Lactams as EP4 prostanoid receptor subtype selective agonists. Part 1: 2-Pyrrolidinones-stereochemical and lower side-chain optimization.

Article abstract of DOI:10.1016/j.bmcl.2004.01.063

A series of 7-[(5R)-substituted 2-oxo-1-pyrrolidinyl]-heptanoic acids were prepared, their isomeric purity determined, and pharmacologically evaluated. Lactams with affinity for the EP(4) receptor displayed agonist behavior. The lower side-chain of the la

Full text of DOI:10.1016/j.bmcl.2004.01.063

Bioorganic & Medicinal Chemistry Letters 14 (2004) 1655–1659
Lactams as EP4 prostanoid receptor subtype selective agonists.
Part 1: 2-Pyrrolidinones-stereochemical and lower
side-chain optimization
Todd R. Elworthy,* Denis J. Kertesz, Woongki Kim, Michael G. Roepel,
Lina Quattrocchio-Setti, David B. Smith, Jahari Laurant Tracy, Audrey Chow, Fujun Li,
Emma R. Brill, Leang K. Lach,y Daren McGee, Diana S. Yang and San-San Chiou{
Roche Palo Alto, Department of Medicinal Chemistry, 3431Hillview Avenue, Palo Alto, CA 94304-1397, USA
Received 18 September 2003; revised 22 January 2004; accepted 22 January 2004
Respectfully and warmly dedicated to the memory of Brian H. Vickery, deceased June 2002.
Abstract—A series of 7-[(5R)-substituted 2-oxo-1-pyrrolidinyl]-heptanoic acids were prepared, their isomeric purity determined,
and pharmacologically evaluated. Lactams with affinity for the EP4 receptor displayed agonist behavior. The lower side-chain of the
lactam template could be substituted to afford ligands (e.g., 17, 24, 30, 31, and 33) of high potency and greater than 1000-fold
affinity for EP4 versus the other EP prostanoid receptors.
# 2004 Elsevier Ltd. All rights reserved.
Biosynthetic products of arachidonic acid, namely
prostaglandin E2 (1, PGE2), are released and exert an
effect(s) at the site where they are produced. PGE2 is a
potent paracrine (tissue) and autocrine (cell) mediator
by acting on at least four pharmacologically distinct
receptors: the prostanoid EP1, EP2, EP3, and EP4
receptors1 which are widely distributed throughout the
body.
gram was initiated based on our preliminary finding that
racemic 8-aza-11-deoxyPGE1 23 behaved as an agonist
at the EP4 receptor.4 The focus of this letter is to
describe the preparation and in vitro pharmacological
evaluation of some o-side-chain derivatives of lactam 6
(Fig. 1).
The functional activity of compounds was assessed by a
gene reporter assay. Recombinant EP4 receptor5 in
conjunction with cAMP response element and lucifer-
ase6 were stably transfected in CHO cells. Table 1
displays the activity for all four stereoisomers of 8-aza-
11-deoxyPGE1 skeleton that were prepared discretely as
previously described.7 Lactam 6 was the most potent
agonist of the four isomers and it was not surprising to
find that it bears the natural configurations (12R, 15S)
of 1.
Suda et al. reported that the EP4 receptor plays a critical
role in bone biology in vitro.2 A current hypothesis in
this arena is that selective stimulation of the EP4 recep-
tor will lead to preferential effects in bone tissue and
spare effects on the cardiovascular, gastrointestinal and
reproductive systems and other tissues that are observed
by systemic administration of PGE2 and other non-
selective agonists. We sought to identify a chemically
simplified class that would possess structure–activity
relationship(s) towards EP4 subtype selectivity. A pro-
To access new compounds, alcohol 77 served as a key
intermediate as outlined in Scheme 1. It was oxidized to
the corresponding aldehyde under Swern conditions and
directly subjected to olefination conditions.8 The
enantiomeric purity of 8 (R0=n-pentyl) was determined
by chiral stationary phase HPLC to be 97% ee [tR 43.8
min with Chiracel1 OJ column, eluant: 5% i-PrOH in
n-hexane; [a]2D2 À1.1ꢀ (c 2.0, EtOH), lit. as the methyl
* Corresponding author. Fax: +1-650-354-2442; e-mail: todd.elworthy@
roche.com
y
Current Address: ARYx Therapeutics, 2338 Walsh Ave., Santa
Clara, CA 95051, USA
Current Address: Elan Pharmaceuticals, 800 Gateway Blvd., South
San Francisco, CA 94080, USA
{
0960-894X/$ - see front matter # 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.01.063

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T. R. Elworthy et al. / Bioorg. Med. Chem. Lett. 14 (2004) 1655–1659
ester [a]2D9 À0.9ꢀ (c 2.0, EtOH)7]. Alcohols 9 and 10
were produced by hydride-based methods depicted in
Scheme 1. The C-15 diastereomers were resolved
(>96% dr) by silica gel chromatography as their ethyl
esters when R0¼aryl (eluant: 1:1 ethyl acetate:toluene or
10% i-PrOH in 1:3 ethyl acetate:hexane). Allylic alcohol
9 (R0¼aryl) was more efficiently prepared by treatment
of 8 with 10–20 mol% (R)-2-methyloxazaborolidine and
70 mol% BH3–SMe2 according to the method of Corey
et al.9 When 8 (R0=aryl) was treated to these asym-
metric conditions, an inseparable mixture of 9 and 10 as
well as the corresponding saturated alcohols was
obtained. The 13,14-dihydro-15-aryl compounds were
synthesized to >95% dr to circumvent this problem
and others (vide infra). Hydrogenation of 8 (R0=aryl)
at 1 atm H2, catalytic Pd-C, EtOAc, 1.5 h, followed by
reduction [10 mol% (S)-2-methyl-CBS, 70 mol% BH3-
SMe2, toluene, 0 ꢀC]9 produced the (15R) configured
benzylic alcohol. The final acids were generated under
standard conditions (5 equiv of LiOH or NaOH in aq
Figure 1. Structures of 1 and 2.
Table 1. EP4 Prostanoid receptor activity: stereochemical relation-
ships of 8-aza-11-deoxyprostanoids
Absolute configurations
Structure
EC50 (nM)a
6.1b
(12R,15S)
1
(12S,15S)
(12S,15R)
(12S,15R)c
(12S,15R)d
>100,000
200,000
6100
ꢀ
MeOH, 0 C to rt).
Scheme 2 displays methods of preparing the b-keto-
phosphonates 11 that were employed in Scheme 1. The
most routine method of preparation is shown in eq 1.10
We identified an additional product 12, when R0=Bn, if
this reaction were allowed to warm above À78 ꢀC.
Phosphonates 11 and 12 were separated by silica chro-
matography. The undesired methylated product likely
formed by subsequent deprotonation of 11 and then
neutral dimethyl methylphosphonate behaved as an
electrophilic source of methyl to result in 12. In some
instances, it was more expedient to use an alternative
method to prepare 11 when R0=alkyl, or cycloalkyl-
alkyl eq 2.11
56 (12)
a The value is the average of a minimum of three determinations except
where noted in parenthesis.
b Slipetz, D.; Buchanan, S.; Mackereth, C.; Brewer, N.; Pellow, V.;
Hao, C.-m.; Adam, M.; Abramovitz, M.; Metters, K. M. Biochem.
Pharmacol. 2001, 62, 997 reported EC50 0.5 nM for 1 (or 3.1 nM
pretreated with 1.0 mM of 1 30 min prior to assay).
c The C-15 dr of 5:6 was determined to be 20:1 by HPLC: tR 5.6 min
(Zorbax SB-Phenyl column, eluant: 20% CH3CN, 0.5% TFA in
water for 1.0 min then linear gradient to 45% CH3CN over 5.0 min).
d The C-15 dr of 5:6 was determined to be 1:120 tR 5.3 min.
Scheme 1. General scheme for elaboration of lactams.
Scheme 2. Preparation of b-ketophosphonates.

T. R. Elworthy et al. / Bioorg. Med. Chem. Lett. 14 (2004) 1655–1659
1657
Table 2. E-Type prostanoid receptor profile of selected lower side chain (12R)-8-Aza-11-deoxy-prostaglandins
Compound
Structure
Binding affinity, Ki (nM)a
Activity, EC50 (nM)a hEP4
EP1
EP2
EP3
EP4
1
6
1
4.5 (2)
6.4 (6)
4500
8.0
0.8 (27)
4.5 (6)
6.1
>100,000 (2)
3000 (18)
56 (12)
13
14
15
ndb
nd
>100,000
71,000
56,000
4.2
7.5
6.1
200 (6)
120
16,000 (6)
100,000 (6)
nd
31,000
140 (6)
16
17
18
19
20
21
22
23
24
25
26
27
28
29
>100,000 (2)
nd
29,000
22,000 (6)
164,000
41,000
68,000
nd
12,000 (6)
13,000
nd
1.6 (6)
16
17 (9)
12 (15)
460 (9)
180 (6)
>10,000
500 (9)
130 (6)
>10,000
40
>100,000 (2)
nd
28,000 (2)
nd
38,000 (6)
20,000 (6)
nd
12 (6)
2,300
140
nd
131,000
12,000
nd
7.4
nd
nd
nd
nd
nd
58,000
nd
4,900
10
nd
nd
nd
42,000 (9)
360 (6)
40 (6)
nd
32,000
42,000
85,000
4200
>100,000
>100,000
>100,000
>100,000
360
nd
6.2
nd
420 (6)
390 (9)
170 (6)
nd
50 (6)
(continued on next page)

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T. R. Elworthy et al. / Bioorg. Med. Chem. Lett. 14 (2004) 1655–1659
Table 2 (continued)
Compound
Structure
Binding affinity, Ki (nM)a
Activity, EC50 (nM)a hEP4
EP1
EP2
EP3
EP4
32
30
31
50,000 (2)
nd
>100,000
85 (9)
nd
nd
nd
>100,000
>100,000
26,000
38,000
3.1
4.9
8.2
0.8 (6)
32
33
>100,000
>100,000
13 (6)
15 (6)
The straight line (at C-15) denotes a dr of 1:1 for the compound.
a The value is the average of a minimum of three determinations except where noted in parentheses.
b nd=Not determined.
Selected lactams bearing the native PGE1 a-chain are
shown in Table 2. Compounds were studied for their
generate agonists of nanomolar potency at the EP4
receptor. This class presents structure–activity relation-
ships in both the 15- and 16-phenyl series. Ligands with
o-chain meta-biphenyl or meta-phenoxyphenyl sub-
stitution can display greater than 1000-fold subtype
selectivity for EP4, as determined by affinity measure-
ments. The 15-biphenyl subclass allows for the removal
of the metabolically labile 13,14-unsaturation and flex-
ibility of the nature of the distal substituent.
5
affinity at the EP1,12 EP2,4b EP3,13 and EP4 receptors
following a determination of their activity at the EP4
(vide supra). The affinity estimates generated for 1 are in
agreement with published reports4 and the lactam 6 was
found to confer subtype selectivity for EP4. Data from
compounds 6, and 13–19 illuminated a SAR aligned
with a published report.14a Data for 16 (1:1 dr at C-15)
and 17 [>96% dr and assigned (15S) based on pre-
cedence9] demonstrated that the greater potency at EP4
resides with the naturally configured isomer. This finding
was also recently reported by Billot et al.15 The 13,14-
dihydro- 18 and the 15-keto- 24 compounds are less
potent at EP4 and are reflections of historical findings for
PGs.
References and notes
1. Abramovitz, M.; Metters, K. M. Ann. Reports Med.
Chem. 1998, 33, 223.
2. Suda, M.; Tanaka, K.; Natsui, K.; Ushi, T.; Tanaka, I.;
Fukushima, M.; Shigeno, C.; Konishi, J.; Narumiya, S.;
Ichikawa, A.; Nakao, K. Endocrinology 1996, 137, 1698.
3. Bolliger, G.; Muchowski, J. M. Tetrahedron Lett. 1975,
2931.
4. (a) Two reports of receptor binding profile with cyclo-
pentane-type ligands were known at the outset of our
program: Kiriyama, M.; Ushikubi, F.; Kobayashi, T.;
Hirata, M.; Sugimoto, Y.; Narumiya, S. Br. J. Pharmacol.
1997, 122, 217. (b) Abramovitz, M.; Adam, M.; Boie, Y.;
Carriere, M.-C.; Denis, D.; Godbout, C.; Lamontagne, S.;
Rochette, C.; Sawyer, N.; Tremblay, N. M.; Belley, M.;
Gallant, M.; Dufresne, C.; Gareau, Y.; Ruel, R.; Juteau,
H.; Labelle, M.; Ouimet, N.; Metters, K. M. Biochim.
Biophys. Acta 2000, 1483, 285.
5. An, S.; Yang, J.; Xia, M.; Goetzl, E. J. Biochim. Biophys.
Res. Commun. 1993, 197, 263.
6. Fitzgerald, L. R.; Mannan, I. J.; Dytko, G. M.; Wu, H.-
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7. Saijo, S.; Wada, M.; Himizu, J.-I.; Ishida, A. Chem.
Pharm. Bull. 1980, 28, 1449.
8. Most enones of this letter were prepared according to:
Blanchette, M. A.; Choy, W.; Davis, J. T.; Essenfeld,
A. P.; Masamune, S.; Roush, W. R.; Sakai, T. Tetra-
hedron Lett. 1984, 25, 2183 Preparation of enone 8, R0=
n-pentyl is representative: A-78ꢀ CH2Cl2 (90 mL) solution
of dimethyl sulfoxide (1.27 mL, 16.5 mmol) was treated
with oxalyl chloride (2 M CH2Cl2, 7.2 mL, 14.4 mmol),
In order to increase activity at EP4, the 15-phenyl com-
pounds were elaborated and activity was found to be
more reliant on meta- substitution. A comparison of the
pairs 15 and 16 versus 20 and 21 demonstrate this find-
ing (Table 2). Compound 24 displayed a favorable pro-
file but was found to be acid sensitive. It degraded
approximately 75% at pH 2 at 40 ꢀC over 3 days as
compared to 21 and 22 which suffered no measurable
loss under the same conditions. Investigation of sub-
stituents of 20 produced the following: meta-phenyl-
(e.g., 26) or-phenoxy-substitution (e.g., 30) restored EP4
activity. Furthermore, a small 20-substituent of the
biphenyl system (e.g., 27) was optimum for EP4 affinity
and activity. It was also found that the presentation of a
13,14-single bond and the (15R)-configured hydroxyl
restored high potency (e.g., 22 and 33) versus their more
rigid counterparts (21 and 32, respectively). The 20,40-
disubstituted biphenyls 31 and 32 could be substituted
with a distal (40-) hydrophobic or polar and potentially
ionizable moiety and retain high subtype selectivity and
excellent activity at the EP4 receptor.
In summary, 8-aza-11-deoxy-(12R)-PGE1 derivatives
can be prepared in high diastereomeric purity. The 1-
heptanoic-2-pyrrolidinone template was utilized to

T. R. Elworthy et al. / Bioorg. Med. Chem. Lett. 14 (2004) 1655–1659
1659
drop wise, and stirred for 15 min. Alcohol 7 (2.8 g, 10.4
mmol) was dissolved in CH2Cl2 (5 mL) and added to the
À78ꢀ solution of activated DMSO and stirred for an
additional 15 min. At which time, Et3N was added rapidly
and the resulting suspension was allowed to warm to rt
before being poured into a separatory funnel containing
aqueous NaHCO3 and CH2Cl2. The combined organic
extract was dried over Na2SO4, filtered, and the volatiles
were removed. 1H NMR analysis of the crude aldehyde
(3.1 g) suggested the purity was 90% which was immedi-
ately treated with CH3CN (15 mL), LiCl (385 mg, 9.1
mmol), and dimethyl 2-oxoheptylphosphonate (1.0 equiv,
1.72 mL, 8.3 mmol) at rt. The suspension was treated with
iPr2NEt (1.5 mL, 8.7 mmol) and stirred at rt for 17 h. The
enone 8 (1.66 g, 4.55 mmol) was isolated by extraction
(H2O and EtOAc 4 ꢁ 50 mL), dried over Na2SO4, and
subjected to SGC (eluant: 1:1 hexane:EtOAc): [a]2D2 À1.1ꢀ
(c 2.0, EtOH), lit. as the methyl ester [a]2D9 À0.9ꢀ (c 2.0,
EtOH).7
9. Corey, E. J.; Bakshi, R. K.; Shibata, S.; Chen, C.-P.;
Singh, V. K. J. Am. Chem. Soc. 1987, 109, 7925.
10. Bindra, J. S.; Johnson, M. R. Chem. Abstr. 1977, 87,
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1993, 36, 243.
12. Funk, C. D.; Furci, L.; FitzGerald, G. A.; Grygorczyk,
R.; Rochette, C.; Bayne, M. A.; Abramovitz, M.; Adam,
M.; Metters, K. M. J. Biol. Chem. 1993, 268, 26767.
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14. (a) Cameron, K. O.; Ke, H.; Lefker, B. A.; Thompson,
D. D. Chem Abstr 2001, 135, 76786. (b) DeFranco, R. J.;
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son, A. J. Chem. Abstr. 1979, 92, 146340.
15. Billot, X.; Chateauneuf, A.; Chauret, N.; Denis, D.;
Greig, G.; Mathieu, M.-C.; Metters, K. M.; Slipetz, D. M.;
Young, R. N. Bioorg. Med. Chem. Lett. 2003, 13, 1129.