Discovery of potent imidazole and cyanophenyl containing farnesyltransferase inhibitors with improved oral bioavailability

Article abstract of DOI:10.1016/S0960-894X(03)00195-1

A pyridyl moiety was introduced into a previously developed series of farnesyltransferase inhibitors containing imidazole and cyanophenyl (such as 4), resulting in potent inhibitors with improved pharmacokinetics.

Full text of DOI:10.1016/S0960-894X(03)00195-1

Bioorganic & Medicinal Chemistry Letters 13 (2003) 1571–1574
Discovery of Potent Imidazole and Cyanophenyl Containing
Farnesyltransferase Inhibitors with Improved Oral Bioavailability
Yunsong Tong,* Nan-Horng Lin, Le Wang, Lisa Hasvold, Weibo Wang,
Nicholas Leonard, Tongmei Li, Qun Li, Jerry Cohen, Wen-Zhen Gu, Haiying Zhang,
Vincent Stoll, Joy Bauch, Kennan Marsh, Saul H. Rosenberg and Hing L. Sham
R47B, AP10, Global Pharmaceutical R&D, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, IL 60064-6101, USA
Received 21 November 2002; accepted 4 February 2003
Abstract—A pyridyl moiety was introduced into a previously developed series of farnesyltransferase inhibitors containing imidazole
and cyanophenyl (such as 4), resulting in potent inhibitors with improved pharmacokinetics.
# 2003 Elsevier Science Ltd. All rights reserved.
Ras proteins play an important role in cell growth and
oncogenesis.1 The first step of Ras processing requires
transferring a 15-carbon farnesyl group to the C terminal
of the protein substrate and is catalyzed by farnesyl-
transferase (FTase).2 Inhibitors of FTase prevent the
key step in the post-translational processing of the Ras
protein. They were developed initially as therapeutic
agents to inhibit cell signaling in Ras-transformed cells
and thus control the oncogenic Ras activity.3 Even
though it is still debatable whether FTase inhibitors
(FTIs) function via Ras blocking,4 many FTIs show
activity in a wide range of preclinical models as well as
efficacy in some early clinical trials.5 Geranylgeranyl-
transferase-I (GGTase-I), which is closely related to
FTase, transfers a 20-carbon group to the C terminal of
Ras protein. A recent observation demonstrated that an
optimal FTI should be selective for FTase over GGTase
to achieve lower toxicity.6
During the early studies in search of FTIs, we and oth-
ers7 found molecules with imidazole and cyanophenyl
moieties, such as 1, to be potent against FTase. Inser-
tion of nitrogen into the ring system of 1 resulted in
compounds 2 and 3 (Table 1) with improved cellular
Ras processing (RP) activity as well as acceptable phar-
macokinetics (PK).8 We also found that elimination of
the fused rings from molecules like 1, along with addi-
tion of an aromatic ring at the lower cyanophenyl moi-
ety, led to another series of potent and more selective
FTIs represented by 4 (Table 1).8 However, compound
4 possesses relatively low oral bioavailability. In an
effort to optimize 4, we developed molecules containing
an additional ring nitrogen (general structure 5), result-
ing in FTIs with better PK profiles while maintaining
high potency and selectivity.
The chemistry of the nitrogen insertion into the lower
cyanophenyl moiety is shown in Scheme 1. 1-Methyl-2-
triethylsilylimidazole9 was treated with t-BuLi followed
by 4-cyanobenzaldehyde to give the key racemic inter-
mediate 6. The ether formation was achieved by the
reaction of 6 with various benzyl bromides using Ag2O.
Alternatively, it could be carried out by the coupling of
6 and alcohol 9 using TsOH. The final compounds for
the SAR study were synthesized with either direct ami-
nations or Suzuki coupling reactions.
The syntheses of the three key intermediates, 9, 12, and
15, are outlined in Scheme 2. Pyridinone 7 was bromi-
nated, then coupled with 3-chlorophenylboronic acid to
afford 8. Sequential treatment of 8 with POCl3 followed
by benzylic bromination and hydrolysis gave compound
*Corresponding author. Tel.: +1-847-935-1252; fax: +1-847-935-
5165; e-mail: yunsong.tong@abbott.com
0960-894X/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0960-894X(03)00195-1

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Y. Tong et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1571–1574
Table 1. Activity and PK comparison of compounds 1–4
Compd
FTase
a
GGTase-I
b
RP
EC50
(nM)
Dog
PKd
F
(%)e
Monkey
PKd F
(%)e
c
IC50
(nM)
IC50
(nM)
1
2
3
4
0.20
2.0
0.43
0.62
18
103
24
110
3.7
6.0
1.2
29
53
56
35
65
92
48
2.3
3900
aCompound concentration needed to cause 50% inhibition of transfer
of [3H]FPP to biotin K-ras peptide (KKSKTKCVIM) catalyzed by
bovine FTase.
bCompound concentration needed to cause 50% inhibition of transfer
of [3H]FPP to biotin K-ras peptide (KKSKTKCVLL) catalyzed by
bovine GGTase-I.
cCompound concentration needed to reduce 50% of farnesylation in
NIH-3T3 H-ras cell line.
d5 mg/kg single dose.
eOral bioavailability.
Scheme 2. Reagents and conditions: (i) NBS, dichloroethane, reflux,
92%; (ii) 3-chlorophenylboronic acid, Pd(PPh3)4, 2 N Na2CO3, LiCl,
toluene, EtOH, 100 ꢀC, 73%; (iii) POCl3, 85 ꢀC, 90%; (iv) NBS, CCl4,
AIBN, reflux; (v) Celite1
, 1,4-dioxane, H2O, reflux; 20%; (vi)
mCPBA, CH2Cl2, rt, 47%; (vii) dimethylcarbamyl chloride, TMSCN,
dichloroethane, reflux, 31%; (viii) 3-chlorophenylboronic acid,
Pd(PPh3)4, Na2CO3, toluene, EtOH, H2O, reflux, 80%; (ix) NaCN,
DMSO, 110 ꢀC, 90%.
Scheme 1. Reagents and conditions: (i) t-BuLi, 4-cyanobenzaldehyde,
THF, À78 ꢀC, 79%; (ii) 12, 15, or 6-bromomethyl-2-chloro-nicotino-
nitrile, Ag2O, CH2Cl2, rt, 22–50%; (iii) 9, TsOH, toluene, Dean–Stark
trap, reflux, 44%; (iv) amines, heating; (v) ArB(OH)2, Pd(PPh3)4, 2 N
Na2CO3, toluene, EtOH, heating.
9. 2-Bromo-3-methylpyridine 10 was converted into the
N-oxide using mCPBA, which, in turn was treated with
dimethylcarbamyl chloride and TMSCN to afford
cyano compound 11. Benzylic bromination led to bro-
mide 12. Suzuki coupling of 2-fluoro-4-iodo-5-methyl-
pyridine10 13 with 3-chlorophenylboronic acid gave the
biaryl molecule 14. The fluoro group of 14 was con-
verted into a cyano upon treatment with NaCN. Stan-
dard bromination gave intermediate 15.
Scheme 3. Reagents and conditions: (i) LAH, THF, 44%; (ii) PCC,
CH2Cl2, 78%; (iii) t-BuLi, 1-methyl-2-triethylsilylimidazole, THF,
À78 ꢀC, 80%; (iv) ArB(OH)2, Pd(PPh3)4, Na2CO3, toluene, H2O,
90 ꢀC; (v) NBS, CCl4, AIBN, 50%; (vi) Ag2O, CH2Cl2, 50%; (vii)
Zn(CN)2, Pd(PPh3)4, DMF, 190 ꢀC, sealed tube, 40%.
The compounds with the nitrogen insertion in the upper
cyanophenyl moiety were prepared using the chemistry
shown in Scheme 3. The methylester of 16 was reduced to
the alcohol with LAH followed by oxidation with PCC to
give aldehyde 17. Treatment of 17 with 5-lithio-1-methyl-
2-triethylsilylimidazole afforded 18. Molecule 21 was
derived from a Suzuki coupling of 19 followed by benzylic
bromination of 20. Compounds 18 and 21 were then cou-
pled via the ether formation described earlier to give 22.
Cyanation of 22 led to the final product 23.
high selectivity over GGTase. Three analogues (23a,
23d, and 23g) possess EC50 values less than 10 nM in
RP. Compound 23a has relatively low oral bioavail-
ability (F=9.4%) in monkey (1 mg/kg dosage).
Compounds 24 with substituents ortho to the lower
cyano group are generally less potent against FTase as
compared to 4 (Table 3). X-ray structures suggest that
these substituents may be too close to the protein resi-
dues in the active site.
The FTIs synthesized were evaluated for their biological
activities. As shown in Table 2, when nitrogen is inser-
ted into the upper cyanophenyl group, the inhibitors
(23) are as potent as 4 against FTase while maintaining

Y. Tong et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1571–1574
1573
Table 2. SAR of pyridyl compounds 23
bioavailability in dog. Compound 25a, which has no
substitution at R, shows reasonable PK in dog
(F=78%), but fails to perform well in monkey
(F=0.9%). A representative X-ray crystallographic
structure with compound 25b bound to the active site of
FTase and hydroxyl farnesyl phosphate (HFP)11 is
shown in Figure 1. The nitrogen in the imidazole moiety
is ligated to the zinc ion with a distance of 2.6 Ang-
strom, a hallmark feature of the imidazole-bearing
FTIs. The lower cyanophenyl and its 3-chlorophenyl
substituent are close to the hydrophobic residues of
FTase. The chloro on the pyridyl ring points to the sol-
vent front, which explains why bulky solubilizing repla-
cements of it (25c to 25h) do not sacrifice the potency of
the inhibitors. The upper cyanophenyl sits between the
hydrophobic residues and the HFP isoprenoid.
Compd
Ar
FTase IC50 GGTase-I IC50 RP EC50
(nM)
(nM)
(nM)
4
0.62
0.75
0.88
0.40
0.84
1.0
2.0
0.64
1.7
3900
1.2
2.1
20
24
3.5
46
25
3.5
46
23a
23b
23c
23d
23e
23f
23g
23h
3-Cl-Ph
3-OMe-Ph
8620
>10,000
990
>10,000
8600
>10,000
960
>10,000
3-OCF3-Ph
3,4-OCH2O-Ph
3-Cl-4-F-Ph
3,5-di-F-Ph
3,5-di-Cl-Ph
1-Naphthyl
The results of the SAR studies on series 25 are shown in
Table 4. All the compounds are potent against FTase
and selective over GGTase. Among them, many have
RP EC50 values below 10 nM. Compound 25d, with a 4-
acyl-piperazine, is three fold more potent than 4 in the
cellular RP assay, but does not result in improved oral
Substitutions on the cyanopyridine 26 led to another
series of potent and selective FTIs (Table 5). The bicyc-
lic substitution (26j) is as active as monocylic analogues.
As compared to 26b, compound 27, which has the 3-
chlorophenyl substitution on the other side of the pyri-
dine nitrogen, is about 10-fold less active in Ras pro-
cessing. Several of the most promising compounds were
tested for their PK profiles. Among them, compound
26d exhibits excellent oral bioavailability (F=90% in
dog, 56% in monkey).
Table 3. SAR of pyridyl compounds 24
In summary, we have synthesized four series of imida-
zole-bearing FTIs with nitrogen inserted into one of the
cyanophenyl moieties. Most of the inhibitors in series
23, 25, and 26 show IC50 values against FTase less than
1 nM and cellular Ras processing EC50 values less than
10 nM. In general, these compounds are at least 2000-
fold selective over GGTase-I. Compound 26d exhibits
desirable oral bioavailability in dog and monkey, a fea-
ture we targeted for improvement from the initial lead
molecule 4. Thus, the nitrogen insertion into the cyano-
phenyl core of 4 represents an effective way to develop
FTIs with balanced properties.
Compd
X
FTase IC50
(nM)
GGTase-I IC50
(nM)
4
0.62
12
58
8.2
8.5
25
3900
1100
—
2600
1600
3900
—
24a
24b
24c
24d
24e
24f
3-Cl-Ph
4-Methyl-piperazin-1-yl
2-Naphthyl
3,5-di-Cl-Ph
4-Cl-Ph
3-Cyano-Ph
68
Table 4. SAR of pyridyl compounds 25
Compds
R
FTase GGTase-I RP
EC50
(nM)
PKa
F
IC50
(nM)
IC50
(nM)
(%)
4
0.62
0.92
0.90
0.99
0.98
3900
4200
2800
650
2100
2400
830
1.2
10
29
4.5
0.40
2.0
3.6
1.5
1.2
35b
78b, 0.9c
14b
25a
25b
25c
25d
25e
25f
25g
25h
H
Cl
4-Boc-piperazin-1-yl
4-Acyl-piperazin-1-yl
2.6b
12b
4-Methyl-piperazin-1-yl 0.57
4-Hydroxy-piperidin-1-yl 0.51
4-Carboxamoyl-piperidin-1-yl 0.73
—
14b
2100
1800
1.5c
—
Morpholin-4-yl
0.25
a5 mg/kg single dose.
bDog PK.
cMonkey PK.
Figure 1.12 X-ray structure of FTI (25b active enantiomer) bound to
active site. 25b is colored yellow. Zn ion is purple. Several key FTase
residues are green. The isoprenoid group of HFP is shown in brown.

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Y. Tong et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1571–1574
Table 5. SAR of pyridyl compounds 26
Acknowledgements
X-ray crystallographic data were collected at beamline
17-ID in the facilities of the Industrial Macromolecular
Crystallography Association Collaborative Access
Team (IMCA-CAT) at the Advanced Photon Source.
These facilities are supported by the compaines of the
Industrial Macromolecular Crystallography Association
through a contract with Illinois Institute of Technology
(IIT), executed through IIT’s Center for Synchrotron
Radiation Research and Instrumentation. Use of the
Advanced Photon Source was supported by the US
Department of Energy, Basic Energy Sciences, Office of
Science, under Contract No. W-31-109-Eng-38.
Compd
R
FTase
IC50
(nM)
GGTase-I
IC50
(nM)
RP
EC50
(nM)
PKa
F
(%)
26a
26b
26c
26d
26e
26f
3.9
>10,000
1700
510
19
—
—
0.82
0.18
0.18
0.51
0.71
1.8
2.0
1.2
4.0
2.2
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26j
27e
1.9
>10,000
5500
88
7.4
17
—
—
—
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1.8
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11. Farnesyl diphosphate (FPP) was replaced by hydroxyl
farnesyl phosphate (HFP) in this study.
12. See PDB ID 1NT1 for coordinates.
a1 mg/kg single dose.
bDog PK.
cMonkey PK.
dOther oral PK data: t1/2=7.6 h; Cmax=0.26 mcg/mL; Tmax=1.0 h;
AUC=2.8 mcg.h/mL.
eSynthesized from the reaction of 6 and 15.