Discovery of diazepane amide DORAs and 2-SORAs enabled by exploration of isosteric quinazoline replacements

Article abstract of DOI:10.1016/j.bmcl.2014.12.081

Dual orexin receptor antagonists (DORAs), or orexin 1 (OX₁) and orexin 2 (OX₂) receptor antagonists, have demonstrated clinical utility for the treatment of insomnia. Medicinal chemistry efforts focused on the reduction of bioactivat

Full text of DOI:10.1016/j.bmcl.2014.12.081

Accepted Manuscript
Discovery of Diazepane Amide DORAs and 2-SORAs Enabled by Exploration
of Isosteric Quinazoline Replacements
Anthony J. Roecker, Swati P. Mercer, Jeffrey M. Bergman, Kevin F. Gilbert,
Scott D. Kuduk, C. Meacham Harrell, Susan L. Garson, Steven V. Fox, Anthony
L. Gotter, Pamela L. Tannenbaum, Thomayant Prueksaritanont, Tamara D.
Cabalu, Donghui Cui, Wei Lemaire, Christopher J. Winrow, John J. Renger,
Paul J. Coleman
PII:
S0960-894X(14)01389-4
DOI:
http://dx.doi.org/10.1016/j.bmcl.2014.12.081
BMCL 22326
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
27 November 2014
22 December 2014
24 December 2014
Please cite this article as: Roecker, A.J., Mercer, S.P., Bergman, J.M., Gilbert, K.F., Kuduk, S.D., Meacham Harrell,
C., Garson, S.L., Fox, S.V., Gotter, A.L., Tannenbaum, P.L., Prueksaritanont, T., Cabalu, T.D., Cui, D., Lemaire,
W., Winrow, C.J., Renger, J.J., Coleman, P.J., Discovery of Diazepane Amide DORAs and 2-SORAs Enabled by
Exploration of Isosteric Quinazoline Replacements, Bioorganic & Medicinal Chemistry Letters (2015), doi: http://
dx.doi.org/10.1016/j.bmcl.2014.12.081
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Discovery of Diazepane Amide DORAs and 2-SORAs Enabled by
Exploration of Isosteric Quinazoline Replacements
Anthony J. Roecker,*,a Swati P. Mercer,a Jeffrey M. Bergman,a Kevin F. Gilbert,a Scott D.
Kuduk,a C. Meacham Harrell,b Susan L. Garson,b Steven V. Fox,b Anthony L. Gotter, b
Pamela L. Tannenbaum,b Thomayant Prueksaritanont,c Tamara D. Cabalu,c Donghui
Cui,c Wei Lemaire,d Christopher J. Winrow,b John J. Renger,b and Paul J. Colemana
Departments of Medicinal Chemistry,a Neuroscience,b Drug Metabolism,c and In Vitro
Pharmacology,d Merck Research Laboratories, P. O. Box 4, Sumneytown Pike, West
Point, PA 19486.
* Corresponding author. Tel.: + 1-215-652-8257; fax: + 1-215-652-3971; e-mail:
anthony_roecker@merck.com
1

Abstract
Dual orexin receptor antagonists (DORAs), or orexin 1 (OX1) and orexin 2 (OX2)
receptor antagonists, have demonstrated clinical utility for the treatment of insomnia.
Medicinal chemistry efforts focused on the reduction of bioactivation potential of
diazepane amide 1 through the modification of the Western heterocycle resulted in the
discovery of suvorexant, a DORA recently approved by the FDA for the treatment of
insomnia. A second strategy towards reducing bioactivation risk is presented herein
through the exploration of monocyclic quinazoline isosteres, namely substituted
pyrimidines. These studies afforded potent DORAs with significantly reduced
bioactivation risk and efficacy in rodent sleep models. Surprisingly, side products from
the chemistry used to produce these DORAs yielded isomeric pyrimidine-containing
diazepane amides possessing selective OX2R antagonist (2-SORA) profiles. Additional
exploration of these isomeric pyrmidines uncovered potent 2-SORA diazepane amides
with sleep efficacy in mouse EEG studies.
2

Results and Discussion
The field of orexin receptor antagonist research began shortly after the discovery
of the orexin receptors, OX1R and OX2R, and their wake-promoting peptides, orexin A
and B, in 1998.1 Proof-of-concept for the treatment of insomnia by dual orexin receptor
antagonists (DORAs, molecules that antagonize both receptors) occurred in under a
decade in 2007,2 and suvorexant (2, Figure 1) was the first DORA to be approved by the
FDA for the treatment of insomnia in 2014.3 Several excellent reviews describing the
state of preclinical and clinical orexin antagonist research have been published and are
beyond the scope of this manuscript.4 Medicinal chemistry efforts that resulted in the
discovery of suvorexant have been published by our group. 5 The reduction of
bioactivation potential was a critical profile element in the optimization of diazepanes
6
7
such as 1 to suvorexant (2). Metabolite identification studies revealed the
fluoroquinazoline motif in 1 was the underlying cause of the bioactivation through the
formation of high levels of GSH adducts in human and rat microsomal incubations.
Suvorexant demonstrated that modification of the nature of the fused Western
heterocycle could significantly reduce bioactivation potential in the same microsomal
GSH trapping experiments. A second strategy targeted utilization of monocyclic isosteric
replacements (3, Figure 1) of the fluoroquinazoline heterocycle in 1 to affect a similar
level of bioactivation risk reduction.
3

Figure 1. Strategic designs focused on reduction of bioactivation potential of diazepane
amide DORA 1.
Analysis of previously disclosed SAR in the diazepane amide DORA series
demonstrated that removal of the distal fused phenyl in the Western heterocycle afforded
essentially inactive compounds at both receptors (data not shown).8 From this data it was
apparent that the lipophilic interactions in this region of the molecule were critical from a
potency perspective. Thus, substituted pyrimidine Western heterocyclic designs filling a
similar amount of lipophilic space compared to DORA 1 were prioritized for synthetic
efforts. The synthesis of selected targets is described in Schemes 1 and 2. Substitution
reactions involving diazepane cores A and B with 5-substituted-2,4-dichloropyrimidines
favor substitution at the 4-position of the pyrimidine except when a strong electron
withdrawing motif is present at the 5-position.9 An example of reversed regioselectivity
in these SNAr reactions is depicted in Scheme 1 as diazepane amines A and B react with
2,4-dichloro-5-trifluoromethylpyrimidine (C) to afford the 2-substituted products 7 and 8
in a 4:1 ratio with regioisomers 13 and 14.10 Both regioisomeric products were then
transformed via a second SNAr reaction or Stille coupling to afford products 9 - 12 and
15 in acceptable yields. The regioselectivity for the initial SNAr reaction was confirmed
by small molecule X-ray analysis of DORA 11 (Scheme 1). A more standard selectivity
profile for these SNAr reactions is depicted in Scheme 2 where 2,4,5-trichloropyrimidine
(F) must be functionalized via selective Stille coupling with tetramethyltin to afford
4

intermediate G.11 This intermediate can then be reacted with diazepane core A to afford
2-substituted pyrimidine compound 4 in high yield. The substitution reaction of F with
diazepane core B was completely selective for the 4-position of the pyrimidine to afford
18. Compound 18 was then regioselectively methylated under Stille conditions to afford
compound 19.
Scheme 1. Representative synthesis of diazepane amide DORAs. Reagents and reaction conditions: (a)
Diazepane A, Et3N, DMF, 25°C, 18h, 67% of 7 and 18% of 13; Diazepane B afforded 56% of 8 and 16%
of 14; (b) Me4Sn, PdCl2(dppf), LiCl, DMF, 110°C, 14h, 70% for 9 86% for 11; (c) NaOMe (4M in MeOH),
DMF, 23°C, 0.5h, 95% for 10 and 96% for 12; (d) Me4Sn, PdCl2(dppf), LiCl, DMF, 110°C, 14h, 19%; See
reference 5a for the synthesis of diazepane cores A and B; Abbreviations: DMF = N,N-dimethylformamide,
dppf = 1,1'-(diphenylphosphino)ferrocene.
5

Scheme 2. Representative synthesis of diazepane amide DORAs and 2-SORAs. Reagents and reaction
conditions: (a) Me4Sn, PdCl2(dppf), DMF, 110°C, 4h, 60%; (b) Diazepane A, Et3N, DMF, 90°C, 15h, 56%;
(c) Diazepane B, Et3N, DMF, 0°C to 23°C, 18h, 73%; (d) Me4Sn (1.05 equiv), Pd(PPh3)4, LiCl, DMF,
115°C, 4h, 43%
Selected potency and pharmacokinetic data for isosteric replacements of the
Western 6-fluoroquinazoline motif are captured in Table 1. While certain designs did not
recapitulate the planar topology of the fused fluorophenyl ring of DORA 1 (i.e.
compounds 7 – 12 containing a trifluoromethyl motif), all designs resided within 20 Å2 of
lipophilic surface area from the lead.12 As shown in Table 1, compound 1 demonstrated
excellent binding (as determined by a radioligand binding assay) and functional (as
determined via FLIPR assay) potency at OX2R and OX1R as well as low clearance in the
dog. 13 This combination of potency and pharmacokinetics provided excellent sleep
efficacy in preclinical models and eventually led to the discovery of suvorexant (2).
Hence, our objective was to duplicate this excellent profile in a monocyclic pyrimidine
DORA.
Replacement of the fluorophenyl motif in DORA 1 with chlorine and methyl
substituents such as 4 and 5 retained excellent binding and functional potency of lead 1
on both receptors. However, clearance in dog increased 3-fold for both compounds.
Concerns around the direct electrophilic potential of the 4-chloropyrimidine motif in
6

DORA 5 encouraged non-electrophilic designs such as 4-methoxy-5-methylpyrimidine 6.
OX1R binding potency and functional potency on both receptors were slightly diminished
for this analog. Analogs such as 7 were designed incorporating a 5-trifluoromethyl motif
to interrogate the relationship between lipophilicity and potency. Gratifyingly, compound
7 demonstrated subnanomolar intrinsic potency against OX2R and OX1R, however,
functional potency significantly diminished and dog clearance increased with the
incorporation of lipophilicity. Reducing lipophilicity via removal of the methyl group (8,
Table 1) on the triazole benzamide did not further improve functional potency, and,
coupled with concerns around direct electrophilicity of compounds 7 and 8, chlorine
replacements were targeted. Analogs 9 through 12 replaced the potentially electophilic
chlorine in compounds 7 and 8 with a methyl or methoxy motif. Both compounds 9 and
10 demonstrated excellent intrinsic potency against both receptors, however, the methoxy
analog 10 displayed improved functional potency and reduced clearance in dog compared
to compound 9. Removing the methyl group from the triazole benzamide afforded 11 and
12 with very comparable functional potency and dog clearance profiles compared to
DORA 10. Consistent with known amide SAR in the diazepane series, compounds 11
and 12 demonstrated reduced OX1R binding potency. Hence, the profile of DORA 10
most closely replicated the potency and pharmacokinetic profile of DORA 1, and this
compound was selected for additional profiling.
Table 1. Potential quinazoline isosteric replacements.a,b
7

OX2R Ki
(nM)a
OX1R Ki
(nM)a
OX2R IC50
(nM)a
OX1R IC50
(nM)a
Heterocycle
(compound #)
Dog Cl
(mL/min/kg)
X
H
0.2
0.6
0.4
1.8
6.1
3.9
27
20
28
27
26
30
3
9
8
(1)
(4)
Me
Me
(5)
Me
Me
H
0.6
0.6
0.7
0.5
0.4
0.5
0.7
14
0.7
5.1
1.6
1.5
11
31
140
88
38
120
99
NA
15
NA
10
3
(6)
(7)
(8)
Me
Me
H
85
52
(9)
27
43
(10)
(11)
(12)
19
27
5
H
6.3
21
44
3
(a) See reference 5a for the details of these assays. All compounds listed were assayed as single
enantiomers; (b) All data reported as an average value from n > 2; for n > 2, standard deviation is < 40% in
all cases.
8

The bioactivation potential of DORA 1 and DORA 10 was assessed in vitro
through glutathione (GSH) trapping experiments in rat and human microsomal
preparations. DORA 10 reduced the amount of GSH-related adducts (determined by
AUC measurements normalized to an internal standard) compared to DORA 1 in both rat
and human preparations by over 80% (Figure 2).14 This reduction in bioactivation
potential was comparable to that achieved by the chloro-benzoxazole motif in suvorexant
(>95% reduction, 2, Figure 1). DORA 10 demonstrated similar plasma protein binding in
rat and human (95% and 96%, respectively), however, it was highly bound in dog
(99.5%). The compound was highly permeable, was not a substrate for rat or human
Pgp, 15 and it owned moderate PSA and relatively high lipophilicity (logD = 3.4)
suggesting high potential for CNS penetration (Figure 3). DORA 10 has moderate
clearance in rat and low clearance in dog with short half-lives in both species consistent
with a short-acting agent for insomnia treatment (Table 2). Although DORA 10 had
limited bioavailability in rat (8%), it demonstrated moderate bioavailability in the dog
(23%). With this information in hand, increased doses were targeted in rat sleep
experiments to evaluate oral efficacy of DORA 10 compared to lead DORA 1.
9

Figure 2. GSH trapping studies of DORAs 1 and 10 in rat and human liver microsomes.a
a
Ratios are AUC measurements normalized to the AUC of an internal standard (IS = labetalol). AUC =
area under curve; RLM = rat liver microsomes; HLM = human liver microsomes.
10

N
O
N
N
N
F3C
MeO
N
N
N
Me
Me
DORA 10
Plasma Protein Binding
Human: 96%
Rat: 95%
Dog: 99.5%
CNS Properties
Pgp ratio (BA/AB): 0.7 (h); 1.2 (r)
Papp: 28 cm * 10-6/s
HPLC log D: 3.4
PSA: 78 Å2
MW: 475 g/mol
Figure 3. Additional properties of DORA 10.
Table 2. Pharmacokinetics of DORA 10 in rat and dog.
IVa
POb
Dose
Cl
Vdss
T1/2
(h)
Dose
AUC
(µM*h)
0.6
Tmax
(h)
Cmax
(µM)
0.2
F
Species (mg/kg) (mL/min/kg) (L/kg)
(mg/kg)
(%)
Rat
Dog
Rat
2
37
3
2.5
0.4
NA
1.1
2.4
NA
10
3c
3.0
0.6
0.8
8
0.125
NA
9.9
2.3
23
19
NA
30 c
5.5
2.5
a vehicle = 100% DMSO in rat and dog (n = 2); b dosed as the free base in 100% PEG200 (n = 2); c dosed as
free base in 20% VitE TPGS in water; satellite rats for sleep study pharmacokinetics (n = 3), PO in dog n =
2.
Figure 4. Sleep architecture effects of DORA 10 and DORA 1 in rat sleep dosed during
their active phase.a
11

Mean time in active wake, light sleep, SWS and REM sleep in rat monitored for two hours post dose. PO
administration of 30mg/kg of DORA 1, 30 mg/kg of DORA 10, or vehicle (20% Vitamin E TPGS)
treatment was administered in a balanced cross-over design such that each subject received drug and
vehicle (3 day treatment). Mean within-subject change relative to vehicle is shown. Data were analyzed
using within-subject ANOVA to determine main effects and one sample t-test to compare to vehicle (N =
12); (*p < 0.05, **p < 0.01, ***p < 0.001).
Comparative efficacy for DORAs 1 and 10 in our previously reported rat sleep
model is depicted in Figure 4. 16 Immediate, significant, and statistically similar
reductions of active wake and concomitant increases in slow wave and REM sleep were
observed for both compounds during the first two hours after oral administration of 30
mpk of each DORA (active-phase dosing). Pharmacokinetics in satellite rats determined
that DORA 10 achieved significant exposure in the sleep experiment with a Cmax of 2.5
µM, an AUC of 5.5 µM●h, and a Tmax of 0.8 h. These exposure levels indicate significant
OX2R occupancy during the course of the experiment as DORA 10 achieved 83%
occupancy in a humanized rat occupancy model at a plasma exposure of 1.0 µM.17 The
12

exposure / occupancy relationship for lead DORA 1 was very similar to that described
above with Cmax of 2.0 µM, an AUC of 4.5 µM●h in rat sleep studies, a Tmax of 1.3 h, and
90% occupancy at 0.35 µM. Hence, from a potency, pharmacokinetic, and efficacy
perspective, the 4-methoxy-5-trifluoromethylpyrimidine motif was a competent isosteric
replacement for 6-fluoroquinazoline substructure with the potential to significantly
reduce bioactivation potential.
In addition to assaying the purposefully designed isosteric replacements of DORA
1, our team also studied the regioisomeric SNAr products from Scheme 1. Previous SAR
as well as SAR established in Table 1 (see matched pairs 9 and 11; 10 and 12, Table 1)
demonstrated that the removal of the methyl group on the benzamide of suvorexant (2,
Figure 1) generally resulted in the reduction of OX1R binding and, in some cases,
functional potency. Hence, it was expected that compounds such as 14 would
demonstrate some level of reduced OX1R potency. Surprisingly, compound 14 had
significantly diminished OX1R binding potency (Ki = 1100 nM, Table 3) and was
essentially functionally inactive on OX1R. Compound 14 displayed moderate binding and
functional potency on OX2R which established this compound as a selective orexin 2
receptor antagonist (2-SORA) lead with selectivity over OX1R of greater than 139-fold.
2-SORAs have recently been of interest to further delineate receptor specific
pharmacology as well as therapeutic entities themselves.18 The 2-chloropyrimidine motif
embedded in compound 14 was a concern due to innate electrophilicity similar to the
DORA effort above, thus a small SAR effort was undertaken to remove this concern and
improve OX2R potency.
13

Replacement of the 2-chloropyrimidine with a 2-methylpyrimidine to remove the
nascent electophilic potential of 14 afforded 2-SORA 15 with diminished both OX2R
binding and functional potency.19 Replacement of the trifluoromethyl motif of 14 with a
methyl group increased OX2R potency in both matched pairs (14 and 16; 15 and 17),
however, 2-SORA 17 still was not in an OX2R potency range comparable to DORA 1
and suvorexant (2, Figure 1). Further modifying the 5-substituent of the pyrimidine to a
chlorine gave a marked OX2R potency increase for both 18 and 19, and 2-SORA 19
possessed OX2R functional potency (48 nM) similar to suvorexant (56 nM) with no
detectable antagonist activity on OX1R (> 200x selectivity). Due to its lack of potentially
overt electrophilicity and favorable potency and selectivity profile, 2-SORA 19 was
selected for additional profiling.
Table 3. Regioisomeric pyrimidines with 2-SORA profiles.a,b
Selectivity
(OX1R IC50
OX2R IC50)
OX2R Ki
(nM)a
OX1R Ki
(nM)a
OX2R IC50
(nM)a
OX1R IC50
(nM)a
Heterocycle
(compound #)
/
7.7
31
1100
4200
72
88
>10000
>10000
> 139
(14)
(15)
> 114
14

2.6
12
760
3600
850
42
82
25
48
2600
>10000
3200
62
(16)
(17)
(18)
(19)
> 122
128
1.1
3.6
1800
>10000
> 208
(a) See reference 5a for the details of these assays. All compounds listed were assayed as single
enantiomers; (b) All data reported as an average value from n > 2; for n > 2, standard deviation is < 40% in
all cases.
2-SORA 19 displayed properties consistent with CNS penetration such as high
permeability, low molecular weight, moderate PSA, and moderate log D (Figure 5). This
compound was not a substrate for rat or human Pgp and possessed acceptable free
fraction across species. Pharmacokinetic evaluation of 2-SORA 19 indicated moderate
clearance in dog and high clearance in rat with short half-lives in both species (Table 4).
Despite high clearance, the compound demonstrated moderate bioavailability in both rat
(%F = 35%) and dog (%F = 19) suggesting that evaluation of oral sleep efficacy would
be possible. Due to high clearance in rat for 2-SORA 19, high doses for in vivo
evaluation were anticipated. Thus, mouse sleep studies were selected to probe efficacy for
this 2-SORA lead to ease material requirements, and active-phase oral dosing at 300 mpk
to telemetrized mice elicited immediate and significant decreases in active wake with
concomitant increases in delta and REM sleep over the course of two hours (Figure 6).
While exposures were somewhat high in this experiment (Cmax = 18 µM),20 these findings
15

are very consistent with sleep architecture profiles for DORA 10, DORA 1, suvorexant,
and 2-SORAs MK-1064 and MK-3697.21
Cl
N
O
N
N
N
N
N
N
Me
2-SORA
Me
19
Plasma Protein Binding
Human: 95%
Rat: 88%
Dog: 95%
CNS Properties
Pgp ratio (BA/AB): 0.7 (h); 1.5 (r)
Papp: 34 cm * 10-6/s
HPLC log D: 2.8
PSA: 74 Å2
MW: 412 g/mol
Figure 5. Additional properties of 2-SORA 19.
Table 4. Pharmacokinetics of 2-SORA 19 in rat and dog.
IVa
POb
Dose
Cl
Vdss
T1/2
(h)
Dose
AUC
(µM*h)
1.2
Tmax
(h)
Cmax
(µM)
0.9
F
Species (mg/kg) (mL/min/kg) (L/kg)
(mg/kg)
(%)
Rat
Dog
2
118
15
7.0
0.8
NA
3.2
0.9
NA
10
3c
0.4
0.4
1.0
35
19
0.5
NA
1.8
1.3
Mouse c
NA
300
NA
18
NA
a vehicle = 100% DMSO in rat and dog (n = 2); b dosed as the hydrochloride salt in 100% PEG200 (n = 2); c
dosed as free base in 20% VitE TPGS in water; satellite rats for sleep study pharmacokinetics (n = 3), PO
in dog n = 2.
16

Figure 6. Sleep architecture effects of 2-SORA 19 in mouse sleep experiments dosed
during their active phase.a
Mean time in active wake, light sleep, SWS and REM sleep in wild type mice monitored for over time. PO
administration of 2-SORA 19 (300 mg/kg; open circles) or vehicle (closed circles; 20% Vitamin E TPGS)
treatment was administered in a balanced cross-over design such that each subject received drug and
vehicle (5 day treatment). Vertical grey bar indicates dose time relative to light/dark period (filled/open
horizontal bar). Significant differences are indicated by gray vertical lines, and black tic marks indicate
significance level (short, medium, long, p < 0.05, 0.01, 0.001).
In conclusion, we have demonstrated that substituted pyrimidines can serve as
competent isosteric replacements for the 6-fluoroquinzaoline motif with the added benefit
of lower bioactivation potential with DORA 10 representing a hallmark example. During
the course of synthesis, we serendipitously discovered that isomeric pyrimidines in the
diazepane amide series owned moderate OX2R potency and significant selectivity over
OX1R making them intriguing 2-SORA leads. Further exploration uncovered 2-SORA 19
17

as an orally efficacious 2-SORA in mouse sleep. Further biological studies on DORAs
and 2-SORAs presented herein will be published in due course.
Acknowledgments
We thank Dr. Charles W. Ross III and Joan S. Murphy for analytical studies in
support of this manuscript. We would like to thank Michael J. Bogusky for NMR support.
We would like to thank Joseph G. Bruno and Rodney A. Bednar for assay support.
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3 Suvorexant (Belsomra®) was approved by the FDA for the treatment of insomnia on August 13, 2014; see
http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm409950.htm
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C. J.; Coleman, P. J. Ann. Rep. Med. Chem. 2013, 48, 73-87; (k) Gatfield, J.; Brisbare-Roch, C.; Jenck, F.;
Boss, C. ChemMedChem 2010, 20, 1539-1542.
5 (a) Cox, C. D.; Breslin, M. J.; McGaughey, G. B.; Whitman, D. B.; Schreier, J. D.; Bogusky, M. J.;
Roecker, A. J.; Mercer, S. P.; Bednar, R. A.; Lemaire, W.; Bruno, J. G.; Reiss, D. R.; Harrell, C. M.;
Murphy, K. L.; Garson, S. L.; Doran, S. M.; Koblan, K. S.; Prueksaritanont, T.; Anderson, W. B.; Tang, C.;
Roller, S.; Cabalu, T. D.; Cui, D.; Ball, R. G.; Hartman, G. D.; Winrow, C. J.; Renger, J. J.; Coleman, P. J.
J. Med. Chem. 2010, 53, 5320 – 5332; (b) Winrow, C. J.; Gotter, A. L.; Cox, C. D.; Doran, S. M.;
18

Tannenbaum, P. L.; Breslin, M. J.; Garson, S. L.; Fox, S. V.; Harrell, C. M.; Stevens, J.; Reiss, D. R.; Cui,
D.; Coleman, P. J.; Renger, J. J. J. Neurogenetics 2011, 25, 52-61.
6 Compound 1 is also known as DORA 12 in reference 5a.
7
The reduction of bioactivation potential is a generally well accepted de-risking strategy in drug
development. For recent reviews, see: a) Stachulski, A. V.; Baillie, T. A.; Park, B. K.; Obach, R. S.; Dalvie,
D. K.; Williams, D. P.; Srivastava, A.; Regan, S. L.; Antoine, D. J.; Goldring, C. E. P; Chia, A. J. L.;
Kitteringham, N. R.; Randle, L. E.; Callan, H.; Castrejon, L.; Farrell, J.; Naisbitt, D. J.; Lennard, M. S.
Medicinal Res. Rev. 2013, 33, 985-1080; b) Stepan, A. F.; Walker, D. P.; Bauman, J.; Price, D. A.; Baillie,
T. A.; Kalgutkar, A. S.; Aleo, M. D. Chem. Res. Toxicol. 2011, 24, 1345-1410.
8 Whitman, D. B.; Cox, C. D.; Breslin, M. J.; Brashear, K. M.; Schreier, J. D.; Bogusky, M. J.; Bednar, R.
A.; Lemaire, W.; Bruno, J. G.; Hartman, G. D.; Reiss, D. R.; Harrell, C. M.; Kraus, R. L.; Li, Y.; Garson, S.
L.; Doran, S. M.; Preuksaritanont, T.; Li, C.; Winrow, C. J.; Koblan, K. S.; Renger, J. J.; Coleman, P. J.
ChemMedChem 2009, 4, 1069 - 1074.
9 Marugan, J. J.; Zheng, W.; Motabar, O.; Southall, N.; Goldin, E.; Westbroek, W.; Stubblefield, B. K.;
Sidransky, E.; Aungst, R. A.; Lea, W. A.; Simeonov, A.; Leister, W.; Austin, C. P. J. Med. Chem. 2011, 54,
1033.
10
Kath, J. C.; Richter, D. T.; Luzzio, M. J. Selective synthesis of CF3-substituted pyrimidines, WO
2005023780.
11 For additional synthetic details regarding the compounds in this manuscript, see: Bergman, J. M.; Breslin,
M. J.; Coleman, P. J.; Cox, C. D.; Mercer, S. P.; Roecker, A. J. Substituted diazepan compounds as orexin
receptor antagonists, WO 2008069997.
12 The lipophilic surface area for DORA 1 is 350 Å2. The isosteric designs represent less than a 10%
deviation from the lead compound.
13 For the details of these in vitro assays, see reference 5a.
14 For the details of the microsomal GSH trapping assay, see reference 5a.
15 Pgp and permeability were assayed as described in: (a) Hochman, J. H.; Yamazaki, M.; Ohe, T.; Lin, J. H.
Curr. Drug Metab. 2002, 3, 257-273; (b) Lin, J. H.; Yamazaki, M. Drug Metab. Rev. 2003, 35, 417-454.
16 For the details of rat and mouse sleep studies, please see reference 5b.
17 For the details of the humanized rat occupancy assay, see reference 5a.
18 (a) Roecker, A. J.; Mercer, S. P.; Schreier, J. D.; Cox, C. D.; Fraley, M. E.; Steen, J. T.; Lemaire, W.;
Bruno, J. G.; Harrell, C. M.; Garson, S. L.; Gotter, A. L.; Fox, S. V.; Stevens, J.; Tannenbaum, P. L.;
Prueksaritanont, T.; Cabalu, T. D.; Cui, D.; Stellabott, J.; Hartman, G. D.; Young, S. D.; Winrow, C. J.;
Renger, J. J.; Coleman, P. J. ChemMedChem 2014, 9, 312-322; (b) Mercer, S. P.; Roecker, A. J.; Garson, S.
L.; Reiss, D. R.; Harrell, C. M.; Murphy, K. L.; Bruno, J. G.; Bednar, R. A.; Lemaire, W.; Cui, D.; Cabalu,
T. D.; Tang, C.; Prueksaritanont, T.; Hartman, G. D.; Young, S. D.; Winrow, C. J.; Renger, J. J.; Coleman,
P. J. Bioorg. Med. Chem. Lett. 2013 23, 6620-6624; (c) Roecker, A. J.; Reger, T. S.; Mattern, M. C.;
Mercer, S. P.; Bergman, J. M.; Schreier, J. D.; Cube, R. V.; Cox, C. D.; Li, D.; Lemaire, W.; Bruno, J. G.;
Harrell, C. M.; Garson, S. L.; Gotter, A. L.; Fox, S. V.; Stevens, J.; Tannenbaum, P. L.; Prueksaritanont, T.;
Cabalu, T. D.; Cui, D.; Stellabott, J.; Hartman, G. D.; Young, S. D.; Winrow, C. J.; Renger, J. J.; Coleman,
P. J. Bioorg. Med. Chem. Lett. 2014, 24, 4884-4890; (d) Lebold, T. P.; Bonaventure, P.; Shireman, B. T.
Bioorg. Med. Chem. Lett. 2013, 23, 4761-4769; (e) Fujimoto, T.; Kunitomo, J.; Tomata, Y.; Nishiyama, K.;
Nakashima, M.; Hirozane, M.; Yohikubo, S.-I.; Hirai, K.; Marui, S. Bioorg. Med. Chem. Lett. 2011, 21,
19

6414-6416; (f) T. Fujimoto, Y. Tomata, J. Kunitomo, M. Hirozane, S. Marui, Bioorg. Med. Chem. Lett.
2011, 21, 6409-6413; (g) Betschart, C.; Hintermann, S.; Behnke, D.; Cotesta, S.; Fendt, M.; Gee, C. E.;
Jacobson, L. H.; Laue, G.; Ofner, S.; Chaudhari, V.; Badiger, S.; Pandit, C.; Wagner, J.; Hoyer, D. J. Med.
Chem. 2013, 56, 7590-7607.
19 The 2-methoxypyrimidine variant of 2-SORA 15 was synthesized and demonstrated an OX2R IC50 of
245 nM and selectivity over OX1R of 7-fold. This further highlights the stringent SAR around orexin
subtype selectivity.
20
While mouse plasma protein binding is unavailable for 2-SORA 19, it is anticipated that the free
concentration at Cmax is well below the OX1R IC50 in this experiment suggesting low OX1R blockade
during this mouse sleep study.
21 For medicinal chemistry details concerning MK-1064 and MK-3697, see references 15a and 15c.
20