Structure-activity relationships of pyrazine-based CK2 inhibitors: Synthesis and evaluation of 2,6-disubstituted pyrazines and 4,6-disubstituted pyrimidines

Article abstract of DOI:10.1002/ardp.200700269

Structually related to the known CK2 inhibitors, 2,6-disubstituted pyrazine and 4,6-disubstituted pyrimidine derivatives were synthesized and their inhibitory activities toward CK2α and CK2α′ were evaluated. Structure-activity relationship study has revealed that several pyrazine derivatives bearing a (pyrrol-3-yl)acetic acid and a monosubstituted aniline possess potent inhibitory activities.

Full text of DOI:10.1002/ardp.200700269

554
Arch. Pharm. Chem. Life Sci. 2008, 341, 554–561
Full Paper
Structure-Activity Relationships of Pyrazine-Based CK2
Inhibitors: Synthesis and Evaluation of 2,6-Disubstituted
Pyrazines and 4,6-Disubstituted Pyrimidines
Yamato Suzuki, Jꢀrꢁme Cluzeau, Takafumi Hara, Akira Hirasawa, Gozoh Tsujimoto, Shinya Oishi,
Hiroaki Ohno, and Nobutaka Fujii
Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan
Structually related to the known CK2 inhibitors, 2,6-disubstituted pyrazine and 4,6-disubstituted
pyrimidine derivatives were synthesized and their inhibitory activities toward CK2a and CK2a9
were evaluated. Structure-activity relationship study has revealed that several pyrazine deriv-
atives bearing a (pyrrol-3-yl)acetic acid and a monosubstituted aniline possess potent inhibitory
activities.
Keywords: CK2 / Glomerulonephritis / Kinase inhibitor / Pyrazine derivatives / SAR study /
Received: Decemer 27, 2007; accepted: February 26, 2008
DOI 10.1002/ardp.200700269
A
number of CK2-specific inhibitors have been
Introduction
reported to date, including quercetin, apigenin (chrysin)
[6], emodin [7, 8], TBB (4,5,6,7-tetrabromo-1H-benztria-
zole) [9, 10], IQA [(5-oxo-5,6-dihydroindolo[1,2-a]quinazo-
lin-7-yl)acetic acid], and their analogues [11] (Fig. 1). These
compounds exhibit ATP-competitive inhibition of CK2
through interaction with a hydrophobic pocket adjacent
to the ATP-binding site [8, 12]. It is generally accepted
that the relatively small hydrophobic pocket of CK2 com-
pared to those of other protein kinases allows selective
binding of CK2 inhibitors [8, 13].
Recently, using a cDNA microarray strategy, we identi-
fied CK2 as a gene product related to the progression of
glomerulonephritis (GN), a disease characterized by renal
inflammation causing destruction of glomeruli and adja-
cent structures and loss of renal function [14]. We have
also revealed that administration of either antisense
CK2a oligodeoxynucleotide or low-molecular-weight
CK2-specific inhibitors, such as emodin and apigenin,
ameliorates the renal dysfunction and histological pro-
gression in rat GN models [14], suggesting that CK2 is a
potential molecular target for GN therapy. In-vitro screen-
ing for CK2 inhibitors, utilizing a compound library
focused on protein kinases, led to identification of two
potent CK2-specific inhibitors 1a, b [15]. Both of these
compounds include a pyrazine nucleus and two substitu-
ents: a (pyrrol-3-yl)acetic acid moiety (fragment A) and a
Protein kinase CK2 (formerly known as casein kinase II) is
a ubiquitous, well conserved and pleiotropic Ser/Thr kin-
ase which has a heterotetrameric structure with two cat-
alytic (a and/or a9) and two regulatory subunits (b) [1, 2].
CK2 is constitutively active in living cells either alone or
combined with b-subunits to phosphorylate over 300 pro-
tein substrates. It is well documented that CK2 plays
important roles in gene expression, DNA repair, RNA and
protein synthesis, and signal transduction from extracel-
lular growth factors [3]. Overexpression or inhibition of
CK2 shows a significant effect on cell proliferation,
which considerably depends on the cell type [4]. It is also
reported that the CK2a9 isoform is highly expressed in
testes, and male mice, in which the gene encoding CK2a9
has been knocked out, are infertile, displaying a defect in
spermatogenesis [5].
Correspondence: Nobutaka Fujii and Hiroaki Ohno, Graduate School of
Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501,
Japan.
E-mail: nfujii@pharm.kyoto-u.ac.jp
hohno@pharm.kyoto-u.ac.jp
Fax: +81 75 753 4570
Abbreviations: dppf (1,19-bis(Diphenylphosphino)ferrocene); glomerulo-
nephritis (GN); structure-activity relationship (SAR)
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Arch. Pharm. Chem. Life Sci. 2008, 341, 554–561
Synthesis of Disubstituted Pyrazines and Pyrimidines
555
Reagents and conditions: (a) indole, cat. CuI/(l)-A, K3PO4, dioxane, reflux, 24 h; (b)
ethyl aminoalkanoate, Cs2CO3, DMF, 1108C, 24 h; (c) (for 4f) ethyl (pyrrol-3-yl)acetate
(5), cat. CuI/(l)-A, K3PO4, dioxane, reflux, 24 h; (d) 1 N NaOH, dioxane, rt, 2 h.
Figure 1. Structures of representative CK2 inhibitors and com-
pounds 1a and 1b.
Scheme 1. Synthesis of compounds 4a–f.
6-aminoindazole moiety (fragment B). The binding of
these compounds to the hydrophobic pocket adjacent to
the ATP binding site of CK2a was verified by X-ray crystal-
lography [unpublished data].
2 was coupled with indole in the presence of catalytic CuI
and Buchwald's diamine ligand A [17] to yield the com-
mon intermediate 3. Amination of 3 with several ethyl
aminocarboxylates followed by hydrolysis afforded the
desired compounds 4a–f.
Synthesis of monosubstituted phenoxy- and phenyla-
mino-pyrazine derivatives 7a–d and 8a–r, respectively,
is shown in Scheme 2. The reaction of 2 with ethyl (pyr-
rol-3-yl)acetate 5 [18], following the same protocol used
in the synthesis of 3, yielded the corresponding (iodopyr-
azinyl)pyrrole derivative 6. Further coupling of 6 with
several monosubstituted phenols in the presence of cata-
lytic copper under microwave irradiation, or various ani-
lines in the presence of catalytic Pd2(dba)36CHCl3 and
dppf (1,19-bis(diphenylphosphino)ferrocene), followed by
hydrolysis of the ester, afforded the corresponding acids
7a–d and 8a–r.
In the present study, we designed and synthesized three
types of analogues of compounds 1a and 1b: Firstly, com-
pounds bearing a cyclic or acyclic amino acid as the frag-
ment A 4a–f; secondly, compounds with a monosubsti-
tuted phenol or aniline as the fragment B, 7a–d and 8a–r,
respectively; and, finally, analoguesinwhichthe pyrazine
nucleus has been replaced by pyrimidine 13a and b. Struc-
ture-activity relationship (SAR) studies of these analogues
revealed highly potent CK2 inhibitory compounds having
an aniline moiety as the fragment B. The importance of
thepyrazine nucleusis alsopresented.
Results and discussion
The synthetic route to compounds 4a–f with a cyclic or
acyclic amino acid as the fragment A is shown in
Scheme 1. In these compounds, 6-aminoindazole (frag-
ment B) is also replaced with an indole for ease of prepa-
ration, because the indole derivative 4f has been already
known as a moderate CK2 inhibitor [15]. Prepared by diio-
dination of 2,6-dichloropyrazine [16], 2,6-diiodopyrazine
Pyrimidine derivatives 13a and 13b were synthesized
as shown in Scheme 3. Introduction of the pyrrole and
indazole moieties into 4,6-diiodopyrimidine 9 [19, 20]
was performed by successive copper-mediated coupling
reactions with ethyl (pyrrol-3-yl)acetate 5 and 6-aminoin-
dazole 11 [21] to give the ester 12. Reductive amination of
cyclopentanone or acetone with 12, followed by hydroly-
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Y. Suzuki et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 554–561
Reagents and conditions: (a) cat. CuI/(l)-A, K3PO4, dioxane, reflux, 24 h; (b) cyclo-
pentanone, NaBH3CN, AcOH, DMF, 508C, 12 h; (c) acetone, NaBH3CN, AcOH, DMF,
508C, 12 h; (d) 1 N NaOH, dioxane, rt, 2 h.
Reagents and conditions: (a) cat. CuI/(l)-A, K3PO4, dioxane, reflux, 24 h; (b) R-
PhOH, Cu, Cs2CO3, DMF, MW, 1208C, 15 min; (c) R-PhNH2, cat. Pd2(dba)36CHCl3/
dppf, Cs2CO3, dioxane, reflux, 24 h; (d) 1 N NaOH, dioxane, rt, 2 h.
Scheme 3. Synthesis of compounds 13a and 13b.
Scheme 2. Synthesis of compounds 7a–d and 8a–r.
derivatives 13a and 13b and found that these two ana-
sis of the ester functionality, afforded the corresponding logues were unable to inhibit CK2a or CK2a9.
pyrimidine analogues 13a and 13b.
The IC50 values of the six compounds 8d, 8e, 8i, 8k, 8l,
We then investigated in vitro inhibitory activities of and 8m having high inhibitory activities were deter-
the synthesized compounds toward CK2a and CK2a9. The mined based on the dose-dependency curve of the SAR
relative activity of CK2 in the presence of 1.0 lM 4a–f, data. Results are summarized in Table 2. The m-chloro, m-
7a–d, 8a and 8b is summarized in Table 1. A series of ali- trifluoromethyl, m-nitro, and o-carboxyl derivatives 8d,
phatic amino acid derivatives 4a–e exhibited little or no 8i, 8k, and 8l, respectively, showed high inhibitory activ-
inhibitory activities toward CK2a nor CK2a9; the known ity toward both CK2a (IC50 = 0.18–0.67 lM) and CK2a9
compound 4f carrying a (pyrrol-3-yl)acetic acid (Fragment (IC50 = 0.04–0.32 lM).
B) showed moderate CK2a9 inhibitory activity. Similar
The results of these SAR studies, summarized in Fig. 2,
results were obtained with several monosubstituted phe- are: (i) the pyrazine nucleus is essential for inhibitory
noxy pyrazine derivatives 7a–d. In contrast, pyrazines 8a activity toward CK2a and CK2a9, and (ii) replacement of a
and 8b possessing an m-substituted aniline moiety (pyrrol-3-yl)acetic acid moiety (fragment A) with aliphatic
showed moderate ability to inhibit CK2a (59.3 and 66.3% amino acids is not suitable, resulting in loss of inhibitory
inhibition, respectively, at 1.0 lM) and CK2a9 (74.0 and activity. On the other hand, (iii) analogues with a mono-
81.1% inhibition, respectively, at 1.0 lM). On the basis of substituted phenylamino group at the 6-position of the
these results, we considered the pyrazines with the origi- pyrazine (fragment B) showed moderate to good inhibi-
nal (pyrrol-3-yl)acetic acid moiety as the fragment A and a tory activities, and (iv) substitution on the phenylamino
monosubstituted aniline as the fragment B to be more group (as the fragment B) by m-chloro or m-nitro shows
promising CK2 inhibitors. We then focused on evalua- the highest activity in these analogues. In contrast, (v)
tion of the inhibitory activities of a series of phenylamino the analogues containing o-substituted aniline exhibit
derivatives 8c–r with a (pyrrol-3-yl)acetic acid moiety. significantly lower activity than the corresponding m-
Almost all of these compounds showed potent inhibitory and p-substituted analogues in most cases, except for o-
activity toward both CK2a and CK2a9. In particular, m-tri- carboxyl derivative (see: 8c, 8h, 8l, and 8q in Table 1). In
fluoromethyl- and m-nitro-phenylamino derivatives 8i addition, (vi) all these analogues inhibit both of the CK2a
and 8k, respectively, exhibited high potency against and CK2a9 isoforms, although some inhibitors such as 8e,
CK2a (91.4 and 91.6% inhibition, respectively, at 1.0 lM) 8i, and 8k show moderate selectivity toward CK2a9. How-
and CK2a9 (82.6 and 86.2% inhibition, respectively, at ever, since CK2 forms a tetramer with two regulatory b-
1.0 lM). We also evaluated the potency of the pyrimidine subunits in living cells, predictions of the in-vivo activity
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Arch. Pharm. Chem. Life Sci. 2008, 341, 554–561
Synthesis of Disubstituted Pyrazines and Pyrimidines
557
Table 1. CK2 inhibitory activity of the synthesized compounds.
Table 2. IC50 values of compounds 8d, 8e, 8i, 8k, 8l, and 8m.
Compound
R
Relative CK2 activitya)
Compound
R
IC50 (lM)
CK2a9
(7 and 8)
at 1.0 lM (%)
CK2a
CK2a
CK2a9
1a
1b
8d
8e
8i
8k
8l
8m
–
–
0.03
0.03
0.38
2.62
0.67
0.18
0.58
4.00
0.007
0.04
0.16
0.50
0.25
0.04
0.32
2.05
1a
1b
4a
4b
4c
4d
4e
4f
7a
7b
7c
7d
8a
8b
8c
8d
8e
8f
8g
8h
8i
8j
8k
8l
–
–
–
–
–
–
–
–
8.5
8.2
5.5
6.4
m-Cl
p-Cl
m-CF3
m-NO2
o-CO2H
m-CO2H
86.9
108.4
103.3
79.3
105.8
76.8
93.9
106.1
94.7
107.0
40.7
33.7
58.2
14.2
25.0
27.4
24.2
90.4
8.6
61.0
82.6
102.9
93.0
94.6
33.4
85.8
89.5
90.2
86.3
26.0
18.9
55.9
15.7
33.6
27.3
23.9
94.1
17.4
25.8
13.8
26.1
42.6
68.6
14.9
22.0
66.6
22.2
99.8
98.5
m-NH2
m-NHiPr
m-CO2H
p-CO2H
m-OMe
m-CN
o-Cl
m-Cl
p-Cl
m-F
p-F
o-CF3
m-CF3
p-CF3
m-NO2
o-CO2H
m-CO2H
p-CO2H
m-SO2NH2
p-SO2NH2
o-Me
m-Me
–
24.6
8.4
Figure 2. Structure-activity relationship of 1 and related com-
pounds.
20.7
57.3
78.6
21.2
24.8
71.9
25.1
105.4
106.2
8m
8n
8o
8p
8q
8r
The authors are indebted to Dr. H. Kawai and Dr. N. Fuchi, Toray In-
dustries, Inc. for their generous donation of the key intermediate 6. This
work was supported by the Program for Promotion of Fundamental
Studies in Health Sciences of the National Institute of Biomedical Inno-
vation (NIBIO). Appreciation is expressed to Mr. M. A. Reback (Kyoto
University) for helpful discussion and proofreading of the manuscript.
13a
13b
–
a)
CK2 activity was assessed by using a CK2 assay kit (Upstate
Biotechnology) according to the manufacturer's instructions
[22].
The authors have declared no conflict of interest.
of these pyrazine-based inhibitors is difficult at the
present stage.
Experimental
IR spectra were recorded on a JASCO FT/IR-4100 spectrometer
(Jasco, Tokyo, Japan). Exact mass (HRMS) spectra were recorded
1
on JMS-HX/HX 110A mass spectrometer (JEOL, Tokyo, Japan). H
Conclusions
NMR spectra were recorded using a JEOL AL-400 or ECA-500 spec-
trometer at 400 or 500 MHz frequency (JEOL). Chemical shifts
are reported in d (ppm) relative to Me4Si as internal standard.
Melting points (uncorrected) were measured by a hot stage melt-
ing point apparatus. For column chromatography, Wakosil C-
300 (Wako Chem. Co., Osaka, Japan) was employed.
In conclusion, we have synthesized various 2,6-disubsti-
tuted pyrazines bearing a cyclic and acyclic amino acid
moiety at the 2-position of the pyrazine ring, based on
the known inhibitors 1a and 1b. Evaluation of these ana-
logues' CK2 inhibitory activity has revealed that the pyra-
zine ring, (pyrrole-3-yl)acetic acid moiety, and the nitro-
gen atom at the 6-position of the pyrazine ring are neces-
sary for inhibition, while the indazole moiety of 1 can be
replaced by appropriately-substituted anilines. These
data should prove useful in the search for CK2 inhibitors
for glomerulonephritis (GN) therapy.
General procedure for coupling reaction of
iodopyrazine derivatives with indole, pyrrole, or
indazole derivatives (Procedure A)
Synthesis of 1-(6-iodopyrazin-2-yl)-1H-indole 3
(l)-trans-N,N9-Dimethylcyclohexane-1,2-diamine
A (50 lL, 0.32
mmol) was added to a mixture of 2,6-diiodopyrazine 2 (500 mg,
1.51 mmol), indole (159 mg, 1.36 mmol), CuI (29 mg, 0.15
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558
Y. Suzuki et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 554–561
mmol), and K3PO4 (672 mg, 3.17 mmol) in dioxane (1 mL) under
argon atmosphere. The reaction container was sealed, heated to
1108C and stirred for 24 h. The resulting mixture was allowed to
reach room temperature, diluted with EtOAc, and filtered. The
filtrate was concentrated in vacuo and the residue was purified
by flash chromatography on silica gel (hexane/EtOAc 4 : 1) to
give the compound 3 (200 mg, 41%); 1H-NMR (500 MHz, CDCl3) d:
6.78 (d, 1H, J = 3.6 Hz), 7.26–7.29 (m, 1H), 7.37 (dd, 1H, J = 7.8,
7.8 Hz), 7.65–7.68 (m, 2H), 8.27 (d, 1H, J = 8.4 Hz), 8.63 (s, 1H),
8.77 (s, 1H); MS (FAB) m/z: 322 [M + H+].
4-{[6-(1H-Indol-1-yl)pyrazin-2-yl]amino}butanoic acid 4d
Yield 65%; 1H-NMR (400 MHz, CD3OD) d: 1.99–2.03 (m, 2H), 2.45
(t, 2H, J = 7.3 Hz), 3.53 (t, 2H, J = 7.0 Hz), 6.69–6.70 (m, 1H), 7.16
(dd, 1H, J = 8.0, 7.4 Hz), 7.26 (dd, 1H, J = 8.0, 7.8 Hz), 7.60 (d, 1H, J =
8.0 Hz), 7.70 (s, 1H), 7.82 (d, 1H, J = 3.7 Hz), 7.97 (s, 1H), 8.33 (d,
1H, J = 8.0 Hz); MS (FAB) m/z: 297 [M + H+]; IR (ATR): 3362 (NH),
1698 (C=O) cm– 1
.
6-{[6-(1H-Indol-1-yl)pyrazin-2-yl]amino}hexanoic acid 4e
Yield 53%; 1H-NMR (400 MHz, CDCl3) d: 1.51–1.76 (m, 6H), 2.32 (t,
2H, J = 7.2 Hz), 3.48 (t, 2H, J = 7.1 Hz), 6.70 (d, 1H, J = 3.4 Hz), 7.16
(dd, 1H, J = 7.8, 7.4 Hz), 7.25 (dd, 1H, J = 7.8, 7.8 Hz), 7.60 (d, 1H, J =
7.8 Hz), 7.68 (s, 1H), 7.81 (d, 1H, J = 3.4 Hz), 7.95 (s, 1H), 8.36 (d,
1H, J = 7.8 Hz); MS (FAB) m/z: 325 [M + H+]; IR (ATR): 3367 (NH),
General procedure for coupling of iodopyrazine
derivatives with aminocarboxylates followed by
hydrolysis (Procedure B)
1704 (C=O) cm– 1
.
Synthesis of 1-[6-(1H-indol-1-yl)pyrazin-2-yl]piperidine-4-
carboxylic acid 4a
2-{1-[6-(1H-Indol-1-yl)pyrazin-2-yl]-1H-pyrrol-3-yl}acetic
Ethyl isonipecotate (0.1 mL, 0.64 mmol) was added to a solution
of 3 (50 mg, 0.16 mmol) and Cs2CO3 (150 mg, 0.46 mmol) in DMF
(0.4 mL) under argon atmosphere. The reaction container was
sealed, heated to 1108C and stirred for 24 h. The reaction mix-
ture was cooled to room temperature, poured into water, and
extracted three times with chloroform. The combined organic
layers were washed with brine, dried over MgSO4, and evapo-
rated. The residue was purified by flash chromatography on
silica gel (hexane/EtOAc 1 : 1). The ester obtained was added to a
solution of 1 N NaOH aq. (0.4 mL) in dioxane (1 mL) and the mix-
ture was stirred at room temperature for 2 h. The reaction mix-
ture was neutralized with 1 N HCl aq. (0.4 mL) and generated
precipitate was filtered, washed with water, and dried to give
the compound 4a (40 mg, 75%); 1H-NMR (400 MHz, CDCl3) d:
1.83–1.92 (m, 2H), 2.12 (dd, 2H, J = 13.4, 3.4 Hz), 2.66–2.74 (m,
1H), 3.18–3.25 (m, 2H), 4.34 (ddd, 2H, J = 13.4, 3.7, 3.7 Hz), 6.72
(d, 1H, J = 3.4 Hz), 7.22 (dd, 1H, J = 8.0, 7.4 Hz), 7.30 (dd, 1H, J = 8.0,
7.4 Hz), 7.66 (d, 1H, J = 8.0 Hz), 7.69 (d, 1H, J = 3.4 Hz), 8.01 (s, 1H),
8.12 (s, 1H), 8.17 (d, 1H, J = 8.0 Hz); MS (FAB) m/z: 323 [M + H+]; IR
acid 4f
Using procedure A, compound 3 (63 mg, 0.20 mmol) was
coupled with compound 5 (30 mg, 0.20 mmol). After purifica-
tion by flash chromatography on silica gel (hexane/EtOAc 3 : 2),
the resulting ester was added to the solution of 1 N NaOH aq.
(0.6 mL) in dioxane (2 mL) and the mixture was stirred at room
temperature for 2 h. The mixture was neutralized with 1 N HCl
aq. (0.6 mL) and the generated precipitate was filtered, washed
with water, and dried to give compound 4f (53 mg, 46%);1H-NMR
(400 MHz, DMSO-d6) d: 3.49 (s, 2H), 6.37 (dd, 1H, J = 2.7, 1.7 Hz),
6.87 (d, 1H, J = 3.7 Hz), 7.25 (dd, 1H, J = 7.8, 7.4 Hz), 7.37 (dd, 1H, J
= 7.8, 7.4 Hz), 7.69 (d, 1H, J = 7.8 Hz), 7.70–7.74 (m, 1H), 7.76 (dd,
1H, J = 2.7, 2.6 Hz), 8.23 (d, 1H, J = 3.7 Hz), 8.45 (d, 1H, J = 7.8 Hz),
8.90 (s, 1H), 8.96 (s, 1H), 12.27 (br s, 1H); MS (FAB) m/z: 319 [M +
H+]; IR (ATR): 1722 (C=O) cm– 1
.
Ethyl-2-[1-(6-iodopyrazin-2-yl)-1H-pyrrol-3-yl]acetate 6
Using procedure A, compound 2 (143 mg, 0.43 mmol) was
coupled with compound 5 (55 mg, 0.36 mmol). Purification by
flash chromatography on silica gel (hexane/EtOAc 3 : 2) gave the
compound 6 (67 mg, 52%); 1H-NMR (500 MHz, CDCl3) d: 1.30 (t,
3H, J = 7.2 Hz), 3.55 (s, 2H), 4.20 (q, 2H, J = 7.2 Hz), 6.38 (dd, 1H, J =
2.8, 1.9 Hz), 7.43–7.44 (m, 2H), 8.58 (s, 1H), 8.61 (s, 1H); MS (FAB)
(ATR): 1714 (C=O) cm– 1
.
The compounds 4b–e were synthesized according to the Pro-
cedure B.
m/z: 358 [M + H+]; IR (ATR): 1735 (C=O) cm– 1
.
1-[6-(1H-Indol-1-yl)pyrazin-2-yl]piperidine-3-carboxylic
acid 4b
General procedure for coupling of iodopyrazine
derivatives with phenols followed by hydrolysis
(Procedure C)
Yield 80%; 1H-NMR (500 MHz, CDCl3) d: 1.66–1.74 (m, 1H), 1.89–
1.96 (m, 2H), 2.14–2.18 (m, 1H), 2.72–2.76 (m, 1H), 3.36 (ddd, 1H,
J = 13.2, 10.0, 2.7 Hz), 3.53 (dd, 1H, J = 13.2, 9.4 Hz), 4.07 (ddd, 1H,
J = 13.2, 4.0, 4.0 Hz), 4.36-4.43 (m, 1H), 6.72 (d, 1H, J = 3.4 Hz), 7.21
(dd, 1H, J = 8.0, 7.3 Hz), 7.30 (dd, 1H, J = 8.0, 7.3 Hz), 7.65 (d, 1H, J =
8.0 Hz), 7.70 (d, 1H, J = 3.4 Hz), 8.04 (s, 1H), 8.13 (s, 1H), 8.21 (d,
1H, J = 8.0 Hz); MS (FAB) m/z: 323 [M + H+]; IR (ATR): 1700 (C=O)
Synthesis of 2-{1-[6-(3-aminophenoxy)pyrazin-2-yl]-1H-
pyrrol-3-yl}acetic acid 7a
Compound 6 (50 mg, 0.14 mmol), N-Boc-3-aminophenol (59 mg,
0.28 mmol), copper powder (1 mg, 0.014 mmol), and Cs2CO3
(137 mg, 0.42 mmol) were mixed in DMF (0.5 mL) under argon
atmosphere. The reaction container was sealed and stirred at
1108C for 15 min under microwave irradiation. The reaction
mixture was cooled to room temperature, diluted with dichloro-
methane, and filtered. The filtrate was evaporated and the resi-
due was purified by flash chromatography on silica gel (hexane/
EtOAc 3 : 2). The resulting product was added to the solution of
1N NaOH aq. (0.4 mL) in dioxane (1 mL) and the mixture was
stirred at room temperature for 2 h. The reaction mixture was
neutralized with 1 N HCl aq. (0.4 mL) and extracted four times
cm– 1
.
1-[6-(1H-Indol-1-yl)pyrazin-2-yl]-1,4,5,6-
tetrahydropyridine-3-carboxylic acid 4c
Yield 61%;1H-NMR (500 MHz, DMSO-d6) d: 1.95–1.99 (m, 2H), 2.31
(t, 2H, J = 6.2 Hz), 3.82 (t, 2H, J = 5.7 Hz), 6.83 (d, 1H, J = 3.6 Hz),
7.20–7.27 (m, 2H), 7.67 (d, 1H, J = 7.3 Hz), 8.13 (d, 1H, J = 3.6 Hz),
8.38 (s, 1H), 8.40 (d, 1H, J = 8.2 Hz), 8.59 (s, 1H), 8.67 (s, 1H), 11.74
(s, 1H); MS (FAB) m/z: 321 [M + H+]; IR (ATR): 1624 (C=O) cm– 1
.
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Arch. Pharm. Chem. Life Sci. 2008, 341, 554–561
Synthesis of Disubstituted Pyrazines and Pyrimidines
559
with EtOAc. Combined organic layers were washed with brine,
dried, and evaporated to give compound 7a (13 mg, 29%); H-
Compounds 8b–r were obtained in the same manner as the
Procedure D.
1
NMR (500 MHz, DMSO-d6) d: 3.38 (s, 2H), 5.31 (br s, 2H), 6.24–6.26
(m, 1H), 6.34 (d, 1H, J = 7.7 Hz), 6.38 (s, 1H), 6.46 (d, 1H, J = 7.4 Hz),
7.07 (dd, 1H, J = 7.7, 7.4 Hz), 7.41–7.43 (m, 1H), 7.47 (dd, 1H, J =
2.6, 2.6 Hz), 8.13 (s, 1H), 8.73 (s, 1H); MS (FAB) m/z: 311 [M + H+]; IR
2-{1-[6-(3-Cyanophenylamino)pyrazin-2-yl]-1H-pyrrol-3-
yl}acetic acid 8b
1
(ATR): 3279, 3081 (NH2, OH), 1698 (C=O) cm– 1
.
Yield 57%; H-NMR (400 MHz, DMSO-d6) d: 3.42 (s, 2H), 6.29 (dd,
1H, J = 2.7, 1.7 Hz), 7.44 (d, 1H, J = 7.3 Hz), 7.53–7.59 (m, 3H), 7.96
(d, 1H, J = 8.3 Hz), 8.06 (s, 1H), 8.12 (s, 1H), 8.38 (s, 1H), 10.04 (s,
1H); MS (FAB) m/z: 320 [M + H+]; IR (ATR): 3302 (NH), 2227 (CN),
Compounds 7b–d were synthesized according to the Proce-
dure C.
1720 (C=O) cm– 1
.
2-{1-[6-(3-[Isopropylamino]phenoxy)pyrazin-2-yl]-1H-
pyrrol-3-yl}acetic acid 7b
2-{1-[6-(2-Chlorophenylamino)pyrazin-2-yl]-1H-pyrrol-3-
Yield 26%; 1H-NMR (500 MHz, DMSO-d6, 100 oC) d: 1.19 (d, 6H, J =
6.4 Hz), 3.39 (s, 2H), 3.57-3.62 (m, 1H), 6.26 (dd, 1H, J = 2.8, 1.6 Hz),
6.61 (d, 1H, J = 7.4 Hz), 6.69 (s, 1H), 6.73 (d, 1H, J = 7.9 Hz), 7.24
(dd, 1H, J = 7.9, 7.4 Hz), 7.37–7.41 (m, 1H), 7.43 (dd, 1H, J = 2.8,
2.6 Hz), 8.16 (s, 1H), 8.67 (s, 1H); MS (FAB) m/z: 353 [M + H+]; IR
yl}acetic acid 8c
1
Yield 78%; H-NMR (400 MHz, DMSO-d6) d: 3.38 (s, 2H), 6.22 (dd,
1H, J = 2.9, 1.7 Hz), 7.15 (dd, 1H, J = 7.7, 7.7 Hz), 7.38 (dd, 1H, J =
7.7, 7.7 Hz), 7.42–7.44 (m, 1H), 7.46 (dd, 1H, J = 2.9, 2.4 Hz), 7.53
(d, 1H, J = 7.7 Hz), 7.91 (d, 1H, J = 7.7 Hz), 8.14 (s, 1H), 8.31 (s, 1H),
9.11 (s, 1H), 12.15 (br s, 1H); MS (FAB) m/z: 329 [M + H+]; IR (ATR):
(ATR): 3122–2862 (NH, OH,iPr), 1729 (C=O) cm– 1
.
3350 (NH), 1732 (C=O) cm– 1
.
3-{6-[3-(Carboxymethyl)-1H-pyrrol-1-yl]pyrazin-2-
yloxy}benzoic acid 7c
2-{1-[6-(3-Chlorophenylamino)pyrazin-2-yl]-1H-pyrrol-3-
Yield 84%; 1H-NMR (500 MHz, DMSO-d6) d: 3.36 (s, 2H), 6.22–6.24
(m, 1H), 7.35–7.37 (m, 1H), 7.40 (dd, 1H, J = 2.6, 2.6 Hz), 7.56 (d,
1H, J = 9.3 Hz), 7.61 (t, 1H, J = 7.7 Hz), 7.79 (s, 1H), 7.86 (d, 1H, J =
7.0 Hz), 8.31 (s, 1H), 8.78 (s, 1H); MS (FAB) m/z: 340 [M + H+]; IR
yl}acetic acid 8d
Yield 71%; 1H-NMR (400 MHz, CD3OD) d: 3.52 (s, 2H), 6.33 (dd, 1H,
J = 3.2, 1.7 Hz), 7.01 (d, 1H, J = 8.0 Hz), 7.31 (dd, 1H, J = 8.2, 8.0 Hz),
7.49–7.55 (m, 3H), 7.91 (dd, 1H, J = 3.2, 2.1 Hz), 7.93 (s, 1H), 8.15
(s, 1H); MS (FAB) m/z: 329 [M + H+]; IR (ATR): 3338 (NH), 1686 (C=O)
(CHCl3): 1708 (C=O) cm– 1
.
cm– 1
.
4-{6-[4-(Carboxymethyl)-1H-pyrrol-1-yl]pyrazin-2-
2-{1-[6-(4-Chlorophenylamino)pyrazin-2-yl]-1H-pyrrol-3-
yloxy}benzoic acid 7d
Yield 87%; 1H-NMR (500 MHz, DMSO-d6) d: 3.33 (s, 2H), 6.15–6.17
(m, 1H, J = 3.2 Hz), 7.08 (d, 2H, J = 8.4 Hz), 7.22–7.24 (m, 1H),
7.26–7.29 (m, 1H), 7.88 (d, 2H, J = 8.4 Hz), 8.10 (s, 1H), 8.65 (s, 1H);
yl}acetic acid 8e
1
Yield 64%; H-NMR (400 MHz, DMSO-d6) d: 3.44 (s, 2H), 6.26 (dd,
1H, J = 2.9, 1.6 Hz), 7.40 (d, 2H, J = 8.8 Hz), 7.52–7.55 (m, 1H), 7.57
(dd, 1H, J = 2.9, 2.2 Hz), 7.71 (d, 2H, J = 8.8 Hz), 8.02 (s, 1H), 8.31 (s,
1H), 9.81 (s, 1H), 12.20 (br s, 1H); MS (FAB) m/z: 329 [M + H+]; IR
MS (FAB) m/z: 340 [M + H+]; IR (ATR): 1693 (C=O) cm– 1
.
(ATR): 3368 (NH), 1708 (C=O) cm– 1
.
General procedure for coupling of iodopyrazine
derivatives with anilines followed by hydrolysis
(Procedure D)
2-{1-[6-(3-Fluorophenylamino)pyrazin-2-yl]-1H-pyrrol-3-
yl}acetic acid 8f
Synthesis of 2-{1-[6-(3-methoxyphenylamino)pyrazin-2-
yl]-1H-pyrrol-3-yl}acetic acid 8a
Yield 56%; 1H-NMR (500 MHz, DMSO-d6) d: 3.43 (s, 2H), 6.29 (dd,
1H, J = 2.9, 1.7 Hz), 6.81 (dd, 1H, J = 8.2 Hz), 7.34–7.43 (m, 2H),
7.52–7.54 (m, 1H), 7.56 (dd, 1H, J = 2.9, 2.4 Hz), 7.66 (d, 1H, J =
12.2 Hz), 8.04 (s, 1H), 8.34 (s, 1H), 9.89 (s, 1H), 12.21 (br s, 1H); MS
Compound 6 (75 mg, 0.21 mmol), m-methoxyaniline (37 mg,
0.29 mmol), Pd2dba36CHCl3 (1 mg, 6 nmol), dppf (10 mg,
0.019 mmol), and Cs2CO3 (137 mg, 0.42 mmol) were mixed in
dioxane (1 mL) under argon atmosphere. The reaction container
was sealed, heated to 1108C and stirred for 24 h. The reaction
mixture was cooled to room temperature, diluted with dichloro-
methane and filtered. The filtrate was evaporated and the resi-
due was purified by flash chromatography on silica gel (hexane/
EtOAc 3 : 2). The resulting product was added to the solution of
1 N NaOH aq. (0.6 mL) in dioxane (1.5 mL) and the mixture was
stirred at room temperature for 2 h. The reaction mixture was
neutralized with 1 N HCl aq. (0.6 mL) and extracted four times
with EtOAc. Combined organic layers were washed with brine,
dried, and evaporated to give the compound 8a (40 mg, 59%);1H-
NMR (400 MHz, DMSO-d6) d: 3.41 (s, 2H), 3.77 (s, 3H), 6.27 (s, 1H),
6.57 (d, 1H, J = 8.0 Hz), 7.18 (d, 1H, J = 8.0 Hz), 7.25 (dd, 1H, J = 8.0,
8.0 Hz), 7.45 (s, 1H), 7.54 (s, 1H), 7.57 (t, 1H, J = 2.4 Hz), 8.02 (s,
1H), 8.28 (s, 1H), 9.69 (s, 1H), 12.06 (br s, 1H); MS (FAB) m/z: 325 [M
(FAB) m/z: 313 [M + H+]; IR (ATR): 3371 (NH), 1709 (C=O) cm– 1
.
2-{1-[6-(4-Fluorophenylamino)pyrazin-2-yl]-1H-pyrrol-3-
yl}acetic acid 8g
1
Yield 55%; H-NMR (400 MHz, DMSO-d6) d: 3.43 (s, 2H), 6.26 (dd,
1H, J = 2.9, 1.7 Hz), 7.20 (dd, 2H, J = 8.9, 8.9 Hz), 7.52 (s, 1H), 7.55
(dd, 1H, J = 2.9, 2.6 Hz), 7.67–7.71 (m, 2H), 7.99 (s, 1H), 8.27 (s,
1H), 9.68 (s, 1H); MS (FAB) m/z: 313 [M + H+]; IR (ATR): 3350 (NH),
1715 (C=O) cm– 1
.
2-{1-[6-(2-Trifluoromethylphenylamino)pyrazin-2-yl]-1H-
pyrrol-3-yl}acetic acid 8h
1
Yield 33%; H-NMR (400 MHz, DMSO-d6) d: 3.35 (s, 2H), 6.18 (dd,
1H, J = 2.9, 1.6 Hz), 7.32-7.34 (m, 1H), 7.37 (dd, 1H, J = 2.9, 2.2 Hz),
7.42 (dd, 1H, J = 7.6, 7.6 Hz), 7.69–7.78 (m, 3H), 8.04 (s, 1H), 8.28
+ H+]; IR (ATR): 3355 (NH), 1682 (C=O) cm– 1
.
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560
Y. Suzuki et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 554–561
(s, 1H), 8.96 (s, 1H), 12.05 (br s, 1H); MS (FAB) m/z: 363 [M + H+]; IR
(ATR): 3397 (NH), 1728 (C=O) cm– 1
2-{1-[6-(4-Sulfamoylphenylamino)pyrazin-2-yl]-1H-pyrrol-
.
3-yl}acetic acid 8p
Yield 26%; 1H-NMR (400 MHz, DMSO-d6) d: 3.45 (s, 2H), 6.28 (dd,
1H, J = 3.0, 1.6 Hz), 7.19 (s, 1H), 7.57 (s, 1H), 7.61 (dd, 1H, J = 3.0,
2.3 Hz), 7.81 (d, 2H, J = 9.0 Hz), 7.83 (d, 2H, J = 9.3 Hz), 8.08 (s, 1H),
8.39 (s, 1H), 10.06 (s, 1H); MS (FAB) m/z: 374 [M + H+]; IR (ATR):
2-{1-[6-(3-Trifluoromethylphenylamino)pyrazin-2-yl]-1H-
pyrrol-3-yl}acetic acid 8i
Yield 49%; 1H-NMR (400 MHz, CD3OD) d: 3.51 (s, 2H), 6.33 (dd, 1H,
J = 2.9, 1.7 Hz), 7.30 (d, 1H, J = 7.8 Hz), 7.50–7.54 (m, 3H), 7.78 (d,
1H, J = 8.3 Hz), 7.96 (s, 1H), 8.18 (s, 1H), 8.31 (s, 1H); MS (FAB) m/z:
3371-3077 [NH(SO2NH2, ArNHAr], 1704 (C=O) cm– 1
.
363 [M + H+]; IR (ATR): 3340 (NH), 1687 (C=O) cm– 1
.
2-{1-[6-(2-Methylphenylamino)pyrazin-2-yl]-1H-pyrrol-3-
yl}acetic acid 8q
Yield 66%;1H-NMR (400 MHz, DMSO-d6) d: 2.25 (s, 3H), 3.38 (s, 2H),
6.20 (s, 1H), 7.07 (dd, 1H, J = 7.7, 7.7 Hz), 7.22 (dd, 1H, J = 7.7,
7.7 Hz), 7.26 (d, 1H, J = 7.7 Hz), 7.41 (s, 1H), 7.44 (s, 1H), 7.60 (d,
1H, J = 7.7 Hz), 7.97 (s, 1H), 8.21 (s, 1H), 8.81 (s, 1H), 12.15 (s, 1H);
2-{1-[6-(4-Trifluoromethylphenylamino)pyrazin-2-yl]-1H-
pyrrol-3-yl}acetic acid 8j
Yield 41%; 1H-NMR (400 MHz, CD3OD) d: 3.53 (s, 2H), 6.34 (d, 1H, J
= 1.7 Hz), 7.52–7.54 (m, 2H), 7.64 (d, 2H, J = 8.8 Hz), 7.88 (d, 2H, J =
8.8 Hz), 7.98 (s, 1H), 8.19 (s, 1H); MS (FAB) m/z: 363 [M + H+]; IR
MS (FAB) m/z: 309 [M + H+]; IR (ATR): 3397 (NH), 1722 (C=O) cm– 1
.
(ATR): 3317 (NH), 1703 (C=O) cm– 1
.
2-{1-[6-(3-Methylphenylamino)pyrazin-2-yl]-1H-pyrrol-3-
yl}acetic acid 8r
2-(1-(6-(3-Nitrophenylamino)pyrazin-2-yl)-1H-pyrrol-3-
Yield 67%;1H-NMR (400 MHz, DMSO-d6) d: 2.32 (s, 3H), 3.43 (s, 2H),
6.26 (dd, 1H, J = 2.6, 1.6 Hz), 6.82 (d, 1H, J = 7.1 Hz), 7.23 (dd, 1H, J
= 8.3, 7.1 Hz), 7.47 (d, 1H, J = 8.3 Hz), 7.54–7.56 (m, 3H), 8.01 (s,
1H), 8.26 (s, 1H), 9.59 (s, 1H), 12.19 (s, 1H); MS (FAB) m/z: 309 [M +
yl)acetic acid 8k
1
Yield 69%; H-NMR (400 MHz, DMSO-d6) d: 3.43 (s, 2H), 6.30 (dd,
1H, J = 2.4, 1.5 Hz), 7.59–7.65 (m, 3H), 7.82 (dd, 1H, J = 8.0,
2.0 Hz), 7.87 (d, 1H, J = 7.6 Hz), 8.07 (s, 1H), 8.40 (s, 1H), 9.00 (s,
1H), 10.21 (s, 1H); MS (FAB) m/z: 340 [M + H+]; IR (ATR): 3317 (NH),
H+]; IR (ATR): 3304 (NH), 1697 (C=O) cm– 1
.
1682 (C=O), 1522 (NO2) cm– 1
.
Ethyl-2-[1-(6-iodopyrimidin-4-yl)-1H-pyrrol-3-yl]acetate
10
2-{6-[3-(Carboxymethyl)-1H-pyrrol-1-yl]pyrazin-2-
Using procedure A, compound 5 (100 mg, 0.65 mmol) was
coupled with 4,6-diiodopyrimidine 9 (260 mg, 0.78 mmol). Puri-
fication by flash chromatography on silica gel (hexane/EtOAc
4 : 1) yielded the compound 10 (87 mg, 38%); 1H-NMR (500 MHz,
CDCl3) d: 1.28 (t, 3H, J = 7.2 Hz), 3.51 (s, 2H), 4.18 (q, 2H, J = 7.2 Hz),
6.36 (dd, 1H, J = 3.2, 1.6 Hz), 7.42–7.44 (m, 1H), 7.46 (dd, 1H, J =
3.2, 2.3 Hz), 7.66 (d, 1H, J = 1.0 Hz), 8.61 (d, 1H, J = 1.0 Hz); MS
ylamino}benzoic acid 8l
Yield 74%; 1H-NMR (400 MHz, DMSO-d6) d: 3.43 (s, 2H), 6.28 (s, 1H),
7.08 (t, 1H, J = 7.6 Hz), 7.55 (s, 1H), 7.59 (t, 1H, J = 2.6 Hz), 7.65 (t,
1H, J = 7.8 Hz), 8.00 (d, 1H, J = 7.8 Hz), 8.16 (s, 1H), 8.42 (s, 1H),
8.49 (d, 1H, J = 8.3 Hz), 10.90 (s, 1H); MS (FAB) m/z: 339 [M + H+]; IR
(ATR): 1712 (C=O) cm– 1
.
(FAB) m/z: 358 [M + H+]; IR (ATR): 1719 (C=O) cm– 1
.
3-{6-[3-(Carboxymethyl)-1H-pyrrol-1-yl]pyrazin-2-
ylamino}benzoic acid 8m
Ethyl 2-{1-[6-(6-amino-1H-indazol-1-yl)pyrimidin-4-yl]-1H-
pyrrol-3-yl}acetate 12
Yield 70%; 1H-NMR (400 MHz, DMSO-d6) d: 3.43 (s, 2H), 6.26 (dd,
1H, J = 2.9, 1.6 Hz), 7.47 (dd, 1H, J = 8.3, 7.8 Hz), 7.57 (d, 1H, J =
7.8 Hz), 7.61–7.63 (m, 1H), 7.64 (dd, 1H, J = 2.9, 2.4 Hz), 7.77 (d,
1H, J = 8.3 Hz), 8.04 (s, 1H), 8.33 (s, 1H), 8.68 (dd, 1H, J = 1.8,
1.6 Hz), 9.92 (s, 1H); MS (FAB) m/z: 337 [M + H+]; IR (ATR): 1700
Using procedure A, compound 10 (95 mg, 0.27 mmol) was
coupled with 6-aminoindazole 11 (39 mg, 0.29 mmol). Purifica-
tion by flash chromatography on silica gel (hexane/EtOAc 4 : 1)
gave the compound 12 (54 mg, 56%);1H-NMR (500 MHz, CDCl3) d:
1.29 (t, 3H, J = 7.2 Hz), 3.54 (s, 2H), 4.07 (br s, 2H), 4.19 (q, 2H, J =
7.2 Hz), 6.37 (dd, 1H, J = 3.1, 1.7 Hz) , 6.71 (dd, 1H, J = 8.4, 2.0 Hz),
7.52 (d, 1H, J = 8.4 Hz), 7.58–7.60 (m, 1H), 7.62 (dd, 1H, J = 3.1,
2.3 Hz), 7.83 (d, 1H, J = 1.0 Hz), 8.07 (d, 1H, J = 0.6 Hz), 8.15 (d, 1H,
J = 2.0 Hz), 8.83 (d, 1H, J = 1.0 Hz); MS (FAB) m/z: 363 [M + H+]; IR
(C=O) cm– 1
.
4-{6-[3-(Carboxymethyl)-1H-pyrrol-1-yl]pyrazin-2-
ylamino}benzoic acid 8n
1
Yield 81%; H-NMR (400 MHz, DMSO-d6) d: 3.46 (s, 2H), 6.28 (dd,
1H, J = 2.9, 1.6 Hz), 7.57–7.59 (m, 1H), 7.61 (dd, 1H, J = 2.9,
2.4 Hz), 7.81 (d, 2H, J = 8.8 Hz), 7.95 (d, 2H, J = 8.8 Hz), 8.10 (s, 1H),
8.38 (s, 1H), 10.10 (s, 1H); MS (FAB) m/z: 337 [M + H+]; IR (ATR):
(ATR): 3416, 3349 (NH2), 1726 (C=O) cm– 1
.
2-(1-{6-[6-(Cyclopentylamino)-1H-indazol-1-yl]pyrimidin-
4-yl}-1H-pyrrol-3-yl)acetic acid 13a
3313 (NH), 1692 (C=O) cm– 1
.
To a stirred solution of the compound 12 (14 mg, 0.039 mmol)
and NaBH3CN (9 mg, 0.14 mmol) in DMF (0.2 mL) were added
cyclopentanone (0.02 mL, 0.20 mmol) and glacial acetic acid
(0.02 mL) at room temperature, and the mixture was heated to
508C and stirred for 12 h. The reaction mixture was cooled to
room temperature, made basic with sat. NaHCO3 aq., and
extracted twice with EtOAc. Combined organic layers were
washed with brine, dried, and evaporated, then the residue was
purified by flash chromatography on silica gel (hexane/EtOAc
2-{1-[6-(3-Sulfamoylphenylamino)pyrazin-2-yl]-1H-pyrrol-
3-yl}acetic acid 8o
Yield 36%; 1H-NMR (400 MHz, DMSO-d6) d: 3.42 (s, 2H), 6.25–6.27
(m, 1H), 7.33 (s, 2H), 7.44 (d, 1H, J = 7.8 Hz), 7.54 (dd, 1H, J = 8.3,
7.8 Hz), 7.60–7.63 (m, 1H), 7.64 (dd, 1H, J = 2.9, 2.4 Hz), 7.71 (d,
1H, J = 8.3 Hz), 8.05 (s, 1H), 8.36 (s, 1H), 8.52 (s, 1H), 10.01 (s, 1H),
12.16 (br s, 1H); MS (FAB) m/z: 374 [M + H+]; IR (ATR): 3345–3077
[NH (SO2NH2, ArNHAr)], 1695 (C=O) cm– 1
.
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Arch. Pharm. Chem. Life Sci. 2008, 341, 554–561
Synthesis of Disubstituted Pyrazines and Pyrimidines
561
4 : 1). The resulting product was added to the solution of 1 N
NaOH (0.06 mL) in dioxane (0.2 mL) and the mixture was stirred
at room temperature for 8 h. The reaction mixture was neutral-
ized with 1 N HCl aq. (0.06 mL) and extracted four times with
EtOAc. Combined organic layers were washed with brine, dried,
and evaporated to yield compound 13a (6 mg, 38%); 1H-NMR
(500 MHz, DMSO-d6) d: 1.52–1.63 (br m, 4H), 1.69–1.71 (br m,
2H), 1.98–2.04 (br m, 2H), 3.45 (s, 2H), 3.79–3.83 (br m, 1H),
6.31–6.33 (m, 1H), 6.37 (d, 1H, J = 5.9 Hz), 6.73 (d, 1H, J = 8.7 Hz),
7.52 (d, 1H, J = 8.7 Hz), 7.72–7.74 (m, 1H), 7.75–7.77 (m, 1H), 7.86
(s, 1H), 7.91 (s, 1H), 8.25 (s, 1H), 8.89 (s, 1H); MS (FAB) m/z: 403 [M +
[5] X. Xu, P. A. Toselli, L. D. Russell, D. C. Seldin, Nat. Genet.
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9–13.
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Biol. Chem. 2000, 275, 29618–29622.
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Biophys. Res. Commun. 1995, 208, 418–424.
H+]; IR (ATR): 3401 (NH), 1726 (C=O) cm– 1
.
[10] P. Zien, M. Bretner, K. Zastapilo, R. Szyszka, D. Shugar, Bio-
chem. Biophys. Res. Commun. 2003, 306, 129–133.
2-{1-[6-(6-[Isopropylamino]-1H-indazol-1-yl)pyrimidin-4-
yl]-1H-pyrrol-3-yl}acetic acid 13b
[11] S. Sarno, M. Ruzzene, P. Frascella, M. A. Pagano, et al., Mol.
Cell. Biochem. 2005, 274, 69–76.
By a procedure similar to the synthesis of 13a, compound 12
(27 mg, 0.075 mmol) was converted to the compound 13b
(20 mg, 71%) using acetone (0.03 mL, 0.375 mmol) for imine for-
mation; 1H-NMR (400 MHz, DMSO-d6) d: 1.20 (d, 6H, J = 6.3 Hz),
3.45 (s, 2H), 3.63-3.68 (br m, 1H), 6.23 (d, 1H, J = 7.8 Hz), 6.32 (dd,
1H, J = 2.9, 1.5 Hz), 6.72 (d, 1H, J = 8.8 Hz), 7.53 (d, 1H, J = 8.8 Hz),
7.72–7.74 (m, 1H), 7.75–7.78 (m, 1H), 7.85 (s, 1H), 7.91 (s, 1H),
8.25 (s, 1H), 8.89 (s, 1H), 12.26 (br s, 1H); MS (FAB) m/z: 377 [M +
[12] S. Sarno, M. Salvi, R. Battistutta, G. Zanotti, L. A. Pinna,
Biochim. Biophys. Acta 2005, 1754, 263–270.
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