Design and Synthesis of Novel Macrocyclic Mer Tyrosine Kinase Inhibitors

Article abstract of DOI:10.1021/acsmedchemlett.6b00221

Mer tyrosine kinase (MerTK) is aberrantly elevated in various tumor cells and has a normal anti-inflammatory role in the innate immune system. Inhibition of MerTK may provide dual effects against these MerTK-expressing tumors through reducing cancer cell survival and redirecting the innate immune response. Recently, we have designed novel and potent macrocyclic pyrrolopyrimidines as MerTK inhibitors using a structure-based approach. The most active macrocycles had an EC₅₀ below 40 nM in a cell-based MerTK phosphor-protein ELISA assay. The X-ray structure of macrocyclic analogue 3 complexed with MerTK was also resolved and demonstrated macrocycles binding in the ATP binding pocket of the MerTK protein as anticipated. In addition, the lead compound 16 (UNC3133) had a 1.6 h half-life and 16% oral bioavailability in a mouse PK study.

Full text of DOI:10.1021/acsmedchemlett.6b00221

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Letter
Design and Synthesis of Novel Macrocyclic Mer Tyrosine Kinase Inhibitors
Xiaodong Wang, Jing Liu, weihe zhang, Michael A. Stashko, James Nichols, Michael J. Miley,
Jacqueline L. Norris-Drouin, Zhilong Chen, Mischa Machius, Deborah DeRyckere, Edgar
R. Wood, Douglas K. Graham, Henry Shelton Earp, Dmitri B. Kireev, and Stephen V. Frye
ACS Med. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acsmedchemlett.6b00221 • Publication Date (Web): 13 Sep 2016
Downloaded from http://pubs.acs.org on September 16, 2016
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Design and Synthesis of Novel Macrocyclic Mer Tyrosine Ki-
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Xiaodong Wang,±* Jing Liu, ±† Weihe Zhang, ±† Michael A. Stashko, ± James Nichols,₸ Michael J Miꢀ
ley,§ Jacqueline NorrisꢀDrouin, ± Zhilong Chen,± Mischa Machius,§ Deborah DeRyckere,ǁ Edgar Wood,₸
Douglas K. Graham,ǁ₸ H Shelton Earp, §₸ Dmitri Kireev, ± Stephen V. Frye ±¶₸
±Center for Integrative Chemical Biology and Drug Discovery, Division of Chemical Biology and Medicinal Chemistry,
Eshelman School of Pharmacy
₸Meryx, Inc., 450 West Dr., Chapel Hill, NC 27599, USA
§ Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
ǁAflac Cancer and Blood Disorders Center of Children’s Healthcare of Atlanta, Department of Pediatrics, School of Mediꢀ
cine, Emory University, Atlanta, GA 30322, USA
¶Lineberger Comprehensive Cancer Center, Department of Medicine, School of Medicine, University of North Carolina at
Chapel Hill, Chapel Hill, NC 27599, USA
KEYWORDS. Mer inhibitors, MerTK, macrocycle, pyrrolopyrimidine, TAM kinase, structure-based drug design.
ABSTRACT: Mer tyrosine kinase (MerTK) is aberrantly elevated in various tumor cells and has a normal antiꢀinflammatory role
in the innate immune system. Inhibition of MerTK may provide dual effects against these MerTKꢀexpressing tumors through reducꢀ
ing cancer cell survival and redirecting the innate immune response. Recently, we have designed novel and potent macrocyclic pyrꢀ
rolopyrimidines as MerTK inhibitors using a structureꢀbased approach. The most active macrocycles had an EC50 below 40 nM in a
cellꢀbased MerTK phosphorꢀprotein ELISA assay. The Xꢀray structure of macrocyclic analogue 3 complexed with MerTK was also
resolved and demonstrated macrocycles binding in the ATP binding pocket of the MerTK protein as anticipated. In addition, the
lead compound 16 (UNC3133) had a 1.6 hr halfꢀlife and 16% oral bioavailability in a mouse PK study.
Mer tyrosine kinase (MerTK) belongs to the TAM (Tyro3,
Axl, MerTK) family and regulates adult tissues and organ
systems that are subject to continuous challenge and renewal
throughout life.1,2 Aberrant expression of MerTK in various
hematological and solid tumors promotes cancer cell survival,
chemoresistance and invasive motility.3,4 In addition, MerTK
triggers macrophage engulfment of apoptotic material (efꢀ
ferocytosis) and promotes an antiꢀinflammatory response,
preventing excessive inflammation and autoimmune disease.
Unfortunately, within the tumor microenvironment this supꢀ
presses antiꢀtumor innate immune responses.5ꢀ9 Therefore,
inhibition of MerTK may provide dual therapeutic effects
against MerTKꢀexpressing tumors by reducing cancer cell
survival, invasion, and metastasis as well as stimulating antiꢀ
tumor immune responses.
In addition, TAM family members are used by many envelꢀ
oped viruses, such as West Nile (WNV), Dengue (DENV),
HIVꢀ1, Ebola, Marburg, Zika, and Chikungunya, to attach and
gain access to cells through apoptotic mimicry (a phosphatiꢀ
dylserine (PtdSer)ꢀdependent process).10ꢀ12 Inhibition of
MerTK may also lower the infectivity of an important class of
enveloped viruses.13
structure of a complex of MerTK protein with UNC2025
failed, the Xꢀray structure of compound UNC569 (2) comꢀ
plexed with MerTK protein kinase domain was successfully
resolved at a resolution of 2.69 Å (Figure 1a & 1b).15 UNC569
formed three hydrogen bonds with MerTK protein, two with
the hinge region of the protein and the third one with R727.
UNC2025 is expected to bind MerTK in a similar fashion.14
One interesting observation from this Xꢀray structure was that
thermal motions of the butyl amine side chain and the 4ꢀ
aminocylcohexylmethyl group could bring them close enough
to be connected by a short linker, thus forming a macrocycle.
However, connecting these two groups directly was synthetiꢀ
cally challenging. Retaining the cyclohexyl ring and the hyꢀ
droxyl group, the key hydrogen bond donor, would introduce
new stereogenic centers in the newly formed macrocycles. To
provide a proof of concept for the macrocycle hypothesis, a
simplified macrocycle 3 with an amide linker was proposed
(Figure 1c). Although UNC569 belongs to the pyrazolopyrimꢀ
idine series, we have previously shown that pyrrolopyrimꢀ
idines have similar structureꢀactivity relationships (SAR) and
better solubility (solubility of the HCl salt of 1 is 47 mg/mL at
pH 7.4).13 Therefore, we used a pyrrolopyrimidine core to
form macrocycle 3.
Recently, we reported UNC2025 (1), a potent MerTK/Flt3
dual inhibitor.14 Although, our attempt to obtain an Xꢀray
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and Tyro3 (IC50 2000 nM), respectively, and similar activity
1
2
3
4
5
6
7
8
against Flt3 (IC50 160 nM) in our inꢀhouse microfluidic capilꢀ
lary electrophoresis (MCE) assay.21ꢀ23 The Xꢀray structure of 3
complexed with the MerTK kinase domain was also resolved
at a 2.55 Å resolution (Figure 2). Overall, the structure was in
agreement with the preliminary docking hypothesis (Figure 1).
The major difference between MerTK binding by 3 and 2, was
that, the amide group of 3, was only able to form a hydrogen
bond with N728 because of its limited freedom of motion,
while the 4ꢀaminocylcohexyl substituent in 2 could simultaneꢀ
ously bind to three residues, R727, N728 and D741 (Figure 2).
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Figure 1. a. The structure of UNC569; b. Xꢀray crystal strucꢀ
ture of UNC569 in complex with MerTK (kinase domain)
(PDB code 3TCP); c. The structure of proposed macrocycle 3.
Macrocycles have been prominent in drug structures for
decades although most macrocyclic drugs on the market are
macrolides or cyclic peptides derived from natural products.
The structural preorganization and incomplete rigidity providꢀ
ed by cyclization with flexible linkers may facilitate interacꢀ
tions with target protein through favorable entropies and nuꢀ
merous, spatially distributed binding interactions, thus, inꢀ
creasing both binding affinity and selectivity.16 Furthermore,
some reports suggest that cyclization has a favorable impact
on other essential properties required for drugs, such as memꢀ
brane permeability,17 metabolic stability, and overall pharmaꢀ
cokinetics.18,19 Currently, a handful de novo designed macroꢀ
cyclic kinase inhibitors are in clinical development.16 Howevꢀ
er, limited opportunities in lead optimization, potential inꢀ
creased costs for scale up, and poor understanding of macroꢀ
cycle absorption, distribution, metabolism, execration, and
toxicity (ADMET) are still concerns for drug discovery efforts
in this field. With this background, we explored introduction
of macrocycles into MerTK inhibitors.20
Figure 2. Xꢀray structure of macrocyclic compound 3 comꢀ
plexed with Mer protein (kinase domain) (PDB code 5K0K).
To improve the hydrogen bonding capability of 3, we inꢀ
stalled an amino or a hydroxyl group in the macrocycle as
shown in structures I & II (Table 1). The closest analogues to
3 from structures I & II were compounds 4 & 10 respectively
which had a similar ring size while 4 had an amino group and
10 had a hydroxyl group attached to the macrocycles (insepaꢀ
rable racemic mixture). As proof of concept, both compounds
were prepared, and indeed were 15ꢀfold more active against
MerTK than 3. Changing the ring size of the macrocycles
would affect not only the conformation of the molecule but
also the location of the amino/hydroxyl group, which is crucial
for forming the desired hydrogen bond. Thus, we next exꢀ
plored the SAR of the ring size of molecules I & II.
Indeed, compound 3 proved active against MerTK (IC50 65
nM) with 20ꢀ and 30ꢀfold selectivity over Axl (IC50 1300 nM)
Table 1. SAR of the ring size
Structure
Compound
m
n
IC50 (nM)a
EC50 (nM)a
pMerTK ELISA
>1000
MerTK
Axl
33 ± 17
Tyro3
Flt3
2
4
6
2
4
6
1
1
1
2
2
2
3.9 ± 2.7
39 ± 16
20 ± 9.6
4
5
6
7
8
9
17 ± 1.9 300 ± 170 110 ± 26 100 ± 11
>1000
30 ± 3.8 170 ± 31
8.9 ± 4.4 150 ± 90
2.2 ± 0.8 11 ± 8.2
0.8 ± 0.1 4.2 ± 1.9
170 ± 28 70 ± 2.6
130 ± 74 130 ± 45
>1000
>1000
13 ± 6.1
12 ± 3.2
34 ± 26
7.5 ± 9.2 2.5 ± 2.6
160 ± 43
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2
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3
3
3
3
4.1 ± 1.4
5.6 ± 3.4
1.8 ± 0.5
9.6 ± 9.4
40 ± 10
50 ± 24
14 ± 11
26 ± 15
53 ± 32
60 ± 40
25 ± 19
12 ± 1.3
13 ± 9.4
7.5 ± 2.0
39 ± 5.9
240 ± 190
43 ± 9.2
190 ± 30
150 ± 0.8
ND
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12
13
14
15b
16
17
18
19
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21
1
2
3
4
5
6
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8
54 ± 5.7 8.9 ± 0.4
8.0 ± 3.2 120 ± 36 170 ± 130 29 ± 1.1
4.0 36 94 12
31 ± 9.2 6.8 ± 2.7
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3.0 ± 1.1 17 ± 6.2
2.6 ± 1.9 9.3 ± 7.1
110 ± 69
72 ± 37
22 ± 22
57 ± 41
44 ± 29
8.1 ± 5.8
6.3 ± 2.1
5.4 ± 1.0
4.1 ± 0.1
28 ± 13
69 ± 17
5.0 ± 0.4 25 ± 8.2
3.1 ± 1.3 18 ± 8.9
4.9 ± 2.5 17 ± 6.9
120 ± 1.1
150 ± 39
400 ± 30
38 ± 3.3 9.6 ± 0.9
49 ± 36 13 ± 7.3
a Values are the mean of two or more independent assays ± SD. b Only test once.
For structure I, when n = 1, ring expansion of the macrocyꢀ
possibly due to the less restricted nature of the alkyl macrocyꢀ
cles in structure II versus the amide linked macrocycles in
structure I.
cle led to weaker MerTK inhibitors. As shown in Table 1,
analogues 5 (m = 4) and 6 (m = 6) were 4 and 8ꢀfold less acꢀ
tive than 4 (m = 2), respectively. However, a larger ring was
better when n = 2. Analogue 9 (m = 6) was 10ꢀfold more acꢀ
tive against MerTK than analogue 7 (m = 4) and 3ꢀfold more
active than 8 (m = 4). Interestingly, analogue 9 was 7ꢀfold
more active against Tyro3 compared with UNC2025 although
their activities against MerTK were similar. These results also
demonstrated the importance of the location of the hydrogen
bond donor. For structure II, when n = 1, the MerTK inhibitoꢀ
ry activity of the analogues varied slightly based on the ring
size (compounds 10‒13). Analogue 12 with a 16ꢀmembered
ring (m = 3) was the most active MerTK inhibitor. However,
when n = 2, a larger ring led to a more MerTK active analogue
(compounds 14‒17) with less selectivity among TAM family
members (compounds 14 (15ꢀfold over Axl & 21ꢀfold over
Tyro3) vs 17 (4ꢀfold over Axl & 8ꢀfold over Tyro3)). For n =
3, analogues 18‒21 (m = 1‒4) were equally potent against Mer
independent on the ring size, possibly due to the flexibility of
the large ring when the hydroxyl group, the hydrogen bond
donor, was at the optimal position. Overall, the ring size had
less effect on the activity of macrocycles with structure II
To evaluate the inhibitory activity of our compounds in a
cellꢀbased assay based on the inhibition of MerTK phosphoryꢀ
lation (pMerTK), a 384ꢀwell plate ELISA assay was develꢀ
oped (pMerTK ELISA) (Table 1 and 2). In this assay,
HEK293 cells expressing chimeric proteins24,25 consisting of
the extracellular and transmembrane domains from the epiꢀ
dermal growth factor receptor (EGFR) and the intracellular
kinase domain from Mer were plated and stimulated with EGF
with and without inhibitors. A chimeric protein was utilized
because consistent stimulation of native MerTK with the comꢀ
plex, natural ligand (GAS6 plus PtdSer) was not practical. In
general, compounds in structure I were more polar due to the
primary amine group (shorter retention time in LC/MS specꢀ
tra), likely less cell permeable, and had weaker cellular activiꢀ
ty than compounds in structure II with the exception of anaꢀ
logue 8, which was very active in this assay (EC50 for
UNC2025 was 12 ± 3.1 nM). The reasons for the exception
are
unclear
and
still
under
investigation.
Table 2. SAR Study of R
Structure
Compound
R
IC50 (nM)a
EC50 (nM)a
MerTK
Axl
Tyro3
Flt3
pMerTK
ELISA
>1000
140 ± 93
810 ± 170 1800 ± 1500 280 ± 130
620 ± 320 1300 ± 1100 370 ± 240
22
23
150 ± 140
>1000
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R
86 ± 40
340 ± 13
940 ± 600
250 ± 130
470 ± 230
>1000
>1000
24
25
1
N
2
3
160 ± 34
920 ± 420
1200 ± 810
N
N
H
N
4
5
6
7
170 ± 20
16 ± 11
910 ± 250
93 ± 22
1100 ± 320
300 ± 250
78 ± 71
550 ± 78
75 ± 70
26 ± 19
>1000
26
27
28
OH
160 ± 2.3
210 ± 23
8.1 ± 7.2
65 ± 37
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
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60
11 ± 8.0
30 ± 30
110 ± 62
180 ± 94
190 ± 120
300 ± 300
32 ± 18
84 ± 87
220 ± 39
490 ± 13
29
30
32 ± 1.7
180 ± 43
350 ± 130
68 ± 7.9
690 ± 48
31
54 ± 9.3
13 ± 6.9
80 ± 94
94 ± 46
390 ± 24
180 ± 37
120 ± 3.7
640 ± 54
690 ± 360
210 ± 53
63 ± 3.4
56 ± 39
>1000
380 ± 160
260 ± 89
>1000
32
33
34
35
170 ± 98
37 ± 1.1
1000 ± 15
1200 ± 650
a Values are the mean of two or more independent assays ± SD
.
Next, as shown in Table 2, we explored the SAR at the R
position while fixing the macrocycle as a 17ꢀmembered ring as
in analogue 16 (UNC3133). The R group projects out of the
MerTK active site (Figure 2). Although it interacts mostly
with the solvent, it can still affect the activity of the inhibitors
and be used for tuning solubility and other pharmacokinetic
properties. Various groups were introduced to this site. When
a phenyl group was at the R position, analogue 22 was active
against MerTK but was much weaker than 16 (47ꢀfold) (Table
1) and had no activity in the pMerTK ELISA assay at a conꢀ
centration of 1.0 µM. A small substituent, such as fluoro or
methoxyl group, on the phenyl ring didn’t affect the MerTK
activity in either the MCE or pMerTK ELISA assays (within
2ꢀfold, see analogues 23ꢀ26). However, a larger substituent on
the phenyl ring significantly increased the MerTK activity.
Analogues 27-29 had similar substituents at the R position,
one phenyl and one heterocycle connected by a one atom linkꢀ
er (CH2, CO or SO2), thus they shared similar activity against
MerTK as analogue 16. A longer linker (an amide bond) and
no linker between the phenyl and the heterocycle led to weakꢀ
er MerTK inhibitors 30 and 31 respectively (10ꢀfold weaker
than 16 in the MCE assay and 5ꢀfolder weaker in the pELISA
assay). Introducing a pyridine ring at the R position led to
analogues that could be very active against MerTK depending
on the position of the nitrogen in the pyridine ring. Analogue
33 with a 3ꢀpyridinyl group at the R position was more active
in the MCE assay than analogues 32 (4ꢀfold) and 34 (6ꢀfold)
with a 2ꢀpyridinyl and a 4ꢀpyridinyl group, respectively. Howꢀ
ever, 34 was equipotent to 33 in the pMerTK ELISA assay
while 32 was inactive at a concentration of 1.0 µM. A 4ꢀ
tetrahydropyran group was also tolerated at the R position and
analogue 35 was equally potent as analogue 22. The change of
the MerTK activity based on the size, shape and electron denꢀ
sity of the R group could not be explained by the
Figure 3. Kinase Tree.
Xꢀray structure of 3 since the R group was in the solvent front
and didn’t have close interactions with the MerTK protein.
Generally, these analogues have some selectivity over Axl (>
5ꢀfold) and Tyro3 (> 10ꢀfold) and similar activity against Flt3
and Mer. Analogue 16 was still one of the most active MerTK
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inhibitors and had a mediumꢀsized ring, thus was chosen for
the further study.
Representative synthetic routes to macrocyclic compounds
are shown in Scheme 1. The synthesis of 4 started with comꢀ
mercially available 5ꢀbromoꢀ2ꢀchloroꢀ7Hꢀpyrrolo[2,3ꢀ
1
2
3
4
5
6
7
8
Analogue 16 was tested in the in vivo pharmacokinetic (PK)
study in mice via both intravenous (IV) and oral (PO) adminꢀ
istration (details in supplemental materials). It had a 1.6 hr
halfꢀlife, 16% oral bioavailability, 106 mL/min/kg systemic
clearance (1.2 fold of the normal liver blood flow in mice) and
6.8 L/kg volume of distribution (Vss) (9.7 fold higher than the
normal volume of total body water) at a dose of 3 mg/kg. Theꢀ
se PK properties are not optimal for an in vivo tool compound
and need to be further improved.
d]pyrimidine (36) as shown in path a. Mitsunobu reaction beꢀ
tween 36 and 37 led to intermediate 38. An SNAr replacement
of the chloride on the pyrimidine ring with butaneꢀ1,4ꢀdiamine
yielded 39. The macrocycle was formed by an intraꢀmolecular
amide bond coupling reaction of the unprotected acid and the
free amine to provide intermediate 40. The final compound 4
was obtained by deprotection of the Boc protecting group of
40 followed by a Suzuki coupling reaction with boronic ester
41. In path b, Nꢀalkylation of 36 with alkyl bromide 42 under
basic conditions followed by an SNAr replacement of the chloꢀ
ride on the pyrimidine ring with butꢀ3ꢀenꢀ1ꢀamine yielded
intermediate 43, a macrocycle precursor. A ring closing meꢀ
tathesis reaction of 43 was then catalyzed by the second genꢀ
eration of Grubbs’ catalyst followed by a Suzuki coupling
reaction with boronic ester 41 to yield the intermediate 44
which was a mixture of cisꢀ and transꢀisomers. Reduction of
the newly formed double bonds and removal of the TBS proꢀ
tecting group led to the desired analogue 16.
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The inhibitory activity mediated by 16 against a panel of 30
kinases was also determined at a concentration 100ꢀfold above
its MerTK IC50 (Figure 3) (details in supplemental materials).
This experiment provides a broad survey of kinase families
emphasizing tyrosine kinases along with a selection of serꢀ
ine/threonine kinases. Surprisingly, the selectivity of 16 across
the kinome was not very high (worse than UNC202514): eight
tyrosine kinases and four serine/threonine kinases were inhibꢀ
ited by greater than 50% in the presence of 300 nM 16. This
may be due to the flexibility of this type of macrocycles,
which would allow it to conformationally adapt to the active
site of disparate kinases.
Scheme 1. The synthetic routes for macrocyclic compounds
Experimental details and characterization of all compounds and
biological methods.
In summary, the first potent macrocyclic MerTK inhibitors
were developed using structureꢀbased drug design. An amide
bond formation or a Ruꢀcatalyzed ring metathesis reaction was
the key step to build up the macrocycles. An Xꢀray structure of
the MerTK protein complexed with analogue 3 showed that
these macrocyclic compounds resided in the ATP binding
pocket. The most active analogues had an EC50 below 40 nM
in our newly developed highꢀthroughput phosphoꢀMer cellular
ELISA assay. These macrocycles were not very selective
across the kinome. The selectivity and PK properties will need
to be improved to develop useful in vivo tool compounds.
The Supporting Information is available free of charge on the
ACS Publications website.
Accession Codes: The atomic coordinates for the Xꢀray crystal
structure of 3 have been deposited with the RCSB Protein
Data Bank under the accession code 5K0K.
AUTHOR INFORMATION
Corresponding Author
* Tel: 919ꢀ843ꢀ8456. Fax: 919ꢀ843ꢀ8465. Eꢀmail:
xiaodonw@unc.edu.
ASSOCIATED CONTENT
Supporting Information
Present Addresses
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9.
Todt, J. C.; Hu, B.; Curtis, J. L., The receptor tyrosine
†
Jing Liu: Icahn School of Medicine at Mount Sinai, 1468
kinase MerTK activates phospholipase C γ2 during recognition of
apoptotic thymocytes by murine macrophages. J. Leukocyte Biol.
2004, 75 (4), 705ꢀ713.
1
2
3
Madison Avenue, New York, NY 10029; Weihe Zhang:
BioCryst Pharmaceuticals, Inc., 2100 Riverchase Center,
Suite 200, Birmingham, AL 35244
.
10.
Jemielity, S.; Wang, J. J.; Chan, Y. K.; Ahmed, A. A.; Li,
4
5
6
7
8
9
W.; Monahan, S.; Bu, X.; Farzan, M.; Freeman, G. J.; Umetsu, D. T.;
Dekruyff, R. H.; Choe, H., TIMꢀfamily proteins promote infection of
Author Contributions
The manuscript was written through contributions of all authors. /
All authors have given approval to the final version of the manuꢀ
script.
multiple
phosphatidylserine. PLoS Pathog 2013, 9 (3), e1003232.
11. Mercer, J.; Helenius, A., Vaccinia virus uses
enveloped
viruses
through
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macropinocytosis and apoptotic mimicry to enter host cells. Science
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Funding Sources
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This work was supported by the University Cancer Research Fund
and Federal Funds from the National Cancer Institute, National
Institute of Health, under Contract No. HHSN261200800001E.
The content of this publication does not necessarily reflect the
views or policies of the Department of Health and Human Serꢀ
vices, nor does mention of trade names, commercial products, or
organizations imply endorsement by the U.S. Government.
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Mercer, J.; Helenius, A., Apoptotic mimicry:
phosphatidylserineꢀmediated macropinocytosis of vaccinia virus. Ann
N Y Acad Sci 2010, 1209, 49ꢀ55.
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Therapeutic Opportunities in Oncology, Virology, and Cardiovascular
Indications. Annu Rep Med Chem, 2014, 49, 301ꢀ314.
Wang, X.; Frye, S., Mer Receptor Tyrosine Kinase:
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Zhang, W.; DeRyckere, D.; Hunter, D.; Liu, J.; Stashko, M.
A.; Minson, K. A.; Cummings, C. T.; Lee, M.; Glaros, T. G.; Newton,
D. L.; Sather, S.; Zhang, D.; Kireev, D.; Janzen, W. P.; Earp, H. S.;
Graham, D. K.; Frye, S. V.; Wang, X., UNC2025, a Potent and Orally
Bioavailable MER/FLT3 Dual Inhibitor. J Med Chem 2014, 57 (16),
7031ꢀ7041.
ACKNOWLEDGMENT
We thank Dr. Brenda Temple for her help in depositing the Xꢀray
crystallographic structure to the Protein Data Bank (PDB).
15.
Liu, J.; Yang, C.; Simpson, C.; DeRyckere, D.; Van, D. A.;
Miley, M. J.; Kireev, D.; NorrisꢀDrouin, J.; Sather, S.; Hunter, D.;
Korboukh, V. K.; Patel, H. S.; Janzen, W. P.; Machius, M.; Johnson,
G. L.; Earp, H. S.; Graham, D. K.; Frye, S. V.; Wang, X., Discovery
of Small Molecule Mer Kinase Inhibitors for the Treatment of
Pediatric Acute Lymphoblastic Leukemia. ACS Med. Chem. Lett.
2012, 3, 129ꢀ134.
ABBREVIATIONS
MerTK, Mer tyrosine kinase; PtdSer, phosphatidylserine;
SAR, structureꢀactivity relationships; ADMET, absorption, disꢀ
tribution, metabolism, execration, and toxicity; MCE, microfluidꢀ
ic capillary electrophoresis; IC50, half maximal inhibitory concenꢀ
tration; pMerTK, phosphorylated Mer tyrosine kinase; ELISA,
enzymeꢀlinked immunosorbent assay; IC50, half maximal effective
concentration.
16.
Giordanetto, F.; Kihlberg, J., Macrocyclic drugs and
clinical candidates: what can medicinal chemists learn from their
properties? J Med Chem 2014, 57 (2), 278ꢀ295.
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diffusion coefficients for matched pairs of macrocyclic and linear
molecules over a drugꢀlike molecular weight range. Org Biomol
Chem 2011, 9 (22), 7727ꢀ7733.
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discovery. Future Med Chem 2012, 4 (11), 1409ꢀ1438.
19. Driggers, E. M.; Hale, S. P.; Lee, J.; Terrett, N. K., The
exploration of macrocycles for drug discovery—an underexploited
structural class. Nature Reviews Drug Discovery 2008, 7 (7), 608ꢀ624.
20.
molecule inhibitors of the TAM family: The point of view of the
chemist. Eur J Med Chem 2015, 105, 220ꢀ237.
21.
Bogdan, A. R.; Davies, N. L.; James, K., Comparison of
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Design and Synthesis of Novel Macrocyclic Mer Tyrosine Ki-
nase Inhibitors
Xiaodong Wang,±* Jing Liu, ±† Weihe Zhang, ±† Michael A. Stashko, ± James Nichols,₸ Michael J Miꢀ
ley,§ Jacqueline NorrisꢀDrouin, ± Zhilong Chen,± Mischa Machius,§ Deborah DeRyckere,ǁ Edgar Wood,₸
Douglas K. Graham,ǁ₸ H Shelton Earp, §₸ Dmitri Kireev, ± Stephen V. Frye ±¶₸
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N
N
16 (UNC3133)
IC50 Mer 3.0 nM
N
Axl 17 nM
N
Tyro3 31 nM
FLT3 6.8 nM
N
H
N
PO Cmax: 0.023
IV T1/2: 1.59 h
%F: 16
M
OH
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