Chemoenzymatic synthesis with lipase catalyzed resolution and evaluation of antitumor activity of (R/S)-2-[2-hydroxy-3-(4-phenylpiperazin-1-yl)propyl]-1H- pyrrolo[3,4-b]quinolin-3(2H)-one

Article abstract of DOI:10.1016/j.ejmech.2011.02.069

Synthesis, characterization, resolution and evaluation of novel (R/S)-2-[2-hydroxy-3-(4-phenylpiperazin-1-yl)propyl]-1H-pyrrolo[3,4-b] quinolin-3(2H)-one derivatives are described. Enantiomerically pure compounds were isolated in good to excellent yield w

Full text of DOI:10.1016/j.ejmech.2011.02.069

European Journal of Medicinal Chemistry 46 (2011) 2152e2156
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Chemoenzymatic synthesis with lipase catalyzed resolution and evaluation of
antitumor activity of (R/S)-2-[2-hydroxy-3-(4-phenylpiperazin-1-yl)propyl]-1H-
pyrrolo[3,4-b]quinolin-3(2H)-one
*
Lingaiah Nagarapu , Hanmant K. Gaikwad, Rajashaker Bantu, Sheeba Rani Manikonda
Organic Chemistry Division II, Indian Institute of Chemical Technology (CSIR), Tarnaka, Hyderabad 500607, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Abstract: Synthesis, characterization, resolution and evaluation of novel (R/S)-2-[2-hydroxy-3-(4-phe-
nylpiperazin-1-yl)propyl]-1H-pyrrolo[3,4-b]quinolin-3(2H)-one derivatives are described. Enantiomeri-
cally pure compounds were isolated in good to excellent yield with high enantiomeric excess under mild
reaction conditions by using Candida antarctica B (CAL-B) and Candida rugosa (CRL) Lipases. Newly
synthesized and resolved compounds were screened for their antitumor activity against cancer cells such
as human neuroblastoma SKeNeSH and human lung carcinoma A549 cell line in vitro. The results have
shown that the compound 1 S-(ꢀ) alcohol was more effective in inhibiting the tumor cell growth.
Ó 2011 Elsevier Masson SAS. All rights reserved.
Received 16 December 2010
Received in revised form
21 February 2011
Accepted 26 February 2011
Available online 5 March 2011
Keywords:
Lipase
Cytotoxicity
Neuroblastoma cell line (SKeNeSH)
Lung carcinoma A549 cell line
1. Introduction
[17e19] on the to discover and develop tumor growth inhibitors
and apoptosis inducers as potential new anticancer agents, we
Cancer is a one of the deathliest disease in the medical field
worldwide, the majority of cancer patients treated today will
receive either preoperative or postoperative chemotherapy over
a past few decades, and drug discovery has played a greater role in
development of therapeutic agents [1e6]. Many antitumor
compounds available in the market, some of in clinical trials which
are natural as well as synthetic. The successes of the new agents
and treatments have limitations related to their side effects and
drug resistance [7]. Active new chiral therapeutic agents with fewer
side effects are still needed [8]. The natural alkaloids such as
Camptothecin, Luotonin A and their analogues contain pyrrolo-
quinolinone ring and they possess cytotoxic activity [9,10].
According to Malawska et al. [11,12] and Williams [13] compound
1-[2-hydroxy-3-(4-phenyl-1-piperazinyl)-propyl]-pyrrolidin-2-one
prevented adrenaline and barium chloride induced arrhythmia, so
it could be considered as a class Ia antiarrhythmic drug [14]. In past
few decades, progress in understanding the biochemical pharma-
obtained a novel compound (R/S)-2-[2-hydroxy-3-(4-phenyl-
piperazin-1-yl)propyl]-1H-pyrrolo[3,4-b]quinolin-3(2H)-one
(1)
which has antitumor activity (Fig. 1).
Chiral drugs have been used as therapeutic agents in their
racemic form in most of the cases. In industries, it is used to
synthesize new chiral drugs eco-friendly synthetic routes and
usages of biocatalysts are being implemented [20e23]. Immobi-
lized enzymes are highly stable in organic solvents and we can
reuse the enzymes which is always interesting in economical terms
[9,24]. Herein we would like to report synthesis of antitumor
therapeutic agents by utilizing chemoenzymatic approach for the
enzymatic resolution of compound 1 in terms of enzyme, acyl
donor and other parameters which have influence on biocatalytic
process and screened their antitumor activity against human
cancer cell lines in vitro.
2. Results and discussion
cology of
b-blockers has lead to a more rational approach in
designing new drug combinations involving this hydroxyl propyl
pyrroloquinolinone [15,16]. In our on-going research programme
2.1. Chemistry
Some of the synthetic procedures available for the preparation
of enantiopure compounds are Sharpless asymmetric dihydrox-
ylation (AD), hydrolytic kinetic resolution (HKR) methods, enzyme
(biocatalysts) catalyzed reactions but as far we know there are only
* Corresponding author. Tel.: þ91 40 27191509/10/11; fax: þ91 40 27193382.
E-mail address: lnagarapuiict@yahoo.com (L. Nagarapu).
0223-5234/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2011.02.069

L. Nagarapu et al. / European Journal of Medicinal Chemistry 46 (2011) 2152e2156
2153
signals arising due to typical secondary alcohol. The spectrum
contained two doublet of doublet, one appeared at 3.51e3.64 for
two proton, second appeared at 3.73e3.86 for two proton and one
multiplet at 5.24e5.34 for one proton. The two multiplets
appeared at 2.55e2.71 and 3.01e3.16 for piperazine protons and
remaining splitting at 6.76e8.60 which were assigned to the 10
d
d
d
d
d
d
aromatic protons, respectively.
Fig. 1. Structure of 2-[2-hydroxy-3-(4-phenylpiperazin-1-yl)propyl]-1H-pyrrolo[3,4-b]
quinolin-3(2H)-one.
2.2. Enzymatic resolution
few reports on the use of biocatalysts [25e27]. The lipase having
high enantioselectivities towards a wide range of secondary alco-
hols and primary amines are used in the preparation of pharma-
ceutical formulations [28e30]. The enzyme catalysed reactions
work at mild reaction conditions such as room temperature,
atmospheric pressure etc.
The enzymatic resolution of ( )-1 was attempted using Candida
antarctica lipase type B (CAL-B) and lipase from Candida rugosa
(CRL) with use of vinyl acetate as a acyl donor at mild reaction
condition (Scheme 3). The enzymatic acylation was performed in
neat vinyl acetate because the poor solubility of ( )-1 in MTBE
(Methyl tert-Butyl Ether), Toluene and there is no conversion
observed in Chloroform, 1,4-Dioxane, Acetonitrile, DMF (Dimethyl
formamide) solvents. Controlling the reaction conditions is very
important in enzymatic process, since it is necessary to adjust time
and conversion. We have analyzed varying the reaction times to
reach 50% conversion values at two different ratios of enzyme with
substrate. Thus the chemoenzymatic resolution of ( )-1 by CAL-B
and CRL in 1:1 ratio led to 1 S-(L) alcohol and 1 R-(D) acetate with
high enantiomeric excess (>98%), in good isolated yield (Table 1).
The enzyme CAL-B shows high enantioselectivity towards resolu-
tion of ( )-1 (Table 1, entry 1). The influence of the enzyme loading
is analyzed by recovering the product as a single enantiomer. When
the amount of enzyme with respect to substrate is decreased the
purity of enantiomer also decreased. The enantiomeric excess of
the compound was determined by HPLC using Chiralcel OD column
[31]. The mobile phases were used for Chiralcel OD column is n-
hexane/EtOH (85/10, v/v), n-hexane/EtOH/H2O (85/10/0.2, v/v/v)
and flow rate was 1.2 mL/min. The absolute configurations of the
products obtained by the lipase-mediated resolution can be
assigned [32] with the help of empirical Kazlauskas rule [33,34] to
predict which enantiomer reacts faster during the resolution of
secondary chiral alcohols.
The synthesis of racemic alcohol ( )-1 was obtained in good
yields from allyl amine. We have synthesized a starting material 2-
allyl-1H-pyrrolo[3,4-b]quinolin-3(2H)-one (7) from the Michael
addition reaction of allyl amine with ethyl acrylate in ethanol, fol-
lowed by pyrrolidine ring formation with diethyl oxalate, sodium
methoxide in diethyl ether at room temperature (87%, yield). Then
hydrolysis followed by decarboxylation of compound (5) with aq.
10% HCl to gave N-allyl pyrrolidin-2,3-dione (6), which on Fried-
lander condensation with o-aminobenzaldehyde to gave
compound (7) (63% yield, Scheme 1). The structure of this
compound was confirmed from its spectral and analytical data.
Based on [M þ H]þ 225 its molecular formula was established as
C12H14N2O. 1H NMR spectrum (300 MHz) of compound (7) recor-
ded in CDCl3 exhibited signals arising due to typical N-allyl pyrro-
loquinolinone. The spectrum contained one doublet appeared at
d
4.3 for two proton, one singlet appeared at
one doublet of doublet at 5.24e5.34 for two olefin proton, one
multiplet appeared at 5.80e5.96 for one olefin proton and
remaining splitting at 7.52e8.31 which were assigned to the five
d 4.44 for two proton,
d
d
d
aromatic protons, respectively.
We have attempted to introduce stereo center by using Sharp-
less asymmetric dihydroxylation [26,27] (AD mix-
compound (7). The oxidation of (7) with commercially available AD
mix- which is a mixture of potassium osmate K3[Fe(CN)6] K2CO3
b) on olefin
b
2.3. Effects of the compounds on the viability of human cancer cells
and (DHQD)2-PHAL gave dihydroxy compound (8). The diol (8)
obtained was easily converted to epoxide (9) using the process
based on acetoxonium ion-mediated formation of acetate ester of
halohydrin, subsequent base mediated ester saponification and
cyclization yields epoxide. The aminolysis of compound (9) with 1-
phenylpiperazine in methanol gave the racemic compound ( )-1 in
about 71% yield (Scheme 2). The structure of compound 1 was
confirmed from their spectral and analytical data. Based on HRMS
[M þ H]þ 403.2134 its molecular formula was established as
C24H26N4O2. 1H NMR spectrum (300 MHz, DMSO-d6) revealed,
The in vitro antitumor activity of these compounds was evalu-
ated against SKeNeSH (human neuroblastoma cell line) and A549
(human lung carcinoma cell line) cells by the standard MTT assay
method [35e37]. The potential of various human tumor cell growth
inhibitors was determined as described [38]. The inhibitory action
was expressed in micro molar concentrations of the compound
which causes 50% inhibition per unit of enzyme (IC50) under the
assay conditions and Doxorubicin (DOX) is used as a reference drug,
it is widely used to treat tumors. The data obtained from MTT assay
Scheme 1. Reagents and Conditions: i) Ethanol, rt, 48 h, 96%; ii) NaOMe, diethyl oxalate, Et2O, rt, 12 h, 70%; ii) 10% HCl, reflux, 2 h, 61%; iv) o-aminobenzaldehyde, p-TSA, toluene,
reflux, 12 h, 63%.

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L. Nagarapu et al. / European Journal of Medicinal Chemistry 46 (2011) 2152e2156
Scheme 2. Reagents and Conditions: i) AD Mix-b
, t-BuOH/H2O, 0 ꢁC, 20 h, 75%; ii) MeC(OMe)3, Me3SiCl/CH2Cl2, 1 h; iii) K2CO3, CH3OH, rt, 2 h, 72%; iv) 1-phenylpiperazine, MeOH,
50 ꢁC, 12 h, 71%.
shows that most of the prepared compounds are exhibiting
significant cytotoxicity against SKeNeSH and A549 cell lines.
Antitumor potency of the compounds was indicated by % cell
viability assay and IC50 values that were calculated by linear
regression analysis. The potency of chiral compound 1S was shown
to be more effective inhibiting the cancer cell growth (IC50 ¼ 16.2).
The chiral compound showed significantly inhibited the SKeNeSH
cell growth than the compound 1 and 1R. (Table 2).
designated as s (singlet), d (doublet), t (triplet), q (quartet), br
(broad), m (multiplet, for unresolved lines), etc.Infrared (IR) spectra
were recorded on a Perkin Elmer FT-IR 400 spectrometer; data are
reported in wave numbers (cmꢀ1). Mass spectra were recorded on
Agilent Technologies 1100 Series (Agilent Chemistation Software).
High-resolution mass spectra (HRMS) were obtained by using ESI-
QTOF mass spectrometry.
4.2. Synthesis of ethyl 3-(allylamino)propanoate (4)
3. Conclusion
To a stirred solution of freshly distilled ethyl acrylate (35 g,
0.35 mol) in absolute ethanol (200 mL), allyl amine (20 g,
0.350 mol) was added and allowed to stand at room temperature
for 48 h. The solvent was concentrated under reduced pressure to
obtain compound 4 (53 g, 96.45%) as yellow oil.. 1H NMR (300 MHz,
In summary, an efficient novel chemoenzymatic approach has
been developed for the preparation of enantiopure compound 1.
The enantiopure R and S enantiomers have been achieved using
CAL-B and CRL in vinyl acetate at mild reaction conditions. The
chiral compounds screened in viability assay against human
neuroblastoma (SKeNeSH) and lung carcinoma (A549) cells in
vitro. The prepared compounds had shown significantly cytotox-
icity activity against human cancer cell lines. Compound 1S has
shown potent antitumor against the SKeNeSH tumor cell line.
CDCl3):
d
1.26 t, J ¼ 7.55 Hz, 3H, CH3), 2.18 (br, 1H, NH), 2.49 (t,
J ¼ 6.79 Hz, 2H, CH2), 2.86 (t, J ¼ 6.79 Hz, 2H, CH2), 3.25 zHH(d,
J ¼ 6.03 Hz, 2H, CH2), 4.13 (q, J ¼ 7.55 Hz, 2H, CH2), 5.06e5.23 (dd,
J ¼ 15.86, 12.08 Hz, 2H, ¼ CH2), 5.79e5.94 (m, 1H, ¼ CH); EI-MS: m/
z ¼ 157 [Mþ].
4. Experimental section
4.3. Synthesis of ethyl 1-allyl-4,5-dioxopyrrolidine-3-carboxylate
4.1. Chemistry
(5)
All commercial reagents and solvents were used as received
without further purification unless specified and reaction solvents
were used distilled. The reactions were monitored and Rf value
were determined using analytical thin layer chromatography (TLC)
with Merck Silica gel 60 and F254 precoated plates (0.25 mm
thickness). Spot on the TLC plates were visualized using ultraviolet
light (254 nm). Flash column chromatography was performed with
Merck silica gel 60 (100e200 mesh). Melting points were deter-
mined in capillaries and are uncorrected. 1H NMR spectra were
recorded on Bruker DRX-300, Varian 400 and Varian-500 NMR
spectrometers. 13C NMR spectra were recorded on Bruker DRX-300.
To a stirred solution of freshly prepared sodium methoxide
(17.2 g, 0.32 mol) in diethyl ether (300 mL), diethyl oxalate
(43.2 mL, 0.32 mol) was added at room temperature, followed by
compound 4 (50 g, 0.32 mol) was added and the resulting reaction
mixture refluxed for 2.0 h. The solvent was removed under reduced
pressure. The residual slurry obtained was diluted with warm water
(300 mL) and acidified with 6N HCl. The reaction mixture was then
cooled and allowed to stand till to complete the precipitation. The
precipitate of compound 5 was filtered out and recrystallized form
ethanol to obtained white needles. Yield 70%, mp 82 ꢁC. IR (KBr, v
cmꢀ1): 2986, 2854, 1737, 1689, 1602, 1557, 1451, 1257, 1160, 1052,
Proton chemical shifts are reported in ppm (
tetramethylsilane (TMS, 0.00 or with the solvent reference rela-
tive to TMS employed as the internal standard (CDCl3, 7.26 ppm;
DMSO-d6 2.54 ppm) and Multiplicities of NMR signals are
d) relative to internal
932, 798, 763. 1H NMR (300 MHz, CDCl3):
d
1.35 (t, J ¼ 7.17 Hz, 3H),
d
3.85 (s, 1H, CH), 3.94 (s, 2H, CH2), 4.10 (d, J ¼ 6.04 Hz, 2H, CH2), 4.31
(q, J ¼ 7.17 Hz, 2H, OCH2), 5.18e5.28 (m, 2H, ¼ CH2), 5.71e5.86 (m,
1H, ¼ CH); ESI-MS: m/z ¼ 212 [M þ H]þ
d
d
Scheme 3. Reagents and Conditions: i) Lipase (CAL-B/CRL), vinyl acetate, rt, 48 h.

L. Nagarapu et al. / European Journal of Medicinal Chemistry 46 (2011) 2152e2156
2155
2H, AreH), 8.07 (s, 1H, AreH), 8.31 (d, J ¼ 8.30 Hz, 1H, AreH); 13C
Table 1
Enzymatic Resolution of ( )-1 using Vinyl Acetate at 30 ꢁC at 210 rpm.
NMR (75 MHz, CDCl3): d 45.24, 46.52, 118.39, 127.36, 127.44, 127.91,
Entry
Enzyme
Ratioa
Time (h)
eep (%)b
eeS (%)b
c (%)c
Ed
129.45(2), 129.94, 130.14, 131.78(2), 148.22, 150.64; ESI-MS: m/
z ¼ 225 [M þ H]þ
1
2
3
4
CAL-B
CRL
CAL-B
CRL
1:1
1:1
1:0.5
1:0.5
48
48
64
64
96(36)
89
92
>98(41)
95
96
50
52
50
51
>200
74
175
70
4.6. Synthesis of 2-(2,3-dihydroxypropyl)-1H-pyrrolo [3,4-b]
quinolin-3(2H)-one (8)
84
89
a
Ratio substrate vs. enzyme in weight.
b
c
Determined by HPLC. Isolated yield in parentheses.
c ¼ ees/(eesþeep).
To a solution of tert-butanol (100 mL) and water (100 mL), 20 g
of AD mix
b was added and stirred at room temperature to produce
d
E ¼ ln[(1ec)(1eees)]/ln[(1ec)(1 þ eep)].
two clear phases. The reaction mixture cooled at 0 ꢁC then
compound 7 (5 g, 0.022 mol) was added at once and the hetero-
geneous slurry was stirred at 0e3 ꢁC for 20 h (Progress of reaction
was monitored by TLC). Solid Na2SO3 (20 g) was added to the
reaction mixture at room temperature and stirred for 30 min. The
reaction mixture was diluted with CH2Cl2, the organic phases was
separated, dried over sodium sulphate and concentrated under
reduced pressure. The residue obtained was purified by column
chromatography over silica gel. Yield 75%, mp 197e199 ꢁC. IR (KBr, v
cmꢀ1): 3413, 3345, 2919, 1690, 1579, 1459, 1405, 1214, 1041, 776,
4.4. Synthesis of 1-allylpyrrolidine-2,3-dione (6)
A solution of compound 5 (25 g, 0.118 mol) in 10% HCl (530 mL)
was refluxed for 2 h. The reaction mixture was cooled to room
temperature and extracted with CH2Cl2 (3 ꢂ 300 mL). The
combined organic phases was dried over sodium sulphate and
concentrated under reduced pressure to afford 6 (10 g, 61%) as
yellow oil. IR (KBr, v cmꢀ1): 3012, 2896, 1692, 1586, 1500, 1445,
628. 1H NMR (300 MHz, DMSO-d6):
d 3.44e3.53 (m, 2H, CH2),
1249, 1163, 1018, 927, 798, 673. 1H NMR (400 MHz, CDCl3):
d 2.69 (t,
3.72e3.85 (m, 2H, CH), 3.89e4.00 (m, 1H, CH), 4.22e4.36 (m, 1H.
CH), 4.79 (s, 2H, CH2), 7.64 (t, J ¼ 7.55 Hz, 1H, AreH), 7.78 (t,
J ¼ 7.55 Hz, 1H, AreH), 7.95 (d, J ¼ 7.93 Hz, 1H, AreH), 8.27 (d,
J ¼ 8.68 Hz, 1H, AreH), 8.33 (s, 1H, AreH); ESI-MS: m/z ¼ 281
[M þ Na]þ
J ¼ 5.86 Hz, 2H, CH2), 3.63 (t, J ¼ 5.86 Hz, 2H, CH2), 4.10 (d,
J ¼ 6.59 Hz, 2H, CH2), 5.25e5.35 (m, 2H, ¼ CH2), 5.72e5.85 (m,
1H, ¼ CH); EI-MS: m/z ¼ 139 [Mþ]
4.5. Synthesis of 2-allyl-1H-pyrrolo [3,4-b]quinolin-3(2H)-one (7)
4.7. Synthesis of 2-(oxiran-2-ylmethyl)-1H-pyrrolo [3,4-b]quinolin-
3(2H)-one (9)
To a stirred solution of compound 6 (9.5 g, 0.068 mol) in toluene
(25 mL), o-aminobenzaldehyde (9.5 g, 0.068 mol) and p-toluene-
sulfonic acid (0.58 mg, 0.0034 mol) was added at room tempera-
ture. The reaction mixture was refluxed under DeaneStark
apparatus until no more water was collected and then reaction
mixture was concentrated under reduced pressure. The residue
obtained was triturated with diethyl ether and the precipitate of
compound 7 was filtered out and purified by column chromatog-
raphy over silica gel to obtained brownish solid. Yield 63%, mp
153e155 ꢁC. IR (KBr, v cmꢀ1): 3028, 2919, 1698, 1572, 1500, 1414,
To a stirred solution of compound 8 (4.5 g, 0.017 mol) in CH2Cl2,
trimethylsilyl chloride (2.2 mL, 0.017 mol) and trimethylorthoace-
tate (2.17 mL, 0.017 mol) was added at 0 ꢁC. The reaction mixture
was stirred for 1 h and then concentrated under reduced pressure.
The crude product obtained was dissolved in dry methanol and
K2CO3 (4.7 g, 0.034 mol) was added to the reaction mixture. The
suspension was stirred for 2 h, then precipitate filtered out. The
filtrate obtained was diluted with water, extracted with ethyl
acetate and then aqueous phase was further extracted with ethyl
acetate. The combined organic phases dried over sodium sulphate
and concentrated under reduced pressure. The residue obtained
was purified by column chromatography over silica gel. Yield 72%,
mp 136e138 ꢁC. IR (KBr, v cmꢀ1): 2936,1699, 1576,1462, 1415, 1304,
1246, 1024, 913, 775, 633. 1H NMR (300 MHz, DMSO-d6):
1239,1133,1001, 925, 785, 628. 1H NMR (300 MHz, CDCl3):
d 4.30 (d,
J ¼ 6.23 Hz, 2H, CH2), 4.44 (s, 2H, CH2), 5.24e34 (m, 2H, ¼ CH2),
5.80e5.96 (m, 1H, ¼ CH), 7.52e7.60 (m, 1H, AreH), 7.69e7.70 (m,
Table 2
In vitro cytotoxicity activity of compounds on SKeNeSH and A549 cell line.a
d
2.65e2.69 (dd, J ¼ 3.02 and 2.64 Hz, 1H, CH), 2.79e2.84 (dd,
J ¼ 4.34 and 4.54 Hz, 1H, CH), 3.24e3.32 (m, 1H, CH), 3.57e3.66 (dd,
J ¼ 6.23 and 6.04 Hz, 1H, CH), 3.97e4.06 (dd, J ¼ 3.39 and 3.40 Hz,
1H, CH), 4.74 (s, 2H, CH2), 7.74 (t, J ¼ 8.09 Hz, 1H, AreH), 7.87 (t,
J ¼ 8.21 Hz, 1H, AreH), 8.13 (d, J ¼ 8.12 Hz, 1H, AreH), 8.21 (d,
J ¼ 8.49 Hz, 1H, AreH), 8.62 (s, 1H, AreH); ESI-MS: m/z ¼ 241
[M þ H]þ
Compounds
Concentration % Cell viability assay
% IC50 (mM)
(mM)
SKeNeSH
A549
SKeNe A549
SH
Control
1
100
100
10
25
50
10
25
50
10
25
50
78.31 ꢃ 1.89 96.52 ꢃ 2.45
e
e
e
73.53 ꢃ 1.48 85.48 ꢃ 2.27
e
70.54 ꢃ 2.68 78.71 ꢃ 3.38 65.1
63.2
e
1R
95.51 ꢃ 0.85 98.43 ꢃ 1.83
84.19 ꢃ 2.68 85.61 ꢃ 2.24
e
e
4.8. Synthesis of 2-[2-hydroxy-3-(4-phenyl-piperazin-1-yl)-
propyl]-1,2-dihydro- pyrrolo [3,4-b]quinolin-3-one (1)
e
79.35 ꢃ 3.55 83.29 ꢃ 4.13 67.8
72.7
e
1S
76.79 ꢃ 3.43 90.66 ꢃ 1.40
e
To a solution of compound 9 (500 mg, 2.08 mmol) and 1-phe-
nylpiperazine (338 mg, 2.08 mmol) in methanol was stirred at 50 ꢁC
for 12 h. Then the solvent was concentrated under reduced pres-
sure and the crude product was cooled down. The residue obtained
was crystallized from a mixture of n-hexane and ethyl acetate to
afford compound ( )-1. Yield 71%, mp 188e190 ꢁC. IR (KBr, v cmꢀ1):
3395, 2937, 1689, 1597, 1501, 1383, 1150, 1116, 750, 687. 1H NMR
69.10 ꢃ 0.64 81.75 ꢃ 2.34 62.5
49.39 ꢃ 1.88 74.66 ꢃ 2.41 16.2
e
54.8
e
Doxorubicinb
0.1
1
5
72.50 ꢃ 0.30 76.60 ꢃ 1.05
e
60.79 ꢃ 0.72 65.33 ꢃ 1.74 43
50.97 ꢃ 3.01 33.88 ꢃ 6.37 19.9
e
e
a
Exponentially growing cells were treated with different concentrations of test
compounds for 48 h and cell growth inhibition was analyzed through MTT assay. A
viability assay was carried out. Experiments were performed in triplicate; Data are
expressed as means means ꢃ SEM from three independent determinations of
a representative experiment, the % cell viability of untreated cells [100%].
(500 MHz, DMSO-d6):
d
2.55e2.71 (m, 4H, 2 ꢂ CH2), 3.01e3.16 (m,
4H, 2 ꢂ CH2), 3.51e3.64 (dd, J ¼ 8.12 and 6.98 Hz, 2H, CH2),
b
Doxorubicin is a reference drug.
3.73e3.86 (dd, J ¼ 3.21 and 4.91 Hz 2H, CH2), 4.01e4.17 (m, 1H, CH),

2156
L. Nagarapu et al. / European Journal of Medicinal Chemistry 46 (2011) 2152e2156
4.76 (s, 2H, CH2), 4.96e5.12 (br, 1H, OeH), 6.76 (t, J ¼ 6.98 Hz, 1H,
AreH), 6.90 (d, J ¼ 8.12 Hz, 2H, AreH), 7.11e7.25 (m, 2H, AreH), 7.72
(t, J ¼ 7.36 Hz, 1H, AreH), 7.86 (t, J ¼ 7.26 Hz, 1H, AreH), 7.11 (d,
J ¼ 8.12 Hz, 1H, AreH), 8.20 (d, J ¼ 8.49 Hz, 1H, AreH), 8.60 (s, 1H,
AreH); HRMS (ESIþ) calcd. for C24H26N4O2 (M þ H)þ: 403.2168;
found: 403.2134.
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25
yield and >98% ee, [
a
]
¼ þ2.3 (c 0.35, CHCl3)} and (S)-(ꢀ) 1{41%
D
25
isolated yield and 94% ee, [
a]
¼ ꢀ2.5 (c 0.31, CHCl3)}.
D
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Appendix. Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.ejmech.2011.02.069.