Discovery of C-imidazole azaheptapyridine FPT inhibitors

Article abstract of DOI:10.1016/j.bmcl.2009.12.013

The discovery of C-linked imidazole azaheptapyridine bridgehead FPT inhibitors is described. This novel class of compounds are sub nM FPT enzyme inhibitors with potent cellular inhibitory activities. This series also has reduced hERG activity versus previ

Full text of DOI:10.1016/j.bmcl.2009.12.013

Bioorganic & Medicinal Chemistry Letters 20 (2010) 1134–1136
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of C-imidazole azaheptapyridine FPT inhibitors
*
Hugh Y. Zhu , Alan B. Cooper, Jagdish Desai, George Njoroge, Paul Kirschmeier, W. Robert Bishop,
Corey Strickland, Alan Hruza, Ronald J. Doll, Viyyoor M. Girijavallabhan
Schering Plough Research Institute, 2015 Galloping Hill Rd, Kenilworth, NJ 07033, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The discovery of C-linked imidazole azaheptapyridine bridgehead FPT inhibitors is described. This novel
class of compounds are sub nM FPT enzyme inhibitors with potent cellular inhibitory activities. This ser-
ies also has reduced hERG activity versus previous N-linked imidazole series. X-ray of compound 10a
bound to FTase revealed strong interaction between bridgehead imidazole 3N with catalytic zinc atom.
Ó 2009 Published by Elsevier Ltd.
Received 21 October 2009
Revised 1 December 2009
Accepted 3 December 2009
Available online 6 December 2009
Keyword:
FPT inhibitors
Farnesyl protein transferase inhibitors (FTI) are designed to in-
hibit post-translational modification of Ras oncogene.1 Ras muta-
tions are observed in 30% of all human tumors and in a very high
percentage (ca. 90%) of pancreatic tumors. There are three forms
of Ras: H-Ras, K-Ras and N-Ras that require prenylation to associ-
ate with the inner plasma membrane for activation. Farnesyl is the
preferred lipid, although N and K forms of Ras can be activated
through alternative geranylgeranylation upon inhibition of farn-
esylation. Several FTIs including Sch 66336 (SARASAR) (1) are
being evaluated in clinical settings and some evidence of antitu-
mor activities were reported.2 Several studies indicate that the anti
cancer effect of FTIs may stem from inhibition of farnesylation of
proteins other than Ras.3
In previous studies, a series of bridgehead N-imidazole substi-
tuted azaheptapyridines were found to be potent FPT inhibitors.4
These compounds, exemplified by 2 ( Fig. 1), demonstrated sub
nM potency in both enzyme and cellular assays. Compound 2
had excellent DMPK profiles and was shown to have superior effi-
cacy in tumor xenograft models. In subsequent pre-clinical toxicol-
ogy studies, heart rate reduction was observed in Guinea pigs at
high dosage possibly due to hERG channel inhibition. In light of
these findings, alternative compounds with different structures
that addressed these deficiencies were targeted.
In the case of 2, imidazole was N-linked while C-linked imidaz-
ole was found in 3 and 4. Therefore C-imidazole linked azahepta-
pyridine analogs of 2 were prepared and evaluated (Scheme 1).
The synthesis started with carbonylation of compound 5 fol-
lowed by CDI/NaBH4 reduction to give alcohol 6.8 NBS bromination
N
N
Br
Cl
N
Cl
N
Br
N
O
NH2
N
N
O
N
CN
O
N
H
1
2
CN
Cl
Cl
N
The imidazole group can be found in a number of other leading
FPT inhibitors such as Janssen R115777 (3) and BMS-214662 (4)
(Fig. 1).5 As shown in X-ray structural analysis of these inhibitors
bound to FPT enzyme, a ternary complex was formed with FPP
and imidazole moiety bound to catalytic Zn in the enzyme active
site.6 The interaction with the zinc likely contributes greatly to
the potency of these compounds.7
S
HN
N
N
S
NH2
O
O
N
N
O
N
3
4
* Corresponding author.
E-mail addresses: hugh.zhu@spcorp.com, hughzhu@hotmail.com (H.Y. Zhu).
Figure 1. Representative FPT inhibitors.
0960-894X/$ - see front matter Ó 2009 Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2009.12.013

H. Y. Zhu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1134–1136
1135
R2
N
R2
N
N
R1
N
R1
HO
Br
Cl
Cl
Cl
N
N
N
Cl
N
c,d,e,f
a,b
N
N
N
N
N
N
N
N
CN
O
CN
O
O
O
O
O
N
H
7
N
H
6
5
8
Scheme 1. Reagents: (a) CO, PdCl2, PPh3, DBU,CH3OH/CH3Ph; (b) (1) LiOH, MeOH; (2) CDI,THF, NaBH4; (c) NBS, CH3CN; (d) 5-I imidazole, EtMgBr, CuCN, LiCl, THF; (e) Chiracel
column separation; (f) CH2Cl2, TFA; then 4-CN PhNCO, TEA, CH2Cl2.
of 6 accompanied by 5-imidazole cuprate coupling installed C-
O
imidazole on the bridgehead. After Chiracel HPLC separation, N-
Boc was removed with TFA and converted to p-CN phenyl urea
derivatives 7 and 8. The FPT enzyme and soft agar activities on this
series of compounds are listed (Table 1).
To our delight, 1N-methyl C5-imidazole compound 7a had com-
parable enzymatic and cellular activities with N-imidazole com-
pound 2. There was 30-fold loss of FPT activity in C11 isomer 8a.
By the analogy to the previous series, the active isomer was as-
signed as 7 with S-configuration at C11.9 1N–H C5-imidazole com-
pound 7b and 7c (mixture) were also very potent in enzymatic
assay although 7b was modest in soft agar cellular assay. 1N-
methyl C5-imidazole was chosen for further studies due to its bet-
ter human Cyp inhibition profiles (Scheme 2).
With successful installation of C-imidazole to the benzocyclo-
heptapyridine core, we decided to add polar functional groups to
the linker that was not previously accessible in N-imidazole series.
Polar groups generally reduce hERG activity.10 The targets were
prepared through 5-imidazole Grignard addition to C11(S) enan-
tiomeric aldehyde 9. The resulting diastereomers were separated
either through careful silica gel column or chiral HPLC. The hydro-
xyl group was further converted to O-acetate and OMe groups to
explore the space at the methylene linker.
H
Cl
N
c,d
a,b
6
N
O
N
O
9
N
N
N
N
R
R
Cl
Cl
N
N
N
N
O
N
N
O
O
O
11
As shown in Table 2, diastereomers 10a and 11a showed over
20-fold difference in enzyme activities. Methylation of the OH
was tolerated with lower inhibitory activity with a less profound
difference between the two diastereoisomers. Therefore it was rea-
sonable to assume hydrogen bonding from the free OH in 10a and
11a played a role in their activity difference. The OAc group had the
similar potency to the OMe group in the enzyme assays. It was
interesting to note that the OAc group had better cellular activity
than enzyme data indicated. This may have been due to in cell
hydrolytic conversion of the acetyl group to the more active OH
compound 10a.
10
Scheme 2. Reagents and conditions: (a) MnO2, CH2Cl2; (b) Chiracel AD column
separation (isomer 1); (c) R = OH 2-I N1-methyl imidazole, EtMgBr, ClCH2CH2Cl; (d)
R = OMe, MeI, NaH, for R = OAc, acetic anhydride, Et3N.
Table 2
FPT, soft agar activities of C-imidazole benzocycloheptapyridine derivatives
N
N
The structure of 10a bound to FPT is shown in Figure 2.11 Com-
pound 10a interacts with the active site zinc through the imidazole
R
Cl
N
N
N
Table 1
FTase, soft agar activities of C-imidazole benzocycloheptapyridine derivatives
R1
R2
FTase IC50 (nM)
Soft agar IC50 (nM)
a
b
O
Compd
O
7a
8a
7b
7c+8c
CH3
CH3
H
H
H
H
CH3
0.29
9.6
0.31
0.52
0.5
NA
4
Compd
R
FTase IC50 (nM)
Soft agar IC50 (nM)
H
NA
10a
11a
10b
11b
10c
OH
OH
OMe
OMe
OAc
0.38
12
4.8
2.1
5.5
0.5
NA
10
4
a
In vitro enzyme assay by measuring the transfer of [H3]farnesyl from [H3]far-
nesyl pyrophosphate to trichloroacetic acid-precipitable HaRas-CVLS.
b
Colony forming assay by evaluating the ability to inhibit anchorage-indepen-
1
dent growth of NIH-H tumor cell lines in soft agar.

1136
H. Y. Zhu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1134–1136
nitrogen. The binding of the tricyclic core is similar to previous
compounds lacking the zinc binding motif.12 Carbonyl of the Boc
group also contributes to the binding with interaction with surface
H2O molecule.
Further modifications on the piperazine moiety of 10a were car-
ried out with representative analogs shown in the Table 3. Urea
and carbamate are suitable substitutions at piperazine 1-N as indi-
cated in the X-ray structure with the carbonyl group contributing
to binding. Various sized alkyl and aromatic groups were generally
tolerated. Most compounds are sub nanomolar FPT inhibitors with
low single digit nM inhibitors in soft agar assays.
The hERG activity of compound 12 was assessed and found to
be 37% inhibition at 1
considering its sub nM FPT cellular potency. This compound had
low rat PK (10 mpk, 0–6 h, AUC = 0.1 M). However rat PK on car-
bamate analogs were generally good with AUC = 2.57 M h
lM. It provided a large therapeutic window
l
l
(10 mpk, 0–6 h) for compound 10a (17% hERG inhibition at
300 nM).
In conclusion, we discovered a novel series of potent FPT inhib-
itors featuring C-linked imidazole as the active site Zn binder. We
also demonstrated that the methylene linker carbon was amend-
able to substitutions. DMPK properties could be modulated with
these groups with notable reduction in hERG inhibition. Optimiza-
tion efforts on this series will be reported in future papers.
Figure 2. Structure of 10a (yellow sticks) bound to FPT. The zinc (Orange sphere),
FPP (blue surface) and several specific interactions (white lines) are illustrated.
References and notes
1. (a) Taveras, A. G.; Kirschmeier, P.; Baum, C. M. Curr. Top. Med. Chem. 2003, 3,
1103; (b) Doll, R. J.; Kirschmeier, P.; Bishop, W. R. Curr. Opin. Drug Discov. Devel.
2004, 7, 478; (c) Bell, I. M. J. Med. Chem. 2004, 47, 1869.
Table 3
FPT, soft agar activities of C-imidazole benzocycloheptapyridine derivatives
2. (a) Adjei, A. A.; Erlichman, C.; Davis, J. N.; Cutler, D. L.; Sloan, J. A.; Marks, R. S.;
Hanson, L. J.; Svingen, P. A.; Atherton, P.; Bishop, W. R.; Kirschmeier, P.;
Kaufmann, S. H. Cancer Res. 2000, 60, 1871; (b) Alsina, M.; Fonseca, R.; Wilson,
E. F.; Belle, A. N.; Gerbino, E.; Price-Troska, T.; Overton, R. M.; Ahmann, G.;
Bruzek, L. M.; Adjei, A. A.; Kaufmann, S. H.; Wright, J. J.; Sullivan, D.;
Djulbegovic, B.; Cantor, A. B.; Greipp, P. R.; Dalton, W. S.; Sebti, S. M. Blood
2004, 1039, 3271; (c) Cohen-Jonathan Moyal, E.; Laprie, A.; Delannes, M.;
Poublanc, M.; Catalaa, I.; Dalenc, F.; Berchery, D.; Sabatier, J.; Bousquet, P.; De
Porre, P.; Alaux, B.; Toulas, C. Int. J. Radiat. Oncol. Biol. Phys. 2007, 68(5), 1396;
(d) Borthakur, G.; Kantarjian, H.; Daley, G.; Talpaz, M.; O’Brien, S.; Garcia-
Manero, G.; Giles, F.; Faderl, S.; Sugrue, M.; Cortes, J. Cancer 2006, 106(2), 346.
3. (a) Basso, A. D.; Mirza, A.; Liu, G.; Long, B. J.; Bishop, W. R.; Kirschmeier, P. J. Biol.
Chem. 2005, 280, 31101; (b) Bishop, W. R.; Bond, R.; Petrin, J.; Wang, L.; Patton,
R.; Doll, R.; Njoroge, G.; Catino, J.; Shwartz, J.; Carr, D.; James, L.; Kirschmeier, P.
J. Biol. Chem. 1995, 270, 30611.
N
N
OH
Cl
N
N
N
O
R
Compd
R
FTase IC50 (nM)
0.38
Soft agar IC50 (nM)
0.5
O
10a
4. Njoroge, G. Manuscript in progress. Examples of bridgehead piperazine
compounds with enhanced FPT activities, see: Njoroge, F. G.; Vibulbhan, B.;
Pinto, P.; Strickland, C.; Bishop, W. R.; Nomeir, A.; Girijavallabhan, V. Bioorg.
Med. Chem. Lett. 2006, 16, 984.
5. (a) Hunt, J. T.; Ding, C. Z.; Batorsky, R.; Bednarz, M.; Bhide, R.; Cho, Y.; Chong, S.;
Chao, S.; Gullo-Brown, J.; Guo, P.; Kim, S. H.; Lee, F. Y. F.; Leftheris, K.; Miller, A.;
Mitt, T.; Patel, M.; Penhallow, B. A.; Ricca, C.; Rose, W. C.; Schmidt, R.;
Slusarchyk, W. A.; Vite, G.; Manne, V. J. Med. Chem. 2000, 43, 3587; (b)
Angibaud, P. R.; Venet, M. G.; Filliers, W.; Broeckx, R.; Ligny, Y. A.; Muller, P.;
Poncelet, V. S.; End, D. W. Eur. J. Org. Chem. 2004, 3, 479.
CN
12
13
N
H
0.5
0.5
2.7
N
H
0.13
N
H
14
15
0.47
0.4
18
6. Reid, T. S.; Beese, L. S. Biochemistry 2004, 43, 6877.
7. Strickland, C. SPRI, Unpublished results.
N
H
0.5
8. Zhu, Hugh Y.; Njoroge, F. George; Cooper, Alan B.; Guzi, Timothy; Rane,
Dinanath F.; Minor, Keith P.; Doll, Ronald J.; Girijavallabhan, Viyyoor M.;
Santhanam, Bama; Pinto, Patrick A.; Vibulbhan, Bancha; Keertikar, Kartik M.;
Alvarez, Carmen S.; Baldwin, John J.; Li, Ge; Huang, Chia-yu; James, Ray A.;
Bishop, W. Robert; Wang, James J.-S.; Desai, Jagdish A. U.S. Pat. Appl. Publ.
2004, US 2004122018.
16
17
18
19
0.75
1.0
0.5
1.0
1.0
0.5
O
O
0.3
9. Zhu, H.Y. et al. unpublished results.
O
O
10. Siu, T.; Li, Y.; Nagasawa, J.; Liang, J.; Tehrani, L.; Chua, P.; Jones, R. E.; Defeo-
Jones, D.; Barnett, S. F.; Robinson, R. G. Bioorg. Med. Chem. Lett. 2008, 18, 4191.
11. Crystallographic data for the inhibitor 10a-FTase complex shown in Figure 2
have been deposited with the RCSB (code RCSB056400) Protein Data Bank as
PDB ID 3KSQ.
0.76
12. Strickland, C. L.; Weber, P. C.; Windsor, W. T.; Wu, Z.; Le, H. V.; Albanese, M. M.;
Alvarez, C. S.; Cesarz, D.; del Rosario, J.; Deskus, J.; Mallams, A. K.; Njoroge, F.
G.; Piwinski, J. J.; Remiszewski, S.; Rossman, R. R.; Taveras, A. G.; Vibulbhan, B.;
Doll, R. J.; Girijavallabhan, V. M.; Ganguly, A. K. J. Med. Chem. 1999, 42, 2125.
N3 nitrogen. The imidazole 1N-methyl is packed against FPP. The R
configuration places the hydroxyl group towards solvent in a posi-
tion to make an intra-molecular hydrogen bond to the piperazine