Discovery of thiochroman derivatives bearing a carboxy-containing side chain as orally active pure antiestrogens

Article abstract of DOI:10.1016/j.bmcl.2006.04.090

In order to search for alternatives to the sulfoxide moiety in the long side chain of pure antiestrogens, several molecules that may interact with water in a fashion similar to ICI164,384 were designed and it was found that compounds with the carboxy, the

Full text of DOI:10.1016/j.bmcl.2006.04.090

Bioorganic & Medicinal Chemistry Letters 16 (2006) 4090–4094
Discovery of thiochroman derivatives bearing a carboxy-containing
side chain as orally active pure antiestrogens
Yoshitake Kanbe,a,* Myung-Hwa Kim,a Masahiro Nishimoto,a Yoshihito Ohtake,a
Toshiaki Tsunenari,a Kenji Taniguchi,a Iwao Ohizumi,a Shin-ichi Kaiho,a
Yoshiaki Nabuchi,a Setsu Kawata,a Kazumi Morikawa,a Jae-Chon Jo,b
Hee-An Kwon,b Hyun-Suk Limb and Hak-Yeop Kimb
aFuji Gotemba Research Laboratories, Chugai Pharmaceutical Co., Ltd, 1-135, Komakado, Gotemba, Shizuoka 412-8513, Japan
bC&C Research Laboratories, 146-141, Annyung, Taean, Hwasung, Kyunggi 445-976, Republic of Korea
Received 2 March 2006; revised 18 April 2006; accepted 28 April 2006
Available online 18 May 2006
Abstract—In order to search for alternatives to the sulfoxide moiety in the long side chain of pure antiestrogens, several molecules
that may interact with water in a fashion similar to ICI164,384 were designed and it was found that compounds with the carboxy,
the sulfamide, or the sulfonamide instead of the sulfoxide moiety also functioned as pure antiestrogens. Interestingly, the compound
possessing the carboxy moiety showed superior antiestrogen activity compared to ICI182,780 when dosed orally. Results of the
pharmacokinetic evaluation indicated that the potent antiestrogen activity at oral dosing attributed to both the improved absorption
from the intestinal wall and the metabolic stability of the compound in liver.
ꢀ 2006 Elsevier Ltd. All rights reserved.
The effects of pure antiestrogens such as ICI182,780,
ICI164,384, and ZM189,154 on estrogen receptor posi-
tive breast tumor are well documented.1–4 In particular,
ICI182,780 demonstrated effectiveness in postmeno-
pausal women with advanced breast cancer progression
after tamoxifen therapy in clinical trials,5–7 and was
launched in 2002 as an intramuscular injection drug.
In the course of our research to develop pure antiestro-
gens, we found thiochroman and chroman derivatives 1
and 2 also functioned as pure antiestrogens,8 having
in vitro/in vivo antiestrogen activities similar to
ICI182,780. One of the structural features of these pure
antiestrogens is the presence of the sulfoxide or the
amide moiety (Fig. 1), and to our knowledge, no alter-
native to these moieties in the long alkyl side chain
has been reported to date. We speculated that com-
pounds 1, 2, ZM189,154, and ICI182,780 would bind
to estrogen receptor ligand binding domain (ER-LBD)
in a fashion similar to ICI164,384 (PDB entry: 1HJ1),9
where the side chain would protrude from ER-LBD,
the sulfoxide moiety would make hydrophilic interac-
tion with water, and the terminal hydrophobic moiety
would be buried in the AF-2 cleft on the surface of
ER-LBD.
In this study, several molecules with different moieties in
the side chain that might interact with water as alterna-
tives to the sulfoxide or the amide moiety were first
designed and evaluated to ascertain whether thiochro-
man or chroman derivatives having these moieties
functioned as pure antiestrogens. After confirming the
pure antiestrogen activity of the thiochroman derivative
having the carboxy moiety, optimization of the total
length of the side chain and the position of the carboxy
moiety was carried out.
The thiochroman and chroman derivatives were
prepared according to the methods described by this
laboratory10,11 and are summarized in Schemes 1–3. In
preparation of thiochroman derivatives 6, 7, 10, and
11 (Scheme 1), a nucleophilic 1,2-addition to ketone
3a12 and 3b12 with lithiated alkyne derivatives, reduction
with NaBH3CN in the presence of ZnI2, and subsequent
catalytic hydrogenation afforded the 4-alkyl derivatives
Keywords: Pure antiestrogen; Thiochroman; Chroman; Estrogen
receptor.
*
Corresponding author. Tel.: +81 550 87 3416; fax: +81 550 87
3637; e-mail: kanbeyst@chugai-pharm.co.jp
0960-894X/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.04.090

Y. Kanbe et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4090–4094
OH OH
4091
O
O
S
CF2CF3
HO
(CH2)7
HO
(CH2)8
N
Me
ICI182,780
ICI164,384
O
S
O
S
F3CF2C
OH
F3CF2C
OH
(CH2)7
(CH2)7
HO
HO
X
1: X = S
2: X = O
ZM189,154
Figure 1. Structure of representative antiestrogens.
R2O2C
(CH2)3CF2CF3
(CH2)8
(CH2)8OTBS
(CH2)8OMs
OMe
OH
OMe
f,g,h,i,j
d,e
a,b,c
MeO
S
HO
S
MeO
S
6 : R2 = H
OR1
5
4a:R1 = Me
O
S
k
7 : R2 = Me
R1O
O2
S
(CH2)3CF2CF3
OH
3a:R1 = Me
3b:R1 = MOM
(CH2)9OTBS
HN
(CH2)9NH2
OR1
OR1
(CH2)9
a,b,c
d,e,l,m
n,j
R1O
S
R1O
S
HO
S
9a:R1 = Me
8a:R1 = Me
8b:R1 = MOM
10
9b:R1 = MOM
O
O2
S
o,p,q
N
H
(CH2)3CF2CF3
OH
HN
(CH2)9
HO
S
11
Scheme 1. Reagents and conditions: (a) HCꢀC–(CH2)nÀ2OTBS, n-BuLi, THF, À20 to 0 ꢁC; (b) ZnI2, NaBH3CN, 1,2-dichloroethane, 0 ꢁC to rt;
(c) 10% Pd–C, H2, 0.2 N NaHCO3 aq, THF, rt, then cis/trans separation with column chromatography; 34–44% from 3a or 3b; (d) TBAF, THF,
rt, 93%–quant.; (e) MsCl, Et3N, CH2Cl2, rt, 94–98%; (f) NaI, acetone, reflux, 94%; (g) NaH, CF3CF2(CH2)3CH(CO2 Et)2, THF, 0 ꢁC to rt, 96%;
(h) KOH aq, EtOH, reflux, quant.; (i) DMSO, 140 ꢁC, 82%; (j) BBr3, CH2Cl2, À78 to À5 ꢁC (R1 = Me), 72–89%; (k) diazomethane, Et2O, 0 ꢁC, 78%;
(l) NaN3, DMF, rt, 86–87%; (m) 10% Pd–C, H2, MeOH, rt, 97%–quant.; (n) CF3CF2(CH2)3SO2Cl, Et3N, CH2Cl2, 0 ꢁC, 80%; (o) ClCO2Ph, pyridine,
THF, rt; (p) CF3CF2(CH2)3SO2NH2, K2CO3, DMF, 70 ꢁC; (q) 6 N HCl aq, MeOH, 70 ꢁC (R1 = MOM), 47% from 9b.
as a mixture of (3RS,4RS)- and (3RS,4SR)-isomers, in
which (3RS,4RS)-isomers 4a, 8a, and 8b were dominant
and separated with column chromatography. The rela-
tive configuration at the 3- and 4-positions was deter-
mined based on NOESY 2D NMR spectroscopy
described by this laboratory.8 Carboxy derivative 6
was obtained as a mixture of diastereomers from mesy-
late 5 by iodination followed by alkylation with 2-perflu-
oroalkyl malonate and subsequent decarboxylation and
deprotection. Methyl ester 7 was prepared from carboxy
derivative 6. Sulfonamide 10 and sulfonylurea 11 were
prepared from amine 9a and 9b by condensation with
perfluoroalkyl sulfonyl chloride and subsequent depro-
tection, and by treatment with phenyl chloroformate,
reaction with perfluoroalkyl sulfonamide and deprotec-
tion, respectively. The chroman derivatives were
prepared using a similar procedure (Scheme 2). 4-Alkyl
chroman derivative 13, the (3RS,4RS)-isomer obtained
as the major product from catalytic hydrogenation,
was converted to amine 14. Sulfamide 15 was prepared
from amine 14 by treatment with tert-butyl N-(chloro-
sulfonyl)carbamate followed by Mitsunobu reaction
with perfluoroalkyl alcohol and subsequent deprotec-
tion. Urea derivative 16 was prepared by reacting amine
14 with phenyl N-(perfluoroalkyl)carbamate followed by
deprotection. In optimizing carboxy-containing side
chains, the thiochroman derivatives in Table 4 were
prepared from ketone 3a through metathesis as the
key reaction11 (Scheme 3). Reduction of ketone 3a with
LAH followed by allylation with allyl trimethylsilane

4092
Y. Kanbe et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4090–4094
O2
S
(CH2)3CF2CF3
OH
HN
N
H
(CH2)9
g,h,i
(CH2)9OTBS
(CH2)9NH2
HO
O
OMOM
OMOM
OMOM
O
15
O
c,d,e,f
a,b
(CH2)3CF2CF3
OH
MOMO
O
MOMO
O
MOMO
O
HN
N
H
j,k
12
13
14
(CH2)9
HO
O
16
Scheme 2. Reagents and conditions: (a) HCꢀC–(CH2)7OTBS, n-BuLi, THF, À20 to 0 ꢁC, 94%; (b) 10% Pd–C, H2, AcOEt, rt, then cis/trans
separation with column chromatography, 57–63%; (c) PPTS, MeOH, rt, quant.; (d) MsCl, Et3N, CH2Cl2, rt, 97%; (e) NaN3, DMF, 50 ꢁC, 93%; (f)
10% Pd–C, H2, MeOH, rt, quant.; (g) ClSO2NHBoc (prepared from ClSO2NCO and t-BuOH), Et3N, CH2Cl2, À78 ꢁC to rt, 36%; (h)
CF3CF2(CH2)3OH, PPh3, DEAD, CH2Cl2, rt, 67%; (i) TFA, CH2Cl2, rt, 54%; (j) CF3CF2(CH2)3NHCO2Ph, K2CO3, MeCN, 70 ꢁC, 67%; (k) PPTS,
MeOH, reflux, 26%.
HO2C
(CH2)m(CF2)lF
(CH2)n
EtO2C
(CH2)m(CF2)lF
(CH2)n
OMe
OMe
O
OH
e,f
OMe
a,b
c,d
MeO
S
MeO
S
HO
S
MeO
S
19a-j
3a
17
18
Scheme 3. Reagents and conditions: (a) LAH, THF, À78 ꢁC; (b) allyl trimethylsilane, ZnI2, 1,2-dichloroethane, 40 ꢁC to rt, 68% from 3a; (c)
CH2@CH(CH2)nÀ3CH(CO2Et)(CH2)m(CF2)lF, benzylidenebis(tricyclohexylphosphine) dichlororuthenium, CH2Cl2, reflux; (d) 10% Pd–C, H2,
AcOEt, rt, 52–72% from 17; (e) BBr3, CH2Cl2, À78 to 0 ꢁC, 84–92%; (f) NaOH aq, EtOH, reflux, 70–93%.
and ZnI2 yielded (3RS,4RS)-4-allyl thiochroman deriva-
tive 17. Ruthenium catalyzed metathesis of allyl thioch-
roman derivative 17 with a variety of alkene derivatives
and subsequent catalytic hydrogenation and deprotec-
tion afforded thiochroman derivatives 19a–j.
as pure antiestrogens, and that the carboxy, the sulfon-
amide, and the sulfamide moieties could be alternatives
to the sulfoxide moiety. Noteworthy is that compound 6
exhibited oral antiestrogen activity superior to com-
pound 1 and ICI182,780 in spite of its lower affinity
for ERa. On the other hand, compounds 11 and 16,
which have the sulfonylurea and the urea moiety,
respectively, displayed both agonist and antagonist
activities with subcutaneous administration, indicating
these compounds are partial agonists. We speculated
that compounds 6, 10, and 15 would bind to ERa-
LBD similar to ICI164,384, suggesting these compounds
are pure antiestrogens. In contrast, the binding mode of
compounds 11 and 16 would be somewhat different,
suggesting these compounds to be partial agonists. As
has been often observed with estrogen ligands, subtle
differences in structure may be critical factors to
determine whether the compounds function as pure
antiestrogens or as partial agonists.
The thiochroman and chroman derivatives thus pre-
pared were assayed in vitro and in vivo to characterize
their biological profiles. In vitro, binding affinity for
ERa was determined by displacement of [3H]estradiol
with the test compound utilizing human recombinant
ERa-LBD. In vivo, estrogen agonist and antagonist
activities were measured by the ability of the test com-
pound to increase the uterine weight and to inhibit
estrogen-stimulated uterine weight gain in an ovariecto-
mized mouse model, respectively.
Based on our speculation that the sulfoxide moiety of
compounds 1 and 2 would make hydrophilic interaction
with water in a fashion similar to ICI164,384,9 several
molecules containing the carboxy, the ester, the
sulfonamide, the sulfamide, the sulfonylurea, and the
urea moieties as alternatives to the sulfoxide moiety
were designed. As can be seen in Table 1, subcutaneous
administration of compounds 6, 10, and 15 at 10 mg/kg
almost completely inhibited estrogen-induced uterine
weight gain and exhibited no significant uterine weight
gain when dosed alone compared to vehicle. These
results indicate that compounds 6, 10, and 15 functioned
The remarkable antiestrogen activity of orally adminis-
tered compound 6 was intriguing because its binding
affinity for ERa was less than 1/100 of compound 1
and ICI182,780. To explore the reason for high activity,
investigations into the absorption from the intestinal
wall and the metabolic stability in liver in a rat model
in which the test compound was administered into
duodenum were carried out. The areas under the
concentration–time curve (AUC) in portal vein and

Y. Kanbe et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4090–4094
Table 1. Biological data of thiochroman and chroman derivatives
4093
Compound
RBAa (%) E2 = 100
Antiestrogen activityb (% inhibition)
Estrogen activityc (% uterine weight gain)
10 mg/kg sc
10 mg/kg po
50 mg/kg po
10 mg/kg sc
6
0.8
7
95
52
77
40
31
n.t.
41
1
94d
n.t.
73
1*
À1
3*
7
10
52
99
33
11
15
1.2
42
n.t.
69
8
1*
100
77
16
1
57
n.t.
94
10
À2*
200
96
101
94
51
66
54
2
ICI 182,780
88
86
1*
138
95
À1*
n.t., not tested.
a Relative binding affinities for the recombinant estrogen receptor (ERa), determined by competitive radiometric binding assay with [3H]estradiol.
b Inhibition of estrogen-stimulated uterine weight gain by the test compound with subcutaneous (sc) or oral (po) administration.
c Stimulation of uterine weight gain by the test compound with sc administration.
d 30 mg/kg.
* No significant difference between the test group and the vehicle group at P < 0.05 using Student’s t test.
peripheral blood within 30 min. after administration
were measured (Table 2). The AUC of compound 6 in
portal vein was 29- and 45-fold higher than compound
1 and ICI182,780, respectively, and this high AUC level
was well maintained in peripheral blood, also. These
outstanding parameters in absorption and the metabolic
stability were surprising and encouraged us to
investigate its pharmacokinetic profile in greater detail.
Table 3 summarizes the pharmacokinetic data in rats.
As can be seen, compound 6 exhibited 58-fold and
125-fold higher AUC in po, and 1/26 and 1/42 lower
clearance in iv than compound 1 and ICI182,780,
respectively. These results, together with the results in
Table 2, indicated that the absorption from intestinal
wall and metabolic stability in liver of compound 6 are
superior to compound 1 and ICI182,780, and lead to
the remarkable antiestrogen activity of compound 6
administered orally. Factors effecting the absorption
and metabolic stability of compound 6 require further
investigation. However, it is noteworthy that although
compounds 1, 6, and ICI182,780 are all highly lipophil-
ic, their Prolog D at pH 7.0 predictions being 8.18, 7.44,
and 8.44, respectively, only compound 6 exhibited im-
proved characteristics in absorption and metabolic
stability.
After confirming that the thiochroman derivative having
the carboxy moiety exhibited remarkable antiestrogen
activity with oral administration, side-chain optimiza-
tion was next carried out (Table 4). Oral antiestrogen
activities of compounds 19a, 6, 19g, and 19j, which have
7-, 8-, 9-, and 10-methylene between the scaffold and the
carboxy moiety, respectively, were first investigated, and
8- and 9-methylene groups were found optimal. Next a
variety of perfluoroalkyl moieties into the terminal of
compounds 6 and 19g were incorporated. As can be seen
in Table 4, compound 19g derivatives, 19f, 19h, and 19i
showed oral antiestrogen activities similar to compound
19g, whereas the oral antiestrogen activities of com-
pound 6 derivatives, especially compounds 19b, 19c,
and 19d, were approximately 2- or 3-fold superior to
that of compound 6. The clear correlation between the
binding affinity for ERa and oral antiestrogen activity
was not observed within the compounds prepared. The
reason has not been fully investigated; however, it is
speculated that thiochroman derivatives 19b–i may
possess high absorption and metabolically stable
pharmacokinetic profiles similar to compound 6, and
the potent oral activities might be mainly due to absorp-
tion and metabolism rather than their binding affinities.
Although the factors effecting oral antiestrogen activities
remained to be further investigated, oral antiestrogen
activities were improved approximately 2- to 3-fold
from the initial lead compound 6 in the course of the
side-chain optimization. In addition, it was confirmed
Table 2. AUC in portal vein and peripheral blood for 30 min after
duodenal administrationa
Compound
AUC in
portal veinb
(ng · h/mL)
AUC in
peripheral bloodc
(ng · h/mL)
6
2509
88
2041
13
1
ICI182,780
56
7
a Compound dosed into duodenal in Sprague–Dawley rats as a solu-
tion in water/PEG200/EtOH (3:6:1).
b AUC of the test compound in portal vein from 0 to 30 min after
duodenal dosing of 10 mg/kg.
c AUC of the test compound in peripheral blood from 0 to 30 min after
duodenal dosing of 10 mg/kg.
Table 3. Pharmacokinetic data in ratsa
Compound
iv administration 10 mg/kg
AUC (lg · h/mL)
Cltotb (mL/h/kg)
228
8.22
5.30
po administration 20 mg/kg
Bioavailability (%)
AUC (lg · h/mL)
6
47
1240
1969
209
46
22
16
1
ICI 182,780
3.59
1.67
a Compound dosed in Sprague–Dawley rats as a solution in water/PEG200/EtOH (3:6:1) for iv and po dosing.
b Total clearance.

4094
Table 4. Biological data of thiochroman derivatives 6 and 19a–19j
HO2C
Y. Kanbe et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4090–4094
(CH2)m(CF2)lF
(CH2)n
OH
Me
HO
S
Compound
n
m
l
RBAa (%) E2 = 100
Antiestrogen activityb (% inhibition)
3 mg/kg po
10 mg/kg po
30 mg/kg po
19a
19b
6
7
8
8
8
8
8
9
9
9
9
3
2
3
3
4
5
2
3
3
4
3
2
4
2
4
2
2
4
2
4
2
2
0.5
0.6
0.8
0.3
1.3
0.8
0.3
0.9
0.4
0.2
0.2
138
n.t.
63
41
61
69
52
38
45
55
53
n.t.
29
20
93
77
93
87
86
85
81
86
79
62
54
n.t.
96
94
99
19c
19d
19e
97
94
19f
99
19g
19h
19i
n.t.
100
96
19j
ICI182,780
10
n.t.
72
n.t., not tested.
a Relative binding affinities for the recombinant estrogen receptor (ERa), determined by competitive radiometric binding assay with [3H]estradiol.
b Inhibition of estrogen-stimulated uterine weight gain by the test compound with po administration.
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effects (unpublished data).
In summary, it was found that the carboxy, the sulfon-
amide, and the sulfamide moieties functioned as alterna-
tives to the sulfoxide moiety in the long side chain of
pure antiestrogens. Surprisingly, compound 6, wherein
the sulfoxide moiety is replaced with the carboxy moie-
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Acknowledgments
The authors thank Frances Ford and Dr. Paul Langman
of Chugai Pharmaceutical Co., Ltd. for their assistance
with English usage.
References and notes
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