N-aminoindoline derivatives as inhibitors of 5-lipoxygenase

Article abstract of DOI:10.1016/S0960-894X(01)00077-4

N-Aminoindoline derivatives were prepared and their 5-lipoxygenase inhibitory activities were evaluated in vitro and compared with those of phenidone and NDGA. Compound 4 presents the most effective 5-LO inhibition.

Full text of DOI:10.1016/S0960-894X(01)00077-4

Bioorganic & Medicinal Chemistry Letters 11 (2001) 845–848
N-Aminoindoline Derivatives as Inhibitors of 5-Lipoxygenase
Corinne Audouin,a,b Nathalie Mestdagh,b Marie-Agnes Lassoie,b Raymond Houssina
and Jean-Pierre Henicharta,*
a
´
Institut de Chimie Pharmaceutique Albert Lespagnol, Universite de Lille 2, BP 83, 59006 Lille, France
bUCB Secteur Pharmaceutique, Chemin du Foriest, 1420 Braine l’Alleud, Belgium
Received 16 November 2000; revised 22 January 2001; accepted 2 February 2001
Abstract—N-Aminoindoline derivatives were prepared and their 5-lipoxygenase inhibitory activities were evaluated in vitro and
compared with those of phenidone and NDGA. Compound 4 presents the most effective 5-LO inhibition. # 2001 Elsevier Science
Ltd. All rights reserved.
The peptidoleukotrienes LTC4, LTD4 and LTE4 are
potent constrictors of human airways, and it has been
widely assumed that they play an important role in
asthma.1 They are responsible for potent pro-inflam-
matory and spasmogenic manifestations, and are pre-
sent in the airways of asthmatic patients at rest and
during an acute crisis. The 5-LO enzyme catalyses two
key steps in the LT biosynthetic pathway: the arachi-
donate-5-HPETE oxidation step followed by the dehy-
drogenation phase resulting in the formation of LTA4.2
Inhibition of 5-LO could provide a novel therapy for
human inflammatory diseases such as asthma.
the substrate mimic procedure.3 The aim of this work
was to synthesise new antioxidants as inhibitors of 5-LO.
Indapamide, a diuretic drug used in cardiovascular dis-
ease treatment, has antioxidant properties: this drug is
effective in the inhibition of LDL oxidation and its
major metabolite, 5-hydroxyindapamide, is even more
active.4 This could be due to capto-dative stabilisation
of the radical5 resulting from the abstraction of a
hydrogen radical. Molecule 1, like indapamide, presents
an N-aminoindoline skeleton substituted by a carbonyl
group. The non-cyclized analogues of this molecule
possessing a carbonyl (2) or a sulfonyl group (3)
should help evaluate the influence of the indoline cycle
opening and may be compared with indapamide and
also with phenidone, another antioxidant inhibitor of
5-LO.6
At least four strategies can be considered for 5-LO
inhibition: (a) the antioxidant and/or free radical sca-
venger mechanism; (b) the iron-chelation process; (c)
the inhibition of the 5-LO translocation reaction; and (d)
*Corresponding author. Tel.: +33-3-2096-4374; fax: +33-3-2096-4361; e-mail: henicha@phare.univ-lille2.fr
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00077-4

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C. Audouin et al. / Bioorg. Med. Chem. Lett. 11 (2001) 845–848
In order to test the influence of an oxygen moiety on
antioxidant properties, different pharmacomodulations
were performed at C5 and led to 4 (R=OH), that could
be considered as an analogue of 5-hydroxyindapamide,
and to 5 (R=OCH3). Compounds 6 and 7,7 with a
chain containing a double bond as does arachidonic
acid, were also tested.
The substituted derivatives 4 and 5 were prepared from
the corresponding indoles (Scheme 3).
After reduction with sodium cyanoborohydride into the
corresponding indolines,10 nitrosation resulted in 9 and
10. These compounds were reduced with LiAlH4 to give
1-aminoindolines which were acylated in situ with ben-
zoyl chloride. Compound 4 was obtained after hydro-
genolysis of 11 in the presence of Raney nickel.
Carboxylic acid 6 was synthesised as shown in Scheme 4.
Ethyl hexynoate was coupled under Castro–Stephens
conditions with p-iodobenzoic acid by palladium cata-
lysis in the presence of catalytic amounts of copper(I)
iodide to give the aryne 12.11 Reduction of the triple
bond with hydrogen over Lindlar catalyst12 did not lead
to pure cis olefin 14, but to a mixture also containing
Compound 1 was prepared as outlined in Scheme 1.
Nitrosoindoline 8 was prepared by nitrosation of indo-
line.8 Reduction with LiAlH4 and acylation of crude
1-aminoindoline with benzoyl chloride9 produced 1.
The reaction of N-methyl-N-phenylhydrazine with ben-
zoyl chloride or benzenesulfonyl chloride led to
compounds 2 and 3, respectively (Scheme 2).
Scheme 1. (a) NaNO2, HCl, H2O, 83%; (b) (i) LiAlH4, anhydrous ether, 0 ꢀC; (ii) C6H5COCl, AcOEt, NEt3, 0 ꢀC, 45%.
Scheme 2. (a) C6H5COCl, CHCl3, NEt3, 0 ꢀC, 59%; (b) C6H5SO2Cl, CHCl3, NEt3, 0 ꢀC, 70%.
Scheme 3. (a) (i) NaBH3CN, AcOH; (ii) NaNO2, aq HCl; (b) (i) LiAlH4, anhydrous ether, 0 ꢀC; (ii) C6H5COCl, AcOEt, NEt3, 0 ꢀC; (c) H2, Raney
Ni, EtOH.
Scheme 4. (a) p-Iodobenzoic acid, NEt3, CuI, Pd(P(C6H5)2)Cl2, 76%; (b) H2, Pd/BaSO4, pyridine, EtOH, 86%; (c) MEMCl, (iPr)2NEt, CH2Cl2,
84%; (d) HPLC, 70%; (e) TFA, CH2Cl2, 98%; (f) (i) EDCI, HOBT, NEt3, 0 ꢀC; (ii) 1-aminoindoline, 0 ꢀC, rt; (g) NaOH, N2, dioxan/H2O (33:67),
95%; (h) (i) EDCI, HOBT, NEt3, 0 ꢀC; (ii) C10H21NH2, 0 ꢀC, rt, 38%.

C. Audouin et al. / Bioorg. Med. Chem. Lett. 11 (2001) 845–848
847
trans olefin and the corresponding alkane. In order to
circumvent this difficulty, separation was performed by
HPLC13 after transforming the carboxylic function into
MEM ester.14 This strategy led to pure cis olefin 13. The
MEM ester was cleaved by TFA and the resulting car-
boxylic acid 14 was coupled with 1-aminoindoline in the
presence of EDCI and HOBT.15 The carboxylate ester
was hydrolysed by NaOH to give compound 6 which
was coupled with N-decylamine under peptidic synthesis
conditions to give amide 7.
compound, and the presence of a sulfonyl group (3)
instead of its bioisosteric carbonyl group (2) seems to
increase the inhibition of 5-LO. Compound 4 is more
potent than the non-hydroxylated analogue 1: C5 sub-
stitution by a hydroxyl enhances 5-LO inhibition and
this group seems to be essential as regards enzyme
binding since compound 5, substituted at C5 by a
methoxy group, is less active. The introduction of the cis
hexenoic chain (6) has no influence. On the other hand,
amide 7, tested at 1 mM concentration because of low
solubility, could be attractive for further investigations.
The activities of these different compounds were eval-
uated in vitro and compared with those of phenidone
and NDGA (nordihydroguiaretic acid),16 the latter
being another antioxidant that inhibits 5-LO. Lipoxy-
genase products synthesised in RBL-1 cells—a rat
basophilic leukemia cell line—were analysed by HPLC.
The cells were harvested by centrifugation, washed with
phosphate buffer saline (PBS), pH 7.4, and resuspended
in PBS. Cells were stimulated and the reaction was
stopped as previously described.17 The 5-LO product
5-HETE was quantified by HPLC separation on a
Chromspher C18 column. Detection of 5-HETE was
carried out by UV absorbance at 130 nm. Compound 4
presented interesting activity (Table 1) and was sub-
mitted to IC50 determination (Scheme 5). Compound 4
is as active as phenidone, but less potent than NDGA in
vitro.
In conclusion, the prepared N-aminoindoline deriva-
tives are only moderately potent in inhibiting 5-LO.
However, further studies in the aminoindoline and ben-
zothiophene series (relative to Zileuton for example18)
are underway taking into account the preliminary and
encouraging results obtained on compounds 4 and 7,
and considering the fact that a sulfonyl group could
induce an increase in activity.
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Table 1.
Compound
Inhibition% 10 mM
IC50 (mM)
NDGA
Phenidone
73Æ8a
0.41Æ0.20
—
2.54Æ0.53
1
2
3
4
5
6
7
15Æ15
n=3
n=3
n=4
n=4
n=4
n=3
n=2
—
—
—
28Æ3
53Æ19
80Æ8
3.47Æ0.93
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meansÆSEM of at least three determinations.

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