Phenylbutyrates as potent, orally bioavailable vitronectin receptor (integrin αvβ3) antagonists

Article abstract of DOI:10.1016/S0960-894X(03)00102-1

In our continuing efforts to identify small molecule vitronectin receptor antagonists, we have discovered a series of phenylbutyrate derivatives, exemplified by 16, which have good potency and excellent oral bioavailability (approximately 100% in rats). T

Full text of DOI:10.1016/S0960-894X(03)00102-1

Bioorganic & Medicinal Chemistry Letters 13 (2003) 1483–1486
Phenylbutyrates as Potent, Orally Bioavailable Vitronectin
Receptor (Integrin ꢀvꢁ3) Antagonists
William H. Miller,a,* Peter J. Manley,a Russell D. Cousins,a Karl F. Erhard,b
Dirk A. Heerding,a Chet Kwon,a Stephen T. Ross,b James M. Samanen,a
Dennis T. Takata,a Irene N. Uzinskas,a Catherine C. K. Yuan,a
R. Curtis Haltiwanger,b Catherine J. Gress,b Michael W. Lark,b
Shing-Mei Hwang,b Ian E. James,b David J. Rieman,b Robert N. Willette,b
Tian-Li Yue,b Leonard M. Azzarano,b Kevin L. Salyers,b Brian R. Smith,b
b
Keith W. Ward,b KyungO. Johanson and William F. Huffmana
aGlaxoSmithKline Pharmaceuticals, 1250 S. Collegeville Rd., PO Box 5089, Collegeville, PA 19426, USA
bGlaxoSmithKline Pharmaceuticals, 709 Swedeland Road, PO Box 1539, King of Prussia, PA 19406, USA
Received 16 October 2002; accepted 17 December 2002
Abstract—In our continuingefforts to identify small molecule vitronectin receptor antagonists, we have discovered a series of
phenylbutyrate derivatives, exemplified by 16, which have good potency and excellent oral bioavailability (approximately 100% in
rats). This new series is derived conceptually from openingof the seven-membered ringof SB-265123.
# 2003 Elsevier Science Ltd. All rights reserved.
Integrin avb3, also referred to as the vitronectin recep-
tor, is a member of the integrin family of heterodimeric
transmembrane glycoprotein complexes that function in
cellular adhesion events and signal transduction pro-
cesses.1 Integrin avb3 is expressed on a variety of cell
types, includingosteoclasts, vascular smooth muscle
cells, and endothelial cells, and is known to mediate
several biologically-relevant processes, including adhe-
sion of osteoclasts to the bone matrix, migration of
vascular smooth muscle cells, and angiogenesis. As a
result, antagonists of integrin avb3 are expected to have
utility in the treatment of several human diseases,
includingosteoporosis, restenosis followingpercuta-
neous transluminal coronary angioplasty (PTCA),
rheumatoid arthritis, cancer, diabetic retinopathy, and
macular degeneration.
the discovery of SB-265123,2 a potent vitronectin
receptor antagonist with very good pharmacokinetics in
rats, includingoral bioavailability of approximately
100%.3 In followingup on this lead, we envisioned
openingthe seven-membered ringto afford a 4-phenyl-
butyrate derivative. This modification would allow us to
determine if the conformational constraint provided by
the seven-membered ringin SB-265123 is required for
potent biological activity. In addition, if 4-phenylbuty-
rates were found to be potent vitronectin receptor
antagonists with good pharmacokinetic properties, they
would be structurally simpler leads that might be more
readily amenable to rapid and thorough investigation.
In this communication, we report the results of our
preliminary studies in this area.
The phenylbutyrate derivatives 7–10 (Table 1) were pre-
pared as described in Scheme 1. Reaction of 2-(4-
methoxyphenyl)-1-phenylethanone (1)4 with the enolate of
ethyl acetate gave the b-hydroxyester 2, which on treat-
ment with Et3SiH and boron trifluoride etherate5 gave a
mixture of 3 and the corresponding a,b-unsaturated ester
(from dehydration of 2). This mixture was hydrogenated
to afford pure 3. Methyl ether deprotection with etha-
The identification of small molecule vitronectin receptor
antagonists is a vigorous area of research, and a wide
variety of potent antagonists have been identified.1 In a
previous report from these laboratories, we described
*Correspondingauthor. Tel.: +1-610-917-7937; fax:+1-610-917-
4206; e-mail: william_h_ miller@gsk.com
0960-894X/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0960-894X(03)00102-1

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W. H. Miller et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1483–1486
Table 1. In vitro activity and rat pharmacokinetics of phenylbutyrate-based vitronectin receptor antagonists
Entry
Compd
avb3 Ki (nM)
4ꢁ1
avb3/HEK IC50 (nM)
T1/2 (min)
Clp (mL/min/kg)
Oral F (%)
SB-265123
60
181–378
3ꢁ1
ꢂ100
7
32ꢁ6
170ꢁ36
12ꢁ3
500
—
—
—
—
—
8
—
—
9
470
330
30
144ꢁ27
310ꢁ167
95ꢁ8
7.2ꢁ0.9
4.9ꢁ1.3
6.0ꢁ1.7
ꢂ100
ꢂ100
ꢂ100
10
16
7ꢁ2
2.5ꢁ0.6
6
nethiol and AlCl3 gave 4, which was resolved by chiral
HPLC7 to give 5 and 6. The absolute configuration of
the phenols was determined by X-ray crystallographic
analysis of the (4-bromophenyl)urethane derivative of
the (S)-phenol 6.8 Compounds 7 and 8 were prepared
from 4 and 5, respectively, accordingto established
methods.2 For the synthesis of 9, the (S)-phenylbutyrate
phenol 6 was treated with 2-[N-(3-methanesulfonyloxy-1
- propyl) - N - (tert - butoxycarbonyl)amino]pyridine - N -
oxide9 in the presence of sodium hydride. Acidic
removal of the Boc group, reduction of the N-oxide,
and saponification gave 9. Compound 10 was prepared
10
from 6 accordingto established methods.
The preparation of phenylbutyrate 16 is shown in
Scheme 2. 2-Methyl-[1,8]naphthyridine (11)11 was selec-
tively hydrogenated12 to afford the tetrahydronaphthy-
ridine 12, which was then protected as its tert-butyl
carbamate (13). Deprotonation of 13 with LDA at 0 ꢀC
.
Scheme 1. (a) EtOAc/LiN(TMS)2, THF (96%); (b) Et3SiH, BF3 OEt2,
CH2Cl2; (c) H2, 10% Pd/C, EtOH (91% for two steps); (d) EtSH,
AlCl3, CH2Cl2 (96%); (e) chiral HPLC; (f) 2-[(3-hydroxy-1-propyl)-
amino]pyridine-N-oxide, DIAD, (Ph)3P, DMF (68% for 7; 51% for
8); (g) cyclohexene, 10% Pd/C, 2-propanol (77% for 7; 87% for 8;
43% for 9;); (h) 1.0 N LiOH, THF, H2O, then acidification (74% for 7;
43% for 8; 43% for 9; 41% for 10); (i) 2-[N-(3-methanesulfonyloxy-1-
propyl)-N-(tert-butoxycarbonyl)amino]pyridine-N-oxide, NaH, DMSO
(38%); (j) TFA, CH2Cl2 (quantitative); (k) 6-(methylamino)-2-pyr-
idylethanol, DIAD, (Ph)3P, DMF (93%).
Scheme 2. (a) H2, 10% Pd/C, EtOH (99%); (b) LiHMDS, (Boc)2O,
THF (83%); (c) LDA, (EtO)2C¼O, THF, 0 ꢀC (100%); (d) LiBH4,
THF, reflux; (e) 4 N HCl/dioxane, CH2Cl2, then 1.0 N NaOH; (f)
HCO2H, Et2O; (g) 1.0 N NaOH (48% for four steps); (h) compound 6,
DIAD, (Ph)3P, THF (71%); (i) 1.0 N LiOH, THF, H2O, then acid-
ification (74%).

W. H. Miller et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1483–1486
1485
in the presence of diethyl carbonate gave ester 14 in
quantitative yield. Reduction and deprotection gave
crude 15, which was conveniently purified by crystal-
lization of the formate salt. Couplingof 15 with 6 fol-
lowed by saponification gave 16.
hydro[1,8]naphthyridine guanidine mimetic,12b has
much improved affinity for avb3, both in the isolated
receptor assay (Ki=2.5 nM) as well as in the cell adhe-
sion assay (IC50=30 nM). Compound 16 is also a
potent antagonist of integrin avb5 (Ki=2.5 nM), but
has good selectivity against integrin aIIbb3 (Ki=36,000
nM). The increased activity of 16 against avb3 may be
related to the increased lipophilicity of the 5,6,7,8-tet-
rahydro[1,8]naphthyridine guanidine mimetic,12b which
might allow for a more favorable interaction with the
receptor. In addition, the conformational restriction
imposed by the piperidine ring, which causes the ami-
dine-like nitrogens of 16 to be more exposed than in
aminopyridines 9 and 10, may also contribute to the
increased activity. Significantly, 16 has very good phar-
macokinetic properties in rats, with a half life of 1.5 h,
clearance of 6.0 mL/min/kg, and very high oral bio-
availability (approximately 100%).
The phenylbutyrate derivatives prepared as described
above were evaluated in our standard integrin binding
assays (Table 1).13ꢃ15 In the interest of synthetic effi-
ciency, we first prepared the racemic phenylbutyrate
derivative 7. In the avb3 bindingassay, 13 7 (Ki=32 nM)
is 8-fold less potent than SB-265123 (Ki=4 nM). In
accord with this level of affinity for the isolated recep-
tor, 7 is a moderate inhibitor (IC50=500 nM) in the
avb3/HEK cell adhesion assay,14 which measures affi-
nity for avb3 in a cellular context. Compound 7 is a
potent antagonist of the related vitronectin receptor
avb5 (Ki=6 nM),13 but selectivity against integrin
aIIbb3 is very g ood (Ki >10,000 nM).15 This selectivity
profile is very similar to that of SB-265123, which has
avb5 Ki=2.6 nM and aIIbb3 Ki=9000 nM.2
The combined results for 16 demonstrate that phe-
nylbutyrate derivatives can be potent vitronectin recep-
tor (avb3 and avb5) antagonists with excellent
pharmacokinetics. In fact, the overall profile of phe-
nylbutyrate 16 is very similar to that of SB-265123. In
further biological testing, phenylbutyrate 16 was found
to be a potent inhibitor of human vascular smooth
muscle cell migration (IC50=26 nM),18 suggesting that
this compound may have utility in the treatment of
restenosis followingPTCA.
Consideringthe encouragingoverall activity and selec-
tivity of 1, we prepared the pure enantiomers 8 and 9. In
accord with previous observations,2,10 the (S)-enantio-
mer 9 is more active than the (R)-enantiomer 8. In the
avb3 bindingassay, 9 (Ki=12 nM) is approximately
3-fold less potent than SB-265123 (Ki=4 nM). How-
ever, despite this relatively good affinity for isolated
avb3, 9 has IC50=470 nM in the avb3/HEK assay,
which is approximately 8-fold less potent than SB-
265123 (IC50=60 nM). These results suggest that the
conformational constraint provided by the seven-mem-
bered ringin SB-265123 contributes singificantly to
potency against cellular avb3. In pharmacokinetic stud-
ies16 in rats, phenylbutyrate 9 has a half life of 2.4 h,
clearance of 7.2 mL/min/kg, and very high oral bio-
availability (approximately 100%). This pharmaco-
kinetic profile is very similar to that of SB-265123,2,3
and shows that the seven-membered ringis not required
for good pharmacokinetic properties.
In conclusion, we have described a new series of potent,
orally bioavailable, nonpeptide vitronectin receptor
(avb3 and avb5) antagonists based on a phenylbutyrate
template, which is derived conceptually from openingof
the seven-membered ringof SB-265123. A representa-
tive of this series, compound 16, has very good affinity
for avb3 and avb5, good selectivity against aIIbb3, and
excellent pharmacokinetics in rats, with oral bioavail-
ability of approximately 100%. Furthermore, com-
pound 16 is a potent inhibitor of vascular smooth
muscle cell migration in vitro, suggesting that this
compound may have utility in the treatment of rest-
enosis followingPTCA. The results of further investi-
gations in this new series, including further lead
optimization studies as well as additional biological
characterization of selected derivatives, will be reported
in due course.
The combined results of biological and pharmacokinetic
evaluation indicate that phenylbutyrate 9 is a promising
new lead, with moderate potency and excellent phar-
macokinetics, includingvery high oral bioavailability.
Our next objective was to determine if potency in this
series could be improved without significantly compro-
misingthe pharmacokinetic profile. Therefore, we initi-
ated a brief investigation towards this end, focused
primarily on the guanidine mimetic.
References and Notes
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Holzemann, G. Idrugs 2001, 4, 72. (c) Miller, W. H.; Keenan,
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One of these derivatives, 10, which contains the
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half life of 5.2 h, clearance of 4.9 mL/min/kg, and very
high oral bioavailability (approximately 100%). The
other derivative, 16, which contains the 5,6,7,8-tetra-

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