Non-peptidic αvβ3 antagonists containing indol-1-yl propionic acids

Article abstract of DOI:10.1016/j.bmcl.2005.01.028

We describe the synthesis and structure/activity relationship of RGD mimetics that are potent inhibitors of the integrin α_vβ ₃. Indol-1-yl propionic acids containing a variety of basic moieties at the 5-position, as well as substitutions alpha and beta to the carboxy terminus were synthesized and evaluated. Novel compounds with improved potency have been identified.

Full text of DOI:10.1016/j.bmcl.2005.01.028

Bioorganic & Medicinal Chemistry Letters 15 (2005) 2679–2684
Non-peptidic avb3 antagonists containing indol-1-yl propionic acids
Kristi Leonard, Wenxi Pan, Beth Anaclerio, Joan M. Gushue, Zihong Guo,
Renee L. DesJarlais, Marge A. Chaikin, Jennifer Lattanze, Carl Crysler,
Carl L. Manthey, Bruce E. Tomczuk and Juan Jose Marugan*
Johnson & Johnson, Pharmaceutical Research and Development, L.L.C., 665, Stockton Drive, Exton, PA 19341, USA
Received 8 November 2004; revised 11 January 2005; accepted 13 January 2005
Available online 12 April 2005
Abstract—We describe the synthesis and structure/activity relationship of RGD mimetics that are potent inhibitors of the integrin
avb3. Indol-1-yl propionic acids containing a variety of basic moieties at the 5-position, as well as substitutions alpha and beta to the
carboxy terminus were synthesized and evaluated. Novel compounds with improved potency have been identified.
Ó 2005 Elsevier Ltd. All rights reserved.
The integrin family is a group of heterodimeric trans-
membrane glycoproteins that are involved in cell
adhesion, signal transduction, and migration.1 The
vitronectin receptor, avb3 is a member of the integrin
family and is predominantly involved in adhesion of
osteoclasts to bone matrix, migration of vascular
smooth muscle cells and angiogenesis of proliferating
endothelium.2 Therefore, inhibitors of avb3 are thought
to be useful in the treatment of many diseases including
osteoporosis, restenosis, cancer, and ocular disease.3
study around this series. To this end, we explored
replacing the basic moieties at the N-terminus, substitut-
ing at positions alpha and beta to the carboxylic acid
terminus and replacing the linker region between the
termini (Fig. 2).
The synthetic routes to various indol-1-yl propionic acid
analogues are outlined in Schemes 1–6. Several different
basic endings were prepared by the procedures outlined
in Scheme 1. Commercially available 2-aminopyridine
was protected with tert-butylchloride and treated with
LDA and DMF, followed by deprotection to give alde-
hyde 2. This was then treated with acetone and base to
give 2-methyl-[1,8]naphthyridine 3, which was hydroge-
nated and subsequently protected with Boc2O to give
4a.5 Alternatively, commercially available 6-methyl-2-
nitropyridin-3-ol was reduced by hydrogenation and
then treated with chloro-acetyl chloride to give lactam
5,6 which was reduced with lithium aluminum hydride,
followed by protection of the amine with Boc2O to give
4b. Compounds 4 were then treated with base and
diethyl carbonate to give the esters 6a,b. Treatment of
ester 6a with selenium dioxide, followed by treatment
We have recently reported an original series of N-substi-
tuted indoles such as compound 1 (Fig. 1) that possess a
number of favorable characteristics including good oral
bioavailability.4 In view of these promising preliminary
results, we maintained the indole scaffold of our first-
generation inhibitor, which provided a good PK profile,
and further explored a structure/activity relationship
H
N
N
O
N
1
OH
linker
basic
O
ending
N
Figure 1. First-generation inhibitor of avb3.
R1
R2
OH
O
Keywords: Integrins; RGD mimetic; avb3 antagonists.
Corresponding author. Tel.: +1 610 458 5264; fax: +1 610 458
8249; e-mail: jmarugal@prdus.jnj.com
*
Figure 2. Second-generation inhibitors of avb3.
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.01.028

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K. Leonard et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2679–2684
N
NH2
H
N
NH2
N
N
d
a,b,c
O
3
2
e,f
N
Boc
N
H
N
O
N
O2N
HO
N
g, h
i, j
O
X
5
4a X=CH2
4b X=O
k
H
N
o
Boc
N
R
R
N
OH
N
OEt
O
O
X
8
6a X=CH2, R=H
6b X=O, R=H
l, m
7a X=CH2, R=F
n
Boc
N
R
R
N
OH
X
9a X=CH2, R=H
9b X=O, R=H
9c X=CH2, R=F
Scheme 1. Reagents and conditions: (a) tert-butylchloride, DIEA, DCM, 67%; (b) LDA, DMF, 95%; (c) 3 N HCl, H2O, 52%; (d) L-proline, acetone,
99%; (e) H2, Pd/C, EtOH, 74%; (f) Boc2O, NaH, THF, 50%; (g) H2, Pd/C, EtOAc, 99%; (h) NaHCO3, 2-butanone, H2O, ClCOCH2Cl, 79%; (i) LAH,
THF, rt, 3 h, 99%; (j) Boc2O, neat, 60 °C, 80%; (k) LDA, (EtO)2CO, THF, 0 °C, 49–75%; (l) selenium dioxide, dioxane, rt, 24 h, 81%; (m) DAST,
DCM, À78 °C, 1 h, 40%; (n) LiBH4, THF, À78 °C, 3 h, 25–94%; (o) (a) NaOH, MeOH, (b) TFA, DCM, 99%.
with DAST yielded the difluoro derivative 7a.7 Alterna-
tively, 6a was saponified with sodium hydroxide fol-
lowed by Boc deprotection with TFA to give
compound 8. Esters 6a,b and 7a were reduced in the
presence of lithium borohydride to give alcohols 9a–c.
with ethyl phenylpropiolate and TBAF, followed by
hydrogenation gave the corresponding alcohol, which
was coupled with N-hydroxyphthalimide in a Mitsun-
obu reaction and then deprotected with methylamine
to give the O-amino derivative 38. This amine was trea-
ted with 2-(3,5-dimethylpyrazolyl)-4,5-dihydroimidazole
hydrobromide and then saponified with LiOH to give
39.
Indoles 13–35 were synthesized from the coupling of
commercially available 3-methyl-4-nitrophenol and
alcohols 9a–c in a Mitsunobu reaction to give nitrophe-
nol esters 10a–c, as depicted in Scheme 2. Subsequent
treatment with N,N-dimethylformamide dimethyl acetal
and pyrrolidine followed by hydrogenation afforded
intermediates 11a–c.8 Michael addition with substituted
aryl ethyl propiolates and cesium fluoride gave ethyl
acrylates 12a–c, which were reduced by hydrogenation,
followed by deprotection of the Boc group with
copper(I) triflate. Finally, the target compounds 13–35
were obtained by the saponification of the correspond-
ing esters 12a–c.
The synthesis of compounds with substitution on the
propionic acid are shown in Scheme 4. Commercially
available 5-benzyloxy-1H-indole was alkylated with 3-
bromopropionic acid ethyl ester followed by treatment
with lithium diisopropylamide and the corresponding
substituted bromide, followed by hydrogenation to give
the corresponding 5-hydroxyindoles 42a–d. Compound
42a–d was coupled with 3-(2-pyridylamino)-propan-1-
ol in a Mitsunobu reaction, followed by saponification
with lithium hydroxide to give the target compounds
45–48. Alternatively, 5-benzyloxy-1H-indole was cou-
pled with either meta- or para-bromobenzoic acid ethyl
ester in the presence of a palladium catalyst9 followed
by hydrogenation to give hydroxyindoles 41a,b. The
Mitsunobu coupling reaction with 3-(2-pyridylamino)-
propan-1-ol followed by subsequent saponification with
sodium hydroxide afforded the target compounds 43
and 44.
A second approach that lead to the synthesis of the O-
guanidine basic endings is shown in Scheme 3. Commer-
cially available 3-methyl-4-nitrophenol and 2-benzyl-
oxyethanol were coupled in a Mitsunobu reaction to
give 36, followed by treatment with N,N-dimethylform-
amide dimethyl acetal and pyrrolidine, followed by
selective hydrogenation to give 37. Michael addition

K. Leonard et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2679–2684
2681
Boc
N
Boc
N
R
R
R R
N
OH HO
+
N
O
a
NO2
X
X
NO2
10a X=O, R=H
10b X=CH2, R=F
10c X=CH2, R=H
9a-c
b, c
Boc
N
R
R
O
Boc
N
R1
R
R
N
O
N
O
OEt
O
N
X
d
OEt
N
X
R1
H
11a X=O, R=H
11b X=CH2, R=F
11c X=CH2, R=H
12a X=O, R=H, R1=5-benzo[1,3]dioxole
12b X=CH2, R=F, R1=3-pyridyl
12c X=CH2, R=H, R1= see table 4
e, f, g
R
R
H
N
N
O
O
N
X
OH
R1
13 X=O, R=H, R1=5-benzo[1,3]dioxole
14 X=CH2, R=F, R1=3-pyridyl
15-35 X=CH2, R=H, R1= see table 4
Scheme 2. Reagents and conditions: (a) PPh3, DIAD, THF, 60–88%; (b) N,N-dimethylformamide dimethyl acetal, pyrrolidine, DMF, 16 h, 120 °C;
(c) EtOAc, MeOH, H2, Pd/C, 27–54% (2 steps); (d) CsF, DMF, 60 °C, 4 h, 40–80%; (e) EtOAc, MeOH, H2, Pd/C, 70–80%; (f) Cu(OTf), 10% DMF/
toluene, 80–90%; (g) LiOH, 70% MeOH/H2O, 40–80%.
HO
BnO
a
Bn
O
O
O
+
NO2
Bn
OH
N
H
NO2
36
c, d, b
HO
a, b
b, c
H2N
O
O
HO
d, e, f, g
O
Bn
O
O
R
N
O
N
OEt
N
38
h,i
O
OEt
N
H
42a R=H
37
OEt
41a meta
41b para
42b R=CH3
42c R=C3H7
42d R=benzyl
e, f
H
H
N
e, f
O
H
N
O
N
N
O
O
O
H
N
O
R
N
N
N
N
OH
45 R=H
39
OH
46 R=CH3
N
O
47 R=C3H7
43 meta
44 para
48 R=benzyl
OH
Scheme 3. Reagents and conditions: (a) PPh3, DIAD, THF, rt, 75%;
(b) N,N-dimethylformamide dimethyl acetal, pyrrolidine, DMF,
120 °C, 16 h; (c) EtOAc, MeOH, H2, Pd/C, 22%; (d) ethyl phenylpro-
piolate, TBAF, 70 °C, 16 h, 69%; (e) EtOAc, MeOH, H2, Pd/C, 80%;
(f) N-hydroxyphthalimide, PPh3, DIAD, THF, 96%; (g) methylamine,
rt, 16 h, 73%; (h) 2-(3,5-dimethylpyrazolyl)-4,5-dihydroimidazole
hydrobromide, MeOH, 5 days, 99%; (i) LiOH, 70% MeOH/H2O, rt,
16 h; 74–80%.
Scheme 4. Reagents and conditions: (a) P(t-Bu)3, Cs2CO3, m- or p-Br–
C6H4CO2Et, Pd2(dba)3, toluene, 16–30%; (b) H2, Pd/C, MeOH, 98%;
(c) (i) NaH, DMF, rt; (ii) 3-bromopropionic acid ethyl ester, reflux,
71%; (d) LDA, THF, RBr, À78 °C, 50–90%; (e) n-Bu3P, ADDP,
3-(pyridin-2-ylamino)-propan-1-ol, THF, rt, 15–54%; (f) (i) NaOH,
MeOH (ii) HCl, 70–85%.
The synthesis of molecules with a modified linker region
between the basic ending and the indole core are shown
in Schemes 5 and 6. Commercially available 5-bromoin-
dole was coupled to 3-cyanopropylzinc bromide in the
presence of a palladium catalyst to give the correspond-
ing cyano derivative, which was protected with TIPS-Cl
in the presence of base to give 50. Compound 50 was
reacted with methyl magnesium bromide followed by
treatment with 2-amino-benzaldehyde and L-proline to
give compound 51. Alkylation with 3-bromohexanoic

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K. Leonard et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2679–2684
N
Br
N
N
c, d
a, b
N
N
H
N
Si
Si
51
50
e
H
N
N
N
N
f, g
O
O
N
N
OH
OEt
53
52
Scheme 5. Reagents and conditions: (a) PdCl2(dppf)2, 3-cyanopropylzinc bromide [0.5 M THF], THF, 18 h, 93%; (b) LHMDS, TIPSCl, THF,
À78 °C to rt, 4 h, 99%; (c) CH3MgBr, THF, À78 °C to rt, 18 h, 95%; (d) 2-amino-benzaldehyde, L-proline, EtOH, 57%; (e) (i) THF, TBAF, rt;
(ii) THF, NaH, rt; (iii) 3-bromohexanoic acid ethyl ester, 17%; (f) H2, Pd/C, MeOH, 80%; (g) LiOH, THF, MeOH, 50 °C, 24 h, 65%.
O2N
a
H2N
O2N
c
b
N
N
N
H
CO2Et
CO2Et
C3H7
C3H7
54
55
H
N
H
N
H
N
H
N
N
N
d
O
N
O
CO2Et
N
CO2H
C3H7
57
56
C3H7
Scheme 6. Reagents and conditions: (a) (i) NaH, DMF, rt; (ii) 3-bromo-hexanoic acid ethyl ester, 34%; (b) H2, 10% Pd/C, MeOH, 78%; (c) 8, BOP,
DIEA, DMF, rt, 67%; (d) (i) NaOH, MeOH (ii) HCl, 81%.
acid ethyl ester gave 52, which was reduced with hydro-
genation and saponified with lithium hydroxide to give
53 (Scheme 5).
This increase in potency is due to the increased rigidity
obtained by placing a phenyl ring in the linker region be-
tween the basic ending and the indole scaffold.12 A fur-
ther 6-fold increase in potency can be obtained with the
THN compound 15, which has a piperidine ring that
fixes the position of the hydrogen in the methylamine
of compound 1 by incorporating it into a ring. This cyc-
lic structure is also more lipophilic.3c Modification of the
THN basic ending with difluoromethylene (14) led to a
decrease in activity due to an unfavorable change in
the pKa of the pyridyl nitrogen. Placing an oxygen in
the THN cyclic structure (13) does not negatively effect
the pKa of the pyridyl nitrogen, but there is an unfavor-
able contact with a carbonyl of a protein residue in this
region, which lowers the potency.11 Finally, the O-ami-
dine derivative 39 exhibited lower potency, similar to
45, possibly due to the increased flexibility of the guan-
idine mimetic.
The synthesis of the amide linker derivative is shown in
Scheme 6. Commercially available 5-nitroindole was
alkylated with 3-bromohexanoic acid ethyl ester to give
nitroindole 54, which was reduced by hydrogenation to
give aminoindole 55. This was coupled with 8 using BOP
and DIEA to give amide 56, which was saponified with
sodium hydroxide to give 57.
Compounds described above were evaluated in a stan-
dard integrin binding assay,4 and the results are outlined
in Tables 1–4.
The crystal structure of avb3 has recently been re-
ported10 and we were able to build a model of this series
of compounds, which explains the SAR observed.11 It
has previously been reported that compounds contain-
ing a tetrahydronaphthyridine (THN) moiety have been
potent avb3 inhibitors and that this basic ending has im-
proved pharmacokinetic properties.5 We attempted to
replace the existing methylaminopyridine of our
first-generation compound with several different basic
endings, including the THN, to increase potency and
improve pharmacokinetic properties. Compounds with
various basic ending groups are shown in Table 1. The
replacement of a pyridylamino group (45) for a methyl-
aminopyridine (1) led to a 13-fold increase in potency.
It is well known that many scaffolds can be used as pep-
tidomimetic inhibitors of avb3,12 since the glycine of
RGD and the peptide backbone do not make any inter-
actions with the protein.10 The importance of the scaf-
fold appears to be the ability to present the aspartate
and guanidine mimetics in the correct orientation for
recognition by avb3 and to modulate the PK profile of
the avb3 antagonist. We have found, however, that sub-
tle changes in the linker region have profound effect on
the activity (Table 2). Substitution of an oxygen (16) for
a carbon (53) led to a greater than 4-fold decrease in

K. Leonard et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2679–2684
2683
Table 1. Antagonists with modification of the N-terminus basic
moiety
Table 3. Antagonists with propionic acid substitutions
H
N
N
O
Y
O
O
N
R
N
OH
R
Compd
R
IC50 (nM) avb3
Compd
Y; R
IC50
(nM) avb3
OH
OH
45
470
460
H
N
O
N
45
; H
470
46
47
H
N
O
N
N
N
N
N
N
N
1
; H
; H
; Ph
36
6
C3H7
OH
OH
2000
H
N
O
15
17
30
21
14
Ph
H
N
48
43
44
1900
>20,000
>20,000
1
O
O
H
N
; 3-pyridyl
0.25
0.38
130
OH
OH
H
N
; 5-benzo-[1,3]dioxole
; 3-pyridyl
O
F
F
H
N
to the ethoxy linker, there is an unfavorable interaction
of the amide carbonyl with a tyrosine residue in this
region, which significantly decreases its activity.
H
N
13
39
; 5-benzo-[1,3]dioxole
; Ph
8
O
H
N
H
N
Compounds with substituents alpha to the carboxylic
acid as well as compounds replacing the propionic acid
with more rigid groups are shown in Table 3. A small
substitution at the alpha position, such as replacement
of a hydrogen (45) with a methyl (46) was tolerated,
but larger substitutions such as n-propyl (47) and benzyl
(48) led to a loss of activity. Also, replacing the prop-
ionic acid of compound 45 with more rigid groups such
meta and para benzoic acids 43 and 44 led to the com-
plete loss of activity.
200
O
N
Table 2. Antagonists with varying linkers
H
X
N
N
O
N
OH
linker
Although we were unable to significantly affect the po-
tency of these molecules by substitutioning alpha to
the carboxy terminus or by replacing the propionic acid
with other acid derivatives, compounds with substitu-
tion beta to the carboxy terminus did show a significant
increase in potency, as shown in Table 4. Substitutions
beta to the carboxylic acid have been described by other
groups13 and our results indicate that various betasub-
stituents can have a significant impact on potency. Sub-
stituents that were particularly potent were the
substituted 3-pyridyl compounds such as 28, 30, 34,
and 35, whereas bulky substituents such as 26 and 27
significantly reduced potency.
Compd
X
IC50 (nM) avb3
O
16
53
5
23
H
N
57
78
O
activity. It is theorized11 that the oxygen and carbon
prefer different conformations and the ethoxy linker is
able to place the basic ending in the correct orientation
for interaction with the protein aspartic acid while main-
taining a low energy conformation. Although the amide
linker (57) can adopt a similar low energy conformation
In conclusion, several compounds were identified with
superior activity to our first-generation compound 1.
We were able to maintain the indole scaffold and signif-
icantly increase potency by replacing the methylamino-

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K. Leonard et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2679–2684
Table 4. Antagonists with substitution beta to the carboxy terminus
pyridine basic ending with the THN moiety, as well as
making substitutions beta to the carboxy terminus. Sev-
eral of these indol-1-yl propionic acids were of interest
to our group. In particular, compound 21, which was
dosed orally and intravenously to mice to give a half-life
of 1.5 h, an F value of 73% and clearance of 13 mL/min/
kg.
H
N
O
N
O
N
OH
R
Compd
R
H
IC50 (nM) avb3
15
16
6.0
3.0
References and notes
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17
1.0
O
18
1.1
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Acad. Sci. 1996, 93, 9764.
O
O
19
20
0.8
0.7
O
21
0.38
O
Cl
´
4. Marugan, J. J.; Manthey, C.; Anaclerio, B.; Lafrance, L.;
22
23
55
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0.5
24
25
0.7
37
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F
26
27
40
37
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NC
28
29
0.26
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N
N
30
31
32
0.25
0.9
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N
N
O
0.38
N
O
S
33
0.46
N
N
34
35
0.3
S
O
O
O
0.25
N