Synthesis and in vitro activity of new tetrahydronaphtho[1,2-b]azepine derivatives against Trypanosoma cruzi and Leishmania chagasi parasites

Article abstract of DOI:10.1016/j.bmcl.2008.05.013

Series of 2-exo-aryl-1,4-epoxy-2,3,4,5-tetrahydronaphtho[1,2-b]azepines 3a-k and cis-2-aryl-4-hydroxy-2,3,4,5-tetrahydronaphtho[1,2-b]azepines 4a-j were synthesized and evaluated against free and intracellular live forms of Trypanosoma cruzi and Leishmani

Full text of DOI:10.1016/j.bmcl.2008.05.013

Bioorganic & Medicinal Chemistry Letters 19 (2009) 2360–2363
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and in vitro activity of new tetrahydronaphtho[1,2-b]azepine
derivatives against Trypanosoma cruzi and Leishmania chagasi parasites
a
b
b
b
Alirio Palma a, , Andrés Felipe Yépes , Sandra Milena Leal , Carlos Andrés Coronado , Patricia Escobar
*
a Laboratorio de Síntesis Orgánica, Escuela de Química, Universidad Industrial de Santander, A. A. 678, Bucaramanga, Santander, Colombia
b Centro de Investigación de Enfermedades Tropicales, Facultad de Salud, Escuela de Medicina, Departamento de Ciencias Básicas, Universidad Industrial de Santander,
A.A. 678, Bucaramanga, Santander, Colombia
a r t i c l e i n f o
a b s t r a c t
Article history:
Series of 2-exo-aryl-1,4-epoxy-2,3,4,5-tetrahydronaphtho[1,2-b]azepines 3a–k and cis-2-aryl-4-hydroxy-
2,3,4,5-tetrahydronaphtho[1,2-b]azepines 4a–j were synthesized and evaluated against free and intracel-
lular live forms of Trypanosoma cruzi and Leishmania chagasi parasites using in vitro assays. Cell toxicity
was also analyzed on Vero and THP-1 mammalian cell lines. The compounds 3c, 3f, and 4d were the most
active against both live forms of T. cruzi parasites with low mammalian cell toxicity. Some compounds
were active on free live forms of L. chagasi parasites but none was active on intracellular amastigotes
of L. chagasi infecting THP-1 macrophages.
Received 1 February 2008
Revised 2 May 2008
Accepted 2 May 2008
Available online 6 May 2008
Keywords:
Trypanosoma cruzi
Leishmania chagasi
Chagas’ disease
Ó 2008 Elsevier Ltd. All rights reserved.
Anti-parasitic agents
Tetrahydronaphtho[1,2-b]azepines
1,4-Epoxytetrahydronaphtho[1,2-b]-
azepines
Drug discovery
American trypanosomiasis (Chagas’ disease) and leishmaniasis
have reemerged over the last few decades as important threats
to human health and economic development. They constitute en-
demic diseases mainly distributed on the tropical and subtropical
areas of the world where millions of people live on permanent risk
of infection. The alternatives of treatment for the parasite-infected
people are few, expensive, variable on clinical efficacy and not al-
ways available.1 They often require long courses of parenteral
administration and are associated with severe side effects and
resistance.2
The chemotherapy for leishmaniasis has been based for over 60
years on the use of pentavalent antimonial drugs and in case of
failure, amphotericine B, pentamidine isethionate, aminosidine
(paromomycin), and miltefosine are commonly used.3 The chemo-
therapy for Chagas’ disease is more precarious, dependent on two
nitroheterocyclic compounds, nifurtimox, now discontinued, and
benznidazole. They are both toxic and restricted only to the acute
phase of the disease.4 There is an urgent need to develop cost-
effective new drugs and discover novel molecules with a potent
The tetrahydro-1-benzazepine derivatives have been exten-
sively investigated synthetically and pharmacologically.7–21 Com-
pounds containing this heterocyclic unit possess a wide range of
biological activities and some derivatives have been active against
promastigotes and intracellular amastigotes of L. mexicana.22 Other
derivatives are considered as promising anti-trypanosomal agents
when used as inhibitors of Trypanosoma cruzi dihydrofolate reduc-
tase.23 Based on this information and, as an extension of our ongo-
ing work toward the synthesis, structural elucidation, and
functionalization of the tetrahydro-1-benzazepine ring system,24,25
in this letter we report the anti-parasitic activity of 2-exo-aryl-1,4-
epoxytetrahydronaphtho[1,2-b]azepines 3a–k and cis-2-aryl-4-
hydroxytetrahydronaphtho[1,2-b]azepines 4a–j against T. cruzi
and Leishmania chagasi parasites and Vero and THP-1 cell lines.
As illustrated in Scheme 1, the evaluated compounds were syn-
thesized starting from the available N-benzyl-a-naphthylamines,
which on reaction with an excess of allyl bromide in the presence
of potassium carbonate in dry acetone under reflux, were con-
verted into N-allyl-N-benzyl-substituted-a-naphthylamines 1a–k
in good yields (70–85%). The introduction of an allyl moiety at
the ortho-position of the amino group was carried out via an aro-
matic amino-Claisen rearrangement of the N-allyl derivatives 1a–
k. Thus, rearrangement of these derivatives by heating in the
presence of stoichiometric amounts of boron trifluoride diethyl
anti-parasitic
activity
and
improved
pharmacological
characteristics.5,6
* Corresponding author. Tel./fax: +57 76 349069.
E-mail addresses: apalma@uis.edu.co, alirio.palma@gmail.com (A. Palma).
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.05.013

A. Palma et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2360–2363
2361
Scheme 1. Reagents and conditions: (i) BF3ꢀOEt2 (1 equiv), 115–125 °C, 1–4 h; (ii) a—30% H2O2 (3 equiv)/Na2WO4ꢀ2H2O (5% mol), methanol, 0–25 °C, 45–50 h; b—toluene,
reflux, 6–10 h; (iii) Zn/80% AcOH, 80–82 °C, 2–5 h.
ether (BF3ꢀEt2O), as acid catalyst, at 115–125 °C gave the rear-
ranged products 2a–k in excellent yields (61–88%).
83.37 10.37 lM; SI > 17.7), 3f (IC50 18.35 0.49 lM and IC90
76.29 16.82 lM; SI > 13.6), and 4d (IC50 9.89 0.10 lM and IC90
29.70 0.08 lM; SI 6.7) compounds were active on T. cruzi
amastigotes infecting Vero cells. None of the tested molecules
was active on intracellular L. chagasi parasites at any of the evalu-
ated concentration (1–100 lM). Intracellular amastigotes of
L. chagasi were susceptible only to the AmB referential drug with
activities of IC50 0.03 0.0009 and IC90 0.19 0.002 lM (data not
shown). About the mammalian cell toxicity, the 2-exo-aryl-1,4-
epoxytetrahydronaphtho[1,2-b]azepines 3a–k were, in general,
less toxic than their reduced analogs 4a–j.
In a search for structural parameters which might enhance the
anti-parasitic activity, we introduced chlorine, bromine, fluorine,
methoxy, methyl, and nitro substituents onto the phenyl ring of
compounds 3 and 4. The presence of the bromine atom on com-
pounds 3d,f and 4d,f showed interesting behavior. Since 3f com-
pound was active on free and intracellular live forms of T. cruzi
and on L. chagasi promastigotes without toxicity on Vero or THP-
1 cells, compound 4d was also active but with moderate toxicity
on mammalian cells. In contrast, compounds 3d and 4f lost activity
on intracellular forms of T. cruzi. Among the chlorine and fluorine
containing molecules, 3c, 4c, 3e, 4e, and 4b were highly active on
epimastigotes of T. cruzi (even higher than the reference nifurtimox
drug). The compounds 3c and 4b showed the best activity, being
active on free and intracellular live forms of T. cruzi and on L. chag-
asi promastigotes without (for 3c) or moderate (for 4b) toxicity on
mammalian cells. The obtained values also indicate that halogen,
methyl, and nitro substitution at 20-position as well as methyl or
methoxy substitution at 30-position resulted in a loss of activity.
Dichloro substitution at 20, 40-positions presented in addition a
higher cell toxicity.
Oxidation and subsequent intramolecular 1,3-dipolar cycload-
dition of 2a–k to obtain the corresponding 1,4-epoxytetrahydro-
naphtho[1,2-b]azepines 3a–k was carried out by reacting
compounds 2a–k with an excess of hydrogen peroxide (30%
H2O2) in the presence of catalytic amounts of sodium tungstate
(Na2WO4ꢀ2H2O) and by heating generated in-situ nitrones in tol-
uene under reflux. Cycloadducts 3a–k were fully characterized
by using 1H and 13C NMR spectroscopy at 400 MHz and
100 MHz, respectively (Bruker AM-400 apparatus), and shown
to be 2-exo-aryl-cycloadducts as evidenced by NOESY experi-
ments.25 Finally, reductive cleavage of the N–O bond of 3a–j by
treating with Zn in 80% acetic acid at 80–82 °C for 2–5 h, gave,
as expected, exclusively cis-2-aryl-4-hydroxytetrahydronaph-
tho[1,2-b]azepines 4a–j in 64–78% yields, after column chroma-
tography purification on silica gel. The cis stereochemistry of
these compounds was also determined on the basis of NOESY
experiments.25
The in vitro anti-parasitic activity of the cycloadducts 3a–k
and their reduced homologues 4a–j were evaluated against T. cru-
zi, L. chagasi (free and intracellular live forms) parasites and on
Vero epithelial cells and THP-1 transformed human macrophages.
Nifurtimox and amphotericine B (AmB) were used as control
drugs under the same assay conditions.26,27 The obtained results
are summarized in Table 1. Many of the tested compounds were
active on free live forms of T. cruzi and L. chagasi parasites. Thus,
fifteen compounds (3c,e,f,h,k and 4a–j) were active on T. cruzi
epimastigotes with inhibitory concentration (IC50) values ranging
from 0.50 0.21 to 38.77 1.71 lM and IC90 values from
11.01 0.21 to 104.73 17.12 lM. Likewise, nine compounds
(3c,f–h,j and 4d,e,g,j) were active on L. chagasi promastigotes with
IC50 values ranging from 5.97 0.64 and 35.37 0.49 lM and IC90
values from 28.20 0.08 and 67.31 4.73 lM. The selectivity in-
dex (SI = CC50 Vero cells/IC50 T. cruzi or CC50 THP-1 cells/IC50
L. chagasi) from the active compounds was higher than 4. Seven
compounds (3c,f,g and 4d,e,g,j) were active on both tested
parasites.
In conclusion, the most active compounds to emerge from this
study were 2-exo-(40-chlorophenyl)-1,4-epoxytetrahydronaph-
tho[1,2-b]azepine 3c, 2-exo-(30-bromophenyl)-1,4-epoxytetrahy-
dronaphtho[1,2-b]azepine 3f, and cis-2-(40-bromophenyl)-4-
hydroxytetrahydronaphtho[1,2-b]azepine 4d. They were active
against free and intracellular forms of T. cruzi with SI higher than
6. Although some of the tested compounds were active on L. chag-
asi promastigotes, none of them was active on intracellular
amastigotes infecting THP-1 cells. The results obtained offer new
On the other side, few compounds were active on parasite intra-
cellular live forms. Only 3c (IC50 16.22 1.12 lM and IC90

2362
A. Palma et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2360–2363
Table 1
In vitro activity of 2-exo-aryl-1,4-epoxytetrahydronaphtho[1,2-b]azepines 3a–k and cis-2-aryl-4-hydroxy-tetrahydronaphtho[1,2-b]azepines 4a–j against Trypanosoma cruzi and
Leishmania chagasi
Compound
R
R1
R2
lM
Trypanosoma cruzia
Epimastigote forms Intracellular amastigotes
Leishmania chagasib
Mammalian cells
Promastigote forms
Vero cellsc
THP-1 cellsd
IC50e/IC90
SIg
IC50/IC90
SI
IC50/IC90
SI
CC50f/CC90
CC50/CC90
3a
4a
3b
4b
3c
H
H
F
H
H
H
11.5
>350
5.7
35.1
90.5
>300
1.1
11.6
38.8
104.7
3.2
24.8
11.4
175.5
10.2
15.9
12.6
80.1
1.4
54.9
17.5
82.3
10.7
19.4
82.7
>300
14.0
48.5
17.0
44.1
16.5
42.7
100.2
292.6
0.5
6.3
>100
>100
19.3
>30
>100
>100
14.8
>30
16.2
83.4
>100
>100
>100
>100
9.9
29.7
13.1
>100
23.4
>30
18.4
76.3
>100
>100
89.6
>100
24.3
>30
>100
>100
33.4
>30
>100
>100
10.6
>30
>250
>250
>30
<0.7
21.2
175.2
46.0
67.1
70.4
112.7
21.0
120.1
35.4
43.1
25.9
52.9
73.4
>250
18.5
37.1
32.7
>300
6.0
67.3
10.4
31.3
18.3
55.7
16.4
49.5
17.9
58.7
35.2
41.2
41.4
134.0
183.8
>300
30.6
64.6
22.1
45.8
11.0
28.2
40.9
208.7
ND
>16.5
72.9
>350
>350
101.9
>300
>300
>300
81.9
>250
>300
>300
36.2
122.2
>250
>250
79.0
>200
>300
>300
43.2
176.8
>250
>250
41.7
>250
>300
>300
195.0
>300
>300
>300
89.9
115.6
>300
>300
66.1
>300
>250
>250
79.4
>350
108.0
>268.3
>300
>300
100.5
>250
286.7
>300
95.0
>250
>250
>250
66.1
>200
>300
>300
30.7
>200
>250
>250
49.5
>250
>300
>300
97.6
>200
>300
>300
87.4
>250
37.2
H
18.9
>3.3
91.4
7.4
5.6
2.2
H
H
>3.0
6.8
>4.3
3.9
F
H
H
Cl
Cl
Br
Br
H
H
H
H
H
H
H
H
H
H
Cl
Cl
H
H
H
>17.7
<1.0
2.5
>8.5
1.4
4c
H
H
29.7
21.9
6.5
3d
4d
3e
4e
3f
H
H
>3.4
4.3
H
H
6.7
Cl
H
>23.8
21.9
>14.3
4.6
>22.9
1.3
>9.2
7.2
Cl
H
Br
Br
OCH3
OCH3
CH3
CH3
H
H
>13.6
0.5
>24.0
2.3
4f
H
3g
4g
3h
4h
3i
H
>3.6
7.0
>3.3
4.0
>18.3
10.9
>8.5
2.2
H
H
>17.6
5.3
>3.0
2.6
H
Cl
Cl
Cl
Cl
NO2
0.4
<0.4
9.1
>1.6
2.2
>300
96.5
>250
55.00
>250
45.4
>200
40.2
>300
113.6
>300
ND
4i
H
193.0
1.0
11.01
52.7
>250
1.0
19.43
1.4
3j
H
<0.2
<1.5
<0.4
81.1
—
>11.3
7.2
4j
H
45.4
28.7
23.7
—
>30
92.7
3k
Nfxh
AmBi
H
>100
>100
1.4
11.0
ND
>7.3
—
>300
>300
ND
ND
0.170
0.180
29.6
4.8
17.0
ND
0.01
0.03
NDk
17.0
a
Trypanosoma cruzi strain 320I04 was treated for 72 h at 27 °C with compounds.
Leishmania chagasi strain MHOM/BR/74/PP75 was treated for 72 h at 27 °C with compounds.
African green monkey kidney cell line (Vero, ATCC) was treated for 72 h at 37 °C with compounds.
Transformed human acute monocytic leukemia cell line (THP-1, ATCC) was treated for 72 h at 37 °C with compounds.
Inhibitory concentration IC50 or IC90 was the concentration required for 50% or 90% growth inhibition. All reported values are representative of one experiment from
b
c
d
e
three.
f
Cytotoxic concentration CC50 or CC90 was the concentration required for 50% or 90% mammalian cell killing.
Selectivity index (SI) was obtained by dividing CC50 of Vero or THP-1 cells by IC50 of T. cruzi and L. chagasi parasites.
Reference drug: nifurtimox (Nfx).
Reference drug: amphotericine B (AmB).
ND, not determined.
g
h
i
k
possibilities for further improvements concerning the anti-para-
sitic activity of other closely related derivatives of these series of
compounds. A more complete structure–activity relationship is
currently pursued in our laboratory.
110240520350), and the Research Center of Excellence CENIVAM
(Contract No. 432).
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