Synthesis and structure-activity relationships of a series of substituted 2-(1H-furo[2,3-g]indazol-1-yl)ethylamine derivatives as 5-HT2C receptor agonists

Article abstract of DOI:10.1016/j.bmc.2007.10.100

A series of novel indazole derivatives were synthesized, and their structure-activity relationships examined in order to identify potent and selective 5-HT_2C receptor agonists. Among these compounds, (S)-2-(7-ethyl-1H-furo[2,3-g]indazol-1-yl)-1-methylethylamine (YM348) had a good in vitro profile, that is, high agonistic activity to the human 5-HT_2C receptor subtype (EC₅₀ = 1.0 nM) and high selectivity over 5-HT_2A receptors. This compound was also effective in a rat penile erection model when administered po.

Full text of DOI:10.1016/j.bmc.2007.10.100

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry 16 (2008) 1966–1982
Synthesis and structure–activity relationships of a series
of substituted 2-(1H-furo[2,3-g]indazol-1-yl)ethylamine
derivatives as 5-HT2C receptor agonists
Itsuro Shimada,a,* Kyoichi Maeno,a Ken-ichi Kazuta,b Hideki Kubota,a
Tetsuya Kimizuka,c Yasuharu Kimura,a Ken-ichi Hatanaka,d Yuki Naitou,a
Fumikazu Wanibuchi,a Shuichi Sakamotoe and Shin-ichi Tsukamotoa
aDrug Discovery Research, Astellas Pharma Inc., 21 Miyukigaoka, Tsukuba, Ibaraki 305-8585, Japan
bDevelopment, Astellas Pharma Inc., 3-17-1 Hasune, Itabashi-Ku, Tokyo 174-8612, Japan
cIntellectual Property, Astellas Pharma Inc., 2-3-11 Nihonbashi-honcho, Chuo-ku, Tokyo 103-8411, Japan
dSales & Marketing, Astellas Pharma Inc., 2-3-11 Nihonbashi-honcho, Chuo-ku, Tokyo 103-8411, Japan
eTechnology, Astellas Pharma Inc., 3-17-1 Hasune, Itabashi-Ku, Tokyo 174-8612, Japan
Received 20 September 2007; revised 29 October 2007; accepted 30 October 2007
Available online 4 November 2007
Abstract—A series of novel indazole derivatives were synthesized, and their structure–activity relationships examined in order to
identify potent and selective 5-HT2C receptor agonists. Among these compounds, (S)-2-(7-ethyl-1H-furo[2,3-g]indazol-1-yl)-1-meth-
ylethylamine (YM348) had a good in vitro profile, that is, high agonistic activity to the human 5-HT2C receptor subtype
(EC50 = 1.0 nM) and high selectivity over 5-HT2A receptors. This compound was also effective in a rat penile erection model when
administered po.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
dysfunction.4–6 Unfortunately, very few 5-HT2C-selec-
tive agonists were known7; therefore, a program to
develop selective 5-HT2C receptor agonists was initiated.
5-Hydroxytryptamine (5-HT), an important neurotrans-
mitter in the central and peripheral nervous systems
(CNS and PNS, respectively), has been implicated in a
variety of important physiological processes. At least
14 distinct serotonin receptor subtypes are expressed in
the mammalian CNS, each of which is assigned to one
of seven families, 5-HT1 to 5-HT7.1 The 5-HT2 receptor
family currently consists of three subtypes termed
5-HT2A, 5-HT2B, and 5-HT2C receptors. Given their
relative brain specificity, regional messenger RNA distri-
bution in the brain,2 and the results from a recent study
using gene-knockout mice,3 5-HT2C receptors are con-
sidered to be attractive targets for the design of novel
drugs for treatment of CNS-related diseases such as
obesity, obsessive compulsive disorder, and sexual
Only a few selective 5-HT2C agonists had been reported
previously, such as Ro60-0175 (1), Ro60-0213 (2)
(Fig. 1), and related compounds.8,9 Therefore, in order
to discover more potent and selective 5-HT2C agonists,
focus was placed upon replacing the indole core with
other heterocycles. Since the indazole ring system is
known to be a viable bioisostere for the indole ring sys-
tem,10 its potential as an 5-HT2C agonist was
investigated.
F
N
N
Cl
MeO
Ro60-0213 (2)
Keywords: 5-HT2C receptor agonist; Binding affinity; Indazole;
YM348.
NH2
Ro60-0175 (1)
NH2
*
Corresponding author. Tel.: +81 29 863 6684; fax: +81 29 852
5387; e-mail: itsuro.shimada@jp.astellas.com
Figure 1. Structures of Ro60-0175 and Ro60-0213.
0968-0896/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2007.10.100

I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
1967
This paper reports on the synthesis and structure–activ-
ity relationships (SAR) of indazole derivatives when
used as 5-HT2C agonists [representative compound:
YM348 (7i)].11 In addition to the binding affinities for
5-HT2C and 5-HT2A receptors, the functional activities
for 5-HT2C, 5-HT2B, and 5-HT2A receptors and a fur-
ther in vivo characterization of a 5-HT2C receptor-med-
iated response, penile erection of YM348 (7i) are shown.
reduction of the azide 6 with LiAlH4 or PPh3, produced
the amines 7. Alternatively, the amines 7 were also ob-
tained via Method B, which started with N-alkylation
of the indazoles 3 with N-Boc-O-Ts-L-alaninol12 fol-
lowed by Boc-deprotection with HCl.
Scheme 2 shows the syntheses of the substituted inda-
zoles 3a–f. A protocol developed by Bartsch and Yang13
was adopted to synthesize the halogenated indazoles 3a–
d. The halogenated o-toluidines 9a–d were diazotized
with sodium nitrite in hydrochloric acid, followed by
the addition of sodium tetrafluoroborate to yield benze-
nediazonium tetrafluoroborates as precipitates. The
crude benzenediazonium tetrafluoroborates were treated
with potassium acetate and 18-crown-6 in chloroform to
give the halogenated indazoles 3a–d in 20%, 19%, 49%,
and 45% yield, respectively. The toluidine 9c was ob-
tained by nitration of 3, 4-dichlorotoluene (10), followed
by reduction of the nitro group with SnCl2. The regio-
2. Chemistry
The desired substituted 2-(indazol-1-yl)-1-methylethyl-
amines (7) were prepared starting from substituted inda-
zoles 3 via two different routes (Scheme 1). Method A
started with the deprotonation of the indazoles 3, fol-
lowed by alkylation with (R)-propylene oxide to afford
the alcohols 4. The SN2 reaction of the corresponding
mesylates 5 with sodium azide, and the subsequent
Method A
a
d
c
N
N
N
N
N
N
N
N
H
R
R
R
R
3
6
7
X
N3
NH2
4 : X = OH
b
5 : X = OMs
Method B
f
e
N
N
3
7
R
8
NHBoc
Scheme 1. Synthetic route to compound 7. Reagents: (a) NaH, (R)-propylene oxide, DMF; (b) MsCl, Et3N, CH2Cl2; (c) NaN3, DMF; (d) LiAlH4,
THF or PPh3, H2O, THF; (e) N-Boc-O-Ts-L–alaninol, Cs2CO3, DMSO; (f) HCl, AcOEt.
Me
a
N
N
H
NH2
R
R
9a : R = 4-F
9b : R = 5-F
3a : R = 5-F
3b : R = 6-F
9c : R = 4,5-diCl
9d : R = 5,6-diCl
3c : R = 5,6-diCl
3d : R = 6,7-diCl
Cl
Me
Cl
Cl
Me
b, c
Cl
Cl
NH2
10
9c
Me
Me
O
d
e
f
O
Cl
NH2
N
H
Cl
NH2
Cl
N
H
Cl
Cl
Cl
9d
Cl
11
12
13
g
i
N
N
N
N
H
N
H
N
H
H2N
HO
h
MeO
R
R
14
3e : R = H
3f : R = Cl
15 : R = H
16 : R = Cl
Scheme 2. Synthetic route to compound 3a–3f. Reagents: (a) 1—NaNO2, c-HCl then NaBF4, H2O; 2—AcOK, 18-crown-6, CHCl3; (b) KNO3,
t
c-H2SO4; (c) SnCl2Æ2H2O, c-HCl, EtOH; (d) PivCl, K2CO3, acetone; (e) BuLi, MeI, TMEDA, BuOMe; (f) KOH, HOCH2CH2OH; (g) NaNO2,
H2SO4, then 10 M H2SO4; (h) NCS, dioxane; (i) MeI, K2CO3, DMF.

1968
I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
isomer of the toluidine 9c, 9d was prepared from
2,3-dichloroaniline (11). o-Lithiation of the pivaloyl-
protected derivative 12 generated an aryllithium inter-
mediate, which was trapped with methyl iodide in a
moderate yield. The obtained 13 was then deprotected
to afford the toluidine 9d. The methoxy indazoles 3e,
3f were prepared from a commercially available 6-amin-
oindazole (14). The hydroxyindazole 15 was obtained by
hydrolyzing the diazonium sulfate derivative of 14.14
The synthesis of 16 was carried out by chlorinating 15
using the N-chlorosuccinimide (NCS). The hydroxy
groups in 15 and 16 were reacted with methyl iodide
to afford 3e and 3f.
prepared from dihydrobenzofuranones 18a, 18c by uti-
lizing the aforementioned synthetic methods with minor
modifications. The 3-methoxy analogues 3p, 3q were
also derived from 18a or 18c first by introducing the eth-
oxycarbonyl group followed by cyclization, O-methyla-
tion, and aromatization.
Scheme 4 shows the syntheses of the thiophene-fused
indazole 3r and the oxazole-fused indazole 3s. The thio-
phene-fused analogue 3r was prepared from commer-
cially available 24 according to the procedure for
synthesizing 3g. The oxazole-fused analogue 3s was syn-
thesized from 6-hydroxyindazole (15) by nitration at the
7-position, followed by reduction and cyclization using
triethyl orthoformate in three steps and an overall yield
of 77%.
Scheme 3 shows the syntheses of the furan-fused inda-
zoles 3g–q. 1,3-Cyclohexanedione (17) was reacted with
chloroacetaldehyde to give 6,7-dihydrobenzofuran-
4(5H)-one (18a)15 in 60% yield. Subsequent a-formyla-
tion of 18a was performed using ethyl formate and
t-BuOK, followed by the addition of hydrazine to afford
4, 5-dihydro-1H-furo[2,3-g]indazole (19a) in 73% yield.
Finally, dehydration with DDQ provided 1H-furo[2,3-
g] indazole (3g) in 40% yield. The 7-methyl analogue
3h and 7-ethyl analogue 3i16 were prepared from the cor-
responding dihydrobenzofuranones 18b, 18c using the
method outlined above. The 7-isopropyl analogue 3j
was derived from 19a first by the acetylation using acetic
acid and trifluoroacetic anhydride, followed by methyl-
ation and dehydration. The 3-alkyl analogues 3k–o were
3. Results and discussion
3.1. In vitro binding assay
The synthesized compounds were evaluated for their
5-HT2C and 5-HT2A receptor binding affinities, which
were determined using the displacement of agonist
([3H]5-HT) radioligand binding to human 5-HT2C and
5-HT2A receptor sites in CHO cell membranes. The
structure–activity relationships of the novel indazole
derivatives are summarized in Tables 1–4.
a or b or c
d, e
f
N
N
H
N
N
H
O
O
O
O
R
O
R
O
R
17
18a : R = H
18b : R = Me
18c : R = Et
19a : R = H
19b : R = Me
19c : R = Et
3g : R = H
3h : R = Me
3i : R = Et
N
N
N
g
h
N
H
N
H
N
H
O
O
O
O
19a
20
3j
R2
R2
i, e
f
N
N
O
O
N
N
H
O
O
H
R1
R1
R
21a : R = H, R2 = Me
3k : R = H, R2 = Me
1
1
18a : R = H
18c : R = Et
21b : R = H, R2 = Et
3l : R = H, R2 = Et
1
1
21c : R = H, R2 = Pr
3m : R = H, R2 = Pr
1
1
21d : R = Et, R2 = Me 3n : R = Et, R2 = Me
1
1
21e : R = Et, R2 = Et
3o : R = Et, R2 = Et
1
1
O
O
OMe
N
OEt
k, f
NH
O
H
j
e
O
O
R
N
N
O
O
R
O
R
H
R
18a : R = H
18c : R = Et
22a : R = H
22b : R = Et
23a : R = H
23b : R = Et
3p : R = H
3q : R = Et
Scheme 3. Synthetic route to compounds 3g–3q. Reagents: (a) ClCH2CHO, NaHCO3, H2O; (b) 1—2,3-dibromopropene, Triton B, MeOH, H2O; 2—
HClO4, HCO2H; (c) 1-bromo-2-butanone, NaHCO3, MeOH, H2O; (d) tBuOK, HCO2Et, THF; (e) H2NNH2ÆH2O, EtOH; (f) DDQ, dioxane or Pd–
C, diethyl fumarate, ethylene glycol; (g) AcOH, TFAA; (h) 1—MeMgCl, THF; 2—I2, benzene; (i) R2CO2Et, KH, NaH, DME; (j) KHMDS,
ClCO2Et, THF; (k) CH2N2, dioxane, MeOH.

I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
1969
a, b
c
N
N
H
N
N
H
O
S
S
S
24
15
25
3r
d
e
f
N
N
H
N
N
H
N
N
H
N
N
H
HO
HO
HO
O
N
NO2
26
NH2
27
3s
Scheme 4. Synthetic route to compound 3r and 3s. Reagents: (a) HCO2Et, tBuOK, THF; (b) H2NNH2ÆH2O, EtOH; (c) DDQ, dioxane; (d) KNO3,
H2SO4; (e) H2, Pd–C, AcOH; (f) HC(OEt)3.
Table 1. Affinities of compounds 1 and 7a-7f for 5-HT2C and 5-HT2A receptors
R1
N
R2
N
R3
NH2
Compound
R1
R2
R3
Kia (nM)
Selectivityb
5-HT2C
5-HT2A
5-HT2A/5-HT2C
1
26
43
39
89
2
2
3
2
9
1
2
7a
7b
7e
7f
7c
7d
F
H
H
H
H
Cl
H
Cl
H
H
H
Cl
H
F
32
16
82
37
OMe
OMe
Cl
140
7.5
4.0
1200
11
Cl
9.1
a Ki for [3H]5-HT binding; human 5-HT2C and 5-HT2A receptors expressed in CHO cells.
b Selectivity = 5-HT2A value/5-HT2C value.
Table 2. Affinities of compounds 7g, 7r, and 7s for 5-HT2C and 5-
HT2A receptors
Table 3. Affinities of compounds 7k, 7l, 7m, and 7p for 5-HT2C and 5-
HT2A receptors
Kia (nM)
Selectivityb
R
Compound
N
5-HT2C
5-HT2A
9.1
5-HT2A/5-HT2C
2
N
O
7d
4.0
NH2
N
Compound
R
Kia (nM)
Selectivityb
N
S
7r
1.4
6.7
5
5-HT2C
5-HT2A
5-HT2A/5-HT2C
NH2
7g
7k
7l
H
0.20
13
0.78
17
4
1
Me
Et
N
N
2.5
25
11
64
4
N
N
O
O
7g
7s
0.2
0.78
4
1
7m
7p
Pr
OMe
3
17
0.51
8.7
NH2
NH2
a Refer to Table 1.
b Refer to Table 1.
59
47
N
a Refer to Table 1.
b Refer to Table 1.
replacement of the indole ring system with the indazole
ring system was acceptable.
3.1.1. Indazole ring substituents. The 6-fluoro derivative
7b was found to be as potent as 7a (Ki = 43 vs 32 nM).
The 6-methoxy derivative 7e was more potent
(Ki = 16 nM) than the 5-fluoro derivative 7a and the 6-
fluoro derivative 7b. However, the introduction of the
chloro group at the 7-position of the compound 7e led
to a loss of binding affinity for the 5-HT2C receptors
(Ki = 140 nM). The dihalogenated compounds 7c, 7d
The replacement of the Ro60-0175 indole ring (1) with
the indazole ring was examined first. As shown in Table
1, the binding of the indazole derivative 7a to the 5-
HT2C and 5-HT2A receptors (Ki = 43 and 89 nM, respec-
tively) was almost equipotent to that of 1 (Ki = 26 and
39 nM, respectively). This result indicated that the

1970
I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
Table 4. Affinities of compounds 7h–7j, 7n, 7o, and 7q for 5-HT2C and
5-HT2A receptors
group (7i) resulted in a slight loss of 5-HT2C affinity
(Ki = 0.30 and 0.89 nM, respectively), and the isopropyl
group (7j) caused a significant drop (Ki = 20 nM). Com-
pared to the non-substituted derivative 7g, the ethyl
derivative 7i showed a slight loss of 5-HT2C binding
affinity (Ki = 0.89 vs 0.20 nM) and a significant drop in
5-HT2A affinity (Ki = 13 vs 0.78 nM). As a result, this
compound 7i showed high 2A/2C selectivity (15-fold).
Thus, out of the substituents introduced at the 7-posi-
tion, the ethyl group was the best. Next, substituents
were introduced at the 3-position while the 7-ethyl
group remained. Introduction of a methyl (7n) or ethyl
group (7o) at the 3-position of the compound 7i resulted
in a reduction of the 5-HT2C binding affinity (Ki = 5.0
and 2.7 nM, respectively). As was the case with com-
pound 7p, the introduction of the methoxy group (7q)
was expected to decrease the affinity for 5-HT2A recep-
tors and improve the 2A/2C selectivity. However, the
introduction of the methoxy group (7q) led to a substan-
tial decrease in 5-HT2C receptor affinity, which resulted
in a decrease in 2A/2C selectivity (Ki = 12 nM, 2A/
2C = 3-fold).
R1
N
N
O
R2
NH2
Compound R1
R2
Kia (nM)
Selectivityb
5-HT2C 5-HT2A 5-HT2A/5-HT2C
7g
7h
7i
H
H
0.20
0.78
2.1
13
4
7
H
Me 0.30
Et 0.89
iPr 20
H
15
4
7j
H
87
46
7n
7o
7q
Me
Et
Et
Et
5.0
2.7
12
9
51
38
19
3
OMe Et
a Refer to Table 1.
b Refer to Table 1.
were examined next. Although the 5, 6-dichloro deriva-
tive 7c had a higher affinity for the 5-HT2C receptors
(Ki = 7.5 nM) than the fluoro derivatives 7a, 7b, this
compound 7c had poor 2A/2C selectivity (1-fold).
Among the compounds evaluated, the 6,7-dicholoro
derivative 7d had the highest affinity for the 5-HT2C
receptors (Ki = 4.0 nM).
In view of its affinity for 5-HT2C receptors and selectiv-
ity for 5-HT2A receptors, the ethyl derivative 7i was con-
sidered to be the most promising compound of those
examined. Therefore compound 7i was subjected to fur-
ther evaluation.
The 6,7-dichloro derivative 7d showed high binding
affinity (Ki = 4.0 nM), which indicated that the introduc-
tion of substituents at the 6- and 7-positions was toler-
ated. Therefore, fused-heteroaromatics were put in
place at the 6- and 7-positions (results shown in Table
2). The affinity of the thiophene-fused analogue 7r
(Ki = 1.4 nM) for the 5-HT2C receptors was greater than
that of the 6,7-dichloroindazole derivative 7d. The fur-
an-fused analogue 7g was identified as the most potent
of the fused analogues, with a Ki value of 0.20 nM at
5-HT2C receptors; however, its selectivity for 5-HT2A
receptors was poor (4-fold). The oxazole-fused analogue
7s had a significantly lower affinity (Ki = 59 nM) for
5-HT2C receptors compared to those of the thiophene-
fused 7r and furan-fused analogue 7g. The
1H-furo[2,3-g]indazole derivative 7g was considered to
be the preferable template because of its affinity for
5-HT2C receptors; thus optimization of the substituents
on this ring was chosen for further improvement of the
selectivity for 5-HT2A receptors.
3.2. In vitro agonist activity
The functional activities of YM348 (7i) and known 5-
HT2C agonists (5-HT, mCPP, and Ro60-0175) of human
5-HT2C, 5-HT2A, and 5-HT2B receptors were determined
by measuring the myo-[3H] inositol turnover in CHO or
HEK 293-EBNA cells. The results are summarized in
Table 5.
The non-selective 5-HT2C receptor agonist, mCPP, had
a potency for 5-HT2C receptors (EC50 = 120 nM) that
was 6-fold lower than that of 5-HT. Its efficacy for 5-
HT2C receptors was also relatively weak (Emax = 63%).
The potency of mCPP for 5-HT2A and 5-HT2B receptors
was also relatively weak (EC50 = 150 and 93 nM, respec-
tively). Their efficacy was also low (Emax = 18% and
21%, respectively). The potency of Ro60-0175 (1) for
5-HT2C receptors was 2-fold lower (EC50 = 52 nM) than
that of 5-HT, but it did have full agonist activity
(Emax = 88%). For 5-HT2A receptors, the potency of
Ro60-0175 (1) was 6-fold lower (EC50 = 400 nM) than
that of 5-HT, but it did show full efficacy (Emax = 91%).
For 5-HT2B receptors, the potency of Ro60-0175 (1) was
2-fold higher (EC50 = 2.4 nM) than that of 5-HT, and it
showed full efficacy (Emax = 130%). Meanwhile, YM348
(7i) exhibited high 5-HT2C potency (EC50 = 1.0 nM),
and its Emax value for 5-HT2C receptors was 76%. For
5-HT2A receptors, YM348 (7i) showed a similar potency
(EC50 = 93 nM) and efficacy (Emax = 97%) to 5-HT. For
5-HT2B receptors, YM348 (7i) showed a similar potency
(EC50 = 3.2 nM) and efficacy (Emax = 110%) to 5-HT.
When YM348 (7i) was compared with Ro60-0175 (1),
it was about 50-fold more potent for 5-HT2C receptors
(1.0 vs 52 nM) and had excellent functional selectivity
The data in Table 3 show the binding affinities for the 3-
substituted furoindazole analogues. Compounds with
methyl (7k), ethyl (7l), or propyl (7m) substitutions at
the 3-position showed decreased affinities for 5-HT2C
receptors (Ki = 13, 2.5, and 25 nM, respectively) com-
pared
to the non-substituted derivative
7g
(Ki = 0.20 nM). In contrast, the 3-methoxy derivative
7p had high 5-HT2C affinity (Ki = 0.51 nM) with a 10-
fold decrease in affinity for 5-HT2A receptors, which re-
sulted in high 2A/2C selectivity (17-fold).
The substituents at the 7-position were investigated next
(Table 4). The introduction of a methyl (7h) or ethyl

I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
1971
Table 5. Functional activities of 7i and known 5-HT2 agonists for the cloned human 5-HT2C, 5-HT2A, and 5-HT2B receptors
Compound
5-HT2C
EC50 (nM)
5-HT2A
EC50 (nM)
5-HT2B
EC50 (nM)
Selectivity
2A/2C 2B/2C
Emax (%)
Emax (%)
Emax (%)
5-HT
mCPP
24
100
63
70
150
400
93
100
18
5.8
93
97
21
2.9
1.3
7.7
93
0.24
0.78
0.05
3.2
120
52
Ro60-0175 (1)
YM348 (7i)
88
76
91
97
2.4
3.2
130
110
1.0
Emax indicates intrinsic activity and is expressed as the percentage of maximal stimulation produced by 10 lM 5-HT.
for 5-HT2C over 5-HT2A (93-fold vs 7.7-fold). More-
over, YM348 (7i) showed higher selectivity than Ro60-
0175 (1) for 5-HT2B over 5-HT2C receptors (0.05-fold
vs 3.2-fold).
4. Conclusion
As part of the search for novel 5-HT2C receptor agonists,
a series of indazole derivatives were synthesized and eval-
uated to determine their in vitro and in vivo 5-HT2C ago-
nist activities. YM348 (7i), (S)-2-(7-ethyl-1H-furo[2,3-g]
indazol-1-yl)-1-methylethylamine, showed high affinity
(Ki = 0.89 nM) and potency (EC50 = 1.0 nM) for the 5-
HT2C receptors. Though its functional selectivity over
the 5-HT2B receptors was not enough (3.2-fold), it had
high functional selectivity over the 5-HT2A receptors
(93-fold). YM348 (7i) showed excellent oral agonistic
activity in the induction of penile erection in rat. Further
refined analogs with high 5-HT2B selectivity have poten-
tial for use in therapy for CNS-related diseases such as
obesity, obsessive compulsive disorder, and sexual
dysfunction.
3.3. In vivo activity
The compounds mentioned above were tested for effi-
cacy in the induction of penile erection in rats. This is
a symptom of the serotonin syndrome, which is a reflec-
tion of 5-HT2C receptor activation in rodents.17 The re-
sults are presented with MED values [minimum effective
dose; that is, the lowest dose that significantly (p < 0.05
as compared with vehicle) affected penile erections] in
Table 6.
First, the in vivo profile of the non-selective 5-HT2C
receptor agonist, mCPP, which has been shown to in-
duce penile erection in rats,18 was evaluated. Indeed,
subcutaneous (sc) and oral (po) administration of mCPP
did induce penile erections. The MED values for sc and
po administration were 0.1 and 3 mg/kg, respectively. sc
administration of Ro60-0175 (1) induced penile erec-
tions at an activity level 3-fold lower than that of mCPP
(MED = 0.3 vs 0.1 mg/kg sc). Compound 7p, which had
a high affinity for 5-HT2C receptors and high 2A/2C
selectivity, induced penile erections via sc administration
(MED = 0.1 mg/kg sc), but not via po administration.
This was probably due to the metabolic weakness of
the methoxy group. On the other hand, YM348 (7i)
showed high 5-HT2C potency and induced penile erec-
tions when administered via both sc and po
(MED = 0.03 and 0.3 mg/kg, respectively). These effects
were completely inhibited by the selective 5-HT2C recep-
tor antagonist, SB242084,19 which indicates that 5-HT2C
activation was the mechanism by which YM348 (7i) in-
duced penile erection.
5. Experimental
5.1. Chemistry
Melting points were determined with a Yanaco MP-
500D or a Buchi B-545 melting point apparatus and
¨
are uncorrected. 1H NMR spectra were recorded on
a JEOL JNM-LA300 or a JNM-EX400 spectrometer
and the chemical shifts are expressed in d (ppm) val-
ues with tetramethylsilane as an internal standard (in
NMR description, s = singlet, br s = broad singlet,
d = doublet, t = triplet, q = quartet, dd = doublet of
doublets, m = multiplet). Mass spectra were recorded
on a Hitachi M-80 or a JEOL JMS-LX2000 spectrom-
eter. Elemental analyses were performed with a Yana-
co MT-5 microanalyzer (C, H, N) and a Yokogawa
IC-7000S ion chromatographic analyzer (halogens),
and the results were within 0.4% of theoretical
values.
Table 6. Effects of representative indazole derivatives and known 5-
HT2C agonists on penile erections in rats after sc or po administration
5.1.1. 5-Fluoro-1H-indazole (3a). To a mixture of 9a
(6.3 g, 50 mmol), H2O (13 mL), and concd HCl
(13 mL) was added a solution of NaNO2 (3.5 g,
50 mmol) in H2O (10 mL) at À10 ꢁC, and the resulting
mixture was stirred for 0.5 h at 0 ꢁC. The insoluble
material was removed by filtration, and to the filtrate
was added a solution of NaBF4 (7.7 g, 70 mmol) in
H2O (20 mL). The resulting precipitate was collected
by filtration and washed with 5% NaBF4 aq, cold
MeOH, and Et2O, after which it was air-dried. This pro-
cess yielded 7.86 g of 4-fluoro-2-methylbenzenediazoni-
um tetrafluoroborate as a slightly violet solid that was
used in the next step without further purification.
Compound
MEDa
sc (mg/kg)
po (mg/kg)
mCPP
0.1
0.3
0.1
0.03
3
Ro60-0175 (1)
7p
YM348 (7i)
NTb
NEc
0.3
a The lowest dose that significantly (p < 0.05 as compared with vehicle)
affected penile erections was considered to be the minimum effective
dose (MED).
b Not tested.
c Not effective.

1972
I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
A mixture of 4-fluoro-2-methylbenzenediazonium tetra-
fluoroborate (7.86 g, 35 mmol), AcOK (6.9 g, 70 mmol),
18-crown-6 (0.48 g, 1.8 mmol), and CHCl3 (500 mL) was
stirred at room temperature for 3 h. The insoluble mate-
rial was removed by filtration, after which the filtrate
was washed with H2O and dried over MgSO4. After re-
moval of the solvent, the residue was purified by column
chromatography on silica gel (AcOEt/toluene = 1:8 to
1:4) to yield 3a (1.36 g, 20%) as a yellow solid. 1H
NMR (CDCl3) d 7.21–7.27 (1H, m), 7.53–7.54 (1H,
m), 7.55–7.57 (1H, m), 8.06 (1H, s); EI-MS m/z 136
[M+].
MeOH = 30:1) to yield 3g (3.63 g, 40%) as a yellow so-
lid.1H NMR (DMSO-d6) d 7.16 (1H, dd, J = 0.7,
2.2 Hz), 7.41 (1H, d, J = 8.8 Hz), 7.66 (1H, d, J = 8.8
Hz), 8.06 (1H, d, J = 2.2 Hz), 8.14 (1H, d, J = 1.5 Hz),
13.39 (1H, br s); FAB-MS m/z 159 [(M+H)+].
5.1.8. 7-Methyl-1H-furo[2,3-g]indazole (3h). Compound
3h was prepared from 19b using a procedure similar to
that described for 3g, in 33% yield as a pale yellow so-
lid.1H NMR (DMSO-d6) d 2.51 (3H, s), 6.78 (1H, s),
7.31 (1H, d, J = 8.7 Hz), 7.55 (1H, d, J = 8.7 Hz), 8.09
(1H, d, J = 1.5 Hz), 13.29 (1H, br s); FAB-MS m/z 173
[(M+H)+].
5.1.2. 6-Fluoro-1H-indazole (3b). Compound 3b was pre-
pared from 9b using a procedure similar to that de-
scribed for 3a, in 19% yield as a pale yellow solid. H
NMR (DMSO-d6) d 6.95–7.04 (1H, m), 7.28–7.35 (1H,
m), 7.80 (1H, dd, J = 5.1, 8.7 Hz), 8.09 (1H, s), 13.12
(1H, br s); EI-MS m/z 136 [M+].
5.1.9. 7-Ethyl-1H-furo[2,3-g]indazole (3i). To a solution
of 19c (500 mg, 2.66 mmol) in ethylene glycol (5 mL)
were added diethyl fumarate (0.44 mL, 2.66 mmol) and
5% Pd on carbon, after which the mixture was heated
at reflux for 5 h. After cooling, the mixture was diluted
with MeOH (50 mL). The catalyst was removed by fil-
tration. The filtrate was concentrated in vacuo, after
which brine was added to the residue. The resulting
aqueous solution was extracted with AcOEt/toluene
(1:3), the organic layer was dried over MgSO4, and con-
centrated. The residue was purified by column chroma-
tography on silica gel (AcOEt/hexane = 1:5) to yield 3i
1
5.1.3. 5,6-Dichloro-1H-indazole (3c). Compound 3c was
prepared from 9c using a procedure similar to that de-
scribed for 3a, in 49% yield as a pale yellow solid.1H
NMR (CDCl3) d 7.86 (1H, s), 8.10–8.11 (2H, m),
13.35 (1H, br s); EI-MS m/z 186 [M+].
1
5.1.4. 6,7-Dichloro-1H-indazole (3d). Compound 3d was
prepared from 9d using a procedure similar to that de-
scribed for 3a, in 45% yield as a pale yellow solid. H
(391 mg, 79%) as a white solid. H NMR (CDCl3) d
1.37 (3H, t, J = 7.5 Hz), 2.87 (2H, dq, J = 0.9, 7.5 Hz),
6.60 (1H, d, J = 0.9 Hz), 7.32 (1H, dd, J = 0.8, 8.7 Hz),
7.54 (1H, d, J = 8.7 Hz), 8.15 (1H, s), 10.85 (1H, br s);
FAB-MS m/z 187 [(M+H)+].
1
NMR (DMSO-d6) d 7.32 (1H, d, J = 8.8 Hz), 7.78
(1H, d, J = 8.8 Hz), 8.22 (1H, d, J = 1.2 Hz), 13.75
(1H, br s); EI-MS m/z 186 [M+].
5.1.10. 7-Isopropyl-1H-furo[2,3-g]indazole (3j). To a
solution of 20 (1.70 g, 8.41 mmol) in THF (50 mL) was
added MeMgCl (8.40 mL, 3 M in THF) at 0 ꢁC, and
then the mixture was stirred for 0.5 h at room tempera-
ture. The resulting mixture was poured into saturated
aqueous NH4Cl and extracted with AcOEt. The com-
bined extracts were washed with H2O and brine, and
then dried over MgSO4. After removal of the solvent,
the residue was purified by column chromatography
on silica gel (CHCl3/MeOH = 100:1 to 50:1) to yield yel-
low amorphous solid (2.36 g).
5.1.5. 6-Methoxy-1H-indazole (3e). To a mixture of 15
(1.90 g, 14.2 mmol), K2CO3 (2.35 g, 17.0 mmol), and
DMF (20 mL) was added MeI (1.06 mL, 17.0 mmol)
at 0 ꢁC and the resulting mixture was stirred at room
temperature for 15 h. To the mixture was added H2O,
which was then extracted with AcOEt and dried over
MgSO4. After removal of the solvent, the residue was
purified by column chromatography on silica gel
(AcOEt/hexane = 1:2) to yield 3e (1.02 g, 48%) as a
1
white solid. H NMR (DMSO-d6) d 3.81 (3H, s), 6.71–
6.76 (1H, m), 6.88–6.92 (1H, m), 7.60 (1H, d,
J = 8.7 Hz), 7.92 (1H, s), 12.80 (1H, br s); FAB-MS
m/z 147 [(MÀH)+].
To this product (2.36 g) was added benzene (20 mL) and
I2 (10 mg), and the resulting mixture was heated at re-
flux for 2 h. The mixture was cooled to room tempera-
ture and concentrated in vacuo. The residue was
purified by column chromatography on silica gel (tolu-
ene/AcOEt = 10:1) to yield 3j (539 mg, 32%) as a white
5.1.6. 7-Chloro-6-methoxy-1H-indazole (3f). Compound
3f was prepared from 16 using a procedure similar to
that described for 3e, in 56% yield as a white solid. H
1
1
NMR (DMSO-d6) d 3.94 (3H, s), 7.09 (1H, d,
J = 9.0 Hz), 7.71 (1H, d, J = 9.0 Hz), 8.08 (1H, s),
13.24 (1H, br s); FAB-MS m/z 183 [(M+H)+].
solid. H NMR (DMSO-d6) d 1.34 (6H, d, J = 6.8 Hz),
3.08–3.22 (1H, m), 6.74 (1H, s), 7.33 (1H, d,
J = 8.4 Hz), 7.56 (1H, d, J = 8.4 Hz), 8.09 (1H, d,
J = 1.6 Hz), 13.27 (1H, br s); FAB-MS m/z 201
[(M+H)+].
5.1.7. 1H-Furo[2,3-g]indazole (3g). To a mixture of 19a
(8.50 g, 53 mmol) and dioxane (150 mL) was added
DDQ (13.4 g, 58.5 mmol), and the resulting mixture
was heated at reflux for 2 h. After cooling, the insoluble
material was removed by filtration. To the filtrate was
added saturated aqueous NaHCO3, which was then ex-
tracted with CHCl3 and dried over MgSO4. After re-
moval of the solvent, the residue was purified by
column chromatography on silica gel (CHCl3/
5.1.11. 3-Methyl-1H-furo[2,3-g]indazole (3k). Com-
pound 3k was prepared from 21a using a procedure sim-
ilar to that described for 3g, in 44% yield as a slightly
1
yellow solid. H NMR (CDCl3) d 2.63 (3H, s), 6.97–
7.01 (1H, m), 7.35–7.40 (1H, m), 7.54 (1H, d,
J = 8.7 Hz), 7.71 (1H, d, J = 2.1 Hz); FAB-MS m/z 173
[(M+H)+].

I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
1973
5.1.12. 3-Ethyl-1H-furo[2,3-g]indazole (3l). Compound 3l
was prepared from 21b using a procedure similar to that
described for 3g, in 26% yield as a pale purple solid. H
NMR (CDCl3) d 1.45 (3H, t, J = 7.5 Hz), 3.06 (2H, q,
J = 7.5 Hz), 6.98 (1H, dd, J = 0.9, 2.4 Hz), 7.36 (1H,
dd, J = 0.9, 8.7 Hz), 7.57 (1H, d, J = 8.7 Hz), 7.70
(1H, d, J = 2.1 Hz); FAB-MS m/z 187 [(M+H)+].
5.1.17. 7-Ethyl-3-methoxy-1H-furo[2,3-g]indazole (3q).
Compound 3q was prepared from 23b using a procedure
similar to that described for 3p, in 30% yield as a yellow
1
1
solid. H NMR (DMSO-d6) d 1.30 (3H, d, J = 7.5 Hz),
2.85 (2H, q, J = 7.5 Hz), 4.00 (3H, s), 6.70 (1H, d,
J = 0.9 Hz), 7.22 (1H, dd, J = 0.9, 8.8 Hz), 7.36 (1H, d,
J = 8.8 Hz), 12.16 (1H, br s); FAB-MS m/z 217
[(M+H)+].
5.1.13. 3-Propyl-1H-furo[2,3-g]indazole (3m). Com-
pound 3m was prepared from 21c using a procedure sim-
ilar to that described for 3g, in 13% yield as a purple
solid. 1H NMR (CDCl3) d 1.03 (3H, t, J = 7.5 Hz),
1.82–1.95 (2H, m), 3.00 (2H, t, J = 7.5 Hz), 6.98 (1H,
dd, J = 1.2, 2.4 Hz), 7.36 (1H, dd, J = 0.6, 9.0 Hz),
7.57 (1H, d, J = 9.0 Hz), 7.70 (1H, d, J = 2.4 Hz);
FAB-MS m/z 201 [(M+H)+].
5.1.18. 1H-Thieno[2,3-g]indazole (3r). Compound 3r was
prepared from 25 using a procedure similar to that de-
scribed for 3g, in 78% yield as a pale yellow solid. H
NMR (DMSO-d6) d 7.66–7.73 (2H, m), 7.83 (1H, d,
J = 5.6 Hz), 7.87 (1H, d, J = 5.6 Hz), 8.16 (1H, s),
13.62 (1H, br s); EI-MS m/z 174 [M+].
1
5.1.19. 1H-[1,3]Oxazolo[5,4-g]indazole (3s). A mixture of
27 (360 mg, 2.41 mmol) and HC(OEt)3 (10 mL) was
heated at reflux for 2 h. After cooling, the solvent was
removed and the residue was purified by column chro-
matography on silica gel (CHCl3/MeOH = 50:1) to yield
3s (310 mg, 81%) as a pale yellow solid. 1H NMR
(DMSO-d6) d 7.55 (1H, d, J = 8.7 Hz), 7.82 (1H, d,
J = 8.7 Hz), 8.23 (1H, s), 8.83 (1H, s), 13.85 (1H, br s);
FAB-MS m/z 160 [(M+H)+].
5.1.14. 7-Ethyl-3-methyl-1H-furo[2,3-g]indazole (3n).
Compound 3n was prepared from 21d using a procedure
similar to that described for 3i, in 34% yield as a yellow
solid. 1H NMR (CDCl3) d 1.37 (3H, t, J = 7.5 Hz), 2.68
(3H, s), 2.87 (2H, q, J = 7.5 Hz), 6.69 (1H, s), 7.33 (1H,
d, J = 9.0 Hz), 7.46 (1H, d, J = 9.0 Hz); FAB-MS m/z
201 [(M+H)+].
5.1.15. 3,7-Diethyl-1H-furo[2,3-g]indazole (3o). Com-
pound 3o was prepared from 21e using a procedure sim-
ilar to that described for 3g, in 33% yield as a yellow
solid. 1H NMR (CDCl3) d 1.37 (3H, t, J = 7.5 Hz),
1.47 (3H, t, J = 7.5 Hz), 2.87 (2H, dq, J = 0.9, 7.5 Hz),
3.11 (2H, q, J = 7.5 Hz), 6.70 (1H, d, J = 0.9 Hz), 7.33
(1H, dd, J = 0.9, 9.0 Hz), 7.50 (1H, d, J = 9.0 Hz);
FAB-MS m/z 215 [(M+H)+].
5.1.20. (2R)-1-(5-Fluoro-1H-indazol-1-yl)propan-2-ol (4a).
To a mixture of 60% NaH (0.48 g, 12 mmol) and DMF
(15 mL) were added 3a (1.5 g, 11 mmol) at room tem-
perature, and the mixture was stirred for 0.5 h. To the
reaction mixture was added (R)-propylene oxide
(0.89 mL, 13 mmol) at 0 ꢁC, and it was stirred at room
temperature for 17 h. The mixture was poured into
water and extracted with AcOEt. The extracts were
dried over MgSO4 and evaporated. The residue was
purified by column chromatography on silica gel
(AcOEt/toluene = 1:4 to 1:2) to yield 4a (0.87 g, 41%)
as a yellow solid. 1H NMR (CDCl3) d 1.28 (3H, d,
J = 6.4 Hz), 3.18 (1H, d, J = 4.0 Hz), 4.20–4.25 (1H,
m), 4.29–4.39 (2H, m), 7.15–7.20 (1H, m), 7.33–7.40
(2H, m), 7.97 (1H, d, J = 0.8 Hz); FAB-MS m/z 195
[(M+H)+].
5.1.16. 3-Methoxy-1H-furo[2,3-g]indazole(3p). To a mix-
ture of 40% aqueous NaOH (15 mL) and Et2O
(30 mL) was added portionwise N-methyl-N-nitrosou-
rea (4.21 g, 10.2 mmol) at 0 ꢁC. After stirring for
0.5 h at this temperature, the ether layer was decanted,
and added to a solution of 23a (1.50 g, 8.51 mmol) in
dioxane (10 mL) and MeOH (20 mL) at 0 ꢁC. After
stirring at room temperature for 15 min, AcOH was
added until the solution became colorless, after which
it was evaporated in vacuo. The residue was diluted
with CHCl3, washed with saturated aqueous NaHCO3,
dried over MgSO4, and evaporated. The residue was
purified by column chromatography on silica gel
(CHCl3/MeOH/satd NH3 aq = 30:1:0.1) to yield 3-
methoxy-4, 5-dihydro-1H-furo[2,3-g]indazole (0.80 g,
49%).
5.1.21. (2R)-1-(6-Fluoro-1H-indazol-1-yl)propan-2-ol (4b).
Compound 4b was prepared from 3b using a procedure
similar to that described for 4a, in 40% yield. H NMR
1
(CDCl3) d 1.28 (3H, d, J = 6.4 Hz), 3.18 (1H, d,
J = 4.0 Hz), 4.15–4.21 (1H, m), 4.30–4.38 (2H, m),
6.92–6.97 (1H, m), 7.07–7.10 (1H, m), 7.68 (1H, dd,
J = 5.2, 8.8 Hz), 8.00 (1H, s); FAB-MS m/z 195
[(M+H)+].
To this product were added dioxane (50 mL) and DDQ
(1.41 g, 6.23 mmol), and the resulting mixture was stir-
red at 60 ꢁC for 0.5 h. After cooling, the insoluble mate-
rial was removed by filtration. To the filtrate was added
saturated aqueous NaHCO3, which was then extracted
with CHCl3 and dried over MgSO4. After removal of
the solvent, the residue was purified by column chroma-
tography on silica gel (AcOEt/hexane = 1:4) to yield 3p
(0.66 g, 85%) as a yellow solid.1H NMR (DMSO-d6) d
4.01 (3H, s), 7.08–7.10 (1H, m), 7.29 (1H, dd, J = 1.2,
8.8 Hz), 7.45 (1H, d, J = 8.8 Hz), 8.03 (1H, d,
J = 2.0 Hz); FAB-MS m/z 189 [(M+H)+].
5.1.22. (2R)-1-(5,6-Dichloro-1H-indazol-1-yl)propan-2-ol
(4c). Compound 4c was prepared from 3c using a proce-
dure similar to that described for 4a, in 43% yield.1H
NMR (DMSO-d6) d 1.08 (3H, d, J = 5.9 Hz), 4.00–
4.08 (1H, m), 4.30–4.32 (2H, m), 4.85 (1H, d,
J = 4.9 Hz), 8.04–8.08 (3H, m); EI-MS m/z 244 [M+].
5.1.23. (2R)-1-(6,7-Dichloro-1H-indazol-1-yl)propan-2-ol
(4d). Compound 4d was prepared from 3d using a pro-
cedure similar to that described for 4a, in 24% yield.
1H NMR (DMSO-d6) d 1.04 (3H, d, J = 5.4 Hz),

1974
I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
4.01–4.12 (1H, m), 4.50–4.57 (1H, m), 4.69–4.76 (1H,
m), 4.88 (1H, d, J = 5.2 Hz), 7.34 (1H, d,
J = 8.4 Hz), 7.78 (1H, d, J = 8.4 Hz), 8.20 (1H, m);
FAB-MS m/z 245 [M+].
28% yield. 1H NMR (CDCl3)
d 1.01 (3H, t,
J = 7.5 Hz), 1.30 (3H, d, J = 6.0 Hz), 1.79–1.91 (2H,
m), 2.96 (2H, t, J = 7.5 Hz), 4.34–4.42 (2H, m), 4.48–
4.58 (1H, m), 7.07 (1H, d, J = 2.1 Hz), 7.33 (1H, d,
J = 9.0 Hz), 7.54 (1H, d, J = 9.0 Hz), 7.72 (1H, d,
J = 2.1 Hz); FAB-MS m/z 259 [(M+H)+].
5.1.24. (2R)-1-(6-Methoxy-1H-indazol-1-yl)propan-2-ol
(4e). Compound 4e was prepared from 3e using a proce-
dure similar to that described for 4a, in 45% yield. H
1
5.1.31. (2R)-1-(3-Methoxy-1H-furo[2,3-g]indazol-1-yl) ro-
pan-2-ol (4p). Compound 4p was prepared from 3p using
a procedure similar to that described for 4a, in 44%
yield. 1H NMR (CDCl3) d 1.29 (3H, d, J = 6.3 Hz),
3.57 (1H, s), 4.09 (3H, s), 4.19–4.44 (3H, m), 7.01 (1H,
dd, J = 0.9, 2.1 Hz), 7.27 (1H, dd, J = 0.9, 8.7 Hz),
7.51 (1H, d, J = 8.7 Hz), 7.70 (1H, d, J = 2.1 Hz);
FAB-MS m/z 247 [(M+H)+].
NMR (DMSO-d6) d 1.06 (3H, d, J = 6.0 Hz), 3.83
(3H, s), 4.05–4.16 (1H, m), 4.10–4.30 (2H, m), 4.85
(1H, d, J = 5.2 Hz), 6.73 (1H, dd, J = 2.0, 8.8 Hz),
7.08–7.11 (1H, m), 7.58 (1H, d, J = 8.8 Hz), 8.22 (1H,
s); FAB-MS m/z 207 [(M+H)+].
5.1.25. (2R)-1-(7-Chloro-6-methoxy-1H-indazol-1-yl)pro-
pan-2-ol (4f). Compound 4f was prepared from 3f using
a procedure similar to that described for 4a, in 57%
5.1.32. (2R)-1-(1H-Thieno[2,3-g]indazol-1-yl)propan-2-ol
(4r). Compound 4r was prepared from 3r using a proce-
dure similar to that described for 4a, in 15% yield. H
1
yield. H NMR (DMSO-d6) d 1.00 (3H, d, J = 6.0 Hz),
1
3.94 (3H, s), 4.04–4.09 (1H, m), 4.46–4.50 (1H, m),
4.65–4.70 (1H, m), 4.84 (1H, d, J = 5.5 Hz), 7.10 (1H,
d, J = 9.0 Hz), 7.71 (1H, d, J = 9.0 Hz), 8.06 (1H, s);
FAB-MS m/z 241 [(M+H)+].
NMR (DMSO-d6) d 1.10 (3H, d, J = 6.4 Hz), 4.03–
4.17 (1H, m), 4.45–4.56 (1H, m), 4.60–4.73 (1H, m),
5.02 (1H, d, J = 5.2 Hz), 7.70–7.80 (2H, m), 7.91 (1H,
d, J = 5.2 Hz), 8.04 (1H, d, J = 5.2 Hz), 8.25 (1H, s);
FAB-MS m/z 233 [(M+H)+].
5.1.26. (2R)-1-(1H-Furo[2,3-g]indazol-1-yl)propan-2-ol
(4g). Compound 4g was prepared from 3g using a proce-
dure similar to that described for 4a, in 51% yield. H
1
5.1.33. (2R)-1-(1H-[1,3]Oxazolo[5,4-g]indazol-1-yl)pro-
pan-2-ol (4s). Compound 4s was prepared from 3s using
a procedure similar to that described for 4a, in 28%
NMR (DMSO-d6) d 1.09 (3H, d, J = 6.3 Hz), 3.99–
4.18 (2H, m), 4.38–4.58 (2H, m), 4.50 (1H, d,
J = 5.1 Hz), 7.39–7.44 (1H, m), 7.45–7.48 (1H, m), 7.63
(1H, d, J = 8.7 Hz), 8.08–8.12 (2H, m); FAB-MS m/z
217 [(M+H)+].
1
yield. H NMR (DMSO-d6) d 1.05 (3H, d, J = 8.0 Hz),
4.20–4.33 (1H, m), 4.52–4.61 (1H, m), 4.63–4.74 (1H,
m), 4.92 (1H, d, J = 8.1 Hz), 7.56 (1H, d, J = 9.0 Hz),
7.80 (1H, d, J = 9.0 Hz), 8.21 (1H, s), 8.87 (1H, s);
FAB-MS m/z 218 [(M+H)+].
5.1.27. (2R)-1-(7-Ethyl-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-ol (4i). Compound 4i was prepared from 3i using
a procedure similar to that described for 4a, in 49%
yield. 1H NMR (CDCl3) d 1.32 (3H, d, J = 6.0 Hz),
1.39 (3H, t, J = 7.8 Hz), 2.88 (2H, q, J = 7.8 Hz), 4.40–
4.60 (3H, m), 6.68 (1H, s), 7.30 (1H, d, J = 8.7 Hz),
7.51 (1H, d, J = 8.7 Hz), 8.04 (1H, s); FAB-MS m/z
245 [(M+H)+].
5.1.34. 1-[(2S)-2-Azidopropyl]-5-fluoro-1H-indazole (6a).
To a solution of 4a (0.80 g, 4.1 mmol) in CH2Cl2
(15 mL) was added triethylamine (1.7 mL, 12.3 mmol)
and MsCl (0.47 mL, 6.2 mmol) at room temperature,
and it was stirred at this temperature for 2 h. The mix-
ture was poured into water and extracted with CHCl3.
The combined extracts were washed with H2O and
brine, and then dried over MgSO4. The solvent was
evaporated in vacuo to give the crude 5a.
5.1.28. (2R)-1-(3-methyl-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-ol (4k). Compound 4k was prepared from 3k
using a procedure similar to that described for 4a, in
49% yield. 1H NMR (CDCl3)
d
1.08 (3H, d,
The residue was dissolved in DMF (15 mL) without fur-
ther purification. To this solution was added NaN3
(0.78 g, 12 mmol), and the mixture was stirred at 70 ꢁC
for 17 h. After cooling to room temperature, the mixture
was poured into water and extracted with Et2O. The
combined extracts were washed with H2O and brine,
and then dried over MgSO4. The solvent was evaporated
J = 5.0 Hz), 3.32 (3H, s), 4.07–4.10 (3H, m), 4.30–4.36
(1H, m), 4.40–4.46 (1H, m), 4.91 (1H, d, J = 5.0 Hz),
7.37 (1H, d, J = 10 Hz), 7.42 (1H, s), 7.56 (1H, d,
J = 10 Hz), 8.07 (1H, s); FAB-MS m/z 226 [(M+H)+].
5.1.29. (2R)-1-(3-Ethyl-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-ol (4l). Compound 4l was prepared from 3l using
a procedure similar to that described for 4a, in 30%
yield. 1H NMR (CDCl3) d 1.29 (3H, d, J = 6.3 Hz),
1.41 (3H, t, J = 7.8 Hz), 3.00 (2H, q, J = 7.8 Hz), 4.32–
4.42 (2H, m), 4.47-4.55 (1H, m), 7.06 (1H, dd, J = 0.9,
2.4 Hz), 7.33 (1H, dd, J = 0.9, 9.0 Hz), 7.53 (1H, d,
J = 9.0 Hz), 7.72 (1H, d, J = 2.4 Hz); FAB-MS m/z 245
[(M+H)+].
1
in vacuo to yield 6a (0.83 g, 92%) as a yellow oil: H
NMR (CDCl3) d 1.33 (3H, d, J = 6.8 Hz), 4.07–4.15
(1H, m), 4.29–4.40 (2H, m), 7.17–7.22 (1H, m), 7.35
(1H, dd, J = 2.0, 8.6 Hz), 7.41 (1H, dd, J = 4.0,
9.0 Hz), 8.00 (1H, d, J = 0.8 Hz); FAB-MS m/z 220
[(M+H)+].
5.1.35. 1-[(2S)-2-Azidopropyl]-6-fluoro-1H-indazole (6b).
Compound 6b was prepared from 4b using a procedure
similar to that described for 6a, in 97% yield. H NMR
1
5.1.30. (2R)-1-(3-Propyl-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-ol (4m). Compound 4m was prepared from 3m
using a procedure similar to that described for 4a, in
(CDCl3) d 1.33 (3H, d, J = 7.2 Hz), 4.08–4.16 (1H, m),
4.23–4.36 (2H, m), 6.92–6.97 (1H, m), 7.09–7.12 (1H,

I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
1975
m), 7.67 (1H, dd, J = 5.6, 8.8 Hz), 8.01 (1H, d,
J = 1.2 Hz); EI-MS m/z 219 [M+].
J = 8.7 Hz), 7.47 (1H, d, J = 8.7 Hz), 8.03 (1H, s);
FAB-MS m/z 270 [(M+H)+].
5.1.36. 1-[(2S)-2-Azidopropyl]-6-methoxy-1H-indazole (6e).
Compound 6e was prepared from 4e using a procedure
similar to that described for 6a, in 80% yield.1H NMR
(DMSO-d6) d 1.24 (3H, d, J = 6.6 Hz), 3.83 (3H, s),
4.06–4.19 (1H, m), 4.42–4.46 (2H, m), 6.77 (1H, dd,
J = 2.1, 9.0 Hz), 7.18–7.21 (1H, m), 7.61 (1H, d,
J = 9.0 Hz), 7.98 (1H, s); FAB-MS m/z 232 [(M+H)+].
5.1.40. 1-[(2S)-2-Azidopropyl]-3-methyl-1H-furo[2,3-g]inda-
zole (6k). Compound 6k was prepared from 4k using a
procedure similar to that described for 6a, in 68% yield.
1H NMR (CDCl3) d 1.30 (3H, d, J = 6.3 Hz), 2.58 (3H,
s), 4.07–4.20 (1H, m), 4.43 (1H, d, J = 6.3 Hz), 7.03 (1H,
d, J = 2.1 Hz), 7.32 (1H, d, J = 8.7 Hz), 7.46 (1H, d,
J = 8.7 Hz), 7.69 (1H, d, J = 2.1 Hz); FAB-MS m/z 256
[(M+H)+].
5.1.37. 1-[(2S)-2-Azidopropyl]-7-chloro-6-methoxy-1H-
indazole (6f). Compound 6f was prepared from 4f using
a procedure similar to that described for 6a, in 60%
5.1.41. 1-[(2S)-2-Azidopropyl]-3-ethyl-1H-furo[2,3-g]inda-
zole (6l). Compound 6l was prepared from 4l using a
procedure similar to that described for 6a, in 81% yield.
1H NMR (CDCl3) d 1.33 (3H, d, J = 6.6 Hz), 1.41 (3H,
t, J = 7.5 Hz), 3.02 (2H, q, J = 7.5 Hz), 4.08–4.24 (1H,
m), 4.48 (2H, d, J = 6.6 Hz), 7.07 (1H, dd, J = 0.9,
2.1 Hz), 7.34 (1H, dd, J = 0.9, 8.7 Hz), 7.54 (1H, d,
J = 8.7 Hz), 7.72 (1H, d, J = 2.1 Hz); FAB-MS m/z 270
[(M+H)+].
1
yield. H NMR (DMSO-d6) d 1.23 (3H, d, J = 6.6 Hz),
3.95 (3H, s), 4.03–4.10 (1H, m), 4.73–4.76 (2H, m),
7.14 (1H, d, J = 9.0 Hz), 7.75 (1H, d, J = 9.0 Hz), 8.14
(1H, s); FAB-MS m/z 266 [(M+H)+].
5.1.38. 1-[(2S)-2-Azidopropyl]-7-methyl-1H-furo[2,3-g]inda-
zole (6h). To a mixture of 60% NaH (213 mg,
5.34 mmol) and DMF (10 mL) was added 3h (835 mg,
4.85 mmol) at 0 ꢁC, and it was stirred at this tempera-
ture for 0.5 h. To the reaction mixture was added (R)-
propylene oxide (0.41 mL, 5.82 mmol) at 0 ꢁC, and it
was stirred at room temperature for 70 h. The mixture
was poured into water and extracted with AcOEt. The
combined extracts were dried over MgSO4 and evapo-
rated. The residue was purified by column chromatogra-
phy on silica gel (AcOEt/hexane = 1:3) to yield a
mixture of 3h and 4h (700 mg).
5.1.42. 1-[(2S)-2-Azidopropyl]-3-propyl-1H-furo[2,3-g]inda-
zole (6m). Compound 6m was prepared from 4m using a
procedure similar to that described for 6a, in 81% yield.
1H NMR (CDCl3) d 1.01 (3H, t, J = 7.5 Hz), 1.32 (3H,
d, J = 6.6 Hz), 1.79–1.93 (2H, m), 2.97 (2H, t, J =
7.5 Hz), 4.09–4.20 (2H, m), 4.48 (2H, d, J = 6.6 Hz),
7.07 (1H, dd, J = 0.9, 2.4 Hz), 7.34 (1H, dd, J = 0.9,
8.7 Hz), 7.53 (1H, d, J = 8.7 Hz), 7.72 (1H, d, J =
2.4 Hz); FAB-MS m/z 284 [(M+H)+].
This mixture was dissolved with CHCl3 (25 mL). To the
solution were added triethylamine (1.26 mL, 9.12 mmol)
and MsCl (0.35 mL, 4.56 mmol) at 0 ꢁC, and it was stir-
red at room temperature for 1 h. The mixture was
poured into water and extracted with CHCl3. The com-
bined extracts were washed with H2O and brine, and
then dried over MgSO4. The solvent was evaporated in
vacuo to give the crude 5h which was used in the next
step without further purification.
5.1.43. 1-[(2S)-2-Azidopropyl]-3-methoxy-1H-furo[2,3-
g]indazole (6p). Compound 6p was prepared from 4p
using a procedure similar to that described for 6a, in
88% yield. 1H NMR (CDCl3)
d 1.31 (3H, d,
J = 6.4 Hz), 4.10 (3H, s), 4.11–4.60 (1H, m), 4.28–4.38
(1H, m), 6.99–7.03 (1H, m), 7.26 (1H, dd, J = 1.2,
8.8 Hz), 7.50 (1H, d, J = 8.8 Hz), 7.70 (1H, d,
J = 2.0 Hz); FAB-MS m/z 272 [(M+H)+].
5.1.44. 1-[(2S)-2-Azidopropyl]-1H-thieno[2,3-g]indazole
(6r). Compound 6r was prepared from 4r using a proce-
dure similar to that described for 6a, in 88% yield. H
NMR (DMSO-d6) d 1.33 (3H, d, J = 6.6 Hz), 3.98–
4.08 (1H, m), 4.10–4.24 (1H, m), 4.69–4.88 (2H, m),
7.70–7.78 (2H, m), 7.94 (1H, d, J = 5.4 Hz), 8.06 (1H,
d, J = 5.4 Hz), 8.20 (1H, s); FAB-MS m/z 258 [(M+H)+].
The crude 5h was dissolved in DMF (15 mL). To this
solution was added NaN3 (0.98 g, 15 mmol), and the
mixture was stirred at 80 ꢁC for 15 h. After cooling to
room temperature, the mixture was poured into water
and extracted with Et2O. The combined extracts were
washed with H2O and brine, and then dried over
MgSO4. The solvent was evaporated in vacuo to yield
the crude product, which was purified by column chro-
matography on silica gel (AcOEt/hexane = 1:10) to give
1
5.1.45. 1-[(2S)-2-Azidopropyl]-1H-[1,3]oxazolo[5,4-g]inda-
zole (6s). Compound 6s was prepared from 4s using a
procedure similar to that described for 6a, in 56%
yield.1H NMR (DMSO-d6) d 1.27 (3H, d, J = 8.8 Hz),
4.24–4.32 (1H, m), 4.77–4.83 (2H, m), 7.61 (1H, d,
J = 9.0 Hz), 7.84 (1H, d, J = 9.0 Hz), 8.29 (1H, s), 8.90
(1H, s); EI-MS m/z 242 [M+].
1
6h (510 mg, 41% from 3h) as a colorless oil. H NMR
(DMSO-d6) d 1.30 (3H, d, J = 6.9 Hz), 2.52 (3H, s),
4.05–4.20 (1H, m), 4.50–4.75 (2H, m), 7.15 (1H, s),
7.36 (1H, d, J = 8.7 Hz), 7.57 (1H, d, J = 8.7 Hz), 8.15
(1H, s); FAB-MS m/z 256 [(M+H)+].
5.1.39. 1-[(2S)-2-Azidopropyl]-7-ethyl-1H-furo[2,3-g]inda-
zole (6i). Compound 6i was prepared from 4i using a
procedure similar to that described for 6a, in 76% yield.
1H NMR (CDCl3) d 1.31 (3H, d, J = 6.6 Hz), 1.37 (3H,
t, J = 7.8 Hz), 2.85 (2H, q, J = 7.8 Hz), 4.05–4.22 (1H,
m), 4.43–4.56 (2H, m), 6.64 (1H, s), 7.28 (1H, d,
5.1.46. (2S)-1-(5-Fluoro-1H-indazol-1-yl)propan-2-amine
(7a). To a stirred suspension of LiAlH4 (218 mg,
5.74 mmol) in THF (10 mL) was added a solution of
6a (630 mg, 2.87 mmol) in THF (5 mL) at 0 ꢁC, and it
was stirred at room temperature for 1 h. The excess re-
agent was quenched by the addition of MeOH, followed

1976
I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
by the addition of water (0.22 mL), 15% aqueous NaOH
(0.22 mL), and water (0.66 mL). After stirring for 1 h,
the resulting mixture was filtered through Celite and
concentrated in vacuo to give the crude product, which
was purified by column chromatography on silica gel
(CHCl3/MeOH = 10:1) to yield 7a (393 mg; 72%). This
compound was subsequently converted to its hydrochlo-
J = 6.8 Hz), 3.50–3.61 (1H, m), 4.42–4.59 (2H, m), 6.49
(2H, s), 8.11 (1H, s), 8.16 (1H, s), 8.21 (1H, s); FAB-
MS m/z 244 [(M+H)+]. Anal. Calcd for C10H11N3Cl2Æ-
C4H4O4: C, 46.68; H, 4.20; N, 11.67; Cl, 19.69. Found:
C, 47.12; H, 4.05; N, 11.71; Cl, 18.17.
5.1.49. (2S)-1-(6,7-Dichloro-1H-indazol-1-yl)propan-2-
amine (7d). Compound 7d was prepared from 3d using
a procedure similar to that described for 7c, in 57%
yield. This compound was subsequently converted to
1
ride to yield a white solid (mp 185–186 ꢁC). H NMR
(DMSO-d6) d 1.19 (3H, d, J = 6.4 Hz), 3.63–3.74 (1H,
m), 4.54–4.75 (2H, m), 7.33–7.39 (1H, m), 7.58 (1H,
dd, J = 2.0, 9.2 Hz), 7.86 (1H, dd, J = 4.4, 9.2 Hz),
8.15 (1H, s), 8.36 (3H, br s); FAB-MS m/z 194
[(M+H)+]. Anal. Calcd for C10H12N3FÆHCl: C, 52.29;
H, 5.70; N, 18.29; Cl, 15.44; F, 8.27. Found: C, 52.18;
H, 5.72; N, 18.27; Cl, 15.25; F, 8.41.
its hemifumarate to yield
a
white solid (mp
183–185 ꢁC). 1H NMR (DMSO-d6) d 1.01 (3H, d,
J = 6.4 Hz), 3.50–3.61 (1H, m), 4.58–4.73 (2H, m) 7.37
(1H, d, J = 8.0 Hz), 7.80 (1H, d, J = 8.0 Hz), 8.25 (1H,
s); FAB-MS m/z 244 [(M+H)+]. Anal. Calcd for
C10H11N3Cl2Æ0.5C4H4O4: C, 47.70; H, 4.34; N, 13.91;
Cl, 23.27. Found: C, 47.82; H, 4.15; N, 13.93; Cl, 23.27.
5.1.47. (2S)-1-(6-Fluoro-1H-indazol-1-yl)propan-2-amine
(7b). Compound 7b was prepared from 6b using a proce-
dure similar to that described for 7a, in 65% yield. This
compound was subsequently converted to its hydrochlo-
5.1.50. (2S)-1-(6-Methoxy-1H-indazol-1-yl)propan-2-amine
(7e). Compound 7e was prepared from 6e using a
procedure similar to that described for 7a, in 86% yield.
This compound was subsequently converted to its
fumarate to yield a white solid (mp 138–139 ꢁC). 1H
NMR (DMSO-d6) d 1.12 (3H, d, J = 6.4 Hz), 3.55–
3.66 (1H, m), 3.85 (3H, s), 4.43 (1H, dd, J = 6.8,
14 Hz), 4.55 (1H, dd, J = 6.0, 14 Hz), 6.48 (2H, s),
6.77 (1H, dd, J = 2.0, 8.8 Hz), 7.23–7.25 (1H, m), 7.62
(1H, d, J = 8.8 Hz), 7.99 (1H, s); FAB-MS m/z 206
[(M+H)+]. Anal. Calcd for C11H15N3OÆC4H4O4Æ0.1H2O:
C, 55.76; H, 5.99; N, 13.00. Found: C, 55.76; H, 5.90; N,
12.96.
1
ride to yield a white solid (mp 160–161 ꢁC). H NMR
(DMSO-d6) d 1.21 (3H, d, J = 6.4 Hz), 3.43–3.47 (1H,
m), 4.50–4.70 (2H, m), 7.04–7.09 (1H, m), 7.72 (1H,
dd, J = 2.4, 9.8 Hz), 7.84 (1H, dd, J = 4.8, 9.0 Hz),
8.18 (1H, s), 8.34 (3H, br s); EI-MS m/z 193 [M+]. Anal.
Calcd for C10H12N3FÆHCl: C, 52.29; H, 5.70; N, 18.29;
Cl, 15.44; F, 8.27. Found: C, 52.46; H, 5.68; N, 18.11;
Cl, 15.36; F, 8.47.
5.1.48. (2S)-1-(5,6-Dichloro-1H-indazol-1-yl)propan-2-
amine (7c). To a solution of 4c (468 mg, 1.91 mmol) in
CH2Cl2 (20 mL) were added triethylamine (1.06 mL,
7.64 mmol) and MsCl (438 mg, 3.82 mmol) at 0 ꢁC,
and it was stirred at room temperature for 0.5 h. The
mixture was poured into water and extracted with
AcOEt. The combined extracts were washed with H2O
and brine, and then dried over MgSO4. The solvent
was evaporated in vacuo to give the crude 5c which
was used in the next step without further purification.
5.1.51. (2S)-1-(7-Chloro-6-methoxy-1H-indazol-1-yl)pro-
pan-2-amine (7f). To
a solution of 6f (260 mg,
0.98 mmol) in THF (20 mL) was added PPh3 (308 mg,
1.18 mmol) at room temperature, and it was stirred at
50 ꢁC for 5 h. To the mixture was added H2O
(0.5 mL), and it was stirred at 50 ꢁC for 15 h. The result-
ing mixture was concentrated in vacuo to give the crude
product, which was purified by column chromatography
on silica gel (CHCl3/MeOH/satd NH3 aq = 30:1:0.1) to
yield 7f (222 mg; 95%). This compound was subse-
quently converted to its fumarate to yield a white solid
The crude 5c was dissolved in DMF (10 mL), to which
NaN3 (373 g, 5.73 mmol) was added. This mixture was
then stirred at 80 ꢁC for 8 h. After cooling to room tem-
perature, the mixture was poured into water and ex-
tracted with AcOEt. The combined extracts were
washed with H2O and brine, and then dried over
MgSO4. Removal of the solvent gave the crude 6c which
was used in the next step without further purification.
1
(mp 166–168 ꢁC). H NMR (DMSO-d6) d 1.04 (3H, d,
J = 6.4 Hz), 3.51–3.61 (1H, m), 3.95 (3H, s), 4.68–4.78
(2H, m), 6.47 (2H, s), 7.14 (1H, d, J = 9.2 Hz), 7.75
(1H, d, J = 9.2 Hz), 8.13 (1H, s); FAB-MS m/z 240
[(M+H)+]. Anal. Calcd for C11H14N3OClÆC4H4O4Æ0.4-
H2O: C, 49.63; H, 5.22; N, 11.58; Cl, 9.77. Found: C,
49.48; H, 4.97; N, 11.54; Cl, 9.73.
To a stirred suspension of LiAlH4 (144 mg, 3.82 mmol)
in THF (5 mL) was added a solution of the crude 6c in
THF (10 mL) at 0 ꢁC, and it was stirred at room temper-
ature for 0.5 h. The excess reagent was quenched by the
addition of MeOH, followed by the addition of water
(0.15 mL), 15% aqueous NaOH (0.15 mL), and addi-
tional water (0.45 mL). After stirring for 0.5 h, the mix-
ture was filtered through Celite, and then concentrated
in vacuo to yield the crude product, which was purified
by column chromatography on silica gel (CHCl3/
MeOH/satd NH3 aq = 10:1:0.1) to yield 7c (393 mg;
85% from 4c). This compound was subsequently con-
verted to its fumarate to yield a white solid (mp 157–
5.1.52. (2S)-1-(1H-Furo[2,3-g]indazol-1-yl)propan-2-amine
(7g). Compound 7g was prepared from 4g using a proce-
dure similar to that described for 7c, in 47% yield. This
compound was subsequently converted to its dihydro-
chloride to yield a white solid (mp 209–210 ꢁC). 1H
NMR (DMSO-d6) d 1.11 (3H, d, J = 6.8 Hz), 3.65–3.78
(1H, m), 4.75–4.96 (2H, m), 7.48 (1H, d, J = 8.8 Hz),
7.69 (1H, d, J = 8.8 Hz), 7.84 (1H, d, J = 2.0 Hz), 8.17
(1H, d, J = 2.0 Hz), 8.57 (3H, br s); FAB-MS m/z 216
[(M+H)+]. Anal. Calcd for C12H13N3OÆ2HClÆ0.1C2H6O:
C, 50.05; H, 5.37; N, 14.35; Cl, 24.22. Found: C, 50.06; H,
5.39; N, 14.28; Cl, 23.99.
160 ꢁC). 1H NMR (DMSO-d6)
d 1.12 (3H, d,

I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
1977
5.1.53. (2S)-1-(7-Methyl-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-amine (7h). Compound 7h was prepared from 6h
using a procedure similar to that described for 7f, in
98% yield. This compound was subsequently converted
to its fumarate to yield a white solid (mp 191–197 ꢁC).
1H NMR (DMSO-d6) d 1.05 (3H, d, J = 6.0 Hz), 2.52
(3H, s), 3.54–3.66 (1H, m), 4.55–4.63 (1H, m), 4.62–
4.68 (1H, m), 6.51 (2H, s), 7.26 (1H, s), 7.37 (1H, d,
J = 8.8 Hz), 7.57 (1H, d, J = 8.8 Hz), 8.14 (1H, s);
FAB-MS m/z 230 [(M+H)+]. Anal. Calcd for
C13H15N3OÆC4H4O4Æ0.1H2O: C, 58.82; H, 5.57; N,
12.10. Found: C, 58.62; H, 5.57; N, 12.20.
4.78–4.86 (1H, m), 6.79 (2H, br s), 7.43 (1H, d,
J = 9.0 Hz), 7.66 (1H, d, J = 9.0 Hz), 7.78–7.79 (1H,
m), 8.14 (1H, d, J = 2.0 Hz), 8.52 (3H, br s); FAB-MS
m/z 244 [(M+H)+]. Anal. Calcd for C14H17N3OÆ1.9H-
ClÆ0.8H2O: C, 51.42; H, 6.32; N, 12.85; Cl, 20.60.
Found: C, 51.50; H, 6.34; N, 12.74; Cl, 20.65.
5.1.58. (2S)-1-(3-Propyl-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-amine (7m). Compound 7m was prepared from
6m using a procedure similar to that described for 7f,
in 48% yield. This compound was subsequently con-
verted to its dihydrochloride to yield a white solid (mp
191–193 ꢁC). 1H NMR (DMSO-d6) d 0.95 (3H, d,
J = 8.7 Hz), 1.11 (3H, t, J = 6.4 Hz), 1.73–1.82 (2H,
m), 2.92 (2H, t, J = 8.7 Hz), 3.62–3.75 (1H, m), 4.65–
4.73 (1H, m), 4.78–4.85 (1H, m), 5.74 (2H, br s), 7.43
(1H, d, J = 8.8 Hz), 7.65 (1H, d, J = 8.8 Hz), 7.74–7.77
(1H, m), 8.15 (1H, d, J = 2.4 Hz), 8.47 (3H, br s);
FAB-MS m/z 258 [(M+H)+]. Anal. Calcd for
C15H19N3OÆ1.8HClÆ0.8H2O: C, 53.40; H, 6.69; N,
12.46; Cl, 18.92. Found: C, 53.19; H, 6.58; N, 12.49;
Cl, 18.78.
5.1.54. (2S)-1-(7-Ethyl-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-amine (7i). Compound 7i was prepared from 6i
using a procedure similar to that described for 7a, in
89% yield. This compound was subsequently converted
to its fumarate to yield a white solid (mp 191–193 ꢁC).
1H NMR (DMSO-d6) d 1.05 (3H, d, J = 6.8 Hz), 1.33
(3H, t, J = 8.0 Hz), 2.86 (2H, q, J = 8.0 Hz), 3.55–3.68
(1H, m), 4.61 (1H, dd, J = 8.0, 14 Hz), 4.76 (1H, dd,
J = 6.0, 14 Hz), 6.50 (2H, s), 7.28 (1H, s), 7.38 (1H, d,
J = 8.8 Hz), 7.58 (1H, d, J = 8.8 Hz), 8.15 (1H, s);
FAB-MS m/z 244 [(M+H)+]. Anal. Calcd for
C14H17N3OÆC4H4O4: C, 60.16; H, 5.89; N, 11.69.
Found: C, 60.13; H, 5.83; N, 12.60.
5.1.59. (2S)-1-(7-Ethyl-3-methyl-1H-furo[2,3-g]indazol-1-
yl)propan-2-amine (7n). Compound 7n was prepared
from 3n using a procedure similar to that described for
7q, in 42% yield. This compound was subsequently con-
verted to its hydrochloride to yield a white solid [mp
>245 ꢁC (dec)]. 1H NMR (DMSO-d6) d 1.12 (3H, d,
J = 6.6 Hz), 1.34 (3H, t, J = 7.5 Hz), 2.51 (3H, s), 2.87
(2H, q, J = 7.5 Hz), 3.60–3.75 (1H, m), 4.63 (1H, dd,
J = 7.9, 14 Hz), 4.74 (1H, dd, J = 5.7, 14 Hz), 7.31–
7.39 (2H, m), 7.53 (1H, d, J = 9.0 Hz), 8.39 (3H, br s);
FAB-MS m/z 258 [(M+H)+]. Anal. Calcd for
C15H19N3OÆ1.05HClÆ0.2H2O: C, 60.21; H, 6.89; N,
14.04; Cl, 12.44. Found: C, 60.29; H, 6.84; N, 14.03;
Cl, 12.34.
5.1.55. (2S)-1-(7-Isopropyl-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-amine (7j). Compound 7j was prepared from 3j
using a procedure similar to that described for 7q, in
17% yield. This compound was subsequently converted
to its dihydrochloride to yield a white solid (mp 243–
249 ꢁC). 1H NMR (DMSO-d6)
d 1.10 (3H, d,
J = 6.8 Hz), 1.37 (3H, d, J = 7.6 Hz), 3.10–3.22 (1H,
m), 3.61–3.79 (1H, m), 4.77 (1H, dd, J = 8.8, 14 Hz),
4.92 (1H, dd, J = 6.4, 14 Hz), 7.40 (1H, d, J = 8.8 Hz),
7.52 (1H, s), 7.59 (1H, d, J = 8.8 Hz), 8.44 (1H, s),
8.68 (1H, br s), 10.29 (1H, br s); FAB-MS m/z 258
[(M+H)+]. Anal. Calcd for C15H19N3OÆ2HClÆ0.3H2O:
C, 53.67; H, 6.49; N, 12.52; Cl, 21.12. Found: C,
53.96; H, 6.36; N, 12.50; Cl, 20.93.
5.1.60. (2S)-1-(3,7-Diethyl-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-amine (7o). Compound 7o was prepared from 3o
using a procedure similar to that described for 7q, in
33% yield. This compound was subsequently converted
to its hydrochloride to yield a white solid [mp >215 ꢁC
5.1.56. (2S)-1-(3-Methyl-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-amine (7k). Compound 7k was prepared from 6k
using a procedure similar to that described for 7f, in
84% yield. This compound was subsequently converted
to its fumarate to yield a white solid (mp 172–174 ꢁC).
1H NMR (DMSO-d6) d 1.07 (3H, d, J = 6.4 Hz), 3.17
(3H, s), 3. 56–3.68 (1H, m), 4.54–4.63 (1H, m), 4.65–
4.75 (1H, m), 6.50 (2H, s), 7.42 (1H, d, J = 8.8 Hz),
7.60 (1H, d, J = 8.8 Hz), 7.62–7.63 (1H, m), 8.12 (1H,
d, J = 2.0 Hz); FAB-MS m/z 230 [(M+H)+]. Anal. Calcd
for C13H15N3OÆC4H4O4ÆH 2O: C, 56.19; H, 5.82; N,
11.56. Found: C, 56.39; H, 5.81; N, 11.36.
(dec)]. 1H NMR (DMSO-d6)
d
1.12 (3H, d,
J = 6.6 Hz), 1.33 (3H, t, J = 7.5 Hz), 1.35 (3H, t,
J = 7.5 Hz), 2.87 (2H, q, J = 7.5 Hz), 2.94 (2H, q,
J = 7.5 Hz), 3.60–3.76 (1H, m), 4.65 (1H, dd, J = 8.3,
14 Hz), 4.78 (1H, dd, J = 5.7, 14 Hz), 7.32–7.40 (2H,
m), 7.55 (1H, d, J = 9.0 Hz), 8.46 (3H, br s); FAB-MS
m/z 272 [(M+H)+]. Anal. Calcd for C15H19N3OÆHClÆ0.3-
H2O: C, 61.35; H, 7.27; N, 13.42; Cl, 11.32. Found: C,
61.21; H, 7.14; N, 13.30; Cl, 11.41.
5.1.61. (2S)-1-(3-Methoxy-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-amine (7p). Compound 7p was prepared from 6p
using a procedure similar to that described for 7f, in
64% yield. This compound was subsequently converted
to its fumarate to yield a white solid (mp 160–162 ꢁC).
1H NMR (DMSO-d6) d 1.13 (3H, d, J = 6.4 Hz), 3.60–
3.71 (3H, m), 4.04 (1H, s), 4.53 (1H, dd, J = 8.0,
14 Hz), 4.63 (1H, dd, J = 6.0, 14 Hz), 6.55 (2H, s),
7.36 (1H, d, J = 8.8 Hz), 7.48 (1H, d, J = 8.8 Hz), 7.63
(1H, d, J = 2.0 Hz), 8.13 (1H, d, J = 2.0 Hz); FAB-MS
5.1.57. (2S)-1-(3-Ethyl-1H-furo[2,3-g]indazol-1-yl)pro-
pan-2-amine (7l). Compound 7l was prepared from 6l
using a procedure similar to that described for 7f, in
61% yield. This compound was subsequently converted
to its dihydrochloride to yield a white solid [mp
>195 ꢁC (dec)]. 1H NMR (DMSO-d6) d 1.12 (3H, d,
J = 6.4 Hz), 1.34 (3H, t, J = 8.0 Hz), 2.97 (2H, q,
J = 8.0 Hz), 3.62–3.75 (1H, m), 4.66–4.74 (1H, m),

1978
I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
m/z 246 [(M+H)+]. Anal. Calcd for C13H15N3O2Æ
C4H4O4Æ1.2H2O: C, 53.32; H, 5.63; N, 10.97;. Found:
C, 53.25; H, 5.39; N, 10.74.
H2SO4 (160 mL) was added portionwise KNO3 (7.0 g,
126 mmol) at 5 ꢁC, and the resulting mixture was stirred
at room temperature for 2 h. After cooling to 0 ꢁC, the
mixture was poured into ice-water. The resulting precip-
itate was collected with filtration and dried in vacuo to
yield an orange solid. This orange solid was dissolved
in Et2O, washed with brine, and dried over MgSO4.
After removal of the solvent, the residue was purified
by column chromatography on silica gel (AcOEt/hex-
ane = 1:100) to yield 3, 4-dichloro-6-nitrotoluene
(17.8 g, 86%) as a slightly yellow solid.
5.1.62. (2S)-1-(7-Ethyl-3-methoxy-1H-furo[2,3-g]indazol-
1-yl)propan-2-amine (7q). To a solution of 3q (295 mg,
1.36 mmol) in DMSO (10 mL) were added (2S)-2-
[(tert-butoxycarbonyl)amino]propyl 4-methylbenzene-
sulfonate (674 mg, 2.04 mmol) and Cs2CO3 (889 mg,
2.72 mmol) at room temperature, and the mixture was
stirred at 60 ꢁC for 7 h. After cooling to room tempera-
ture, the mixture was poured into ice-water and ex-
tracted with AcOEt. The organic extracts were washed
with brine, dried over MgSO4, and evaporated in vacuo.
The residue was purified by column chromatography on
silica gel (AcOEt/hexane = 1:5) to yield 8q.
To a mixture of 3, 4-dichloro-6-nitrotoluene (9.20 g,
44.7 mmol), conc. HCl (40 mL), and EtOH (40 mL)
was added a solution of SnCl2Æ2H2O (50 g, 222 mmol)
in concd HCl (40 mL), and the mixture was stirred at
room temperature for 17 h. The reaction was quenched
with aqueous NaOH solution and extracted with
CHCl3. The combined extracts were washed with H2O
and brine, dried over MgSO4, and concentrated in vacuo
to yield 9c (7.0 g, 88%) as a white solid. 1H NMR
(CDCl3) d 2.10 (3H, s), 3.63 (2H, br s), 6.73 (1H, s),
7.09 (1H, s); EI-MS m/z 175 [M+].
To a solution of 8q in AcOEt (5 mL) was added 4 M
HCl–AcOEt (5 mL) at 0 ꢁC, and the mixture was stirred
for 2 h at room temperature. After removal of the sol-
vent, to the residue was added saturated aqueous NaH-
CO3 and extracted with CHCl3. The extracts were dried
over MgSO4 and evaporated. The residue was purified
by column chromatography on silica gel (CHCl3/
MeOH/satd NH3 aq = 30:1:0.1) to yield 7q (201 mg,
66%). This compound was subsequently converted to
its fumarate to yield a white solid (mp 202–205 ꢁC).
1H NMR (DMSO-d6) d 1.09 (3H, d, J = 6.4 Hz), 1.32
(3H, t, J = 7.6 Hz), 2.85 (2H, q, J = 7.6 Hz), 3.50–3.66
(1H, m), 4.02 (1H, s), 4.43 (1H, dd, J = 7.6, 14 Hz),
4.55 (1H, dd, J = 6.0, 14 Hz), 6.50 (2H, s), 7.21 (1H,
s), 7.27 (1H, d, J = 8.8 Hz), 7.39 (1H, d, J = 8.8 Hz);
FAB-MS m/z 274 [(M+H)+]. Anal. Calcd for
C15H19N3O2ÆC4H4O4: C, 58.60; H, 5.95; N, 10.79;.
Found: C, 58.44; H, 5.86; N, 10.79.
5.1.66. 5,6-Dichloro-2-methylaniline (9d). To a mixture
of 13 (6.55 g, 25.2 mmol) and ethylene glycol (200 mL)
was added KOH (7.0 g, 126 mmol), and the resulting
mixture was heated at 170 ꢁC for 7 h. After cooling to
room temperature, the mixture was poured into water
and extracted with AcOEt. The combined extracts were
washed with H2O and brine, and then dried over
MgSO4. After removal of the solvent, the residue was
purified by column chromatography on silica gel
(AcOEt/toluene = 1:10) to yield 9d (4.23 g, 95%) as pale
1
yellow oil. H NMR (DMSO-d6) d 2.12 (3H, s), 5.36
(2H, s), 6.70 (3H, d, J = 8.0 Hz), 6.93 (1H, d,
5.1.63. (2S)-1-(1H-Thieno[2,3-g]indazol-1-yl)propan-2-
amine (7r). Compound 7r was prepared from 6r using
a procedure similar to that described for 7f, in 71%
yield. This compound was subsequently converted to
its fumarate to yield a white solid (mp 179–181 ꢁC).
1H NMR (DMSO-d6) d 1.05 (3H, d, J = 6.4 Hz), 3.50–
3.66 (1H, m), 4.65–4.80 (2H, m), 6.49 (2H, s), 7.69–
7.79 (2H, m), 7.95 (1H, d, J = 6.0 Hz), 8.13 (1H, d,
J = 5.2 Hz), 8.19 (1H, s); FAB-MS m/z 232 [(M+H)+].
Anal. Calcd for C12H13N3SÆ1.1C4H4O4Æ 0.25H2O: C,
54.19; H, 4.96; N, 11.56; S, 8.82. Found: C, 53.95; H,
4.67; N, 11.54; S, 8.82.
J = 8.0 Hz); EI-MS m/z 175 [M+].
5.1.67. N-(2,3-Dichlorophenyl)-2,2-dimethylpropanamide
(12). To a mixture of 2,3-dichloroaniline 11 (25.0 g,
154 mmol) and K2CO3 (44 g, 318 mmol) in acetone
(600 mL) was added pivaloyl chloride (19.5 g,
162 mmol), and the resulting mixture was refluxed for
8 h. The mixture was cooled to room temperature and
then filtered through Celite. The filtrate was concen-
trated in vacuo and diluted with AcOEt. This solution
was washed with 1 M aqueous HCl, H2O, and brine,
and then dried over MgSO4. After removal of the sol-
vent, the residue was purified by column chromatogra-
phy on silica gel (AcOEt/hexane = 3:1) to yield 12
5.1.64. (2S)-1-(1H-[1,3]Oxazolo[5,4-g]indazol-1-yl)pro-
pan-2-amine (7s). Compound 7s was prepared from 6s
using a procedure similar to that described for 7f, in
78% yield. This compound was subsequently converted
to its fumarate to yield a white solid (mp 160–162 ꢁC).
1H NMR (DMSO-d6) d 1.09 (3H, d, J = 6.4 Hz), 3.74–
3.86 (1H, m), 4.78–4.86 (2H, m), 6.49 (2H, s), 7.61
(1H, d, J = 8.8 Hz), 7.84 (1H, d, J = 8.8 Hz), 8.29 (1H,
s), 8.91 (1H, s); FAB-MS m/z 217 [(M+H)+]. Anal.
Calcd for C11H12N4OÆ1. 2C4H4O4Æ0.1H2O: C, 53.11;
H, 4.80; N, 15.68. Found: C, 53.10; H, 5.16; N, 15.51.
1
(13.6 g, 37%) as a white solid. H NMR (DMSO-d3) d
1.24 (9H, s), 7.35 (1H, t, J = 8.4 Hz), 7.46 (1H, dd,
J = 1.6, 8.4 Hz), 7.50 (1H, dd, J = 1.6, 8.4 Hz), 9.16
(1H, s); FAB-MS m/z 246 [(M+H)+].
5.1.68.
propanamide (13). To
N-(2,3-Dichloro-6-methylphenyl)-2,2-dimethyl-
mixture of 12 (10.22 g,
a
38.7 mmol) and TMEDA (3.15 mL, 27.1 mmol) in
t-BuOMe (100 mL) was added BuLi (62 mL, 1.55 M in
hexane) over 20 min at À20 ꢁC. After stirring at this
temperature for 1 h, a solution of MeI (4.82 mL,
77.4 mmol) in t-BuOMe (10 mL) was added over 1 h
at À20 ꢁC. The reaction was quenched with ice-water
5.1.65. 4,5-Dichloro-2-methylaniline (9c). To a mixture
of 3, 4-dichlorotoluene 10 (16.1 g, 100 mmol) and conc.

I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
1979
and the aqueous phase was extracted with Et2O. The
combined extracts were washed with H2O and brine,
dried over MgSO4, and concentrated in vacuo to give
the crude product. This was then washed with i-Pr2O
to yield 13 (5.92 g, 59%) as a white solid. 1H NMR
(CDCl3) d 1.37 (9H, s), 2.20 (3H, s), 7.08 (1H, d,
J = 8.7 Hz), 7.15–7.23 (1H, m), 7.27 (1H, d,
J = 8.7 Hz); FAB-MS m/z 260 [(M+H)+].
combined extracts were washed with H2O and brine,
dried over MgSO4, and concentrated in vacuo. The res-
idue was purified by crystallization from i-Pr2O to yield
2-(2-bromoprop-2-en-1-yl)cyclohexane-1,3-dione
(10.5 g, 48%) as a white solid.
HCO2H (300 mL) and HClO4 (30 mL) were added to
this product, and then the solution was stirred at
80 ꢁC for 4 h. After cooling and removal of the solvent,
to the residue was added H2O, after which it was ex-
tracted with Et2O. The combined extracts were dried
over MgSO4 and concentrated in vacuo. The residue
was purified by column chromatography on silica gel
(AcOEt/hexane = 1:5) to yield 18b (4.70 g, 70%) as pale
5.1.69. 1H-Indazol-6-ol (15). To a mixture of 14 (2.13 g,
16.0 mmol), H2SO4 (16 mL), and H2O (20 mL) was
added dropwise
a
solution of NaNO2 (1.21 g,
17.5 mmol) in H2O (5 mL) at 0 ꢁC. After stirring at this
temperature for 0.5 h, the mixture was cautiously
poured into boiling 10 M aqueous H2SO4 (70 mL). After
boiling for 10 min, the mixture was diluted with water
and cooled to room temperature. The resulting solution
was extracted with AcOEt and the combined extracts
were washed with brine, dried over MgSO4, and concen-
trated in vacuo to give 1.78 g of crude product as brown
solid. This crude product was recrystallized from
i-PrOH–Et2O to yield 15 (885 mg, 41%) as a brown so-
lid. 1H NMR (DMSO-d6) d 6.40 (1H, dd, J = 2.0,
8.4 Hz), 6.75–6.78 (1H, m), 7.52 (1H, d, J = 8.4 Hz),
7.86 (1H, s), 9.52 (1H, s), 13.42 (1H, br s); FAB-MS
m/z 135 [(M+H)+].
1
yellow oil. H NMR (DMSO-d6) d 2.02–2.09 (2H, m),
2.26 (3H, s), 2.34–2.38 (2H, m), 2.82 (2H, t,
J = 6.4 Hz), 6.25 (1H, d, J = 1.6 Hz); FAB-MS m/z 151
[(M+H)+].
5.1.73. 2-Ethyl-6,7-dihydro-1-benzofuran-4(5H)-one (18c).
To a mixture of 1-bromobutan-2-one (25.0 g, 166 mmol)
and NaHCO3 (55.8 g, 332 mmol) in MeOH (250 mL)
and H2O (500 mL) was added a solution of 1,3-cyclo-
hexanedione 17 (37.1 g, 332 mmol) in H2O (500 mL)
dropwise at 0 ꢁC. The resulting mixture was stirrred at
room temperature for 65 h. Subsequently, 1 M aqueous
HCl (500 mL) was added and the crude mixture was ex-
tracted with AcOEt. The combined extracts were dried
over MgSO4 and concentrated in vacuo. To the crude
residue was added H2SO4 (150 mL) dropwise at
À20 ꢁC. After stirring at room temperature for 15 min,
the mixture was poured onto ice and extracted with
AcOEt. The extracts were washed with water, saturated
aqueous NaHCO3, and brine. The organic layer was
dried over MgSO4 and concentrated. The residue was
purified by column chromatography on silica gel
(AcOEt/hexane = 1:4) to yield 18c (13.6 g, 50%) as pale
5.1.70. 7-Chloro-1H-indazol-6-ol (16). To a solution of
15 (2.50 g, 18.7 mmol) in dioxane (100 mL) was added
NCS (2.74 g, 20.5 mmol), and the resulting mixture
was heated at 60 ꢁC for 12 h. The reaction mixture
was concentrated in vacuo, and the residue was purified
by column chromatography on silica gel (CHCl3/
MeOH = 30:1) to yield 16 (1.70 g, 54%) as a white solid.
1H NMR (DMSO-d6) d 6.84 (1H, d, J = 8.8 Hz), 7.51
(1H, d, J = 8.8 Hz), 7.97–7.99 (1H, m), 10.25 (1H, s),
13.08 (1H, br s); FAB-MS m/z 168 [(M+H)+].
yellow oil. 1H NMR (CDCl3)
d 1.23 (3H, t,
5.1.71. 6,7-Dihydro-1-benzofuran-4(5H)-one (18a). To a
mixture of chloroacetaldehyde (40 mL, 40% in water)
and NaHCO3 (20 g, 240 mmol) in H2O (160 mL) was
added a solution of 1,3-cyclohexanedione 17 (22.4 g,
200 mmol) in H2O (230 mL) dropwise at 0 ꢁC. The
resulting mixture was stirred at room temperature for
70 h. Following the addition of AcOEt (200 mL), to
the mixture was added H2SO4 in order to adjust the
pH of the aqueous layer to 1. After 1 h, the mixture
was extracted with AcOEt. The combined extracts were
dried over MgSO4 and concentrated in vacuo, and the
residue was purified by column chromatography on sil-
ica gel (AcOEt/hexane = 1:4) to yield 18a (16.4 g, 60%)
J = 7.8 Hz), 2.10–2.21 (2H, m), 2.43–2.51 (2H, m), 2.63
(2H, q, J = 7.8 Hz), 2.83 (2H, t, J = 6.3 Hz), 6.25 (1H,
s); FAB-MS m/z 165 [(M+H)+].
5.1.74. 4,5-Dihydro-1H-furo[2,3-g]indazole (19a). To a
suspension of t-BuOK (16.5 g, 146 mmol) in THF
(200 mL) was added a solution of 18a (10 g, 73 mmol)
and HCO2Et (23.7 mL, 292 mmol) in THF (150 mL)
dropwise at 0 ꢁC, and the resulting mixture was stirred
at this temperature for 2 h. To the reaction mixture
was added hydrazine monohydrate (3.9 mL, 81 mmol)
and 1 M aqueous HCl (150 mL) at 0 ꢁC, and it was stir-
red for 20 h at room temperature. The reaction mixture
was extracted with AcOEt, washed with brine, and dried
over MgSO4. After removal of the solvent, the residue
was purified by column chromatography on silica gel
(CHCl3/MeOH = 30:1) to yield 19a (8.51 g, 73%) as a
yellow solid. 1H NMR (DMSO-d6) d 2.84–2.86 (4H,
m), 6.63 (1H, d, J = 2.2 Hz), 7.43 (1H, s), 7.58 (1H, d,
J = 1.8 Hz); EI-MS m/z 160 [M+].
1
as a white solid. H NMR (CDCl3) d 2.12–2.20 (2H,
m), 2.57 (2H, t, J = 6.9 Hz), 2.78 (2H, t, J = 6.9 Hz),
6.42 (1H, d, J = 1.5 Hz), 7.56 (1H, d, J = 1.5 Hz); EI-
MS m/z 136 [M+].
5.1.72. 2-Methyl-6,7-dihydro-1-benzofuran-4(5H)-one (18b).
To a solution of 17 (10.0 g, 89.2 mmol) in H2O (45 mL)
was added a solution of Triton B (37.9 mL, 40% in
MeOH), followed by the addition of 2,3-dibromopro-
pene (21.4 g, 107 mmol). This reaction mixture was stir-
red at room temperature for 6 days, and then diluted
with water, followed by extraction with AcOEt. The
5.1.75. 7-Methyl-4,5-dihydro-1H-furo[2,3-g]indazole (19b).
Compound 19b was prepared from 18b using a proce-
dure similar to that described for 19a (59%). H NMR
1
(DMSO-d6) d 2.27 (3H, s), 2.77–2.83 (4H, m), 6.23

1980
I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
(1H, s), 7.40 (1H, s), 12.20 (1H, br s); FAB-MS m/z 175
(AcOEt/hexane = 1:5) to yield 21a (2.32 g, 29%) as a yel-
low solid. H NMR (CDCl3) d 2.23 (3H, s), 2.77–2.84
1
[(M+H)+].
(2H, m), 2.89–2.97 (2H, m), 6.66 (1H, d, J = 1.8 Hz),
7.31–7.34 (1H, m); FAB-MS m/z 175 [(M+H)+].
5.1.76. 7-Ethyl-4,5-dihydro-1H-furo[2,3-g]indazole (19c).
To a suspension of t-BuOK (35.3 g, 314 mmol) in THF
(400 mL) was added a solution of 18c (25.8 g, 157 mmol)
and HCO2Et (50.6 mL, 628 mmol) in THF (300 mL)
dropwise at 0 ꢁC. The mixture was then stirred at this
temperature for an additional 1.5 h. Subsequently, 1 M
aqueous HCl (350 mL) was added, and the crude mix-
ture was extracted with AcOEt. The combined extracts
were washed with brine, dried over MgSO4, and concen-
trated in vacuo. Without further purification the residue
was dissolved in EtOH (600 mL). This solution was
added dropwise to a solution of hydrazine monohydrate
(9.08 mL, 187 mmol) in EtOH (600 mL) over a period of
1 h and then stirred at room temperature for an addi-
tional 17 h. After removal of the solvent, the residue
was diluted with AcOEt and washed with brine. The or-
ganic layer was dried over MgSO4 and concentrated.
The residue was purified by column chromatography
on silica gel (AcOEt/hexane = 1:4) to yield 19c (23.5 g,
5.1.79. 3-Ethyl-4,5-dihydro-1H-furo[2,3-g]indazole (21b).
To a suspension of 35% KH (420 mg, 3.67 mmol) and
60% NaH (7.36 g, 184 mmol) in DME (200 mL) was
added a solution of 18a (5.0 g, 36.7 mmol) in DME
(30 mL) at 0 ꢁC. The resulting mixture was stirred at this
temperature for 0.5 h, followed by the addition of ethyl
propionate (12.7 mL, 111 mmol). The resulting mixture
was refluxed for 1 h. After cooling, it was diluted with
AcOEt, washed with saturated aqueous NH4Cl, water,
and brine. The combined extracts were dried over
MgSO4 and concentrated in vacuo. The residue was
purified by column chromatography on silica gel
(AcOEt/hexane = 1:7) to yield a yellow oil. To this com-
pound were added EtOH (50 mL) and hydrazine mono-
hydrate (5.10 mL, 104 mmol), and it was stirred for 2 h
at room temperature. The reaction mixture was concen-
trated in vacuo, diluted with AcOEt, washed with H2O
and brine, and then dried over MgSO4. After removal
of the solvent, the residue was purified by column chro-
matography on silica gel (AcOEt/hexane = 1:3) to yield
1
80%) as a pale yellow solid. H NMR (CDCl3) d 1.25
(3H, t, J = 7.5 Hz), 2.66 (2H, q, J = 7.5 Hz), 2.88–2.94
(4H, m), 6.27 (1H, s), 7.27 (1H, s); FAB-MS m/z 189
[(M+H)+].
1
21b (5.85 g, 85%) as a yellow solid. H NMR (CDCl3)
d 1.24 (3H, t, J = 7.8 Hz), 2.63 (2H, q, J = 7.8 Hz),
2.80–2.96 (4H, m), 6.66 (1H, d, J = 2.4 Hz), 7.32 (1H,
d, J = 2.4 Hz); FAB-MS m/z 189 [(M+H)+].
5.1.77. 1-(4,5-Dihydro-1H-furo[2,3-g]indazol-7-yl)etha-
none (20). To a solution of 19a (5.0 g, 31.2 mmol) in
AcOH (5 mL) was added TFAA (26.2 g, 125 mmol) at
room temperature. The resulting mixture was stirred at
room temperature for 4 h, and then concentrated in va-
cuo. The residue was diluted with 15% aqueous NaOH
and extracted with AcOEt. The combined extracts were
washed with H2O and brine, dried over MgSO4, and
concentrated in vacuo. The residue was purified by col-
umn chromatography on silica gel (CHCl3/
MeOH = 100:1 to 10:1), and then was washed with hot
ethanol to yield 20 (1.74 g, 28%) as a pale yellow solid.
1H NMR (DMSO-d6) d 2.42 (3H, s), 2.85–3.02 (4H,
m), 7.51 (1H, s), 7.61 (1H, s); FAB-MS m/z 203
[(M+H)+].
5.1.80. 3-Propyl-4,5-dihydro-1H-furo[2,3-g]indazole (21c).
To a suspension of 35% KH (420 mg, 3.67 mmol) and
60% NaH (7.36 g, 184 mmol) in DME (200 mL) was
added a solution of 18a (5.0 g, 36.7 mmol) in DME
(30 mL) at 0 ꢁC. The resulting mixture was stirred at this
temperature for 0.5 h, followed by addition of ethyl
butyrate (14.5 mL, 111 mmol). The resulting mixture
was refluxed for 2 h. After cooling, it was diluted with
AcOEt, washed with saturated aqueous NH4Cl, water,
and brine. The combined extracts were dried over
MgSO4 and concentrated in vacuo. The residue was
purified by column chromatography on silica gel
(AcOEt/hexane = 1:4) to yield a yellow oil. To this com-
pound was added EtOH (50 mL) and hydrazine mono-
hydrate (7.13 mL, 147 mmol), and it was stirred for
12 h at room temperature. The reaction mixture was
concentrated in vacuo, diluted with AcOEt, washed with
H2O and brine, and then dried over MgSO4. After re-
moval of the solvent, the residue was purified by column
chromatography on silica gel (AcOEt/hexane = 1:4) to
yield 21c (6.30 g, 85%) as a yellow solid. 1H NMR
(CDCl3) d 0.94 (3H, t, J = 7.5 Hz), 1.58–1.70 (2H, m),
2.57 (2H, t, J = 7.5 Hz), 2.79–2.96 (4H, m), 6.58–6.62
(1H, m), 7.33 (1H, d, J = 2.1 Hz); FAB-MS m/z 203
[(M+H)+].
5.1.78. 3-Methyl-4,5-dihydro-1H-furo[2,3-g]indazole (21a).
To a suspension of 35% KH (1.35 g, 11.8 mmol) and
60% NaH (9.12 g, 228 mmol) in DME (300 mL) was
added a solution of 18a (6.20 g, 45.6 mmol) in DME
(300 mL) at 0 ꢁC. The resulting mixture was stirred at
this temperature for 0.5 h, followed by addition of
AcOEt (13.4 mL, 137 mmol). The resulting mixture
was refluxed for 3 h. After cooling, it was diluted with
AcOEt, and then washed with saturated aqueous
NH4Cl, water, and brine. The combined extracts were
dried over MgSO4 and concentrated in vacuo. The resi-
due was purified by column chromatography on silica
gel (AcOEt/hexane = 1:10) to yield a pale yellow oil.
To this compound were added EtOH (50 mL) and
hydrazine monohydrate (3.60 mL, 74 mmol), and it
was stirred at room temperature for 2 h. The reaction
mixture was concentrated in vacuo, diluted with AcOEt,
washed with H2O and brine, and then dried over
MgSO4. After removal of the solvent, the residue was
purified by column chromatography on silica gel
5.1.81. 7-Ethyl-3-methyl-4,5-dihydro-1H-furo[2,3-g]inda-
zole (21d). Compound 21d was prepared from 18c using
a procedure similar to that described for 21a, in 16%
1
yield as a yellow solid. H NMR (CDCl3) d 1.24 (3H,
t, J = 7.5 Hz), 2.25 (3H, s), 2.65 (2H, q, J = 7.5 Hz),
2.75–2.94 (4H, m), 6.26 (1H, s), 8.53 (1H, br s); FAB-
MS m/z 203 [(M+H)+].

I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
1981
5.1.82. 3,7-Diethyl-4,5-dihydro-1H-furo[2,3-g]indazole
(21e). Compound 21e was prepared from 18c using a
procedure similar to that described for 21b, in 14% yield
as a yellow solid. 1H NMR (CDCl3) d 1.24 (3H, t,
J = 7.5 Hz), 1.26 (3H, t, J = 7.5 Hz), 2.60–2.70 (4H,
m), 2.78–2.94 (4H, m), 6.25 (1H, s), 8.59 (1H, br s);
FAB-MS m/z 217 [(M+H)+].
5.1.88. 7-Nitro-1H-indazol-6-ol (26). To a mixture of 15
(500 mg, 3.37 mmol) and H2SO4 (5.0 mL) was added
KNO3 (375 mg, 3.71 mmol) portionwise at 0 ꢁC, and
it was stirred at this temperature for 0.5 h. To the
reaction mixture was added ice (70 g), and it was stir-
red at 0 ꢁC for 1 h. The resulting precipitate was col-
lected by filtration and rinsed with water to yield 26
(575 mg, 95%) as a pale yellow solid. 1H NMR
(DMSO-d6) d 6.94 (1H, d, J = 8.4 Hz), 8.06 (1H, d,
J = 8.4 Hz), 8.18 (1H, s), 11.60 (1H, br s); FAB-MS
m/z 180 [(M+H)+].
5.1.83. Ethyl 4-oxo-4,5,6,7-tetrahydro-1-benzofuran-5-
carboxylate (22a). To a solution of KHMDS (11.0 g,
55.1 mmol) in THF (100 mL) was added dropwise a
solution of 18a (3.00 g, 22.0 mmol) and THF
(50 mL) at À40 ꢁC, and it was stirred for 10 min. To
the reaction mixture was added dropwise ethyl chloro-
formate (2.32 mL, 24.2 mmol) at À40 ꢁC. It was stir-
red at this temperature for 0.5 h, and then at room
temperature for 2 h. The reaction mixture was poured
into ice-water, added 1 M HCl (200 mL), and then ex-
tracted with AcOEt. The combined extracts were dried
over MgSO4 and evaporated. The residue was purified
by column chromatography on silica gel (AcOEt/tolu-
ene = 1:10) to yield 22a (3.88 g, 85%) as a pale yellow
oil. 1H NMR (CDCl3) d 1.28 (3H, t, J = 7.2 Hz),
2.14–2.62 (2H, m), 2.81–3.14 (2H, m), 3.45–3.53 (1H,
m), 4.22 (1H, q, J = 7.2 Hz), 6.69 (1H, d,
J = 2.1 Hz), 7.34 (1H, d, J = 2.1 Hz); FAB-MS m/z
209 [(M+H)+].
5.1.89. 7-Amino-1H-indazol-6-ol (27). To a solution of
26 (460 mg, 2.56 mmol) in AcOH (30 mL) was added
Pd on carbon (10%, 50 mg). The mixture was stirred
for 20 h under H2 at 40 psi. The catalyst was removed
by filtration through Celite and the solvent was re-
moved in vacuo. The resulting residue was washed
with i-Pr2O to yield 27 (380 mg, 100%) as a pale yel-
low solid. 1H NMR (DMSO-d6) d 4.51 (2H, br s),
6.66 (1H, d, J = 8.4 Hz), 6.83 (1H, d, J = 8.4 Hz),
7.79 (1H, s), 8.40 (1H, br s), 12.24 (1H, br s); FAB-
MS m/z 148 [(M+H)+].
6. Biological procedures
6.1. Receptor binding assay
5.1.84. Ethyl 2-ethyl-4-oxo-4,5,6,7-tetrahydro-1-benzofu-
ran-5-carboxylate (22b). Compound 22b was prepared
from 18c using a procedure similar to that described
The membrane preparation was washed once with
50 mM Tris–HCl buffer (pH 7.4) containing 4 mM
CaCl2 just before it was used for the binding assays.
The 5-HT2C and 5-HT2A receptor binding assays with
[3H]5-HT were carried out using the methods of Pazos
et al.20 with a slight modification; reaction medium
[50 mM Tris–HCl buffer (pH 7.4) containing 4 mM
CaCl2, 10 lM pargyline, and 0.1 mg/mL L-(+)-ascorbic
acid] containing [3H]5-HT, membrane preparation,
and test compounds was incubated at 37 ꢁC for
30 min. Non-specific binding was determined in the
presence of 10 lM 5-HT, and specific binding was calcu-
lated as total binding minus non-specific binding. After
incubation, 4 mL of 50 mM Tris–HCl buffer (pH 7.4)
containing 4 mM CaCl2 was added, and the medium
was filtered under vacuum through Whatman GF/B
glass filter pre-treated with 0.1% polyethyleneimine.
The filter was washed with the same buffer solution
(4· 3 mL). The GF/B glass filter was immersed in
6 mL of liquid scintillator (Packard, Aquasol-2), and
the radioactivities were measured with a liquid scintilla-
tion counter (Packard, Tri-Carb-2500TR). The amounts
of protein were measured according to the method
established by Lowry et al.21 Dissociation constants
(Kd value) were obtained by Scatchard analysis using
SAS (ver. 6.11) together with an application software
developed by our company (5-HT2C; 1.6 nM and 5-
HT2A; 9.8 nM). Concentrations of compounds showing
50% inhibition of receptor binding, IC50 values, were
obtained by non-linear analysis using SAS (ver. 6.11) to-
gether with an application software developed by our
company. Ki values indicating affinity for receptors were
calculated by using a formula developed by Cheng and
Prussoff.22
1
for 22a, in 37% yield. H NMR (CDCl3) d 1.23 (3H, t,
J = 7.2 Hz), 1.28 (3H, t, J = 7.2 Hz), 2.29–2.38 (1H,
m), 2.49–2.58 (1H, m), 2.63 (1H, q, J = 7.2 Hz), 2.79–
2.88 (1H, m), 2.97–3.06 (1H, m), 3.43–3.48 (1H, m),
4.22 (1H, q, J = 7.2 Hz), 6.26 (1H, s); FAB-MS m/z
237 [(M+H)+].
5.1.85. 1,2,4,5-Tetrahydro-3H-furo[2,3-g]indazol-3-one
(23a). To
a solution of hydrazine monohydrate
(0.78 mL, 15.9 mmol) in EtOH (30 mL) was added
dropwise a solution of 22a (3.00 g, 14.4 mmol) in EtOH
(20 mL), and it was stirred for 14 h at room tempera-
ture. After removal of the solvent, the residue was
washed with EtOH to yield 23a (2.08 g, 82%) as a yellow
1
solid. H NMR (DMSO-d6) d 2.66 (3H, t, J = 8.4 Hz),
2.83 (1H, d, J = 8.4 Hz), 6.54 (1H, s), 7.56 (1H, s);
FAB-MS m/z 177 [(M+H)+].
5.1.86. 7-Ethyl-1,2,4,5-tetrahydro-3H-furo[2,3-g]indazol-
3-one (23b). Compound 23b was prepared from 22b
using a procedure similar to that described for 23a, in
1
84% yield as a yellow solid. H NMR (DMSO-d6) d
1.17 (3H, t, J = 7.5 Hz), 2.55–2.69 (4H, m), 2.72–2.81
(2H, m), 6.14 (1H, s), FAB-MS m/z 205 [(M+H)+].
5.1.87. 4,5-Dihydro-1H-thieno[2,3-g]indazole (25). Com-
pound 25 was prepared from 24 using a procedure sim-
ilar to that described for 19a, in 78% yield as a pale
yellow solid. 1H NMR (DMSO-d6) d 2.80 (2H, t,
J = 7.6 Hz), 2.94 (2H, t, J = 7.6 Hz), 7.26 (1H, d,
J = 4.8 Hz), 7.36 (1H, d, J = 4.8 Hz), 7.50 (1H, s),
12.41 (1H, br s); EI-MS m/z 176 [M+].

1982
I. Shimada et al. / Bioorg. Med. Chem. 16 (2008) 1966–1982
6.2. PI hydrolysis assay
References and notes
1. Hoyer, D.; Martin, G. Neuropharmacology 1997, 36, 419.
2. Kennett, G. A. Curr. Opin. Invest. Drugs 1993, 2, 317.
3. Tecott, L. H.; Sun, L. M.; Akanas, F.; Strack, A. M.;
Lowenstein, D. H.; Dallman, M. F.; Julius, D. Nature
1995, 374, 542.
4. Isaac, M. Drugs Future 2001, 26, 383.
5. Roth, B. L.; Shapiro, D. A. Exp. Opin. Ther. Targets 2001,
5, 685.
6. Bishop, M. J.; Nilsson, B. M. Exp. Opin. Ther. Patents
2003, 13, 1691.
7. Chang-Fong, J.; Addo, J.; Dukat, M.; Smith, C.; Mitchell,
N. A.; Herrick-Davis, K.; Teitler, M.; Glennon, R. A.
Bioorg. Med. Chem. Lett. 2002, 12, 155.
8. Bo¨s, M.; Jenck, F.; Martin, J. R.; Moreau, J.-L.; Sleight,
A. J.; Wichmann, J.; Widmer, U. J. Med. Chem. 1997, 40,
2762.
9. Bo¨s, M.; Wichmann, J. Patent EP 0657426, 1995; Chem.
Abstr. 1995, 123, 339731.
10. Fludzinski, P.; Evrard, D. A.; Bloomquist, W. E.; Lace-
field, W. B.; Pfeifer, W.; Jones, N. D.; Deeter, J. B.;
Cohen, M. L. J. Med. Chem. 1987, 30, 1537.
11. Kimura, Y.; Hatanaka, K.; Naitou, Y.; Maeno, K.;
Shimada, I.; Koakutsu, A.; Wanibuchi, F.; Yamaguchi,
T. Eur. J. Pharmacol. 2004, 483, 37.
PI hydrolysis assay was carried out using the methods
of Aramori and Nakanishi 23 with a slight modification.
CHO cells expressing human 5-HT2C or 5-HT2A recep-
tors and HEK 293-EBNA cells expressing 5-HT2B
receptors were seeded onto a 24-well plate (approxi-
mately 1 · 105 cells/well), and cultured for 1 day. After
the addition of myo-[3H]inositol (3 lCi/mL), they were
incubated for 24 h for labeling. After the cells were
washed two times with phosphate buffered saline
(PBS), they were incubated with PBS for 20 min, and
then further incubated with PBS–LiCl solution for
20 min. After 20 min incubation with PBS–LiCl solu-
tion containing the test compound, the reaction was
terminated by adding 0.2 M PCA, after which the reac-
tion mixture was allowed to stand at 4 ꢁC for 1–3 h.
After 2 M KOH and 100 mM EDTA-2Na solution
were added, the plate was centrifuged (2000 rpm,
5 min). The supernatant (1 mL) was added to a Bio-
Rad AG1-X8 column, and washed with GPI solution
(5 mM disodium tetraborate, 60 mM sodium formate)
(3.5· 2 mL), and eluted with 4 mL of IP3 solution
(0.1 M formate, 1 M ammonium formate). The elute
was added to a liquid scintillator (Aquasol-2) and mea-
sured with the liquid scintillation counter. EC50 values
and Emax (%) were calculated by non-linear analysis
using SAS (ver.6.11) together with an application soft-
ware developed by our company. Emax (%) indicated
intrinsic activity and the response produced by 10 lM
5-HT was defined as 100%.
´
12. van den Broek, L. A. G. M.; Lazaro, E.; Zylicz, Z.;
Fennis, P. J.; Missler, F. A. N.; Lelieveld, P.; Garzotto,
M.; Theo Wagener, D. J.; Ballesta, J. P. G.; Ottenheijm,
H. C. J. J. Med. Chem. 1989, 32, 2002.
13. Bartsch, R. A.; Yang, I. W. J. Heterocycl. Chem. 1984, 21,
1063.
14. Fieser, L. F. J. Am. Chem. Soc. 1926, 48, 1097.
15. Matsumoto, M.; Watanabe, N. Heterocycles 1994, 22,
2313.
16. Shimada, I.; Maeno, K.; Kimizuka, T.; Goto, S.; Takah-
ashi, T.; Nakamura, A.; Miyafuji, A.; Tsukamoto, S.;
Sakamoto, S. Heterocycles 2004, 62, 807.
17. Berendsen, H. H. G.; Jenck, F.; Broekkamp, C. L.
Psychopharmacology 1990, 101, 57.
18. Millan, M. J.; Peglion, J.-L.; Lavielle, G.; Perrin-Mon-
neyron, S. Eur. J. Pharmacol. 1997, 325, 9.
19. Kennett, G. A.; Wood, M. D.; Bright, F.; Trail, B.; Riley,
G.; Holland, V.; Avenell, K. Y.; Stean, T.; Upton, N.;
Bromidge, S.; Forbes, I. T.; Brown, A. M.; Middlemiss, D.
N.; Blackburn, T. P. Neuropharmacology 1997, 36, 609.
20. Pazos, A.; Hoyer, D.; Palacios, J. M. Eur. J. Pharmacol.
1985, 106, 539.
6.3. Behavioral studies
All experiments were carried out during 13:00–19:00.
Rats were placed individually in transparent acrylic
plastic cages to count the number of penile erections.
A penile erection was defined as previously described24:
repeated pelvic thrusts immediately followed by assum-
ing an upright position (on hind limbs), an emerging, en-
gorged penis, and licking it. The number of penile
erections was observed for 30 min immediately after test
compounds sc or po administration.
21. Lowry, O. H.; Rosebrough, N. J.; Farr, A. L.; Randall, R.
J. J. Biol. Chem. 1951, 193, 265.
22. Cheng, Y. C.; Prussoff, W. H. Biochem. Pharmacol. 1973,
22, 3099.
Acknowledgment
The authors are grateful to the staff of the Division of
Analytical Science Laboratories for the elemental analy-
sis and spectral measurements.
23. Aramori, I.; Nakanishi, S. Neuron 1992, 8, 757.
24. Berendsen, H. H. G.; Gower, A. J. Neuroendocrinology
1986, 42, 185.