1-Aryl-tetrahydroisoquinoline analogs as active anti-HIV agents in vitro

Article abstract of DOI:10.1016/j.bmcl.2008.02.040

A series of 1-aryl-6,7-dihydroxyl(methoxy)-1,2,3,4-tetrahydroisoquinolines (compounds 1-36) were synthesized via Pictet-Spengler cyclization. All the synthesized compounds were assayed for activities against HIV-1_IIIB in C8166 cell cultures by

Full text of DOI:10.1016/j.bmcl.2008.02.040

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 18 (2008) 2475–2478
1-Aryl-tetrahydroisoquinoline analogs as active
anti-HIV agents in vitro
Pi Cheng,a,c Ning Huang,b Zhi-Yong Jiang,a Quan Zhang,a,c Yong-Tang Zheng,b
Ji-Jun Chen,a,* Xue-Mei Zhanga and Yun-Bao Maa
aState Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany,
The Chinese Academy of Sciences, Kunming, Yunnan 650204, PR China
bLaboratory of Molecular Immunopharmacology, Key Laboratory of Animal Models and Human Diseases Mechanisms,
Kunming Institute of Zoology, The Chinese Academy of Sciences, Kunming, Yunnan 650223, PR China
cGraduate School of the Chinese Academy of Sciences, Beijing 100039, PR China
Received 27 November 2007; revised 25 January 2008; accepted 14 February 2008
Available online 19 February 2008
Abstract—A series of 1-aryl-6,7-dihydroxyl(methoxy)-1,2,3,4-tetrahydroisoquinolines (compounds 1–36) were synthesized via Pic-
tet–Spengler cyclization. All the synthesized compounds were assayed for activities against HIV-1IIIB in C8166 cell cultures by
MTT method for the first time. The results of the anti-HIV screening revealed that 6,7-dihydroxytetrahydroisoquinolines possessed
higher selective index than 6,7-dimethoxyl analogs due to the significantly decreased cytotoxicities. Compounds 6, 24, and 36
showed potent anti-HIV activities with EC50 values of 8.2, 4.6, and 5.3 lM respectively, and the cytotoxicities (CC50) of these three
compounds were 784.3, 727.3, and 687.3 lM, which resulted in SI values larger than 95, 159, and 130 respectively.
ꢀ 2008 Elsevier Ltd. All rights reserved.
1,2,3,4-Tetrahydroisoquinoline (THIQ) was a common
core structure of many alkaloids isolated from natural
sources and showed antitumor,1 antimicrobial,2 and
other biological activities.3–7 The recent success in total
synthesis of ecteinascidin 7438,9 and its human clinical
trials10,11 have shed light on this class of natural
products.
(selective index > 125).14 Besides, Iwasa and colleagues
reported that 1-methyl-6,7-dihydroxytetrahydroisoquin-
oline (compound A, Fig. 1) still possessed an EC50 value
of 0.117 lg/mL (SI = 181) in H9 cell.2 During the course
of our continuous search for anti-HIV compounds from
natural sources, it was suggested that compound B, an
isomer of A, showed 48% inhibitory ratio against
HIV-1 RT at 210 lg/mL.15
Prompted by a report of the anti-human immunodefi-
ciency virus (HIV) activity of michellamine B (Fig. 1),
a naphthylisoquinoline alkaloid dimmer from Ancistro-
cladus korupenis,12 evaluations of natural THIQs as
inhibitors of HIV-1 were continuously reported in the
literatures. The rigid THIQ derivatives chelidoneme,13
O-methyl psychotrine sulfate,4 and magnoflorine13
inhibited HIV-1 target at reverse transcriptase (RT).
More recently, a series of active anti-HIV benzyl THIQ
derivatives were isolated from the leaves of Nelumbo
nucifera, among which R-coclaurine inhibited HIV rep-
lication in H9 cell with an EC50 value of 0.8 lg/mL
Based on the anti-HIV activities of THIQs derivatives
reported previously, our interest in this study was to
synthesize simple 1-aryl-tetrahydroisoquinoline analogs
(C) and assess these compounds as anti-HIV agents to
identify active compounds and reveal structure–activity
relationship (SAR) trends. The syntheses of compounds
C focused on the replacement of methyl (C-1) and hy-
droxyl (C-6 and C-7) in compound A by various aro-
matic moieties and methoxyl group, respectively.
THIQs were generally prepared as racemates by acid
catalyzed Pictet–Spengler cyclization.16,17 On the basis
of this method, compounds C (1–36) (Table 1) were syn-
thesized as outlined in Scheme 1. When R was hydroxyl
group, dopamine hydrochloride and aromatic aldehyde
were selected as starting materials. A solution of dopa-
Keywords: 1-Aryl-tetrahydroisoquinoline; Anti-HIV activity; Pictet–
Spengler cyclization.
*
Corresponding author. Tel./fax: +86 871 5223265; e-mail:
chenjj@mail.kib.ac.cn
0960-894X/$ - see front matter ꢀ 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.02.040

2476
P. Cheng et al. / Bioorg. Med. Chem. Lett. 18 (2008) 2475–2478
OH
HN
OH
OH OCH3
O
MeO
MeO
O
OMe
Me
H
N
OCH3OH
N
H
OMe
H
N
HO
O
H
OH
NH
H2SO4
OH
Me
O-Methyl psychotrine sulfate
Michellamine B
Chelidoneme
MeO
H3CO
HO
+
5
N
NH
HO
R
HO
HO
4
1
6
3
H
7
NH
NH
NH
HO
R
8
HO
OH
Ar
MeO
HO
R = OH or OMe
A
B
C
Magnoflorine
R-Coclaurine
Figure 1. Structures of some THIQ derivatives.
mine hydrochloride and aromatic aldehyde in dichloro-
methane (DCM) was stirred under nitrogen atmosphere
for 72 h to afford the target compounds in moderate to
good yields after column chromatography separation
(Table 1).
compounds were summarized in Table 1. The results
suggested that the 6,7-dimethoxy derivatives only exhib-
ited weak anti-HIV activities (SI < 10) except compound
7. O-Demethylation led to significantly decreased cyto-
toxicities with higher SI values. For example, 1-para-
methylphenyl-6,7-dihydroxytetrahydroisoquinoline (6)
showed a CC50 value of >784.3 lM (SI > 95), while its
methoxyl derivative 5 possessed a CC50 of 280.7 lM.
In addition, hydroxyl groups bond to C-6 and C-7 might
play an important role in potent anti-HIV activity as to
the title compounds. For example, compound 24 exhib-
ited an EC50 of 4.6 lM (SI > 159), but its methoxyl
derivative 23 only showed an EC50 of 31.8 lM. When
Ar moiety located at C-1 changed to 2-furyl, 2-pyridinyl
or naphthyl, compounds 30, 32, and 36 still had antiviral
activities. Especially, compound 36 showed anti-HIV
activity with EC50 and CC50 values of 5.3
and >687.3 lM, respectively, resulting in a SI value of
>130.
When the starting material changed to 3,4-dimethoxy-
phenylethylamine, the one-pot procedure only afforded
the target compounds in poor yields after a screening
of various Bronsted acid catalysts including 4-methyl-
phenylsulfonic acid,18 trifluoroacetic acid (TFA),19 and
trifluoromethylsulfonic acid (TFSA).20 A further litera-
ture survey demonstrated that Pictet–Spengler cycliza-
tion would be favored if the imine was used as
substrate directly.21–23 As a result, the methoxyl THIQs
were synthesized in two steps: imine intermediates were
obtained without further purification. Then, the already
usable imines were dissolved in TFA and heated to re-
flux23 or 120 ꢁC in Schelenk sealed tube for 4 h to afford
target compounds in good yields after column chroma-
tography. It should be noted that refluxing the corre-
sponding imines in TFA for 4 h at normal boiling
temperature only afforded the compounds 7, 9, 11, and
29 in very poor yields. The reactions performed at high-
er temperature (120 ꢁC in Schelenk sealed tube for 4 h)
gave good yields for the electron-rich imines.
The above-mentioned anti-HIV activity information
suggested the importance of hydroxyl groups at C-7
and C-8 for minimal cytotoxicities and potent antiviral
activities. But there were exceptions, which were the
cases for the inactive hydroxyl compounds 14 and34.
Compound
14
(Ar = para-trifluoromethylphenyl)
showed EC50 and CC50 values of 8.52 and 13.07 lg/
mL respectively (SI = 1.5), indicating that the trifluoro-
methyl group was a cytotoxic moiety compared with
compound 6 (Ar = para-methylphenyl). Compound 34,
the 1-naphthyl analogue, only exhibited SI value of
1.9 (CC50 = 47.4 lM). Interestingly, the 2-naphthyl
derivative 36 showed an obviously increased SI value
According to the previous literatures reported by other
research groups, 1-aryl-tetrahydroisoquinolines dis-
played various biological activities including antibacte-
rial,23
bronchodilator,24
and
anticonvulsant25
properties. Herein, Compounds 1–36 were evaluated
for activity against HIV-1IIIB in C8166 cell cultures for
the first time. AZT (zidovudine) was included as a refer-
ence compound. The anti-HIV activities (EC50), cyto-
toxicities (CC50), and selective index (SI) for the tested
of >130 due to the decreased cytotoxicity (CC50
687.3 lM) and increased anti-HIV activity (EC50
5.3 lM).
>
=

P. Cheng et al. / Bioorg. Med. Chem. Lett. 18 (2008) 2475–2478
Table 1. Structures, physical data, and anti-HIV activities of compounds Ca
2477
c
Compound C
R
Ar
–OMe Phenyl
–OH Phenyl
–OMe 2-Methylphenyl
–OH 2-Methylphenyl
–OMe 4-Methylphenyl
–OH 4Methylphenyl
–OMe 2-Methoxyphenyl
–OH 2-Methoxyphenyl
–OMe 4-Methoxyphenyl
–OH 4-Methoxyphenyl
–OMe 2,4-Dimethoxyphenyl
–OH 2,4-Dimethoxyphenyl
Yields (%)b State
Mp (ꢁC) EC50 (lM) CC50 (lM)d SIe (CC50/EC50
)
123
224
3
72
65
75
59
60
77
78
85
77
68
73
55
White solid
77–80
115–117 67.3
68–70 42.5
109–113 61.9
84–86 67.3
112–115 8.2
119.6
293.5
>829.9
197.0
>784.3
280.7
>784.3
555.1
>738.0
312.1
>738.0
227.3
>664.4
30.9
2.4
Yellow solid
White solid
Yellow solid
White solid
White solid
Viscous oil
Yellow solid
Viscous oil
>12
4.6
4
>13
4.2
526
627
728
8
>95
12
— 45.9
220–222 42.2
>18
2.5
929
1030
11
—
127.2
34.1
43.8
Pale yellow solid 94–96
Viscous oil
>22
5.2
—
12
Pale yellow solid 109–112 46.5
>14
<1
1326
14
–OMe 4-Trifluoromethylphenyl 71
–OH 4-Trifluoromethylphenyl 80
–OMe 4-Bromphenyl
–OH 4-Bromphenyl
–OMe 3-Bromophenyl
–OH 3-Bromophenyl
–OMe 2-Bromophenyl
–OH 2-Bromophenyl
–OMe 2-Fluorophenyl
–OH 2-Fluorophenyl
–OMe 3-Chlorophenyl
–OH 3-Chlorophenyl
–OMe 2-Chlorophenyl
–OH 2-Chlorophenyl
–OMe 4-Nitrilephentyl
–OH 4-Nitrilephentyl
–OMe 2-Furyl
–OH 2-Furyl
–OMe Pyridin-2-yl
–OH Pyridin-2-yl
–OMe 1-Naphthyl
–OH 1-Naphthyl
–OMe 2-Naphthyl
White solid
White solid
White solid
137–139 27.8
78–80 27.6
109–113 16.9
42.3
37.9
1.5
2.2
1531
16
72
75
74
62
73
67
75
61
64
62
77
56
76
78
68
63
76
80
76
68
76
63
—
Pale yellow solid 116–118 36.2
>625.0
106.7
>625
>18
2.4
1725
18
White solid
Yellow solid
Viscous oil
Yellow solid
Viscous oil
Yellow solid
White solid
Yellow solid
Viscous oil
Yellow solid
White solid
White solid
Viscous oil
Yellow solid
Viscous oil
Yellow solid
Viscous oil
Yellow solid
White solid
80–82
93–96
—
43.5
53.5
31.3
>12
2.8
1932
20
89.0
>625
112–114 23.7
69.0
183–185 58.4
83–85 31.8
114–116 4.6
>26
2.8
21
—
175.4
>772.2
183.6
>727.3
248.7
>727.3
46.2
22
>13
5.9
2325
24
>159
4.3
2528
2629
2726,33
2834
29
—
58.4
109–111 51.8
110–112 60.1
208–210 53.7
>14
7.7
>751.9
572.5
>865.8
444.5
>826.4
64.8
>14
3.8
—
83–85
—
152.4
61.7
171.2
30
>14
2.8
3135
32
215–217 48.4
22.6
236–238 33.2
93–96 6.9
Pale yellow solid 110–113 5.3
0.011
>11
2.9
33
34
—
47.4
54.6
1.9
7.9
35
36
AZTf
–OH
—
2-Naphthyl
—
>687.3
>749
>130
>68,091
—
—
a Anti-HIV data represent the mean values of two separate experiments.
b Isolated yields.
c Effective concentration required to protect C8166 cells against the cytopathogenicity of HIV by 50%.36
d Cytostatic concentration required to reduce C8166 cell proliferation by 50% tested by MTT method.36
e Selectivity index; ratio CC50/EC50
.
f AZT (zidovudine) was used as positive control.
HO
HO
HO
HO
MS4A
DCM
CHO
+
HCl
Ar
NH2
NH
Ar
MeO
MeO
MeO
MeO
MeO
CHO
MS4A
DCM
TFA
+
Ar
NH
N
NH2
reflux
MeO
imine
Ar
Ar
Scheme 1. Synthesis of target compounds C.
Structure modification of compounds C had led to three
active anti-HIV compounds 6, 24, and 36. Based on the
previous literature,37 THIQs generally inhibited HIV-1
replication as non-nucleoside reverse transcriptase
inhibitors (NNRTIs). These three compounds that
showed potent anti-HIV-1 activity were also evaluated
on their inhibitory activity of recombinant HIV-1 RT,
but they only showed 28%, 20%, and 30% inhibitory rate

2478
P. Cheng et al. / Bioorg. Med. Chem. Lett. 18 (2008) 2475–2478
19. Ashley, E. R.; Cruz, E. G.; Stoltz, B. M. J. Am. Chem.
Soc. 2003, 125, 15000.
20. Nakamura, S.; Tanaka, M.; Taniguchi, T.; Uchiyama, M.;
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tively. The suboptimal enzymatic activities of these as-
sayed compounds suggested that further study on the
possible mechanisms of action is needed to provide the
detailed properties of 1-aryl THIQ as anti-HIV agents.
23. Rakesh Kumar, T. R.; Devender, S.; Jaspal, S.; Anil
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Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.bmcl.2008.02.040.
26. Karri, N.; Ferenc, F.; Helmi, N.; Andreas, K.; Erich, K.;
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with 10% heat-inactivated newborn calf serum (Gibco),
The cells used in all experiments were in log-phase growth.
30-Azido-30-deoxythymidine (AZT), the positive control,
was purchased from Sigma (USA).
Syncytium reduction assay: In the presence of 100 lL of
various concentrations of compounds, C8166 cells
(4 · 105 mLꢀ1) were infected with HIV-1IIIB at a multi-
plicity of infection (MOI) of 0.06. The final volume per
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3 days of culture, the cytopathic effect (CPE) was mea-
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giant cell) in each well under an inverted microscope.
Percentage inhibition of syncytial cell number in treated
culture to that in infected control culture and 50% effective
concentration (EC50) was calculated.
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C8166 cells was assessed by MTT methods. Briefly, cells
were seeded on a microplate in the absence or presence of
various concentrations of compounds in triplicate and
incubated at 37 ꢁC in a humid atmosphere of 5% CO2 for
72 h. The supernatants were discarded and MTT reagent
(5 mg/mL in PBS) was added to each well, then incubated
for 4 h, 100 lL of 50% DMF-20% SDS was added. After
the formazan was dissolved completely, the plates were
read on a Bio-Tek ELx 800 ELISA reader at 595/630 nm.
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viable cells by 50% (CC50) was calculated from dose–
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