Optimization of Preclinical Metabolism for Somatostatin Receptor Subtype 5-Selective Antagonists

Article abstract of DOI:10.1021/acsmedchemlett.8b00306

A series of structurally diverse azaspirodecanone and spirooxazolidinone analogues were designed and synthesized as potent and selective somatostatin receptor subtype 5 (SSTR5) antagonists. Four optimized compounds each representing a subseries showed imp

Full text of DOI:10.1021/acsmedchemlett.8b00306

Subscriber access provided by University of Sunderland
Letter
Optimization of preclinical metabolism for somatostatin
receptor subtype 5 (SSTR5) selective antagonists
Weiguo Liu, Zahid Hussain, Yi Zang, Ramzi F Sweis, F. Anthony Romero, Paul E. Finke, Remond
Moningka, Jianming Bao, Michael A. Plotkin, Jin Shang, Karen H. Dingley, Gino Salituro, Beth
Ann Murphy, Andrew D. Howard, Feroze Ujjainwalla, Harold B. Wood, and Joseph L Duffy
ACS Med. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acsmedchemlett.8b00306 • Publication Date (Web): 05 Oct 2018
Downloaded from http://pubs.acs.org on October 8, 2018
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 7
ACS Medicinal Chemistry Letters
1
2
3
4
5
6
7
8
9
Optimization of preclinical metabolism for somatostatin receptor subtype
5 (SSTR5) selective antagonists
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Weiguo Liu*, Zahid Hussain, Yi Zang, Ramzi F. Sweis, F. Anthony Romero, Paul E. Finke, Remond
Moningka, Jianming Bao, Michael A. Plotkin, Jin Shang, Karen H. Dingley, Gino Salituro, Beth Ann
Murphy, Andrew D. Howard, Feroze Ujjainwalla, Harold B. Wood, Joseph L. Duffy
Merck & Co., Inc., Kenilworth, New Jersey 07033, USA
ABSTRACT: A series of structurally diverse azaspirodecanone and spirooxazolidinone analogs were designed and synthesized as
potent and selective somatostatin receptor subtype 5 (SSTR5) antagonists. Four optimized compounds each representing a sub-
series showed improvement in their metabolic stability and pharmacokinetic profiles compared to the original lead compound 1
while maintaining pharmacodynamic efficacy. The optimized
Head Group Core Group
Tail Group
cyclopropyl analog 13 demonstrated efficacy in mouse OGTT and
an improved metabolic profile and pharmacokinetic properties
in rhesus monkey studies. In this communication, we discuss the
relationship between structure, in vitro and in vivo activity,
metabolic stability, and ultimately the potential of these
compounds as therapeutic agents for treatment of type 2
O
N
OH
N
OH
N
N
O
O
O
CF3
O
F
O
O
13
1
diabetes. Furthermore, we show how the use of focused libraries significantly expanded the structural class and provided new
directions for structure-activity relationship optimization.
KEYWORDS: Somatostatin, SSTR5 antagonists, Type 2 diabetes mellitus (T2DM), Glucose-dependent insulin secretion
(GDIS), Metabolic stability
Somatostatin (SST) is a peptide hormone that exists in two
isoforms of 14 and 28 amino acids (SST-14 and SST-28),
respectively,1 and is widely distributed throughout the body.2
The SST-mediated biological effects involve a broad range of
functional regulation and hormonal secretion control, and are
effected through interaction with five distinct G-protein-
coupled receptors (SSTR1-5). The target SSTR5 is prominently
expressed in pancreatic islet  cells as well as in
enteroendocrine cells of the gastrointestinal (GI) tract,3
inhibiting the secretion of both insulin and the insulinotropic
glucagon-like peptide 1 (GLP-1).4 SSTR5 knock-out (KO) mice
displayed decreased susceptibility to high-fat-diet (HFD)–
demonstrated a significant glucose lowering effect in a dose-
dependent manner in rodent diabetic models, and instigated
increased pancreatic insulin secretion as well as total and
active GLP-1 release. This SSTR5 antagonist also showed
synergistic effects in combination with a dipeptidyl peptidase
IV (DPP-4) inhibitor.
Unfortunately, advanced profiling of 1 revealed impediments
to developing the compound as a clinical candidate. The
metabolic turnover of 1 was low in liver microsomes from
human, rat, and dog, with > 80% of the parent compound
remaining intact following 30 minute incubation in
microsomes from each species. Therefore, dogs were
investigated as a non-rodent species for safety assessment
studies. However, we found persistent emesis in dogs in a 7
induced insulin resistance5
and SSTR5 selective small
molecular antagonists have been reported to lower glucose
and insulin excursion during an oral glucose tolerance test
(OGTT) in both mice and rats.6,7,8 Based on these cellular and
preclinical pharmacology studies, SSTR5 is an attractive
investigational target for treatment of type 2 diabetes mellitus
(T2DM).
day tolerability study at
5 – 45 minutes post oral
administration for doses of 20 mg/kg or greater.10 This
persistent canine emesis would confound preclinical safety
observations in this species and limit exposure of 1 in
advanced profiling investigations.
In the preceding manuscript in this issue, we reported the
discovery of the azaspirodecanone analog 1 as a novel, and
highly potent and selective SSTR5 antagonist.9 Compound 1
Preclinical profiling in rhesus monkeys was pursued. We
found significantly greater metabolic turnover of 1 in rhesus
ACS Paragon Plus Environment
1

ACS Medicinal Chemistry Letters
Page 2 of 7
1
2
3
4
5
6
7
8
Figure 1. Representative HPLC chromatogram of plasma from a rhesus
monkey treated with 50 mg/kg of compound 1 QD (day 5).
monkey microsomes as compared to other species, with only
28% of the parent compound remaining following 30 minute
incubation. In rhesus oral dose tolerability studies,
administration of 1 for five days (50 mg/kg QD) was well
tolerated without emesis. Metabolite identification was
performed using LC-MS-MS plasma analysis on day 5 (Figure
1), showing significant metabolism in vivo. Glucuronidation
was observed on the carboxylic acid, resulting in metabolite
M6 and a small amount of hydroxylation on the benzoic acid
(M5). However, the majority of metabolites were from
oxidation on the biphenyl ring and de-ethylation of the
ethoxyl group (M1-4). We suspected that the biphenyl ring
was activated by the two electron donating ethoxyl groups and
became susceptible to oxidation catalyzed by cytochrome
P450 bioactivation. The multiple reactive phenols, biphenols,
or triphenols generated from oxidation, hydroxylation, and de-
ethylation of 1 posed a potential safety risk for the compound
as a development candidate.11
This biaryl tail piece in 1 was first reported by Mohr and
coworkers as an optimal SSTR5 potency enhancing
substituent,12 and this moiety has been utilized in multiple
subsequent studies.7,8,12 In light of the metabolic liabilities
associated with this substituent in preclinical safety species,
our focus turned to exploring the structure-activity
relationship (SAR) of the tail piece of 1 with the objective of
improving metabolic stability while maintaining SSTR5
antagonistic activity and other desired properties.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Small and focused libraries of analogs were designed with
different replacements for the biaryl tail piece. Electron
withdrawing groups such as Cl, F, and CF3 were introduced to
limit oxidation on aromatic ring. Positioning such as ortho,
meta, and para were explored to optimize potency,
cyclopropyl groups were introduced to replace aromatic rings
in order to limit CYP induced aromatic oxidation. The
members of these libraries were synthesized and characterized
R
N
OH
N
O
X
O
as individual compounds, and libraries in this sense refers to
collections of compounds prepared using solution-phase
parallel synthetic techniques. The results from the synthesis
and testing of these compounds are shown in Table 1. We
monitored rhesus microsome stability to identify a suitable
preclinical safety candidate with a development advantage
over compound 1.
Table 1. Representative analogs from four subclasses of spiropiperidine type of SSTR5 antagonists
hSSTR5 Bindinga
IC50 (nM) (%
max)b
hSSTR5 cAMPc
IC50 (nM ) (%
max)d
mSSTR5 cAMP
IC50 (nM) (%
max)
Ligand Efficiency
(LE)
Microsomal stabilitye
(H / Rh)
Structure
R =
Compound
X
OEt
1
2
CH2
O
1.2 (99)
0.8 (100)
1.1 (78)
1.5 (66)
0.9 (80)
0.3 (75)
92 / 28
90 / N.D.
0.30
0.31
OEt
F
Cl
3
CH2
N.D.
78 (50)
994 (65)
N.D.
--
OCF3
Cl
Cl
F
4
5
O
0.2 (100)
17 (102)
0.4 (90)
36 (54)
1.7 (97)
64 (61)
78 / 28
86 / 76
0.34
0.29
F
Me
CH2
Me
N
F
6
O
2.9 (97)
0.8 (71)
21 (88)
86 / 81
0.31
Me
CF3
ACS Paragon Plus Environment
2

Page 3 of 7
ACS Medicinal Chemistry Letters
F
1
2
3
4
5
6
7
F
F
7
8
O
CH2
1.2 (98)
4.9 (94)
3.2 (112)
20 (43)
232 (104)
120 (63)
88 / 86
100 / 94
0.30
0.28
Me
CF3
Cl
Cl
9
O
O
2.4 (95)
5.5 (93)
3.2 (64)
1.0 (95)
174 (81)
49 (84)
89 / 89
N.D.
0.29
0.30
8
Me
9
10
11
CF3
N
Me
N
10
12
13
14
CF3
Cl
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
11
O
O
95 (96)
1.8 (98)
66 (83)
1.2 (67)
>3000
N.D.
0.28
0.35
OCF3
Cl
CF3
12
9.3 (90)
N.D. / 45
13
14
O
O
2.1 (100)
4.1 (99)
2.4 (111)
3.2 (36)
43 (78)
42 (51)
99 / 94
81 / 59
0.35
0.34
CF3
CF3
15
16
O
CH2
0.7 (98)
19 (93)
0.4 (87)
37 (62)
57 (86)
298 (72)
100 / 92
N.D. / 88
0.36
0.30
Cl
CF3
OMe
N
17
O
8.2 (108)
5.7 (105)
46 (90)
N.D. / 88
0.34
Me Me
18
19
CH2
O
24 (94)
7.9 (98)
30 (68)
112 (37)
90 / 77
0.31
0.33
O
Cl
Me
Me
O
8.4 (114)
399 (85)
N.D. / 78
Me
Me
20
21
O
CH2
1.5 (94)
161 (64)
1.1 (83)
109 (80)
21 (89)
335 (77)
90 / 83
N.D.
0.36
0.28
O
S
Me
Me
22
23
O
O
0.6 (81)
31 (62)
1.5 (76)
30 (115)
39 (107)
283 (113)
81 / 13
0.38
--
Me
Me
94 / 79
S
O
O
Me
Me
24
CH2
33 (93)
28 (113)
18 (78)
100 / 95
0.30
N
Me
ACS Paragon Plus Environment
3

ACS Medicinal Chemistry Letters
Page 4 of 7
F
1
F
F
2
3
25
O
0.2 (87)
0.5 (85)
1.0 (83)
53 / 17
0.31
4
5
N
Me
Me
6
7
8
9
26
27
O
CH2
0.3 (93)
0.8 (114)
0.1 (76)
0.7 (59)
6.0 (81)
25 (82)
78 / 61
92 / 83
0.36
0.34
N
Me
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Me
F
28
29
O
O
0.4 (92)
222 (80)
0.4 (81)
17 (94)
N/D. / 76
N.D.
0.32
0.23
N
N
Me
Me
F
276 (69)
15670 (9.8)
N
N
Me
Me
a IC50 values were calculated as the mean of minimally duplicate experiments with less than threefold variance for acceptance of
results.
b Binding inhibition at 10 M compound concentration.
c Inhibition of forskolin-induced cAMP in CHO cells expressing human (h) or mouse (m) SSTR5.
d Maximal inhibition at 8.3 mM compound concentration.
e Percent parent compound after incubation at 1 M for 30 minutes in 250 mg protein / mL microsomes from human (H) or rhesus
monkey (Rh). N.D. = not determined
Scheme 1. Synthetic route of spiropiperidine analogsa
identified with 1. However, these microsomal assays do not
inform on the propensity for Phase 2 glucuronidation.
NH
N
a
R
HO2C
HOOC
O
R
+
N
O
N
O
The biaryl series (2-10) was explored with halogens,
trifluoromethyl, and alkyl groups replacing the diethoxy
groups in 1 and at different positions to limit metabolism. The
tolerated connection point of the biaryl was found to be either
the para- (2-5) or ortho-(6-10) positions, and the second
phenyl group can be substituted by pyridines (6) or other
heterocycles such as a pyrazole (10). The ortho-connected
biaryls are generally more potent than the para-connected
biaryls, and larger alkyl substitutions in the meta position on
the proximal aromatic ring (cyclopropyl or trifluromethyl) are
necessary for potency. These SAR iterations demonstrated that
X
X = CH2, O
X
a Reagents and conditions: (a) Na(OAc)3BH, AcOH, (Method
A) or MP-BH3CN resin, AcOH (Method B) as described in SI,
yields ranging from 48-95%
The typical synthetic procedure is outlined in Scheme 1, and
involved reductive amination of the appropriate aryl aldehyde
to the spiropiperidine core piece. Details on the synthesis of
the spiropiperidine substituent and representative tail pieces
are described in the preceding report9 and supporting
information. From over 200 analogs prepared, four structural
classes of compounds emerged as lead series: the biaryls,
monoaryls, chromanes, and indoles. Each of these four classes
was explored with traditional medicinal chemistry iteration.
the metabolically labile diethoxyl groups of
1 can be
eliminated or replaced. However, the resulting analogs (3, 5,
and 8) were less potent in SSTR5 agonist functional (cAMP)
activity. The loss of potency against the human receptor could
be compensated for by modification of the spiropiperidine
core group by replacing the -lactam CH2 substituent with
oxygen. This permutation afforded compounds with similar
SSTR5 potency (1 vs. 2) or improved potency (7 vs. 8) in SSTR5
functional activity. The potency gained by modification of the
core group permitted the use of more diverse tail substituents
that impart improved microsomal stability compared to 1 and
Table 1 lists representative examples from each of the 4 sub-
classes of analogs. All compounds from these libraries were
tested in SSTR5 ligand binding assay and cell-based cAMP
functional assays to measure SSTR5 antagonism. Once the
tractable SAR was established with a series, further analogs
were prepared and evaluated for their metabolic stability in
liver microsome incubation assays. Test compounds were
incubated with microsomes from human, rat, dog, and / or
rhesus monkey liver preparations. The results from human and
rhesus monkey microsomes are presented in Table 1 as a
comparator to the Phase I oxidative metabolism issues
2
and are devoid of the metabolically labile ethoxy
substituents.13
The monoaryl series represented by 11-17 evolved from our
SAR work on the biaryl series, where we noticed that
replacement of the distal aryl by a cyclopropyl group retained
ACS Paragon Plus Environment
4

Page 5 of 7
ACS Medicinal Chemistry Letters
1
2
3
4
5
6
7
8
most of the SSTR5 activity of the resulting compounds.
Rat PKb
Cl
(mL/min/kg)
AUC (M•hr)
F (%)
Previous efforts removing or replacing the distal aryl with
other groups such as simple alkyl, alkoxyl, and halogen had all
resulted in some loss of potency (11). Therefore, a focused
library of these monoaryls with cyclopropyl substitutions was
designed and synthesized in the form of individual analogs.
Meta-cyclopropyl analogs (12) are slightly more potent than
the ortho-(13) or para-(14) substituted analogs. Similar to the
biphenyl series, compounds with spiro-oxazolidinone core
group are more potent than their lactam counterparts (15 vs
16). Electron withdrawing groups such as F, Cl, and CF3 groups
were introduced to minimize metabolism as well as increase
potency. Replacement of the phenyl with pyridyl (17) was
tolerated.
15.2
1.67
41
4.6
6.6
21
3.4
8.5
85
19.6
1.94
100
2.8
14.4
0.66
28
1.9
1.9
1.6
0.84
t1/2 (hr)
OGTTc
% (mg/kg)
-94 (3) -101 (10)
-65 (10)
2.3
0.018
-73 (10)
56
0.228
-69 (10)
31
0.356
9
mPPB: Fu (%) 4.6
0.016
6.2
0.057
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
[3 hr]u (M)
a Lipophilic ligand efficiency was calculated using the hSSTR5
biding potency and LogP determined by HPLC.
b Rat Sprague; 2 mg/kg PO, 1 mg/kg IV; n = 2;
c % Decreased glucose AUC t=0-120 min compared to vehicle in
male C57BL/6 mice fed with high-fat-diet (D12492) for 21 days,
compound (mg/kg) dosed 60 minutes prior to glucose, n=3. mPPB
= mouse plasma free fraction. [3 hr]u = Free drug 3 hr post dose.
The chromane and indole series were first identified through
synthesis and screening of libraries where a diverse set of aryl
groups from commercial sources and our internal collections
were attached to the spiro-piperidine core group. Potent
compounds from this library were followed up with traditional
medicinal chemistry, resulting in 30 chromane analogs for
SAR exploration. The most potent derivatives are the
dihydrobenzopyrans with attachment positions at 6-(18) or 8-
(19). Gem-dimethyl substitutions at  or  dihydropyran and
alkyl or chloro-substitution on phenyl ring next to pyran
oxygen were introduced to block potential metabolic soft
spots. The oxygen of dihydrobenzopyran can be substituted
by sulphur (22), and sulphone (23). Again, the spiro-
oxazolidinone analog was more potent than the corresponding
lactam (20 vs 21).
A representative compound from each of the four sub-classes
was chosen for more advanced PK and efficacy profiling. Table
2 lists the relative potency, pharmacokinetic, and efficacy data
of these compounds (4, 13, 18, and 27) and compares them to
the reference compound 1.14 Each of the four chosen
compounds preserves the head group and core group in 1 that
was optimized previously to reduce ancillary pharmacology.9
As a result, each of the compounds is devoid of significant
potency against cardiovascular ion channels (hERG, Cav1.2,
and Nav1.5 IC50 > 10 M) or metabolic targets (CYP3A4, 2C9,
2D6, or activation of PXR). Each compound represents a
different structural subclass of biaryls (4), monoaryls (13),
chromanes (18), and indoles (27). All four compounds
demonstrated good hSSTR5 antagonist activity as evaluated by
LE / LLE, but exhibited significantly diminished mSSTR5
potency as compared to 1 (Table 1). The compounds exhibited
moderate to good oral bioavailability, and a wide range of
unbound fraction (Fu) in mouse plasma.
The indole series represented by 24-29 includes some of the
most potent SSTR5 antagonists in this work. The original lead
was a simple 1-isopropyl indole with attachment point at the
3-position (24). SAR optimization quickly led to 1-alkyl-4-
arylindole analogs (25) with sub-nanomolar IC50 in SSTR5
binding but poor microsomal stability. Replacing the 4-aryl
with cyclopropyl (26) yielded equally potent antagonists. Once
again, the spiro-oxazolidinone analog (26) was more potent
than the corresponding lactam (27), with the later displaying a
better microsomal metabolic profile. Focused sub-libraries
with different 1-alkyl or 4 or 5-aryl groups were synthesized to
optimize potency and metabolic stability. Isosteres of indole
such as azaindole (28) are well tolerated while the analogous
indazole (29) lost potency.
Mouse oral glucose tolerance test (OGTT) experiments were
carried out with these compounds, and the results from the 10
mg/kg dose (formulated in 0.5% methylcellulose suspension)
are shown in Table 2. Compound 13, 18 and 27 were less
efficacious than
1
in this assay,9 due to significantly
diminished functional potency against the mouse SSTR5
receptor. However, compound 4, which is potent in the
mSSTR5 cAMP assay (Table 1) showed similar efficacy to 1.
Notably, all four of these compounds maintain comparable
potency to 1 against the hSSTR5 receptor, and as such could be
anticipated to have comparable intrinsic clinical efficacy.
Although the primary goal of this lead optimization was to
improve the metabolic stability of 1, particularly the rhesus
microsomal stability, improvements were also achieved in
ligand efficiency (Table 1). Several members of the monoaryl
series (12-17) chromane series (18-20, 22), and indole series
(24-28) afforded similar or better binding potency to 1 with
similar or reduced molecular weight. No clear correlation was
discerned between ligand efficiency and microsomal stability.
From these optimized compounds, 13 exhibited the greatest
metabolic stability in rhesus liver microsomes (Table 1), and
the compound was further evaluated in vivo in rhesus
monkeys for metabolic stability and pharmacokinetic
properties. Dosed orally at 5 mg/kg, 13 reached a Cmax of 2.99
M with 31.2 M·hr total AUC and a residual (24 h) plasma
concentration of 0.47 M. Analysis of pooled plasma samples
from 0.5-24h in this experiment revealed that only the parent
molecule (81%) and glucuronidated 13 (19%) were present. No
oxidized metabolites were detected.
Table 2. Activity, metabolism, PK and efficacy of optimized lead
compounds from each subseries
Compound
1
4
13
18
27
Potencya
LE/LLE
0.3/6.3 0.34/4.9
0.35/6.0
0.31/5.9
0.34/7.1
ACS Paragon Plus Environment
5

ACS Medicinal Chemistry Letters
Page 6 of 7
1
2
3
4
5
6
7
8
In conclusion, we have developed novel series of highly
selective and potent SSTR5 antagonists with diverse structural
features. Building on the chemotype of lead compound 1,
identified in the preceding report, we significantly expanded
the SAR of the tail group and identified four sub-series of
analogs with minimal off-target activity profiles. Metabolic
stability of these SSTR5 antagonists was optimized to achieve
minimal oxidative metabolism through multi-species liver
microsome incubation screens, which ultimately resulted in
good oral bioavailability, exposure, and clearance in rat
pharmacokinetic studies. We also demonstrated that these
antagonists can significantly lower glucose excursions in a
mouse diabetic model. The improved metabolic profile of one
antagonist is confirmed in rhesus monkey pharmacokinetic
studies with 13. These results provide a strong foundation for
further investigation and development of selective SSTR5
antagonists as potential therapeutics for treatment of type 2
diabetes and other metabolic disorders.
receptors. Regul. Pept. 2000, 90, 1–18.
(3) Ludvigsen, E.; Olsson, R.; Stridsberg, M.; Janson, E. T.; Sandler,
S. Expression and distribution of somatostatin receptor subtypes in
the pancreatic islets of mice and rats. J. Histochem. Cytochem. 2004,
52, 391–400.
(4) Chisholm, C.; Greenberg, G. R. Somatostatin-28 regulates GLP-1
secretion via somatostatin receptor subtype 5 in rat intestinal
cultures. Am. J. Physiol. Endocrinol. Metab. 2002, 283, E311–E317.
(5) Tirone, T. A.; Norman, M. A.; Moldovan, S.; DeMayo, F. .J;
Wang, X P; Brunicardi, F. C. Pancreatic somatostatin inhibits insulin
secretion via SSTR-5 in the isolated perfused mouse pancreas model.
Pancreas. 2003, 26, e67–e73.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(6) Sprecher, U.; Mohr, P.; Martin, R. E.; Maerki, H. P.; Sanchez, R.
A.; Binggeli, A.; Kuennecke, B.; Christ, A. D. Novel, non-peptidic
somatostatin receptor subtype
5 antagonists improve glucose
tolerance in rodents. Regul. Pept. 2010, 159, 19–27.
(7) Yamasaki, T.; Hirose, H.; Yamashita, T.; Takakura, N.;
Morimoto, S.; Nakahata, T.; Kina, A.; Nakano, Y.; Tamura, Y. O.;
Sugama, J.; Odani, T.; Shimizu, Y.; Iwasaki, S.; Watanabe, M.;
Maekawa, T. Discovery of novel somatostatin receptor subtype 5
(SSTR5) antagonists: Pharmacological studies and design to improve
pharmacokinetic profiles and human Ether-a-go-go-related gene
(hERG) inhibition. Bioorg. Med. Chem. 2017, 25, 4153–4162.
(8) Hirose, H.; Yamasaki, T.; Ogino, M.; Mizojiri, R.; Tamura-
Okano, Y.; Yashiro, H.; Muraki, Y.; Nakano, Y.; Sugama, J.; Hata, A.;
Iwasaki, S.; Watanabe, M.; Maekawa, T.; Kasai, S. Discovery of novel
5-oxa-2,6-diazoaspiro[3.4]oct-6-ene derivatives as potent, selective,
and orally available somatostatin receptor subtype
antagonists for the treatment of type 2 diabetes mellitus. Bioorg. Med.
Chem. 2017, 25, 4175–4193.
(9) Liu, W.; Shao, P. P.; Liang, G.-B.; Bawiec, J.; He, J.; Aster, S. D.;
Wu, M; Chicchi, G.; Wang, J.; Tsao, K.-L.; Shang, J.; Salituro, G.;
Zhou, Y.-P.; Li, C.; Akiyama, T. E.; Metzger, D. E.; Murphy, B. E.;
Howard, A. D.; Weber, A. E.; Duffy, J. L. Discovery and pharmacology
of a novel somatostatin subtype 5 (SSTR5) antagonist: Synergy with
DPP-4 inhibition. ACS Med. Chem. Lett. 2018, preceding manuscript
in this issue.
ASSOCIATED CONTENT
Supporting Information
Supporting information is available free of charge on the ACS Publications
website at http://pubs.acs.org.
Experimental procedures for the preparation of all compounds and full
characterization of compounds 4, 13, 18 and 27; in vitro and in vivo assay
protocols (PDF).
5 (SSTR5)
AUTHOR INFORMATION
Corresponding Author
*(U.S.) Phone: 908-740-3782
E-mail: weiguo_liu@merck.com
Author Contributions
The manuscript was written through contributions of all authors. All
authors have given approval to the final version of the manuscript.
(10) The cause of canine emesis is unknown.
Funding
(11) Gonzalez, F. J. Role of cytochromes P450 in chemical toxicity
and oxidative stress: studies with CYP2E1. Mutat. Res. 2005, 569, 101–
110.
(12) Alker, A.; Binggeli, A.; Christ, A. D.; Green, L.; Maerki, H. P.;
Martin, R. E.; Mohr, P. Piperidinyl-nicotinamides as potent and
selective somatostatin receptor subtype 5 antagonists. Bioorg. Med.
Chem. Lett. 2010, 20, 4521-4525.
(13) The preclinical pharmacology profile of 2 was recently reported
independently by other investigators. See Briere, D. A.; Bueno, A. B.;
Gunn, E. J.; Michael, M. D.; Sloop, K. W. Mechanisms to elevate
endogenous GLP-1 beyond injectable GLP1 analogs and metabolic
surgery. Diabetes, 2018, 67, 309-320.
(14) Duffy, J. L.; Bao, J.; Ondeyka, D. L.; Tyagarajan, S.; Shao, P.; Ye,
F.; Katipally, R.; Zwicker, A.; Sherer, E. C.; Plotkin, M. A.; Moningka,
R.; Hussian, Z.; Wood, H. B.; Ujjainwalla, F.; Romero, A.; Finke, P.;
Zang, Y.; Liu, W. Preparation of substituted spirocyclic amine,
particularly spiroxazolidinone compounds, as SSTR5 antagonists. WO
2012024183.
All authors were employees of Merck Sharp & Dohme Corp., a
subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA during the
time this research was conducted. All research was funded by
Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc.,
Kenilworth, NJ, USA.
ABBREVIATIONS
SSTR5, somatostatin receptor subtype 5; OGTT, oral glucose tolerance
test; GLP-1, glucagon-like peptide 1; SST, somatostatin; GI,
gastrointestinal; KO, genetic knockout; GDIS, glucose-dependent insulin
secretion; WT, genetic wild type; HFD, high fat diet; T2DM, type 2
diabetes mellitus; DPP-4, dipeptidyl peptidase-IV; QD, dosed once daily;
AUC, area under the curve; SAR, structure activity relationship; CYP,
cytochrome P450; CHO, Chinese hamster ovary; LE, ligand efficiency;
LLE, lipophilic ligand efficiency.
References
(1) Patel, Y. C.; Greenwood, M. T.; Warszynska, A.; Panetta, R.;
Srikant, C. B. All five cloned human somatostatin receptors (hSSTR1–
5) are functionally coupled to adenyl cyclase. Biochem. Biophys. Res.
Commun. 1994, 198, 605–612.
(2) Selmer, I.-S.; Schindler, M.; Allan, J. P.; Humphrey, P. P. A.;
Emson P. C. Advances in understanding neuronal somatostatin
ACS Paragon Plus Environment
6

Page 7 of 7
ACS Medicinal Chemistry Letters
For table of contents use only
1
2
3
4
5
6
7
8
9
Optimization of preclinical metabolism for somatostatin
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
receptor subtype 5 (SSTR5) selective antagonists
Weiguo Liu*, Zahid Hussain, Yi Zang, Ramzi F. Sweis, F. Anthony Romero, Paul E. Finke,
Remond Moningka, Jianming Bao, Michael Plotkin, Vincent J. Colandrea, Jin Shang, Katie
Raustad, Karen Dingley, Gino Salituro, Beth Ann Murphy, Andrew D. Howard, Feroze
Ujjainwalla, Harold B. Wood, Joseph L. Duffy
Merck & Co., Inc., Kenilworth, New Jersey 07033, USA
ACS Paragon Plus Environment