Biarylpyrazolyl oxadiazole as potent, selective, orally bioavailable cannabinoid-1 receptor antagonists for the treatment of obesity

7216

J. Med. Chem. 2008, 51, 7216–7233

Biarylpyrazolyl Oxadiazole as Potent, Selective, Orally Bioavailable Cannabinoid-1 Receptor

Antagonists for the Treatment of Obesity

Suk Ho Lee,^†Hee Jeong Seo,^†Sung-Han Lee,^†Myung Eun Jung,^†Ji-Hyun Park,^†Hyun-Ju Park,^‡Jakyung Yoo,^‡Hoseop Yun,^§

Jooran Na,^§Suk Youn Kang,^†Kwang-Seop Song,^†Min-ah Kim,^†Chong-Hwan Chang,^†Jeongmin Kim,^†and Jinhwa Lee*^,†

Central Research Laboratories, Green Cross Corporation, 303 Bojeong-dong, Giheung-gu, Yongin 446-770, Korea, College of Pharmacy,

Sungkyunkwan UniVersity, Suwon 440-746, Korea, DiVision of Energy Systems Research and Department of Chemistry,

Ajou UniVersity, Suwon 443-749, Korea

ReceiVed July 10, 2008

Since the CB1 cannabinoid receptor antagonist 1 (SR141716, rimonabant) was previously reported to modulate

food intake, CB1 antagonism has been considered as a new therapeutic target for the treatment of obesity.

In the present study, biarylpyrazole analogues based on a pyrazole core coupled with 1,3,4-oxadiazole were

synthesized and tested for CB1 receptor binding afﬁnity. Thorough SAR studies to optimize pyrazole

substituents as well as 1,3,4-oxadiazole ring led to several novel CB1 antagonists with IC₅₀∼ 1 nM for the

CB1 receptor binding. Among these analogues, we identiﬁed 2-(4-((1H-1,2,4-triazol-1-yl)methyl)-5-(4-

bromophenyl)-1-(2,4-dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-(triﬂuoromethyl)cyclopropyl)-1,3,4-oxa-

diazole 43c as a promising precandidate for the development as an antiobesity agent.

Introduction

The prevalence of obesity has rapidly increased over the past

decade. Obesity is not a simply cosmetic concern but a serious

health problem. Thus, the World Health Organization (WHO)

recently declared that obesity has become a global epidemic.^1,2

Obesity is characterized by excess of body fat and includes a

pro-inﬂammatory state eventually resulting in type 2 diabetes,

coronary heart disease, and hypertension. Furthermore, obesity

elevates the relative risk of mortality owing to cardiovascular

disease,³and obesity now ranks as the second leading cause of

preventable death after smoking in the United States.⁴Treatment

of obesity involves a combination of diet, exercise, and

pharmacotherapy. However, there is growing evidence that

short-term dietary changes or exercise alone cannot adequately

address obesity as a chronic disease. Only two drugs are

currently approved for chronic weight loss treatment: orlistat

(1-(3-hexyl-4-oxo-oxetan-2-yl)tridecan-2-yl 2-formylamino-4-

methyl-pentanoate) and sibutramine (1-(4-chlorophenyl)-N,N-

dimethyl-a-(2-methylpropyl)-cyclobutanemethanamine). How-

ever, both of these agents have different adverse event proﬁles

that limit more widespread use.⁵

Numerous studies on causes of obesity have been made to

identify new potential targets that could be exploited to create

novel types of antiobesity drugs. Eventually, the discovery was

made that modulation of the endocannabinoid system by

speciﬁcally blocking the cannabinoid receptor 1 (CB1)^ain both

the brain and periphery can provide a novel target for the

treatment of obesity.^6aThe endocannabinoid system includes

endogenous ligands (such as anandamide and 2-AG)^6band two

cannabinoid receptor subtypes (CB1 and CB2). These receptors

Figure 1. Structures of CB1R antagonists or inverse agonists.

(CB1 and CB2) belong to the G-protein coupled receptor

superfamilyandwereﬁrstclonedin1990and1993,respectively.^7-9

The CB1 receptors are mainly expressed in several brain areas

including the limbic system (amygdala, hippocampus), hypo-

thalamus, cerebral cortex, cerebellum, and basal ganglia. It has

been known that CB1 receptors, especially in the limbic

system-hypothalamus axis cannabinoids, have an important role

in the control of appetite. In contrast, CB2 receptors are almost

exclusively expressed in cells of the immune system.^10,11The

physiological role of both CB receptors is not yet completely

understood, although they seem to be involved in certain

pathophysiological processes. In particular, the physiological

role of CB1 receptors has been of interest since the clinical

results of 1 (SR141716, rimonabant, Figure 1),^15athe ﬁrst

commercial CB1 antagonist, were reported for the treatment of

obesity and metabolic disorders in 2001. Since then, antagonism

of CB1 receptors has been pursued as a highly promising

strategy for the treatment of obesity. Considering the important

impact of obesity on public health, the increasing incidence of

its worldwide prevalence, and the lack of highly efﬁcient and

well-tolerated drugs for treatment, it is not surprising that CB1

antagonism or inverse agonism is the subject of considerable

interest.¹²Although 1 is currently marketed by Sanoﬁ-Aventis

* To whom correspondence should be addressed. Phone: +82-31-260-

9892. Fax: +82-31-260-9870. E-mail: jinhwalee@greencross.com.

†

Central Research Laboratories, Green Cross Corporation.

College of Pharmacy, Sungkyunkwan University.

Division of Energy Systems Research and Department of Chemistry,

‡

§

Ajou University.

^aAbbreviations: CB1, cannabinoid-1; CB2, cannabinoid-2; 2-AG, 2-arachi-

donoylglycerol; DAST, diethylaminosulfur triﬂuoride; SAR, structure-activity

relationships; NBS, N-bromosuccinimide; AIBN, azobisisobutyronitrile;

CHO cells, Chinese hamster ovary cells; DIO mice, Diet-induced obese

mice; DMSO, dimethyl sulfoxide.

10.1021/jm800843r CCC: $40.75

2008 American Chemical Society

Published on Web 10/28/2008

Biarylpyrazolyl Oxadiazole as CB1 Receptor Antagonists

Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7217

product C using a dehydrating agent (i.e., Burgess reagent)²⁴

to obtain a 1,3,4-oxadiazole 4. Alternatively, the acylhydrazide

intermediate C was also available through the coupling of the

hydrazide 6 with a corresponding acid 7 mediated by coupling

reagents such as DMAP, EDCI or EDCI, HOBt, and NMM.

For this sequence, the requisite hydrazide 6 was prepared by

treating the known ester 5 with hydrazine in reﬂuxing EtOH as

shown in Scheme 1.

Further functionalization was initiated with the activated

4-pyrazole intermediate 8, which was prepared from 4h via a

benzylic bromination-type reaction²⁵as illustrated in Scheme

2. The alcohol functionality of 10 was then introduced by

treating bromide 8 with sodium acetate, followed by basic

hydrolysis of the resulting acetate.

Figure 2. 1 and its receptor-ligand interaction.

As shown in Scheme 3, alcohol 10 could be alkylated with

an alkyl iodide or an alkyl bromide in the presence of sodium

hydride (Williamson ether synthesis conditions) to furnish the

corresponding ether 12. Aternatively, alcohol 10 could be

converted into the corresponding ﬂuoride 13 through the use

of a ﬂuorinating agent such as diethylaminosulfur triﬂuoride

(DAST).²⁶In another variation, the Burgess reagent could be

employed to transform alcohol 10 to the corresponding car-

bamate 14.²⁷Ultimately, however, oxidation of the alcohol 10

to aldehyde 11 was achieved through the use of Dess-Martin

periodinane²⁸as described in Scheme 2.

Aldehyde 11 (Scheme 2) proved to be a versatile intermediate.

This compound could be treated with DAST to provide the

corresponding diﬂuoromethylpyrazole 15. Alternatively, alde-

hyde 11 could be further oxidized to acid 16 by use of sodium

chlorite and monobasic potassium phosphate in aqueous

t-BuOH. Aldehyde 11 could also be treated with a Grignard

reagent such as methylmagnesium bromide to afford the

corresponding alcohol 17. Analogous to the transformations

depicted in Scheme 3, alcohol 17 was also transformed into

ether 18, ﬂuoride 19, and ketone 20, respectively. Interestingly,

treatment of 17 with Burgess reagent produced carbamate 22

along with oleﬁn 21 as described in Scheme 4.

As shown in Scheme 5, ketone 20 could be further treated

with a Grignard reagent to provide alcohol 23, which was then

treated with Burgess reagent to afford oleﬁn 24.

For SAR investigations, bromide 8 was key to the synthesis

of substituted pyrazole derivatives as shown in Scheme 6. Thus,

acetate 9, thioacetate 25, cyanide 26, aryl ether 27, various

secondary or tertiary amine 28, pyrrolidin-2-one 29, succinimide

30, and 2-oxazolidinone 31 could all be smoothly prepared.

Additionally, bromide 8 could be reacted with pyrrole and

various azoles including pyrazole, imidazole, 1,2,4-triazole,

1,2,3-triazole, and tetrazole in the presence of a base to provide

substituted pyrazole derivatives 32a-g as shown in Scheme 7.

in the European Union, many research groups, including major

pharmaceutical companies, are still searching for novel CB1

antagonists with improved physicochemical properties and

decreased adverse effects, such as depression or anxiety.^13,14

Several CB1 receptor antagonists (Figure 1), including 1, 2

(CP-945,598, otenabant),^15band 3 (MK-0364, taranabant),^16,17

have been reported to be in various phase of clinical trials.

Several reviews describe recent medicinal chemistry research

around pyrazolyl derivatives and other new chemotypes as CB1

receptor antagonists.^3,11However, on the basis of recent

literature and patent application reports, 1 appears to be widely

used as a lead template for the design of new compounds.

A pharmacophore model for the binding of a low energy

conformation of 1 in the CB1 receptor has been well-docu-

mented.^11,18The key receptor-ligand interaction is known to

be a hydrogen bond between the carbonyl group of 1 and the

Lys192-Asp366 residue of the CB1 receptor, thereby exerting

a stabilizing effect on the Lys192-Asp366 salt bridge as shown

in Figure 2.¹¹

To date, various analogues of 1 have been designed for the

purpose of enhancing binding afﬁnity and selectivity for the

CB1 receptor, employing strategies such as conformational

constraint or scaffold hopping.¹¹In general, replacement of the

pyrazole core with 5- or 6-membered ring scaffolds has been

an active area of research. We envisioned that the key carbonyl

group of 1 might be replaced to the corresponding imine-type

moiety or “imine”-containing heterocycle. Among many het-

erocycles involving “imine-type” functionality, we were par-

ticularly interested in the 1,3,4-oxadiazole heterocycle as a viable

amide surrogate. We speculated that replacement of the amide

moiety into a 1,3,4-oxadiazole ring could impart a favorable

balance of potency and physicochemical properties to allow for

further in vivo efﬁcacy evaluation. We note that similar

approaches have already been successfully demonstrated with

imidazoles^19a,band tetrazoles.²⁰Subsequently, we also discov-

ered that the 1,3,4-oxadiazole^21,22scaffold has also been

employed for this purpose, although there are clear differences

evident between the current work and these prior examples.

Herein, we describe the design, synthesis, and biological

evaluation of biarylpyrazolyl oxadiazole analogues as novel CB1

receptor antagonists. Through a process of lead optimization,

we successfully identiﬁed 2-(4-((1H-1,2,4-triazol-1-yl)methyl)-

5-(4-bromophenyl)-1-(2,4-dichlorophenyl)-1H-pyrazol-3-yl)-5-

(1-(triﬂuoromethyl)cyclopropyl)-1,3,4-oxadiazole (43c) as a

promising precandidate for development as an antiobesity agent.

Chemistry. The synthesis of the biarylpyrazolyl oxadiazole

analogues commenced with the generic acid A.²³Compounds

of general structure 4 were prepared by (i) reacting a carboxylic

acid A with a hydrazide compound B in the presence of coupling

reagent, e.g., EDCI, DMAP, and (ii) cyclizing the resulting

The compounds containing 1,2,4-triazole could also be

obtained by a reaction sequence involving key intermediate

bromide 33. Thus, bromide 33, obtained by reaction of pyrazole

5 with NBS in the presence of catalytic AIBN, was reacted with

1,2,4-triazole in the presence of cesium carbonate to provide

34. Hydrolysis of ester 34, activation of acid 35, followed by

coupling with a hydrazide in the presence of triethylamine, then

afforded acylhydrazide 36. Alternatively, hydrazynolysis of ester

34 produced the corresponding hydrazide, which could then be

coupled with an acid to give acylhydrazide 36. Cyclization was

then performed using the Burgess reagent under microwave

irradiation to give oxadiazole 32d as illustrated in Scheme 8.

The 4-cyclopropyl pyrazole compound 41 was prepared as

shown in Scheme 9. In the event, 4-bromo-pyrazole of structure

38, prepared by following a generic procedure,⁴¹was coupled

7218 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22

Lee et al.

Scheme 1

Scheme 2

afﬁnity, showing an approximately 2-fold increase in CB1

binding afﬁnity of 4r (IC₅₀) 10.9 nM) and 4s (IC₅₀) 8.42

nM). Cyclization of the gem-dimethyl group at the benzylic

position to generate a cyclopropane is also tolerated without

detriment to in vitro CB1 binding afﬁnity (entry 20). Chlorine

substitution on the phenyl ring also maintained similar levels

of CB1 receptor binding afﬁnity, indicating that a halogen atom

appears to be well tolerated at this position. The same is true

for (4-chlorophenyl)cyclopropyl 4v, which displays virtually

identical binding afﬁnity (IC₅₀) 8.61 nM), suggesting the

importance of a nonpolar moiety in order to optimally bind to

a hydrophobic area of the CB1 receptor. Furan and thiophene

groups showed only modest CB1 receptor binding afﬁnity,

indicating that biaryls at this domain decrease binding afﬁnity

compared with aliphatic chains or carbocycles at this domain.

Neither pyridine (entry 25) nor pyrazine (entry 26) improve CB1

binding afﬁnity, although an interesting exception to this

observation is pyridin-2-ylmethyl oxadiazole 4aa (entry 27).

Insertion of a methylene unit at the pyridine ring resulted in a

dramatic improvement in binding afﬁnity, and this compound

almost regains the potency of benzyl oxadiazole 4q.

with a cyclopropylboronic acid under Suzuki-Miyaura coupling

reaction conditions²⁹to afford a 4-cyclopyrazole 39. The ester

39 then underwent a series of reactions as previously described

to generate oxadiazole 41.

It was encouraging to note that considerable CB1 receptor

binding afﬁnity was already evident in lead compound 4h.³⁸

At this juncture, we proceeded to explore C-4 region of pyrazole

core by using t-butyl oxadiazole as a lead scaffold.³⁹The binding

afﬁnity data of selected key biarylpyrazolyl oxadiazoles for the

CB1 receptor is shown in Table 2. Homologation of the methyl

substituent to give 4ha resulted in a slight improvement in

binding potency as compared to 4h. However, as the size of

carbon chain is increased, binding afﬁnity decreases 3- to 5-fold

(see Table 2: 4hb, 4hc, and 41). Surprisingly, various functional

groups such as hydroxyl (10, 17, and 23), ﬂuoro (13, 15, and

19), vinyl groups (21, 24), carbamate (14, 22), ether (12, 27),

acetate 9, ethanethiolate 25, and nitrile 26 appeared to be

tolerated. Thus, the methyl group of the pyrazole ring can be

extensively modiﬁed. However, substitution with amines (28)

as well as 2-pyrrolidinone 29, succinimide 30, and 2-oxazoli-

dinone 31 resulted in decreased potency relative to the simple

methyl 4h or ethyl group 4ha. Moreover, carboxylic acid 16

demonstrated a complete loss of activity, implying that acidic

functionality in the region is not tolerated. Additionally,

substitution with pyrrole 32a, pyrazole 32b, and imidazole 32c

could be performed. These analogues showed moderate CB1

binding afﬁnity, but none improved potency relative to the

simple methyl group analogue 4h. Five-membered ring hetero-

Results and Discussion

The target analogues were evaluated in vitro at a rat CB1

binding assay,³⁰and the results are shown in Table 1. The results

demonstrate that as the size of the carbon chain is increased,

an increase in binding afﬁnity is observed up to the C-4 or C-5

chain. Branched aliphatic chains are usually more potent than

the corresponding counterparts as shown in entries 1 vs 5, or

entries 4 vs 6. For cyclic analogues, the size of the carbocycle

appears to affect binding afﬁnity. Thus, four-or six-membered

rings (entries 12 and 13) are slightly more potent than the

corresponding seven-membered carbocycle (entry 14), suggest-

ing that there might be a size requirement for the oxadiazole

alkyl region to bind with high afﬁnity to the CB1 receptor. As

shown in oxadiazole 4k, the (triﬂuoromethyl)cyclopropyl moiety

appears to augment CB1 binding afﬁnity, indicating that the

ﬂuorine substituents might be involved in a hydrogen bond

interaction with the receptor that fosters high afﬁnity. A aryl

moiety (entry 16) does not appear to be tolerated because 4p

shows dramatic decrease in binding afﬁnity to IC₅₀) 281 nM.

In contrast, a benzyl substituent (entry 17) improved binding

afﬁnity approximately 15-fold. Importantly, addition of methyl

groups alpha to the oxadiazole ring improved CB1 binding

Biarylpyrazolyl Oxadiazole as CB1 Receptor Antagonists

Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7219

Scheme 3

Scheme 4

cycles with three or more heteroatoms proved to be more potent

CB1 receptor ligands as shown in Table 2 (entries 37-40).

Among the tested compounds in Table 2, 1,2,4-triazole 32d

demonstrated the superior CB1 receptor binding afﬁnity (IC₅₀

) 2.36 nM), implying that one of nitrogen in triazole ring might

be involved in hydrogen bond formation with the backbone of

the receptor, thereby promoting higher afﬁnity.³¹

Binding afﬁnity was also measured for the CB2 receptor

expressed in CHO cells, employing [3H]44 ([³H]WIN55,212-

2, [³H] (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmeth-

yl)pyrrolo[1,2,3-de)-1,4-benzoxazin-6-yl]-1-napthalenylmetha-

none])³²as a radio ligand. Virtually all of our pyrazole-based

compounds were devoid of activity in this CB2 binding assay,

indicating high selectivity for CB1 over CB2 for these ana-

logues. Selected examples of the above analogues are sum-

marized in Table 2.

Because the addition of a hydrophilic 1,2,4-triazole substituent

resulted in increased CB1 receptor binding afﬁnity in the

biarylpyrazolyl oxadiazole series, 1,2,4-triazole substituted

derivatives of 32d were prepared and tested (Table 3). A

7220 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22

Lee et al.

Scheme 5

Scheme 6^a

^aReagents: (a) NaOAc; (b) KSAc, DMF, rt; (c) NaCN, DMF; (d) RR′NH, DIPEA, CH₂Cl₂; (e) 2-oxazolidinone, K₂CO₃, DMF; (f) succimide, K₂CO₃,

DMF; (g) 2-pyrrolidinone, K₂CO₃, DMF; (h) phenol or 2-hydroxypyridine, Cs₂CO₃.

methylcyclopropyl substituent (42b) was selected for the direct

comparison with t-butyl-oxadiazole 32d. Indeed, 42b showed

the similar levels of CB1 receptor binding afﬁnity, indicating

that the cyclopropyl group is interchangeable with the corre-

sponding gem-dimethyl group and possibly acts as a gem-

dimethyl surrogate.⁴⁰Next, triﬂuoromethylcyclopropyl 42c,

which should confer lower lipophilicity and possibly enhanced

water solubility, was selected for bioassay. As shown for

oxadiazole 4k (Table 1), the (triﬂuoromethyl)cyclopropyl group

appears to augment CB1 receptor binding afﬁnity. To our

delight, compounds with the (triﬂuoromethyl)cyclopropyl group

also showed more than 1000-fold CB2/CB1 receptor selectivity

as demonstrated by 42c and 43c in Table 3. In addition,

p-tolylcyclopropyl oxadiazole 42e displayed outstanding binding

afﬁnity, implying that increased lipophilicity can improve in

vitro activity. When chlorine (entries 3-8) was exchanged for

bromine (entries 9-14) as shown in Table 3, several compounds

reached subnanomolar CB1 receptor binding afﬁnity. Of note

is that 4-bromophenylcyclopropyl oxadiazole 43f was shown

to be the most potent in vitro CB1 biarylpyrazolyl oxadiazole

receptor ligand (IC₅₀) 0.57 nM) prepared to date. Compound

43f also showed the highest CB2/CB1 receptor selectivity

(∼1842) as demonstrated in Table 3. Some selected promising

compounds have been tested on animal models for in vivo

efﬁcacy.

In vivo efﬁcacy was evaluated on DIO mice.³⁷Male

C57BL/6J mice weighing over 38 g were housed 1 per cage

on a 12 h/12 h light/dark cycle, had free access to food

(rodent sterilized diet), and water and were experimentally

native before testing. Mice were allowed at least 7 days to

habituate to the experimental room prior to testing, and testing

was conducted during the light period. Mice were maintained

and experiments were conducted in accordance with Insti-

tutional Animal Care. The reference (1) and the inventive

compounds of compounds 42c and 43c were prepared fresh

daily by dissolving them in deionized water containing 10%

Biarylpyrazolyl Oxadiazole as CB1 Receptor Antagonists

Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7221

Scheme 7

Scheme 8^a

^aReagents: (a) NBS, AIBN, CCI₄; (b) 1,2,4-triazole, Cs₂CO₃, DMF; (c) LiOH, THF-H₂O; (d) (i) (COCI)₂, (ii) NH₂NH (CO)t-Bu, Et₃N, CH2Cl2; (e)

Burgess reagent, THF, reﬂux or microwave.

Scheme 9

DMSO. By oral administration, animals received at a volume

of 10 mL/kg for 14 days. All control animals received 10%

DMSO dissolved in deionized water. The vehicles 10%

DMSO-treated groups comprised ﬁve mice in oral test. There

were six mice in each of the other experimental groups (n )

6 in each group). By oral administration, the losing weight

was checked every day for the drug treated group and the

control group.

observed on all days at 10 mg/kg of example 4k compound, at

10 mg/kg of example 42c compound, at 10 mg/kg of example

43c compound, and at 10 mg/kg of 1. Each value is the mean

( SEM of 5 mice. *P < 0.05, **P < 0.01 vs corresponding

vehicle (ANOVA with Dunnett’s test).

Figure 3 shows that compounds 42c and 43c are substantially

more efﬁcacious than 1 in in vivo efﬁcacy study on the DIO

mice model (29.5 ( 1.9% and 29.3 ( 0.5% reduction in body

weight after 14 days, respectively), while 4k reduces body

weight moderately (22.8 ( 2.4%). Substitution of methyl with

Figure 3 shows chronic effects of compounds 4k, 42c, 43c,

and 1 in DIO mice. Body weight change from day 0 was

7222 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22

Lee et al.

Table 1. Structures and Binding Afﬁnities of Selected Ligands for Rat CB1 Receptors^a

^arCB1 receptor was collected from brain tissue of SD rat. These data were obtained by single determinations. 1 is estimated to have CB1 binding afﬁnity

(IC₅₀) 5.0 nm) via in-house assay. Units: nM.

triazolylmethyl group on C-4 pyrazole ring improved in vitro

binding afﬁnity, in turn leading to excellent in vivo efﬁcacy on

DIO mouse model.³³

amino acid residues in the active site, facilitating the ligand

bind deeper into binding pockets.

Two aryl groups of 43c, commonly existent in CB1 antago-

nists analogous to 1, are in close contacts with aromatic amino

acid residues (Phe 200, Tyr 275, Trp 279, and Trp 356), forming

π-stacking and hydrophobic interactions. In accord with the

results of published modeling studies, Lys 192 is involved in a

salt bridge with Asp 366, stabilizing the inactive state of

hCB1.^16c,34cIn the case of 1, the carboxamide oxygen formed

a hydrogen bond (H-bond) with Lys 192, which should be

responsible for the high afﬁnity to the inactive state of receptor.

In our model, the 1,3,4-oxadiazole ring of 43c, a bioisostere of

amide, forms a bidentate H-bond with Lys 192, and this may

contribute to increase the binding selectivity toward the active

site. The ﬂuorine atom of triﬂuoromethyl group of 43c plays a

role in H-bond acceptor and is involved in H-bond with OH of

Ser 383. The signiﬁcance of the interaction with Ser 383 was

revealed in previous combined mutagenesis and modeling

studies on 3.^16cIt is noticeable that the ((triﬂuoromethyl)cy-

clopropyl) oxadiazole substituent in 43c can form H-bonds

observed in the binding model of both 1 and 3. In addition, the

The identity of compound 43c was further secured through

single-crystal X-ray analysis, as demonstrated in Figure 4.

Crystallographic data (excluding structure factors) for the

structure have been deposited with the Cambridge Crystal-

lographic Data Centre as supplementary publication no.

CCDC694371.

To explain the potent, selective CB1 binding afﬁnity of 43c,

we built a docking model of CB1:43c complex using our

homology model of the inactive state of human CB1. We

initially constructed a 1-CB1 binding model by taking into

account the interactions between 1 and the active site of CB1

obtained from the published molecular modelings and mutagen-

esis studies.³⁴Compound 43c was docked into CB1 by deﬁning

the bound 1 as a reference. As demonstrated in Figure 5 and 6,

43c is well superimposed over the docked pose of 1 occupying

hydrophobic pocket of CB1. All the substituents attached to

the central pyrazole ring of 43c form various interactions with

Biarylpyrazolyl Oxadiazole as CB1 Receptor Antagonists

Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7223

Table 2. Structures and Binding Afﬁnities of Selected Ligands to Rat CB1 and Human CB2 Receptors, and CB2/CB1 Selectivity of the Ligands^a

^aThese data were obtained by single determinations. 1 is estimated to have CB1 binding afﬁnity (IC₅₀) 5.0 nM) via in-house assay.

N2 of triazole substituent forms a bidentate H-bond with side

chain OH and backbone NH of Thr 197, which is an exclusive

interaction observed in the binding model of 43c.

Signiﬁcantly, the binding mode of 43c generated by docking

analysis conclusively reveals that the structure of the ligand

binds with high potency to hCB1 by forming additional

interactions than 1 and 3 and provides further insight into the

design of more potent and selective hCB1 antagonists.

study also suggested that the 1,3,4-oxadiazole ring participates

in a bidentate H-bond interaction with Lys 192. This interaction

is predicted to be stronger than the analogous monodentate

H-bond interaction formed by the amide carbonyl oxygen of 1

that is hydrogen-bonded to Lys 192. In addition, we have

demonstrated that incorporation of a 1,2,4-triazole ring onto the

pyrazole scaffold via a methylene linker leads to a potent CB1

receptor antagonist with a signiﬁcant antiobesity effect in the

animal model. Importantly, these analogues also display good

selectivity for CB1R over CB2R. Thus, the biarylpyrazolyl

oxadiazole class of compounds bearing a methyl-triazole as the

optimal side chain possesses a promising therapeutic potential

as a CB1 receptor antagonist for the treatment of obesity.

Conclusion

In the present study, we investigated a series of biarylpyra-

zolyl oxadiazole derivatives as antagonists to the cannabinoid

CB1 and CB2 receptors. Several of the compounds in this series

exceeded the potency of known CB1 antagonists, validating the

hypothesis that a 1,3,4-oxadiazole could act as a bioisostere of

the amide moiety in 1. A subsequently conducted modeling

Experimental Section

All references to ether are to diethyl ether; brine refers to a

saturated aqueous solution of NaCl. Unless otherwise indicated,

7224 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22

Lee et al.

Table 3. Structures and Binding Afﬁnities of Selected Ligands to Rat CB1 and human CB2 Receptors and CB2/CB1 Selectivity of the Ligands^a

^aThese data were obtained by single determinations. 1 and 3 were estimated to have CB1 binding afﬁnity via in-house assay.

Figure 3. In vivo efﬁcacy study of compounds 4k, 42c, 43c and 1 in DIO mouse.

Biarylpyrazolyl Oxadiazole as CB1 Receptor Antagonists

Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7225

(400 MHz, CDCl₃) δ 7.41 (d, J ) 2.3 Hz, 1H), 7.34-7.28 (m,

4H), 7.09-7.13 (m, 2H), 2.90 (t, J ) 7.6 Hz, 2H), 2.45 (s, 3H),

1.88 (m, 2H), 1.03 (t, J ) 7.6 Hz, 3H). MH+ 447.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-isopropyl-1,3,4-oxadiazole (4b). ¹H NMR (400

MHz, CDCl₃) δ 7.41 (d, J ) 2.28 Hz, 1H), 7.38-7.29 (m, 4H),

7.13-7.09 (m, 2H), 3.28 (m, 1H), 2.44 (s, 3H), 1.46 (d, J ) 6.88

Hz, 6H). MH+ 447.

2-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-meth-

1

yl-1H-pyrazol-3-yl)-1,3,4-oxadiazole (4c). H NMR (400 MHz,

CDCl₃) δ 7.43 (d, J ) 1.84 Hz, 1H), 7.37-7.29 (m, 4H), 7.12 (dt,

J ) 2.28, 8.24 Hz, 2H), 2.94 (t, J ) 7.56 Hz, 2H), 2.46 (s, 3H),

1.85 (m, 2H), 1.45 (m, 2H), 0.96 (t, J ) 7.36 Hz, 3H). MH+ 461.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-pentyl-1,3,4-oxadiazole (4d). ¹H NMR (400 MHz,

CDCl₃) δ 7.43-7.42 (m, 1H), 7.37-7.30 (m, 4H), 7.13-7.10 (m,

2H), 2.93 (t, J ) 7.8 Hz, 2H), 2.46 (s, 3H), 1.90-1.83 (m, 2H),

1.45-1.32 (m, 4H), 0.91 (t, J ) 7.3 Hz, 3H). MH+ 475.

2-sec-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

methyl-1H-pyrazol-3-yl)-1,3,4-oxadiazole (4e). ¹H NMR (400

MHz, CDCl₃) δ 7.42-7.41 (m, 1H), 7.36 (d, J ) 8.2 Hz, 1H),

7.34-7.30 (m, 3H), 7.13-7.09 (m, 2H), 3.16-3.07 (m, 1H), 2.45

(s, 3H), 2.00-1.89 (m, 1H), 1.80-1.70 (m, 1H), 1.43 (d, J ) 6.9

Hz, 3H), 0.97 (t, J ) 7.4 Hz, 3H). MH+ 461.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(hexan-2-yl)-1,3,4-oxadiazole (4f). ¹H NMR (400

MHz, CDCl₃) δ 7.42-7.41 (m, 1H), 7.38-7.30 (m, 4H), 7.13-7.09

(m, 2H), 3.22-3.13 (m, 1H), 2.45 (s, 3H), 1.95-1.89 (m, 1H),

1.73-1.64 (m, 1H), 1.42 (d, J ) 6.9 Hz, 3H), 1.38-1.25 (m, 4H),

0.91-1.87 (m, 3H). MH+ 489.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(pentan-3-yl)-1,3,4-oxadiazole (4g). ¹H NMR (400

MHz, CDCl₃) δ 7.42 (d, J ) 2.28 Hz, 1H), 7.38-7.30 (m, 4H),

7.13-7.10 (m, 2H), 2.96 (m, 1H), 2.46 (s, 3H), 1.93-1.79 (m,

2H), 0.94 (t, J ) 7.32 Hz, 3H). MH+ 475.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

methyl-1H-pyrazol-3-yl)-1,3,4-oxadiazole (4h). ¹H NMR (400

MHz, CDCl₃) δ 7.42-7.41 (m, 1H), 7.38 (d, J ) 8.2 Hz, 1H),

7.34-7.30 (m, 3H), 7.12-7.09 (m, 2H), 2.45 (s, 3H), 1.52 (s, 9H).

¹³C NMR (100 MHz, CDCl₃) δ 173.0, 160.3, 143.2, 138.6, 136.4,

136.1, 135.3, 133.3, 131.1, 131.0, 130.5, 129.2, 128.2, 127.2, 117.4,

32.7, 28.5, 10.0. MH+ 461.

Figure 4. X-ray structure of compound 43c.

all temperatures are expressed in °C (degrees centigrade). All

reactions are conducted under an inert atmosphere at room

temperature unless otherwise noted, and all solvents are of the

highest available purity unless otherwise indicated. Microwave

reaction was conducted with a Biotage microwave reactor. ¹H NMR

spectra were recorded on either a Jeol ECX-400 or a Jeol JNM-

LA300 spectrometer. Chemical shifts were expressed in parts per

million (ppm, δ units). Coupling constants are in units of hertz

(Hz). Splitting patterns describe apparent multiplicities and are

designated as s (singlet), d (doublet), t (triplet), q (quartet), quint

(quintet), m (multiplet), br (broad). Mass spectra were obtained

with either a Micromass, Quattro LC triple quadruple tandem mass

spectometer ESI or Agilent 1200LC/MSD ESI, and high resolution

mass spectra were determined by Jeol, JMS-700 Mstation. For

preparative HPLC, ca. 100 mg of a product was injected in 1 mL

of DMSO onto a SunFire Prep C18 OBD 5 µm 19 mm × 100 mm

column with a 10 min gradient from 10% CH₃CN to 90% CH₃CN

in a H₂O Biotage SP1 Flash puriﬁcation system was used for normal

phase column chromatography with ethyl acetate and hexane. Flash

chromatography was carried using Merck silica gel 60 (230-400

mesh). Most of the reactions were monitored by thin-layer

chromatography on 0.25 mm E. Merck silica gel plates (60F-254),

visualized with UV light using a 5% ethanolic phosphomolybdic

acid or p-anisaldehyde solution.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

ethyl-1H-pyrazol-3-yl)-1,3,4-oxadiazole (4ha). ¹H NMR (300

MHz, CDCl₃) δ 7.42-7.40 (m, 1H), 7.37-7.28 (m, 4H), 7.15-7.11

(m, 2H), 2.89-2.82 (m, 2H), 1.50 (s, 9H), 1.23 (t, J ) 7.3 Hz,

3H). ¹³C NMR (100 MHz, CDCl₃) δ 173.1, 160.1, 143.1, 138.0,

136.4, 136.0, 135.5, 133.4, 131.1, 131.0, 130.5, 129.2, 128.1, 127.3,

124.0, 32.7, 28.5, 17.4, 15.5. MH+ 475.

N-Butanoyl-N′-[5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

methyl-1H-pyrazole-3-carbonyl]-hydrazine (C). Added to a solu-

tion of 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)- 4-methyl-1H-

pyrazole-3-carboxylic acid (A) (0.40 g, 1.05 mmol), N-butanoyl-

hydrazine (B) (0.11 g, 1.05 mmol), and EDCI (0.24 g, 1.26 mmol)

dissolved in DCM (11 mL) was DMAP (0.15 g, 1.26 mmol) in

one portion at room temperature. The reaction mixture was stirred

at room temperature for 6 h and then treated with 10% aq HCl.

The organic layer was collected and evaporated under a vacuum.

The crude mixture was further puriﬁed by preparative HPLC to

obtain 0.38 g (0.81 mmol, 77%) of the title compound as yellow

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

1

propyl-1H-pyrazol-3-yl)-1,3,4-oxadiazole (4hb). H NMR (400

MHz, CDCl₃) δ 7.40 (d, J ) 2.4 Hz, 1H), 7.37-7.27 (m, 4H),

7.11 (d, J ) 8.4 Hz, 2H), 2.81-2.77 (m, 2H), 1.66-1.57 (m, 2H),

1.49 (s, 9H), 0.88 (t, J ) 7.2 Hz, 3H). ¹³C NMR (100 MHz, CDCl₃)

δ 173.0, 160.2, 143.3, 138.2, 136.3, 136.0, 135.4, 133.4, 131.2,

131.0, 130.4, 129.2, 128.1, 127.4, 122.5, 32.7, 28.5, 25.9, 24.1,

14.3. MH+ 489.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

isopropyl-1H-pyrazol-3-yl)-1,3,4-oxadiazole (4hc). ¹H NMR (400

MHz, CDCl₃) δ 7.38 (d, J ) 2.0 Hz, 1H), 7.31-7.24 (m, 4H),

7.14 (d, J ) 8.8 Hz, 2H), 3.48-3.43 (m, 1H), 1.49 (s, 9H), 1.26

(d, J ) 7.2 Hz, 6H). ¹³C NMR (100 MHz, CDCl₃) δ 173.2, 160.3,

142.6, 137.2, 136.4, 135.8, 135.6, 133.6, 131.9, 131.1, 130.4, 128.9,

128.2, 128.0, 127.9, 32.7, 28.5, 24.9, 22.6. MH+ 489.

1

solid. H NMR (400 MHz, CDCl₃) δ 7.40 (br s, 1H), 7.31-7.27

(m, 4H), 7.08-7.03 (m, 2H), 2.33 (s, 3H), 2.31 (t, J ) 7.8 Hz,

2H), 1.72 (m, 2H), 0.97 (t, J ) 7.3 Hz, 3H). MH+ 463.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-propyl-1,3,4-oxadiazole (4a). N-Butanoyl-N′-[5-

(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-

carbonyl]-hydrazine (C) (0.35 g, 0.75 mmol) was added to a

microwave reactor containing Burgess reagent (0.45 g, 1.88 mmol)

in THF (2 mL). The capped reactor was placed in a microwave

reactor, and the mixture was irradiated at 140 °C for 15 min. The

reaction product was puriﬁed by preparative HPLC to provide the

title compound (0.21 g, 0.46 mmol, 61%) as yellow solid. ¹H NMR

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

1

pyrazol-3-yl)-5-tert-pentyl-1,3,4-oxadiazole (4i). H NMR (400

MHz, CDCl₃) δ 7.42-7.31 (m, 5H), 7.12-7.10 (m, 2H), 2.44 (s,

3H), 1.83 (q, J ) 7.6 Hz, 2H), 1.47 (s, 6H), 0.87 (t, J ) 7.6 Hz,

3H). MH+ 475.

7226 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22

Lee et al.

Figure 5. Docked pose of 43c in the hCB1 homology model, in comparison with that of 1 (yellow). Solvent-accessible protein surfaces are colored

by lipophilicity potential. Lipophilicity increases from blue (hydrophilic) to brown (lipophilic).

143.2, 138.6, 136.4, 136.1, 135.3, 133.3, 131.0, 130.9, 130.5, 129.1,

128.1, 127.1, 117.3, 35.4, 30.4, 25.8, 25.6, 10.0. MH+ 487.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-cycloheptyl-1,3,4-oxadiazole (4n). ¹H NMR (400

MHz, CDCl₃) δ 7.43-7.41 (m, 1H), 7.37-7.29 (m, 4H), 7.13-7.10

(m, 2H), 3.23-3.16 (m, 1H), 2.45 (s, 3H), 2.21-2.14 (m, 4H),

1.98-1.89 (m, 2H), 1.85-1.79 (m, 2H), 1.68-1.53 (m, 4H). MH+

501.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(cyclohexylmethyl)-1,3,4-oxadiazole (4o). ¹H NMR

(400 MHz, CDCl₃) δ 7.43-7.42 (m, 1H), 7.37-7.29 (m, 4H),

7.13-7.10 (m, 2H), 2.82 (d, J ) 7.3 Hz, 2H), 2.46 (s, 3H),

1.98-1.87 (m, 1H), 1.79-1.63 (m, 4H), 1.31-1.03 (m, 6H). MH+

501.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-phenyl-1,3,4-oxadiazole (4p). ¹H NMR (300 MHz,

CDCl₃) δ 8.22-8.18 (m, 2H), 7.57-7.49 (m, 3H), 7.45-7.44 (m,

1H), 7.41-7.32 (m, 4H), 7.16-7.12 (m, 2H), 2.51 (s, 3H). MH+

483.

2-Benzyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-

Figure 6. Binding pose of 43c in the active site cavity of hCB1 overlaid

over 1 (yellow). Key amino acid residues within the binding site are

rendered in line form (magenta). Yellow dotted lines are hydrogen

bonding interactions (<2.5 Å).

1H-pyrazol-3-yl)-1,3,4-oxadiazole (4q). ¹H NMR (400 MHz,

CDCl₃) δ 7.41 (d, J ) 1.84 Hz, 1H), 7.38-7.27 (m, 9H), 7.12-7.08

(m, 2H), 4.29 (s, 2H), 2.43 (s, 3H). MH+ 495.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

1

pyrazol-3-yl)-5-(1-phenylethyl)-1,3,4-oxadiazole (4r). H NMR

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(2-methylhexan-2-yl)-1,3,4-oxadiazole (4j). ¹H

NMR (400 MHz, CDCl₃) δ 7.43-7.38 (m, 2H), 7.34-7.30 (m,

3H), 7.15-7.09 (m, 2H), 2.44 (s, 3H), 1.78 (m, 2H), 1.47 (s, 6H),

1.25 (m, 4H), 0.87 (t, J ) 7.0 Hz, 3H). MH+ 503.

(400 MHz, CDCl₃) δ 7.40 (d, J ) 2.3 Hz, 1H), 7.37-7.23 (m,

9H), 7.12-7.09 (m, 2H), 4.45 (m, 1H), 2.42 (s, 3H), 1.82 (d, J )

7.3 Hz, 3H). (M + Na)+ 531.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(2-phenylpropan-2-yl)-1,3,4-oxadiazole (4s). ¹H

NMR (400 MHz, CDCl₃) δ 7.40-7.38 (d, J ) 2 Hz, 1H),

7.36-7.27 (m, 7H), 7.26-7.21 (m, 1H), 7.10-7.07 (m, 2H), 2.42

(s, 3H), 1.90 (s, 6H). MH+ 523.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(1-phenylcyclopropyl)-1,3,4-oxadiazole (4t). ¹H

NMR (400 MHz, CDCl₃) δ 7.49-7.46 (m, 2H), 7.41-7.27 (m,

8H), 7.15-7.08 (m, 2H), 2.38 (s, 3H), 1.78 (dd, J ) 7.0, 5.0 Hz,

2H), 1.48 (dd, J ) 7.0, 5.0 Hz, 2H). MH+ 521.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(2-(4-chlorophenyl)propan-2-yl)-1,3,4-oxadiaz-

ole (4u). ¹H NMR (400 MHz, CDCl₃) δ 7.40-7.38 (m, 1H),

7.35-7.27 (m, 6H), 7.26-7.21 (m, 1H), 7.10-7.07 (m, 2H), 2.42

(s, 3H), 1.88 (s, 6H). MH+ 559.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(1-(triﬂuoromethyl)cyclopropyl)-1,3,4-oxadiaz-

1

ole (4k). H NMR (400 MHz, CDCl₃) δ 7.41 (br d, J ) 2.0 Hz,

1H), 7.38-7.30 (m, 4H), 7.10 (m, 2H), 2.42 (s, 3H), 1.63 (m, 2H),

1.61 (m, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 162.6, 161.1, 143.4,

137.9, 136.5, 136.0, 135.5, 133.2, 131.0, 130.9, 130.5, 129.2, 128.2,

127.0, 124.5 (d, J ) 272 Hz), 117.6, 21.2 (q, J ) 37 Hz), 12.4,

9.9. ΜΗ+ 513.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

1

pyrazol-3-yl)-5-cyclobutyl-1,3,4-oxadiazole (4l). H NMR (400

MHz, CDCl₃) δ 7.43 (d, J ) 2.3 Hz, 1H), 7.34-7.28 (m, 4H),

7.13-7.09 (m, 2H), 4.01 (m, 1H), 2.62-2.52 (m, 2H), 2.49 (s,

3H), 2.47-2.39 (m, 2H), 2.20-2.00 (m, 2H). MH+ 459.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-cyclohexyl-1,3,4-oxadiazole (4m). ¹H NMR (400

MHz, CDCl₃) δ 7.41 (d, J ) 1.84 Hz, 1H), 7.37-7.29 (m, 4H),

7.11 (dt, J ) 2.28, 8.24 Hz, 2H), 3.00 (m, 1H), 2.44 (s, 3H),

2.16-2.12 (m, 2H), 1.87-1.81 (m, 2H), 1.78-1.65 (m, 3H),

1.44-1.28 (m, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 169.8, 160.0,

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(1-(4-chlorophenyl)cyclopropyl)-1,3,4-oxadiaz-

ole (4v). ¹H NMR (400 MHz, CDCl₃) δ 7.42-7.39 (m, 3H),

7.35-7.29 (m, 6H), 7.08 (m, 2H), 2.38 (s, 3H), 1.79 (dd, J ) 7.1,

4.6 Hz, 2H), 1.45 (dd, J ) 7.1, 4.6 Hz, 2H). ¹³C NMR (100 MHz,

Biarylpyrazolyl Oxadiazole as CB1 Receptor Antagonists

Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7227

CDCl₃) δ 168.9, 160.3, 143.2, 138.3, 137.6, 136.4, 136.0, 135.4,

133.8, 133.3, 131.2, 131.0, 130.9, 130.5, 129.2, 129.0, 128.1, 127.1,

117.4, 22.1, 16.3, 9.9. MH+ 555.

(m, 2H), 1.52 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ 185.8, 174.1,

158.8, 147.7, 140.5, 137.4, 136.9, 134.6, 133.2, 131.6, 130.8, 130.7,

129.0, 128.4, 124.9, 119.7, 32.9, 28.5. MH+ 475.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(furan-2-yl)-1,3,4-oxadiazole (4w). MH+ 471.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(thiophen-2-yl)-1,3,4-oxadiazole (4x). MH+ 487.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazole (4y). ¹H NMR

(400 MHz, CDCl₃) δ 8.78 (d, J ) 7.43 Hz, 1H), 8.01 (d, J ) 5.04

Hz, 1H), 7.41 (d, J ) 1.84 Hz, 1H), 7.37-7.29 (m, 4H), 7.11 (d,

J ) 8.72 Hz, 2H), 2.48 (s, 3H). MH+ 482.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(pyrazin-2-yl)-1,3,4-oxadiazole (4z). ¹H NMR

(400 MHz, CDCl₃) δ 9.53 (s, 1H), 8.76 (m, 1H), 7.43 (d, J ) 1.84

Hz, 1H), 7.39 (d, J ) 8.68 Hz, 1H), 7.36-7.30 (m, 4H), 7.15 (d,

J ) 8.24 Hz, 2H), 2.55 (s, 3H). MH+ 483.

2-(5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-

pyrazol-3-yl)-5-(pyridin-2-ylmethyl)-1,3,4-oxadiazole (4aa). ¹H

NMR (400 MHz, CDCl₃) δ 8.55 (d, J ) 4.12 Hz, 1H), 7.66 (dt, J

) 1.84, 7.80 Hz, 1H), 7.41 (d, J ) 1.84 Hz, 1H), 7.35-7.29 (m,

5H), 7.20 (dd, J ) 5.04, 7.32 Hz, 1H), 7.13-7.09 (m, 2H), 4.52

(s, 2H), 2.45 (s, 3H). MH+ 496.

2-(4-(Bromomethyl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-

1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-oxadiazole (8). To the solution

of methyl pyrazole (4h) (18.7 g, 40.5 mmol) in CCl₄(400 mL) was

added N-bromosuccinimide (9.3 g, 52.6 mmol) and AIBN (340 mg,

2.0 mmol). The reaction mixture was heated for 12 h at 80 °C. Reaction

mixture was ﬁltered. Filtrate was washed with H₂O and brine. The

organic layer was dried over anhydrous MgSO₄, ﬁltered, and concen-

trated in vacuo to provide 17 g (yield: 78%) of desired bromide as a

solid. The obtained bromide was used without further puriﬁcation.

(3-(5-tert-butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)methyl acetate (9). To the

solution of bromide (8) (2.86 g, 5.29 mmol) in DMF (15 mL) was

added sodium acetate (1.30 g, 15.87 mmol). The reaction mixture

was stirred for 12 h at room temperature. The reaction mixture

was diluted with EtOAc and washed with brine. The organic

layer was dried over anhydrous MgSO₄, ﬁltered, and concentrated

in vacuo. Puriﬁcation by silica gel column chromatography (eluent:

hexane/EtOAc ) 3/1) provided 1.75 g (63%) of desired acetate as

solid. ¹H NMR (400 MHz, CDCl₃) δ 7.44-7.43 (m, 1H), 7.40-7.38

(m, 2H), 7.35-7.32 (m, 3H), 7.17-7.13 (m, 2H), 5.31 (s, 2H),

2.03 (s, 3H), 1.50 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ 173.4,

170.8, 159.4, 145.8, 139.0, 136.8, 136.2, 135.5, 133.3, 131.1, 130.9,

130.6, 129.4, 128.3, 125.9, 115.7, 56.6, 32.7, 28.4, 21.1. MH+ 519.

(3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)methanol (10). To the solu-

tion of acetate (9) (1.57 g, 3.020 mmol) in THF (9 mL)/MeOH (9

mL)/H₂O (2 mL) was added LiOH monohydrate (380 mg, 9.060

mmol). The reaction mixture was stirred for 12 h at room temperature.

The reaction mixture was diluted with EtOAc and washed with brine.

The organic layer was dried over anhydrous MgSO₄, ﬁltered, and

concentrated in vacuo to provide 1.37 g (95%) of desired alcohol (10)

as a solid. The obtained alcohol was used without further puriﬁcation.

¹H NMR (400 MHz, CDCl₃) δ 7.45-7.44 (m, 1H), 7.34-7.32 (m,

4H), 7.16-7.14 (m, 2H), 4.82-4.78 (m, 1H), 4.72-4.70 (m, 2H), 1.51

(s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ 173.8, 160.5, 143.7, 138.4,

136.7, 136.0, 135.6, 133.4, 131.3, 130.9, 130.6, 129.3, 128.3, 126.0,

122.0, 54.6, 32.8, 28.4. MH+ 478.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

methoxymethyl)-1H-pyrazol-3-yl)-1,3,4-oxadiazole (12b). To the

suspension of alcohol (10) (120 mg, 0.251 mmol), NaH (20 mg,

60% dispersion in mineral oil) in DMF (5 mL) was stirred at room

temperature. After 1 h, the reaction mixture was added MeI (40

µL, 0.33 mmol) and stirred for 12 h. The reaction mixture was

ﬁltered off the white solid and then extracted with EtOAc (50 mL).

The organic layer was dried over anhydrous MgSO₄, ﬁltered, and

concentrated in vacuo. Puriﬁcation by silica gel column chroma-

tography (eluent: hexane/EtOAc ) 4/1) provided 103 mg (84%)

1

of desired ether (12b) as a solid. H NMR (400 MHz, CDCl₃) δ

7.45-7.44 (m, 1H), 7.36-7.31 (m, 4H), 7.26-7.23 (m, 2H), 4.66

(s, 2H), 3.48 (s, 3H), 1.50 (s, 9H). ¹³C NMR (100 MHz, CDCl₃)

δ 173.3, 159.8, 145.7, 139.0, 136.6, 135.9, 135.8, 133.4, 131.1,

130.9, 130.6, 129.2, 128.2, 126.4, 118.0, 63.6, 58.7, 32.7, 28.5.

MH+ 491.

2-(4-(Butoxymethyl)-5-(4-chlorophenyl)-1-(2,4-dichlorophe-

nyl)-1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-oxadiazole (12a). ¹H NMR

(400 MHz, CDCl₃) δ 7.45-7.36 (m, 1H), 7.34-7.31 (m, 4H),

7.28-7.26 (m, 2H), 4.70 (s, 2H), 3.60 (t, J ) 6.4 Hz, 2H),

1.66-1.57 (m, 2H), 1.50 (s, 9H), 1.41-1.26 (m, 2H), 0.91 (t, J )

7.6 Hz, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 173.2, 159.8, 145.6,

138.9, 136.5, 135.9, 135.8, 133.3, 131.1, 130.9, 130.6, 129.1, 128.2,

126.5, 118.3, 70.8, 62.0, 32.7, 31.9, 28.5, 19.6, 14.1. MH+ 533.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

(ﬂuoromethyl)-1H-pyrazol-3-yl)-1,3,4-oxadiazole (13). To the

solution of alcohol (10) (200 mg, 0.418 mmol) in CH₂Cl₂(5 mL)

in Falcon tube was added (diethylamino)sulfur triﬂuoride (DAST,

110 µL, 0.836 mmol). The reaction mixture was stirred for 2 h at

room temperature. Saturated NaHCO₃(30 mL) was added to the

reaction mixture. After 1 h, the organic extract was dried over

anhydrous MgSO₄, ﬁltered, and concentrated in vacuo. Puriﬁcation

by silica gel column chromatography (eluent: hexane/EtOAc ) 4/1)

provided 106 mg (53%) of desired ﬂuoride (13) as a solid. ¹H NMR

(400 MHz, CDCl₃) δ 7.47-7.46 (m, 1H), 7.38-7.32 (m, 4H),

7.24-7.20 (m, 2H), 5.67 (d, J ) 48.8 Hz, 2H), 1.50 (s, 9H). ¹³C

NMR (100 MHz, CDCl₃) δ 173.5, 159.3, 146.8, 139.1, 136.9, 136.4,

135.5, 133.3, 131.1, 130.9, 130.7, 129.4, 128.3, 125.6, 116.0 (d, J

) 20 Hz), 74.2 (d, J ) 162 Hz), 32.8, 28.5. MH+ 479.

Methyl (3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophe-

nyl)-1-(2,4-dichlorophenyl)-1H-pyrazol-4-yl)methylcarbamate

(14). To the solution of alcohol (10) (100 mg, 0.209 mmol) and

Burgess reagent (55 mg, 0.230 mmol) in THF (5 mL) was irradiated

in a microwave reactor (Biotage) for 60 min at 120 °C. The organic

extract was dried over anhydrous MgSO₄, ﬁltered, and concentrated

in vacuo. Puriﬁcation by Prep-LC (Gilson) provided 45 mg (40%)

as a solid. ¹H NMR (400 MHz, CDCl₃) δ 7.44-7.41 (m, 1H),

7.38-7.27 (m, 6H), 6.86-6.78 (m, 1H), 4.41 (d, J ) 6.8 Hz, 2H),

3.60 (s, 3H), 1.50 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ 173.6,

160.3, 157.2, 144.0, 138.3, 136.6, 136.0, 135.7, 133.4, 131.6, 130.9,

130.6, 129.3, 128.2, 125.9, 119.1, 52.2, 34.8, 32.8, 28.4. MH+ 534.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

(diﬂuoromethyl)-1H-pyrazol-3-yl)-1,3,4-oxadiazole (15). To the

solution of aldehyde (11) (50 mg, 0.105 mmol) in CH₂Cl₂(5 mL)

in Falcon tube was added (diethylamino)sulfur triﬂuoride (DAST,

30 µL, 0.210 mmol). The reaction mixture was stirred for 2 h at

room temperature. Saturated NaHCO₃(30 mL) was added to the

reaction mixture. After 1 h, the organic extract was dried over

anhydrous MgSO₄, ﬁltered, and concentrated in vacuo. Puriﬁcation

by silica gel column chromatography (eluent: hexane/EtOAc ) 4/1)

provided 25 mg (48%) of desired diﬂuoride (15) as a solid. ¹H

NMR (400 MHz, CDCl₃) δ 7.56 (d, J ) 53.6 Hz, 1H), 7.45-7.44

(m, 1H), 7.37-7.30 (m, 4H), 7.27-7.24 (m, 2H), 1.50 (s, 9H).

¹³C NMR (100 MHz, CDCl₃) δ 173.5, 158.9, 145.6, 137.4, 137.2,

136.6, 134.9, 133.4, 131.4, 130.9, 130.7, 129.1, 128.3, 125.6, 115.4

(t, J ) 26 Hz), 110.4 (t, J ) 232 Hz), 32.8, 28.4. MH+ 497.

3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazole-4-carbaldehyde (11). To the solu-

tion of alcohol (10) (100 mg, 0.209 mmol) and Dess-Martin

periodinane (132 mg, 0.313 mmol) in CH₂Cl₂(5 mL) was stirred

at room temperature. The reaction mixture was ﬁltered off the white

solid and then diluted with CH₂Cl₂(50 mL) and washed with brine.

The organic layer was dried over anhydrous MgSO₄, ﬁltered, and

concentrated in vacuo. Puriﬁcation by silica gel column chroma-

tography (eluent: hexane/EtOAc ) 3/1) provided 78 mg (78%) of

1

desired aldehyde (11) as a solid. H NMR (400 MHz, CDCl₃) δ

10.65 (s, 1H), 7.46-7.45 (m, 1H), 7.38-7.31 (m, 4H), 7.36-7.23

7228 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22

Lee et al.

3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazole-4-carboxylic acid (16). To the

solution of aldehyde (11) (1.0 g, 2.10 mmol) in t-BuOH (60 mL)

was added 2-methyl-2-butene (12.0 mL, 99.0 mmol), KH₂PO₄(2.2

g, 14.7 mmol), and NaClO₂(2.4 g, 18.9 mmol in H₂O (35 mL)).

The reaction mixture was stirred for 12 h at rt. The reaction mixture

was acidiﬁed with AcOH and extracted with EtOAc. The organic

layer was dried over anhydrous MgSO₄, ﬁltered, and concentrated

in vacuo to provide 981 mg (95%) of desired acid as a solid. The

obtained acid was used without further puriﬁcation. MH+ 491.

1-(3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)ethanol (17). To the solu-

tion of aldehyde (11) (100 mg, 0.210 mmol) in THF (5 mL) was

added methyl magnesium bromide (200 µL, 3.0 M solution in

diethylether). The reaction mixture was stirred for 12 h at room

temperature. H₂O (20 mL) was added to the reaction mixture and

then extracted with CH₂Cl₂(50 mL). The organic layer was dried

over anhydrous MgSO₄, ﬁltered, and concentrated in vacuo.

Puriﬁcation by silica gel column chromatography (eluent: hexane/

EtOAc ) 2/1) provided 83 mg (80%) of desired secondary alcohol

(17) as a solid. ¹H NMR (400 MHz, CDCl₃) δ 7.42-7.41 (m, 1H),

7.34-7.29 (m, 4H), 7.13-7.10 (m, 2H), 5.72 (d, J ) 11.6 Hz,

1H), 4.86-4.78 (m, 1H), 1.61 (d, J ) 7.2 Hz, 3H), 1.51 (s, 9H).

¹³C NMR (100 MHz, CDCl₃) δ 173.6, 161.0, 142.3, 136.7, 136.3,

136.0, 135.5, 133.4, 131.4, 130.9, 130.6. 129.3, 128.2, 126.5, 126.4,

62.6, 32.8, 28.4, 24.4. MH+ 491.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-(1-

methoxyethyl)-1H-pyrazol-3-yl)-1,3,4-oxadiazole (18). To the

suspension of secondary alcohol (17) (50 mg, 0.101 mmol), NaH

(25 mg, 60% dispersion in mineral oil) in DMF (5 mL) was stirred

at room temperature. After 1 h, the reaction mixture was added

MeI (20 µL, 0.33 mmol) and stirred for 12 h. The reaction mixture

was ﬁltered off the white solid and then extracted with EtOAc (50

mL). The organic extract was dried over anhydrous MgSO₄, ﬁltered,

and concentrated in vacuo. Puriﬁcation by silica gel column

chromatography (eluent: hexane/EtOAc ) 2/1) provided 42 mg

(82%) of desired product (18) as a solid. ¹H NMR (400 MHz,

CDCl₃) δ 7.41-7.40 (m, 1H), 7.30-7.22 (m, 6H), 5.27 (q, J )

6.4 Hz, 1H), 3.27 (s, 3H), 1.50 (s, 9H), 1.39 (d, J ) 6.8 Hz, 3H).

¹³C NMR (100 MHz, CDCl₃) δ 173.3, 160.0, 143.9, 137.9, 136.6,

135.7, 135.6, 133.5, 131.8, 131.0, 130.5, 128.7, 128.1, 127.5, 123.1,

71.0, 56.6, 32.7, 28.5, 21.5. MH+ 505.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-(1-

ﬂuoroethyl)-1H-pyrazol-3-yl)-1,3,4-oxadiazole (19). To the solu-

tion of secondary alcohol (17) (50 mg, 0.101 mmol) in CH₂Cl₂(3

mL) in Falcon tube was added DAST (27 µL, 0.202 mmol). The

reaction mixture was stirred for 2 h at room temperature. Saturated

NaHCO₃(30 mL) was added to the reaction mixture. After 1 h,

the organic layer was dried over anhydrous MgSO₄, ﬁltered, and

concentrated in vacuo. Puriﬁcation by silica gel column chroma-

tography (eluent: hexane/EtOAc ) 2/1) provided 40 mg (80%) of

desired product (19) as a solid. ¹H NMR (400 MHz, CDCl₃) δ

7.42 (bs, 1H), 7.32-7.29 (m, 4H), 7.25-7.22 (m, 2H), 6.49 (q, J

) 6.8 Hz, 1H), 1.61 (d, J ) 6.4 Hz, 3H), 1.50 (s, 9H). ¹³C NMR

(100 MHz, CDCl₃) δ 173.5, 159.5, 144.3, 136.9, 136.8, 136.1,

135.4, 133.5, 131.8, 131.0, 130.5, 128.9, 128.1, 126.8, 121.5 (d, J

) 23 Hz), 84.0 (d, J ) 164 Hz), 32.7, 28.5, 21.7 (d, J ) 26 Hz).

MH+ 493.

δ 194.7, 174.1, 158.9, 146.0, 137.6, 137.2, 136.7, 134.9, 133.3,

131.5, 130.9, 130.6, 129.2, 128.3, 125.9, 123.1, 32.8, 31.4, 28.5.

MH+ 489.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

vinyl-1H-pyrazol-3-yl)-1,3,4-oxadiazole (21). To the solution of

secondary alcohol (17) (200 mg, 0.41 mmol) and Burgess reagent

(193 mg, 0.81 mmol) in THF (5 mL) was irradiated in a microwave

reactor (Biotage) for 10 min at 150°. The organic extract was dried

over anhydrous MgSO₄, ﬁltered, and concentrated in vacuo.

Puriﬁcation by silica gel column chromatography (eluent: hexane/

EtOAc ) 4/1) provided 50 mg (21, 26%) and 100 mg (22, 44%)

as a solid. ¹H NMR (400 MHz, CDCl₃) δ 7.42-7.41 (m, 1H),

7.34-7.28 (m, 4H), 7.20-7.18 (m, 2H), 7.12-7.04 (m, 1H), 5.41

(dd, J ) 18.0, 1.2 Hz, 1H), 5.25 (dd, J ) 11.6, 1.2 Hz, 1H), 1.50

(s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ 173.3, 160.0, 142.6, 137.2,

136.7, 135.8, 135.5, 133.6, 131.5, 131.0, 130.5, 129.4, 128.1, 127.2,

125.5, 119.6, 118.7, 32.7, 28.5. MH+ 473.

Methyl 1-(3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophe-

nyl)-1-(2,4-dichlorophenyl)-1H-pyrazol-4-yl)ethylcarbamate

(22). ¹H NMR (400 MHz, CDCl₃) δ 7.52-7.49 (m, 2H), 7.42-7.30

(m, 6H), 5.05-5.00 (m, 1H), 3.63 (s, 3H), 1.52-1.48 (m, 12H).

¹³C NMR (100 MHz, CDCl₃) δ 173.5, 160.7, 156.8, 143.1, 136.6,

136.5, 136.0, 135.6, 133.4, 131.6, 130.9, 130.6, 129.4, 128.1, 126.1,

124.1, 52.1, 42.4, 32.8, 28.4, 21.6. MH+ 473.

2-(3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)propan-2-ol (23). To the

solution of ketone (20) (40 mg, 0.082 mmol) in THF (5 mL) was

added methyl magnesiumbromide (100 µL, 3.0 M solution in

diethylether). The reaction mixture was stirred for 12 h at room

temperature. H₂O (20 mL) was added to the reaction mixture and

then extracted with CH₂Cl₂(50 mL). The organic layer was dried

over anhydrous MgSO₄, ﬁltered, and concentrated in vacuo.

Puriﬁcation by silica gel column chromatography (eluent: hexane/

EtOAc ) 2/1) provided 33 mg (80%) of desired tertiary alcohol

(23) as a solid. ¹H NMR (400 MHz, CDCl₃) δ 7.39-7.38 (m, 1H),

7.29-7.17 (m, 6H), 6.77 (s, 1H), 1.51 (s, 9H), 1.42 (s, 6H). ¹³C

NMR (100 MHz, CDCl₃) δ 173.5, 161.5, 141.2, 136.8, 136.2, 136.1,

135.5, 134.0, 132.1, 131.1, 130.4, 130.3, 128.9, 128.7, 127.9, 68.4,

32.8, 31.4, 28.4. MH+ 505.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

(prop-1-en-2-yl)-1H-pyrazol-3-yl)-1,3,4-oxadiazole (24). To the

solution of tertiary alcohol (23) (52 mg, 0.103 mmol) and Burgess

reagent (50 mg, 0.206 mmol) in THF (5 mL) was irradiated in a

microwave reactor (Biotage) for 10 min at 150°. The organic layer

was washed with brine and dried over anhydrous MgSO₄, ﬁltered,

and concentrated in vacuo. Puriﬁcation by silica gel column

chromatography (eluent: hexane/EtOAc ) 4/1) provided 49 mg

(98%) of desired product (24) as a solid. ¹H NMR (400 MHz,

CDCl₃) δ 7.42 (d, J ) 2.4 Hz, 1H), 7.39 (d, J ) 8.4 Hz, 1H), 7.32

(dd, J ) 8.4, 2.4 Hz, 1H), 7.28-7.26 (m, 2H), 7.14-7.10 (m, 2H),

5.28-5.27 (m, 1H), 4.99-4.98 (m, 1H), 2.02 (s, 3H), 1.48 (s, 9H).

¹³C NMR (100 MHz, CDCl₃) δ 173.3, 159.7, 142.4, 137.1, 136.5,

135.9, 135.5, 135.2, 133.3, 131.0, 130.9, 130.5, 129.0, 128.1, 127.1,

124.5, 119.7, 32.7, 28.5, 24.2. MH+ 487.

S-(3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)methyl ethanethioate (25).

To the solution of bromide (8) (150 mg, 0.28 mmol) in DMF (3

mL) was added KSAc (48 mg, 0.42 mmol). The reaction mixture

was reﬂuxed for 12 h at room temperature. The reaction mixture

was diluted with EtOAc (25 mL) and washed with brine. The

organic layer was dried over anhydrous MgSO₄, ﬁltered, and

concentrated in vacuo. Puriﬁcation by Prep-LC (Gilson) provided

45 mg (30%) of desired thioacetate as a solid. ¹H NMR (400 MHz,

CDCl₃) δ 7.40 (d, J ) 2.4 Hz, 1H), 7.38-7.26 (m, 5H), 7.16-7.12

(m, 2H), 4.40 (s, 2H), 2.26 (s, 3H), 1.49 (s, 9H). ¹³C NMR (100

MHz, CDCl₃) δ 195.1, 173.3, 159.6, 144.4, 138.4, 136.7, 136.0,

135.6, 133.3, 131.2, 130.9, 130.5, 129.3, 128.2, 126.2, 116.7, 32.7,

30.4, 28.5, 23.4. MH+ 535.

1-(3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)ethanone (20). To the solu-

tion of secondary alcohol (17) (150 mg, 0.305 mmol) and

Dess-Martin periodinane (155 mg, 0.366 mmol) in CH₂Cl₂(5 mL)

was stirred at room temperature. The reaction mixture was ﬁltered

off the white solid and then diluted with CH₂Cl₂(50 mL) and

washed with brine. The organic layer was dried over anhydrous

MgSO₄, ﬁltered, and concentrated in vacuo. Puriﬁcation by silica

gel column chromatography (eluent: hexane/EtOAc ) 2/1) provided

1

117 mg (78%) of desired ketone (20) as a solid. H NMR (400

2-(3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)acetonitrile (26). To the

solution of bromide (8) (1.0 g, 1.85 mmol) in CH₃CN (20 mL)

MHz, CDCl₃) δ 7.44-7.43 (m, 1H), 7.35-7.30 (m, 4H), 7.23-7.19

(m, 2H), 2.40 (s, 3H), 1.50 (s, 9H). ¹³C NMR (100 MHz, CDCl₃)

Biarylpyrazolyl Oxadiazole as CB1 Receptor Antagonists

Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7229

was added KCN (0.24 g, 3.70 mmol) and 18-crown-6 (0.20 g, 0.74

mmol). The reaction mixture was reﬂuxed for 12 h. The reaction

mixture was cooled to room temperature and diluted with brine.

The aqueous layer was extracted with EtOAc. The organic layer

was dried over anhydrous MgSO₄, ﬁltered, and concentrated in

vacuo. Puriﬁcation by normal phase column chromatography

(Biotage) provided 0.66 g (74%) of desired cyanide as a solid. ¹H

NMR (400 MHz, CDCl₃) δ 7.45-7.32 (m, 5H), 7.21-7.18 (m,

2H), 4.05 (s, 2H), 1.51 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ

173.5, 159.3, 144.8, 138.0, 137.1, 136.7, 135.2, 133.3, 131.0, 130.9,

130.7, 129.8, 128.4, 125.3, 117.3, 110.5, 32.8, 28.5, 13.8. MH+

488.

MHz, CDCl₃) δ 173.6, 160.2, 144.6, 138.3, 136.6, 135.9, 135.8,

133.4, 131.4, 131.0, 130.5, 130.4, 129.2, 128.2, 126.4, 49.0, 40.4,

32.8, 28.4, 22.4. MH+ 518.

1-((3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)methyl)pyrrolidine-2,5-di-

one (30). To the suspension of bromide (8) (150 mg, 0.28 mmol)

in acetone (10 mL) was added succinimide (35 mg, 0.33 mmol)

and K₂CO₃(60 mg, 0.42 mmol). The reaction mixture was reﬂuxed

for 12 h and cooled to room temperature. H₂O (25 mL) was added

to the reaction mixture and then extracted with EtOAc (50 mL).

The organic extract was dried over anhydrous MgSO₄, ﬁltered, and

concentrated in vacuo. Puriﬁcation by Prep-LC (Gilson) provided

1

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

(phenoxymethyl)-1H-pyrazol-3-yl)-1,3,4-oxadiazole (27a). To the

solution of bromide (8) (150 mg, 0.277 mmol) in DMF (5 mL)

was added phenol (40 mg, 0.415 mmol) and Cs₂CO₃(202 mg, 0.622

mmol). The reaction mixture was reﬂuxed for 12 h at room

temperature. Reaction mixture was ﬁltered off the white solid and

then extracted with EtOAc (50 mL). The organic extract was dried

over anhydrous MgSO₄, ﬁltered, and concentrated in vacuo.

Puriﬁcation by silica gel column chromatography (eluent: hexane/

EtOAc ) 5/1) provided 86 mg (56%) of desired ether (27a) as a

99 mg (64%) of desired product as a solid. H NMR (400 MHz,

CDCl₃) δ 7.36-7.16 (m, 7H), 4.99 (s, 2H), 2.33 (s, 4H), 1.47 (s,

9H). ¹³C NMR (100 MHz, CDCl₃) δ 176.8, 173.3, 159.6, 143.2,

137.5, 136.8, 136.1, 135.3, 133.6, 131.6, 131.1, 130.4, 129.0, 128.0,

126.4, 115.1, 34.2, 32.7, 28.5, 28.2. MH+ 560.

1-((3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)methyl)pyrrolidin-2-one

(29). Similar procedure with preparation of 30 proceeded with

2-pyrrolidinone, instead of succinimide. ¹H NMR (400 MHz,

CDCl₃) δ 7.42 (d, J ) 2.0 Hz, 1H), 7.36-7.27 (m, 4H), 7.13-7.09

(m, 2H), 4.87 (s, 2H), 3.26 (t, J ) 6.8 Hz, 2H), 2.12 (t, J ) 8.0

Hz, 2H), 1.68-1.65 (m, 2H), 1.50 (s, 9H). ¹³C NMR (100 MHz,

CDCl₃) δ 174.6, 173.4, 159.8, 144.5, 138.6, 136.7, 136.0, 135.6,

133.4, 131.1, 130.9, 130.5, 129.0, 128.2, 126.1, 116.2, 46.8, 36.6,

32.7, 30.9, 28.5, 17.8. MH+ 544.

3-((3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)methyl)oxazolidin-2-one

(31). Similar procedure with preparation of 30 proceeded with

2-oxazolidinone, instead of succinimide. ¹H NMR (400 MHz,

CDCl₃) δ 7.45-7.41 (m, 1H), 7.37-7.28 (m, 4H), 7.18-7.15 (m,

2H), 4.75 (s, 2H), 4.13 (t, J ) 8.0 Hz, 2H), 3.62 (t, J ) 8.0 Hz,

2H), 1.50 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ 173.6, 159.8,

158.1, 145.4, 138.5, 136.8, 136.3, 135.6, 133.4, 131.2, 130.9, 130.6,

129.3, 128.2, 125.8, 115.8, 62.1, 45.1, 38.2, 32.8, 28.5. MH+ 546.

Ethyl 4-(Bromomethyl)-5-(4-chlorophenyl)-1-(2,4-dichlorophe-

nyl)-1H-pyrazole-3-carboxylate (33). To the solution of ester (5)

(29.5 g, 72.0 mmol) in CCl₄(500 mL) was added N-bromosuc-

cinimide (15.3 g, 86.4 mmol) and AIBN (0.6 g, 3.6 mmol). The

reaction mixture was heated for 12 h at 80 °C. Reaction mixture

was ﬁltered. Filtrate was washed with H₂O and brine. The

organic layer was dried over anhydrous MgSO₄, ﬁltered, and

concentrated in vacuo to provide 31.8 g (yield: 90%) of desired

bromide as a solid. The obtained bromide was used without

further puriﬁcation.

1

solid. H NMR (400 MHz, CDCl₃) δ 7.45 (d, J ) 2.0 Hz, 1H),

7.39 (d, J ) 8.4 Hz, 1H), 7.33 (dd, J ) 8.4, 2.0 Hz, 1H), 7.30-7.22

(m, 6H), 6.97-6.95 (m, 3H), 5.27 (s, 2H), 1.44 (s, 9H). ¹³C NMR

(100 MHz, CDCl₃) δ 173.4, 159.6, 158.7, 146.0, 138.9, 136.7,

136.0, 135.7, 133.4, 131.1, 131.0, 130.6, 129.7, 129.3, 128.3, 126.2,

121.5, 116.7, 115.4, 60.3, 32.7, 28.4. MH+ 553.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

((pyridin-2-yloxy)methyl)-1H-pyrazol-3-yl)-1,3,4-oxadiazole

(27b). ¹H NMR (400 MHz, CDCl₃) δ 8.11-8.09 (m, 1H),

7.56-7.53 (m, 1H), 7.44-7.41 (m, 2H), 7.34-7.32 (m, 1H),

7.28-7.19 (m, 4H), 6.88-6.86 (m, 1H), 6.73-6.71 (m, 1H), 5.52

(s, 2H), 1.52 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ 173.3, 163.5,

159.6, 147.0, 145.9, 139.2, 138.8, 136.7, 135.9, 135.7, 133.3, 131.1,

131.0, 130.6, 129.2, 128.2, 126.3, 117.2, 116.9, 111.2, 57.9, 32.7,

28.4. MH+ 554.

N-((3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)methyl)-N-methyletha-

namine (28b). To the suspension of bromide (8) (150 mg, 0.28

mmol) in CH₂Cl₂(5 mL) was added N-ethylmethylamine (30 µL,

0.33 mmol) and DIPEA (63 µL, 0.36 mmol). The reaction mixture

was stirred for 12 h at room temperature. H₂O (25 mL) was added

to the reaction mixture and then extracted with EtOAc (50 mL).

The organic extract was dried over anhydrous MgSO₄, ﬁltered, and

concentrated in vacuo. Puriﬁcation by Prep-LC (Gilson) provided

1

83 mg (58%) of desired amine as a solid. H NMR (400 MHz,

Ethyl 4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-chlorophenyl)-

1-(2,4-dichlorophenyl)-1H-pyrazole-3-carboxylate (34). NaH (0.37

g, 9.21 mmol, 60% dispersion in mineral oil) was added to the

solution of 1,2,4-triazole (0.51 g, 7.37 mmol) in THF (30 mL)

at 0 °C. The reaction mixture was stirred for 1 h at 0 °C. The

solution of bromide (33) (3 g, 6.14 mmol) in THF (15 mL) was

added to the reaction mixture. The reaction mixture was warmed

up to room temperature, stirred for 1 h at room temperature and

for 12 h at 45 °C. The reaction mixture was cooled to room

temperature. H₂O (100 mL) was added to the reaction mixture

and then extracted with EtOAc (150 mL). The organic extract

was dried over anhydrous MgSO₄, ﬁltered, and concentrated in

vacuo. Puriﬁcation by silica gel column chromatography (Biotage,

eluent: 12% EtOAc/hexane f EtOAc (gradient)) provided 1.35 g

CDCl₃) δ 7.42-7.27 (m, 7H), 3.78 (s, 2H), 2.51-2.43 (m, 2H),

2.13 (s, 3H), 1.51 (s, 9H), 0.99 (t, J ) 6.8 Hz, 3H). ¹³C NMR (100

MHz, CDCl₃) δ 173.1, 160.1, 145.1, 139.3, 136.4, 136.1, 135.5,

133.3, 131.6, 131.0, 130.5, 128.9, 128.1, 127.2, 119.2, 51.5, 49.5,

40.9, 32.7, 28.5, 12.5. MH+ 518.

2-tert-Butyl-5-(5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-

(piperidin-1-ylmethyl)-1H-pyrazol-3-yl)-1,3,4-oxadiazole (28a).

¹H NMR (400 MHz, CDCl₃) δ 7.44-7.26 (m, 7H), 3.58 (s, 2H),

2.38 (br s, 4H), 1.60-1.45 (m, 15H). ¹³C NMR (100 MHz, CDCl₃)

δ 173.1, 160.2, 145.1, 139.3, 136.4, 136.1, 135.4, 133.3, 131.6,

130.9, 130.5, 128.8, 128.1, 127.3, 118.9, 54.0, 51.1, 32.7, 28.5,

26.3, 24.5. MH+ 546.

4-((3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)methyl)morpholine (28c).

¹H NMR (400 MHz, CDCl₃) δ 7.43-7.41 (m, 1H), 7.38-7.27 (m,

4H), 6.98-6.81 (m, 2H), 4.92 (s, 2H), 3.77-3.51 (m, 8H),

2.51-2.39 (m, 8H), 1.50 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ

173.2, 160.0, 145.2, 139.2, 136.5, 135.9, 135.6, 133.3, 131.4, 130.9,

130.5, 128.9, 128.2, 127.1, 117.9, 67.3, 53.1, 50.8, 32.7, 28.5. MH+

548.

N-((3-(5-tert-Butyl-1,3,4-oxadiazol-2-yl)-5-(4-chlorophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-4-yl)methyl)propan-2-amine

(28d). ¹H NMR (400 MHz, CDCl₃) δ 7.43-7.31 (m, 7H), 3.95 (s,

2H), 3.20-3.07 (m, 1H), 1.51 (s, 9H), 1.05 (s, 6H). ¹³C NMR (100

1

(46%) of desired triazole (34) as a solid. H NMR (400 MHz,

CDCl₃) δ 8.76 (s, 1H), 8.09 (s, 1H), 7.41-7.27 (m, 7H), 5.48

(s, 2H), 4.44 (quartet, J ) 7.2 Hz, 2H), 1.398 (t, J ) 7.2 Hz,

3H). MH+ 478.

4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazole-3-carboxylic acid (35). To the

solution of ester (34) (500 mg, 1.05 mmol) in THF (5 mL)/H₂O

(15 mL) was added LiOH monohydrate (132 mg, 3.15 mmol). The

reaction mixture was reﬂuxed for 2 h and cooled to room

temperature. The reaction mixture was acidiﬁed with aq 1N HCl

solution and extracted with 30% MeOH/CHCl₃. The organic extract

7230 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22

Lee et al.

was dried over anhydrous MgSO₄, ﬁltered, concentrated and dried

in vacuo to provide 470 mg (100%) of desired acid (35) as a solid.

The obtained acid was used without further puriﬁcation.

135.3, 133.4, 131.1, 130.9, 130.6, 129.5, 128.3, 125.2, 112.7, 47.0,

32.7, 28.4. MH+ 531.

2-(4-((1H-Tetrazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-oxadiazole

(32g). ¹H NMR (400 MHz, CDCl₃) δ 9.26 (s, 1H), 7.46-7.29 (m,

7H), 5.78 (s, 2H), 1.49 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ

173.8, 159.4, 146.6, 144.2, 138.0, 137.1, 136.9, 135.2, 133.3, 131.7,

130.8, 130.7, 129.7, 128.4, 124.9, 113.9, 41.9, 32.8, 28.4. MH+

531.

Ethyl 4-Bromo-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-1H-

pyrazole-3-carboxylate (38). To a solution of ethyl 5-(4-chlo-

rophenyl)-1-(2,4-dichlorophenyl)-1H-pyrazole-3-carboxylate (37) (1

g, 2.4 mmol) in methylene chloride (30 mL) at room temperature

was added bromine (4.9 mL, prepared 1.0 M solution in methylene

chloride, 4.9 mmol) dropwise. The reaction mixture was stirred at

room temperature for 1 h, and the resulting solution was diluted

with ethyl ether (50 mL). The reaction mixture was quenched with

saturated sodium bicarbonate solution (30 mL) and extracted with

ethyl ether (50 mL twice). The organic solution was evaporated

under reduced pressure, and crude residue was puriﬁed with silica

gel column (hexane/ethyl acetate ) 5/1) to recover starting material

(37) (401 mg, 40%) and produce the title compound (38) (520 mg,

45% yield) as white solid. ¹H NMR (400 MHz, CDCl₃) δ 7.41 (d,

J ) 2.0 Hz, 1H), 7.37 (d, J ) 8.4, 2H), 7.35-7.31 (m, 3H),

7.21-7.19 (m, 2H), 4.50 (q, J ) 7.2 Hz, 2H), 1.44 (t, J ) 7.2 Hz,

3H). MH+ 473.

Ethyl 5-(4-Chlorophenyl)-4-cyclopropyl-1-(2,4-dichlorophe-

nyl)-1H-pyrazole-3-carboxylate (39). To a solution of ethyl

4-bromo-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-1H-pyrazole-

3-carboxylate (38) (500 mg, 1.1 mmol) in aqueous toluene,

tetrakis(triphenylphsophine)palladium (122 mg, 0.11 mmol) and

potassium carbonate (510 mg, 3.9 mmol) were added. The reaction

mixture was placed under microwave irradiation with the temper-

ature set to 140 °C. The resulting solution was ﬁltered with syringe

ﬁlter, and then the solvent was evaporated under reduced pressure.

The residue was puriﬁed with silica gel column chromatography

to obtain the title compound (283 mg, 44%) as white solid. ¹H

NMR (400 MHz, CDCl₃) δ 7.46-7.43 (m, 1H), 7.38-7.35 (m,

4H), 7.13-7.11 (m, 2H), 4.48 (q, J ) 7.1 Hz, 2H), 2.02-1.98 (m,

1H), 1.44 (t, J ) 7.1, 3H), 1.26-1.23 (m, 1H), 0.89-0.86 (m, 1H).

MH+ 436.

2-tert-Butyl-5-(5-(4-chlorophenyl)-4-cyclopropyl-1-(2,4-dichlo-

rophenyl)-1H-pyrazol-3-yl)-1,3,4-oxadiazole (41). Similar pro-

cedure with preparation of 4h proceeded with 39, instead of 5. ¹H

NMR (400 MHz, CDCl₃) δ 7.55-7.50 (m, 2H), 7.37-7.31 (m,

2H), 7.22-7.20 (m, 1H), 7.15-7.10 (m, 2H), 1.45 (m, 1H), 1.34

(s, 9H), 0.62-0.59 (m, 2H), 0.38-0.34 (m, 2H). ¹³C NMR (100

MHz, CDCl₃) δ 173.2, 160.0, 139.7, 136.4, 136.0, 135.3, 133.4,

131.4, 131.1, 130.5, 129.3, 128.8, 128.1, 127.3, 122.7, 32.7, 28.5,

7.8, 5.7. MH+ 489.

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-methylcyclopropyl)-1,3,4-

oxadiazole (42b). ¹H NMR (400 MHz, DMSO-d₆) δ 8.41 (s, 1H),

7.89 (s, 1H), 7.83 (d, J ) 8.8 Hz, 1H), 7.60 (d, J ) 2.4 Hz, 1H),

7.59 (dd, J ) 8.8 Hz, 2.4 Hz, 1H), 7.50-7.76 (m, 4H), 5.50 (s,

2H), 1.50 (s, 3H), 1.26-1.19 (m, 2H), 1.05-0.99 (m, 2H). ¹³C

NMR (100 MHz, CDCl₃) δ 171.0, 158.8, 151.9, 146.1, 144.8, 138.1,

136.9, 136.5, 135.4, 133.4, 131.7, 130.8, 130.7, 129.4, 128.3, 125.4,

114.9, 43.0, 20.5, 17.0, 13.1. ESI-MS m/z: 526 [M + H]⁺. Positive

HR-FAB-MS m/z: 526.0731 [M + H]⁺(calcd for C₂₄H₁₈Cl₃N₇O:

526.0717).

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-(triﬂuoromethyl)cyclo-

propyl)-1,3,4-oxadiazole (42c). ¹H NMR (400 MHz, CDCl₃) δ

9.13 (s, 1H), 8.14 (s, 1H), 7.45-7.32 (m, 7H), 5.62 (s, 2H), 1.64

(s, 4H). ¹³C NMR (100 MHz, CDCl₃) δ 163.0, 160.0, 152.0, 146.3,

144.7, 137.4, 137.0, 136.6, 135.3, 133.3, 131.7, 130.8, 130.6, 129.4,

128.3, 125.3, 124.3 (d, J ) 272 Hz), 115.2, 42.9, 21.2 (q, J ) 37

Hz), 12.7. ESI-MS m/z: 580 [M + H]⁺; Positive HR-FAB-MS m/z:

580.0435 [M + H]⁺(Calcd for C₂₄H₁₅Cl₃F₃N₇O: 580.0434).

4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-N′-pivaloyl-1H-pyrazole-3-carbohydrazide (36).

To the solution of acid (35) (330 mg, 0.74 mmol) in CH₂Cl₂(10

mL) was added oxalyl chloride (77 µL, 0.88 mmol) and the catalytic

amount of DMF. The reaction mixture was stirred for 1 h and

concentrated in vacuo. The residue (crude acyl chloride) was diluted

with CH₂Cl₂(10 mL) and pivalohydrazide (128 mg, 1.10 mmol),

and triethylamine (0.31 mL, 2.21 mmol) was added. The reaction

mixture was stirred for 2 h at room temperature. The reaction

mixture was concentrated in vacuo and diluted with EtOAc (50

mL). The organic layer was washed with aq 1N HCl and aq sat

NaHCO₃solution, dried over anhydrous MgSO₄, ﬁltered, and

concentrated in vacuo. Puriﬁcation by Prep-LC (Gilson) provided

244 mg (61%) of desired diamide to target compound.

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-oxadiazole

(32d). NaH (15 mg, 0.36 mmol, 60% dispersion in mineral oil)

was added to the solution of 1,2,4-triazole (23 mg, 0.33 mmol) in

THF (5 mL) at 0 °C. The reaction mixture was stirred for 30 min

at 0 °C. The solution of bromide (8) (150 mg, 0.28 mmol) in THF

(5 mL) was added to the reaction mixture. The reaction mixture

was warmed up to room temperature and stirred for 12 h at room

temperature. H₂O (25 mL) was added to the reaction mixture and

then extracted with EtOAc (50 mL). The organic extract was dried

over anhydrous MgSO₄, ﬁltered, and concentrated in vacuo.

Puriﬁcation by Prep-LC (Gilson) provided 70 mg (47%) of desired

1

product as a solid. H NMR (400 MHz, CDCl₃) δ 8.79 (s, 1H),

7.99 (s, 1H), 7.49-7.44 (m, 3H), 7.49-7.29 (m, 4H), 5.59 (s, 2H),

1.48 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ 173.5, 159.4, 151.9,

146.2, 144.8, 138.2, 136.9, 136.5, 135.4, 133.4, 131.7, 130.9, 130.7,

129.4, 128.3, 125.4, 115.1, 43.0, 32.8, 28.4. ESI-MS m/z: 528 [M

+ H]⁺; positive HR-FAB-MS m/z: 528.0884 [M + H]⁺(calcd for

C₂₄H₂₀Cl₃N₇O: 528.0873).

2-(4-((1H-Pyrrol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-dichlo-

rophenyl)-1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-oxadiazole (32a).

¹H NMR (400 MHz, CDCl₃) δ 7.45-7.27 (m, 7H), 6.45-6.39 (m,

2H), 5.92-5.85 (m, 2H), 5.53 (s, 2H), 1.51 (s, 9H). MH+ 528.

2-(4-((1H-Pyrazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-dichlo-

rophenyl)-1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-oxadiazole (32b).

¹H NMR (400 MHz, CDCl₃) δ 7.78 (d, J ) 2.0 Hz, 1H), 7.49-7.47

(m, 1H), 7.42-7.28 (m, 7H), 6.18 (t, J ) 2.0 Hz, 1H), 5.54 (s,

2H), 1.47 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ 173.4, 159.6,

145.9, 139.5, 138.4, 136.7, 136.2, 135.7, 133.4, 131.7, 130.9, 130.8,

130.6, 129.2, 128.2, 125.8, 116.4, 105.3, 45.1, 32.7, 28.4. MH+

527.

2-(4-((1H-Imidazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-oxadiazole

(32c). ¹H NMR (400 MHz, CDCl₃) δ 7.59 (s, 1H), 7.43-7.33 (m,

5H), 7.10-7.05 (m, 2H), 7.01 (t, J ) 6.8 Hz, 1H), 6.92 (t, J ) 1.2

Hz, 1H), 5.47 (s, 2H), 1.49 (s, 9H). ¹³C NMR (100 MHz, CDCl₃)

δ 173.6, 159.4, 145.6, 138.2, 137.2, 137.0, 136.7, 135.2, 133.3,

131.1, 130.8, 130.6, 129.7, 129.4, 128.3, 125.6, 119.2, 116.5, 39.8,

32.8, 28.4. MH+ 527.

2-(4-((1H-1,2,3-Triazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-oxadiazole

1

(32e). H NMR (400 MHz, CDCl₃) δ 8.21 (d, J ) 1.2 Hz, 1H),

7.66 (d, J ) 0.8 Hz, 1H), 7.44 (dd, J ) 1.6 Hz, 0.8 Hz, 1H),

7.42-7.29 (m, 6H), 5.76 (s, 2H), 1.48 (s, 9H). ¹³C NMR (100 MHz,

CDCl₃) δ 173.7, 159.5, 146.3, 138.1, 136.9, 136.6, 135.4, 133.5,

133.4, 131.7, 130.8, 130.7, 129.5, 128.3, 125.6, 125.3, 115.1, 43.5,

32.8, 28.4. MH+ 530.

2-(4-((2H-tetrazol-2-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-dichlo-

rophenyl)-1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-oxadiazole (32f).

¹H NMR (400 MHz, CDCl₃) δ 8.43 (s, 1H), 7.44-7.43 (m, 1H),

7.36 (d, J ) 0.4 Hz, 1H), 7.33 (d, J ) 2.4 Hz, 1H), 7.31-7.27 (m,

2H), 7.16-7.13 (m, 2H), 6.07 (s, 2H), 1.47 (s, 9H). ¹³C NMR (100

MHz, CDCl₃) δ 173.5, 159.2, 153.0, 146.3, 138.8, 137.0, 136.7,

Biarylpyrazolyl Oxadiazole as CB1 Receptor Antagonists

Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7231

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-phenylcyclopropyl)-1,3,4-

oxadiazole (42d). ¹H NMR (400 MHz, DMSO-d₆) δ 8.38 (s, 1H),

7.94 (s, 1H), 7.89-7.78 (m, 2H), 7.60-7.55 (m, 1H), 7.48-7.26

(m, 8H), 5.52 (s, 2H), 1.69-1.64 (m, 2H), 1.55-1.47 (m, 2H).

¹³C NMR (100 MHz, CDCl₃) δ 170.0, 159.2, 151.9, 146.1, 144.8,

138.6, 138.0, 136.9, 136.5, 135.4, 133.3, 131.7, 130.8, 130.6, 130.0,

129.4, 128.9, 128.3, 128.1, 125.4, 115.0, 42.9, 22.7, 16.5. ESI-MS

m/z: 588 [M + H]⁺. positive HR-FAB-MS m/z: 588.0896 [M +

H]⁺(calcd for C₂₉H₂₀Cl₃N₇O: 588.0873).

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-p-tolylcyclopropyl)-1,3,4-

oxadiazole (42e). ¹H NMR (400 MHz, DMSO-d₆) δ 8.37 (s, 1H),

7.88 (s, 1H), 7.84-7.76 (m, 2H), 7.57 (dd, J ) 8.4 Hz, 2.4 Hz,

1H), 7.48-7.43 (m, 2H), 7.43-7.36 (m, 8H), 7.30-7.24 (m, 2H),

7.18-7.12 (m, 2H), 5.52 (s, 2H), 2.26 (s, 3H), 1.65-1.59 (m, 2H),

1.48-1.41 (m, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 170.3, 159.1,

151.9, 146.1, 144.8, 138.0, 137.9, 136.9, 136.5, 135.7, 135.4, 133.3,

131.7, 130.8, 130.6, 129.9, 129.6, 128.3, 125.4, 115.0, 42.9, 22.4,

21.4, 16.5. ESI-MS m/z: 602 [M + H]⁺. Positive HR-FAB-MS

m/z: 602.1028 [M + H]⁺(calcd for C₃₀H₂₂Cl₃N₇O: 602.1030).

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-bromophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-p-tolylcyclopropyl)-

1,3,4-oxadiazole (43e). ¹H NMR (400 MHz, CDCl₃) δ 8.49 (s,

1H), 7.89 (s, 1H), 7.54-7.52 (m, 2H), 7.45-7.41 (m, 3H),

7.38-7.30 (m, 4H), 7.19-7.17 (m, 2H), 5.50 (s, 2H), 2.35 (s, 3H),

1.77-1.74 (m, 2H), 1.49-1.46 (m, 2H). ¹³C NMR (100 MHz,

CDCl₃) δ 170.3, 159.1, 151.9, 146.1, 144.8, 138.1, 137.9, 136.9,

135.7, 135.4, 133.3, 132.4, 131.9, 130.8, 130.7, 129.9, 129.6, 128.3,

125.9, 124.9, 115.0, 42.9, 22.4, 21.4, 16.5. ESI-MS m/z: 646 [M

+ H]⁺. Positive HR-FAB-MS m/z: 646.0522 [M + H]⁺(calcd for

C₃₀H₂₂BrCl₂N₇O: 646.0525).

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-bromophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-(4-chlorophenyl)cy-

clopropyl)-1,3,4-oxadiazole (43f). ¹H NMR (400 MHz, CDCl₃) δ

8.51 (s, 1H), 7.89 (s, 1H), 7.54-7.52 (m, 2H), 7.45-7.40 (m, 5H),

7.36-7.30 (m, 4H), 5.52 (s, 2H), 1.81-1.78 (m, 2H), 1.50-1.47

(m, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 169.6, 159.3, 152.0, 146.2,

144.8, 137.9, 137.1, 137.0, 135.4, 134.0, 133.3, 132.4, 131.9, 131.4,

130.8, 130.7, 129.1, 128.3, 125.8, 124.9, 115.0, 42.9, 22.2, 16.6.

ESI-MS m/z: 666 [M + H]⁺. Positive HR-FAB-MS m/z: 665.9971

[M + H]⁺(calcd for C₂₉H₁₉BrCl₃N₇O: 665.9978).

HPLC Analysis Data. All ﬁnal compounds were determined

by Agilent 1200 series high performance liquid chromatography

with UV detection at 254 nm (Xterra MS C18 3.5 µm, 2.1 ( 50

mm, 12 min, 0.3 mL/min ﬂow rate, 50-100% 0.05% TFA in

CH₃CN/100-50% 0.05% TFA in H₂O) (Table 4).

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-chlorophenyl)-1-(2,4-

dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-(4-chlorophenyl)cyclopro-

1

pyl)-1,3,4-oxadiazole (42f). H NMR (400 MHz, CDCl₃) δ 8.76

(s, 1H), 7.99 (s, 1H), 7.46-7.28 (m, 11H), 5.54 (s, 2H), 1.78 (m,

2H), 1.47 (m, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 169.6, 159.3,

152.0, 146.2, 144.8, 137.9, 137.1, 136.9, 136.5, 135.4, 134.0, 133.3,

131.7, 131.4, 130.8, 130.7, 129.4, 129.1, 128.3, 125.4, 115.0, 42.9,

22.2, 16.6. ESI-MS m/z: 622 [M + H]⁺. Positive HR-FAB-MS

m/z: 622.0491 [M + H]⁺(Calcd for C₂₉H₁₉Cl₄N₇O: 622.0483).

Table 4. HPLC Analysis Data

HPLC: retention

time (min)

HPLC: retention

time (min)

entry compd

1

2

3

4

5

6

7

8

4h

4ha

4hb

4hc

4k

9

10

11

12a

12b

13

14

15

16

17

18

19

20

21

8.013

9.038

10.012

9.770

8.571

7.067

5.103

6.550

10.555

7.307

7.577

6.164

8.212

3.866

6.264

7.767

8.209

6.216

8.786

7.633

6.902

8.881

8.294

6.508

9.990

8.190

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

28a

28b

28c

28d

29

30

31

1.442

1.248

1.103

1.265

4.293

4.416

4.255

8.660

6.861

1.354

4.220

4.327

5.915

5.096

8.696

3.559

4.714

5.976

7.106

7.259

4.598

3.927

4.712

6.299

7.395

7.548

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-bromophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-oxadia-

1

zole (43a). H NMR (400 MHz, CDCl₃) δ 8.59 (s, 1H), 7.91 (s,

1H), 7.55-7.53 (m, 2H), 7.47-7.43 (m, 3H), 7.38-7.32 (m, 2H),

5.57 (s, 2H), 1.50 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) δ 173.5,

159.4, 151.9, 146.1, 144.8, 138.2, 136.9, 135.4, 133.4, 132.4, 131.9,

130.8, 130.7, 128.3, 125.9, 124.9, 115.1, 43.0, 32.8, 28.4. ESI-MS

m/z: 572 [M + H]⁺. Positive HR-FAB-MS m/z: 572.0375 [M +

H]⁺(calcd for C₂₄H₂₀BrCl₂N₇O: 572.0368).

32a

32b

32c

32d

32e

32f

32g

41

42b

42c

42d

42e

42f

43a

43b

43c

43d

43e

43f

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-bromophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-methylcyclopropyl)-

1

1,3,4-oxadiazole (43b). H NMR (400 MHz, CDCl₃) δ 8.55 (s,

1H), 7.89 (s, 1H), 7.54-7.52 (m, 2H), 7.45-7.41 (m, 3H),

7.35-7.30 (m, 2H), 5.55 (s, 2H), 1.61 (s, 3H), 1.42-1.39 (m, 2H),

1.00-0.97 (m, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 171.0, 158.8,

151.9, 146.1, 144.8, 138.1, 136.9, 135.4, 133.4, 132.4, 131.9, 130.8,

130.7, 128.3, 125.9, 124.9, 114.9, 43.0, 20.5, 17.0, 13.1. ESI-MS

m/z: 570 [M + H]⁺. Positive HR-FAB-MS m/z: 570.0220 [M +

H]⁺(calcd for C₂₄H₁₈BrCl₂N₇O: 570.0211).

22

23

24

25

26

27a

27b

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-bromophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-(triﬂuoromethyl)cy-

1

clopropyl)-1,3,4-oxadiazole (43c). H NMR (400 MHz, DMSO-

d₆) δ 8.43 (s, 1H), 7.89 (s, 1H), 7.85 (d, J ) 8.8 Hz, 1H), 7.80 (d,

J ) 2.4 Hz, 1H), 7.63-7.55 (m, 3H), 7.38-7.30 (m, 2H), 5.52 (s,

2H), 1.73 (s, 4H). ¹³C NMR (100 MHz, CDCl₃) δ 163.0, 160.0,

152.0, 146.4, 144.7, 137.5, 137.0, 135.3, 133.3, 132.4, 131.9, 130.8,

130.7, 128.3, 125.7, 125.0, 124.3 (d, J ) 272 Hz), 42.9, 21.2 (q, J

) 37 Hz), 12.7. ESI-MS m/z: 624 [M + H]⁺. Positive HR-FAB-

MS m/z: 623.9928 [M + H]⁺(calcd for C₂₄H₁₅BrCl₂F₃N₇O:

623.9929).

CB1 and CB2 Receptor Binding Assay. For CB1 receptor

binding studies, rat cerebellar membranes were prepared as previ-

ouslydescribedbythemethodsofKusteretal.³⁰MaleSprague-Dawley

rats (200-300 g) were sacriﬁced by decapitation and the cerebella

rapidly removed. The tissue was homogenized in 30 volumes of

TME buffer (50 mM Tris-HCl, 1 mM EDTA, 3 mM MgCl₂, pH )

7.4) using a Dounce homogenizer. The crude homogenates were

immediately centrifuged (48000g) for 30 min at 4 °C. The resultant

pellets were resuspended in 30 volumes of TME buffer, and protein

concentration was determined by the method of Bradford and stored

at -70 °C until use.³¹

2-(4-((1H-1,2,4-Triazol-1-yl)methyl)-5-(4-bromophenyl)-1-

(2,4-dichlorophenyl)-1H-pyrazol-3-yl)-5-(1-phenylcyclopropyl)-

1

1,3,4-oxadiazole (43d). H NMR (400 MHz, CDCl₃) δ 8.48 (s,

1H), 7.88 (s, 1H), 7.53-7.51 (m, 2H), 7.48-7.29 (m, 10H), 5.50

(s, 2H), 1.79-1.76 (m, 2H), 1.52-1.49 (m, 2H). ¹³C NMR (100

MHz, CDCl₃) δ 170.0, 159.2, 151.9, 146.1, 144.8, 138.6, 138.0,

136.9, 135.4, 133.3, 132.4, 131.9, 130.8, 130.7, 130.0, 129.0, 128.3,

128.1, 125.9, 124.9, 115.0, 42.9, 22.7, 16.5. ESI-MS m/z: 632 [M

+ H]⁺. Positive HR-FAB-MS m/z: 632.0361 [M + H]⁺(calcd for

C₂₉H₂₀BrCl₂N₇O: 632.0368).

For CB2 receptor binding studies, CHO K-1 cells were trans-

fected with human CB2 receptor as previously described, and cell

membranes were prepared as described above.³²

Competitive binding assays were performed as described.³³

Brieﬂy, approximately 10 µg of rat cerebella membranes (containing

7232 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22

Lee et al.

CB1 receptor) or cell membranes (containing CB2 receptor) were

incubated in 96-well plate with TME buffer containing 0.5%

essentially fatty acid free bovine serum albumin (BSA),

Molecular Docking. Structures of 1 and 43c were energy-

minimized by the conjugated gradient method with Gasteiger-Hu¨ckel

charge until a convergence value of 0.001 kcal/(Å·mol), using the

Tripos force ﬁeld. The model for 1 complex was generated by

manual docking in the active site of the hCB1 homology model

considering the key ligand-receptor interactions. The model was

optimized using the FlexiDock utility in the Biopolymer module

of Sybyl to determine the most energetically favorable binding

conformation and orientation. After the hydrogen atoms were added

to the hCB1 receptor, atomic charges were recalculated by Kollman

all-atom for the protein and Gasteiger-Hu¨ckel for 1. H-bond sites

were marked for all residues in the binding pocket (6.5 Å cavity

centered by 1) and for ligands that were able to act as H-bond

donors or acceptors. During the Flexi-Dock run, single bonds in

the ligand and the residues of the binding pocket were deﬁned as

rotatable. Default FlexiDock parameters were set at 30000 genera-

tion for genetic algorithms. Finally, the complex structure was

minimized by Powell method with a gradient of 0.05 kcal/(mol ·Å).

Compound 43c was docked into hCB1 with Surﬂex-Dock³⁶after

the active site region was deﬁned by using protocol that reproduces

the interactions made by 1 with hCB1. Subsequent scoring for

Surﬂex-Dock solution was performed by a consensus scoring

function (CScore³⁵). The binding modes of conformers with high

CScore value (3-5) were visually inspected. A conformer with

the top D-score rank showed the most favorable binding mode in

complex with hCB1, and it is displayed in Figures 5 and 6.

Three nM [3H]44 (for CB2 receptor, NEN; speciﬁc activity

50-80 Ci/mmol) or 3 nM 45 ([³H]CP55,940, [³H]2-[(1S,2R,5S)-

5-hydroxy-2-(3-hydroxypropyl) cyclohexyl]-5-(2-methyloctan-2-

yl)phenol, for CB1 receptor, NEN; speciﬁc activity 120-190 Ci/

mmol) and various concentrations of the synthesized cannabinoid

ligands in a ﬁnal volume of 200 µL. The assays were incubated

for 1 h at 30 °C and then immediately ﬁltered over GF/B glass

ﬁber ﬁber ﬁlter (PerkinElmer Life and Analytical Sciences, Boston,

MA) that had been soaked in 0.1% PEI for 1 h by a cell harvester

(PerkinElmer Life and Analytical Sciences, Boston, MA). Filters

were washed ﬁve times with ice-cold TBE buffer containing 0.1%

essentially fatty acid free BSA, followed by oven-dried for 60 min

and then placed in 5 mL of scintillation ﬂuid (Ultima Gold XR;

PerkinElmer Life and Analytical Sciences, Boston, MA), and

radioactivity was quantitated by liquid scintillation spectrometry.

In CB1 and CB2 receptor competitive binding assay, nonspeciﬁc

binding was assessed using 1 µM 1 and 1 µM 44 (WIN55,212-2),

respectively. Speciﬁc binding was deﬁned as the difference between

the binding that occurred in the presence and absence of 1 µM

concentrations of 1 or 44 and was 70-80% of the total binding.

IC₅₀was determined by nonlinear regression analysis using Graph-

Pad PRISM. All data were collected in triplicate and IC₅₀was

determined from three independent experiments.

Measurements of in Vivo Activity Analysis. Male C57BL/6J

mice weighing over 38 g were housed 1 per cage on a 12 h/12 h

light/dark cycle, had free access to food (rodent sterilizable diet)

and water, and were experimentally native before testing. Mice were

allowed at least 7 days to habituate to the experimental room prior

to testing, and testing was conducted during the light period. Mice

were maintained and experiments were conducted in accordance

with Institutional Animal Care. The reference (1) and the com-

pounds 4k, 42c, and 43c were prepared daily by dissolving it in

deionized water containing 10% DMSO. By oral administration,

animals received at a volume of 10 mL/kg for 14 days. All control

animals received 10% DMSO dissolved in deionized water. The

vehicles 10% DMSO treated group were comprised of ﬁve mice in

oral test. There were six mice in each of the other experimental groups

(n ) 6 in each group). By oral administration, the losing weight was

checked everyday for the drug treated group and the control group.

Acknowledgment. We are grateful to Drs. Jae-Wook Huh

and Eun Chul Huh for their many valuable discussions

throughout research programs at Central Research Laboratories,

Green Cross Corp. (GCC). This research was in part (H.-J.P.

and J.Y.) supported by a grant (CBM32-B2000-01-02-00) from

the Center for Biological Modulators of the 21st Century

Frontier R&D Program, the Ministry of Science, Republic of

Korea. This work was partially (H.Y. and J.N.) supported by

the Korea Research Foundation Grant funded by the Korean

Government (MOEHRD) (KRF-2007-412-J04001). Finally, we

are grateful to Dr. Andrew B. Benowitz (GlaxoSmithKline,

Collegeville, USA) for his prudent proofreading this manuscript.

Supporting Information Available: Elemental analyses data

for compounds 42c, 43c; HRMS and HPLC purity data for

compounds 32d, 42b-42f, 43a-43f; ¹H NMR and ¹³C NMR

spectrum data for compounds 4k, 32d, 42b-42f, 43a-43f; HRMS

and HPLC spectrum data for compounds 42c, 43c; single-crystal

X-ray analysis data for 43c. This material is available free of charge

via the Internet at http://pubs.acs.org.

Protein modeling and docking experiments have been performed

with the Sybyl 7.3 software package (Tripos, Inc., St. Louis, MO)³⁵

based on Linux CentOS 4.0.

Homology Modeling of hCB1 Receptor. The sequence of human

CB1 receptor was taken from the Swiss-Prot Database (entry P21554;

http://us.expasy.org/sprot/). The crystal structure of bovine rhodopsin

at 2.80 Å resolution (PDB entry 1F88) from the HOMSTRAD, a

database containing thousands of 3D protein structures clustered into

related families, was used as a template. The ﬁrst alignment is based

on an automatic alignment created in FUGUE, structural homologues

of hCB1 were identiﬁed by sequence-structure comparison using

protein database. Additional manual adjustments were performed to

eliminate unwanted gaps in the produced alignment for hCB1. Using

the ORCHESTRAR, aligned sequence of hCB1 was built using

structure of bovine rhodopsin. Loops were then modeled by knowledge-

based or ab initio approaches, and side chains were added.

The conserved disulﬁde bond between residues Cys257 and Cys264

in the middle of extracellular loop 2 was also created and kept as a

constraint in the geometric optimization. The resultant structure of the

hCB1 receptor was optimized using Powell methods with the following

parameters: a distance-dependent dielectric constant of 1.0, nonbounded

cutoff 8 Å, Powell and Kollman all-atom charges, and conjugate

gradient minimization until the maximum derivative is less than 0.05

kcal/(mol·Å). The side chains of the resulting minimized structure

underwent simulated annealing to relieve any steric clashes and correct

unfavorable torsion angle. Stereochemical feature of the minimized

structure was evaluated by inspection of the Ramachandran plots

obtained from PROCHECK analysis.

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JM800843R

Article Doi

Biarylpyrazolyl oxadiazole as potent, selective, orally bioavailable cannabinoid-1 receptor antagonists for the treatment of obesity

DOI: 10.1021/jm800843r

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Article abstract of DOI:10.1021/jm800843r

Full text of DOI:10.1021/jm800843r

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