PF-04859989 as a template for structure-based drug design: Identification of new pyrazole series of irreversible KAT II inhibitors with improved lipophilic efficiency

Article abstract of DOI:10.1016/j.bmcl.2013.02.039

The structure-based design, synthesis, and biological evaluation of a new pyrazole series of irreversible KAT II inhibitors are described herein. The modification of the inhibitor scaffold of 1 and 2 from a dihydroquinolinone core to a tetrahydropyrazolopyridinone core led to discovery of a new series of potent KAT II inhibitors with excellent physicochemical properties. Compound 20 is the most potent and lipophilically efficient of these new pyrazole analogs, with a k_inact/K_i value of 112,000 M^-1 s ^-1 and lipophilic efficiency (LipE) of 8.53. The X-ray crystal structure of 20 with KAT II demonstrates key features that contribute to this remarkable potency and binding efficiency.

Full text of DOI:10.1016/j.bmcl.2013.02.039

Bioorganic & Medicinal Chemistry Letters 23 (2013) 1961–1966
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
PF-04859989 as a template for structure-based drug design:
Identification of new pyrazole series of irreversible KAT II inhibitors
with improved lipophilic efficiency
,
⇑
Amy B. Dounay , Marie Anderson, Bruce M. Bechle, Edelweiss Evrard, Xinmin Gan, Ji-Young Kim,
Laura A. McAllister, Jayvardhan Pandit, SuoBao Rong, Michelle A. Salafia, Jamison B. Tuttle,
Laura E. Zawadzke, Patrick R. Verhoest
Pfizer Worldwide Research and Development, Neuroscience Medicinal Chemistry, Groton Laboratories, Eastern Point Road, Groton, CT 06340, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The structure-based design, synthesis, and biological evaluation of a new pyrazole series of irreversible
KAT II inhibitors are described herein. The modification of the inhibitor scaffold of 1 and 2 from a dihy-
droquinolinone core to a tetrahydropyrazolopyridinone core led to discovery of a new series of potent
KAT II inhibitors with excellent physicochemical properties. Compound 20 is the most potent and lipo-
philically efficient of these new pyrazole analogs, with a kinact/Ki value of 112,000 MÀ1 sÀ1 and lipophilic
efficiency (LipE) of 8.53. The X-ray crystal structure of 20 with KAT II demonstrates key features that con-
tribute to this remarkable potency and binding efficiency.
Received 7 January 2013
Accepted 7 February 2013
Available online 15 February 2013
Keywords:
Kynurenine pathway
Kynurenic acid
Kynurenine aminotransferase
Irreversible inhibitor
Mechanism-based inactivator
Lipophilic efficiency
Schizophrenia
Ó 2013 Elsevier Ltd. All rights reserved.
The kynurenine pathway has been implicated in the pathophys-
iology of a number of psychiatric and neurological disorders,
including schizophrenia and bipolar disorder.1–3 Initial interest in
pharmacological modulation of the kynurenine pathway was
prompted, in part, by reports that kynurenic acid (KYNA) antago-
nizes both the a7 nicotinic acetylcholine receptor4 and the N-
for preclinical exploration of this mechanism. For example, (S)-
ESBA and BFF-122 have been investigated as centrally-adminis-
tered tool compounds.13,14 Our team recently reported the discov-
ery of PF-04859989 (1), a potent, brain-penetrant inhibitor of KAT
II with in vivo activity.15 The X-ray crystal structure and 13C NMR
studies of 1 bound to KAT II have demonstrated that this com-
pound forms a covalent adduct with the cofactor, pyridoxal phos-
phate (PLP), in the enzyme active site. This covalent interaction
irreversibly inhibits the enzyme, but without formation of a
covalent bond to the protein, thus alleviating the risk of hapten-
mediated immunotoxicity. Our preliminary structure–activity rela-
tionship (SAR) studies on this scaffold have also shown that sub-
stituents at the C6 and C7 positions provide the best
opportunities for improved potency. In a recent follow-up report,
we have demonstrated that compound 2, a 6-benzyl-7-methoxy-
substituted analog of 1, is significantly more potent (kinact/Ki) than
the parent compound.16
The key binding features of compound 2 that account for its
remarkable KAT II potency are illustrated in Figure 2.17 Compound
2, like compound 1, employs its primary amine functionality in a
covalent enamine linkage with PLP, which is bound to KAT II via
a network of non-covalent interactions. Additionally, the hydroxa-
mate functionality of 2 engages Arg399 and Asn202 in critical
hydrogen-bonding interactions. Compound 2 also gains binding
methyl-D
-aspartate (NMDA) receptor.5 More recently, KYNA has
also been identified as the only known native agonist of the aryl
hydrocarbon receptor (AHR).6 Elevated KYNA levels have been de-
tected in the cerebrospinal fluid in small cohorts of schizophre-
nia7,8 and bipolar patients,9 as well as in the postmortem
prefrontal cortex of schizophrenia patients.10 Thus, reduction of
central KYNA levels via modulation of the kynurenine pathway
may provide a new therapeutic approach for schizophrenia and
other diseases of the central nervous system.
Inhibition of kynurenine aminotransferase (KAT) II, one of sev-
eral enzymes in the kynurenine pathway, provides a novel mecha-
nism for reduction of KYNA levels in the brain.11,12 A number of
new KAT II inhibitors have been utilized as pharmacological tools
⇑
Corresponding author. Tel.: +1 719 389 6438; fax: +1 719 389 6182.
E-mail address: amy.dounay@coloradocollege.edu (A.B. Dounay).
Present address: The Colorado College, Department of Chemistry and Biochem-
istry, 14 East Cache La Poudre, Colorado Springs, CO 80903, United States.
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.02.039

1962
A. B. Dounay et al. / Bioorg. Med. Chem. Lett. 23 (2013) 1961–1966
affinity from van der Waals interactions between the C6-benzyl
group and hydrophobic residues, including Leu293, in the ‘lipo-
philic pocket’ of KAT II. Unique interactions between KAT II and 2
that further enhance this inhibitor’s potency include an apparent
HN
Arg399
Asn202
O
N
H2
H
N
2
cation–
p interaction between the aromatic ring of the C6-benzyl
N
H2
H
O
N
O
group and Arg20, which is further stabilized by a hydrogen bond
between Arg20 and the C7-methoxy oxygen. Unfortunately,
in vivo efficacy studies of 2 were hampered by rapid clearance of
this compound. Although O-glucuronidation is a primary clearance
mechanism for all compounds in this series, the more lipophilic
compounds, such as 2, are also susceptible to cytochrome P450
(CYP)-mediated metabolism, resulting in high drug clearance and
low exposure.
In order to enable exploration of analogs similar to 2 in which
lipophilic phenyl or benzyl substituents are utilized for significant
potency gains, our goal was to identify a modified core structure
with reduced lipophilicity. A pyrazolopyridinone ring system was
envisioned as a viable alternative to the quinolinone core of 1
and 2 (Fig. 1). This new scaffold would afford a drug with more
favorable overall physicochemical properties, and preliminary
modeling suggested that benzyl or phenyl substituents on the pyr-
azole ring (R1 or R2) could access the lipophilic pocket of KAT II.
Appropriately substituted pyrazole analogs might also be able to
replicate the unique bidentate interaction of 2 with Arg20 that
contributes to the remarkable potency of this compound.
Arg20
H3C
O
NH
HN
H
N
O
2
N
H
O
O
N
H2
Asp230
O3PO
lipophilic
pocket
NH2
N
H2
Leu293
Arg270
NH
Figure 2. Key interactions of the 2-PLP adduct in the KAT II active site.
ative (13) with a benzaldehyde hydrazone (14). Oxidation of the
amino group was accomplished using sodium perborate tetrahy-
drate in trifluoroacetic acid, and subsequent ester hydrolysis
yielded carboxylic acid 16. The conversion of 16 to pyrazole ana-
logs 19 and 20 used the same general route and methods described
in Scheme 1 for analogs 10–12.
Pyrazole analogs 10–12 were synthesized according to the gen-
eral route shown in Scheme 1.18 This synthetic sequence began
with the appropriately substituted methoxymethylidene malono-
nitrile 3, which was condensed with methylhydrazine in ethanol
under reflux to afford the corresponding 5-amino-1-methyl-1H-
pyrazole-4-carbonitrile 4. Nitrile hydrolysis followed by oxidation
of the 5-amino group yielded nitropyrazole 6. Reduction of the car-
boxylic acid using borane-dimethylsulfide provided a primary
alcohol, which was converted to bromide 7 using carbon tetrabro-
mide and triphenylphosphine. Asymmetric alkylation of 7 was
accomplished using phase-transfer-catalyzed alkylation with a gly-
cinate Schiff base to afford 8 with high enantioselectivity.19,20 Acti-
vation of the carboxylic acid functionality as the trifluoroethyl
ester was critical to the success of the reductive cyclization in this
series.20,21 Thus, global deprotection of 8 using TFA was followed
by protection of the amine functionality as its Boc derivative. Sub-
sequent activation of the carboxylic acid via esterification with
2,2,2-trifluoroethanol provided 9. Finally, reductive cyclization
using platinum on carbon in pyridine was followed by deprotec-
tion of the Boc group to give pyrazole analogs 10–12.
New pyrazole analogs were initially assessed for IC50 in our KAT
II screening assay.15 The IC50 values were used in a primary triage
step to discriminate between ‘actives’ and ‘inactives’. Compounds
with IC50 6100 nM were advanced to the kinact/Ki assay, which
was used for more rigorous evaluation of the SAR in the series (Ta-
ble 1). Pyrazole 10 was prepared as an unadorned analog of 1 to
preliminarily assess the compatibility of the pyrazole scaffold with
KAT II. Capping of the pyrazole with a methyl substituent avoids
the introduction of an additional hydrogen-bond donor, thereby
keeping the overall physicochemical properties in reasonable
space for CNS-penetrant compounds.23 Pyrazole 10 showed mod-
erate potency (329 nM) in the preliminary KAT II assay, suggesting
that further follow-up on this scaffold was warranted. The methyl
substitutent in 10 was actually better tolerated than in the analo-
gous C8-methyl analog of 1 (1050 nM),15 suggesting that maintain-
ing this N-methyl group could be feasible as the substitution
pattern on the scaffold was further optimized. Our previous struc-
ture-based drug design around compound 2 had demonstrated
that significant potency gains were achieved by appending the
C6-benzyl group. To test the translatability of this finding to the
pyrazole series, pyrazole 11 was prepared and evaluated. Once
again, the benzyl substitution provided a significant improvement
in potency (64 nM), and the kinact/Ki for compound 11
(16,000 MÀ1 sÀ1) was comparable to that of our initial lead com-
pound 1 (18,500 MÀ1 sÀ1). In the previous series, additional modest
The synthesis of pyrazole analogs 19 and 20 was completed
using an analogous route, as shown in Scheme 2. To achieve this
substitution pattern on the pyrazole core, the general method of
Xia and co-workers was applied.22 The desired regioselectivity
was achieved by condensation of the appropriately activated
methylidene malononitrile or analogous ethyl cyanoacetate deriv-
OH
N
OH
N
OH
7
8
5
O
N
MeO
O
O
X
7
6
R1
Y
6
Z
NH2
NH2
NH2
5
R2
Ph
1
: IC50: 23 nM
2
: IC50: 37 nM
Targeted pyrazole analogs
:
kinact/Ki:18,500 M-1s-1
kinact/K :129,000 M-1s-1
i
X = Y = N; Z = C
or
X = C; Y = Z = N
R1 or R2 = Ph, Bn
Figure 1. Design of new pyrazole series based on KAT II inhibitors 1 and 2.

A. B. Dounay et al. / Bioorg. Med. Chem. Lett. 23 (2013) 1961–1966
1963
OMe
N
N
NH2
CN
N
N
NO2
NH2
NO2
Br
a
b
c
d,e
N
N
N
N
CN
O
R2
Ph
R2
CO2H
CO2H
R2
R2
R2
CN
3
4
5
6
7
OH
N
N
O
N
N
N
OtBu
NO2
NO2
N
N
Ph
N
3
g-i
j,k
NH2
f
R2
Ph
R2
R2
OtBu
OCH2CF3
N
BocHN
10 R2 = H
O
O
11 R2 = Bn
Ph
12 R2 = 3-MeO-Bn
9
8
Scheme 1. Synthesis of compounds 10–12. Reagents and conditions: (a) methylhydrazine, ethanol, reflux; (b) NaOH (aq), reflux; (c) NaNO2, HBF4 (aq); Cu/NaNO2; (d)
BH3ÁDMS, THF, À20 °C to reflux; (e) CBr4, PPh3, CH2Cl2; (f) O-allyl-N-(9-anthracenylmethyl)cinchonidinium bromide, CsOHÁH2O, CH2Cl2, À30 °C; (g) TFA, CH2Cl2; (h) Boc2O,
NaOH, THF; (i) 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride, DMAP, 2,2,2-trifluoroethanol, CH2Cl2; (j) 5% Pt/C, H2 (30 psi), pyridine; (k) HCl, dioxane.
NNHR1
NO2
X
N
N
R1
R1
NH2
CN
a, b
N
N
+
Ref 21
CN
R2
Ph
R2
CO2H
Y
R2
16
14
15
Y = CN or CO2Et
X = Cl, OMe, or OEt
OH
13
N
O
d-k
N
R1
N
NH2
R2
19 R1 = Bn; R2 = H
20
R
1 = Ph; R2 = H
Scheme 2. General synthetic approach toward pyrazole analogs 19–20. Reagents and conditions (a) sodium perborate tetrahydrate, TFA; (b) LiOH (aq.), MeOH; (d–k): see
Scheme 1.
potency gains were achieved with substituents on the benzyl
group, but the same trends were not observed in the pyrazole ser-
ies (e.g., compound 12, Table 1).
The X-ray crystal structure of pyrazole 20 with KAT II provides
useful insights into the unique potency of this inhibitor (Fig. 3).
Like all of our active irreversible inhibitors, the primary amine of
20 reacts with the aldehyde functionality of PLP in the active site
of KAT II to form an enamine adduct.15 Likewise, as in our previous
X-ray structures of KAT II inhibitors, the hydroxamate functional
group is involved in a number of hydrogen bonding interactions
with Arg399 and Asn202. Our selection of the N-phenyl group to
optimize lipophilic interactions plays out well with 20, in which
the phenyl group interacts with multiple hydrophobic residues
that line the entrance tunnel to the substrate-binding site, includ-
ing Ile19, Leu40, and Tyr74. Although the phenyl group of 20 does
An isomeric pyrazole scaffold (compounds 1724 and 18,25 Ta-
ble 1) was also explored. This structural variation was designed
to project the benzyl substituent into the lipophilic pocket of
KAT II, in analogy to analogs 2 and 11, without requiring the N-
methyl group to cap the 1H-pyrazole. Although the trifluoromethyl
group of 17 was tolerated, pyrazole 18, which is unsubstituted at
the 7 position, achieved comparable potency to 11 while providing
slightly improved ligand efficiency.
The phenyl group was next examined on the 6-position of the
pyrazole scaffold. In the expectation that this substitution pattern
would continue to project the phenyl into the lipophilic pocket of
KAT II, pyrazoles 19–21 were prepared and evaluated (Table 1).
Pyrazole 19, which is isomeric with pyrazole 18, showed a slight
loss in potency (10,500 MÀ1 sÀ1) relative to 18 (16,200 MÀ1 sÀ1).
Remarkably, the N-Ph pyrazole 20, which differs from 19 only in
not appear to form a cation–
served in the X-ray structure of 2, the domain consisting of Ile19
to Gly29 of KAT II forms an ordered -helical structure, a feature
p interaction with Arg20 as was ob-
a
that has generally been observed in co-structures of KAT II with
our most potent inhibitors.16 The X-ray structure of 20 also pro-
vides an explanation for the dramatic potency difference between
20 and the isomeric pyrazole analog 21. The N7-nitrogen atom of
20 (see Fig. 1) is appropriately positioned (3.0 Å) to interact with
a water molecule in the active site, thereby further enhancing
the potency of this inhibitor. Likewise, the unsubstituted C5 carbon
of the pyrazole ring is well accommodated in the lipophilic pocket
bounded by Tyr 74. In contrast, the isomeric pyrazole 21 cannot
take advantage of a similar water molecule interaction. Further-
more, pyrazole 21 projects its nitrogen atom at position 5 (see
Fig. 1) into the lipophilic pocket bounded by Tyr74. Thus, pyrazole
21 is doubly penalized for this reversal of polarity in its pyrazole
scaffold.
the deletion of one methylene group, provided
a dramatic
improvement in kinact/Ki (112,000 MÀ1 sÀ1). Pyrazole 20 thus
emerged as one of our most potent KAT II inhibitors discovered
to date, approaching the potency of compound 2. The subtlety of
the SAR in this series is further highlighted by pyrazole 21,26 which
is isomeric with 20, but is significantly less potent in the kinact/Ki
assay (8580 MÀ1 sÀ1). Pyrazoles 20 and 21 confirm that the pyra-
zole core not only serves as a scaffold to project the phenyl substi-
tuent into an optimal position in the lipophilic pocket, but that the
atoms in the pyrazole ring can also provide either favorable or
unfavorable interactions with KAT II.

1964
A. B. Dounay et al. / Bioorg. Med. Chem. Lett. 23 (2013) 1961–1966
Table 1
Selected data for KAT II inhibitors
b
Compound
Structure
OH
hKAT IIa IC50 (nM)
kinact/Kib (MÀ1 sÀ1
)
kinact (minÀ1
)
Kia (nM)
cSF logDc
LipEd
7.77
N
O
1 (PF-04859989)
23
18,500
0.0156
14
0.079
NH2
OH
N
O
MeO
2
37
129,000
0.0146
1.6
ND
2.07
6.73
ND
NH2
Ph
OH
N
O
N
10
329
ND
ND
À0.67
N
NH2
OH
N
O
N
N
11
12
17
64
66
74
16,000
0.0349
0.0116
0.0227
32
22
48
0.29
0.61
1.17
7.20
7.04
6.15
NH2
OH
N
O
N
N
8710
MeO
NH2
OH
N
F3C
N
O
7920
N
NH2
OH
N
O
N
18
19
23
47
16,200
10,500
0.0116
0.0147
12
23
0.22
0.16
7.70
7.48
N
NH2
OH
N
O
N
N
NH2
OH
N
O
N
20
21
25
85
112,000
8580
0.0125
0.0144
1.9
41
0.20
0.37
8.53
6.99
N
N
NH2
OH
N
O
N
NH2
a
b
c
Values are geometric means of two or more experiments conducted in duplicate. See Ref. 15 for detailed assay protocols.
Values are arithmetic of two or more experiments conducted in duplicate.
Calculated shake flask (SF) distribution coefficient at pH 7.4.
Calculated LipE = Àlog(Ki) À cSF logD.
d
Further evaluation of the kinact/Ki data set provides additional
largely driven by differences in the Ki term, which describes the
non-covalent binding affinity; the kinact term, which describes the
rate of covalent bond formation, remained relatively constant
across compounds in the series.15,16 The same trend is observed
insights on this novel pyrazole series of KAT II inhibitors. Our pre-
vious evaluation of kinact/Ki trends for inhibitors 1 and 2 and their
analogs showed that the potency differences among analogs were

A. B. Dounay et al. / Bioorg. Med. Chem. Lett. 23 (2013) 1961–1966
1965
Figure 3. X-ray structure of adduct formed by 20 with PLP in the KAT II active site. The surface is colored by increasing hydrophobicity, from blue to green to brown.
3. Potter, M. C.; Elmer, G. I.; Bergeron, R.; Albuquerque, E.; Guidetti, P.; Wu, H.-Q.;
Schwarcz, R. Neuropsychopharmacology 2010, 35, 1734.
4. Hilmas, C.; Pereira, E. F.; Alkondon, M.; Rassoulpour, A.; Schwarcz, R.;
for the new series of pyrazole analogs (Table 1). The most potent
new analog, pyrazole 20, has a Ki of 1.9 nM, which is comparable
to the Ki of compound 2 (1.6 nM), our most potent analog from
the original series.
Albuquerque, E. X. J. Neurosci. 2001, 21, 7463.
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Engberg, G.; Erhardt, S.; Landen, M. J. Psychiatry Neurosci. 2010, 35, 195.
10. Schwarcz, R.; Rassoulpour, A.; Wu, H.-Q.; Medoff, D.; Tamminga, C. A.; Roberts,
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13. Rossi, F.; Valentina, C.; Garavaglia, S.; Sathyasaikumar, K. V.; Schwarz, R.;
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15. Dounay, A. B.; Anderson, M.; Bechle, B. M.; Campbell, B. M.; Claffey, M. M.;
Evdokimov, A.; Evrard, E.; Fonseca, K. R.; Gan, X.; Ghosh, S.; Hayward, M. M.;
Horner, W.; Kim, J.-Y.; McAllister, L. A.; Pandit, J.; Paradis, V.; Parikh, V. D.;
Reese, M. R.; Rong, S.; Salafia, M. A.; Schuyten, K.; Strick, C. A.; Tuttle, J. B.;
Valentine, J.; Wang, H.; Zawadzke, L. E.; Verhoest, P. R. ACS Med. Chem. Lett.
2012, 3, 187.
In order to evaluate progress against our original goal of identify-
ing a less lipophilic core structure for elaboration to potent KAT II
inhibitors, the lipophilicity of these analogs was assessed using cal-
culated shake flask logD (cSF logD) values (Table 1).27,28 This lipo-
philicity term was used in conjunction with the potency term Ki to
calculate lipophilic ligand efficiency (LipE), a parameter that nor-
malizes potency differences relative to a compound’s lipophilicity,
allowing for a direct comparison between compounds.29 A compar-
ison of the LipE of our new pyrazole analogs demonstrates that these
compounds generally achieve comparable lipophilic efficiency to
lead compound 1 and improved efficiency relative to compound 2
(Table 1). Notably, pyrazole 20 shows significantly improved LipE
(8.53) over compounds 1 (7.77) and 2 (6.73) and emerges as our
most efficient KAT II inhibitor identified to date. As anticipated,
the lower logD of 20 relative to 2 also results in reduction of CYP-
mediated clearance. The measured clearance (intrinsic, apparent)
in a human liver microsome assay30 improved from 26.0
mg for compound 2 to <8.0 L/min/mg for compound 20.
lL/min/
l
16. Tuttle, J. B.; Anderson, M.; Bechle, B. M.; Campbell, B. M.; Chang, C.; Dounay, A.
B.; Evrard, E.; Fonseca, K. R.; Gan, X.; Ghosh, S.; Horner, W.; James, L. C.; Kim, J.-
Y.; McAllister, L. A.; Pandit, J.; Parikh, V. D.; Rago, B. J.; Salafia, M. A.; Strick, C.
A.; Zawadzke, L. E.; Verhoest, P. R. ACS Med. Chem. Lett. 2013, 4, 37.
17. For X-ray structure of 2 bound to KAT II, see Ref. 16.
18. Full experimental details are contained within the following patent
application: Dounay, A. B.; McAllister, L. A.; Parikh, V. D.; Rong, S.; Verhoest,
P. R. PCT Int. Appl. 2012, WO 2012073143.
In summary, our structure-based drug design approach has en-
abled the identification of a new pyrazole series of irreversible KAT
II inhibitors. Optimization within this new series led to the discov-
ery of 20, which displays significantly improved LipE and provides
a new template for further preclinical investigation of KAT II as a
novel mechanism for treatment of CNS disorders.
19. Corey, E. J.; Noe, M. C.; Xu, F. Tetrahedron Lett. 1998, 39, 5347.
20. McAllister, L. A.; Bechle, B. M.; Dounay, A. B.; Evrard, E.; Gan, X.; Ghosh, S.; Kim,
J.-Y.; Parikh, V. D.; Tuttle, J. B.; Verhoest, P. R. J. Org. Chem. 2011, 76, 3484.
21. The ester activation step was necessary to prevent over-reduction to a lactam
by-product under the reductive cyclization conditions.
22. Xia, Y.; Chackalamannil, S.; Czarniecki, M.; Tsai, H.; Vaccaro, H.; Cleven, R.;
Cook, J.; Fawzi, A.; Watkins, R.; Zhang, H. J. Med. Chem. 1997, 40, 4372.
23. Wager, T. T.; Villalobos, A.; Verhoest, P. R.; Hou, X.; Shaffer, C. L. Expert Opin.
Drug Discov. 2011, 6, 371.
Acknowledgment
We would like to thank Brian Campbell, Christine Strick, and
Scot Mente for helpful discussions and Katherine Brighty for care-
ful editing of this manuscript.
24. Prepared in analogy to compound 18, starting from 3-methyl-5-
(trifluoromethyl)-1H-pyrazole as described by Acker, B. A.; Hughes, R. O.;
Jacobsen, E. J.; Lu, H.-F.; Rogers, T. E.; Tollefson, M. B.; Walker, J. K. PCT Int. Appl.
2006, WO 2006046135.
25. Prepared from methyl 1-benzyl-4-nitro-1H-pyrazole-5-carboxylate using the
general methods described in Schemes 1 and 2. Commercially available 4-
nitro-1H-pyrazole-3-carboxylic acid was converted to 1-benzyl-4-nitro-1H-
pyrazole-5-carboxylate over two steps.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2013.02.
039.
26. Pyrazole 21 was prepared following the general route shown in Scheme 1. In
this case, arylation of methyl 4-nitro-1H-pyrazole-3-carboxylate followed by
ester hydrolysis provides 4-nitro-1-phenyl-1H-pyrazole-3-carboxylic acid,
following the method of Miller, T. A. Sloman, D. L.; Stanton, M. G.; Wilson, K.
J.; Witter, D. J. PCT Int. Appl. 2007, WO 2007087129. Subsequent conversion of
the carboxylic acid moiety to a primary bromide may be effected as described
References and notes
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in Scheme 1. The resulting 3-(bromomethyl)-4-nitro-1-phenyl-1H-pyrazole
28. The experimental shake-flask logD values for compounds in this series have
shown excellent correlation with in silico SF logD values calculated with our
new model (Christopher Keefer, Pfizer, unpublished results.)
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a
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