Synthesis and cytotoxic evaluation of N2-benzylated quaternary β-carboline amino acid ester conjugates

Article abstract of DOI:10.1016/j.ejmech.2009.12.060

The β-carboline alkaloids have been characterized as a class of potential antitumor agents. To further enhance the cytotoxic potency and improve water solubility of β-carboline, a series of new β-carboline amino acid ester, β-carboline amino acid and N²-benzylated quaternary β-carboline amino acid ester conjugates were designed and synthesized, and the cytotoxic activities of these compounds were evaluated using a panel of human tumor cell lines. The N²-benzylated quaternary β-carboline amino acid ester conjugates represented the most interesting cytotoxic activities. Particularly, compounds 8b and 8g were found to be the most potent compounds with IC₅₀ values lower than 20?μM against all human tumor cell lines investigated. These results confirmed that the N²-benzyl substituent on the β-carboline ring played an important role in the modulation of the cytotoxic potencies.

Full text of DOI:10.1016/j.ejmech.2009.12.060

European Journal of Medicinal Chemistry 45 (2010) 1515–1523
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and cytotoxic evaluation of N2-benzylated quaternary
b-carboline
amino acid ester conjugates
,
a
a
a
a
b
Chunming Ma a, Rihui Cao a , Buxi Shi , Shaoxue Li , Zhiyong Chen , Wei Yi , Wenlie Peng ,
*
Zhenhua Ren b, Huacan Song a
,
*
a School of Chemistry and Chemical Engineering, Sun Yat-sen University, 135 Xin Gang West Road, Guangzhou 510275, PR China
b School of Life Science, Sun Yat-sen University, 135 Xin Gang West Road, Guangzhou 510275, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The
enhance the cytotoxic potency and improve water solubility of
amino acid ester,
-carboline amino acid and N2-benzylated quaternary
conjugates were designed and synthesized, and the cytotoxic activities of these compounds were
evaluated using a panel of human tumor cell lines. The N2-benzylated quaternary
-carboline amino acid
ester conjugates represented the most interesting cytotoxic activities. Particularly, compounds 8b and 8g
b
-carboline alkaloids have been characterized as a class of potential antitumor agents. To further
-carboline, a series of new -carboline
-carboline amino acid ester
Received 7 February 2009
Received in revised form
24 December 2009
Accepted 29 December 2009
Available online 13 January 2010
b
b
b
b
b
were found to be the most potent compounds with IC50 values lower than 20 mM against all human
Keywords:
Synthesis
tumor cell lines investigated. These results confirmed that the N2-benzyl substituent on the
b-carboline
ring played an important role in the modulation of the cytotoxic potencies.
b
-Carboline
Ó 2010 Elsevier Masson SAS. All rights reserved.
Amino acid
Cytotoxic activity
SARs
1. Introduction
topoisomerase II resulting in potent antitumor effects [9], and b-
carboline amino acid ester conjugates were found to display
prominent cytotoxic potencies [10].
The
b-carboline core is the common structural unit of many
naturally occurring and synthetic indole alkoloids associated with
a broad spectrum of biochemical and pharmacological properties
[1]. Previously, considerable attention focused on the effects of
Our previous reports also described the syntheses of numerous
b
-carboline derivatives bearing various substituents at position-1,
2, 3, 7 and 9 of -carboline nucleus and evaluated their antitumor
activities in vitro [11–16] and in vivo [11,13]. The SARs analysis
revealed that (1) the common -carboline moiety was very
b
b-carboline alkoloids on the central nervous system (CNS) including
their affinity with benzodiazepine (BZ) [2], 5-hydroxytryptamine
(5-HT) [3], dopamine (DA) [4], and imidazoline receptors [5]. Recent
b
important for their potent antitumor activities; (2) the introduction
of appropriate substituents into position C-1, N-2, C-3 and N-9 of
-carboline ring enhanced the antitumor activities; and the n-butyl,
benzyl and phenylpropyl substituents at position-9 and the benzyl
group at position-2 played a vital role in facilitating their antitumor
potencies.
interests in
potential antitumor activities. Several groups have investigated the
syntheses, cytotoxic activities of -carbolines bearing various
-carboline nucleus. Ishida
-carboline analogues dis-
b-carboline alkoloids have been stimulated by their
b
b
substituents at postion-1, 3, 7 and 9 of
et al. [6] reported that harmine and its
b
b
played significant cytotoxic activities against a panel of tumor cell
lines. Xiao et al. [7] described that -carbolines bearing a flexible
alkylamine side chain at position-3 exhibited potent cytotoxic
activities. Shen et al. [8] observed that 1-substituted 1,2,3,4-tetra-
It is well known that amino acids are attractive substrates
because there are not only the fundamental building blocks of
biological systems and many natural products, but also they are
commercially available and possess structurally diverse side chain
[9]. So far, amino acids have been introduced into many leading
compounds aiming to develop potential bioactive agents with low
toxicity [10,17–20]. In addition, amino acids, as prodrugs, can
significantly improve oral bioavailability of the parent drugs [21],
such as melphalan [22] and gabapentin [23], which is ascribed to
their advantages of being able to be efficiently delivered by the
human peptide transporter.
b
hydro- and 3,4-dihydro-
cytotoxic potencies. Moreover, some amino acid functionalized
1,2,3,4-tetrahydro- -carbolines were reported to inhibit
b-carboline demonstrated remarkable
b
* Corresponding authors. Tel.: þ86 20 84110918; fax: þ86 20 84112245.
E-mail addresses: caorihui@mail.sysu.edu.cn (R. Cao), yjhxhc@mail.sysu.edu.cn
(H. Song).
0223-5234/$ – see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.12.060

1516
C. Ma et al. / European Journal of Medicinal Chemistry 45 (2010) 1515–1523
Table 1
In our continuing search for novel and effective antitumor
agents, we designed and synthesized a series of novel b-carboline
Chemical structure of compounds 6a–n
amino acid ester conjugates. The design of substituents at position-
9 of -carboline ring was based on the previous SARs analysis [1],
and the choice of -amino acid was limited to -alanine, -valine,
-methionine, -phenylalanine and -tyrosine. The focus of this
CONHCHR
b
COOR'
L
L
L
N
L
L
L
investigation was to probe the optimal structural requirement of
these compounds with regard to antitumor activities, and further
N
R1
R9
develop new antitumor
solubility and bioavailability. To the best of our knowledge, all
carboline amino acid ester conjugates are novel. We report herein
b-carbolines with improved water
b
-
.
the preparation of novel
activities.
b-carboline derivatives and their cytotoxic
Compounds
R1
R9
R
R0
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
H
H
H
H
H
H
H
H
H
H
H
H
CH3
CH3
n-C4H9
n-C4H9
n-C4H9
n-C4H9
n-C4H9
n-C4H9
CH2Ph
CH3
CH3
CH3
C2H5
CH3
C2H5
CH3
C2H5
C2H5
CH3
C2H5
C2H5
C2H5
C2H5
C2H5
CH(CH3)2
CH2CH2SCH3
CH2Ph
2. Chemistry
CH2Ph
The synthetic routes of
outlined in Scheme 1. 9-Substituted-
1–4 were prepared from the -tryptophan via five steps including
the Pictet–Spengler condensation, esterification, aromatization,
N-alkylation or N-benzylation and hydrolyzation as previously
b
-carboline amino acid conjugates are
CH2Ph(p-OH)
CH2CH2SCH3
CH2Ph
b-carboline-3-carboxylic acids
CH2Ph
L
(CH2)3Ph
(CH2)3Ph
(CH2)3Ph
(CH2)3Ph
n-C4H9
n-C4H9
CH3
CH(CH3)2
CH2CH2SCH3
CH2Ph
CH2CH2SCH3
CH2Ph
described [11,12]. Esterification of various
L-amino acid with
methanol or ethanol in the presence of SOCl2 at ꢀ5 ꢁC gave the
corresponding L-amino acid esters 5 in good yield.
The conversion of compounds 1–4 to
ester conjugates 6a–n (Table 1) was carried out via different ami-
dating approach either by activation of -carboline-3-carboxylic
acid 1–4 with N,N’-dicyclohexxylcarbodiimide (DCC) in anhydrous
THF [10], benzotriazole-1-yl-oxytri-pyrrolidino phosphonium
hexafluorophosphate (Py-BOP) in anhydrous CH2Cl2 [9], and N,
N’-carbonyldiimidazole (CDI) in anhydrous DMF. And the CDI was
b-carboline amino acid
proven to be the most efficient and convenient reagent with mild
reaction conditions, and compounds 1–4 were coupled to amino
acid esters 5 using CDI in anhydrous DMF to provide the target
compounds 6a–n in 82–96% yield. Refluxing of the corresponding
b
b-carboline amino acid ester 6 with aqueous sodium hydroxide for
CO2H
CONHCHR
COOR'
N
R
H2N
COOR'
N
N
N
5
R1
R1
R9
R9
1 R1=H R9=n-C4H9
2 R1=H R9=CH2Ph
3 R1=H R9=(CH2)3Ph
4 R1=CH3 R9=n-C4H9
6a-n
H
O
a
N
PhCH2Br
CONHCHR
CO2R'
CH2Ph
CONHCHR
COOH
N
N
N
R1
N
Br
R1
R9
R9
8a-h
7a-h
CONHCHR
CONHCHR
CO2Et
CH2Ph
PhCH2Br
CO2Et
N
N
N
N
Br
CH3
CH3
C4H9
C4H9
6 m
6 n
R = (CH2)2SCH3
R = CH2Ph
Scheme 1. Synthesis of b-carboline amino acid ester derivatives.

C. Ma et al. / European Journal of Medicinal Chemistry 45 (2010) 1515–1523
1517
Table 3
1h almost quantitatively generated
gates 7a–h (Table 2), while the amide bonds of b-carboline amino
b
-carboline amino acid conju-
Chemical structure of compounds 8a–h
acid ester conjugates were not affected.
CONHCHR
CO2R'
CH2Ph
The N2-benzylated
b
-carbolinium bromate derivatives 8a–h
(Table 3) was prepared from the corresponding -carboline amino
b
N
acid ester conjugates 6 by the addition of benzyl bromide in
refluxing ethyl acetate [15]. Compared with the N2-benzylated
N
Br
R1
reaction of other
b-carbolines [15] with benzyl bromide,
R9
compounds 8a–h were obtained with longer reaction time and
lower yield (32–62%), which might be attrituted to the inaccessi-
bility of the sterically hindered amino acid side chains. Unfortu-
nately, the same synthetic procedure was used for the preparation
of N2-benzylated compounds 6m and 6n but failed to afford the
.
Compounds
R1
R9
R
R0
8a
8b
8c
8d
8e
8f
H
H
H
H
H
H
H
H
n-C4H9
n-C4H9
n-C4H9
CH2Ph
CH(CH3)2
CH2CH2SCH3
CH2Ph
CH(CH3)2
CH2Ph
C2H5
C2H5
C2H5
C2H5
C2H5
C2H5
C2H5
C2H5
expected b-carbolinium bromates. The chemical structures of all
the synthesized novel compounds were characterized by elemental
analysis, MS, IR, 1H NMR, and 13C NMR spectra.
CH2Ph
(CH2)3Ph
(CH2)3Ph
(CH2)3Ph
CH(CH3)2
CH2CH2SCH3
CH2Ph
8g
8h
3. Results and discussion
All compounds were evaluated for their cytotoxic activity in
vitro against a panel of human tumor cell lines using cisplatin and
paclitaxel as the reference drug. In order to enhance the solubility
in aqueous solution, compounds 6a–n were prepared in the form of
hydrochloride and compounds 7a–h were converted into their
water-soluble sodium salts by the usual methods before use. The
IC50 results were summarized in Table 4.
b
-carboline-3-amino acid ester conjugates 8a–h displayed a broad
spectrum of cytotoxic activities against all human tumor cell lines
with IC50 values of lower than 50 M.
Of all -carboline-3-amino acid conjugates 7a–h, compounds 7f,
m
b
7g and 7h bearing a phenylpropyl substituent at position-9 of
Our efforts to improve the water solubility and cytotoxic potency
of b-carboline derivatives resulted in the compounds 6a–n, 7a–h and
8a–h. As predicted, compounds 7a–h displayed improved water
Table 4
Cytotoxicity of
a
b
-carboline derivatives in vitroc (IC50
,
mM).
Compounds
769-Pb
BGCb
KBb
786-0b
A375b
ClogPd
solubility with ClogP values ranged from 3.88 to 6.04 (Table 4).
Interestingly, N2-benzylated quaternary
b-carboline-3-amino acid
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
7a
7b
7c
7d
7e
7f
7g
7h
8a
8b
8c
8d
27.2
>200
>200
>200
32.5
>200
>200
>200
>200
>200
>200
187
>200
>200
105
114
>200
145
120
78.3
116
8.0
13.7
7.5
19.2
12.5
13.5
14.0
7.6
22.9
19.2
7.1
>200
>200
>200
>200
>200
>200
>200
>200
148
>200
>200
>200
>200
>200
>200
>200
>200
>200
162
>200
>200
>200
>200
113
>200
>200
>200
>200
>200
176
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
191
>200
>200
78.3
84.6
70.0
52.7
14.4
1.7
15.0
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
160
4.40
5.32
5.07
5.81
6.34
5.15
5.25
6.52
5.28
6.74
5.96
7.23
5.57
6.84
3.88
5.15
4.48
4.06
4.62
5.55
4.77
6.04
2.16
1.38
2.65
2.34
2.84
3.05
2.28
3.54
–
ester conjugates 8a–h exhibited excellent water solubility with
ClogP values ranged from 1.38 to 3.54. However, compounds 6a–n
were almost insoluble in aqueous solution.
Unfortunately, as shown in Table 4, the
ester conjugates 6a–n were almost inactive to all tumor cell lines
investigated at the concentration of 200 M. This was in disagree-
b-carboline amino acid
m
ment with earlier findings [10]. The poor water solubility of these
compounds might be significantly affected their potencies in vitro.
Whereas, their corresponding hydrolyzed congener 7a–h, bearing
a free carboxyl group at the side chain of amino acid residue,
exhibited moderate to weak cytotoxic activities against all tested
human tumor cell lines. Noticeably, most of the N2-benzylated
89.2
>200
>200
>200
155
>200
135
179
106
96.6
38.8
28.4
10.8
11.3
25.3
51.4
12.5
9.4
121
156
Table 2
96.3
58.0
58.9
33.8
22.5
8.2
41.7
15.8
25.8
10.4
7.3
Chemical structure of compounds 7a–h
139
136
76.1
CONHCHR
44.2
13.4
21.4
21.9
92.5
17.8
12.0
23.7
13.4
1.5
COOH
N
10.8
69.4
4.0
10.1
23.4
4.9
<0.08
N
8e
8f
8g
R1
R9
8h
Cisplatin
Paclitaxel
18.2
4.6
21.3
9.4
0.81
.
0.08
–
Compounds
R1
R9
R
a
Cytotoxicity as IC50 for each cell line is the concentration of compound, which
reduced by 50% the optical density of treated cells with respect to untreated using
the MTT assay.
7a
7b
7c
7d
7e
7f
H
H
H
H
H
H
H
H
n-C4H9
n-C4H9
n-C4H9
CH2Ph
(CH2)3Ph
(CH2)3Ph
(CH2)3Ph
(CH2)3Ph
CH2CH2SCH3
CH2Ph
CH2Ph(p-OH)
CH2CH2SCH3
CH3
CH(CH3)2
CH2CH2SCH3
CH2Ph
b
Cell lines include renal carcinoma (769-P), gastric carcinoma (BGC-823),
epidermoid carcinoma of the nasopharynx (KB), renal carcinoma (786-0), mela-
noma (A375).
c
The data represent the mean values of three independent determinations.
ClogP represent the calculated n-octanol/water partition coefficient (log Pow),
7g
7h
d
and the values produced by Chemdraw software.

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C. Ma et al. / European Journal of Medicinal Chemistry 45 (2010) 1515–1523
b
-carboline core displayed moderate cytotoxic activities. However,
improving water solubility and bioavailability, the synthesis of
the others only had marginal or no cytotoxic effects in any cell lines.
more N2-benzylated quaternary
b-carboline amino acid ester
Noticeably, compound 7h showed the best activity with, for
conjugates is needed.
example, 50% growth inhibition, IC50 8.0 mM against 769-P renal
carcinoma cell lines. Our previous reports [15] and the above-
mentioned results further confirmed that the phenylpropyl
5. Experimental
substituent represented the optimal structure at postion-9 of
b
-
5.1. Reagents and general procedures
carboline core for this class of compounds to exhibit potent cyto-
toxic activities.
All reagents were purchased from commercial suppliers and
were dried and purified when necessary. Melting points were
determined with a Kofler micromelting point apparatus without
correction. ESI-MS spectra were obtained from VG ZAB-HS spec-
trometer. 1H NMR and 13C NMR spectra were recorded on
a Mercury-Plus 300 spectrometer at 300 MHz and 75 MHz
respectively, using TMS as internal standard and CDCl3 or DMSO-d6
As predicted, the incorporating a benzyl substituent into posi-
tion-2 of
-carboline-3-amino acid ester conjugates 8a–h, which repre-
b
-carboline core led to the N2-benzylated quaternary
b
sented the most interesting cytotoxic activities. Compounds 8b, 8f
and 8g exhibited significant cytotoxic activities against all human
tumor cell lines with IC50 value of lower than 20
further confirmed that the N2-benzylated substituent on the
-carboline ring played a very vital role in the modulation of the
cytotoxic activities. Particularly, compounds 8b and 8g, having
a common methionine residue at position-3 of -carboline nucleus
but bearing an n-butyl and phenylpropyl substituent at position-9
of -carboline core, respectively, demonstrated the most potent
cytotoxic activities with IC50 value of 1.7 M and 4.0 M against
mM. These results
as solvent and chemical shifts (d) were expressed in ppm. Elemental
b
analyses were carried out on an Elementar Vario EL CHNS
Elemental Analyzer. Silica gel F254 were used in analytical thin-
layer chromatography (TLC) and silica gel were used in column
chromatography, respectively.
b
b
m
m
5.2. Gerneral procedure for the preparation of amino acid methyl/
786-0 renal carcinoma cell lines, respectively. This observation
indicated that methionine side chain might be more favorable for
ethyl esters 5
the cytotoxic potency of N2-benzylated quaternary
b-carboline
To the solution of L-amino acid (10 mmol) and anhydrous
amino acid ester conjugates.
methanol/ethanol (100 mL), SOCl2 (1.0 mL, 12 mmol) was added
slowly at ꢀ5 ꢁC for about 10–30 min until clear. And then the
reaction mixture was stirred for about 5 h at room temperature.
After the reaction was completed, the superfluous SOCl2 and
methanol/ethanol were removed on the rotary evaporator to give
4. Conclusions
A series of new N2-benzylated quaternary
b-carboline amino
acid ester conjugates described in this paper were proved to be
significantly cytotoxic activities. Current investigation corroborated
our previous observations that (1) the cytotoxic potencies of
the L-amino acid methyl/ethyl ester hydrochloride in 96–98% yield
as white solid.
To the mixture of the above-mentioned amino acid methyl/ethyl
ester hydrochlorides and anhydrous methanol/ethanol (100 mL),
anhydrous baryta (20 mmol) was added, and the reaction mixture
was stirred at room temperature overnight. After filtration and
evaporation, the amino acid esters were obtained as oil or solid,
which could be used directly for the next step without further
purification.
b
-carbolines were substituent-dependant; (2) introducing appro-
priate substituents into position-9 of -carboline nucleus enhanced
their cytotoxic activities; (3) the N2-benzyl substituent on the
-carboline core played a very important role in the modulation of
b
b
the cytotoxic potencies.
Some important molecular mechanisms of action of b-carbo-
lines have recently been reviewed [1]. However, the underlying
mechanism and the cellular target molecules responsible for such
5.3. Gerneral procedure for the preparation of compounds 6a–n
activity has not been completely understood. Some
were reported to have DNA intercalating activity [7,24] and inhib-
itory activity of topoisomerase [9], other -carbolines were iden-
tified as inhibitors of CDK [25] and MAPKAP-K2 [26]. Our previous
investigations reported that the ability of -carbolines to act as DNA
intercalating agents and Topoisomerase I inhibitors was related to
their potent antitumor activities [27], and -carbolines can pass
b-carbolines
A mixture of
1.1 mmol) and anhydrous DMF (15 mL) was stirred at room
temperature until clear, and then -amino acid ester (1.2 mmol) was
b-carboline-3-carboxylic acid (1 mmol), CDI (0.18 g,
b
L
b
added and stirred at room temperature for 3–8 h. After completion
of the reaction as indicated by TLC, the resulting solution was
poured into H2O (100 mL), and extracted with ethyl acetate
(3 ꢂ 50 mL). The organic phase was washed with water and brine,
then dried over anhydrous sodium sulfate, filtered, and evaporated.
The oil obtained was purified by silica column chromatography
with ethyl acetate/petroleum ether as the eluent to give
compounds 6a–n as white crystals.
b
through cell membrane and penetrate into cell nucleus quickly
resulting in intercalating into DNA in cells [28]. Moreover, our
group also found that some
HepG2 cells and other -carbolines can inhibit the expression of
Bcl-2 gene and upregulate the expression of death receptor Fas [29].
Unfortunately, the weak effects of -carbolines on the above-
b-carbolines can induce apoptosis in
b
b
mentioned cellular molecules indicated that they are unlikely to be
the targets for the potent inhibition of tumor cell growth. There is
no doubt that further investigation is urgently required to
5.3.1. N-(9-Butyl-b-carboline-3-carbonyl)-L-alanine methyl
ester (6a)
Yield 91%, mp 110–112 ꢁC; ESI-MS m/z 354 [M þ H]þ; IR (KBr):
3402 (N ꢀ H), 3049, 2962, 2931, 2853, 1739 (C]O), 1666 (C]O),
completely elucidate the mechanisms of action of
b
-carbolines.
-carboline
In order to confirm the utility of the N2-benzylated
b
1624, 1588, 1496, 1211, 748 cmꢀ1; 1H NMR (300 MHz, CDCl3)
d: 8.89
amino acid ester conjugates as an interesting antitumor agent,
compounds 8b, 8f and 8g are now selected and submitted to
further acute toxicity and antitumor activity studies in animal
models, and the relative possible results will be reported in due
course. Moreover, to acquire more information about the struc-
tural requirements for enhancing cytotoxic potencies and
(1H, s, ArH), 8.78 (1H, s, ArH), 8.59 (1H, d, J ¼ 7.8 Hz, CONH), 8.20
(1H, d, J ¼ 7.8 Hz), 7.62 (1H, t, J ¼ 7.2 Hz, ArH), 7.49 (1H, d, J ¼ 8.4 Hz,
ArH), 7.34 (1H, t, J ¼ 7.5 Hz, ArH), 4.90 (1H, m, CH), 4.42 (2H, t,
J ¼ 7.2 Hz, NCH2), 3.80 (3H, s, OCH3), 1.91 (2H, m, CH2), 1.61 (3H, d,
J ¼ 6.9 Hz, CHCH3),1.40 (2H, m, CH2), 0.96 (3H, t, J ¼ 7.2 Hz, CH3); 13
C
NMR (75 MHz, CDCl3)
d: 173.59 (C]O), 165.02 (C]O), 141.85,

C. Ma et al. / European Journal of Medicinal Chemistry 45 (2010) 1515–1523
1519
139.76, 137.99, 131.74, 129.39, 128.44, 123.00, 121.34, 120.82, 114.70,
111.18, 52.80, 48.57, 43.38, 31.67, 20.53, 18.31, 14.45. Anal. Calc. for
C20H23N3O3: C, 67.97; H, 6.56; N, 11.89. Found: C, 67.85; H, 6.74; N,
11.80.
CDCl3) d: 171.62 (C]O), 162.41 (C]O), 143.42, 137.83, 136.91, 134.17,
131.42, 130.75, 129.80, 129.26, 128.91, 127.24, 123.48, 122.13, 120.69,
116.37, 111.93, 61.63, 55.30, 44.01, 37.22, 31.73, 20.42, 14.85, 14.47.
Anal. Calc. for C27H29N3O3: C, 73.11; H, 6.59; N, 9.47. Found: C,
73.28; H, 6.70; N, 9.40.
5.3.2. N-(9-Butyl-b-carboline-3-carbonyl)-L-valine methyl
ester (6b)
5.3.6. N-(9-Butyl-b-carboline-3-carbonyl)-L-tyrosine methyl
Yield 83%, mp 99–101 ꢁC; ESI-MS m/z 382 [M þ H]þ; IR (KBr):
3384 (N ꢀ H), 3035, 2968, 2931, 2863, 1735 (C]O), 1669(C]O),
ester (6f)
Yield 88%, mp 145–147 ꢁC; ESI-MS m/z 447 [M þ H]þ; IR (KBr):
3373 (N ꢀ H), 3240, 3059, 3030, 2958, 2930, 2872, 1723 (C]O),
1621, 1586, 1497, 1201, 749 cmꢀ1; 1H NMR (300 M Hz, CDCl3)
d: 8.87
(1H, s, ArH), 8.75 (1H, s, ArH), 8.59 (1H, d, J ¼ 7.8 Hz, CONH), 8.19
(1H, d, J ¼ 7.8 Hz), 7.63 (1H, t, J ¼ 7.2 Hz, ArH), 7.51 (1H, d, J ¼ 8.4 Hz,
ArH), 7.36 (1H, t, J ¼ 7.5 Hz, ArH), 4.85 (1H, m, CH), 4.40 (2H, t,
J ¼ 7.2 Hz, NCH2), 3.78 (3H, s, OCH3), 3.11 (1H, m, CH), 1.41 (2H, m,
CH2), 1.21 (6H, s, CH (CH3)2), 0.96 (3H, t, J ¼ 7.2 Hz, CH3); 13C NMR
1622 (C]O), 1589, 1515, 1216, 828, 750 cmꢀ1 1H NMR (300 MHz,
;
CDCl3)
d
: 8.86 (1H, s, ArH), 8.74 (1H, s, ArH), 8.65 (1H, d, J ¼ 8.1 Hz,
CONH), 8.17 (1H, d, J ¼ 7.5 Hz, ArH), 7.61 (1H, t, J ¼ 7.8 Hz, ArH), 7.48
(1H, d, J ¼ 8.1 Hz, ArH), 7.32 (1H, t, J ¼ 7.5 Hz, ArH), 7.07 (2H, d,
J ¼ 7.8 Hz, 2ArH), 6.74 (1H, d, J ¼ 7.8 Hz, 2ArH), 6.17 (1H, s, OH), 5.11
(1H, q, CH), 4.39 (2H, t, J ¼ 7.2 Hz, NCH2), 3.74 (1H, s, OCH3), 3.20
(2H, m, CHCH2), 1.89 (2H, m, CH2), 1.39 (2H, m, CH2), 0.96 (3H, t,
(75 MHz, CDCl3) d: 171.61 (C]O), 162.57 (C]O), 143.43, 136.96,
134.24, 131.36, 130.83, 129.09, 123.66, 122.08, 120.77, 116.78, 111.91,
61.42, 59.42, 44.00, 31.74, 30.72, 20.43,19.84,19.58,14.47. Anal. Calc.
for C22H27N3O3: C, 69.27; H, 7.13; N, 11.02. Found: C, 69.17; H, 7.16;
N, 10.95.
J ¼ 7.2 Hz, CH3); 13C NMR (75 MHz, CDCl3)
d: 172.30 (C]O), 162.73
(C]O), 156.73, 143.16, 137.04, 134.89, 131.14, 130.71, 130.37, 129.61,
127.67, 123.40, 121.96, 120.74, 116.03, 115.84, 111.82, 55.34, 52.91,
43.90, 36.49, 31.72, 20.45, 14.49. Anal. Calc. for C26H27N3O4: C,
70.09; H, 6.11; N, 9.43. Found: C, 69.94; H, 6.20; N, 9.37.
5.3.3. N-(9-Butyl-b-carboline-3-carbonyl)-L-methionine ethyl
ester (6c)
Yield 95%, mp 100–102 ꢁC; ESI-MS m/z 428 [M þ H]þ; IR (KBr):
3372 (N ꢀ H), 3050, 2956, 2927, 2858, 1730 (C]O), 1674 (C]O),
5.3.7. N-(9-Benzyl-b-carboline-3-carbonyl)-L-methionine ethyl
ester (6g)
1625, 1518, 1495, 1211, 745 cmꢀ1; 1H NMR (300 MHz, CDCl3)
d
: 8.91
Yield 87%, mp 105–107 ꢁC; ESI-MS m/z 462 [M þ H]þ; IR (KBr):
3312 (N ꢀ H), 3058, 2971, 2918, 1741 (C]O), 1654 (C]O), 1586,
(1H, s, ArH), 8.80 (1H, s, ArH), 8.70 (1H, d, J ¼ 8.7 Hz, CONH), 8.21
(1H, d, J ¼ 7.8 Hz, ArH), 7.64 (1H, t, J ¼ 7.2 Hz, ArH), 7.51 (1H, d,
J ¼ 8.4 Hz, ArH), 7.35 (1H, t, J ¼ 7.5 Hz, ArH), 5.00 (1H, m, CH), 4.43
(2H, t, J ¼ 7.2 Hz, NCH2), 4.27 (2H, q, OCH2), 2.67 (2H, m, SCH2),
2.41–2.17 (2H, m, CHCH2), 2.14 (3H, s, SCH3), 1.92 (2H, m, CH2), 1.42
(2H, m, CH2), 1.33 (3H, t, J ¼ 7.2 Hz, CH3), 0.97 (3H, t, J ¼ 7.2 Hz, CH3);
1521, 1458, 1208, 746, 696 cmꢀ1; 1H NMR (300 MHz, CDCl3)
d: 8.92
(1H, s, ArH), 8.73 (1H, s, ArH), 8.63 (1H, d, J ¼ 8.1 Hz, CONH), 8.23
(1H, d, J ¼ 7.8 Hz, ArH), 7.61 (1H, t, J ¼ 7.5 Hz, ArH), 7.49 (1H, d,
J ¼ 8.1 Hz, ArH), 7.38 (1H, t, J ¼ 7.5 Hz, ArH), 7.29–7.09 (5H, m, 5ArH),
5.63 (2H, s, NCH2Ph), 4.99 (1H, m, CH), 4.26 (2H, q, OCH2), 2.63 (2H,
m, SCH2), 2.32–2.16 (2H, m, CHCH2), 2.13 (3H, s, SCH3), 1.32 (3H, t,
13C NMR (75 MHz, CDCl3)
d: 172.36 (C]O), 165.51 (C]O), 141.88,
139.72, 138.03, 131.83, 129.45, 128.45, 123.07, 121.34, 120.88, 114.81,
111.27, 61.56, 52.05, 43.42, 31.71, 31.44, 30.63, 20.56, 15.47, 14.94,
14.52. Anal. Calc. for C23H29N3O3S: C, 64.61; H, 6.84; N, 9.83. Found:
C, 64.50; H, 6.95; N, 9.76.
J ¼ 7.2 Hz, CH3); 13C NMR (75 MHz, CDCl3)
d: 172.12 (C]O), 163.63
(C]O), 143.02, 137.57, 137.32, 136.55, 130.96, 130.46, 130.19, 129.36,
128.30, 127.49, 123.50, 122.04, 121.18, 116.16, 111.99, 61.65, 52.54,
47.26, 30.98, 30.66, 15.39, 14.95. Anal. Calc. for C26H27N3O3S: C,
67.65; H, 5.90; N, 9.10. Found: C, 67.47; H, 6.02; N, 9.05.
5.3.4. N-(9-Butyl-b-carboline-3-carbonyl)-L-phenylalanine methyl
ester (6d)
5.3.8. N-(9-Benzyl-b-carboline-3-carbonyl)-L-phenylalanine ethyl
Yield 95%, mp 102–104 ꢁC; ESI-MS m/z 431 [M þ H]þ; IR (KBr):
3368 (N ꢀ H), 3031, 2955, 2882, 1737 (C]O), 1668 (C]O), 1624,
ester (6h)
Yield 96%, mp 147–149 ꢁC; ESI-MS m/z 478 [M þ H]þ; IR (KBr):
3383 (N ꢀ H), 3060, 3031, 2979, 2931, 2867, 1734 (C]O), 1665
(C]O), 1619, 1584, 1513, 1459, 1205, 734, 697 cmꢀ1;1H NMR
1588, 1511, 1491, 1203, 748, 700 cmꢀ1; 1H NMR (300 MHz, CDCl3)
d:
8.86 (1H, s, ArH), 8.71 (1H, s, ArH), 8.60 (1H, d, J ¼ 8.4 Hz, CONH),
8.16 (1H, d, J ¼ 7.8 Hz, ArH), 7.59 (1H, t, J ¼ 7.5 Hz, ArH), 7.45 (1H, d,
J ¼ 8.4 Hz, ArH), 7.30–7.22 (6H, m, 6ArH), 5.17 (1H, m, CH), 4.35 (2H,
t, J ¼ 7.2 Hz, NCH2), 3.74 (3H, s, OCH3), 3.30 (2H, m, CHCH2), 1.88
(2H, m, CH2),1.38 (2H, m, CH2), 0.94 (3H, t, J ¼ 7.2 Hz, CH3); 13C NMR
(300 MHz, CDCl3) d: 8.91 (1H, s, ArH), 8.70 (1H, s, ArH), 8.58 (1H, d,
J ¼ 8.1 Hz, CONH), 8.23 (1H, d, J ¼ 7.8 Hz, ArH), 7.60 (1H, t, J ¼ 7.8 Hz,
ArH), 7.48 (1H, d, J ¼ 8.1 Hz, ArH), 7.36 (1H, t, J ¼ 7.5 Hz, ArH),
7.29–7.13 (10H, m, 10ArH), 5.62 (2H, s, NCH2Ph), 5.12 (1H, m, CH),
4.19 (2H, q, OCH2), 3.28 (2H, d, J ¼ 6.3 Hz, CHCH2), 1.24 (3H, t,
(75 MHz, CDCl3) d: 172.02 (C]O), 162.53 (C]O), 143.35, 137.92,
136.97, 134.25, 131.37, 130.78, 129.85, 129.35, 128.90, 127.21, 123.53,
122.10, 120.73, 116.29, 111.88, 55.25, 48.90, 43.95, 37.53, 31.76,
20.34, 14.48. Anal. Calc. for C26H27N3O3: C, 72.71; H, 6.34; N, 9.78.
Found: C, 72.63; H, 6.40; N, 9.68.
J ¼ 7.2 Hz, CH3); 13C NMR (75 MHz, CDCl3)
d: 171.94 (C]O), 165.03
(C]O), 142.01, 140.00, 138.14, 137.69, 132.08, 129.79, 129.62, 129.35,
128.94, 128.82, 128.21, 127.51, 127.24, 123.12, 121.54, 121.20, 114.78,
111.47, 61.57, 54.27, 47.00, 37.65, 14.87. Anal. Calc. for C30H27N3O3: C,
75.45; H, 5.70; N, 8.80. Found: C, 75.27; H, 5.82; N, 8.70.
5.3.5. N-(9-Butyl-b-carboline-3-carbonyl)-L-phenylalanine ethyl
ester (6e)
5.3.9. N-(9-Phenylpropyl-b-carboline-3-carbonyl)-L-alanine
Yield 92%, mp 107–108 ꢁC; ESI-MS m/z 444 [M þ H]þ; IR (KBr):
3370 (N ꢀ H), 3063, 3028, 2959, 2928, 2872, 1735 (C]O), 1665
methyl ester (6i)
Yield 93%, mp 141–143 ꢁC; ESI-MS m/z 416 [M þ H]þ; IR (KBr):
3315 (N ꢀ H), 3054, 2944, 2853, 1748 (C]O), 1652 (C]O), 1588,
(C]O), 1624, 1586, 1516, 1494, 1199, 750, 702 cmꢀ1 1H NMR
;
(300 MHz, CDCl3)
d: 8.88 (1H, s, ArH), 8.76 (1H, s, ArH), 8.61 (1H, d,
1518, 1459, 1215, 749, 699 cmꢀ1; 1H NMR (300 MHz, CDCl3)
d: 8.91
J ¼ 8.1 Hz, CONH), 8.20 (1H, d, J ¼ 7.8 Hz, ArH), 7.62 (1H, t, J ¼ 7.8 Hz,
ArH), 7.49 (1H, d, J ¼ 8.1 Hz, ArH), 7.36–7.20 (6H, m, 6ArH), 5.13 (1H,
q, CH), 4.42 (2H, t, J ¼ 7.5 Hz, NCH2), 4.19 (2H, q, OCH2), 3.29 (2H, d,
J ¼ 6.3 Hz, CHCH2Ph), 1.92 (2H, m, CH2), 1.42 (2H, m, CH2), 1.25 (3H,
t, J ¼ 7.2 Hz, CH3), 0.98 (3H, t, J ¼ 7.2 Hz, CH3); 13C NMR (75 MHz,
(1H, s, ArH), 8.69 (1H, s, ArH), 8.63 (H, d, J ¼ 7.2 Hz, CONH), 8.22 (1H,
d, J ¼ 7.8 Hz, ArH), 7.62 (1H, t, J ¼ 7.8 Hz, ArH), 7.42–7.15 (7H, m,
7ArH), 4.89 (1H, m, CH), 4.44 (2H, t, J ¼ 7.2 Hz, NCH2), 3.81 (3H, s,
OCH3), 2.74 (2H, t, J ¼ 7.5 Hz, CH2Ph), 2.29 (2H, m, CH2), 1.62 (3H, d,
J ¼ 7.2 Hz, CHCH3); 13C NMR (75 MHz, CDCl3)
d: 173.60 (C]O),

1520
C. Ma et al. / European Journal of Medicinal Chemistry 45 (2010) 1515–1523
165.01 (C]O), 141.83, 141.67, 139.77, 137.91, 131.69, 129.50, 128.99,
128.75, 128.54, 126.56, 123.14, 121.37, 120.95, 114.80, 111.18, 52.84,
48.56, 43.35, 33.17, 31.19, 18.25. Anal. Calc. for C25H25N3O3: C, 72.27;
H, 6.06; N, 10.11. Found: C, 72.10; H, 6.11; N, 10.02.
132.31, 131.64, 131.03, 123.06, 122.40, 120.19, 115.76, 111.80, 61.66,
53.18, 45.38, 33.35, 30.81, 30.54, 20.25, 19.42, 15.34, 14.98, 14.42.
Anal. Calc. for C24H31N3O3S: C, 65.28; H, 7.08; N, 9.52. Found: C,
65.38; H, 7.04; N, 9.43.
5.3.10. N-(9-Phenylpropyl-
b-carboline-3-carbonyl)-
L
-valine ethyl
5.3.14. N-(1-Methyl-9-butyl-
b-carboline-3-carbonyl)-L-
ester (6j)
phenylalanine ethyl ester (6n)
Yield 82%, mp 123–125 ꢁC; ESI-MS m/z 459 [M þ H]þ; IR (KBr):
3366 (N ꢀ H), 3061, 3027, 2960, 1730 (C]O), 1669 (C]O), 1588,
Yield 92%, mp 110–111 ꢁC; ESI-MS m/z 459 [M þ H]þ; IR (KBr):
3379 (N ꢀ H), 3060, 2952, 2910, 2870, 1740 (C]O), 1655 (C]O),
1518, 1463, 1193, 746, 699 cmꢀ1; 1H NMR (300 MHz, CDCl3)
d: 8.90
1621, 1581, 1515, 1192, 750 cmꢀ1; 1H NMR (300 MHz, CDCl3)
d: 8.64
(1H, s, ArH), 8.71 (1H, s, ArH), 8.63 (1H, d, J ¼ 8.4 Hz, CONH), 8.20
(1H, d, J ¼ 7.8 Hz, ArH), 7.60 (1H, t, J ¼ 7.8 Hz, ArH), 7.41–7.15 (7H, m,
7ArH), 4.81 (1H, m, CH), 4.43 (2H, t, J ¼ 6.9 Hz, NCH2), 4.26 (2H, q,
OCH2), 2.74 (2H, t, J ¼ 7.2 Hz, CH2Ph), 2.40–2.26 (3H, m, CH2, CH
(s, 1H, ArH), 8.58 (1H, d, J ¼ 8.1 Hz, CONH), 8.06 (1H, d, J ¼ 7.8 Hz,
ArH), 7.49 (1H, t, J ¼ 7.8 Hz, ArH), 7.36 (1H, d, J ¼ 8.4 Hz, ArH),
7.23–7.14 (6H, m, 6ArH), 5.02 (1H, q, CH), 4.44 (2H, t, J ¼ 7.8 Hz,
NCH2), 4.10 (2H, q, OCH2), 3.19 (2H, m, CHCH2), 2.93 (3H, s, ArCH3),
1.72 (2H, m, CH2), 1.36 (2H, m, CH2), 1.15 (3H, t, J ¼ 7.2 Hz, CH3),
(CH3)2), 1.33 (3H, t, J ¼ 6.9 Hz, CH3), 1.07 (6H, t, J ¼ 6.9 Hz, 2CH3); 13
C
NMR (75 MHz, CDCl3)
d
: 171.99 (C]O), 165.05 (C]O), 141.87,
0.90 (3H, t, J ¼ 7.2 Hz, CH3).; 13C NMR (75 MHz, CDCl3)
d: 171.94
141.65, 139.49, 137.98, 131.91, 129.50, 128.94, 128.73, 128.61, 126.52,
123.13, 121.37, 120.96, 114.73, 111.15, 61.53, 57.93, 43.45, 33.23,
31.43, 31.20, 19.82, 18.85, 14.97. Anal. Calc. for C28H31N3O3: C, 73.50;
H, 6.83; N, 9.18. Found: C, 73.28; H, 6.99; N, 9.20.
(C]O), 164.86 (C]O), 142.10, 140.65, 138.51, 137.48, 136.38,
129.85, 129.24, 129.16, 128.98, 127.35, 122.45, 121.41, 120.87,
112.93, 111.26, 61.57, 54.01, 44.82, 37.75, 33.38, 24.09, 20.34, 14.86,
14.47. Anal. Calc. for C28H31N3O3: C, 73.50; H, 6.83; N, 9.18. Found:
C, 73.41; H, 6.99; N, 9.10.
5.3.11. N-(9-Phenylpropyl-b-carboline-3-carbonyl)-L-methionine
ethyl ester (6k)
5.4. General procedure for the preparation of compounds 7a–h
Yield 84%, mp 113–115 ꢁC; ESI-MS m/z 491 [M þ H]þ; IR (KBr):
3323 (N–H), 3055, 2974, 2918, 2855,1743 (C]O),1653 (C]O),1588,
A mixture of the corresponding b-carboline-3-carbonyl-L-amino
1517, 1500, 1214, 749, 699 cmꢀ1; 1H NMR (300 MHz, CDCl3)
d
: 8.91
acid ester 6 (1 mmol), NaOH (5 mmol), ethanol (10 mL) and H2O
(10 mL) was stirred for 1 h at refluxing, and then the ethanol was
removed on the rotary evaporator. The mixture was neutralized to
pH 5 with 5M hydrochloride and cooled. The precipitate was
collected, washed well with H2O and dried to give compounds 7a–h
as yellow solid. The solid was further crystallized from ethanol.
(1H, s, ArH), 8.74–870 (2H, ArH, CONH), 8.21 (1H, d, J ¼ 7.8 Hz, ArH),
7.62 (1H, t, J ¼ 7.5 Hz, ArH), 7.43–7.15 (7H, m, 7ArH), 4.98 (1H, m,
CH), 4.45 (2H, t, J ¼ 7.2 Hz, NCH2), 4.27 (2H, q, OCH2), 2.75 (2H, t,
CH2Ph), 2.67 (2H, m, CHCH2), 2.40–2.18 (4H, m, SCH2, CH2), 2.14
(3H, s, SCH3), 1.34 (3H, t, J ¼ 7.2 Hz, CH3); 13C NMR (75 MHz, CDCl3)
d: 172.19 (C]O), 165.52 (C]O), 141.67, 140.52, 139.59, 137.88,
130.28, 129.14, 128.95, 128.80, 128.43, 126.56, 122.47, 121.77, 120.72,
114.78, 109.95, 61.87, 52.08, 43.30, 33.51, 32.88, 30.64, 30.58, 15.92,
14.63. Anal. Calc. for C28H31N3O3S: C, 68.68; H, 6.38; N, 8.58. Found:
C, 68.81; H, 6.40; N, 8.47.
5.4.1. N-(9-Butyl-
b
-carboline-3-carbonyl)-
L
-methionine (ꢀ7a)
Yield 95%, mp 195–196 ꢁC; ESI-MS m/z 420 [M ꢀ H] ; IR (KBr):
33 375 (N ꢀ H), 3030, 2966, 2937, 2868, 1733 (C]O), 1670 (C]O),
1624, 1510, 1496, 1201, 745 cmꢀ1; 1H NMR (300 MHz, DMSO-d6)
d:
9.07 (1H, s, ArH), 8.84 (1H, s, ArH), 8.79 (1H, d, J ¼ 8.4 Hz, CONH),
8.41 (1H, d, J ¼ 7.8 Hz, ArH), 7.77 (1H, d, J ¼ 8.4 Hz, ArH), 7.65 (1H, t,
J ¼ 8.4 Hz, ArH), 7.33 (1H, t, J ¼ 7.5 Hz, ArH), 4.67 (1H, q, CH), 4.58
(2H, t, J ¼ 6.6 Hz, NCH2), 2.55 (2H, m, CHCH2), 2.16 (2H, q, SCH2),
2.05 (3H, s, SCH3), 1.82 (2H, m, CH2), 1.27 (2H, m, CH2), 0.87 (3H, t,
5.3.12. N-(9-Phenylpropyl-
phenylalanine ethyl ester (6l)
b-carboline-3-carbonyl)-L-
Yield 89%, mp 109–111 ꢁC; ESI-MS m/z 507 [M þ H]þ; IR (KBr):
3381 (N ꢀ H), 3034, 2935, 2862, 1741 (C]O), 1661 (C]O), 1590,
1509, 1459, 1197, 746, 700 cmꢀ1; 1H NMR (300 MHz, CDCl3)
d
: 8.88
J ¼ 7.2 Hz, CH3); 13C NMR (75 MHz, DMSO-d6)
d: 173.87 (C]O),
(1H, s, ArH), 8.66 (1H, s, ArH), 8.61 (1H, d, J ¼ 8.1 Hz, CONH), 8.19
(1H, d, J ¼ 7.8 Hz, ArH), 7.61 (1H, t, J ¼ 7.8 Hz, ArH), 7.41–7.15 (12H,
m, 12ArH), 5.14 (1H, m, CH), 4.41 (2H, t, J ¼ 7.2 Hz, NCH2), 4.20 (2H,
q, OCH2), 3.29 (2H, d, J ¼ 6.0 Hz, CHCH2), 2.73 (2H, t, J ¼ 7.5 Hz,
CH2Ph), 2.28 (2H, m, CH2), 1.25 (3H, t, J ¼ 6.9 Hz, CH3); 13C NMR
165.32 (C]O), 141.86, 139.80, 137.99, 131.79, 129.42, 128.45, 123.05,
121.34, 120.86, 114.70, 111.23, 51.95, 43.41, 31.70, 30.69, 20.56, 15.48,
14.50. Anal. Calc. for C21H25N3O3S: C, 63.13; H, 6.31; N,10.52. Found:
C, 63.00; H, 6.47; N, 10.45.
(75 MHz, CDCl3)
d
: 171.86 (C]O), 165.29 (C]O), 141.61, 140.56,
5.4.2. N-(9-Butyl-b-carboline-3-carbonyl)-L-phenylalanine (7b)
139.65, 137.82,136.60, 130.34, 129.65, 129.04, 128.91, 128.80,128.69,
128.45, 127.14, 126.56, 122.43, 121.76, 120.68, 114.66, 109.94, 61.69,
53.96, 43.26, 38.97, 33.51, 30.65,14.59. Anal. Calc. for C32H31N3O3: C,
76.02; H, 6.18; N, 8.31. Found: C, 75.90; H, 6.28; N, 8.28.
Yield 94%, mp 190–192 ꢁC; ESI-MS m/z 436 [M ꢀ H]ꢀ; IR (KBr):
3346, 3030, 2927, 2853, 1734 (C]O), 1636 (C]O), 1590, 1521, 1500,
1201, 742, 698 cmꢀ1 1H NMR (300 MHz, DMSO-d6)
; d: 9.03 (1H, s,
ArH), 8.80 (1H, s, ArH), 8.63 (1H, d, J ¼ 8.1 Hz, CONH), 8.39 (1H, d,
J ¼ 7.5 Hz, ArH), 7.75 (1H, d, J ¼ 8.4 Hz, ArH), 7.63 (1H, t, J ¼ 7.5 Hz,
ArH), 7.31 (1H, t, J ¼ 7.5 Hz, ArH), 7.26–7.14 (5H, m, 5ArH), 4.82 (1H,
q, CH), 4.55 (2H, t, J ¼ 6.9 Hz, NCH2), 3.25 (2H, m, CHCH2), 1.80 (2H,
m, CH2), 1.26 (2H, m, CH2), 0.86 (3H, t, J ¼ 7.2 Hz, CH3); 13C NMR
5.3.13. N-(1-Methyl-9-butyl-b-carboline-3-carbonyl)-L-methionine
ethyl ester (6m)
Yield 91%, mp 104–105 ꢁC; ESI-MS m/z 442 [M þ H]þ; IR (KBr):
3363 (N ꢀ H), 3054, 2957, 2915, 2856, 1727 (C]O), 1675 (C]O),
(75 MHz, DMSO-d6) d: 173.24 (C]O), 162.87 (C]O), 143.27, 138.01,
1620, 1560, 1514, 1211, 745 cmꢀ1
;
1H NMR (300 MHz, CDCl3)
d:
136.78, 135.37, 131.43, 130.82, 129.76, 128.98, 128.93, 127.03, 122.76,
122.59, 120.45, 115.28, 111.86, 55.35, 44.05, 37.50, 31.65, 20.22,
14.52. Anal. Calc. for C25H25N3O3: C, 72.27; H, 6.06; N, 10.11. Found:
C, 72.05; H, 6.24; N, 10.10.
8.75–8.73 (2H, ArH, CONH), 8.17 (1H, d, J ¼ 8.1 Hz, ArH), 7.60 (1H, t,
J ¼ 8.1 Hz, ArH), 7.48 (1H, d, J ¼ 8.4 Hz, ArH), 7.32 (1H, t, J ¼ 7.8 Hz,
ArH), 4.98 (1H, m, CH), 4.58 (2H, t, J ¼ 7.8 Hz, NCH2), 4.27 (2H, q,
OCH2), 3.08 (3H, s, ArCH3), 2.65 (2H, m, SCH2), 2.36–2.18 (2H, m,
CHCH2), 2.14 (3H, s, SCH3), 1.86 (2H, m, CH2), 1.47 (2H, m, CH2), 1.34
(3H, t, J ¼ 7.2 Hz, CH3),1.01(3H, t, J ¼ 7.2 Hz, CH3); 13C NMR (75 MHz,
5.4.3. N-(9-Butyl-
b
-carboline-3-carbonyl)-
L
-tyrosine (7c)ꢀ
Yield 94%, mp 183–185 ꢁC; ESI-MS m/z 430 [M ꢀ H] ; IR (KBr):
CDCl3)
d: 172.00 (C]O), 161.59 (C]O), 143.86, 141.08, 134.66,
3373 (N ꢀ H), 3240, 3059, 3030, 2958, 2930, 2872, 1723 (C]O),

C. Ma et al. / European Journal of Medicinal Chemistry 45 (2010) 1515–1523
1521
1622 (C]O), 1589, 1515, 1216, 828, 750 cmꢀ1
;
1H NMR (300 MHz,
CH), 4.61 (2H, t, J ¼ 7.2 Hz, NCH2), 2.65 (2H, t, J ¼ 7.8 Hz, CH2Ph),
2.53 (2H, m, CHCH2), 2.20–2.11 (4H, m, SCH2, CH2), 2.05 (3H, s,
DMSO-d6) : 9.06 (1H, s, ArH), 8.84 (1H, s, ArH), 8.61 (1H, d,
d
J ¼ 8.1 Hz, CONH), 8.41 (1H, d, J ¼ 7.8 Hz, ArH), 7.77 (1H, d, J ¼ 8.1 Hz,
ArH), 7.65 (1H, t, J ¼ 7.8 Hz, ArH), 7.33 (1H, t, J ¼ 7.5 Hz, ArH), 7.01
(2H, d, J ¼ 7.8 Hz, 2ArH), 6.62 (1H, d, J ¼ 7.8 Hz, 2ArH), 4.73 (1H, q,
CH), 4.57 (2H, t, J ¼ 6.9 Hz, NCH2), 3.11 (2H, m, CHCH2), 1.81 (2H, m,
CH2), 1.28 (2H, m, CH2), 0.87 (3H, t, J ¼ 7.2 Hz, CH3); 13C NMR
SCH3); 13C NMR (75 MHz, DMSO-d6)
d: 173.84 (C]O), 165.31
(C]O), 141.83, 141.64, 139.89, 137.91, 131.69, 129.45, 128.95, 128.73,
128.55, 126.53, 123.08, 121.39, 120.91, 114.73, 111.13, 51.97, 43.37,
33.20, 31.74, 31.18, 30.70, 15.49. Anal. Calc. for C26H27N3O3S: C,
67.65; H, 5.90; N, 9.10. Found: C, 67.77; H, 5.88; N, 9.11.
(75 MHz, DMSO-d6) d: 173.46 (C]O), 164.37 (C]O), 156.66, 142.12,
138.67, 137.73, 131.34, 130.78, 129.78, 128.83, 127.81, 123.05, 121.16,
121.09, 115.82, 114.76, 111.28, 54.44, 43.51, 36.83, 31.68, 20.53, 14.46.
Anal. Calc. for C25H25N3O4: C, 69.59; H, 5.84; N, 9.74. Found: C,
69.50; H, 6.03; N, 9.63.
5.4.8. N-(9-Phenylpropyl-b-carboline-3-carbonyl)-L-
phenylalanine (7h)
Yield 97%, mp 179–180 ꢁC; ESI-MS m/z 477 [M ꢀ H]ꢀ; IR (KBr):
3376 (N ꢀ H), 3027, 2929, 2860, 1735 (C]O), 1626 (C]O), 1591,
1526, 1500, 1210, 746, 699 cmꢀ1 1H NMR (300 MHz, DMSO-d6)
; d:
5.4.4. N-(9-Benzyl-
b
-carboline-3-carbonyl)-
L
-methionineꢀ(7d)
9.02 (1H, s, ArH), 8.86 (1H, s, ArH), 8.73 (1H, d, J ¼ 8.1 Hz, CONH),
8.40 (1H, d, J ¼ 7.8 Hz, ArH), 7.72 (1H, d, J ¼ 8.1 Hz, ArH), 7.65 (1H, t,
J ¼ 7.5 Hz, ArH), 7.33 (1H, t, J ¼ 7.5 Hz, ArH), 7.25–7.14 (10H, m,
10ArH), 4.90 (1H, m, CH), 4.60 (2H, t, J ¼ 6.9 Hz, NCH2), 3.24 (2H, m,
CHCH2), 2.65 (2H, t, J ¼ 7.8 Hz, CH2Ph), 2.13 (2H, m, CH2); 13C NMR
Yield 96%, mp 233–234 ꢁC; ESI-MS m/z 454 [M ꢀ H] ; IR (KBr):
3428, 3037, 2925, 1732 (C]O), 1634 (C]O), 1530, 1501, 1459, 1181,
748 cmꢀ1 1H NMR (300 MHz, DMSO-d6)
; d: 9.10 (1H, s, ArH), 8.85
(1H, s, ArH), 8.79 (1H, d, J ¼ 8.1 Hz, CONH), 8.43 (1H, d, J ¼ 7.5 Hz,
ArH), 7.78 (1H, d, J ¼ 7.5 Hz, ArH), 7.62 (1H, t, J ¼ 7.5 Hz, ArH), 7.33
(1H, t, J ¼ 7.5 Hz, ArH), 7.27–7.19 (5H, m, 5ArH), 5.84 (2H, s,
NCH2Ph), 4.65 (1H, q, CH), 2.52 (2H, m, CHCH2), 2.14 (2H, q, SCH2),
(75 MHz, DMSO-d6) d: 173.29 (C]O), 164.36 (C]O), 142.13, 141.59,
138.63, 138.00, 137.68, 131.20, 129.83, 129.03, 128.89, 128.70, 127.16,
126.49, 123.11, 121.24, 121.16, 114.91, 111.24, 54.26, 43.49, 37.52,
33.15, 31.12. Anal. Calc. for C30H27N3O3: C, 75.45; H, 5.70; N, 8.80.
Found: C, 75.31; H, 5.85; N, 8.72.
2.04 (3H, s, SCH3); 13C NMR (75 MHz, DMSO-d6)
d: 173.83 (C]O),
165.27 (C]O), 142.00, 140.24, 138.12, 137.70, 132.03, 129.63, 129.37,
128.85, 128.23, 127.53, 123.16, 121.57, 121.21, 114.79, 111.50, 51.97,
46.99, 31.68, 30.70, 15.47. Anal. Calc. for C24H23N3O3S: C, 66.49; H,
5.35; N, 9.69. Found: C, 66.25; H, 5.55; N, 9.71.
5.5. General procedure for the preparation of compounds 8a–h
A mixture of N-(b-carboline-3-carbonyl)-L-amino acid esters
5.4.5. N-(9-Phenylpropyl-
b
-carboline-3-carbonyl)-
L
-alaniꢀne (7e)
(2 mmol) and benzyl bromide (20 mmol) in ethyl acetate (10 mL)
was refluxed for 24–36 h. The reaction mixture was monitored by
TLC and then cooled at 0 ꢁC. The yellow solid was filtered under
reduced pressure and washed well with ethyl acetate, and then
recrystallized from ethanol, dried in vacuum to give yellow crystals
8a–h.
Yield 94%, mp 178–179 ꢁC; ESI-MS m/z 423 [M ꢀ H] ; IR (KBr):
3383 (N ꢀ H), 3028, 2932, 1733 (C]O), 1627 (C]O), 1528,
1505,1457, 1213, 745 cmꢀ1 1H NMR (300 MHz, DMSO-d6)
; d: 12.80
(1H, s, COOH), 9.02 (1H, s, ArH), 8.84 (1H, s, ArH), 8.75 (1H, d,
J ¼ 7.5 Hz, CONH), 8.42 (1H, d, J ¼ 7.8 Hz, ArH), 7.72 (1H, d, J ¼ 8.1 Hz,
ArH), 7.64 (1H, t, J ¼ 8.1 Hz, 0.9 Hz, ArH), 7.32 (1H, t, J ¼ 7.5 Hz, ArH),
7.26–7.14 (4H, m, 4ArH), 4.61 (2H, t, J ¼ 6.9 Hz, NCH2), 4.54 (1H, m,
CH), 2.65 (2H, t, J ¼ 7.8 Hz, CH2Ph), 2.14 (2H, m, CH2), 1.46 (3H, d,
5.5.1. 2-Benzyl-9-butyl-3-(carbonyl-valine ethyl ester)-b-
carbolinium bromate (8a)
J ¼ 7.2 Hz, CHCH3); 13C NMR (75 MHz, DMSO-d6)
d: 176.63 (C]O),
Yield 39%, mp 174–175 ꢁC; ESI-MS m/z 487 [M ꢀ Br] þ; IR (KBr):
3429 (N ꢀ H), 3173, 2963, 2934, 2874, 1739 (CO2Et), 1668 (CONH),
164.12 (C]O), 141.66, 141.45, 140.83, 137.61, 131.53, 129.26, 128.81,
128.57, 128.46, 126.41, 122.76, 121.33, 120.74, 114.06, 110.86, 50.98,
43.20, 33.10, 31.05, 20.52. Anal. Calc. for C24H23N3O3: C, 71.80; H,
5.77; N, 10.47. Found: C, 71.73; H, 5.89; N, 10.40.
1635, 1536, 1513, 1461, 756, 714 cmꢀ1 1H NMR (300 MHz, DMSO-
;
d6)
d
: 10.00 (1H, s, ArH), 9.53 (1H, d, J ¼ 7.5 Hz, CONH), 8.94 (1H, s,
ArH), 8.64 (1H, d, J ¼ 7.8 Hz, ArH), 8.03 (1H, d, J ¼ 8.4 Hz, ArH), 7.91
(1H, t, J ¼ 8.1 Hz, ArH), 7.54 (1H, t, J ¼ 7.5 Hz, ArH), 7.56–7.29 (5H, m,
5ArH), 6.13 (2H, q, NþCH2Ph), 4.69 (2H, t, J ¼ 6.9 Hz, NCH2), 4.31
(1H, t, J ¼ 7.2 Hz, CH), 4.16 (2H, m, OCH2), 2.11 (1H, m, CHMe2), 1.84
(2H, m, CH2), 1.27 (2H, m, CH2), 1.22 (3H, t, J ¼ 7.2 Hz, CH3), 0.91–
5.4.6. N-(9-Phenylpropyl-b-carboline-3-carbonyl)-L-valine (7f)
Yield 96%, mp 93–95 ꢁC; ESI-MS m/z 429 [M ꢀ H]ꢀ; IR (KBr):
3379 (N ꢀ H), 3029, 2962, 2883, 1730 (C]O), 1628 (C]O), 1523,
1510, 1460, 1208, 745 cmꢀ1
;
1H NMR (300 MHz, DMSO-d6)
d: 9.02
0.83 (9H, m, CH3, CH(CH3)2); 13C NMR (75 MHz, DMSO-d6)
d: 171.04
(1H, s, ArH), 8.81 (2H, ArH, CONH), 8.23 (1H, d, J ¼ 7.5 Hz, ArH), 7.64
(1H, t, J ¼ 7.8 Hz, ArH), 7.41–7.13 (7H, m, 7ArH), 4.72 (1H, m, CH),
4.46 (2H, t, J ¼ 6.9 Hz, NCH2), 2.76 (2H, t, J ¼ 7.2 Hz, CH2Ph),
(C]O), 162.74 (C]O), 145.31, 136.82, 135.89, 135.33, 133.46, 132.07,
131.55, 129.48, 128.49, 124.88, 123.12, 119.96, 119.62, 112.53, 61.79,
61.65, 59.42, 44.52, 31.64, 30.52, 20.45, 19.11, 14.97, 14.49. Anal. Calc.
for C30H36BrN3O3: C, 63.60; H, 6.40; N, 7.42. Found: C, 63.65; H,
6.51; N, 7.37.
2.31–2.26 (3H, m, CH2, CH(CH3)2), 1.14 (6H, t, J ¼ 6.3 Hz, 2CH3); 13
C
NMR (75 MHz, DMSO-d6) d: 173.41 (C]O), 164.49 (C]O), 142.19,
141.66, 138.69, 137.80, 131.45, 129.88, 129.05, 128.95, 128.74, 126.53,
123.24, 121.29, 121.20, 114.95, 111.32, 57.94, 43.56, 33.20, 31.35,
31.20, 20.01, 18.73. Anal. Calc. for C26H27N3O3: C, 72.71; H, 6.34; N,
9.78. Found: C, 72.60; H, 6.50; N, 9.74.
5.5.2. 2-Benzyl-9-butyl-3-(carbonyl-methionine ethyl ester)-b-
carbolinium bromate (8b)
Yield 46%, mp 138–140 ꢁC; ESI-MS m/z 519 [M ꢀ Br] þ; IR (KBr):
3428 (N ꢀ H), 3160, 2593, 2932, 2870, 1739 (CO2Et), 1671 (CONH),
5.4.7. N-(9-Phenylpropyl-
b
-carboline-3-carbonyl)-
L
-
1633, 1577, 1513, 1458, 1215, 754, 714 cmꢀ1 1H NMR (300 MHz,
;
methionine (7g)
DMSO-d6)
d
: 9.96 (1H, s, ArH), 9.44 (1H, d, J ¼ 7.5 Hz, CONH), 9.17
Yield 96%, mp 192–194 ꢁC; ESI-MS m/z 483 [M ꢀ H]ꢀ; IR (KBr):
3430, 3376 (N ꢀ H), 3027, 2926, 1732 (C]O), 1635 (C]O), 1534,
(1H, s, ArH), 8.42 (1H, s, ArH), 8.05 (1H, d, J ¼ 8.1 Hz, ArH), 7.57 (1H,
t, J ¼ 7.8 Hz, ArH), 7.32–7.05 (6H, m, 6ArH), 6.12 (2H, q, NþCH2Ph),
4.64 (1H, q, CH), 4.24 (2H, t, J ¼ 6.9 Hz, NCH2), 4.02 (2H, q, OCH2),
2.10 (2H, m, CH2), 1.55 (4H, m, 2CH2), 1.06 (3H, t, J ¼ 7.2 Hz, CH3),
1502, 1460, 1170, 747 cmꢀ1; 1H NMR (300 MHz, DMSO-d6)
d: 12.88
(1H, s, COOH), 9.02 (1H, d, J ¼ 0.9 Hz, ArH), 8.84 (H, d, J ¼ 0.6 Hz,
ArH), 8.81 (1H, d, J ¼ 8.1 Hz, CONH), 8.42 (1H, d, J ¼ 7.8 Hz, ArH),
7.73 (1H, d, J ¼ 8.1 Hz, ArH), 7.64 (1H, dt, J ¼ 7.2 Hz, 0.9 Hz, ArH), 7.33
(1H, dt, J ¼ 7.8 Hz, 0.6 Hz, ArH), 7.26–7.14 (4H, m, 4ArH), 4.67 (1H, m,
0.62 (3H, t, J ¼ 6.9 Hz, CH3); 13C NMR (75 MHz, DMSO-d6)
d: 171.27
(C]O), 162.57 (C]O), 145.28, 136.32, 135.88, 135.42, 133.47, 132.03,
131.93, 129.04, 128.59, 127.49, 124.78, 123.18, 119.96, 119.63, 112.59,

1522
C. Ma et al. / European Journal of Medicinal Chemistry 45 (2010) 1515–1523
61.96, 61.68, 52.93, 44.61, 35.70, 31.69, 31.01, 28.03, 20.45, 14.89,
14.51. Anal. Calc. for C30H36BrN3O3S: C, 60.19; H, 6.06; N, 7.02.
Found: C, 60.00; H, 6.27; N, 6.95.
2.20 (2H, m, CH2), 2.10 (1H, m, CHMe2), 1.23 (3H, t, J ¼ 6.9 Hz, CH3),
0.91 (6H, d, J ¼ 6.3 Hz, CH(CH3)2); 13C NMR (75 MHz, DMSO-d6)
d:
171.04 (C]O), 162.75 (C]O), 145.28, 141.42, 136.79, 135.88, 135.35,
133.42, 132.12, 131.65, 131.27, 129.46, 129.26, 128.88, 128.59, 126.53,
124.86, 123.11, 120.02, 119.58, 112.45, 61.65, 59.43, 44.60, 33.08,
31.02, 30.50, 19.69, 19.13, 14.97. Anal. Calc. for C35H38BrN3O3: C,
66.87; H, 6.09; N, 6.68. Found: C, 66.78; H, 6.23; N, 6.60.
5.5.3. 2-Benzyl-9-butyl-3-(carbonyl-phenylalanine ethyl ester)-b-
carbolinium bromate (8c)
Yield 62%, mp 155–157 ꢁC; ESI-MS m/z 535 [M ꢀ Br] þ; IR (KBr)
3427(N ꢀ H), 3169, 3060, 2960, 1741 (CO2Et), 1670 (CONH), 1634,
1513, 1458, 1216, 753, 714 cmꢀ1
;
1H NMR (300 MHz, DMSO-d6)
d:
5.5.7. 2-Benzyl-3-(carbonyl-methionine ethyl ester)-9-
10.07 (1H, s, ArH), 9.82 (1H, d, J ¼ 7.2 Hz, CONH), 8.69 (1H, s, ArH),
8.53 (1H, d, J ¼ 7.8 Hz, ArH), 8.03 (1H, d, J ¼ 8.7 Hz, ArH), 7.91 (1H, t,
J ¼ 7.2 Hz, ArH), 7.55 (1H, t, J ¼ 7.2 Hz, ArH), 7.31–7.27 (8H, m, 8ArH),
6.00 (2H, q, NþCH2Ph), 4.71 (3H, m, CH, NCH2), 4.10 (2H, q, OCH2),
3.17–2.94 (2H, m, CH2Ph), 1.80 (2H, m, CH2), 1.25 (2H, m, CH2), 1.13
(3H, t, J ¼ 7.2 Hz, CH3), 0.85 (3H, t, J ¼ 7.2 Hz, CH3); 13C NMR
phenylpropyl-b-carbolinium bromate (8g)
Yield 32%, mp 134–136 ꢁC; ESI-MS m/z 581 [M ꢀ Br] þ; IR (KBr)
3428, 3161, 3027, 2980, 2940, 1739 (C]O), 1669 (C]O), 1632, 1578,
1514, 1456, 1340, 1213, 749, 707 cmꢀ1 1H NMR (300 MHz, DMSO-
;
d6)
d
: 10.17 (1H, d, J ¼ 4.2 Hz, ArH), 9.75 (1H, dd, J ¼ 28.8, 7.2 Hz),
8.97 (1H, d, J ¼ 21.0 Hz, ArH), 8.60 (1H, t, J ¼ 7.8 Hz, ArH), 8.01 (1H, d,
J ¼ 8.1 Hz, ArH), 7.91 (1H, t, J ¼ 7.8 Hz, ArH), 7.54 (1H, t, J ¼ 7.8 Hz,
ArH), 7.35–7.06 (10H, m, 10ArH), 6.20 (2H, m, NþCH2Ph), 4.79 (2H, t,
J ¼ 6.6 Hz, NCH2), 4.57 (1H, q, CH), 4.16 (2H, q, OCH2), 2.66 (2H, t,
J ¼ 7.8 Hz, CH2Ph), 2.40–2.20 (4H, m, 2CH2), 1.98 (2H, m, CH2), 1.21
(75 MHz, DMSO-d6) d: 171.05 (C]O), 162.28 (C]O), 145.23, 137.32,
136.39, 135.35, 133.44, 131.80, 129.86, 129.43, 129.09, 128.73, 127.51,
124.54, 123.21, 119.86, 119.40, 112.59, 61.84, 61.48, 55.31, 44.63,
37.33, 31.72, 20.45, 14.82, 14.53. Anal. Calc. for C34H36BrN3O3: C,
66.45; H, 5.90; N, 6.84. Found: C, 66.46; H, 6.03; N, 6.70.
(3H, t, J ¼ 7.2 Hz, CH3); 13C NMR (75 MHz, DMSO-d6)
d: 172.89
(C]O), 162.37 (C]O), 145.13, 141.47, 135.78, 135.51, 135.38, 133.33,
132.28, 131.93,129.48,129.27, 128.90,128.78,128.59,126.43,124.72,
123.11, 120.04, 119.69, 112.40, 61.61, 61.47, 53.00, 49.74, 44.72, 35.64,
33.02, 31.11, 28.39, 14.70. Anal. Calc. for C35H38BrN3O3S: C, 63.63; H,
5.80; N, 6.36. Found: C, 63.42; H, 5.90; N, 6.40.
5.5.4. 2,9-Dibenzyl-3-(carbonyl-valine ethyl ester)-b-carbolinium
bromate (8d)
Yield 36%, mp 195–196 ꢁC; ESI-MS m/z 521 [M ꢀ Br] þ; IR (KBr)
3429 (N ꢀ H), 3151, 3030, 2966, 2934, 1737 (CO2Et), 1667 (CONH),
1632, 1536, 1512, 1202, 756, 712 cmꢀ1; 1H NMR (300 MHz, DMSO-
d6)
d
: 10.07 (1H, s, ArH), 9.56 (1H, d, J ¼ 6.3 Hz, CONH), 8.98 (1H, s,
5.5.8. 2-Benzyl-3-(carbonyl-phenylalanine ethyl ester)-9-
ArH), 8.66 (1H, d, J ¼ 7.8 Hz, ArH), 8.01 (1H, d, J ¼ 8.7 Hz, ArH), 7.89
(1H, t, J ¼ 7.8 Hz, ArH), 7.54 (1H, t, J ¼ 7.5 Hz, ArH), 7.33–7.26 (10H,
m, 10ArH), 6.10 (2H, q, NþCH2Ph), 5.96 (2H, s, NCH2Ph), 4.34 (1H, t,
J ¼ 6.3 Hz, CH), 4.17 (2H, q, OCH2), 2.14 (1H, m, CHMe2), 1.22 (3H, t,
J ¼ 6.6 Hz, CH3), 0.92 (6H, d, J ¼ 6.0 Hz, CH(CH3)2); 13C NMR
phenylpropyl-b-carbolinium bromate (8h)
Yield 40%, mp 188–189 ꢁC; ESI-MS m/z 597 [M ꢀ Br] þ; IR (KBr)
3410, 3181, 3027, 2983, 2939, 2851, 1736 (C]O), 1670 (C]O), 1633,
1541, 1515, 1457, 1341, 1244, 748, 704 cmꢀ1 1H NMR (300 MHz,
;
DMSO-d6)
d
: 9.98 (1H, s, ArH), 9.80(1H, d, J ¼ 7.5 Hz, CONH), 8.65 (1H,
(75 MHz, DMSO-d6)
d: 171.03 (C]O), 162.70 (C]O), 145.29, 137.49,
s, ArH), 8.52 (1H, d, J ¼ 8.1 Hz, ArH), 8.01 (1H, d, J ¼ 8.1 Hz, ArH), 7.92
(1H, t, J ¼ 7.5 Hz, ArH), 7.56 (1H, t, J ¼ 7.5 Hz, ArH), 7.33–7.04 (15H, m,
15ArH), 6.00 (2H, m, NþCH2Ph), 4.75 (3H, m, CH, NCH2), 4.11 (2H, q,
OCH2), 3.05 (2H, m, CHCH2), 2.63 (2H, t, J ¼ 7.5 Hz, CH2Ph), 2.19 (2H,
136.52, 136.16, 135.18, 133.67, 132.65, 131.35, 129.52, 129.47, 128.66,
127.71, 125.01, 123.40, 120.21, 119.66, 112.77, 61.85, 61.70, 59.45,
47.83, 30.53, 19.71, 19.07, 14.98. Anal. Calc. for C33H34BrN3O3: C,
66.00; H, 5.71; N, 7.00. Found: C, 65.71; H, 5.93; N, 7.08.
m, CH2), 1.13 (3H, t, J ¼ 6.6 Hz, CH3); 13C NMR (75 MHz, DMSO-d6)
d:
171.06 (C]O), 162.31 (C]O), 145.22, 141.46, 137.37, 136.39, 135.86,
135.37, 133.42, 131.92, 131.82, 129.86, 129.44, 129.08, 128.80, 128.59,
127.50, 126.47, 124.51, 123.24, 119.97, 119.38, 112.51, 61.86, 61.47,
55.32, 44.71, 37.32, 33.03, 31.05, 14.81. Anal. Calc. for C39H38BrN3O3:
C, 69.23; H, 5.66; N, 6.21. Found: C, 69.22; H, 5.65; N, 6.03.
5.5.5. 2,9-Dibenzyl-3-(carbonyl-phenylalanine ethyl ester)-b-
carbolinium bromate (8e)
Yield 43%, mp 189–190 ꢁC; ESI-MS m/z 569 [M ꢀ Br] þ; IR (KBr)
3427 (N ꢀ H), 3156, 3057, 2977, 1738 (CO2Et), 1671 (CONH), 1632,
1541, 1514, 1456, 1220, 743, 700 cmꢀ1 1H NMR (300 MHz, DMSO-
;
d6)
d
: 10.01 (1H, s, ArH), 9.83 (1H, d, J ¼ 7.5 Hz, CONH), 8.72 (1H, s,
5.6. Cytotoxicity assays in vitro
ArH), 8.56 (1H, d, J ¼ 8.1 Hz, ArH), 7.99 (1H, d, J ¼ 8.4 Hz, ArH), 7.89
(1H, t, J ¼ 7.2 Hz, ArH), 7.56 (1H, t, J ¼ 7.5 Hz, ArH), 7.33–7.29 (5H, m,
5ArH), 7.25–7.22 (5H, m, 5ArH), 5.94 (4H, m, NþCH2Ph, NCH2Ph),
4.75 (1H, m, CH), 4.11 (2H, q, OCH2), 3.19–2.94 (2H, m, CH2Ph), 1.13
Cytotoxicity assays in vitro were carried out using 96 microtitre
plate cultures and MTT staining according to the procedures
described in our previous report [11]. Briefly, cells were grown in
(3H, t, J ¼ 7.2 Hz, CH3); 13C NMR (75 MHz, DMSO-d6)
d: 171.03
RPMI-1640 medium containing 10% (v/v) fetal calf serum and 50
mg/
(C]O), 162.20 (C]O), 145.28, 137.22, 137.10, 136.40, 136.14, 135.11,
133.76, 132.51, 131.48, 129.84, 129.51, 129.13, 128.70, 127.70, 127.56,
124.66, 123.58, 120.10, 119.35, 112.81, 61.92, 61.80, 55.25, 47.86,
37.37,14.78. Anal. Calc. for C37H34BrN3O3: C, 68.52; H, 5.28; N, 6.48.
Found: C, 68.28; H, 5.48; N, 6.22.
ml penicillin and 50 g/ml streptomycin. Cultures were propagated
m
at 37 ꢁC in a humified atmosphere containing 5% CO2. Cell lines were
obtained from Shanghai Cell Institute, Chinese Academy of Science.
Drug stock solutions were prepared in DMSO. The final concentra-
tion of DMSO in the growth medium was 2% (v/v) or lower,
concentration without effects on cell replication. The human tumor
cell line panel consisted of renal carcinoma (769-P), gastric carci-
noma (BGC-823), epidermoid carcinoma of the nasopharynx (KB),
renal carcinoma (786-0), melanoma (A375). In all of these experi-
ments, three replicate wells were used to determine each point.
5.5.6. 2-Benzyl-3-(carbonyl-valine ethyl ester)-9-phenylpropyl-b-
carbolinium bromate (8f)
Yield 40%, mp 148–150 ꢁC; ESI-MS m/z 549 [M ꢀ Br] þ; IR (KBr)
3428 (N ꢀ H), 3166, 2970, 1738 (CO2Et), 1668 (CONH), 1634, 1514,
1460, 1198, 749 cmꢀ1; 1H NMR (300 MHz, DMSO-d6)
d: 10.04 (1H, s,
ArH), 9.52 (1H, d, J ¼ 7.2 Hz, NH), 8.92 (1H, s, ArH), 8.63 (1H, d,
J ¼ 8.1 Hz, ArH), 8.00 (1H, d, J ¼ 7.5 Hz, ArH), 7.92 (1H, t, J ¼ 6.9 Hz,
ArH), 7.54 (1H, t, J ¼ 7.5 Hz, ArH), 7.47–7.08 (10H, m, 10ArH), 6.15
(2H, q, NþCH2Ph), 4.77 (2H, t, J ¼ 6.0 Hz, NCH2), 4.32 (1H, t,
J ¼ 6.9 Hz, CH), 4.17 (2H, q, OCH2), 2.64 (2H, t, J ¼ 7.5 Hz, CH2Ph),
Acknowledgment
This work was supported by Xinjiang Huashidan Pharmaceu-
tical Co. Ltd. and the Open Project of the State Key Labortory of
Biocontrol (2007-01).

C. Ma et al. / European Journal of Medicinal Chemistry 45 (2010) 1515–1523
1523
[13] R. Cao, H. Chen, W. Peng, Y. Ma, X. Hou, H. Guan, X. Liu, A. Xu, Eur. J. Med.
Chem. 40 (2005) 991–1001.
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