Structure-based design of imidazo[1,2-a]pyrazine derivatives as selective inhibitors of Aurora-A kinase in cells

Article abstract of DOI:10.1016/j.bmcl.2010.08.091

Co-crystallisation of the imidazo[1,2-a]pyrazine derivative 15 (3-chloro-N-(4-morpholinophenyl)-6-(pyridin-3-yl)imidazo[1,2-a]pyrazin-8-amine) with Aurora-A provided an insight into the interactions of this class of compound with Aurora kinases. This led to the design and synthesis of potent Aurora-A inhibitors demonstrating up to 70-fold selectivity in cell-based Aurora kinase pharmacodynamic biomarker assays.

Full text of DOI:10.1016/j.bmcl.2010.08.091

Bioorganic & Medicinal Chemistry Letters 20 (2010) 5988–5993
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Structure-based design of imidazo[1,2-a]pyrazine derivatives as selective
inhibitors of Aurora-A kinase in cells
Nathalie Bouloc a, Jonathan M. Large a, Magda Kosmopoulou b, Chongbo Sun a, Amir Faisal a,
Mizio Matteucci a, Jóhannes Reynisson a, Nathan Brown a, Butrus Atrash a, Julian Blagg a, Edward McDonald a,
Spiros Linardopoulos a,c, Richard Bayliss b, Vassilios Bavetsias a,
⇑
a Cancer Research UK Cancer Therapeutics Unit, The Institute of Cancer Research, 15 Cotswold Road, Sutton, Surrey SM2 5NG, United Kingdom
b Section of Structural Biology, The Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, London SW3 6JB, United Kingdom
c The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, Fulham Road, London SW3 6JB, United Kingdom
a r t i c l e i n f o
a b s t r a c t
Article history:
Co-crystallisation of the imidazo[1,2-a]pyrazine derivative 15 (3-chloro-N-(4-morpholinophenyl)-6-
(pyridin-3-yl)imidazo[1,2-a]pyrazin-8-amine) with Aurora-A provided an insight into the interactions
of this class of compound with Aurora kinases. This led to the design and synthesis of potent Aurora-A
inhibitors demonstrating up to 70-fold selectivity in cell-based Aurora kinase pharmacodynamic
biomarker assays.
Received 30 June 2010
Revised 16 August 2010
Accepted 17 August 2010
Available online 21 August 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Aurora-A
Selectivity
Kinases
The Aurora proteins A, B, and C belong to a small family of
highly homologous serine/threonine kinases that play a critical
role in regulating mitosis.1–3 Aurora-A has been reported to be
overexpressed in a wide range of tumours such as breast, colorec-
tal, ovarian, and glioma.4–7 Likewise, Aurora-B is overexpressed in
human tumours including glioma, thyroid carcinoma, seminoma,
and colorectal cancer.8–10 During the last decade, the discovery
of small-molecule inhibitors of Aurora kinases as potential anti-
cancer agents has been the goal of numerous research groups,11,12
and has resulted in a number of compounds (e.g., VX-680 (MK-
0457),13 PHA-739358,14,15 AT9283,16 SNS-314,17 MLN8054,18 and
AZD115219) being assessed in clinical trials. Herein, we report
the discovery of imidazo[1,2-a]pyrazine derivatives as inhibitors
of Aurora kinases, and the structure-based design of potent inhib-
itors demonstrating isoform selectivity for Aurora-A kinase in cell
based pharmacodynamic biomarker assays.
High-throughput screening (HTS) of our in-house compound
collection versus Aurora-A provided the imidazopyrazine deriva-
tives 1 and 2 as promising hits (Fig. 1).20 Having confirmed
the Aurora-A inhibitory activity of 1 and 2 as 6.70 and 2.12 lM,
Table 1
Effect of C8–NH and C8–NMe on Aurora-A inhibition
Compound
R
Aurora-A IC50
6.70 2.46
(lM)
1
16
H
Me
27% Inhibition at 10 l
Ma, 64.0a
Figure 1. HTS hits, inhibition of Aurora-A.
Results shown are mean values of two independent determinations or mean ( SD)
⇑
Corresponding author. Tel.: +44 (0) 2086438901x4601.
E-mail address: vassilios.bavetsias@icr.ac.uk (V. Bavetsias).
for n >2 unless specified otherwise.
a
Results shown are mean values for samples run in triplicate.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.08.091

N. Bouloc et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5988–5993
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Table 2
Table 3
Effect of C8-substituent on Aurora-A inhibition
Effect of C6-substituent on Aurora-A inhibition
Compound R2
Aurora-A IC50
2.90
(
l
M) Ligand
Compound R1
Aurora-A IC50
(
lM)
Ligand
efficiencyb
efficiencyb
1
6.70 2.46
2.12 0.63
2.90
0.33
0.28
0.32
0.32
6a
0.32
36%, 30% inhibition
at 10
Ma
n.d.c
n.d.c
n.d.c
0.29
2
7a
7b
7c
7d
l
38%, 28% inhibition
at 10
Ma
6a
6b
l
5.5a
42%, 32% inhibition
at 10
l
Ma
6c
2.5a
0.30
9.70a
41%, 38% inhibition
at 10
Ma
7e
7f
n.d.c
n.d.c
l
6d
6e
6f
3.75
0.24
n.d.c
n.d.c
46% inhibition at
10
Ma
l
41% inhibition at
10
Ma
l
7g
7h
5.48 2.37
7.31 3.35
0.29
0.24
35% inhibition at
10
Ma
l
33% inhibition at
10
Ma
6g
6h
n.d.c
n.d.c
l
48%, 22% inhibition
7i
7j
n.d.c
0.21
32% inhibition at
10
Ma
a
at 10
lM
l
Results shown are mean values of two independent determinations or mean ( SD)
for n >2 unless specified otherwise.
7.20a
a
Results shown are mean values for samples run in triplicate.
b
Calculated using the formula: LE = [À1.4 Â log10 (IC50 (M))]/(number of heavy
atoms).
c
7.90a
6.70
0.20
0.20
n.d. = not determined.
7k
7l
respectively, we initiated a hit-to-lead programme aimed at estab-
lishing clear structure–activity relationship (SAR) trends in relation
to enzyme inhibition and identifying a compound series meriting
further optimisation towards a preclinical development candidate.
To achieve these goals, we first attempted to establish the role of
the C8–NH of the imidazo[1,2-a]pyrazine template for enzyme
inhibition. Subsequently, we investigated the Aurora-A inhibitory
effect of C6, C8 and C3 substituents on the scaffold (Fig. 1).
Starting from 6,8-dibromoimidazo[1,2-a]pyrazine (4) which
was synthesised by modifying a previously reported preparation,21
access was readily gained to 6,8-disubstituted derivatives 1 and 2
(Fig. 1), 6a–h (Table 2) and 7a–g (Table 3), by first introducing the
amino group at C8 via a SNAr substitution reaction22 followed by
7m
4.50
0.22
Results shown are mean values of two independent determinations or mean ( SD)
for n >2 unless specified otherwise.
a
Results shown are mean values for samples run in triplicate.
Calculated using the formula: LE = [À1.4 Â log10 (IC50 (M))]/(number of heavy
b
atoms).
c
n.d. = not determined.
Scheme 1. Reagents and conditions: (a) (i) 48% aq HBr, H2O, 90 °C, 1 h, then cool to rt, (ii) NaHCO3, iPrOH, 2-amino-3,5-dibromopyrazine, 90 °C, 5 h; (b) ArNH2, iPr2NEt, NMP,
microwave, 190 °C, 30 min or benzyl/aliphatic amine, iPr2NEt, BuOH, microwave, 110 °C, 30 min; (c) R2B(OH)2, Pd(PPh3)2Cl2, 2 M aq Na2CO3, CH3CN, microwave, 150 °C, 15–
30 min; for compounds 7a–g: R2B(OH)2/pinacol ester, Pd(dppf)Cl2, 2 M aq Na2CO3, CH3CN, microwave, 150 °C, 20 min.

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N. Bouloc et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5988–5993
Table 4
methoxybenzenesulfonyl chloride and pyridine-3-sulfonyl chlo-
ride, respectively, in pyridine/CHCl3 (v/v; 1:1).
Effect of C3-substituent on Aurora-A and cell growth inhibition
The 3-methylimidazo[1,2-a]pyrazine derivative 8 (Table 4) was
accessed via the route shown in Scheme 1 by replacing 4 with 6,8-
dibromo-3-methylimidazo[1,2-a]pyrazine which was prepared
from 2-amino-3,5-dibromopyrazine in a manner similar to that
reported for the synthesis of 8-bromo-6-chloro-3-methylimi-
dazo[1,2-a]pyrazine.23 The syntheses of the 3-bromo-, 3-chloro-,
and
3-(pyrid-3-yl)-imidazo[1,2-a]pyrazine-based
analogues
(compounds 11, 15, 12) are shown in Scheme 2. 3,6,8-Tribromoim-
idazo[1,2-a]pyrazine (compound 9, Scheme 2) was obtained from
6,8-dibromoimidazo[1,2-a]pyrazine (4) upon treatment with
NBS.21,24 Access to 6,8-dibromo-3-chloroimidazo[1,2-a]pyrazine
(compound 13, Scheme 2) was accomplished in a similar manner
to 9 but using NCS.23,25,26 A Suzuki cross-coupling between 10
and 3-pyridylboronic acid pinacol ester gave the 3-Br derivative
11 in 41% yield, and the 3-(pyrid-3-yl) analogue 12 in 22% yield
(Scheme 2). The assignment of regiochemistry in 11 was confirmed
by a Pd-catalysed debromination of 11 with triethylsilane (Scheme
2).27,28 The product of this reaction had a 1H NMR identical to that
of a sample of 2 obtained via the route shown in Scheme 1.
In an effort to establish the importance of C8–NH for enzyme
binding, the C8-N-methyl derivative of 1 (compound 16, Table 1)
was prepared via the route shown in Scheme 1. Compound 16 dis-
played reduced Aurora-A inhibitory potency relative to 1, indicat-
ing that C8–NH plays a role in binding to Aurora-A, a plausible
explanation being a hydrogen bonding interaction with the hinge
region of the kinase. Docking studies based on the crystal structure
of Aurora-A in complex with adenosine29 suggested that com-
pound 2 could occupy the ATP binding site with the N1 of the
imidazo[1,2-a]pyrazine core and C8–NH forming hydrogen bond-
ing interactions with Ala213 in the hinge region of the kinase.
Compound R3
Aurora-A
IC50 M)
Ligand
HCT116
M) GI50
M)
Hela
(l
efficiencya GI50
(l
(
l
2
8
11
H
Me
Br
2.12 0.63
0.208 0.052 0.32
0.152 0.090 0.33
0.28
n.db
7.2
n.db
6.5
2.3
13.4
12
15
4.20
0.22
n.db
3.9
n.db
28
Cl
0.190 0.138 0.32
Aurora-A IC50 results are mean values of two independent determinations or mean
( SD) for n >2.
a
Calculated using the formula: LE = [À1.4 Â log10 (IC50 (M))]/(number of heavy
atoms).
b
n.d = not determined.
C6–C bond formation under standard Suzuki cross-coupling condi-
tions (Scheme 1). The amide derivatives 7h, 7i (Table 3) were
obtained from the aniline 7g by reaction with the requisite acid
chloride in the presence of diisopropylethylamine. The ureas 7j
and 7k (Table 3) were synthesised by reacting the aniline 7g with
the appropriate aryl isocyanate in CHCl3. The sulfonamides 7l and
7m (Table 3) were prepared by treating the aniline 7g with 4-
Scheme 2. Reagents and conditions: (a) NBS, CH3CN/CH2Cl2, rt, 6 h; (b) NCS, CH3CN/DCE (v/v; 3:1), reflux; (c) 4-(4-morpholino)aniline, iPr2NEt, dioxane/DMF (v/v; 8:1),
microwave, 180 °C, 30 min; (d) 4-(4-morpholino)aniline, iPr2NEt, dioxane, microwave, 180 °C, 30 min; (e) 3-pyridylboronic acid, Pd(PPh3)2Cl2, 2 M aq Na2CO3, CH3CN,
microwave, 150 °C, 30 min; (f) 3-pyridylboronic acid pinacol ester, Pd(dppf)Cl2, 2 M aq Na2CO3, CH3CN, microwave, 150 °C, 25 min; (g) 10% Pd–C, Et3SiH, EtOH.

N. Bouloc et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5988–5993
5991
Figure 2. Co-crystal structures of compounds 15 and 17 bound to Aurora-A. A standard colour scheme is used throughout the figure: nitrogen, blue; oxygen, red; sulfur,
orange; chlorine, green; protein carbon atoms, light blue; compound carbon atoms, yellow. Putative hydrogen bonds are shown as dashed, black lines. Residues that differ
between Aurora-A and Aurora-B/C are highlighted in green. (A) Co-crystal structure of compound 15 bound to the catalytic domain of D274 N mutant of Aurora-A (PDB code
2XNE). (B) Sequence alignment of the hinge region of human Auroras -A, -B and -C shows the three residues which differ. (C) Chemical structure of compound 17. (D) Co-
crystal structure of compound 17 bound to the catalytic domain of wild-type Aurora-A (PDB code 2XNG). (E) Co-crystal structure of 17/Aurora-A shown in a view rotated by
45° around the vertical axis with respect to that shown in (D). In this view, the interaction between Thr217 and one of the two conformations of 17 is clearly shown.
Subsequently, working on the hypothesis that the imidazo[1,2-
a]pyrazine N1 and C8–NH bind to the hinge region of the protein,
we investigated the Aurora-A inhibitory effect of the C6, C8, and
finally the C3-substituent (Fig. 1).
of 3-aminophenyl as a C6-substituent was better tolerated; com-
pound 7g displayed comparable potency (IC50 = 5.48 M) to that
l
of 6a (Table 3). Subsequent utilisation of NH2 in 7g as a tether
for additional functionalisation provided the amides 7h, 7i, ureas
7j, 7k and sulfonamides 7l, 7m; all but 7i inhibited Aurora-A kinase
with IC50 values similar to that of 7g. Overall, the data in Table 3
pointed to the pyrid-3-yl as the optimum, most ligand efficient,31
C6-substituent.
The final part of this exploration was focussed at the C3-posi-
tion of the imidazo[1,2-a]pyrazine scaffold, an area of investigation
that proved more promising. Introduction of a 3-Me group in 2
provided a significant benefit on Aurora-A inhibition. Compound
8 was an approximately 10-fold more potent inhibitor of Aurora-
A compared with 2 (Table 4). A similar trend was observed with
the C3-bromo and C3-chloro analogues (compounds 11 and 15,
Table 4) that inhibited Aurora-A with IC50 values of 0.152 and
We began by exploring substitution at the C8-position in an at-
tempt to improve enzyme inhibitory activity. Compound 2 was a
slightly more potent inhibitor of Aurora-A kinase compared with
1 (Fig. 1, Table 2), prompting us to introduce a range of p-substit-
uents on C8–NHPh of 1 (compounds 6a–d, Table 2). As shown in
Table 2, analogues 6a–d exhibited similar Aurora-A inhibitory
potencies to that of the unsubstituted parent compound 1. The
IC50 values30 varied between 2.5 and 5.5
lM with the morpholino,
methoxy, and NHCOCH3 derivatives being the most potent inhibi-
tors of the enzyme. The introduction of a substituted benzyl (com-
pounds 6e, 6f; Table 2) or a substituted alkyl (6g, 6h, Table 2) had a
detrimental effect on inhibitor potency. The data in Table 2 pointed
to phenyl, 4-(morpholin-4-yl)phenyl and 4-methoxyphenyl as the
preferred C8-substituents.
Subsequently, the effect of the C6-substituent on Aurora-A inhi-
bition was explored in more detail. Replacement of the pyrid-3-yl
in 6a with a substituted pyrid-3-yl group (compounds 7a–c,
Table 3), 1-methyl-1H-pyrazole (compound 7d), 1-benzyl-1H-pyr-
azole (compound 7e), and 3-chlorophenyl (compound 7f) provided
no Aurora-A inhibitory benefit (Table 3). However, the introduction
0.190
id-3-yl substituent in 2 (compound 12, Table 4) led to a slight drop
in potency (Aurora-A IC50 = 4.20 M, Table 4). In relation to Aurora
isoform selectivity, compound 15 inhibited recombinant human
Aurora-C with an IC50 value of 1.95
M,32 less potently compared
lM, respectively. In contrast, the introduction of a C3-pyr-
l
l
with Aurora-A. Aurora isoform selectivity was also determined in
a cell-based assay in which the autophosphorylation of T288 in
Aurora-A was used as a biomarker for Aurora-A inhibition and

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N. Bouloc et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5988–5993
the phosphorylation of histone H3 at S10 as a biomarker for Aur-
ora-B inhibition.18 The cellular Aurora-A and Aurora-B IC50 values
for 15 were determined as 0.381 and 7.48 lM, respectively, indi-
by the introduction of a C6-phenyl ring bearing an electron rich
substituent capable of forming a hydrogen bond with Thr217 in
Aurora-A, which would sterically clash with the equivalent residue
in Aurora-B/C. On this basis, the sulfonamide derivative 17 (Figs.
2C and 4) was prepared from 14, by first reacting with 3-(amino-
methyl)phenylboronic acid under the conditions described in
Scheme 2, and then treating the cross-coupling product with
CH3SO2Cl in pyridine/CH2Cl2.
cating an approximately 19-fold selectivity in inhibiting Aurora-A.
Encouraged by the significant increase in Aurora-A inhibitory
potency with analogues 8, 11, and 15, we studied their cell growth
inhibitory activity in two cancer cell lines (Table 4). All three com-
pounds displayed cellular potency with GI50 values between 2.3
and 28
l
M (Table 4).33
Compound 17 inhibited recombinant human Aurora-A and Aur-
The binding mode of this class of imidazo[1,2-a]pyrazine-based
kinase inhibitors was elucidated by co-crystallisation of Aurora-A
catalytic domain D274N mutant with 15 to a resolution of 2.8 Å
(Fig. 2A, Supplementary data Table S1).34 As we hypothesised, 15
occupies the ATP-binding site with the imidazo[1,2-a]pyrazine
N1 and C8–NH forming hydrogen bonding interactions with the
Ala213 in the hinge region of the kinase. Imidazo[1,2-a]pyrazine
N1 is hydrogen bonded to the main chain NH of Ala213 (3.0 Å)
and the C8–NH to the carbonyl of Ala213 (2.8 Å) as shown in Figure
2A. The chlorine atom of the inhibitor sits in a hydrophobic pocket
formed from the gatekeeper residue (Leu210), and also Val147,
Leu194 and Leu263. Importantly, the C6-pyridyl-3-yl substituent
resides in close proximity to Thr217 of Aurora-A (3.5 Å closest con-
tact), whereas the equivalent residue in Aurora-B/C is a glutamic
acid (Fig. 2B). This is one of the three active site sequence differ-
ences between Aurora-A and Aurora-B/C. The Leu215 side chain
in Aurora-A (arginine in Aurora-B/C) points away from the active
site. There is little selectivity to be gained from targeting the side
chain of Arg220 (lysine in Aurora-B/C) which is highly mobile
and disordered in our co-crystal structure. We exploited this obser-
vation in the design of compounds with substantially enhanced
selectivity in inhibiting Aurora-A over isoforms -B and -C. It was
envisaged that isoform selectivity for Aurora-A could be achieved
ora-C with IC50 values of 0.060 and 2.35
17 displayed a 70-fold selectivity in inhibiting Aurora-A over Aur-
ora-B, the cellular IC50 values determined as 0.15 and 10.54 M,
lM, respectively. In cells,
l
respectively. In the same cellular assay, we found that the Aur-
ora-A inhibitor MLN805418 was 90-fold selective for Aurora-A over
Aurora-B. The crystal structure of 17 bound to Aurora-A was deter-
mined to a resolution of 2.6 Å, and shows that 17 occupies the ATP-
binding site in a mode similar to that observed for 15 (Fig. 2D). The
sulfonamide group in 17 is flexible and adopted two conformations
in the crystal structure, one of which showed the predicted hydro-
gen bond interaction with the side chain of Thr217 (Fig. 2E). We
propose that the selectivity of 17 for inhibition of Aurora-A is
attributable to the interaction of the sulfonamide group with
Thr217 in Aurora-A, and the likely clash of this group with the
more bulky equivalent glutamic acid in Aurora-B/C. In line with
this proposal, the acetamide counterpart of 17 (18, Fig. 4) was
46-fold selective in inhibiting Aurora-A in cells. In contrast, the
PhCH2NH2 derivative 19 (Fig. 4) was considerably less selective
for Aurora-A in cells compared with 17 (20-fold vs 70-fold). Addi-
tional evidence supporting the hypothesis that the observed selec-
tivity is driven by Thr217 came from experiments with T217E
mutant Aurora-A. As described earlier, inhibition of Aurora-A auto-
phosphorylation at T288 was used as a biomarker in cellular as-
says. As shown in Fig. 3, the T217E mutant Aurora-A was
resistant to inhibition by 17 and MLN8054, an Aurora-A selective
inhibitor. These results are in line with recent studies showing that
T217E and T217D mutants of Aurora-A are less sensitive to inhibi-
tion by MLN8054.35,36 It should be noted that Coumar et al. re-
cently reported a pyrazole-based Aurora-A selective inhibitor,
and rationalised the selectivity for inhibition of Aurora-A over Aur-
ora-B/C by proposing a similar argument, that is, hydrogen bond-
ing interaction with the backbone NH of Thr217 in Aurora-A and
steric clash with the equivalent residue (Glu) in Aurora B/C.37
In summary, HTS of our in-house compound collection against
recombinant human Aurora-A kinase provided 6,8-disubstituted
imidazo[1,2-a]pyrazine derivatives as promising hits for a hit-to-
lead exploration programme. It was found that the introduction
of C3–Cl, C3–Br or C3–Me substituent in 2 improved Aurora-A
inhibitory activity by approximately 10-fold. Co-crystallisation of
15 with Aurora-A provided
a clear understanding of the
interactions for this class of compound with Aurora kinases. Based
on this knowledge, we designed compound 17 that showed high
Figure 3. Aurora-A T217E mutant is resistant to inhibition by 17 and MLN8054. (A)
Western blot analysis showing inhibition of Aurora-A WT and T217E autophoph-
orylation (P-T288) by 17 and MLN8054. Hela cells transfected with Myc-Aurora-A
WT and T217E were treated with indicated concentrations of 17 and MLN8054 for
two hours. After protein extraction and separation by SDS–PAGE, autophosphory-
lation was detected using anti-phosphoThr288 antibodies (AuroraA-pThr288), total
Myc-Aurora-A protein was detected using an anti Myc antibody, and anti-GAPDH
was used as a loading control. (B) Quantification of the Western blots. P-T288 blots
were quantified and normalised to myc-Aurora-A. Results are represented as
percentage of untreated.
Figure 4. Compound 17 and analogues 18 and 19.

N. Bouloc et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5988–5993
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Matthews, J. E.; McMenamin, R. L.; Navarro, E. F.; O’Brien, M. A.; O’Reilly, M.;
selectivity for Aurora-A in cellular assays, comparable to that of
MLN8504. We propose that the observed Aurora isoform selectiv-
ity is driven by Thr217 in Aurora-A, the equivalent residue in Aur-
ora-B/C is a glutamic acid. We observed that in the crystal
structure of 17 bound to Aurora-A, the sulfonamide group of 17
interacts with Thr217. It was also shown that the T217E mutant
Aurora-A is considerably less sensitive to inhibition by compound
17. Finally, 17 inhibited the HCT116 cell growth with a GI50 value
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of 2.4 lM, and is a useful chemical tool for investigating the role of
selective Aurora-A inhibition.
Acknowledgments
We acknowledge NHS funding to the NIHR Biomedical Research
Centre. This work was supported by Cancer Research UK [CUK]
Grant number C309/A8274, and also the Breakthrough Breast Can-
cer. R.B. is a Royal Society University Research Fellow and acknowl-
edges the support of Breakthrough Breast Cancer Project Grant
AURA 05/06 and infrastructural support for Structural Biology at
the ICR from Cancer Research UK and the staff of ESRF beamline
ID14.1 for assistance with data collection. We also thank Dr. A. Mir-
za, and M. Richards for assistance with compound characterisation.
24. Sablayrolles, C.; Bonnet, P.-A.; Cros, G.; Chapat, J.-P.; Boucard, M. WO8804298
A1, 1988; Chem. Abst. 109, 231072.
25. For reviews on the synthesis and reactions of imidazo[1,2-a]pyrazines, see: (a)
Regan, A. C.. In Comprehensive Heterocyclic Chemistry III; Katritzky, A. R.,
Ramsden, C. A., Scriven, E. F. V., Taylor, R. J. K., Eds.; Elsevier: Oxford, 2008; Vol.
11, pp 551–586; (b) Montgomery, J. A.; SecristIII, J. A.. In Comprehensive
Heterocyclic Chemistry; Katritzky, A. R., Rees, C. W., Eds.; Pergamon Press:
Elsevier, 1984; Vol. 5, pp 607–668.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.08.091.
26. The characterisation data for compound 15 is as follows: 1H NMR (500 MHz,
DMSO-d6) 3.10 (t, 4H, J = 9.0 Hz, morpholine-CH), 3.75 (t, 4H, J = 8.8 Hz,
morpholine-CH), 6.99 (d, 2H, J = 9.0 Hz, 2,6-ArH or 3,5-ArH), 7.51 (dd, 1H,
J = 4.7 Hz, 7.9 Hz, pyridyl 5-H), 7.78 (s, 1H, imidazo[1,2-a]pyrazine 2-H), 7.94
(d, 2H, J = 8.8 Hz, 2,6-ArH or 3,5-ArH), 8.40 (s, 1H, imidazo[1,2-a]pyrazine 5-H),
8.43 (d, 1H, J = 7.8 Hz, pyridyl 4-H), 8.59 (d, 1H, J = 3.9 Hz, pyridyl 6-H), 9.27 (d,
1H, J = 2.0 Hz, pyridyl 2-H), 9.69 (s, 1H, NH); LC–MS (ESI, m/z) Rt = 7.29 min—
407, 409 [(M+H)+, Cl isotopic pattern]; ESI-HRMS calcd for C21H20ClN6O
(M+H)+: 407.1387, found: 407.1384.
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