Synthesis and cannabinoid activity of a variety of 2,3-substituted 1-benzo[b]thiophen derivatives and 2,3-substituted benzofuran: Novel agonists for the CB1 receptor

Article abstract of DOI:10.1071/CH07412

An exploratory chemical effort has been undertaken to develop a novel series of compounds as selective CB₁ agonists. It is hoped that compounds of this type will have clinical utility in pain control and cerebral ischaemia following stroke or traumatic head injury. We report here medicinal chemistry studies directed towards the investigation of several classes of 1-benzo[b]thiophen and benzofuran derivatives as novel CB₁ agonists. We have discovered a novel series of compounds, which contain a 1-benzo[b]thiophen or a benzofuran group as the central aromatic group. Our investigation of this series of compounds has enhanced our understanding of the importance of binding sites within the CB₁ receptor for favourable CB₁ potency. Our understanding of these factors allowed us to modify the structure of a 1-benzothiophen derivative and improve its potency at the CB₁ receptor. CSIRO 2008.

Full text of DOI:10.1071/CH07412

Full Paper
CSIRO PUBLISHING
Aust. J. Chem. 2008, 61, 484–499
www.publish.csiro.au/journals/ajc
Synthesis and Cannabinoid Activity of a Variety
of 2,3-Substituted 1-Benzo[b]thiophen Derivatives
and 2,3-Substituted Benzofuran: Novel Agonists
for the CB1 Receptor
Gerard P. Moloney,A,E James A. Angus,B Alan D. Robertson,C
Martin J. Stoermer,A Michael Robinson,A Lucy Lay,B Christine E. Wright,B
Ken McRae,A and Arthur ChristopoulosD
ADepartment of Medicinal Chemistry, Victorian College of Pharmacy (Monash University),
381 Royal Parade, Parkville VIC 3052, Australia.
BCardiovascular Therapeutics Unit, Department of Pharmacology, University of Melbourne,
VIC 3010, Australia.
CAMRAD Corporation Limited (now known as Zenyth Therapeutics Limited),
576 Swan Street, Richmond VIC 3121, Australia.
DDrug Discovery Laboratory, Department of Pharmacology, Monash University,
VIC 3800, Australia.
ECorresponding author. Email: gerard.moloney@vcp.monash.edu.au
An exploratory chemical effort has been undertaken to develop a novel series of compounds as selective CB1 agonists. It
is hoped that compounds of this type will have clinical utility in pain control and cerebral ischaemia following stroke or
traumatic head injury. We report here medicinal chemistry studies directed towards the investigation of several classes of
1-benzo[b]thiophen and benzofuran derivatives as novel CB1 agonists. We have discovered a novel series of compounds,
which contain a 1-benzo[b]thiophen or a benzofuran group as the central aromatic group. Our investigation of this series
of compounds has enhanced our understanding of the importance of binding sites within the CB1 receptor for favourable
CB1 potency. Our understanding of these factors allowed us to modify the structure of a 1-benzothiophen derivative and
improve its potency at the CB1 receptor.
Manuscript received: 29 November 2007.
Final version: 31 May 2008.
O
Introduction
HO
N
There are two cannabinoid receptors designated neuronal (CB1)
and peripheral (CB2).[1,2] Activation of both receptors leads
to inhibition of adenylate cyclase and activation of mitogen-
activated protein kinases. Activation of CB1 receptors also leads
to the gating of a variety of ion channels, including the inhibition
of N-type voltage-dependent calcium channels. As a conse-
quence of these cellular effects, together with the distribution of
the receptors in neuronal tissues, cannabinoid CB1 agonists have
been suggested to offer significant therapeutic potential in vari-
ous conditions including chronic neuropathic pain.[3–5] In 1992,
it was discovered that the endogenous ligand for the CB1 receptor
is anandamide.[6] Anandamide 1 and a range of other structurally
unrelated cannabinoid agonists have been shown to block the
N-type calcium channel. Given that blockade of these channels
by certain conotoxin peptides has already demonstrated clinical
potential for the treatment of neuropathic pain,[7] there is con-
siderable interest for the development of anandamide analogues
as one means for achieving a similar therapeutic outcome.[8–13]
Molecular modelling studies on anandamide[14] have resulted
OH
H
N
H
O
1
1
Scheme 1.
in a proposed conformation for activity at the CB1 receptor
(Scheme 1).[15,16]
In recent times, it has been demonstrated that the activ-
ity of a series of aminoalkylindole (AAI) antinociceptive
agents, originally designed as non-ulcerogenic, non-steroidal
anti-inflammatory drugs (NSAIDs) is associated with a second
mechanism of action manifested by potent activity at inhibit-
ing electrically induced contractions of mouse vas deferens
(MVD).[12,17–20] StudiesonWIN-55,212–22, Pravadoline3, and
related compounds have shown that compounds from this struc-
turally unrelated indole-based series(relative to the non-classical
© CSIRO 2008
10.1071/CH07412
0004-9425/08/070484

Novel Agonists for the CB1 Receptor
485
H3CO
H3CO
O
OH
N
HO
NH
OH
O
N
O
O
N
Cl
Cl
CH3
CH3
N
N
N
Cl
O
SR141716A
CP-55,940
N
N
N
7
8
O
O
Scheme 4.
O
2
3
4
O
O
Scheme 2.
N
N
H3CO
H3CO
H3CO
CH3
CH3
N
O
N
O
O
O
CH3
CH3
Cl
N
I
N
Br
Cl
L-768,242
L-759,787
N
N
9
10
O
Scheme 5.
O
Bromopravadoline
WIN-54,461
AM630
AM630 6 behaved as a competitive antagonist of CP-55,940
8, WIN-55,212–2 2, and anandamide 1 but was more markedly
potent as an antagonist of (−)-ꢀ9-THC and CP-55,940 8
(Scheme 4) than as an antagonist of WIN-55,212–2 2 or anan-
damide. These differences imply that the MVD may contain
more than one type of cannabinoid receptor. The results also
indicate that the receptors for which AM-630 6 has the high-
est affinity may not be the cannabinoid CB1 receptors, as the
CB1 selective antagonist SR141716A 7 is known to be equally
potent in attenuating the inhibitory effects of CP-55,940 8 and
anandamide 1 on the twitch response of the MVD.
In 1993, a human peripheral cannabinoid (CB2) receptor was
disclosed.[22] Several workers have put forward the hypothesis
that a selective and potent ligand for the CB2 receptor would
show therapeutically useful effects,[19] including a series of
analogues selected through a topological search using WIN-
55,212–2 2 as the template.[17,18] The work of D’Ambra et al.
and Gallant et al. led to the discovery of a range of N1-benzoyl
and N1-naphthoyl indole analogues.[17,18] Two of the more
potent compounds from the research of Adams et al. included
L-768,242 9 and L-759,787 (Scheme 5).[12]
5
6
Scheme 3.
cannabinoids or to anandamide 1 and other arachidonic acid
derivatives) are capable of producing pharmacological responses
in a fashion resembling the profile exhibited by (−)-ꢀ9-THC.
Additionally the AAI drug class produces its cannabimimetic
actions in a stereoselective manner as shown by the results for
the optical isomers of WIN-55,212–2.[21]
WIN-55,212–2 (CB1, median inhibition concentration
(IC50) 2.0 nM) 2, Pravadoline (CB1, IC50 453 nM) 3,
and (4-methoxyphenyl)(3-morpholinomethyl)-2,3-dihydro-1H-
pyrrolo[1,2-a]indol-9-yl)methanone 4[17] (CB1, IC50 320.0 nM)
are all potent CB1 receptor agonists (Scheme 2).[2,17,22] The
key structural features for potent cannabinoid activity in this
series are a 3-keto group, an aryl or bicyclic (naphthyl) sub-
stituent at the 3-position, a small (H or CH3) substituent at
the 2-position, and an ethylene-linked morpholine group at the
1-position. Molecular modelling studies have been performed to
develop a pharmacophore and to compare AAI structures with
those of classical cannabinoids.[23] Within the work of Eissen-
statetal., aCB1 antagonistWIN-54,4615(orbromopravadoline)
was also identified. A separate group identified a related com-
pound AM630 6 (or iodopravadoline) (Scheme 3) that is also
found to be a competitive cannabinoid receptor antagonist.[24]
In conjunction with the synthesis of novel compounds as
potential CB1 agonists, we have performed preliminary mod-
elling studies in an attempt to build up a pharmacophore
for the CB1 receptor. A comparison was made between the
aminoalkylindoles, anandamide 1 and the classical and non-
classical cannabinoids. We extrapolated from work carried out
by Thomas and coworkers[15] using the proposed conformation

486
G. P. Moloney et al.
1
1
OH
HO
HN
O
O
3
3
4
4
9
Anandamide 1
(ꢀ)-ꢁ -THC
2
2
O
HO
1
N
1
CH3
O
OH
N
O
O
3
3
4
4
HU210 11
WIN-55,212 2
Scheme 6.
Fig. 2. Proposed mode of binding for a low-energy conformation of anan-
damide at the CB1 pharmacophore model. The four proposed binding sites
are shown as coloured spheres.
Fig. 1. Proposed mode of binding for a low-energy conformation of
HU210 at the CB1 pharmacophore model.
N
N
anandamide adopts for binding. Scheme 6 illustrates the four
proposed important binding sites within the CB1 pharmacophore
using anandamide, (−)-ꢀ9-THC, HU210 11, and WIN-55,212–
2 2. The proposed binding sites are a hydrogen-bond donor or
acceptor site 1, and two further hydrogen-bonding sites 2 and 3,
and a hydrophobic pocket 4. The pharmacophore is further illus-
trated in Figs 1 and 2. The proposed mode of binding of a low
energy conformer of HU210 11 and anandamide 1 are shown in
Figs 1 and 2 respectively.
O
N
N
We recently reported the results of a drug discovery
program directed toward a series of 1-substituted indole-3-
oxadiazole derivatives.[25] The work of Moloney and Robert-
son resulted in the discovery of several exciting compounds
including 3-(3-benzyl-[1,2,4]oxadiazol-5-yl)-1-(2-pyrrolidin-1-
ylethyl)-1H-indole 12 (Scheme 7), which had good CB1 potency
(pKb 7.2).
As part of the present research program, it was our intention
to investigate a variety of 1-benzo[b]thiophen- and benzofuran-
based molecules in our effort to discover novel CB1 ligands and
understand fully the binding characteristics of CB1 ligands.
12
Scheme 7.
Results and Discussion
Synthesis
Our decision to investigate several benzofuran and
1-benzo[b]thiophen derivatives was based on several previously

Novel Agonists for the CB1 Receptor
487
CN
O
O
CN
OCH3
OCH3
S
O
H3CO
H3CO
LY820186
LY320136[26]
Fig. 3. 2,3,6-Trisubstituted-1-benzo[b]thiophen and benzofuran derivatives LY820186 and LY320136,
which have been previously reported to inhibit cannabinoid receptors.[26]
O
O
O
X
OCH3
OH
(a)
(b)
R
R
R
XH
OCH3
XH
OH
(c)
14 X ꢄ O, R ꢄ 5-OCH3
21 X ꢄ S, R ꢄ H
15 X ꢄ O, R ꢄ 5-OCH3
22 X ꢄ S, R ꢄ H
O
O
O
X
X
X
(e)
(d)
R
R
R
Rꢃ
OH
OCH3
O
O
O
Rꢂ
Rꢂ
Rꢂ
18 X ꢄ O, R ꢄ 5-OCH3, Rꢂ ꢄ Bn, Rꢃ ꢄ N(CH3)2
19 X ꢄ O, R ꢄ 5-OCH3, Rꢂ ꢄ Bn, Rꢃ ꢄ NH-pip
25 X ꢄ S, R ꢄ H, Rꢂ ꢄ Bn, Rꢃ ꢄ NH-pip
17 X ꢄ O, R ꢄ 5-OCH3, Rꢂ ꢄ Bn
24 X ꢄ S, R ꢄ H, Rꢂ ꢄ Bn
28 X ꢄ O, R ꢄ 5-OCH3, Rꢂ ꢄ i-Pr
16 X ꢄ O, R ꢄ 5-OCH3, Rꢂ ꢄ Bn
23 X ꢄ S, R ꢄ H, Rꢂ ꢄ Bn
27 X ꢄ O, R ꢄ 5-OCH3, Rꢂ ꢄ i-Pr
26 X ꢄ S, R ꢄ H, Rꢂ ꢄ Bn, Rꢃ ꢄ N(CH3)2
31 X ꢄ O, R ꢄ 5-OCH3, Rꢂ ꢄ (CH2)2morpholine 30 X ꢄ O, R ꢄ 5-OCH3, Rꢂ ꢄ (CH2)2morpholine
29 X ꢄ O, R ꢄ 5-OCH3, Rꢂ ꢄ i-Pr, Rꢃ ꢄ NH-tetrazole
32 X ꢄ O, R ꢄ 5-OCH3, Rꢂ ꢄ (CH2)2morpholine, Rꢃ ꢄ NHBn
Scheme 8. Reagents: (a) SOCl2, MeOH; (b) KOBut, THF, ClCH2CO2CH3; (c) DMSO, KOBut, alkyl halide; (d) KOH, MeOH; (e) amine, DMF, TBTU,
DIPEA or CDI, THF, 5-aminotetrazole.
reported 1-benzo[b]thiophen and benzofuran derivatives that
inhibit cannabinoid receptors in mammals (Fig. 3).[26]
The substituted benzofuran derivatives were synthesized
by two general methods. In the first (Scheme 8), the substi-
tuted salicylic acid or thiosalicylic acid (14, 15) derivatives
were alkylated with methyl 2-chloroacetate in the presence of
potassium tert-butoxide, with the di-ester intermediates under-
going a Diekmann-type condensation to afford the heterocyclic
2-carboxylates,[27] which were then alkylated and hydrolyzed
to form the 3-alkoxybenzofuran and benzo[b]thiophen-2-
carboxylicacids.Thecarboxylicacidderivativescouldbereadily
amide-coupled with a range of amines to form the amide
inhibitors 18, 19, 25, 26, 29, and 32.
The second general method for the preparation of the 1-
benzo[b]thiophen derivatives is illustrated in Scheme 9 and
starts with the substituted cinnamic acids 38 and 45. Reaction
with thionyl chloride in pyridine/DMF generated the 3-chloro-
1-benzo[b]thiophen-2-carbonyl chloride intermediates 29 and
46. The carbonyl chloride intermediate could then be treated
with the alcohol of choice to simultaneously introduce the
alkoxy group at C3 and to form the ester intermediates 41, 48,
53, 56, and 60. The esters were then hydrolyzed to form the
1-benzo[b]thiophen-2-carboxylic acid derivatives 42, 49, 54, 57,
and 61, which were then amide-coupled to the amine of choice
to form the 1-benzo[b]thiophen-2-carboxamides 43, 44, 55, 58,
and 62–64.
We also synthesized the known central cannabinoid antag-
onist SR141716 for comparison with our novel CB1 agonists
(Scheme 10). The synthesis begins with condensation of
4-chloropropiophenone 33 with diethyl oxalate, which is pro-
moted by lithium hexamethydisilazide[29] to afford the lithium
enolate 34. Condensation of 34 with (2,4-dichlorophenyl)
hydrazine in ethanol at reflux[30] afforded the pyrrole ester 35.
The pyrrole ester 35 was then heated with ethanolic sodium
hydroxide to afford the pyrazole carboxylic acid 36. Amide
coupling of 36 with N-aminopiperidine afforded the desired
SR141716 37 in good yield.
Biological Results
The compounds were investigated and their biological data are
shown in Table 1. To explain the biological data, we referred
to our theoretical receptor model for the CB1 receptor, shown
in Fig. 1 using the preferred conformation of the cannabinoid
mimetic HU210 (11) fitted to the proposed CB1 receptor model.
The theoretical receptor model is composed of four binding sites.
To build our CB1 receptor model, we compared potential com-
monality between aminoalkyl indoles and other cannabinoids.
We initially built the structure for anandamide 1 and minimized
the conformation anandamide adopts for binding to the CB1
receptor.WethenrecognizedthatwhenwecomparedHU210and
anandamide 1, it was possible to overlay the phenolic hydroxyl
of HU210 with the amido ethyl alcohol of anandamide 1 (bind-
ing site 1). Binding site 1 is represented by the red sphere
and is a hydrogen-bonding site, which the phenolic hydroxyl
The nitro analogue 51 was synthesized in the same method
by first nitrating the carboxylic acid intermediate 49 followed by
amide coupling with 5-aminotetrazole.[28]

488
G. P. Moloney et al.
O
O
O
O
S
S
(a)
(b)
OH
R
R
R
Cl
Rꢂ
Cl
O
38 R ꢄ 4-OCH3
45 R ꢄ 3-OCH3
39 R ꢄ 6-OCH3
46 R ꢄ 5-OCH3
Rꢂ
41 R ꢄ 6-OCH3, Rꢂ ꢄ c-C6H11
48 R ꢄ 5-OCH3, Rꢂ ꢄ i-Pr
(c)
53 R ꢄ 6-OCH3, Rꢂ ꢄ 4-MeOC6H4
56 R ꢄ 5-OCH3, Rꢂ ꢄ OBn
60 R ꢄ 6-OCH3, Rꢂ ꢄ OBn
O
O
S
S
(d)
R
R
OH
HN Rꢃ
O
O
Rꢂ
Rꢂ
43 R ꢄ 6-OCH3, Rꢂ ꢄ c-C6H11, Rꢃ ꢄ tetrazole
44 R ꢄ 6-OCH3, Rꢂ ꢄ c-C6H11, Rꢃ ꢄ CH2-2-furyl
42 R ꢄ 6-OCH3, Rꢂ ꢄ c-C6H11
49 R ꢄ 5-OCH3, Rꢂ ꢄ i-Pr
55 R ꢄ 6-OCH3, Rꢂ ꢄ 4-MeOC6H4, Rꢃ ꢄ tetrazole
58 R ꢄ 5-OCH3, Rꢂ ꢄ OBn, Rꢃ ꢄ CH2-2-furyl
59 R ꢄ 5-OCH3, Rꢂ ꢄ OBn, Rꢃ ꢄ CH2-2-thienyl
62 R ꢄ 6-OCH3, Rꢂ ꢄ OBn, Rꢃ ꢄ CH2-2-thienyl
63 R ꢄ 6-OCH3, Rꢂ ꢄ OBn, Rꢃ ꢄ tetrazole
64 R ꢄ 6-OCH3, Rꢂ ꢄ OBn, Rꢃ ꢄ CH2-2-furyl
54 R ꢄ 6-OCH3, Rꢂ ꢄ 4-MeOC6H4
57 R ꢄ 5-OCH3, Rꢂ ꢄ OBn
61 R ꢄ 6-OCH3, Rꢂ ꢄ OBn
(e)
O
S
O
S
(f)
R
R
OH
HN Rꢃ
O
O
NO2
NO2
Rꢂ
Rꢂ
51 R ꢄ 5-OCH3, Rꢂ ꢄ i-Pr, Rꢃ ꢄ tetrazole
50 R ꢄ 5-OCH3, Rꢂ ꢄ i-Pr
Scheme 9. Reagents: (a) SOCl2, DMF, pyridine; (b) RꢀOH, THF; (c) NaOH, MeOH; (d) amine, TBTU, DMF, DIPEA or CDI, THF,
5-aminotetrazole; (e) CH3CO2H, HNO3; (f) CDI, THF, 5-aminotetrazole.
O
O
OCH2CH3
OLi
O
H3CH2CO
(a)
O
O
O
CH3
Cl
33
Cl
34
Cl
Cl
(b)
O
N
NHNH2
O
H3C
H3C
OH
(c)
OCH2CH3
N
N
N
Cl
Cl
Cl
Cl
Cl
Cl
35
36
Scheme 10. Reagents and conditions: (a) LiHMS (1 M inTHF),THF −78◦C; (b) 2,4-dichlorophenyl
hydrazine hydrochloride, ethanol; (c) 2 M NaOH, EtOH.
of HU210 can interact with (Fig. 1). Binding site 2 is repre-
sented by the purple sphere in Fig. 1 and the 9-hydroxymethyl
group of HU210 interacts with this binding site and is an impor-
tant binding site for the aminoalkyl indole series[12,20,26] and
our novel 2,3-substituted-1-benzo[b]thiophen- and benzofuran-
based compounds. Binding site 3 is a hydrogen-bonding site and
is represented by the orange sphere (Fig. 1) and is accessed by the
pyran oxygen of HU210 and the amide carbonyl of anandamide 1

Novel Agonists for the CB1 Receptor
489
Table 1. Percentage inhibition of CB1: 1-substituted-indole-3-oxadiazole derivatives
MVD, mouse vas deferens bioassay; IC50, negative logarithm of the concentration of compound required to inhibit
50% of the specific binding of the radioligand. Affinity values are the average of at least four different estimates.
Negative values connote stimulation rather than inhibition
Compound no.
Structure
CB1 (MVD)A
CB1 (Binding)
O
OH
Anandamide 1
N
H
pKB 8.52
OH
OH
CP-55,940
HO
HO
OH
HU210 11
IC50 3.22 µM
O
OH
(−)-ꢀ9-THC
pKB 8.74
O
O
CH3
WIN-55,212 2
pKB 8.6
IC50 1.007 µM
N
O
N
O
O
O
N
H3CO
18
19
12.2% inhibition at 1.0 µM
11.0% inhibition at 1.0 µM
O
O
O
N
HN
H3CO
O
O
S
OH
O
24
25
17.5% inhibition at 1.0 µM
18.8% inhibition at 1.0 µM
S
O
HN
N
O
(Continued)

490
G. P. Moloney et al.
Table 1. (Continued)
Compound no.
Structure
CB1 (MVD)A
CB1 (Binding)
S
O
N
CH3
CH3
O
26
22% inhibition at 1.0 µM
O
O
N
N
N
H C
3
H
N
O
29
30
35.71% inhibition at 1.0 µM
10.3% inhibition at 1.0 µM
30% inhibition at 1.0 µM
N
H
O
O
O
OCH3
H3CO
O
N
O
O
O
HN
H3CO
O
32
20.3% inhibition at 1.0 µM
IC50 1.84 µM
N
O
O
N
H3C
N
H
N
N
SR141716A 37
pKB 8.4–8.6
IC50 3.92 nM
Cl
Cl
Cl
H3CO
S
O
N
N
HN
N
43
25.0% inhibition at 1.0 µM
N
H
O
S
O
O
H3C
N
H
O
O
44
51
31.1% inhibition at 1.0 µM
29.3% inhibition at 1.0 µM
20% inhibition at 1.0 µM
O
N
S
N
N
H
O
N
O
N
H
NO2
O
S
O
H3C
N
N
N
HN
O
N
H
55
3.33% inhibition at 1.0 µM
O
(Continued)

Novel Agonists for the CB1 Receptor
491
Table 1. (Continued)
Compound no.
Structure
CB1 (MVD)A
CB1 (Binding)
S
O
HN
O
O
58
−21.0% inhibition at 1.0 µM
O
S
O
H3C
HN
O
S
O
59
63
64
29.7% inhibition at 1.0 µM
22.7% inhibition at 1.0 µM
−59.2% inhibition at 1.0 µM
20% inhibition at 1.0 µM
O
S
O
H
N
H3C
N
HN
N
O
Inactive
N
O
S
O
H3C
HN
S
O
Inactive
AAffinity (pKB = − log10 KB, the dissociation equilibrium constant) estimates for novel compounds at the CB1
receptor in the MVD. Standard errors are omitted for clarity but in all cases were ≤0.2 log10 unit.
(Fig. 2). A low-energy conformation of HU210 is shown in
Fig. 1.
The proposed conformation anandamide 1 adopts for binding
to the CB1 receptor is shown in Fig. 2.
25 showing 18.8% inhibition of CB1 at 1.0 µM. The dimethyl
derivative 24 showed a similar lack of potency with 22.0%
inhibition of CB1. The 1-benzo[b]thiophen-2-carboxylic acid
derivative 24 exhibited 17.5% inhibition of CB1.
In the current study, we decided to investigate a novel series
of 1-benzo[b]thiophen-based compounds in an attempt to suc-
cessfully replace the indole nucleus of the aminoalkyl indole
series. A review of the structural requirements for good inter-
action with the CB1 receptor binding sites revealed to us that it
would be more difficult to produce compounds from this series
that contained appropriate functionality to interact with the four
main binding sites of the CB1 receptor, Scheme 6. In a previous
study,[25] we discovered an aminoalkyl indole, 3-benzyl-5-(1-
pentyl-1H-indol-3-yl)-1,2,4-oxadiazole 12, which inhibits CB1
100% at 1.0 µM. 12 does not contain functionality to interact
with binding site 2, Scheme 6. With this information, we decided
to synthesize several 1-benzo[b]thiophen-based compounds that
contained functionality to interact with binding sites 1, 3, and 4.
To begin our investigation of the benzo[b]thiophen series,
we synthesized several simple 3-benzyloxy-1-benzo[b]thiophen
derivatives. Our preliminary modelling studies suggested that
compounds such as 24, 25, and 26 would be able to adopt con-
formations that allow the 3-benzyloxy substituent to occupy the
hydrophobic pocket (binding site 4), whereas the 2-carbonyl
group could interact with the hydrogen-bonding site (bind-
ing site 1) and the central 1-benzo[b]thiophen nucleus could
interact with binding site 3. The results for these simple
1-benzo[b]thiophen derivatives were lower than expected, with
A similar lack of potency was observed for 5-methoxy-
benzofuran derivatives with the same substituents at the 2
position. 18, a dimethylbenzofuran-2-carboxamide derivative,
exhibited a similar lack of potency, with 12.2% inhibition of
CB1. Similarly the piperidin-1-yl benzofuran-2-carboxamide
derivative 19 exhibited similar lack of activity, showing 11.0%
inhibition of CB1. It became clear that in order to obtain
potent compounds within this series of compounds, we would
be required to include functionality to interact with binding
site 2, Scheme 6. Molecular modelling studies showed that if
we incorporated a heterocyclic moiety into the 2-carboxamide
substituent, a heteroatom would be able to interact with the
hydrogen-bonding site designated as binding site 2. These
preliminary modelling studies led us to the amido tetrazole
derivative 29. Our computational studies indicated that as 29
adopts a low-energy conformation for interaction with CB1,
functional groups are able to interact with binding sites 1, 3,
and 4 whereas one of the tetrazole nitrogens should be able to
interact with binding site 2. The biological results in Table 1
revealthatalthough 29isnotsuper-potent, inclusionoftheamido
tetrazole moiety increased the potency of this compound to up
to 35.71% inhibition of CB1 at 1.0 µM. The 3-isopropyl group
is able to interact with binding site 4, the hydrophobic pocket,
and the amide carbonyl is able to interact with binding site 1.

492
G. P. Moloney et al.
Similarly, the 4-nitro analogue 51 exhibited a similar profile to
29, inhibiting CB1 29.3% at 1.0 µM.
the binding sites of the CB1 receptor. Our results revealed that
32 lacked potency at CB1, inhibiting CB1 20.3%. We also exam-
ined one of the intermediates, the 2-methyl ester 30, which was
equally as inactive, inhibiting CB1 10.3%. The lack of potency
for this series of compounds appears to be due to inappropriate
distance between the morpholine nitrogen, which interacts with
binding site 2, and the benzoyloxy phenyl group, which interacts
with the hydrophobic pocket binding site 4. Future work within
this series of 2,3,5-substituted 1-benzo[b]thiophen derivatives
will involve incorporating a longer linking chain between the
morpholine moiety and the central 1-benzo[b]thiophen group.
Alkylation with 4-(3-chloropropyl)morpholine will allow such
an analogue to adopt a conformation that allows more accurate
interaction with all the binding sites of the CB1 receptor.
We then decided to explore some 3-cyclohexyloxy deriva-
tives, as our molecular modelling studies suggested that the
cyclohexyl group might be able to interact with the hydropho-
bic pocket, binding site 4 more accurately. The 3-cyclohexyloxy
derivative 43 was observed to inhibit CB1 with similar potency to
29 showing 25.0% inhibition. Our preliminary modelling stud-
ies suggested that the 2-carboxamidotetrazole moiety was not
able to interact accurately with binding site 2. In an attempt
to overcome this problem, we decided to replace the tetrazole
group with a furan-2-ylmethyl group, which is able to inter-
act with hydrogen-bonding sites such as binding site 2 while
the cyclohexyl group interacts with the hydrophobic site. Our
results showed that the inclusion of a 2-(furan-2-ylmethyl) car-
boxamide group did improve potency, with 31.1% inhibition
of CB1 observed. The marginally improved potency is likely
to be due to the ability of the methyl-linked morpholine sub-
stituent to interact with the hydrogen-bonding site, binding site 2,
while the 3-cyclohexyloxy group interacts with the hydropho-
bic pocket, binding site 4, as well as the ability of the more
hydrophobic 2-(furan-2-ylmethyl) carboxamide group of 44 to
interact with the proposed additional hydrophobic pocket[31]
in the region between the central 1-benzo[b]thiophen moiety
and the hydrogen-bonding site, binding site 2 (Scheme 6). We
previously suggested that this proposed hydrophobic region
may be where the six-membered rings of (−)-ꢀ9-THC and
HU210 are placed when these compounds are interacting
with the CB1 receptor.[31] We envisage that future work on
compounds from this series will involve the synthesis and
assessment of an analogue of 44 with an ethyl linking chain
betweenthe morpholine moietyandthe1-benzo[b]thiophen cen-
tral nucleus. Such a compound would be expected to interact
more closely with the hydrophobic pocket and binding site 2.
In addition, such an analogue would be more hydrophobic
in the region between the central 1-benzo[b]thiophen nucleus
and binding site 2, which might enhance affinity at the CB1
receptor.
We decided to investigate several 3-benzyloxy derivatives,
with various 2-carboxamido substituents for interaction with
binding site 2. Initially we examined the 2-carboxamidotetrazole
derivative 63, which displayed 22.7% inhibition of CB1,
which is a similar lack of potency to the 3-isopropoxy and
3-cyclohexyloxy derivatives. It was encouraging to observe
that replacement of the tetrazole group with a (thiophen-2-
yl)methyl group had the same effect of marginally improving
CB1 inhibition, as 59 was observed to inhibit CB1 29.7%. We
also investigated other hydrophobic groups to interact with the
hydrophobic pocket, binding site 4.
We synthesized one 3-(4-methoxyphenoxy) derivative, which
proved to be totally inactive. Clearly the 3-phenoxy group is not
ideal to combine with a 2-carboxamido tetrazole group. It has
become evident that for optimum CB1 activity with this family of
compounds, an extended 2-carboxamido side chain is required
for optimal interaction with the four identified binding sites of
the CB1 receptor. Future work with the 3-phenoxy series would
involve incorporation of alternative 2-carboxamido groups.
We decided at this point to examine several 1-benzo
[b]thiophen derivatives incorporating an ethyl-linked morpho-
line side chain at the 3-position in an attempt to more closely
mimic the aminoalkyl indole family of CB1 inhibitors. Our mod-
elling studies suggested that our first compound from this family,
the 2-benzylamide derivative 32, should be able to interact with
Conclusions
In the present study, we have identified a novel class of 1-
benzo[b]thiophen and benzofuran derivatives as agonists of the
CB1 receptor. We have successfully designed and synthesized a
novel series of compounds using a 1-benzo[b]thiophen group as
the central aromatic group. The inclusion of suitable function-
ality to this central aromatic group has allowed us to produce a
series of CB1 agonists. The 1-benzo[b]thiophen and benzofuran
ring systems have previously been used to produce CB1 antag-
onists. Although many of the molecules in our study have not
exhibited high CB1 affinity in many cases, our design strategy
based on our understanding of the CB1 pharmacophore has
allowed improvement in CB1 affinity of the compounds. We
were able to improve the affinity of a 3-cyclohexyloxy derivative
with a 2-carboxamidotetrazole group 43, which exhibited 25.0%
inhibition, by replacing the 2-carboxamido group with a longer
and more lipophilic 2-amide side chain, a 2-(furan-2-ylmethyl)
carboxamide group, 44. We propose that the heteroatom of the
furan ring is able to interact with binding site 2 more accurately
than the nitrogens. This was reflected in a marginally increased
CB1 inhibition of 44, 31.1%. We envisage that this class of
molecule with proposed structural improvements will be useful
pharmacological probes for the CB1 receptor.
Experimental
Biological Methods
Radioligand binding assays were conducted using rat cerebellum
(CB1 receptors[32,33]) or rat spleen (CB1 and CB2, with the lat-
ter predominating[34,35]). Functional activity of the compounds
was assayed using the mouse electrically stimulated vas deferens
bioassay, a measure of CB1 receptor function.[36,37] Compounds
showing appreciable activity in this assay and the ability to
be antagonized by the CB1-selective antagonist SR141716A 7
were deemed to be CB1 agonists. The remaining compounds
were classed as cannabinoid ligands. CB2 functionality may
be investigated using assays such as those described in US
6013648.[38]
Radioligand Binding
Sprague Dawley rats of either sex (200–300 g) were killed by
gassing with 80% CO2 in O2 and decapitation, and the entire
brain and spleen were excized rapidly and placed in ice-cold
Tris–HCl buffer (Tris 50 mM, MgCl2 3 mM, ethylene glycol
tetraacetic acid 0.2 mM, pH to 7.4 with HCl). On ice, the
cerebellum was dissected away from the rest of the brain, the
spleen was diced using a scalpel and both were weighed and

Novel Agonists for the CB1 Receptor
493
homogenized (PT-DA 1205/2EC Polytron Aggregate; Kinemat-
ica, Luzern, Switzerland) in 10 volumes of ice-cold Tris–HCl
buffer. Homogenates were then made up to 20 volumes with
Tris–HCl buffer and centrifuged at either 31000g for 15 min at
4◦C (cerebellum) or 12600g for 5 min, 4◦C (spleen). For the
spleen membranes, the pellet was discarded, the supernatant
was retained and was subjected to a second centrifugation step
(23800g, 20 min, 4◦C). Subsequently, supernatants from both
cerebellar and spleen preparations were discarded, the pellets
were resuspended in buffer, assayed for protein content using
the method of Bradford[39] with bovine serum albumin as a stan-
dard, and stored in 500 µL aliquots at −80◦C until used for the
binding assays.
Ligand binding assays were performed in polypropylene
tubes in a total volume of 1.0 mL containing Tris–HCl buffer,
a final concentration of 1.0 mg mL−1 bovine serum albumen
(BSA), and varying concentrations of drugs. Tubes contained
30.0 µg of membrane protein and incubation was started by the
addition of 100 µL of either 0.5 nM [3H]SR141716A or 0.2 nM
[3H]WIN-55,212–2. Experiments were carried out in triplicate
at 30◦C for 90 min with non-specific binding being defined
as radioligand binding in the presence of 1.0 µM unlabelled
WIN-55,212–2. Incubations were terminated by rapid filtra-
tion with an M-24 Cell Harvester (Brandel, Gaithersburg, MD,
USA) using ice-cold Tris–HCl buffer containing 0.5 mg mL−1
BSA. Filters (Wattman GR/B) were soaked for 2 h before fil-
tering in a solution of Tris–HCl buffer containing 3.0 mg mL−1
BSA and 0.5% w/w polyethyleneimine (PEI). Filters were left
to dry thoroughly before placement into scintillation vials with
5.0 mL of scintillation cocktail (Ultima Gold LSC-cocktail;
Packard Bioscience, Meridian, CT, USA) added. Vials were left
to stand overnight before the radioactivity was determined using
a model 1409 DSA Liquid Scintillation counter (EG&E Wallac,
Gaithersburg, MD, USA).
Chemical Methods: General Directions
Computational chemistry was performed on a Silicon Graphics
Iris indigo II using the Sybyl[40] molecular modelling software.
Unless otherwise stated, all 1H NMR spectra were recorded at
300 MHz on a BrukerAM 300 spectrometer. Chemical shifts are
in ppm relative to TMS. Deuterated dimethylsulfoxide (99.9%)
was used as solvent unless otherwise stated. Mass spectra and
high-resolution mass spectra (HRMS) were obtained on a Kratos
Concept IS (electron ionization mass spectrometer), a Kratos
MS50 (fast atom bombardment mass spectrometer or a Joel
JMX DX-300 double-focussing instrument. Melting points were
determined on a Gallenkamp melting point apparatus and are
uncorrected. Methanol and ethanol were distilled from iodine
and magnesium and stored over 3 Å molecular sieves.Anhydrous
THF was freshly distilled over potassium and benzophenone.
Anhydrous DMF, diethyl ether, and toluene were stored over
4 Å molecular sieves.Triethylamine, diisopropylethylamine, and
pyridine were stored over sodium hydroxide. All solutions were
driedoverMgSO4 orNa2SO4 andconcentratedonaBuchirotary
evaporator. Column chromatography was performed on silica gel
(Merck Kieselgel 60 F254). IR spectra were run in KBr disks on
a Bruker IFS66 Fourier transform infrared (FTIR) spectrometer.
Microanalyses were performed on a VG Platform spectrometer
and are within 0.4% of the theoretical values unless otherwise
stated. HPLC was performed on a Waters Millennium system
comprising a 490E Multi-wavelength detector, 600 Controller,
and a series 600 pump with a 717 Plus Autosampler. A Zorbax
4.6 mm × 250 mm, 5 µm column was used for analytical work
whereas a 22.4 mm × 250 mm, 7 µm C18 column was used for
preparative work.
Methyl 2-Hydroxy-5-methoxy Benzoate 14[41]
Thionyl chloride (500.0 µL, 6.85 mmol) was added slowly to
methanol (30.0 mL) followed by 5-methoxysalicylic acid (2.0 g,
11.9 mmol), and the reaction mixture was heated at reflux
overnight. The reaction mixture was allowed to cool and the
solvent was evaporated under reduced pressure to afford an
oil, which was purified by column chromatography with ethyl
acetate/hexane (1:9) as eluent to afford 2.03 g (94.0%) of
the desired methyl 2-hydroxy-5-methoxy benzoate 14 as clear
colourless oil. m/z 183 (M + 1)+. δH ([D6]DMSO) 3.78 (3H, s,
OCH3), 3.97 (3H, s, OCH3), 6.91 (1H, d, J 9.0, H6), 7.08 (1H,
dd, J 3.1, 9.0, H5), 7.29 (1H, d, J 3.2, H3).
The resulting radioligand binding curves were analyzed by
non-linear regression using the program PRISM 3.0 (Graphpad
Software, San Diego, CA, USA) to derive ligand affinity
estimates for the cannabinoid receptor(s).
Mouse Isolated Vasa Deferentia
Swiss white mice (35–50 g) were killed by exposure to 80% CO2
in O2 and exsanguination. Mouse vasa deferentia were dissected
with capsular connective tissue intact and set up in 20-mL organ
baths at 37◦C in Mg2+-free physiological salt solution.[36] The
upper (epididymal) end was attached to an isometric force trans-
ducer (Grass FTO3C) and lower (prostatic) end tied to a fixed
support between two parallel field electrodes (5 mm apart, 5 mm
long).The tissue was initially stretched by 0.5g force and allowed
to equilibrate for 10 min.The tissues were stimulated (Grass S88
stimulator) to contract using trains of electrical field stimulation
of three pulses (4 Hz), 0.5 ms duration, 100V (80% maximal
voltage) every 20 s for 10 min. This electrical stimulation period
was applied before and after both antagonist and agonist addi-
tion. Output from the transducer amplifier was recorded on a
flatbed recorder (Gould BS 272, Cleveland, OH, USA).All drugs
were dissolved in dimethyl sulfoxide (DMSO; Sigma, St Louis,
MO, USA) and allowed to equilibrate with the tissue for 30 min
before the responses to field stimulation were assessed. Drug
effects were measured as the percentage decrease of the pre-drug
twitch force. In experiments where only a single drug concentra-
tion was tested, the resulting effect was expressed as a percentage
of that observed in the presence of vehicle.
Methyl 3-Hydroxy-5-methoxybenzofuran-
2-carboxylate 15[27]
Potassium tert-butoxide (1.1 g, 8.2 mmol) was added to methyl
5-methoxysalicylate (1.5 g, 8.2 mmol) in anhydrous THF
(15.0 mL) at room temperature. The resulting yellow mixture
was stirred at room temperature for 30 min. Methyl chloroacetate
(800.0 µL, 9.12 mmol) was added and the reaction mixture was
stirred at room temperature for 15 min. After this time, the
reaction mixture was heated to reflux for 60 min. The reaction
mixture was allowed to cool to room temperature and potas-
sium tert-butoxide (1.1 g, 8.2 mmol) was added and the resulting
mixture heated at reflux for 4 h and then allowed to stir at
room temperature over 2 days. The thick slurry was poured into
water and then acidified with concentrated hydrochloric acid
and the resulting precipitate was collected by filtration. The
resulting off-white powder was recrystallized from methanol
to afford 367.2 mg (20.1%) of the desired methyl 3-hydroxy-
5-methoxybenzofuran-2-carboxylate 15 as white crystals. m/z

494
G. P. Moloney et al.
223 (M + 1)+. δH ([D6]DMSO) 3.87 (3H, s, OCH3), 4.02
(3H, s, OCH3), 7.04–7.17 (2H, m, ArH), 7.36 (1H, d, J 9.9,
H7). HPLC retention time Rt 4.47 min, isocratic 50% B (90%
CH3CN/H2O)/50% D (0.05% H3PO4/H2O).
By the above method was also prepared methyl 3-hydroxy-
1-benzo[b]thiophen-2-carboxylate 22[42] as a pink powder, mp
106–108◦C. m/z 209 (M + 1)+. δH ([D6]DMSO) 2.48 (3H, s,
CH3), 6.06–6.11 (1H, m, ArH), 6.19 (1H, t, ArH, J 8.1,), 6.55–
6.59 (1H, m, ArH), 6.63–6.69 (1H, m, ArH), 9.32 (1H, s, OH).
Found C 57.3, H 3.8. C10H8O3S requires C 57.7, H 3.9%.
potassium hydroxide (96.0 mg, 0.2 mmol) was added. The reac-
tion mixture was heated to reflux for 2 h. The reaction mixture
was allowed to cool, the methanol was evaporated under reduced
pressure, water was added, and the reaction mixture was acidi-
fied with concentrated hydrochloric acid.The aqueous phase was
extracted with ethyl acetate, dried, filtered, and evaporated under
reduced pressure to afford an orange oil, which was purified with
preparative HPLC to afford 17 (174.2 mg, 75%) as an off-white
solid. m/z 299 (M + 1)+. δH ([D6]DMSO) 3.72 (3H, s, OCH3),
5.39 (2H, s, CH2), 7.04–7.89 (8H, m, 8 ArH). Found C 64.96,
H 4.47. C17H14O4S requires C 64.95, H 4.49%. Rt 4.47 min,
isocratic conditions 50% B (90% CH3CN/10% H2O)/50% D
(0.01% TFA in H2O).
Methyl 3-(Benzyloxy)-5-methoxybenzofuran-
2-carboxylate 16[42]
By the above method were also prepared the following
compounds.
Methyl
3-hydroxy-5-methoxybenzofuran-2-carboxylate
(333.0 mg, 1.5 mmol) and potassium tert-butoxide (202.0 mg,
1.8 mmol) were dissolved in anhydrous DMSO (5.0 mL). Ben-
zyl bromide (399.0 µL, 3.3 mmol) was added and the reaction
mixture was heated to 100◦C for 2 h. The reaction mixture
was allowed to cool, water was added, and the aqueous phase
was extracted with ethyl acetate, dried, filtered, and evaporated
under reduced pressure to afford a viscous yellow oil, which was
purified by column chromatography with chloroform/methanol
(99:1) as eluent to afford 16 (280.6 mg, 60%) as a pale yellow
oil. m/z 313.1 (M + 1)+. δH ([D6]DMSO) 3.75 (3H, s, OCH3),
3.85 (3H, s, OCH3), 5.45 (2H, s, CH2), 6.91–7.54 (8H, m, ArH),
7.36 (1H, d, J 9.9, H7). Rt 10.14 min, isocratic conditions 50%
B (90% CH3CN/10% H2O)/50% D (0.01% TFA in H2O).
By the above method were also prepared the following
compounds.
3-(Benzyloxy)-1-benzo[b]thiophen-2-carboxylic Acid 24[25]
White powder. m/z 285 (M + 1)+. δH (CDCl3) 5.19 (2H, s,
OCH2), 6.49 (1H, m, ArH), 6.7 (1H, m, ArH), 6.78–6.82 (2H,
d, 2 ArH), 6.88–7.15 (3H, m, 3 ArH), 7.62 (1H, m, ArH), 10.05
(1H, s, OH). Found C 67.6, H 4.2. C16H12O3S requires C 67.6, H
4.3%. Found (M + 1)+ 285.0507. C16H12O3S requires(M + 1)+
285.05071.
3-Isopropoxy-5-methoxybenzofuran-2-carboxylic
Acid 28[27,42]
The crude product was recrystallized from methanol/water to
afford 28 (311.0 mg, 28.0%) as cream crystals, mp 138–140◦C.
m/z 250 (M)+. δH ([D6]DMSO) 1.3 (6H, d, J 6.0, CH(CH3)2),
3.81 (3H, s, OCH3), 4.79 (1H, m, J 6.0, CH(CH3)2), 7.08–7.11
(2H, m, ArH), 7.15–7.52 (1H, d, J 9.6, ArH), 13.16 (1H, s, OH).
Found C 62.5, H 5.6. C13H14O5 requires C 62.4, H 5.6%. HPLC
Rt 7.33 min (10% B/90% D) to (90% B/10% D) over 20 min
(B 90% CH3CN/10% H2O; D 0.1 M NH4OAc (pH 4)).
Methyl 3-(Benzyloxy)-1-benzo[b]thiophen-
2-carboxylate 23[25]
Yellow powder. m/z 299 (M + 1)+. δH ([D6]DMSO) 3.8 (2H, s,
OCH2), 3.81 (3H, s, OCH3), 7.01–7.04 (2H, m, ArH), 7.05–
7.4 (2H, m, 2 ArH), 7.57–7.67 (4H, m, 4 ArH). Found C 68.4,
H 4.71. C17H14O3S requires C 68.44, H 4.73%. Found (M + 1)+
299.06636. C17H14O3S requires (M + 1)+ 299.06637.
3-(2-Morpholinoethoxy)-5-methoxybenzofuran-
2-carboxylic Acid 31[43]
Light orange powder. m/z 322 (M + 1)+. δH ([D6]DMSO) 2.35
(3H, m, CH2, CH), 2.65 (2H, m, CH2), 3.4 (3H, m, 2 CH2), 3.81
(2H, d, J 4.2, NHCH2), 4.53 (3H, m, CH2, CH), 7.06 (1H, dd, J
2.2, 6.4, H6), 7.24 (1H, d, J 2.7, H4), 7.49 (1H, d, J 9.0, H7), 8.56
(1H, m, NH). Rt 8.87 min, gradient conditions 30% B/70% A to
90% B/10% A over 20 min (B 90% CH3CN/10% H2O; A 0.1%
TFA in H2O).
Methyl 3-Isopropoxy-5-methoxybenzofuran-
2-carboxylate 27[42]
White powder, mp 66–67◦C [lit. 66–68◦C[18]]. m/z 265
(M + 1)+. δH ([D6]DMSO) 1.39 (6H, d, J 6.0, CH(CH3)2),
3.89 (3H, s, OCH3), 3.96 (3H, s, OCH3), 4.17 (1H, m, J 6.0,
CH(CH3)2), 7.14–7.79 (3H, m, ArH).
3-Cyclohexyloxy-6-methoxy-1-benzo[b]thiophen-
2-carboxylic Acid 42
Methyl 3-(2-Morpholinoethoxy)-5-methoxybenzofuran-
2-carboxylate 30
White powder. m/z 307 (M + 1)+ δH (CDCl3) 1.2–1.39 (3H, m,
CH2, CH), 1.58–1.68 (3H, m, CH2, CH), 1.8–1.85 (2H, m, CH2),
2.0–2.14 (2H, m, CH2), 3.88 (3H, s, OCH3), 4.49 (1H, m, J 3.9,
CH(CH3)2), 7.13(1H, dd, J2.5, 8.6,ArH), 7.23(1H, m,ArH), 7.7
(1H, m, ArH). Found (M + 1)+ 307.09255. C16H18O4S requires
(M + 1)+ 307.09258.
The crude product was purified by column chromatography
with chloroform/methanol (99:1) as eluent to afford the title
compound as a yellow waxy solid. m/z 336 (M + 1)+. δH
([D6]DMSO) 3.16–3.23 (8H, m, 4 CH2), 3.46 (2H, t, J 5.5, CH2),
4.24 (4H, m, 2 CH2), 4.47 (3H, s, OCH3), 4.59 (3H, s, OCH3),
5.23 (2H, t, J 5.5, OCH2), 7.88 (1H, dd, J 2.6, 9.0,ArH), 7.9 (1H,
d, J 2.8, ArH), 8.29 (1H, d, J 9.0, ArH). Rt 4.47 min, isocratic
conditions 50% B (90% CH3CN/H2O)/50% D (0.05% H3PO4
in H2O).
3-Isopropoxy-5-methoxy-1-benzo[b]thiophen-
2-carboxylic Acid 49[28]
The crude product was recrystallized from acetonitrile to
afford 140.8 mg (25%) of the desired 3-isopropoxy-5-methoxy-
1-benzo[b]thiophen-2-carboxylic acid as a white powder, mp
76–80◦C. m/z 266 (M)+. δH (CDCl3) 3.85 (3H, s, OCH3), 7.09
(1H, dd, J 2.5, 8.8, ArH), 7.26 (1H, d, J 2.5, ArH), 7.59 (1H, d, J
8.8, ArH). Found C 54.5, H 4.6. C13H13ClO3S requires C 54.9,
3-(Benzyloxy)-5-methoxybenzofuran-2-carboxylic
Acid 17[42]
Methyl
3-(benzyloxy)-5-methoxybenzofuran-2-carboxylate
(244.0 mg, 0.8 mmol) was dissolved in methanol (3.0 mL), and

Novel Agonists for the CB1 Receptor
495
H 4.5%. Rt 5.37 min, linear gradient over 10 min. 10% B/90% D
to 90% B/10% D (B 90% CH3CN, 10% H2O; D 0.1 N NH4OAc
(pH 4)).
3-(Benzyloxy)-N-(piperidin-1-yl)-1-benzo[b]thiophen-
2-carboxamide 25
The crude product was purified by column chromatography
with chloroform as eluent to afford 25 as clear viscous oil. m/z
367 (M + 1)+. δH ([D6]DMSO) 3.31 (10H, m, 5 CH2), 5.16
(2H, s, OCH2), 7.32–7.92 (9H, m, ArH). Rt 12.01 min, isocratic
conditions 50% B (90% CH3CN/10% H2O)/50% B/D (0.05%
H3PO4/H2O). Found (M + 1)+ 367.147. C21H22N2O2S requires
(M + 1)+ 367.14801.
3-(4-Methoxyphenoxy)-6-methoxy-1-benzo[b]thiophen-
2-carboxylic Acid 54
The crude product was recrystallized from methanol to
afford 98.8 mg (65%) of the desired 3-(4-methoxyphenoxy)-
6-methoxy-1-benzo[b]thiophen-2-carboxylic acid as a cream
solid, mp 169–172◦C (dec.). m/z 368 (M + 1)+. δH ([D6]DMSO)
3.69 (3H, s, OCH3), 3.83 (3H, s, OCH3), 6.92 (3H, m, ArH),
7.3 (3H, m, ArH), 7.81 (1H, d, J 2.0, ArH). Found (M + 1)+
331.05600. C17H14O5S requires (M + 1)+ 331.05619.
3-(Benzyloxy)-N,N-dimethyl-1-benzo[b]thiophen-
2-carboxamide 26
The crude product was purified by column chromatography with
chloroform as eluent to afford 3-(benzyloxy)-N,N-dimethyl-1-
benzo[b]thiophen-2-carboxamide as a white powder. m/z 312
(M)+. δH ([D6]DMSO) 2.96 (6H, s, 2 NCH3), 5.16 (2H,
s, OCH2), 7.32–7.92 (9H, m, ArH), 9.66 (1H, s, OH). Rt
18.82 min, isocratic conditions 50 B (90% CH3CN/H2O)/50 D
(0.05% H3PO4 in H2O).
3-(Benzyloxy)-5-methoxy-1-benzo[b]thiophen-
2-carboxylic Acid 57[27,44]
Pink solid. m/z 315 (M + 1)+. δH (CDCl3) 3.5 (3H, s, OCH3), 5.0
(2H, s, OCH2), 6.4–6.9 (5H, m, ArH), 7.2–7.3 (2H, m, 2 ArH),
7.4 (1H, d, J 8.5, ArH).
N-Benzyl-3-(2-morpholinoethoxy)-5-methoxybenzofuran-
2-carboxamide 32[43]
3-(Benzyloxy)-6-methoxy-1-benzo[b]thiophen-
2-carboxylic Acid 61[44]
Pink powder. m/z 315 (M + 1)+. δH (CDCl3) 3.49 (3H, s, OCH3),
4.95 (2H, s, CH2), 6.57 (1H, m, ArH), 6.81 (2H, m, ArH), 6.98
(1H, m, ArH), 7.11 (1H, m, ArH), 7.23 (1H, d, J 8.9, H4).
The crude product was purified by column chromatography
with chloroform/methanol (99:1) as eluent to afford 21.4 mg
(34%) of the desired N-benzyl-3-(2-morpholinoethoxy)-5-
methoxybenzofuran-2-carboxamide as yellow crystals, mp 118–
120◦C. m/z 411 (M + 1)+. δH ([D6]DMSO) 2.35 (3H, m, CH2,
CH), 2.65 (2H, m, CH2), 3.4 (4H, m, 2 CH2), 3.81 (2H, d, J
4.2, NHCH2), 4.53 (3H, m, CH2, CH), 7.06 (1H, dd, J 2.2, 6.4,
H6), 7.24 (1H, d, J 2.6, H4), 7.49 (1H, d, J 9.0, H7), 8.56 (1H,
m, NH). Rt 8.87 min, gradient conditions 30% B/70% A to 90%
B/10% A over 20 min (B 90% CH3CN, 10% H2O; A 0.1% TFA
in H2O).
3-(Benzyloxy)-5-methoxy-N,N-dimethylbenzofuran-
2-carboxamide 18
3-(Benzyloxy)-5-methoxy-1-benzofuran-2-carboxylic
acid
(128.0 mg, 0.4 mmol), N-aminopiperidine (47.0 mg, 50.0 µL,
47.0 mmol), andO-benzotriazole-N,N,Nꢀ,Nꢀ-tetramethyluronium
hexafluorophosphate (TBTU) (152.0 mg, 0.5 mmol) were dis-
solved in anhydrous DMF (5.0 mL). The solution was stirred
for 15 min under an atmosphere of nitrogen after which
diisopropylethylamine (89.8 µL, 0.5 mmol) was added. The
solution was stirred overnight at room temperature under nitro-
gen.The DMF was evaporated under reduced pressure to afford a
residue. Water was added to the residue and the aqueous solution
was extracted with ethyl acetate, then dried, filtered, and evapo-
rated under reduced pressure to afford a yellow solid.The yellow
solid was purified by column chromatography with chloro-
form as eluent to afford 18 as yellow oil. m/z 326 (M + 1)+.
δH (CDCl3) 3.02 (6H, s, 2 NCH3), 3.81 (3H, s, OCH3), 5.29
(2H, s, OCH2), 6.87–7.65 (8H, m, ArH). Rt 9.99 min, isocratic
conditions 50 B (90% CH3CN/10% H2O)/50 D (0.05% H3PO4
in H2O).
3-Cyclohexyloxy-6-methoxy-N-(furan-2-ylmethyl)-
1-benzo[b]thiophen-2-carboxamide 44
The crude product was purified by column chromatography with
ethyl acetate/hexane (1:9 to 1:1) as eluent to afford 130.0 mg
(98.0%) of the desired 3-cyclohexyloxy-6-methoxy-N-(furan-2-
ylmethyl)-1-benzo[b]thiophen-2-carboxamideaspalepinkcrys-
tals, mp 115–117◦C. m/z 386 (M + 1)+. δH (CDCl3) 1.18 (2H, m,
CH2), 1.38 (1H, m, CH), 1.54 (3H, s, OCH3), 3.87 (2H, s, CH2),
4.33 (1H, m, CH), 4.64 (2H, d, J 8.9, NHCH2). Rt 2.66 min,
isocratic 100% B (90% CH3CN/H2O).
3-Cyclohexyloxy-5-methoxy-N-(furan-2-ylmethyl)-
1-benzo[b]thiophen-2-carboxamide 58
By the above method were also prepared the following
compounds.
The crude product was purified by column chromatography with
hexane/ethyl acetate (1:9 to 1:1) as eluent to afford 55.5 mg
(88.0%) of the desired 3-cyclohexyloxy-5-methoxy-N-(furan-2-
ylmethyl)-1-benzo[b]thiophen-2-carboxamide as a yellow gum.
m/z 386 (M + 1)+. δH ([D6]DMSO) 1.04–1.24 (3H, m, 3 CH),
1.32–1.5 (3H, m, 3 CH), 1.63–1.67 (2H, m, 2 CH), 1.89–1.98
(2H, m, 2 CH), 3.83 (3H, s, OCH3), 4.32 (1H, m, OCH), 4.52
(2H, d, J 5.5, CH2NH), 6.34 (1H, s, furan ArH), 6.42 (1H, s,
furan ArH), 7.12 (3H, m, ArH), 7.83–7.85 (1H, m, ArH), 8.17
(1H, t, J 5.9, NH). Found C 65.4, H 6.0, N 3.6. C21H23NO4S
requires C 65.4, H 6.0, N 3.6%.
3-(Benzyloxy)-5-methoxy-N,N-(piperidin-1-yl)benzofuran-
2-carboxamide 19
The crude product was purified by column chromatography with
chloroform as eluent to afford 19 (65.3 mg, 40%) as a yellow oil.
m/z 381 (M + 1)+. δH (CDCl3) 1.51–1.54 (6H, m, 3 CH2), 2.8
(4H, m, 2 CH2), 3.8 (3H, s, OCH3), 5.1 (2H, s, CH2), 7.0–7.48
(6H, m, ArH), 7.5 (1H, d, J 2.2, H4), 7.6 (1H, d, J 8.0, H7).
Found (M + 1)+ 381.17363. C22H24N2O4 requires (M + 1)+
381.17361.

496
G. P. Moloney et al.
3-(Benzyloxy)-5-methoxy-N-(thiophen-2-ylmethyl)-
1-benzo[b]thiophen-2-carboxamide 59
H 5.4, N 18.6. C17H19N5O3S requires C 54.7, H 5.1, N 18.8%.
Rt 12.62 min, 10% B/90% D to 90% B/10% D over 20 min (B
90% CH3CN, 10% H2O; D 0.1 N NH4OAc (pH 4)).
The crude product was purified by column chromatography with
hexane/ethyl acetate (8:2 to 3:1) as eluent to afford 151.0 mg
(57.0%) of the desired 3-(benzyloxy)-5-methoxy-N-(thiophen-
2-ylmethyl)-1-benzo[b]thiophen-2-carboxamide as an off-white
solid. m/z 410 (M + 1)+. δH ([D6]DMSO) 3.79 (3H, s, OCH3),
4.6 (2H, d, NHCH2), 5.25 (2H, s, OCH2), 6.85–7.45 (11H, m,
11 ArH), 8.43 (1H, t, NH). Rt 2.82 min, isocratic 100% B (90%
CH3CN/H2O).
3-(4-Methoxyphenoxy)-6-methoxy-N-(1H-1,2,3,4-tetrazol-
5-yl)-1-benzo[b]thiophen-2-carboxamide 55
The crude product was recrystallized from methanol/DMF/water
to afford 106.0 mg (86.0%) of the desired 3-(4-methoxy-
phenoxy)-6-methoxy-N-(1H-1,2,3,4-tetrazol-5-yl)-1-benzo[b]
thiophen-2-carboxamide as a fine white powder, mp 267–268◦C.
m/z 368 (M + 1)+. δH (CDCl3) 1.18 (2H, m, CH2), 1.38 (1H, m,
CH), 1.54 (3H, s, OCH3), 3.87 (2H, s, CH2), 4.33 (1H, m, CH),
4.64 (2H, d, J 8.9, NHCH2). Rt 2.16 min, isocratic 100% B (90%
CH3CN/H2O).
3-Benzyloxy-6-methoxy-N-(thiophen-2-ylmethyl)-
1-benzo[b]thiophen-2-carboxamide 62
The crude product was purified by column chromatography
with ethyl acetate/hexane (2:8) as eluent to afford 149.0 mg
(57.0%) of the desired 3-benzyloxy-6-methoxy-N-(thiophen-
2-ylmethyl)-1-benzo[b]thiophen-2-carboxamide as pale pink
crystals. m/z 410 (M + 1)+. δH (CDCl3) 3.88 (3H, s, OCH3),
4.61 (2H, d, J 1.8, NHCH2), 5.19 (2H, s, PhCH2), 6.85–6.89
(2H, m, ArH), 7.21–7.23 (3H, m, 3 ArH), 7.31 (3H, m, ArH),
7.61 (1H, m, NHCH2), 7.65 (2H, m, ArH).
3-(Benzyloxy)-6-methoxy-N-(1H-1,2,3,4-tetrazol-5-yl)-
1-benzo[b]thiophen-2-carboxamide 63[44]
Pale pink powder. m/z 382 (M + 1)+. δH (CDCl3) 3.63 (3H, s,
OCH3), 5.19 (2H, s, OCH2), 6.25–7.75 (8H, m,ArH), 10.01 (1H,
s, NH). Rt 2.16 min, isocratic 100% B (90% CH3CN/H2O).
3-Isopropoxy-4-nitro-5-methoxy-N-(1H-1,2,3,4-tetrazol-
5-yl)-1-benzo[b]thiophen-2-carboxamide 51[28]
3-(Benzyloxy)-6-methoxy-N-(thiophen-2-ylmethyl)-
1-benzo[b]thiophen-2-carboxamide 64
The crude product was recrystallized from methanol/DMF/water
to afford 36.3 mg (30.0%) of the desired 3-isopropoxy-4-nitro-5-
methoxy-N-(1H-1,2,3,4-tetrazol-5-yl)-1-benzo[b]thiophen-2-
carboxamide as a white powder, mp 236–238◦C. m/z 379
(M + 1)+. δH ([D6]DMSO) 1.15 (6H, d, J 6.0, 2 CH3), 3.97
(3H, s, OCH3), 4.49 (1H, m, CH), 7.65 (1H, d, J 9.2, H7), 8.25
(1H, d, J 9.0, H6). Found C 55.6, H 5.1, N 4.9. C13H15NO4S
requires C 55.5, H 5.4, N 5.0%. Found (M + 1)+ 282.08002.
C13H15NO4S requires (M + 1)+ 282.08.
The crude product was purified by column chromatography
with ethyl acetate/hexane (2:8) as eluent to afford 150.0 mg
(57.3%) of the desired 3-(benzyloxy)-6-methoxy-N-(thiophen-
2-ylmethyl)-1-benzo[b]thiophen-2-carboxamide as pale pink
crystals. m/z 411 (M + 1)+. δH (CDCl3) 3.9 (3H, s, OCH3), 4.62
(2H, d, NHCH2), 5.19 (2H, s, OCH2), 7.0 (4H, m, ArH), 7.36
(3H, m, ArH), 7.64 (2H, d, NHCH2). Rt 2.85 min, 100% B (90%
CH3CN/H2O).
Lithium 1-(4-Chlorophenyl)-4-ethoxy-2-methyl-
3-Isopropoxy-5-methoxy-N-(1H-1,2,3,4-tetrazol-
5-yl)benzofuran-2-carboxamide 29[27,42]
3,4-dioxobutan-1-olate 34[44]
1,1ꢀ-Carbonyldiimidazole (120.0 mg, 0.74 mmol) was added to
a solution of 3-isopropoxy-5-methoxybenzofuran-2-carboxylic
acid (150.0 mg, 0.6 mmol) dissolved in anhydrousTHF (5.0 mL)
at room temperature. The reaction mixture was heated to
reflux for 90 min. The reaction mixture was partially cooled, 5-
aminotetrazole (60.0 mg, 0.7 mmol) was added, and the reaction
mixture was heated to reflux overnight.The reaction mixture was
allowed to cool, then poured into water (200.0 mL), and acidi-
fied with concentrated hydrochloric acid. The precipitate was
collected by filtration and recrystallized from acetonitrile/water
to afford 29 (158.0 mg, 83.0%) as a cream crystalline solid, mp
236–238◦C. m/z 318 (M + 1)+. δH (CDCl3) 1.37 (6H, d, J 6.0, 2
CH3), 3.85 (3H, s, OCH3), 5.07 (1H, m, CH(CH3)2), 7.17–7.21
(2H, m, H4, H6), 7.57 (1H, d, J 8.9, H7), 11.8 (1H, s, NH).
By the above method were also prepared the following
compounds.
Lithium hexamethyl disilazide (1.0 N in THF) (29.6 mL,
30.0 mmol) was added to anhydrous THF (120.0 mL). The
solution was then cooled to −78◦C under an atmosphere of nitro-
gen. After 30 min, 4-chloropropiophenone (5.0 g, 30.0 mmol) in
anhydrous THF (25.0 mL) was added to the reaction mixture.
The solution was then allowed to warm up to room temperature
overnight. The solvent was evaporated under reduced pressure
to afford a gum, which was recrystallized from acetone to afford
2.41 g (30.0%) of the desired lithium 1-(4-chlorophenyl)-4-
ethoxy-2-methyl-3,4-dioxobutan-1-olate as yellow crystals. m/z
269 (M + 1)+. δH ([D6]DMSO) 1.13 (3H, t, J 7.1, CH3), 1.27
(3H, d, J 6.9, CH3), 4.18 (2H, q, J 6.9, CH2), 5.28 (1H, q, J 6.9,
CH), 7.66 (1H, d, J 6.8, ArH), 7.69 (1H, d, J 7.8, ArH), 8.01 (1H,
d, J 8.3, ArH), 8.03 (1H, d, J 8.6, ArH).
Ethyl 5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-
4-methyl-1H-pyrazole-3-carboxylate 35[44]
3-Cyclohexyloxy-6-methoxy-N-(1H-1,2,3,4-tetrazol-5-yl)-
1-benzo[b]thiophen-2-carboxamide 43
Ethyl 3-(4-chlorophenyl)-2-methyl-3-oxopropanoate (1.31 g,
4.9 mmol) was dissolved in anhydrous ethanol (40.0 mL) and
2,4-dichlorophenyl hydrazine hydrochloride (1.04 g, 4.9 mmol)
was added. The reaction mixture was stirred at room tempera-
ture under an atmosphere of nitrogen for 48 h. The solvent was
evaporated under reduced pressure and the residue was puri-
fied by column chromatography with hexane/chloroform (1:1)
leading to chloroform as eluent to afford 498.0 mg (24.0%) of
the desired ethyl 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-
methyl-1H-pyrazole-3-carboxylate as a yellow solid. m/z 431
The crude product was recrystallized from methanol/water
to afford 30.0 mg (87.0%) of the desired 3-cyclohexyloxy-6-
methoxy-N-(1H-1,2,3,4-tetrazol-5-yl)-1-benzo[b]thiophen-2-
carboxamide as a white solid, mp 219–222◦C. m/z 373 (M)+.
δH (CDCl3) 1.28 (3H, m, 3 CH), 1.54–1.66 (3H, m, 3 CH),
1.85–1.88 (2H, m, 2 CH), 2.15–2.29 (2H, m, 2 CH), 3.91 (3H,
s, OCH3), 4.65 (1H, m, OCH), 7.05 (1H, dd, J 2.2, 8.9, ArH),
7.24 (1H, d, J 2.2, ArH), 7.71 (1H, d, J 8.9, ArH). Found C 54.7,

Novel Agonists for the CB1 Receptor
497
(M + 1)+ (cyclizes in the source). δH ([D6]DMSO) 1.05 (3H, t,
J 6.9, CH3), 1.25 (2H, q, J 6.9, CH2), 1.36 (3H, d, J 4.2, CH3),
3.05 (1H, q, J 4.2, CH), 7.2–8.02 (7H, m, ArH).
Cyclohexyl 3-Chloro-6-methoxy-1-benzo[b]thiophen-
2-carboxylate 40
3-Chloro-6-methoxy-1-benzo[b]thiophen-2-carbonyl chloride
(16.3 g, 62.4 mmol) was dissolved in anhydrous benzene
(20.0 mL) and anhydrous cyclohexanol (20.0 mL) and the reac-
tion mixture was heated to reflux for 3 h under an atmosphere
of nitrogen and then stirred at room temperature for 17 h. After
this time, the reaction mixture was evaporated under reduced
pressure to afford a yellow oil, which was purified by column
chromatography with hexane/dichloromethane (1:9) as eluent
to afford a yellow solid, which was recrystallized from hexane
to afford 19.94 g (98.0%) of the desired cyclohexyl 3-chloro-6-
methoxy-1-benzo[b]thiophen-2-carboxylate as a yellow powder.
m/z 326 (M + 1)+. δH (CDCl3) 1.4–1.44 (2H, m, CH2), 1.46–
1.49 (2H, m, CH2), 1.62–1.73 (2H, m, CH2), 1.8–1.86 (2H, m,
CH2), 1.9–1.97 (2H, m, CH2), 3.9 (3H, s, OCH3), 5.1 (1H, m,
CH), 7.1 (1H, dd, J 2.0, 9.0, H6), 7.21 (1H, d, J 2.0, H4), 7.83
(1H, d, J 9.0, H7). Found (M + 1)+. 325.0586. C16H17ClO3S
requires (M + 1)+ 325.05869.
5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-
1H-pyrazole-3-carboxylic Acid 36[44]
(Z)-Ethyl4-(4-chlorophenyl)-2-(2,4-dichlorophenyl)hydrazone-
3-methyl-4-oxobutanoate (33.5 mg, 0.08 mmol) was dissolved
in ethanol (2.0 mL) and 2 M NaOH (980.0 µL, 1.9 mmol) was
added and the reaction mixture was heated to reflux for 6 h,
then allowed to stir at room temperature overnight. The sol-
vent was evaporated under reduced pressure and water was
added; the aqueous phase was acidified with 2 M HCl and
extracted with ethyl acetate, dried, filtered and the solvent
evaporated under reduced pressure to afford 3.1 mg (10.0%)
of the desired 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-
methyl-1H-pyrazole-3-carboxylic acid as a yellow solid. m/z 381
(M)+. δH ([D6]DMSO) 2.1 (3H, s, CH3), 7.1 (2H, d, J 8.4, ArH),
7.34 (2H, d, J 8.4, ArH), 7.45 (1H, m, ArH), 7.58 (1H, m, ArH),
7.69 (1H, m, ArH).
Cyclohexyl 3-Cyclohexyloxy-6-methoxy-
1-benzo[b]thiophen-2-carboxylate 41
Cyclohexanol (8.3 mL, 80.0 mmol) was added dropwise to a
stirred suspension of sodium hydride (60%, 3.2 g, 80.0 mmol) in
anhydrousTHF (60.0 mL) under an atmosphere of nitrogen. The
reaction mixture was stirred for 90 min. After this time, a solu-
tion of cyclohexyl 3-chloro-6-methoxy-1-benzo[b]thiophen-
2-carboxylate (13.0 g, 40.0 mmol) in warm anhydrous THF
(100.0 mL) was added slowly to the stirred sodium hydride
mixture over 5 min. The reaction mixture was then heated to
reflux for 17 h under an atmosphere of nitrogen. After this
time, the reaction mixture was allowed to cool to room tem-
perature and the cyclohexanol and THF were evaporated under
reduced pressure to afford a brown solid, which was dis-
solved in diethyl ether (500.0 mL) and washed with water.
The diethyl ether phase was then dried, filtered and evaporated
under reduced pressure to afford 14.19 g (91.0%) of the desired
cyclohexyl 3-cyclohexyloxy-6-methoxy-1-benzo[b]thiophen-2-
carboxylate as a yellow oil. m/z 389 (M + 1)+. δH (CDCl3)
1.18–1.3 (10H, m, 5 CH2), 1.46–1.99 (10H, m, 5 CH2),
4.5 (1H, m, CH), 4.99 (1H, m, CH), 6.95 (1H, dd, J 2.2,
8.9, H6), 7.13 (1H, d, J 2.0, H4), 7.7 (1H, d, J 9.0, H7).
Found (M + 1)+ 389.17081. C22H28O4S requires (M + 1)+
389.17083.
5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-
N-piperidino-1H-pyrazole-3-carboxamide 37[44]
1-(2,4-Dichlorophenyl)-4-methyl-5-(4-chlorophenyl) pyrazole-
3-carboxylic acid (433.0 mg, 11.1 mmol) was dissolved in
anhydrous DMF (25.0 mL) and N-aminopiperidine (125.0 mg,
1.3 mmol) and TBTU (400.0 mg, 1.3 mmol) were added and
the reaction mixture was stirred under an atmosphere of nitro-
gen for 30 min, and diisopropylethylamine (238.0 µL, 1.4 mmol)
was added and the reaction was stirred for 72 h. The DMF
was evaporated under reduced pressure, water was added and
the aqueous phase was extracted with ethyl acetate, dried,
filtered, and evaporated under reduced pressure to afford a
dark brown oil, which was purified by column chromato-
graphy with chloroform as eluent to afford 346.0 mg (68.0%)
of the desired 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-
methyl-N-piperidino-1H-pyrazole-3-carboxamide as a light yel-
low glassy solid. m/z 464 (M + 1)+. δH ([D6]DMSO) 1.33 (2H,
m, CH2), 1.55 (3H, m, CH3), 2.76 (4H, m, 2 CH2), 7.21 (2H, d,
J 8.4, ArH), 7.45 (2H, d, J 8.4, 2 ArH), 7.57 (1H, dd, J 2.3, 8.5,
ArH), 7.74 (2H, m, 2 ArH), 9.03 (1H, s, NH).
3-Chloro-6-methoxy-1-benzo[b]thiophen-2-carbonyl
Chloride 39[45–47]
Isopropyl 5-Methoxy-3-chloro-1-benzo[b]thiophen-
2-carboxylate 47[28]
To a mixture of 4-methoxycinnamic acid (10.0 g, 56.1 mmol)
and anhydrous pyridine (560.0 µL, 6.9 mmol) was added drop-
wise with stirring thionyl chloride (30.0 mL, 0.41 mmol) and
the reaction mixture was heated to 105◦C for 48 h. The reac-
tion mixture was allowed to cool and the volatiles were
removed by evaporation under reduced pressure to afford
a yellow solid, which was recrystallized from ButOCH3 to
afford 6.75 g (46.0%) of the desired 3-chloro-6-methoxy-1-
benzo[b]thiophen-2-carbonyl chloride as yellow needles, mp
120◦C. m/z 261 (M + 1)+. δH (CDCl3) 3.89 (3H, s, OCH3),
7.19–7.3 (2H, m, ArH), 7.66 (1H, d, J 9.0, ArH).
3-Chloro-5-methoxy-1-benzo[b]thiophen-2-carbonyl chloride
(7.32 g, 28.0 mmol) was added to a mixture of anhydrous THF
(30.0 mL) and isopropyl alcohol (30.0 mL) and the reaction mix-
ture was stirred at reflux for 5 h. The reaction was allowed to
cool and the solvent was evaporated under reduced pressure to
afford a yellow residue, which was purified by column chromato-
graphy with dichloromethane/hexane (2:3) as eluent to afford a
yellow solid, which was recrystallized from hexane to afford
1.39 g (17.0%) of the desired isopropyl 5-methoxy-3-chloro-1-
benzo[b]thiophen-2-carboxylate as pale fluffy yellow crystals,
mp 76–80◦C. m/z 319 (M + 1)+. δH ([D6]DMSO) 1.32 (6H,
d, J 6.2, CH(CH3)2), 4.03 (3H, s, OCH3), 5.15 (1H, m, J 6.2,
CH(CH3)2), 7.55 (1H, d, J 9.0, ArH), 8.05 (1H, d, J 8.9, ArH).
Found C 54.5, H 4.6. C13H13ClO3S requires C 54.9, H 4.5%.
By the above method was also prepared 3-chloro-5-methoxy-
1-benzo[b]thiophen-2-carbonyl chloride 46[28,48] as a yellow
solid. m/z 260 (M)+. δH (CDCl3) 3.9 (3H, s, OCH3), 7.2–7.3
(2H, m, ArH), 7.69 (1H, d, J 8.8, ArH).

498
G. P. Moloney et al.
Isopropyl 3-Isopropoxy-5-methoxy-1-benzo[b]thiophen-
2-carboxylate 48[28]
7.26 (1H, d, J 2.2,ArH), 7.88 (1H, d, J 9.0,ArH). Found (M + 1)+
349.02231. C17H13ClO4S requires (M + 1)+ 349.02231.
Sodium hydride (60%, 600.0 mg, 4.0 mmol) was suspended in
anhydrous THF (2.0 mL) and stirred under an atmosphere of
nitrogen for 10 min. A solution of isopropyl alcohol (350.0 µL,
4.6 mmol) dissolved in anhydrous THF (2.0 mL) was slowly
added to the sodium hydride in THF. The reaction mixture was
then stirred at room temperature for 1.5 h under an atmosphere
of nitrogen. After this time, isopropyl 3-chloro-5-methoxy-1-
benzo[b]thiophen-2-carboxylate (600.0 mg, 2.1 mmol) in anhy-
drous THF (3.0 mL) was slowly added. The reaction mixture
was heated to reflux for 17 h. After this time, the THF and iso-
propanol were evaporated under reduced pressure to afford a
residue, which was partitioned between hexane and water. The
aqueous phase wasextractedwith hexane andthehexane extracts
were dried, filtered, and evaporated under reduced pressure to
afford (325.0 mg, 50.0%) of the desired isopropyl 3-isopropoxy-
5-methoxy-1-benzo[b]thiophen-2-carboxylate as yellow oil. m/z
309 (M + 1)+. δH (CDCl3) 1.24 (6H, d, J 3.8, 2 CH3), 2.1 (6H,
s, J 6.9, 2 CH3), 3.89 (3H, s, OCH3), 7.06 (1H, dd, J 2.4, 9.0,
ArH), 7.24 (1H, d, J 2.4, ArH), 7.5 (1H, d, J 9.0, ArH).
4-Methoxyphenyl 3-(4-Methoxyphenoxy)-6-methoxy-
1-benzo[b]thiophen-2-carboxylate 53
Potassium hydroxide (100.0 mg, 1.78 mmol) and 4-methoxy-
phenol (240.0 mg, 1.93 mmol) in anhydrous toluene (60.0 mL)
were heated to reflux under Dean–Stark conditions for 17 h.
After this time, the reaction mixture was allowed to cool to
room temperature, then DMSO (5.0 mL) was added and the
toluene was evaporated under reduced pressure. The DMSO
solution was brown. 4-Methoxyphenyl 3-chloro-6-methoxy-
1-benzo[b]thiophen-2-carboxylate (300.0 mg, 0.86 mmol) was
added to the DMSO solution and the reaction mixture was heated
to 100◦C for 17 h. After this time, the reaction mixture was
allowed to cool to room temperature, then poured into 0.25 N
aqueous potassium carbonate solution (100.0 mL) and stirred
for 2 h. A precipitate formed and was collected by filtration and
dried under reduced pressure to afford 212.3 mg (57.0%) of the
desired 4-methoxyphenyl 3-(4-methoxyphenoxy)-6-methoxy-1-
benzo[b]thiophen-2-carboxylate as a cream powder. m/z 437
(M + 1)+. δH (CDCl3) 3.77 (3H, s, OCH3), 3.79 (3H, s, OCH3),
3.91 (3H, s, OCH3), 6.78–6.9 (5H, m, ArH), 6.91–7.04 (6H,
m, ArH), 7.53 (1H, d, J 8.9, ArH). Found (M + 1)+ 437.09804.
C24H24O6S requires (M + 1)+ 437.09806.
3-Isopropoxy-4-nitro-5-methoxy-1-benzo[b]thiophen-
2-carboxylic Acid 50[28]
A solution of 3-isopropoxy-5-methoxy-1-benzo[b]thiophen-2-
carboxylic acid (500.0 mg, 1.87 mmol) in acetic acid (10.0 mL)
was cooled in ice-water and concentrated nitric acid (1.5 mL)
was added dropwise over 2 min.The reaction mixture was stirred
at room temperature for 60 min. After this time, the reaction
mixture was poured into water (150.0 mL) and a precipitate
formed, which was collected by filtration and washed well with
water, then dried under reduced pressure to afford a yellow
solid, which was recrystallized from dichloromethane/hexane to
afford 289.0 mg (50.0%) of the desired 3-isopropoxy-4-nitro-
5-methoxy-1-benzo[b]thiophen-2-carboxylic acid as a yellow
powder, mp 197–200◦C. m/z 312 (M + 1)+. δH (CDCl3) 1.32
(6H, d, J 6.0, 2 CH3), 3.99 (3H, s, OCH3), 5.04 (1H, m,
CH(CH3)2), 7.32 (1H, d, J 9.0, H6), 7.8 (1H, d, J 8.9, H7).
Found C 50.1, H 4.2, N 4.4. C13H13NO6S requires C 50.2, H
4.2, N 4.5%. Rt 6.39 min, 10% B/90% D to 90% B/10% D (B
90% CH3CN/10% water; D 0.1 N NH4OAc (pH 4)).
Benzyl 3-(Benzyloxy)-5-methoxy-1-benzo[b]thiophen-
2-carboxylate 56[44]
Benzyl alcohol (9.0 mL, 70.0 mmol) in anhydrous THF
(10.0 mL)wasaddeddropwisetoasuspensionofsodiumhydride
(60%, 2.8 g, 70.0 mmol) in anhydrous THF (40.0 mL) under an
atmosphere of nitrogen.The reaction mixture was stirred at room
temperature for 90 min. After this time, 3-chloro-5-methoxy-
1-benzo[b]thiophen-2-carbonyl chloride (8.0 g, 30.0 mmol) was
added and the reaction mixture was heated to reflux for 17 h
under an atmosphere of nitrogen. After this time, the THF was
evaporated under reduced pressure to afford a solid, which was
purified by column chromatography, eluting with hexane/ethyl
acetate (8:2) to afford 6.07 g (49.0%) of the desired benzyl
3-(benzyloxy)-5-methoxy-1-benzo[b]thiophen-2-carboxylateas
a yellow solid, m/z 405 (M + 1)+. δH ([D6]DMSO) 3.88 (3H, s,
OCH3), 5.32 (2H, s, OCH2), 5.4 (2H, s, OCH2), 7.0–7.22 (2H, m,
2 ArH), 7.28–7.29 (3H, m, ArH), 7.29 (1H, dd, J 2.5, 8.9, ArH),
7.34 (1H, d, J 2.3, ArH), 7.37–7.44 (2H, m, ArH), 7.45–7.58
(3H, m, ArH). Found (M + 1)+ 405.10821. C24H20O4S requires
(M + 1)+ 405.10823.
4-Methoxyphenyl 3-Chloro-6-methoxy-
1-benzo[b]thiophen-2-carboxylate 52
2-Chloroethyl formate (250.0 µL, 2.61 mmol) was added
to 3-chloro-6-methoxy-1-benzo[b]thiophen-2-carboxylic acid
(500.0 mg, 2.1 mmol) and triethylamine (350.0 µL, 2.51 mmol)
in acetone (5.0 mL) at 0◦C. The reaction mixture was stirred at
0◦C for 15 min, then a solution of 4-methoxyphenol (400.0 mg,
3.22 mmol) and triethylamine (450.0 µL, 3.23 mmol) in acetone
(1.5 mL) was added slowly over 2 h. The reaction mixture was
allowed to stir to room temperature for 2 h. The reaction mixture
became very thick, so a further quantity of acetone (5.0 mL) was
added and stirring was continued for a further 60 min. After this
time, the reaction mixture was poured onto water (200.0 mL)
and a precipitate formed, which was collected by filtration. The
solid was then recrystallized from hexane/dichloromethane to
afford 461.2 mg (64.0%) of the desired 4-methoxyphenyl 3-
chloro-6-methoxy-1-benzo[b]thiophen-2-carboxylate as white
fluffy crystals, mp 160–161.5◦C. m/z 349 (M + 1)+. δH (CDCl3)
3.83 (3H, s, OCH3), 3.92 (3H, s, OCH3), 6.92 (2H, d, J 9.7,
2ArH), 7.13 (1H, dd, J 2.3, 9.0, ArH), 7.18 (2H, d, J 9.0, 2ArH),
By the above method was also prepared benzyl 3-benzyloxy-
6-methoxy-1-benzo[b]thiophen-2-carboxylate 60, which was
purified by column chromatography, with ethyl acetate/hexane
(5:95 to 2:8) as eluent, to afford 60 (6.78 g, 67.4%) as an orange
oil. δH (CDCl3) 3.76 (3H, s, OCH3), 5.27 (2H, s, CH2), 5.4
(2H, s, CH2), 7.03 (1H, dd, J 2.1, 9.0, H5), 7.18–7.45 (11H, m,
11 ArH), 7.54 (1H, d, J 9.0, H4).
Biological Methods
Experiments using rat or mouse tissues were approved by the
University of Melbourne Animal Ethics Committee in accor-
dance with the Australian Code of Practice for the Care and
Use of Animals for Scientific Purposes (Australian Govern-
ment, National Health and Medical Research Council, Canberra,
2004).

Novel Agonists for the CB1 Receptor
499
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