A. M. Jordan et al. / Bioorg. Med. Chem. Lett. xxx (2016) xxx–xxx
5
Table 3
Cl
N
Cl
N
i)
In vitro metabolic stability data for selected derivatives
OMe
OH
OMe
OR
N
Compound Human microsomal half-life
(min)
Human hepatocyte half-life
(min)
N
57
7
220
58
4.7
2.7
32
50
2900
68
66
160
—
41
42
43
44
48
49
50
OH
—
60
83
59
99
ii)
NH
N
F
OMe
N
R
O
45-49
Ar
Cl
Scheme 3. Synthesis of compounds 45–49. Reagents and conditions: (i) alcohol,
triphenylphosphine, DIAD, THF, 35 °C, 16 h, 33–91%; (ii) 3-amino-4-fluoro-2-
methylphenol, acetic acid, 120 °C, 2 h, 11–67%.
NH
i)
OMe
OMe
OMe
N
N
N
N
OMe
51
8-18
tended to maintain activity in the cellular systems, giving data
comparable to 7. This finding, along with the data for 43, indicates
that permeability and physicochemical parameters may be a limit-
ing factor for these derivatives and that further modification of
both the pKa of the tailgroup and the overall Log P of the derivative
may potentially allow further improvement in this area.
To investigate whether these present modifications had miti-
gated the metabolic deficiencies experienced with the phenol war-
head, the seven most cell-active compounds were investigated in
in vitro human metabolic stability assays (Table 3). Whilst 49
was exceptionally stable in a microsomal (Phase I) metabolic assay,
most compounds failed to show an improvement relative to com-
pound 7. However, an interesting disconnect in stability was
observed between microsomal stability and stability in hepato-
cytes, where both Phase I and II metabolism occurs. Whilst some
compounds, such as 44, behaved similarly to the parent compound
7 and showed diminished stability in hepatocytes compared to
microsomes (as may be anticipated for a phenolic moiety), we
were pleased to find that compounds 41, 48 and 50 were observed
to be relatively metabolically stable.
Scheme 1. Preparation of bioisosteres 8–18. Reagents and conditions: (i) aromatic
amine, acetonitirile, microwave, 100 °C, 1 h, 11–93%.
NC
N
OMe
O
NC
N
OMe
.TFA
OH
i)
Cl
(Me)2N
(Me)2N
n
52
n = 2; 53
n = 3; 54
OH
OH
NH
NH
N
ii)
ii)
F
OMe
F
OMe
N
N
R1
n
N
O
Cl
O
n
n = 2; 55
n = 3; 56
21-44, 50
Scheme 2. Synthesis of compounds 21–44, 50. Reagents and conditions:
(i) bromochloroalkane, potassium carbonate, acetonitirile, 50–80 °C, 6 h, 61–63%;
(ii) 3-amino-4-fluoro-2-methylphenol, acetic acid, 120 °C, 2 h, 24–48%; (iii) amine,
microwave, 110 °C, 2–24 h, 5–87%.
Incorporation of a pendant, basic tail group has previously been
demonstrated to deliver an improvement in phenol metabolism. In
this setting, this strategy does not appear to be universally benefi-
cial to mitigate hepatic metabolism. Whilst derivatives such as
compound 43 displayed improved cell potency compared to the
parent derivative, concomitant improvements in metabolic stabil-
ity were not generally observed. However, compounds such as 41,
48 and 50 maintained cellular potency and selectivity whilst show-
ing some improvement in the overall metabolic profile of these
agents. These data suggest that further improvements to this ser-
ies, through modification of physicochemical properties, may offer
additional potential for improvements in both metabolic stability
and cellular potency.
The described derivatives were synthesized according to the
following schemes. As detailed in Scheme 1, the commercially
available chloroquinazoline 51 was functionalized through an SNAr
displacement of the 4-chloro moiety with the required aromatic
amine to yield the desired bioisosteres 8–18.
However, the majority of the derivatives for this study were
prepared as described in Scheme 2. The previously described imine
adduct 5222 was readily alkylated with either 1-chloro-2-bro-
moethane or 1-chloro-3-bromopropane to yield intermediates 53
and 54. Cyclisation with the requisite anilinophenol16 yielded the
advanced chloroalkyloxy anilinoquinazolines 55 and 56 in moder-
ate yield. These alkyl halides could then be further elaborated
without intermediate purification simply by SN2 alkylation with
the desired amine, and the target compounds purified by preparative
HPLC, to yield 21–44 and 50.
translate to the cellular environment, with many compounds
failing to display potency in this more relevant context. Given
the biochemical assay was conducted at an ATP concentration
close to Km for the RET kinase domain, we had anticipated a much
closer correlation between the enzyme and cellular assays and we
therefore attributed this disconnect to be due to limited perme-
ability of these compounds, or potential differences in the binding
conformation of the kinase domain in the biochemical and cellular
assay systems.16
Indeed, most of the basic derivatives were found to be inactive
(>10 lM) in our KDR cellular selectivity assay, though seven of the
prepared derivatives displayed cell activity against RET compara-
ble to the parent derivative. Amongst the latter compounds, only
the trifluoromethylpiperazine derivative 43 displayed a significant
improvement in activity and was the only compound found to dis-
play sub-micromolar RET activity in our cell-based systems.
To test the hypothesis that polar functionality, rather than a
basic centre, may also improve metabolic stability whilst
enhancing cellular permeability, a limited number of non-basic
derivatives, exemplified by 48–50, were also prepared. These
derivatives tended to show similar potencies and selectivities to
the basic derivatives when tested in our biochemical assay, but