Bioorganic & Medicinal Chemistry Letters
Discovery and SAR of a novel series of potent, CNS penetrant M PAMs
4
based on a non-enolizable ketone core: Challenges in disposition
a,c,y
a,b,y
a,y
d
a
a
Michael R. Wood
, Meredith J. Noetzel
, James C. Tarr , Alice L. Rodriguez , Atin Lamsal ,
Sichen Chang , Jarrett J. Foster , Emery Smith , Peter Chase , Peter S. Hodder , Darren W. Engers a,b,
a
a
d
e
a,b,g
, Nicholas J. Brandon , Michael W. Wood , Mark E. Duggan , P. Jeffrey Conn a,b,g,
f
f
f
Colleen M. Niswender
a,b,
⇑
a,b,c,
⇑
Thomas M. Bridges
, Craig W. Lindsley
a
Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
Department of Chemistry, Vanderbilt University, Nashville, TN 37232, USA
The Scripps Research Institutes Molecular Screening Center, Department of Molecular Therapeutics, The Scripps Research Institute, Scripps Florida, Jupiter, FL 33458, USA
Amgen Inc., Thousand Oaks, CA 91320, USA
b
c
d
e
f
Neuroscience Innovative Medicines, Astra Zeneca, 141 Portland Street, Cambridge, MA 02139, USA
Vanderbilt Kennedy Center, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
g
a r t i c l e i n f o
a b s t r a c t
Article history:
This Letter describes the chemical optimization of a novel series of M4 PAMs based on a non-enolizable
ketone core, identified from an MLPCN functional high-throughput screen. The HTS hit was potent, selec-
tive and CNS penetrant; however, the compound was highly cleared in vitro and in vivo. SAR provided
Received 18 July 2016
Accepted 19 July 2016
Available online xxxx
analogs for which M
4
PAM potency and CNS exposure were maintained; yet, clearance remained high.
Metabolite identification studies demonstrated that this series was subject to rapid, and near quantita-
Keywords:
tive, reductive metabolism to the corresponding secondary alcohol metabolite that was devoid of M
PAM activity.
4
M
4
Muscarinic acetylcholine receptor
Positive allosteric modulator (PAM)
Schizophrenia
Ó 2016 Elsevier Ltd. All rights reserved.
Structure–Activity Relationship (SAR)
Selective activation of the M
has emerged as a very promising, and mechanistically distinct,
therapeutic approach for the treatment of numerous neuropsychi-
4
muscarinic acetylcholine receptor
4
MLSMR collection, and four structurally novel M PAMs were iden-
tified. Of the hits, VU0009153 (7, CID: 682264) represented an
interesting lead (Fig. 2), as it was similarly potent on both human
4
and rat M (EC50s of 120 nM (76% ACh Max) and 76 nM (71% ACh
2
2
1–8
9
atric and rare genetic CNS disorders.
Until recently, the M
4
PAMs reported to date have been primarily within a single
Max), respectively (using DMSO stock from the source plates). In
addition to no apparent species differences, 7 was also inactive
amide-bearing chemotype (Fig. 1),1
0–19
wherein non-obvious, sub-
tle structural modifications engender steep SAR, species differ-
on both human M
re-synthesis of 7,
EC50 = 138 nM, pEC50 = 6.86 ± 0.07, ACh Max = 76.8 ± 4.1 and rM
1
and M
5
(built-in HTS counterscreen). Upon
ences in PAM potency as well as affinity/cooperativity and
M
4
PAM potency remained intact (hM
4
subtype selectivity, solubility, and/or P-gp efflux.1
0–21
As such, all
4
of the known chemotypes of M
4
PAMs (1–6) pose one or more
EC50 = 145 nM, pEC50 = 6.84 ± 0.10, ACh Max = 80.5 ± 6.3). More-
over, it was a des-NH variant of the prototypical M PAM chemo-
major challenges en route to a clinical development candidate. In
this Letter, we detail the identification, SAR and DMPK profile of
a new, non-enolizable ketone chemotype, related to 1, 2 and 4,
identified in a high-throughput screening (HTS) campaign.
Under the auspice of the MLPCN, we performed a functional M
HTS in 1536-well assay format against the ꢀ360,000 compound
4
types 1, 2, and 4, replacing the amide linker with a non-
enolizable ketone. PAM 7 displayed very high in vitro intrinsic
clearance (CLint) in both rat and human hepatic microsomes with
predicted hepatic clearance (CLhep) near hepatic blood flow rates
(Qhep), but was this due to the trimethyl moiety, or an inherent fea-
ture of the ketone-linker? Figure 2 also highlights the three regions
of 7 targeted for SAR exploration with focus on alternate aryl/het-
eroaryl moieties, evaluating our preferred aza systems of 2 and 4,
while also exploring ketone bioisosteres.
2
2
4
⇑
y
These authors contributed equally.
0
960-894X/Ó 2016 Elsevier Ltd. All rights reserved.