Synthesis and biological evaluation of novel tetrahydroisoquinoline derivatives as antitumor agents

Article abstract of DOI:10.14233/ajchem.2014.16064

Fifteen novel tetrahydroisoquinoline derivatives have been synthesized via a mild synthetic route. The structures of all the compounds were confirmed by ¹H NMR spectra, ¹³C NMR spectra and mass spectra. Their antitumor activities were evaluated in four human tumor cell lines, including human colon carcinoma (HCT116), non-small cell lung cancer (H1975), human lung adenocarcinoma (A549) and human pancreatic cancer (BxPC-3). Among them, compounds 4i and 4j exhibited remarkable growth inhibitory activity against the subtotal tested subpanel tumor cell lines particularly H1975 with GI values of 59.1 and 63.0 %, respectively.

Full text of DOI:10.14233/ajchem.2014.16064

Asian Journal of Chemistry; Vol. 26, No. 12 (2014), 3493-3495
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.16064
Synthesis and Biological Evaluation of Novel Tetrahydroisoquinoline Derivatives as Antitumor Agents
*
DAO-CAI WANG, HANG SONG and SHUN YAO
Department of Pharmaceutical and Biological Engineering, Sichuan University, Chengdu 610065, P.R. China
*Corresponding author: Tel/Fax: +86 28 85405221; E-mail: cusack@scu.edu.cn
Received: 18 July 2013;
Accepted: 23 October 2013;
Published online: 5 June 2014;
AJC-15279
Fifteen novel tetrahydroisoquinoline derivatives have been synthesized via a mild synthetic route. The structures of all the compounds
were confirmed by 1H NMR spectra, 13C NMR spectra and mass spectra. Their antitumor activities were evaluated in four human tumor
cell lines, including human colon carcinoma (HCT116), non-small cell lung cancer (H1975), human lung adenocarcinoma (A549) and
human pancreatic cancer (BxPC-3). Among them, compounds 4i and 4j exhibited remarkable growth inhibitory activity against the
subtotal tested subpanel tumor cell lines particularly H1975 with GI values of 59.1 and 63.0 %, respectively.
Keywords: Synthesis, Tetrahydroisoquinoline derivatives, Antitumour activity.
Cancer Institute (NCI) in-vitro disease-oriented human cells
screening panel assay.
INTRODUCTION
Inspite of obtaining much progress in our understanding
of the biological processes associated with cancer, there is still
a tremendous need for new and effective agents to treat this
disease well. Therefore, the design of new lead structures for
the screen of antitumor agents is significant in contemporary
medicinal chemistry. Among the kinds of pharmacologically
active heterocycles, isoquinoline and related derivatives have
attracted great attention over the past years. A considerable
variety of natural products containing an isoquinoline skeleton
exhibit anticancer activity1,2, and more isoquinoline derivatives
derived from the parent bicyclic system have caused great
interest, especially tetrahydroisoquinoline derivatives3,4. With
the increasing attention of tetrahydroisoquinoline family, the
development of efficient synthetic approaches for tetrahydro-
isoquinoline and related derivatives can be considered of great
importance.
EXPERIMENTAL
All aromatic aldehydes and 1-methylpiperidin-4-one were
obtained from Kelong Chemical Reagent Co., Ltd. (Chengdu,
China) and used as supplied. Unless otherwise indicated, other
chemicals were purchased from commercial sources and used
without further purification. Column chromatography was
performed on silica gel (200-300 mesh, Qingdao Marine
Chemical Ltd., Qingdao, China). Thin layer chromatography
(TLC) was carried out on TLC silica gel 60 F254 plates.
Melting points were determined on YRT-3 melting point
measuring apparatus (Precision Instrument Plant, Tianjin
University). The 1H NMR and 13C NMR spectra were recorded
on a BrukerAM400 NMR spectrometer and the chemical shifts
in ppm were reported relative to residual solvent peaks or
internal tetramethylsilane (TMS). Mass spectrometry (ESI-
MS) data were measured using a Bruker Daltonics amaZon
SL mass spectrometer. All products were recrystallized from
95 % ethanol.
Recently, 1-methylpiperidin-4-one derivatives have been
effectively used as a base for design of new lead molecules
and pharmacologically active compounds5.Among them, tetra-
hydroisoquinoline structural motif is particularly interesting
with the construction of the benzene ring from a heterocyclic
precursor6.Although the above methods offered several synthe-
tic approaches to this class of important compounds, there is
enough space to lower the reaction temperature. In our investi-
gation, we would like to report a novel mild procedure for the
synthesis of tetrahydroisoquinoline derivatives using 1-
methylpiperidin-4-one as a starting material. Their in-vitro
antitumor activity was evaluated according to the National
General procedure for the aldol condensation reaction
of 1-methylpiperidin-4-one with aromatic aldehydes: A
solution of 1-methyl-4-piperidone (565.8 mg, 5 mmol) and
tetrahydro pyrrole (0.5 mL, 6 mmol) in dichloromethane (10
mL) was stirred at room temperature, to which aromatic
aldehydes (5 mmol) was added. Subsequently, the resulting
mixture was reacted at 40 °C for 4 h to obtain α, β-unsaturated
ketones. The solvent was concentrated under reduced pressure
and the product was isolated by column chromatography on

3494 Wang et al.
Asian J. Chem.
silica gel (200-300 mesh) using petroleum ether/ethyl acetate/
triethylamine (16:8:1, v/v/v).
(2H, t, CH2), 5.12 (2H, s, NH2), 7.45 (1H, d, ArH), 7.51 (1H,
s, ArH), 7.65 (1H, t, ArH), 7.76 (1H, d, ArH); 13C NMR (100
MHz, CDCl3): δ = 29.7, 45.9, 51.3, 55.7, 96.4, 97.0, 114.8,
115.0, 124.1, 125.0, 125.1, 126.1, 126.2, 129.7, 131.6, 136.6,
144.8, 146.5, 150.1. MS (ESI): m/z = 357.1 [M + H]+.
6-Amino-8-(3-bromophenyl)-2-methyl-1,2,3,4-tetra-
hydroisoquinoline-5,7-dicarbonitrile (4g): Flavescens solid.
1H NMR (400 MHz, CDCl3): δ = 2.34 (3H, s, NCH3), 2.68
(2H, m, CH2), 3.08 (4H, m, 2CH2), 5.12 (2H, s, NH2), 7.18
(1H, m, ArH), 7.38 (2H, m, ArH), 7.62 (1H, m, ArH); 13C
NMR (100 MHz, CDCl3): δ = 29.6, 45.9, 51.3, 55.7, 96.4,
96.8, 114.9, 115.1, 123.0, 124.0, 126.8, 130.6, 131.0, 132.4,
137.8, 144.6, 146.6, 150.1. MS (ESI): m/z = 367.0 [M + H]+.
6-Amino-8-(2-bromophenyl)-2-methyl-1,2,3,4-tetra-
hydroisoquinoline-5,7-dicarbonitrile (4h): Yellowish green
solid. 1H NMR (400 MHz, CDCl3): δ = 2.32 (3H, s, NCH3),
2.69 (2H, qt, CH2), 3.01 (2H, s, CH2), 3.10 (2H, m, CH2), 5.09
(2H, s, NH2), 7.18 (1H, dd, ArH), 7.36 (1H, td, ArH), 7.46
(1H, td, ArH), 7.73 (1H, dd, ArH); 13C NMR (100 MHz,
CDCl3): δ = 29.6, 45.8, 51.2, 55.0, 96.6, 97.1, 114.8, 114.9,
122.1, 124.5, 128.1, 129.6, 130.9, 133.4, 136.8, 144.5, 147.0,
150.0. MS (ESI): m/z = 367.1 [M + H]+.
General procedure for the reaction of α,β-unsaturated
ketones with malononitrile: A solution of α,β-unsaturated
ketones (1 mmol), malononitrile (132.1 mg, 2 mmol), DBU
(304.5 mg, 2 mmol) in dichloromethane (4 mL) was stirred at
room temperature for 6 h.After the completion of the reaction,
dichloromethane was removed under reduced pressure. Further
purification of the desired product was accomplished by column
chromatography on silica gel, eluting with petroleum ether/
ethyl acetate/ triethylamine (16:8:1, v/v/v).
6-Amino-2-methyl-8-[4-(trifluoromethyl)phenyl]-
1,2,3,4-tetrahydroisoquinoline-5,7-dicarbonitrile (4a):
Yellowish green solid. 1H NMR (400 MHz, CDCl3): δ = 2.33
(3H, s, NCH3), 2.68 (2H, t, CH2), 3.04 (2H, s, CH2), 3.11 (2H,
t, CH2), 5.13 (2H, s, NH2), 7.38 (2H, d, ArH), 7.77 (2H, d, ArH
); 13C NMR (100 MHz, CDCl3): δ = 29.7, 45.9, 51.3, 55.7,
96.2, 97.0, 114.8, 115.1, 123.9, 126.0, 126.1, 128.7, 131.6,
139.5, 144.7, 146.7, 150.1. MS (ESI): m/z = 357.1 [M + H]+.
6-Amino-2-methyl-8-(naphthalen-2-yl)-1,2,3,4-tetra-
hydroisoquinoline-5,7-dicarbonitrile (4b): Pale yellowish
1
green solid. H NMR (400 MHz, CDCl3): δ = 2.28 (3H, s,
NCH3), 2.69 (2H, t, CH2), 3.12 (4H, t, 2CH2), 5.10 (2H, s,
NH2), 7.32 (1H, dd, ArH), 7.57 (2H, m, ArH ), 7.73 (1H, s,
ArH), 7.90 (2H, td, ArH), 7.97 (1H, d, ArH); 13C NMR (100
MHz, CDCl3): δ = 29.7, 45.9, 51.4, 55.9, 96.4, 96.8, 115.1,
115.5, 124.5, 125.4, 126.9, 127.1, 127.7, 127.9, 128.4, 128.9,
133.1, 133.3, 144.3, 148.4, 150.1. MS (ESI): m/z = 339.2
[M + H]+.
6-Amino-8-(3-methoxyphenyl)-2-methyl-1,2,3,4-tetra-
hydroisoquinoline-5,7-dicarbonitrile (4i): Flavescens solid.
1H NMR (400 MHz, CDCl3): δ = 2.33 (3H, s, NCH3), 2.67
(2H, t, CH2), 3.09 (4H, m, 2CH2), 3.84 (3H, s, OCH3), 5.08
(2H, s, NH2), 6.74 (1H, s, ArH), 6.80 (1H, d, ArH ), 7.00 (1H,
dd, ArH), 7.40 (1H, t, ArH); 13C NMR (100 MHz, CDCl3): δ =
29.7, 45.9, 51.4, 55.4, 55.7, 96.3, 96.6, 113.8, 114.6, 115.1,
115.4, 120.3, 124.2, 130.1, 137.1, 144.2, 148.3, 150.0, 159.7.
MS (ESI): m/z = 319.1 [M + H]+.
6-Amino-8-(2,4-dichlorophenyl)-2-methyl-1,2,3,4-
tetrahydroisoquinoline-5,7-dicarbonitrile (4c): Green solid.
1H NMR (400 MHz, CDCl3): δ = 2.33 (3H, s, NCH3), 2.69
(2H, m, CH2), 3.00 (2H, m, CH2), 3.10 (2H, t, CH2), 5.10 (2H,
s, NH2), 7.13 (1H, d, ArH), 7.40 (1H, dd, ArH), 7.57 (1H, d,
ArH); 13C NMR (100 MHz, CDCl3): δ = 29.6, 45.8, 51.2, 55.0,
96.5, 97.4, 114.7, 114.8, 124.6, 128.0, 130.3, 130.6, 133.2,
133.4, 136.2, 144.3, 144.7, 150.0. MS (ESI): m/z = 357.0
[M + H]+.
6-Amino-8-(3,5-difluorophenyl)-2-methyl-1,2,3,4-
tetrahydroisoquinoline-5,7-dicarbonitrile (4j): Green solid.
1H NMR (400 MHz, CDCl3): δ = 2.35 (3H, s, NCH3), 2.68
(2H, t, CH2), 3.09 (4H, m, 2CH2), 5.12 (2H, s, NH2), 6.79 (2H,
m,ArH), 6.94 (1H, tt,ArH); 13C NMR (100 MHz, CDCl3): δ =
29.7, 45.9, 51.3, 55.5, 96.1, 97.2, 105.0, 111.5, 111.7, 111.8,
114.7, 114.8, 123.9, 144.8, 145.5, 150.0, 161.8, 164.3. MS
(ESI): m/z = 325.1 [M + H]+.
6-Amino-2-methyl-8-(thiophen-2-yl)-1,2,3,4-tetra-
hydroisoquinoline-5,7-dicarbonitrile (4d):Yellowish brown
1
solid. H NMR (400 MHz, CDCl3): δ = 2.37 (3H, s, NCH3),
6-Amino-2-methyl-8-(4-nitrophenyl)-1,2,3,4-tetra-
hydroisoquinoline-5,7-dicarbonitrile (4k):Yellow solid. 1H
NMR (400 MHz, CDCl3): δ = 2.32 (3H, s, NCH3), 2.69 (2H, t,
CH2), 3.03 (2H, s, CH2), 3.11 (2H, t, CH2), 5.16 (2H, s, NH2),
7.46 (2H, d, ArH), 8.38 (2H, d, ArH); 13C NMR (100 MHz,
CDCl3): δ = 29.7, 45.9, 51.2, 55.7, 95.8, 97.4, 114.6, 114.9,
123.7, 124.3, 129.5, 142.4, 145.0, 145.7, 148.4, 150.1. MS
(ESI): m/z = 334.1 [M + H]+.
2.68 (2H, t, CH2), 3.08 (2H, t, CH2), 3.25 (2H, s, CH2), 5.10
(2H, s, NH2), 7.09 (1H, m, ArH), 7.17 (1H, dd, ArH), 7.52
(1H, m, ArH); 13C NMR (100 MHz, CDCl3): δ = 29.7, 45.9,
51.3, 55.9, 97.1, 97.7, 114.9, 115.3, 125.7, 127.6, 128.0, 128.8,
135.0, 141.1, 144.2, 150.0. MS (ESI): m/z = 295.2 [M + H]+.
6-Amino-2-methyl-8-m-tolyl-1,2,3,4-tetrahydro-
isoquinoline-5,7-dicarbonitrile (4e): Pale yellowish green
6-Amino-8-(4-isopropylphenyl)-2-methyl-1,2,3,4-
tetrahydroisoquinoline-5,7-dicarbonitrile (4l): Green solid.
1H NMR (400 MHz, CDCl3): δ = 1.31 (6H, d, 2CH3), 2.33
(3H, s, NCH3), 2.67 (2H, t, CH2), 2.98 (1H, m, CH), 3.09 (4H,
m, 2CH2), 5.06 (2H, s, NH2), 7.15 (2H, d, ArH), 7.33 (2H, d,
ArH); 13C NMR (100 MHz, CDCl3): δ = 23.9, 29.6, 33.9, 45.9,
51.4, 55.9, 96.1, 96.7, 115.2, 115.6, 124.3, 126.9, 128.1, 133.1,
144.0, 148.8, 149.8, 150.2. MS (ESI): m/z = 331.2 [M + H]+.
6-Amino-8-(4-tert-butylphenyl)-2-methyl-1,2,3,4-tetra-
hydroisoquinoline-5,7-dicarbonitrile (4m): Green solid. 1H
NMR (400 MHz, CDCl3): δ = 1.37 (9H, s, 3CH3), 2.34 (3H, s,
NCH3), 2.68 (2H, t, CH2), 3.09 (4H, m, 2CH2), 5.07 (2H, s,
1
solid. H NMR (400 MHz, CDCl3): δ = 2.32 (3H, s, NCH3),
2.41 (3H, s, CH3), 2.67 (2H, t, CH2), 3.09 (4H, m, 2CH2), 5.07
(2H, s, NH2), 7.02 (2H, m, ArH), 7.27 (1H, m, ArH), 7.37
(1H, m, ArH); 13C NMR (100 MHz, CDCl3): δ = 21.5, 29.6,
45.9, 51.4, 55.8, 96.2, 96.7, 115.1, 115.5, 124.2, 125.1, 128.6,
128.8, 129.9, 135.8, 138.7, 144.1, 148.8, 150.0. MS (ESI): m/
z = 303.2 [M + H]+.
6-Amino-2-methyl-8-[3-(trifluoromethyl)phenyl]-
1,2,3,4-tetrahydroisoquinoline-5,7-dicarbonitrile (4f): Pale
yellowish green solid. 1H NMR (400 MHz, CDCl3): δ = 2.33
(3H, s, NCH3), 2.69 (2H, m, CH2), 3.04 (2H, s, CH2), 3.10

Vol. 26, No. 12 (2014)
Synthesis and Biological Evaluation of Novel Tetrahydroisoquinoline Derivatives as Antitumor Agents 3495
TABLE-1
NH2), 7.16 (2H, m, ArH), 7.48 (2H, m, ArH); 13C NMR (100
MHz, CDCl3): δ = 29.6, 31.3, 34.8, 45.9, 51.5, 55.9, 96.1,
96.7, 115.2, 115.6, 124.3, 125.8, 127.8, 132.8, 144.0, 148.8,
150.2, 152.2. MS (ESI): m/z = 345.3 [M + H]+.
SYNTHETIC RESULTS OF TETRAHYDRO-
ISOQUINOLINE DERIVATIVES
Entry
1
R
Product
4a
Yield (%)
51
m.p. (°C)
180-183
226-228
211-214
229-232
187-190
183-184
176-177
175-178
215-218
220-223
218-221
184-187
220-222
235-238
226-228
4-CF3C6H4
2-Naphthyl
2,4-Cl2C6H3
2-Thienyl
6-Amino-2-methyl-8-(pyridin-3-yl)-1,2,3,4-tetra-
hydroisoquinoline-5,7-dicarbonitrile (4n):Yellowish green
1
solid. H NMR (400 MHz, CDCl3): δ = 2.33 (3H, s, NCH3),
2
4b
4c
44
3
41
4
4d
4e
40
2.69 (2H, m, CH2), 3.08 (4H, m, 2CH2), 5.15 (2H, s, NH2),
7.47 (1H, dd, ArH), 7.62 (1H, dt, ArH), 8.53 (1H, d, ArH ),
8.75 (1H, dd, ArH); 13C NMR (100 MHz, CDCl3): δ = 29.7,
45.9, 51.2, 55.9, 96.6, 97.2, 114.8, 115.1, 123.7, 124.4, 131.9,
135.9, 144.4, 144.8, 148.7, 150.2, 150.5. MS (ESI): m/z =
290.2 [M + H]+.
5
3-CH3C6H4
3-CF3C6H4
3-BrC6H4
52
6
4f
43
7
4g
68
8
2-BrC6H4
4h
4i
59
9
3-CH3OC6H4
3,5-F2C6H3
4-NO2C6H4
4-iPrC6H4
61
10
11
12
13
14
15
4j
40
4k
4l
43
6-Amino-8-(4-bromo-2-fluorophenyl)-2-methyl-1,2,3,4-
tetrahydroisoquinoline-5,7-dicarbonitrile (4o): Yellowish
1
brown solid. H NMR (400 MHz, CDCl3): δ = 2.34 (3H, s,
45
4-tert-Butylphenyl
3-Pyridyl
4m
4n
4o
42
77
2-F-4-BrC6H3
43
NCH3), 2.69 (2H, m, CH2), 3.08 (4H, m, 2CH2), 5.11 (2H, s,
NH2), 7.10 (1H, m, ArH), 7.44 (2H, m, ArH); 13C NMR (100
MHz, CDCl3): δ = 29.6, 45.8, 51.2, 55.1, 96.7, 97.5, 114.7,
114.9, 120.1, 122.3, 124.3, 124.9, 128.3, 131.3, 140.9, 144.7,
150.0, 159.9. MS (ESI): m/z = 384.9 [M + H]+.
of treated cells and presented as percentage growth inhibition
(GI %) caused by 20 µM of the test compounds (Table-2).
The obtained data revealed that compounds 4i and 4j exhibited
noticeable growth inhibitory activity against the subtotal tested
subpanel tumor cell lines particularly H1975 with GI values
of 59.1 and 63.0 %, respectively. Other compounds also showed
moderate activity against H1975, especially compound 4f (GI
46.8 %). These heterocycles could be used as new lead struc-
tures for future derivatization or modification to obtain more
potent and selective antitumor agents.
RESULTS AND DISCUSSION
To explore conditions of the synthesis of tetrahydroiso-
quinoline derivatives, various reaction conditions were investi-
gated. When 1-methylpiperidin-4-one was converted to corres-
ponding α,β-unsaturated ketones, the reaction time should not
exceed 4 h to avoid the formation of by-products. In the second
step, the reaction of α,β-unsaturated ketones and malononitrile
was examined using different strong bases, including NaOH,
EtONa, DBU. However, the reaction occurred suiting our needs
perfectly only when DBU was used as strong base. Therefore,
DBU was chosen as the most suitable strong base for all further
reactions. The progress of the reaction was monitored by TLC
and 6 h was enough. The optimized reaction route was shown
in Scheme-I.
TABLE-2
in-vitro PERCENTAGE GROWTH INHIBITION (GI %)
CAUSED BY THE TEST COMPOUNDS AT DOSE OF 20 µM
Subpanel tumor cell lines (% growth inhibitory activity)
Compound
HCT116
23.7
21.2
13.3
5.6
H1975
12.9
28.4
22.2
24.2
8.5
A549
17.5
12.0
3.4
BxPC-3
4a
4b
4c
4d
4e
4f
3.9
3.5
3.9
19.1
9.8
18.8
15.4
22.7
16.2
2.7
NH
2
2.2
O
O
N
NC
CN
R
0.5
46.8
30.6
13.6
59.1
63.0
18.1
11.6
20.7
6.4
17.5
20.7
10.8
41.4
39.3
10.3
2.9
tetrahydro pyrrole
CH Cl
malononitrile
DBU, CH Cl
R
+
R
CHO
2a-o
4g
4h
4i
15.2
5.4
2
2
2
2
N
N
4.8
40.9
10.7
10.6
7.6
1
3a-o
4a-o
4j
39.7
20.0
8.5
Scheme-I: Synthetic route for compounds 3a-o and 4a-o
4k
4l
Based on these optimized conditions, a series of tetra-
4m
4n
4o
0.8
5.8
6.8
hydroisoquinoline derivatives were synthesized. The results
(Table-1, entries 1-15) indicated that for aromatic aldehydes
bearing different functional groups such as trifluoromethyl,
chloro, bromo, fluoro, nitro, methoxyl, methyl, isopropyl or
tert-butyl the reaction proceeded smoothly in all cases.
The compounds were screened for their in vitro antitumor
activity in the full NCI 60 cell panel, including human colon
carcinoma (HCT116), non-small cell lung cancer (H1975),
human lung adenocarcinoma (A549) and human pancreatic
cancer (BxPC-3). In the protocol, all compounds were tested
initially at three high doses, i.e., 10, 20 and 40 µM. After the
primary biological tests, only compounds which had better
antitumor activities were chosen to carry out the five-dose screen.
The data are reported as a mean graph of the percent growth
3.2
1.8
21.0
0.9
3.2
25.4
18.7
REFERENCES
1. X.Y. Zhang, Z.J. Liu, B. Xu, Z.L. Sun, Y.Q. Gong and C.S. Shao, Eur.
J. Pharmacol., 677, 47 (2012).
2. A. Burgeiro, A.C. Bento, C. Gajate, P.J. Oliveira and F. Mollinedo,
Eur. J. Pharmacol., 705, 109 (2013).
3. H.R. Lin, M.K. Safo and D.J. Abraham, Bioorg. Med. Chem. Lett., 17,
2581 (2007).
4. Q.Q. Huang, L.H. Chen and F.J. Nan, Tetrahedron Lett., 49, 5141
(2008).
5. R.R. Kumar, S. Perumal, J.C. Menéndez, P. Yogeeswari and D. Sriram,
Bioorg. Med. Chem., 19, 3444 (2011).
6. K. Balamurugan,V. Jeyachandran, S. Perumal and J.C. Menéndez, Tetra-
hedron, 67, 1432 (2011).