Probing the cannabinoid CB1/CB2 receptor subtype selectivity limits of 1,2-diarylimidazole-4-carboxamides by fine-tuning their 5-substitution pattern

Article abstract of DOI:10.1016/j.bmcl.2010.03.068

The cannabinoid CB₁/CB₂ receptor subtype selectivity in the 1,2-diarylimidazole-4-carboxamide series was boosted by fine-tuning its 5-substitution pattern. The presence of the 5-methylsulfonyl group in 11 led to a greater than ～840-f

Full text of DOI:10.1016/j.bmcl.2010.03.068

Bioorganic & Medicinal Chemistry Letters 20 (2010) 2770–2775
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Probing the cannabinoid CB1/CB2 receptor subtype selectivity limits of
1,2-diarylimidazole-4-carboxamides by fine-tuning their 5-substitution pattern
*
Jos H. M. Lange , Martina A. W. van der Neut, Alice J. M. Borst, Mahmut Yildirim,
Herman H. van Stuivenberg, Bernard J. van Vliet, Chris G. Kruse
Solvay Pharmaceuticals, Research Laboratories, C. J. van Houtenlaan 36, 1381 CP Weesp, The Netherlands
a r t i c l e i n f o
a b s t r a c t
Article history:
The cannabinoid CB1/CB2 receptor subtype selectivity in the 1,2-diarylimidazole-4-carboxamide series
was boosted by fine-tuning its 5-substitution pattern. The presence of the 5-methylsulfonyl group in
11 led to a greater than ꢀ840-fold CB1/CB2 subtype selectivity. The compounds 10, 18 and 19 were found
more active than rimonabant (1) in a CB1-mediated rodent hypotension model after oral administration.
Our findings suggest a limited brain exposure of the P-glycoprotein substrates 11, 12 and 21.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 21 January 2010
Revised 16 March 2010
Accepted 16 March 2010
Available online 19 March 2010
Keywords:
Cannabinoid CB1 receptor
Site of metabolism prediction
Metasite
Rimonabant
Subtype selectivity
Polar surface area
Lipophilicity
P-Glycoprotein
Cannabinoids constitute an area of intensive research since the
endocannabinoid system plays an important role in many physio-
logical processes.1 Cannabinoid CB1 receptor antagonists showed
clinical efficacy in the treatment of obesity and improved cardio-
vascular and metabolic risk factors.2 They have in addition good
prospects in other therapeutic areas,3 including cognitive disor-
ders.4 Although the risk of psychiatric side-effects has terminated5
many development programs of CB1 receptor blockers such as 1,6
2,7 38 and 49,10 (Fig. 1) for obesity treatment, suggestions have been
made to focus on possible therapeutic applications in peripheral
pathologies11 and adapted clinical trials.12 Very recently, more po-
lar derivatives of 1 were reported13 which showed significantly de-
creased CNS/plasma ratios in combination with pronounced
weight reduction in obese mice. The majority of the reported14,15
CB1 receptor antagonists/inverse agonists can be described in
terms of a general pharmacophore model.16–20
1,2-Diarylimidazole-4-carboxylates resulted from scaffold hop-
ping, based on the 1,5-diarylpyrazole 1. Such imidazoles21–23
showed comparable CB1 antagonistic/inverse agonistic properties
as compared to their pyrazole counterparts. However, it was ob-
served that they were in general less CB1/CB2 receptor subtype
selective. For example, 5 and 6 exhibited ꢀ20–30-fold CB1/CB2
selectivity values, whereas in the same CB1 and CB2 receptor as-
says, 1 showed >60-fold CB1/CB2 selectivity (Table 1). This some-
what lower CB1/CB2 selectivity in the 1,2-diarylimidazole class
can be attributed to their higher CB2 receptor affinities. Recently,
we used this observation in the design of a novel imidazole class
as selective CB2 receptor antagonists.24
In considering options to designing agents that would poten-
tially have an improved CB1/CB2 selectivity profile relative to the
imidazoles 5 and 6, it was chosen to focus on their 5-substitution
since the 5-cyano-substituted 7 showed a slightly improved
(ꢀ53-fold) CB1/CB2 selectivity ratio as compared to 5 and 6.
Previously, we published an efficient regioselective lithiation25
reaction,21 enabling the efficient exploration of other substitu-
tions at the 5-position of the 1,2-diarylimidazole-4-carboxamide
class. First, a set of larger substituents (methylsulfanyl, ethyl-
sulfanyl, iodo) was chosen to investigate the potential steric im-
pact of substitution. Second, a set of more polar substituents
(methylsulfinyl, methylsulfonyl and hydroxymethyl) which all
contain at least one strongly electronegative oxygen atom were
selected in order to study in more detail the impact of electro-
negative substituents, including effects due to potential hydrogen
bonding. This led to the synthesis of the target compounds 8–17.
In addition, a smaller set of 4-substituted 1,5-diarylpyrazoles
18–22 was designed in order to compare the structure–activity
relationship (SAR) of the most selective 5-substituted-imida-
zoles with the corresponding 4-substituted 1,5-diarylpyrazole
pharmacophore.
* Corresponding author. Tel.: +31 (0)294 479731; fax: +31 (0)294 477138.
E-mail address: jos.lange@solvay.com (J.H.M. Lange).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.03.068

J. H. M. Lange et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2770–2775
2771
Cl
CF3
Cl
O
R
N
N
O
N
N
H
N
N
N
N
N
N
N
H
O
Cl
Cl
N
N
N
N
O
N
Cl
Cl
Cl
H
Cl
NH
N
Cl
N
Cl
5 R = CH3
S
O
N
NC
Cl
O
O
H
NH2
6 R = C2H5
7 R = CN
Otenabant (2)
Rimonabant (1)
Taranabant (3)
Ibipinabant (4)
Figure 1. Representative CB1 antagonists 1–4 progressed to clinical development and the preclinical imidazoles 5–7.
Table 1
Pharmacological in vitro results of compounds 1 and 5–21
Compound
Ki(CB1)a (nM)
pA2(CB1)b
Ki(CB2)c (nM)
CB1/CB2 ratiod
1
5
6
7
8
25 15 (11.5)6
30 1621
8.6 0.1
8.6 0.121
9.0 0.121
8.6 0.121
8.8 0.1
8.6 0.1
9.0 0.3
8.5 0.2
8.2 0.3
7.9 0.3
8.1 0.3
8.5 0.2
8.9 0.2
8.4 0.2
8.8 0.1
9.0 0.2
8.6 0.6
8.4 0.1
1580 150 (1640)6
608 16121
430 14121
1590 46721
1811 550
>1000
1072 278
>10,000
>1000
>1000
>1000
>1000
325 73
63 (143)
20
31
14 1221
30 621
53
10
51
5
7
181
>19
88
>840
>20
>77
>50
>112
27
221
211
62
14
20
9
10
11
12
13
14
15
16
17
18
19
20
21
12.2 1.6
11.9 4.9
49 14
12.9 3.2
20
7
8.9 4.3
12.0 5.1
34 14
3.0 0.8
13.0 3.6
7504 2496
634 204
804 222
371 27
27
20
6
9
398e
a
Displacement of specific CP-55,940 binding in CHO cells stably transfected with human CB1 receptor, expressed as Ki SEM (nM). The values represent the mean result
based on at least three independent experiments.
b
[3H]-Arachidonic acid release in CHO cells expressed as pA2 SEM values. The values represent the mean result based on at least three independent experiments.
Displacement of specific CP-55,940 binding in CHO cells stably transfected with human CB2 receptor, expressed as Ki SEM (nM). The values represent the mean result
c
based on three independent experiments, unless otherwise noted.
d
CB1/CB2 selectivity values are provided as single values instead of their ranges based on the underlying CB1 and CB2 affinity SEM values.
Result of duplicate measurement (individual values 398 and 398 nM).
e
Due to the presence of the metabolically vulnerable 4-meth-
ylsulfanyl substituent, compound 19 might be regarded as a meta-
bolically less stable analog of 1. This is of particular relevance since
it was reported that 1 had a very long terminal half-life in non-obese
subjects (6–9 days) and 16 days in obese subjects.26 Moreover, the
metabolic degradation of 1 is characterized by oxidation at its piper-
idine moiety27—to produce metabolites such as SR142923—and
amidohydrolysis. The latter process theoretically could lead to the
formation of the corresponding carboxylic acid metabolite
SR141715 and the mutagenic 1-aminopiperidine,28 although there
is no evidence that 1—or one of its metabolites—is carcinogenic.
Therefore, a metabolically less stable and structurally related
derivative of 1 with a retained cannabinoid CB1 activity and selec-
tivity profile would be of interest.
The synthesis of the target compounds 8–16 is depicted in
Scheme 1. The tert-butyl ester21 24 was lithiated with LDA in anhy-
drous THF, followed by the reaction with a number of electrophiles
RX as shown in Scheme 1 to give 25–27. The methylsulfonyl ana-
logue 28 was obtained from 27 using more than 2 mol equiv of m-
CPBAin74%yield. Themethylsulfoxide 29wasobtainedanalogously
from 27 using 1 mol equiv of m-CPBA. Acidic hydrolysis of the t-bu-
tyl ester moiety in 25–29 with TFA in the presence of a small amount
of triethylsilane in CH2Cl2 provided the carboxylic acids 30–34 in
high yields. These acids were amidated with 1-aminopiperidine in
the presence of a coupling reagent (HBTU) to yield the target com-
pounds 8–12, respectively. The chiral sulfoxide 12 in this series
was separated into its enantiomers (+)-13 and (ꢁ)-14 by using chiral
preparative HPLC. The acid 32 was amidated with 1-aminopyrrol-
idine and 1-amino-azepane in the presence HBTU to yield the target
compounds 15 and 16, respectively.
The synthesis of the target compound 17 is shown in Scheme 2.
The 5-bromomethyl substituted 3521 was converted under basic
conditions into 36, followed by coupling with 1-aminopiperidine
in the presence of HBTU and Hünig’s base.
The synthesis of the 3-substituted 1,5-diarylpyrazoles 18–21 is
depicted in Scheme 3. Initial attempts to couple the methylsulfanyl
group to the pyrazole nucleus analogously to the regioselective
lithiation method described hereinabove for the imidazoles
(Scheme 1) proved to be troublesome. Eventually, we succeeded
to perform a 4-bromo-lithium exchange of the carboxylic acid29
37 by applying excess n-butyllithium and convert it subsequently
into 38 by treatment with dimethyldisulfide. Compound 19 was
obtained by amidating 38 with 1-aminopiperidine in the presence
of HOAt/EDCI.
In the meantime our attention had shifted to an alternative route
wherein the methylsulfanylgroup is already present in the reagents
from which the pyrazole ring is formed6 via a cycloaromatization
reaction. This versatile synthetic approach to the pyrazole-based

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J. H. M. Lange et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2770–2775
O
O
O
O
Cl
Cl
N
N
Cl
Cl
OH
O-t-Bu
O-t-Bu
N
H
N
d
N
N
c
a, b
Cl
Cl
R
Cl
Cl
R
N
R
N
N
N
RX
Cl
Cl
Cl
Cl
a F(CH2)2I
b (SC2H5)2
c (SCH3)2
8 R = I
9 R = SC2H5
10 R = SCH3
11 R = SO2CH3
12 R = SOCH3
30 R = I
31 R = SC2H5
32 R = SCH3
33 R = SO2CH3
34 R = SOCH3
24
25 R = I
26 R = SC2H5
27 R = SCH3
28 R = SO2CH3
29 R = SOCH3
e
f
g
O
Cl
N
N
N
H
h
n
(+)-13 R = SOCH3
(-)- 14 R = SOCH3
Cl
SCH3
32
N
Cl
15 n = 1
16 n = 3
Scheme 1. Reagents and conditions: (a) LDA, anhydrous THF, ꢁ20 °C, 1 h; (b) RX, ꢁ40 °C?rt, 16 h (61–90%); (c) TFA, cat. Et3SiH, CH2Cl2, rt, 16 h (78%-quantitative);
(d) 1-aminopiperidine, HBTU, DIPEA, CH3CN, rt, 16 h (54–84%); (e) 2.2 mol equiv m-CPBA, CH2Cl2, rt, 16 h (89%); (f) 1 mol equiv m-CPBA, CH2Cl2, rt, 16 h (84%); (g) chiral
preparative HPLC separation, stationary phase: ChiralpakÒ AD 20
DIPEA, CH3CN, rt, 16 h (35/73%).
lm, mobile phase: 25% ethanol/heptane (25/75 (v/v); (h) 1-aminopyrrolidine or 1-amino-azepane, HBTU,
O
O
O
Cl
Cl
Cl
OH
OH
N
N
OEt
N
N
N
H
a
b
Br
Cl
Cl
Cl
OH
N
N
N
Cl
Cl
Cl
35
17
36
Scheme 2. Reagents and conditions: (a) 2 N NaOH, THF, reflux, 16 h (63%); (b) 1-aminopiperidine, HBTU, DIPEA, CH3CN, rt, 16 h (37%).
target compounds 18–22 is depicted in Scheme 3. The bromoaceto-
phenone congener 39 was converted to the corresponding meth-
ylsulfanyl analogue 40. Reaction of 40 with diethyloxalate under
basic conditions and subsequent treatment with 2,4-dichlorophen-
ylhydrazineꢂHCl led to the formation of the pyrazole ester 41 in a
modest yield. This ester was hydrolyzed with LiOH under basic con-
ditions to the corresponding lithium carboxylate which was con-
verted in situ—in the presence of the coupling reagent TBTU—with
a set of amines to the target compounds 18–20, respectively. The
sulfoxide 21 was obtained from 19 using 1 mol equiv of m-CPBA.
However, treatment of 19 with excess m-CPBA did not furnish the
correspondingsulfone22. Although22is anticipatedtobeaccessible
via oxidation of the ester 41 with excess m-CPBA -analogously to the
sequence 27?28?33?11 in the imidazole series (Scheme 1)—no
further attempts were undertaken to synthesize 22.
The pharmacological results of the compounds 1 and 5–21 are
given in Table 1. They were evaluated in vitro at the human CB1
and CB2 receptor, stably expressed into Chinese Hamster Ovary
(CHO) cells,9 utilizing radioligand binding studies (displacement
of the specific binding of [3H]-CP-55,940). CB1 receptor antago-
nism9 was measured using a CP-55,940 induced arachidonic acid
release functional assay, using the same recombinant cell line.
The known21 imidazoles 5–7 showed ꢀ20–50-fold CB1/CB2
receptor subtype selectivity values which were somewhat lower
as compared to the pyrazole 1. Introduction of larger 5-substitu-
ents without strongly electronegative atoms (iodo (8), ethylsulfa-
nyl (9) and methylsulfanyl (10)) at the imidazole core in all three
cases led to >1000 nM CB2 receptor affinity values. For both 8
and 10 high CB1 receptor affinities were observed (Table 1), there-
by resulting into increased CB1/CB2 receptor subtype selectivity
values, whereas in 9 the larger ethylsulfanyl substituent led to a
decrease in CB1 receptor affinity (51 nM).
Since the observed steric impact on CB1/CB2 receptor subtype
selectivity apparently is relatively low, more polar substituents
(methylsulfonyl (11), methylsulfinyl (12) and hydroxymethyl
(17)) were incorporated. Surprisingly, compound 11 turned out
to be very CB1/CB2 receptor selective (>ꢀ840-fold). A shift to the
sulfinyl moiety (12) led to a decrease in CB1 receptor affinity. The
enantiopure dextrorotatory 13 showed a somewhat higher CB1
receptor affinity than its levorotatory counterpart 14, thereby indi-
cating that these chiral ligands bind with a relatively low degree of
stereoselectivity at the CB1 receptor. The presence of the polar
hydroxymethyl group in 17 also led to a high degree of CB1/CB2
receptor selectivity (ꢀ221-fold). These findings revealed that the
presence of one or two electronegative oxygen atoms in the imid-
azole 5-substituent can lead to lower CB2 receptor affinities, there-
by enhancing the resulting CB1/CB2 receptor selectivity, provided
that the CB1 receptor affinity is retained, such as in 11. Apparently,
the CB2 receptor cannot easily accommodate such a polar substitu-
ent at this specific position of the imidazole moiety. The effect of
ring size on the SAR in this series was also studied (10 vs 15 and
16). The pyrrolidinyl analogue 15 was found somewhat more

J. H. M. Lange et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2770–2775
Table 2
2773
O
O
Cl
Cl
In vivo pharmacological data and physicochemical parameters of compounds 1,
10–12, 18, 19 and 21
OH
OH
N
N
c
a,b
Cl
N
Cl
19
N
Compound Hypotension rat,a ID50 PGPb
cPSAc A log P Log PHPLC
d
S
Br
1
10
11
12
18
19
21
3.2
1.9
29
>30
1.9
1.5
>30
1.2 0.1 50
1.4 0.1 75
6.0 1.3 93
6.6
6.3
5.3
5.2
6.2
6.7
5.6
5.4
4.8
3.5
3.7
4.7
5.1
3.7
7.7e
86
75
Cl
Cl
n. d.f
37
38
1.5 0.1 75
8.0 0.8 86
O
O
Cl
Antagonism of CB agonist (CP-55,940) induced hypotension9 (anaesthetized
rat), expressed as ID50 (mg/kg, po administration).
a
Cl
R
OEt
N
N
N
N
H
n
O
Cl
N
b
Cl
N
P-Glycoprotein-based membrane transport factor, expressed as the ratio of the
S
S
bottom to top transport and top to bottom transport.9
g,h
e,f
Calculated polar surface area (Å2).
c
d
Experimental log P value determined by a validated RP-HPLC method, deter-
mined at pH 7.9
Cl
Cl
e
Cl
Result of duplicate measurement (individual values 7.7 and 8.3).
n. d. = not determined.
f
39 R = Br
40 R = SCH3
41
18 n = 1
19 n = 2
20 n = 3
d
In order to support whether pharmacokinetic properties are
responsible for this difference in the observed in vivo oral poten-
cies, we determined their propensity to undergo P-glycoprotein-
mediated transport, calculated their polar surface area (PSA) and
lipophilicity (A log P).
O
O
Cl
Cl
N
H
N
N N
N
N
i
j
H
Cl
Cl
N
N
19
19
S
S
O
O
O
The P-glycoprotein pump is known to lower the CNS levels of
certain compounds by actively extruding them from the brain.30
Therefore, the affinities of 1, 10–12, 18, 19 and 21 for this efflux
pump were examined. Compounds 1, 10 and 19 were shown to
be devoid of significant P-glycoprotein pump substrate affinity.
However, the compounds 11 and 21—possessing the additional
electronegative oxygen-atom containing substituent—were P-gly-
coprotein substrates (Table 2). As a consequence, 11, 12 and 21
are expected to attain limited brain/plasma ratios. It is of interest
to note from a SAR viewpoint that relatively small modifications
of the 5-methylsulfanyl substituent in 10 which is no P-glycopro-
tein substrate, led to the P-glycoprotein substrates 11 and 12,
respectively. Analogously, replacement of the methylsulfanyl
group in 19 by the more polar methylsulfinyl moiety gave rise to
the P-glycoprotein substrate 21.
Cl
Cl
21
22
Scheme 3. Reagents and conditions: (a) excess n-BuLi, anhydrous THF, ꢁ78 °C,
15 min; (b) (CH3S)2, THF, ꢁ78 °C, 16 h; (c) 1-aminopiperidine, HOAt, EDCI, CH2Cl2,
rt, 16 h (10%); (d) NaSCH3, MeOH, rt, 2 h (32%); (e) diethyloxalate, NaOEt, EtOH, rt,
20 h; (f) 2,4-dichlorophenylhydrazineꢂHCl, AcOH, 60 °C, 3 h (27%); (g) LiOH, H2O,
THF, 35 °C, 20 h; (h) amine, TBTU, Et3N, DMF, 50 °C, 18 h (50–58%); (i) 1.4 mol equiv
m-CPBA, CH2Cl2, rt, 20 h (21%); (j) excess m-CPBA, CH2Cl2, rt, 100 h.
CB1/CB2 selective than 10 and much more selective than 16.
Apparently, an increase in ring size leads to a decreased CB1/CB2
selectivity in this series.
The SAR in the related pyrazole series showed the same trend as
compared to the imidazoles. The CB1 and CB2 receptor affinities and
the functional CB1 antagonistic potencies of 10 and 19 are in the
same order of magnitude. Comparisonof the sulfoxides 12 and 21re-
vealed that the pyrazole 21 elicited higher CB1 and CB2 receptor
affinities. Interestingly, in the pyrazole series the pyrrolidinyl-
substituted 18 behaved as a very strong CB1 receptor binder
(3 nM), which in addition gave a high CB1/CB2 selectivity value
(ꢀ211-fold). The effect on the CB1/CB2 selectivity by increasing the
ring size in the 1,5-diarylpyrazole series from five to seven (18–20)
was in line with the observed order in the 1,2-diarylimidazole series
(10, 15 and 16), respectively.
PSA values have been shown to closely correlate with drug trans-
port properties, such as intestinal absorption or blood–brain barrier
(BBB) penetration. Compounds having a PSA value <65 Å2 generally
readily cross the BBB, whereas compounds above a threshold of
90 Å2 been shown to have a low probability to cross the BBB.31–33
It should be noted that 11, 12 and 21 have relatively high calculated
PSA values, which are nearby or higher than this threshold of 90 Å.2
The highly CB1/CB2 selective 11 might be considered as a prototypic
pharmacologicaltooltostudy peripherally-mediatedCB1 antagonis-
tic effects,13 because it is a P-glycoprotein substrate, in combination
with a relatively high calculated PSA value. It should be born in mind
that due to the very high abundance of CB1 receptors in the brain34 it
would a priori be expected that only CB1 receptor antagonists with a
very low CNS exposure will be devoid of centrally mediated side-
effects.
The compounds 5–21 elicited significant functional CB1 antago-
nistic potencies. In particular the compounds 10 and 19 behaved as
potent CB1 receptor antagonists (pA2 = 9.0).
The in vivo activities of a smaller set of compounds 1, 10–12,
18, 19 and 21 after oral administration were investigated in our
CB1 agonist-induced anaesthetized rat hypotension model.9
Some of the novel compounds were very potent in this mecha-
nistic model (Table 2). It is interesting to note that three of our no-
vel compounds (the imidazole 10 and the pyrazoles 18 and 19)
were found more potent in this model than rimonabant (1)9
(ID50 = 3.2 mg/kg). The corresponding sulfoxides and sulfones were
less active in vivo although these compounds also showed high
activities in vitro.
Log P is an important Lipinski parameter.35–37 The values for the
selected compounds were calculated (A Log P)38 and in parallel
determined by applying our RP-HPLC method at neutral pH.9 Typ-
ically, a 1–2 log unit distance was observed between the calculated
A log P and our experimentally determined values throughout the
whole compound range. This can be rationalized by invoking an
intramolecular hydrogen bond potential39 between the N–H of
the hydrazide and the N2 atom of the pyrazole ring, c.q. the N3
atom of the imidazole moiety.40 In line with expectation, the sulf-
oxides and sulfones showed significantly lower log P values than

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J. H. M. Lange et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2770–2775
References and notes
1. Lambert, D. M.; Fowler, M. J. Med. Chem. 2005, 48, 5059.
2. van Gaal, L. F.; Rissanen, A. M.; Scheen, A. J.; Ziegler, O.; Roessner, S. Lancet
2005, 365, 1389.
3. Lange, J. H. M.; Kruse, C. G. Chem. Rec. 2008, 8, 156.
4. De Bruin, N. M. W. J.; Prickaerts, J.; Lange, J. H. M.; Akkerman, S.;
Andriambeloson, E.; de Haan, M.; Wijnen, J.; van Drimmelen, M.; Hissink, E.;
Heijink, L.; Kruse, C. G. Neurobiol. Learn. Memory, in press. doi:10.1016/
j.nlm.2010.01.010.
5. Jones, D. Nat. Rev. Drug Discovery 2008, 7, 961.
6. Lan, R.; Liu, Q.; Fan, P.; Lin, S.; Fernando, S. R.; McCallion, D.; Pertwee, R.;
Makriyannis, A. J. Med. Chem. 1999, 42, 769.
7. Griffith, D. A.; Hadcock, J. R.; Black, S. C.; Iredale, P. A.; Carpino, P. A.; DaSilva-
Jardine, P.; Day, R.; DiBrino, J.; Dow, R. L.; Landis, M. S.; O’Connor, R. E.; Scott, D.
O. J. Med. Chem. 2009, 52, 234.
8. Lin, L. S.; Lanza, T. J.; Jewell, J. P.; Liu, P.; Shah, S. K.; Qi, H.; Tong, X.; Wang, J.;
Xu, S. S.; Fong, T. M.; Shen, C.-P.; Lao, J.; Xiao, J. C.; Shearman, L. P.; Stribling, D.
S.; Rosko, K.; Strack, A.; Marsh, D. J.; Feng, Y.; Kumar, S.; Samuel, K.; Yin, W.;
van der Ploeg, L. H. T.; Goulet, M. T.; Hagmann, W. K. J. Med. Chem. 2006, 49,
7584.
9. Lange, J. H. M.; Coolen, H. K. A. C.; van Stuivenberg, H. H.; Dijksman, J. A. R.;
Herremans, A. H. J.; Ronken, E.; Keizer, H. G.; Tipker, K.; McCreary, A. C.;
Veerman, W.; Wals, H. C.; Stork, B.; Verveer, P. C.; den Hartog, A. P.; de Jong, N.
M. J.; Adolfs, T. J. P.; Hoogendoorn, J.; Kruse, C. G. J. Med. Chem. 2004, 47, 627.
10. Lange, J. H. M.; van Stuivenberg, H. H.; Veerman, W.; Wals, H. C.; Stork, B.;
Coolen, H. K. A. C.; McCreary, A. C.; Adolfs, T. J. P.; Kruse, C. G. Bioorg. Med. Chem.
Lett. 2005, 15, 4794.
11. Bifulco, M.; Pisanti, S. Nat. Rev. Drug Discovery 2009, 8, 594.
12. Le Foll, B.; Gorelick, D. A.; Goldberg, S. R. Psychopharmacology 2009, 205, 171.
13. Receveur, J.-M.; Murray, A.; Linget, J.-M.; NØrregaard, P. K.; Cooper, M.;
Bjurling, E.; Nielsen, P. A.; Högberg, T. Bioorg. Med. Chem. Lett. 2010, 20, 453.
14. Jagerovic, N.; Fernandez-Fernandez, C.; Goya, P. Curr. Top. Med. Chem. 2008, 8,
205.
Figure 2. MetaSite™ prediction of the sites of metabolism of 19.
the corresponding sulfanes but their values remain in a favorable
range to enable efficient cell membrane passage.
The involvement of the central nervous system in the complex
effects of cannabinoids on blood pressure has been studied previ-
ously. Initially, it was found that blood pressure significantly de-
creased after central injection of
D
9-tetrahydrocannabinol in
anaesthetized animals.41,42 More recently, it has also been reported
that hypotension is caused by activation of peripheral cannabinoid
CB1 receptors.43 These diverse findings suggest that the observed
effects in our CB1 agonist-induced anaesthetized rat hypotension
model9 can be either centrally or peripherally mediated or by a
combination of both. Interestingly, 11, 12 and 21 all were found
poorly orally active in our rodent hypotension assay, whereas 1,
10 and 19 all elicited potent activity therein. The observed lower
activity of 11, 12 and 21 in our hypotension model may be either
attributed to a lower CNS exposure of these compounds or to their
lower oral bioavailability. Determination of their CNS and plasma
levels after oral administration will be mandatory to resolve this
issue.
15. Lee, H.-K.; Choi, E. B.; Pak, C. S. Curr. Top. Med. Chem. 2009, 9, 482.
16. Reggio, P. H. Curr. Pharm. Des. 2003, 9, 1607.
17. Lange, J. H. M.; Kruse, C. G. Curr. Opin. Drug Discovery Dev. 2004, 7, 498.
18. Lange, J. H. M.; Kruse, C. G. Drug Discovery Today 2005, 10, 693.
19. Wang, H.; Duffy, R. A.; Boykow, G. C.; Chackalamannil, S.; Madison, V. S. J. Med.
Chem. 2008, 51, 2439.
20. Foloppe, N.; Benwell, K.; Brooks, T. D.; Kennett, G.; Knight, A. R.; Misra, A.;
Monck, N. J. T. Bioorg. Med. Chem. Lett. 2009, 19, 4183.
21. Lange, J. H. M.; van Stuivenberg, H. H.; Coolen, H. K. A. C.; Adolfs, T. J. P.;
McCreary, A. C.; Keizer, H. G.; Wals, H. C.; Veerman, W.; Borst, A. J. M.; De Looff,
W.; Verveer, P. C.; Kruse, C. G. J. Med. Chem. 2005, 48, 1823.
22. Dyck, B.; Goodfellow, V. S.; Phillips, T.; Grey, J.; Haddach, M.; Rowbottom, M.;
Naeve, G. S.; Brown, B.; Saunders, J. Bioorg. Med. Chem. Lett. 2004, 14, 1151.
23. Smith, R. A.; Fathi, Z.; Achebe, F.; Akuche, C.; Brown, S. E.; Choi, S.; Fan, J.;
Jenkins, S.; Kluender, H. C. E.; Konkar, A.; Lavoie, R.; Mays, R.; Natoli, J.;
O’Connor, S. J.; Ortiz, A. A.; Su, N.; Taing, C.; Tomlinson, S.; Tritto, T.; Wang, G.;
Wirtz, S. N.; Wong, W.; Yang, X. F.; Ying, S.; Zhang, Z. Bioorg. Med. Chem. Lett.
2007, 17, 2706.
As postulated above, the presence of the metabolically vulnera-
ble methylsulfanyl moiety in 19 was anticipated be of interest with
respect to its cytochrome P450 Phase I metabolism.44
24. Lange, J. H. M.; van der Neut, M. A. W.; Wals, H. C.; Kuil, G. D.; Borst, A. J. M.;
Mulder, A.; den Hartog, A. P.; Zilaout, H.; Goutier, W.; van Stuivenberg, H. H.;
van Vliet, B. Bioorg. Med. Chem. Lett. 2010, 20, 1084.
Cruciani’s Metasite™ is a computational tool45 to predict the
preferred sites of metabolism related to cytochrome-mediated
reactions in Phase I metabolism. Metasite™ was applied46 to pre-
dict the primary sites of metabolism of 19. In accordance with
our expectations, 19 was predicted to indeed metabolize primarily
via oxidation at its sulfur atom (as represented by the large green
bar in Fig. 2), but also to some extend by oxidation at the methyl
part of its methylsulfanyl group, its piperidinyl group and the
ortho-positions of its 4-chlorophenyl group.
25. Snieckus, V. Chem. Rev. 1990, 90, 879.
26. Gadde, K. M.; Allison, D. B. Circulation 2006, 114, 974.
27. Zhang, Q.; Ma, P.; Wang, W.; Cole, R. B.; Wang, G. Drug Metab. Dispos. 2005, 33,
508.
28. European Medicines Agency Report on Acomplia: http://www.ema.europa.eu/
humandocs/PDFs/EPAR/acomplia/H-666-en6.pdf, p 10).
29. Katoch-Rouse, R.; Pavlova, O. A.; Caulder, T.; Hoffman, A. F.; Mukhin, A. G.;
Horti, A. G. J. Med. Chem. 2003, 46, 642.
30. Schinkel, A. H.; Wagenaar, E.; van Deemter, L.; Mol, C. A. A. M.; Borst, P. J. Clin.
Invest. 1995, 96, 1698.
31. Kelder, J.; Grootenhuis, P. D. J.; Bayada, D. M.; Delbressine, L. P. C.; Ploemen, J.-
P. Pharm. Res. 1999, 16, 1514.
In conclusion, the CB1/CB2 receptor subtype selectivity in the
1,2-diarylimidazole-4-carboxamide series47 was boosted by fine-
tuning their 5-substitution pattern. The presence of the methylsul-
fonyl group in 11 led to a greater than ꢀ840-fold CB1/CB2 subtype
selectivity. The methylsulfanyl substituted pyrazoles 18 and 19
showed potent oral activities in vivo. Our findings suggest a limited
brain exposure of the more polar compounds 11, 12 and 21, which
all were found to act as P-glycoprotein substrates.
32. Clark, D. E. Drug Discovery Today 2003, 8, 927.
33. Bendels, S.; Kansy, M.; Wagner, B.; Huwyler, J. Eur. J. Med. Chem. 2008, 43, 1581.
34. Irving, A. J.; McDonald, N. A.; Harkany, T. Cannabinoids and the brain; Köfalvi, A.,
Ed.; Springer US; New York, 2008, p 59.
35. Lipinski, C. A.; Lombardo, F.; Dominy, B. W.; Feeney, P. J. Adv. Drug Delivery Rev.
1997, 23, 3.
36. Leeson, P. D.; Springthorpe, B. Nat. Rev. Drug Discovery 2007, 6, 881.
37. Waring, M. J. Expert Opin. Drug Discovery 2010, 5, 235.
38. Ghose, A. K.; Viswanadhan, V. N.; Wendoloski, J. J. J. Phys. Chem. A 1998, 102,
3762.
39. Lange, J. H. M.; van der Neut, M. A. W.; den Hartog, A. P.; Wals, H. C.;
Hoogendoorn, J.; van Stuivenberg, H. H.; van Vliet, B. J.; Kruse, C. G. Bioorg. Med.
Chem. Lett. 2010, 20, 1752.
Acknowledgments
40. Dow, R. L.; Hadcock, J. R.; Scott, D. O.; Schneider, S. R.; Paight, E. S.; Iredale, P. A.;
Carpino, P. A.; Griffith, D. A.; Hammond, M.; DaSilva-Jardine, P. Bioorg. Med.
Chem. Lett. 2009, 19, 5351.
41. Cavero, I.; Solomon, T.; Buckley, J. P.; Jandhyala, B. S. Res. Commun. Chem.
Pathol. Pharmacol. 1973, 6, 527.
Jan Jeronimus and Hugo Morren are gratefully acknowledged
for supply of the analytical data. Syncom BV (The Netherlands) is
acknowledged for synthetic support.

J. H. M. Lange et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2770–2775
2775
42. Vollmer, R. R.; Cavero, I.; Ertel, R. J.; Solomon, T. A.; Buckley, J. P. J. Pharm.
Pharmacol. 1974, 26, 186.
43. Wagner, J. A.; Jarai, Z.; Batkai, S.; Kunos, G. Eur. J. Pharmacol. 2001, 423, 203.
44. Brown, C. M.; Reisfeld, B.; Mayeno, A. N. Drug Metab. Rev. 2008, 40, 1.
45. Cruciani, G.; Carosati, E.; De Boeck, B.; Ethirajulu, K.; Mackie, C.; Howe, T.;
Vianello, R. J. Med. Chem. 2005, 48, 6970.
46. Metasite™ version 3.0.6 (2009) was used. Validation of the method by the
originators has shown that the primary site of metabolism was found in the top
three Metasite predictions for more than 85% of the cases.
chromatography (silicagel, EtOAc) and triturated with MTBE to give 11 in 84%
yield, mp 181–185 °C (dec); 1H NMR (600 MHz, DMSO-d6) d 1.35–1.41 (m, 2H),
1.61–1.66 (m, 4H), 2.80–2.84 (m, 4H), 3.52 (s, 3H), 7.38 (d, J = 8 Hz, 2H), 7.42
(dd, J = 8 and 2 Hz, 1H), 7.46 (d, J = 8 Hz, 2H), 7.57 (d, J = 2 Hz, 1H), 7.62 (d,
J = 8 Hz, 1H), 9.40 (s, 1H); HRMS exact mass calcd for C22H22Cl3N4O3S 527.0478
[MH]+, found m/z 527.0469. Compound 13: mp 243–245 °C; 1H NMR (400 MHz,
CDCl3) d 1.40–1.48 (m, 2H), 1.72–1.80 (m, 4H), 2.82–2.90 (m, 4H), 3.10 (s, 3H),
7.18–7.27 (m, 4H), 7.29 (br d, J = 8 Hz, 2H), 7.38 (d, J = 2 Hz, 1H), 7.92 (br s, 1H);
ESI+-MS exact mass calcd for C22H2235Cl3N4O2S m/z, 511.0529 ([MH+]), found:
47. Yields refer to isolated pure products unless otherwise noted and were not
maximized. Selected data for target compounds 8, 10, 11, 13, 14, 17, 19 and 21,
synthesis of key intermediate 41 and selected data for the intermediates 25, 30,
32 and 36. Compound 8: mp 196–201 °C (dec); 1H NMR (600 MHz, DMSO-d6) d
1.34–1.40 (m, 2H), 1.60–1.66 (m, 4H), 2.77–2.82 (m, 4H), 7.32 (d, J = 8 Hz, 2H),
7.41 (dd, J = 8 and 2 Hz, 1H), 7.47 (d, J = 8 Hz, 2H), 7.53 (d, J = 2 Hz, 1H), 7.63 (d,
J = 8 Hz, 1H), 8.90 (s, 1H); 13C NMR (150 MHz, DMSO-d6) d 23.32, 25.68, 55.90,
82.22, 127.46, 128.69, 129.07, 129.42, 130.59, 134.55, 134.73, 134.82, 135.30,
136.12, 136.47, 146.15, 158.81; HRMS exact mass calcd for C21H19Cl3IN4O m/z
574.9669 [MH]+, found 574.9694. Anal. Calcd for C21H18Cl3IN4Oꢂ1/2H2O: C,
43.14; H, 3.28; N, 9.58. Found: C, 43.06; H, 2.94; N, 9.51. Compound 10: mp
170 °C (dec); 1H NMR (600 MHz, DMSO-d6) d 1.35–1.42 (m, 2H), 1.62–1.67 (m,
4H), 2.35 (s, 3H), 2.80–2.84 (m, 4H), 7.29 (d, J = 8 Hz, 2H), 7.42 (dd, J = 8 and
2 Hz, 1H), 7.45 (d, J = 8 Hz, 2H), 7.52 (d, J = 2 Hz, 1H), 7.62 (d, J = 8 Hz, 1H), 8.90
(s, 1H); 13C NMR (150 MHz, DMSO-d6) d 19.26, 23.32, 25.63, 55.98, 127.52,
128.61, 129.14, 129.23, 129.86, 130.12, 130.18, 133.86, 134.45, 134.66, 136.01,
137.12, 144.04, 158.98; HRMS exact mass calcd for C22H22Cl3N4OS m/z
511.0513; ½a 2D5
ꢃ
= +23 c 0.94 (g/100 ml, CH3OH): ee = 99.5%. Compound 14: mp
242–244 °C; 1H NMR (400 MHz, CDCl3) d 1.40–1.48 (m, 2H), 1.72–1.80 (m, 4H),
2.82–2.90 (m, 4H), 3.10 (s, 3H), 7.18–7.27 (m, 4H), 7.29 (br d, J = 8 Hz, 2H), 7.38
(d, J = 2 Hz, 1H), 7.92 (br s, 1H); ESI+-MS exact mass calcd for C22H2235Cl3N4O2S
m/z, 511.0529 ([MH+]), found: 511.0540; ½a 2D5
= ꢁ19, c 0.94 (g/100 ml, CH3OH):
ꢃ
ee = 97.2%. Compound 17: mp 212–214 °C; 1H NMR (600 MHz, DMSO-d6) d
1.34–1.41 (m, 2H), 1.61–1.66 (m, 4H), 2.80–2.84 (m, 4H), 4.61–4.64 (m, 2H),
5.43–5.47 (m, 1H), 7.34 (d, J = 8 Hz, 2H), 7.41–7.46 (m, 3H), 7.52 (d, J = 2 Hz,
1H), 7.61 (d, J = 8 Hz, 1H), 9.00 (s, 1H); 13C NMR (150 MHz, DMSO-d6) d 23.29,
25.63, 52.57, 55.95, 127.53, 128.61, 129.13, 129.40, 129.58, 131.88, 133.78,
134.29, 134.69, 134.73, 135.88, 137.41, 142.66, 160.46; HRMS exact mass calcd
for C22H22Cl3N4O2 m/z 479.0808 [M+H]+, found: 479.0832. Anal. Calcd for
C22H21Cl3N4O2ꢂ1/2H2O: C, 54.06; H, 4.54; N, 11.46. Found: C, 54.14; H, 4.25; N,
11.49. Compound 19: mp 110–112 °C. 1H NMR (CDCl3, 400 MHz) d 1.41–1.49
(m, 2H), 1.72–1.81 (m, 4H), 2.40 (s, 3H), 2.83–2.95 (m, 4H), 7.15 (br d, J = 8 Hz,
2H), 7.28–7.35 (m, 4H), 7.42 (br d, J = 2 Hz, 1H), 7.94 (br s, 1H); 13C NMR
(CDCl3, 100 MHz) d 20.03, 23.32, 25.29, 57.02, 113.66, 126.20, 127.99, 128.74,
130.36, 130.48, 131.24, 132.85, 135.59, 135.64, 136.41, 147.08, 147.30, 158.62;
ESI+-MS exact mass calcd for C22H2235Cl3N4OS m/z, 495.0580 ([MH+]), found:
495.058. Compound 21: 1H NMR (CDCl3, 400 MHz) d 1.41–1.49 (m, 2H), 1.72–
1.81 (m, 4H), 2.84–2.96 (m, 4H), 3.11 (s, 3H), 7.15 (br d, J = 8 Hz, 2H), 7.27–7.32
(m, 4H), 7.43 (br s, 1H), 8.70 (br s, 1H); 13C NMR (CDCl3, 100 MHz) d 23.28,
25.22, 41.84, 56.97, 122.91, 124.67, 128.03, 128.66, 130.41, 130.63, 131.60,
133.01, 134.54, 136.51, 136.98, 144.62, 144.85, 157.60; ESI+-MS exact mass
calcd for C22H2235Cl3N4O2S m/z, 511.0529 ([MH+]), found: 511.0550. Synthesis
of 41: To a magnetically stirred solution of 39 (16.8 g, 72 mmol) in CH3OH
(200 ml) was added NaSCH3 (5.23 g, 72 mmol) to give an exothermic reaction.
The resulting mixture was reacted for 2 h at rt, concentrated and suspended in
CH2Cl2 (150 ml) and washed with water, dried over MgSO4, filtered and
concentrated to give 40 (5.1 g, 32% yield). 1H NMR (CDCl3, 400 MHz) d 2.13 (s,
3H), 3.72 (s, 2H), 7.44 (br d, J = 8 Hz, 2H), 7.92 (br d, J = 8 Hz, 2H). Sodium metal
(2 g, 87 mmol) was slowly dissolved in EtOH (80 ml). The resulting solution
was added to a magnetically stirred solution of diethyl oxalate (6 g, 41 mmol)
and 40 (8.0 g, 40 mmol). The resulting mixture was reacted for 20 h at rt and
subsequently poured into HCl (200 ml, 1 N). The resulting mixture was
extracted twice with MTBE (200 ml), dried over MgSO4, filtered and
concentrated. The resulting residue was dissolved in AcOH (200 ml), 2,4-
dichlorophenylhydrazineꢂHCl (8.6 g, 40 mmol) was added and the resulting
mixture was heated at 60 °C for 3 h. The reaction mixture was allowed to attain
rt, concentrated to ꢀ50 ml and poured into water (200 ml), followed by
extraction with MTBE (3 ꢄ 150 ml). The combined organic layers were washed
with 5% aqueous NaHCO3, dried over MgSO4, filtered and concentrated.
Purification by column chromatography (silica gel, heptane/EtOAc = 90/10 (v/
v)) gave 41 (4.9 g, 27% yield). 1H NMR (CDCl3, 300 MHz) d 1.44 (t, J = 7 Hz, 3H),
2.32 (s, 3H), 4.46 (q, J = 7, 2H), 7.10–7.45 (m, 7H). Compound 25: mp 234–
237 °C; 1H NMR (200 MHz, CDCl3) d 1.65 (s, 9H), 7.08 (br d, J ꢀ 8 Hz, 2H), 7.20–
7.45 (m, 5H). Compound 30: mp 182–186 °C; 1H NMR (200 MHz, CDCl3) d 3.50
(br s, 1H), 7.12 (br d, J ꢀ 8 Hz, 2H), 7.22–7.45 (m, 5H). Compound 32: 1H NMR
(400 MHz, CDCl3) d 2.41 (s, 3H), 3.60 (br s, 1H), 7.08 (br d, J ꢀ 8 Hz, 2H), 7.26
(dd, J = 8 and 2 Hz, 1H), 7.30 (d, J = 8 Hz, 1H), 7.35 (d, J = 2 Hz, 1H), 7.37 (br d, J
ꢀ 8 Hz, 2H). Compound 36: mp 138 °C; 1H NMR (200 MHz, CDCl3): d 3.05 (br s,
1H), 4.67 (s, 2H), 7.05–7.42 (m, 7H).
495.0580 [MH]+, found 495.0592. Synthesis of compound 11: To
a cooled
(ꢁ20 °C) and magnetically stirred solution of 24 (10.59 g, 25.0 mmol), in
anhydrous THF (100 ml) was added LDA (15.0 ml, 2 M solution in heptane/THF,
30.0 mmol) and the resulting mixture was stirred for 1 h under N2. A solution
of (CH3S)2 (2.7 ml, 30.0 mmol) in anhydrous THF (20 ml) was added and the
resulting solution was successively stirred at ꢁ40 °C for 1 h, allowed to attain
rt and stirred for another 16 h. A saturated aqueous NH4Cl solution (250 ml)
was added and the resulting solution was extracted twice with EtOAc. The
combined organic layers were washed with water, dried over MgSO4, filtered
and concentrated to give 27 in 90% yield as an oil which slowly solidified; 1H
NMR (200 MHz, CDCl3) d 1.66 (s, 9H), 2.28 (s, 3H), 7.05 (br d, J ꢀ 8 Hz, 2H), 7.25
(dd, J = 8 and 2 Hz, 1H), 7.28 (d, J = 2 Hz, 1H), 7.32–7.41 (m, 3H). To
a
magnetically stirred solution of 27 (6.00 g, 12.8 mmol) in CH2Cl2 (25 ml) was
slowly added a solution of m-CPBA (6.90 g, 70% grade, 0.282 mol) in CH2Cl2 and
the resulting mixture was stirred for 16 h. The reaction mixture was twice
washed with 2 N NaOH solution and dried over Na2SO4, filtered and
concentrated. The residue was purified by flash chromatography (silicagel,
Et2O/petroleum ether = 2/1 (v/v)) to give 28 (4.76 g, 74% yield) as a white solid,
mp 130 °C; 1H NMR (400 MHz, CDCl3) d 1.66 (s, 9H), 3.34 (s, 3H), 7.15 (br d, J ꢀ
8 Hz, 2H), 7.20–7.26 (m, 2H), 7.32–7.41 (m, 3H). To a magnetically stirred
solution of 28 (4.76 g, 9.49 mmol) in CH2Cl2 (60 ml) was added excess TFA
(9.40 ml, 0.2124 mol) and Et3SiH (3.8 ml, 0.0238 mol). The solution was
reacted at rt for 16 h and concentrated in vacuo. Water was added and the
formed precipitate was collected by filtration and subsequently dried to give
33 in quantitative yield, mp ꢀ130 °C (dec); 1H NMR (400 MHz, CDCl3) d 3.45 (s,
3H), 3.50 (br s, 1H), 7.40 (br d, J ꢀ 8 Hz, 2H), 7.42 (dd, J = 8 and 2 Hz, 1H), 7.50
(br d, J ꢀ 8 Hz, 2H), 7.59 (d, J = 2 Hz, 1H), 7.61 (d, J = 8 Hz, 1H). To
a
magnetically stirred suspension of 33 (2.23 g, 5.01 mmol) in anhydrous
CH3CN (50 ml) was successively added N,N-diisopropylethylamine (Hünig’s
base) (1.90 ml, 11.0 mmol), O-benzotriazol-1-yl-N,N,N0,N0-tetramethyluronium
hexafluorophosphate (HBTU) (2.27 g, 5.99 mmol) and 1-aminopiperidine
(0.65 ml, 6.03 mmol). After stirring for 16 h at rt, the resulting mixture was
concentrated. The residue was dissolved in EtOAc, successively washed with
aqueous NaHCO3 solution, water and brine, dried over Na2SO4, filtered and
concentrated to give a crude solid. This solid was further purified by flash