Synthesis and biological evaluation of 4-[3-biphenyl-2-yl-1-hydroxy-1-(3-methyl-3H-imidazol-4-yl)-prop-2-ynyl]-1- yl-benzonitrile as novel farnesyltransferase inhibitor

Article abstract of DOI:10.1016/S0960-894X(03)00122-7

Farnesyltransferase inhibitors (FTIs) have emerged as a novel class of anti-cancer agents. Analogues of the potent FTI, 4-[3-biphenyl-1-hydroxy-1-(3-methyl-3H-imidazol-4-yl)-prop-2-ynyl]-1-yl- benzonitrile, were synthesized and tested in vitro for their inhibitory activities. The synthesis and detailed biological data of this series of analogues are presented.

Full text of DOI:10.1016/S0960-894X(03)00122-7

Bioorganic & Medicinal Chemistry Letters 13 (2003) 1293–1296
Synthesis and Biological Evaluation of 4-[3-biphenyl-2-yl-1-
hydroxy-1-(3-methyl-3H-imidazol-4-yl)-prop-2-ynyl]-1-yl-
benzonitrile as Novel Farnesyltransferase Inhibitor
Nan-Horng Lin,* Le Wang, Jerry Cohen, Wen-Zhen Gu, David Frost, Haiying Zhang,
Saul Rosenberg and Hing Sham
Cancer Research, D-47B, Global Pharmaceutical Products Division, Abbott Laboratories, 100 Abbott Park Road,
Abbott Park, IL 60064-3500, USA
Received 19 November 2002; accepted 17 January 2003
Abstract—Farnesyltransferase inhibitors (FTIs) have emerged as a novel class of anti-cancer agents. Analogues of the potent FTI,
4-[3-biphenyl-1-hydroxy-1-(3-methyl-3H-imidazol-4-yl)-prop-2-ynyl]-1-yl-benzonitrile, were synthesized and tested in vitro for their
inhibitory activities. The synthesis and detailed biological data of this series of analogues are presented.
# 2003 Elsevier Science Ltd. All rights reserved.
Ras proteins play an important role in normal cellular
physiology and pathophysiology and are also com-
monly found in human tumors.1,2 An essential pre-
requisite for the function of the Ras protein is its
association with the plasma membrane. Ras proteins are
initially synthesized in the cytoplasmwhere they
undergo posttranslational farnesylation of the cysteine
unit of the so-called CAAX box (C, cysteine; A, any
aliphatic amino acid; X, serine or methionine) in the
pre-Ras protein by the enzyme protein: farnesyl-
transferase (FT).3 Once the protein substrate is farnesy-
lated, the AAX tripeptide is cleaved and the new C-
terminal cysteine carboxylate is methylated. The pro-
cessed proteins become localized to the cell membrane,
a step that is essential for their function. This associ-
ation transmits extracellular signals to the nucleus and
leads to cell proliferation.4,5
exhibit antitumor activity. Instead, inhibiting Rho-B
and possibly other cellular proteins might also account
for the efficacy against malignant tumors.10ꢀ13 Although
the mechanism of action of these agents is still debated,
FTIs have shown impressive efficacy in preclinical
models of human cancers.
Abbott’s first generation FTI, ABT-839, was potent and
selective, but low selectivity was observed between
FTase and GGTase-1. The goal of our research is to
identify a structurally distinct FTI that maintains or
exceeds the potency of ABT-839 and has high selectivity
favoring FT inhibition as well.
The antitransforming properties of farnesyltransferase
inhibitors (FTIs), a novel class of cancer therapeutics,
has been widely investigated in the past decade.6ꢀ9 FTIs
were originally developed with the aimof inhibiting the
posttranslational prenylation and oncogenic activity of
Ras. It has become apparent that inhibition of Ras
prenylation is not necessary for these compounds to
Tolyl and naphthyl analogues were prepared based on
the reaction sequences shown in Scheme 1. The starting
aldehyde 1 was prepared fromthe corresponding bro-
mide by Suzuki reaction with various phenylboronic
acids. (Scheme 1) Formation of secondary alcohols 2
may be accomplished by formation of imidazole anion
with n-butyl lithiumfollowed by addition of the anion
to the aldehyde. The TES group was then removed with
*Corresponding author. Fax:+1-847-935-5466; e-mail: nanhorng.
lin@abbott.com
0960-894X/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0960-894X(03)00122-7

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N.-H. Lin et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1293–1296
In this study, tolyl, naphthyl and biphenyl analogues of
imidazole acetylenic alcohol were tested for their inhi-
bitory activity against both FTase and GGTase-1
enzymes. The effects of varying the substituents at the
C3- and C4-positions of the phenyl ring of the naphthyl
series as shown in Table 1 have been studied in detail.
Table 1 reveals that the 4-CN analogue (19) is the most
potent compound to inhibit FTase in the naphthyl ser-
ies. For the inhibition against FTase, both electron-
donating and withdrawing groups are tolerated at the
C4- position. In contrast, introduction of the electron-
donating NH2 group to the C3- position provided the
compound with weak inhibitory potency against
GGTase-1 (14 vs 12).
The inhibitory activity at the C4-position appears to be
governed by steric effects. Analogue (16) which pos-
sesses a large pentyl group at the C4-position is less
potent than either the Et (18) or acetylene (15) sub-
stitutions. The same trend is observed for the inhibition
of the GGTase-1 enzyme (Table 1).
Scheme 1. (i) n-BuLi, TBAF, ꢀ78 ꢁC; (ii) MnO2, CH2Cl2; (iii) t-BuLi,
(Trimethylsilyl)acetylene; (iv) K2CO3, MeOH; (v) Pd(PPh3)2Cl2, bro-
mobenzene.
TBAF. Oxidation followed by addition of an acetylenic
anion that was generated by reaction of acetylene with
t-butyl lithiumprovided the desired tertiary alcohol 3.
Removal of the trimethylsilyl group with potassium
carbonate gave the common intermediate 4 that was
coupled with various phenyl bromides utilizing Heck
reaction conditions.
Table 1 also demonstrates that introduction of a nitro-
gen atomto the naphthyl ring results in decreased
potency in both the FTase and GGTase-1 assays (17
vs 19). In general, the naphthyl series shows poor selec-
tivity with the exception of compound 14 that has 131-
fold selectivity in favor of Ftase inhibition. It has also
been revealed that introduction of a Cl, CN or acetylene
group at the C4-position of the phenyl ring in the
naphthyl series results in a 17–170-fold increase in Ras
processing potency compared with analogue 12.
Scheme 2 illustrates that biphenyl analogues may be
synthesized using a route similar to that shown in
Scheme 1. Thus, coupling of a substituted phenyl iodide
5 with a substituted phenylboronic acid 6 provided the
phenol 7 after the removal of the methyl group with
boron tribromide. Conversion of the phenol into the
corresponding triflate 8 followed by the Heck reaction
with acetylene gave the protected acetylene 9. Removal
of the trimethylsilyl group with base provided the acet-
ylene 10 which is easily converted to the corresponding
Table 1. FTase inhibition, GGTase-1 inhibition, and Ras processing
data for biphenyl analogues 12–20
lithiumacetylide by treatment with n-butyl lithium.
Addition of lithiumacetylide to the imidazole ketone
generated the desired alcohol 11.
Cmpds
R1
X
Y
FTase GGTase Selectivity Ras
IC50
IC50
(nM)b
(GGT
/FT)
EC50
(nM)c
(nM)a
12
13
14
15
16
17
18
19
20
H
4-Cl
CH CH
CH CH
0.8
0.8
0.7
0.7
3.1
9.5
92
16
360
83
18
10
40
4
12
131
23
30
83
26
36
170
9.5
NT
<1.0
3.8
<1.0
130
7.9
3-NH2 CH CH
4-CCH CH CH
4-C5H11 CH CH 12
1
4-CN
4-Et
N
CH
CH CH
CH CH
0.7
0.28
1.0
4-CN
4-Me
CH
N
40
49
aConcentration of compound required to reduce the human FTase-
catalyzed incorporation of [3H]FPP into recombinant Ras CVIM by
50%.
bConcentration of compound required to reduce the human GGTase-
catalyzed incorporation of [3H]GGPP into biotinylated peptide corre-
sponding to the C-terminal of human K-Ras by 50%.
cCompound concentration needed to reduce 50% of farnesylation in
NIH-3T3H-ras cell line.
Scheme 2. (i) Pd(PPh3)4; (ii) BBr3, CH2Cl2; (iii) PhN(Tf)2, i-PrNEt2; (iv)
Pd(PPh3)2Cl2, (trimethylsilyl)acetylene; (v) K2CO3, MeOH; (vi) n-BuLi.

N.-H. Lin et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1293–1296
1295
To improve the selectivity against FTase, we have also
synthesized several biphenyl analogues as shown in
Table 2. It reveals that both electron-donating and
withdrawing groups are tolerated at the R1- and R2-
positions with the 3,5-Cl analogue (26) being the most
potent compound against FTase in the biphenyl series.
In general, compounds having the biphenyl structure
are the most selective, whereas the naphthyl analogues
(Table 1) are the least selective.
effect on FTase (cf. 27, 22 and28) activity. However, a
decrease in inhibitory potency against GGTase-1 is
observed. (Table 2) Replacing the 3-OMe with Cl in the
biphenyl series causes a 25-fold reduction in Ras pro-
cessing activity. In contrast, little effect is observed
when the 4-CN group is replaced with a Cl atom. (27 vs
21; 27 vs 22)
We then turned our attention to the effect of the acet-
ylenic linker on the inhibitory potency. Table 3 indi-
cates that reduction of the acetylene moiety of the tolyl
analogue to a saturated bond results in a 10-fold
decrease in potency in the inhibition of both the FTase
and GGTase-1 enzymes (23 vs 24). A similar SAR
trend is observed when the acetylene moiety is
removed (25 vs 26). In contrast to the tolyl analogue,
reduction of the acetylene moiety in the biphenyl series
has little effect on the inhibition of FTase (22 vs 27).
However, a 5-fold decrease in potency is observed in
Table 2 also reveals that replacement of the chloro atom
(21) at the C30-position of the phenyl ring with a meth-
oxy group (27) causes a 150-fold increase in selectivity.
Further increase in selectivity was observed when the
chloro atomwas replaced with a CN at C4- position of
the phenyl ring (27 vs 22).
Introduction of various groups such as Cl, CN and CO-
n-Bu to the C4-position in the biphenyl series has little
Table 2. FTase inhibition, GGTase-1 inhibition, and Ras processing data for biphenyl analogues 21–28
Compd
R1
R2
FTase
IC50 (nM)a
GGTase
IC50 (nM)b
Selectivity
(GGT /FT)
Ras
EC50 (nM)c
21
22
23
24
25
26
27
28
Cl
CN
CN
CN
CN
CN
Cl
CO-n-Bu
3-Cl
3-OMe
3,4-OCH2O–
3-OEt
3-OCF3
3,5-Cl
3-OMe
1.4
100
4100
5600
2400
430
1100
7
11,100
8200
3290
1050
14,000
1070
>9100
100
2.74
1.4
0.37
0.68
0.73
0.41
0.079
0.69
1.1
0.1
NT
3.86
4.0
740
>10,000
3-OMe
<0.1
aConcentration of compound required to reduce the human FTase-catalyzed incorporation of [3H]FPP into recombinant Ras CVIM by 50%.
bConcentration of compound required to reduce the human GGTase-catalyzed incorporation of [3H]GGPP into biotinylated peptide corresponding
to the C-terminal of human K-Ras by 50%.
cCompound concentration needed to reduce 50% of farnesylation in NIH-3T3H-ras cell line.
Table 3. FTase inhibition, GGTase-1 inhibition, and Ras processing data for biphenyl analogues 23–27 and 22
Compd
R1
R2
R3
A
FTase
IC50 (nM)za
GGTase
IC50 (nM)b
Selectivity
(GGT /FT)
Ras
EC50 (nM)c
23
24
25
26
27
22
H
H
4-CN
4-CN
4-CN
4-CN
H
H
H
2-Me-Ph
2-Me-Ph
2-Me-Ph
2-Me-Ph
H
CH2CH2
CꢂC
33
1800
240
210
1200
870
4100
54
73
250
200
1318
11100
NT
NT
9.8
<1.0
1.24
2.74
3.3
0.84
6
0.66
0.37
CꢂC
H
bond
CH2CH2
CꢂC
3-OMe-Ph
3-OMe-Ph
H
aConcentration of compound required to reduce the human FTase-catalyzed incorporation of [3H]FPP into recombinant Ras CVIM by 50%.
bConcentration of compound required to reduce the human GGTase-catalyzed incorporation of [3H]GGPP into biotinylated peptide corresponding
to the C-terminal of human K-Ras by 50%.
cCompound concentration needed to reduce 50% of farnesylation in NIH-3T3H-ras cell line.

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N.-H. Lin et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1293–1296
the inhibition of GGTase-1 (Table 3). It has also been
demonstrated that reduction of the acetylene moiety
has little effect on the Ras processing activity in the
biphenyl series.
References and Notes
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stituent pattern at the phenyl or naphthyl rings of
an imidazole acetylenic alcohol such as compound
12 alters the inhibitory properties of these com-
pounds. The inhibitory activity (Tables 1–3) indicates
that large substituents are not well tolerated at the
C4-position of the phenyl ring. In general, com-
pounds having the biphenyl structure as shown in
3. Zhang, F. L.; Casey, P. J. Annu. Rev. Biochem. 1996, 65, 241.
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Table
1 possess the weakest inhibitory activities
against the GGTase-1 enzyme. In contrast, the
naphthyl analogues possess the most potent activity
against GGTase-1. The selectivity for FTase inhibi-
tion over GGTase-1 is highest in the biphenyl series
as shown in Table 2. This study has also shown
that reduction of the acetylene moiety decreases the
potency in the tolyl series. However, only a small
effect is observed in the biphenyl series. The most
potent analogue identified fromthis study is com-
pound 26 which is 50-fold more potent than ABT-
839, a potent FTase inhibitor identified previously
(IC50=3.9 nM).
10. Prendergast, G. Curr. Opin. Cell Biol. 2000, 166.
11. Du, W.; Lebowitz, P. F.; Prendergast, G. C. Mol. Cell.
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12. Prendergast, G. C.; Du, W. Drug Resistance Update 1999,
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