Design and synthesis of a series of indole glycoprotein IIb/IIIa inhibitors

Article abstract of DOI:10.1016/S0223-5234(01)01325-3

Synthesis of 1,3-disubstituted indoles derivatives as potential glycoprotein (GP) IIb/IIIa antagonists was reported. Substitution of the indolic nitrogen atom by piperidino or benzamidino moieties was used as mimics of an arginine residue. The acid carboxylic group was linked to the indole scaffold in position-3 via a methylene unit (compounds 4, 9, 10). Introduction of a β-alanine chain was carried out on the acids (17-22) which after deprotection and basic hydrolysis afforded the final compounds 39-46. The distance between the indole scaffold and the amide bond was modulated from no methylene unit (compound 39) to 1 (compounds 40, 41) or 2 methylene units (compounds 42-46). The presence of a tosylamino group on the β-alanine chain (compound 56) slightly increased the inhibiting action on platelet aggregation initiated by collagen.

Full text of DOI:10.1016/S0223-5234(01)01325-3

Eur. J. Med. Chem. 37 (2002) 45–62
Laboratory note
Design and synthesis of a series of indole glycoprotein IIb/IIIa
inhibitors
Vale´rie Grumel a, Jean-Yves Me´rour a,*, Brigitte Lesur b, Thierry Giboulot b,
Armand Frydman b, Ge´rald Guillaumet a
a Institut de Chimie Organique et Analytique, UMR CNRS 6005, Uni6ersite´ d’Orle´ans, BP 6759, F-45067 Orle´ans, France
b Laboratoire L. Lafon, 19 A6enue du Professeur Cadiot, F-94701 Maisons-Alfort, France
Received 25 September 2001; received in revised form 27 November 2001; accepted 29 November 2001
Abstract
Synthesis of 1,3-disubstituted indoles derivatives as potential glycoprotein (GP) IIb/IIIa antagonists was reported. Substitution
of the indolic nitrogen atom by piperidino or benzamidino moieties was used as mimics of an arginine residue. The acid carboxylic
group was linked to the indole scaffold in position-3 via a methylene unit (compounds 4, 9, 10). Introduction of a b-alanine chain
was carried out on the acids (17–22) which after deprotection and basic hydrolysis afforded the final compounds 39–46. The
distance between the indole scaffold and the amide bond was modulated from no methylene unit (compound 39) to 1 (compounds
40, 41) or 2 methylene units (compounds 42–46). The presence of a tosylamino group on the b-alanine chain (compound 56)
´
slightly increased the inhibiting action on platelet aggregation initiated by collagen. © 2002 Editions scientifiques et me´dicales
Elsevier SAS. All rights reserved.
Keywords: Indole derivatives; Amino acids; Glycoprotein IIb/IIIa; Platelet aggregation
this recognition [6,7]. Subsequent studies have shown
that incorporating the RGD motif into constrained
cyclic peptides was a successful approach to the disco-
very of fibrinogen receptor antagonists [8]. Conforma-
tional studies of such peptides gave information about
the conformation for biological activity depending on
the RGD framework. Those informations were used to
design potent non-peptide RGD mimetics with im-
proved bioavailability [9–11].
Numerous scaffolds have been used such as 3-oxo-
1,4-benzodiazepine [12–19], benzimidazole [20], ben-
zoxazole [20], pyrrolidone [21], benzopyran [22],
2-amino-4-phenylthiazole [23] for designing new GPIIb/
IIIa antagonists (Fig. 1).
Recently isoindolinone [24,25] has been used as tem-
plate for the synthesis of new GPIIb/IIIa antagonists.
At the beginning of this program a few years ago we
decided to use the indole as bicyclic scaffold and to add
a basic moiety and an aspartic acid surrogate in order
to fullfill the requirements for a biological activity. The
1. Introduction
The aggregation of platelets is a critical step in
hemostasis and arterial thrombosis. Platelets are acti-
vated by a variety of agonists including adenosine
diphosphate (ADP), collagen, thrombin, adrenaline,
thromboxane A2, vasopressin, platelet activating factor
(PAF) and the final common stage resulting in platelet
aggregation is the binding of fibrinogen to glycoprotein
(GP) IIb/IIIa receptors located on the surface of acti-
vated platelets [1–3] (fibrinogen bridging of membrane
platelet receptors GPIIb/GPIIIa). In this binding pro-
cess it is known that: (i) the RGD sequence in fibrino-
gen is responsible for the recognition [4,5] of
GPIIb/IIIa; and (ii) the guanidino group of the Arg
residue and the b-carboxylic acid of the Asp residue in
the RGD sequence are the essential functionalities in
* Correspondence and reprints.
E-mail address: jean-yves.merour@univ-orleans.fr (J.-Y. Me´rour).
´
0223-5234/02/$ - see front matter © 2002 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
PII: S0223-5234(01)01325-3

46
V. Grumel et al. / European Journal of Medicinal Chemistry 37 (2002) 45–62
Fig. 1. Chemical structures of GPIIb/IIIa antagonists.
best compounds known in the literature when you build
mimics of RGD sequence are ‘linear model’ and the
modelisation of these compounds confirm the obtained
biological data [1–3]. Also, biological results in this
paper were attempted with the ‘curved type’ derivatives.
During the course of this work, indole derivatives
with antagonistic activity towards GPIIb/GPIIIa ap-
peared in the literature essentially by the Merck’s group
which published [26] and patented [27] 3,5-, 2,5- and
3,6-disubstituted indole derivatives. Taking into ac-
count this new situation it was decided to refocus the
research work on the preparation and biological evalua-
tion of ‘curved type’ derivatives namely the 1,3- (struc-
tures A and B, Fig. 2) disubstituted indole derivatives.
The chemical work and the biological activity studies
reported here will deal with the preparation and optimi-
sation of compounds in the 1,3 indole family.
bonyl)aminoiminomethyl]aniline [30] using EDCI/
DMAP in dichloromethane at room temperature to
afford compound 3 in 58% yield. Hydrogenolysis of the
CbZ group under 2 atm of hydrogen in presence of
palladium (80% yield), followed by saponification of
the ester group with lithium hydroxide at room temper-
ature and formation of the hydrochloride salt gave 4
(55% for the two steps) (Fig. 3).
The piperidine derivatives 8–10 were prepared in a
similar way by reacting the sodium salt of methyl
indole-3-acetate (1) or methyl indole-3-carboxylate (5)
with the benzyl-4-(2-iodoethyl)-1-piperidinecarboxylate
(6) or benzyl-4-(2-iodopropyl)-1-piperidinecarboxylate
(7) in DMF to afford the corresponding N-alkylated
derivatives 8–10. Yields being ranged from 54 to 87%
and best yields were obtained with the more reactive
ester 5 (Fig. 4).
In order to increase the distance between the acidic
and basic functions we planned first to alkylate the
nitrogen atom of methyl 3-(1H-3-indolyl)propanoate
with the iodoalkylpiperidine 6 or 7 but without success.
2. Chemistry
2.1. Preparation of ‘cur6ed type’ deri6ati6es: synthesis
of 1,3-deri6ati6es
Indole 3-acetic acid was esterified with methyl alco-
hol at reflux (85% yield) to give the methyl ester 1 [28].
Alkylation on the nitrogen atom with tert-butyl bro-
moacetate afforded 2 (81% yield). The use of NaH as a
base, in DMF [29] at room temperature, allowed the
exclusive N-alkylation without C-alkylation in a-posi-
tion of the methyl ester. Trifluoroacetic acid (TFA)
deprotection generated the acid, in quantitative yield,
which was further condensed with 4-[N(benzyloxycar-
Fig. 2. Structures A and B.

V. Grumel et al. / European Journal of Medicinal Chemistry 37 (2002) 45–62
47
The piperidino compounds 8–10, 14–16 obtained
were hydrolysed to the corresponding saturated 17–19
or unsaturated acids 20–22 with lithium hydroxide in
ethanol or methanol at room temperature or under
reflux (Table 1).
Condensation of acids 17–22 with ethyl ester of
b-alanine or methyl 3-aminobutanoate in presence of
EDCI and DMAP at room temperature afforded the
corresponding amido-esters 23–30 (Table 1).
The piperidino nitrogen atom of 23–25 was depro-
tected by hydrogenolysis over palladium, at atmo-
spheric pressure, in ethanol to afford 31–33. The
double bond of 26–30 was also reduced during the
deprotection step to give the saturated aminoesters
34–38. Finally acidic hydrolysis (3 N HCl) afforded the
corresponding aminoacids 39–46, as hydrochloride salt
(Table 1).
Fig. 3. (a) NaH, DMF, tert-butyl bromoacetate, r.t. (81%); (b) TFA,
CH2Cl2, r.t. (99%); (c) EDCI, DMAP, 4-aminobenzamidineCbz, r.t.
(58%); (d) H2, Pd/C, MeOH, HCl, r.t. (80%); (e) LiOH, r.t.; (f) 3 N
HCl (two steps, 55%).
2.2. Optimisation of 1,3-deri6ati6es: h-sulfonamides
It has been reported [26,34] that the introduction of a
NHSO2C6H5 group in position a of a terminal car-
boxylic function considerably enhances the GPIIb/GPI-
IIa antagonist activity. Therefore, we have first
prepared the methyl 2-(S)-tosylamino-3-aminopro-
panoate (47) according to the procedure of Moore [32]
and Kato [33] and further reacted that compound with
19 to obtain 48.
Fig. 4. Synthesis of piperidinyl derivatives 8–10.
Reaction of substituted piperidino compound 19 with
the methyl 2(S)-methylphenylsulfonyl-3-aminopro-
panoate (47) afforded derivative 48 (70% yield). The
piperidino nitrogen atom was deprotected by hy-
drogenolysis (49, 71% yield) and reacted with Boc2O to
give 50 (90% yield). Saponification of ester 50 afforded
acid 51 (92% yield) which upon treatment with HCl 4 N
led to the hydrochloride salt (52) (76% yield) (Fig. 6).
Fig. 5. (a) Potassium carbonate, 6, acetonitrile, reflux, (12); (b)
potassium carbonate, 7, acetonitrile, reflux, (13); (c) (Ph)3PꢀCHꢁ
COOC2H5, 12, toluene, reflux, (14); (d) (Ph)3PꢀCHꢁCOOC2H5, 13,
toluene, reflux, (15); (e) (EtO)2P(O)ꢁCH(CH3)COOC2H5, NaH, 12,
THF, r.t., (16).
We decided then to use a more reactive indolic deriva-
tive, the 3-formylindole 11 (pKa=12) [31], commer-
cially available. Compounds 12 and 13 were obtained in
good yields, respectively 99 and 93%, by reacting 11
with the iododerivative 6 or 7 in presence of sodium
hydride. They were further reacted with the Wittig
reagent (Ph)3PꢀCHꢁCOOC2H5 to afford 14 and 15,
respectively in 87 and 97% yields. The aldehydic deriva-
tive 12 was also submitted to a Horner–Emmons reac-
tion with triethyl-2-phosphonopropanoate to give 16
(91% yield) (Fig. 5).
Fig. 6. (a) H2NꢁCH2ꢁCH(NHTos)ꢁCOOCH3 (47), EDCI, DMAP,
HOBt, CH2Cl2, r.t.; (b) H2, Pd/C 10%, MeOH, r.t.; (c) Boc2O, Et3N,
dioxane, r.t.; (d) LiOH, MeOH, r.t.; (e) 4 N HCl, dioxane, 0 °C.

48
V. Grumel et al. / European Journal of Medicinal Chemistry 37 (2002) 45–62

V. Grumel et al. / European Journal of Medicinal Chemistry 37 (2002) 45–62
49
Table 2
one reported by the Merck’s group for the correspon-
ding 2,5-disubstituted indole derivatives [26] and re-
mains insufficient for translating into an in vivo an-
tithrombotic activity consistent with any expectation of
therapeutic effect.
In vitro antiplatelet activity of indole derivatives under study on
guinea-pig PRP aggregation induced by collagen
Compound
IC50 (mM)
4
31
32
33
\1000
\1000
140
4. Conclusions
25
34
120
35
36
37
38
39
40
41
42
43
44
45
46
520
230
170
350
New indole derivatives bearing different structural
features on the indole moiety have been prepared as
potential inhibitors of platelet GPIIb/IIIa. Among the
18 derivatives tested on their ability to inhibit platelet
aggregation induced by collagen, some 1,3-disubstituted
indoles derivatives show low micromolar activity. How-
ever, compared to the results reported in the literature
for 3,5- and 2,5-disubstituted indole analogues, in-
hibitory potency of our compounds appears to be
relatively weaker.
\1000
210
34
160
520
320
540
340
49
6.2
52
4.5
L756-568
0.0058
5. Experimental
5.1. Chemistry
3. Pharmacology
M.p.s were determined on a Ko¨fler melting point
apparatus and are uncorrected. 1H- and 13C-NMR
spectra were recorded in the indicated solvent on a
Bruker Advance DPX250 (250 MHz for proton and
The in vitro inhibiting action on platelet aggregation
initiated by collagen in guinea-pig platelet-rich-plasma
(PRP) was investigated. IC50 values were reported on
Table 2.
1
62.9 MHz for carbon). Chemical shifts for H are given
relative to internal TMS, while the 13C chemical shifts
were obtained with the solvent signal set to
l(CHCl3)=77.0. The J values were expressed in Hertz.
IR spectra were recorded in the range of 4000–600
cm−1 on a Perkin–Elmer spectrometer FT PARAGON
1000 PC. MS spectra were recorded under ionspray or
heat nebuliser conditions on a Perkin–Elmer mass
spectrometer SCIEX API 300 or Nermag R 1010 (70
eV): (CI–NH3). Column chromatographic separation
were performed on Merck silica gel 60 (0.040–0.063
mm) using the indicated solvents (Table 3).
3.1. 1,3-Disubstituted indoles
Benzamidino derivative 4 was totally inactive and we
rapidly focused on the piperidino group as substitute
for the amidino group.
Among the 18 piperidino derivatives prepared in this
series 16 of them are unsubstituted on the a-position of
the terminal carboxylic moiety and most of them have
IC50 only in the submillimolar range in our in vitro test,
which is quite unsatisfactory for that type of com-
pound. We can see from data presented in Table 1, that
in our assay system, acid or ester derivatives have
similar IC50 values.
5.1.1. Methyl 2-{1-[2-(tert-butoxy)-2-oxoethyl]-1H-3-
indolyl}acetate (2)
Ester 33, and the corresponding acid 41 have the
lowest IC50 of the series, respectively 25 and 34 mM.
This pattern prompted us to keep the backbone of
those compounds and to try to improve the potency by
adding a tosylsulfonamido group on the a-position of
the terminal carboxylic moiety as it is generally re-
ported for that type of compound. However, only an
improvement by a factor of less than 10 was observed:
IC50 of 4.5 mM for acid 52 compared to 34 mM for
parent compound 41 and 6.2 mM for ester 49 compared
to 25 mM for parent compound 33. This potency en-
hancement is unfortunately not as spectacular as the
To a suspension of NaH (38 mg, 1.59 mmol) in DMF
(0.5 mL) cooled in an ice-bath indole ester 1 (200 mg,
1.06 mmol) in DMF (1 mL) was dropwise added. The
mixture was stirred for 45 min at 0 °C and transferred
via a needle to a solution of tert-butyl bromoacetate
(309 mg, 1.59 mmol) in DMF (1 mL) at 0 °C. The
mixture was stirred for 2 h at room temperature (r.t.).
After evaporation of the DMF under reduced pressure
water–EtOAc was added. Decantation and extraction
with EtOAc followed by drying of the organic layers
over MgSO4 and evaporation leave an oil which was
purified by column chromatography on silica gel using

50
V. Grumel et al. / European Journal of Medicinal Chemistry 37 (2002) 45–62
EtOAc–PE 1:9 as eluent; a yellow oil was obtained;
m=260 mg (81%). Analysed for C17H21NO4 (C, H, N).
9.22 (br s, 2H, NH2); 11.02 (s, 1H, NH). 13C-NMR
(DMSO-d6): l 33.2 (CH2); 51.8 (NCH2); 54.4 (OCH3);
109.6 (C); 112.6 (CH); 121.4 (2CH); 121.5 (CH); 121.7
(CH); 124.2 (CH); 124.7 (CH); 130.3 (C); 131.4 (C);
132.1 (2CH); 139.4 (C); 146.6 (C); 167.5 (NꢀCN); 170.2
(CO); 174.7 (CO). MS (IS): m/z 365 [MH+].
5.1.2. Methyl 2-(1-{2-[4-amino{(benzyloxy)carbonyl]-
imino}methyl)anilino]-2-oxoethyl}-1H-3-indolyl)acetate
(3)
5.1.3.2. 2-[1-(2-{4-Amino(imino)methyl]anilino}-2-oxo-
ethyl)-1H-3-indolyl]acetic acid, hydrochloride (4). A
suspension of methyl 2-[1-(2-{4-amino(imino)methyl]-
anilino}-2-oxoethyl)-1H-3-indolyl]acetate (290 mg, 0.80
mmol) in water (3 mL) was adjusted to pH 12 with a
solution of 1 M LiOH and stirred for 24 h at r.t.; pH
was adjusted to 7 by addition of diluted aq. HCl. After
filtration the solid obtained was stirred, as a suspen-
sion, in water (1 mL) and 3 N HCl (350 mL) for 2 h at
0 °C. Filtration gave a solid, HCl salt, which was dried
over P2O5; m=170 mg (55%); m.p. 240–242 °C (dec.).
Analysed for C19H18N4O3, HCl (C, H, N).
5.1.2.1.
2-[3-(2-Methoxy-2-oxoethyl)-1H-1-indolyl]-
acetic acid. A solution of 2 (2 g, 6.59 mmol) and
trifluoroacetic acid (3 mL) in CH2Cl2 (10 mL) was
stirred at r.t. for 24 h. Water was added and the organic
layer was extracted with a saturated aq. solution of
sodium hydrogencarbonate. After acidification of the
aq. layer, extraction with CH2Cl2 and drying over
MgSO4, an oil was obtained after evaporation; m=
1.63 g (quantitative yield). IR (film) w (cm−1): 1731
1
(CꢀO); 2600–3700 (OH). H-NMR (CDCl3): l 3.77 (s,
3H, OCH3); 3.85 (s, 2H, CH2); 4.82 (s, 2H, NCH2); 7.10
(s, 1H, H2); 7.20–7.32 (m, 3H, H5, H6, H7); 7.68 (d, 1H,
H4, J=7.5 Hz); 10.0 (br s, 1H, COOH). 13C-NMR
(CDCl3): l 31.0 (CH2); 47.2 (NCH2); 52.1 (CH3); 108.5
(C); 109.0 (CH); 119.3 (CH); 120.0 (CH); 122.5 (CH);
127.2 (CH); 127.9 (C); 136.6 (C); 172.6 (CO); 173.6
(CO). MS (IS): m/z 248 [MH+].
5.1.4. Benzyl 4-(2-iodoethyl)-1-piperidinecarboxylate
(6)
To a solution of benzyl 4-(2-hydroxyethyl)-1-pipe-
ridinecarboxylate [35] (1.2 g, 4.56 mmol) in C6H5CH3–
MeCN (18/9 mL) cooled at 0 °C was added
triphenylphosphine (1.79 g, 6.84 mmol), imidazole (930
mg, 13.7 mmol) and iodine (1.73 g, 6.84 mmol). The
mixture was stirred for 3 h at r.t. After evaporation of
the solvent, water was added to the residue which was
extracted with CH2Cl2. Drying over MgSO4 and evapo-
ration leave a residue which was purified by column
chromatography on silica gel using EtOAc–PE 1:4 as
eluent to give an oil; m=1.59 g (93%). Analysed for
C15H20INO3 (C, H, N).
5.1.2.2. Methyl 2-(1-{2-[4-amino{(benzyloxy)carbonyl]-
imino}methyl)anilino]-2-oxoethyl}-1H-3-indolyl)acetate
(3). A mixture of 4-aminobenzamidineCbz (240 mg,
0.89 mmol), DMAP (118 mg, 0.97 mmol), 2-[3-(2-
methoxy-2-oxoethyl)-1H-1-indolyl]acetic acid (200 mg,
0.81 mmol), EDCI (170 mg, 0.89 mmol) in CH2Cl2 (20
mL) was stirred for 24 h at r.t. Water was added and
the mixture was extracted with CH2Cl2. After drying of
the organic extracts over MgSO4 and evaporation, the
residue was purified by column chromatography on
silica gel using EtOAc–PE 1:1 as eluent; a white solid
was obtained; m=230 mg (58%); m.p. 174–175 °C.
Analysed for C28H26N4O5 (C, H, N).
5.1.5. Benzyl 4-(2-iodopropyl)-1-piperidinecarboxylate
(7)
Same procedure as for 6 starting from benzyl 4-(2-hy-
droxypropyl)-1-piperidinecarboxylate [36]; chromato-
graphy (eluent: EtOAc–EP, 3:7); oil; m=8.7 g (89%).
Analysed for C17H22INO3 (C, H, N).
5.1.3. 2-[1-(2-{4-Amino(imino)methyl]anilino}-2-
oxoethyl)-1H-3-indolyl]acetic acid, hydrochloride (4)
5.1.6. General procedure for alkylation: compounds
8–13
5.1.3.1. Methyl 2-[1-(2-{4-amino(imino)methyl]anilino}-
2-oxoethyl)-1H-3-indolyl]acetate. To a solution of com-
pound 3 (1 g, 2 mmol) in MeOH (100 mL) and 4 N
HCl (2.5 mL in Et2O), Pd/C 10% (750 mg) was added.
The suspension was stirred for 1 h under 2 atm of
hydrogen at r.t. Filtration and evaporation leave a solid
as HCl salt which was crystallised in MeOH; m=650
mg (80%); m.p. 238–240 °C (dec.). IR (KBr) w (cm−1):
5.1.6.1. Method A: synthesis of compounds 8–10. A
solution of indole 1 or 5 (1 equiv.) in DMF (1 mL for
1 mmol) was dropwise added to a suspension of NaH
(1.5 equiv.) in DMF (1 mL for 1 mmol) at 0 °C. The
mixture was stirred for 30 min at 0 °C and transferred
slowly to a solution of halogeno derivatives 6 or 7 in
DMF (1 mL for 1 mmol). The mixture was stirred at
r.t. until disappearance of the indole 1 or 5 and evapo-
rated under reduced pressure. Water was added to the
residue and the mixture was extracted with EtOAc.
Drying over MgSO4 and evaporation leave a residue,
which was chromatographed on a silica gel column.
1
1673 (CꢀO), 1728 (CꢀO); 3334, 3384 (NH2, NH). H-
NMR (DMSO-d6): l 3.64 (s, 3H, OCH3); 3.78 (s, 2H,
CH2); 5.13 (s, 2H, NCH2CO); 7.06 (t, 1H, H5 or H6,
J=7.3 Hz); 7.15 (2t, 1H, H5 or H6, J=7.3 Hz); 7.34 (s,
1H, H2); 7.43 (d, 1H, H7, J=7.3 Hz); 7.53 (d, 1H, H4,
J=7.0 Hz); 7.75 (m, 4H, Harom.); 8.89 (br s, 2H, NH2);

V. Grumel et al. / European Journal of Medicinal Chemistry 37 (2002) 45–62
51
8: Eluent: CH2Cl2–MeOH, 95:5; oil; m=4.2 g (87%).
Analysed for C25H28N2O4 (C, H, N).
9: Eluent: CH2Cl2; oil; m=2.12 g (54%). Analysed
for C26H30N2O4 (C, H, N).
10: Eluent: EtOAc–EP, 3:7; oil; m=330 mg (55%).
Analysed for C27H32N2O4 (C, H, N).
mmol) in MeOH or EtOH (2 mL for 1 mmol) was
stirred at r.t. until disappearance of the starting indolic
ester. After evaporation under reduced pressure, water
was added and the mixture was made acidic with 1 M
HCl. The precipitated acid was collected.
5.1.10.2. Method B. Similar to Method A except reflux-
ing of the solvent.
5.1.6.2. Method B: synthesis of deri6ati6es 12, 13. A
suspension of indole-3-carboxaldehyde (11) (1 equiv.),
of halogeno derivative 6 or 7 and K2CO3 (1.5 equiv.) in
MeCN (1 mL for 3 mmol of 11) was refluxed. After
disappearance of 11 the solvent was evaporated and
water was added to the residue. Extraction with EtOAc,
drying over MgSO4 and evaporation leave a solid,
which was chromatographed on a silica gel column.
17: Method A; m=3.50 g (90%); solid, m.p. 168–
170 °C. Analysed for C24H26N2O4 (C, H, N).
18: Method A; m=1.84 g (92%); solid, m.p. 134–
135 °C. Analysed for C25H28N2O4 (C, H, N).
19: Method A; m=2.20 g (80%); solid, m.p. 115–
116 °C. Analysed for C26H30N2O4 (C, H, N).
20: Method B; m=1.1 g (80%); m.p. 65 °C (dec.).
Analysed for C26H28N2O4 (C, H, N).
21: Method B; m=2.68 g (90%); m.p. 85 °C (dec.).
Analysed for C27H30N2O4 (C, H, N).
22: Method B; m=2.50 g, (86%); m.p. 70 °C (dec.).
Analysed for C27H30N2O4 (C, H, N).
12: Time reaction 24 h; eluent: EtOAc–PE 1:1; oil;
m=5.32 g (99%). Analysed for C24H26N2O3 (C, H, N).
13: Time reaction 46 h; eluent: AcOEt–PE, 1:1; oil;
m=4.88 g (93%). Analysed for C25H28N2O3 (C, H, N).
5.1.7. Benzyl 4-(2-{3-[(E)-3-ethoxy-3-oxo-1-propenyl]-
1H-1-indolyl}-ethyl)-1-piperidinecarboxylate (14)
A solution of aldehyde 12 (2.0 g, 5.1 mmol) and
(carbethoxymethylene)triphenylphosphorane (3.93 g,
11.3 mmol) in C6H5CH3 (50 mL) was refluxed 17 h.
Evaporation of the solvent was followed by column
chromatography (eluent: AcOEt–PE, 4:6); oil; m=2.04
g (87%). Analysed for C28H32N2O4 (C, H, N).
5.1.11. General procedure for amidification: compounds
23–30
A solution of b-alanine ethyl ester hydrochloride (1.1
equiv.) in CH2Cl2 (20 mL for 1 mmol) was cooled at
0 °C. DMAP (1.65 equiv.), acids 17–22 (1 equiv.),
EDCI (1.1 equiv.) were added to the mixture and
stirred at r.t. until disappearance of the acid. Water was
added and the organic layer dried over MgSO4 and
evaporated under reduced pressure. The residue was
purified by column chromatography on silica gel.
5.1.8. Benzyl 4-(2-{3-[(E)-3-ethoxy-3-oxo-1-propenyl]-
1H-1-indolyl}-propyl)-1-piperidinecarboxylate (15)
Obtained from 13 using similar conditions as for 14.
Chromatography (eluent: EtOAc–PE, 4:6); oil; m=
3.18 g (97%). Analysed for C29H34N2O4 (C, H, N).
23: Eluent: CH2Cl2–MeOH, 98:2; oil; m=2.0 g
(89%). Analysed for C29H35N3O5 (C, H, N).
24: Eluent: CH2Cl2–MeOH, 97:3, v/v; oil; m=750
mg (88%). Analysed for C30H37N3O5 (C, H, N).
25: Eluent: EtOAc–PE, 7:3; oil; m=2.65 g (92%).
Analysed for C31H39N3O5 (C, H, N).
26: Eluent: EtOAc–PE, 8:2; oil; m=800 mg (86%).
Analysed for C31H37N3O5 (C, H, N).
27: Eluent: EtOAc–PE, 7:3; oil; m=960 mg (79%).
Analysed for C32H39N3O5 (C, H, N).
28: Eluent: EtOAc–PE, 8:2; oil; m=1.65 g (77%).
Analysed for C31H37N3O5 (C, H, N).
29: Eluent: EtOAc–PE, 7:3; oil; m=470 mg (73%).
Analysed for C32H39N3O5 (C, H, N).
30: Eluent: EtOAc–PE, 7:3 ; oil; m=1.90 g (78%).
Analysed for C32H39N3O5 (C, H, N).
5.1.9. Benzyl 4-(2-{3-[(E)-3-ethoxy-2-methyl-3-oxo-1-
propenyl]-1H-1-indolyl}-ethyl)-1-piperidinecarboxylate
(16)
A solution of triethyl-2-phosphonopropanoate (1.9 g,
9.2 mmol) in THF (10 mL) was dropwise added to a
suspension of NaH (202 mg, 8.45 mmol) in THF (30
mL) at 0 °C. After 30 min, a solution of aldehyde 12 (3
g, 7.7 mmol) in THF (20 mL) was dropwise added to
the mixture which was stirred at r.t. for 2 h. Evapora-
tion of the solvent, addition of water and extraction
with EtOAc leave after drying over MgSO4 and evapo-
ration of a residue which was chromatographed on
silica gel column (eluent: EtOAc–PE, 3:7); oil; m=3.32
g (91%). Analysed for C29H34N2O4 (C, H, N).
5.1.10. General procedure of esters hydrolysis:
compounds 17–22
5.1.12. General procedure for debenzylation:
compounds 31–38
5.1.10.1. Method A. A solution of indolic esters 8–10 or
14–16 (1 mmol) and aq. 1 M LiOH (2.5 mL for 1
Compounds 23–30 were dissolved in EtOH or
MeOH (5 mL for 1 mmol) and a catalytic amount of

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V. Grumel et al. / European Journal of Medicinal Chemistry 37 (2002) 45–62
Pd/C 10% (10% in weight) was added. The suspension
was stirred under 1 atm of hydrogen at r.t. until the
disappearance of the starting material (2–12 h). After
filtration the solvent was evaporated and the crude
residue chromatographed on silica gel column.
5.1.17. 3-[({1-[2-(4-Piperidyl)ethyl]-1H-3-indolyl}-
propanoyl)amino]propanoic acid, hydrochloride (42)
White solid; m=335 mg (70%); m.p. 96–98 °C
(chlorhydrate). Analysed for C21H29N3O3, HCl (C, H,
N).
5.1.18. 3-[({1-[2-(4-Piperidyl)propyl]-1H-3-indolyl}-
propanoyl)amino]propanoic acid, hydrochloride (43)
White solid; m=327 mg (80%); m.p. 120–122 °C
(chlorhydrate). Analysed for C22H31N3O3, HCl (C, H,
N).
31: Eluent: CH2Cl2–MeOH–NH4OH 30%, 100:30:3;
oil; m=1.0 g (85%); m.p. 219–221 °C (oxalate).
Analysed for C21H29N3O3 (C, H, N).
32: Eluent: CH2Cl2–MeOH–NH4OH 30%, 100:10:1
then 100:20:2; oil; m=610 mg (90%); m.p. 213–215 °C
(oxalate). Analysed for C22H31N3O3 (C, H, N).
33: Eluent: CH2Cl2–MeOH–NH4OH 30%, 100:20:2;
oil; m=1.73 g (91%); m.p. 208–210 °C (oxalate).
Analysed for C23H33N3O3 (C, H, N).
5.1.19. 3-[(3-{1-[2-(4-Piperidyl)ethyl]-1H-3-indolyl}-
propanoyl)amino]butanoic acid, hydrochloride (44)
White solid; m=374 mg (88%); m.p. 96 °C (dec.)
(chlorhydrate). Analysed for C22H31N3O3; HCl (C, H,
N).
34: Eluent: CH2Cl2–MeOH–NH4OH 30%, 100:20:2;
oil; m=430 mg (65%); m.p. 210–212 °C (oxalate).
Analysed for C23H33N3O5 (C, H, N).
35: Eluent: CH2Cl2–MeOH–NH4OH 30%, 100:20:2;
oil; m=570 mg (88%); m.p. 205–206 °C (oxalate).
Analysed for C24H35N3O5 (C, H, N).
36: Eluent: CH2Cl2–MeOH–NH4OH 30%, 100:20:2;
oil; m=695 mg (80%); m.p. 210–212 °C (oxalate).
Analysed for C23H33N3O3 (C, H, N).
5.1.20. 3-[(3-{1-[2-(4-Piperidyl)propyl]-1H-3-indolyl}-
propanoyl)amino]butanoic acid, hydrochloride (45)
White solid; m=335 mg (76%); m.p. 106 °C (dec.)
(hydrochloride). Analysed for C23H33N3O3, HCl (C, H,
N).
37: Eluent: CH2Cl2–MeOH–NH4OH 30%, 100:20:2;
oil; m=265 mg (87%); m.p. 204–206 °C (oxalate).
Analysed for C24H35N3O3 (C, H, N).
38: Eluent: CH2Cl2–MeOH–NH4OH 30%, 100:20:2;
oil; m=1.22 g (84%); m.p. 212–213 °C (oxalate).
Analysed for C24H35N3O3 (C, H, N).
5.1.21. 3-[(2-Methyl-3-{1-[2-(4-piperidyl)ethyl]-1H-3-
indolyl}propanoyl)amino]propanoic acid, hydrochloride
(46)
White solid; m=300 mg (60%); m.p. 119 °C (dec.)
(chlorhydrate). Analysed for C22H31N3O3, HCl (C, H,
N).
5.1.13. Hydrolysis of esters: compounds 31–38
A solution of esters 31–38 (1.50 mmol) in 3 N HCl (3
mL) was stirred for 7 days at r.t. After addition of Et2O
to the reaction mixture a solid was obtained to afford
acids 39–46 as hydrochloride.
5.1.22. Benzyl 4-[3-(3-{2-[(3-methoxy-2-{[(4-methyl-
phenyl)-sulphonyl]amino}-3-oxopropyl)amino]-2-oxo-
ethyl}-1H-1-indolyl)propyl]-1-piperidinecarboxylate
(48)
Compound 19 (2 g, 4.6 mmol), EDCI (971 mg, 5.06
mmol), HOBt (775 mg, 5.06 mmol), DMAP (928 mg,
3.3 mmol) were added to the aminoacid 47 as hydro-
chloride salt (1.56 g, 5.06 mmol) in CH2Cl2 (100 mL) at
0 °C. After stirring for 24 h at r.t. water was added and
the organic layer was dried over MgSO4. Evaporation
leaves a residue which was chromatographed on a silica
gel column (eluent: EtOAc–PE, 7:3); white solid; m=
2.2 g (70%); m.p. 74–76 °C. [h]D: +20.8° (c 0.5,
CHCl3). Analysed for C37H44N4O7S (C, H, N).
5.1.14. 3-[({1-[2-(4-Piperidyl)ethyl]-1H-3-indolyl}-
methanoyl)amino]propanoic acid, hydrochloride (39)
White solid; m=435 mg (82%); m.p. 132 °C (dec.)
(chlorhydrate). Analysed for C19H25N3O3, HCl (C, H,
N).
5.1.15. 3-[({1-[2-(4-Piperidyl)ethyl]-1H-3-indolyl}-
ethanoyl)amino]propanoic acid, hydrochloride (40)
Yellow solid; m=250 mg (42%); m.p. 120–122 °C
(dec.) (chlorhydrate). Analysed for C20H27N3O3, HCl
(C, H, N).
5.1.23. Methyl 2-{[(4-methylphenyl)sulfonyl]amino}-
3-[(2-{1-[3-(4-piperidinyl)propyl]-1H-3-indolyl}acetyl)-
amino]propanoate (49)
5.1.16. 3-[({1-[2-(4-Piperidyl)propyl]-1H-3-indolyl}-
ethanoyl)amino]propanoic acid, hydrochloride (41)
Yellow solid; m=250 mg (35%); m.p. 80 °C (dec.)
(chlorhydrate). Analysed for C21H29N3O3, HCl (C, H,
N).
Obtained by hydrogenolysis of 48 according to the
general procedure. Chromatography (eluent: CH2Cl2–
MeOH–NH4OH 30%, 100:20:2); white solid; m=800
mg (71%); m.p. 118–120 °C. [h]D: +16.3° (c 0.3,
MeOH). Analysed for C29H38N4O5S (C, H, N).

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5.1.24. tert-Butyl 4-[3-(3-{2-[(3-methoxy-2-{[(4-
methylphenyl)sulfonyl]amino}-3-oxopropyl)amino]-2-
oxo-ethyl}-1H-1-indolyl)propyl]-1-piperidinecarboxylate
(50)
trophotometrically (Chronolog Aggregometer models
490-4D or 560-VS). Aggregation was initiated with
collagen (1 mg mL−1) 5 min after infusion of the
studied compound (or vehicle) and was measured for 15
min. Percent inhibition was calculated from control
aggregation of PRP only containing vehicle. IC50 values
were obtained from the mean-dose–response curve
computed for four pools of PRP in a 1–1000 mM
concentration range.
To a solution of 49 (430 mg, 0.78 mmol) in a mixture
of dioxane–water (8 mL, 1:1) were added Et3N (120
mL, 0.85 mmol, 86 mg) and di-tert-butoxycarbonyle
dicarbonate (211 mg, 0.97 mmol). After stirring for 24
h at r.t., the mixture was evaporated, water was added
and the residue extracted with EtOAc. Drying over
MgSO4 of the organic extracts and evaporation leave a
solid which was chromatographied on silica gel column
(eluent: EtOAc–PE, 7:3); white solid; m=455 mg
(90%); m.p. 92–94 °C. [h]D: +12.5° (c 1.1, CHCl3).
Analysed for C34H49N4O7S (C, H, N).
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