Syntheses of novel indole lipoic acid derivatives and their antioxidant effects on lipid peroxidation

Article abstract of DOI:10.1002/ardp.200400932

The aim of the study was to examine antioxidant properties of conjugates based on indole and lipoic acid moieties. The design and syntheses of novel indole α-lipoic acid derivatives were performed. The antioxidant properties of target compounds were investigated using rat liver microsomal, NADPH-dependent lipid peroxidation inhibition. Some of the target compounds, especially those containing amide linker at position 5 of indole ring, proved to be highly effective in inhibiting lipid peroxidation as compared to α-lipoic acid.

Full text of DOI:10.1002/ardp.200400932

Arch. Pharm. Chem. Life Sci. 2005, 338, 67−73
DOI 10.1002/ardp.200400932
67
Syntheses of Novel Indole Lipoic Acid Derivatives
and Their Antioxidant Effects on Lipid Peroxidation
A. Selen Gurkana, Arzu Karabayb, Zeliha Buyukbingolb, Adeboye Adejarec,
Erdem Buyukbingola
a Department of Pharmaceutical Chemistry, Ankara University, Faculty of Pharmacy, Turkey
b Department of Biochemistry, Ankara University, Faculty of Pharmacy, Turkey
c Department of Pharmaceutical Sciences, Philadelphia College of Pharmacy, University of the Sciences in
Philadelphia, Philadelphia, PA, USA
The aim of the study was to examine antioxidant properties of conjugates based on indole and lipoic
acid moieties. The design and syntheses of novel indole α-lipoic acid derivatives were performed. The
antioxidant properties of target compounds were investigated using rat liver microsomal, NADPH-
dependent lipid peroxidation inhibition. Some of the target compounds, especially those containing
amide linker at position 5 of indole ring, proved to be highly effective in inhibiting lipid peroxidation
as compared to α-lipoic acid.
Keywords: α-Lipoic acid; Indole; Lipid peroxidation; Antioxidant
Received: August 10, 2004; Accepted: February 12, 2005 [FP932]
Introduction
α-LA [8]. The antioxidant properties of α-lipoic acid can be
related to four categories: its ability to scavenge free rad-
icals; metal ion chelating activity; capacity to regenerate en-
dogenous antioxidants for example glutathione and tocoph-
erol; and the ability to repair oxidative damage in macro-
molecules [9, 10]. On the other hand, the indole nucleus
is an important element in many pharmacologically active
endogenous and exogenous compounds. Tryptophane is an
indole amino acid found in the constitution of numerous
proteins. Another well-known indole derivative is the neuro-
transmitter serotonin which displays a wide range of physio-
logical actions including protection of biological tissues
against radiation injury [11]. The mechanism for this protec-
tion is thought to include inhibition of excessive free radical
formation. Melatonin is also a well-known indole com-
pound having the properties of scavenging free radicals [11]
that protects against DNA strand breaks and lipid peroxi-
dation [12].
Impaired antioxidant defense mechanisms are important
features in the pathogenesis of various diseases including
diabetes, cancer, and neurological disorders. Antioxidants
are required to prevent cellular damage observed in many
of these diseases. Impairment of these defense mechanisms
may be due to increased oxidative stress. α-Lipoic acid
(α-LA; 1,2-dithiolane-3-pentanoic acid; thioctic acid) is a
natural multifunctional antioxidant [1] and acts as a co-
enzyme in biological group transfer reactions [2Ϫ4]. Its
main function is to increase production of glutathione,
which eliminates toxic substances in the liver.
α-LA (α-Lipoic acid) is found endogenously as lipoamide
in animals and plants [5]. Its carboxylic group is covalently
bound by amide linkage to the ε-amino group of lysine
residues. It functions as a cofactor of mitochondrial en-
zymes in catalyzing oxidative decarboxylation of α-keto ac-
ids such as pyruvate, α-ketoglutarate, and branched-chain
α-keto acids [6]. α-LA is readily absorbed and rapidly con-
verted to reduced form, dihydrolipoic acid (DHLA) in many
tissues [7]. Usually, antioxidant substances exhibit antioxi-
dant properties in their reduced form. α-LA is unique, be-
cause it retains protective functions in both its reduced and
oxidized forms, although DHLA is the more effective than
This study was designed to determine whether novel indole-
lipoic acid derivatives will be able to provide certain antioxi-
dant properties compared to α-lipoic acid which has been
shown to have substantial multifunctional antioxidant
properties.
Results and discussion
Correspondence: Erdem Buyukbingol, Department of Pharma-
ceutical Chemistry, Faculty of Pharmacy (ECZACILIK),
Ankara University, Tandogan 06100, Ankara, Turkey. Phone:
ϩ90 312 212-6805, ext. 2306, Fax: ϩ90 312 213-1081, e-mail:
erdem@pharmacy.ankara.edu.tr
Several novel α-lipoic acid-indole (α-LAI) derivatives were
synthesized. The target compounds were evaluated for anti-
oxidant properties using in vitro non-enzymatic lipid peroxi-
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Buyukbingol et al.
Arch. Pharm. Chem. Life Sci. 2005, 338, 67−73
dation of rat hepatic microsomal membranes by measure-
ment of the formation of 2-thiobarbituric acid (TBA) reac-
tive substances. Lipid peroxidation consists of a radical-in-
itiated reaction that serves for the evaluation of the
antioxidant properties of a compound. The compounds ex-
hibited significant lipid peroxidation inhibitory effects at the
concentration of 1.0 mM with exception of compounds I-4f
and II-3d, which showed 14.7% and 16.1% inhibition,
respectively.
pound has a bare benzyl substitution and the activity ob-
served was significantly less than for the fluorobenzyl com-
pound. This difference in terms of inhibitory levels for two
similar substitution patterns generated some interest and
assays were repeated several times. However, the difference
seems to be due to the significance of the fluoro group being
located at the para position of the benzyl ring. The 2,4-
dichlorobenzyl derivative in this series also gave moderate
inhibitory activity with confirmation of the important role
of halogen substitution on the benzyl ring. A feasible ap-
proach to continuing studies in this area might be rational-
ized based on the difference between the halogens, including
size and electronegativity, and the location. Removal of
alkyl substitution (except I-4d) from the indole nitrogen re-
sulted in a slight drop in the inhibitory activity. The i-propyl
derivative (I-4d) might contain the optimal braching feature
for the alkyl substitution. In order to perceive the activity
of α-LA conjugation to indole moiety at the first (1) posi-
tion, we synthesized α-LA derivatives of indole in which
the indole nitrogen was maintained to establish the α-LA
integration while at position 5 of indole moiety was further
modified by substituting electron donating (OCH3, Br, CH3)
and electron withdrawing (NO2) groups in order to optimize
the electronic and lipophilic characteristics. The amino
linker at the position 1 of the indole ring was required for
the conjugation of α-LA, due to the failure of direct bond-
ing of α-LA to indole nitrogen.
For the first series of compounds (Scheme 1), substitution
at the amine of 5-nitroindole followed by reduction gener-
ated the amine intermediate. Conjugation of this with α-LA
through amide bond formation was then conducted. The
second series involved introduction of amine at position 1
followed by conjugation. The third series involved introduc-
tion of ethylamine at position 3 via formylation and methyl
nitrite followed by conjugation to the nitrogen. The conju-
gation of α-LA to indole moiety resulted in substitution
patterns which were classified in three groups. The first
group involved amidation of 5-amino indoles with α-LA.
The subtitution pattern for this group lies on the indole
nitrogen where alkyl homologues and various benzyl substi-
tents were employed. The most active compound within the
first group was 4-fluoro benzyl derivative (compound I-4g)
which exerted lipid peroxidation (LPO) inhibitory activity
as 90.7% inhibition. However, inconsistency was found with
compound I-4f which exhibited 14.7% inhibition. This com-
Scheme 1. Reaction scheme of the first series of compounds. (i) alkyl / benzyl /substituted benzyl halogenid, NaH, DMF, r.t.;
(ii) 10% Pd/C, H2; (iii) N,NЈ-CDI, DMF, r.t.
R = -H, -CH3, -C2H5, -2-Pr, -n-Bu, Bn, 4-F-Bn, 2,4-diCl-Bn
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Arch. Pharm. Chem. Life Sci. 2005, 338, 67−73
Novel Indole Lipoic Acid Derivatives
69
Scheme 2. Reaction scheme for the second series of compounds. (i) H-O-SA, KOH, DMF, 0°C; (ii) N,NЈ-CDI, DMF, r.t.
R = -H, -OCH3, -Br, -NO2, -CH3
Scheme 3. Reaction scheme for the third series of compounds. (i) POCl3, DMF, 0°C; (ii) CH3NO2, CH3COONH4, 70°C, reflux;
(iii) LiAlH4, THF, reflux; (iv) N,NЈ-CDI, DMF, r.t.
R = -H, -OCH3
The reaction depicted in Scheme 2 was used for preparation
of the second series of α-LA-indole conjugates. All com-
pounds showed good inhibitory activity except compound
II-3d (16.1% LPO inhibition) which bears a nitro substitu-
ent at position 5. The non-substituted derivative, II-3a
showed good activity (89.6%), higher than those with elec-
tron donating substituents. These data illustrate that the
presence of substituents might not be necessary to obtain
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70
Buyukbingol et al.
Arch. Pharm. Chem. Life Sci. 2005, 338, 67−73
Table 1. 1-Substituted-5-nitro/5-amino-1H-indole and 5-sub-
stituted-1H-indole-1-amino derivatives.
good potency while electron-withdrawing substitution
might be involved in significant alteration of the electron
density of the indole ring to cause major loss in LPO inhi-
bition activity. However, further studies are needed to eluci-
date the impact of such modifications or the influence of
such substitution patterns for α-LA-indole compounds on
lipid peroxidation inhibitory activity. The 5-substituted
tryptamine conjugates synthesized as shown in Scheme 3
also exhibited greater than 75% inhibition.
Comp.
R
mp [°C]
yield [%]
I-2b
I-2c
CH3
C2H5
i-C3H7
n-C4H9
Bn
4-F-Bn
2,4-diCl-Bn
CH3
164 (165Ϫ167, [14])
77 (78Ϫ81, [14])
66Ϫ-67
94
61
21
77
73
78
82
I-2d†
I-2e†
I-2f
46Ϫ47
102 (100Ϫ103, [14])
120Ϫ121 (114Ϫ115, [15])
149Ϫ151
I-2g
I-2h†
I-3b
I-3c
In conclusion, this study designed and synthesized α-LA-
indole conjugates. These compounds possess good inhibi-
tory activities on lipid peroxidation. These findings become
significant in that α-lipoic acid is less active than some of
the synthesized compounds. This could indicate a new strat-
egy in designing α-LA derivatives with improved antioxi-
dant capacity which could have an indirect beneficial effect
on the human antioxidant defence system.
104 (105, [16])
oil [17]
C2H5
I-3d
I-3e
I-3f
i-C3H7
n-C4H9
Bn
oil
oil
oil [17]
I-3g
4-F-Bn
2,4-diCl-Bn
H
OCH3
Br
oil [no ref. in Sci Finder]
oil
40 (41Ϫ41.5, [19])
115 (115Ϫ117, [20])
85 (oil, [20])
165 (166Ϫ167, [20])
84
I-3h
II-2a
II-2b
II-2c
II-2d
II-2e†
29
8
33
8
NO2
CH3
34
†
Acknowledgments
Detailed properties of novel compounds are given in Experi-
mental.
This study was supported by Ankara University Research
Fund (2001-08-03-029) and USA NIH-NINDS Grant
# 2R15NS36393-03A1.
Table 2. Physicochemical properties of synthesized com-
pounds as 1st, 2nd, 3rd group and their inhibition of lipid
peroxidation (LPO).
Experimental
Comp.
R
†Rf
yield
[%]
mp [°C]
‡LPO
[% inh]
(10Ϫ4M)
General
I-4a
I-4b
I-4c
I-4d
I-4e
I-4f
I-4g
I-4h
II-3a
II-3b
II-3c
II-3d
II-3e
III-5a
III-5b
H
CH3
C2H5
i-C3H7
n-C4H9
Bn
4-F-Bn
2,4-diCl-Bn
H
OCH3
Br
0.62
0.68
0.76
0.82
0.89
0.85
0.86
0.94
0.88
0.84
0.82
0.54
0.83
0.16
0.16
62
36
9
96Ϫ98
116Ϫ117
93Ϫ95
130
65Ϫ66
105
82.1
60.4
77.4
88.7
78.1
14.7
90.7
64.6
89.6
78.2
79.3
16.1
63.4
83.3
75.7
The structures of all synthesized compounds were assigned on the
basis of IR, 1H-NMR, and Mass Spectra analyses. Silica gel 60
(Merck, 230-400 Mesh; Merck, Darmstadt, Germany) was used for
column chromatography. Precoated silica gel plates (Merck, Kiesel-
gel 60 GF256, 0.20 mm) were used for TLC. Melting points were
determined with Büchi SMP-20 and Büchi 9100 melting point ap-
paratus and are uncorrected (Büchi Labortechnik, Flawil, Switzer-
land). IR spectra were recorded on a Jasco FTIR-420 spectrophoto-
meter (JASCO Research Ltd., Victoria, British Columbia, Canada),
1H-NMR (400 MHz) spectra were obtained on a Varian Mercury-
400 spectrometer (Varian Inc., Palo Alto, CA, USA), and MS were
recorded on a Waters ZQ micromass LC-MS spectrometer by the
method of ESϩ (Waters Corporation, Milford, MA, USA).
52
69
61
51
29
32
25
27
21
50
54
38
111
69Ϫ71
105Ϫ107
88Ϫ90
118
124Ϫ126
43Ϫ44
58Ϫ60
oil
NO2
CH3
H
OCH3
†
Ethylacetate/n-Hexane (1:1).
α-LA; LPO inh.: 45%.
Chemistry
‡
Commercially available α-lipoic acid (racemic mixture) and appro-
priate indole compounds served as starting materials. Fifteen α-LA
derivatives were designed and synthesized, composing three series
bearing substituents at positions 1, 3, and 5 of the indole ring. Con-
jugation of the two moieties was through amide bond which is be-
tween the carboxyl group of α-LA and the amine group on position
1, 3, or 5 of the indole ring (Tables 1 and 2). Fourteen out of fifteen
conjugates are novel α-LA compounds. Designed compounds are
shown as three groups in Schemes 1Ϫ3.
Syntheses of compounds I-4 (aϪh) comprising the 1st group
Designed compounds bearing substituent at position 1 were synthe-
sized in three steps (Scheme 1). Syntheses of 1-substituted-5-nitro-
1H-indole derivatives I-2(b؊h) (Table 1) were obtained according
to the procedure described by Mor et al. [13], starting from I-1 and
using an alkylating agent (Scheme 1). Catalytic hydrogenation of
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Arch. Pharm. Chem. Life Sci. 2005, 338, 67−73
Novel Indole Lipoic Acid Derivatives
Spectral analyses of synthesized compounds
71
the aromatic nitro group in ethanol was conducted at room tem-
perature and under a pressure of 35 psi with 10% Pd/C as catalyst.
The reaction was filtered through celite to remove the Pd/C, and
the solvent evaporated. The compounds (I-3 (c؊h)) (Table 1) ob-
tained as brown oils were used in situ and without purification in
the next step. The amide compounds I-4 (b؊h) (Table 2) were pre-
pared from α-LA and appropriate amine as illustrated above after
activation of N,NЈ-Carbonyldiimidazole (N,NЈ-CDI) according to
the method described by Tomihisa [18]. The same method was used
to synthesize the compound I-4a starting from α-LA and
5-amino-indole.
5-[1,2]Dithiolane-3-yl-penthanoic acid (1H-indole-5-yl)-amide
(I-4a)
1H-NMR δ ppm (DMSO-d6, 400 MHz): 1.39Ϫ3.65 [1.42 (m, 2H),
1.57Ϫ1.72 (m, 4H), 1.87 (m, 1H), 2.29 (t, 2H), 2.44 (m, 1H), 3.15
(m, 2H), 3.64 (m, 1H); α-LA-protons], 6.35Ϫ7.86 [6.35 (m, 1H), 7.17
(m, 1H), 7.28 (m, 2H), 7.86 (d, 1H); Ar-H], 9.66 (s, 1H, indole-NH),
10.98 (s, 1H, NH-CO) ; LC-MS m/z 321 (MϩH)ϩ; IR (KBr, cmϪ1):
3271 (NH), 1653 (CϭO).
5-[1,2]Dithiolane-3-yl-penthanoic acid (1-methyl-1H-indole-5-yl)-
amide (I-4b)
Syntheses of compounds II-3 (aϪe) comprising the 2nd group
1H-NMR δ ppm (DMSO-d6, 400 MHz): 1.38Ϫ3.64 [1.41 (m, 2H),
1.56Ϫ1.69 (m, 4H), 1.86 (m, 1H), 2.27 (t, 2H), 2.38 (m, 1H), 3.13
(m, 2H), 3.61 (m, 1H); α-LA-protons], 3.74 (s, 3H, N-CH3),
6.33Ϫ7.86 [6.33 (d, 1H), 7.24 (m, 2H), 7.32 (d, 1H), 7.86 (d, 1H);
Ar-H], 9.69 (s, 1H, NH-CO); LC-MS m/z 335 (MϩH)ϩ; IR (KBr,
cm-1): 3254 (NH), 1637 (CϭO).
Designed compounds bearing substituent at position 5 were synthe-
sized in two steps (Scheme 2). Syntheses of 5-substituted-1H-indole-
1-amine derivatives II-2 (a؊e) (Table 1) were achieved following the
procedure described by Somei and Natsume [19], starting from 5-
substituted-1H-indoles II-1 (a؊e) and using Hydroxylamine-O-sul-
fonic acid (H-O-SA) as amination agent. The amide compounds
II-3 (a؊e) (Table 2) were prepared from α-LA and appropriate
amine after activation of N,NЈ-CDI in accordance with the litera-
ture [18].
5-[1,2]Dithiolane-3-yl-penthanoic acid (1-ethyl-1H-indole-5-yl)-
amide (I-4c)
1H-NMR δ ppm (DMSO-d6, 400 MHz): 1.33 (t, 3H, N-CH2CH3),
1.41Ϫ3.64 [1.42 (m, 2H), 1.67 (m, 4H), 1.87 (m, 1H), 2.29 (t, 2H),
2.42 (m, 1H), 3.15 (m, 2H), 3.63 (m, 1H); α-LA-protons], 4.15 (m,
2H, N-CH2CH3), 6.35Ϫ7.86 [6.35 (m, 1H), 7.22 (d, 1H), 7.35 (m,
2H), 7.86 (s, 1H); Ar-H], 9.69 (s, 1H, NH-CO); LC-MS m/z 349
(MϩH)ϩ; IR (KBr, cmϪ1): 3255 (NH), 1639 (CϭO).
Syntheses of compounds III-5 (aϪb) comprising the 3rd group
Designed compounds bearing substituent at position 5 were synthe-
sized in four steps (Scheme 3). By treating III-1 (a؊b) with DMF
and POCl3 [13], the corresponding aldehydes III-2 (a؊b) were ob-
tained. These aldehydes were condensed with nitromethane to give
III-3 (a؊b) as described by Mor et al. [13]. 3-2Ј-vinylindoles were
reduced to the subsequent aminoethylindoles III-4 (a؊b) by LiAlH4
[21]. The amide compounds III-5 (a؊b) (Table 2) were prepared
from α-LA and aforementioned amine as described above after acti-
vation of N,NЈ-CDI.
5-[1,2]Dithiolane-3-yl-penthanoic acid (1-isopropyl-1H-indole-5-yl)-
amide (I-4d)
1H-NMR
δ ppm (DMSO-d6, 400 MHz): 1.41 (d, 6H, N-
CH(CH3)2), 1.40Ϫ3.62 [1.40 (m, 2H), 1.65 (m, 4H), 1.86 (m, 1H),
2.28 (t, 2H), 2.40 (m, 1H), 3.14 (m, 2H), 3.62 (m, 1H); α-LA-pro-
tons], 4.67 (m, 1H, N-CH(CH3)2), 6.36Ϫ7.85 [6.36 (s, 1H), 7.19 (d,
1H), 7.39 (m, 2H), 7.85 (s, 1H); Ar-H], 9.67 (s, 1H, NH-CO); LC-
MS m/z 363 (MϩH)ϩ; IR (KBr, cmϪ1): 3258 (NH), 1645 (CϭO).
Spectral analyses of intermediate compounds
1-Isopropyl-5-nitro-1H-indole (I-2d)
1H-NMR δ ppm (CDCl3, 400 MHz): 1.57 (d, 6H, N-CH(CH3)2),
4.72 (m, 1H, N-CH(CH3)2), 6.70 (d, 1H, J ϭ 3.6), 7.38 (d, 1H, J ϭ
3.2), 7.40 (s, 1H), 8.11 (dd, 1H, Jm ϭ 2.4, Jo ϭ 9.2), 8.59 (d, 1H,
J ϭ 2); LC-MS m/z 204 (MϩH)ϩ.
5-[1,2]Dithiolane-3-yl-penthanoic acid (1-n-butyl-1H-indole-5-yl)-
amide (I-4e)
1H-NMR δ ppm (DMSO-d6, 400 MHz): 0.87 (t, 3H, -CH3), 1.21
(m, 2H, -CH2CH3), 1.39Ϫ3.65 [1.42 (m, 2H), 1.57Ϫ1.73 (m, 4H),
1.87 (m, 1H), 2.29 (t, 2H), 2.41 (m, 1H), 3.15 (m, 2H), 3.63 (m,
1H); α-LA-protons], 1.57Ϫ1.73 (m, 2H, N-CH2CH2-), 4.12 (t, 2H,
N-CH2-), 6.34Ϫ7.87 [6.34 (d, 1H), 7.22 (d, 1H), 7.31 (d, 1H), 7.36
(d, 1H), 7.87 (s, 1H); Ar-H], 9.70 (s, 1H, NH-CO); LC-MS m/z 377
(MϩH)ϩ; IR (KBr, cmϪ1): 3253 (NH), 1635 (CϭO).
1-n-Butyl-5-nitro-1H-indole (I-2e)
1H-NMR δ ppm (CDCl3, 400 MHz): 0.95 (t, 3H, -CH3), 1.34 (m,
2H, -CH2CH3), 1.83 (m, 2H, N-CH2CH2-), 4.16 (t, 2H, N-CH2-),
6.66 (d, 1H, J ϭ 3.6), 7.24 (d, 1H, J ϭ 3.2), 7.34 (d, 1H, Jϭ8.8),
8.10 (dd, 1H, Jm ϭ 2, Jo ϭ 9.2), 8.57 (d, 1H, Jϭ2); LC-MS m/z
218 (MϩH)ϩ.
5-[1,2]Dithiolane-3-yl-penthanoic acid (1-benzyl-1H-indole-5-yl)-
amide (I-4f)
1-(2,4-dichloro benzyl)-5-nitro-1H-indole (I-2h)
1H-NMR δ ppm (DMSO-d6, 400 MHz): 1.39Ϫ3.56 [1.40 (m, 2H),
1.65 (m, 4H), 1.86 (m, 1H), 2.28 (t, 2H), 2.40 (m, 1H), 3.12 (m,
2H), 3.56 (m, 1H); α-LA-protons], 5.36 (s, 2H, N-CH2-), 6.41Ϫ7.88
[6.41 (s, 1H), 7.16Ϫ7.31 (m, 7H), 7.45 (s, 1H), 7.88 (s, 1H); Ar-H],
9.68 (s, 1H, NH-CO); LC-MS m/z 411 (MϩH)ϩ; IR (KBr, cmϪ1):
3248 (NH), 1644 (CϭO).
1H-NMR δ ppm (CDCl3, 400 MHz): 5.42 (s, 2H, N-CH2-), 6.56 (d,
1H, J ϭ 8), 6.77 (d, 1H, J ϭ 3.2), 7.11 (dd, 1H, Jm ϭ 2.4, Jo
ϭ
8.8), 7.27 (m, 2H), 7.46 (d, 1H, J ϭ 2), 8.09 (dd, 1H, Jm ϭ 2.4, Jo ϭ
8), 8.61 (d, 1H, J ϭ 2.4).
5-Methyl-1H-indole-1-amine (II-2e)
5-[1,2]Dithiolane-3-yl-penthanoic acid [1-(4-fluorobenzyl)-1H-in-
dole-5-yl]-amide (I-4g)
1H-NMR δ ppm (CDCl3, 400 MHz): 2.44 (s, 3H, -CH3), 4.74 (s,
2H, -NH2), 6.29 (d, 1H, J ϭ 2.8), 7.06 (dd, 1H, J ϭ 8.4), 7.12
(d, 1H, J ϭ 3.2), 7.29 (d, 1H, J ϭ 8.4), 7.37 (s, 1H); LC-MS m/z
146 (MϩH)ϩ.
1H-NMR δ ppm (DMSO-d6, 400 MHz): 1.39Ϫ3.61 [1.40 (m, 2H),
1.65 (m, 4H), 1.86 (m, 1H), 2.27 (t, 2H), 2.39 (m, 1H), 3.12 (m,
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Buyukbingol et al.
Arch. Pharm. Chem. Life Sci. 2005, 338, 67−73
2H), 3.61 (m, 1H); α-LA-protons], 5.35 (s, 2H, N-CH2-), 6.40Ϫ7.88
[6.40 (s, 1H), 7.11Ϫ7.21 (m, 5H), 7.34 (d, 1H), 7.45 (s, 1H), 7.88 (s,
1H); Ar-H], 9.69 (s, 1H, NH-CO); LC-MS m/z 429 (MϩH)ϩ; IR
(KBr, cmϪ1): 3315 (NH), 1686 (CϭO).
5-[1,2]Dithiolane-3-yl-penthanoic acid [2-(1H-indole-3-yl)ethyl]-
amide (III-5a)
1H-NMR δ ppm (DMSO-d6, 400 MHz): 1.30Ϫ3.55 [1.30 (m, 2H),
1.51 (m, 3H), 1.61 (m, 1H), 1.82 (m, 1H), 2.06 (t, 2H), 2.36 (m,
1H), 2.82 (m, 2H), 3.12 (m, 2H), 3.34 (m, 2H), 3.55 (m, 1H); α-LA-
protons and ϪCH2CH2NH], 6.66Ϫ7.53 [6.66 (t, 1H), 7.06 (t, 1H),
7.14 (s, 1H), 7.33 (d, 1H), 7.53 (d, 1H); Ar-H], 7.92 (s, 1H, indole-
NH), 10.82 (s, 1H, NH-CO); LC-MS m/z 349 (MϩH)ϩ; IR (KBr,
cmϪ1): 3291 (NH), 1648 (CϭO).
5-[1,2]Dithiolane-3-yl-penthanoic acid [1-(2,4-dichlorobenzyl)-1H-
indole-5-yl]-amide (I-4h)
1H-NMR δ ppm (DMSO-d6, 400 MHz): 1.39Ϫ3.65 [1.42 (m, 2H),
1.63 (m, 4H), 1.87 (m, 1H), 2.29 (t, 2H), 2.42 (m, 1H), 3.15 (m,
2H), 3.63 (m, 1H); α-LA-protons], 5.47 (s, 2H, N-CH2-), 6.47Ϫ7.93
[6.47 (d, 1H), 6.55 (d, 1H), 7.17Ϫ7.32 (m, 3H), 7.41 (d, 1H), 7.68
(d, 1H), 7.93 (d, 1H); Ar-H], 9.73 (s, 1H, NH-CO); LC-MS m/z 479
(MϩH)ϩ; IR (KBr, cmϪ1): 3254 (NH), 1639 (CϭO).
5-[1,2]Dithiolane-3-yl-penthanoic acid [2-(5-methoxy-1H-indole-3-
yl)ethyl]-amide (III-5b) [18]
1H-NMR δ ppm (DMSO-d6, 400 MHz): 1.30Ϫ3.56 [1.30 (m, 2H),
1.49 (m, 3H), 1.62 (m, 1H), 1.83 (m, 1H), 2.05 (m, 2H), 2.36 (m,
1H), 2.76 (m, 2H), 3.13 (m, 2H), 3.30 (m, 2H), 3.56 (m, 1H); α-LA-
protons and -CH2CH2NH], 3.74 (s, 3H, O-CH3), 6.69Ϫ7.20 [6.69
(d, 1H), 6.99 (s, 1H), 7.08 (s, 1H), 7.20 (d, 1H); Ar-H], 7.89 (s, 1H,
indole-NH), 10.63 (s, 1H, NH-CO); LC-MS m/z 379 (MϩH)ϩ; IR
(KBr, cmϪ1): 3298 (NH), 1647 (CϭO).
5-[1,2]Dithiolane-3-yl-penthanoic acid indole-1-yl-amide (II-3a)
1H-NMR δ ppm (DMSO-d6, 400 MHz): 1.44Ϫ3.66 [1.47 (m, 2H),
1.60Ϫ1.71 (m, 4H), 1.89 (m, 1H), 2.34 (t, 2H), 2.42 (m, 1H),
3.11Ϫ3.19 (m, 2H), 3.66 (m, 1H); α-LA-protons], 6.44Ϫ7.54 [6.44
(m, 1H), 7.05 (t, 1H), 7.15 (m, 2H), 7.25 (d, 1H), 7.54 (d, 1H); Ar-
H], 11.10 (s, 1H, NH-CO); LC-MS m/z 321 (MϩH)ϩ; IR (KBr,
cmϪ1): 3195 (NH), 1667 (CϭO).
Assay of lipid peroxidation
NADPH-dependent lipid peroxidation was determined under the
optimum conditions as earlier described [22]. Male Wistar rats
(200Ϫ225 g) were fed with standard laboratory rat chow and tap
water ad libitum. The animals were starved for 24 h prior to sacrifice
and then killed by decapitation under anaesthesia. Livers were re-
moved immediately and washed in ice-cold distilled water, and
microsomes were prepared using literature methods [23]. NADPH-
dependent lipid peroxidation was measured spectrophotometrically
by estimation of thiobarbituric acid reactive substances (TBARS).
Amounts of TBARS were expressed in terms of nmol malondial-
dehyde (MDA) per mg protein. A typical optimized assay mixture
contained 0.2 mM Feϩϩ, 90 mM KCl, 62.5 mM potassium phos-
phate buffer, pH 7.4, a NADPH generating system consisting of
0.25 mM NADPϩ, 2.5 mM MgCl2, 2.5 mM glucose-6-phosphate
buffer, pH 7.8, and 0.2 mg microsomal protein in a final volume of
1.0 mL. Protein was measured by the method of Lowry et al., using
bovine serum albumin as standard [24].
5-[1,2]Dithiolane-3-yl-penthanoic acid (5-methoxy-indole-1-yl)-
amide (II-3b)
1H-NMR δ ppm (DMSO-d6, 400 MHz): 1.45Ϫ3.67 [1.46 (m, 2H),
1.63 (m, 4H), 1.90 (m, 1H), 2.33 (t, 2H), 2.45 (m, 1H), 3.14 (m,
2H), 3.67 (m, 1H); α-LA-protons], 3.74 (s, 3H, O-CH3), 6.35Ϫ7.20
[6.35 (d, 1H), 6.78 (m, 1H), 7.06 (m, 2H), 7.20 (m, 1H); Ar-H],
11.06 (s, 1H, NH-CO); LC-MS m/z 351 (MϩH)ϩ; IR (KBr, cmϪ1):
3180 (NH), 1668 (CϭO).
5-[1,2]Dithiolane-3-yl-penthanoic acid (5-bromo-indole-1-yl)-amide
(II-3c)
1H-NMR δ ppm (DMSO-d6, 400 MHz): 1.45Ϫ3.69 [1.47 (m, 2H),
1.67 (m, 4H), 1.91 (m, 1H), 2.36 (t, 2H), 2.44 (m, 1H), 3.15Ϫ3.31
(m, 2H), 3.68 (m, 1H); α-LA-protons], 6.47Ϫ7.78 [6.47 (d, 1H), 7.18
(d, 1H), 7.28 (d, 1H), 7.35 (s, 1H), 7.78 (s, 1H); Ar-H], 11.22 (s, 1H,
NH-CO); LC-MS m/z 400 (MϩH)ϩ, 401 (Mϩ2); IR (KBr, cmϪ1):
3187 (NH), 1674 (CϭO).
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