From Oxadiazole to Triazole Analogues: Optimization toward a Dual Orexin Receptor Antagonist with Improved in vivo Efficacy in Dogs

Article abstract of DOI:10.1002/cmdc.201900618

The orexin system is responsible for regulating the sleep-wake cycle. Suvorexant, a dual orexin receptor antagonist (DORA) is approved by the FDA for the treatment of insomnia disorders. Herein, we report the optimization efforts toward a DORA, where our starting point was (5-methoxy-4-methyl-2-[1,2,3]triazol-2-yl-phenyl)-{(S)-2-[5-(2-trifluoromethoxy-phenyl)-[1,2,4]oxadiazol-3-yl]-pyrrolidin-1-yl}methanone (6), a compound which emerged from our in-house research program. Compound 6 was shown to be a potent, brain-penetrating DORA with in vivo efficacy similar to suvorexant in rats. However, shortcomings from low metabolic stability, high plasma protein binding (PPB), low brain free fraction (f_u brain), and low aqueous solubility, were identified and hence, compound 6 was not an ideal candidate for further development. Our optimization efforts addressing the above-mentioned shortcomings resulted in the identification of (4-chloro-2-[1,2,3]triazol-2-yl-phenyl)-{(S)-2-methyl-2-[5-(2-trifluoromethoxy-phenyl)-4H-[1,2,4]triazol-3-yl]-pyrrolidin-1-yl}l-methanone (42), a DORA with improved in vivo efficacy compared to 6.

Full text of DOI:10.1002/cmdc.201900618

Full Papers
DOI: 10.1002/cmdc.201900618
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From Oxadiazole to Triazole Analogues: Optimization
toward a Dual Orexin Receptor Antagonist with Improved
in vivo Efficacy in Dogs
Christine Brotschi,*[a] Martin H. Bolli,[a] John Gatfield,[a] Bibia Heidmann,[a] Francois Jenck,[a]
Catherine Roch,[a] Thierry Sifferlen,[a] Alexander Treiber,[a] Jodi T. Williams,[a] and
Christoph Boss[a]
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The orexin system is responsible for regulating the sleep-wake
cycle. Suvorexant, a dual orexin receptor antagonist (DORA) is
approved by the FDA for the treatment of insomnia disorders.
Herein, we report the optimization efforts toward a DORA,
where our starting point was (5-methoxy-4-methyl-2-[1,2,3]
triazol-2-yl-phenyl)-{(S)-2-[5-(2-trifluoromethoxy-phenyl)-[1,2,4]
shortcomings from low metabolic stability, high plasma protein
binding (PPB), low brain free fraction (fu brain), and low aqueous
solubility, were identified and hence, compound 6 was not an
ideal candidate for further development. Our optimization
efforts addressing the above-mentioned shortcomings resulted
in the identification of (4-chloro-2-[1,2,3]triazol-2-yl-phenyl)-{(S)-
2-methyl-2-[5-(2-trifluoromethoxy-phenyl)-4H-[1,2,4]triazol-3-yl]-
pyrrolidin-1-yl}l-methanone (42), a DORA with improved in vivo
efficacy compared to 6.
oxadiazol-3-yl]-pyrrolidin-1-yl}methanone (6),
a
compound
which emerged from our in-house research program. Com-
pound 6 was shown to be a potent, brain-penetrating DORA
with in vivo efficacy similar to suvorexant in rats. However,
Introduction
Insomnia is a sleep disorder defined by difficulties in initiating
or maintaining sleep or when the sleep that is obtained is non-
refreshing or of poor quality. Current standard insomnia
medications[1–2] are benzodiazepines or gamma-amino-butyric
acid (GABA) modulators, both associated with negative side
effects. A mechanistically unique sleep medication is suvorexant
(1)[3–5] (Figure 1), a dual orexin receptor antagonist (DORA).
Suvorexant, developed by Merck is on the market since 2014
and no other orexin receptor antagonist had been approved by
the FDA since. Intense research led to compounds currently
investigated in late stage clinical trials for the treatment of
insomnia, e.g. lemborexant (2)[6] from Eisai or daridorexant
(3)[7–9] from Idorsia, both DORA’s inhibiting orexin 1 and orexin
Figure 1. Compounds in preclinical or clinical development.
2 receptors (OX1R and OX2R, respectively). Seltorexant (4),[10–11]
a
selective OX2R antagonist co-developed by Janssen and Miner-
va Neurosciences is as well in clinical development for the
treatment of insomnia.[12] The therapeutic potential of selective
OX1R antagonists is also investigated[13] such as SB-334867
(5)[14–15] from GlaxoSmithKline, JNJ-61393215[16] from Janssen,
and ACT-539313[17–19] from Idorsia. Selective OX1R blockage may
be useful for the treatment of addiction or anxiety disorders.[20]
Herein, we describe our efforts toward the discovery of an
orally active, brain-penetrating novel dual orexin receptor
antagonist 42, with increased metabolic stability compared to
our earlier DORA compound 6. These efforts translated into an
improved in vivo sleep efficacy in a canine EEG/EMG experi-
ment.
[a] Dr. C. Brotschi, Dr. M. H. Bolli, Dr. J. Gatfield, Dr. B. Heidmann, Dr. F. Jenck,
Dr. C. Roch, Dr. T. Sifferlen, Dr. A. Treiber, Dr. J. T. Williams, Dr. C. Boss
Drug Discovery and Preclinical Research & Development
Idorsia Pharmaceuticals Ltd.
Results and Discussion
Recently, we published the discovery of compound 6[21] (Fig-
ure 2), a potent DORA, exhibiting sleep-promoting effects in
rats at oral doses of 30 mg/kg and 100 mg/kg. However, this
compound was ineffective in promoting sleep in male Beagle
dogs when dosed at 30 and 90 mg/dog. The lack of efficacy in
Hegenheimermattweg 91
4123 Allschwil, BL (Switzerland)
E-mail: christine.brotschi@idorsia.com
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/cmdc.201900618
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Figure 2. The optimization route.
the dog experiment was attributed to the compound’s low
metabolic stability (intrinsic clearance measured in dog liver
microsomes (DLM) 543 μLminÀ 1 mgÀ 1), its high plasma protein
binding (PPB 99.8%), low brain free fraction (fu brain 0.3%), and
low aqueous solubility (<1 μgmLÀ 1). In addition, suboptimal
physicochemical and human in vitro DMPK properties (intrinsic
clearance in human liver microsomes (HLM) 282 μLminÀ 1 mgÀ 1,
hPPB>99.9%), yielded an inappropriate predicted human PK
profile with a short half-life of around 1.3 h and therefore
compound 6 would not fulfill the requirements for further
development as a sleep promoting drug. Further optimization
work was clearly needed, therefore we embarked on a program
aiming to find compounds with improved properties.
The following assays were used to characterize our com-
pounds as well as to establish the SAR’s with respect to
potency, physicochemical properties, metabolic stability and
in vivo efficacy. Inhibitory activity of the compounds was
determined using fluorometric imaging plate reader (FLIPR)
technology. Compound inhibition of the orexin-A induced Ca2+
flux was measured in CHO cells overexpressing either the hOX1
or the hOX2 receptor and the results are expressed as IC50 values
in nM (geomean of at least three measurements). In a first step,
we assessed the lipophilicity of our compounds by calculating
the clogP. We envisaged reducing the lipophilicity of our
compounds compared to compound 6, since high PPB, low fu
brain, and low aqueous solubility are parameters which are
often associated with high lipophilicity, even though there is no
strict correlation between these parameters. To address the
high clearance predicted for compound 6 in human, we
measured the intrinsic clearance in HLM, assuming a correlation
between in vitro and in vivo clearance. Our goal was to obtain
compounds with a lower intrinsic clearance in HLM than
compound 6 (<282 μLminÀ 1 mgÀ 1). For compounds fulfilling
the above-mentioned objective, physicochemical parameters,
such as PPB in human and rat, fu brain, and solubility were
measured. Compounds were assessed for their brain-penetrat-
ing potential in an in vivo experiment in male Wistar rats, where
brain and plasma concentrations were measured 3 h after oral
dosing (100 mgkgÀ 1). The human multidrug resistant protein
transporter assay (MDR1) was used to determine substrate
susceptibility for the P-glycoprotein (P-gp). The most promising
compounds were tested for their in vivo efficacy on sleep-wake
parameters in male Wistar rats and male Beagle dogs using
electroencephalography/electromyography (EEG/EMG) recorded
by a telemetric system.
When we set out to optimize compound 6, we first focused
on improving its physicochemical properties and in vitro
stability by altering the oxadiazole moiety. Heteroaryls such as
oxazoles, isoxazoles, pyrazoles, imidazoles, or triazoles were
investigated and the triazoles were found to improve the
above-mentioned liabilities. However, such triazole-analogues
were found to be human P-gp substrates and a methyl group
at the C1-position of the pyrrolidine needed to be inserted to
resolve this issue. Further optimization work included the fine
tuning of the peripheral substituents to boost potency on both
orexin receptors as well as to maximize brain exposure
(Figure 2). Combining these efforts resulted in the discovery of
compound 42, a dual orexin receptor antagonist with improved
in vivo efficacy in EEG/EMG experiments in male Beagle dogs,
when compared to compound 6.
In detail, compound 6 showed IC50 values of 28 nM and
4 nM for OX1R and OX2R, respectively (Figure 2). Previous SAR
investigations had shown that the pyrrolidine-core structure is
beneficial for potency on both OXR’s, with preference for the
OX2R. While the substitution patterns of the biaryl moiety and
the aryl moiety linked to the oxadiazole in 6 were previously
optimized for in vivo exposure, little work was performed on
the oxadiazole moiety, and only the two asymmetrical as well
as the symmetrical oxadiazoles had been studied so far. We
therefore evaluated the effect of exchanging the oxadiazole
moiety on the above-mentioned parameters. Our goal was to
replace the oxadiazole by
a less lipophilic 5-membered
heteroaryl system, and we envisaged that by reducing the
lipophilicity of our compound we would either directly or
indirectly alter parameters such a metabolic stability, PPB, fu
brain, and aqueous solubility. We therefore calculated clogP
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Table 1. SAR studies of heteroaromatic replacements.
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2
3
X
4
5
6
7
8
Compd
OX1R[a]
OX2R[a]
clogP[b]
HLM[c]
7
8
9
10
226
49
3.5
140
11
12
13
426
140
3.1
38
486
76
3.1
50
2088
1122
3.0
1062
152
3.5
225
163
3.5
119
311
3.5
nd
13
141
125
9
X
10
11
12
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16
17
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19
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21
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Compd
OX1R[a]
OX2R[a]
clogP[b]
HLM[c]
14
15
16
17
18
19
73
477
2.2
43
20
392
113
3.1
1267
351
3.1
390
210
3.0
47
1210
1023
2.4
2388
1377
2.1
617
158
2.6
32
332
124
nd
nd
[a] IC50 in nM; data are the geometric mean (�2-fold) of at least three independent experiments and were determined by FLIPR assay (see Supporting
Information for assay details). [b] clogP values were calculated using ChemBioDraw Ultra 14.0. [c] Intrinsic metabolic clearance (μLminÀ 1 mgÀ 1) in human liver
microsomes at 1 μM.
values as an indicator of the lipophilicity of the compound and
we measured the intrinsic clearance in HLM to assess whether
the modification led to more stable compounds and was
tolerated by the OXRs, especially on the OX2R. For this exercise,
the pyrrolidine-core, the biaryl carboxamide, and the unsub-
stituted phenyl ring were fixed, resulting in compound 7
(Table 1) a simplified version of compound 6, which served as
the basis for our comparison. In Table 1, a selection of
compounds with 5-membered heteroaromatic oxadiazole re-
placements are listed for which the clogP was calculated to be
in the range of 2.1 to 3.5. Even though we were most interested
in compounds with a lower clogP than the one of compound 7
(3.1), being aware that there is no strict correlation between
lipophilicity and the parameters we intended to alter, it felt too
restrictive to eliminate compounds with a similar or slightly
higher clogP than compound 7. Oxadiazole pyrrolidine isomers
7 and 8 (same clogP) were similar in potency whereas the
symmetrical oxadiazole analogue 9 was at least 5-fold less
potent. Isoxazole 10 and 11, as well as oxazoles 12 and 13,
were tolerated by the OXRs, however neither the clogP nor the
intrinsic clearance were improved when compared to com-
pound 7, and these modifications were therefore not further
pursued. Imidazoles 14 and 15 (same clogP as compound 7)
were of no interest to us, due to their increased in in vitro
clearance in HLM. Pyrazole 16 (clogP of 3.0) was moderately
potent on both OXRs and equally stable in HLM (CLint=47) and
therefore a candidate for further studies. However, further
optimization work to regain potency by introducing substitu-
ents to the aryl-moiety was unsuccessful (data not shown). N-
linked pyrazole analogue 17 and N-linked [1,2,3]-triazole 18,
both exhibiting a lower clogP of around 2, were not well
tolerated by the OXRs. The N-linked [1,2,4]-triazole 19 had an
interesting clogP value of 2.2 and showed low intrinsic
clearance in HLM (CLint=43), but its OX1R preference was not of
interest to us. Most promising seemed [1,2,4]-triazole 20 with
an OX2R preferential profile, a rather low intrinsic clearance in
HLM of 32 and a clogP (2.6).
To evaluate whether this triazole indeed serves as a
promising oxadiazole replacement we compared PPB, fu brain,
aqueous solubility (pH=4) and intrinsic clearance in HLM of
compound 6 with its direct triazole analogue 21 (Table 2).
Replacing the oxadiazole in 6 by the triazole in 21, had no
impact at the OXRs’s potencies and both compounds are
equally potent DORA’s, with a slightly higher potency at OX2R
vs OX1R.
Table 2. Comparison of 6 versus 21.
Compd
6
21
34
2
4.1
OX1R[a]
28
4
OX2R[a]
clogP[b]
4.5
4.0
logD[c]
3.4
PPB
>99.9/99.7
99.9/98.5
human/rat %[d]
fu brain %[e]
Solubility
water pH=4[f]
FaSSIF/FeSSIF
0.3
<1
26/32
1.8
120
156/633
[g]
CLint
HLM/DLM/RLM
282/543/>1250
183/444/613
[a] IC50 in nM; data are the geometric mean (�2-fold) of at least three
independent experiments and were determined by FLIPR assay (see
Supporting Information for assay details). [b] clogP values were calculated
using ChemBioDraw Ultra 14.0. [c] measured. [d] plasma protein binding in
%. [e] brain free fraction in %. [f] solubility measured at pH 4 in a high-
throughput solubility assay in [μgmLÀ 1)]. [g] Intrinsic metabolic clearance
[μMminÀ 1 mgÀ 1] with human, dog, and rat liver microsomes at 1 μM.
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The clogP and the measured logD values clearly showed
that the lipophilicity of compound 21 was reduced compared
to compound 6 (4.1 vs 4.5 and 3.4 vs 4.0). As hypothesized, PPB
(human and rat), fu brain, and aqueous solubility were indeed
improved for the less lipophilic compound 21. For compound 6,
human PPB was greater than 99.9%, whereas for compound 21,
PPB was 99.9%. A more obvious effect was visible in rat, where
PPB decreased from 99.7% to 98.5%. The fu brain (rat) increased
from 0.3 to 1.8% for the less lipophilic compound 21. At pH 4,
the aqueous solubility increased from less than 1 to
1
2
3
4
5
6
7
8
9
120 μgmLÀ 1 for 6 versus 21, respectively.
Based on these promising data for triazole derivative 21, we
resumed SAR studies of the aromatic moieties (Tables 3 and 4)
keeping the [1,2,4]-triazole constant.
To explore the substitution pattern of the aryl attached to
the triazole, we kept the pyrrolidine core, the triazole and the
biaryl carboxamide fixed (Table 3). The unsubstituted phenyl
(20, see above) was slightly more potent on OX2R compared to
OX1R. A 2-methoxy substituent (22) improved the potency on
both receptors and elongation to a 2-ethoxy (23) further
increased the affinity for OX2R. Introduction of a nitrogen
leading to pyridine analogue (24) was tolerated. An additional
substituent such as a 3-chloro (25) slightly improved potency
on OX2R, but not on OX1R. The disubstituted 2-methyl,3-chloro
analogue 26 was inferior especially at OX1R when compared to
25. As had already been observed in the oxadiazole series (e.g.
compound 6), the most potent compound at OX2R was the
trifluoromethoxy derivative 27.
For the next round of optimization, we kept the 2-
(trifluoromethoxyphenyl)-substituted (S)-3-(pyrrolidin-2-yl) 4H-
1,2,4-triazole scaffold constant (Table 4) and screened various
substitutions on the 2-triazol-2-yl benzamide moiety. The
unsubstituted triazolyl benzamide 28 showed weaker affinity at
both OXRs than 27. The 5-methyl derivative 29 was less potent,
while the 3-methyl compound 30 was slightly more potent at
both receptors, when compared to 27. This was different in the
oxadiazole series where the 4-position was the most favorable
position for an additional substituent. A methyl or a chlorine
substituent had little influence on potency (27 versus 32 and 30
versus 33). Further improvement in potency on both receptors
was obtained by combining two substituents, resulting in a 3,4-
dimethyl (31) or a 4-chloro,3-methyl substitution (34). Di-
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14
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16
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20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
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49
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Table 3. SAR studies of triazole pyrrolidine analogues with various R
moieties.
R
Compd
OX1R[a]
OX2R[a]
20
617
158
22
49
124
23
39
38
24
57
50
R
Compd
OX1R[a]
OX2R[a]
25
145
17
26
1143
29
27
98
10
[a] IC50 in nM; data are the geometric mean (�2-fold) of at least three
independent experiments and were determined by FLIPR assay.
Table 4. SAR studies of triazoleÀ pyrrolidine-analogues with different biaryl R.
R
Compd
OX1R[a]
OX2R[a]
HLM[b]
28
156
27
29
477
53
27
98
10
84
30
27
4
31
9
2
nd
nd
nd
244
R
Compd
OX1R[a]
OX2R[a]
HLM[b]
32
109
9
33
17
3
34
8
2
35
22
3
21
29
3
48
73
190
91
183
[a] IC50 in nM; data are the geometric mean (�2-fold) of at least three independent experiments and were determined by FLIPR assay. [b] Intrinsic metabolic
clearance (mLminÀ 1 mgÀ 1) in human.
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substituted triazolyl benzamides (35 and 21) also resulted in
highly potent compounds, however no improvement over
mono-substituted analogues was observed (35 versus 33 and
21 versus 30). In addition, not only was the potency maintained,
but also the in vitro clearance in HLM was reduced when
compared to the oxadiazole analogues (e.g., 21 versus 6).
A similar SAR exploration was performed for pyrazole
analogue 16 (Table 1). Unfortunately, fine tuning of compound
16 did not result in potent orexin receptor antagonists, and
therefore pyrazole analogues were not further pursued (data
not shown).
To assess whether triazole analogues penetrate into brain
tissue, a series of in vivo experiments were performed in male
Wistar rats (Table 5). Absolute brain and plasma concentrations
were determined 3 h after oral dosing (100 mgkgÀ 1). These
results were compared to those of the corresponding oxadia-
zole analogues. When compared to oxadiazole 6, the more
polar triazole 21 reached 10-fold lower plasma concentrations
and showed a low brain concentration of 21 nggÀ 1 at the 3 h
timepoint after dosing. A second pair of compounds was
analyzed (36 v. 27). This time, the plasma concentration for the
triazole analogue 27 was higher than for the oxadiazole 36.
However, the brain to plasma ratio was still lower for
compound 27 than for 36, resulting in lower absolute
concentration in the brain for 27 when compared to 36
(395 nggÀ 1 versus 629 nggÀ 1). Similarly, absolute plasma con-
centrations were higher for the triazole compounds 31 and 33
when compared to their corresponding oxadiazole analogues
37 and 38, respectively.
The triazole 33 reached brain concentrations that were
comparable to the ones observed with compound 6 and we
therefore investigated this compound in vivo for its sleep
promoting effects. We used freely moving male Wistar rats
implanted with radiotelemetric transmitters for continuous
recording of EEG/EMG signals. Compound 33 and 6 were tested
orally at the dose of 100 mgkgÀ 1 and administered at the
beginning of the nocturnal active phase, when endogenous
orexin levels increase. Over the 12 h night period following
administration, compound 33 showed a similar sleep promoting
effect as compound 6 when tested under the same experimen-
tal conditions (+66 min and +54 min of sleep compared to
matched vehicle, respectively; Figure 3).
Compared to vehicle treated rats, 33 significantly decreased
the time spent in active wake (À 19.4%, p=0.0029 and À 24.0%,
p<0.001 versus matched vehicle for 33 and 6, respectively;
paired t-test), and significantly increased both the time spent in
non-REM (rapid eye movement) sleep (+24.2%, p=0.0022 and
+14.3%, p<0.001 for 33 and 6; paired t-test) and the time
spent in REM sleep (+47.0%, p=0.0077 and +35.2%, p=
0.0195 for 33 and 6; paired t-test). The time spent in quiet wake
was not significantly changed for either compound (p=0.6390
for 33 and p=0.1356 for 6, paired t-test). As usually observed
with DORAs,[20–29] the relative proportion of the time spent in
non-REM and REM sleep over the total sleep time did not
significantly change with 80–83% of non-REM sleep (compared
to matched-vehicle treated rats; p=0.0914 for 33 and p=
0.1697 for 6, paired t-test).
1
2
3
4
5
6
7
8
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
Table 5. Brain penetration properties for a selection of compounds.
R
Compd
SF[a]
OX1R[b]
OX2R[b]
[P][c]
[B][c]
[B]/[P] ratio[d]
MDR1
Efflux
ratio[e]
6
21
A
B
28
29
4
3
1763
141
1585
21
0.90
0.14
2.1
nd
36
27
A
B
13
98
4
503
1024
629
395
1.25
0.39
2.3
11
10
37
31
A
B
4
9
3
2
49
773
42
306
0.86
0.40
nd
9.2
38
33
A
B
23
17
11
3
1042
2773
1794
1639
1.72
0.59
1.7
6.5
[a] SF= scaffold; [b] IC50 in nM; data are the geometric mean (�2-fold) of at least three independent experiments and were determined by FLIPR assay. [c]
Brain penetration experiment was performed in rats (n=3) by sampling plasma [P] in (ngmLÀ 1) and brain [B] (nggÀ 1), 3 h following administration of
100 mgkgÀ 1 p.o., formulated in 100% polyethylene glycol 400 (PEG400). [d] Brain/plasma ratios were calculated assuming a brain density around 1 gmLÀ 1. [e]
multidrug resistant protein 1 (MDR1) efflux ratio of (Papp B!A/Papp A!B). nd=not determined.
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ing bulk close by, such as a methyl group in the 2-position of
the pyrrolidine core. Indeed, this subtle modification resulted in
a reduction of the MDR1 efflux ratio (Table 6).
All compounds with a 2-methyl-pyrrolidine (scaffold C), had
a 2-fold lower efflux ratio when compared to their analogue
with scaffold B (see Table 6). This structural modification was
tolerated by the OXRs, with a slight loss at OX2R and a minor
increase at OX1R potency. This contrasts with a 2-methyl
1
2
3
4
5
6
7
8
9
oxadiazoleÀ pyrrolidine analogue where
a 10-fold loss in
potency at both receptors was observed (data not shown).
These in vitro results translated into in vivo. In the rat,
compound 42 showed high brain penetration potential with a
B/P ratio of 1.05 (brain concentrations of 1123 nggÀ 1 and
plasma concentration of 1073 ngmLÀ 1) whereas compound 33
had a B/P ratio of only 0.59 (brain concentrations of 1639 nggÀ 1
and plasma concentrations of 2773 ngmLÀ 1). In combination
with the human MDR1 data, 2-methyl-pyrrolidine 42 clearly was
the most interesting compound.
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
Figure 3. Effect of 33 and 6 on the time spent in sleep and wake stages (%
of total time) during the 12 h night active period post administration in male
Wistar rats. Rats were administered a single oral dose of vehicle (PEG 400) or
compound at 100 mgkgÀ 1. Data are expressed as mean�SEM. *p<0.05,
**p<0.01, ***p<0.001 (n=7 for 33, n=8 for 6).
Compounds 6 and 42 were shown to be potent DORA’s and
equipotent across species such as human, rat and dog (see
Table 7).
The observation that the triazoles showed a clear trend for
lower brain to plasma ratios in the rat, led us speculate whether
these analogues are substrates for the human P-gp transporter.
Indeed, compounds with a triazole pyrrolidine scaffold B
showed an increased human P-gp susceptibility. Measured
efflux ratios (Papp B!A/Papp A!B) for 31 and 33 were 9.2 and
6.5. respectively; still having a high apparent passive perme-
ability (Papp A!B) of 8.5 to 9.7×10À 6 cmsÀ 1. In contrast, the
efflux ratios of oxadiazole compounds (scaffold A) were around
2. We hypothesized that the P-gp transporter recognizes the
NÀ H of the triazole and that this motif could be the culprit for
an increased efflux ratio, therefore we methylated the triazole.
Unfortunately, this modification resulted in a complete loss of
potency at both OXRs (data not shown). Another way of
masking the hydrogen bond donor was envisaged by introduc-
Both compounds were tested in the EEG/EMG rat pharma-
cology experiment at 30 mgkgÀ 1 p.o. Over the 12 h night
period following administration, compound 6 and compound
42 increased significantly the time spent asleep by 25 min (p=
0.0321, paired t-test) and 33 min (p=0.0045, paired t-test)
respectively, compared to matched vehicle treated rats. This
was reflected by an increase of 8.0% (p=0.0248) and 19.4%
(p=0.0194) of the time spent in non-REM sleep and 17.1% (p=
0.1084) and 5.6% (p=0.3114) for the time spent in REM sleep
for compound 6 and compound 42, respectively (Figure 4). In a
next step, we characterized compounds 6 and 42 in freely
moving male Beagle dogs implanted with radiotelemetric
transmitters for continuous recording of EEG/EMG signals. Dogs
were treated with a single oral dose of vehicle, 90 mg of
Table 6. Brain penetration properties for a selection of compounds.
R1
R2
Compd
SF[a]
OX1R[b]
OX2R[b]
MDR1[c]
app A!B
MDR1[d]
Efflux
ratio
P
31
39
B
C
9
4
2
8
8.5
8.9
9.2
4.7
40
41
B
C
58
13
3
11
10.2
20.4
5.3
2.7
33
42
B
C
17
5
3
8
9.7
15.1
6.5
3.3
[a] SF= scaffold. [b] IC50 in nM; data are the geometric mean (�2-fold) of at least three independent experiments and were determined by FLIPR assay. [c]
(human) multidrug resistant protein 1 (MDR1) passive permeability. [d] MDR1 efflux ratio of (Papp B!A/Papp A!B). nd=not determined.
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Table 7. Inhibition of human (h), rat (r), and dog (d) orexin receptors.
1
2
3
[a]
[a]
[b]
[b]
[b]
[b]
[b]
[b]
Compd
IC50
IC50
Kb
Kb
Kb
Kb
Kb
Kb
hOX1R
hOX2R
hOX1R
hOX2R
rOX1R
rOX2R
dOX1R
dOX2R
4
5
6
42
28
5
4
8
17
4.6
1.3
2.4
10
4.6
1.3
2.5
12
5.0
0.8
4.5
6
7
[a] Data are the geometric mean (�2-fold) of at least three independent experiments and were determined by FLIR assay. [b] apparent Kb values are in nM
and calculated via the Cheng-Prusoff equation from single FLIPR experiments run in duplicates.
8
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
The time spent in non-REM and REM sleep increased by
96% (p=0.0039) and 48%, (p=0.3420) respectively, although
not statistically significantly for REM sleep. Total sleep time was
divided into ~87% non-REM sleep and 13% REM sleep in all
groups, meaning that the physiological non-REM/REM propor-
tions were unchanged (one-way ANOVA; p=0.9683). In parallel,
the time spent in active wake dose-dependently decreased
(one-way ANOVA, p=0.0337) with significant effect at 90 mg
(À 21.5% or À 27 min compared to vehicle treated dogs, p=
0.0015). Time spent in quiet wake did not significantly change
(+9.6% or +2 min, p=0.7482).
In parallel, the time spent in active wake dose-dependently
Figure 4. Effect of 6 and 42 on the time spent in sleep and wake stages (%
decreased (one-way ANOVA, p=0.0337) with significant effect
of total time) during the 12 h night active period post administration. Male
at 90 mg (À 21.5% or À 27 min compared to vehicle treated
Wistar rats were administered a single oral dose of vehicle (PEG 400) or
compound at 30 mgkgÀ 1. Data are expressed as mean�SEM. *p<0.05 (n=8
dogs, p=0.0015). Time spent in quiet wake did not significantly
per group).
change (+9.6% or +2 min, p=0.7482).
compound 6 or, 30 mg and 90 mg of compound 42. Com- Conclusions
pounds were given in capsules during their active phase, when
endogenous orexin levels are naturally rising.
Whereas compound at 90 mg was inactive on all
In summary, we successfully optimized compound 6 into
compound 42. Table 8 compiles the properties we set out to
optimize at the beginning of our discovery efforts starting from
compound 6.
Short comings of compound 6 are low metabolic stability
(HLM of 282 μMminÀ 1 mgÀ 1), high plasma protein binding
(hPPB>99.9%), low brain free fraction (fu brain 0.3%), and low
aqueous solubility (<1 μgmLÀ 1). The triazole 33 represents a
landmark in our studies as it ameliorated several short comings
of compound 6.
Specifically, while potency at both OXRs was maintained,
aqueous solubility, metabolic stability, free plasma and brain
concentrations were higher for the triazole 33. However, this
compound showed an efflux ratio in MDCK cells overexpressing
human MDR1 that was too high for the compound’s use as a
CNS drug. Further optimization led to the discovery of the 2-
methyl-pyrrolidine 42 that showed a reduced efflux ratio. In
addition, the introduction of the 2-methyl substituent on the
pyrrolidine core led to improved metabolic stability in rat, dog,
and human microsomes. Unfortunately, this additional methyl
group negatively affected aqueous solubility and free fraction
in plasma and brain. The gain in aqueous solubility obtained
when the oxadiazole in 6 was replaced with the triazole in 33
was lost with the introduction of the 2-methyl group at the
pyrrolidine scaffold. Similarly, the higher plasma free fraction
and higher fu brain measured for triazole 33 dropped to
comparably low values for triazole 42.
6
parameters, compound 42 dose dependently decreased the
time spent in wakefulness and increased the time spent in sleep
over the 3 h period following administration (one-way ANOVA,
p=0.0194). At 90 mg, sleep time was significantly increased by
87.6% (+25 min) compared to vehicle-treated dogs (p=0.0022)
(Figure 5).
Figure 5. Effect of compounds 6 and 42 on the time spent in sleep and
wake stages (% of total time) during the 3 h day active period post
administration in male Beagle dogs. Dogs were administered a single oral
dose of vehicle, compound 6 at 90 mg or compound 42 at 30 mg or 90 mg.
Data are expressed as mean�SEM. **p<0.01 (n=8 per group).
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Table 8. Comparison of properties for compound 6, 33, and 42.
1
2
3
4
5
6
7
8
9
Compd
6
33
42
OX1R[a]
28
4
17
5
8
OX2R[a]
3
PPB[b] human/dog/rat %
fu brain % [c]
[B][d]
>99.9/99.8/99.7
99.8/98.8/98.6
1.4
1639
103
169/343
>99.9/99.7/99.4
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
0.3
1585
<1
0.5
1123
<1
Solubility
Sol. water pH 4[e]
FaSSIF/FeSSIF
clogP[f]
26/32
28/68
4.5
4.0
4.4
3.6
4.9
4.1
logD measured
[g]
CLint
HLM/DLM/RLM
282/543/>1250
73/150/189
28/143/136
[a] IC50 in nM; data are the geometric mean (�2-fold) of at least three independent experiments and were determined by FLIPR assay. [b] plasma protein
binding in %. [c] brain free fraction in %. [d] Brain penetration experiments were performed in rats (n=3) by sampling brain [B] (nggÀ 1), 3 h following
administration of 100 mgkgÀ 1 p.o., [e] solubility measured at pH 4 (Citrate), FaSSIF and FeSSIF in a high-throughput solubility assay in [μgmLÀ 1)]. [f] clogP
values were calculated using ChemBioDraw Ultra 14.0. [g] intrinsic metabolic clearance [μMminÀ 1 mgÀ 1] with human, dog, and rat liver microsomes at 1 μM.
In summary, with triazole 42 we identified a potent DORA
with similar physicochemical properties to oxadiazole 6, but
clearly improved metabolic stability and sleep promotion in the
canine EEG/EMG experiment.
racemization cannot be excluded. For compound 8, racemiza-
tion was ruled out by chiral chromatography. However, for
triazoles-analogue 33 partial racemization was observed. Im-
portantly, racemization can be ruled out for lead compound 42,
due to the quaternary carbon on the stereocenter. Previous
studies[21] have shown that the S-enantiomer is more potent
than the R-enantiomer. For compounds where racemization
occurs, the reported IC50 underestimates the potency of the
pure enantiomer.
Chemistry
The syntheses of compounds 7–42 are summarized in
Scheme 1–10.
For simplicity, in the reaction schemes below, the stereo-
chemistry was kept constant even though the possibility of
Compound 7 was synthesized starting with an amide
coupling of commercially available (S)-pyrrolidine-2-carbonitrile
HCl and 43a. The obtained nitrile 44 was converted to
°
Scheme 1. Synthesis of oxadiazoles: a) TBTU, DIPEA, CH2Cl2, RT, 45 min to16 h; b) hydroxylamine HCl, KOtBu, MeOH, 75 C, 18 h; c) 1. PyBOP, DIPEA, CH2Cl2, RT,
3–24 h, 2. dioxane, 60–100 C for hours to days; d) 2 N aqueous NaOH solution in MeOH/THF, RT, 45 min; e) TFA, CH2Cl2, RT, 4 h; f) 1H-1,2,3-triazole, CuI, Cs2CO3,
DMF, RT, 1.5 h.
°
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hydroxyamidine 45. Amide coupling with benzoic acid 46a
followed by thermal cyclization yielded compound 7.
First, coupling of hydrazine 50a, then cyclization in presence of
the Burgess reagent at elevated temperature yielded 51. After
Boc deprotection with TFA, amide coupling of 52 and 43a
yielded symmetric oxadiazole 9. The biaryl carboxylic acid 43a
was synthesized in a cooper mediated reaction from commer-
cially available 53 and 1,2,3-triazole.
Alternatively, oxadiazole analogues (6, 36–38) were synthe-
sized according to Scheme 2. Commercially available nitrile 54
was converted to the hydroxyamidine 55. First, coupling of 55
with commercially available carboxylic acid 46b, followed by
thermal cyclization in dioxane yielded 57. Boc deprotection
resulted in amine 58 which upon amide coupling with the
corresponding biaryl carboxylic acid yielded final compounds
(6, 36–38).
1
2
3
4
5
6
7
8
9
a
Compound 8 was synthesized using commercially available L-
proline methyl ester HCl, which upon amide coupling with 43a
afforded intermediate 47. Saponification of the ester function
under basic conditions yielded compound 48. Amide coupling
with hydroxyamidine 49, followed by a thermal cyclization
yielded compound 8. For the synthesis of compound 9,
commercially available (tert-butoxycarbonyl)-L-proline and 50a
was converted in a two-step procedure to intermediate 51.
10
11
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13
14
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17
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19
20
21
22
23
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27
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29
30
31
32
33
34
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36
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Isoxazole analogues 10 and 11 were synthesized according
to Scheme 3. Commercially available Boc-L-prolinal 59 was
converted to the oxime 60 using hydroxylamine HCl and NaOAc
in MeOH. Isoxazoles 62 was synthesized by click chemistry of 60
and commercially available alkyne 61 in the presence of
chloramine T trihydrate. Boc deprotection of 62, followed by
amide coupling of 63 with 43a yielded 10. For the synthesis of
isoxazole isomer 11, Boc-L-prolinal 59 was converted to alkyne
64, then click chemistry of alkyne 64 and commercially available
oxime 65, in the presence of chloramine T trihydrate resulted in
66. After Boc deprotection the obtained amine 67 was coupled
to carboxylic acid 43a yielding isoxazole 11. Oxazole analogues
12 and 13 were synthesized according to Scheme 4. Compound
Scheme 2. Synthesis of oxadiazoles: a) hydroxylamine HCl, NaHCO3, MeOH,
°
°
70 C, 3 h; b) 1. TBTU, DIPEA, CH2Cl2, RT, 1.5 h to 16 h, 2. dioxane, 80 C,
2.5 days; c) 4 N HCl, CH2Cl2, RT, 4.5 h; d) TBTU, DIPEA, CH2Cl2, RT, 20 min.
°
Scheme 3. Synthesis of isoxazoles: a) NaOAc, MeOH, RT, 18 h; b) Chloramine T trihydrate, MeOH, 1 h, then 60 C, 1–18 h; c) 4 N HCl in dioxane, RT, 1.5 h; d)
TBTU, DIPEA, DMF, RT, 18 h; e) dimethyl (diazomethyl)phosphonate, K2CO3, MeOH, RT, 18 h
°
Scheme 4. Synthesis of oxazoles: a) K2CO3, DMF, RT, 18 h; b) BF3 ·OEt2 Et2O/o-xylene, 120–140 C, 1 d; c) TBTU, DIPEA, CH2Cl2, RT, 18 h; d) polyphosphoric acid,
°
150 C, 1 h.
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48 reacted with commercially available bromoÀ ketone 68 under
basic conditions to intermediate 69, which was cyclized to
oxazole 12. Amide coupling of 48 with 70 yielded 71, which
upon cyclization resulted in oxazole 13.
K2CO3 to yield 77. Boc deprotection and amide coupling with
the biaryl carboxylic acid 43a yielded imidazole 15.
1
2
3
4
5
6
7
8
9
Pyrazole analogue 16 (Scheme 6) was synthesized from
commercially available Weinreb amide 79 and alkyne 61 in the
presence of ethylmagnesium bromide to yield alkyne 80.
Pyrazole 81 was synthesized from 80 and hydrazine at elevated
temperature. Boc-deprotection and amide coupling with the
biarylic acid 43a yielded imidazole 16.
The synthesis of pyrazole analogue 17 is outlined in
Scheme 7. Commercially available 83 was converted to Weinreb
amide 84, then converted in a Grignard reaction to acetal 86.
Acetal cleavage resulted in aldehyde 87, which upon reductive
amination and thermal cyclization yielded intermediate 89.
Deprotection and amide coupling with the biarylic acid 43a
yielded 17.
Imidazole analogues 14 and 15 (Scheme 5) were synthe-
sized from commercially available nitrile 54. After formation of
amidine 72 in the presence of NaOMe and ammonium bromide,
72 was coupled with bromoÀ ketone 68, followed by cyclization
to yield 73. Boc-deprotection and amide coupling with the
biaryl carboxylic acid 43a yielded imidazole 14. Isomer 15 was
synthesized from starting materials with inverted functional
groups. Compound 75 was prepared from the corresponding
commercially available Boc-L-proline. In a two-step reaction,
first, carboxylic acid 50 reacted with commercially available
benzylÀ amidine 76, followed by cyclization in the presence of
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
Scheme 5. Synthesis of imidazoles: a) 1. NaOMe in MeOH, RT, 18 h; 2. NH4Br, RT, 18 h; b) K2CO3, DMF, RT, 3 days; c) 4 N HCl in dioxane, CH2Cl2, RT, 4.5 h; d)
°
°
HATU, DIPEA, DMF, RT, 18 h; e) 1. isobutyl chloroformate, DIPEA 0 C, 4 h, 2. (trimethylsilyl)diazomethane solution (2.0 M in hexane), THF/MeCN, 0 C, 3.5 h, 3.
°
°
HBr (33% in AcOH), À 55 to À 25 C, 2.5 h; f) K2CO3, DMF, 65 C, 7 h; g) EDC HCl, HOBT, DMF, RT, 1.5 h.
°
°
°
Scheme 6. Synthesis of pyrazoles: a) 1. EtMgBr (1 M in THF), THF, 0 C to RT, 1 h; 2. 79, THF, 0 C to RT, 18 h; b) hydrazine hydrate (50%) EtOH, 85 C, 1.5 h; c)
4 N HCl in dioxane, CH2Cl2, RT, 4.5 h; d) HATU, DIPEA, DMF, RT, 18 h.
Scheme 7. Synthesis of N-pyrazoles: a) EDC HCl, HOBT, N,O-dimethylhydroxylamine HCl, DMF, RT, 1.5 h; b) 1. 3-bromo-1,1-dimethoxypropane (85), Mg, I2, THF,
°
°
°
RT, 2 h, 2. 84, 0 C to RT, 30 min; c) 2 N HCl, THF, RT, 20 min; d) NaBH(OAc)3, À 78 C to RT, 1 h; e) TFA, 100 C, microwave irradiation; f) TBTU, DIPEA, DMF, RT,
18 h.
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1
2
3
4
5
6
7
8
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
°
Scheme 8. Synthesis of 1,2,3-triazoles and 1,2,4-triazoles: a) DMF, 150 C to RT, 10 h; b) 4 N HCl in dioxane, CH2Cl2, RT, 3 h; c) HATU, DIPEA, DMF, RT, 18 h; d)
°
NaOMe in MeOH, RT, 18 h; e) 1. TEA, MeOH, RT, 4 d; 2. triethyl orthoformate, pyridine, 120 C, 1.5 h; f) TFA, CH2Cl2, RT, 18 h; g) TBTU, DIPEA, DMF, RT, 1.5 h.
Triazole analogue 18 was synthesized from alkyne 64
(Scheme 8). Click chemistry with azide 91 yielded 92, which
upon Boc deprotection and amide coupling resulted in 18.
Triazole 19 was synthesized from commercially available nitrile
54 (Scheme 8). Imidate 94 was synthesized from 54 in presence
of NaOMe and converted to triazole 96 in a two-step procedure.
Hydrazine 95 was reacted in the presence of triethylamine with
94, then subsequent addition of triethyl orthoformate at
elevated temperature yielded triazole 96. Boc-deprotection and
amide coupling with the biarylic acid 43a yielded 19.
Triazole analogues 20–35 and 40 were synthesized accord-
ing to Scheme 9. Compound 98 was synthesized from commer-
cially available nitrile 54 and hydrazides 50a–g (either commer-
cially available or synthesized from their corresponding
carboxylic acid), in presence of K2CO3 at elevated temperature.
Boc deprotection and amide coupling with the corresponding
biaryl carboxylic acid 43a–h, yielded final compounds 20–35
and 40.
As an example of a trizaole-2-methyl pyrrolidine-analogue
(scaffold C), the synthesis of compound 42 is depicted in
Scheme 10.
Compound 39 and 41 were synthesized in analogy to 42.
The commercially available compound 100 was converted via
amide formation to nitrile 101. The nitrile 101 reacted with
commercially available hydrazide 51g in the presence of K2CO3
to compound 102. Boc deprotection, followed by amide
coupling of amine 103 with biaryl carboxylic acid 43e yielded
compound 42. The biarylic carboxylic acid 43b was synthesized
in a copper catalyzed reaction from commercially available 104
and 1H-1,2,3-triazole in presence of CuI, Cs2CO3 and trans-N,N’-
dimethylcyclohexane-1,2-diamine.
°
Scheme 9. Synthesis of 1,2,4-triazoles: a) 1. K2CO3, nBuOH, 135 C, 2.5 h, 2.
EDC HCl, HOBT, CH2Cl2, RT, 10 min; b) 4 N HCl in dioxane, RT, 1.5 h to 18 h; c)
EDC HCl, HOBT, CH2Cl2, RT, 10 min to 18 h.
Experimental Section
Commercially available starting materials were used as received
without further purification. All reactions were carried out under an
atmosphere of nitrogen or argon. Compounds were purified by
flash chromatography on silica gel, or by preparative HPLC.
Compounds described below are characterized by LC-MS data
(retention time tR is given in min, molecular weight obtained from
the mass spectrum is given in gmolÀ 1 using the conditions below.
In cases where compounds appeared as a mixture of conforma-
tional isomers, as visible in their LC-MS spectra, the retention time
of the most abundant conformer was given.
LC-MS under acidic conditions
Scheme 10. Synthesis of compound 42: a) 1. ethyl chloroformate, TEA, THF
0 C, 2. ammonia 0 C to RT; b) trifluoroacetic anhydride, TEA, CH2Cl2, 0 C to
°
°
°
Method A: Agilent 1100 series with mass spectrometry detection
(MS: Finnigan single quadrupole). Column: Zorbax SB-aq (3.5 μm,
4.6×50 mm). Conditions: MeCN [eluent A]; H2O+0.04% TFA [eluent
°
RT; c) hydrazide 50b, K2CO3, nBuOH, 125 C, for days, or microwave
°
irradiation, 150 C, 1 h; c) TFA or HCl; d) 1H-1,2,3-triazole, CuI, Cs2CO3,
°
DMCDA, DMF, microwave irradiation, 105 C, 15 min; e) HATU, DIPEA, DMF,
RT, 18 h.
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1
B]. Gradient: 95% B!5% B over 1.5 min (flow: 4.5 mL/min).
Detection: UV/Vis+MS.
diazepane series reported by Merck,[22] therefore full H NMR and
13C NMR spectra are reported in some cases rather than peak lists
(see Supporting Information).
1
2
3
4
5
6
7
8
9
Method B: Agilent 1100 series with mass spectrometry detection
(MS: Finnigan single quadrupole). Column: Waters XBridge C18
(2.5 μm, 4.6×30 mm). Conditions: MeCN [eluent A]; H2O+0.04%
TFA [eluent B]. Gradient: 95% B!5% B over 1.5 min (flow: 4.5 mL/
min). Detection: UV/Vis+MS.
clogP values were calculated using ChemBioDraw Ultra 14.0.
Abbreviations used: AcOH, acetic acid; DIPEA, diisopropylethyl-
amine; DMCDA, trans-N,N’-dimethylcyclohexane-1,2-diamine; DMF,
dimethylformamide; DMSO, dimethylsulfoxide; EDC, N-(3-dimeth-
ylaminopropyl)-N’-ethyl-carbodiimide; Et2O, diethyl ether; EtOAc,
ethyl acetate; EtOH, ethanol; HATU, (1-[bis(dimethylamino)meth-
ylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophos-
phate, HOBt, 1-hydroxybenzotriazole; HPLC, high performance
liquid chromatography; nBuOH, n-butanol; MeCN, acetonitrile;
MeOH, methanol; min, minutes; PyBOP, (benzotriazol-1-yloxy)
tripyrrolidinophosphonium hexafluorophosphate; RT, room temper-
ature; TBTU, 2-(1H-benzotriazole-1-yl)-1,2,3,3-tetramethyluronium
tetrafluoroborate; THF, tetrahydrofuran; tR, retention time.
LC-MS under basic conditions
Method C: Agilent 1100 series with mass spectrometry detection
(MS: Finnigan single quadrupole). Column: Waters XBridge C18
(5 μm, 4.6×50 mm). Conditions: MeCN [eluent A]; 13 mmol/L NH3 in
H2O [eluent B]. Gradient: 95% B!5% B over 1.5 min (flow: 4.5 mL/
min). Detection: UV/Vis+MS.
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LC-HRMS parameters were the following: analytical pump Waters
Acquity binary, Solvent Manager, MS, SYNAPT G2 MS, source
°
°
temperature of 150 C, desolvation temperature of 400 C, desolva-
tion gas flow of 400 L/h; cone gas flow of 10 L/h, extraction cone of
4 RF; lens 0.1 V; sampling cone 30; capillary 1.5 kV; high resolution
mode; gain of 1.0, MS function of 0.2 s per scan, 120–1000 amu in
full scan, centroid mode. Lock spray: keucine enkephalin, 2 ng/mL
(556.2771 Da), scan time of 0.2 s with interval of 10 s and average
of 5 scans; DAD: Acquity UPLC PDA detector. Column was an
Acquity UPLC BEH C18 1.7 μm, 2.1 mm×50 mm from Waters,
(5-Methyl-2-[1,2,3]triazol-2-yl-phenyl)-[(S)-2-(5-phenyl-[1,2,4]
oxadiazol-3-yl)-pyrrolidin-1-yl]-methanone (7)
Step 1: (S)-1-(5-methyl-2-(2H-1,2,3-triazol-2-yl)benzoyl)pyrroli-
dine-2-carbonitrile (44). TBTU (2.66 g, 8.27 mmol) was added to a
RT solution of 43a (1.40 g, 6.89 mmol) and DIPEA (3.54 mL,
20.7 mmol) in CH2Cl2 (10 mL). After 5 min at RT, (S)-pyrrolidine-2-
carbonitrile HCl (914 mg, 6.89 mmol) was added and stirring was
continued at RT overnight. The reaction mixture was washed with
water, the inorganic layer extracted with CH2Cl2 (2×100 mL) and
the combined organic layers were dried (MgSO4), filtered, and
concentrated. Purification by Biotage FC (EtOAc/hexane 3:7 to 1:1,
Rf =0.21 in 1:1) yielded 44 (1.53 g, 79%) as a white solid. LC-MS A:
°
thermostated in the Acquity UPLC column manager at 60 C.
Eluents were the following: H2O+0.05% formic acid; B, acetonitrile
+0.05% formic acid. Gradient was 2% to 98% B over 3.0 min. Flow
was 0.6 mL/min. Detection was at UV 214 nm. In cases where final
compounds appear as a mixture of conformational isomers, visible
in their LC-MS spectra, the retention time of the most abundant
conformer is given.
1
tR =0.74 min; [M+H]+ =282.19. H NMR (400 MHz, DMSO) δ: 8.04
(s, 2 H), 7.83 (d, J=8.3 Hz, 1 H), 7.46–7.49 (m, 1 H), 7.34 (d, J=
1.2 Hz, 1 H), 4.84 (dd, J1 =4.0 Hz, J2 =7.8 Hz, 1 H), 2.99–3.22 (m, 2 H),
2.41 (s, 3 H), 2.12–2.29 (m, 2 H), 1.83–1.97 (m, 2 H).
Preparative HPLC under acidic conditions
Step 2: (S)-N-Hydroxy-1-(5-methyl-2-[1,2,3]triazol-2-yl-benzoyl)-
pyrrolidine-2-carboxamidine (45). Hydroxylamine HCl (663 mg,
9.54 mmol) was added to a RT suspension of KOtBu (1.25 g,
10.80 mmol) in MeOH (20 mL) and the mixture was stirred at RT for
20 min, then a solution of 44 (895 mg, 3.18 mmol) in MeOH (10 mL)
Method D: Column: Waters XBridge (10 μm, 75×30 mm). Condi-
tions: MeCN [eluent A]; H2O+0.5% HCOOH [eluent B]; Gradient:
90% B!5% B over 6.4 min (flow: 75 mL/min). Detection: UV/Vis+
MS.
°
was added and the resulting suspension was refluxed at 75 C. After
Method E: Column: Waters Atlantis (10 μm, 75×30 mm). Condi-
tions: MeCN [eluent A]; H2O+0.5% HCOOH [eluent B]; Gradient:
90% B!5% B over 6.4 min (flow: 75 mL/min). Detection: UV/Vis+
MS.
18 h, KOtBu (220 mg) and hydroxylamine HCl (133 mg) were added
and stirred for another 18 h. The reaction mixture was filtered and
concentrated. The residue was dissolved in CH2Cl2 and washed with
1 N HCl (2×10 mL). The inorganic layer was basified with saturated
aqueous NaHCO3, followed by 1 N aqueous NaOH solution and
extracted with CH2Cl2. The combined organic layers were washed
with brine, dried (MgSO4), filtered, and concentrated to yield 45
(0.84 g, 84%) as a white solid, which was used as such in the next
step. LC-MS A: tR =0.56 min; [M+H]+ =315.07.
Preparative HPLC under basic conditions
Method F: Column: Waters XBridge (10 μm, 75×30 mm). Condi-
tions: MeCN [eluent A]; H2O+0.5% NH4OH (25% aqueous) [eluent
B]; Gradient: 90% B!5%
B over 6.5 min (flow: 75 mL/min).
°
Step 3: PyBOP (124 mg, 0.24 mmol) was added to a 0 C solution of
Detection: UV/Vis+MS
45 (50 mg, 0.16 mmol), benzoic acid (46a) (30 mg, 0.246 mmol) and
DIPEA (82 μL, 0.48 mmol) in CH2Cl2 (2.0 mL) and the resulting
reaction mixture was stirred at RT for 3 h. The reaction mixture was
washed with water, the inorganic layer was re-extracted with
CH2Cl2 (2×15 mL) and the combined organic layers were dried
(MgSO4), filtered, and concentrated. To the residue (227 mg) was
added dioxane (2.0 mL) and the reaction mixture was stirred at
Synthesis
Flash column chromatography (FC) was performed either conven-
tional or by using Biotage SNAP cartridges (10–340 g) and elution
was with a Biotage Isolera system. Merck pre-coated thin layer
chromatography (TLC) plates were used for TLC analysis.
°
80 C overnight. The mixture was concentrated and purified directly
by preparative HPLC (Method F) yielding 7 (13 mg, 20%) as an off-
white solid. LC-MS C: tR =0.94 min; [M+H]+ =401.02; LC-HRMS: tR =
1.17 min; m/z=401.1721, found=401.1725.
1H NMR and 13C NMR spectra were recorded on a Bruker (400 or
500 MHz) spectrometer in the indicated deuterated solvent. Chem-
ical shifts are reported in ppm relative to solvent peaks as the
internal reference. Due to hindered rotation, our compounds exist
in multiple conformations on the NMR time-scale, similar to the
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dissolved in CH2Cl2 (30 mL) and basified with 1 N aqueous NaOH
solution. The layers were separated, and the inorganic layer was
extracted with CH2Cl2 (1×30 mL). The combined organic layers
were dried (MgSO4), filtered, and concentrated to yield 52 (203 mg,
60% over 2 steps) as a yellow oil, which was used as such in the
next step. LC-MS B: tR =0.38 min; [M+H]+ =216.30. 1H NMR
(400 MHz, DMSO) δ: 7.99 (d, J=7.1 Hz, 2 H), 7.62 (s, 3 H), 4.48 (dd,
J1 =5.8 Hz, J2 =7.6 Hz, 1 H), 2.89–2.95 (m, 2 H), 2.05–2.17 (m, 2 H),
1.85–1.98 (m, 1 H), 1.68–1.81 (m, 1 H).
(5-Methyl-2-[1,2,3]triazol-2-yl-phenyl)-[(S)-2-(3-phenyl-[1,2,4]
oxadiazol-5-yl)-pyrrolidin-1-yl]-methanone (8)
1
2
3
4
5
6
7
8
9
Step 1: (S)-1-(5-Methyl-2-[1,2,3]triazol-2-yl-benzoyl)-pyrrolidine-2-
carboxylic acid methyl ester (47). TBTU (7.11 g, 22.1 mmol) was
added to a RT solution of 5-methyl-2-(2H-1,2,3-triazol-2-yl)benzoic
acid 43a (3.00 g, 14.8 mmol) and DIPEA (10.1 mL, 59.1 mmol) in
CH2Cl2 (100 mL). After stirring for 10 min at RT, commercially
available L-proline methyl ester (3.19 g, 15.4 mmol) was added and
stirring was continued at RT for 1.5 h. The reaction mixture was
diluted with CH2Cl2 and water. The layers were separated, the
inorganic layer was extracted with CH2Cl2 (2×100 mL). The
combined organic layers were washed with brine, dried (MgSO4),
filtered, and concentrated. Purification by FC (EtOAc/heptane 7:3)
yielded 47 (4.46 g, 94%) as a white solid. LC-MS B: tR =0.75 min; [M
+H]+ =315.30.
Step 3: TBTU (55.8 mg, 0.174 mmol) was added to a RT solution of
43a (29 mg, 0.15 mmol), DIPEA (74 μL, 0.43 mmol) in DMF (1 mL).
After 5 min at RT, 52 (31 mg, 0.15 mmol) was added and the
reaction mixture was stirred at RT for 18 h. The mixture was directly
purified by preparative HPLC (Method F), followed by preparative
TLC (EtOAc/heptane 9:1) to yield 9 (37 mg, 64%) as a white foam.
LC-MS B: tR =0.77 min; [M+H]+ =401.16; LC-HRMS: tR =1.05 min;
m/z=401.1721, found=401.1728.
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Step 2: (S)-1-(5-Methyl-2-[1,2,3]triazol-2-yl-benzoyl)-pyrrolidine-2-
carboxylic acid (48). 2 N aqueous NaOH solution (20 mL, 40 mmol)
was added to a RT solution of 47 (5.00 g, 15.9 mmol) in MeOH
(20 mL) and THF (20 mL). The mixture was stirred for 45 min at RT,
then concentrated and the residue acidified with 1 N aqueous HCl.
The inorganic layer was extracted with CH2Cl2 (3×150 mL) and the
combined organic layers were dried (MgSO4), filtered, and concen-
trated to yield 48 (4.8 g, 100%) as a white solid, which was used as
such in the next step. LC-MS B: tR =0.57 min; [M+H]+ =301.05.
(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-[(S)-2-(5-phenyl-isoxazol-3-yl)-pyrrolidi-
n-1-yl]-methanone (10)
Step 1: (S)-2-(Hydroxyimino-methyl)-pyrrolidine-1-carboxylic acid
tert-butyl ester (60). Hydroxylamine HCl (355 mg, 5.11 mmol) was
added to a RT solution of (S)-N-Boc-prolinal (59) (1.00 g, 5.02 mmol)
and NaOAc (423 mg, 5.15 mmol) in MeOH (4.5 mL). The mixture
was stirred at RT for 18 h. The reaction mixture was concentrated
and take up in CH2Cl2 (60 mL) and water (20 mL). The layers were
separated, and the inorganic layer was extracted with CH2Cl2 (1×
30 mL). The combined organic layers were washed with brine (1×
10 mL), dried (MgSO4), filtered, and concentrated to yield 60
(1.35 g, 126%) as a colorless oil, which was used in the next step.
LC-MS A: tR =0.66 min; [M+H]+ =215.21.
Step 3: PyBOP (260 mg, 0.50 mmol) was added to a RT solution of
48 (100 mg, 0.33 mmol) and DIPEA (0.17 mL, 1.00 mmol) in CH2Cl2
(3 mL) and the reaction mixture was stirred for 10 min at RT, then
benzamidoxime 49 (69 mg, 0.43 mmol) was added and the
resulting mixtures stirred at RT for 18 h. The mixture was quenched
with water and extracted with CH2Cl2 (2×10 mL). The combined
organic layers were washed with brine, dried (MgSO4), filtered, and
concentrated to obtain the crude product as a brown oil. LC-MS A:
tR =0.80 min; [M+H]+ =419.34. To the crude was added dioxane
Step 2: (S)-2-(5-Phenyl-isoxazol-3-yl)-pyrrolidine-1-carboxylic acid
tert-butyl ester (62). Chloroamine T trihydrate (319 mg, 1.4 mmol)
was added to a RT solution of 60 (300 mg, 1.4 mmol) in MeOH
(6.5 mL) and the mixture was stirred at RT for 5 min before a
solution of phenylacetylene 61 (143 mg, 1.4 mmol) in MeOH
(6.5 mL) was added. The resulting mixture was stirred at RT for 1 h,
°
(4 mL) and the reaction mixture was stirred at 90 C for 2 days. The
mixture was concentrated, the residues dissolved in DMF and
purified by preparative HPLC (Method E) to yield 8 (54 mg, 41%) as
a beige solid. LC-MS A: tR =0.93 min; [M+H]+ =401.13; LC-HRMS:
tR =1.19 min; m/z=401.1721, found=401.1721.
°
then heated to 60 C for 3 h. The reaction mixture was concen-
(5-Methyl-2-[1,2,3]triazol-2-yl-phenyl)-[(S)-2-(5-phenyl-[1,3,4]
oxadiazol-2-yl)-pyrrolidin-1-yl]-methanone (9)
trated, dissolved in CH2Cl2, washed with saturated NaHCO3 and
brine. The organic layer was dried (MgSO4), filtered, and concen-
trated. Purification by FC (EtOAc/hexane 2:3, Rf = 0.45) yielded 62
(155 mg, 35%) as a colorless oil. LC-MS A: tR =0.93 min; [M+H]+ =
315.04.
Step 1: tert-butyl (S)-2-(5-phenyl-1,3,4-oxadiazol-2-yl)pyrrolidine-
°
1-carboxylate (51). PyBOP (945 mg, 1.81 mmol) was added to a 0 C
solution of Boc-L-proline (300 mg, 1.39 mmol), benzohydrazide
(50a) (190 mg, 1.39 mmol) and DIPEA (0.72 mL, 4.18 mmol) in
CH2Cl2 (5.0 mL) and the resulting reaction mixture was stirred at RT
for 3 h. The reaction mixture was washed with water, the inorganic
layer was re-extracted with CH2Cl2 (2×30 mL) and the combined
organic layers were dried (MgSO4), filtered, and concentrated.
Purification by FC (EtOAc/hexane 3:7 to 1:1) yielded 399 mg of
intermediate, which was dissolved in dioxane (10 mL) and Burgess
reagent (456 mg, 1.91 mmol) was added at RT. The reaction mixture
Step 3: 5-Phenyl-3-(S)-pyrrolidin-2-yl-isoxazole HCl (63). 4 N HCl in
°
dioxane (1 mL) was added to a 0 C solution of 62 (150 mg,
0.477 mmol) in CH2Cl2 (1 mL). The mixture was stirred at RT for
2.5 h, then the solvent was removed and 63 (125 mg) was obtained
as an oil which was used as such in the next step. LC-MS A: tR =
0.57 min; [M+H]+ =215.17.
Step 4: TBTU (38.5 mg, 0.12 mmol) was added to a RT solution of
43a (20.3 mg, 0.1 mmol) and DIPEA (96 μL, 0.4 mmol) in DMF
(1.0 mL). The mixture was stirred at RT for 5 min, before 63
(25.1 mg, 0.1 mmol) dissolved in DMF (0.2 mL) was added and
stirred at RT overnight. Purification by preparative HPLC (Method F)
yielded 10 (24 mg, 59%) as yellow solid. LC-MS A: tR =0.93 min; [M
+H]+ =400.09; LC-HRMS: tR =1.17 min; m/z=400.1768, found=
400.1771.
°
was irradiated in the microwave for 20 min at 110 C, then the
mixture was diluted with saturated sol. NaHCO3 and extracted with
EtOAc (2×20 mL). The combined organic layers were dried
(MgSO4), filtered, and concentrated to yield 51 (500 mg) as an oil,
which was used as such in the next step. LC-MS B: tR =0.79 min; [M
+H]+ =316.31.
Step 2: 2-Phenyl-5-(S)-pyrrolidin-2-yl-[1,3,4]oxadiazole (52). TFA
°
(1.5 mL, 19.5 mmol) was added to a 0 C solution of 51 (500 mg) in
CH2Cl2 (15.0 mL) and the resulting reaction mixture was stirred at
RT for 4 h. The excess TFA was removed in vacuo, the residue was
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°
overnight, followed by heating to 140 C for another 24 h. The
(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-[(S)-2-(3-phenyl-isoxazol-5-yl)-pyrrolidi-
n-1-yl]-methanone (11)
1
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residue was dissolved in EtOAc and water, the organic layer was
separated, and the inorganic layer extracted with EtOAc (1x). The
combined organic layers were dried (MgSO4), filtered, and concen-
trated. Purification by preparative HPLC (Method F) yielded 12
(107 mg, 40%) as an off-white solid. LC-MS A: tR =0.90 min; [M+
H]+ =400.13; LC-HRMS: tR =1.16 min; m/z=400.1768, found=
400.1762.
Step 1: (S)-2-Ethynyl-pyrrolidine-1-carboxylic acid tert-butyl ester
(64). Dimethyl (diazomethyl)phosphonate (2.48 g, 12.9 mmol) was
added to
a RT solution of (S)-N-Boc-prolinal (59) (2.02 mL,
10.8 mmol) and K2CO3 (2.98 g, 21.6 mmol) in MeOH (100 mL). The
resulting suspension was stirred at RT overnight. The reaction
mixture was concentrated, then the residue was dissolved in CH2Cl2
(100 mL) and washed with saturated aqueous NaHCO3-solution
(30 mL). The organic layer was dried (MgSO4), filtered, and
concentrated to yield 64 (2.09 g, 100%) as a yellow oil which was
used as such in the next step. LC-MS B: tR =0.76 min; [M+H]+ =
196.21.
(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-[(S)-2-(5-phenyl-oxazol-2-yl)-pyrrolidin-1--
yl]-methanone (13)
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Step 1: (S)-1-(5-methyl-2-(2H-1,2,3-triazol-2-yl)benzoyl)-N-(2-oxo-
2-phenylethyl)pyrrolidine-2-carboxamide (71). TBTU (192 mg,
0.60 mmol) was added to a RT solution of 48 (150 mg, 0.50 mmol),
DIPEA (0.43 mL, 2.5 mmol) in CH2Cl2 (2 mL). After 10 min at RT, 2-
amino-1-phenylethan-1-one HCl (70) (89.3 mg, 0.50 mmol) was
added and stirred at RT overnight. The reaction mixture was
washed with saturated aqueous NaHCO3, and the organic layer was
dried (MgSO4), filtered, and concentrated to yield 71 (337 mg) as a
brown oil. LC-MS A: tR =0.81 min; [M+H]+ =417.90.
Step 2: (S)-2-(3-Phenyl-isoxazol-5-yl)-pyrrolidine-1-carboxylic acid
tert-butyl ester (66). Chloramine T trihydrate (741 mg, 3.26 mmol)
was added to a RT solution of benzaldehyde oxime 65 (394 mg,
3.26 mmol) in MeOH (15.0 mL). After 5 min at RT, a solution of 64
(636 mg, 3.26 mmol) in MeOH (15.0 mL) was added and the
°
reaction mixture stirred at RT for 1 h, then at 60 C for 1 h, followed
°
by 50 C for 18 h. The reaction mixture was concentrated, dissolved
in CH2Cl2 and washed with saturated aqueous NaHCO3. The
combined organic layers were dried (MgSO4), filtered and concen-
trated. Purification by Biotage FC (EtOAc/hexane 1:9, Rf =0.1)
yielded 66 (393 mg, 38%) as a yellow oil. LC-MS B: tR =0.89 min; [M
+H]+ =315.21.
Step 2: Polyphosphoric acid (4.08 g, 17 mmol) was added to the
crude 71 (337 mg) and the mixture was heated to 150 C for 1 h.
°
The reaction mixture was poured onto ice water and basified with
saturated aqueous Na2CO3. The layers were separated, and the
inorganic layer was extracted with EtOAc (2×30 mL). The combined
organic layers were dried (MgSO4), filtered, and concentrated.
Purification by preparative HPLC (Method F) yielded 13 (40.1 mg,
20% over 2 steps) as a yellow solid. LC-MS A: tR =0.90 min; [M+H]
+ =400.14; LC-HRMS: tR =1.13 min; m/z=400.1768, found=
400.1769.
Step 3: 3-Phenyl-5-(S)-pyrrolidin-2-yl-isoxazole (67). TFA (1.2 mL,
15.7 mmol) was added to a RT solution of 66 (393 mg, 1.25 mmol)
in CH2Cl2 (10.0 mL) and the resulting reaction mixture was stirred at
RT for 3 h. The excess TFA was removed in vacuo, the residue was
dissolved in CH2Cl2 and basified with 1 N aqueous NaOH solution.
The layers were separated, and the inorganic layer was extracted
with CH2Cl2 (1x). The combined organic layers were dried (MgSO4),
filtered, and concentrated to yield 67 (244 mg, 91% over 2 steps) as
a brown solid, which was used as such in the next step. LC-MS B:
(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-[(S)-2-(5-phenyl-1H-imidazol-2-yl)-pyrroli-
din-1-yl]-methanone (14)
tR =0.44 min; [M+H]+ =215.23. H NMR (400 MHz, DMSO) δ: 7.84–
7.87 (m, 2 H), 7.50 (m, 3 H), 6.85 (s, 1 H), 4.32 (dd, J1 =4.7 Hz, J2 =
7.6 Hz, 1 H), 3.10–3.52 (bm, 2 H), 2.91 (t, J=6.8 Hz, 2 H), 2.02–2.19
(m, 1 H), 1.71–1.86 (m, 3 H).
1
Step 1: tert-butyl (S)-2-carbamimidoylpyrrolidine-1-carboxylate
(72). NaOMe solution (0.5 M in MeOH, 2.35 mL) was added to a RT
solution of (S)-1-N-boc-2-cyanopyrrolidine (54) (2.30 g, 11.7 mmol)
in MeOH (8 mL) and the reaction mixture was stirred at RT
overnight, before ammonium bromide (1.15 g, 11.7 mmol) was
added and stirring was continued at RT overnight. The reaction
mixture was concentrated, then EtO2 was added and stirred at RT
for 30 min. The resulting white solid was filtered off and dried in
vacuo to yield 72 (1.99 g, 58%) as a white foam. LC-MS B: tR =
0.37 min; [M+H]+ =214.27.
Step 4: TBTU (58 mg, 0.18 mmol) was added to a RT solution of 43a
(30.5 mg, 0.15 mmol), and DIPEA (77 μL, 0.45 mmol) in DMF
(1.0 mL). The mixture was stirred at RT for 5 min, before 67
(32.1 mg, 0.15 mmol) was added and stirred at RT overnight
Purification by preparative HPLC (Method F) yielded 11 (31 mg,
52%) as an off-white foam. LC-MS B: tR =0.85 min; [M+H]+ =
400.10; LC-HRMS: tR =1.17 min; m/z=400.1768, found=400.1777.
Step 2: (S)-2-(5-phenyl-1H-imidazol-2-yl)-pyrrolidine-1-carboxylic
acid tert-butyl ester (73). K2CO3 (953 mg, 6.89 mmol) was added to
a RT solution of 72 (1.01 g, 3.45 mmol) in DMF (6 mL). After stirring
for 5 min at RT, 2-bromoacetophenone (68) (350 mg, 1.72 mmol)
was added and the reaction mixture stirred at RT for 3 days. The
reaction mixture was extracted with EtOAc and washed with water.
The organic layer was dried (MgSO4), filtered, and concentrated.
Purification by preparative HPLC (Method F) yielded 73 (235 mg,
44%) as a yellow solid. LC-MS A: tR =0.63 min; [M+H]+ =314.14.
(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-[(S)-2-(4-phenyl-oxazol-2-yl)-pyrrolidin-1--
yl]-methanone (12)
Step 1: 2-Oxo-2-phenylethyl (5-methyl-2-(2H-1,2,3-triazol-2-yl)
benzoyl)-L-prolinate (69). 2-bromoacetophenone (68) (135 mg,
0.67 mmol) was added to a RT solution of 48 (200 mg, 0.67 mmol),
K2CO3 (107 mg, 0.78 mmol) in DMF (6.0 mL) and the suspension
was stirred at RT overnight. The reaction mixture was washed with
H2O, and the inorganic layer was extracted with EtOAc (2x). The
combined organic layers were dried (MgSO4), filtered, and concen-
trated to yield 69 (413 mg) as a yellow oil, which was used as such
in the next step.
Step 3: 5-Phenyl-2-(S)-pyrrolidin-2-yl-1H-imidazole HCl (74). 4 N
HCl in dioxane (1.5 mL, 6.04 mmol) was added dropwise to a RT
solution of 73 (235 mg, 0.75 mmol) in CH2Cl2 (12 mL) and the
resulting mixture was stirred at RT for 4.5 h. The mixture was
concentrated and the obtained solid was triturated with Et2O to
yield 74 (52 mg, 24%) as a white solid. LC-MS A: tR =0.45 min; [M+
Step 2: BF3 ·OEt2 (5 drops) were added to a RT solution of 69
(413 mg, 0.67 mmol) and acetamide (204 mg, 3.45 mmol) in Et2O
(2.5 mL) and o-xylene (1.5 mL). The solution was stirred at 120 C
H]+ =214.22. H NMR (400 MHz, CDCl3) δ: 7.69–7.71 (bs, 2 H), 7.39
1
°
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(t, J=7.6 Hz, 2 H), 7.23–7.29 (m, 4 H), 4.47 (dd, J1 =6.0 Hz, J2 =
7.8 Hz, 1 H), 3.05–3.09 (m, 2 H), 2.22–2.40 (m, 1 H), 2.02–2.18 (m, 1
H), 1.78–1.95 (m, 2 H).
(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-(S)-2-(5-phenyl-2H-pyrazol-3-yl)-pyrrolidi-
n-1-yl]-methanone (16)
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Step 4: HATU (47.9 mg, 0.13 mmol) was added to a RT solution of
43a (24.4 mg, 0.12 mmol), 74 (41.2 mg, 0.144 mmol) in DMF (1 mL)
and stirring was continued at RT overnight. The reaction mixture
was directly purified by preparative HPLC (Method F) to yield 14
(34 mg, 72%) as a yellow oil. LC-MS A: tR =0.68 min; [M+H]+ =
399.09. LC-HRMS: tR =0.71 min; m/z=399.1928, found=399.1957.
Step 1: (S)-2-(3-Phenyl-propynoyl)-pyrrolidine-1-carboxylic acid
tert-butyl ester (80). Ethylmagnesium bromide (1 M in THF (3.9 mL,
3.89 mmol) was added dropwise to a 0 C solution of phenyl-
acetylene 61 (374 mg, 3.66 mmol) in THF (10.0 mL). The reaction
mixture was stirred at 0 C for 10 min, then at RT for 1 h. The
°
°
°
reaction mixture was cooled to 0 C and a solution of commercially
available (S)-2-(methoxy-methyl-carbamoyl)-pyrrolidine-1-carboxylic
acid tert-butyl ester 79 (700 mg, 2.71 mmol) in THF (9.0 mL) was
added. The resulting reaction mixture was allowed to warm to RT
overnight. The reaction mixture was quenched with saturated
aqueous NH4Cl and extracted with EtOAc (2×30 mL). The combined
organic layers were washed with water and brine, dried (MgSO4),
filtered, and concentrated to yield 80 (859 mg) as a yellow oil which
was used as such in the next step. LC-MS A: tR =0.94 min; [M+H]+
=244.16.
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(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-[(S)-2-(2-phenyl-3H-imidazol-4-yl)-pyrroli-
din-1-yl]-methanone (15)
Step 1: (S)-2-(2-Bromo-acetyl)-pyrrolidine-1-carboxylic acid tert-
butyl ester (75). Isobutyl chloroformate (1.82 mL, 13.9 mmol) was
°
added to a 0 C solution of Boc-L-proline (50) (2.00 g, 9.29 mmol)
and DIPEA (2.75 mL, 16.1 mmol) in THF (20 mL) and stirring was
°
continued at 0 C for 4 h. The mixture was diluted with MeCN
Step 2: (S)-2-(5-Phenyl-2H-pyrazol-3-yl)-pyrrolidine-1-carboxylic
acid tert-butyl ester (81). Hydrazine hydrate (50%) (0.145 mL,
2.38 mmol) was added to a RT solution of 80 (659 mg, 1.98 mmol)
(10 mL) until a clear solution was obtained, then a solution of
(trimethylsilyl)diazomethane (2.0 M in hexane; 9.3 mL, 18.6 mmol)
in THF (6.4 mL) and MeCN (6.4 mL) was added dropwise over
°
in EtOH (18.0 mL) and the mixture was heated to 85 C for 1.5 h.
°
10 min. The mixture was stirred at 0 C for 3.5 h, followed by stirring
The reaction mixture was concentrated and to the residue was
added CH2Cl2 and water, then the organic layer was separated, and
the inorganic layer extracted with CH2Cl2 (1×30 mL). The combined
organic layers were dried (MgSO4), filtered, and concentrated.
Purification by Biotage FC (EtOAc/hexane. 3:7 to 1:1; Rf =0.55 (in
1:1) yielded 81 (576, mg, 89% over 2 steps) as an off-white foam.
LC-MS A: tR =0.84 min; [M+H]+ =314.19.
at RT overnight. The mixture was concentrated in vacuo and the
crude was purified by FC (EtOAc/heptane 3:7) to yield 763 mg
(34%) of intermediate which was dissolved in EtOAc (17.5 mL) and
°
cooled to À 50 C, then HBr (33% in AcOH; 0.39 mL, 2.23 mmol) was
added slowly and the resulting mixture was stirred for 2.5 h at À 55
°
to À 25 C. The reaction mixture was diluted with TBME (54 mL) and
after the reaction mixture reached RT, it was washed with saturated
NaHCO3 and brine. The organic layer was dried (MgSO4), filtered,
and concentrated to yield 75 (613 mg, 66%) as a colorless oil which
was used in the next step. LC-MS A: tR =0.81 min; [M+H]+ =
292.17.
Step 3: 3-Phenyl-5-(S)-pyrrolidin-2-yl-1H-pyrazole HCl (82). 4 N HCl
in dioxane (5.0 mL, 20.1 mmol) was added dropwise to a RT
solution of 81 (758 mg, 2.42 mmol) in CH2Cl2 (10 mL) and the
°
resulting mixture was stirred at RT for 18 h. At 0 C, another portion
of 4 N HCl in dioxane (1.5 mL, 6 mmol) was added and the mixture
was stirred at RT for 3 h. The mixture was concentrated to obtained
82 (506 mg, 73%) as a off-white solid. LC-MS A: tR =0.53 min; [M+
H]+ =214.13.
Step 2: (S)-2-(2-Phenyl-3H-imidazol-4-yl)-pyrrolidine-1-carboxylic
acid tert-butyl ester (77). A solution of 75 (231 mg, 0.672 mmol) in
DMF (1.3 mL) was added dropwise to
a RT suspension of
benzamidine (76) (170 mg, 1.34 mmol) and K2CO3 (372 mg,
2.69 mmol) in DMF (1 mL). The resulting mixture was stirred at RT
Step 4: HATU (90.0 mg, 0.24 mmol) was added to a RT solution of
43a (40.0 mg, 0.20 mmol), 82 (56.3 mg, 0.20 mmol) in DMF (0.7 mL)
and stirring was continued at RT overnight. The reaction mixture
was directly purified by preparative HPLC (Method F) to yield 16
(35 mg, 45%) as a yellow oil. LC-MS A: tR =0.86 min; [M+H]+ =
399.10. LC-HRMS: tR =1.06 min; m/z=399.1928, found=399.1939.
°
for 1 h, then heated to 65 C for 7 h. To the reaction mixture was
added EtOAc (20 mL) and water (10 mL), the organic layer was
separated, and the inorganic layer extracted with EtOAc (1×10 mL).
The combined organic layers were dried (MgSO4), filtered, and
concentrated. Purification by FC (EtOAc/heptane 3:2) yielded 77
(152 mg, 72%) as an oil. LC-MS A: tR =0.63 min; [M+H]+ =314.21.
Step 3: 2-Phenyl-5-(S)-pyrrolidin-2-yl-1H-imidazole HCl (78). 4 N
HCl in dioxane (1.2 mL, 4.8 mmol) was added dropwise to a RT
solution of 77 (152 mg, 0.49 mmol) in CH2Cl2 (2 mL) and the
resulting mixture was stirred at RT for 1 h. The mixture was
concentrated to obtained 78 (135 mg, 100%) as a brownish solid.
LC-MS A: tR =0.35 min; [M+H]+ =214.13. 1H NMR (400 MHz, DMSO)
δ: 9.30–9.75 (bs, 1 H), 9.95–10.03 (bs, 1 H), 8.18 (d, J=6.6 Hz, 2 H),
7.90 (s, 1 H), 7.63 (m, 3 H), 4.83–4.86 (m, 1 H), 3.34 (m, 2 H), 1.98–
2.43 (m, 4 H).
(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-[(S)-2-(1-phenyl-1H-pyrazol-4-yl)-pyrrolidi-
n-1-yl]-methanone (17)
Step 1: N-methoxy-N-methyl-1-phenyl-1H-pyrazole-4-carboxa-
mide (84). EDC HCl (611 mg, 3.19 mmol) was added to a RT solution
of 1-phenyl-1H-pyrazole-4-carboxylic acid (83) (500 mg, 2.66 mmol),
HOBT (431 mg, 3.19 mmol), TEA (1.11 mL, 7.97 mmol) in CH2Cl2
(9.0 mL) and DMF (1.8 mL), after 5 min at RT, N,O-dimeth-
ylhydroxylamine HCl (317 mg, 3.19 mmol) was added and the
resulting suspension was stirred at RT overnight. The mixture was
washed with saturated aqueous NaHCO3 and brine. The organic
layer was dried (MgSO4), filtered, and concentrated to yield 84
(645 mg, 105%) as an oil, which was used as such in the next step.
LC-MS A: tR =0.61 min; [M+H]+ =232.05.
Step 4: EDC HCl (63.6 mg, 0.332 mmol) was added to a RT solution
of 43a (27 mg, 0.13 mmol), HOBT (24.4 mg, 0.16 mmol), and DIPEA
(46 μL, 0.27 mmol) in DMF (1 mL). After stirring for 10 min at RT, 78
(34 mg, 0.132 mmol) was added and stirring was continued at RT
for 1.5 h. The reaction mixture was directly purified by preparative
HPLC (Method E) yielding 15 (34 mg, 35%) as a white solid. LC-MS
A: tR =0.66 min; [M+H]+ =399.12. LC-HRMS: tR =0.68 min; m/z=
399.1928, found=399.1942.
Step 2: 4,4-Dimethoxy-1-(1-phenyl-1H-pyrazol-4-yl)butan-1-one
(86). Preparation of the Grignard reagent: A solution of commer-
cially available 3-bromo-1,1-dimethoxypropane 85 (1.25 g,
6.83 mmol) in THF (2.4 mL) was added to a RT suspension of Mg
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(217 mg, 8.91 mmol) and I2 (151 mg, 0.594 mmol) in THF (2.4 mL).
The reaction mixture was stirred at RT for 2 h, where the mixture
turned from red to grey. The freshly prepared Grignard reagent was
Step 2. (S)-2-(1-Phenyl-1H-1,2,3-triazol-4-yl)pyrrolidine-1-carbox-
ylic acid tert-butyl ester (92). Freshly prepared 91 (from step 1)
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6
7
8
9
°
was added in 3 portions (15 min apart) to a pre-heated (150 C)
°
°
cooled to 0 C, then added to a 0 C solution of 84 (645 mg,
2.79 mmol) in THF (3.0 mL) via cannula. The mixture was allowed to
solution of 64 (100 mg, 0.51 mmol) in DMF (1.0 mL). The reaction
mixture was allowed to reach RT, then directly purified by
preparative HPLC (Method F) (separation from the undesired
isomer) to give 92 (72 mg, 45%) as a brown oil. LC-MS A: tR=
0.85 min; [M+H]+ =315.18.
°
warm to RT and stirred at RT for 30 min. At 0 C, the mixture was
quenched with saturated aqueous NH4Cl, followed by some
addition of water and EtOAc. The organic layer was separated, and
the inorganic layer was extracted with EtOAc (1×50 mL). The
combined organic layers were dried (MgSO4), filtered, and concen-
trated to yield 86 (957 mg, 125%) as a yellow solid, which was used
as such in the next step. LC-MS B: tR =0.69 min; [M+H]+ =275.02.
Step 3: (S)-1-phenyl-4-(pyrrolidin-2-yl)-1H-1,2,3-triazole (93). 4 N
°
HCl in dioxane (0.62 mL, 2.47 mmol) was added to a 0 C solution of
92 (72 mg, 0.23 mmol) in CH2Cl2 (3 mL) and the resulting mixture
was stirred at RT for 3 h. The reaction mixture was concentrated in
vacuo to yield 93 as a brown oil which was used as such in the next
step. LC-MS A: tR=0.49 min; [M+H]+ =215.12.
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Step 3: 4-Oxo-4-(1-phenyl-1H-pyrazol-4-yl)-butyraldehyde (87).
2 N HCl (7 mL, 14 mmol) was added dropwise to a RT solution of 86
(952 mg, 2.78 mmol) in THF (5.0 mL) and the resulting reaction
mixture was stirred at RT for 20 min. The reaction mixture was
quenched with saturated aqueous NaHCO3 and extracted with
EtOAc (2×50 mL). The combined organic layers were dried
(MgSO4), filtered, and concentrated to yield 87 (587 mg, 93%) as a
yellow solid, which was used as such in the next step. LC-MS B: tR =
0.61 min; [M+H]+ =228.25.
Step 4: HATU (45.6 mg, 0.12 mmol) was added to a RT solution of
43a (20.3 mg, 010 mmol) and DIPEA (86 μL, 0.5 mmol) in DMF
(0.5 mL), after 5 min at RT, 93 (30.1 mg, 0.12 mmol) in DMF (0.5 mL)
was added and stirred at RT overnight. The reaction mixture was
directly purified by preparative HPLC (Method F) to give 18 (10 mg,
26%) as an orange oil. LC-MS A: tR =0.85 min; [M+H]+ =400.05.
LC-HRMS: tR =1.03 min; m/z=400.1881, found=400.1887.
Step 4: 4-{(S)-1-[(R)-1-(4-Methoxy-phenyl)-ethyl]-pyrrolidin-2-yl}-1-
phenyl-1H-pyrazole (89). NaBH(OAc)3 (1.63 g, 7.71 mmol) was
(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-[(S)-2-(1-phenyl-1H-[1,2,4]
triazol-3-yl)-pyrrolidin-1-yl]-methanone (19)
°
added to a À 78 C solution of 87 (587 mg, 2.57 mmol) in CH2Cl2
°
(30.0 mL), then AcOH (0.29 mL) was added and after 1 h at À 78 C,
commercially available (R)-(+)-4-methoxy-alpha-methylbenzylamine
(88) (0.36 mL, 2.44 mmol) was added and the mixture was allowed
to warm to RT. After 1 h at RT, the reaction mixture was quenched
with saturated aqueous NaHCO3. The organic layer was separated,
and the inorganic layer extracted with CH2Cl2 (2x). The combined
organic layers were dried (MgSO4), filtered, and concentrated to
yield 89 (868 mg, 97%) as a yellow oil, which was used as such in
the next step. LC-MS B: tR =0.58 min; [M+H]+ =348.08.
Step 1: (S)-2-Methoxycarbonimidoyl-pyrrolidine-1-carboxylic acid
tert-butyl ester (94). A solution of Boc-(S)-pyrrolidine-2-carbonitrile
(54) (100 mg, 0.51 mmol) in MeOH (1.8 mL) was added to a RT
solution of NaOMe (5.4 M in MeOH, 105 μL) in MeOH (2 mL) and
the resulting mixture was stirred at RT overnight. The reaction was
quenched with saturated aqueous KH2PO4 until pH 6. The reaction
mixture was concentrated in vacuo and the residue was taken up in
CH2Cl2 and H2O. The organic layer was separated, and the inorganic
layer was extracted with CH2Cl2 (1×20 mL). The combined organic
layers were dried (MgSO4), filtered, and concentrated to give 94
(94 mg, 75%) as an oil, which was used as such in the next step. LC-
MS A: tR=0.51 min; [M+H]+ =229.11.
Step 5: 1-Phenyl-4-(S)-pyrrolidin-2-yl-1H-pyrazole (90). TFA (3 mL,
39.2 mmol) was added to 89 (140 mg, 0.40 mmol) and the yellow
°
solution was irradiated in the microwave at 100 C for 30 min. The
dark red solution was concentrated (removal of TFA) and the
residue was diluted with CH2Cl2, then basified with 1 N aqueous
NaOH solution. The organic layer was separated, and the inorganic
layer was extracted with CH2Cl2 (1×20 mL). The combined organic
layers were dried (MgSO4), filtered, and concentrated to yield 90
(126 mg, 146%) as a brown oil, which was used as such in the next
step. LC-MS B: tR =0.43 min; [M+H]+ =214.15.
Step 2: (S)-2-(1-Phenyl-1H-[1,2,4]triazol-3-yl)-pyrrolidine-1-carbox-
ylic acid tert-butyl ester (96). Phenylhydrazine (95) (42 μL,
0.412 mmol) was added to a RT solution of 94 (94 mg, 0.41 mmol)
and TEA (172 μL, 1.24 mmol) in MeOH (1.5 mL). The resulting
mixture was stirred at RT for 4 days. The mixture was concentrated
in vacuo, then the residue dissolved in pyridine (1.53 mL,
18.9 mmol) and triethyl orthoformate (1.54 mL, 9.06 mmol) was
Step 6: TBTU (77 mg, 0.24 mmol) was added to a RT solution of 43a
(41 mg, 0.20 mmol) and DIPEA (103 μL, 0.60 mmol) in DMF (0.5 mL).
The mixture was stirred at RT for 5 min, before 90 (62 mg,
0.20 mmol) in DMF (0.5 mL) was added and stirred at RT overnight.
The reaction mixture was directly purified by preparative HPLC
(Method F) yielding 17 (20 mg, 25%) as a yellow oil. LC-MS B: tR =
0.81 min; [M+H]+ =398.99. LC-HRMS: tR =1.11 min; m/z=399.1928,
found=399.1935.
°
added. The mixture was heated to 120 C for 1.5 h, then the
reaction mixture was concentrated and dissolved in CH2Cl2, washed
with saturated aqueous citric acid, saturated aqueous NaHCO3 and
brine. The organic layer was dried (MgSO4), filtered, and concen-
trated. The crude was purified by FC (EtOAc/heptane 2:3) to yield
96 (75 mg, 58%) as an oil. LC-MS A: tR=0.82 min; [M+H]+ =315.17.
Step 3: 1-phenyl-3-(S)-pyrrolidin-2-yl-1H-[1,2,4]triazole (97). TFA
(180 μL, 2.39 mmol) was added to a RT solution of 96 (75 mg,
0.24 mmol) in CH2Cl2 (1.0 mL) and the resulting mixture was stirred
(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-[(S)-2-(1-phenyl-1H-[1,2,3]
triazol-4-yl)-pyrrolidin-1-yl]-methanone (18)
°
at RT overnight. The reaction mixture was cooled to 0 C, then
diluted with CH2Cl2 and basified with 4 N aqueous NaOH solution.
The layers were separated, and the inorganic layer was extracted
with CH2Cl2 (1×20 mL). The combined organic layers were dried
(MgSO4), filtered, and concentrated to yield 97 (37 mg, 72%), which
was used as such in the next step. LC-MS A: tR=0.48 min; [M+H]+ =
215.13.
Step 1: Phenylazide (91). tert-Butyl nitrite (0.4 mL, 3 mmol),
followed by trimethylsilylazide (0.33 mL, 2.4 mmol) was added to a
°
0 C solution of phenylamine (0.18 mL, 2 mmol) in MeCN (4.0 mL)
and the resulting mixture was stirred at RT for 2 h. The reaction
mixture was carefully concentrated (not completely) in vacuo to
yield 91, which was used immediately in the next step. LC-MS A: tR=
0.8 min; [M+H]+ =no ionization.
Step 4: TBTU (62.4 mg, 0.19 mmol) was added to a RT solution of
43a (32 mg, 0.15 mmol) and DIPEA (64 μL, 0.37 mmol) in DMF
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(0.6 mL). The mixture was stirred at RT for 5 min, before 97
(51.3 mg, 0.18 mmol) in DMF (0.5 mL) was added and stirred at RT
for 1.5 h. The reaction mixture was directly purified by preparative
HPLC (Method E) to yield 19 (27 mg, 45%) as a white solid. LC-MS
A: tR =0.83 min; [M+H]+ =400.14. LC-HRMS: tR =1.00 min; m/z=
400.1881, found=400.1896.
24.5 mmol) was added to a RT solution of 2-(trifluoromethoxy)
benzoic acid (46b) (4.00 g, 18.8 mmol) and DIPEA (18.06 mL,
47.1 mmol) in CH2Cl2 (32 mL). The reaction mixture was stirred at RT
for 10 min, then 55 (5.01 g, 20.3 mmol) was added and stirring was
continued for 4 h at RT. The reaction mixture was concentrated and
to the residue was added dioxane (22 mL) and the reaction mixture
1
2
3
4
5
6
7
8
9
°
was stirred at 80 C for 2 days. The reaction mixture was concen-
trated, CH2Cl2 was added, and the organic layer was washed with
aqueous saturated NaHCO3 solution. The organic layer was dried
(MgSO4), filtered, and concentrated. Purification by Biotage FC
(EtOAc/hexane 1:9 to 3:7; Rf =0.38 in EtOAc/heptane 3:7) yielded
57 (6.54 g, 87%) as an orange oil. LC-MS A: tR =0.99 min; [M+H]+ =
400.12.
(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-[(S)-2-(5-phenyl-4H-[1,2,4]
triazol-3-yl)-pyrrolidin-1-yl]-methanone (20)
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Step 1: (S)-2-(5-Phenyl-4H-[1,2,4]triazol-3-yl)-pyrrolidine-1-carbox-
ylic acid tert-butyl ester (98a). Benzohydrazide (50a) (150 mg,
1.1 mmol) was added to a RT solution of (S)-1-boc-2-cyanopyrroli-
dine (54) (649 mg, 3.31 mmol) and K2CO3 (76.1 mg, 0.551 mmol) in
Step 3. 3-(S)-Pyrrolidin-2-yl-5-(2-trifluoromethoxyphenyl)-[1,2,4]
oxadiazole (58). 4 N HCl in dioxane (2.1 mL, 8.4 mmol) was added
°
°
dropwise to a 0 C solution of 57 (1.30 g, 3.26 mmol) in CH2Cl2
nBuOH (4.4 mL) and the mixture was refluxed (125 C) for 2.5 h. The
(13 mL) and the resulting mixture was stirred at RT for 2 h. The
mixture was poured into an ice-cold solution of 4 N aqueous NaOH
solution (8 mL), then the mixture was extracted with CH2Cl2 (2×
30 mL). The combined organic layers were dried (MgSO4), filtered,
and concentrated to yield 58 (903 mg, 93%) as a white solid. LC-MS
A: tR =0.63 min; [M+H]+ =300.12. 1H NMR (400 MHz, DMSO) δ: 8.23
(dd, J1 =1.9 Hz, J2 =8.3 Hz, 1 H), 7.84–7.88 (m, 1 H), 7.66–7.70 (m, 2
H), 4.37–4.40 (m, 1 H), 3.04–3.45 (bs, 1 H), 2.90–3.06 (m, 2 H), 2.09–
2.18 (m, 1 H), 1.71–1.97 (m, 3 H).
reaction mixture was concentrated in vacuo, then CH2Cl2 and H2O
was added, and the solution was brought to pH 7 (1 N aqueous
HCl). The organic layer was separated, and the inorganic layer
extracted with CH2Cl2 (2×20 mL). The combined organic layers
were dried (MgSO4), filtered, and concentrated. Purification by FC
(EtOAc/heptane 7:3) yielded 98a (285 mg, 85%) as a white solid.
LC-MS A: tR =0.75 min; [M+H]+ =315.17.
Step 2: 3-Phenyl-5-(S)-pyrrolidin-2-yl-4H-[1,2,4]triazole (99a). 4 N
HCl in dioxane (2.1 mL, 8.4 mmol) was added dropwise to a RT
solution of 98a (240 mg, 0.765 mmol) in CH2Cl2 (5 mL) and the
resulting mixture was stirred at RT for 45 min. The mixture was
concentrated to obtained 99a (204 mg, 93%) as a white solid. LC-
MS A: tR =0.46 min; [M+H]+ =215.18.
Step 4. TBTU (1.13 g, 3.52 mmol) was added to a RT solution of 43b
(550 mg, 2.71 mmol) and DIPEA (3.08 mL, 18 mmol) in CH2Cl2
(12 mL) and the reaction mixture was stirred for 15 min before 58
(2.37 g, 7.92 mmol) dissolved in CH2Cl2 (6 mL) was added and the
resulting mixture was stirred at RT for 18 h. The reaction mixture
was diluted with CH2Cl2 and water. The layers were separated, and
the organic layer was dried (MgSO4), filtered, and concentrated.
Purification by FC (EtOAc/heptane 3:7) yielded 36 (1.08 g, 82%) as
an off-white foam. LC-MS A: tR =0.99 min; [M+H]+ =484.80; LC-
HRMS: tR =1.27 min; m/z=485.1544, found=485.1551.
Step 3: EDC HCl (130 mg, 0.67 mmol) was added to a RT solution of
43a (55 mg, 0.27 mmol), HOBT (44 mg, 0.33 mmol) in CH2Cl2
(0.7 mL). After stirring for 5 min at RT, 99a (68 mg, 0.32 mmol) in
CH2Cl2 (1.0 mL) was added and stirring was continued at RT for
10 min. The reaction mixture was diluted with CH2Cl2 and H2O, the
organic layer was separated, and the inorganic layer extracted with
CH2Cl2 (1×10 mL). The combined organic layers were dried
(MgSO4), filtered, and concentrated. Purification by preparative
HPLC (Method E) yielded 20 (55 mg, 51%) as a white solid. LC-MS
A: tR =0.80 min; [M+H]+ =400.07; LC-HRMS: tR =0.97 min; m/z=
400.1881, found=400.1890.
Compounds 37 and 38 were synthesized in a manner analogous to
the procedure described for compound 36. Compound 41 was
synthesized in a manner analogous to the procedure described for
compound 42 (see Supporting Information).
Compounds 21–35 and 40 were synthesized in a manner analo-
gous to the procedure described for compound 20 (see Supporting
Information).
(4-Chloro-2-[1,2,3]
triazol-2-yl-phenyl)-{(S)-2-meth-
yl-2-[5-(2-trifluoromethoxy-phenyl)-4H-[1,2,4]
triazol-3-yl]-pyrrolidin-1-yl}-methanone (42)
(5-Methyl-2-[1,2,3]
triazol-2-yl-phenyl)-{(S)-2-[5-(2-trifluoromethoxy-pheny-
l)-[1,2,4]oxadiazol-3-yl]-pyrrolidin-1-yl}-methanone (36)
Step 1: (S)-2-Cyano-2-methyl-pyrrolidine-1-carboxylic acid tert-
°
butyl ester (101). TEA (17 mL, 122 mmol) was added to a À 5 C
solution of commercially available (S)-1-(tert-butoxycarbonyl)-2-
methylpyrrolidine-2-carboxylic acid (100) (14.00 g, 61.1 mmol) in
THF (150 mL) and the brown solution was stirred for 15 min before
ethyl chloroformate (7 mL, 72.5 mmol) was added dropwise. The
Step 1. (S)-2-(N-Hydroxycarbamimidoyl)pyrrolidine-1-carboxylic
acid tert-butyl ester (55). Hydroxylamine·HCl (4.95 g, 69.9 mmol)
was added to a RT solution of commercially available (S)-1-boc-2-
cyanopyrrolidine (54) (9.14 g, 46.6 mmol) and Na2CO3 (5.87 g,
69.9 mmol) in MeOH (90 mL) and the resulting suspension was
°
mixture was stirred at 0 C for 30 min, then aqueous 25% NH4OH
(95 mL, 755 mmol) was added and the resulting mixture was
allowed to warm to RT, where stirring was continued for 1 h. The
mixture was concentrated in vacuo. The residue was taken up in
CH2Cl2 and H2O. The layers were separated, and the inorganic layer
was re-extracted with CH2Cl2 (1×150 mL). The combined organic
layers were washed with brine, dried (MgSO4), filtered, and
concentrated. The crude orange solid (9.27 g) was dissolved in
CH2Cl2 (120 mL) and TEA (17 mL, 122 mmol) was added. The
°
stirred at 70 C for 1.5 h. The reaction mixture was filtered, and the
filter cake was washed with MeOH. The filtrate was concentrated to
a residue and dissolved in EtOAc and H2O. The organic layer was
separated, and the inorganic layer was extracted with EtOAc (1×
200 mL). The combined organic layers were dried (MgSO4), filtered,
and concentrated to yield 55 (9.15 g of 86%) as a greyish solid,
which was used as such in the next step. LC-MS A: tR =0.45 min; [M
+H]+ =230.23.
°
solution was cooled to 0 C, then trifluoroacetic anhydride (10.5 mL,
73.3 mmol) was added dropwise and the resulting mixture was
°
stirred at 0 C for 30 min, then at RT overnight. The mixture was
Step 2. (S)-2-[5-(2-Trifluoromethoxyphenyl)-[1,2,4]oxadiazol-3-yl]
pyrrolidine-1-carboxylic acid tert-butyl ester (57). TBTU (7.857 g,
diluted with CH2Cl2 (100 mL) and washed with H2O (1×20 mL). The
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°
organic layer was dried (MgSO4), filtered, and concentrated.
Purification by Biotage FC (EtOAc/hexane. 1:1, Rf =0.63) yielded
101 (6.94 g, 81%) as a yellow oil. LC-MS A: tR =0.80 min; [M+H]+ =
211.24.
mixture was cooled to 0 C and hydrazine (1 M in THF; 18.8 mL,
18.8 mmol) was added, the ice bath removed, and the solution
stirred at RT for 2 h. The reaction mixture was diluted with CH2Cl2,
washed with saturated aqueous NaHCO3, and the inorganic layers
were re-extracted with CH2Cl2 (1×50 mL). The combined organic
layers were dried (MgSO4), filtered, and concentrated. Purification
by Biotage FC (CH2Cl2/MeOH 95:5+0.2% NH4OH) yielded 50b
(920 mg, 86%) as an off-white solid. LC-MS A: tR =0.50 min; [M(35Cl)
+H]+ =201.05.
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Step 2: (S)-2-Methyl-2-[5-(2-trifluoromethoxy-phenyl)-4H-[1,2,4]tria-
zol-3-yl]-pyrrolidine-1-carboxylic acid tert-butyl ester (102). 2-(Tri-
fluoromethoxy)benzoic acid hydrazide (50b) (13.85 g, 62.9 mmol)
was added to a RT solution of 102 (13.23 g, 62.9 mmol) and K2CO3
(4.35 g, 31.4 mmol) in n-butanol (120 mL). The reaction mixture was
°
stirred at 125 C for 51 h, then the reaction mixture was allowed to
reach RT before it was concentrated in vacuo. To the residue was
added CH2Cl2 (150 mL) and H2O (10 mL), then the mixture was
acidified with 2 N HCl. The organic layer was separated, and the
inorganic layer was extracted with CH2Cl2 (2×30 mL). The combined
organic layers were dried (MgSO4), filtered, and concentrated.
Purification by preparative HPLC (Method D) yielded 102 (4.46 g,
17%) as a yellow foam. LC-MS A: tR =0.87 min; [M+H]+ =413.07.
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Acknowledgements
The authors gratefully thank Stephanie Bazire, Jeanine Thanner,
Dr. Markus Gude, Celia Müller-Grandjean, Katalin Menyhart,
Thomas Sasse, Cedric Fischer, Stephane Delahaye, Isabelle Weber,
Fabienne Drouet, Eric Soubieux, Rolf Wuest, Julia Khobzaoui, René
Vogelsanger, Claus Müller, and Sandrine Chopinet.
Step 3: 3-((S)-2-Methyl-pyrrolidin-2-yl)-5-(2-trifluoromethoxy-
phenyl)-4H-[1,2,4]triazole (103). 4 N HCl in dioxane (45 mL,
°
180 mmol) was added dropwise to a 0 C solution of 102 (4.46 g,
10.8 mmol) in CH2Cl2 (100 mL), then the reaction was stirred at RT
for 1.5 h. The reaction mixture was concentrated, to the residue
was added CH2Cl2 and the mixture was basified with 4 N aqueous
NaOH solution. The organic layer was separated, and the inorganic
layer extracted with CH2Cl2 (2×100 mL). The combined organic
layers were washed with brine, dried (MgSO4), filtered, and
concentrated to yield 103 (3.64 g, 108%) as a yellow oil. LC-MS A:
tR =0.57 min; [M+H]+ =313.17.
Keywords: drug design · dual orexin receptor antagonists ·
insomnia · sleep disorders · structure-activity relationships
[1] Y. Choi, B. K. Raymer, Bioorg. Med. Chem. Lett. 2019, 29, 2025–2033.
[2] P. C. Bollu, H. Kaur, Mo. Med. 2019, 116, 68–75.
[3] L. Citrome, Int. J. Clin. Pract. 2014, 68, 1429–1441.
[4] A. K. Dubey, S. S. Handu, P. K. Mediratta, J. Pharmacol. Pharmacother.
2015, 6, 118–121.
[5] C. D. Cox, J. J. Renger, P. J. Coleman, C. J. Winrow, Med. Chem. Rev. 2015,
Step 4: HATU (3.06 g, 8.05 mmol) was added to a RT solution of
43b (1.50 g, 6.71 mmol) in DMF (10.0 mL). After 5 min at RT, a
solution of 103 (2.30 g, 7.36 mmol) and DIPEA (3.5 mL, 20.4 mmol)
in DMF (10.0 mL) was added and the reaction mixture was stirred at
RT overnight. To the reaction was added EtOAc and H2O, then the
organic layer was separated, and the inorganic layer was extracted
with EtOAc (2×50 mL). The combined organic layers were dried
(MgSO4), filtered, and concentrated. Purification by preparative
HPLC (Method D) yielded 42 (2.43 g, 70%) as an off-white solid. LC-
MS A: tR =0.94 min; [M+H]+ =518.08. LC-HRMS: tR =1.26 min; m/
z=518.1314, found=518.1327.
50, 419–432.
[6] Y. Yoshida, Y. Naoe, T. Terauchi, F. Ozaki, T. Doko, A. Takemura, T.
Tanaka, K. Sorimachi, C. T. Beuckmann, M. Suzuki, T. Ueno, S. Ozaki, M.
Yonaga, J. Med. Chem. 2015, 58, 4648–4664.
[7] https://clinicaltrials.gov/ct2/show/NCT02919319.
[8] A. Treiber, R. de Kanter, C. Roch, J. Gatfield, C. Boss, M. von Raumer, B.
Schindelholz, C. Muehlan, J. van Gerven, F. Jenck, J. Pharm. Exp. Ther.
2017, 362, 489–503.
[9] C. Muehlan, S. Brooks, R. Zuiker, J. van Gerven, J. Dingemanse, European
neuropsychopharmacology : the journal of the European College of
Neuropsychopharmacology 2019, 29, 847–857.
[10] Press Release Minerva Bioscience: www.minervaneurosciences.com:
“Minerva Neurosciences Announces Achievement of Primary and Key
Secondary Objectives in Phase 2b Clinical Trial of Seltorexant (MIN-202)
in Insomnia” 2019.
[11] S. Brooks, G. E. Jacobs, P. de Boer, J. M. Kent, L. Van Nueten, G.
van Amerongen, R. Zuiker, I. Kezic, R. Luthringer, P. van der Ark, J. M.
van Gerven, W. Drevets, J. Psychopharmacol. 2019, 33, 202–209.
[12] A. L. Gotter, M. S. Forman, C. M. Harrell, J. Stevens, V. Svetnik, K. L. Yee,
X. Li, A. J. Roecker, S. V. Fox, P. L. Tannenbaum, S. L. Garson, I. D.
Lepeleire, N. Calder, L. Rosen, A. Struyk, P. J. Coleman, W. J. Herring, J. J.
Renger, C. J. Winrow, Sci. Rep. 2016, 6, 27147.
[13] D. A. Perrey, Y. Zhang, Brain Research 2018.
[14] D. Smart, C. Sabido-David, S. J. Brough, F. Jewitt, A. Johns, R. A. Porter,
J. C. Jerman, Br. J. Pharmacol. 2001, 132, 1179–1182.
[15] J. Wiskerke, M. H. James, G. Aston-Jones, Brain Research 2019.
[16] S. B. Giacomo Salvadore, C. Bleys, K. Tatikola, B. Remmerie, Gabriel, J. M.
Jacobs, A. Nash, L. Van Nueten, W. Drevets, ASCP 2019 Meeting, May28–
31, 2019 Scottsdale, Arizona 2019.
[17] J. T. Williams, 20th SCI/RSC Medicinal Chemistry Symposium (September
8–11, Cambridge, UK) 2019.
4-Chloro-2-[1,2,3]triazol-2-yl-benzoic acid (43b). CuI (75.7 mg,
0.34 mmol) was added to a RT solution of commercially available 4-
chloro-2-iodobenzoic acid (104) (2.25 g), 1H-1,2,3-triazol (0.92 mL,
15.9 mmol), Cs2CO3 (5.19 g, 15.9 mmol) and DMCDA (0.26 mL,
1.59 mmol) in DMF (10 mL). The mixture was irradiated in the
°
microwave to 105 C for 15 min (with cooling). The reaction mixture
was diluted with aqueous 1 N HCl and EtOAc was added. The
organic layer was separated, and the inorganic layer was extracted
with EtOAc (2×20 mL). The combined organic layers were dried
(MgSO4), filtered, and concentrated. Purification by FC (CH2Cl2/
MeOH 20:1 with 0.2% acetic acid; Rf =0.3) yielded 43b (1.24 g,
70%) as a brown oil. The undesired isomer eluted with Rf =0.25.
LC-MS A: tR =0.66 min; [M+H]+ =224.1.
The synthesis of biaryl-carboxylic acids 43a–h are synthesized in a
manner analogous to the procedure described for compound 43b.
The SM are either prepared from the corresponding commercially
available o-iodo or o-bromo carboxylic acid. (see Supporting
Information).
[18] P. Kaufmann, B. Berger, R. Kornberger, J. Dingemanse, 120th Annu Meet
Am Soc Clin Pharmacol Ther (ASCPT) (March 13–16, Washington, D. C.)
2019, Abst LB-018 2019.
[19] P. Kaufmann, R. Kornberger, J. Dingemanse, 119th Annu Meet Am Soc
Clin Pharmacol Ther (ASCPT) (March 21–24, Orlando) 2018, Abst PII-068
2018.
3-Chloro-2-methoxybenzohydrazide (50b)
TBTU (2.07 g, 6.43 mmol) was added to a RT solution of 3-chloro-2-
methoxybenzoic acid (1.00 g, 5.36 mmol) and DIPEA (2.75 mL,
16.1 mmol) in DMF (20.0 mL). After stirring for 5 min, the reaction
[20] E. Merlo Pich, S. Melotto, Front. Neurosci. 2014, 8, 26.
ChemMedChem 2020, 15, 1–20
www.chemmedchem.org
18
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��
These are not the final page numbers!

Full Papers
[21] C. Brotschi, C. Roch, J. Gatfield, A. Treiber, J. T. Williams, T. Sifferlen, B.
Heidmann, F. Jenck, M. H. Bolli, C. Boss, ChemMedChem 2019, 14, 1257–
1270.
[22] C. D. Cox, M. J. Breslin, D. B. Whitman, J. D. Schreier, G. B. McGaughey,
M. J. Bogusky, A. J. Roecker, S. P. Mercer, R. A. Bednar, W. Lemaire, J. G.
Bruno, D. R. Reiss, C. M. Harrell, K. L. Murphy, S. L. Garson, S. M. Doran, T.
Prueksaritanont, W. B. Anderson, C. Tang, S. Roller, T. D. Cabalu, D. Cui,
G. D. Hartman, S. D. Young, K. S. Koblan, C. J. Winrow, J. J. Renger, P. J.
Coleman, J. Med. Chem. 2010, 53, 5320–5332.
[23] C. J. Winrow, A. L. Gotter, C. D. Cox, P. L. Tannenbaum, S. L. Garson, S. M.
Doran, M. J. Breslin, J. D. Schreier, S. V. Fox, C. M. Harrell, J. Stevens, D. R.
Reiss, D. Cui, P. J. Coleman, J. J. Renger, Neuropharmacology 2012, 62,
978–987.
[26] C. Boss, C. Brisbare-Roch, F. Jenck, H. Aissaoui, R. Koberstein, T. Sifferlen,
T. Weller, Chimia 2008, 62, 974–979.
[27] T. Sifferlen, R. Koberstein, E. Cottreel, A. Boller, T. Weller, J. Gatfield, C.
Brisbare-Roch, F. Jenck, C. Boss, Bioorg. Med. Chem. Lett. 2013, 23, 3857–
3863.
[28] C. Boss, C. Roch-Brisbare, M. A. Steiner, A. Treiber, H. Dietrich, F. Jenck,
M. von Raumer, T. Sifferlen, C. Brotschi, B. Heidmann, J. T. Williams, H.
Aissaoui, R. Siegrist, J. Gatfield, ChemMedChem 2014, 9, 2486–2496.
[29] T. Sifferlen, A. Boller, A. Chardonneau, E. Cottreel, J. Gatfield, A. Treiber,
C. Roch, F. Jenck, H. Aissaoui, J. T. Williams, C. Brotschi, B. Heidmann, R.
Siegrist, C. Boss, Bioorg. Med. Chem. Lett. 2015, 25, 1884–1891.
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39
40
41
42
43
44
45
46
47
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49
50
51
52
53
54
55
56
57
[24] T. Sifferlen, C. Boss, E. Cottreel, R. Koberstein, M. Gude, H. Aissaoui, T.
Weller, J. Gatfield, C. Brisbare-Roch, F. Jenck, Bioorg. Med. Chem. Lett.
2010, 20, 1539–1542.
[25] H. Aissaoui, R. Koberstein, C. Zumbrunn, J. Gatfield, C. Brisbare-Roch, F.
Jenck, A. Treiber, C. Boss, Bioorg. Med. Chem. Lett. 2008, 18, 5729–5733.
Manuscript received: November 1, 2019
Revised manuscript received: December 13, 2019
Version of record online: ■■■, ■■■■
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Dr. C. Brotschi*, Dr. M. H. Bolli, Dr. J.
Gatfield, Dr. B. Heidmann, Dr. F.
Jenck, Dr. C. Roch, Dr. T. Sifferlen,
Dr. A. Treiber, Dr. J. T. Williams, Dr. C.
Boss
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DORA explorers: The orexin system
plays an important role in regulating
the sleep-wake cycle. Herein we
report our optimization efforts toward
a novel dual orexin receptor antago-
nist (DORA) with improved properties
over compound 6. Replacing the oxa-
diazole by a triazole resulted in
intrinsic metabolic stability, lower
plasma protein binding, higher brain
free fraction, and increased solubility.
Further optimization was needed to
decrease the compounds P-glycopro-
tein susceptibility. Our work led to the
identification of compound 42, a
potent, brain-penetrating DORA with
improved in vivo efficacy in dogs
compared with compound 6.
From Oxadiazole to Triazole
Analogues: Optimization toward a
Dual Orexin Receptor Antagonist
with Improved in vivo Efficacy in
Dogs
compounds (e.g. compound 33) with
improved properties, such as higher