1-(5-Carboxy- and 5-carbamoylindol-1-yl)propan-2-ones as inhibitors of human cytosolic phospholipase A2α: Bioisosteric replacement of the carboxylic acid and carboxamide moiety

Article abstract of DOI:10.1016/j.bmc.2007.02.016

Indole-5-carboxylic acids and -carboxamides with 3-aryloxy-2-oxopropyl residues in position 1 were previously reported to be potent inhibitors of cytosolic phospholipase A₂α (cPLA₂α) isolated from human platelets. In continuation of

Full text of DOI:10.1016/j.bmc.2007.02.016

Bioorganic & Medicinal Chemistry 15 (2007) 2883–2891
1-(5-Carboxy- and 5-carbamoylindol-1-yl)propan-2-ones
as inhibitors of human cytosolic phospholipase A2a:
Bioisosteric replacement of the carboxylic acid
and carboxamide moiety
Mark Hess, Alwine Schulze Elfringhoff and Matthias Lehr*
Institute of Pharmaceutical and Medicinal Chemistry, University of Mu¨nster, Hittorfstrasse 58-62, D-48149 Mu¨nster, Germany
Received 21 September 2006; revised 1 February 2007; accepted 9 February 2007
Available online 13 February 2007
Abstract—Indole-5-carboxylic acids and -carboxamides with 3-aryloxy-2-oxopropyl residues in position 1 were previously reported
to be potent inhibitors of cytosolic phospholipase A2a (cPLA2a) isolated from human platelets. In continuation of our attempts to
develop novel cPLA2a inhibitors, a number of derivatives of these substances characterized by bioisosteric replacement of the car-
boxylic acid and carboxamide functionality, respectively, were prepared. The results of the biological evaluation of the obtained
compounds enabled us to gain further insight into structural features critical for cPLA2a inhibition.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
structurally related to 2, as compounds 3–5, are also po-
tent inhibitors of cPLA2a.8 Structure–activity relation-
ship studies revealed that a carboxylic acid or
carboxamide moiety in position 5 of the indole nucleus
is important for a pronounced inhibition of the enzyme
by these substances.
Cytosolic phospholipase A2a (cPLA2a) is an esterase that
selectively cleaves the sn-2 position of arachidonoyl-glyc-
erophospholipids of biomembranes to generate free ara-
chidonic acid and lysophospholipids.1 Arachidonic acid
in turn is metabolized to a variety of inflammatory medi-
ators including prostaglandins and leukotrienes. Lyso-
phospholipids with an alkyl ether moiety at the sn-1
position can be acetylated to platelet activating factor
(PAF), another mediator of inflammation.2 Thus, inhibi-
tion of cPLA2a is considered as an attractive target for the
design of new anti-inflammatory drugs.3–5
Since bioisosteric replacement is a valuable tool in lead
optimization and structure–activity relationship stud-
ies,9 we now replaced the carboxylic acid and carboxam-
ide substituents of 4 and 5, respectively, by bioisosteric
groups.
First-generation inhibitors of cPLA2a were analogues of
arachidonic acid with the COOH group replaced by
COCF3 (AACOCF3, 1) or PO(OCH3)F (MAFP).3
Compounds with very high in vitro cPLA2a-inhibitory
potency reported later are thiazolidinedione compounds
from Shionogi6 and propan-2-ones, such as 2, from
AstraZeneca (Fig. 1).7 Recently, we have found that 1-
[3-(4-octylphenoxy)-2-oxopropyl]indoles, which are
2. Chemistry
Indole-5-carboxamide derivatives 12 and 13 were synthe-
sized by the route outlined in Scheme 1. Indole-5-carbox-
ylic acid (6) was reacted with N,N0-carbonyldiimidazole
to give the stable imidazolide 7,10 which upon reaction
with methylamine and dimethylamine, respectively, affor-
ded the N-methylated indole-5-carboxamides 8 and 9.11,12
These compounds were coupled with 2-(4-octylphe-
noxy)methyloxirane8 in DMF in the presence of NaH.
The alcohol moieties of the obtained intermediates 10
and 11 were oxidized by the Albright–Goldman proce-
dure with acetic anhydride/DMSO to provide the target
compounds 12 and 13.
Keywords: Cytosolic phospholipase A2a inhibitors; Indol-1-ylpropan-
2-ones; Bioisosteric replacement.
*
Corresponding author. Tel.: +49 251 83 33331; fax: +49 251 83
32144; e-mail: lehrm@uni-muenster.de
0968-0896/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2007.02.016

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M. Hess et al. / Bioorg. Med. Chem. 15 (2007) 2883–2891
O
CF3
1
R1
O
O
O
O
O
N
R2
C10H21
O
COOH
C8H17
2
3 R1 = COOCH3, R2 = COOH
4 R1 = H, R2 = COOH
5 R1 = H, R2 = CONH2
Figure 1.
Scheme 1. Reagents and conditions: (a) N,N0-Carbonyldiimidazole, THF, room temperature; (b) methylamine HCl or dimethylamine HCl,
triethylamine, THF, aqueous NaHCO3, room temperature; (c) 2-(4-octylphenoxymethyl)oxirane, NaH, DMF, 100 ꢁC; (d) acetic anhydride, DMSO,
room temperature.
The preparation of morpholinocarbonyl-substituted in-
dole derivative 17 is shown in Scheme 2. Treatment of
indole-5-carboxylic acid with N,N0-carbonyldiimidazole
and morpholinium chloride/triethylamine gave 5-mor-
pholinocarbonylindole (14).13 This compound was
further reacted with epichlororhydrin to afford the epoxy
intermediate 15. Ring opening of 15 with 4-octylphenol
was achieved without solvent in the presence of catalytic
amounts of 4-dimethylaminopyridine. Oxidation of the
resulting alcohol intermediate 16 to the desired ketone
17 was carried out with Dess–Martin reagent.
Indole-5-sulfonamides 19–2114–16 were synthesized start-
ing from 1-acetylindoline by known reaction sequences
involving chlorosulfonation with chlorosulfonic acid,
sulfonamide formation with ammonia, methylamine
or dimethylamine, deacetylation with concentrated
HCl, and rearomatization of the indoline to the indole
with 2,3-dichloro-5,6-dicyanobenzoquinone (Scheme 3).
Reaction of 19–21 with 2-(4-octylphenoxy)methyloxirane
as described for the synthesis of 10 and subsequent oxida-
tion with acetic anhydride/DMSO or Dess–Martin
reagent led to the target sulfonamides 22–24.
Scheme 2. Reagents and conditions: (a) N,N0-Carbonyldiimidazole, THF, morpholinium chloride, triethylamine, room temperature; (b)
epichlorohydrin, KOH, Bu4N+Brꢀ, room temperature; (c) 4-octylphenol, 4-dimethylaminopyridine, 95 ꢁC; (d) Dess–Martin reagent, CH2Cl2, room
temperature.

M. Hess et al. / Bioorg. Med. Chem. 15 (2007) 2883–2891
2885
Scheme 3. Reagents and conditions: (a) Chlorosulfonic acid, 70 ꢁC; (b) aqueous NH3, THF, room temperature, or methylamine HCl, triethylamine,
THF, aqueous NaHCO3, reflux, or dimethylamine HCl, triethylamine, THF, aqueous NaHCO3, reflux; (c) conc. HCl, dioxane, reflux; (d) 2,3-
dichloro-5,6-dicyanobenzoquinone, dioxane, 80 ꢁC; (e) 2-(4-octylphenoxymethyl)oxirane, NaH, DMF, 60 ꢁC or room temp; (f) acetic anhydride,
DMSO, room temperature, or Dess–Martin reagent, CH2Cl2, room temperature.
Indol-5-ylmethylidenethiazolidine-2,4-dione derivative
26 was prepared by treatment of indole-5-carbaldehyde
25 with thiazolidine-2,4-dione in toluene in the presence
of catalytical amounts of piperidine and acetic acid, fol-
lowed by oxidation with Dess–Martin reagent (Scheme
4).
3. Evaluation of inhibitors
All newly synthesized indole derivatives were evaluated
in an assay applying cPLA2a isolated from human plate-
lets.19 Like other lipases, cPLA2a has evolved to work
optimally at a lipid–water interface. For this reason,
sonicated covesicles consisting of 1-stearoyl-2-arachido-
noyl-sn-glycero-3-phosphocholine and 1,2-dioleoyl-sn-
glycerol were used as enzyme substrate. A possible
problem of assays using such an aggregated form of
phospholipids is that a test compound could inhibit
the enzyme not by binding to its active site but merely
by altering the substrate assembly and hence causing
the enzyme to desorb from the lipid–water-interface.
To exclude this way of action, the mole fraction of
inhibitor in the interface has to be kept low.20 Thus,
the highest concentration of test compounds evaluated
was 10 lM, while the concentration of the vesicle form-
ing lipids was 300 lM. The enzyme activity was deter-
mined by measuring the enzyme product arachidonic
acid formed after an incubation time of 60 min with
HPLC and UV-detection at 200 nm.
Oxadiazoles 30 and 31 were synthesized in the same
way as 12 starting from 5-(3-benzyl- and 3-ethyl-1,2,4-
oxadiazol-5-yl)indole (28 and 29) (Scheme 5). The
preparation of the latter compounds was achieved by
reaction of methyl indole-5-carboxylate with N-hy-
droxy-2-phenylacetamidine17 and N-hydroxypropio-
namidine,18 respectively.
Scheme 6 outlines the synthesis of the target compounds
with 4,5-dihydro-1,2,4-oxadiazol-5-one and 1H-tetra-
zole moieties 36 and 38. Indole-5-carbonitrile (32) was
alkylated in position 1 with epichlorohydrin to afford
33. Coupling of this compound with 4-octylphenol in a
fashion similar to that described for the synthesis of 16
provided the hydroxy intermediate 34. This was convert-
ed to the oxadiazol-5-one 35 by subsequent treatment
with hydroxylammonium chloride/NaOH and diethyl
carbonate, and to the 1H-tetrazole 37 by reaction with
4. Results and discussion
trimethylsilyl
azide/tetrabutylammonium
fluoride.
Dess–Martin-oxidation of 35 and 37 gave the desired
compounds 36 and 38.
Bioisosteric replacement is a well-known medicinal
chemistry technique. It consists of replacing one frag-
Scheme 4. Reagents and conditions: (a) Thiazolidine-2,4-dione, acetic acid, piperidine, toluene, reflux; (b) Dess–Martin reagent, CH2Cl2, THF, room
temperature.
Scheme 5. Reagents and conditions: (a) N-Hydroxy-2-phenylacetamidine or N-hydroxypropionamidine, NaH, THF, reflux; (b) 2-(4-octylphen-
oxymethyl)oxirane, NaH, DMF, 60 ꢁC; (c) acetic anhydride, DMSO, room temperature.

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M. Hess et al. / Bioorg. Med. Chem. 15 (2007) 2883–2891
Scheme 6. Reagents and conditions: (a) Epichlorohydrin, KOH, Bu4N+Brꢀ, room temperature; (b) 4-octylphenol, 4-dimethylaminopyridine, 60 ꢁC;
(c) hydroxylammonium chloride, methanol, aqueous NaOH, reflux; (d) diethyl carbonate, NaOEt, ethanol, reflux; (e) Dess–Martin reagent, CH2Cl2,
THF, room temperature; (f) trimethylsilyl azide, Bu4N+Fꢀ hydrate, 120 ꢁC.
ment in a bioactive molecule with another fragment
possessing similar spatial and electronic character.
Bioisosteric transformation has been extensively and
successfully used in the optimization of lead candidates
in drug discovery.9
of these inhibitors, we now replaced these functionalities
by several bioisosteric groups. First, we synthesized the
N-methylated and N,N-dimethylated carboxamides 12
and 13. With IC50-values of 0.37 and 0.84 lM these
compounds were about threefold and sevenfold less ac-
tive than the unsubstituted parent 5 (Table 1). Replace-
ment of the amide nitrogen by a morpholino substituent
(17) decreased activity to a similar extent. Introduction
of unsubstituted and methyl substituted sulfonamide
residues also did not result in more active compounds.
The sulfonamides 22, 23, and 24 possessed an IC50
against cPLA2a in the range of 0.3–0.5 lM. In contrast
Indole-5-carboxylic acid 4 and its carboxamide deriva-
tive 5 have been found to be potent inhibitors of cPLA2a
with IC50-values of 0.035 and 0.12 lM against the en-
zyme isolated from human platelets.8 Since the carbox-
ylic acid and carboxamide moieties of 4 and 5,
respectively, are important parts of the pharmacophore
Table 1. Inhibition of cPLA2a-activity
O
O
N
R
C8H17
a
Compound
R
Vesicle assay IC50 (lM)
4
5
COOH
CONH2
0.035
0.12
0.37
0.84
0.50
0.39
0.31
0.50
>10b
n.a.c
n.a.c
3.5
12
13
17
22
23
24
26
30
31
36
38
1
CONHCH3
CON(CH3)2
Morpholin-4-ylcarbonyl
SO2NH2
SO2NHCH3
SO2N(CH3)2
2,4-Dioxothiazolidin-5-ylidenemethyl
3-Benzyl-1,2,4-oxadiazol-5-yl
3-Ethyl-1,2,4-oxadiazol-5-yl
5-Oxo-4,5-dihydro-1,2,4-oxadiazol-3-yl
1H-Tetrazol-5-yl
1.1
2.3
2
0.011
0.005
3
a Values are means of at least two independent determinations; errors are within 20%.
b 29% inhibition at 10 lM.
c n.a., not active at 10 lM.

M. Hess et al. / Bioorg. Med. Chem. 15 (2007) 2883–2891
2887
to the corresponding amides, the unsubstituted sulfon-
amide 22 was not significantly more active than the
N-methylated compounds 23 and 24.
COCF3) was purchased from Biomol, Hamburg,
Germany. The reference inhibitor AR-C70484XX (4-
[3-(4-decyloxyphenoxy)-2-oxopropoxy]benzoic acid, 2),
was sythesized according to published procedures.7
Since a series of 3-methylidenethiazolidine-2,4-dione
derivatives had been found to inhibit cPLA2a very
potently,6 we synthesized a compound with such a resi-
due in position 5 of the indole scaffold (26). This modi-
fication led to a drastic decrease of enzyme inhibition in
our case. The IC50-value of 26 was greater than 10 lM.
3-Benzyl- and 3-ethyl-1,2,4-oxadiazole residues, known
as bioisosteric to amide groups, even led to a total loss
of activity at a concentration of 10 lM when introduced
instead of the 5-carboxamide residue. With the introduc-
tion of a 4,5-dihydro-1,2,4-oxadiazol-5-one system some
inhibitory potency could be regained; the IC50 of com-
pound 36 was 3.5 lM.
5.1. (Imidazol-1-yl)indol-5-ylmethanone (7)10
A solution of indole-5-carboxylic acid (1.0 g, 6.2 mmol) in
dry THF (15 mL) was treated under a nitrogen atmo-
sphere with N,N0-carbonyldiimidazole (1.0 g, 6.2 mmol),
and the mixture was stirred at room temperature until the
gas development was finished. After addition of water, the
reaction mixture was extracted exhaustively with diethyl
ether. The combined organic phases were dried (Na2SO4)
and concentrated. The residue was recrystallized from
acetone/toluene (1:1) to give 7 as a solid (1.1 g, 81%);
1
mp 162 ꢁC. H NMR (DMSO-d6): d 6.66–6.67 (m, 1H),
7.16 (m, 1H), 7.55–7.56 (m, 1H), 7.59 (m, 2H), 7.71 (m,
1H), 8.13 (s, 1H), 8.23–8.24 (m, 1H), 11.66 (br, 1H). MS
(EI) m/z (%): 211 (4) [M]+, 144 (100).
Since the tetrazole group possesses bioisosteric relation-
ships to the carboxylic acid moiety, we finally synthe-
sized 1H-tetrazole 38. With an IC50 of 1.1 lM this
compound was about 30-fold less active than the lead
compound 4.
5.2. N-Methylindole-5-carboxamide (8)11
To a solution of 7 (211 mg, 1 mmol) in THF were added
subsequently methylamine hydrochloride (135 mg,
2 mmol), triethylamine (0.28 mL), and a saturated aque-
ous NaHCO3 solution (2 mL). The mixture was stirred
at room temperature for 1 h. Then, methylamine hydro-
chloride (135 mg, 2 mmol) and saturated aqueous NaH-
CO3 solution (2 mL) were added a second time, and
stirring was continued for additional 2 h. After dilution
with water, the mixture was extracted exhaustively with
diethyl ether. The combined organic phases were dried
(Na2SO4) and concentrated. The residue was purified
by chromatography on silica gel (hexane/ethyl acetate,
In conclusion, in contrast to many other medicinal
chemistry investigations,9 in our case bioisosteric
replacement of a carboxylic acid and carboxamide func-
tionality, respectively, did not lead to more potent bio-
active molecules.
5. Experimental
Column chromatography was performed on Merck sili-
ca gel 60, 230–400 mesh (=flash chromatography) or 70–
230 mesh. Preparative HPLC was performed on a RP18
column (Kromasil 100, 5 lm, 10 mm (ID) · 250 mm
protected with an analogously filled guard column
10 mm (ID) · 50 mm, CS-chromatographie service,
Langerwehe, Germany). Melting points were deter-
1
3:2) to give 8 as a solid (142 mg, 82%); mp 144 ꢁC. H
NMR (DMSO-d6): d 2.77–2.78 (m, 3H), 6.50 (m, 1H),
7.38–7.40 (m, 2H), 7.58–7.60 (m, 1H,), 8.08 (s, 1H),
8.25 (br, 1H), 11.28 (br, 1H). MS (EI) m/z (%): 174
(60) [M]+, 144 (100).
mined on a Buchi B-540 apparatus and are uncorrected.
¨
1H NMR spectra were recorded on a Varian Mercury
Plus 400 spectrometer (400 MHz). Mass spectra were
obtained on Finnigan GCQ and LCQ apparatuses
applying electron beam ionization (EI) and electrospray
ionization (ESI), respectively. For ESI-MS a mixture of
acetonitrile/H2O/formic acid (85:15:0.1) containing
ammonium formiate (12 mM) was used.21 The purity
of the target compounds was determined using two di-
verse HPLC systems with UV detection at 254 nm.
The first one applied an amino phase (Spherisorb
NH2, 5 lm, 4.0 mm (ID) · 250 mm, Latek, Heidelberg,
Germany) eluting the compounds with an isohexane/
THF gradient at a flow rate of 0.75 mL/min. In the sec-
ond system separation was performed using a cyano
phase (LiChrospher 100 CN, 5 lm, 3.0 mm
(ID) · 250 mm, Merck, Darmstadt, Germany) with an
isohexane/THF gradient containing 0.1% trifluoroacetic
acid at a flow rate of 0.5 mL/min. With exception of 24
and 38, all target compounds showed purities greater
than 97% in both HPLC systems. The purity evaluated
for 24 was 95%, and for 38 96% each time. The reference
inhibitor arachidonyltrifluoromethyl ketone (AA-
5.3. N,N-Dimethylindole-5-carboxamide (9)12
Compound 7 was reacted with dimethylamine hydro-
chloride according to the methodology described for 8
1
to give 9 as a solid; mp 237 ꢁC. H NMR (DMSO-d6):
d 2.96 (s, 6H), 6.46–6.47 (m, 1H), 7.12 (dd, 1H), 7.38–
7.40 (m, 2H), 7.59–7.60 (m, 1H), 11.25 (br, 1H). MS
(EI) m/z (%): 188 (27) [M]+, 144 (100).
5.4. 1-[2-Hydroxy-3-(4-octylphenoxy)propyl]-N-methyl-
indole-5-carboxamide (10)
Under a nitrogen atmosphere a suspension of NaH
(60% in mineral oil; 29 mg, 0.72 mmol) in dry DMF
(7 mL) was stirred at room temperature for 10 min.
After addition of a solution of 8 (115 mg, 0.66 mmol)
in dry DMF (7 mL), the mixture was further stirred
for 1 h. Then, a solution of 2-(4-octylphenoxymeth-
yl)oxirane8 (173 mg, 0.66 mmol) in dry DMF (10 mL)
was added, and the reaction mixture was heated at
100 ꢁC for 3 h. After it was cooled to room temperature,
the mixture was treated with half-saturated brine and

2888
M. Hess et al. / Bioorg. Med. Chem. 15 (2007) 2883–2891
extracted exhaustively with diethyl ether. The combined
organic phases were washed three times with half-
saturated brine, dried (Na2SO4), and the solvent was
evaporated. The residue was purified by silica gel
chromatography (1) hexane/ethyl acetate, 1:1; (2) ethyl
6H), 4.62 (s, 2H), 5.20 (s, 2H), 6.62 (d, 1H), 6.83 (d,
2H), 7.09 (d, 1H), 7.12–7.15 (m, 3H), 7.29 (dd, 1H),
7.73 (d, 1H). MS (EI) m/z (%): 448 (92) [M]+, 244 (100).
5.8. (Indol-5-yl)morpholin-4-ylmethanone (14)13
1
acetate) to give 10 as an oil (150 mg, 52%). H NMR
(CDCl3): d 0.88 (t, 3H), 1.26–1.30 (m, 10H), 1.55–1.58
(m, 2H), 2.54 (t, 2H), 2.86 (br, 1H), 3.01 (d, 3H), 3.84
(dd, 1H), 3.91 (dd, 1H), 4.28–4.33 (m, 2H), 4.40–4.44
(m, 1H), 6.21 (d, 1H), 6.55 (d, 1H), 6.79 (d, 2H), 7.08
(d, 2H), 7.21 (d, 1H), 7.36 (d, 1H), 7.56 (d, 1H), 8.03
(s, 1H). MS (EI) m/z (%): 436 (100) [M]+.
A solution of indole-5-carboxylic acid (6) (300 mg,
1.86 mmol) in dry THF (10 mL) was treated under a
nitrogen atmosphere with N,N0-carbonyldiimidazole
(302 mg, 1.86 mmol), and the mixture was stirred at
room temperature until the gas development was fin-
ished. After addition of morpholinium chloride
(460 mg, 3.72 mmol) and triethylamine (0.52 mL,
3.75 mmol), the reaction mixture was stirred at room
temperature for 10 h, treated with water, and extracted
exhaustively with diethyl ether. The combined organic
layers were dried (Na2SO4), and the solvent was evapo-
rated. The residue was purified by silica gel chromatog-
raphy (hexane/ethyl acetate, 1:1) to give 14 as a solid
5.5. 1-[2-Hydroxy-3-(4-octylphenoxy)propyl]-N,N-dime-
thylindole-5-carboxamide (11)
Compound 9 was reacted with 2-(4-octylphenoxymeth-
yl)oxirane for 50 h at 100 ꢁC following the procedure
for the synthesis of 10 to give 11 as an oil in 60% yield.
1H NMR (CDCl3): d 0.88 (t, 3H), 1.26–1.30 (m, 10H),
1.56 (quint, 2H), 2.53 (t, 2H), 3.06 (br, 6H), 3.17 (d,
1H), 3.78 (dd, 1H), 3.85 (dd, 1H), 4.24–4.30 (m, 2H),
4.37–4.43 (m, 1H), 6.51 (d, 1H), 6.77 (d, 2H), 7.06 (d,
2H), 7.18–7.20 (m, 2H), 7.30 (d, 1H), 7.68 (d, 1H). MS
(EI) m/z (%): 450 (100) [M]+.
1
(340 mg, 79%); mp 128 ꢁC. H NMR (CDCl3): d 3.71
(br, 8H), 6.57–6.59 (m, 1H), 7.25–7.27 (m, 2H), 7.38
(dd, 1H), 7.72–7.73 (m, 1H), 8.50 (br, 1H). MS (EI) m/
z (%): 230 (21) [M]+, 144 (100).
5.9. (Morpholin-4-yl)-1-oxiranylmethylindol-5-ylmetha-
none (15)
5.6. N-Methyl-1-[3-(4-octylphenoxy)-2-oxopropyl]indole-
5-carboxamide (12)
A
mixture of powdered KOH (85%; 182 mg,
2.76 mmol), compound 14 (310 mg, 1.35 mmol), tetra-
butylammonium bromide (42 mg, 0.13 mmol), and epi-
chlorohydrin (3 mL) was stirred under a nitrogen
atmosphere at room temperature for 1 h, diluted with
a small amount of CH2Cl2, and subjected to chromatog-
raphy on silica gel (hexane/ethyl acetate, 2:3) to give 15
Acetic anhydride (1.0 mL, 10 mmol) was added to dry
DMSO (5 mL), and the mixture was stirred under a
nitrogen atmosphere at room temperature for 10 min.
Then, this solution was added to a solution of 10
(120 mg, 0.27 mmol) in dry DMSO (7 mL). The mixture
was stirred under a nitrogen atmosphere for 18 h, and
poured into a mixture of 5% aqueous NaHCO3 and brine
(1:2). After being stirred for 5 min, the mixture was
extracted exhaustively with diethyl ether. The
combined organic phases were washed three times with
half-saturated brine, dried (Na2SO4), and the solvent
was distilled off. The residue was purified by silica gel
chromatography (CHCl3/methanol, 49:1). The product
fractions were concentrated, and the residue was crystal-
lized from ethyl acetate/hexane. The product was further
purified by RP-HPLC applying acetonitrile/H2O (85:15)
as mobile phase. The eluates were concentrated under re-
duced pressure until most of the acetonitrile was distilled
off. The remaining solvent was removed by freeze-drying
to give 12 as a solid (83 mg, 71%); mp 138 ꢁC. 1H NMR
(CDCl3): d 0.88 (t, 3H), 1.26–1.30 (m, 10H), 1.58 (quin,
2H), 2.57 (t, 2H), 3.03 (d, 3H), 4.62 (s, 2H), 5.21 (s,
2H), 6.20 (br, 1H), 6.64 (d, 1H), 6.83 (d, 2H), 7.09–7.10
(m, 2H), 7.14 (d, 2H), 7.63 (dd, 1H), 8.07 (d, 1H). MS
(EI) m/z (%) 434 (57) [M]+, 230 (100).
1
as an oil (368 mg, 95%). H NMR (CDCl3): d 2.44 (dd,
1H), 2.81 (dd, 1H), 3.27–3.29 (m, 1H), 3.70 (br, 8H),
4.18 (dd, 1H), 4.49 (dd, 1H), 6.56 (dd, 1H), 7.20 (d,
1H), 7.30 (dd, 1H), 7.40 (d, 1H), 7.71 (d, 1H). MS
(EI) m/z (%): 286 (70) [M]+, 200 (100).
5.10. {1-[2-Hydroxy-3-(4-octylphenoxy)propyl]indol-5-
yl}morpholin-4-ylmethanone (16)
Compound 15 (300 mg, 1.05 mmol), 4-octylphenol
(216 mg, 1.05 mmol), and 4-dimethylaminopyridine
(20 mg) were mixed thoroughly, and heated at 95 ꢁC
for 1.5 h stirring up the mixture several times. The
cooled reaction mixture was dissolved in CH2Cl2 and
subjected to chromatography on silica gel (hexane/ethyl
acetate, 2:3) to give 16 as an oil (331 mg, 64%). 1H NMR
(CDCl3): d 0.87 (t, 3H), 1.24–1.29 (m, 10H), 1.56 (quint,
2H), 2.54 (t, 2H), 2.61 (d, 1H), 3.69 (br, 8H), 3.82 (dd,
1H), 3.90 (dd, 1H), 4.31–4.35 (m, 2H), 4.40–4.44 (m,
1H), 6.55 (d, 1H), 6.79 (d, 2H), 7.08 (d, 2H), 7.20–7.26
(m, 2H), 7.38 (d, 1H), 7.70 (m, 1H). MS (EI) m/z (%):
492 (61) [M]+, 406 (100).
5.7. N,N-Dimethyl-1-[3-(4-octylphenoxy)-2-oxopropyl]in-
dole-5-carboxamide (13)
5.11. 1-[5-(Morpholine-4-carbonyl)indol-1-yl]-3-(4-octyl-
phenoxy)propan-2-one (17)
Compound 11 was oxidized using the procedure de-
scribed for the preparation of 12. Silica gel chromatog-
raphy (hexane/ethyl acetate, 1:1) afforded 13 as a solid;
mp 136 ꢁC. 1H NMR (CDCl3): d 0.88 (t, 3H), 1.27–
1.30 (m, 10H), 1.58 (quint, 2H), 2.56 (t, 2H), 3.08 (br,
A solution of 16 (270 mg, 0.55 mmol) in dry CH2Cl2
(5 mL) was treated with Dess–Martin periodinane

M. Hess et al. / Bioorg. Med. Chem. 15 (2007) 2883–2891
2889
reagent (349 mg, 0.82 mmol), and stirred under a nitro-
gen atmosphere at room temperature for 3 h. A solution
of sodium thiosulfate (1.0 g) in saturated sodium bicar-
bonate solution (20 mL) was added. After stirring for
10 min, the reaction mixture was extracted exhaustively
with diethyl ether. The combined organic layers were
dried (Na2SO4), and the solvent was evaporated. The
residue was purified by silica gel chromatography (hex-
ane/ethyl acetate, 2:3) to give 17 as an oil (217 mg,
methyl)oxirane at room temperature for 24 h, followed
by oxidation of the obtained intermediate with
DMSO/acetic anhydride applying procedures similar
to those described above for the synthesis of 10 and
12. Purification by silica gel chromatography (hexane/
1
ethyl acetate, 7:3) gave 24 as a solid; mp 133 ꢁC. H
NMR (CDCl3): d 0.88 (t, 3H), 1.27–1.32 (m, 10H),
1.58 (quint, 2H), 2.58 (t, 2H), 2.70 (s, 6H), 4.68 (s,
2H), 5.28 (s, 2H), 6.73 (d, 1H), 6.86 (d, 2H), 7.15–7.19
(m, 4H), 7.59 (dd, 1H), 8.12 (d, 1H). MS (EI) m/z (%):
484 (30) [M]+, 438 (100).
1
80%). H NMR (CDCl3): d 0.88 (t, 3H), 1.27–1.30 (m,
10H), 1.58 (quin, 2H), 2.57 (t, 2H), 3.70 (br, 8H), 4.63
(s, 2H), 5.21 (s, 2H), 6.63 (d, 1H), 6.83 (d, 2H), 7.09–
7.15 (m, 4H), 7.26–7.28 (m, 1H), 7.72 (d, 1H). MS
(EI) m/z (%): 490 (21) [M]+, 286 (100).
5.15. 5-{1-[3-(4-Octylphenoxy)-2-oxopropyl]indol-5-
ylmethylidene}thiazolidine-2,4-dione (26)
A solution of 1-[2-hydroxy-3-(4-octylphenoxy)propyl]in-
dole-5-carbaldehyde8 (25) (270 mg, 0.66 mmol) in tolu-
ene (10 mL) was treated with thiazolidine-2,4-dione
(78 mg, 0.66 mmol) and catalytic amounts of acetic acid
and piperidine. The mixture was refluxed for 4 h, cooled,
poured into water, and extracted exhaustively with ethyl
acetate. The combined organic phases were dried
(Na2SO4) and concentrated under reduced pressure until
crystallization occurred. The solid was sucked off and
recrystallized from hexane/ethyl acetate (2:3) to yield
the thiazolidine-2,4-dione derivative of 25 (180 mg,
54%). An aliquot of this compound (150 mg, 0.30 mmol)
was oxidized in a similar way as described above for the
synthesis of 17. The crude product was purified by silica
gel chromatography ((1) hexane/ethyl acetate, 2:3; (2)
ethyl acetate) to yield 26 as a solid (111 mg); mp 203–
205 ꢁC (decomp.). 1H NMR (DMSO-d6): d 0.88 (t,
3H), 1.27–1.29 (m, 10H), 1.56 (m, 2H), 2.54 (m, 2H),
5.02 (s, 2H), 5.46 (s, 2H), 6.66 (d, 1H), 6.92 (d, 2H),
7.15 (d, 2H), 7.39 (dd,1H), 7.43 (d, 1H), 7.54 (d, 1H),
7.88 (m, 2H), 12.50 (br, 1H). MS (EI) m/z (%): 504
(59) [M]+, 257 (100).
5.12. 1-[3-(4-Octylphenoxy)-2-oxopropyl]indole-5-sulfon-
amide (22)
Compound 22 was prepared by coupling indole-5-sulfon-
amide14 (19) with 2-(4-octylphenoxymethyl)oxirane at
60 ꢁC for 6 h, followed by oxidation of the obtained inter-
mediate with Dess–Martin periodinane reagent applying
procedures similar to those described above for the syn-
thesis of 10 and 17. The crude product was purified by sil-
ica gel chromatography (hexane/ethyl acetate, 1:1),
followed by RP-HPLC (acetonitrile/H2O, 85:15). The
eluates were concentrated under reduced pressure until
most of the acetonitrile was distilled off. The remaining
solvent was removed by freeze-drying yielding 22 as a
1
solid; mp 180 ꢁC (decomp.). H NMR (CDCl3): d 0.88
(t, 3H), 1.26–1.30 (m, 10H), 1.60 (quint, 2H), 2.58 (t,
2H), 4.67 (s, 2H), 4.71 (s, 2H), 5.29 (s, 2H), 6.71 (d, 1H),
6.86 (d, 2H), 7.16–7.18 (m, 4H), 7.73 (dd, 1H), 8.28 (d,
1H). MS (EI) m/z (%): 456 (35) [M]+, 107 (100).
5.13. N-Methyl-1-[3-(4-octylphenoxy)-2-oxopropyl]in-
dole-5-sulfonamide (23)
5.16. 5-(3-Benzyl-1,2,4-oxadiazol-5-yl)indole (28)
Compound 23 was prepared by coupling N-methylin-
dole-5-sulfonamide15 (20) with 2-(4-octylphenoxymeth-
yl)oxirane at room temperature for 24 h, followed by
oxidation of the obtained intermediate with DMSO/ace-
tic anhydride applying procedures similar to those
described above for the synthesis of 10 and 12. The
crude product was purified by silica gel chromatography
((1) hexane/ethyl acetate/triethylamine, 1:1:0.02; (2) hex-
ane/ethyl acetate/formic acid, 1:1:0.02). The product
fractions were washed with 10% aqueous NaHCO3 solu-
tion, concentrated, and the residue was cleaned up by
RP-HPLC as described for the purification of 22 to give
To a solution of N-hydroxy-2-phenylacetamidine17
(1.68 g, 11.2 mmol) in dry THF (20 mL) was added un-
der a nitrogen atmosphere NaH (60% in mineral oil;
438 mg, 11.2 mmol). The mixture was stirred at room
temperature for 1 h and then treated with a solution of
methyl indole-5-carboxylate (27) (980 mg, 5.6 mmol) in
dry THF (20 mL). The resulting mixture was heated un-
der reflux for 2 h, cooled, poured into water, and
extracted exhaustively with diethyl ether. The combined
organic layers were dried (Na2SO4), and the solvent was
evaporated. The residue was purified by silica gel chro-
matography (hexane/ethyl acetate, 4:1) to give 28 as a
solid (1.0 g, 65%); mp 135 ꢁC. 1H NMR (CDCl3): d
4.17 (s, 2H), 6.63–6.64 (m, 1H), 7.23–7.42 (m, 7H),
7.92 (dd, 1H), 8.45 (m, 1H), 8.66 (br, 1H). MS (EI)
m/z (%): 275 (46) [M]+, 144 (100).
1
23 as a solid; mp 130 ꢁC. H NMR (CDCl3): d 0.88 (t,
3H), 1.27–1.36 (m, 10H), 1.59 (quint, 2H), 2.58 (t,
2H), 2.64 (d, 3H), 4.28 (m, 1H), 4.68 (s, 2H), 5.28 (s,
2H), 6.71 (d, 1H), 6.86 (d, 2H), 7.15–7.25 (m, 4H),
7.65 (dd, 1H), 8.21 (d, 1H). MS (EI) m/z (%): 470 (35)
[M]+, 265 (100).
5.17. 5-(3-Ethyl-1,2,4-oxadiazol-5-yl)indole (29)
5.14. N,N-Dimethyl-1-[3-(4-octylphenoxy)-2-oxopropyl]
indole-5-sulfonamide (24)
N-Hydroxypropionamidine18 was reacted with methyl
indole-5-carboxylate following the procedure for the
synthesis of 28. Purification by silica gel chromatogra-
phy (hexane/ethyl acetate, 7:3) gave 29 as a solid in
Compound 24 was prepared by coupling N,N-dimethy-
lindole-5-sulfonamide16 (21) with 2-(4-octylphenoxy-

2890
M. Hess et al. / Bioorg. Med. Chem. 15 (2007) 2883–2891
54% yield; mp 159 ꢁC. 1H NMR (CDCl3): d 1.41 (t, 3H),
2.84 (q, 2H), 6.68 (m, 1H), 7.30–7.32 (m, 1H), 7.50 (d,
1H), 7.97 (dd, 1H), 8.47 (br, 1H), 8.48 (m, 1H). MS
(EI) m/z (%): 213 (70) [M]+, 144 (100).
atmosphere at 60 ꢁC for 2 h. The cooled reaction mix-
ture was dissolved in a small amount of CH2Cl2 and
subjected to chromatography on silica gel ((1) hexane/
ethyl acetate, 9:1; (2) hexane/ethyl acetate, 4:1) to give
1
34 as an oil (1.04 g, 85%). H NMR (CDCl3): d 0.88
5.18. 1-[5-(3-Benzyl-1,2,4-oxadiazol-5-yl)indol-1-yl]-3-(4-
octylphenoxy)propan-2-one (30)
(t, 3H), 1.27–1.30 (m, 10H), 1.58 (m, 2H), 2.55 (t, 2H),
3.85 (dd, 1H), 3.92 (dd, 1H), 4.33–4.35 (m, 2H), 4.43–
4.47 (m, 1H), 6.60 (d, 1H), 6.80 (d, 2H), 7.11 (d, 2H),
7.29 (d, 1H), 7.39 (d, 1H), 7.45 (d, 1H), 7.94 (s, 1H).
MS (EI) m/z (%): 404 (100) [M+].
Compound 30 was prepared by coupling 28 with 2-(4-
octylphenoxymethyl)oxirane at 60 ꢁC for 16 h, followed
by oxidation of the obtained intermediate with DMSO/
acetic anhydride applying procedures similar to those
described above for the synthesis of 10 and 12. The
crude product was purified by flash chromatography
on silica gel (hexane/ethyl acetate, 4:1) to give 30 as a
5.22. 3-{1-[2-Hydroxy-3-(4-octylphenoxy)propyl]indol-5-
yl}-4,5- dihydro-1,2,4-oxadiazol-5-one (35)
A solution of 34 (290 mg, 0.72 mmol) in methanol
(5 mL) was treated with a mixture of solutions of
hydroxylammonium chloride (50 mg, 0.72 mmol) in
methanol (3 mL) and NaOH (29 mg, 0.72 mmol) in
water (3 mL). The resulting mixture was heated under
reflux for 24 h. Then, another portion of a mixture of
hydroxylammonium chloride (50 mg, 0.72 mmol) in
methanol (3 mL) and NaOH (29 mg, 0.72 mmol) in
water (3 mL) was added, and the reaction mixture was
heated under reflux for another 24 h. The solvent was re-
moved under reduced pressure, and the residue chro-
matographed on silica gel eluting with ethyl acetate to
yield crude carboxamidine of 34 (280 mg). Without fur-
ther purification, a solution of an aliquot of this inter-
mediate (200 mg) in dry ethanol was treated with a
sodium ethanolate solution, prepared from sodium
(21 mg, 0.91 mmol) and dry ethanol (5 mL). When gas
development had ceased, diethyl carbonate (0.22 mL,
1.83 mmol) was added, and the reaction mixture was
heated under reflux overnight. After cooling to room
temperature, the mixture was poured into water and
extracted exhaustively with diethyl ether. The combined
organic layers were dried (Na2SO4), and the solvent was
evaporated. The residue was purified by silica gel chroma-
tography (hexane/ethyl acetate, 2:3) to give 35 as a solid
(80 mg). 1H NMR (DMSO-d6): d 0.88 (t, 3H), 1.26–1.28
(m, 10H), 1.54 (m, 2H), 2.50–2.53 (m, 2H), 3.86–3.88
(m, 2H), 4.18–4.19 (m, 1H), 4.32 (dd, 1H), 4.47 (dd,
1H), 5.46 (d, 1H), 6.62 (d, 1H), 6.87 (d, 2H), 7.11 (d,
2H), 7.53 (d, 1H), 7.57 (dd, 1H), 7.71 (d, 1H), 8.07 (m, 1H).
1
solid; mp 148 ꢁC. H NMR (CDCl3): d 0.88 (t, 3H),
1.26–1.32 (m, 10H), 1.55–1.60 (m, 2H), 2.57 (t, 2H),
4.15 (s, 2H), 4.66 (s, 2H), 5.24 (s, 2H), 6.70 (dd, 1H),
6.85 (d, 2H), 7.11 (d, 1H), 7.14–7.17 (m, 3H), 7.25–
7.28 (m, 1H), 7.32–7.36 (m, 2H), 7.40–7.42 (m, 2H),
7.93 (dd, 1H), 8.45 (d, 1H). MS (EI) m/z (%): 535 (25)
[M]+, 330 (100).
5.19. 1-[5-(3-Ethyl-1,2,4-oxadiazol-5-yl)indol-1-yl]-3-(4-
octylphenoxy)propan-2-one (31)
Compound 31 was prepared by coupling 29 with 2-(4-
octylphenoxymethyl)oxirane at 60 ꢁC for 3 h, followed
by oxidation of the obtained intermediate with DMSO/
acetic anhydride applying procedures similar to those de-
scribed above for the synthesis of 10 and 12. The crude
product was purified by silica gel chromatography (hex-
ane/ethyl acetate, 4:1) and recrystallized from hexane/eth-
yl acetate (7:3) to give 31 as a solid; mp 112 ꢁC. 1H NMR
(CDCl3): d 0.88 (t, 3H), 1.27–1.32 (m, 10H), 1.40 (t, 3H),
1.57–1.61 (m, 2H), 2.58 (t, 2H), 2.84 (q, 2H), 4.67 (s, 2H),
5.25 (s, 2H), 6.71 (d, 1H), 6.85 (d, 2H), 7.12 (d, 1H),
7.15–7.19 (m, 3H), 7.95 (dd, 1H), 8.46 (d, 1H). MS (EI)
m/z (%): 473 (55) [M]+, 268 (100).
5.20. 1-Oxiranylmethylindole-5-carbonitrile (33)
A mixture of powdered KOH (85%; 440 mg,
7.84 mmol), indole-5-carbonitrile (32) (500 mg,
3.52 mmol), tetrabutylammonium bromide (113 mg,
0.35 mmol), and epichlorohydrin (5 mL) was stirred un-
der a nitrogen atmosphere at room temperature for 1 h,
diluted with a small amount of CH2Cl2, and subjected to
chromatography on silica gel ((1) hexane/ethyl acetate,
9:1; (2) hexane/ethyl acetate, 7:3) to give 33 as a solid
(630 mg, 90%); mp 92–93 ꢁC. 1H NMR (CDCl3): d
2.45 (dd, 1H), 2.83–2.85 (m, 1H), 3.27–3.30 (m, 1H),
4.15 (dd, 1H), 4.54 (dd, 1H), 6.61 (d, 1H), 7.26–7.27
(m, 1H), 7.44–7.45 (m, 2H), 7.97 (s, 1H). MS (EI) m/z
(%) 198 (75) [M]+, 142 (100).
5.23. 3-{1-[3-(4-Octylphenoxy)-2-oxopropyl]indol-5-yl}-
4,5-dihydro-1,2,4-oxadiazol-5-one (36)
Compound 35 was oxidized in a similar way as de-
scribed above for the synthesis of 17. The crude product
was purified by silica gel chromatography (hexane/ethyl
1
acetate, 2:3) to yield 36 as a solid; mp 201–203 ꢁC. H
NMR (DMSO-d6): d 0.88 (t, 3H), 1.26–1.28 (m, 10H),
1.54 (m, 2H), 2.52–2.54 (m, 2H), 5.02 (s, 2H), 5.48 (s,
2H), 6.66 (d, 1H), 6.91 (d, 2H), 7.13 (d, 2H), 7.45 (d,
1H), 7.58 (m, 2H), 8.08 (s, 1H), 12.81 (s, 1H). MS (EI)
m/z (%): 461 (29) [M]+, 107 (100).
5.21. 1-[2-Hydroxy-3-(4-octylphenoxy)propyl]indole-5-
carbonitrile (34)
5.24. 1-(4-Octylphenoxy)-3-[5-(1H-tetrazol-5-yl)indol-1-
yl]propan-2-ol (37)
Compound 33 (600 mg, 3.03 mmol), 4-octylphenol
(625 mg, 3.03 mmol), and 4-dimethylaminopyridine
(20 mg) were dissolved in CH2Cl2 (4 mL). The solvent
was distilled off, and the residue heated under a nitrogen
A mixture of 34 (250 mg, 0.62 mmol), trimethylsilyl
azide (0.12 mL, 0.93 mmol), and tetrabutylammonium

M. Hess et al. / Bioorg. Med. Chem. 15 (2007) 2883–2891
2891
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fluoride hydrate (81 mg, 0.31 mmol) was heated under a
nitrogen atmosphere at 120 ꢁC for 12 h. The reaction
mixture was purified by silica gel chromatography ((1)
hexane/ethyl acetate, 2:3; (2) ethyl acetate) to give 37 as
1
a solid (160 mg, 58%). H NMR (DMSO-d6): d 0.88 (t,
3H), 1.27–1.28 (m, 10H), 1.54 (m, 2H), 2.51–2.54 (m,
2H), 3.90 (d, 2H), 4.20–4.21 (m, 1H), 4.33 (dd, 1H), 4.48
(dd, 1H), 5.47 (d, 1H), 6.65 (d, 1H), 6.89 (d, 2H), 7.12
(d, 2H), 7.53 (d, 1H), 7.74 (d, 1H), 7.81 (d, 1H), 8.29 (s,
1H). MS (EI) m/z (%): 447 (76) [M]+, 403 (100).
7. Connolly, S.; Bennion, C.; Botterell, S.; Croshaw, P. J.;
Hallam, C.; Hardy, K.; Hartopp, P.; Jackson, C. G.; King,
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5.25. 1-(4-Octylphenoxy)-3-[5-(1H-tetrazol-5-yl)indol-1-
yl]propan-2-one (38)
Compound 37 was oxidized in a similar way as de-
scribed above for the synthesis of 17. The crude product
was purified by silica gel chromatography (hexane/ethyl
acetate, 2:3) to yield 38 as a solid; mp 170–172 ꢁC (de-
comp.). 1H NMR (DMSO-d6): d 0.87 (t, 3H), 1.26–
1.28 (m, 10H), 1.54 (m, 2H), 2.52–2.54 (m, 2H), 5.00
(s, 2H), 5.37 (s, 2H), 6.52 (d, 1H), 6.90 (d, 2H), 7.13
(d, 2H), 7.27 (d, 1H), 7.36 (d, 1H), 7.82 (dd, 1H), 8.16
(m, 1H). MS (ESI) m/z (%): 444 [MꢀH]+.
5.25.1. Assay of cPLA2a inhibition. The inhibition of
cPLA2a isolated from human platelets was performed
as previously described.19 Briefly, sonicated covesicles
consisting of 1-stearoyl-2-arachidonoyl-sn-glycero-3-
phosphocholine (0.2 mM) and 1,2-dioleoyl-sn-glycerol
(0.1 mM) were used as enzyme substrate. cPLA2a activ-
ity was determined by measuring the arachidonic acid
released by the enzyme with reversed-phase HPLC and
UV-detection at 200 nm after cleaning up the samples
with solid phase extraction.
16. Terentev, A. P.; Preobrazhenskaya, M. N. Zh. Obshch.
Khim. 1960, 30, 1218.
17. Moloney, G. P.; Martin, G. R.; Mathews, N.; MacLen-
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C 1970, 270, 2062.
19. Schmitt, M.; Lehr, M. J. Pharm. Biomed. Anal. 2004, 35,
135.
References and notes
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Castro, R.; Clark, J. D.; Dennis, E. A.; Gelb, M. H.
Biochim. Biophys. Acta 1999, 1420, 45.
1. Kudo, I.; Murakami, M. Prostaglandins Other Lipid
Mediat. 2002, 68–69, 3.
21. Fabian, J.; Lehr, M. J. Pharm. Biomed. Anal. 2007, 43,
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2. Serhan, C. N.; Haeggstro¨m, J. Z.; Leslie, C. C. FASEB J.
1996, 10, 1147.