Lead optimization of purine based orally bioavailable Mps1 (TTK) inhibitors

Article abstract of DOI:10.1016/j.bmcl.2012.04.131

Efforts to optimize biological activity, novelty, selectivity and oral bioavailability of Mps1 inhibitors, from a purine based lead MPI-0479605, are described in this Letter. Mps1 biochemical activity and cytotoxicity in HCT-116 cell line were improved. On-target activity confirmation via mechanism based G2/M escape assay was demonstrated. Physico-chemical and ADME properties were optimized to improve oral bioavailability in mouse.

Full text of DOI:10.1016/j.bmcl.2012.04.131

Bioorganic & Medicinal Chemistry Letters 22 (2012) 4377–4385
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Lead optimization of purine based orally bioavailable Mps1 (TTK) inhibitors
D. Vijay Kumar a, , Christophe Hoarau a, Matthew Bursavich a, Paul Slattum a, David Gerrish a,
⇑
Kraig Yager a, Michael Saunders a, Mark Shenderovich a, Bruce L. Roth b, Rena McKinnon b, Ashley Chan b,
Daniel M. Cimbora b, Chad Bradford c, Leslie Reeves c, Scott Patton c, Damon I. Papac c, Brandi L. Williams b,
Robert O. Carlson b
a Department of Medicinal Chemistry, Myrexis Inc., 305 Chipeta Way, Salt Lake City, UT 84108, USA
b Department of Discovery Biology, Myrexis Inc., 305 Chipeta Way, Salt Lake City, UT 84108, USA
c ADME Department, Myrexis Inc., 305 Chipeta Way, Salt Lake City, UT 84108, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Efforts to optimize biological activity, novelty, selectivity and oral bioavailability of Mps1 inhibitors, from
a purine based lead MPI-0479605, are described in this Letter. Mps1 biochemical activity and cytotoxicity
in HCT-116 cell line were improved. On-target activity confirmation via mechanism based G2/M escape
assay was demonstrated. Physico-chemical and ADME properties were optimized to improve oral bio-
availability in mouse.
Received 28 February 2012
Revised 27 April 2012
Accepted 30 April 2012
Available online 5 May 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Mps1 kinase
TTK kinase
Lead optimization
Cancer
Kinase selectivity
Mitotic kinases such as CDKs, Auroras, and PLKs, which are
overexpressed in proliferative cancer cells, play a critical role dur-
ing cell division1 and are considered attractive targets for inhibi-
tion of cancer cell proliferation. There are several mitotic kinase
inhibitors that are currently being investigated in the clinic. In this
context, we were interested in developing orally bioavailable
inhibitors of the mitotic kinase, Mps1 (also known as TTK). Mps1
kinase is a dual specificity serine/threonine and tyrosine protein ki-
nase2 and is essential for the proper attachment of chromosomes
to the mitotic spindle. Inhibiting Mps1 has been shown to cause
chromosomal missegregations followed by cell death.3 Since we
started working on this program, several Mps1 kinase inhibitors
were reported in the literature such as Reversine,4 NMS-P715,5
MPS1-IN-1,6 and AZ 31467 (Fig. 1).
Based on the in-house as well as invitrogen kinase profiling it
had acceptable selectivity against other kinases.3
Significantly, MPI-0479605 dosed intra-peritoneally (IP), dem-
onstrated dose dependent and statistically significant tumor
growth inhibition (75% TGI @ 150 mg/kg, Q4DX6; 49% TGI @
30 mg/kg, QDX15) in HCT-116 xenograft studies in mice.3 As far
as ADME data is concerned, 1 has solubility of 16 l
M (pH 7.4)9
and low metabolic stability in mouse liver microsomes (20%
remaining at 40 min)10 and some permeability in the PAMPA assay
(Papp = 400 Â 10À6 cm/s).11 This was reflected in low (ꢀ20%) oral
bioavailability in mouse with solubility limited oral
pharmacokinetics.12
Docking13 of compound 1 in the ATP-binding site of Mps1 crys-
tal structure 3H9F reveals a three-point hinge binding motif with
hydrogen bond acceptor C=O of hinge i+1-th residue Glu603
(where i-th residue is the gatekeeper Met602), donor NH of i+3-
th residue Gly605 and acceptor C=O of Gly605 interaction with
two nitrogens of the purine core and with C-6 aniline NH, respec-
tively (Fig. 3). These crucial interactions anchor the molecule in the
active site, while orienting the C-6 cyclohexyl ring toward the ri-
bose binding pocket, and the C-2 aniline group towards a largely
solvent exposed region of the active site.
Recently, we disclosed biological data for one of our earlier
Mps1 inhibitors, MPI-0479605 (1) (Fig. 2).3 It has potent activity
against the Mps1 enzyme (IC50 = 0.004
(HCT-116; IC50 = 0.1 M). Commensurate activity in the mecha-
nism-based G2/M escape assay (EC50 = 0.3
M)8 suggests that cyto-
lM) and good cytotoxicity
l
l
toxicity of this compound is due to inhibition of the Mps1 kinase.
Since compound 1 shared structural similarity with Reversine
(Fig. 1), a known multi-kinase (including Mps1) inhibitor,4 we
needed to structurally modify compound 1 to improve novelty.
⇑
Corresponding author. Tel.: +1 801 214 7883; fax: +1 801 214 7992.
E-mail address: dvijayku@hotmail.com (D. Vijay Kumar).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.04.131

4378
D. Vijay Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4377–4385
O
O
S
N
O
HN
N
HN
N
N
F3CO
N
N
N
H
OH
N
H
N
H
O
O
NH
N
MPS-1-IN-1
NMS-P715
N
O
HN
O
N
N
N
N
O
N
N
N
N
H
N
N
H
N
N
H
O
AZ 3146
Reversine
Figure 1. Structures some of the disclosed Mps1 inhibitors.
aqueous solubility, metabolic stability and permeability were also
assessed.
HN
O
Optimization efforts were begun at the C-6 position and were
aimed at identifying a more hydro/amphiphilic replacement for
the cyclohexylamino group of compound 1. Keeping the C-2 group
constant as 2-methyl-4-morpholino aniline, systematic changes to
the C-6 position were made. The effects of these changes on po-
tency and solubility are summarized in Table 1. Compounds not
meeting a 30 nM potency threshold against the Mps1 kinase did
not advance into cell-based assays. Introduction of solubilizing
groups at the C-6 position, as in compounds 2, 4 and 7 for example,
resulted in significantly diminished activity against Mps1 kinase.
Changes to the linking element were similarly deleterious to po-
tency, where N-disubstitution (compounds 5), and linking through
carbon and oxygen, (compounds 3 and 8, respectively) were not
tolerated. Replacement of the cyclohexyl group with short-chain
aliphatic, cycloalkyl and aromatic groups led to compounds with
significant loss of activity against Mps1 kinase (data not shown).
With C-6 proving intolerant to significant change, we settled on
cyclohexyl and refocused on modifications to the C-2 aniline moi-
ety as an avenue to improved physico-chemical properties and oral
pharmacokinetics.
6
N
N
N
N
H
N
N
H
2
(1)
Figure 2. Structure of MPI-0479605 (1).
The presence of an ortho-substituted aniline at the purine C-2
position is an essential selectivity element of this class of Mps1
inhibitors. This ‘ortho selectivity’ effect is illustrated in Table 2
where 1 and des-methyl derivative Reversine 10 were assayed
against the related mitotic kinases Aurora A and B, and PLK1. In
each instance the selectivity of compound 1 for Mps1 was at least
1000-fold.
The role of the ortho substituent in influencing selectivity can be
rationalized by molecular modeling studies (Fig. 4). The aniline
ortho group makes van der Waals contacts with the side chain of
hinge residue Cys604, along with the backbone of hinge residue
Asn606 and with the d-methyl group of non-hinge residue Ile531
(see Fig. 3). In Aurora A, respective positions are occupied by resi-
dues Tyr212, Pro214 and Leu139.
The steric demands imparted by the Tyr212 hydroxyphenyl
group are significantly greater than that presented by the Cys605
thiomethyl group present in Mps1. Tyr212 4-OH group and espe-
cially the ring 3-CH position make unfavorable contacts with the
aniline ortho group. The presence of a proline residue in position
i+4 significantly changes the backbone conformation of hinge res-
idues i+4 and i+5 in Aurora A. In addition, the second d-methyl
Figure 3. Compound 1 docked in Mps1 crystal structure 3H9F. Protein residues and
ligand are displayed as sticks colored by atom type with protein carbons colored
gold and ligand carbons colored white.
With 1 as the lead compound, we initiated efforts toward identify-
ing novel, potent, and selective Mps1 kinase inhibitors with im-
proved oral pharmacokinetics.
During this phase of lead optimization efforts, we opted to con-
serve the three hinge-binding interactions presented by the purine
core, and instead focused on specific changes to the C-6 and C-2
positions. Since the primary goal of this optimization campaign
was improved oral bioavailability, the effects of substitution on

D. Vijay Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4377–4385
4379
Table 1
SAR of the purine C-6 substituenta
R
N
O
N
N
N
N
H
N
H
8
#
R
Mps1 IC50
0.36
(l
M)
HCT 116 Cytotoxic IC50
(l
M)
G2/M Chkpt Esc. EC50
(l
M)
Sol. pH 7.29
(lM)
O
N
2
38
H
H
N
H
3
4
0.17
19
47
NH2
0.035
3.2
2.7
HN
O
5
6
0.13
23
10
N
O
H
O
N
N
0.028
0.79
1.3
H
H
N
7
8
9
0.23
69
19
23
N
0.014
0.001
0.13
0.69
0.31
1.5
O
OH
H
N
a
Mean of triplicates values with standard deviation of 10%.
group of the Leu139 side chain in Aurora A overlaps with the posi-
tion of ortho substituent of compound 1 bound to Mps1 that con-
tains Ile531 residue in the same position (see Fig. 4). As a result
the Aurora A ATP binding site does not present a sufficiently large
cavity in the hinge loop region to accommodate any heavy atom
(non-hydrogen) at the ortho position of the C-2 aniline.
In general, compounds with an ortho substituent are expected
to demonstrate selectivity for Mps1 versus kinases possessing a
large side chain residue (Tyr, Phe) in the i+3 hinge loop position.
For instance Aurora B has active site residues almost identical
to those of Aurora A with bulky Phe residue in position i+3,
which contributes to the observed selectivity for compound 1.
Moderate selectivity is anticipated against kinases containing
medium-size side chains (Leu, Ile, Met) at position i+3. On the
other hand, low sequence identity between Mps1 and PLK1 (25%)
explains lack of activity at PLK1 for both Mps1 inhibitors 1 and
10 (see Table 2).
significantly lower potency. Surprisingly, the trifluoromethoxy
and trifluoromethyl derivatives 12 and 17, demonstrated unac-
ceptably poor cellular activities despite very good biochemical po-
tency (IC50 = 0.001 lM and 0.003 lM, respectively). Based on these
studies, the ortho-methoxy group present in 15 was deemed opti-
mal, and was therefore held constant during subsequent investiga-
tions. Not surprisingly, 15 had a similar selectivity profile against
related mitotic kinases such as Aurora A & B and PLK1 as observed
for compound 1.
With the optimal ortho selectivity element identified, our atten-
tion was focused on optimizing the remaining C-2 aniline substit-
uents. We knew from previous studies that only para substituents
(to the aniline nitrogen) preserved potency against Mps1. All other
regio-isomers explored, di-ortho or meta anilino for example,
exhibited significantly diminished Mps1 inhibition (by 50- to
100-fold, data not shown). As a result, the search for enhanced
physico-chemical properties and oral bioavailability were neces-
sarily focused on modifications to the para-position of the C-2 ani-
line. To this end, numerous para-position modifications were
assessed. It was determined that replacement of the morpholine
group, with a substituted piperazine or piperdine, resulted in a ser-
ies of promising inhibitors, Tables 4 and 5.
Various ortho groups on the aniline moiety were investigated
and the results are summarized in Table 3. Relatively small groups
such as those present in compounds 1 (methyl), 15 (methoxy) and
16 (ethoxy), were well-tolerated by the Mps1 enzyme and exhib-
ited the desired cellular phenotypes (less than 0.1 lM activity in
HCT-116 toxicity and G2/M escape assay). Inhibitors bearing larger
substituents, such as, methylsulfone 13 or methyl sulfide 14, had
Table 4 highlights some of the numerous para-position pipera-
zine analogs that were prepared during this SAR investigation.

4380
D. Vijay Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4377–4385
Table 2
Table 3
Effect of ortho substitution on selectivitya
C-2 Aniline ortho substitution SARa
H N
O
H N
N
O
N
N
N
N
N
N
N
N
H
N
N
H
N
H
H
R
R
R
Mps IC50
M)
Aur A IC50
M)
Aur B IC50
M)
PLK1 IC50
M)
R
Mps1 IC50
M)
HCT 116 IC50
M)
G2/M Chkpt Esc. EC50
(l
M)8
(
l
(
l
(
l
(l
(
l
(
l
10
1
H
0.004
0.11
>10
0.075
>5
>5
>5
1
-Me
0.004
0.001
1
0.1
0.54
0.3
0.38
Me 0.004
12
13
14
15
16
17
-OCF3
-SO2Me
-SMe
-OCH3
-OCH2CH3
-CF3
a
Mean of triplicates values with standard deviation of 10%.
0.51
0.004
0.001
0.003
0.033
0.07
0.52
0.023
0.041
1
Modifications to the piperazine group were generally well toler-
ated by the enzyme and had little impact on the Mps1 biochemical
and cellular activities suggesting minimal interactions between the
protein and this distal portion of the molecule. This assumption is
supported by Mps1 docking studies which orient the C-2 aniline,
and specifically the para substituents, toward the solvent exposed
region of the ATP-binding site. Therefore, we viewed this region as
a potential fertile ground for optimization of physico-chemical
properties.
Although improvements in solubility were modest, many of the
compounds in this series, for example 19, 20, 21, 23, 25 and 27
demonstrated substantially improved metabolic stability and
PAMPA permeability, and these compounds were advanced into
mouse PK studies. Compound 22 had good solubility owing to its
basic substituent; however, not surprisingly this compound had
poor permeability in the PAMPA assay.
a
Mean of triplicates values with standard deviation of 10%.
odds of good oral absorption, we opted to reduce TPSA by replacing
the piperazine with a piperidine moiety.
Selected compounds from the piperidine subseries are shown in
the Table 5. As mentioned previously, and based on our binding
model, substituents in this region of the inhibitor extend into the
solvent exposed area of the protein and exert little effect on inhib-
itory activity. Certain substitutions on the piperidine ring, as exem-
plified by compounds 30–32, 34 and 36, resulted in significantly
enhanced solubility, PAMPA permeability and metabolic stability.
These compounds were advanced into mouse PK studies. Here
again, basic amine derivatives, for example 29 and 35, had good
aqueous solubility but at the expense of permeability. Azetidine
37 had lower than desired activity in the mechanism-based assay
(G2/M escape assay).
Most of the compounds in the piperazine subseries (Table 4)
had one or two violations (molecular weight and/or total polar
surface area, TPSA) of the Lipinski ‘rule of five’.14 To increase the
In vitro and mouse xenograft3 data suggest that a 24 h constant
exposure to an Mps1 inhibitor is required for robust responses. With
Figure 4. Overlay of ATP binding sites of Mps1 crystal structure 3H9F and Aurora A crystal structure 2NP8 with Compound 1 docked to Mps1. Protein residues and ligand are
displayed as sticks colored by atom type with carbons of Mps1 colored gold, carbons of Aurora A colored grey and ligand carbons colored white. Residue labels are shown for
Aurora A structure only.

D. Vijay Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4377–4385
4381
Table 4
C-2 Piperazine substitution SARa
R
1
HN
N
N
N
N
N
N
H
N
H
O
8
#
R
Mps1 IC50
0.001
(l
M) HCT 116 Cytotoxic IC50
0.088
(
l
M) G2/M Chkpt Esc. EC50
(l
M) Sol. pH 7.29
19
(l
M) PA MPAb MLM stability % remc
18
H
O
0.16
NA
NA
77
O
S
19
0.002
0.011
0.001
0.015
10
848
O
O
O
20
0.002
0.022
10
725
81
28
68
S
N
O
21
0.003
0.015
0.014
19
OH
O
22
23
0.003
0.009
0.017
0.022
0.018
0.029
75
19
Low
978
46
50
N
O
N
O
O
H
N
N
N
24
25
0.003
0.009
0.023
0.051
0.019
0.089
10
38
NA
17
38
976
O
26
27
0.005
0.009
0.027
0.066
0.1
19
5
Low
47
59
N
OH
O
0.17
1874
a
b
c
Mean of triplicates values with standard deviation of 10%.
PAMPA permeability Papp 10À6 cm/s.7
% Remaining in mouse liver microsomal stability assay.
prolonged exposure appearing critical for efficacy, we adopted an
abbreviated, mouse PK screening paradigm in which compound
plasma levels were evaluated at 4 and 8 h following oral administra-
tion at 10 mg/kg.15 This abbreviated protocol obviated the need for
individual IV and oral PK analyses on all compounds meeting the po-
tency and ADME criteria (such as compounds shortlisted for PK
studies from Tables 4 and 5). This approach improved the through-
put of the compounds going through the PK studies. Table 6 shows
the list of compounds along with plasma concentration data at the 4
and 8 h time points.
Compounds demonstrating a plasma concentration of less than
10 ng/ml exposure at 8 h were abandoned, since they were not
likely to have sufficient exposure to see a biological response.
Compound 1 in this study had oral plasma exposure of 105 ng/ml
and 72.3 ng/ml at 4 h and 8 h time point respectively. Six Mps1
inhibitors 20, 28, 31, 32, 33 and 36 (Table 6) demonstrated
acceptable plasma levels at the 4 and 8 h time points post oral
administration, and these compounds were chosen for more exten-
sive PK studies.16
exposure at the 8 h time point also showed improved bioavailability
over Compound 1. Importantly, compounds 28, 31 and 36 exhibited
oral bioavailability values of 28%, >83%, and 38%, respectively, all of
which were improvements over 1. Compound 31, which had the
highest exposure at the 8 h time point, exhibited slightly higher
clearance than desired, but had the highest oral bioavailability
(>83%) and a good IV half life in the mouse. As a consequence of these
studies, further support for the correlation between PAMPA perme-
ability and oral bioavailability was established. For example, com-
pound 29 had virtually no measurable permeability by PAMPA and
it was undetectable in plasma at the 4 and 8 h time points.
A multi-faceted lead optimization strategy resulted in several
novel purine-based Mps1 inhibitors with improved physico-chem-
ical properties, for example aqueous solubility, permeability, and
oral bioavailability, while maintaining potent and selective activity
against the Mps1 target. Details of the efficacy demonstrated by
these compounds in tumor xenografts will be communicated in fu-
ture publications.
The Mps1 inhibitors described in this Letter were prepared
according to the synthetic procedures previously described17 and
were adequately characterized.18
Data from the two point assay format translated well into data ob-
tained from full PK studies (Table 6). Compounds with the highest

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D. Vijay Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4377–4385
Table 5
C-2 Piperidine substitution SARa
R1
H N
N
N
N
N
H
N
N
H
O
Sol. pH 7.29
10
(lM)
PAMPAb
700
MLM stability %c
53
8
#
R1
Mps1 IC50
0.011
(lM)
HCT 116 Cytotoxic IC50
0.022
(lM)
G2/M Esc. EC50
0.031
(
lM)
O
28
N
O
29
0.004
0.058
0.077
38
0.0
60
N
N
O
30
31
32
0.004
0.005
0.003
0.05
0.13
0.12
0.07
19
38
19
744
70
68
61
N
N
O
0.049
0.036
2087
409
O
O
N
N
N
O
33
0.005
0.051
0.065
38
530
43
O
N
34
35
0.004
0.007
0.074
0.059
0.055
0.097
19
75
480
47
48
N
N
N
Low
O
O
36
37
0.007
0.004
0.015
0.05
0.026
0.26
19
19
1688
NA
59
65
O
N
OH
a
b
c
Mean of triplicates values with standard deviation of 10%.
PAMPA permeability Papp 10À6 cm/s.7
% Remaining in mouse liver microsomal stability assay.
Table 6
Mouse IV and Oral PK parameters
#
4 h Conc. (ng/ml)
8 h Conc. (ng/ml)
IV Cla
IV T1/2 (h)
PO AUCb
PO Cmax
(lM)
%F
20
25
28
29
30
31
32
33
36
155.8
66.3
104.7
BQL
17.5
2.9
1032
NA
1810
1.5
NA
2.2
1730
NA
1714
1.0
NA
2.6
17.9
NA
31
44.2
BQL
1.68
186.8
20.9
39.9
69.2
16.7
NA
NA
2.9
0.9
2.8
2.0
NA
NA
2.6
1.4
0.3
1.8
NA
>83
23.1
6.9
36
435.2
97.04
179.7
137.6
1048
1398
1255
2051
10686
1651
547
1774
a
ml/h/kg.
h.ng/ml.
b
Briefly, the inhibitors illustrated in Tables 1–3 were prepared
amines such as morpholine followed by palladium catalyzed
reduction of nitro group gave desired aniline derivatives 39a–h.
2,6-dichloropurine 40 was treated under thermal conditions with
various amines such as cyclohexyl amine, to get 6-substituted
purine derivatives 41, which upon THP-protection provided key
according to the synthesis as described in Scheme 1 from appropri-
ate starting materials.17 Nucleophilic substitution of fluoro group
in 4-fluoro-1-nitrobenzene 38 (with suitable ortho substituent
such as methyl, methoxy etc, next to the nitro group) with various

D. Vijay Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4377–4385
4383
O
HN
N
O
N
(b)
N
F
N
(a)
N
N
H
N
H
O2N
H2N
X
X
X
X = Me
X = H
1
X = Me
X = H
39a
39b
39c
38
10
12
X = OCF3
X = OCF3
X= SO2Me 13
X= SO2Me 39d
X = SMe
X= OMe
14
15
X = SMe
X= OMe
39e
39f
X = OC2H5 16
X = OC2H5 39g
X = CF3
17
X = CF3
39h
R1
N
Cl
R1
N
N
(e)
N
(d)
(c)
N
N
N
N
Cl
N
H
N
Cl
N
H
N
Cl
O
40
41
R1 = NHC6H12
42a
42b
42c
R1 = 4-morpholinocyclohexanamine
R1 = Morpholine
O
R1
N
N
R1 = N-[(4-aminocyclohexyl)methyl]-2,2,2-trifluoro-
N
N
acetamide
42d
N
H
N
R1 = ethyl 4-aminopiperidine-1-carboxylate 42e
H
Me
R1 = 4-aminocyclohexanol
42f
R1 = NHC6H12
1
2
R1 = 4-morpholinocyclohexanamine
R1 = 4-(aminomethyl)cyclohexanamine
R1 = Morpholine
4
5
6
7
9
R1 = ethyl 4-aminopiperidine-1-carboxylate
R1 = 4-aminopiperidine
(f)
R1 = 4-aminocyclohexanol
Scheme 1. Reagents and conditions: (a) (i) Morpholine neat, 80 °C, quant.; (ii) 10% Pd/C, MeOH, H2, balloon, quant.; (b) (i) 42a, Pd(OAc)2, BINAP, Cs2CO3, toluene, 80–100 °C,
60–90%; (ii) 4M HCl in 1,4-dioxane, MeOH, RT, 60–80%; (c) Amine, Et3N, 80 °C, EtOH, 60–80%; (d) dihydropyran (DHP), p-TSA (cat), reflux, THF, 50–75%; (e) (i) Aniline 39a,
Pd(OAc)2, BINAP, Cs2CO3, toluene, 80–100 °C, 60–90%; (ii) 4M HCl in 1,4-dioxane, MeOH, rt, 60–80%; (f) 4 NaOH, MeOH, THF, 65–75%.
intermediates 42a–f. Buchwald coupling of various intermediates
42a–f with aniline derivative 39a and subsequent THP deprotec-
O
tion under acidic conditions gave the desired products 1, 2, 4–7
and 9. On the other hand, compounds 12–17 in Table 3 were pre-
pared via Buchwald coupling of aniline derivatives 39b–h with
purine intermediate 42a (Scheme 1) followed by deprotection.
Compound 3 from Table 2 was prepared according to Scheme 2,
where Suzuki coupling19 with cyclohexylmethylboronic acid with
THP protected 2,6-dichloro purine gave intermediate 43. Buchwald
coupling of 43 with aniline 39a furnished desired compound 3.
Compound 8 was obtained via treatment of 2,6-dichloro purine
with cyclohexanol in sodium, followed by acid catalyzed C-6 chlo-
rine displacement with aniline 39a under microwave conditions.
Generally, the microwave based acid catalyzed method of intro-
ducing aniline group at C-6 position on the purine was less efficient
than Buchwald coupling methods.
The piperazine analogs shown in the Table 4 were prepared
according to Scheme 3. Buchwald coupling of 42a with tert-butyl
4-(4-amino-3-methoxy-phenyl)piperazine-1-carboxylate (pre-
pared employing similar procedure as described for aniline 39f
using tert-butyl piperazine-1-carboxylate) followed by deprotec-
tion gave key intermediate 18, which was used for preparing var-
ious derivatives shown in the Table 4.
N
N
N
N
(b)
N
(a)
N
40
N
H
N
N
H
N
Cl
Me
O
3
43
(c)
O
N
O
O
N
N
N
(d)
N
N
N
N
H
N
N
H
Cl
H
Me
44
8
Scheme 2. Reagents and conditions: (a) (i) Dihydropyran (DHP), p-TSA (cat), reflux,
THF, 75%; (ii) cyclohexylmethylboronic acid, Pd(PPh3)4, dioxane, 80–110 °C, 55%;
(b) (i) Aniline 39a, Pd(OAc)2, BINAP, Cs2CO3, toluene, 80–100 °C, 60–70%; (ii) 4M HCl
in 1,4-dioxane, MeOH, 80%; (c) cyclohexanol, Na, 90 °C, 53%; (d) 39a, p-TSA (cat),
microwave, 135–150 °C, 30 min, 12–30%.
obtained similarly using aniline derivative with appropriate piper-
idine carboxylic acid ester in the coupling reaction. Finally, amide
coupling of acid 46 with various amines such as morpholine fol-
lowed by hydrolysis of the THP protecting group gave the desired
amides 29, 30, 32, 33, 35, 36 and 37. Some of these amides were
reduced with LiAlH4 to give aminoalkyl piperadine derivatives
such as 31 and 34.
N-linked piperidine analogs shown in the Table 5 were pre-
pared according to Scheme 4. Compound 28 was obtained via
Buchwald coupling of 2-methoxy-4-(4-morpholino-1-piperi-
dyl)aniline with purine derivative 42a. Key intermediate 46 was

4384
D. Vijay Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4377–4385
O
NH
HN
N
O
HN
N
N
N
(a)
N
(b)
N
N
N
42a
N
N
H
N
H
N
N
H
OMe
OMe
O
18
45
(c)
O
R2
N
HN
N
N
R2
HN
N
N
N
(d)
N
N
N
N
H
N
H
N
H
N
N
H
OMe
OMe
R2 = 2-pyridyl
R2 = 3-tetrahydrofuranyl
25
27
R2 = 4-hydroxycyclohexyl 21
R2 = 2-pyridyl
24
R2 = 3-tetrahydrofuranyl
27a
O
O
N
O
R3
S
HN
N
N
R4
HN
N
N
N
(g)
N
N
N
(e)
18
N
H
N
H
N
H
N
H
N
OMe
OMe
(f)
R3 = -Me
19
R4 = N-Methyl piperazine 22
R4 = 3-hydroxypyrrolidine 26
R3 = -CH2CH2CH2N(CH2)4O 20
O
NH
N
HN
N
O
N
N
N
H
N
N
H
OMe
23
Scheme 3. Reagents and conditions: (a) tert-butyl 4-(4-amino-3-methoxy-phenyl)-piperazine-1-carboxylate, BINAP, Pd(OAc)2, Cs2CO3, toluene, 90 °C, 74%; (b) 4M HCl in 1,4-
dioxane, MeOH, 80%; (c) Acid, EDCI, HOBt, DIEA, DMF; (d) LiAlH4, THF, rt; (e) Amine, p-nitro phenylchloroformate, Et3N, NMP or Isocyanate, DIEA, DMF, 50–70%; (f) 2-
methylamino-2-oxo-acetic acid, EDCI, HOBt, DMF, 65%; (g) sulfonyl chloride, DIEA, DMF, 50–68%.
n = 0, 1
O
O
OH
N
HN
N
HN
N
N
N
N
N
N
(b)
(a)
N
N
42a
N
H
N
H
N
H
O
O
O
28
46
n = 0, 1
O
R6
R6
HN
HN
N
N
(d)
N
(c)
N
N
N
N
N
H
N
N
N
H
N
H
O
H
O
R6 = Morpholine
31
34
R6 = N,N-dimethylpyrrolidin-3-amine
R6 = N,N-dimethylpyrrolidin-3-amine
R6 = Morpholine
29 (n=0)
35 (n=1)
30 (n=0)
32 (n=1)
36 (n=1)
33 (n=1)
37 (n=0)
34a (n=0)
R6 = Diethylamine
R6 = Morpholine
R6 = Pyrrolidine
R6 = N-Methylpiperazine
R6 = azetidin-3-ol
R6 = diethylamine
Scheme 4. Reagents and conditions: (a) (i) 2-Methoxy-4-(4-morpholino-1-piperidyl)aniline, Pd(OAc)2, BINAP, Cs2CO3, 80–100 °C, toluene, 60–80%; (ii) 4M HCl 1,4-dioxane,
MeOH, 75%; (b) (i) methyl 2-(4-piperidyl)acetate or methyl piperidine-4-carboxylate, Pd(OAc)2, BINAP, Cs2CO3, toluene, 80–100 °C, 60–75%; (ii) 4M NaOH, MeOH, 50 °C, THF,
70–80%; (c) (i) Amine, DIEA, HATU, DMF, 60–75%; (ii) 4M HCl 1,4-dioxane, MeOH, 75%; (d) LiAlH4, THF, 30–70%.

D. Vijay Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4377–4385
4385
incubation with Alexa Fluor-conjugated secondary antibodies (Invitrogen).
Cells were subsequently stained with Hoechst 33342 dye. The percentage of
pHH3-positive cells was quantified by image analysis (BD Pathway High
Content Imaging system).
Acknowledgments
We would like to thank Hit to Lead team for early leads in the
project and Analytical team for compound purifications.
9. Kinetic solubility measurements were obtained using pION instrument at pH
7.4.
10.
%
Of compound remaining after 40 min of incubation in mouse liver
References and notes
micosomes at 1 M and the quantitation was done by mass spectrometry.
l
11. Permeability measurements were obtained using PAMPA assay.
12. Lead identification efforts leading up to MPI-0479605 including its mouse oral
PK data will be disclosed in the future publications.
1. (a) Musacchio, A.; Salmon, E. D. Nat. Rev. Mol. Cell Bio. 2007, 8, 379; (b) Liu, S. T.;
Chan, G. K.; Hittle, J. C.; Fujii, G.; Lees, E.; Yen, T. J. Mol. Biol. Cell 2003, 14, 1638;
(c) Malumbres, M. Physiol. Rev. 2011, 91(3), 973.
2. (a) De Cárcer, G.; Pérez de Castro, I.; Malumbres, M. Curr. Med. Chem. 2007,
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(c) Kang, J.; Yu, H. J. Biol. Chem. 2009, 284(23), 15359.
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Ostanin, K.; Papac, D. I.; Baichwal, V.; McAlexander, I.; Willardsen, J. A.;
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Williams, B. L. Mol. Cancer Ther. 2011, 10, 2267.
13. Molecular docking studies were performed using Schrodinger program Glide: Glide
5.0 User Manual, Schrodinger Press, Schrodinger, L.L.C.: New York, NY 2008.
Crystal structure of Mps1 complex with a small molecule inhibitor (PDB ID
3H9F, Ref.6) solved with resolution 2.60 Å was used as a target for docking.
Docking model of Mps1 complex with compound 1 was further refined using
Schrodinger Induced Fit Docking protocol: Sherman, W.; Day, T.; Jacobson,
M.P.; Friesner, R.A.; Farid, R.; J. Med. Chem., 2006, 49,534–553. The images were
made with Accelrys Discovery Studio Visualizer, release 3.2, Accelrys Software
Inc., San Diego, USA, 2011.
14. Lipinski, C. A.; Lombardo, F.; Dominy, B. W.; Feeney, P. J. Adv. Drug Deliv. Rev.
2001, 46, 3.
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15. Compounds were dosed in DMA/PEG 400 solution formulation orally in CD-1
mice at 10 mg/kg and the plasma concentrations were determined at 4 and 8 h
time points.
5. Caldarelli, M.; Angiolini, M.; Disingrini, T.; Donati, D.; Guanci, M.; Nuvoloni, S.;
Posteri, H.; Quartieri, F.; Silvagni, M.; Colombo, R. Bioorg. Med. Chem. Lett. 2011,
21, 4507.
16. IV PK: CD-1 mice were dosed in DMA/PEG 400 at 2.5 mg/kg and PO PK: CD-1
mice were dosed in DMA/PEG 400 at 10 mg/kg.
17. Kumar, D. V.; McAlexander, I; Bursavich, M.; Hoarau, C.; Slattum, P.; Gerrish,
D.; Lockman, J.; Judd, W.; Saunders, M.; Parker, D.;. Zigar, D.; Kim, I.;
Willardsen, J.; Yager, K.; Shenderovich, M.; Williams, B.; Tardiff, K. WO 2010/
111406.
18. All the compounds reported in the paper were purified by reverse phase HPLC and
characterized by NMR and HRMS. Characterization data for compound 31: 1H
NMR (400 MHz, DMSO-d6): d 9.50 (s, 1H), 8.19 (s, 1H), 7.74 (s, 1H), 6.71 (s, 1H),
6.57 (s, 1H), 3.98 (d, J = 12.8 Hz, 2H), 3.96 (s, 1H), 3.84 (s, 3H), 3.74 (t,
J = 11.2 Hz, 4H), 3.48 (d, J = 12 Hz, 2H), 3.10 (m, 4H), 2.72 (s, 1H), 2.0–1.3 (m,
17H). Mass Spec.: Calculated: 521.3347 (M+H) and found 521.3348 (M+H).
19. Molandar, G. A.; Yun, C. S. Tetrahedron 2002, 58, 1465.
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8. G2/M Checkpoing Escape Assay: To measure phosphohistone H3 (pHH3),
nocodazole-arrested cells were treated for 4 h with MPI-0479605. Cells were
fixed with 4% paraformaldehyde for 15 min at 37 °C, permeabilized in 0.2%
Triton-X 100 for 5 min, incubated with primary antibodies (rabbit polyclonal
anti-phosphohistone H3 (diluted 1:200; Upstate) and mouse monoclonal anti-
b-tubulin (diluted 1:2000; Sigma)) for 45 min at 37 °C, followed by a 45 min