Synthesis and antioxidant activity of new tetrahydro-naphthalene-indole derivatives as retinoid and melatonin analogs

Article abstract of DOI:10.1002/ardp.200500177

A number of retinoid-related compounds represent classes of antioxidative and proapoptotic agents with promising potential in the treatment of neoplastic diseases. Indeed, the synthetic retinoid amide fenretinide [N-(4-hydroxyphenyl) retinamide] induces apoptosis of cancer cells and acts as a chemotherapeutic drug in cancer therapy. In the present work, and as a continuation of our studies on retinoid-type compounds, the synthesis of melatonin retinamide derivatives was studied as a novel series of melatonin retinoids, using the condensation reaction sequence involving tetrahydrotetramethylnaphthalene carboxylic acid and appropriate melatonin-type moieties. Despite of the weak DPPH inhibition activity pattern of the synthesized compounds, some of them showed a strong inhibition on lipid peroxidation (IVa-b, Va, and VIIa-c, 88, 96, 90, 94, 93, and 86%, respectively at 10^-4 M concentration) when melatonin (85% at 10^-4 M concentration) was used as a reference compound.

Full text of DOI:10.1002/ardp.200500177

Arch. Pharm. Chem. Life Sci. 2006, 339, 193–200
Z. Ates-Alagoz et al.
193
Full Paper
Synthesis and Antioxidant Activity of New Tetrahydro-
Naphthalene-Indole Derivatives as Retinoid and Melatonin
Analogs
Zeynep Ates-Alagoz1, Tulay Coban2, Erdem Buyukbingol1
1 Ankara University, Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Ankara, Turkey
2 Ankara University, Faculty of Pharmacy Department of Toxicology, Ankara, Turkey
A number of retinoid-related compounds represent classes of antioxidative and proapoptotic
agents with promising potential in the treatment of neoplastic diseases. Indeed, the synthetic
retinoid amide fenretinide [N-(4-hydroxyphenyl)retinamide] induces apoptosis of cancer cells
and acts as a chemotherapeutic drug in cancer therapy. In the present work, and as a continua-
tion of our studies on retinoid-type compounds, the synthesis of melatonin retinamide deriv-
atives was studied as a novel series of melatonin retinoids, using the condensation reaction
sequence involving tetrahydrotetramethylnaphthalene carboxylic acid and appropriate melato-
nin-type moieties. Despite of the weak DPPH inhibition activity pattern of the synthesized com-
pounds, some of them showed a strong inhibition on lipid peroxidation (IVa–b, Va, and VIIa–c,
88, 96, 90, 94, 93, and 86%, respectively at 10– 4 M concentration) when melatonin (85% at 10– 4
M concentration) was used as a reference compound.
Keywords: Synthesis / Indoles / Antioxidant activity /
Received: July 25, 2005; accepted: November 14, 2005
DOI 10.1002/ardp.200500177
differentiation/proliferation [3] and lipid peroxidase
inhibition [4]. It has been shown that Am580 (Fig. 1), a
stable retinobenzoic derivative, originally synthesized as
a retinoic acid receptor (RAR) alpha agonist, is a powerful
inducer of granulocytic maturation in NB4, an APL-
derived cell line [5]. Am580 is a potent synthetic retinoic
acid derivative showing selectivity towards one of the
retinoic acid receptors. It is known that several RAR ago-
nists have therapeutic activity against a variety of cancer
types. However, unacceptable toxicity profiles have hin-
dered their development as drugs [6]. RAR agonists pre-
senting novel structural and chemical features could
therefore open new avenues for the discovery of leads
against breast, lung, and prostate cancer or leukemia.
On the other hand, previous studies have shown that
fenretinide [N-(4-hydroxyphenyl)retinamide], a synthetic
retinoid amide, exhibits antioxidant activities that
include scavenging DPPH (2,2,diphenyl-1-picrylhydrazyl)
radicals, inhibiting linoleic acid peroxidation initiated
by hydroxyl radicals and reducing lipid peroxidation in
rat liver microsomes to the same extent or greater than
Introduction
Vitamin A (retinol) plays an important role in the control
of differentiation and proliferation of various epithelia
of the body [1]. Absence of vitamin A can lead to uncon-
trolled proliferation of epithelial stem cells that fail to
differentiate into the normal phenotype in many lining
epithelia. Retinol and its metabolites are essential for
growth and cell differentiation, particularly of epithelial
tissues [2]. Retinoic acid is the physiologically most active
metabolite of vitamin A that modulates biological pro-
cesses involved in embryogenesis, skeletal development,
cellular differentiation, and growth – in addition, it can
modulate programmed cell death. Retinoids play essen-
tial roles in many diverse biological events including cell
Correspondence: Zeynep Ates-Alagoz, Department of Pharmaceutical
Chemistry, Faculty of Pharmacy (ECZACILIK), University of Ankara, Tan-
dogan 06100, Ankara, Turkey.
E-mail: zates@pharmacy.ankara.edu.tr
Fax: + 90 312 213-1081
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194
Z. Ates-Alagoz et al.
Arch. Pharm. Chem. Life Sci. 2006, 339, 193–200
namide derivatives (containing the melatonin moiety
integrated with the structure of retinoic acid and
Am580) which can be classified into three sets (Schemes
1–3). The antioxidant activities of these compounds are
also reported here.
Results and discussion
Superoxide anion, DPPH-free radical scavencing activ-
ities, and inhibition of lipid peroxidation (LP) assays were
used to determine the antioxidative activities of the com-
pounds synthesized. Scavenging effects of synthesized
compounds on superoxide anion and DPPH radical and
inhibitory effect on the lipid peroxidation are shown in
Table 1. The compounds had a strong effect on the lipid
peroxidation and did not show a strong effect on the
DPPH radical, whereas they showed moderate scavenger
effect on superoxide anion when compared with melato-
nin. The scavenger effects of synthesized compounds on
DPPH radical and inhibitory effect on the lipid peroxida-
tion were not similar. Since the mechanisms of these
methods are different in manner, it is quite difficult to
explain the observed different effects of synthesized com-
pounds unless the fact that further mechanistic studies
should be considered. However, the conflicting results
obtained from antioxidative capacity and activity may be
dependent on several factors: 1) the physical structure of
the test systems, 2) the mode of initiating oxidation, 3)
Figure 1. Structures of all-trans-retinoic acid, Am 580, Am 80,
melatonin, and N-(4-hydroxyphenyl)retinamide.
a-tocopherol [7]. Melatonin is also a well-known indole
compound having the properties of scavenging free radi-
cals [8], protecting against DNA strand breaks, and lipid
peroxidation [9]. Melatonin stimulates several antioxida-
tive enzymes, namely superoxide dismutase (SOD), glu-
tathione peroxidase (GPx), and glutathione reductase
(GRd), increasing their antioxidant effectiveness [10]. Its
potential usefulness in a number of therapeutic areas
such as those related to the desynchronization of biologi-
cal rhythms e.g. jet-lag, disturbed sleep-wake cycles [11],
seasonal disorders, and depression, is known [12]. Melato-
nin may also play a role in the cardiovascular system [13].
In this study, we have synthesized novel melatonin reti-
Scheme 1. Synthesis of the compounds I-4 (a–c).
R1 = –H, –OCH3, –Br. a) POCl3, DMF; b) CH3NO2,
AcONH4; c) LiAlH4
Scheme 2. Synthesis of compounds II-3 (a–h)
comprising the 2nd group. R2 = –H, –CH3, –C2H5, -i-
pr, n-Bu, -Bn, p-fluor-Bn, o, p-dichlor-Bn. a) R2X,
DMF, NaH; b) Pd/C (10%), H2; a9) trifluoroacetic
anhydride, DMF, 08C; b9) Pd/C (10%), H2
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Arch. Pharm. Chem. Life Sci. 2006, 339, 193–200
Synthesis/Antioxidant Activity of some Indole Derivatives
195
Scheme 3. Synthesis of compounds III-5 comprising the 3rd group. a) HCl, H2SO4, EtOH; b) toluene,
AlCl3, CHCl2; c) KMnO4, pyridin, NaOH; c9) HNO3, H2SO4; d9) Pd/C (10%), EtOH
Scheme 4. Amidification reactions of
compound (III-5a). SOCl2, benzene,
CHCl2, triethylamine. R1 = –H,
–OCH3, –Br; R2 = –H, –CH3, –C2H5,
-i-Pr, n-Bu, -Bn, p-F-Bn, o, p-diCl-Bn
the nature of the substrate for oxidation [31]. Com- methyl portion of the melatonin side chain (Compound
pounds Ve, Vg, VIIa, VIIc, Vh, and VI (see Schemes 4 and IVb) produced a compound of high interest in view of its
5) slightly scavenged the level of the DPPH radical at 10– 3 LP inhibitory activity. A difference exists between the
M concentration by about 35, 68, 34, 48, and 19%, respec- substitution pattern on the phenyl ring of the com-
tively. Compounds IVa–c, Va–b, Vg, and VIIa–c (see pounds IVa–c, in that the non-substituted IVa and that
Schemes 4 and 5) showed a strong inhibitory effect on substituted with Br, IVc, cannot be considered as devoid
the lipid peroxidation at the 10– 3 M concentration and of LP inhibitory activity, whereas the compound IVb
the inhibition rates were in the range of 90–99%. In addi- retained the best activity within these three compounds
tion, these compounds showed even better activity than at both, 10– 3 and 10– 4 M concentrations. In contrast, we
melatonin at 10– 3 M concentration. Our results indicate found that the compounds Va–h in which the amide
that introduction of a retinoid moiety (1,1,4,4-tetrahy- moiety of the retinoid portion is linked to the indole ring
dro-1,1,4,4-tetramethylnaphthalene) in place of the from the fifth position, showed variable results on the
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Scheme 5. Amidification reactions of
compound (III-5b). Reaction conditions:
N,N9-CDI, DMF
Table 1. Effects of the compounds IVa–VIIc on LP levels and
scavenging activity of superoxide and DPPH radical*.
concentrations which are 99% and 90%, respectively.
This might indicate the importance of the alkyl chain
inclusion at the 1st position on the indole ring. When the
benzyl substitution at the 1st position of the indole ring,
only the p-fluoro compound among them (Vg) showing a
significant result (94% LP inhibition at 10– 3 M). The alkyl
substitution of the indole ring obviously decresaed the
LP inhibition. When compared, for compounds IV and V,
different than the alkyl subsitution on the indole ring, it
seemed that extending the chain between retinoid amide
moiety and the indole ring did not have any influence on
the activity in which the compounds from both series
had similar LP inhibitory activity, except for those having
alkyl substitution on the indole ring.
On the other hand, the results obtained from the com-
pounds VIIa–c also showed good LP inhibitory activity in
that compound VIIa shows extremely high LP inhibition
(96% and 94% inh., at 10– 3 and 10– 4 M, respectively) in
comparison with compounds VIIb–c. From these data we
can conclude that structural requirements for optimal
LP inhibitory activity are rather strict, in particular that
(a) the presence of the linker group (amide) between the
retinoid head and indole moiety might be required for
activity and (b) alkyl residues linked to the indole moiety
may be more critical for antioxidant activity than with
linker chain. The magnitude of the alkyl substitution
seemed also to be a critical factor as the increased volume
of substitution led to decrease in activity, with the excep-
tion that benzyl substitution showed rather better activ-
ity at 10– 3 M among other bulky substituents examined.
However, further investigations are necessary to clarify
this issue.
Compound
No
Concentration Superoxide
in incubation anion (O9 –
LP [%
DPPH free
)
Inhibition] radical scaven-
ging activity
2
medium [M]
scavenging
capacity
[% Inhibition]
[% Inhibition]
IVa
IVb
IVc
Va
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
10 – 3
10 – 4
63 l 2a)
5 l 5a)
63 l 3a)
NEc)
93 l 1
88 l 2
98 l 1
96 l 2
90 l 1
26 l 2a)
99 l 2
90 l 1
99 l 1
23 l 4a)
18 l 5a)
12 l 7
12 l 8
1 l 2
6 l 2
NEc)
14 l 3
2 l 1
2 l 2a)
4 l 3
10 l 5
3 l 2
NEc)
47 l 4a)
39 l 2a)
69 l 2
59 l 2a)
71 l 5
4 l 5a)
64 l 3
4 l 4a)
73 l 2
15 l 4a)
71 l 3
NEc)
Vb
NEc)
Vc
5 l 5
1 l 4
4 l 2a)
1 l 4
35 l 3
1 l 4
9 l 2
NEc)
68 l 2a)
2 l 1
19 l 2
NEc)
19 l 1
NEc)
34 l 3
NEc)
14 l 2
NEc)
48 l 4
NEc)
Vd
Ve
11 l 3a)
NEc)
Vf
72 l 2
NEc)
7 l 5a)
NEc)
94 l 2
5 l 5a)
14 l 1b)
NEc)
31 l 3a)
16 l 4a)
96 l 2
94 l 3
98 l 1
93 l 2
96 l 2
86 l 2
87 l 2
85 l 2
Vg
67 l 4
9 l 6a)
34 l 4a)
28 l 5
58 l 2a)
15 l 8
52 l 4a)
12 l 1b)
59 l 12a)
10 l 6a)
40 l 10
5 l 12
87 l 3
86 l 4
Vh
VI
VIIa
VIIb
VIIc
Melatonin
30 l 4
5 l 2
*
cf. Experimental section.
a)
Significantly different from that of melatonin (p a 0.05).
Significantly different from that of melatonin (p a 0.001).
NE = No effect.
b)
c)
The superoxide anion radical scavenging activities of
the synthesized compounds at different concentration
were also investigated. The results showed that all
synthesized compounds expressed superoxide anion
scavenging activity to a certain extent, and the scaven-
ging rates were in the range of 34–73%. Compounds
IVa–b and Va–g have some scavenger effect on superox-
ide anion at 10– 3 M concentration (63–73%). Addition-
lipid peroxidation. Compounds Vc–e h and VI had
slightly inhibited lipid peroxidation by about 18%, 12%,
11%, 14%, and 31%, respectively, at 10– 3 M concentration,
but compound Vf had no effect on lipid peroxidation at
the same concentration.
Only compound Va possessed a notable inhibitory
activity when compared to melatonin at 10– 3 and 10– 4
M
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Arch. Pharm. Chem. Life Sci. 2006, 339, 193–200
Synthesis/Antioxidant Activity of some Indole Derivatives
197
ally, these compounds had comparable scavenger effects Chemistry
Conjugation of the two moieties was through an amide bond
which is located between the carboxyl group of 1,1,4,4-tetra-
methyl-6-carboxy-1,2,3,4-tetrahydro-naphthalene and the amine
group on position 3 or 5 of the indole ring.
on superoxide radical as that of melatonin (87% and 86%
inhibitor at 10– 3 and 10– 4 M concentrations, respec-
tively). Compounds IVc and Va have also decreased the
level of superoxide anion by about 39% and 59% at 10– 4
M concentration. Compound Va has optimal scavenging
activity for a superoxide radical as it showed 63% and
59% scavenging activity at 10– 3 and 10– 4 M concentra-
tions, respectively.
Our studies have revealed information about synthe-
sized melatonin retinamide inhibition of oxygen free
radicals in which such retinamides might be of impor-
tance in the context of the prevention of cancer diseases,
in which the reactive oxygen species may directly or
indirectly trigger the expression of redox-sensitive genes
in the organism and, consequently, changes in the cellu-
lar redox system, have impact on the regulation of gene
expression. Despite the promising results of the studys, it
is difficult at the moment to directly relate available
experimental data to human pathophysiology in terms
of chemotherapy of cancer. Nevertheless, and in consid-
eration of the great impact of retinoid antioxidants on
cancer disease prevention, further studies in this field
are required.
Syntheses of compounds I-4 (a–c) comprising
the 1st group
The syntheses of the compounds I-4 (a–c) was carried out as
shown in Scheme 1. The indole-3-aldehyde was obtained by
direct formylation of indole with dimethylformamide, using
phosphorus oxychloride as a catalyst [14–15]. Indole-3-carboxal-
dehydes were refluxed in nitromethane and ammonium acetate
to produce 3-(2-nitroethenyl)-1H-indoles [16]. This was followed
by synthesizing 3-indole-ethylamines using LiAlH4 as described
by Faust et al. [17–18].
Syntheses of compounds II-3 (a–h) comprising
the 2nd group
Syntheses of 1-substituted 5-nitro-1H-indole derivatives II-3 (a–
h) were obtained according to the procedure described by Mor et
al. [18–19], starting from II-1 and using an alkylating agent. The
trifluoroacetic anhydride was added to a solution of 5-nitro-1H-
indole in dry dimethylformamide at 08C. The solution was
allowed to warm to room temperature and then heated at reflux
for 24 h. The reaction mixture was cooled and poured into
water. The resulting mixture was filtered and dried. Catalytic
hydrogenation of the aromatic nitro group in ethanol was con-
ducted at room temperature and under a pressure of 35 psi
using Pd/C (10%) as catalyst. The reaction was filtered through
celite to remove the Pd/C, and the solvent was evaporated [20]. II-
19 and II-29 are original compounds. M+1 peaks in mass spectra of
these compounds are 259, 229, melting points are 243, 1988C,
and yields for these compounds are 62 and 68%, respectively.
This work is supported by Ankara University Research Fund
(2001-08-03-029).
Experimental
Syntheses of compounds III-5 comprising the 3rd group
The starting material was the 2,5-dichloro-2,5-dimethylhexane,
which was prepared in 56% yield by passing dry hydrochloride
gas over 2,5-dimethyl-2,5-hexandiole as described by Boehm et
al. [21]. Toluene was alkylated by 2,5-dichloro-2,5-dimethyl hex-
ane in dichloromethane catalyzed with aluminum chloride to
produce 1,2,3,4-tetrahydro-1,1,4,4,6-pentamethylnaphthalene,
in 91% yield [21–23]. 1,1,4,4-tetramethyl-6-carboxy-1,2,3,4-tetra-
hydro-naphthalene, obtained by oxidation of 1,2,3,4-tetrahydro-
1,1,4,4,6-pentamethylnaphthalene with KMnO4 in 80% yield
[24].
A mixture of HNO3 and H2SO4 was added to 1,2,3,4-tetrahydro-
1,1,4,4,6-pentamethylnaphthalene (III-3) at –108C to give
1,2,3,4-tetrahydro-1,1,4,4,6-pentamethyl-7-nitronaphthalene in
50% yield. This nitro compound was hydrogenated by the usual
method (10% Pd-C in EtOH, 48%) [25].
General
Melting points were determined with a Bꢀchi SMP-20 and Buchi
9100 melting point apparatus (Bꢀchi Labortechnik, Flawil, Swit-
zerland) and are uncorrected. The 1H-NMR spectra were recorded
with a Varian Mercury-400 spectrophotometer (Varian Inc., Palo
Alto, CA, USA), in DMSO-d6 or CDCl3 unless otherwise stated,
using the d scale (ppm) from internal standard TMS. The IR spec-
tra were recorded on a Jasco FT/IR-420 spectrophotometer
(JASCO Research Ltd., Victoria, BC, Canada) as potassium bro-
mide pellets. The mass spectra were recorded with a Waters ZQ
micromass LC-MS spectrometer (Waters Corporation, Milford,
MA, USA) by the method of ES+. Elemental analyses were per-
formed on LECO 932 CHNS instrument (Leco, St. Joseph, MI,
USA) and were within l0.5% of the theoretical values. Analyses
were performed at Scientific and Technical Research Council of
Turkey, Instrumental Analysis Center, Ankara, Turkey. Analyti-
cal thin-layer chromatography (TLC) was run on Merck silica gel
plates (Kieselgel 60F-254). Column chromatographies were
accomplished on silica gel 60 (40–63 lm particle size) (Merck,
Darmstadt, Germany). All starting materials and reagents were
high-grade commercial products purchased from Aldrich (Stein-
heim, Germany), Merck or Fluka (Buchs, Switzerland). Physical
and spectral data for compounds IVa–VIIc are summarized in
Table 2.
1,1,4,4-Tetramethyl-6-carboxy-1,2,3,4-tetrahydro-naphthalene
was acylated with SOCl2 in dry benzene [26]. A crude oil of
amines I-4 (a–c) and compounds II-3(a–h), II-29 which was then
used for amidification with 5,5,8,8-tetramethyl-1,2,3,4-tetrahy-
dronaphthalene-6-carboxylic acid without purification.
A
mixture of appropriate acide and 1,2,3,4-tetrahydro-
1,1,4,4,6-pentamethyl-7-aminonaphthalene (III-5b) was amidifi-
cation with N,N9-CDI [27]. Compounds VIII, IX, and X are com-
mercially avaliable.
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Arch. Pharm. Chem. Life Sci. 2006, 339, 193–200
Table 2. Physical and spectral data for compounds IVa-VIIc
No
R
Mp.
[8C]
Yield
[%]
Formulas
1H- and 13C-NMR
Mass
(ESI+)
IR
[cm – 1
Isolation
]
IVa
H
220
190
92
28
30
42
C25H30N2O N 0.8 H2O
1H-NMR (CDCl3) d 1.3 (s, 12H), 1.65 (s, 4H), 3.1
(t, 2H), 3.8 (m, 2H), 6.15 (s, 1H), 7.1 – 7.7 (m, 8H),
8.1 (s, 1H); 13C-NMR (DMSO-d6) d 166.09, 147.42,
144.18, 136.16, 131.81, 127.21, 126.21, 125.12,
124.25, 122.49, 120.80, 118.21, 118.13, 111.89,
111.27, 34.42, 34.29, 33.97, 33.94, 31.44, 31.32,
25.18
1H-NMR (CDCl3) d 1.33 (d, 12H), 1.69 (s, 4H), 3.08
(t, 2H), 3.77 (s, 3H), 3.8 (q, 2H), 6.22 (s, 1H),
6.87 – 8.1 (m, 7H), 8.25 (s, 1H);13C-NMR (CDCl3)
d 167.98, 154.34, 148.90, 145.62, 132.07, 131.82,
128.02, 126.97, 125.84, 123.77, 123.18, 113.09,
112.79, 112.33, 100.58, 55.98, 40.64, 35.17, 35.05,
34.69, 34.59, 31.93, 25.58
375
(M+1, 100)
Amid I, 1638
Amid II, 1530
CHCl3 : n-hexane
(3 : 1), cc
IVb
IVc
OCH3
C26H32N2O2
405
(M+1, 100)
Amid I, 1632
Amid II, 1539
CHCl3
Br
C25H29BrN2O
1H-NMR (CDCl3) d 1.28 (s, 12H), 1.68 (s, 4H), 3.04
(t, 2H), 3.77 (m, 2H), 6.16 (s, 1H), 7.16 – 7.8 (m,
7H), 8.24 (s, 1H);13C-NMR (DMSO-d6) d 166.11,
147.43, 144.18, 134.82, 131.75, 129.12, 126.22,
125.10, 124.35, 124.20, 123.24, 120.54, 113.29,
111.81, 110.86, 34.41, 34.29, 33.97, 33.93, 31.44,
31.31, 24.90
455 (M+2, 100), Amid I, 1630
456 (M+3, 60) Amid II, 1541
CHCl3 : n-hexane
(7 : 1), cc
Va
Vb
H
177
196
60
32
C23H26N2O N 0.5 H2O
1H-NMR (CDCl3) d 1.34 (d, 12H), 1.74 (s, 4H), 6.52 (t, 347 (M+1, 100) Amid I, 1630
CHCl3
1H), 7.2 – 7.9 (m, 8H), 8.25 (s, 1H); 13C-NMR (DMSO-
d6) d 165.90, 148.44, 145.12, 133.69, 133.38, 131.63,
128.11, 127.12, 126.55, 126.25, 125.43, 117.08,
113.19, 111.64, 101.80, 35.26, 35.10, 34.88, 34.81,
32.25, 32.16
Amid II, 1541
CH3
C24H28N2O N 0.3 H2O
1H-NMR (CDCl3) d 1.3 (d, 12H), 1.75 (s, 4H), 3.8 (s,
3H), 6.45 (d, 1H), 7.1 – 7.95 (m, 8H );13C-NMR (DMSO-
d6) d 165.87, 148.45, 145.10, 134.24, 133.28, 131.79,
130.79, 128.41, 127.10, 126.23, 125.39, 116.98,
113.33, 109.93, 100.94, 35.21, 35.07, 34.82, 34.78,
33.21, 32.22, 32.11
361 (M+1, 100) Amid I, 1647
Amid II, 1531
EtOAc
crystallization
Vc
C2H5
181
88
19
33
C25H30N2O N 0.4 H2O
1H-NMR (CDCl3) d 1.33 (d, 12H), 1.48 (t, 3H) 1.72 (
s, 4H), 4.18 (q, 2H) 6.47 (d, 1H), 7.12 – 7.97 (m, 8H);
13C-NMR (DMSO-d6) d 165.87, 148.45, 145.10,
133.27, 131.74, 129.13, 128.57, 127.10, 126.23,
125.40, 116.94, 113.46, 109.94, 101.16, 41.02,
35.22, 35.07, 34.82, 34.77, 32.22, 32.12, 16.17
1H-NMR (CDCl3) d 1.32 (d, 12H), 1.53 (d, 6H) 1.72
(s, 4H), 4.65 (m, 1H), 6.48 (d, 1H), 7.2 – 7.95 (m, 8H);
13C-NMR (DMSO-d6) d 165.87, 148.47, 145.12,
133.30, 133.05, 131.79, 128.52, 127.11, 126.26,
125.85, 125.42, 116.84, 113.43, 110.12, 101.46,
47.26, 41.60, 35.23, 35.09, 34.84, 34.79, 32.24,
32.14, 23.21
375 (M+1, 100) Amid I, 1640
Amid II, 1535
n-hexane: EtOAc
(3 : 1), cc
Vd
i-C3H7
C26H32N2O N 0.1 H2O
389 (M+1, 100) Amid I, 1636
Amid II, 1536
CHCl3 : n-hexane
(2 : 1), cc
Ve
Vf
n-butyl
149
105
78
29
C
27H34N2O N 0.3 H2O
1H-NMR (CDCl3) d 0.9 (t, 3H), 1.33 (d, 12H), 1.33
(m, 2H), 1.6 (s, 4H), 1.85 (m, 2H), 4.1 (t, 2H) 6.45 (d,
1H), 7.1 – 7.95 (m, 8H);13C-NMR (DMSO-d6) d 165.86,
148.44, 145.09, 133.55, 133.28, 131.70, 129.80,
128.48, 127.08, 126.23. 125.39, 116.94, 113.45,
110.04, 101.03, 45.95, 35.21, 35.07, 34.81, 34.77,
32.67, 32.22, 32.11, 20.16, 14.22
403 (M+1, 100) Amid I, 1637
Amid II, 1541
n-hexane : EtOAc
(5 : 1), cc
benzyl
C
30H32N2O N 0.25 C4H8O2 1H-NMR (CDCl3) d 1.3 (d, 12H), 1.72 (s, 4H), 5.35
(s, 2H), 6.55 (d, 1H), 7.1 – 8.0 (m, 13H);13C-NMR
(CDCl3) d 166.21, 149.09, 145.86, 137.64, 134.10,
132.88, 129.42, 129.14, 128.98, 127.85, 127.14,
126.90, 126.04, 123.77, 116.44, 113.33, 110.12,
102.12, 50.46, 35.17, 35.05, 34.75, 34.69, 32.02,
31.93
437 (M+1, 100) Amid I, 1643
Amid II, 1536
n-hexane : EtOAc
(4 : 1), cc
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Arch. Pharm. Chem. Life Sci. 2006, 339, 193–200
Table 2. Continued
Synthesis/Antioxidant Activity of some Indole Derivatives
199
No
R
Mp.
[8C]
Yield
[%]
Formulas
1H- and 13C-NMR
Mass
(ESI+)
IR
[cm – 1
Isolation
]
Vg
p-fluoro-
benzyl
173
63
C30H31FN2O
N 0.1 C2H5OH N 0.2 H2O
1H-NMR (CDCl3) d 1.3 (d, 12H), 1.75 (s, 4H), 5.3
(s, 2H), 6.55 (d, 1H), 6.95 – 8.0 (m, 12H);13C-NMR
(DMSO-d6) d 165.89, 163.28, 160.87, 148.47, 145.10,
135.22, 133.47, 133.24, 132.05, 130.23, 129.73,
129.65, 128.78, 127.09, 126.23, 125.37, 117.18,
116.06, 115.85, 113.49, 110.43, 101.82, 49.08,
35.20, 35.06, 34.81, 34.76, 32.21, 32.10
455 (M+1, 70),
456 (M+2, 25)
Amid I, 1644
Amid II, 1530
n-hexane : EtOAc
(3 : 1), cc
ethanol
crystallization
Vh
VI
o,p-dichloro- 183
benzyl
24
29
C
30H30Cl2N2O
25H25F3N2O2
1H-NMR (CDCl3) d 1.33 (d, 12H), 1.75 (s, 4H), 5.36
(s, 2H), 6.6 (d, 1H), 7.1 – 8.05 (m, 11H)
505 (M+1, 94),
507 (M+3, 65),
508 (M+4, 22)
443 (M+1, 100) 1723 (ketone)
Amid I, 1643
Amid I, 1634
Amid II, 1535
n-hexane : EtOAc
(5 : 1), cc
–
227
C
1H-NMR (DMSO-d6) 1.3 (d, 12H), 1.65 (s, 4H),
7.4 – 8.6 (m, 7H), 10.2 (s, 1H), 10.7 (s, 1H )
n-hexane : EtOAc
(3 : 1), cc
N 0.2 C4H8O2 N 0.4 H2O
Amid II, 1555
VIIa
VIIb
–
–
135
131
19
22
C
24H28N2O N 0.3 C6H14
1H-NMR (CDCl3) d 1.32 (d, 12H), 1.7 (s, 4H), 2.33
(s, 3H), 6.97 (s, 1H), 7.11 – 7.87 (m, 7H), 9.7 (s, 1H)
1H-NMR (CDCl3) d 1.25 (d, 12H), 1.65 (s, 4H), 1.92
(s, 3H), 2.8 (t, 2H), 3.25 (t, 2H) 6.75 (s, 1H), 7.1 – 7.7
(m, 7H), 8.1 (s, 1H)
1H-NMR (CDCl3) d 1.3 (d, 12H), 1.65 (s, 4H), 2.2
(s, 3H), 2.2 (m, 2H), 2.42 (t, 2H), 2.9 (t, 2H), 6.81
(s, 1H), 7.1–7.75 (m, 7H), 8.05 (s, 1H)
361 (M+1, 100) Amid I, 1638
Amid II, 1537
389 (M+1, 100) Amid I, 1644
Amid II, 1522
n-hexane : EtOAc
(3 : 1), cc
n-hexane : EtOAc
(2 : 1), cc
N 0.3 C4H8O2
C26H32N2O N 0.2 H2O
VIIc
–
158
25
C27H34N2O N 0.7 H2O
403 (M+1, 100) Amid I, 1711
Amid II, 1536
n-hexane : EtOAc
(3 : 1), cc
ESI: Elektrospray ionization, cc: column chromatography, C6H14: n-hexane, C4H8O2: EtOAc, C2H5OH: ethanol.
Elemental analyses were within l0.5%.
trically on the basis of inhibition of cytochrome c reduction
according to the modified method of McCord et al. [28]. Superox-
ide anion was generated in the xanthine/xanthine oxidase sys-
tem. The reaction mixture contained in a final volume of 1 mL,
0.05 M phosphate buffer pH 7.8, 0.32 U xanthine oxidase, 50 lM
xanthine, 60 mM ctytochrome c, and different concentrations of
synthesized compounds at 100 lL. The absorbance was meas-
ured spectrophotometrically at 550 nm for cytochrome c reduc-
tion. Each experiment was performed in triplicate, and the
results are expressed as a percent of the control.
General method for 5,5,8,8-tetramethyl-5,6,7,8-tetra-
hydro-naphthalene-2-carboxylic acid-(substituted-1H-
indol)-amide derivatives
A mixture of 1,1,4,4-tetramethyl-6-carboxy-1,2,3,4-tetrahydro-
naphthalene (III-4a) (1 mmol), thionyl chloride (2 mL), and ben-
zene (6 mL) was heated at reflux for 4 h. After removal of the sol-
vent, a mixture of substituted-indole-amine (1 mmol), chloro-
form (5 mL), triethylamine (0.5 mL) was added to the residue and
the whole mixture was stirred and refluxed overnight. The reac-
tion mixture was evaporated, washed with Na2CO3 (5%),
extracted with ethyl acetate, and washed with water. The
organic layer was dried over Na2SO4 and evaporated. The residue
was purified by silica gel flash column chromatography [26].
DPPH radical scavenging assay
The free radical scavenging activities of these compounds were
tested by their ability to bleach the stable radical 2,2,diphenyl-1-
picrylhydrazyl (DPPH) [29]. Because of its odd electron, DPPH
gives a strong absorption band at 517 nm in visible spectro-
scopy. The reaction mixture contained 100 lM DPPH in metha-
nol and different concentrations of synthesized compounds.
Absorbance at 517 nm was determined after 30 min at room
temperature and the scavenging activity was calculated as a per-
centage of the radical reduction. Each experiment was perform-
ed in triplicate. Melatonin was used as a reference compound.
General method for indol-(3,5,5,8,8-pentamethyl-5,6,7,8-
tetrahydro-naphthalene-2yl)-amide derivatives
A
mixture of appropriate acid (0.6 mmol) and N,N9-CDI
(0.65 mmol) in DMF (10 mL) was stirred for 4 h. 1,2,3,4-Tetrahy-
dro-1,1,4,4,6-pentamethyl-7-amine-naphthalene (III-5b) (0.6
mmol) was added and stirred for 3 h. The reaction mixture was
evaporated, extracted with ethyl acetate, and washed with
water. The organic layer was dried over Na2SO4, and evaporated.
The residue was purified by silica gel flash column chromatogra-
phy [27].
Assay of lipid peroxidation
The effect of synthesized compounds on rat liver homogenate
induced with FeCl2-ascorbic acid and lipid peroxidation was
determined by the method modified by Mihara et al. [30]. Wistar
rats (200–225 g; Refik Saydam Hygiene Center, Ankara, Turkey)
were fed with standard laboratory rat chow and tap water ad libi-
tum. The animals were starved for 24 h prior to sacrifice and
then killed by decapitation under anaesthesia. The livers were
removed immediately, washed in ice-cold distilled water, and
homogenized immediately with teflon homogenizer in chilled
ice. LP was measured spectrophotometrically by estimation of
thiobarbituric acid reactant substances (TBARS). Amounts of
TBARS were expressed in terms of nmol malondialdehyde
Antioxidant activity studies
Chemicals used in these experiments include: xanthine,
xanthine oxidase, cytochrome c, 2,2,diphenyl-1-picrylhydrazyl
(DPPH), butylated hydroxytoluene, and a-tocopherol thiobarbi-
turic acid (TBA) which were purchased from Sigma Chemical Co.
(St Louis, MO, USA).
Superoxide radical scavenging activity
The capacity of melatonin retinoid compounds to scavenge
superoxide anion formation was determined spectrophotome-
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www.archpharm.com

200
Z. Ates-Alagoz et al.
Arch. Pharm. Chem. Life Sci. 2006, 339, 193–200
(MDA)/g tissue. A typical optimized assay mixture contained
0.5 mL of liver homogenate, 0.1 mL of Tris-HCl buffer (pH 7.2),
0.05 mL of 0.1 mM ascorbic acid, 0.05 mL of 4 mM FeCl2, and
0.05 mL of various concentrations of synthesized compounds, or
a-tocopherol incubated for 1 h at 378C. After incubation, 3.0 mL
of H3PO4 and 1 mL of 0.6% TBA were added and shaken vigor-
ously. The mixture was boiled for 30 min. After cooling, n-buta-
nol was added and the mixture was shaken vigorously. The n-
butanol phase was separated by centrifugation at 3000 rpm for
10 min. The absorbance of the supernatant was read at 532 nm
against a blank, which contained all reagents except liver homo-
genate.
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