Synthesis, acute toxicities, and antitumor effects of novel 9-substituted β-carboline derivatives

Article abstract of DOI:10.1016/j.bmc.2004.06.038

A series of novel 9-substituted β-carboline derivatives was synthesized from the starting material harmine and l-tryptophan, respectively. Cytotoxic activities, acute toxicities, and antitumor effects of these compounds were investigated. A series of nove

Full text of DOI:10.1016/j.bmc.2004.06.038

Bioorganic & Medicinal Chemistry 12 (2004) 4613–4623
Synthesis, acute toxicities, and antitumor effects of novel
9-substituted b-carboline derivatives
Rihui Cao, Qi Chen, Xuerui Hou, Hongsheng Chen, Huaji Guan, Yan Ma,
Wenlie Peng and Anlong Xu*
Department of Biochemistry and Center for Biopharmaceutical Research, College of Life Sciences,
Sun Yat-sen (Zhongshan) University, 135 Xin Gang Xi Road, Guangzhou 510275, PR China
Received 3 May 2004; revised 27 June 2004; accepted 28 June 2004
Abstract—A series of novel 9-substituted b-carboline derivatives was synthesized from harmine and L-tryptophan, respectively. Cy-
totoxic activities of these compounds in vitro were investigated. The results showed that most compounds of 9-substituted b-carb-
oline derivatives had more remarkable cytotoxic activities in vitro than their corresponding parent compounds. Acute toxicities and
antitumor effects of the selected b-carboline derivatives in mice were also examined. The results demonstrated that a short alkyl or
benzyl substituent at position-9 increased the antitumor activities significantly and a ethoxycarbonyl or carboxyl substituent at posi-
tion-3 reduced the acute toxicity and neurotoxicity of these b-carboline derivatives dramatically. Moreover the compounds both
with an alkoxycarbonyl or carboxyl substituent at position-3 and a short alkyl or benzyl substituent at positon-9 exhibited more
significant antitumor activities and lower acute toxicities and neurotoxicities than the other compounds. The compound 8c, having
an n-butyl and a carboxyl substituent at position-9 and 3, respectively, was found to have the highest antitumor effect and the lowest
acute toxicity and neurotoxicity. These data suggested that (1) appropriate substituents at both position-9 and 3 of b-carboline
derivatives might play a crucial role in determining their enhanced antitumor activities and decreased acute toxicities and neurotoxic
effects; (2) the b-carboline derivatives have the potential to be used as antitumor drug leads.
ꢀ 2004 Published by Elsevier Ltd.
1. Introduction
our preliminary investigation results demonstrated that
the compounds with b-carboline nucleus have potential
antitumor activities. Yet we also found that this class of
compounds caused remarkable acute neurotoxicity
characterized by tremble, twitch, and jumping in exper-
imental mice models.
b-Carbolines are a large group of naturally occurring
and synthetic indole alkaloids with different degrees of
aromaticity, some of which are widely distributed in nat-
ure, including various plants,1–3 marine creatures,4 in-
sects,5 mammalians as well as human tissues and body
fluids.6–9 These compounds are of great interest due to
their various biological activities such as intercalating
into DNA,10,11 inhibiting CDK,12 and Topisom-
erase,13,14 inhibiting monoamine oxidase15,16 as well as
interacting with benzodiazepine receptors17–19 and 5-
hydroxy serotonin receptors,20 and their broad spectrum
pharmacological properties including anxiolytic, hyp-
notic, anticonvulsant,21–23 parasiticidal,24 antiviral25 as
well as antimicrobial activities.30 Recent work26–28 and
Many previous reports focused on the effects of these
compounds on the central nervous system (CNS), such
as their affinity with benzodiazepine receptors,17–19 5-
HT2A and 5-HT2C receptors20 and imidazoline recep-
tor32, and so on. However so far there have been few
such literatures about their cytotoxic activities of these
compounds in vitro, even no reports are available deal-
ing with systematic and detailed studies of structure–
activity relationships on both antitumor activities and
neurotoxic activities in vivo. A probable reason for this
is that many of the b-carboline derivatives of interest are
not readily available. One goal of the present investiga-
tions was to synthesize a series of novel b-carboline
derivatives and elucidate their preliminary relationships
between structures and antitumor activities as well as
Keywords: b-Carboline; Synthesis; Acute toxicity; Antitumor; Neuro-
toxicity.
*
Corresponding author. Tel.: +86-20-84113655; fax: +86-20-
84038377; e-mail: ls36@zsu.edu.cn
0968-0896/$ - see front matter ꢀ 2004 Published by Elsevier Ltd.
doi:10.1016/j.bmc.2004.06.038

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R. Cao et al. / Bioorg. Med. Chem. 12 (2004) 4613–4623
COOR3
N
COOR3
N
neurotoxicities, and the other aim of this study was to
increase the antitumor activities and decrease the neuro-
toxic activities of these compounds. The work would
help search for new antitumor leading compounds with
significant antitumor activities and lower neurotoxicities
by simple chemical structural modifications on the basis
of b-carboline ring. To the best of our knowledge, all 9-
substituted b-carboline derivatives except 2a–c are novel
compounds, and this is the first time to report the anti-
tumor activities and acute toxicities as well as neurotoxi-
cities of this class of compounds in mice.
DMF/ THF
NaH, RI or RBr
N
N
H
R9
5a R3=CH3 R9=CH3
5 R3=CH3
5b R3=CH3 R9=CH2CH3
6 R3=CH2CH3
7 R3=n-C4H9
5c R3=CH3 R9=n-C4H9
5d R3=CH3 R9=CH2C6H5
6a R3=CH2CH3 R9=CH3
6b R3=CH2CH3 R9=CH2CH3
6c R3=CH2CH3 R9=n-C4H9
6d R3=CH2CH3 R9=CH2C6H5
6e R3=CH2CH3 R9=CH2C6F5
6f R3=CH2CH3 R9=(CH2)3C6H5
7a R3=n-C4H9 R9=CH3
7b R3=n-C4H9 R9=CH2CH3
7c R3=n-C4H9 R9=n-C4H9
7d R3=n-C4H9 R9=CH2C6H5
2. Results and discussion
2.1. Synthetic approach
N-alkylation and N-benzylation derivatives of harmine
1 could be easily obtained in a good yield through react-
ing with alkyl or benzyl bromide in the presence of so-
dium hydride in DMF and THF (see Scheme 1). The
starting material L-tryptophan reacted with formalde-
hyde via well-known Pictet–Spengler condensation and
then the products were esterified with relevant alcohol
to produce 1,2,3,4-tetrahydro-b-carboline-3-carboxy-
lates, respectively. The 1,2,3,4-tetrahydro-b-carboline-
3-carboxylates reacted with SeO2 in acetic acid solution
by oxidative decarboxylation to produce b-carboline 3
and reacted with sulfur in anhydrous xylene by dehydro-
genation to afford b-carboline-3-carboxylate 5, 6, 7,
respectively. The N-9 position of compound 3, 5, 6, 7
was further alkylated or benzylated by the action of so-
dium hydride in anhydrous DMF followed by addition
of the relevant appropriate alkylating and benzylating
agents (see Schemes 2 and 3) to produce various 9-sub-
Scheme 3. Synthesis of 9-substituted b-carboline-3-carboxylate deriv-
atives.
COOC2H5
N
COOH
N
NaOH
N
R9
N
R9
8
R9=H
8a R9=CH3
8b R9=CH2CH3
8c R9=n-C4H9
8d R9=CH2C6H5
8e R9=CH2C6F5
8f R9=(CH2)3C6H5
6, 6a-6f
Scheme 4. Synthesis of 9-substituted b-carboline-3-carboxylic acid
derivatives.
DMF/ THF
N
N
H3CO
H3CO
NaH, RI or RBr
N
N
R9
CH3
CH3
H
stituted b-carboline-3-carboxylate (5a–d, 6a–e, 7a–d).
The compounds 6 and 6a–f were hydrolyzed in sodium
hydroxide solution to afford the compounds 8 and 8a–
f (see Scheme 4). In our studies, we found that N-alkyl-
ation and N-benzylation of b-carboline-3-carboxylate
would be accompanied by ester exchange and ester
hydrolysis unexpectedly. As a result, separating and
purifying the products would become difficult. Conse-
quently, the key step was to use anhydrous DMF so
as to guarantee the dryness of reaction system of alkyla-
tion and benzylation of b-carboline-3-carboxylate 5, 6,
7. The chemical structures of all the synthesized novel
2a R9=CH3
1
2b R9=CH2CH3
2c R9=n-C4H9
2d R9=CH2CH2OH
2e R9=CH2C6H5
2f R9=CH2C6F5
2g R9=(CH2)3C6H5
Scheme 1. Synthesis of 9-substituted harmine derivatives.
1
compounds were confirmed by FAB-MS, UV, IR, H
NMR, and elemental analyses data.
DMF/ THF
N
N
NaH, RI or RBr
N
R9
N
H
2.2. Cytotoxicity assays
4a R9=CH3
3
Thirty-seven b-carboline derivatives were examined for
cytotoxic activities against a panel of human tumor cell
lines. In order to enhance the solubility in aqueous solu-
tion, compounds 8 and 8a–f were converted into their
water-soluble sodium salts and the other compounds
4b R9=CH2CH3
4c R9=n-C4H9
4d R9=CH2C6H5
Scheme 2. Synthesis of 9-substituted b-carbolines.

R. Cao et al. / Bioorg. Med. Chem. 12 (2004) 4613–4623
4615
a
Table 1. Cytotoxicity of b-carboline derivatives in vitroc (IC50
,
lM)
Compounds
PLA-801b
HepG2b
Bel-7402b
BGC-823b
Helab
6066
Lovob
Harmine
2a
2b
2c
2d
2e
2f
45
29
46
16
54
63
68
52
8
17
43
170
87
22
14
62
28
58
45
69
111
78
28
25
313
85
244
57
204
95
27
65
42
27052
28
27
46
43
22
31
2g
3
5036
17
44
46
24
228
102
311
99
379
302
171
164
77
274
204
234
101
73
353
327
159
88
35
220
4a
4b
4c
4d
5
219
130167
133
124
295
125
25
134
123
160
175
107
107
241
119
117
464
>1000
>1000
48
293
195
124
433
>1000
>1000
278
181
79
100
181
17
5a
5b
5c
5d
6
136
>1000
275
310289
>1000
>1000
166
>1000
567
312
>1000
6a
6b
6c
6d
6e
6f
8
17010260141
136
69
87
71
109
476
107
784
108
760487
38
137
173
77
78
47
38
116
45
13
78
122
37
9
387
52
>1000
>1000
675
109
>1000
994
327
267
212
92
>1000
>1000
266
>1000
>1000
394
>1000
>1000
295
>1000
>1000
104
7
>1000
313
74
7a
7b
7c
7d
8
70
82
72
67
954
83
45
>1000
>1000
354
>1000
>1000
369
>1000
330262
126
>1000
198
89
>1000
8a
8b
8c
8d
8e
8f
147
179
226
88
130163
92
112
183
62
6011
73
102
116
52
100
86
86
44
41
13
5
31
31
61
53
35
28
57
100
aCytotoxicity 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 cells using the MTT assay.
b Cell lines include nonsmall cell lung carcinoma (PLA-801), liver carcinoma (HepG2 and Bel-7402), gastric carcinoma (BGC-823), cervical carci-
noma (Hela), colon carcinoma (Lovo).
c Data represent the mean values of three independent determinations.
investigated were all prepared in the form of hydrochlo-
ride by the usual methods before use. The results were
summarized in Table 1.
pound 7 were found to be less active with IC50 values of
more than 100lM against tumor cell lines, suggesting
that the substitution of 7-methoxy and 1-methyl groups
might contribute to their increased cytotoxic activities
while a long chain alkoxy at 3-position might not be
preferable. Compared with the IC50 values of other com-
pounds, the IC50 values of the compounds 2a, 2b, 2f,
and 2g was lower than 50lM, which implicated that
the alkyl and benzyl substituents had almost equal po-
tency to enhance their cytotoxic activities in vitro.
As shown in Table 1, most studied compounds showed
significant cytotoxic activities against several human tu-
mor cell lines. 9-Substituted harmines, b-carbolines, b-
carboline-3-carboxylates, and b-carboline-3-carboxylic
acids (except 5d, 6f, and 7d) displayed more remarkable
cytotoxic activities than their parent compounds, respec-
tively, indicating that the introduction of an appropriate
alkyl or benzyl group into 9-position of b-carboline ring
system facilitates the increase of their cytotoxic activi-
ties.
As for the harmine series, the compound 2b with an
ethyl group at 9-position exhibited the highest cytotoxic
activities (except for Lovo cell line). The compound 2a
having a methyl at position-9 showed selective cytotoxic
activities against the screened tumor cell lines with the
lowest IC50 value (8lM) against Hela. The compounds
2f and 2g with a pentafluorobenzyl and a phenylpropyl
at position-9, respectively, demonstrated the prominent
Among all the compounds investigated, 9-substituted
harmine series demonstrated the highest cytotoxicities
while 9-substituted butyl b-carboline-3-carboxylates 7a,
7c, 7d (except 7b), and their corresponding parent com-

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R. Cao et al. / Bioorg. Med. Chem. 12 (2004) 4613–4623
Table 2. Acute toxic effects of b-carboline derivatives in mice
and broader spectrum of cytotoxic activities against all
six human tumor cell lines with IC50 values of all lower
than 50lM.
Compound
Acute toxicity
LD50 (mg/kg, 95% CL)
Neurotoxic effect
1
59.00 (43.50–110.00)
24.25 (22.24–26.44)
26.45 (23.91–29.26)
147.82 (132.55–164.85)
70.61 (64.17–77.70)
240.38 (211.38–273.50)
135.22 (121.62–150.34)
>500
++a
++
++
++
+
In contrast to the harmine series, 9-substituted b-carbo-
line series failed to exhibit obviously increased cytotoxi-
cities. The compound 3 having no substituent on ring
system showed a good cytotoxic activity against PLA-
801 and Lovo cell lines. Compounds 4a–d displayed al-
most equal cytotoxic activities while the compound 4d
showed higher and selective cytotoxic activity against
Lovo cells with IC50 values of 48lM.
2b
2c
2e
5a
6d
8
ꢀ
ꢀ
8c
8d
8e
ꢀ
163.48 (141.56–188.76)
219.19 (193.25–248.61)
ꢀ
ꢀ
a Acute neurotoxic manifestation were denoted by Ô+Õ and ÔꢀÕ. A Ô+Õ
represents toxic reactions including tremble, twitch, jumping, teta-
nus, and supination, Ô++Õ means the same reactions with more
severity, while ÔꢀÕ means no such reaction.
Of all 9-substituted b-carboline-3-carboxylate deriva-
tives, the compound 6d having a benzyl at position-9
displayed strong cytotoxic activities against HepG2,
Bel-7402, BGC-823, and Hela with IC50 values of 38,
45, 38, and 13lM, respectively. However compounds
5d and 7d, having a benzyl at 9-position, had little or
even no cytotoxic effects on the tested cell lines, indicat-
ing that ethoxycarbonyl substituent was preferable for
improving cytotoxic activities of this type of com-
pounds. The compounds 5b, 6b, and 7b with an ethyl
at position-9, respectively, displayed higher cytotoxic
activities against human tumor cell lines tested. Mean-
while the compound 5b showed highly selective cytotox-
ic effects against PLA-801 and Hela with IC50 values 25
and 17lM, respectively. All these results, together with
the cytotoxic activity of the compound 2b, confirmed
that the ethyl group at position-9 might play a crucial
role in eliciting distinct cytotoxic activities of these com-
pounds.
receiving the b-carboline derivatives via intraperitoneal
(i.p.) route. All the tested compounds resulted in acute
toxic manifestation. Of all the compounds investigated,
1, 2b, 2c, 2e, and 5a caused remarkable acute toxic
effects including tremor, twitch, jumping, tetanus, and
supination. Death occurred mostly in high dosage group
within 1min after administration and then reached a
peak 1h later. For survived animals, the tremor and
jumping lasted for about 20min and then relieved grad-
ually and returned to normal in the next day. Animals
were drowsy and exhibited a decrease in locomotor
activity after the administration of the compound 8,
6d, 8d, and 8f. Death only occurred in high dosage
group 10–20min after administration and reached a
peak 1h later. However, the compounds 8c caused no
obvious neurotoxic reaction and no death at tested dos-
age. Autopsy of the animals that died in the course of
experiment and the necropsy findings in surviving ani-
mals at the end of experimental period (14days) revealed
no apparent changes in any organs. The results of toxi-
cities suggested that an alkoxycarbonyl or carboxyl sub-
stituent at position-3 of the b-carboline ring might play
a vital role in determining their decreased acute toxici-
ties and neurotoxicities, and perhaps the carboxyl sub-
stituent is more favorable.
For the b-carboline-3-carboxylic acid series (8 and 8a–
e), the cytotoxic activities were also enhanced by intro-
duction of short alkyl or benzyl substituent into posi-
tion-9 of the b-carboline ring. The compounds 8c and
8e, having an n-butyl and a benzyl at positon-9, respec-
tively, showed remarkable cytotoxic activities against
Lovo cell lines with IC50 values of 11 and 13lM, respec-
tively, furthermore the compound 8f exhibited the most
significant cytotoxic activity against Lovo cell lines with
IC50 values 5lM.
A total analysis of the cytotoxic activities of b-carboline
derivatives in vitro clearly suggested that (1) the b-carb-
oline nucleus might be an important basis for the design
and synthesis of new antitumor drugs; (2) the cytotoxic
potencies of b-carboline derivatives depended upon the
presence and location and nature of the subtituents,
which were introduced into the b-carboline ring. (3)
The cytotoxic activities of b-carboline derivatives were
enhanced by the introduction of an appropriate substit-
uent into position-9 of b-carboline ring; (4) the Lovo cell
lines were more sensitive to the tested compounds than
other tumor cells.
2.4. Evaluation of antitumor activity
The tumor inhibition rates of the selected b-carboline
derivatives in mice bearing Lewis lung cancer and Sar-
coma180(S180) were summarized in Table 3. Harmine
(compound 1) only showed a moderate antitumor effect
(34.1% and 15.3% against Lewis lung cancer and S180,
respectively), however the selected 9-substituted b-carb-
oline derivatives all exhibited more potent antitumor
activities. Compounds 2c, 2d, 2e, 6d, and 8c displayed
remarkable antitumor activities with the tumor inhibi-
tion rate of more than 40% against mice bearing Lewis
lung cancer and S180. Moreover the compounds 2e
and 8c demonstrated the highest antitumor effect with
the tumor inhibition rate of 46.9% against mice bearing
Lewis lung cancer among all the tested compounds. The
results indicated that short alkyl or benzyl substituent at
2.3. Assessment of acute toxicity
The LD50 values and scores for neurotoxicity of the se-
lected b-carboline derivatives in mice after administra-
tion were summarized in Table 2. Neurotoxicities were
the principal acute toxic effects observed in mice after

R. Cao et al. / Bioorg. Med. Chem. 12 (2004) 4613–4623
4617
Table 3. Antitumor effects of b-carboline derivatives against mice
bearing Sarcoma 180and Lewis lung carcinoma
thesis of more new b-carboline derivatives with
different substituents at other positions is needed.
Compound
Tumor inhibition rate (%)
Lewis lung carcinoma Sarcoma180
4. Experimental
4.1. Materials
1
34.1
15.3
2b
.29c
2e
5a
6d
8
42.037.6
44.040
46.9
45.2
All reagents were purchased from commercial suppliers
and were dried and purified when necessary. Compound
1 (Harmine) was extracted from Peganum multisectum
Maxim, a plant indigenous to western China, according
to the method by Duan et al.2 Compounds 3 and 5–8
were synthesized from the starting material L-trypto-
phan according to the procedures described by Hagen
et al.19 and Lippke et al.18 with a slight modification,
respectively.
35.031.1
43.3
33.4
42.1
32.2
43.1
34.4
32.2
87.5
8c
8d
8e
CTX
46.9
43.2
39.6
88.6
position-9 of the b-carboline ring facilitated the increase
of their antitumor activities.
Melting points were determined in capillary tubes on an
electrothermal PIF YRT-3 apparatus and without cor-
rection. UV spectra were measured on Shimadzu UV
2501PC Spectrometer. FAB-MS spectra were obtained
from VG ZAB-HS spectrometer. FTIR were run on a
Bruker Equinox 55 Fourier Transformation Infarred
Spectrometer. 1H NMR spectra were recorded on a Var-
ian INOVA 500NB spectrometer. Elemental analyses
were carried out on an Elementar Vario EL CHNS Ele-
mental Analyzer. Silica gel F254 were used in analytical
thin-layer chromatography (TLC) and silica gel were
used in column chromatography, respectively.
3. Conclusions
The present investigation reported for the first time that
b-carboline derivatives had significant antitumor activi-
ties in mice bearing Lewis lung cancer and Sarcoma 180
but also exhibited remarkable acute neurotoxicity in
experimental mice models. Alkyl or benzyl substituent
at position-9 of b-carboline ring might facilitate their
antitumor activities and minimize their acute toxicities
but not neurotoxicities. However alkoxycarbonyl or
carboxyl substituent at position-3 played a crucial role
in determining their decreased acute toxicities and neu-
rotoxicities. Furthermore, the compounds with appro-
priate substituents both at positon-3 and 9 displayed
enhanced antitumor activities and decreased neurotoxi-
cities simultaneously. The compound 8c, having an n-
butyl and a carboxyl at position-9 and 3, respectively,
exhibited the highest antitumor effect and the lowest
acute neurotoxicity and was found to be the most prom-
ising leading compound for further investigation. These
data suggested that (1) appropriate substituents at both
position-9 and 3 of b-carboline derivatives might play a
crucial role in determining their enhanced antitumor
activities and decreased acute toxicities and neurotoxic
effects; (2) the b-carboline derivatives have the potential
to be used as antitumor drug leads.
4.1.1. 7-Methoxy-1,9-dimethyl-b-carboline (2a). A mix-
ture of Harmine 1 (2.12g, 10mmol), anhydrous DMF
(50mL), and anhydrous THF (50mL) was stirred at rt
until clear, and then 60% NaH (0.6g, 15mmol) and
iodomethane (2mL, 30mmol) were added and stirred
at rt for 30min. Later the mixture was evaporated in re-
duced pressure. The resulting solution was poured into
H2O (100mL), and extracted with ethyl acetate
(3·150mL). The organic phase was washed with water
and brine, then dried over anhydrous sodium sulfate, fil-
tered, and evaporated. The oil obtained was purified by
silica column chromatography with ethyl acetate as the
eluent. Upon recrystallization, white crystals of 2a were
obtained (1.8g, 80%), mp 121–123ꢁC (from ether);
FAB-MS m/e 227 (M+1); UV kmax 345, 332, 302, 264,
244, 214nm; IR (KBr): 3380, 2744, 1628, 1570, 1469,
1
1348, 1249, 1152, 1045, 810cmꢀ1; H NMR (500MHz,
CDCl3): 8.24–8.25 (1H, m, H-5), 7.93–7.96 (1H, m, H-
3), 7.69–7.71 (1H, m, H-4), 6.86–6.89 (1H, m, H-8),
6.81–6.83 (1H, m, H-6), 4.04–4.07 (3H, m, NCH3),
3.94–3.95 (3H, m, OCH3), 3.04–3.05 (3H, m, CH3).
Anal. Calcd for C14H14N2O: C, 74.33; H, 6.19; N,
12.39. Found: C, 74.21; H, 6.37; N, 12.31.
Although the antitumor effects of the studied b-carbo-
line derivatives presented here remained relatively mod-
est, it should be noted that the acute neurotoxicities of
some compounds decreased dramatically by introduc-
tion of an alkoxycarbonyl or carboxyl substituent into
position-3 of the b-carboline ring. This investigation
and finding would be helpful to further design and de-
velop more potent antitumor agents together with low
neurotoxicities. Further investigations are in progress
in our laboratory to elucidate the molecular mechanisms
involved in antitumor activities and neurotoxicities of b-
carboline derivatives. To acquire more information
about the structural requirements for enhancing antitu-
mor activities and minimizing neurotoxicities, the syn-
4.1.2. 7-Methoxy-9-ethyl-1-methyl-b-carboline (2b). A
mixture of Harmine 1 (2.12g, 10mmol), anhydrous
DMF (50mL), and anhydrous THF (50mL) was stirred
at rt until clear, and then 60% NaH (0.6g, 15mmol) and
iodoethane (2.5mL, 30mmol) were added. Later the
mixture was treated in a manner similar to that de-
scribed for 2a to afford 2b (2.0, 83%), mp 99–101ꢁC
(from ether); FAB-MS m/e 241 (M+1); UV kmax 345,

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R. Cao et al. / Bioorg. Med. Chem. 12 (2004) 4613–4623
332, 303, 265, 244, 213nm; IR (KBr): 3362, 3128, 1622,
1565, 1451, 1346, 1217, 1136, 812cmꢀ1 1H NMR
H-8, H-6, Ar–H), 6.98–7.00 (1H, d, J=7.0Hz, Ar–H),
6.90–6.92 (1H, m, Ar–H), 6.76 (1H, s, Ar–H), 5.75
(2H, s, NCH2Ar), 3.85 (3H, s, OCH3), 2.88 (3H, s,
CH3). Anal. Calcd for C20H18N2O: C, 79.47; H, 5.96;
N, 9.27. Found: C, 79.29; H, 6.19; N, 9.21.
;
(500MHz, CDCl3): 8.26–8.27 (1H, d, J=5Hz, H-5),
7.96–7.98 (1H, d, J=5Hz, H-3), 7.74–7.75 (1H, d,
J=4.5Hz, H-4), 6.86–6.90(2H, m, H-8, H-6), 4.52–
4.57 (2H, m, CH2CH3), 3.95 (3H, s, OCH3), 3.05 (3H,
s, CH3), 1.43–1.46 (3H, m, CH2CH3). Anal. Calcd for
C15H16N2O: C, 75.00; H, 6.67; N, 11.67. Found: C,
74.89; H, 6.87; N, 11.59.
4.1.6.
9-(20,30,40,50,6-Pentafluoro)benzyl-7-methoxy-1-
methyl-b-carboline (2f). A mixture of Harmine 1
(0.53g, 2.5mmol), anhydrous DMF (15mL), and anhy-
drous THF (15mL) was stirred at rt until clear, and then
60% NaH (0.15g, 3.8mmol) and a-bromo-2,3,4,5,6-pen-
tafluorotoluene (0.7mL, 4.5mmol) were added. Later
the mixture was treated in a manner similar to that
described for 2a to afford 2f (0.64g, 65%), mp 173–
174ꢁC (from ether); FAB-MS m/e 393 (M+1); UV
kmax 338, 325, 300, 241, 209nm; IR (KBr): 2961, 1622,
4.1.3. 7-Methoxy-9-butyl-1-methyl-b-carboline (2c). A
mixture of Harmine 1 (2.12g, 10mmol), anhydrous
DMF (50mL), and anhydrous THF (50mL) was stirred
at rt until clear, and then 60% NaH (0.6g, 15mmol) and
n-butyl iodide (6mL, 50mmol) were added and refluxed
for 1h. Later the resulting mixture was treated in a man-
ner similar to that described for 2a to afford 2c (2.1,
78%), mp 104–105ꢁC (from ether); FAB-MS m/e 269
(M+1); UV kmax 346, 334, 303, 265, 244, 213nm; IR
(KBr): 3428, 2959, 2927, 1621, 1563, 1497, 1448, 1356,
1
1502, 1446, 1256, 1026, 816cmꢀ1; H NMR (500MHz,
CDCl3): 8.32–8.33 (1H, d, J=5Hz, H-5), 7.94–7.95
(1H, d, J=7.5Hz, H-3), 7.72–7.73 (1H, d, J=5.5Hz,
H-4), 7.26 (1H, s, H-8), 6.87–6.89 (1H, m, H-6), 5.85
(2H, s, CH2Ar), 3.88 (3H, s, OCH3), 3.05 (3H, s,
CH3). Anal. Calcd for C20H13F5N2O: C, 61.22; H,
3.32; N, 7.14. Found: C, 61.09; H, 3.46; N, 7.06.
;
1243, 1197, 1137, 812cmꢀ1 1H NMR (500MHz,
CDCl3): 8.26–8.28 (1H, d, J=5.5Hz, H-5), 7.95–7.97
(1H, d, J=9Hz, H-3), 7.71–7.72 (1H, d, J=5Hz, H-4),
6.85–6.88 (2H, m, H-8, H-6), 4.43–4.46 (2H, m,
J=8Hz, CH2CH2CH2CH3), 3.94 (3H, s, OCH3), 3.01
(3H, s, CH3), 1.78–1.84 (2H, m, CH2CH2CH2CH3),
1.41–1.48 (2H, m, CH2CH2CH2CH3), 0.97–1.00 (3H,
m, CH2CH2CH2CH3). Anal. Calcd for C17H20N2O: C,
76.12; H, 7.46; N, 10.45. Found: C, 75.96; H, 7.69; N,
10.53.
4.1.7.
9-Phenylpropyl-7-methoxy-1-methyl-b-carboline
(2g). A mixture of Harmine 1 (1.05g, 5mmol), anhy-
drous DMF (25mL), and anhydrous THF (25mL) were
stirred at rt until clear, and then 60% NaH (0.3g,
7.5mmol) and 1-bromo-3-phenylpropane (3mL,
20mmol) were added and refluxed for 3h. Later the mix-
ture was treated in a manner similar to that described
for 2a to afford 2g (0.84g, 51%), mp 117–118ꢁC (from
ether); FAB-MS m/e 331 (M+1); UV kmax 346, 332,
302, 265, 244, 211nm; IR (KBr): 2995, 2931, 1623,
4.1.4. 7-Methoxy-9-hydroxyethyl-1-methyl-b-carboline
(2d). A mixture of Harmine 1 (1.05g, 5.0mmol) and
anhydrous DMF (25mL), and anhydrous THF
(25mL) was stirred at rt until clear, and then 60%
NaH (0.3g, 7.5mmol) and 2-iodoethanol (3mL,
40mmol) were added and refluxed for 5h. Then the
resulting mixture was treated in a manner similar to that
described for 2a to afford 2d (0.7g, 54%), mp 204–206ꢁC
(from ether); FAB-MS m/e 257 (M+1); UV kmax 328,
304, 249, 211nm; IR (KBr) 3295, 2696, 1629, 1569,
1563, 1449, 1238, 1156, 1043, 801cmꢀ1 1H NMR
;
(500MHz, CDCl3): 8.25–8.26 (1H, d, J=5Hz, H-5),
7.92–7.94 (1H, d, J=8.5Hz, H-3), 7.69–7.70(1H, d,
J=5Hz, H-4), 7.29–7.32 (2H, m, H-8, H-6), 7.20–7.25
(3H, m, Ar–H), 6.84–6.86 (1H, m, Ar–H), 6.63–6.64
(1H, m, Ar–H), 4.42–4.45 (2H, m, NCH2CH2CH2Ar),
3.84–3.85 (3H, s, OCH3), 2.88 (3H, s, CH3), 2.74–2.77
(2H, m, NCH2CH2CH2Ar), 2.12–2.18 (2H, m,
NCH2CH2CH2Ar). Anal. Calcd for C22H22N2O: C,
80.00; H, 6.67; N, 8.48. Found: C, 79.87; H, 6.82; N,
8.39.
1
1467, 1352, 1155, 1051, 810cmꢀ1; H NMR (500MHz,
CDCl3): 8.15–8.16 (1H, d, J=4Hz, H-5), 7.93–7.94
(1H, d, J=3.5Hz, H-3), 7.63–7.64 (1H, d, J=5.0Hz,
H-4), 6.88–6.95 (2H, m, H-8, H-6), 4.66–4.71 (2H, t,
J=5.5Hz, NCH2CH2OH), 4.06–4.08 (2H, m,
NCH2CH2OH), 3.94 (3H, s, OCH3), 2.99 (3H, s,
CH3). Anal. Calcd for C15H16N2O2: C, 70.31; H, 6.25;
N, 10.94. Found: C, 70.13; H, 6.46; N, 10.87.
4.1.8. 9-Methyl-b-carboline (4a). A mixture of norhar-
man 3 (1.68g, 10mmol) and anhydrous DMF (50mL)
was stirred at rt till clear. Then 60% NaH (0.6g,
15mmol) and iodomethane (2mL, 30mmol) were
added, and the mixture was stirred at rt for 30min. La-
ter the resulting mixture was poured into H2O (150mL),
and extracted with ethyl acetate (3·150mL). The organ-
ic phase was washed with water and brine, then dried
over anhydrous sodium sulfate, filtered, and evaporated.
The oil obtained was purified by silica column chroma-
tography with petroleum ether–acetone (2:1) as the elu-
ent. Upon recrystallization, white crystals of 4a were
obtained (1.4g, 77%), mp 108–109ꢁC (from petroleum
ether–acetone); FAB-MS m/e 183 (M+1); UV kmax
360, 346, 289, 236, 216nm; IR (KBr): 2509, 1638,
4.1.5. 9-Benzyl-7-methoxy-1-methyl-b-carboline (2e). A
mixture of Harmine 1 (2.12g, 10mmol), anhydrous
DMF (50mL), and anhydrous THF (50mL) was stirred
at rt until clear, and then 60% NaH (0.6g, 15mmol) and
benzyl bromide (5mL, 40mmol) were added. Later the
mixture was treated in a manner similar to that de-
scribed for 2a to afford 2e (2.2, 67%), mp 131–133ꢁC
(from ether); FAB-MS m/e 303 (M+1); UV kmax 343,
330, 301, 244, 210nm; IR (KBr): 3421, 2958, 1620,
1565, 1498, 1447, 1361, 1256, 1197, 1172, 1044,
1
825cmꢀ1; H NMR (500MHz, CDCl3): 8.29–8.30(1H,
d, J=5.5Hz, H-5), 8.01–8.02 (1H, d, J=8.5Hz, H-3),
7.80–7.81 (1H, d, J=5.5Hz, H-4), 7.23–7.30(3H, m,
1504, 1335, 1259, 835cmꢀ1 1H NMR (500MHz,
;
CDCl3): 8.88 (1H, s, H-4), 8.46–8.47 (1H, d, J=5Hz,

R. Cao et al. / Bioorg. Med. Chem. 12 (2004) 4613–4623
4619
H-1), 8.13–8.14 (1H, d, J=6Hz, H-8), 7.94–7.95 (1H, d,
J=5Hz, H-3), 7.59–7.62 (1H, m, H-5), 7.45–7.46 (1H, d,
J=8.5Hz, H-6), 7.25–7.30(1H, m, H-7), 3.93 (3H, s,
CH3). Anal. Calcd for C12H10N2: C, 79.12; H, 5.49; N,
15.38. Found: C, 78.93; H, 5.71; N, 15.45.
added. Later the mixture was stirred at rt for 30min.
The resulting mixture was poured into iced-water
(150mL) and extracted with ethyl acetate (3 ·100mL).
The combined organic phase was washed with water and
brine. Then dried over anhydrous sodium sulfate, filtered,
and evaporated. The yellow oil obtained was purified by
silica column chromatography with ethyl acetate as the
eluent. After that the solid was collected, it was recrystal-
lized from ethyl ether to give a white crystals (1.8g, 75%),
mp 215–216ꢁC (from ether); FAB-MS m/e 241 (M+1); UV
4.1.9. 9-Ethyl-b-carboline (4b). A mixture of norharman
3 (1.68g, 10mmol) and anhydrous DMF (50mL) was
stirred at rt till clear, and then 60% NaH (0.6g, 15mmol)
and iodoethane (2.5mL, 30mmol) were added. Later the
mixture was treated following the method described for
4a to afford yellow oil 4b (1.5g, 76%), FAB-MS m/e 197
(M+1); UV kmax 365, 342, 291, 239, 218nm; IR(KBr):
kmax 358, 343, 307, 272, 236, 219nm; IR (KBr): 3387, 2548,
2056, 1730, 1631, 1334, 1282, 1207cmꢀ1 1H NMR
;
(500MHz, CDCl3): 8.94 (1H, s, H-4), 8.88 (1H, s, H-1),
8.20–8.21 (1H, d, J=7.5Hz, H-8), 7.65–7.68 (1H, m, Ar–
H), 7.50–7.52 (1H, d, J=8Hz, Ar–H), 7.36–7.39 (1H, m,
J=8Hz, Ar–H), 4.0 6 (3H, s, OHC3), 4.00 (3H, s,
NCH3). Anal. Calcd for C14H12N2O2: C, 70 .0 0 ; H, 5.0 0 ;
N, 11.67. Found: C, 69.83; H, 5.23; N, 11.59.
1
2485, 2022, 1633, 1500, 1462, 1355, 1239, 831cmꢀ1; H
NMR (500MHz, CDCl3): 8.84 (1H, s, H-4), 8.42–8.43
(1H, d, J=5Hz, H-1), 8.04–8.05 (1H, d, J=8Hz, H-8),
7.85–7.86 (1H, d, J=5Hz, H-3), 7.50–7.53 (1H, m, H-
5), 7.34–7.36 (1H, d, J=8Hz, H-6), 7.20–7.23 (1H, m,
H-7), 4.26–4.30(2H, m, C H2CH3), 1.35–1.38 (3H, m,
CH2CH3). Anal. Calcd for C13H12N2: C, 79.59; H,
6.12; N, 14.29. Found: C, 79.32; H, 6.43; N, 14.13.
4.1.13. Methyl 9-ethyl-b-carboline-3-carboxylate (5b). A
mixture of 5 (2.26g, 10mmol) and anhydrous DMF
(60mL) was stirred at rt for 10min, then 60% NaH
(0.6g, 2mmol) and iodoethane (2.5mL, 30mmol) were
added. Later the mixture was treated in a manner similar
to that described for 5a to afford white crystals 5b (2.0g,
79%), mp 155–156ꢁC (from ether); FAB-MS m/e 255
(M+1); UV kmax 358, 345, 306, 273, 236, 205nm; IR
4.1.10. 9-Butyl-b-carboline (4c). A mixture of norharman
3 (1.68g, 10mmol) and anhydrous DMF (50mL) was
stirred at rt till clear, and then 60% NaH (0.6g, 15mmol)
and n-butyl iodide (6mL, 50mmol) were added and ref-
luxed for 1h. Later the mixture was treated following
the method described for 4a to afford white crystals 4c
(1.6g, 71%), mp 108–109ꢁC (from light petroleum
ether–acetone); FAB-MS m/e 225 (M+1); UV kmax
362, 348, 290, 237, 217nm; IR (KBr): 2525, 2030,
(KBr): 3248, 1694, 1629, 1337, 1250cmꢀ1 1H NMR
;
(500MHz, CDCl3): 8.90–9.00 (2H, m, H-4, H-1), 8.21–
8.23 (1H, d, J=8Hz, H-8), 7.65–7.68 (1H, m, H-5),
7.52–7.54 (1H, d, J=8Hz, H-6), 7.36–7.39 (1H, m, H-
7), 4.51 (2H, s, NCH2CH3), 4.07 (3H, s, OCH3), 1.52
(3H, s, NCH2CH3). Anal. Calcd for C15H14N2O2: C,
70.87; H, 5.51; N, 11.02. Found: C, 70.65; H, 5.68; N,
10.93.
1632, 1500, 1458, 1355, 1235, 823cmꢀ1 1H NMR
;
(500MHz, CDCl3): 8.86 (1H, s, H-4), 8.43–8.44 (1H,
d, J=5.5Hz, H-1), 8.06–8.08 (1H, d, J=8Hz, H-8),
7.88–7.89 (1H, d, J=4.5Hz, H-3), 7.52–7.55 (1H, m,
H-5), 7.38–7.40(1H, d, J=8.5Hz, H-6), 7.21–7.25 (1H,
m, H-7), 4.25–4.28 (2H, m, CH2CH2CH2CH3),
1.79–1.85 (2H, m, CH2CH2CH2CH3), 1.30–1.38 (2H,
m, CH2CH2CH2CH3), 0.86–0.91 (3H, m, CH2CH2-
CH2CH3). Anal. Calcd for C15H16N2: C, 80.36; H,
7.14; N, 12.50. Found: C, 80.15; H, 7.35; N, 12.39.
4.1.14. Methyl 9-butyl-b-carboline-3-carboxylate (5c). A
mixture of 5 (2.26g, 10mmol) and anhydrous DMF
(60mL) was stirred at rt for 10min, then 60% NaH
(0.6g, 2mmol) and n-butyl iodide (6mL, 50mmol) were
added and refluxed for 1h. Later the mixture was treated
in a manner similar to that described for 5a to afford
white crystals 5c (2.3g, 82%), mp 181–183ꢁC (from
petroleum ether–ethyl ether 1:2); FAB-MS m/e 283
(M+1); UV kmax 358, 344, 306, 273, 236, 222nm; IR
4.1.11. 9-Benzyl-b-carboline (4d). A mixture of norhar-
man 3 (1.68g, 10mmol) and anhydrous DMF (50mL)
was stirred at rt till clear, and then 60% NaH (0.6g,
15mmol) and benzyl bromide (5mL, 40mmol) were
added and refluxed for 3h. Later the mixture was trea-
ted following the method described for 4a to afford
white crystals 4d (1.8g, 69%), mp 118–120ꢁC (from
ether); FAB-MS m/e 259 (M+1); UV kmax 358, 344,
289, 237, 213nm; IR (KBr): 3023, 1619, 1448, 1332,
(KBr): 2959, 1735, 1625, 1361, 1246cmꢀ1 1H NMR
;
(500MHz, CDCl3): 8.94 (1H, s, H-4), 8.89 (1H, s, H-1),
8.19–8.21 (1H, d, J=7Hz, H-8), 7.62–7.65 (1H, m, H-
5), 7.50-7.52 (1H, d, J=7.5Hz, H-6), 7.34–7.37 (1H, m,
H-7), 4.41–4.44 (2H, m, CH2CH2CH2CH3), 4.06 (3H,
s, OCH3), 1.87–1.93 (2H, m, CH2CH2CH2CH3), 1.35–
1.42 (2H, m, CH2CH2CH2CH3), 0.93–0.96 (3H, m,
CH2CH2CH2CH3). Anal. Calcd for C17H18N2O2: C,
72.34; H, 6.38; N, 9.93. Found: C, 72.21; H, 6.57; N,
9.86.
1258, 821cmꢀ1 1H NMR (500MHz, CDCl3): 8.84
;
(1H, s, H-4), 8.48 (1H, s, H-1), 8.15–8.16 (1H, d,
J=8Hz, H-8), 7.98 (1H, s, H-3), 7.53–7.56 (1H, m, H-
5), 7.41–7.43 (1H, d, J=8Hz, H-6), 7.13–7.31 (6H, m,
J=8Hz, H-7, Ar–H), 5.55 (2H, s, CH2Ar). Anal. Calcd
for C18H14N2: C, 83.72; H, 5.43; N, 10.85. Found: C,
83.57; H, 5.69; N, 10.76.
4.1.15. Methyl 9-benzyl-b-carboline-3-carboxylate (5d). A
mixture of 5 (2.26g, 10mmol) and anhydrous DMF
(60 mL) was stirred at rt for 10 min, then 60 % NaH
(0.6g, 2mmol) and benzyl bromide (5mL, 40mmol) were
added and refluxed for 3h. Later the mixture was treated
4.1.12. Methyl 9-methyl-b-carboline-3-carboxylate (5a). A
mixture of 5 (2.26g, 10mmol) and anhydrous DMF
(60 mL) was stirred at rt for 10 min, then 60 % NaH in a manner similar to that described for 5a to afford white
(0.6g, 2mmol) and iodomethane (2mL, 30mmol) were
crystals 5d (2.3g, 73%), mp 187–188ꢁC (from petroleum

4620
R. Cao et al. / Bioorg. Med. Chem. 12 (2004) 4613–4623
ethyl ether); FAB-MS m/e 317 (M+1); UV kmax 356, 341,
304, 272, 235, 205nm; IR (KBr): 3026, 2945, 1731, 1622,
4.1.19. Ethyl 9-benzyl-b-carboline-3-carboxylate (6d). A
mixture of 5 (2.4g, 10mmol) and anhydrous DMF
(60mL) was stirred rt for 10min, then 60% NaH (0.6g,
2mmol) and benzyl bromide (5mL, 40mmol) were
added and refluxed for 3h. Later the mixture was treated
in a manner similar to that described for 5a to afford
white crystals 6d (2.4g, 70%), mp 126–127ꢁC (from ethyl
ether); FAB-MS m/e 331 (M+1); UV kmax 356, 342, 305,
273, 234nm; IR (KBr): 3425, 3060, 3027, 2974, 1723,
1335, 1242cmꢀ1 1H NMR (500MHz, CDCl3): 8.89–
;
8.90(2H, d, J=4Hz, H-4, H-1), 8.21–8.22 (1H, d,
J=8Hz, H-8), 7.58–7.61 (1H, m, H-5), 7.47–7.48 (1H, d,
J=8.5Hz, H-6), 7.35–7.38 (1H, m, H-7), 7.24–7.28 (3H,
m, Ar–H), 7.13–7.15 (2H, m, Ar–H), 5.60(2H, s, C H2Ar),
4.05 (3H, s, OCH3). Anal. Calcd for C20H16N2O2: C,
75.95; H, 5.06; N, 8.86. Found: C, 75.75; H, 5.29; N, 8.78.
1622, 1335, 1214cmꢀ1 1H NMR (500MHz, CDCl3):
;
4.1.16. Ethyl 9-methyl-b-carboline-3-carboxylate (6a). A
mixture of 6 (2.4g, 10mmol) and anhydrous DMF
(60mL) was stirred at rt for 10min, then 60% NaH
(0.6g, 15mmol) and iodomethane (2mL, 30mmol) were
added. Later the mixture was treated in a manner similar
to that described for 5a to afford white crystals 6a (1.9g,
75%), mp 139–140ꢁC (from ethyl ether); FAB-MS m/e
255 (M+1); UV kmax 358, 342, 306, 272, 236, 219nm;
IR (KBr): 3446, 3398, 2603, 1721, 1628, 1328,
8.91 (2H, m, H-4, H-1), 8.23–8.25 (1H, d, J=8Hz, H-
8), 7.59–7.62 (1H, m, H-5), 7.49–7.50(1H, d, J=8Hz,
H-6), 7.36–7.39 (1H, m, H-7), 7.25–7.27 (3H, s, Ar–H),
7.14–7.16 (2H, m, Ar–H), 5.62 (2H, s, CH2Ar), 4.51–
4.55 (2H, m, OCH2CH3), 1.47–1.50(3H, m, OCH 2CH3).
Anal. Calcd for C21H18N2O2: C, 76.36; H, 5.45; N, 8.48.
Found: C, 76.19; H, 5.67; N, 8.38.
4.1.20. Ethyl 9-(20,30,40,50,60-pentafluoro)benzyl-b-carbo-
line-3-carboxylate (6e). A mixture of 5 (2.4g,10mmol)
and anhydrous DMF(60mL) was stirred at rt for
10min, then 60% NaH (0.6g, 15mmol) and a-bromo-
2,3,4,5,6-pentafluorotoluene (3mL, 20mmol) were
added. Later the mixture was treated in a manner simi-
lar to that described for 5a to afford white crystals 6d
(2.6g, 62%), mp 153–154ꢁC (from ethyl ether); FAB-
MS m/e 421 (M+1); UV kmax 350, 335, 299, 271, 236,
217nm; IR (KBr): 3399, 3065, 2987, 1709, 1627, 1337,
1
1280cmꢀ1; H NMR (500MHz, CDCl3): 8.94 (1H, s,
H-4), 8.86 (1H, s, H-1), 8.19–8.20(1H, d, J=7.5Hz, H-
8), 7.66–7.67 (1H, m, H-5), 7.49–7.51 (1H, d, J=8.5Hz,
H-6), 7.35–7.37 (1H, m, H-7), 4.52–4.56 (2H, m,
OCH2CH3), 3.98 (3H, s, NCH3), 1.48–1.51 (3H, s,
OCH2CH3). Anal. Calcd for C15H14N2O2: C, 70.87; H,
5.51; N, 11.02. Found: C, 70.73; H, 5.73; N, 11.09.
4.1.17. Ethyl 9-ethyl-b-carboline-3-carboxylate (6b). A
mixture of 6 (2.4g, 10mmol) and anhydrous DMF
(60mL) was stirred rt for 10min, then 60% NaH
(0.6g, 2mmol) and iodoethane (2.5mL, 30mmol) were
added. Later the mixture was treated in a manner simi-
lar to that described for 5a to afford white crystals 6b
(1.8g, 67%), mp 117–118ꢁC (from ethyl ether); FAB-
MS m/e 269 (M+1); UV kmax 359, 344, 306, 273, 237,
221nm; IR (KBr): 3413, 2984, 1717, 1633, 1334,
1
1245cmꢀ1; H NMR (500MHz, CDCl3): 9.07 (1H, s,
H-4), 8.86 (1H, s, H-1), 8.19–8.21 (1H, d, J=8Hz, H-
8), 7.65–7.68 (1H, m, H-5), 7.59–7.61 (1H, d,
J=8.5Hz, H-6), 7.38–7.41 (1H, m, H-7), 5.67 (2H, s,
CH2Ar), 4.52–4.56 (2H, m, OCH2CH3), 1.49–1.51 (3H,
m, OCH2CH3). Anal. Calcd for C21F5H13N2O2: C,
60.00; H, 3.10; N, 6.67. Found: C, 59.87; H, 3.29; N,
6.58.
1
1257cmꢀ1; H NMR (500MHz, CDCl3): 8.93 (1H, s,
H-4), 8.86 (1H, s, H-1), 8.18–8.21 (1H, d, J=8Hz, H-
8), 7.62–7.64 (1H, m, H-5), 7.48–7.50(1H, d, J=8Hz,
H-6), 7.33–7.36 (1H, m, H-7), 4.42–4.56 (4H, m,
OCH2CH3, NCH2CH3), 1.46–1.52 (6H, m, OCH2CH3,
NCH2CH3). Anal. Calcd for C16H16N2O2: C, 71.64;
H, 5.97; N, 10.45. Found: C, 71.41; H, 6.21; N, 10.38.
4.1.21. Ethyl 9-phenylpropyl-b-carboline-3-carboxylate
(6f). A mixture of 5 (2.4g, 10mmol) and anhydrous
DMF (60mL) was stirred at rt for 10min, then 60%
NaH (0.6g, 2mmol) and 1-bromo-3-phenylpropane
(6mL, 40mmol) were added and refluxed for 3h. Later
the mixture was treated in a manner similar to that de-
scribed for 5a to afford white crystals 6e (2.0g, 56%),
mp 140–142ꢁC (from ethyl ether); FAB-MS m/e 359
(M+1); UV kmax 358, 343, 306, 273, 236, 217nm; IR
4.1.18. Ethyl 9-butyl-b-carboline-3-carboxylate (6c). A
mixture of 6 (2.4g, 10mmol) and anhydrous DMF
(60mL) was stirred rt for 10min, then 60% NaH
(0.6g, 15mmol) and n-butyl iodide (6mL, 50mmol) were
added and refluxed for 1h. Later the mixture was trea-
ted in a manner similar to that described for 5a to afford
white crystals 6c (2.3g, 78%), mp 76–77ꢁC (from petro-
leum ether–ethyl ether 1:2); FAB-MS m/e 297 (M+1);
UV kmax 359, 343, 307, 273, 235, 221nm; IR (KBr):
(KBr): 3026, 2983, 2933, 1724, 1622, 1333, 1246cmꢀ1
;
1H NMR (500MHz, CDCl3): 8.89 (2H, m, H-4, H-1),
8.20–8.22 (1H, d, J=7.5Hz, H-8), 7.61–7.64 (1H, m,
H-5), 7.41–7.42 (1H, m, H-6), 7.34–7.37 (1H, m, H-7),
7.26–7.30(2H, m, Ar–H), 7.19–7.22 (1H, m, Ar–H),
7.13–7.15 (2H, m, Ar–H), 4.52–4.57 (2H, m,
NCH2CH2CH2Ar), 4.41–4.44 (2H, m, NCH2CH2-
CH2Ar), 2.70–2.73 (2H, m, OCH2CH3), 2.24–2.30(2H,
m, NCH2CH2CH2Ar), 1.49–1.52 (3H, m, OCH2CH3).
Anal. Calcd for C23H22N2O2: C, 77.09; H, 6.15; N,
7.82. Found: C, 76.88; H, 6.38; N, 7.75.
3438, 2956, 1731, 1623, 1333, 1242cmꢀ1 1H NMR
;
(500MHz, CDCl3): 8.98 (1H, s, H-4), 8.89 (1H, s, H-
1), 8.21–8.23 (1H, d, J=8Hz, H-8), 7.63–7.66 (1H, m,
H-5), 7.51–7.53 (1H, d, J=8.5Hz, H-6), 7.36–7.38 (1H,
m, H-7), 4.52–4.56 (2H, m, OCH2CH3), 4.42–4.44 (2H,
m, CH2CH2CH2CH3), 1.88–1.94 (2H, m, CH2CH2-
CH2CH3), 1.49–1.52 (3H, m, OCH2CH3), 1.35–1.42
(2H, m, CH2CH2CH2CH3), 0.93–0.96 (3H, m, CH2CH2-
CH2CH3). Anal. Calcd for C18H20N2O2: C, 72.97; H,
6.76; N, 9.46. Found: C, 72.78; H, 6.98; N, 9.37.
4.1.22. Butyl 9-methyl-b-carboline-3-carboxylate (7a). A
mixture of 7 (2.68g, 10mmol) and anhydrous DMF
(80mL) was stirred at rt for 10min, then 60% NaH
(0.6g, 15mmol) and iodomethane (2mL, 30mmol) were
added and stirred at rt for 30min. Later the mixture was

R. Cao et al. / Bioorg. Med. Chem. 12 (2004) 4613–4623
4621
treated in a manner similar to that described for 5a to af-
ford white crystals 7a (2.0g, 70%), mp 235–238 ꢁC (from
ethyl ether); FAB-MS m/e 283 (M+1); UV kmax 358, 343,
305, 272, 236, 219nm; IR (KBr): 3402, 2956, 2869, 1726,
(from ethyl ether); FAB-MS m/e 359 (M+1); UV kmax
356, 342, 305, 273, 235, 205nm; IR (KBr): 3051, 2959,
2930, 2869, 1700, 1620, 1362, 1246cmꢀ1 1H NMR
;
(500MHz, CDCl3): 8.89 (1H, s, H-4), 8.85 (1H, s, H-
1), 8.19–8.20(1H, d, J=8Hz, H-8), 7.56–7.59 (1H, m,
H-5), 7.45–7.46 (1H, d, J=8.5Hz, H-6), 7.33–7.36 (1H,
m, H-7), 7.22–7.26 (3H, m, ArH), 7.11–7.13 (2H, m,
ArH), 5.56 (2H, s, CH2Ar), 4.45–4.48 (2H, m,
OCH2CH2CH2CH3), 1.82–1.88 (2H, m, OCH2-
CH2CH2CH3), 1.47–1.54 (2H, m, OCH2CH2CH2CH3),
0.98–1.01 (3H, m, OCH2CH2CH2CH3). Anal. Calcd
for C23H22N2O2: C, 77.09; H, 6.15; N, 7.82. Found: C,
76.89; H, 6.35; N, 7.75.
1625, 1333, 1238cmꢀ1 1H NMR (500MHz, CDCl3):
;
8.94 (1H, s, H-4), 8.83 (1H, s, H-1), 8.18–8.20(1H, d,
J=7.5Hz, H-8), 7.63–7.66 (1H, m, H-5), 7.48–7.50
(1H, d, J=8.5Hz, H-6), 7.34–7.37 (1H, m, H-7), 4.46–
4.49 (2H, m, OCH2CH2CH2CH3), 3.97 (3H, s, NCH3),
1.84–1.90(2H, m,
J=7.0Hz, OCH2CH2CH2CH3),
1.48–1.56 (2H, m, OCH2CH2CH2CH3), 0.99–1.02 (3H,
m, OCH2CH2CH2CH3). Anal. Calcd for C17H18N2O2:
C, 72.34; H, 6.38; N, 9.93. Found: C, 72.25; H, 6.58;
N, 9.85.
4.1.26. General procedure for the preparation of b-carb-
oline-3-carboxylic acids 8a–e. A mixture of the corre-
sponding b-carboline-3-carboxylate (6a–f, 10mmol),
NaOH (50mmol), ethanol (50mL), and H 2O (100mL)
was refluxed for 1h, and the ethanol was removed on
the rotary evaporator. The mixture was neutralized
(pH5) with 5M HCl and cooled. The precipitate was
collected, washed well with H2O, and dried in vacuo.
4.1.23. Butyl 9-ethyl-b-carboline-3-carboxylate (7b). A
mixture of 6 (2.4g, 10mmol) and anhydrous DMF
(60mL) was stirred at rt for 10min, then 60% NaH
(0.6g, 15mmol) and iodoethane (2.5mL, 30mmol) were
added. Later the mixture was treated in a manner simi-
lar to that described for 5a to afford white crystals 6b
(2.0g, 65%), mp 76–77 ꢁC (from ethyl ether); FAB-MS
m/e 297 (M+1); UV kmax 360, 345, 306, 273, 240,
220nm; IR (KBr): 3053, 2963, 2401, 1999, 1722, 1627,
4.1.27. 9-Methyl-b-carboline-3-carboxylic acid (8a). Yel-
low solid was obtained (2.32g, 99%). Mp 267–269ꢁC;
FAB-MS m/e 227 (M+1); UV kmax 384, 360, 273, 241,
217nm; IR (KBr): 3250–2100, 1716, 1630, 1405,
1337, 1269cmꢀ1 1H NMR (500MHz, CDCl3): 9.02
;
(1H, s, H-4), 8.86 (1H, s, H-1), 8.20–8.22 (1H, d,
J=8Hz, H-8), 7.63–7.67 (1H, m, H-5), 7.51–7.53 (1H,
d, J=7.5Hz, H-6), 7.35–7.38 (1H, m, H-7), 4.47–4.51
(4H, m, OCH2CH2CH2CH3, NCH2CH3), 1.84–1.90
(2H, m, OCH2CH2CH2CH3), 1.49–1.56 (2H, m, OCH2-
CH2CH2CH3), 0.99–1.02 (3H, m, OCH2CH2CH2CH3).
Anal. Calcd for C18H20N2O2: C, 72.97; H, 6.76; N,
9.46. Found: C, 72.83; H, 6.97; N, 9.39.
1200cmꢀ1 1H NMR (500MHz, DMSO-d6) d 12.15
;
(1H, s, COOH), 9.19 (1H, s, H-4), 9.12 (1H, s, H-1),
8.42–8.44 (1H, d, J=8.0Hz, H-8), 7.81–7.88 (2H, m, H-
5, H-6), 7.50–7.53 (1H, m, H-7), 4.16 (1H, s, NCH3).
Anal. Calcd for C13H10N2O2: C, 69.03; H, 4.42; N,
12.39. Found: C, 68.96; H, 4.57; N, 12.31.
4.1.24. Butyl 9-butyl-b-carboline-3-carboxylate (7c). A
mixture of 6 (2.4g, 10mmol) and anhydrous DMF
(60mL) was stirred at rt for 10min, then 60% NaH
(0.6g, 15mmol) and n-butyl iodide (6mL, 50mmol) were
added and refluxed for 1h. Later the mixture was trea-
ted in a manner similar to that described for 5a to afford
white crystals 6c (2.2g, 74%), mp 94–95ꢁC (from petro-
leum ether–ethyl ether 1:2); FAB-MS m/e 325 (M+1);
UV kmax 359, 344, 307, 274, 238, 221nm; IR (KBr):
4.1.28. 9-Ethyl-b-carboline-3-carboxylic acid (8b). Yel-
low solid was obtained (2.41g, 98%). Mp 201–202ꢁC;
FAB-MS m/e 241 (M+1); UV kmax 387, 359, 273, 239,
220nm; IR (KBr): 3250–2250, 1713, 1630, 1407, 1336,
1198cmꢀ1 1H NMR (500MHz, DMSO-d6) d 12.10
;
(1H, s, COOH), 9.16 (1H, s, H-4), 8.97 (1H, s, H-1),
8.31–8.33 (1H, d, J=8.0Hz, H-8), 7.75–7.81(2H, m, H-
5, H-6), 7.43–7.46 (1H, m, H-7), 4.63–4.67 (2H, s,
NCH2CH3), 1.46–1.52 (3H, s, NCH2CH3). Anal. Calcd
for C14H12N2O2: C, 70.00; H, 5.00; N, 11.67. Found: C,
69.89; H, 5.19; N, 11.59.
3061, 2956, 2866, 1728, 1624, 1358, 1247cmꢀ1 1H
;
NMR (500MHz, CDCl3): 8.95 (1H, s, H-4), 8.85 (1H,
s, H-1), 8.19–8.20(1H, d, J=7Hz, H-8), 7.60–7.64
(1H, m, H-5), 7.49–7.50(1H, d, J=8.5Hz, H-6), 7.32–
7.36 (1H, m, H-7), 4.47–4.49 (2H, m, OCH2CH2CH2-
CH3), 4.37–4.42 (2H, m, NCH2CH2CH2CH3), 1.84–
1.92 (4H, m, OCH2CH2CH2CH3, NCH2CH2CH2CH3),
1.49–1.56 (2H, m, OCH2CH2CH2CH3), 1.34–1.40(2H,
m, NCH2CH2CH2CH3), 0.99–1.02 (3H, m, OCH2CH2-
CH2CH3), 0.92–0.95 (3H, m, NCH2CH2CH2CH3).
Anal. Calcd for C20H24N2O2: C, 74.07; H, 7.41; N,
8.64. Found: C, 73.88; H, 7.65; N, 8.57.
4.1.29. 9-n-Butyl-b-carboline-3-carboxylic acid (8c). Yel-
low solid was obtained (2.71g, 99%). Mp 182–184ꢁC;
FAB-MS m/e 269 (M+1); UV kmax 387, 359, 272, 238,
221nm; IR (KBr): 3250–2250, 1710, 1630, 1334,
1213cmꢀ1 1H NMR (500MHz, DMSO-d6) d 12.11
;
(1H, s, COOH), 9.14 (1H, s, H-4), 8.94 (1H, s, H-1),
8.42–8.44 (1H, d, J=8.0Hz, H-8), 7.77–7.79 (1H, d,
J=8.5Hz, H-5), 7.65–7.68 (1H, m, H-6), 7.34–7.37 (1H,
m, H-7), 4.56–4.59 (2H, m, NCH2CH2CH2CH3), 1.79–
1.85 (2H, m, NCH2CH2CH2CH3), 1.28–1.32 (2H, m,
4.1.25. Butyl 9-benzyl-b-carboline-3-carboxylate (7d). A
mixture of 5 (2.4g, 10mmol) and anhydrous DMF
(60mL) was stirred at rt for 10min, then 60% NaH
(0.6g, 15mmol) and benzyl bromide (5mL, 40mmol)
were added and refluxed for 3h. Later the mixture was
treated in a manner similar to that described for 5a to
afford white crystals 7d (2.4g, 67%), mp 105–106ꢁC
NCH2CH2CH2CH3),
0.87–0.90
(3H,
m,
NCH2CH2CH2CH3). Anal. Calcd for C16H16N2O2: C,
71.64; H, 5.97; N, 10.45. Found: C, 71.45; H, 6.19; N,
10.36.
4.1.30. 9-Benzyl-b-carboline-3-carboxylic acid (8d). Yel-
low solid was obtained (2.96g, 98%). Mp 261–262ꢁC;

4622
R. Cao et al. / Bioorg. Med. Chem. 12 (2004) 4613–4623
FAB-MS m/e 303 (M+1); UV kmax 355, 342, 267,
239nm; IR (KBr): 3457, 3409, 3250–2250, 1683, 1624,
approximately 24 2ꢁC, with a relative humidity 60–
70%, and in 12h light-dark cycle. The sterile food and
water were provided according to institutional guide-
lines. All animals were provided by Shanghai Labora-
tory Animal Center of Chinese Academy of Science.
All animal procedures were approved by the Animal
Ethical Committee of the Sun Yat-sen University. Prior
to each experiment, mice were fastened overnight and al-
lowed free access to water. Various doses of the b-carb-
oline derivatives ranging from 10to 300mg/kg dissolved
in 0.5% carboxymethyl cellulose sodium (CMC-Na) salt
solution were given via intraperitoneal (i.p.) to different
groups of healthy C57BL/6 mice, and each group con-
tained 10mice (five males and five females). After the
administration of the compounds, mice were observed
continuously for the first 2h for any gross behavioral
changes and deaths, then intermittently for the next
24h and occasionally thereafter for 14days, and for
the onset of any delayed effects. All animals were sacri-
ficed at the 14th day after drug administration and
checked macroscopically for possible damage to the
heart, liver, and kidneys. Mice of immediate death fol-
lowing drug administration were also examined for
any possible organ damage. LD50 values were calculated
graphically as described.31
1334, 1225cmꢀ1 1H NMR (500MHz, DMSO-d6) d
;
12.18 (1H, s, COOH), 9.15 (1H, s, H-4), 8.96 (1H, s,
H-1), 8.44–8.45 (1H, d, J=8.0Hz, H-8), 7.79–7.80 (1H,
d, J=8.0Hz, H-5), 7.63–7.66 (1H, m, H-6), 7.35–7.38
(1H, m, H-7), 7.22–7.31 (5H, m, Ar–H), 5.85 (2H, s,
NCH2Ar). Anal. Calcd for C19H14N2O2: C, 75.50; H,
4.64; N, 9.27. Found: C, 75.38; H, 4.85; N, 9.18.
4.1.31. 9-(20,30,40,50,60-Pentafluoro)benzyl-b-carboline-3-
carboxylic acid (8e). White solid was obtained (3.84g,
98%). Mp >270ꢁC; FAB-MS m/e 393 (M+1); UV kmax
351, 338, 261, 239, 218nm; IR (KBr): 3500–2250,
1714, 1628, 1335cmꢀ1 1H NMR (500MHz, DMSO-
;
d6) d 12.14 (1H, s, COOH), 9.10(1H, s, H-4), 8.83
(1H, s, H-1), 8.45–8.47 (1H, d, J=8Hz, H-8), 7.65–
7.68 (1H, m, H-5), 7.59–7.61 (1H, d, J=8.5Hz, H-6),
7.38–7.41 (1H, m, H-7), 5.67 (2H, s, CH2Ar). Anal. Cal-
cd for C19F5H9N2O2: C, 58.16; H, 2.30; N, 7.14. Found:
C, 58.03; H, 2.39; N, 7.18.
4.1.32. 9-Phenylpropyl-b-carboline-3-carboxylic acid (8f).
Yellow solid was obtained (3.2g, 97%). Mp 213–215ꢁC;
FAB-MS m/e 331 (M+1); UV kmax 358, 346, 268, 239,
218nm; IR mmax 3500–2250, 1692, 1629, 1335,
1215cmꢀ1 1H NMR (500MHz, DMSO-d6) d 12.09
;
4.4. Assay of antitumor activity
(1H, s, COOH), 9.13 (1H, s, H-4), 9.00 (1H, s, H-1),
8.46–8.48 (1H, d, J=7.5Hz, H-8), 7.76–7.78 (1H, d,
J=8.0Hz, H-5), 7.69–7.72 (1H, m, H-6), 7.38–7.41
(1H, m, H-7), 7.21–7.26 (2H, m, ArH), 7.13–7.17 (3H,
m, Ar–H), 4.63–4.66 (2H, m, NCH2CH2CH2Ar), 2.49–
2.51 (2H, m, NCH2CH2CH2Ar), 2.14–2.20(2H, m,
NCH2CH2CH2Ar). Anal. Calcd for C21H18N2O2: C,
76.36; H, 5.45; N, 8.48. Found: C, 76.22; H, 5.69; N,
8.38.
Lewis lung cancer and S180sarcoma cell lines were pro-
vided by Shanghai Institute of Pharmaceutical Industry.
Tumor cells of Lewis lung cancer and S180sarcoma
were inoculated to mice. After 7days, tumors were taken
out and cells harvested. Viable tumor cells (2·106 cells/
mouse) were inoculated to the armpit of mice by subcu-
taneous injection. Each compound was injected by intra-
peritoneal (i.p.) to different group mice (each group
containing 10female mice) 24h after the inoculation at
a dosage of 7.5mg/kg once a day for consecutive 7days.
This dose was the maximum tolerated dose for most
compounds based on our preliminary studies. Cyto-
phosphane (CTX) at 30mg/kg was used as a positive
control and vehicle as negative control. The weights of
animals were recorded every 3days. All animals were
sacrificed at the 21st day after tumor inoculation and
the tumors were excised and weighed. The inhibition
rate was calculated as follows:
4.2. In vitro cytotoxicity assays
Cytotoxicity assays in vitro were carried out using 96
microtiter plate cultures and MTT staining according
to the procedures described by Al-Allaf and Rashan26
with a slight modification. Cells were grown in RPMI-
1640medium containing 1%0 (v/v) fetal calf serum
and 100lg/mL penicillin and 100lg/mL streptomycin.
Cultures were propagated at 37ꢁC in a humified atmos-
phere containing 5% CO2. Cell lines were obtained from
Shanghai Cell Institute, Chinese Academy of Science.
Drug stock solutions were prepared in DMSO. The final
concentration of DMSO in the growth medium was 2%
(v/v) or lower, concentration without effects on cell rep-
lication. The human tumor cell line panel consisted of
nonsmall cell lung carcinoma (PLA-801), liver carci-
noma (HepG2 and Bel-7402), gastric carcinoma
(BGC-823), cervical carcinoma (Hela), colon carcinoma
(Lovo). In all of these experiments, three replicate wells
were used to determine each point.
ðC ꢀ T Þ=C ꢁ 100
T: average tumor weight of treated group; C: average
tumor weight of negative control group.
Acknowledgements
We are thankful for the financial support of this work
by Xinjiang Huashidan Pharmaceutical Co. Ltd and
Guangzhou Commission of Science and Technology
(97-Z-12-01). We are also grateful to Prof. Huifang
Yan and co-workers for performance of the antitumor
and acute toxic assays in mice.
4.3. Assay of acute toxicities
Healthy C57BL/6 mice (9–12weeks) weighing 18–22g
were housed in rooms where the temperature was

R. Cao et al. / Bioorg. Med. Chem. 12 (2004) 4613–4623
4623
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