M. G. Bursavich et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6829–6833
6831
R1
N
R1
HN
Cl
HN
N
a
b
Br
EtO
Br
N
N
Cl
N
N
Cl
X
N
Cl
10
11
12
R1
N
R1
N
N
c
d or e
N
N
Cl
N
N
H
R2
13a : R1 = H
14
13b : R1 = cyclohexyl
Scheme 2. Reagents and conditions: (a) ammonia, THF or cyclohexylamine, THF,
50 °C (b) B(OH)2CHCHOEt, NaHCO3, Pd(PPh3)4, DME, reflux; (c) AcOH, 120 °C; (d) (i)
Ar/HetArBr, CuI, K3PO4, ( )-trans-1,2-diaminocyclohexane, 90 °C; (ii) aniline, Cs2-
CO3, Pd(OAc)2, BINAP, toluene, reflux; (e) aniline, Cs2CO3, Pd(OAc)2, BINAP, toluene,
reflux.
Figure 5. Binding model overlay with quinazoline structure (pink) and Mps1 lead
structure 1b.
X
X
X
Kinase inhibition activity was determined as previously
described using full-length Mps1 enzyme at 2xKm ATP concentra-
tions. Cellular proliferation activity was determined by monitoring
cell growth densities in HCT116 cell cultures.4
a
b
c
N
N
NO2
N
OH
N
Cl
H
O
The importance of combined R1, R2 substituents was immedi-
ately evident. The unsubstituted compound (6: R1, R2 = H) was
shown to be inactive, but substitution of an R2 methyl group (7)
provided a potent starting point (IC50 = 35 nM). Incorporating an
R1 methyl group on the pyrimidine ring with an unsubstituted R2
group (8) provided a slightly more potent analog (IC50 = 28 nM).
While 7 and 8 are not as potent as purine 2, these analogs possess
reduced MW, reduced TPSA, and only slightly reduced LE as com-
pared with purine lead 2. Interestingly, the disubstituted com-
pound (9: R1, R2 = Me) was shown to be inactive, presumably due
to a unproductively biased conformation.
22
23
21
R1
N
X
Y
Y
d
N
N
N
N
N
N
H
N
H
OMe
OMe
24
25
Scheme 3. Reagents and conditions: (a) (i) Fe, AcOH, HCl, EtOH, 70 °C; (ii) urea,
180 °C; (b) POCl3, 110 °C; (c) aniline–HCl, IPA, 100 °C; (d) Ar/HetArB(OH)2, Na2CO3,
Pd(PPh3)4, DME or cyclohexylamine, Cs2CO3, Pd(OAc)2, BINAP, toluene, reflux.
Encouraged by the diaminopyrimidine results, and realizing the
potential for conformational restriction, a series of pyrrolopyrimi-
dines were designed and modeled. The binding model overlay of
the N-cyclohexyl pyrrolopyrimidine scaffold with purine lead com-
pound 2 is shown in Figure 4.8
(R1 = H) into 14 required an initial Buchwald reaction to function-
alize the indole NH and introduce the R1 substituent followed by a
second Buchwald–Hartwig reaction to incorporate the desired ani-
line.12,13 Conversion of 13b (R1 = cyclohexyl) into 14 required the
same Buchwald–Hartwig reaction to install the desired aniline.13
In the case of the pyrrolopyrimidines (Table 2) all the R1 = cyclo-
hexyl analogs (15–17) were shown to be potent Mps1 inhibitors.
The 2-methyl-morpholine analog 16 (R2 = Me, X = O) provided an
attractive starting point (IC50 = 22 nM) with a MW under 400, TPSA
The synthesis of the pyrrolopyrimidine inhibitors9 (Scheme 2)
begins with reaction of commercially available 5-bromo-2,4-
dichloropyrimidine 10 with either ammonia or cyclohexylamine
to provide 11. Suzuki reaction with the vinyl ether borane reagent
provided the pyrrolopyrimidine precursor 12.11 Cyclization under
acidic conditions afforded both 13a and 13b. Conversion of 13a
Table 2
Structure–activity relationships of pyrrolopyrimidines
R1
N
X
N
N
N
N
H
R2
Compd
R1
R2
X
Mps1a IC50 (nM)
HCT116a IC50
(l
M)
MW
TPSA
LEb
15
16
17
18
19
20
Cyclohexyl
Cyclohexyl
Cyclohexyl
Phenyl
2-Pyridyl
3-Pyridyl
OMe
Me
OMe
OMe
OMe
OMe
O
O
46
22
20
>100
32
7.5
8.6
0.75
—
10
—
408
392
485
479
480
480
64
55
101
101
114
114
0.24
0.26
0.23
—
0.22
—
NSO2Me
NSO2Me
NSO2Me
NSO2Me
>100
a
Values are means of two experiments, standard deviations are 10%.
LE = ÀLog(Mps1 IC50)/# of heavy atoms.
b