Design, synthesis, and activity of 4-quinolone and pyridone compounds as nonthiol-containing farnesyltransferase inhibitors

Article abstract of DOI:10.1016/j.bmcl.2004.08.012

As a part of our efforts to identify potent inhibitors of farnesyltransferase (FTase), modification of the structure of tipifarnib through structure-based design was undertaken by replacing the 2-quinolones with 4-quinolones and pyridones, and subsequent

Full text of DOI:10.1016/j.bmcl.2004.08.012

Bioorganic & Medicinal Chemistry Letters 14 (2004) 5367–5370
Design, synthesis, and activity of 4-quinolone
and pyridone compounds as nonthiol-containing
farnesyltransferase inhibitors
Qun Li,* Akiyo Claiborne, Tongmei Li, Lisa Hasvold, Vincent S. Stoll,
Steven Muchmore, Clarissa G. Jakob, Wendy Gu, Jerry Cohen, Charles Hutchins,
David Frost, Saul H. Rosenberg and Hing L. Sham
Cancer Research, GPRD, Abbott Laboratories, Abbott Park, IL 60064-6101, USA
Received 29 June 2004; revised 6 August 2004; accepted 6 August 2004
Available online 3 September 2004
Abstract—As a part of our efforts to identify potent inhibitors of farnesyltransferase (FTase), modification of the structure of tipi-
farnib through structure-based design was undertaken by replacing the 2-quinolones with 4-quinolones and pyridones, and subse-
quent relocation of the D-ring to the N-methyl group on the imidazole ring. This study has yielded a novel series of potent and
selective FTase inhibitors. The X-ray structure of tipifarnib (1) in complex with FTase was described.
Ó 2004 Elsevier Ltd. All rights reserved.
Prenylation, a process of covalently attaching either a
15-carbon farnesyl moiety or a 20-carbon geranylgera-
nyl moiety to the conserved cysteine residues at the the
C-terminus of certain proteins, plays a major role in a
number of intracellular signaling pathways that control
cell proliferation.1 Among the important oncoproteins
that require posttranslational prenylation for their activ-
ity is a family of Ras proteins.2 Activating mutations of
Ras are among the most common in human tumors.3
The discovery that farnesylation is required for Ras
transforming activity has led to an intense search for
farnesyltransferase (FTase) inhibitors (FTIs) as antican-
cer agents.4,5 Many FTIs have demonstrated excellent
antitumor efficacy in preclinical human xenograft mod-
els and several compounds are now in Phase II/III clin-
ical trials.6,7 However, recent studies have shown that
other farnesylated protein targets other than Ras, such
as RhoB, may be more important for the antitumor ef-
fects of FTIs.8
of 80–90% of prenylated proteins. Because FTIs have
been shown to be sufficient for achieving growth inhibi-
tion in tumor cells and this effect is not enhanced with
co-application of GGTase inhibitors,9 selective FTIs
Cl
Cl
H2N
X2
Cl
C
D
N
D
N
A
N
A
Me
Me
B
A
B
X1
O
O
N
N
D
N
2
O
Me
1
X2
X2
Cl
Cl
D
N
A
L
1L2
L
1L2
Me
Me
N
A
N
Me
N
X1
N
N
O
3
4
NC
Het
Cl
Related to FTase is geranylgeranyltransferase
(GGTase I), which is responsible for the prenylation
I
N
N
N
NC
Me
NC
L3
Het
O
7
O
N
Keywords: Farnesyltransferase inhibitors; Anticancer; Tipifarnib; Quino-
lone; Pyridone.
5
6
*
Figure 1. Modifications of tipifarnib (1) lead to novel inhibitors of
FTase 2–7.
Corresponding author. Tel.: +1 8479377125; fax: +1 8479361550;
e-mail: qun.li@abbott.com
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.08.012

5368
Q. Li et al. / Bioorg. Med. Chem. Lett. 14 (2004) 5367–5370
pound 10 was reacted with DMF–DMA to provide
Cl
Cl
the N,N-dimethylenamine, which was further reacted
with 3-chloroaniline then cyclized with K2CO3 in reflux-
ing pentanol to afford cyano-4-quinolone 11 in 34%
overall yield. The desired compound 2a was prepared
in 26% yield by the addition of 1-methyl-2-triethylsilyl-
5-imidazolyl lithium12 to the ketone (11) and subsequent
removal of the triethylsilyl group with HCl in methanol.
F
Br
a
b
F
F
O
O
MeO2C
NC
HO2C
Cl
8
9
O
10
Cl
HO
Cl
Cl
Preparation of the required monocyclic 4-quinolone
intermediates 16 and 17 is illustrated in Scheme 2. 4-
Quinolone-3-carboxylic acid 14 was prepared from pyr-
one 12 in 59% overall yield by the method of Bassini
et al.13 Transformation of acid 14 to cyanide 15 was
achieved in 91% yield by dehydration of the intermediate
amide with POCl3. Direct free radical promoted bromi-
nation of 15 gave the desired bromide 16 in low yield
(65%). The bromomethyl quinolone (16) was prepared
alternatively from 15 in 26% yield by a three-step se-
quence involving oxidation to the aldehyde with SeO2
in refluxing dioxane, reduction of the aldehyde to the
alcohol with NaBH(OAc)3, and reaction of the alcohol
with PBr3. Bromide 16 was then reacted with NaN3 and
the azido intermediate reduced with triphenylphosphine
in refluxing THF/water to give amine 17 in 81% yield.
N
O
c
N
O
Me
d
O
N
NC
N
NC
11
2a
Scheme 1. Reagents and conditions: (a) (i) 4-Chlorophenylboronic
acid, CO, PdCl2 (dppf), K2CO3, anisole, 80°C, overnight, 67%, (ii)
LiOH, THF/H2O, 70°C, 1.5h, 95%; (b) (i) SOCl2, 80°C, 15min, (ii) t-
BuO2CCH2CN, NaH, toluene, rt, (iii) TFA, CH2Cl2, 3h; 61%; (c) (i)
DMF–DMA, toluene, rt, 3h, (ii) 3-chloroaniline, CH2Cl2, rt, (iii)
K2CO3, pentanol, 110°C, overnight, 34%; (d) (i) 1-methyl-2-TES-
imidazole, t-BuLi, THF, À78°C, 3h, (ii) MeOH, 1N HCl, rt, 0.5h,
26%.
are sought in order to avoid potential undesirable
toxicities.
Reaction of aldehyde 18 with 1-methyl-2-triethylsilyl-5-
imidazolyl lithium in the same way as described for 2a
provided alcohol 19 in 89% yield (Scheme 3). Coupling
Tipifarnib (R115777, 1) is one of the most potent and
selective nonthiol FTIs currently in Phase III clinical
trials.10 As a part of our efforts to identify novel and
nonthiol FTIs, we report here our design and synthesis
of a series of quinolone based FTIs (2–7) using the struc-
ture of tipifarnib as a template.
CN
CN
Cl
CN
Synthesis of bicyclic 4-quinolone analog 2a is illustrated
in Scheme 1. The carbonylative cross-coupling of bro-
mide 8 with 4-chlorophenylboronic acid using the condi-
tion of Ishiyama et al.11, followed by saponification of
the ester gave ketone 9 in 64% yield. Acid 9 was con-
verted to cyanoacetone 10 in 61% yield via the reaction
of its acid chloride with t-butyl cyanoacetate, and subse-
quent hydrolysis, and decarboxylation in TFA. Com-
a
b
N
O
HO
O
Me
Me
N
N
CHO
NC
N
N
18
4a
19
Scheme 3. Reagents and conditions: (a) (i) 1-methyl-2-TES-imidazole,
t-BuLi, THF, À78°C, 1h, (ii) MeOH, 1N HCl, rt, 0.5h, 89%; (b) 16,
AgO, CH2Cl2, rt, 18h, 44%.
Cl
Cl
Cl
O
O
CH3
O
O
CH3
a
b
CO2Et
N
O
CH3
Me2N
CO2Et
CO2Et
a
b
EtO2C
O
12
O
13
HO2C
Cl
EtO2C
CN
O
N
14
20
d
22
21
Me
c
Cl
Cl
CN
Cl
c
d
or e
N
CH3
f
N
N
19
Br
NH2
O
H2N
Me
N
NC
NC
NC
N
Me
O
15
O
16
O
17
N
H
N
23
O
N
Me
N
3a
Scheme 2. Reagents and conditions: (a) DMF–DMA, toluene, rt, 4h,
75%; (b) 3-chloroaniline, t-BuONa, EtOH, 90°C, 18h, 78%; (c) (i)
CDI, DMF, 110°C, 18h, then NH3, 4°C, 18h, 91%, (ii) POCl3, NMP,
rt, 3h, 38%; (d) NBS, CCl4, PhCO3H, reflux, 18h, 5%; (e) (i) SeO2,
dioxane, reflux, overnight, 77%, (ii) NaBH(OAc)3, MeOH, rt, 4h, 69%,
(iii) PBr3, LiBr, DMF, 0°C, 4h, 49%; (f) (i) NaN3, acetone, reflux, 1h,
91%, (ii) PPh3, THF/H2O, reflux, 1h, 89%.
Scheme 4. Reagents and conditions: (a) 3-chloroiodobenzene,
Pd(OAc)2, NaOAc, DMF, 100°C, 21h, 20%; (b) (i) HCO2Et, NaH,
ether, rt, 2h, 96%, (ii) MeNH2, EtOH, reflux, 0.5h, then, K2CO3, rt,
18h, 41%; (c) (i) LiOH, THF/H2O, 60°C, 8h, 77%, (ii) (COCl)2,
CH2Cl2, 0°C to rt, 2h, (iii) 23, THF, rt, 18h, 67%; (d) (i) SOCl2,
CH2Cl2, rt, 4h, 100%, (ii) NH4OH, THF, rt, 2h, 77%.

Q. Li et al. / Bioorg. Med. Chem. Lett. 14 (2004) 5367–5370
5369
Table 1. Activity of quinolone based farnesyltransferase inhibitors
NC
NC
NC
O
Cl
Compd
IC50 (nM)
GGTc
EC50 (nM)
Ras processinga
FTb
N
O
51%d
nte
N
N
a
2a
3a
12
16,000
nte
N
b
N
N
HO
H
R
685
12
NC
4%d
0%d
nte
N
N
25
4a
6a
>10,000
>10,000
nte
6a, R=H
6b, R=SO2Me
c
24
7.9
160
17
NC
Cl
6b
7a
Cl
Cl
>10,000
1100
>10,000
21%d
Tipifarnib (1)f
Lonafarnibf,21
0.65
8.3
1.6
100
e
d
Br
Me
NH2
N
N
H
N
a In H-Ras NIH-3T3 cells.
b Bovine farnesyltransferase.
c Bovine geranylgeranyltransferase.
d Inhibition at 100nM.
e Not tested.
f Data from racemic mixtures.
N
NC
N
NC
Me
N
NC
Me
7a
O
O
O
26
27
Scheme 5. (a) MnO2, dioxane, 85°C, overnight, 43%; (b) 17, AcOH,
MeOH rt, 1h; then NaBH3CN, rt, 1h, 100%; (c) MeSO2Cl, Et3N,
CH2Cl2, rt, 2h, 18%; (d) (i) NaN3, acetone, reflux, 1h, 70%, (ii) PPh3,
THF/H2O, reflux, 1h, 83%; (e) 25, AcOH, MeOH rt, 1h; then
NaBH3CN, rt, 1h, 71%.
amine is not interacting directly with the protein, but
is solvent exposed.
Having a carbonyl group rather than a methyl group
facing solvent front, the X-ray structure suggests the
4-quinolone (2) should be a good mimic of 1. A carbonyl
group in 2 now faces the solvent front versus a methyl
group in 1 and the cyano group in 4-quinolone now re-
places the 2-carbonyl group in 1. Indeed, 2a was found
to be a potent and selective inhibitor of FTase, with
IC50 values20 of 12nM and 16lM against FTase and
GGTase, respectively (Table 1). The inhibition of Ras
processing in H-Ras transformed cells20 was determined
as a measure of intracellular potency. Compound 2a
shows an EC50 of about 100nM.
of alcohol 19 with bromomethane 16 in the presence of
silver oxide gave desired 4-pyridone analog 4a in 44%
yield.
Preparation of 3a is shown in Scheme 4. The glutaconate
(20) was converted to pyridone ester 22 according to the
procedure of Kvita and Sauter in 8% overall yield.14 In
our hands, ester 22 could not be reduced to the alcohol
without reducing the ring double bond. Thus it was
hydrolyzed and converted to the acid chloride, which
was coupled with amine 23 to furnish 3a in 67% yield.
Synthesis of the analogs with the three-atom linkers (6a
and b, and 7a) is shown in Scheme 5. Thus 4-hydroxy-
methylimidazole 2415 was oxidized with MnO2 to form
aldehyde 25 (43% yield), which underwent reductive
amination with 17 in the presence of sodium cyanoboro-
hydride to give the desired product 6a in 100% yield
(Scheme 5). Reaction of 6a with methanesulfonyl chlo-
ride produced sulfonamide 6b in 18% yield. Reaction
of bromomethyl 2-pyridone 2616 with sodium azide
(70% yield) and subsequent reduction with triphenyl-
phosphine gave amine 27 in 83% yield. Reductive alkyl-
ation of 27 with 25 furnished the desired product 7a in
71% yield. In our hands, we were unable to couple alco-
hol 24 with either bromide 16 or 26 to form the ether-
Structure analysis revealed that it might be possible
to maintain the desired conformation by deleting the
B-ring in 1 and 2, provided that an appropriate and
accessible linker is used. Thus pyridones 3a and 4b were
designed and synthesized, wherein the pyridone and imi-
dazole moieties are connected via amide bond and ether
linkages, respectively. The amide 3a is significantly less
potent than 1 with an IC50 of 685nM against FTase.
Unlike the amide, ether 4a displays very good FTase
activity (IC50 12nM) that is identical to 4-quinolone 2
and only about 17-fold higher than 1. EC50 of Ras
processing for one of the compounds tested (4a) was
determined to be over 100nM.
bridged compounds under
conditions.
a
variety of reaction
Examination of the structures of 3 and 4 revealed that
the D-ring (Fig. 1) could be attached to the adjacent
N-methyl group on the imidazole ring without signifi-
cantly affecting its binding to the hydrophobic pocket
of FTase. This modification not only simplifies the syn-
thesis, but also makes the compounds achiral. 4-Pyr-
idone analog 6a is the most potent FTase inhibitor
synthesized with an IC50 of 8nM, which is slightly more
active than its parent 4a. 2-Pyridone 7a is about 2-fold
less potent than the 4-pyridone (6a). Attaching a meth-
anesulfonyl group on the linker nitrogen in 6a resulted
in a 20-fold drop in FTase activity. Compound 6a shows
poor activity in Ras processing assay and has an EC50
over 100nM. None of the compounds in this series are
active against GGTase with IC50 values over 10lM.
The X-ray structure of tipifarnib in complex with FTase
was obtained (Fig. 2a).17,18 The result is similar to a re-
cent work by Reid and Beese.19 The imidazole serves as
a replacement of the thiol of the CaaX tetrapeptide sub-
strate by coordinating with the catalytic zinc that is crit-
ical to the farnesylation process. The 2-quinolone ring
extends over the loop consisting of Asp359, Phe360,
and Tyr361 and is lined from above the plane by resi-
dues Leu96 and Tyr93 via van der Waals interactions.
The two chlorophenyl rings (rings C and D) occupy
the two adjacent hydrophobic pockets and stack to-
gether forming a strong p/p interaction. The primary

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Q. Li et al. / Bioorg. Med. Chem. Lett. 14 (2004) 5367–5370
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Figure 2. Stereo views of (A) tipifarnib and (B) an overlay of a model
of compound 2a (in green) over the X-ray crystal structure of tipifarnib
(1) (in purple) in complex with FTase in the active site. Zn+2 is shown
in grey and hydroxy farnesylpyrophosphate in blue.
15. Williams, T. M.; Bergman, J. M.; Brashear, K.; Breslin,
M. J.; Dinsmore, C. J.; Hutchinson, J. H.; MacTough, S.
C.; Stump, C. A.; Wei, D. D.; Zartman, C. B.; Bogusky,
M. J.; Culberson, J. C.; Buser-Doepner, C.; Davide, J.;
Greenberg, I. B.; Hamilton, K. A.; Koblan, K. S.; Kohl,
N. E.; Liu, D.; Lobell, R. B.; Mosser, S. D.; OÕNeill, T. J.;
Rands, E.; Schaber, M. D.; Wilson, F.; Senderak, E.;
Motzel, S. L.; Gibbs, J. B.; Graham, S. L.; Heimbrook, D.
C.; Hartman, G. D.; Oliff, A. I.; Huff, J. R. J. Med. Chem.
1999, 42, 3779–3784.
Stereo view of an overlay of a model of 2a, which was
modeled based on the crystal structure of a close chem-
ical analog22 and the X-ray crystal structure of tipifarnib
(1) is shown in Figure 2b. The model of 2a superimposes
very well with tipifarnib. The important cyano group of
2a binds to the main chain loop consisting of residues
Asp359, Phe360 and Tyr361 through a combination of
electrostatic and van der Waals interaction.
16. Hasvold, L. A.; Wang, W.; Gwaltney, S. L.; Rockway, T.
W., II; Nelson, L. T. J.; Mantei, R.; Fakhoury, S.;
Sullivan, G.; Li, Q.; Lin, N.-H.; Wang, L.; Zhang, H.;
Cohen, J.; Gu, W.-Z.; Marsh, K.; Bauch, J.; Rosenberg,
S.; Sham, H. Bioorg. Med. Chem. Lett. 2003, 13, 4001–
4005.
In summary, we have used the structure of tipifarnib to
design a series of novel inhibitors of FTase. The com-
pounds demonstrate potent activity against FTase with
IC50 values in the nanomolar range. The current series
of compounds are highly selective and their IC50 values
against GGTase are in the double-digit micromolar
range. The successful discovery of 4-quinolone 2 as a po-
tent FTase inhibitor has opened a door for future
opportunities to extend further into other 4-quinolones
and bicyclic 2-pyridones.23 However, further structural
modifications are needed in order to improve the cellular
activity of the current series. These efforts have led to the
discovery of more potent FTase inhibitors, the detailed
of which will be presented elsewhere16,22,24 and in the
subsequent paper in the current journal.
17. Protein of the Rat Ftase was purified and crystallized in
the presence of HFP and Ac-CVIM peptide according to
the methods outlined in Strickland et al.18 Crystals of
Ftase were soaked in a solution containing 0.1M KCl,
0.1M sodium acetate pH4.7 saturated with tipifarnib. The
˚
structure was refined to 3.5A resolution with an
R = 22.31% and Rfree = 29.19%. Crystallographic data
for structure of tipifarnib in complex with FTase in this
paper have been deposited with PDB (ID: 1X81).
18. Strickland, C.; Windsor, W. T.; Syto, R.; Wang, L.; Bond,
Ri.; Wu, Z.; Schwartz, J.; Le, H. V.; Beese, L. S.; Weber,
P. C. Biochemistry 1998, 37, 16601–16611.
19. Reid, T. S.; Beese, L. S. Biochemistry 2004, 43, 6877–6884.
20. Assay methods described in: Vogt, A.; Qian, Y.; Blaskov-
ich, M. A.; Fossum, R. D.; Hamilton, A. D.; Sebti, S. M.
J. Biol. Chem. 1995, 270, 660–664.
21. Wang, L.; Johnson, W. W. Chemotherapy 2003, 49, 303–308.
22. Wang, L.; Wang, G. T.; Wang, X.; Tong, Y.; Sullivan, G.;
Park, D.; Leonard, N.; Li, Q.; Cohen, J.; Gu, W.-Z.;
Zhang, H.; Bauch, J.; Jacob, C. G.; Hutchins, C. W.; Stoll,
S. V.; Marsh, K.; Rosenberg, S. H.; Sham, H.; Lin, N.-H.
J. Med. Chem. 2004, 47, 612–626.
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 companies of the Indus-
trial Macromolecular Crystallography Association.
23. Li, Q.; Mitscher, L. A.; Shen, L. L. Med. Res. Rev. 2000,
20, 231–293.
References and notes
24. Tong, Y.; Lin, N.-H.; Wang, L.; Hasvold, L.; Wang, W.;
Leonard, N.; Li, T.; Li, Q.; Cohen, J.; Gu, W.-Z.; Zhang,
H.; Stoll, V.; Bauch, J.; Marsh, K.; Rosenberg, S. H.;
Sham, H. L. Bioorg. Med. Chem. Lett. 2003, 13, 1571–
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