Discovery of 3(S)-thiomethyl pyrrolidine ERK inhibitors for oncology

Article abstract of DOI:10.1016/j.bmcl.2018.04.063

Compound 5 (SCH772984) was identified as a potent inhibitor of ERK1/2 with excellent selectivity against a panel of kinases (0/231 kinases tested @ 100 nM) and good cell proliferation activity, but suffered from poor PK (rat AUC PK @10 mpk = 0 μM h; F% =

Full text of DOI:10.1016/j.bmcl.2018.04.063

Accepted Manuscript
Discovery of 3(S)-thiomethyl pyrrolidine ERK inhibitors for oncology
Sobhana Babu Boga, Abdul-Basit Alhassan, Alan B. Cooper, Ronald Doll,
Neng-Yang Shih, Gerald Shipps, Yongqi Deng, Hugh Zhu, Yang Nan, Robert
Sun, Liang Zhu, Jagdish Desai, Mehul Patel, Kiran Muppalla, Xiaolei Gao,
James Wang, Xin Yao, Joseph Kelly, Subrahmanyam Gudipati, Sunil Paliwal,
Hon-Chung Tsui, Tong Wang, Bradley Sherborne, Li Xiao, Alan Hruza, Alexei
Buevich, Li-Kang Zhang, David Hesk, Ahmed A. Samatar, Donna Carr, Brian
Long, Stuart Black, Priya Dayananth, William Windsor, Paul Kirschmeier,
Robert Bishop
PII:
S0960-894X(18)30373-1
https://doi.org/10.1016/j.bmcl.2018.04.063
BMCL 25810
DOI:
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
22 February 2018
10 April 2018
25 April 2018
Please cite this article as: Boga, S.B., Alhassan, A-B., Cooper, A.B., Doll, R., Shih, N-Y., Shipps, G., Deng, Y.,
Zhu, H., Nan, Y., Sun, R., Zhu, L., Desai, J., Patel, M., Muppalla, K., Gao, X., Wang, J., Yao, X., Kelly, J., Gudipati,
S., Paliwal, S., Tsui, H-C., Wang, T., Sherborne, B., Xiao, L., Hruza, A., Buevich, A., Zhang, L-K., Hesk, D.,
Samatar, A.A., Carr, D., Long, B., Black, S., Dayananth, P., Windsor, W., Kirschmeier, P., Bishop, R., Discovery
of 3(S)-thiomethyl pyrrolidine ERK inhibitors for oncology, Bioorganic & Medicinal Chemistry Letters (2018),
doi: https://doi.org/10.1016/j.bmcl.2018.04.063
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Bioorganic & Medicinal Chemistry Letters
Discovery of 3(S)-thiomethyl pyrrolidine ERK inhibitors for oncology#
Sobhana Babu Bogaa, *, Abdul-Basit Alhassana, Alan B. Cooper a, Ronald Doll a, Neng-Yang Shih a, Gerald Shipps b,Yongqi Deng b, Hugh Zhu a, Yang
a
Nan b, Robert Sun a, Liang Zhu b, Jagdish Desai a, Mehul Patel b, Kiran Muppalla b, Xiaolei Gao a, James Wang a, Xin Yao a, Joseph Kelly
,
Subrahmanyam Gudipati a, Sunil Paliwal a, Hon-Chung Tsui a, Tong Wangb, Bradley Sherborne a Li Xiao a, Alan Hruza a, Alexei Buevich a, Li-Kang
Zhanga, David Hesk a, Ahmed A. Samatar a, Donna Carr a, Brian Long a, Stuart Black a, Priya Dayananth a, William Windsor , Paul Kirschmeier a,
a
Robert Bishop a
a Discovery Chemistry, Merck & Co., Inc.,2015 Galloping Hill Rd, Kenilworth, NJ 07033, United States
b Discovery Chemistry, Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, MA 02115, United States
#Dedicated to Professor Dale L. Boger, Professor The Scripps Research Institute, San Diego, CA, USA on the occasion of his 65th birthday
ARTICLE INFO
ABSTRACT
Article history:
Received
Revised
Accepted
Available online
Compound 5(SCH772984) was identified as a potent inhibitor of ERK1/2 with excellent
selectivity against a panel of kinases (0/231 kinases tested @ 100 nM) and good cell
proliferation activity, but suffered from poor PK (rat AUC PK @10 mpk= 0 uM.h; F %= 0)
which precluded further development. In an effort to identify novel ERK inhibitors with
improved PK properties with respect to 5, a systematic exploration of sterics and composition at
the 3-position of the pyrrolidine led to the discovery of a novel 3(S)-thiomethyl pyrrolidine
analog 28 with vastly improved PK (rat AUC PK @10 mpk= 26 uM.h; F % = 70).
Keywords:
ERK inhibitor
ATP competitive
MAP kinases
Kinase selectivity
Oncology
2009 Elsevier Ltd. All rights reserved.
Aberrant and hyper activation of the RAS/RAF/MEK/ERK signaling
pathway, a member of the MAPK kinase pathway, plays a central
role in the underlying proliferation mechanisms of several human
tumor subtypes. ERK is the downstream target of the MAPK kinase
pathway and is constitutively activated in many tumor cells
(Melanoma: 60% BRAF mutant; 15-20% NRAS, Colon: 50% KRAS
mutant, 15% BRAF, Pancreatic: 90% KRAS, NSCLC: 30%
KRAS).1 ERK inhibition selectively induces many cellular events
including cell differentiation, cell proliferation and apoptosis.2 Of
late, several highly optimized ERK inhibitors such as the pyrrole 1
An excellent review7 by Samatar and Poulikakos describes the
discovery and development of various RAS-ERK inhibitors that are
being studied at various phases in both clinical and pre-clinical
development. The seminal work by these groups has led to the
development of more effective therapies for patients with tumors
dependent on the ERK signaling pathway. The goal of our research
effort was to overcome RAS-ERK resistance believed to be tied to
down field effectors in the MAPK pathway. Designing potent and
selective RAS-ERK inhibitors that could mediate drug resistance is a
daunting challenge that has been a major focus for both academia
and the pharmaceutical industry.8 We reported9 the discovery of a
highly potent, kinase selective ERK1/2 inhibitor 5 (SCH772984) that
displayed unique dual mechanism of action (inhibits both
phosphorylation of ERK and RSK) and demonstrated anti-tumor
efficacy in both the BRAF/RAS mutant cell line xenograft models
(Figure 1).
by Vertex/Biomed Valley Discoveries,3 the pyridone
2 by
Genentech4, fused pyrrolo-diazepanone 3 by Novartis5 and most
recently, the irreversible acrylate inhibitor 4 by Astrazeneca6 have
been reported (Figure 1).
Compound 5 is a potent ERK inhibitor (ERK2 IC50= 1 nM),
exhibiting high kinase selectivity (0/231 kinases tested @ 100 nM),
which was derived from an initial high throughput screening hit
6(ERK2 IC50=18.6 µM) (Figure 2). Compound 6 was obtained
through an in-house neomorph small molecule library which was
screened against the unphosphorylated (in-active) form of the target
protein ERK2 utilizing an automated ligand identification system
(ALIS). Subsequent SAR following hit validation from 6 afforded
compound 7 (ERK2 IC50=2.7 µM).10 Introduction of the indazole
pharmacophore provided enhanced potency and selectivity giving
rise to compound 5; however, compound 5 suffered from both poor
absorption and bioavailability in rat, as seen in the plasma drug
concentration measured by area under the concentration-time curve
Figure 1. Representative structures of ERK inhibitors 1-5.

(AUC) (Rat AUC @ 10 mpk=0 nM.h; F %= 0), that precluded this
target for further development. Based upon our interest in developing
an oral ERK compound for in-vivo biological studies, we chose to
further explore the SAR of this novel class of ERK inhibitors. Herein
we report our research efforts toward this aim (Figure 2).
Asp104
Gln103
G-loop
Lys52
Hinge
Met106
Tyr62
Tyr34
Lys112
Figure 3. X-ray crystal structure of 5 in the active site of ERK2 with
hydrogen bond interactions to the key residues highlighted in dashed
lines
Based on the X-ray studies, the pyrrolidine amide linkage is involved
in pivotal hydrogen bonding interactions in the active site with the
gate keeper residues (Asp165, Gln103 Glu69) of the ERK protein
vis-à-vis a water hydrogen bond network (depicted in Figure 3). We
began our SAR studies by replacing the unsubstituted pyridine
(potentially susceptible to N-oxide formation mediated by
cytochrome P450 enzymes) at the 3-position of the indazole, which
has a key interaction with the lysine 112 residue of ERK, with a p-
fluoro phenyl group to afford compound 8. Compound 8 maintained
ERK potency ERK2 IC50= 5.5 nM, but did not show any sign of
improving pharmacokinetics (PK) in the rat (Rat AUC @ 10 mpk=0
nM.h) Table 1.
In order to better understand the underlying mechanism for poor
bioavailability for this class of compounds, metabolic identification
studies with compound 8 were undertaken. Incubation of compound
3H-8 in cryo-preserved rat and human hepatocytes at 10 µM and 1
µCi/mL for 0, 2 and 4 hours at 37°C followed by metabolite
characterization identified the indazole amide linkage as the major
metabolic pathway giving rise to metabolites 9 and 10 (Figure-4).
Figure 2. Hit to lead identification of ERK inhibitor 5(SCH772984).
To enable our structure based drug design (SBDD) effort, we
obtained the X-ray crystal structure of 5 bound to ERK2, shown in
Figure 4. The binding mode is similar to other inhibitors in the series
and has been extensively discussed previously10. Briefly, the two
indazole nitrogen atoms of 5 form hydrogen bonds with Asp104 and
Met106 at the hinge region of the ERK2 ATP binding site. The
pyridine N atom forms an H-bond with Lys112, while the two amide
carbonyl O atoms, along with the protonated pyrrolidine N atom, are
involved in an H-bond network with gatekeeper Gln103 and catalytic
Lys52. In addition, upon binding of 5 to ERK2, the G-loop
undergoes a large conformation change which flips the Try34 side-
chain and generates a new side pocket for 5 to extend into, thus
produces a novel binding conformation where aromatic pi-pi
stacking interactions between the pyrrolidine and Tyr34, and the
distal phenyl pyrimidine and Tyr62, were observed. This unique
binding conformation leads to excellent kinase selectivity for 5 and
its analogs.
Figure 4. Metabolic pathway and strategies for mitigating the amide bond
cleavage liability of 8
Guided by in-silico modeling, an initial chemistry strategy was
aimed at structural modifications (viz., elimination, disposition,
isostere and steric hindrance) around the pyrrolidine amide region in
an effort to mitigate this metabolic pathway. We first investigated the
simple elimination of the carbonyl group (compound 11) and
disposition of the amide as the N-acetyl (compound 12), both of
which caused significant loss in ERK activity compared to
compound 8. Incorporation of a triazole as an amide isostere,
(compound 13) was unfortunately shown to be completely devoid of
ERK activity illustrating the significance of the pyrrolidine amide
group with respect to ERK inhibition.

explore similar groups in the hope that they might provide further
improved PK properties. Attempted ring expansion to morpholine
compound 30 and thiomorpholine compound 31 led to a loss of
ERK2 potency, potentially disturbing the close interaction with the
gate keeper region of the active site of the ERK protein.
Interestingly, the opposite enantiomer 3(R)-thiomethoxy compound
3212 was shown to be completely devoid of ERK potency,
highlighting the stereospecific constraints and stringent structural
composition requirements for this class of inhibitors to maintain
ERK potency.
Table 1. Significance of pyrrolidine amide group towards ERK potency
ERK2
IC50
Rat AUC
@10 mpk
(nM.hr)
#
R
(nM)
8
5.5
0
11
12
960
ND
574
ND
ND
Table 2. Exploration of center core toward ERK activity and PK.
R2 =
R2 =
Centre core
R1 =
13
>1000
#; ERK2 IC50 (nM) /
Rat AUC (nM.h)$
#; ERK2 IC50 (nM) /
Rat AUC (nM.h)$
ND Not Determined
8; 5.5/0
14; 15.5/ND
We then chose to determine whether electronic and steric
interactions could affect amide metabolism and as such provide a
path forward for this promising chemo type, lead 5. A systematic
SAR at the 3- position of the pyrrolidine amide (centre core) while
keeping the same p-flouro phenyl indazole Left Hand Side (LHS)
15; 24/65
-
and in combination with two of the Right Hand Sides (RHS) (R2
=
pipirazine 8 and pipiridine-ene 14) was explored as depicted in Table
2. In general smaller substitutions at the 3-position of the pyrrolidine
(viz., methyl 15 and fluoro methyl 16) retained ERK potency but did
not show any significant improvement in rat AUC levels.
Incorporation of heteroatom polar functionality such as hydroxy
methyl 17 and N, N-dimethyl compound 18 had slightly weaker ERK
potency. However, introduction of the 3(R)-methoxy moiety,
compound 19 resulted in a modest measurable AUC of 352 nM in rat
following 10 mpk dose, while retaining ERK potency. Notably,
16; 5.8/28
-
-
-
17; 14/ND
18; 21/ND
compound 20 (R2 pipiridine-ene RHS) showed
a 5 fold
=
improvement in rat PK (AUC=1.8 µM.h) while retaining single digit
nanomolar ERK potency. Increasing the length and size of the
alkoxy group, such as ethoxy 21, isopropoxy 22 and phenoxy 23,
seemed to be very sensitive and generally not well tolerated leading
to loss in ERK potency but/albeit showed some improvement in rat
AUC levels. Attempted substitutions of methoxymethyl compounds
24, 25 and ethyl compound 26 resulted in a 5 to 20 fold loss in ERK
potency compared to compound 8.
19; 2.1/352
21; 9.7/150
22; 90/712
20; 4.8/1880
-
-
Further SAR exploration led to the incorporation of a thiomethoxy
group at the 3-position of the pyrrolidine to afford compounds 27
and 28. The 3(S)-thiomethoxy pyrrolidine analogs 27 and 28 showed
a dramatic 10-14 fold improvement in rat AUC levels at 10 mpk PO
dose (AUC=3.6 µM.h for 27; 26 µM at 10 mpk for 28) compared to
the corresponding 3(R)-methoxy pyyrolidine analogs (AUC=0.35
µM.h for 19; AUC=1.8 µM.h for 20) while retaining single digit
nanomolar ERK potency. Although sterically hindered tertiary 3(S)-
thiomethoxy pyrrolidine compound 28 was stable to aerial oxidation
at ambient temperature, the corresponding sulfone methyl analog 29
was detected following chemical oxidation with mCPBA11. Sulfone
methyl compound 29 displayed weaker ERK potency and did not
have a significant PK advantage when compared to thiomethyl
compound 28. To capitalize on the observed PK enhancements
observed following the substitution of the 3(S)-methoxy and 3(S)-
thiomethoxy groups at the 3-position of the pyrrolidine we chose to
23; >3000/938
-
24; 25/1216
25; 41/ND
-
26; 115/ND

t½ (h)
Mean residence time (hr.)
Bioavailability F %
Dog AUC @ 10 mpk (nM.hr.)
Clp (mL/min/kg)
t½ (h)
ND
ND
0
ND
ND
ND
ND
ND
ND
ND
ND
4528
ND
ND
ND
ND
2.5
2.5
70
17200
7.6
2.0
27; 5.6/3657
28; 7/25914
29; 12/4091
Mean residence time (hr.)
F %
5.1
75
-
ND Not Determined
-
-
30; 119/ND
31; 1311/ND
-
32; >3000/ND
ND Not Determined $ Rapid Rat PK dosed @ 10 mpk
As depicted in Table 2, 3(S)-thiomethoxy pyrrolidine compound 28
emerged as a lead ERK inhibitor with single digit nanomolar potency
and an improved PK profile. Further evaluations of compound 28
versus the 3(S)-methoxy pyrrolidine compound 20 and the initial
proof of concept lead pyrrolidine compound 5 were conducted across
various parameters (viz., enzymatic, cellular potency, CYP, hERG,
Caco-2 permeability and PK) and are summarized in Table 3.
Compound 28 maintained good ERK enzymatic activity (ERK IC50
=
7 nM) and cellular activity in BRAF/KRAS mutant wildtype cancer
cell lines (HT-29/Caspase IC50 (nM) = 118/80 nM) compared to
compounds 20 and 5. Interestingly, swapping the methoxy to a
thiomethoxy group reduced hERG inhibitory activity (hERG
%I@1.5/5 mg/ml = 8/21) and human/dog hepatocyte clearance (Hu
& Dog hep. CL mL/min/M = 18 & 7), but CYP 3A4 activation still
needed to be addressed. The 3(S)-thiomethoxy pyrrolidine compound
28 was selected for full in vivo PK evaluation in both and rat at 10
mpk PO; 3 mpk IV and in dog at 10 mpk PO; 2 mpk IV, 2mpk IPT
(via portal vein infusion). Compound 28 displayed excellent
Figure 5. Rat and dog Plasma concentration (Mean ± SD) of compound 28
We hypothesized that the observed dramatic enhancement of PK for
the 3(S)-thiomethoxy pyrrolidine ERK inhibitor 28 over compounds
5 and 20 could be due to the combination of both steric hindrance
and electronic effects. We envisioned that the thiomethyl group
could participate in a strong coordination with zinc in the
metalloprotease active site13, thereby shifting the equilibrium more
towards intermediate 34, reducing the formation of the tetrahedral
intermediate 33, resulting in minimized potential for amide
hydrolysis and thus mitigating the amide metabolic liability (Figure
6). To the best of our knowledge, this is first reported example of an
improvement in PK profile resulting from the substitution of a sulfur
based group (e.g., thiomethyl) adjacent or in close proximity to an
amide functional group.
pharmacokinetic profiles with total clearance of 8.4 mL/min/kg, t of
½
2.5 h, with 70% bioavailability in the rat and a total clearance of 7.6
mL/min/kg, t of 2 h, and 75% bioavailability in the dog (Figure 5).
½
Table 3. Comparison of analogs 5, 20 and 28 toward overall ERK profile.
5
20
28
Parameter (units)
R = H
1
59/96
7.8/5.7
12/3
R = OMe
4.8
88/79
31/2.2
56/70
R = SMe
7
118/80
>30/2
8/21
ERK2 IC50 (nM)
HT-29/Caspase IC50 (nM)
CYP 3A4 (co/pre) (mM)
hERG Rb (%I) @1.5/5 mg/ml
Hu & Dog hep. CL
Figure 6. Plausible rationale for the PK enhancements of compound 28
To understand how 3(S)-thiomethoxy group interacts with ERK2, the
X-ray structure of ERK2/27 was determined (Figure 7, PDB:6CPW).
Not surprising, 27 showed a similar binding mode as 5. The 3(S)-
thiomethoxy group points into the binding region where Asn152,
Leu154, Cys164, and Asp165 serve as the floor, G-loop as the
ND
36/33
18/7
(mL/min/M)
106Caco II (Papp/cm.S-1)
4
60
Rat AUC @ 10 mpk (nM.hr.)
Clp (mL/min/kg)
0
ND
1880
ND
25914
8.4

ceiling, making hydrophobic contacts with Asn152, Cys164, and
Try34.
51 in good yield. Global deprotection of 51 using TFA and
alkylation of RHS fragment 50 afforded the 3(S)-thiomethoxy
pyrrolidine ERK inhibitor 2817 in good yield.
Figure 7. X-ray crystal structure of 27(PDB:6CPW ) in the active
site of ERK2 with hydrogen bond interactions to the key residues
highlighted in dashed lines.
Since 28 is a close analog of 27, we expected a similar binding mode
of 28 in ERK2 as 27. A structural model14 of ERK2/28 (Figure 8),
constructed using the X-ray structure of ERK2/27, displayed the
binding conformation of 3(S)-thiomethoxy that allows 28 to retain
strong binding to ERK2, while offers improved PK profile.
Scheme 1. Synthesis of ERK inhibitor 28. Reagents and conditions: (a)
1) Br2, MeOH, 88%; (b) (Boc)2O, DMF, 100%; (c) p-flouorphenyl boronic
acid, PdCl2(dppf), K3PO4, Dioxane/H2O, 80%; (d) H2, Pd/C, 100%; (e) 41,
PdCl2(dppf), K3PO4, Dioxane/H2O, 73%; (f) 4.0 N HCl/Dioxane; (g) Chloro
acetyl chloride, DIPEA, 80% (two steps); (h) Mont-K-10, 10% w/w, rt,
CH2Cl2, 3 d, 60%; (i) 1-chloroethyl chloroformate, proton sponge, CH2Cl2,
86%; (j) CH2N2, MeOH, 100%; (k) LDA, (SMe)2, THF, -78°C, 60%; (l) TFA,
CH2Cl2, 90%; (m) L-tartaric acid, MeOH, 78%; (n) (Boc)2O, DMF, 100%; (o)
aq. LiOH (2.0M), THF/MeOH, 100%; (p) 39, HATU, DIPEA, DMF, 60%;
(q) TFA, CH2Cl2, 100%; (r) 43, Et3N, CH2Cl2, 60-80%.
Gln103
Asp104
Lys52
G-loop
Hinge
Met106
Tyr62
Tyr34
Cys164
Leu154
Asp165
Asn152
In summary, systematic exploration of sterics and composition at
the C-3 position of the pyrrolidine of lead compound 5 led to the
discovery of the novel 3(S)-thiomethyl pyrrolidine centre core,
intermediate 50, which was shown to play a critical role in achieving
vastly improved PK and proved critical in identifying orally
bioavailable ERK inhibitors such as compound 28. In addition,
single X-ray crystallography of 3(S)-thiomethyl pyrrolidine 27 bound
to ERK illustrated a unique binding mode for this class of inhibitors.
Finally, the 3(S)-thiomethyl pyrrolidine core identified in the work
described herein, prominently featured in the development of clinical
candidate18 ERK Inhibitor MK-8353, work which will be reported in
due course.
Figure 8. A structural model of 28 in the active site of ERK2. It
displays a similar binding mode of 5, while it’s 3(S)-thiomethoxy
group points towards the binding region defined by residues Asn152
and Cys164.
Synthesis of these ERK inhibitors relied upon on a convergent
approach utilizing three fragments viz., substituted indazole (LHS),
piperidine-ene synthon (RHS), and 3(S)-thiomethyl pyrrolidine
centre core as depicted for compound 28 in Scheme 1. Commercial
3-nitro indazole 37 was brominated followed by Boc protection to
afford compound 38 in good yield. Suzuki coupling of 38 with p-
fluoro phenyl boronic acid followed by hydrogenation using Pd/C
generated the LHS 39 in overall good yield. Suzuki coupling of Boc-
protected piperidine-ene boronic acid 41 with pyrimidine compound
40 afforded 42 in good yield. Deprotection under acidic conditions
followed by chloroacetylation generated the RHS 43 in good yield.
Novel achiral 3-thiomethoxy pyrrolidine 49 was prepared based on
our previously reported synthetic methodolgy15 involving two
synthetic approaches viable for scale-up. Acid catalyzed [3+2]
cycloaddition between acrylate 44 and azomethine ylide precursor 45
and thiomethylation of 47 with dimethyl disulfide/LDA at _78oC
followed by deprotection gave the 3-thiomethyl Pyrrolidine 48 in
moderated yield. Chiral resolution of 49 by crystallization with L-
tartaric acid in MeOH led to the synthesis of novel center core 3(S)-
thiomethyl pyrrolidine 50 in >99% purity.16 Boc protection and
hydrolysis of methyl ester 3(S)-thiomethyl pyrrolidine 50 followed
by HATU coupling with indazole 43 led to the assembly of fragment
Acknowledgments
We thank Drs. John Piwinski, Cathy Strader, Cecil Pickett at
Merck & Co., Inc., Kenilworth, NJ USA for their support and
encouragement.
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compound 29
12. Crystallization of methyl 3-(methylthio)pyrrolidine-3-carboxylate
49 with D-tartaric acid gave the 3(R)-thiomethyl pyrrolidine core
for the synthesis of compound 32.
13. (a) Matthews, B. W. Acc. Chem. Res. 1988, 21, 333 (b) Lipscomb,
W. N., Strater, N. Chem. Rev. 1996, 96, 2375.
14. The binding conformation of compound 27 in ERK2 was taken as
a template to mode compound 28. The change from pipirazine to
dihydro-pyridine was made using Maestro (Schrodinger). The
structure of the ERK2/28 complex was further minimized using
Macromodel (Schrodinger). Small-Molecule Drug Discovery
Suite 2017 , Schrödinger, LLC, New York, NY, 2018.
15. Boga, S. B.; Alhassan, A. B.; Cooper, A. B. Shih, N-Y.; Doll, R. J.
Tetrahedron Lett., 2009, 50,5315
16. methyl (S)-3-(methylthio)pyrrolidine-3-carboxylate 50:1H NMR
(599 MHz, DMSO-d6): δ 3.98 (s, 1H), 3.69 (s, 2H), 3.53 (d, J =
12.4 Hz, 1H), 3.23 – 3.10 (m, 2H), 2.41 (dt, J = 13.7, 8.2 Hz, 1H),
2.02 – 1.94 (m, 1H). 13C NMR (151 MHz, DMSO-d6): δ 173.81,
170.95, 71.40, 55.39, 52.45, 52.25, 44.41, 33.67, 12.95.
17. (S)-N-(3-(4-fluorophenyl)-1H-indazol-5-yl)-3-(methylthio)-1-(2-
oxo-2-(4-(4-(pyrimidin-2-yl)phenyl)-3,6-dihydropyridin-1(2H)-
yl)ethyl)pyrrolidine-3-carboxamide 28: 1H NMR (599 MHz,
DMSO-d6): δ 13.21 (s, 1H), 10.61 (s, 1H), 10.20 – 9.89 (m, 1H),
8.88 (d, J = 4.6 Hz, 2H), 8.42 – 8.29 (m, 3H), 7.93 (m, 3H), 7.69
(dd, J = 8.9, 1.7 Hz, 1H), 7.64 – 7.54 (m, 3H), 7.41 (t, J = 4.7 Hz,
1H), 7.36 (m, 3H), 6.34 (m, 1H), 4.57 (m, 3H), 4.28 – 4.17 (m,
2H), 4.12 (d, , 1H), 3.98 (m, 1H), 3.91 – 3.78 (m, 1H), 3.76 (m,
1H), 3.67 – 3.25 (m, 3H), 2.97 – 2.52 (m, 4H), 2.44 – 2.30 (m,
1H), 2.14 (s, 3H). 13C NMR (151 MHz, DMSO-d6): δ 168.16,
163.40, 163.17, 162.83, 162.38, 160.75, 157.50, 141.95, 141.57,
138.77, 136.02, 135.99, 134.25, 133.85, 132.25, 130.15, 128.28,

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Discovery of 3(S)-thiomethyl pyrrolidine ERK
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inhibitors for oncology
Sobhana Babu Bogaa, * Abdul-Basit Alhassan, Alan B. Cooper, Ronald Doll, Neng-Yang Shih, Gerald Shipps,Yongqi Deng, Hugh Zhu,
Yang Nan, Robert Sun, Liang Zhu, Jagdish Desai, Mehul Patel, Kiran Muppalla, Xiaolei Gao, James Wang, Xin Yao, Joseph Kelly,
Subrahmanyam Gudipati, Sunil Paliwal, Hon-Chung Tsui, Tong Wang, Bradley Sherborne, Li Xiao, Alan Hruza, Alexei Buevich, Li-
Kang Zhang, David Hesk, Ahmed A. Samatar, Donna Carr, Brian Long, Stuart Black, Priya Dayananth, William Windsor, Paul
Kirschmeier, Robert Bishop
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Discovery of potent, selective and orally bioavailable ERK
inhibitor for oncology
Synthesis of tert 3-(S)thiomethyl pyrrolidine based ERK
inhibitors
Improved PK due to sulfur substitution-mitigation of amide
bond cleavage