Design and synthesis of a selective EP4-receptor agonist. Part 1: Discovery of 3,7-dithiaPGE1 derivatives and identification of their ω chains

Article abstract of DOI:10.1016/S0968-0896(01)00351-0

Improvement of EP4-receptor selectivity and the agonist activity by introduction of heteroatoms into the α chain of PGE₁ was investigated. Among the compounds tested, 3,7-dithiaPGE₁ 4a exhibited good EP4-receptor selectivity and agonist activity. Further modification of the ω chain of 3,7-dithiaPGE₁ was performed to improve EP4-receptor selectivity and agonist activity. Of the compounds produced, 16-phenyl-ω-tetranor-3,7-dithiaPGE₁ 4p possessing moderate EP4-receptor selectivity and agonist activity, was identified as a new chemical lead for further optimization by modification of the aromatic moiety. Copyright

Full text of DOI:10.1016/S0968-0896(01)00351-0

Bioorganic & Medicinal Chemistry 10 (2002) 975–988
Design and Synthesis of a Selective EP4-Receptor Agonist.
Part 1: Discovery of 3,7-DithiaPGE1 Derivatives and
Identification of Their ! Chains
Toru Maruyama,* Masaki Asada, Tai Shiraishi, Hiromu Egashira, Hideyuki Yoshida,
Takayuki Maruyama, Shuichi Ohuchida, Hisao Nakai, Kigen Kondo and Masaaki Toda
Minase Research Institute, Ono Pharmaceutical Co., Ltd., Shimamoto, Mishima, Osaka 618-8585, Japan
Received 6 August 2001; accepted 4 October 2001
Abstract—Improvement of EP4-receptor selectivity and the agonist activity by introduction of heteroatoms into the a chain of
PGE1 was investigated. Among the compounds tested, 3,7-dithiaPGE1 4a exhibited good EP4-receptor selectivity and agonist
activity. Further modification of the o chain of 3,7-dithiaPGE1 was performed to improve EP4-receptor selectivity and agonist
activity. Of the compounds produced, 16-phenyl-o-tetranor-3,7-dithiaPGE1 4p possessing moderate EP4-receptor selectivity and
agonist activity, was identified as a new chemical lead for further optimization by modification of the aromatic moiety. # 2002
Elsevier Science Ltd. All rights reserved.
Introduction
Chemical modification of 3 was carried out with the
introduction of another heteroatom into the a chain and
further chemical development (Scheme 1). In this
report, we describe identification and biological
evaluation of 3,7-dithiaPGE1 derivatives as new selective
EP4-receptor agonists. Structure–activity relationships
(SARs) are also discussed.
Prostaglandins have been known to have diverse biolo-
gical activities that are mediated by all the receptor
subtypes.1 The EP4-receptor subtype, which is located
in thymus, lung, heart, kidney, bone, womb, liver and
other organs, has been characterized with relaxation of
the porcine and dog saphenous vein and of the rabbit
jugular vein.2 The biological effects have been con-
sidered to be correlated with an enhancement of the
intracellular cAMP concentration. Novel biological
roles of the EP4-receptor are expected to be revealed by
experiments using subtype selective ligands. Some PG
congeners have been used as probes for EP4-receptor
ligands,3 however, their subtype selectivities were poor.
As such, identification of a highly selective EP4-receptor
agonist is an attractive approach to disclose the biolo-
gical role of the EP4-receptor and develop clinically
useful drugs.
Chemistry
The 7-thiaPGE analogues described here were synthe-
sized according to the method4 reported previously with
minor modifications. Synthesis of 4,7-dithiaPGE1 is
outlined in Scheme 2. Monoalkylation of ethanedithiol
6 afforded 7. Ring opening reaction of the epoxide 84
with 7 followed by dehydration provided 9. Conjugate
addition reaction of higher order vinyl cuprate prepared
from commercially available vinyliodide 10a and
lithium (2-thienyl)cyanocuprate5 to the enone 9 gave 11.
Deprotection of t-butyldimethylsilyl (TBS) groups of 11
afforded 12. Enzymatic hydrolysis of 12 with porcine
liver esterase (PLE) in phosphate buffer provided 13.
In the course of a screening program to find an EP4-
receptor selective agonist, 7-thia PGE1 derivative 3 was
found to exhibit potent affinity for EP4-receptor
although it also showed affinities for other receptors.
Synthesis of 3,6-dithiaPGE1 19 is outlined in Scheme 3.
Treatment of 1,2-ethanedithiol 6 with dibutyltin oxide
in benzene afforded 14, monoalkylation of which pro-
*Corresponding author. Tel.: +81-75-961-1151; fax: +81-75-962-
9314; e-mail: to.maruyama@ono.co.jp
0968-0896/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(01)00351-0

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T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
vided 15. Conjugate addition of 15 to the enone 165,6 in
the presence of piperidine gave 17, TBS groups of which
were deprotected to afford 18. Enzymatic hydrolysis of
18 provided 3,6-dithiaPGE1 19.
Synthesis of 3-oxa-7-thiaPGE1 is outlined in Scheme 4.
O-Alkylation of 3-bromopropanol 20 afforded 21, sub-
stitution of which with thiourea followed by hydrolysis
provided the thiol 22. Ring opening of the epoxide 8
with 22 in the presence of alumina afforded 23, which
was converted to 26 according to the same procedures
as described for the synthesis of 13 from 9.
Syntheses of 3,7-dithiaPGE1 are outlined in Schemes 5
and 6. Treatment of 1,3-propanedithiol 27 with dibu-
tyltin oxide in benzene afforded 28, monoalkylation of
which with methyl bromoacetate provided 29. Ring
opening reaction of the epoxide 8 with the thiol 29 fol-
lowed by dehydration provided 30. Compound 30 was
converted to 4a–r and 36a–c according to the same
procedure as described for the synthesis of 13.
The optically active vinyl iodides 10 were prepared from
racemic allyl alcohols by the Sharpless kinetic resolu-
tion,7 except for the commercially available product.
Results and Discussion
The effects of introduction of heteroatom(s) such as
oxygen and sulfur atoms into the a chain of PGE1 on
EP4-receptor selectivity and agonist activity were inves-
tigated. Among the compounds tested, 3,7-dithiaPGE1
4a exhibited good EP4-receptor selectivity and agonist
Scheme 1. Discovery of 16-phenyl-o-tetranor-3,7-dithiaPGE1 4p.
Scheme 2. Synthesis of 4,7-dithiaPGE1 13. Reagents: (a) methyl acrylate, piperidine, EtOH; (b) 8, alumina, hexane; (c) 10a, t-BuLi, lithium 2-thie-
nylcyanocuprate, THF, ether; (d) (HF)n-py, pyridine, CH3CN; (e) PLE, EtOH, phosphate buffer.
Scheme 3. Synthesis of 3,6-dithiaPGE1 20. Reagents: (a) dibutyltinoxide, benzene; (b) methyl bromoacetate, DMF; (c) piperidine, MeOH; (d)
(HF)n-py, pyridine, CH3CN; (e) PLE, EtOH, phosphate buffer.

T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
977
Scheme 4. Synthesis of 3-oxa-7-thiaPGE1 26. Reagents: (a) methyl bromoacetate, NaH, DMF; (b) thiourea, EtOH, then 1 N NaOH, 1 N HCl; (c) 8,
alumina, hexane; (d) 10a, t-BuLi, lithium 2-thienylcyanocuprate, ether, THF; (e) (HF)n-py, pyridine, CH3CN; (f) PLE, EtOH, phosphate buffer.
Scheme 5. Synthesis of 3,7-dithiaPGEs 4a–r. Reagents: (a) dibutyltinoxide, benzene; (b) methyl bromoacetate, DMF; (c) 8, alumina, hexane; (d) 10,
t-BuLi, lithium 2-thienylcyanocuprate, ether, THF; (e) (HF)n-py, pyridine, CH3CN; (f) PLE, EtOH, phosphate buffer.
Scheme 6. Synthesis of 3,7-dithiaPGE1 possessing miscellaneous o chain 36a–c. Reagents: (a) 33a–c, t-BuLi, lithium 2-thienylcyanocuprate, ether,
THF; (b) (HF)n-py, pyridine, CH3CN; (c) PLE, EtOH, phosphate buffer.

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T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
activity as shown in Table 1. Although the selectivity
(KiEP3/KiEP4) was excellent, 4a showed potent EP3-
receptor agonist activity for its described Ki value. Che-
mical modification of the o chain of 3,7-dithiaPGE1 was
continued to further improve both of EP4-receptor
selectivity and agonist activity. Of the resulting com-
pounds, 16-phenyl-o-tetranor-3,7-dithiaPGE1 4p with
moderate EP4-receptor selectivity and agonist activity
was identified as a new chemical lead for further opti-
mization because of the ease of further modification of
its aromatic moiety (Scheme 1).
7-thiaPGE1 analogue 3 exhibited better EP4-receptor
selectivity than PGE1 2 or PGE2 1. As shown in Table 1,
7-thiaPGE1 demonstrated affinity not only to the EP3-
receptor but also to the IP-receptor. For its relatively
weak affinity (Ki=870 nM) to the IP-receptor, 3 showed
potent agonist activity (EC50=26 nM). Since both of
the subtypes (EP4 and IP) are involved in increases in
intracellular cAMP concentration, it was important to
remove the IP-receptor agonist activity in 3 to disclose
the physiological roles of the EP4-receptor. According
to our internal data,9 3-thiaPGE1 did not show affinity
to the IP-receptor at 10 mM. As such, structural hybri-
dization of these thiaPGE analogues was expected to be
effective to remove the IP-receptor affinity from 7-
thiaPGE1 analogues.
Binding assay was conducted according to the reported
method8 with minor modifications. The binding con-
stants were determined by competitive binding assay of
the test compounds using radiolabeled ligands such as
[3H] PGE2 (EP-receptors) and [3H] Iloprost (IP-recep-
tor).
Introduction of another sulfur atom into position-3 of 3
provided 4a with no affinity to the IP-receptor. Besides,
4a was found to demonstrate a markedly increased EP4-
receptor selectivity maintaining excellent EP4-receptor
agonist activity. On the other hand, the corresponding
3-oxa-analogue 26 exhibited less EP4-receptor selectiv-
ity. As illustrated in the profile of 13, introduction of
another sulfur atom into position-4 of 3 did not
improve the EP4-receptor selectivity to the EP3-recep-
tor (KiEP3/KiEP4=1.3) with marked loss of the agonist
activity. Shifting the sulfur atom at position-7 of 4a to
position-6 (19) resulted in marked reduction of the
Agonist activities of the compounds for EP4-receptor
and EP3-receptor were evaluated based on their effects
on intracellular cAMP production using EP4-receptor
expressing CHO cells and on intracellular Ca2+ con-
centration using EP3-receptor expressing CHO cells,
respectively.
We began our molecular design with introduction
of heteroatoms into the a chain of PGE1 because
Table 1. Optimization of a chain
Compound
R
Binding Ki (nM)
mEP2mEP3 mEP4
EC50 (nM)
mEP1
6.0
hlP
mEP4
4
1
2
22
41
5.0
5.0
3.1
3.3
>10
3.6
2.5
22
120
610
50
150
870
3
100
1200
1000
150
4.5
4.4
3.5
0.7
3.2
3.7
170
7800
7.7
13
19
26
4a
>104
>104
510
28
1200
610
11
2.3
0.7
280
220
>104
4.3
Using membrane fractions of CHO cells expressing the prostanoid receptors, the mouse (m) EP-receptor or human (h) IP-receptor, Ki values were
determined by competitive binding assay, which was performed according to the method of Kiriyama et al. with some modifications.8 With regard to
the subtype-receptor agonist activity, EC50 values were determined based on the effects of the test compounds on the increase in intracellular cAMP
production in EP4 receptor expressing cells.

T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
979
agonist activity. The EP4-receptor selectivity was also
markedly deteriorated (KiEP3/KiEP4=0.13). The EP1 and
EP3 receptor affinities were restored by this modification.
3,7-DithiaPGE1 4a seemed to be the most potent and most
selective of the series as described in Table 1. However, the
EP3-receptor agonist activity of 4a (EC50=1.1 nM) was
fairly potent for its described Ki value. Thus, the a chain
with a 3,7-dithia moiety might be one of the most pro-
mising entries for chemical synthesis for the develop-
ment of selective EP4-receptor agonists.
tion to find a new EP4-receptor agonists. Detailed
structural modification of the o chain in 4a led to the
discovery of a new chemical lead 4p, which demon-
strated a balanced profile with regard to receptor selec-
tivity, agonist activities17 (EC50: EP3=530 nM,
EP4=34 nM) and the ease of further modification of
the phenyl moiety as illustrated in Scheme 7. Further
optimization of 4p to obtain more potent and selective
EP4-receptor agonists will be reported in the following
paper.
For the purpose of further optimization of the EP4-
receptor agonist, we focused our attention on chemical
modification of the o chain of 4a because there have
been many successful examples of o-chain modification
to improve biological activities of PG derivatives. As
described in Table 2, replacement of the 15-n-pentyl
moiety with a butyl, hexyl, 4-pentenyl and 3-cyclopro-
pylpropyl groups afforded 4b, 4c, 4d and 4e, respec-
tively. All four analogues demonstrated increased EP3-
receptor affinity relative to 4a, while they showed simi-
lar EP4-receptor affinity. Their EP4-receptor agonist
activity was not markedly affected by this chemical
modification except in the case of 4c. Introduction of a
16(S)- or 16(R)-methyl moiety10 into 4a provided 4f and
4g, respectively, which decreased the EP4-receptor
selectivity although they retained potent agonist activ-
ity. In the case of 16(S)-methyl derivative 4f, however,
EP4-receptor selectivity (KiEP3/KiEP4) was preserved
to some extent. Reduction of the EP4-receptor selectiv-
ity was also observed by the introduction of a 17(R)- or
17(S)-methyl moiety.4,11 Replacement of the 15-pentyl
moiety of 4a with a 3-methylbutyl or 2-ethylbutyl group
afforded 4j and 4k, respectively, without improvement
of the EP4-receptor selectivity especially to the EP3-
receptor. Both the 15-cyclopentyl and 15-cyclohexyl4,12
derivatives 4l and 4m demonstrated the most reduced
EP4-receptor affinity and agonist activity. 16-Cyclo-
pentyl and 16-cyclohexyl derivatives 4n and 4o exhibited
6-fold less potent EP4-receptor affinity than 4a without
improvement of their EP4-receptor selectivity to their
EP3-receptor. 16-Phenyl derivative13 4p demonstrated
moderate EP4-receptor selectivity with moderate ago-
nist activity. 17-Phenyl derivative14 4q and 16-phenoxy
derivative15 4r showed more potent affinity for the EP3-
receptor than the EP4-receptor.
Scheme 7. Plausible modification of the aromatic moiety of 4q.
Experimental
General procedures
Analytical samples were homogeneous as confirmed by
TLC, and afforded spectroscopic results consistent with
the assigned structures. Proton nuclear magnetic reso-
nance spectra (1H NMR) were obtained on a Varian
Gemini-200 or VXR-200s spectrometer using deuter-
ated chloroform (CDCl3) or deuterated methanol
(CD3OD) as the solvent. Fast atom bombardment mass
spectra (FAB-MS) and electron ionization (EI) were
obtained on a JEOL JMS-DX303HF spectrometer.
Atmospheric pressure chemical ionization (APCI) was
determined on a Hitachi M1200H spectrometer. Infra-
red spectra (IR) were measured on a Perkin-Elmer FT-
IR 1760Â spectrometer. Melting points and results of
elemental analyses were uncorrected. Column chroma-
tography was carried out on silica gel [Merck silica gel
60 (0.063–0.200 mm), Wako gel C200 or Fuji Silysia
BW235]. Thin layer chromatography was performed on
silica gel (Merck TLC or HPTLC plates, silica gel 60
F254). The following abbreviations for solvents and
reagents are used: tetrahydrofuran (THF), ethyl acetate
(EtOAc), dimethylformamide (DMF), dichloromethane
(CH2Cl2), chloroform (CHCl3), methanol (MeOH),
acetic acid (AcOH), pyridinium poly(hydrogen fluoride)
.
13,14-Dihydro-3,7-dithiaPGE1 36a, 15(S)-methyl-3,7-
dithiaPGE1 derivative 36b and 16(R)-methyl-16(S)-
[(HF)n py, Aldrich], porcine liver esterase (PLE).
16
hydroxy-15-deoxy-3,7-dithiaPGE1 36c were prepared
Methyl 6-mercapto-4-thiahexanate 7. To a stirred mix-
ture of 1, 2-ethanedithiol (1.17 g, 12.4 mmol) and methyl
acrylate (1.67 mL, 18.6 mmol) was added piperidine
(0.05 mL) at room temperature (exothermic). Stirring
was continued for 5 min until the exothermic reaction
subsided. The reaction mixture was directly subjected to
column chromatography on silica gel (EtOAc/hexane,
1:10–1:7) to afford 7 as a colorless oil (1.06 g, 47%). H
NMR (200 MHz, CDCl3) d 3.72(s, 3H), 2.85–2.60 (m,
8H).
and biologically evaluated (Table 3). Hydrogenation of
the 13,14-double bond of 4a gave 36a with a marked
increase in EP3-receptor affinity, while its agonist activ-
ity was less potent than 4a. Introduction of a 15(S)-
methyl group into 4a provided 36b, which showed
reduced EP3/EP4-receptor selectivity. Shifting the two
functional groups of position-15 in 36b to position-16
afforded 36c without improvement of the selectivity
(KiEP3/KiEP4=1). Among them, 36b exhibited the
good EP4-receptor selectivity and agonist activity.
1
2-(6-Carbomethoxy-1, 4-dithiahexyl)-4-(R)-t-butyldime-
thylsilyloxy-2-cyclopentenone 9. A solution of epoxide 8
and thiol 7 (235 mg, 1.3 mmol) in hexane (10 mL) and
In summary, we have identified 3,7-dithiaPGE1 4a as a
unique chemical lead to restart our chemical modifica-

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T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
Table 2. Effect of the chemically modified o chain on biological activites
Compound
R
Binding Ki (nM)
mEP4
EC50 (nM)
4.3
mEP1
610
mEP2mEP3
280
hlP
mEP4
4a
4b
4c
4d
4e
4f
220
0.7
1.4
0.3
1.6
0.4
0.2
0.2
0.8
0.6
1.9
8.5
>104
>104
530
240
800
94
23
2.5
6.8
4.7
25
3.9
1100
24
2100
760
300
>104
10
130
Not tested
680
2.1
110
250
0.8
4g
4h
4i
3500
940
150
2.1
10
Not tested
350
1.4
83
1.4
15
110
4.5
22
220
18
4j
2500
250
840
Not tested
>104
32
4k
4l
540
50
140
600
1300
55
>104
1200
>104
610
3000
390
660
610
47
74
>104
4m
4n
4o
4p
4q
4r
22
1400
3900
7000
3900
>104
>104
4.2
>104
83
4.2
7
>104
140
34
2600
360
130
4.6
4.3
>104
6.0
>104
69
45
12
>104
Not
tested.

T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
Table 3. Biological evaluation of 3,7-dithia PGE1 possessing miscellaneous o chains
981
Binding Ki (nM)
mEP2mEP3 mEP4
EC50 (nM)
Compound
R
mEP1
310
hlP
mEP4
4
36a
1200
850
8.3
1.6
0.7
>10
84
36b
36c
310
34
>104
>104
2.2
>104
330
6.3
5.6
Not
tested
CH2Cl2 (1 mL) was stirred at room temperature in the
presence of activated alumina (1 g). After the reaction
was completed, alumina was removed by filtration and
washed repeatedly with CH2Cl2. The filtrate was eva-
porated and the residue was purified by column chro-
matography on silica gel (EtOAc/hexane, 1:5) to give 9
was washed with 1 N HCl, H2O and brine, and dried
over Na2SO4. After removal of the solvent by evapora-
tion, the residue was purified by column chromato-
graphy on silica gel (EtOAc/hexane, 1/1–3/1–1/0) to
1
give 12 as a pale brown oil (56 mg, 60%). H NMR
(200 MHz, CDCl3) d 5.8–5.6 (m, 2H), 4.5–4.4 and 4.25–
4.10 (m, 2H), 3.71 (s, 3H), 3.5–3.4 and 3.1–2.2 (m, 12H),
1.7–1.2(m, 8H), 0.90 (t, J=7 Hz, 3H).
1
as a colorless oil (389 mg, 77%). H NMR (200 MHz,
CDCl3) d 6.90 (d, J=2Hz, 1H), 5.0–4.9 (m, 1H), 3.72(s,
3H), 3.1–3.0 (m, 2H), 2.95–2.75 (m, 5H), 2.7–2.6 (m,
2H), 2.36 (d, J=18 Hz, 1H), 0.92(s, 9H), 0.16 (s, 6H).
4,7-DithiaPGE1 13. To a stirred mixture of 13 (54 mg,
0.13 mmol) in ethanol (1 mL) and phosphate buffer (pH
7.4, 5 mL) was added porcine liver esterase (PLE)
(Sigma, 20,000 U, 0.1 mL) at room temperature. The
reaction mixture was stirred vigorously for 1.5 h. The
resulting clear solution was poured into saturated aqu-
eous (NH4)2SO4 solution and then extracted with
EtOAc twice, dried (Na2SO4) and evaporated. Purifica-
tion by column chromatography on silica gel (EtOAc/
hexane, 1/1–EtOAc/hexane/AcOH, 30/10/1–EtOAc/
AcOH, 40/1) provided 13 as a pale yellow oil (48 mg,
95%). IR (neat) 3392, 2930, 2859, 1734, 1407, 1246,
4,7-DithiaPGE1 methyl ester 11,15-bis(t-butyldimethylsi-
lyl ether) 11. To a stirred solution of 3-(S)-t-butyldi-
methylsilyloxy-1-iodo-1-octene 10a (188 mg, 0.51 mmol)
in freshly distilled dry diethylether (4 mL) was slowly
added t-butyllithium (1.57 M in pentane, 0.65 mL,
1.02mmol) at À70 ꢀC under Ar and stirring was con-
tinued for 1 h at that temperature. To the resulting
suspension was added dropwise lithium 2-thienylcyano-
cuprate (0.25 M in THF, 2.0 mL, 0.51 mmol) in 5 min.
The gray suspension was stirred for an additional
25 min and 2-(6-carbomethoxy-3-oxa-1-thiahexyl)-4-
(R)-t-butyldimethylsilyloxy-2-cyclopentenone 9 (200 mg,
0.51 mmol) in THF (3 mL) was added dropwise in
8 min. The resulting yellowish mixture was allowed to
warm to À20 ꢀC over 1 h and then poured into a mix-
ture of hexane (10 mL) and saturated aqueous NH4Cl
(10 mL) under stirring. The separated organic layer was
washed with aqueous NH4Cl, H2O and brine, dried over
Na2SO4, and evaporated. The residue was purified by
column chromatography on silica gel (EtOAc/hexane,
1/10–1/6) to afford 11 as a pale yellow oil (151 mg,
1
1150, 1079, 969 cmÀ1; H NMR (200 MHz, CDCl3) d
5.85–5.55 (m, 2H), 4.8–4.0 (br, 3H), 4.25–4.05 (m, 2H),
3.55–3.45 and 3.2–2.2 (m, 12H), 1.7–1.2 (m, 8H), 0.91 (t,
J=7 Hz, 3H); MS (FAB) m/z 373 (MÀH2O+H)+.
2,2-Dibutyl-[1,3,2]dioxastannolane 14. A solution of 1,2-
ethanedithiol (1.0 g, 10.6 mmol) and dibutyltinoxide
(2.64 g, 10.6 mmol) in benzene (10 mL) was stirred under
reflux for 48 h. After the reaction was completed, the
solvent was removed by evaporation to give 14 as a
white solid (3.37 g, 98%).
1
47%). H NMR (200 MHz, CDCl3) d 5.8–5.4 (m, 2H),
4.2–4.0 (m, 2H), 3.68 (s, 3H), 3.0–2.3 (m, 12H), 1.6–1.2
(m, 8H), 1.0–0.8 (m, 21H), 0.1–0.0 (m, 12H).
Methyl 5-mercapto-3-thiapentanoate 15. To a stirred
solution of 14 (500 mg, 1.54 mmol) in DMF (5 mL) was
added methyl bromoacetate (283 mg, 1.85 mmol) at
room temperature under Ar. The reaction mixture was
stirred at 100 ꢀC for 5 h. After cooling to room tem-
perature, the reaction mixture was treated with water
and stirred for 1 h. The mixture was extracted with
EtOAc and the organic layer was washed with brine,
and dried over Na2SO4. After removal of solvents by
evaporation, the residue was purified by column chro-
4,7-DithiaPGE1 methyl ester 12. A stitrred solution of
11 (148 mg, 0.23 mmol) and pyridine (0.5 mL) in aceto-
nitrile (5 mL) was cooled in an ice-bath and treated with
.
(HF)n py (Aldrich, 0.5 mL). After stirring for 3 h at
room temperature, the reaction mixture was slowly
poured into saturated aqueous NaHCO3. The mixture
was extracted with EtOAc twice and the EtOAc layer

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T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
1
matography on silica gel (EtOAc/hexane, 1/20–1/10) to
afford 15 as a colorless oil (210 mg, 82%).
as a colorless oil (0.51 g, 25%). H NMR (200 MHz,
CDCl3) d 4.10 (s, 2H), 3.76 (s, 3H), 3.67 (t, J=7 Hz,
2H), 3.54 (t, J=7 Hz, 2H), 2.25–2.10 (m, 2H); MS
(APCI) m/z 213 (M+H)+.
4, 6-DithiaPGE1 methyl ester 11,15-bis(t-butyldimethyl-
silyl ether) 17. To a stirred solution of 16 (211 mg,
0.45 mmol) and 15 (50 mg, 0.30 mmol) in MeOH (4 mL)
was added two drops of piperidine at À78 ꢀC under Ar.
The reaction mixture was stirred at that temperature for
5 min, at 0 ꢀC for 10 min and then diluted with EtOAc.
The solution was washed with water, brine and dried
(Na2SO4). The solvent was removed by evaporation and
the residue was purified by column chromatography on
silica gel (EtOAc/hexane, 1/20–1/10) to afford 17 as a
colorless oil (110 mg, 60%). 1H NMR (200 MHz,
CDCl3); d 5.65 (dd, J=15, 7 Hz, 1H), 5.50 (dd, J=15,
8 Hz, 1H), 4.10 (m, 2H), 3.74 (s, 3H), 3.26 (s, 2H), 2.96–
2.57 (m, 8H), 2.22 (m, 2H), 1.6–1.1 (m, 8H), 0.88 (m,
21H), 0.05 (m, 12H).
Methyl 6-mercapto-3-oxahexanate 22. A suspension of
21 (0.51 g, 2.4 mmol) and thiourea (0.46 g, 6.0 mmol) in
ethanol (10 mL) was stirred under reflux for 5 h. The
resulting clear solution was treated with 2N NaOH
(5.0 mL, 10 mmol) at that temperature and then stirred
for 30 min. Then, the mixture was cooled to 0 ꢀC and
neutralized with 2N HCl. The mixture was extracted
with EtOAc repeatedly and the combined organic layer
was washed with brine, and dried over MgSO4. After
removal of the solid by filtration, the filtrate was treated
with CH2N2 and concentrated. The residue was purified
by column chromatography on silica gel (EtOAc/hex-
ane, 1/6) to afford 22 as a colorless oil (147 mg, 37%).
1H NMR (200 MHz, CDCl3) d 4.09 (s, 2H), 3.74 (s, 3H),
3.63 (t, J=7 Hz, 2H), 2.68 (q, J=7 Hz, 2H), 1.91 (pent,
J=7 Hz, 2H), 1.43 (t, J=7 Hz, 1H).
4,7-DithiaPGE1 methyl ester 18. A stirred solution of 17
(94 mg, 0.15 mmol) and pyridine (0.4 mL) in acetonitrile
(4 mL) was cooled in an ice-bath and treated with
.
(HF)n py (Aldrich, 0.8 mL). The reaction mixture was
2-(6-Carbomethoxy-5-oxa-1-thiahexyl)-4-(R)-t-butyldi-
methylsilyloxy-2-cyclopentenone 23. A solution of epox-
ide 8 and thiol 22 (145 mg, 0.88 mmol) in hexane
(10 mL) was stirred at room temperature in the presence
of activated alumina (1 g). After the reaction was com-
pleted, alumina was removed by filtration and washed
with CH2Cl2 repeatedly. The filtrate was evaporated
and purified by column chromatography on silica gel
(EtOAc/hexane=1:4) to afford enone 23 as a colorless
stirred for 2h at room temperature and then slowly
poured into saturated aqueous NaHCO3 solution.
Then, the mixture was extracted with EtOAc twice and
the organic layer was washed with 1 N HCl, H2O and
brine, and dried over Na2SO4. After removal of solvent
by evaporation, the residue was purified by column chro-
matography on silica gel (CHCl3/MeOH, 1/0–50/1–25/1)
1
to give 12 as a pale yellow oil (50 mg, 85%). H NMR
1
(200MHz, CDCl3) d 5.75 (1H, dd, J=15, 7 Hz), 5.59 (1H,
dd, J=15, 8 Hz), 4.12 (m, 2H), 3.75 (s, 3H), 3.26 (s, 2H),
3.2–2.6 (m, 8H), 2.28 (m, 2H), 1.8–1.2 (m, 8H), 0.90 (3H, t,
J=6Hz); MS (APCI) m/z 387 (MÀH2O+H)+.
oil (202 mg, 61%). H NMR (200 MHz, CDCl3) d 6.86
(d, J=2Hz, 1H), 5.0–4.9 (m, 1H), 4.07 (s, 2H), 3.76 (s,
3H), 3.65 (t, J=7 Hz, 2H), 2.97 (t, J=7 Hz, 2H), 2.85
(dd, J=19, 6 Hz, 1H), 2.37 (dd, J=19, 2Hz, 1H), 2.05–
1.90 (m, 2H), 0.90 (s, 9H), 0.15 (s, 6H).
4, 6-DithiaPGE1 19. To a stirred mixture of 18 (40 mg,
0.10 mmol) in ethanol (0.5 mL) and phosphate buffer
(pH 7.4, 5 mL) was added PLE (0.1 mL) at room tem-
perature. The reaction mixture was stirred vigorously
for 1.5 h and the resulting clear solution was poured
into saturated aqueous (NH4)2SO4. The reaction mix-
ture was extracted with EtOAc twice, dried (Na2SO4)
and evaporated. Purification by column chromato-
graphy on silica gel (CHCl3/MeOH, 20/1–9/1) provided
19 as a pale yellow oil (48 mg, 95%). IR (neat) 3391,
2929, 2858, 2649, 1739, 1407, 1277, 1157, 1075, 973,
3-Oxa-7-thiaPGE1 methyl ester 11,15-bis(t-butyldime-
thylsilyl ether) 24. To a stirred solution of 3-(S)-t-butyl-
dimethylsilyloxy-1-iodo-1-octene 10a (195 mg, 0.53
mmol) in freshly distilled dry diethyl ether (3 mL) was
slowly added t-butyllithium (1.57 M in pentane,
0.68 mL, 1.06 mmol) at À70 ꢀC under Ar. The reaction
mixture was stirred for 1 h at that temperature. To the
resulting suspension was added lithium 2-thienylcyano-
cuprate (0.25 M in THF, 2.2 mL, 0.53 mmol) dropwise
over 5 min. The gray suspension was stirred for an
additional 25min and 2-(6-carbomethoxy-5-oxa-1-thia-
hexyl)-4-(R)-t-butyldimethylsilyloxy-2-cyclopentenone 23
(200 mg, 0.51 mmol) in THF (3 mL) was added dropwise
in 8 min. The resulting yellowish mixture was allowed to
warm to À20 ꢀC over 1 h and then poured into a mix-
ture of hexane (10 mL) and saturated aqueous NH4Cl
(10 mL) under stirring. The organic layer was washed
with aq NH4Cl, H2O and brine, and dried over Na2SO4.
The solvent was removed by evaporation and the resi-
due was purified by column chromatography on silica
gel (EtOAc/hexane, 1/10–1/6) to afford 24 as a pale
yellow oil (64 mg, 20%). 1H NMR (200 MHz, CDCl3) d
5.75–5.45 (m, 2H), 4.1-4.0 (m, 4H), 3.73 (s, 3H), 3.62 (t,
J=6 Hz, 2H), 2.9–2.5 (m, 5H), 2.38 (dd, J=19, 8 Hz,
1H), 2.0–1.8 (m, 2H), 1.6–1.2 (m, 8H), 0.9–0.8 (m, 21H),
0.1–0.0 (m, 12H).
758 cmÀ1 1H NMR (200 MHz, CDCl3) d 5.76 (dd,
;
J=15, 7 Hz, 1H), 5.63 (dd, J=15, 8 Hz, 1H), 4.4 (br,
3H), 4.14 (m, 2H), 3.25 (s, 2H), 3.05–2.55 (m, 8H), 2.45–
2.20 (m, 2H), 1.8–1.1 (m, 8H), 0.89 (t, J=6 Hz, 3H); MS
(FAB) m/z 373 (MÀH2O+H)+.
Methyl 6-bromo-3-oxahexanate 21. To a stirred solution
of 3-bromo-1-propanol 20 (1.33 g, 9.6 mmol) and
methyl bromoacetate (1.47 g, 9.6 mmol) in dry DMF
(10 mL) was added sodium hydride (60% in oil, 384 mg,
9.6 mmol) in several portions at 0 ꢀC. After stirring for
2h, the resulting yellow suspension was poured into ice-
cooled 1 N HCl. The mixture was extracted with EtOAc
and the organic layer was washed with brine, dried and
evaporated. The residue was purified by column chro-
matography on silica gel (EtOAc/hexane, 1/8) to give 21

T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
983
3-Oxa-7-thiaPGE1 methyl ester 25. A solution of 24
(64 mg, 0.10 mmol) and pyridine (0.5 mL) in acetonitrile
(5 mL) was cooled in an ice-bath and treated with
was purified by column chromatography on silica gel
(EtOAc/hexane, 1/10–1/4) to give 30 as a colorless oil
(4.19 g, 83%). H NMR (200 MHz, CDCl3) d 6.87 (d,
J=3 Hz, 1H), 4.96 (m, 1H), 3.75 (s, 3H), 3.23 (s, 2H),
2.96 (t, J=7 Hz, 2H), 2.85 (dd, J=18, 6 Hz, 1H), 2.77 (t,
J=7 Hz, 2H), 2.37 (dd, J=18, 2Hz, 1H), 1.98 (m, 2H),
0.91 (m, 9H), 0.13 (m, 6H).
1
.
(HF)n py (Aldrich, 0.5 mL). The reaction mixture was
stirred for 3 h at room temperature and then slowly
poured into saturated aqueous NaHCO3 solution. The
reaction mixture was extracted with EtOAc twice and
the EtOAc layer was washed with 1 N HCl, H2O and
brine, and dried over Na2SO4. After removal of sol-
vent by evaporation, the residue was purified by
column chromatography on silica gel (EtOAc/
AcOH, 20/1) to give 25 as a pale brown oil (30 mg,
65%). 1H NMR (200 MHz, CDCl3) d 5.8–5.6 (m,
2H), 4.5–4.4 and 4.25–4.10 (m, 2H), 3.71 (s, 3H),
3.5–3.4 and 3.1–2.2 (m, 12H), 1.7–1.2 (m, 8H), 0.90 (t,
J=7 Hz, 3H).
3,7-DithiaPGE1 methyl ester 11,15-bis(t-butyldimethylsi-
lyl ether) 31a. To a stirred solution of 3-(S)-t-butyldi-
methylsilyloxy-1-iodo-1-octene 10a (368 mg, 1.0 mmol)
in freshly distilled dry diethylether (4 mL) was slowly
added t-butyllithium (1.57 M in pentane, 1.27 mL,
2.0 mmol) at À70 ꢀC under Ar and the reaction mixture
was stirred for 1 h at that temperature. To the resulting
suspension was added dropwise lithium 2-thienylcyano-
cuprate (0.25 M in THF, 4.4 mL, 1.1 mmol) in 4 min.
The gray suspension was stirred for an additional
15 min and 2-(6-carbomethoxy-1,5-dithiahexyl)-4-(R)-t-
butyldimethylsilyloxy-2-cyclopentenone 30 (300 mg,
0.84 mmol) in THF (3.5 mL) was added dropwise in
8 min. The resulting yellowish mixture was allowed to
warm to À20 ꢀC over 1 h and then poured into hexane
(10 mL) and saturated aqueous NH4Cl (10 mL) with
stirring. The aqueous layer was extracted with hexane
and the combined organic layer was washed with satu-
rated aqueous NH4Cl, H2O and brine, and dried over
Na2SO4. The solvent was removed by evaporation and
the residue was purified by column chromatography on
silica gel (EtOAc/hexane, 1/20–1/9) to afford 31a as a
pale yellow oil (342mg, 64%). 1H NMR (200 MHz,
CDCl3) d 5.67 (dd, J=16, 5 Hz, 1H), 5.53 (dd, J=16,
7 Hz, 1H), 4.08 (m, 2H), 3.73 (s, 3H), 3.22 (s, 2H), 2.9–
2.3 (m, 8H), 1.87 (m, 2H), 1.6–1.2 (m, 8H), 1.0–0.8 (m,
21H), 0.1–0.0 (m, 12H).
3-Oxa-7-thiaPGE1 26. To a stirred mixture of 25
(30 mg, 0.065 mmol) in ethanol (1 mL) and phosphate
buffer (pH 7.4, 5 mL) was added PLE (0.1 mL) at room
temperature. The reaction mixture was stirred vigor-
ously for 1.5 h and the resulting clear solution was
poured into saturated aqueous (NH4)2SO4. The mixture
was extracted with EtOAc twice, dried over Na2SO4 and
evaporated. Purification by column chromatography on
silica gel (EtOAc/hexane, 1/1–EtOAc/hexane/AcOH,
30/10/1–EtOAc/AcOH, 40/1) provided 13 as a pale yel-
low oil (22 mg, 65%). IR (neat) 3369, 2930, 1741, 1403,
1225, 1132, 1077 cmÀ1 1H NMR (200 MHz, CDCl3)
;
d 5.8–5.5 (m, 2H), 5.0–4.4 (3H, br), 4.5–4.4 and 4.2–
4.0 (m, 2H), 4.10 (s, 2H), 3.8–3.5 (m, 2H), 3.5–3.4
and 3.2–2.3 (m, 6H), 2.0–1.8 (m, 2H), 1.7–1.2 (m,
8H), 1.0–0.8 (m, 3H); MS (FAB) m/z 357
(MÀH2O+H)+.
2,2-Dibutyl-[1,3,2]dioxastanninane 28. A solution of 1,3-
propanedithiol 27 (6.0 g, 55.4 mmol) and dibutyltin-
oxide (13.8 g, 55.4 mmol) in benzene (60 mL) was azeo-
tropically stirred under reflux for 3 h. After the reaction
was completed, the solvent was evaporated to give 28 as
a white solid (18.7 g, 100%). 1H NMR (200 MHz,
CDCl3) d 2.94 (t, J=6 Hz, 4H), 1.88 (m, 2H), 1.69 (m,
4H), 1.6–1.3 (m, 8H), 0.93 (t, J=7 Hz, 6H).
3,7-Dithia-!-norPGE1 methyl ester 11,15-bis(t-butyldi-
1
methylsilyl ether) 31b. 64% yield; H NMR (200 MHz,
CDCl3) d 5.8–5.4 (m, 2H), 4.2–4.0 (m, 2H), 3.73 (s, 3H),
3.21 (s, 2H), 2.9–2.2 (m, 8H), 2.0–1.8 (m, 2H), 1.6–1.2
(m, 6H), 1.0–0.8 (m, 21H), 0.1–0.0 (m, 12H).
3,7-Dithia-!-homoPGE1 methyl ester 11,15-bis(t-butyl-
dimethylsilyl ether) 31c. 71% yield; 1H NMR
(200 MHz, CDCl3) d 5.7–5.5 (m, 2H), 4.4–4.0 (m, 2H),
3.73 (s, 3H), 3.22 (s, 2H), 3.45–2.8 (m, 1H), 2.9–2.3 (m,
7H), 1.95–1.75 (m, 2H), 1.6–1.1 (m, 10H), 1.0–0.8 (m,
21H), 0.1–0.0 (m, 12H).
Methyl 6-mercapto-3-thiahexanate 29. To a solution of
28 (18.7 g, 55.4 mmol) in DMF (40 mL) was added
methyl bromoacetate (7.87 mL, 83.1 mmol) at room
temperature. The reaction mixture was stirred at 100 ꢀC
for 5 h. After cooling to room temperature, the reaction
mixture was treated with water and stirred for 1 h. The
mixture was extracted with EtOAc and the organic layer
was washed with brine, and dried over Na2SO4. After
removal of solvents, the residue was purified by column
chromatography on silica gel (EtOAc/hexane, 1/20–1/9–
1/4) to afford 29 as a colorless oil (5.59 g, 56%).
3,7-Dithia-19-D-PGE1 methyl ester 11,15-bis(t-butyldi-
1
methylsilyl ether) 31d. 71% yield; H NMR (200 MHz,
CDCl3) d 5.8–5.6 (m, 3H), 5.1–4.8 (m, 2H), 4.4–4.05 (m,
2H), 3.73 (s, 3H), 3.22 (s, 2H), 3.5–2.2 (m, 8H), 2.1–1.8
(m, 4H), 1.7–1.3 (m, 4H), 0.89 (s, 9H), 0.88 (s, 9H), 0.1–
0.0 (m, 12H).
2-(6-Carbomethoxy-1,5-dithiahexyl)-4-(R)-t-butyldime-
thylsilyloxy-2-cyclopentenone 30. A solution of 8 (3.0 g,
13 mmol) and 29 (2.46 g, 13.7 mmol) in CH2Cl2 (45 mL)
was stirred at room temperature in the presence of acti-
vated alumina (13 g). After stirring for 12h, alumina
was removed by filtration and washed with CH2Cl2
repeatedly. The filtrate was evaporated and the residue
3,7-Dithia-19,20-methanoPGE1 methyl ester 11,15-bis(t-
butyldimethylsilyl ether) 31e. 41% yield; 1H NMR
(200 MHz, CDCl3) d 5.7–5.5 (m, 2H), 4.4–4.1 (m, 2H),
3.73 (s, 3H), 3.22 (s, 2H), 3.5–2.2 (m, 8H), 2.0–1.8 (m,
2H), 1.6–1.0 (m, 6H), 0.89 (s, 9H), 0.87 (s, 9H), 0.7–0.5
(m, 1H), 0.45–0.3 (m, 2H), 0.05 (s, 6H), 0.03 (s, 6H),
0.05–0.0 (m, 2H).

984
T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
3,7-Dithia-16-(S)-methylPGE1 methyl ester 11,15-bis(t-
butyldimethylsilyl ether) 31f. 64% yield; 1H NMR
(200 MHz, CDCl3) d 5.7–5.4 (m, 2H), 4.2–4.0 (m, 1H),
4.0–3.9 (m, 1H), 3.73 (s, 3H), 3.22 (s, 2H), 2.9–2.3 (m,
2H), 2.0–1.8 (m, 2H), 1.5–1.1 (m, 7H), 1.0–0.8 (m, 24H),
0.1–0.0 (m, 12H).
3,7-Dithia-16-cyclohexyl-!-tetranorPGE1 methyl ester
1
11,15-bis(t-butyldimethylsilyl ether) 31o. 52% yield; H
NMR (200MHz, CDCl3) d 5.76–5.36 (m, 2H), 4.42–4.00
(m, 3H), 3.74 (s, 3H), 3.22 (s, 2H), 3.06–2.10 (m, 7H), 1.98–
1.06 (m, 15H), 0.92–0.85 m, 18H), 0.08–0.00 (m, 12H).
3,7-Dithia-16-phenyl-!-tetranorPGE1
methyl
ester
1
3,7-Dithia-16-(R)-methylPGE1 methyl ester 11,15-bis(t-
butyldimethylsilyl ether) 31g. 72% yield; 1H NMR
(200 MHz, CDCl3) d 5.7–5.4 (m, 2H), 4.2–3.9 (m, 2H),
3.72 (s, 3H), 3.22 (s, 2H), 2.9–2.3 (m, 8H), 2.0–1.8 (m,
2H), 1.7–1.0 (m, 7H), 1.0–0.8 (m, 24H), 0.1–0.0 (m,
12H).
11,15-bis(t-butyldimethylsilyl ether) 31p. 65% yield; H
NMR (200 MHz, CDCl3) d 7.33–7.12(m, 5H), 5.79–
5.65 (m, 1H), 5.52(dd, J=15.7, 8.1 Hz, 1H), 4.38–3.42
(m, 6H), 3.22 (s, 2H), 3.00–2.05 (m, 9H), 2.00–1.70 (m,
2H), 0.89 (s, 9H), 0.85 (s, 9H), 0.12–0.05 (m, 6H), 0.06
(s, 3H), 0.08 (s, 3H), 0.23 (s, 3H), 0.25 (s, 3H).
3,7-Dithia-17-(R)-methylPGE1 methyl ester 11,15-bis(t-
butyldimethylsilyl ether) 31h. 57% yield; 1H NMR
(200 MHz, CDCl3) d 5.75–5.39 (m, 2H), 4.41–4.00 (m,
2H), 3.73 (s, 3H), 3.22 (s, 2H), 3.48–2.11 (m, 8H), 1.98–
1.78 (m, 2H), 1.71–1.02 (m, 9H), 1.0–0.8 (m, 24H), 0.1–
0.0 (m, 12H).
3,7-Dithia-17-phenyl-!-trinorPGE1 methyl ester 11,15-
1
bis(t-butyldimethylsilyl ether) 31q. 62% yield; H NMR
(200 MHz, CDCl3) d 7.3–7.1 (m, 5H), 5.73 (dd, J=16,
5 Hz, 1H), 5.55 (dd, J=16, 7 Hz, 1H), 4.3–4.0 (m, 2H),
3.72 (s, 3H), 3.19 (s, 2H), 2.9–2.5 (m, 9H), 2.37 (dd,
J=19, 8 Hz, 1H), 2.0–1.7 (m, 4H), 1.0–0.8 (m, 18H),
0.2–0.0 (m, 12H).
3,7-Dithia-17-(S)-methylPGE1 methyl ester 11,15-bis(t-
butyldimethylsilyl ether) 31i. 56% yield; 1H NMR
(200 MHz, CDCl3) d 5.67 (dd, J=16, 5 Hz, 1H), 5.53
(dd, J=16, 7 Hz, 1H), 4.4–4.0 (m, 2H), 3.73 (s, 3H), 3.22
(s, 2H), 3.5–2.3 (m, 8H), 2.0–1.7 (m, 2H), 1.6–1.0 (m,
9H), 1.0–0.8 (m, 24H), 0.05 (m, 12H).
3,7-Dithia-16-phenoxy–!-tetranorPGE1 methyl ester
1
11,15-bis(t-butyldimethylsilyl ether) 31r. 35% yield; H
NMR (200 MHz, CDCl3) d 7.35–7.20 (m, 2H), 6.94 (t,
J=8 Hz, 1H), 6.87 (d, J=7 Hz, 2H), 5.85–5.75 (m, 2H),
4.75–4.65 and 4.65–4.50 (m, 1H), 4.45–4.35 and 4.15–
4.00 (m, 1H), 3.95–3.80 (m, 2H), 3.74 (s, 3H), 3.22 (S,
2H), 3.45–3.40 and 3.0–2.5 (m, 7H), 2.5–2.1 (m, 1H),
2.0–1.7 (m, 2H), 1.0–0.8 (m, 18H), 0.2–0.0 (m, 12H).
3,7-Dithia-18-methyl-!-norPGE1 methyl ester 11,15-
1
bis(t-butyldimethylsilyl ether) 31j. 75% yield; H NMR
(200 MHz, CDCl3) d 5.7–5.5 (m, 2H), 4.4–4.05 (m, 2H),
3.73 (s, 3H), 3.22 (s, 2H), 3.5–2.2 (m, 8H), 2.0–1.8 (m,
2H), 1.6–1.4 (m, 3H), 1.3–1.1 (m, 2H), 1.0–0.8 (m, 24H),
0.1–0.0 (m, 12H).
3,7-DithiaPGE1 methyl ester 32a. A solution of 31a
(947 mg, 1.5 mmol) and pyridine (4.5 mL) in acetonitrile
(30 mL) was cooled in an ice-bath and treated with
.
(HF)n py (Aldrich, 9 mL). The reaction mixture was
3,7-Dithia-17-ethyl-!-norPGE1 methyl ester 11,15-bis(t-
butyldimethylsilyl ether) 31k. 64% yield; 1H NMR
(200 MHz, CDCl3) d 5.8–5.4 (m, 2H), 4.25–4.00 (m,
2H), 3.73 (s, 3H), 3.21 (s, 2H), 2.9–2.2 (m, 8H), 2.0–1.8
(m, 2H), 1.5–1.2 (m, 7H), 0.90 (s, 9H), 0.88 (s, 9H), 0.83
(t, J=7 Hz, 6H), 0.1–0.0 (m, 12H).
stirred for 30 min at room temperature and then slowly
poured into a heterogeneous solution of EtOAc (60 mL)
and saturated aqueous NaHCO3 (200 mL) with stirring.
The aqueous layer was extracted with EtOAc twice and
the combined organic layer was washed with 1 N HCl,
H2O and brine, dried over Na2SO4, and evaporated.
The residue was purified by column chromatography on
silica gel (EtOAc/hexane, 1/1–3/1 then EtOAc/AcOH,
100/1) to afford 3,7-dithiaPGE1 methyl ester 32a as a
yellow oil (560 mg, 92%). IR (neat) 3392, 2929, 2858,
1741, 1437, 1283, 1137, 1080, 1016, 969 cmÀ1; 1H NMR
(200 MHz, CDCl3) d 5.85–5.55 (m, 2H), 4.5–4.4 and
4.25–4.05 (m, 2H), 3.74 (s, 3H), 3.22 (s, 2H), 3.45–3.40
and 3.05–2.20 (m, 8H), 2.0–1.8 (m, 2H), 1.6–1.2 (m,
8H), 0.89 (t, J=7 Hz, 3H); MS (EI) m/z 404 (M)+.
3,7-Dithia-15-cyclopentyl-!-pentanorPGE1 methyl ester
1
11,15-bis(t-butyldimethylsilyl ether) 31l. 58% yield; H
NMR (200 MHz, CDCl3) d 5.76–5.32 (m, 2H), 4.42–
3.82 (m, 3H), 3.73 (s, 3H), 3.22 (s, 2H), 3.06–2.20 (m,
8H), 2.04–1.14 (m, 10H), 0.92–0.85 (m, 18H), 0.08–0.01
(m, 12H).
3,7-Dithia-15-cyclohexyl-!-pentanorPGE1 methyl ester
1
11,15-bis(t-butyldimethylsilyl ether) 31m. 32% yield; H
NMR (200 MHz, CDCl3) d 5.7–5.3 (m, 2H), 4.4–3.8 (m,
2H), 3.73 (s, 3H), 3.22 (s, 2H), 3.5–2.1 (m, 8H), 2.0–1.5
(m, 7H), 1.4–0.9 (m, 6H), 0.9–0.8 (m, 18H), 0.1–0.0 (m,
12H).
3,7-Dithia-!-norPGE1 methyl ester 32b. 85% yield; IR
(neat) 3401, 2930, 1740, 1437, 1282, 1138, 1079 cmÀ1
;
1H NMR (200 MHz, CDCl3) d 5.85—5.55 (m, 2H), 4.5–
4.4 and 4.2–4.0 (m, 2H), 3.74 (s, 3H), 3.45–3.40 and 3.1–
2.2 (m, 8H), 3.22 (s, 2H), 2.0–1.8 (m, 2H), 1.7–1.2 (m,
6H), 0.92(3H, t, J=7 Hz); MS (EI) m/z 390 (M)+.
3,7-Dithia-16-cyclopentyl-!-tetranorPGE1 methyl ester
1
11,15-bis(t-butyldimethylsilyl ether) 31n. 52% yield; H
NMR (200 MHz, CDCl3) d 5.70 (dd, J=15, 5.5 Hz,
1H), 5.54 (dd, J=15, 7.7 Hz, 1H), 4.36 (m, 1H), 4.10
(m, 1H), 3.73 (s, 3H), 3.22 (s, 2H), 3.48–2.22 (m, 8H),
1.97–1.00 (m, 13H), 1.0–0.8 (m, 18H), 0.1–0.0 (m,
12H).
3,7-Dithia-!-homoPGE1 methyl ester 32c. 89% yield;
1H NMR (200 MHz, CDCl3) d 5.75–5.55 (m, 2H), 4.5–
4.1 (m, 2H), 3.74 (s, 3H), 3.23 (s, 2H), 3.4–2.2 (m, 8H),
2.0–1.2 (m, 12H), 0.89 (t, J=6 Hz, 3H); MS (FAB) m/z
401 (MÀH2O+H)+.

T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
985
1
3,7-Dithia-19-D-PGE1 methyl ester 32d. 78% yield; H
NMR (200 MHz, CDCl3) d 5.85–5.6 (m, 3H), 5.1–4.9
(m, 2H), 4.5–4.1 (m, 2H), 3.74 (s, 3H), 3.23 (s, 2H), 3.4–
3,7-Dithia-16-cyclopentyl-!-tetranorPGE1 methyl ester
1
32n. 84% yield; H NMR (200 MHz, CDCl3) d 5.8–5.6
(m, 2H), 4.43 (m, 1H), 4.15 (m, 1H), 3.74 (s, 3H), 3.23
(s, 2H), 3.42–2.17 (m, 8H), 2.00–1.40 (m, 11H), 1.2–1.0
(m, 2H).
2.2 (m, 8H), 2.2–2.0 (m, 2H), 1.95–1.85 (m, 2H), 1.6–1.4
+
(m, 4H); MS (EI) m/z 402(M)
.
3,7-Dithia-19,20-methanoPGE1 methyl ester 32e. 67%
1
3,7-Dithia-16-cyclohexyl-!-tetranorPGE1 methyl ester
1
yield; H NMR (200 MHz, CDCl3) d 5.8–5.6 (m, 2H),
32o. 63% yield; H NMR (200 MHz, CDCl3) d 5.80–
4.45–4.1 (m, 2H), 3.73 (s, 3H), 3.21 (s, 2H), 3.4–2.2 (m,
8H), 2.0–1.8 (m, 2H), 1.6–1.4 (m, 4H), 1.25–1.15 (m,
2H), 0.7–0.6 (m, 1H), 0.5–0.3 (m, 2H), 0.05–0.0 (m, 2H);
MS (EI) m/z 416 (M)+.
5.40 (m, 2H), 4.48–3.94 (m, 3H), 3.71 (s, 3H), 3.20 (s,
2H), 3.10–2.10 (m, 9H), 2.00–1.54 (m, 6H), 1.54–0.76
(m, 8H).
3,7-Dithia-16-phenyl-!-tetranorPGE1 methyl ester 32p.
79% yield; 1H NMR (200 MHz, CDCl3) d 7.38–7.15
(m, 5H), 5.78 (dd, J=15.4, 5.8 Hz, 1H), 5.56 (dd,
J=15.4, 8.0 Hz, 1H), 4.46–4.28 (m, 2H), 4.12–3.94 (m,
1H), 3.73 (s, 3H), 3.22 (s, 2H), 3.06–2.14 (m, 9H), 2.00–
1.70 (m, 2H).
3,7-Dithia-16-(S)-methylPGE1 methyl ester 32f. 72%
yield; 1H NMR (200 MHz, CDCl3) d 5.9–5.5 (m,
2H), 4.5–4.4 and 4.1–4.0 (m, 1H), 4.3–4.1 (m, 1H),
3.73 (s, 3H), 3.22 (s, 2H), 3.5–3.4 and 3.1–2.3 (m,
10H), 2.0–1.8 (m, 2H), 1.6–1.0 (m, 7H), 1.0–0.8 (m,
6H).
3,7-Dithia-17-phenyl-!-trinorPGE1 methyl ester 32q.
80% yield; 1H NMR (200 MHz, CDCl3) d 7.35–7.15
(m, 5H), 5.85–5.55 (m, 2H), 4.5–4.4 and 4.2–4.0 (m,
2H), 3.72 (s, 3H), 3.00 (s, 2H), 3.45–3.40 and 3.05–2.20
(m, 10H), 2.0–1.8 (m, 4H).
3,7-Dithia-16-(R)-methylPGE1 methyl ester 32g. 82%
1
yield; H NMR (200 MHz, CDCl3) d 5.8–5.5 (m, 2H),
4.5–4.4 and 4.2–4.0 (m, 2H), 3.73 (s, 3H), 3.23 (s, 2H),
3.5–3.4 and 3.1–2.3 (m, 8H), 2.0–1.8 (m, 2H), 1.7–1.2
(m, 7H), 1.0–0.8 (m, 6H).
3,7-Dithia-16-phenoxy-!-tetranorPGE1 methyl ester
1
3,7-Dithia-17-(R)-methylPGE1 methyl ester 32h. 64%
yield; 1H NMR (200 MHz, CDCl3) d 5.76 (1H, dd,
J=16, 6 Hz), 5.61 (1H, dd, J=16, 8 Hz), 4.4–4.1 (m,
2H), 3.74 (s, 3H), 3.23 (s, 2H), 3.42–2.17 (m, 8H), 1.88
(m, 2H), 1.58 (m, 2H), 1.23 (m, 7H), 0.91 (m, 6H); MS
(FAB) m/z; 415 (MÀH2O+H)+.
32r. 61% yield; H NMR (200 MHz, CDCl3) d 7.4–7.1
(m, 2H), 6.98 (t, J=8 Hz, 1H), 6.92(d, J=7 Hz, 2H),
5.9–5.8 (m, 2H), 4.6–4.5 (m, 1H), 4.5–4.4 and 4.2–4.1
(m, 1H), 4.07 and 4.05 (d, J=9 Hz, 1H), 3.95 and 3.91
(d, J=9 Hz, 1H), 3.74 (s, 3H), 3.21 (S, 2H), 3.4–3.3 and
3.1–2.3 (m, 8H), 2.0–1.8 (m, 2H).
3,7-Dithia-17-(S)-methylPGE1 methyl ester 32i. 88%
1
3,7-DithiaPGE1 4a. To a stirred mixture of 32a (370 mg,
0.91 mmol) in ethanol (5 mL) and phophate buffer (pH
7.4, 25 mL) was added PLE (0.5 mL) at room tempera-
ture. The reaction mixture was stirred for 1 h. The
resulting clear solution was poured into saturated aqu-
eous (NH4)2SO4 and then extracted with EtOAc twice.
The combined organic layer was dried (Na2SO4) and
evaporated. Purification by column chromatography on
silica gel (EtOAc/hexane, 3/1 to EtOAc/AcOH, 50/1)
provided 4a as a pale yellow oil (372mg, 92%). IR
(neat) 3392, 2929, 2858, 1733, 1417, 1262, 1135, 1077,
yield; H NMR (200 MHz, CDCl3) d 5.70 (m, 2H), 4.5–
4.1 (m, 2H), 3.74 (s, 3H), 3.23 (s, 2H), 3.4–2.2 (m, 8H),
2.0–1.0 (m, 11H), 1.0–0.8 (m, 6H); MS (FAB) m/z; 432
(M)+.
3,7-Dithia-18-methyl-!-norPGE1 methyl ester 32j. 79%
1
yield; H NMR (200 MHz, CDCl3) d 5.8–5.6 (m, 2H),
4.5–4.1 (m, 2H), 3.74 (s, 3H), 3.23 (s, 2H), 3.4–2.2 (m,
8H), 2.0–1.8 (m, 2H), 1.6–1.4 (m, 3H), 1.3–1.1 (m, 2H),
0.90 (d, J=7 Hz, 6H).
1
969 cmÀ1; H NMR (200 MHz, CDCl3) d 5.9–5.6 (m,
3,7-Dithia-17-ethyl-!-norPGE1 methyl ester 32k. 79%
yield; 1H NMR (200 MHz, CDCl3) d 5.85–5.55 (m, 2H),
4.5–4.4 and 4.3–4.1 (m, 2H), 3.77 (s, 3H), 3.24 (s, 2H),
3.45—3.40 and 3.1–2.2 (m, 8H), 2.0–1.2 (m, 9H), 0.89 (t,
J=7 Hz, 6H).
2H), 5.2–4.5 (br, 3H), 4.5–4.4 and 4.3–4.1 (m, 2H), 3.22
(s, 2H), 3.45–3.40 and 3.1–2.3 (m, 8H), 2.0–1.8 (m, 2H),
1.7–1.5 (m, 2H), 1.5–1.2 (m, 6H), 0.92 (t, J=7 Hz, 3H);
MS (EI) m/z 372(M ÀH2O)+.
3,7-Dithia-!-norPGE1 4b. 85% yield; IR (neat) 3382,
3,7-Dithia-15-cyclopentyl-!-pentanorPGE1 methyl ester
1
2928, 1733, 1417, 1262, 1134, 1077, 970, 909, 732 cmÀ1
;
32l. 58% yield; H NMR (200 MHz, CDCl3) d 5.88–
1H NMR (200 MHz, CDCl3) d 5.85–5.60 (m, 2H), 5.6–
5.2 (3H, br), 4.5–4.4 and 4.25–4.05 (m, 2H), 3.23 (s,
2H), 3.45–3.40 and 3.1–2.2 (m, 8H), 2.0–1.8 (m, 2H),
1.7–1.2(m, 6H), 0.92(3H, t, J=7 Hz); MS (EI) m/z 358
(MÀH2O)+.
5.48 (m, 2H), 4.56–3.84 (m, 3H), 3.72 (s, 3H), 3.20 (s,
2H), 3.14–2.20 (m, 9H), 2.20–1.10 (m, 9H); MS (FAB)
m/z 385 (MÀH2O+H)+.
3,7-Dithia-15-cyclohexyl-!-pentanorPGE1 methyl ester
1
32m. 67% yield; H NMR (200 MHz, CDCl3) d 5.74
3,7-Dithia-!-homoPGE1 4c. 70% yield; IR (neat) 3368,
2927, 2857, 2654, 1732, 1417, 1345, 1262, 1137, 1078,
(dd, J=15, 7 Hz, 1H,), 5.56 (dd, J=15, 8 Hz, 1H), 4.4–
3.8 (m, 2H), 3.74 (s, 3H), 3.22 (s, 2H), 3.4–2.1 (m, 8H),
2.0–1.5 (m, 7H), 1.5–0.8 (m, 6H); MS (FAB) m/z 399
(MÀH2O+H)+.
1
969, 757 cmÀ1; H NMR (200 MHz, CDCl3) d 5.8–5.6
(m, 2H), 5.6–5.2 (br), 4.5–4.1 (m, 2H), 3.4–3.0 (m, 1H),
3.23 (s, 2H), 3.0–2.2 (m, 7H), 1.95–1.75 (m, 2H), 1.65–

986
T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
1.5 (m, 2H), 1.5–1.2 (m, 8H), 0.89 (t, J=6 Hz, 3H); MS
(APCI) m/z 403 (MÀH)À.
3,7-Dithia-15-cyclopentyl-!-pentanorPGE1 4l. 25%
yield; IR (neat) 3700–3100, 2926, 2856, 1739, 1403,
1
1385, 1261, 1153, 1076, 1024, 801, 734 cmÀ1; H NMR
3,7-Dithia-19-D-PGE1 4d. 69% yield; IR (neat) 3392,
2928, 2649, 1733, 1640, 1417, 1262, 1148, 1078, 970,
(200 MHz, CDCl3) d 5.86–5.48 (m, 2H), 4.70–3.20 (m,
6H), 3.15 (s, 2H), 3.08–1.00 (m, 18H); MS (APCI) m/z
387 (MÀH)À.
1
914 cmÀ1; H NMR (200 MHz, CDCl3) d 5.9–5.5 (m,
3H), 5.1–4.9 (m, 2H), 4.45–4.1 (m, 2H), 3.4–3.0 (m, 1H),
3.22 (s, 2H), 3.0–2.3 (m, 7H), 2.2–2.0 (m, 2H), 1.95–1.85
(m, 2H), 1.65–1.35 (m, 4H); MS (APCI) m/z 387
(MÀH)À.
3,7-Dithia-15-cyclohexyl-!-pentanorPGE1 4m. 72%
yield; IR (neat) 3392, 2956, 2926, 2872, 1733, 1715,
;
1417, 1381, 1271, 1144, 1080, 970 cmÀ1 1H NMR
(200 MHz, CDCl3) d 5.77 (dd, J=15, 6 Hz, 1H), 5.61
(dd, J=15, 8 Hz, 1H), 4.85–4.65 (br, 3H), 4.5–4.1 (m,
1H), 3.92 (m, 1H), 3.4–2.3 (m, 8H), 3.23 (s, 2H), 2.0–1.6
(m, 7H), 1.5–0.9 (m, 6H); MS (APCI) m/z 401 (MÀH)À.
3,7-Dithia-19,20-methanoPGE1 4e. 84% yield; IR (neat)
3392, 3076, 2998, 2927, 2857, 2653, 1732, 1417, 1265,
1
1148, 1078, 970 cmÀ1; H NMR (200 MHz, CDCl3) d
5.8–5.6 (m, 2H), 4.5–4.1 (m, 2H), 3.4–3.0 (m, 1H), 3.23
(s, 2H), 3.0–2.2 (m, 7H), 2.0–1.8 (m, 2H), 1.7–1.1 (m,
6H), 0.7–0.6 (m, 1H), 0.5–0.3 (m, 2H), 0.05–0.0 (m, 1H);
MS (APCI) m/z 401 (MÀH)À.
3,7-Dithia-16-cyclopentyl-!-tetranorPGE1 4n. 89%
yield; IR (neat) 3392, 2947, 2867, 2649, 1731, 1715,
1
1417, 1265, 1148, 1078, 971 cmÀ1; H NMR (200 MHz,
CDCl3) d 5.9–5.6 (m, 5H), 4.44 (m, 1H), 4.18 (m, 1H),
3.42–3.03 (m, 1H), 3.23 (s, 2H), 2.96–2.20 (m, 7H),
2.01–1.38 (m, 11H), 1.2–1.0 (m, 2H); MS (EI) m/z 384
(MÀH2O)+.
3,7-Dithia-16-(S)-methylPGE1 4f. 89% yield; IR (neat)
1
3368, 2926, 1733, 1417, 1262, 1148, 1078, 733 cmÀ1; H
NMR (200 MHz, CDCl3) d 5.85–5.60 (m, 2H), 4.5–4.4
and 4.2–4.0 (m, 2H), 4.6–3.8 (br, 3H), 3.22 (s, 2H),
3.45–3.40 and 3.1–2.2 (m, 8H), 2.0–1.8 (m, 2H), 1.7–1.1
(m, 7H), 1.0–0.8 (m, 6H); MS (EI) m/z 386 (MÀH2O)+.
3,7-Dithia-16-cyclohexyl-!-tetranorPGE1 4o. 34%
yield; IR (neat) 3600–3100, 2922, 2852, 1732, 1448,
1417, 1261, 1142, 973, 897, 757 cmÀ1
;
1H NMR
3,7-Dithia-16-(R)-methylPGE1 4g. 72% yield; IR (neat)
(200 MHz, CDCl3) d 5.90–5.52(m, 2H), 5.04–4.40 (br),
4.40–3.92 (m, 3H), 3.22 (s, 2H), 3.12–2.24 (m, 7H),
2.24–0.70 (m, 15H); MS (FAB) m/z 399
(MÀH2O+H)+.
3401, 2928, 1730, 1417, 1262, 1147, 1078, 971, 733 cmÀ1
;
1H NMR (200 MHz, CDCl3) d 5.9–5.6 (m, 2H), 4.5–4.4
and 4.3–4.0 (m, 2H), 4.7–3.9 (br, 3H), 3.23 (s, 2H),
3.45–3.40 and 2.9–2.2 (m, 8H), 2.0–1.8 (m, 2H), 1.7–1.0
(m, 7H), 1.0–0.8 (m, 6H); MS (EI) m/z 386 (MÀH2O)+.
3,7-Dithia-16-phenyl-!-tetranorPGE1 4p. 28% yield; IR
(neat) 3700–3100, 2921, 2856, 1732, 1495, 1455, 1407,
1
3,7-Dithia-17-(R)-methylPGE1 4h. yield; IR (neat) 3392,
2955, 2926, 2872, 2858, 2648, 1732, 1715, 1417, 1383,
1266, 1148, 1080, 1029, 911, 735, 702 cmÀ1; H NMR
(200 MHz, CDCl3) d 7.38–7.16 (m, 5H), 5.90–5.50 (m,
2H), 4.56–3.70 (m, 7H), 3.21 (s, 2H), 3.10–2.26 (m,
10H), 2.0–1.8 (m, 2H); MS (MALDI) m/z 449
(M+K)+, 433 (M+Na)+.
1271, 1151, 1080, 970 cmÀ1
;
1H NMR (200 MHz,
CDCl3) d 5.85–5.65 (m, 2H), 5.2–5.0 (3H, br), 4.5–4.05
(m, 2H), 3.4–2.2 (m, 8H), 3.23 (s, 2H), 2.0–1.8 (m, 2H),
1.60–1.02(m, 9H), 1.0–0.8 (m, 6H); MS (EI) m/z 400
(MÀH2O)+.
3,7-Dithia-17-phenyl-!-trinorPGE1 4q. 72% yield; IR
(neat) 3392, 2923, 1730, 1406, 1264, 1152, 1076, 911,
734, 702cm À1; 1H NMR (200 MHz, CDCl3) d 7.35–7.15
(m, 5H), 5.9–5.6 (m, 2H), 4.5–4.4 and 4.3–4.0 (m, 2H),
4.3–3.6 (br, 3H), 3.03 (s, 2H), 3.45–3.40 and 3.05–2.20
(m, 10H), 2.0–1.8 (m, 4H); MS (EI) m/z 406
(MÀH2O)+.
3,7-Dithia-17-(S)-methylPGE1 4i. yield; IR (neat) 3392,
2927, 2872, 1730, 1715, 1404, 1265, 1151, 1079, 969,
;
758 cmÀ1 1H NMR (200 MHz, CDCl3) d 5.74 (dd,
J=15, 6 Hz, 1H), 5.67 (dd, J=15, 8 Hz, 1H), 4.9–4.6
(br), 4.5–4.15 (m, 2H), 3.4–2.2 (m, 8H), 3.23 (s, 2H),
2.0–1.75 (m, 2H), 1.6–1.0 (m, 9H), 1.0–0.8 (m, 6H); MS
(APCI) m/z 417 (MÀH)À.
3,7-Dithia-16-phenoxy-!-tetranorPGE1 4r. 58% yield;
IR (neat) 3392, 2925, 1730, 1599, 1495, 1406, 1245,
;
1147, 1080, 1040, 972, 908, 757 cmÀ1 1H NMR
(200 MHz, CDCl3) d 7.29 (t, J=8 Hz, 2H), 6.98 (t,
J=8 Hz, 1H), 6.92(d, J=8 Hz, 2H), 6.0–5.8 (m, 2H),
4.7–4.6 (m, 1H), 4.6–4.4 and 4.2–3.9 (m, 3H), 4.7–3.7
(br, 3H), 3.22 (S, 2H), 3.45–3.40 and 3.1–2.3 (m, 8H),
2.0–1.8 (m, 2H); MS (FAB) m/z 427 (MÀH2O)+.
3,7-Dithia-18-methyl-!-norPGE1 4j. 92% yield; IR
(neat) 3392, 2954, 2869, 1732, 1417, 1385, 1262, 1147,
1
1077, 970 cmÀ1; H NMR (200 MHz, CDCl3) d 5.8–5.6
(m, 3H), 4.5–4.1 (m, 2H), 3.4–3.0 (m, 1H), 3.23 (s, 2H),
3.0–2.2 (m, 7H), 2.0–1.8 (m, 2H), 1.7–1.5 (m, 3H), 1.3–
1.1 (m, 2H), 0.90 (d, J=7 Hz, 6H); MS (APCI) m/z 389
(MÀH)À.
3,7-Dithia-13,14-dihydroPGE1 methyl ester 11,15-bis(t-
butyldimethylsilyl ether) 34a. To a stirred solution of 3-
(S)-t-butyldimethylsilyloxy-1-iodo-1-octene 33a (90 mg,
0.243 mmol) in freshly distilled dry ether (0.5 mL) was
slowly added t-butyllithium (1.57 M in pentane,
0.31 mL, 0.49 mmol) at À70 ꢀC under Ar and the reac-
tion mixture was stirred for 1 h at that temperature. To
3,7-Dithia-17-ethyl-!-norPGE1 4k. 59% yield; IR (neat)
3392, 2964, 2927, 1731, 1417, 1263, 1148, 1077, 972 cmÀ1
;
1H NMR (200 MHz, CDCl3) d 5.9–5.6 (m, 2H), 5.6–5.0
(3H, br), 4.6–4.0 (m, 2H), 3.23 (s, 2H), 3.45–3.40 and
3.1–2.2 (m, 8H), 2.0–1.8 (m, 2H), 1.6–1.2 (m, 7H), 0.83
(6H, t, J=7 Hz); MS (EI) m/z 386 (MÀH2O)+.

T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
987
the resulting suspension was added dropwise lithium
2-thienylcyanocuprate (0.25 M in THF, 1.0 mL, 0.25
mmol) in 4 min. The gray suspension was stirred for an
additional 15 min and 2-(6-carbomethoxy-1,5-dithia-
hexyl)-4-(R)-t-butyldimethylsilyloxy-2-cyclopentenone 30
(73 mg, 0.19 mmol) in THF (3 mL) was added dropwise
in 4 min. The resulting yellowish mixture was allowed to
warm to À20 ꢀC over 1 h and then poured into a stirred
mixture of hexane (10 mL) and saturated aqueous
NH4Cl (10 mL). The aqueous layer was extracted with
hexane and the combined organic layer was successively
washed with saturated aqueous NH4Cl, H2O, brine and
dried over Na2SO4. The solvent was removed by eva-
poration and the residue was purified by column chro-
matography on silica gel (EtOAc/hexane, 1/20–1/9) to
3,7-Dithia–15 -deoxy-16-(S)-hydroxy-16-methylPGE1
methyl ester 35c. 66% yield; 1H NMR (200 MHz,
CDCl3) d 5.85–5.70 (m, 1H), 5.6–5.4 (m, 1H), 4.5–4.4
and 4.2–4.0 (m, 1H), 3.74 (s, 3H), 3.22 (s, 2H), 3.5–3.4
and 3.0–2.2 (m, 12H), 2.0–1.8 (m, 2H), 1.6–1.1 (m, 9H),
0.92(t, J=7 Hz, 3H).
3,7-Dithia-13,14-dihydroPGE1 36a. To a stirred mixture
of 32a (30 mg, 0.074 mmol) in ethanol (0.4 mL) and
phosphate buffer (pH 7.4, 4.0 mL) was added PLE
(0.1 mL) at room temperature. The reaction mixture
was stirred for 1 h. The resulting clear solution was
poured into saturated aqueous (NH4)2SO4 and extrac-
ted with EtOAc twice. The combined organic layer was
dried (Na2SO4) and evaporated. Purification by column
chromatography on silica gel (EtOAc/hexane, 3/1 to
EtOAc/AcOH, 50/1) provided 36a as a pale yellow oil
(18 mg, 64%). IR (neat) 3418, 2928, 2858, 2649, 1731,
1455, 1417, 1266, 1186, 1143, 1076, 911 cmÀ1; 1H NMR
(200 MHz, CDCl3) d 5.4–5.1 (br), 4.4–4.3 (m, 1H), 4.2–
4.1 (m, 1H), 3.75–3.7 (m, 1H), 3.23 (s, 2H), 3.4–2.4 (m,
7H), 2.3–2.2 (m, 1H), 2.1–1.1 (m, 14H), 0.90 (t, J=6 Hz,
3H); MS (APCI) m/z 391 (MÀH)À.
1
afford 34a as a pale yellow oil (81 mg, 53%). H NMR
(200 MHz, CDCl3) d 4.25–4.15 (m, 1H), 4.05–3.95 (m,
1H), 3.74 (s, 3H), 3.7–3.6 (m, 1H), 3.23 (s, 2H), 3.3–2.3
(m, 7H), 2.0–1.0 (m, 15H), 1.0–0.8 (m, 21H), 0.1–0.0 (m,
12H).
3,7-Dithia-15-Me-PGE1 methyl ester 11,15-bis(t-butyldi-
1
methylsilyl ether) 34b. 65% yield; H NMR (200 MHz,
CDCl3) d 5.69 (d, J=15.4 Hz, 1H), 5.5–5.4 (m, 1H),
4.44–4.30 (m, 1H), 4.15–3.98 (m, 1H), 3.74 (s, 3H), 3.21
(s, 2H), 3.00–2.10 (m, 8H), 2.00–1.76 (m, 2H), 1.60–1.14
(m, 11H), 0.93–0.82(m, 12H), 0.11 (s, 9H), 0.06 (s, 3H),
0.05 (s, 3H).
3,7-Dithia-15-Me-PGE1 36b. 39% yield; IR (neat) 3600–
3100, 2931, 2861, 1732, 1417, 1381, 1262, 1127, 1082,
1
974, 918, 758, 667 cmÀ1; H NMR (200 MHz, CDCl3) d
5.84–5.46 (m, 2H), 5.36–4.70 (br), 4.47–3.98 (m, 2H),
3.15 (s, 2H), 3.06–2.20 (m, 7H), 2.04–1.72 (m, 2H),
1.60–1.40 (m, 2H), 1.32–1.10 (m, 9H), 0.81 (t,
J=6.4 Hz, 3H); MS (FAB) m/z: 387 (MÀH2O+H)+.
3,7-Dithia-15-deoxy-16-(S)-hydroxy-16-methylPGE1
methyl ester 11,15-bis(t-butyldimethylsilyl ether) 34c.
34% yield; 1H NMR (200 MHz, CDCl3) d 5.67 (dt,
J=16, 7 Hz, 1H), 5.34 (dd, J=16, 8 Hz, 1H), 4.04 (q,
J=7 Hz, 1H), 3.73 (s, 3H), 3.20 (S, 2H), 2.9–2.2 (m,
10H), 2.0–1.8 (m, 2H), 1.5–1.2 (m, 9H), 1.0–0.8 (m,
12H), 0.2–0.0 (m, 12H).
3,7-Dithia-15-deoxy-16-(S)-hydroxy-16-methylPGE1 36c.
75% yield; IR (neat) 3392, 2932, 1714, 1403, 1262,
1
1147, 1079, 974, 908, 733 cmÀ1; H NMR (200 MHz,
CDCl3) d 5.9–5.7 (m, 1H), 5.7–5.5 (m, 1H), 4.6–4.4 and
4.2–4.0 (m, 1H), 4.1–3.7 (br) 3.24 (s, 2H), 3.5–3.4 and
3.2–2.2 (m, 10H), 2.0–1.8 (m, 2H), 1.6–1.1 (m, 9H),
0.93 (t, J=7 Hz, 3H); MS (FAB) m/z 405
(MÀH2O+H)+.
3,7-Dithia-13,14-dihydroPGE1 methyl ester 35a. A solu-
tion of bis(t-butyldimethylsilyl ether) 34a (68 mg,
0.11 mmol) and pyridine (0.4 mL) in CH3CN (2.5 mL)
.
was cooled in an ice-bath and treated with (HF)n py
(Aldrich, 0.8 mL). The reaction mixture was stirred for
30 min at room temperature and then slowly poured
into a stirred mixture of EtOAc and saturated aqueous
NaHCO3. The aqueous layer was extracted with EtOAc
twice and the combined EtOAc layer was succes-
sively washed with 1 N HCl, H2O, brine and dried
over Na2SO4. The solvent was removed by eva-
poration and the residue was purified by column
chromatography on silica gel (EtOAc/hexane, 1/1–3/
1 then EtOAc/AcOH, 100/1) to afford 35a as a
yellow oil (37 mg, 84%). 1H NMR (200 MHz,
CDCl3) d 4.4–4.3 (m, 1H), 4.2–4.1 (m, 1H), 3.75 (s,
3H), 3.7–3.6 (m, 1H), 3.24 (s, 2H), 3.4–2.4 (m, 7H),
2.3–2.2 (m, 1H), 2.1–1.1 (m, 14H), 0.90 (t, J=6 Hz,
3H).
Prostanoid EP and IP receptor binding assay
Membranes from CHO cells expressing the prostanoid
receptors were incubated with radioligand (2.5 nM of
[3H]PGE2 for EP1-4 or 5.0 nM of [3H]Iloprost for IP)
and the test compounds at various concentrations in
assay buffer (10 mM Kpi (KH2PO4, KOH; pH 6.0),
1 mM EDTA and 0.1 mM NaCl, for EP1-4-receptors;
50 mM Tris–HCl (pH 7.5), 1 mM EDTA and 10 mM
MgCl2 for IP-receptor). Incubation was carried out at
25 ꢀC for 60 min except for EP1 (20 min) and IP (30 min)
receptors. The incubation was terminated by filtration
through Whatman GF/B filters. The filters were then
washed with ice-cold buffer [10 mM Kpi (KH2PO4,
KOH; pH 6.0), 0.1 mM NaCl for EP1-4; 10 mM Tris–
HCl (pH 7.5), 0.1 mM NaCl for IP], and the radio-
activity on the filter was measured in 6 mL of
liquid scintillation (ACSII) mixture with a liquid
scintillation counter. Nonspecific binding was deter-
mined by incubation of 10 mM unlabeled PGE2 (for
EP1-4) or 1 mM unlabeled Iloprost (for IP) with
assay buffer.
3,7-Dithia-15-Me-PGE1 methyl ester 35b. 48% yield; 1H
NMR (200 MHz, CDCl3) d 5.78 (d, J=15.4 Hz, 1H),
5.7–5.5 (m, 1H), 4.49–4.34 (m, 1H), 4.20–4.02 (m, 1H),
3.72 (s, 3H), 3.21 (s, 2H), 3.06–2.00 (m, 9H), 2.00–1.86
(m, 2H), 1.60–1.44 (m, 2H), 1.40–1.18 (m, 9H), 0.87 (t,
J=6.5 Hz, 3H).

988
T. Maruyama et al. / Bioorg. Med. Chem. 10 (2002) 975–988
4. Tanaka, T.; Okamura, N.; Bannai, K.; Hazato, A.;
Measurement of cAMP production
Sugiura, S.; Manabe, K.; Kamimoto, F.; Kurozumi, S. Chem.
Pharm. Bull. 1985, 33, 2359.
5. Okamoto, S.; Kobayashi, Y.; Kato, H.; Hori, K.; Takaha-
shi, T.; Tsuji, J.; Sato, F. J. Org. Chem. 1988, 53, 5590.
6. The enone 16 was obtained commercially from Nissan
Chemical Industries, Co, Ltd.
Chinese hamster ovary (CHO) cells expressing EP4- or
IP-receptors were cultured in 24-well plates (1Â105 cells/
well). After 2days, the media were removed and cells
were washed with 500 mL of Minimum Essential Med-
ium (MEM) and preincubated for 10 min in 450 mL of
assay buffer (MEM containing 1 mM of IBMX, 1% of
BSA) at 37 ꢀC. Then reaction was started with the
addition of each test compound in 50 mL of assay buffer.
After incubation for 10 min at 37 ꢀC, the reaction was
terminated by addition of 500 mL of ice-cold 10% tri-
chloroacetic acid. The cAMP production was measured
by radioimmunoassay using a cAMP assay kit (Amer-
sham).
7. Kitano, Y.; Matsumoto, T.; Wakasa, T.; Okamoto, S.;
Shimazaki, T.; Kobayashi, Y.; Sato, F.; Miyaji, K.; Arai, K.
Tetrahedron Lett. 1987, 28, 6351 The optical purity of the
1
obtained allyl alcohols was >95% ee by H NMR analysis of
(R)- and (S)-MTPA ester.
8. Kiriyama, M.; Ushikubi, F.; Kobayashi, T.; Hirata, M.;
Sugimoto, Y.; Narumiya, S. Br. J. Pharmacol. 1997, 122, 217.
9. The detailed biological profiles of 3-thiaPGE1 will be
reported in the following paper.
10. 16-(R)- and 16-(S)-Methyl-PGE2 was reported to exhibit
more potent inhibitory activity against gastric juice excretion
than PGE2 Hayashi, M.; Miyake, H.; Tanouchi, T.; Iguchi, S.;
Iguchi, Y.; Tanouchi, F. J. Org. Chem. 1973, 38, 1250.
11. (a) 17-(S)-Methyl moiety was used as the o chain moiety
of Limaprost and Ornoprostil. Drugs Future 1982, 7, 116. (b)
Drugs Future 1978, 3, 536.
12. (a) 15-Cyclopentyl and 15-cyclohexyl derivatives were
reported to exhibit potent inhibitory activity against platelet
aggregation Morley, J.; Page, C. P.; Paul, W.; Mongelli, N.;
Cesarini, R.; Gandorlfi, C. Prostaglandins, Leukotrienes, Med.
1983, 11, 391. (b) ref 4. (c) Caldwell, A. G.; Harris, C. J.;
Stepney, R.; Whittaker, N. J. Chem. Soc., Perkin Trans. 1,
1980, 495.
13. 13,14-Dihydro-16-phenyl-o-tetranor-PGE2 was reported
to display a tissue-selective hypotensive profile: Johnson,
M. R.; Schaaf, T. K.; Constantine, J. W.; Hess, H.-J. Prosta-
glandins 1980, 20, 515.
Measurement of intracellular Ca2+ production
Intracellular Ca2+ concentration was measured using
Jasco CAM220 Spectrofluorometer. CHO cells expres-
sing EP3-receptor were cultured for 2days. After the
media were removed, the cells were washed with PBS
and centrifuged at 800 rpm for 3 min. The cells were
incubated at 37 ꢀC for 60 min with fura 2-AM in the
conditioned medium consisting of MEM containing
20 mM indomethacin, 10% FCS and 10 mM Hepes–
NaOH (pH 7.4). The medium containing the cells was
centrifuged at 800 rpm for 3 min and the cells were sus-
pended in assay buffer consisting of MEM containing
2 mM indomethacin, 0.1% BSA and 10 mM Hepes–
NaOH (pH 7.4). The test compound was added to the
suspension of the cells under stirring. Intracellular Ca2+
production was calculated from the ratio of the fluores-
cence intensities at 340 and 380 nm.
14. 17-Phehyl-o-trinor-PGE2 was often used as a selective
EP1- and/or EP3-receptor agonist in the biological evaluation.
Miller, W. L.; Weeks, J. R.; Lauderdale, J. W.; Kirton, K. T.
Prostaglandins 1975, 9, 9.
15. A 16-phenoxy moiety was used as the o chain moiety of
Sulprostone. Drugs Future 1978, 3, 59.
16. A 16(R)-methyl-16(S)-hydroxy-15-deoxy moiety was used
as the o chain moiety of Misoprostol. Collins, P. W.; Dajani,
E. Z.; Pappo, R.; Gasiecki, A. F.; Bianchi, R. G.; Woods,
E. M. J. Med. Chem. 1983, 26, 786.
References and Notes
1. Coleman, R. A.; Smith, W. L.; Narumiya, S. Pharmacol.
Rev. 1994, 46, 205.
2. Coleman, R. A.; Grix, S. P.; Head, S. A.; Louttit, J. B.;
Mallett, A.; Sheldrick, R. L. G. Prostaglandins 1994, 47, 152.
3. Narumiya, S.; Sugimoto, Y.; Ushikubi, F. Physiol. Rev.
1999, 79, 1193.
17. Subtype selectivity of 4p (EC50EP3/EC50EP4) was recon-
firmed by measuring both of the EP3- and EP4-receptor ago-
nist activities because of its interesting biological profile as a
new chemical lead.