepin-5(4 H )-one (3b). Obtained from

2b in 81% yield. Mp: 123–124 C. IR (KBr disc, cm1): 3054, 2973,

2940, 2841, 1704, 1586, 1493, 1325, 1143, 1107. 1H NMR: d 7.31

(AA0

MM0

X, 2H), 7.18 (AA0

MM0

X, 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.

4.1.2.3. 1,2-Dihydro-4,7,8-trimethoxy-2-phenyl-6-propoxy-1,4-

etheno-3,2-benzoxazepin-5(4 H )-one (3c). Obtained from

2c in 69% yield. Mp: 98–100 C. IR (KBr disc, cm1): 3069, 2978,

2945, 2845, 1696, 1589, 1491, 1324, 1141, 1112. 1H NMR: d 7.31


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,

Table 2

Growth inhibitory activity of compounds 5a– j

Compound GI50 (lM)

MCF-7 A-549 HeLa

5a 0.002 0.005 0.110

5b 0.020 0.010 0.050

5c 0.010 0.110 0.100

5d 0.020 0.098 0.100

5e 0.040 0.025 0.200

5f 0.005 0.008 0.010

5g 0.008 0.008 0.020

5h 0.008 0.010 0.011

5i 0.006 0.010 0.009

5j 0.007 0.006 0.006

Camptothecin 0.002 0.007 0.050

S. Chakrabarty et al./ Bioorg. Med. Chem. 21 (2013) 1143–1149 1145



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,

53.3, 23.8, 10.9. HR-MS (ASAP): m/z calcd for C23H26NO6

([M+H]+): 412.1760, found: 412.1760.

4.1.2.4. 1,2-Dihydro-6-butoxy-4,7,8-trimethoxy-2-phenyl-1,4-etheno-3,2-benzoxazepin-5(4 H )-one (3d). Obtained from

2d in 87% yield. Mp: 78–79 C. IR (KBr disc, cm1): 3063, 2959,

2942, 2872, 1696, 1585, 1489, 1322, 1138, 1105. 1H NMR: d 7.31


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,


for C24H28NO6 ([M+H]+): 426.1911, found: 426.1909.

4.1.2.5. 1,2-Dihydro-6-allyloxy-4,7,8-trimethoxy-2-phenyl-1,4-

etheno-3,2-benzoxazepin-5(4 H )-one (3e). Obtained from

2e in 38% yield. Mp: 91–92 C. IR (KBr disc, cm1): 3053, 2989,

2941, 2842, 1702, 1586, 1493, 1323, 1142, 1105. 1H NMR: d 7.31


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.

4.1.2.6. 1,2-Dihydro-6-benzyloxy-4,7,8-trimethoxy-2-phenyl-

1,4-etheno-3,2-benzoxazepin-5(4 H )-one (3f). Obtained

from 2f in 89% yield. Mp: 116–117 C. IR (KBr disc, cm1): 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,


for C27H26NO6 ([M+H]+): 460.1760, found: 460.1765.

4.1.2.7. 1,2-Dihydro-6- p-fluorobenzyloxy-4,7,8-trimethoxy-2-

phenyl-1,4-etheno-3,2-benzoxazepin-5(4 H )-one

(3g). Obtained from 2g in 79% yield. Mp: 130–131 C. IR (KBr

disc, cm1): 3077, 3003, 2947, 2838, 1685, 1585, 1488, 1322, 1136,

1108. 1H NMR: d 7.64 (AA0MM0X, 4 J HF = 5.5, 2H), 7.31 (AA0MM0X,

2H), 7.17 (AA0MM0X, 2H), 7.09 (AA0MM0X, 3 J HF = 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

(s, 3H), 3.69 (s, 3H). 13C NMR: d 190.2, 163.1 (d, 1 J CF = 246.2),

156.8, 156.3, 150.7, 144.4, 136.9, 135.9, 133.5 (d, 4 J CF = 3.3), 131.4

(d, 3 J CF = 8.3), 129.3, 127.7, 123.5, 120.8, 118.4, 115.6 (d,2

J CF = 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.

4.1.2.8. 1,2-Dihydro-6-o-fluorobenzyloxy-4,7,8-trimethoxy-2-


(3h). Obtained from 2h in 81% yield. Mp: 105–106 C. IR (KBr

disc, cm1): 3064, 2994, 2945, 2840, 1691, 1586, 1490, 1324, 1137,

1107. 1H NMR: d 7.84 (ddd, 4 J HF = 7.5, J = 7.5, J = 1.8, 1H), 7.32

(dddd, J = 8.2, J = 7.5, 4 J HF = 5.4, J = 1.8, 1H), 7.31 (AA0MM0X, 2H),

7.21 (ddd, J = 8.2, J = 7.5, J = 1.2, 1H), 7.18 (AA0MM0X, 2H), 7.08

(ddd, 3 J HF

= 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 = 10.5,4 J HF = 1.0, 1H), 5.16 (ABX, J = 10.5, 4 J HF = 1.0, 1H), 3.98 (s, 3H),

3.87 (s, 3H), 3.69 (s, 3H). 13C NMR: d 190.1, 161.2

(d, 1 J CF = 248.0), 156.8, 156.3, 150.7, 144.4, 136.7, 135.7, 131.8 (d,3 J CF = 4.1), 130.2 (d, 3 J CF = 8.1), 129.3, 127.8, 124.9 (d, 2 J CF = 14.5),

124.5 (d, 4 J CF = 3.6), 123.5, 120.8, 118.4, 115.5 (d, 2 J CF = 21.5),

109.6, 102.7, 69.7, 69.6 (d, 4 J CF = 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-


(3i). Obtained from 2i in 78% yield. Mp: 82–84C. IR (KBr disc,

cm1): 3059, 2981, 2937, 2842, 1696, 1584, 1491, 1321, 1142,

1108. 1H NMR: d 7.59 (AA0XX0, 2H), 7.38 (AA0XX0, 2H), 7.31


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,


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(4 H )-one

(3j). Obtained from 2j in 86% yield. Mp: 122–123 C. IR (KBr

disc, cm1): 3078, 3006, 2944, 2839, 1685, 1587, 1487, 1317,1132, 1106. 1H NMR: d 7.60 (AA0XX0, 2H), 7.31 (AA0MM0X, 2H),

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.

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 solventwas 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.

4.1.3.1. Methyl 1,2,3-trimethoxy-11-oxo-5,10,10a,11-tetrahydro-

4b H -indeno[1,2-b]quinoline-10-carboxylate (4a). Obtained

from 3a in 35% yield. Mp: 187–188 C (lit.16 193.3–194.5 C). IR

(KBr disc, cm1): 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).13

C 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,

1146 S. Chakrabarty et al. / Bioorg. Med. Chem. 21 (2013) 1143–1149



50.9, 45.7. HR-MS (ASAP): m/z calcd for C21H22NO6 ([M+H]+):

384.1447, found: 384.1432.

4.1.3.2. Methyl 1-ethoxy-2,3-dimethoxy-11-oxo-5,10,10a,11-tetrahy-

dro-4b H -indeno[1,2-b]quinoline-10-carboxylate (4b). Obtained

from 3b in 40% yield. Mp: 109–111 C. IR (KBr disc, cm1):

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

C22H24NO6 ([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-4b H -indeno[1,2-b]quinoline-10-carboxylate (4c). Obtained

from 3c in 39% yield. Mp: 162–163 C. IR (KBr disc, cm1):

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,


([M+H]+): 412.1760, found: 412.1751.

4.1.3.4. Methyl1-butoxy-2,3-dimethoxy-11-oxo-5,10,10a,11-tetrahy-

dro-4b H -indeno[1,2-b]quinoline-10-carboxylate (4d). Obtainedfrom 3d in 25% yield. Mp: 171–172 C. IR (KBr disc, cm1):

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


426.1895.

4.1.3.5. Methyl 1-allyloxy-2,3-dimethoxy-11-oxo-5,10,10a,

11-tetrahydro-4b H -indeno[1,2-b]quinoline-10-carboxylate

(4e). Obtained from 3e in 27% yield. Mp: 135–137 C. IR (KBr

disc, cm1): 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


410.1954.

4.1.3.6. Methyl 1-benzyloxy-2,3-dimethoxy-11-oxo-5,10,10a,11-tetra-

hydro-4b H -indeno[1,2-b]quinoline-10-carboxylate (4f). Obtained

from 3f in 30% yield. Mp: 157–158 C. IR (KBr disc, cm1): 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.

4.1.3.7. Methyl 1-p-fluorobenzyloxy-2,3-dimethoxy-11-oxo-

5,10,10a,11-tetrahydro-4b H -indeno[1,2-b]quinoline-10-carbox-

ylate (4g). Obtained from 3g in 36% yield. Mp: 108–110

C. IR (KBr disc, cm1): 2946, 2929, 2848, 1375, 1701, 1591, 1483, 1337,

1256, 1195, 1146. 1H NMR: d 7.55 (AA0MM0X, 4 J HF = 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

(AA0MM0X, 3 J HF = 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,

163.0 (d, 1 J CF = 245.8), 160.3, 152.1, 150.2, 145.6, 142.8, 133.6

(d, 4 J CF = 3.1), 131.0 (d, 3 J CF = 8.3), 129.8, 129.1, 124.0, 123.4,

121.1, 116.7, 115.5 (d, 2 J CF = 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.

4.1.3.8. Methyl 1-o-fluorobenzyloxy-2,3-dimethoxy-11-oxo-


ylate (4h). Obtained from 3h in 32% yield. Mp: 150–151 C. IR

(KBr disc, cm1): 2955, 2930, 2855, 1731, 1703, 1590, 1465, 1341,

1270, 1195, 1145. 1H NMR: d 7.73 (ddd, 4 J HF = 7.5, J = 7.5, J = 1.8,

1H), 7.40 (dd, J = 7.6, J = 1.5, 1H), 7.30 (dddd, J = 8.2, J = 7.5,4 J HF = 5.4, J = 1.8, 1H), 7.19 (ddd, J = 7.8, J = 7.5, J = 1.5, 1H), 7.16

(ddd, J = 7.5, J = 7.5, J = 1.2, 1H), 7.06 (ddd, 3 J HF = 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,

1H), 6.81 (dd, J = 7.8, J = 1.2, 1H), 5.42 (ABX, J = 11.9, 4 J HF = 1.2,

1H), 5.33 (ABX, J = 11.9, 4 J HF = 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,

160.3, 161.2 (d, 1 J CF

= 247.7), 152.0, 150.2, 145.6, 142.8, 131.5

(d, 3 J CF = 4.2), 130.1 (d, 3 J CF = 8.2), 129.8, 129.1, 125.0 (d,2 J CF = 14.7), 124.5 (d, 4 J CF = 3.6), 123.9, 123.4, 121.0, 116.7, 115.4

(d, 2 J CF = 21.3), 102.9, 70.2 (d, 4 J CF = 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.

4.1.3.9. Methyl 1-p-chlorobenzyloxy-2,3-dimethoxy-11-oxo-


ylate (4i). Obtained from 3i in 27% yield. Mp: 145–147 C. IR

(KBr disc, cm1): 2952, 2926, 2874, 1735, 1701, 1592, 1481, 1341,

1252, 1195, 1146. 1H 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),




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.

4.1.3.10. Methyl 2,3-dimethoxy-1-p-methoxybenzyloxy-11-oxo-5,10,10a,11-tetrahydro-4b H -indeno[1,2-b]quinoline-10-carbox-

ylate (4j). Obtained from 3j in 28% yield. Mp: 114–115 C. IR

(KBr disc, cm1): 2961, 2931, 2870, 1735, 1701, 1590, 1481, 1326,

1249, 1174, 1144. 1H 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. 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.

4.1.4.1. Methyl 1,2,3-trimethoxy-11-oxo-11 H -indeno[1,2-b]qui-noline-10-carboxylate (5a). Obtained from 4a in 81% yield.

Mp: 198–199 C. IR (KBr disc, cm1): 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,


([M+H]+): 380.1129, found: 380.1133.

4.1.4.2. Methyl 1-ethoxy-2,3-dimethoxy-11-oxo-11 H -indeno[1,

2-b]quinoline-10-carboxylate (5b). Obtained from 4b in 62%

yield. Mp: 170–172C. IR(KBr disc, cm1

): 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,

16.2. HR-MS (ASAP): m/z calcd for C22H20NO6 ([M+H]+):

394.1285, found: 394.1282.

4.1.4.3. Methyl 2,3-dimethoxy-11-oxo-1-propoxy-11 H -indeno[1,

2-b]quinoline-10-carboxylate (5c). Obtained from 4c in 71%

yield. Mp: 190–191C. IR(KBr disc, cm1): 2958, 2874, 1726, 1696,

1619, 1578, 1465, 1350, 1237, 1138. 1

H 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

(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

C23H22NO6 ([M+H]+): 408.1442, found: 408.1461.

4.1.4.4. Methyl 1-butoxy-2,3-dimethoxy-11-oxo-11 H -indeno[1,2-b]quinoline-10-carboxylate (5d). Obtained from 4d in 49%

yield. Mp: 179–181 C.IR (KBr disc, cm1): 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.

4.1.4.5. Methyl 1-allyloxy-2,3-dimethoxy-11-oxo-11 H -indeno[1,

2-b]quinoline-10-carboxylate (5e). Obtained from 4e in 65%yield. Mp: 186–187 C.IR (KBr disc, cm1): 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


406.1285.

4.1.4.6. Methyl 1-benzyloxy-2,3-dimethoxy-11-oxo-11 H -indeno

[1,2-b]quinoline-10-carboxylate (5f). Obtained from 4f in

77% yield. Mp: 201–203 C. IR (KBr disc, cm1): 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

C27H22NO6 ([M+H]+): 456.1442, found: 456.1459.

4.1.4.7. Methyl 1-p-flurorobenzyl-2,3-dimethoxy-11-oxo-11 H -

indeno[1,2-b]quinoline-10-carboxylate (5g). Obtained from

4g in 50% yield. Mp: 171–173 C. IR (KBr disc, cm1

): 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,4 J HF = 5.4, 2H), 7.57 (ddd, J = 8.2, J = 7.0, J = 1.2, 1H), 7.44 (s, 1H),

7.08 (AA0MM0X, 3 J HF = 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,1 J CF = 246.4), 160.9, 160.7, 151.9, 150.7, 145.5, 141.4, 135.9, 133.2

(d, 4 J CF = 3.2), 132.5, 130.8 (d, 3 J CF = 8.2), 130.4, 128.2, 127.3,

124.1, 123.9, 123.1, 115.7 (d, 2 J CF = 21.4), 101.3, 75.9, 61.8, 57.2,

53.7. HR-MS (ASAP): m/z calcd for C27H21FNO6 ([M+H]+):

474.1347, found: 474.1364.

4.1.4.8. Methyl 1-o-flurorobenzyl-2,3-dimethoxy-11-oxo-11 H -

indeno[1,2-b]quinoline-10-carboxylate (5h). Obtained from4h in 62% yield. Mp: 232–234 C. IR (KBr disc, cm1): 2930, 2824,

1148 S. Chakrabarty et al. / Bioorg. Med. Chem. 21 (2013) 1143–1149



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, 4 J HF = 7.5,

J = 7.5, J = 1.8, 1H), 7.58 (ddd, J = 8.2, J = 7.1, J = 1.2, 1H), 7.46 (s,

1H), 7.34 (dddd, J = 8.2, J = 7.5, 4 J HF = 5.4, J = 1.8, 1H), 7.21 (ddd,

J = 7.5, J = 7.5, J = 1.2, 1H), 7.08 (ddd, 3 J HF = 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

185.9, 166.5, 161.2 (d, 1 J CF

= 247.6), 160.9, 160.7, 151.9, 150.7,

145.5, 141.3, 135.9, 132.5, 131.3 (d, 3 J CF = 3.9), 130.4 (d,3 J CF = 8.1), 130.3, 128.2, 127.3, 124.7 (d, 2 J CF = 14.9), 124.6 (d,4 J CF = 3.8), 124.1, 124.0, 123.0, 115.6 (d, 2 J CF = 21.3), 101.3, 70.3

(d, 3 J CF = 4.2), 61.9, 57.2, 53.7. HR-MS (ASAP): m/z calcd for

C27H21FNO6 ([M+H]+): 474.1347, found: 474.1364.

4.1.4.9. Methyl 1-p-chlorobenzyl-2,3-dimethoxy-11-oxo-11 H -

indeno[1,2-b]quinoline-10-carboxylate (5i). Obtained from

4i in 81% yield. Mp: 184–186 C. IR (KBr disc, cm1): 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.

4.1.4.10. Methyl 2,3-dimethoxy-1-p-methoxybenzyloxy-11-oxo-

11 H -indeno[1,2-b]quinoline-10-carboxylate (5j). Obtained

from 4j in 71% yield. Mp: 169–171 C. IR (KBr disc, cm1): 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.

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

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 SpectraMax Plus384

microplate reader (Molecular Devices, Sunnyvale, CA). The%

growth inhibition (GI%

) was calculated as GI%

= [(1 At) /

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.

Acknowledgments

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.

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.

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