Structure-based design of potent and selective CK1γ inhibitors

Article abstract of DOI:10.1021/ml300278f

Aberrant activation of the Wnt pathway is believed to drive the development and growth of some cancers. The central role of CK1γ in Wnt signal transduction makes it an attractive target for the treatment of Wnt-pathway dependent cancers. We describe a structure-based approach that led to the discovery of a series of pyridyl pyrrolopyridinones as potent and selective CK1γ inhibitors. These compounds exhibited good enzyme and cell potency, as well as selectivity against other CK1 isoforms. A single oral dose of compound 13 resulted in significant inhibition of LRP6 phosphorylation in a mouse tumor PD model.

Full text of DOI:10.1021/ml300278f

Letter
pubs.acs.org/acsmedchemlett
Structure-Based Design of Potent and Selective CK1γ Inhibitors
Hongbing Huang,*,† Lisa Acquaviva,§ Virginia Berry,‡ Howard Bregman,† Nagasree Chakka,†
Anne O’Connor,∥ Erin F. DiMauro,† Jennifer Dovey,§ Oleg Epstein,† Barbara Grubinska,§ Jon Goldstein,§
Hakan Gunaydin,∥ Zihao Hua,† Xin Huang,∥ Liyue Huang,‡ Jason Human,† Alex Long,∥ John Newcomb,§
Vinod F. Patel,†,⊥ Doug Saffran,§ Randy Serafino,§ Steve Schneider,∥ Craig Strathdee,§ Jin Tang,∥
Susan Turci,§ Ryan White,† Violeta Yu,∥ Huilin Zhao,∥ Cindy Wilson,§ and Matthew W. Martin†
†
‡
§
∥
Departments of Medicinal Chemistry; Pharmacokinetics and Drug Metabolism; Oncology Research; and Molecular Structure,
Amgen Inc., 360 Binney Street, Cambridge, Massachusetts 02142, United States
S
* Supporting Information
ABSTRACT: Aberrant activation of the Wnt pathway is
believed to drive the development and growth of some
cancers. The central role of CK1γ in Wnt signal transduction
makes it an attractive target for the treatment of Wnt-pathway
dependent cancers. We describe a structure-based approach
that led to the discovery of a series of pyridyl pyrrolopyr-
idinones as potent and selective CK1γ inhibitors. These
compounds exhibited good enzyme and cell potency, as well as
selectivity against other CK1 isoforms. A single oral dose of
compound 13 resulted in significant inhibition of LRP6
phosphorylation in a mouse tumor PD model.
KEYWORDS: Wnt pathway, CK1γ, cancer, pyridyl pyrrolopyridinone
he canonical Wnt pathway regulates the ability of the β-
catenin protein to activate specific target genes.1 The level
family are shown to regulate the Wnt pathway through
interactions with various proteins.12,13 For instance, phosphor-
ylation of Ser45 in β-catenin by CK1α is an obligate priming for
subsequent phosphorylation by GSK3β, which is a key step
leading to β-catenin degradation.14,15 Additionally, phosphor-
ylation of APC by CK1δ/ε alters its binding affinity with β-
catenin and regulates the assembly of the destruction complex.
Because of complex positive and negative regulation of the Wnt
pathway by CK1 family members, we sought to pursue CK1γ
inhibitors with selectivity over other CK1 isoforms.16 Given the
role of GSK3β in regulating β-catenin, selectivity over GSK3β
was also deemed important. To date, there are no reports of
selective CK1γ inhibitors that demonstrate good cellular
activity.16
The compounds presented in this study were examined for
their ability to inhibit the activity of CK1 kinases (α, δ, and γ)
using enzyme assays with recombinant CK1 kinase catalytic
domains. Two cellular assays were developed to aid evaluation
of CK1γ inhibitors. First, a proximal PO4-LRP6 cellular assay
was used to measure the inhibition of CK1γ-mediated
phosphorylation of LRP6 in HEK293 cells. Second, a
transcriptional Wnt reporter assay driven by multimerized
TCF binding sites in the RKO colon cell line (RKO-STF) was
T
of the transcriptional activator β-catenin is tightly controlled by
a destruction complex, which consists of adenomatous
polyposis coli (APC), Axin, casein kinase 1α (CK1α), and
glycogen synthase kinase 3β (GSK3β).2 In the absence of a
Wnt signal, the Axin and APC proteins form a scaffold that
facilitates the sequential phosphorylation of β-catenin by CK1α
and GSK3β. These events lead to ubiquitination and ultimately
degradation of β-catenin in the proteasome. Interaction of a
Wnt ligand with specific receptor complexes containing a
Frizzled (Fzd) family member and LDL receptor-related
proteins 5 and 6 (LRP5/6) coreceptor triggers the phosphor-
ylation of the cytoplasmic tail of LRP 5/6 proteins by CK1γ,
which creates high-affinity binding sites for Axin and facilitates
relocation of Axin to the cell membrane. Recruitment of the
low abundance Axin protein to the cell membrane disrupts the
destruction complex and leads to the accumulation and nuclear
translocation of β-catenin and to subsequent activation of Wnt
target genes including c-MYC,3 Cyclin D1,4,5 and survivin.6,7
The central role of CK1γ in Wnt signal transduction makes it
an attractive target for the treatment of Wnt-pathway
dependent cancers.8−10
The casein kinase 1 (CK1) family of serine/threonine
protein kinases is highly conserved and includes six human
isoforms α, γ1, γ2, γ3, δ, and ε.11 The CK1 proteins have the
highest degree of homology in their kinase domains but differ
substantially in the length and amino acid sequence of their N-
and C-terminal extensions. Multiple members of the CK1
Received: September 9, 2012
Accepted: October 18, 2012
Published: October 18, 2012
© 2012 American Chemical Society
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Figure 1. (A) Structure and activity of compound 1. (B) Cocrystal structure of CK1γ complexed with 1. The C-terminal insertion of CK1-γ is
colored yellow.
Table 1. SAR of Pyrimidinyl Pyrrolopyridinones
a
Values represent the mean of at least of two experiments.
employed to assess the effect of CK1γ inhibition on
downstream Wnt signaling events.
Leu119 in the hinge region of the kinase. The methoxy group is
in close contact with Pro100 and the gatekeeper Leu116. The
pyrrolopyridinone ring interacts with the protein through direct
hydrogen bonds or through water-bridged hydrogen bond
networks. The NH of the pyridinone is within the hydrogen
bonding distance of Asp185, while the carbonyl group of the
pyridinone directly interacts with Lys72 and engages in water-
mediated hydrogen bond interactions with Glu86 and Tyr90.
Intriguingly, the quinoline ring points toward the C-terminal
extension that contains Pro331 and Pro333, which is unique to
the CK1γ protein.17 Because of the low homology among CK1
isoforms in their C-terminal tails, we hypothesized that
interactions of small molecules with the C-terminal extension
could provide the basis for selectivity over other CK1 isoforms
and even greater selectivity over other kinases.18
Starting from HTS hits, pyrimidinyl pyrrolopyridinone (1)
was identified as a potent pan-CK1 inhibitor with modest
selectivity over GSK3β. In enzyme assays, it was equally potent
on CK1α and CK1γ and slightly less potent on CK1δ (Figure
1A). Compound 1 also exhibited robust cellular activity as
measured by inhibition of PO4-LPR6. However, it was much
less potent in the RKO-STF assay, which reflects its weak
ability to inhibit the downstream transcription. We hypothe-
sized that the disconnection between the two cellular assays
may be due to inhibition of other CK1 isoforms acting
downstream of LRP5/6. To aid the design of selective
inhibitors, a cocrystal structure of 1 with CK1γ protein was
obtained at 2.3 Å. The cocrystal structure reveals several key
interactions between the inhibitor and the protein (Figure 1B.).
The N1 of the pyrimidine core is hydrogen bonded to the
We postulated that modifying the rigid bicyclic quinoline to a
more flexible side chain with general structure 2 might provide
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Table 2. SAR of Pyridyl Pyrrolopyridinones
a
b
Values represent the mean of at least of two experiments. ND = not determined.
a platform for discovery of compounds that could induce
interactions with the C-terminal extension of CK1γ protein
(Figure 1A). Also, varying the linkage between the pyrimidine
ring and the A-ring would allow access to compounds with
different dihedral angles between the two aromatic rings. Thus,
a focused library of compounds with various linkers on the left-
hand side of the molecule was prepared. Selected results are
summarized in Table 1. In general, potency against CK1γ was
not impacted significantly by these changes. A wide range of
linkers showed similar potency on CK1γ with the exception of
compound 8. The isoform selectivity against other CK1
enzymes, however, was influenced by the nature of the linker.
For instance, 4-fluorostyryl pyrimidine (3) showed low
selectivity against CK1α (7-fold) and CK1δ (3-fold). A close
analog with a saturated linkage, 4-fluorophenethyl pyrimidine
(4), exhibited improved selectivity against both CK1α and
CK1δ (30-fold and 7-fold, respectively), albeit at the expense of
potency. It was also noted that compounds having an NH
group connected to the pyrimidine core, such as compounds 5
and 6, showed undesired inhibitory activity on GSK3β.
To further improve isoform selectivity, we then investigated
structural modification of the central heteroaromatic B-ring.
The fact that only the N1 of the pyrimidine ring of 1 was
shown to make a critical hydrogen bond interaction with CK1γ
protein in the cocrystal structure prompted us to investigate
whether a pyridine ring could induce conformational changes
that could improve isoform selectivity. This line of investigation
led to the discovery of a series of pyridyl pyrrolopyridinones
that were very potent on CK1γ and highly selective against
other CK1 isoforms. The results are summarized in Table 2.
For compounds with a two-methylene linkage between the A-
ring and the central B-ring, the change from a pyrimidine to a
pyridine had no effect on either potency or selectivity. For
instance, 2-(4-fluorophenethyl)pyridine (10) showed similar
CK1γ potency and isoform selectivity to its pyrimidine
congener 4. The pyridine ring, however, in combination with
a −CH2O− linkage provided compounds with improved
potency and isoform selectivity. For example, 2-(4-
fluorophenoxymethyl)pyridine (11) (CK1γ IC50 0.005 μM
and CK1α selectivity 35-fold) was significantly more potent
and selective against CK1α compared to its pyrimidine
counterpart 9 (CK1γ IC50 0.024 μM and CK1α selectivity 6-
fold). Intrigued by the improved isoform selectivity, further
investigations were conducted on 2-phenoxymethyl pyridine by
modification of the phenyl ring.
It was found that both CK1γ potency and isoform selectivity
were affected by substituents. Ortho-substitution on the phenyl
ring enhanced isoform selectivity, as 2-((2,4-difluorophenoxy)-
methyl)pyridine (12) was considerably more selective against
both CK1α and CK1δ (75-fold and 12-fold, respectively).
Increase in the size of the substituent led to more selective
compound 2-((2-fluoro-3-methylphenoxy)methyl)pyridine
(14). Meta-substitution improved both isoform selectivity and
cellular potency. For instance, 2-((3,4-difluorophenoxy)-
methyl)pyridine (13) exhibited better selectivity against both
CK1α and CK1δ (50-fold and 8-fold, respectively) and superior
potency in the RKO-STF cell assay (IC50 0.254 μM).
Importantly, these substitution effects appear to be additive,
as a combination of ortho- and meta-substitutions led to 2-
((3,4-difluoro-2-methylphenoxy)methyl)-pyridine (15), which
demonstrated excellent cellular potency and was one of the
most selective CK1γ inhibitors. In addition, both 13 and 15
demonstrated good kinase selectivity against a broad panel of
kinases (Ambit KINOMEscan).19
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Figure 2. X-ray cocrystal structures. (A) 13 bound to CK1γ protein. The C-terminal insertion of CK1γ is colored yellow. (B) 13 bound to CK1δ
protein. (C) 13 bound to CK1δ protein. (D) Overlay of different conformations of 13 as bound to CK1γ and CK1δ.
Table 3. Pharmacokinetic Parameters of Compounds 13 and 15
a
e
μL/(min·mg)
mouse po PK
b
,
c
d
f
compd
RLM
HLM
rPPB
mPPB
dose (mg/kg)
Cmax (μM)
t1/2 (h)
Tmax (h)
AUC (μM·h)
13
15
46
59
96.9%
ND
95.1%
99.2%
30
30
9.72
0.56
2.7
1.4
0.33
15.4
2.1
106
177
1.17
a
b
c
Compounds were incubated with microsomes for 30 min at a concentration of 1 μM. rPPB = rat plasma protein binding. ND = not determined.
d
e
mPPB = mouse plasma protein binding. Pharmacokinetic parameters following administration of compound 13 or 15 in male Mouse_CD1:3
f
animals per study. Dosed in 10.0%Pluronic F68_30.0%HPBCD_60.0%water/MSA_pH2.5.
To understand the structural basis for the selectivity observed
with these CK1γ inhibitors, cocrystal structures of compound
13 with CK1γ and CK1δ were obtained. The structures were
resolved at 2.4 and 1.8 Å, respectively (Figure 2). Not
surprisingly, compound 13 binds very similarly to the two
proteins in the ATP binding pocket, as it is highly conserved
among CK1 proteins. The pyrrolopyridinone moiety of 13 in
both CK1γ and CK1δ cocrystal structures engages the same
hydrogen bond interactions in the ATP binding pocket as
compound 1, and as a result it adopts almost identical
conformations in both crystal structures. In the hinge region,
the pyridyl nitrogen atom of 13 hydrogen bonds to a leucine
residue, Leu119 in CK1γ and Leu116 in CK1δ, respectively.
The methoxy group of 13 engages in a very similar
hydrophobic interaction with the gatekeeper residues in both
structures: Leu85 in CK1γ and Met 82 in CK1δ. The significant
conformational difference was observed in the phenoxy-
methylene moiety of 13. In the CK1γ cocrystal structure
(Figure 2A), the difluorophenyl ring engages in a “face-to-face”
interaction with Pro333 and an “edge-to-face” interaction with
Pro331. Since these residues are unique to the CK1γ isoform,
hydrophobic interactions with them may account for the
increased CK1γ potency of 13 compared to compound 1, as a
productive hydrophobic interaction with the Pro-rich c-
terminal tail was not observed in the cocrystal structure of 1
with the CK1γ protein.
There are two different conformations of the difluoro phenyl
ring of 13 present in the CK1δ/13 cocrystal structure (Figure
2B and 2C), where the c-terminal tail unique to CK1γ is absent.
The difluorophenyl ring of 13 is rotated by ∼60° in the CK1δ/
13 complex, and the meta-fluorine is flipped compared with
that in the CK1γ/13 complex. In one conformation, the
difluorophenyl ring engages in hydrophobic interactions with
the side chain of Ile15 from the glycine rich loop and the meta-
F atom points to the solvent front (Figure 2B). In the other
conformation, the meta-F atom of the difluoro phenyl ring
hydrogen bonds to Arg13 (Figure 2C). The CK1δ/13 cocrystal
structure suggests that compound 15 will have to adopt
different conformations in binding with the CK1δ protein than
compound 13, because the methyl group at the 2-position of
the phenyl ring in 15 would bump into the hinge region of the
protein if it binds the same way as 13. Consequently, in the
absence of the favorable interactions of the phenyl ring with the
protein observed in the CK1δ/13 complex, compound 15 is
expected to bind to the CK1δ protein less favorably than 13.
This may explain the significant loss of CK1δ potency of 15.
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a
In light of their excellent enzyme and cellular potencies,
compounds 13 and 15 were evaluated in vivo in pharmaco-
kinetic (PK) studies in rodents. The key PK parameters of
compounds 13 and 15 are summarized in Table 3. Compound
13 demonstrated low turnover in human and rat liver
microsomes. It provided a reasonable plasma exposure when
dosed orally in mice at 30 mg/kg. On the other hand,
compound 15 exhibited high intrinsic clearance in human and
rat liver microsomes and demonstrated low oral exposure in
mice at 30 mg/kg. The ortho-methyl group may account for the
higher intrinsic clearance, as compound 14 also exhibited
similarly high turnover in human and rat liver microsomes
[HLM/RLM 123/88 μL/(min·mg)].
Scheme 1. Synthesis of Compounds 11−15
Compound 13 was then evaluated in a pharmacodynamic
(PD) assay measuring the inhibition of CK1γ-mediated LRP6
phosphorylation in a human tumor xenograft mouse model.
Subcutaneous tumors were formed in athymic nude mice using
a HEK293 cell line that constitutively expressed LPR6 and had
doxycycline-inducible expression of CK1γ. Mice were treated
for 24 h with doxycycline (DOX, 0.5 mg/mL) in the drinking
water to stimulate LRP6 phosphorylation before compound 13
was dosed orally at 50 mg/kg. The tumor tissues and plasma
were collected 6 h postdosing, and LRP6 phosphorylation
levels were quantified by an electrochemiluminescent assay.
Significant inhibition (42%) of LRP6 phosphorylation was
observed with an associated plasma exposure of 13 of
approximately 2.7 μM (Figure 3) and a plasma unbound
concentration of 13 at 0.13 μM, which is consistent with its
PO4-LRP6 cellular potency (IC50 0.20 μM, Table 2).
a
Reagents: (a) CO, Et3N, PdCl2dppf, MeOH, 95 °C; (b) DIBAL-H,
DCM, 65%; (c) SOBr2, DMF, 45%; (d) ArOH, K2CO3, DMF. (e) 2-
((4,5-difluoro-2-methylphenoxy)methyl)-4,4,5,5-tetramethyl-1,3,2-di-
oxaborolane, PdCl2AmPhos, K2CO3, dioxane, 120 °C; 40%.
model. Further investigations into the effects of selective
pharmacological inhibition of CK1γ in disease relevant models
will be disclosed in future communications.
ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental details, synthesis of compound 16, biological
assays, kinase selectivity, and X-ray crytstallographic informa-
tion. This material is available free of charge via the Internet at
http://pubs.acs.org.
Accession Codes
The PDB accession codes for the X-ray cocrystal structures of
CK1γ + 1, CK1γ + 13, and CK1δ + 13 are 4HGL, 4HGS, and
4HGT, respectively.
AUTHOR INFORMATION
Corresponding Author
*Tel: 617-444-5197. E-mail: hongbing.huang@amgen.com.
■
Present Address
⊥Sanofi-Aventis, 270 Albany Street, Cambridge, Massachusetts
02139.
Notes
Figure 3. Effect of compound 13 on CK1γ-mediated LRP6
phosphorylation in the human tumor xenograft model.
The authors declare no competing financial interest.
ABBREVIATIONS
Compounds 11−15 were synthesized according to the routes
outlined in Scheme 1. The synthesis commenced with
carbonylation of pyridyl pyrrolopyridinone 16. The resulting
methyl ester was reduced to primary alcohol 17, which was
subsequently converted to corresponding bromide 18.20
Nucleophilic substitution of 18 with phenols led to compounds
11−14. Alternatively, a Suzuki coupling of 16 with the
corresponding boronic ester furnished 15.
We have described the design, synthesis, and biological
evaluation of a novel series of pyridyl pyrrolopyridinones as
selective CK1γ inhibitors. Compound 13 demonstrated
excellent CK1γ potency in both enzyme and cell assays, and
it exhibited good selectivity against other CK1 isoforms. X-ray
cocrystal structures revealed significantly different binding
conformations of 13 in CK1γ and CK1δ proteins. The
binding-mode differences were used to formulate a general
hypothesis for the observed selectivity of this series of
inhibitors. A single dose of compound 13 resulted in significant
inhibition of LRP6 phosphorylation in a mouse tumor PD
■
APC, adenomatous polyposis coli; CK1, casein-kinase 1;
GSK3β, glycogen synthase kinase 3β; LRP5/6, LDL receptor-
related proteins 5 and 6; PPB, plasma protein binding; STF,
Super TOP-Flash
REFERENCES
■
(1) Gordon, M. D.; Nusse, R. Wnt signaling: multiple pathways,
multiple receptors, and multiple transcription factors. J. Biol. Chem.
2006, 281, 22429−22433.
(2) Kimelman, D.; Xu, W. beta-catenin destruction complex: insights
and questions from a structural perspective. Oncogene 2006, 25, 7482−
7491.
(3) Yochum, G. S.; Sherrick, C. M.; Macpartlin, M.; Goodman, R. H.
A beta-catenin/TCF-coordinated chromatin loop at MYC integrates 5′
and 3′ Wnt responsive enhancers. Proc. Natl. Acad. Sci. U. S. A. 2010,
107, 145−150.
(4) Mirando, A. J.; Maruyama, T.; Fu, J.; Yu, H. M.; Hsu, W. beta-
catenin/cyclin D1 mediated development of suture mesenchyme in
calvarial morphogenesis. BMC Dev. Biol. 2010, 10, 116.
1063
dx.doi.org/10.1021/ml300278f | ACS Med. Chem. Lett. 2012, 3, 1059−1064

ACS Medicinal Chemistry Letters
Letter
(5) Tetsu, O.; McCormick, F. Beta-catenin regulates expression of
cyclin D1 in colon carcinoma cells. Nature 1999, 398, 422−426.
(6) Ma, H.; Nguyen, C.; Lee, K. S.; Kahn, M. Differential roles for the
coactivators CBP and p300 on TCF/beta-catenin-mediated survivin
gene expression. Oncogene 2005, 24, 3619−3631.
(7) Kim, P. J.; Plescia, J.; Clevers, H.; Fearon, E. R.; Altieri, D. C.
Survivin and molecular pathogenesis of colorectal cancer. Lancet 2003,
362, 205−209.
(8) Davidson, G.; Wu, W.; Shen, J.; Bilic, J.; Fenger, U.; Stannek, P.;
Glinka, A.; Niehrs, C. Casein kinase 1 gamma couples Wnt receptor
activation to cytoplasmic signal transduction. Nature 2005, 438, 867−
872.
(9) Barker, N.; Clevers, H. Mining the Wnt pathway for cancer
therapeutics. Nat. Rev. Drug Discovery 2006, 5, 997−1014.
(10) Klaus, A.; Birchmeier, W. Wnt signalling and its impact on
development and cancer. Nat. Rev. Cancer 2008, 8, 387−398.
(11) Price, M. A. CKI, there’s more than one: casein kinase I family
members in Wnt and Hedgehog signaling. Genes Dev. 2006, 20, 399−
410.
(12) McKay, R. M.; Peters, J. M.; Graff, J. M. The casein kinase I
family in Wnt signaling. Dev. Biol. 2001, 235, 388−396.
(13) Thorne, C. A.; Hanson, A. J.; Schneider, J.; Tahinci, E.; Orton,
D.; Cselenyi, C. S.; Jernigan, K. K.; Meyers, K. C.; Hang, B. I.;
Waterson, A. G.; Kim, K.; Melancon, B.; Ghidu, V. P.; Sulikowski, G.
A.; LaFleur, B.; Salic, A.; Lee, L. A.; Miller, D. M., 3rd; Lee, E. Small-
molecule inhibition of Wnt signaling through activation of casein
kinase 1alpha. Nat. Chem. Biol. 2010, 6, 829−836.
(14) Liu, C.; Li, Y.; Semenov, M.; Han, C.; Baeg, G. H.; Tan, Y.;
Zhang, Z.; Lin, X.; He, X. Control of beta-catenin phosphorylation/
degradation by a dual-kinase mechanism. Cell 2002, 108, 837−847.
(15) Amit, S.; Hatzubai, A.; Birman, Y.; Andersen, J. S.; Ben-Shushan,
E.; Mann, M.; Ben-Neriah, Y.; Alkalay, I. Axin-mediated CKI
phosphorylation of beta-catenin at Ser 45: a molecular switch for
the Wnt pathway. Genes Dev. 2002, 16, 1066−1076.
(16) Hua, Z.; Huang, X.; Bregman, H.; Chakka, N.; Dimauro, E. F.;
Doherty, E. M.; Goldstein, J.; Gunaydin, H.; Huang, H.; Mercede, S.;
Newcomb, J.; Patel, V. F.; Turci, S. M.; Yan, J.; Wilson, C.; Martin, M.
W. 2-Phenylamino-6-cyano-1H-benzimidazole-based isoform selective
casein kinase 1 gamma (CK1gamma) inhibitors. Bioorg. Med. Chem.
Lett. 2012, 22, 5392−5395.
(17) http://kinase.com/human/kinome/ (accessed June 2012).
(18) Long, A.; Zhao, H.; Huang, X. Structural basis for the
interaction between casein kinase 1 delta and a potent and selective
inhibitor. J. Med. Chem. 2012, 55, 956−960.
(19) See the Supporting Information for details.
(20) Nagle, A. S. S., R. N.; Chong, B. D.; Jung, K. W. Efficient
synthesis of β-amino bromides. Tetrahedron Lett. 2000, 41, 3011−
3014.
1064
dx.doi.org/10.1021/ml300278f | ACS Med. Chem. Lett. 2012, 3, 1059−1064