2,5-Diketopiperazines as potent, selective, and orally bioavailable oxytocin antagonists. 2. Synthesis, chirality, and pharmacokinetics

Article abstract of DOI:10.1021/jm050557v

A short stereoselective synthesis of a series of chiral 7-aryl-2,5-diketopiperazines oxytocin antagonists is described. Varying the functionality and substitution pattern of substituents in the 7-aryl ring and varying the chirality of this exocyclic ring have produced potent oxytocin antagonists (pK_i > 8.5). SAR and pharmacokinetic profiling of this series of (3R,6R,7R)-2,5-diketopiperazines together with the introduction of an ortho F group in the 7-aryl ring to improve rat pK has culminated in the 2′,4′-difluorophenyldiketopiperazine derivative 37, a highly potent oxytocin antagonist against the human oxytocin receptor (pK_i = 8.9) that has > 1000-fold selectivity over all three vasopressin receptors V1a, V2, and V1b. It has good bioavailability (46%) in the rat and moderate bioavailability (13-31%) in the dog and is more active in vivo in the rat than atosiban (rat DR₁₀ = 0.44 mg/kg iv).

Full text of DOI:10.1021/jm050557v

6956
J. Med. Chem. 2005, 48, 6956-6969
2,5-Diketopiperazines as Potent, Selective, and Orally Bioavailable Oxytocin
Antagonists. 2. Synthesis, Chirality, and Pharmacokinetics
Alan D. Borthwick,*,† Dave E. Davies,† Anne M. Exall,† David G. Livermore,† Steve L. Sollis,† Fabrizio Nerozzi,†
Michael J Allen,# Marion Perren,# Shalia S. Shabbir,‡ Patrick M. Woollard,‡ and Paul G. Wyatt§
Departments of Medicinal Chemistry and DMPK, Cardiovascular and Urogenital Centre of Excellence for Drug Discovery,
GlaxoSmithKline Research and Development, Medicines Research Centre, Gunnels Wood Road, Stevenage, Herts SG1 2NY,
U.K., and Department of Assay Development and Compound Profiling, Harlow Research 2, GlaxoSmithKline, New Frontiers,
Science Park, Third Avenue, Harlow, Essex CM19 5AD, U.K.
Received June 13, 2005
A short stereoselective synthesis of a series of chiral 7-aryl-2,5-diketopiperazines oxytocin
antagonists is described. Varying the functionality and substitution pattern of substituents in
the 7-aryl ring and varying the chirality of this exocyclic ring have produced potent oxytocin
antagonists (pKi > 8.5). SAR and pharmacokinetic profiling of this series of (3R,6R,7R)-2,5-
diketopiperazines together with the introduction of an ortho F group in the 7-aryl ring to
improve rat pK has culminated in the 2′,4′-difluorophenyldiketopiperazine derivative 37, a
highly potent oxytocin antagonist against the human oxytocin receptor (pKi ) 8.9) that has
>1000-fold selectivity over all three vasopressin receptors V1a, V2, and V1b. It has good
bioavailability (46%) in the rat and moderate bioavailability (13-31%) in the dog and is more
active in vivo in the rat than atosiban (rat DR10 ) 0.44 mg/kg iv).
Introduction
all with different levels of vasopressin antagonist activ-
ity. Although several tocolytics (uterine contraction
inhibtors) have already been approved in clinical prac-
tice, they have harmful maternal or fetal side effects.2b
The first clinically tested oxytocin antagonist atosiban
(Tractocile) has a more tolerable side effect profile and
has recently been approved for use in Europe. However,
atosiban is a peptide and a mixed oxytocin/vasopressin
V1a antagonist that has to be given by iv infusion and
is less likely to be suitable for long-term maintenance
treatment because it is not orally bioavailable.4 Our
target was a potent, orally active oxytocin antagonist
with high levels of selectivity over vasopressin receptors,
which would safely delay labor by greater than 7 days
and improve infant outcome.
We recently reported8 on the identification of a novel
series of 2,5-diketopiperazine derivatives with antago-
nist activity at the human oxytocin receptor. The initial
structure-activity relationships and stereochemistry
were defined, and the most potent template was identi-
fied as the (3R,6R,7R)-6-indanyl-3-isobutyl-2,5-dike-
topiperazine-7-arylisopropylamide 1.
Preterm labor is a major clinical problem leading to
death and disability in newborns. It accounts for 10%
of all births and causes 70% of all infant mortality and
morbidity.1 It is the major cause of long-term handicap,
particularly cerebral palsy. Intensive care in incubators
is usually required, and even those diagnosed as healthy
need long-term medical support. Preterm labor has been
characterized as labor between 24 and 36 weeks of
gestation, with fetal survival increasing from 15% at 24
weeks gestation to 95% at 32 weeks. There is a huge
health burden associated with it, and delaying prema-
ture labor could dramatically reduce mortality, morbid-
ity, and healthcare costs. Hence, there is an unmet need
for an effective long-term treatment of uncomplicated
preterm labor.2,3
Oxytocin, a nonapeptide hormone, is a potent stimu-
lant of uterine contractions and is responsible for the
initiation of labor via the interaction with the oxytocin
receptors in the mammalian female uterus. The oxytocin
receptor is a seven-transmembrane (7TM) (Gq-coupled)
receptor with no subtypes but related to the vasopressin
receptors.17 Oxytocin antagonists have been shown to
inhibit uterine contractions and delay preterm delivery.2c
Hence, there is increasing interest in oxytocin antago-
nists as a result of their potential application in the
prevention of preterm labor. Several templates have
been investigated as potential oxytocin antagonists,5-7
* To whom correspondence should be addressed. Phone: +44 (0)-
1438 763422. Fax: +44 (0)1438 768483. E-mail: alan.d.borthwick@
gsk.com.
† Department of Medicinal Chemistry, Cardiovascular and Urogeni-
tal Centre of Excellence for Drug Discovery, Stevenage, U.K.
# Department of Assay Development and Compound Profiling,
Harlow, U.K.
We now report on the synthesis, further SAR studies,
and preliminary pharmacokinetics of these novel 2,5-
diketopiperazine oxytocin antagonists. This has given
orally active compounds that are >1000-fold selective
for the human oxytocin receptor relative to all three
‡ Department of DMPK, Cardiovascular and Urogenital Centre of
Excellence for Drug Discovery, Stevenage, U.K.
§ Current address: Astex-Technology, 436 Cambridge Science Park,
Milton Road, Cambridge CB4 0QA, U.K.
10.1021/jm050557v CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/08/2005

2,5-Diketopiperazines Oxytocin Antagonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22 6957
Scheme 1a
a Reagents and conditions: (a) (Ph)2CHdNCH2CO2CMe3, LDA, THF; (b) TFA, CH2Cl2; (c) KOCN, H2O, 90 °C, 3 h, then concen-
trated HCl, 20 °C, 1.3 h, then at 90 °C, 15 h; (d) D-hydantoinase, pH 10.5; (e) D-carbamoylase, pH 8.5; (f) (Boc)2O, THF, Et3N, 16 h, room
temp.
vasopressin receptors V1a, V2, and V1b, with greater
in vivo potency than atosiban in animal models.
The stereochemistry of the tertiary butylamide 17 was
determined to be 3R,6R,7R by an alternative stereospe-
cific synthesis,12 and the configuration of this amide 17
was confirmed as 3R,6R,7R for C104, C102, C125 by
single-crystal X-ray analysis (Figure 1). It is of interest
to note the presence of two unique molecules of 17 per
asymmetric unit, molecule A and molecule B, which
differ in the conformation of the indanyl side chain
relative to the 2,5-diketopiperazine ring. The main
distinguishing feature between the two molecules is the
magnitude of the torsion angle between the plane of the
indane ring and the 2,5-diketopiperazine ring. For
molecule A, ω1 is 93.8° for torsion angle C107-C106-
C105-C104. For molecule B, ω1 is 157.4° for torsion
angle C207-C206-C205-C704 (Figure 1). To assess
the relative energies of the two conformations, molecular
orbital calculations13 were conducted and the energies
of the two distinct conformers in the unit cell were
compared. The energy-optimized structure calculated for
each conformer was comparable to that of the solid
state, confirming that both molecules of the unit cell
are low-energy conformers. The two energy-optimized
conformations were shown to have an energy difference
of 1.1 kcal/mol.
Comparison of the CD spectra of 17 and 37 showed
that the configuration of the 7-aryl substituent and the
3,6-substituents on the diketopiperazine ring were the
same (RRR) in both compounds and different from the
3R,6R,7S isomer 18.
Reduction of 15 with LiAlH4 gave the monoketopip-
erazine 45 in 31% yield (Scheme 3). Alkylation of 15
with allyl iodide gave 44 selectively in 35% yield. This
occurred at the 1-position of the diketopiperazine ring.
In contrast, alkylation of 15 with methyl iodide gave
the tertiary amide 43 in 32% yield where the smaller
methyl group had preferentially alkylated the exocyclic
amide.
Chemistry
The synthesis of the Boc-protected homochiral R-
indanylglycine is outlined in Scheme 1. The known
racemic indanylglycine 49 was prepared by alkylation
of the benzhydrylimine of Boc-glycine with 2-iodoindane
2 to give 3, followed by acid hydrolysis.9 Reaction of 4
with potassium cyanate gave an intermediate urea that
cyclized under acidic conditions at 90 °C to give the
racemic hydantoin 5 in 91% yield. Dynamic kinetic
resolution of the racemic hydantoin 5 with D-hydantoi-
nase10,11 gave the chiral urea 6 (90% ee, 93% yield),
which was converted by D-carbamoylase to the R-
indanylglycine 7 (>99% ee, 85% yield). Boc protection
of 7 gave N-tert-butoxycarbonyl-D-indanylglycine 8 in
95% yield.
The two-stage synthesis of indanyldiketopiperazines
is outlined in Scheme 2. The first stage used a four-
component Ugi reaction where the imine formed by the
initial reaction of the arylaldehyde 9 and amine 10
D-leucine methyl ester reacted with the isonitrile 11 (R1
) isopropyl or tertiary butyl), and the resulting inter-
mediate imminium ion then further reacted with the
acid 8 (Boc-protected indanyl-R-glycine), which rear-
ranged to give the tripeptide 12. In the second stage
deprotection of the Boc-amine in 12 with TFA followed
by cyclization in the presence of Et3N gave a 1:3 mixture
of the 3R,6R,7R 13-42 and 3R,6R,7S 14-38, isomers,
respectively. The minor 3R,6R,7R isomers 13-42 were
isolated in e25% yield. Changing the methyl ester of
leucine to the more bulky tertiary butyl ester improved
the ratio of (3R,6R,7R)/(3R,6R,7S) isomers from ∼1:3
to ∼2:3. Changing the solvent of the reaction from
methanol to trifluoroethanol shortened the time of the
reaction and decreased the volume required. However,
attempts to increase further the isomer ratio in favor
of the required (3R,6R,7R) isomer by changing the
reaction time and temperature or by further changing
solvent were unsuccessful.
Results and Discussions
SAR, Structure, and Stereochemistry. The most
potent homochiral template recently identified8 from a

6958 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22
Borthwick et al.
Scheme 2a
a Reagents and conditions: (a) Et3N, methanol, room temp, 16 h; (b) TFA, CH2Cl2, then Et3N, room temp, 16 h.
Figure 1. Molecules A and B.
series of 2,5-diketopiperazine oxytocin antagonists is
exemplified by the (3R,6R,7R)-6-indanyl-3-isobutyl-2,5-
diketopiperazine-7-phenylisopropylamide 15. Some ini-
tial SAR analysis of this template established that
6-indanyl > 6-phenethyl > 6-benzyl in terms of potency,
and a four-carbon branched alkyl was optimal for
potency at the 3-position. Also, for this semirigid
molecule the relative stereochemistry of the substituents
and their chirality was crucial for potency. For both the
3,6-subsituents the potency of cis was greater than that
of trans and for the 7-phenyl substituent the potency
of R was greater than that of S by an order of

2,5-Diketopiperazines Oxytocin Antagonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22 6959
Scheme 3a
) 8.6-8.0 for a range of electron-withdrawing and
-donating substituents at this position except 29
(CONH2), pKi ) 7.6. All R isomers were greater in
potency in the range of 1.8-1.1 log units compared to
the S isomers. A similar level of potency was exhibited
by the isopropylamides and tertiary butylamides (15
and 17) and (13 and 39). The meta-substituted deriva-
tives 40 and 42 were less active than the corresponding
para-substituted analogues 39 and 41. Hence, a whole
range of substituents at the para position of the aryl
ring maintain potency and the para-substituted aro-
matic rings are more potent than meta-substituted
aromatic rings and the R isomers are more potent than
the S isomers.
In addition to the chirality of the exocyclic 7-phenyl
substituent, the relative stereochemistry of the 3- and
6-substituents is crucial for potency. To verify the
stereochemistry of the substituents and conformation
of the diketopiperazine ring,12 an X-ray crystal structure
of 17 was obtained (Figures 1 and 2). This confirmed
the relative stereochemistry as cis for the 3 and 6
centers, which was supported in solution by strong
NOEs between the protons at the 2′ position of the
indane ring and the methylene of the 3-isobutyl group.
The X-ray crystal structure of 17 showed that the 3 and
the 6 substituents are on the same face of the DKP ring,
which is puckered. Also, strong NOEs between the
protons at the 3 and 7 positions and the 7 position and
the methylene of the 3-isobutyl substituent support the
buttressing effect on the leucine seen in the X-ray
crystal structure of 17 (Figure 2). The key functionality
of the puckered diketopiperazine ring, the lactam car-
bonyl and NH groups at the 1 and 2 positions, are also
a Reagents and conditions: (a) LiAlH4 (3 equiv)/THF, -78 °C;
(b) LHMDS (1.3 equiv)/THF, -78 °C, then MeI (17 equiv); (c)
LHMDS (1.3 equiv)/THF, -78 °C, then allyl iodide (17 equiv).
magnitude. An aromatic group at the 7-position with R
chirality was required for good potency. To extend the
SAR and find out what functionality was tolerated, an
additional set of chirally pure single isomers of the
indanyldiketopiperazines with a wide spread of elec-
tronic properties, lipophilic properties, and size was
prepared and tested for activity against the human
oxytocin receptor (Table 1).
Exploration of the para position of the aryl ring
revealed that the acetamide 13 (NHCOMe) was more
potent than carboxamide 29 (CONH2) and was similar
in potency to our previous lead,15 the benzoxazine 46
(Scheme 4), while the rest had a similar potency of pKi
Table 1. Inhibition of the Binding of Oxytocin by 7-Aryl-(R)- and 7-Aryl-(S)-2,5-diketopiperazines at the Human Oxytocin (hOT)
Receptora
compd
R
chirality
R1
pKi hOTb
compd
R
chirality
R1
pKi hOTb
13
15
19
21
23
25
27
29
17
31
33
35
39
40
NHCOMe
H
3R,6R,7R
3R,6R,7R
3R,6R,7R
3R,6R,7R
3R,6R,7R
3R,6R,7R
3R,6R,7R
3R,6R,7R
3R,6R,7R
3R,6R,7R
3R,6R,7R
3R,6R,7R
3R,6R,7R
3R,6R,7R
CHMe2
CHMe2
CHMe2
CHMe2
CHMe2
CHMe2
CHMe2
CHMe2
CMe3
8.8
8.4
8.4
8.3
8.4
8.5
8.0
7.5
8.3
8.6
8.6
8.3
8.7
8.2
14
16
20
22
24
26
28
30
18
32
34
36
NHCOMe
H
3R,6R,7S
3R,6R,7S
3R,6R,7S
3R,6R,7S
3R,6R,7S
3R,6R,7S
3R,6R,7S
3R,6R,7S
3R,6R,7S
3R,6R,7S
3R,6R,7S
3R,6R,7S
CHMe2
CHMe2
CHMe2
CHMe2
CHMe2
CHMe2
CHMe2
CHMe2
CMe3
6.9
7.3
7.0
7.1
7.3
7.6
7.0
6.8
7.1
6.8
7.4
6.8
F
F
CF3
Me
NMe2
SO2Me
CONH2
H
Cl
OMe
OCF3
NHCOMe
3′-NHCOMe
CF3
Me
NMe2
SO2Me
CONH2
H
Cl
OMe
OCF3
CMe3
CMe3
CMe3
CMe3
CMe3
CMe3
CMe3
CMe3
41
3R,6R,7R
CMe3
7.6
42
46
3R,6R,7R
CMe3
6.8
8.7
benzoxazinec
a Displacement of [3H]oxytocin from hOT by the test compound.14 b pKi values are reported as the mean value of three or more
determinations, and all results were obtained in binding assays with a standard deviation in pKi of less than 0.25. c Standard from previous
series.15

6960 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22
Borthwick et al.
Figure 2. X-ray crystal structures of 2,5-diketopiperazine 17 and deamino-oxytocin.16
Table 2. Activity of Ring Modified Diketopiperazines
important for activity. Removal of the 6-carbonyl from
15 to give the monoketopiperazine 45 resulted in a
greater than 10-fold loss in potency (Table 2). Similarly,
alkylation of 15 with allyl iodide to give the N-allyl
lactam 44 resulted in a loss in potency by 10-fold.
Interestingly, the tertiary amide 43 retained activity.
In these diketopiperazine oxytocin antagonists the
RRR stereochemistry of the three chiral centers at the
3, 6, and 7 postions and the key functionality (the
carbonyl at the 2-position and the NH at the 1-position)
of the diketopiperazine ring are essential for high
antagonist potency and hence must be crucial elements
in binding to the oxytocin receptor.
The oxytocin receptor contains seven transmembrane
domains and is a member of the class 1 family of
G-protein-coupled receptors (GPCRs). The agonist oxy-
tocin binds to the extracellular region and transmem-
brane domain of the receptor, which enables the intra-
cellular part to couple to the G proteins and initiate a
cascade of events liberating Ca2+, which causes contrac-
tions.17 The 2-Tyr and 3-Ile are the key amino acids in
oxytocin (Figure 2) for this interaction with the receptor,
generating agonist activity. Modification at the 2-posi-
tion of oxytocin produces antagonist activity. The deam-
ino OEt-Tyr2 oxytocin analogue is a potent antagonist
of oxytocin-induced contractions in the rat uterus in
vitro and in vivo.18 Modification of the 4 and 8 positions
of this deamino OEt-Tyr2 oxytocin analogue gave the
antagonist atosiban.19 In addition, structure-activity
studies of oxytocin analogues have revealed that the
antagonist property depends on a specific conformation,
and the appropriate modification of the Tyr2 plays a
crucial role in this function. The incorporation of bulky
apolar side chain amino acids in position 2 increased
potency and made more effective oxytocin antagonists.
The use of D-indanylglycine (D-IgL) as a rigid homophe-
nylalanine analogue resulted in OT receptor affinity
higher than that of D-Phe2 with greater selectivity for
the oxytocin over the vasopressin receptors.20 This
agrees with what we have found in the diketopiperazine
series of oxytocin antagonists where 6-indanyl > 6-phen-
ethyl > 6-benzyl in terms of potency.
To understand the importance of the stereochemistry
of the three chiral centers for activity in the diketopip-
erazine oxytocin antagonists, the X-ray crystal structure
of the anatagonist 17 was compared to the known
crystal structure of the agonist deamino oxytocin16
(Figure 2). This shows that they have similar phara-
macophores (those in bold) that can be overlaid. Hence,
there is a similar stereochemical relationship of the
required aryl ring, peptide backbone, and isoleucine in
oxytocin and the required aryl ring, part of diketopip-
erazine and leucine in our diketopiperazines. However
the 2,5-diketopiperazine template with three chiral
centers is a more rigid system, where the stereochem-
istry of 3,6 substituents and the vectors these take up
are highly important for potency.
The phenyl ring with the R configuration in the
exocyclic phenylisopropylamide restricts the conforma-
tional mobility of the leucine (3-isobutyl) group which

2,5-Diketopiperazines Oxytocin Antagonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22 6961
Table 3. Pharmacokinetics of Monoaryl-Substituted (3R,6R,7R)-2,5-Diketopiperazines in the Rat
ratb
compd
R
R1
pKi hOTa
AUC po
Cl
Vdss
t1/2
F, %
CHI log D c
sold
39
15
19
21
23
31
33
35
25
27
29
NHCOMe
H
CMe3
8.7
8.4
8.4
8.3
8.4
8.6
8.6
8.3
8.5
8.0
7.5
59
2.4
3.2
3.2
3.7
3.5
4.0
3.4
4.1
3.4
2.4
1.8
0.079
0.02
CHMe2
CHMe2
CHMe2
CHMe2
CMe3
114
421
280
nde
95
29
23
0.8
0.8
1.0
0.9
5
F
13
0.03
CF3
0.001
0.02
0.001
0.001
0.001
0.02
Me
37
43
0.6
0.4
0.6
0.7
Cl
2
OMe
OCF3
NMe2
SO2Me
CONH2
CMe3
CMe3
CHMe2
CHMe2
CHMe2
101
85
287
60
44
48
21
2.3
0.7
1.2
1.5
5
3
0.22
0.25
a Displacement of [3H]oxytocin from hOT by the test compound.14 pKi values are reported as the mean of three or more determinations,
and all results were obtained in binding assays with a standard deviation in pKi of less than 0.25. b Rat PK (n ) 2): AUC (h ng mL-1
)
at 5 mg kg-1, 5% DMSO/95% PEG400 formulation; Cl in mL min-1 kg-1; Vdss in L kg-1; t1/2 in h. c An HPLC method based measurement
of lipophilicity.21 d Solubility (µg/mL), a precipitation/HPLC based measurement.22 e nd ) not determined.
Table 4. Pharmacokinetic Profile of 2′,5′-Diketopiperazine Oxytocin Antagonists in the Rat and Dog and the Inhibition of OT
Binding at the Human OT (hOT) and Vasopressin at the Human (V1a, V1b, and V2) Receptorsa
vasopressin pKia
ratb,c
Cl
dogc,d
Cl
oxytocin
compd
R
pKi hOTa
hVIa
hVIb
hV2
AUC po
Vdss
F, %
AUC po
Vdss
F, %
19
25
37
4-F
4-NMe2
2,4-diF
8.4
8.5
8.9
<5.2
<4.4
5.2
<5.2
<4.3
<5.2
5.9
<4.1
6.2
421
287
1088
23
48
36
0.8
2.3
2
13
5
46
259
335
121
291e
5
15
11
0.8
1.7
1.2
13
50
13
33e
a Displacement of [3H]oxytocin from hOT or vasopressin from hV1a, hV1b, and hV2 by the test compound.14 pKi values are reported as
mean values of three or more determinations, and all results were obtained in binding assays with a standard deviation in pKi of less
than 0.25. b Rat PK (n ) 2): AUC (h ng mL-1) at 5 mg/kg, 5% DMSO/95% PEG400 formulation. c Cl in mL min-1 kg-1. Vdss in L kg-1
.
d Dog PK(n ) 1): AUC (h ng mL-1) at 0.6 mg/kg, 5% DMSO/95% PEG400 formulation. e AUC (h ng mL-1) at 0.6 mg/kg, 5% DMSO/95%
labrafil formulation.
facilitates its interaction at the oxytocin receptor. The
R configuration of the exocyclic phenylisopropylamide
allows the exocyclic amide (which is below the plane of
the diketopiperazine ring) to occupy the same space as
the hexapeptide in oxytocin, whereas in the 3R,6R,7S
diastereoisomer the inversion of the exocyclic center
does not allow these favorable interactions.
Pharmacokinetics. Because the potency was found
to be associated with the R isomer of a 4′-substituted
phenyl ring, a range of these (3R,6R,7R)-diketopipera-
zine derivatives were looked at in the rat to estimate
their pharmacokinetic profiles (Table 3). These were
chosen to give a spread of polarity, lipophiliciy (chro-
matographic hydrophobicity index (CHI) log D21), and
solubility.22 All these compounds had a lower rat oral
exposure than the F derivative 19 (AUC 421 h‚ng/mL).
Also, with the exception of the primary amide 27, all
the derivatives measured had a higher clearance than
19, and this compound was the best in this group with
a bioavailability of 13%. Although it would be useful to
increase water solubility, it can be seen from the data
that hydrophilic electron-withdrawing groups gave low
values for rat oral exposure.
The two diketopiperazines with the largest exposure
in the rat, the 4′-fluorophenyl derivative 19 and the 4′-
dimethylaminophenyl derivative 25, were tested in the
dog (Table 4). Whereas the 4′-fluorophenyl derivative
19 had similar bioavailability in both species, the 4′-
dimethylaminophenyl derivative 25 had much better
bioavailability in the dog than the rat.
The highly potent mono-4′-substituted phenyldike-
topiperazines with the best pharmacokinetic profile
were the 4′-F and 4′-NMe2 derivatives, but they had low
bioavailability in the rat. The question of how to improve
the bioavailability of this template was addressed by
analogy with a previous class of oxytocin antagonists15
where an aromatic fluoro substituent next to the ring
junction had a dramatic effect on the bioavailability,
increasing it from 46 (16%) to 47 (54%) (Scheme 4). This
is due to the increased permeability of 47 (AUC ) 7901

6962 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22
Borthwick et al.
Scheme 4
Table 5. Protein Binding and Potency of OT Antagonists at
h‚ng/mL) compared to 46 (AUC ) 1360 h‚ng/mL)
because the clearance of these are essentially the same
(11 and 10 mL min-1 kg-1, respectively). A similar
situation was seen recently28 where an ortho fluoro
substitution in a aryl ring of factor Xa inhibitors
significantly improved Caco-2 permeability. This sug-
gested that the 2′,4′-difluorophenyldiketopiperazine de-
rivative should have increased bioavailability. This
proved to be the case; the ortho fluoro effect improved
the bioavailability of the diketopiperazine template in
the rat (Table 3) where the 13% seen in the 4′-
fluorophenyl derivative 19 was increased to 46% in the
2′,4′-difluorophenyl analogue 37 (Scheme 4). A different
formulation (DMSO/labrafil) gave higher oral exposures
and improved the bioavailability to 33% for 37 in the
dog compared with 13% obtained with conventional
formulation (DMSO/PEG400) (Table 4). Overall, 37 has
good pharmacokinetics (PK) in rat (Cl 36 mL min-1
kg-1, t1/2 ) 2 h, F ) 46%, oral formulation (DMSO/
PEG400) and dogs (Cl 10 mL min-1 kg-1, t1/2 ) 1 h, F
) 33%, oral formulation (DMSO/labrafil).
Selectivity vs Human Vasopressin Receptors
and Activity in the Presence of HSA. Selectivity
relative to human vasopressin receptors for a range of
diketopiperazines (Table 4) has been established by
measuring the pKi against the human vasopressin
receptors V1a, V1b, and V2. The 2′,4′-difluorophe-
nyldiketopiperazine derivative 37 was >104-fold selec-
tive for the human oxytocin receptor over the vaso-
pressin V1a in the SPA receptor assay. All the diketo-
piperazines measured (Table 4) are >1000-fold selective
for the human oxytocin receptor relative to all three
vasopressin receptors V1a, V2, and V1b.
the hOT Receptor
hOT IC50 CHIe
%
%
pKi
shift + log D,
compd
R
R1
HSAa RSAb hOTc
HSAd
46
pH 7.4
46
25
19
37
benzoxazine
4-NMe2
4-F
95.3 90.1 8.7
2.2
3.4
3.2
3.4
CHMe2 93.8 90.7 8.5
CHMe2 90.3 87.0 8.4
CHMe2 93.4 90.2 8.9
2.2
2.2
2,4-diF
a Human serum albumin binding.23 b Rat serum albumin
binding.23 c Displacement of [3H]oxytocin from hOT by the test
compound.14 pKi values are reported as mean values of three or
more determinations, and all results were obtained in binding
assays with a standard deviation in pKi of less than 0.25. d HSA
shift ) ratio of displacement of [3H] oxytocin from hOT by the test
compound in the presence and absence of 50 mg/mL human serum
albumin.24 e An HPLC method based measurement of lipophilic-
ity.21
also carried out using rat serum albumin (RSA), and
rat was seen to parallel human protein binding (Table
5). This did not, however, differentiate between the
classes of oxytocin antagonists, so the activity of a range
of diketopiperazines against the human oxytocin recep-
tor was also measured in the presence and absence of
physiological concentrations of HSA and the loss in
activity was represented as a shift in hOT IC50 (Table
5). The diketopiperazines as a class have a minimal loss
in human oxytocin antagonist activity in the presence
of HSA (hOT IC50 shift < 2.3, relative to the previous
class lead benzoxazine, e.g., 46 hOT IC50 shift ) 46).
Human serum albumin showed little effect on the
potency of the lead 2′,4′-difluorophenyldiketopiperazine
derivative 37 with a shift of only 2.2 in its hOT IC50.
In Vivo Potency. The in vivo efficacy of the 2′,4′-
difluorophenyldiketopiperazine derivative 37 was esti-
mated in an anesthetized rat model where uterine
contractions were elicited by iv administration of oxy-
The lead compound 46 in our previous class of
oxytocin antagonists had insufficient in vivo activity to
be progressed because of the influence of protein bind-
ing. Therefore, activity in the presence of human serum
albumin (HSA) became an essential part of the screen-
ing protocol for the advancement of lead compounds. A
range of 2,5-diketopiperazine derivatives binding to
purified human serum albumin (HSA) was measured
on a HSA immobilized column. A similar exercise was

2,5-Diketopiperazines Oxytocin Antagonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22 6963
Table 6. Potency at the Human Oxytocin Receptor Compared
with the Efficacy Obtained in the Rat Uterine Contractility
Model
uncorrected. All purifications by flash chromatography were
performed using Kieselgel 60, Merck 9385 silica gel. Prepara-
tive plate chromatography was performed using Whatman
PK6F silica gel 60A plates, with the sample eluting with ethyl
acetate/cyclohexane or 2-propanol/dichloromethane mixtures.
Monitoring of reactions by TLC used Merck 60 F254 silica gel
glass backed plates (5 × 10 cm), with samples eluting with
mixtures of ethyl acetate and cyclohexane and visualized by
UV light followed by heating with aqueous phosphomolybdic
acid. Analytical HPLC experiments were run on a Hewlett-
Packard 1090 HPLC instrument, equipped with a Intersil M
column ODS2. Standard conditions were eluent systems A
(H2O, 0.1% H3PO4) and B (95% MeCN/H2O, 0.1% H3PO4):
gradient 0% B in 2 min, 0-100% B in 40 min, 100% B in 10
min, flow rate ) 1 mL/min, λ ) 215 nm). Retention times (tr)
are given in minutes. LCMS were run on a Hewlett-Packard
1050 coupled with a Micromass Platform II equipped with a
Supelco ABZplus column. Standard conditions were eluent
systems A (H2O, 0.1% formic acid, 10 mmol of ammonium
acetate) and B (MeCN, 0.05% formic acid): gradient 1 100%
A in 0.7 min, 100% A to 100% B in 3.5 min, 100% B in 3.5
min, 100-0% B in 0.3 min, flow rate ) 1 mL/min); gradient 2,
100% A in 0.7 min, 100% A to 100% B in 4.2 min, 100% B in
1.1 min, 100-0% B in 0.2 min, flow rate ) 1 mL/min); gradient
3, 100% A in 3 min, 100% A to 100% B in 20 min, 100% B in
5 min, 100-0% B in 2 min, flow rate ) 1 mL/min). All NMR
spectra were run on a Bruker 400 MHz instrument generally
as solutions in CDCl3 unless otherwise stated. IR spectra were
recorded on a Bio-rad FTS7 spectrometer from thin films on
NaCl plates, a KBr mix, or solutions in the solvent specified.
Mass spectra were run by an electrospray Hewlett-Packard
5989B instrument. CD spectra were recorded in acetonitrile
on a Jasco J-720A spectropolarimeter. Optical rotations were
taken with a Perkin-Elmer model 241 polarimeter. Enantio-
meric excess (% ee) was determined by chiral HPLC anaylsis
using a Chiracel OJ or Chiral Pak AD464 column with a UV
detector, λ ) 215 nm, and with eluents and flow rates as
indicated in each case. Final organic solutions were dried over
MgSO4 before filtration and evaporation using a Buchi Ro-
tavapor. Ambient temperature was 20 °C. All solvents used
were Fisons analytical reagents except for pentane (Aldrich
Chemical Co.) and anhydrous THF (Fluka sureseal). All other
reagents were usually obtained from Aldrich, Fluka, or Lan-
caster. Elemental microanalyses were determined by the
Microanalytical Laboratory, GlaxoSmithKline Stevenage.
rat, iv
compd
R
DR10,a mg/kg
IC50,b ng/mL
pKi hOTc
37
F
H
0.44
0.61
0.63
8.9
8.4
7.4
19
50
140
atosiban
25
a DR10 determination.26 b Plasma IC50
.
c Displacement of
[3H]oxytocin from hOT by the test compound.14 pKi values are
reported as mean values of three or more determinations, and all
results were obtained in binding assays with a standard deviation
in pKi of less than 0.25.
tocin. The reduction in uterine contractility was mea-
sured after subsequent iv administrations of increasing
doses of 37. Two methods were used for the measure-
ment of in vivo activity, plasma IC50 determination25
(plasma concentration that causes 50% inhibition of
response to standard OT dose), and DR10 determination
(dose that shifts agonist dose response to oxytocin 10-
fold).26 The 2′,4′-difluorophenyldiketopiperazine deriva-
tive 37 was more potent than atosiban in vitro and in
vivo (Table 6).
Conclusions
Substitution in the para position of the 7-aryl ring of
the (3R,6R,7R)-diketopiperazines has produced a wide
range of potent oxytocin antagonists with pKi values
greater than 8.5. SAR studies have shown that the
potency of compounds with R chirality at the 7-position
is greater than the corresponding S isomers and that
the potency at the oxytocin receptor with para substitu-
tion is greater than that with meta substitution in the
7-aryl ring. The relative stereochemistry and chirality
of the substituents on the semirigid DKP ring, shown
to be important for antagonist potency at the oxytocin
receptor, have been rationalized as mimicking the 2-Tyr
and 3-Ile key amino acids in oxytocin required for
agonist binding. Pharmacokinetic profiling of the
(3R,6R,7R)-diketopiperazines identified the 4′-F and 4′-
NMe2 phenyl derivatives with moderate oral exposures
in the rat. Increased bioavailability was achieved by
substitution in the 2′ position with fluorine, which gave
the 2′,4′-difluorophenyldiketopiperazine derivative 37.
This is highly potent against the human oxytocin
receptor (pKi ) 8.9), is active in the presence of HSA
(only a 2.2-fold shift in IC50), and has good bioavailabil-
ity (46%) in rat and moderate bioavailability (13-31%)
in the dog. It is >1000-fold selective for the human
oxytocin receptor relative to all three vasopressin recep-
tors V1a, V2, and V1b and is more active in vivo in the
rat than atosiban (rat DR10 ) 0.44 mg/kg iv). It is also
available in a short two-stage synthesis from Boc-
protected homochiral R-indanylglycine.
tert-Butyl N-(Diphenylmethylene)-2-(2-indanyl)glyci-
nate (3). To a solution of N-(diphenylmethylene)glycine tert-
butyl ester (20 g, 68 mmol, 1 equiv) in dry THF (340 mL) at
-70 °C was added a solution of 1.6 M LDA (108.5 mL, 1.1
equiv) in THF/hexane (1:1) over 10 min. After the addition
was complete, the cooling was removed and the mixture was
allowed to warm to 10 °C over 1.5 h. A solution of iodoindane
2
27 (19.9 g, 81.6 mmol, 1.2 equiv) in THF (210 mL) was added
over 30 min. The mixture was then allowed to stir at ambient
temperature overnight. The reaction was quenched with
glacial acetic acid (5.2 mL). The mixture was washed with
water (130 mL), and the aqueous portion was extracted with
EtOAc (250 mL). The combined organics were washed with
saturated NaHCO3 (400 mL), then brine (400 mL). The organic
phases was separated, dried (Na2SO4), filtered, and evaporated
to give the crude product as an orange oil. Flash chromatog-
raphy (Merck 9385 silica, eluting with 12:1 cyclohexane/
EtOAc) and evaporation gave, after trituration under cyclo-
hexane, the pure product 3 as an off-white solid (9.1 g, 33%).
1H NMR (CDCl3) δ 7.69-7.07 (m, 14H, arylH), 4.03 (d, J )
6.9 Hz, NCHindanyl), 3.27-3.15, 3.07-2.92, and 2.75-2.62
(3m, 5H, indanyl-3H, -1H, -2H), 1.46 (s, 9H, But); LCMS m/z
412 (MH+) single component 99.8%, gradient 2 (tR ) 4.24 min);
HRMS calcd for C28H29NO2 (MH+) 412.2277, found 412.2278;
HPLC 100% (tR ) 20.79 min).
rac-Indanylglycine (4). To diphenyliminoindanylglycine
tert-butyl ester 3 (79.9 g, 0.19 mol) was added 10:1 TFA/water
(242 mL). The mixture was stirred at room temperature for
5.5 h, at which point TFA (73 mL, 5 equiv) was added and the
Experimental Procedures
General Procedures. Melting points were obtained using
an Electrothermal digital melting point apparatus and are

6964 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22
Borthwick et al.
mixture was stirred at ambient temperature overnight. The
mixture was poured into water (1.5 L), and the pH was
adjusted to 8. A precipitate formed. This was filtered and
washed with diethyl ether. The cake was slurried in diethyl
ether, filtered, and washed. Drying under vacuum gave the
remained (20 min). The resin was filtered throught Celite, and
concentrated aqueous sodium hydroxide was added to the
filtrate until pH 7.0 was obtained. The prepcipate that formed
was left at 18 °C for 1 h, filtered, and dried under vacuum at
room temperature overnight to give the chiral indanylglycine
7 as a beige solid (73.8 g, 85%). 1H NMR (DMSO-d6 + TFA) δ
8.37 (br s, 3H (+water)), 7.19-7.16 and 7.11-7.06 (2m, 4H,
arylH), 4.06-3.99 (m,1H, NCHindanyl), 3.03-2.80 (m, 5H,
indanyl-3H, -1H, -2H); HPLC 97.5% (tR ) 0.93 min) (generic
fast method); chiral HPLC 100% (tR ) 5.42min) (Chirobotic T,
20% MeCN/TEAA (0.1%), pH 4.1); LCMS m/z 192 (MH+) single
component, gradient 2 (tR ) 1.43min); HRMS calcd for C11H13-
NO2 (MH+) 192.1025, found 192.1023; [R]23D -28° (c 0.20 in 1
N aqueous HCl, 10 cm cell).
1
product 4 as a white solid (32.1 g, 86%). H NMR (DMSO-d6
+ TFA) δ 8.41 (s,3H, NH3+), 7.26-7.12 (m, 4H, arylH), 4.12-
4.04 (m, 1H, NCHindanyl), 3.05-2.88 (m, 5H, indanyl-3H, -1H,
-2H); LCMS m/z 192 (MH+) single component, gradient 2 (tR
) 1.42min); HRMS calcd for C11H13NO2 (MH+) 192.1025, found
192.1025; HPLC 99.52% (tR ) 2.32 min).
rac-Indanylglycine Hydantoin (5). To a solution of
potassium cyanate (127.5 g, 1.57 mol) and water (1.6 L) was
added racemic indanylglycine 4 (100 g, 0.52 mol), and the
mixture was heated to 90 °C over 1 h and held at this
temperature for 2 h (92.8% conversion. HPLC analysis). The
mixture was cooled to 20 °C, and concentrated aqueous
hydrochloric acid (400 mL) was added over 1 h, maintaining
the temperature at 20 °C ((2 °C). After being stirred at 21 °C
for 20 min, the mixture was heated to 90 °C over 1.25 h and
held at this temperature for 15 h. The mixture was cooled to
37 °C, and water (1 L) was added to the thick white slurry.
After cooling at 10 °C for 4 h, the mixture and vessel washings
with water (500 mL) were filtered and the cake was washed
with water (2 × 500 mL). The cake was dried under vacuum
at 45 °C overnight to give the title compound 5 as a white
solid (102.8 g, 91%). 1H NMR (DMSO-d6) δ 10.71 (br s, 1H,
CONHCO), 8.09 (br s, 1H, CONH), 7.21-7.06 (m, 4H, arylH),
4.20-4.17 (m, 1H, NCHindanyl), 3.04-2.96 and 2.89-2.69
N-tert-Butoxycarbonyl-D-2-indanylglycine (8). To a
stirred suspention of R-indanylglycine (15.1 g, 79 mmol) in
tetrahydrofuran (75 mL) and water (75 mL) at room temper-
ature was added triethylamine (13 mL, 93.3 mmol, 1.18 equiv).
The mixture was cooled to 2 °C, and a solution of di-tert-butyl
dicarbonate (27.9 g, 127.8 mmol, 1.62 equiv) in tetrahydrofuran
(50 mL) was added over 40 min. The mixture was sitrred at
room temperature for 16 h. Water (150 mL) and ethyl acetate
(700 mL) were added. The pH was adjusterd to pH 5 by the
addition of 0.5 M citric acid (75 mL), and the organic phase
was separated. The aqueous phase was extracted with ethyl
acetate (2 × 300 mL), and the combined organic phase was
washed with brine (400 mL), dried (NaSO4), and evaporated.
The residue was dissolved in ether (140 mL), hexane (650 mL)
was added, and the organic phase was washed with sodium
bicarbonate (158 mmol, 2 equiv) in water (2 L). The aqueous
phase was acidified with 0.5 M citric acid (280 mL) to pH 5
and extracted with ether (3 × 650 mL), and the combined
organic phase was washed with brine (500 mL), dried (NaSO4),
(2m, 5H, indanyl-3H, -1H, -2H); chiral HPLC 49.77% (tR
)
10.26 min) and 50.23% (tR ) 13.85 min) (Chiralpak AD, 30%
EtOH/heptane); LCMS m/z 234 (MNH4+) single component,
gradient 2 (tR ) 2.46min); HRMS calcd for C12H12N2O2 (MH+)
217.0977, found 217.0973; HPLC 99.08% (tR ) 1.20 min).
1
and evaporated to give 8 (23.81 g, 96%). H NMR (DMSO-d6)
δ 12.58 (br s,1H, CO2H), 7.26 (d, J ) 8 Hz,1H, BocNH), 7.19-
7.16 and 7.11-7.06 (2m, 4H, arylH), 3.99 (t, J ) 8 Hz,1H,
NCHindanyl), 2.96-2.85 and 2.78-2.72 (2m, 5H, indanyl-3H,
-1H, -2H), 1.39(s, 9H, But); HPLC 98.10% (tR ) 1.61 min);
chiral HPLC 100.00%, (tR ) 9.98 min) (Chiralpak ADRHCD-
JE039 50% MeCN/H3PO4 0.1% at 215 nm) 100.0% ee; LCMS
m/z 292 (MH+) single component, gradient 2 (tR ) 3.26min);
HRMS calcd for C16H21NO4 (MNa+) 314.1368, found 314.1368.
R-N-Carbamylindanylglycine (6). To a solution of Borax
(disodium tetraborate decahydrate) (104 g, 0.272mol) and
water (2.75 L) at 43 °C was added dropwise concentrated
aqueous sodium hydroxide (∼40 mL) until the pH was 10.5.
To this solution was added racemic indanylglycine hydantoin
5 (103.6 g, 0.479 mol) in dimethylsulfoxide (690 mL), a white
precipitate formed. Polymer-supported hydantoinase (69 g)
was added, and the slurry was stirred at 45 °C for 23 h. A
further charge of polymer-supported hydantoinase (69 g) was
added, and the mixture was stirred for 22 h (91% conversion
HPLC). The mixture was filtered hot through a Celite pad,
and the filter bed was washed with water (1.5 L). The
temperature of the filtrate was adjusted to 25 °C, and
concentrated aqueous hydrochloric acid (∼100 mL) was slowly
added until pH 1.53 was obtained. The white precipitate
formed was stirred for 45 min, filtered, washed with water,
and dried under vacuum at room temperature overnight to
give the crude indanylglycine carbamate 6 as a white solid
(106.4 g). 1H NMR (DMSO-d6) δ 12.64 (br s,1H, CO2H), 7.28-
7.16 and 7.13-7.08 (2m, 4H, arylH), 6.40 (d, J ) 9 Hz, 1H,
NHCONH2), 5.61(s, 2H, NHCONH2), 4.20 (dd, J ) 9 Hz, 6 Hz,
1H, NCHindanyl), 2.95-2.82 and 2.80-2.70 (2m, 5H, indanyl-
3H, -1H, -2H); chiral HPLC 90.2% (tR ) 7.62 min) and 9.8%
(tR ) 8.41 min) (Chiracel OD-R, 20% MeCN/HClO4/NaClO4 (0.5
M), aqueous, pH 2); LCMS m/z 235 (MH+) single component,
gradient 2 (tR ) 2.41min); HRMS calcd for C12H14N2O3 (MH+)
235.1083, found 235.1084.
R-Indanylglycine (7). A solution of Borax (disodium
tetraborate decahydrate) (243 g, 0.637 mol) and water (6.40
L) was heated to 42 °C, and the pH was adjusted to 8.02 using
dropwise addition of concentrated aqueous hydrochloric acid
(∼70 mL). To this solution was added crude indanylglycine
carbamate (106.4 g, 0.454mol) in dimethyl sulfoxide (700 mL).
Resin-supported d-carbamoylase was filtered, and 120 g was
added to the mixture. The mixture was stirred at 45 °C for 36
h under an air atmosphere. The mixture was cooled to 25 °C
and left overnight. After division into into two equal halves,
each was worked up as follows. Dimethyl sulfoxide (900 mL)
was added followed by concentrated aqueous hydrochloric acid
(200 mL), and the mixture was stirred until no white solid
[R]23 -11° (c 1.0 in MeOH, 10 cm cell).
D
(2R)-2-[(3R,6R)-3-(2,3-Dihydro-1H-inden-2-yl)-6-isobu-
tyl-2,5-dioxopiperazin-1-yl]-N-isopropyl-2-phenylethan-
amide (15) and ((2S)-2-[(3R,6R)-3-(2,3-Dihydro-1H-in-
den-2-yl)-6-isobutyl-2,5-dioxopiperazin-1-yl]-N-isopropyl-2-
phenylethanamide (16). To a solution of D-leucine methyl
ester hydrochloride (182 mg) in methanol (3 mL) was added
triethylamine (140 µL) and benzaldehyde (102 µL). The
mixture was stirred for 2.5 h before the acid 8 (291 mg) and
isopropylisonitrile (150 µL) were sequentially added. After the
mixture was stirred for 16 h, the solvent was removed in vacuo
and the residue was dissolved in dichloromethane (20 mL).
This solution was washed with a saturated aqueous sodium
hydrogen carbonate solution (×2), dried over magnesium
sulfate, and evaporated in vacuo. The residue was dissolved
in dichloromethane (3 mL) and trifluoroacetic acid (4 mL), and
the mixture was stirred for 3 h at ambient temperature. After
this time, the solvent was removed in vacuo and the residue
was re-evaporated from dichloromethane (10 mL × 2). The
residue was treated with triethylamine in dioxane (5% solu-
tion, 10 mL) and was left to stir overnight. After this time,
the dioxane was removed in vacuo and the residue was
dissolved in dichloromethane (50 mL). The solution was
washed with 0.1 M hydrochloric acid solution (10 mL × 2),
and the organic phase was separated using a hydrophobic frit
and evaporated in vacuo to give a yellow gum. This crude
material was purified by preparative plate chromatography,
eluting with 2.5% 2-propanol in dichloromethane (×3) to give
the less polar diastereomer 15 as a colorless solid (81 mg,
17.6%). 1H NMR (400 MHz, CDCl3) δ 7.45-7.41 (m, 5H,
phenyl-arylH), 7.24-7.14 (m, 4H, indanyl-arylH), 6.58 (d, J
) 4.0 Hz, 1H, lactamNH), 5.59 (d, J ) 8.0 Hz, 1H, NHCHMe2),

2,5-Diketopiperazines Oxytocin Antagonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22 6965
5.20 (s, 1H, NCHphenyl), 4.15-4.06 (m, 1H, NHCHMe2), 4.00-
3.95 (m, 2H, NCHisobutyl, NCHindanyl), 3.20-3.02 (m, 3H,
indanyl-3H, -1H), 2.97-2.85 (m, 1H, indanyl-2H), 2.82-2.73
(m, 1H, indanyl-1H), 1.86-1.65 (m, 2H, CHHCHMe2, CH2-
CHMe2), 1.42-1.34 (m, 1H, CHHCHMe2), 1.13 and 1.12 (2d,
J ) 6.5 Hz, NHCHMe2), 0.81 and 0.74 (2d, J ) 6.5 Hz, 3H,
CH2CHMe2); LCMS m/z 462 (MH+) single component, gradient
2 (tR ) 3.40 min); HRMS calcd for C28H35N3O3 (MH+) 462.2757,
found 462.2765; HPLC 100% (tR ) 13.62 min).
The more polar diastereomer 16 (162 mg, 35.2%) was
isolated as a colorless solid. 1H NMR (400 MHz, CDCl3) δ 7.59
(broad s, 1H, lactamNH), 7.45-7.34 (m, 5H, phenyl-arylH),
7.20-7.10 (m, 4H, indanyl-arylH), 6.08 (broad s, 1H, NH-
CHMe2), 5.51 (s, 1H, NCHphenyl), 4.17-4.07 (m, 1H, NH-
CHMe2), 4.00-3.93 (m, 1H, NCHindanyl), 3.71-3.65 (m, 1H,
NCHisobutyl), 3.17-2.78 (m, 5H, indanyl-3H, -1H, indanyl-
2H), 1.98-1.89 (m, 1H, CHHCHMe2), 1.78-1.65 (m, 2H,
CHHCHMe2, CH2CHMe2), 1.16 and 1.13 (2d, J ) 6.5 Hz,
NHCHMe2), 0.80 and 0.62 (2d, J ) 6.5 Hz, 6H, CH2CHMe2);
LCMS m/z 462 (MH+) single component, gradient 2 (tR ) 3.36
min); HRMS calcd for for C28H35N3O3 (MH+) 462.2757, found
462.2765; HPLC 100% (tR ) 13.53 min).
The diastereomer 18 (40%) was isolated as a white solid.
1H NMR (CDCl3) δ 7.45-7.38 (m, 5H, phenylH), 7.24-7.13 (m,
4H, indanyl arylH), 6.67 (d, 1H, J ) 4 Hz, lactamNH), 5.80
(s, 1H CONHBut), 5.42 (s, 1H, NCHphenyl), 3.98, (dd, 1H, J
) 9.5 Hz, 4 Hz, NCHindanyl), 3.75 (m, 1H, NCHisobutyl),
3.18-2.76 (m, 5H, indanyl-3H, -1,H, -2H), 1.91-1.65 (m, 3H,
CH2CHMe2, CH2CHMe2), 1.36 (s, 9H), 0.80 and 0.64 (2d, J )
6.5 Hz 6H, CH2CHMe2); LCMS m/z 476 (MH+) (tR ) 3.59min);
HRMS calcd for C29H38N3O3 (MH+) 476.2913, found 476.2915;
HPLC >99.5% (tR )14.5min); circular dichroism (CH3CN) λmax
) 206.0 nm, dE 2.92, E28846, λmax ) 219.0 nm, dE -3.17,
E13945, λmax ) 226.6 nm, dE -3.47, E3857.
(2R)-2-[(3R,6R)-3-(2,3-dihydro-1H-inden-2-yl)-6-isobu-
tyl-2,5-dioxopiperazin-1-yl]-2-(4-fluorophenyl)-N-isopro-
pylethanamide (19) and (2S)-2-[(3R,6R)-3-(2,3-Dihydro-
1H-inden-2-yl)-6-isobutyl-2,5-dioxopiperazin-1-yl]-2-(4-
fluorophenyl)-N-isopropylethanamide (20). Compound 8
was reacted with 4-fluorobenzaldehyde as described for com-
pound 15 to give 19 as a colorless solid (18%). 1H NMR (CDCl3)
δ 7.46-7.41 (m, 2H, fluorophenyl-2H, -6H), 7.25-7.07 (m, 6H,
fluorophenyl-3H, -5H, indanyl-arylH), 6.51 (d, J ) 3.5 Hz, 1H,
lactamNH), 5.60 (d, J ) 7.5 Hz, 1H, NHCHMe2), 5.10 (s, 1H,
NCHfluorophenyl), 4.15-4.05 (m, 1H, NHCHMe2), 3.98-3.93
(m, 2H, NCHisobutyl, NCHindanyl), 3.20-3.02 (m, 3H, inda-
nyl-3H, -1H), 2.96-2.84 (m, 1H, indanyl-2H), 2.82-2.73 (m,
1H, indanyl-1H), 1.82-1.63 (m, 2H, CHHCHMe2, CH2CHMe2),
1.47-1.39 (m, 1H, CHHCHMe2), 1.14-1.10 (m, 6H, NH-
CHMe2), 0.84 and 0.79 (2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS
m/z 480 (MH+) single component, gradient 2 (tR 3.42 min);
HRMS calcd for C28H35FN3O3 (MH+) 480.2662, found 480.2661;
HPLC 100% (tR ) 13.71 min).
The diastereomer 20 (33%) was isolated as a colorless solid.
1H NMR (CDCl3) δ 7.47-7.42 (m, 2H, fluorophenyl-2H, -6H),
7.24-7.08 (m, 6H, fluorophenyl-3H, -5H, indanyl-arylH), 6.75
(d, J ) 4.0 Hz, 1H, lactamNH), 5.84 (d, J ) 7.5 Hz, 1H,
NHCHMe2), 5.49 (s, 1H, NCHfluorophenyl), 4.15-4.06 (m, 1H,
NHCHMe2), 3.99 (dd, J ) 9.5 Hz, 4.0 Hz, 1H, NCHindanyl),
3.73 (dd, J ) 11.0 Hz, 4.0 Hz, 1H, NCHisobutyl), 3.18-2.88
(m, 4H, indanyl-3H, -1H, indanyl-2H), 2.83-2.76 (m, 1H,
indanyl-1H), 1.91-1.65 (m, 3H, CH2CHMe2, CH2CHMe2), 1.16
(pseudo-t, 2 overlapping d, J ) 6.5 Hz, 6H, NHCHMe2), 0.82
and 0.72 (2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS m/z 480
(MH+) single component, gradient 2 (tR ) 3.42 min); HRMS
calcd for C28H35FN3O3 (MH+) 480.2662, found 480.2645; HPLC
100% (tR ) 13.68 min).
The following compounds were similarly prepared.
(2R)-2-[4-(Acetylamino)phenyl]-2-[(3R,6R)-3-(2,3-dihy-
dro-1H-inden-2-yl)-6-isobutyl-2,5-dioxopiperazin-1-yl]-N-
isopropylethanamide (13) and (2S)-2-[4-(Acetylamino)-
phenyl]-2-[(3R,6R)-3-(2,3-dihydro-1H-inden-2-yl)-6-(2-meth-
ylpropyl)-2,5-dioxo-1-piperazinyl]-N-(1-methylethyl)ethan-
amide (14). Compound 8 was reacted with 4-acetamidoben-
zaldehyde as described for compound 15 to give 13 as a
colorless solid (14%). 1H NMR (CD3OD) δ 8.36 (s, 1H, AcNH),
7.59 and 7.38 (pseudo-ABq, J ) 8.5 Hz, 4H, acetamidophenyl-
H), 7.24-7.13 (m, 4H, indanyl-arylH), 7.10 (d, J ) 4.0 Hz,
lactamNH), 5.92 (d, J ) 8.0 Hz, 1H, NHCHMe2), 5.20 (s, 1H,
NCHacetamidopheny), 4.11-4.00 (m, 1H, NHCHMe2), 3.98-
3.92 (m, 2H, NCHisobutyl, NCHindanyl), 3.19-3.00 (m, 3H,
indanyl-3H, -1H), 2.93-2.75 (m, 2H, indanyl-2H, indanyl-1H),
2.18 (s, 3H, MeCO), 1.80-1.61 (m, 2H, CHHCHMe2, CH2-
CHMe2), 1.37-1.28 (m, 1H, CHHCHMe2), 1.10 (pseudo-t, 2
overlapping d, J ) 6.5 Hz, 6H, NHCHMe2), 0.78 and 0.68 (2d,
J ) 6.5 Hz, 6H, CH2CHMe2); LCMS m/z 519 (MH+) single
component, gradient 2 (tR ) 3.02 min); HRMS calcd for
C30H39N4O4 (MH+) 519.2971, found 519.2966; HPLC 100% (tR
) 13.60 min).
The diastereomer 14 (34%) was isolated as a white solid.
1H NMR (CDCl3) δ 8.36 (s, 1H, AcNH), 7.58 and 7.33 (pseudo-
ABq, J ) 8.5 Hz, 4H, acetamidophenyl-H), 7.23-7.13 (m, 4H,
indanyl-arylH), 6.05 (broad s, 1H, lactamNH), 5.46 ((s, 1H,
NCHacetamidopheny), 4.14-4.04 (m, 1H, NHCHMe2), 3.94 (d,
J ) 10.0 Hz, 1H, NCHindanyl), 3.74-3.69 (m, 1H, NCHisobu-
tyl), 3.19-2.75 (m, 5H, indanyl-3H, -1,H, -2H), 2.18 (s, 3H,
MeCO), 1.94-1.64 (m, 3H, CH2CHMe2, CH2CHMe2), 1.15 and
1.13 (2d, J ) 6.5 Hz, 6H, NHCHMe2), 0.79 and 0.68 (2d, J )
6.5 Hz, 6H, CH2CHMe2); LCMS m/z 519 (MH+) single compo-
nent, gradient 2 (tR ) 2.93 min); HRMS calcd for C30H39N4O4
(MH+) 519.2971, found 519.2974; HPLC 100% (tR ) 13.46 min).
(2R)-N-(tert-Butyl)-2-[(3R,6R)-3-(2,3-dihydro-1H-in-
den-2-yl)-6-isobutyl-2,5-dioxopiperazin-1-yl]-2-phenylethan-
amide (17) and (2S)-N-(tert-Butyl)-2-[(3R,6R)-3-(2,3-di-
hydro-1H-inden-2-yl)-6-isobutyl-2,5-dioxopiperazin-1-yl]-
2-phenylethanamide (18). Compound 8 was reacted with
benzaldehyde as described for compound 15 to give 17 as a
white solid (19%). 1H NMR (CDCl3) δ 7.45-7.38 (m, 5H,
phenylH), 7.24-7.13 (m, 4H, indanyl arylH), 6.72 (d, 1H, J )
4 Hz, lactamNH), 5.67 (s, 1H, CONHBut), 5.21 (s, 1H,
NCHphenyl), 4.01-3.94 (m, 2H, NCHisobutyl, NCHindanyl),
3.19-2.75 (m, 5H, indanyl-3H, -1,H, -2H), 1.83-1.64 (m, 2H,
CHHCHMe2, CH2CHMe2), 1.68 (m, 1H), 1.37-1.28 (m, 1H,
CHHCHMe2), 1.32 (s, 9H, But), 0.80 and 0.71 (2d, J ) 6.5 Hz,
6H, CH2CHMe2); LCMS m/z 476 (MH+) (tR ) 3.54 min); HRMS
calcd for C29H38N3O3 (MH+) 476.2913, found 476.2906; HPLC
((2R)-2-[(3R,6R)-3-(2,3-Dihydro-1H-inden-2-yl)-6-isobu-
tyl-2,5-dioxopiperazin-1-yl]-N-isopropyl-2-[4-(trifluoro-
methyl)phenyl]ethanamide (21) and ((2S)-2-[(3R,6R)-
3-(2,3-Dihydro-1H-inden-2-yl)-6-isobutyl-2,5-dioxopiper-
azin-1-yl]-N-isopropyl-2-[4-(trifluoromethyl)phenyl]ethan-
amide (22). Compound 8 was reacted with 4-trifluorometh-
ylbenzaldehyde as described for compound 15 to give 21 as a
1
colorless solid (18%). H NMR (CDCl3) δ 7.75 (d, J ) 3.5 Hz,
1H, lactamNH), 7.68 and 7.56 (pseudo-ABq, J ) 8.0 Hz, 4H,
trifluoromethylphenyl-H), 7.22-7.13 (m, 4H, indanyl-arylH),
6.01 (d, J ) 8.0 Hz, 1H, NHCHMe2), 5.22 ((s, 1H, NCHtri-
fluoromethylphenyl), 4.16-4.06 (m, 1H, NHCHMe2), 4.02-3.97
(m, 2H, NCHisobutyl, NCHindanyl), 3.17-2.98 (m, 3H, inda-
nyl-3H, -1H), 2.95-2.78 (m, 2H, indanyl-2H, indanyl-1H),
1.89-1.71 (m, 2H, CHHCHMe2, CH2CHMe2), 1.47-1.39 (m,
1H, CHHCHMe2), 1.15 and 1.14 (2d, J ) 6.5 Hz, 6H, NH-
CHMe2), 0.85 and 0.79 (2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS
m/z 530 (MH+) single component, gradient 2 (tR ) 3.77 min);
HRMS calcd for C29H35F3N3O3 (MH+) 530.2631, found 530.2629;
HPLC 100% (tR ) 16.85 min).
The diastereomer 22 (47%) was isolated as a white solid.
1H NMR (CDCl3) δ 8.23 (d, J ) 3.5 Hz, 1H, lactamNH), 7.68
and 7.55 (pseudo-ABq, J ) 8.0 Hz, 4H, trifluoromethylphenyl-
H), 7.20-7.10 (m, 4H, indanyl-arylH), 6.53 (d, J ) 5.0 Hz, 1H,
NHCHMe2), 5.56 ((s, 1H, NCHtrifluoromethylphenyl), 4.16-
4.06 (m, 1H, NHCHMe2), 3.99 (dd, J ) 9.5 Hz, 4.5 Hz, 1H,
NCHindanyl), 3.73-3.67 (m, 1H, NCHisobutyl), 3.19-2.84 (m,
5H, indanyl-3H, -1H, -2H), 1.97-1.68 (m, 3H, CH2CHMe2,
CH2CHMe2), 1.47-1.39 (m, 1H, CHHCHMe2), 1.16 and 1.12
>99.5% (tR ) 14.3min); circular dichroism (CH3CN) λmax
)
204.0 nm, dE 22.73, E31923, λmax ) 228.2 nm, dE -15.52,
E4355.

6966 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22
Borthwick et al.
(2d, J ) 6.5 Hz, 6H, NHCHMe2), 0.82 and 0.65 (2d, J ) 6.5
Hz, 6H, CH2CHMe2); LCMS m/z 530 (MH+) single component,
gradient 2 (tR ) 3.77 min); HRMS calcd for C29H35F3N3O3
(MH+) 530.2631, found 530.2630; HPLC 100% (tR ) 16.73 min).
Dihydro-1H-inden-2-yl)-6-isobutyl-2,5-dioxopiperazin-1-
yl]-N-isopropyl-2-[4 (methylsulfonyl)phenyl]ethanamide
(28). Compound 8 was reacted with 4-methylsulfonylbenzal-
dehyde as described for compound 15 to give 27 as a colorless
solid (13%). 1H NMR (CDCl3) δ 7.99 and 7.64 (pseudo-ABq, J
) 8.5 Hz, 4H, methylsulfonylphenyl-H), 7.25-7.16 (m, 4H,
indanyl-arylH), 6.30 (d, J ) 4.0 Hz, lactamNH), 5.97 (d, J )
8.0 Hz, 1H, NHCHMe2), 5.00 ((s, 1H, NCHmethylsulfonylphe-
nyl), 4.17-4.08 (m, 1H, NHCHMe2), 4.00-3.94 (m, 2H,
NCHisobutyl, NCHindanyl), 3.22-3.15 (m, 1H, indanyl-3H),
3.09-3.03 (m, 5H, MeSO2, indanyl-3H, -1H), 2.97-2.75 (m, 2H,
indanyl-2H, indanyl-1H), 1.95-1.78 (m, 2H, CHHCHMe2,
CH2CHMe2), 1.65-1.56 (m, 1H, CHHCHMe2), 1.16 (d, J ) 6.5
Hz, 6H, NHCHMe2), 0.89 and 0.86 (2d, J ) 6.5 Hz, 6H, CH2-
CHMe2); LCMS m/z 540 (MH+) single component, gradient 2
(tR ) 3.00 min); HRMS calcd for C29H37N3O5S (MH+) 540.2532,
found 540.2534; HPLC 100% (tR ) 12.12 min).
The diastereomer 28 (41%) was isolated as a white solid.
1H NMR (CDCl3) δ 7.79 and 7.65 (pseudo-ABq, J ) 8.5 Hz,
4H, methylsulfonylphenyl-H), 7.25-7.16 (m, 4H, indanyl-
arylH), 6.43 (d, J ) 4.5 Hz, lactamNH), 6.09 (d, J ) 8.0 Hz,
1H, NHCHMe2), 5.55 (s, 1H, NCHmethylsulfonylphenyl),
4.16-4.06 (m, 1H, NHCHMe2), 4.04 (dd, J ) 9.5 Hz, 4.0 Hz,
1H, NCHindanyl), 3.88-3.83 (m, 1H, NCHisobutyl), (m, 1H,
indanyl-3H), 3.22-2.91 (m, 7H, MeSO2, indanyl-3H, -1H, -2H),
2.85-2.77 (m, 1H, indanyl-1H), 1.85-1.68 (m, 3H, CH2CHMe2,
CH2CHMe2), 1.18 and 1.16 (2d, J ) 6.5 Hz, 6H, NHCHMe2),
0.84 and 0.77 (2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS m/z
540 (MH+) single component, gradient 2 (tR ) 3.25 min);
HRMS calcd for C29H37N3O5S (MH+) 540.2532, found 540.2523;
HPLC 100% (tR ) 12.16 min).
4-[(1R)-1-[(3R,6R)-3-(2,3-Dihydro-1H-inden-2-yl)-6-isobu-
tyl-2,5-dioxopiperazin-1-yl]-2-(isopropylamino)-2-oxoeth-
yl]benzamide (29) and 4-{(1S)-1-[(3R,6R)-3-(2,3-Dihydro-
1H-inden-2-yl)-6-(2-methylpropyl)-2,5-dioxo-1-piperazi-
nyl]-2-[(1-methylethyl)amino]-2-oxoethyl}benzamide (30).
Compound 8 was reacted with 4-carboxamidobenzaldehyde as
described for compound 15 to give 29 as a colorless solid (10%).
1H NMR (CD3OD) δ 7.91 and 7.53 (pseudo-ABq, J ) 8.5 Hz,
4H, carboxamidophenyl-H), 7.25-7.15 (m, 4H, indanyl-arylH),
6.75 (d, J ) 8.0 Hz, 1H, NHCHMe2), 5.47 ((s, 1H, NCHcar-
boxamidophenyl), 4.10-3.94 (m, 3H, NHCHMe2, NCHisobutyl,
NCHindanyl), 3.20-3.00 (m, 3H, indanyl-3H, -1H), 2.91-2.78
(m, 2H, indanyl-2H, indanyl-1H), 1.72-1.67 (m, 2H, CHH-
CHMe2, CH2CHMe2), 1.21-1.12 (m, 4H, CHHCHMe2, NHCH-
MeMe), 1.09 (d, J ) 6.5 Hz, 3H, NHCHMeMe), 0.74 and 0.59
(2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS m/z 505 (MH+) single
component, gradient 2 (tR ) 3.57 min); HRMS calcd for
C29H36N4O4 (MH+) 505.2815, found 505.2825; HPLC 100% (tR
) 11.07 min).
The diastereomer 30 (37%) was isolated as a white solid.
1H NMR (CDCl3) δ 7.86 and 7.49 (pseudo-ABq, J ) 8.0 Hz,
4H, carboxamidophenyl-H), 7.23-7.05 (m, 6H, indanyl-arylH,
lactam NH, NHCHMe2), 6.45-5.90 (broad m, 2H, CONH2),
5.58 (broad s, 1H, NCHcarboxamidophenyl), 4.16-4.06 (m, 1H,
NHCHMe2), 3.97 (dd, J ) 9.0 Hz, 4.0 Hz, 1H, NCHindanyl),
3.77-3.69 (m, 1H, NCHisobutyl), 3.21-2.79 (m, 5H, indanyl-
3H, -1H, -2H), 2.04-1.66 (m, 3H, CH2CHMe2, CH2CHMe2),
1.16 and 1.12 (2d, J ) 6.5 Hz, 6H, NHCHMe2), 082 and 0.71
(2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS m/z 505 (MH+) single
component, gradient 2 (tR ) 3.12 min); HRMS calcd for
C29H36N4O4 (MH+) 505.2815, found 505.2823; HPLC 100% (tR
) 11.20 min).
(2R)-2-[(3R,6R)-3-(2,3-Dihydro-1H-inden-2-yl)-6-isobu-
tyl-2,5-dioxopiperazin-1-yl]-N-isopropyl-2-(4-methylphen-
yl)ethanamide (23) and (2S)-2-[(3R,6R)-3-(2,3-Dihydro-
1H-inden-2-yl)-6-isobutyl-2,5-dioxopiperazin-1-yl]-N-iso-
propyl-2-(4-methylphenyl)ethanamide (24). Compound 8
was reacted with 4-methylbenzaldehyde as described for
compound 15 to give 23 as a colorless solid (19%). 1H NMR
(CDCl3) δ 7.33-7.13 (m, 7H, methylphenyl-H, indanyl-arylH),
6.99 (d, J ) 4.0 Hz, 1H, lactamNH), 5.62 (d, J ) 8.0 Hz, 1H,
NHCHMe2), 5.16 ((s, 1H, NCHmethylphenyl), 4.14-4.04 (m,
1H, NHCHMe2), 3.99-3.93 (m, 2H, NCHisobutyl, NCHinda-
nyl), 3.18-3.01 (m, 3H, indanyl-3H, -1H), 2.95-2.75 (m, 2H,
indanyl-2H, indanyl-1H), 2.37 (s, 3H, methylphenyl), 1.84-
1.65 (m, 2H, CHHCHMe2, CH2CHMe2), 1.43-1.35 (m, 1H,
CHHCHMe2), 1.12 and 1.11 (2d, J ) 6.5 Hz, 6H, NHCHMe2),
0.81 and 0.74 (2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS m/z
476 (MH+) single component, gradient 2 (tR ) 3.65 min);
HRMS calcd for C29H38N3O3 (MH+) 476.2913, found 476.2914;
HPLC 100% (tR ) 16.47 min).
The diastereomer 24 (38%) was isolated as a white solid.
1H NMR (CDCl3) δ 7.33-7.04 (m, 9H, methylphenyl-H, inda-
nyl-arylH, NHCHMe2), 5.81 (d, J ) 4.0 Hz, 1H, lactamNH),
5.48 (s, 1H, NCHmethylphenyl), 4.16-4.06(m, 1H, NHCHMe2),
4.01-3.94 (m, 1H, NCHindanyl), 3.72-3.66 (m, 1H, NCHisobu-
tyl), 3.18-2.75 (m, 5H, indanyl-3H, -1H, -2H), 2.37 (s, 3H,
methylphenyl), 1.96-1.64 (m, 3H, CH2CHMe2, CH2CHMe2),
1.20-1.10 and 1.10 (m, 6H, NHCHMe2), 0.80 and 0.66 (2d, J
) 6.0 Hz, 6H, CH2CHMe2); LCMS m/z 476 (MH+) single
component, gradient 2 (tR ) 3.65 min); HRMS calcd for
C29H38N3O3 (MH+) 476.2913, found 476.2912; HPLC 100% (tR
) 16.28 min).
((2R)-2-[(3R,6R)-3-(2,3-Dihydro-1H-inden-2-yl)-6-isobu-
tyl-2,5-dioxopiperazin-1-yl]-2-[4-(dimethylamino)phenyl]-
N-isopropylethanamide (25) and ((2S)-2-[(3R,6R)-3-(2,3-
Dihydro-1H-inden-2-yl)-6-isobutyl-2,5-dioxopiperazin-
1-yl]-2-[4-(dimethylamino)phenyl]-N-isopropylethan-
amide (26). Compound 8 was reacted with 4-dimethylami-
nobenzaldehyde as described for compound 15 to give 25 as a
colorless solid (12%). 1H NMR (CDCl3) δ 730-7.26 (m, 2H,
dimethylaminophenyl-2H, -6H), 7.25-7.14 (m, 4H, indanyl-
arylH), 6.72-6.68 (m, 2H, dimethylaminophenyl-3H, -5H), 6.11
(d, J ) 3.5 Hz, 1H, lactamNH), 5.45 (d, J ) 8.0 Hz, 1H,
NHCHMe2), 5.11 ((s, 1H, NCHdimethylaminophenyl), 4.14-
4.04 (m, 1H, NHCHMe2), 3.97-3.91 (m, 2H, NCHisobutyl,
NCHindanyl), 3.20-3.06 (m, 3H, indanyl-3H, -1H), 2.98 (s, 6H,
Me2N), 2.96-2.71 (m, 2H, indanyl-2H, indanyl-1H), 1.84-1.63
(m, 2H, CHHCHMe2, CH2CHMe2), 1.42-1.34 (m, 1H, CHH-
CHMe2), 1.12 and 1.10 (2d, J ) 6.5 Hz, 6H, NHCHMe2), 0.80
and 0.75 (2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS m/z 505
(MH+) single component, gradient 2 (tR ) 2.78 min); HRMS
calcd for C30H40N4O3 (MNa+) 527.2998, found 527.3000; HPLC
100% (tR ) 12.87 min).
The diastereomer 26 (18%) was isolated as a colorless solid.
1H NMR (CDCl3) δ 7.25-7.14 (m, 6H, dimethylaminophenyl-
2H, -6H, indanyl-arylH), 6.70 (1/2 pseudo-ABq, J ) 8.5 Hz,
2H, dimethylaminophenyl-3H, -5H), 6.29 (d, J ) 3.5 Hz, 1H,
lactamNH), 5.59 (d, J ) 8.0 Hz, 1H, NHCHMe2), 5.49 (s, 1H,
NCHdimethylaminophenyl), 4.15-4.06 (m, 1H, NHCHMe2),
3.96 (dd, J ) 9.5 Hz, 4.0 Hz, 1H, NCHindanyl), 3.72-3.68 (m,
1H, NCHisobutyl), 3.19-2.94 (m, 10H, Me2N, indanyl-3H, -1H,
indanyl-2H), 2.81-2.73 (m, 1H, indanyl-1H), 1.97-1.89 (m,
1H, CHHCHMe2), 1.79-1.65 (m, 2H, CHHCHMe2, CH2CHMe2),
1.15 and 1.14 (2d, J ) 6.5 Hz, 6H, NHCHMe2), 0.83 and 0.70
(2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS m/z 505 (MH+) single
component, gradient 2 (tR ) 3.55 min); HRMS calcd for
C30H40N4O3 (MNa+) 527.2998, found 527.3000; HPLC 100% (tR
) 13.71 min).
(2R)-N-(tert-Butyl)-2-(4-chlorophenyl)-2-[(3R,6R)-3-(2,3-
dihydro-1H-inden-2-yl)-6-isobutyl-2,5-dioxopiperazin-1-
yl]ethanamide (31) and (2S)-N-(tert-Butyl)-2-(4-chlo-
rophenyl)-2-[(3R,6R)-3-(2,3-dihydro-1H-inden-2-yl)-6-
isobutyl-2,5-dioxopiperazin-1-yl]ethanamide(32).Compound
8 was reacted with 4-chlorobenzaldehyde as described for
compound 15 to give 31 as a colorless solid (3%). 1H NMR
(CDCl3) δ 7.41-7.35 (m, 4H, chlorophenyl-H), 7.24-7.15 (m,
4H, indanyl-arylH), 6.26 (d, J ) 3.5 Hz, 1H, lactam NH), 5.76
(s, 1H, NHCMe3), 5.04 (s, 1H, NCHchlorophenyl), 3.98-3.92
(m, 2H, NCHisobutyl, NCHindanyl), 3.20-3.04 (m, 3H, inda-
(2R)-2-[(3R,6R)-3-(2,3-Dihydro-1H-inden-2-yl)-6-isobu-
tyl-2,5-dioxopiperazin-1-yl]-N-isopropyl-2-[4-(methylsul-
fonyl)phenyl]ethanamide (27) and (2S)-2-[(3R,6R)-3-(2,3-

2,5-Diketopiperazines Oxytocin Antagonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22 6967
nyl-3H, -1H), 2.95-2.73 (m, 2H, indanyl-2H, indanyl-1H),
1.86-1.68 (m, 2H, CHHCHMe2, CH2CHMe2), 1.47-1.40 (m,
1H, CHHCHMe2), 1.33 (s, 9H, NHCMe3), 0.84 and 0.78 (2d, J
) 7.0 Hz, 3H, CH2CHMe2); LCMS m/z 510/512 (MH+) single
component, gradient 2 (tR ) 3.85 min); HRMS calcd for C29H37-
4H, indanyl-arylH), 6.94-6.90 (m, 2H, trifluoromethoxyphen-
yl-3H, -5H), 6.46 (s, 1H, NHCMe3), 5.64 (s, 1H, NCHtrifluo-
romethoxyphenyl), 3.96 (dd, J ) 9.0 Hz, 4.0 Hz, 1H, NCHin-
danyl), 3.69 (dd, J ) 10.5 Hz, 3.5 Hz, 1H, NCHisobutyl), 3.17-
2.84 (m, 5H, indanyl-3H, -1H, -2H), 1.94-1.66 (m, 3H,
CH2CHMe2, CH2CHMe2), 1.36 (s, 9H, NHCMe3), 0.81 and 0.60
(2d, J ) 7.0 Hz, 6H, CH2CHMe2); LCMS m/z 560 (MH+) single
component, gradient 2 (tR ) 3.79 min); HRMS calcd for
C30H37F3N3O4 (MH+) 560.2736, found 560.2737; HPLC 100%
(tR ) 18.48 min).
(2R)-2-(2,4-Difluorophenyl)-2-[(3R,6R)-3-(2,3-dihydro-
1H-inden-2-yl)-6-isobutyl-2,5-dioxopiperazin-1-yl]-N-iso-
propylethanamide (37) and (2S)-2-(2,4-Difluorophenyl)-
2-[(3R,6R)-3-(2,3-dihydro-1H-inden-2-yl)-6-isobutyl-2,5-
dioxopiperazin-1-yl]-N-isopropylethanamide(38).Compound
8 was reacted with 2,4-difluorobenzaldehyde as described for
compound 15 to give 37 as a colorless solid (7%). 1H NMR
(CDCl3) δ 7.71-7.64 (m, 1H, difluorophenyl-6H), 7.24-7.14 (m,
4H, indanyl-arylH), 6.98-6.86 (m, 2H, difluorophenyl-3H,
-5H), 6.69 (d, J ) 3.5 Hz, 1H, lactamNH), 5.89 (d, J ) 8.0 Hz,
1H, NHCHMe2), 5.34 (s, 1H, NCHdifluorophenyl), 4.17-4.08
(m, 1H, NHCHMe2),4.02 (dd, J ) 10.0 Hz, 3.5 Hz, 1H,
NCHisobutyl), 3.93 (dd, J ) 9.5 Hz, 4.0 Hz, 1H, NCHindanyl),
3.20-3.03 (m, 3H, indanyl-3H, -1H), 2.97-2.85 (m, 1H, inda-
nyl-2H), 2.82-2.74 (m, 1H, indanyl-1H), 1.90-1.74 (m, 2H,
CHHCHMe2, CH2CHMe2), 1.53-1.45 (m, 1H, CHHCHMe2),
1.16 (pseudo-t, 2 overlapping d, J ) 6.5 Hz, 6H, NHCHMe2),
0.87 and 0.82 (2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS m/z
498 (MH+) single component, gradient 2 (tR ) 3.57 min);
HRMS calcd for C28H33F2N3O3 (MH+) 498.2568, found 498.2578;
HPLC 100% (tR ) 14.11 min); circular dichroism (CH3CN) λmax
) 202.0 nm, dE 12.75, E38105, λmax ) 228.0 nm, dE -7.33,
E4077.
The diastereomer 38 (26%) was isolated as a white solid.
1H NMR (CDCl3) δ 7.72-7.65 (m, 1H, difluorophenyl-6H),
7.24-7.14 (m, 4H, indanyl-arylH), 7.07 (d, J ) 3.5 Hz, 1H,
lactamNH), 6.99-6.86 (m, 2H, difluorophenyl-3H, -5H), 5.97
(d, J ) 7.8 Hz, 1H, NHCHMe2), 5.37 (s, 1H, NCHdifluorophe-
nyl), 4.17-4.08 (m, 1H, NHCHMe2), 4.03 (dd, J ) 10.6 Hz,
3.5 Hz, 1H, NCHisobutyl), 3.93 (dd, J ) 9.4 Hz, 4.0 Hz, 1H,
NCHindanyl), 3.20-3.03 (m, 3H, indanyl-3H, -1H), 2.97-2.85
(m, 1H, indanyl-2H), 2.82-2.74 (m, 1H, indanyl-1H), 1.90-
1.74 (m, 2H, CHHCHMe2, CH2CHMe2), 1.52-1.43 (m, 1H,
CHHCHMe2), 1.16 (pseudo-t, 2 overlapping d, J ) 6.5 Hz, 6H,
NHCHMe2), 0.87 and 0.82 (2d, J ) 6.5 Hz, 6H, CH2CHMe2);
LCMS m/z 498 (MH+) single component, gradient 2 (tR ) 3.36
min); HRMS calcd for C28H33F2N3O3 (MH+) 498.2568, found
498.2556; HPLC 100% (tR ) 13.82 min).
(2R)-2-[4-(Acetylamino)phenyl]-N-(tert-butyl)-2-[(3R,6R)-
3-(2,3-dihydro-1H-inden-2-yl)-6-isobutyl-2,5-dioxopiper-
azin-1-yl]ethanamide (39). Compound 8 was reacted with
4-acetamidobenzaldehyde and tert-butylisonitrile as described
for compound 15 to give 39 as a colorless solid (19%). 1H NMR
(CDCl3) δ 8.48 (s, 1H, AcNH), 7.59 and 7.32 (pseudo-ABq, J )
8.5 Hz, 4H, acetamidophenyl-H), 7.24-7.13 (m, 5H, indanyl-
arylH, lactamNH), 5.90 (s, 1H, NHCMe3), 5.21 (s, 1H, NCHac-
etamidophenyl), 3.98-3.92 (m, 2H, NCHisobutyl, NCHinda-
nyl), 3.18-3.00 (m, 3H, indanyl-3H, -1H), 2.92-2.75 (m, 2H,
indanyl-2H, indanyl-1H), 2.18 (s, 3H, MeCO), 1.77-1.58 (m,
2H, CHHCHMe2, CH2CHMe2), 1.33-1.22 (m, 10H, CHH-
CHMe2, NHCMe3), 0.76 and 0.64 (2d, J ) 6.5 Hz, 6H, CH2-
CHMe2); LCMS m/z 533 (MH+) single component, gradient 2
(tR ) 3.27 min); HRMS calcd for C31H40N4O4 (MH+) 533.3128,
found 533.3120; HPLC 100% (tR ) 12.34 min).
ClN3O3 (MH+) 510.2523, found 510.2529; HPLC 100% (tR
)
17.85 min).
The diastereomer 32 (12%) was isolated as a white solid.
1H NMR (CDCl3) δ 7.43-7.37 (m, 4H, chlorophenyl-H), 7.25-
7.16 (m, 4H, indanyl aryl-H), 6.44 (d, J ) 4.0 Hz, lactam NH),
5.94 (s, 1H, NHCMe3), 5.42 (s, 1H, NCHchlorophenyl), 4.00
(dd, J ) 9.5 Hz, 4.0 Hz, 1H, NCHindanyl), 3.78 (dd, J ) 11.0
Hz, 3.0 Hz, 1H, NCHisobutyl), 3.20-2.89 (m, 4H, indanyl-3H,
-1H, -2H), 2.82-2.74 (m, 1H, indanyl-1H), 1.87-1.65 (m, 3H,
CH2CHMe2, CH2CHMe2), 1.36 (s, 9H, NHCMe3), 0.83 and 0.74
(2d, J ) 6.0 Hz, 6H, CH2CHMe2); LCMS m/z 510/512 (MH+)
single component, gradient 2 (tR ) 364 min); HRMS calcd for
C29H37ClN3O3 (MH+) 510.2523, found 510.2521; HPLC 100%
(tR ) 17.42 min).
(2R)-N-(tert-Butyl)-2-[(3R,6R)-3-(2,3-dihydro-1H-in-
den-2-yl)-6-isobutyl-2,5-dioxopiperazin-1-yl]-2-(4-methoxy-
phenyl)ethanamide (33) and (2S)-N-(tert-Butyl)-2-[(3R,6R)-
3-(2,3-dihydro-1H-inden-2-yl)-6-isobutyl-2,5-dioxopiper-
azin-1-yl]-2-(4-methoxyphenyl)ethanamide (34). Com-
pound 8 was reacted with 4-methoxybenzaldehyde and tert-
butylisonitrile as described for compound 15 to give 33 as a
colorless solid (8%). 1H NMR (CDCl3) δ 7.38-7.34 (m, 2H,
methoxyphenyl-2H, -6H), 7.23-7.14 (m, 4H, indanyl-arylH),
6.94-6.90 (m, 2H, methoxyphenyl-3H, -5H), 6.30 (d, J ) 3.5
Hz, 1H, lactam NH), 5.56 (s, 1H, NHCMe3), 5.14 (s, 1H,
NCHmethoxyphenyl), 3.98-3.92 (m, 2H, NCHisobutyl, NCHin-
danyl), 3.83 (s, 3H, OMe), 3.19-3.05 (m, 3H, indanyl-3H, -1H),
2.95-2.72 (m, 2H, indanyl-2H, indanyl-1H), 1.83-1.65 (m, 2H,
CHHCHMe2, CH2CHMe2), 1.37-1.29 (m, 10H, CHHCHMe2,
NHCMe3), 0.80 and 0.72 (2d, J ) 7.0 Hz, 3H, CH2CHMe2);
LCMS m/z 505 (MH+) single component, gradient 2 (tR ) 3.50
min); HRMS calcd for C30H40N3O4 (MH+) 506.3024, found
506.3017; HPLC 100% (tR ) 14.08 min).
The diastereomer 34 (11%) was isolated as a white solid.
1H NMR (CDCl3) δ 7.38-7.34 (m, 2H, methoxyphenyl-2H,
-6H), 7.23-7.14 (m, 4H, indanyl-arylH), 6.94-6.90 (m, 2H,
methoxyphenyl-3H, -5H), 6.27 (d, J ) 3.5 Hz, 1H, lactam NH),
5.78 (s, 1H, NHCMe3), 5.42 (s, 1H, NCHmethoxyphenyl), 3.97
(dd, J ) 9.5 Hz, 4.0 Hz, 1H, NCHindanyl), 3.83 (s, 3H, OMe),
3.74 (dd, J ) 10.5 Hz, 3.5 Hz, 1H, NCHisobutyl), 3.19-2.90
(m, 4H, indanyl-3H, -1H, -2H), 2.80-2.73 (m, 1H, indanyl-1H),
1.90-1.63 (m, 3H, CH2CHMe2, CH2CHMe2), 1.36-1.29 (s, 9H,
NHCMe3), 0.81 and 0.69 (2d, J ) 6.5 Hz, 6H, CH2CHMe2);
LCMS m/z 505 (MH+) single component, gradient 2 (tR ) 3.50
min); HRMS calcd for C30H40N3O4 (MH+) 506.3024, found
506.3023; HPLC 100% (tR ) 17.02 min).
(2R)-N-(tert-Butyl)-2-[(3R,6R)-3-(2,3-dihydro-1H-in-
den-2-yl)-6-isobutyl-2,5-dioxopiperazin-1-yl]-2-[4-(trifluo-
romethoxy)phenyl]ethanamide (35) and (2S)-N-(tert-
butyl)-2-[(3R,6R)-3-(2,3-dihydro-1H-inden-2-yl)-6-isobu-
tyl-2,5-dioxopiperazin-1-yl]-2-[4-(trifluoromethoxy)phen-
yl]ethanamide (36). Compound 8 was reacted with 4-tri-
fluoromethoxybenzaldehyde and tert-butylisonitrile as de-
scribed for compound 15 to give 35 as a colorless solid (21%).
1H NMR (CDCl3) δ 8.08 (d, J ) 3.5 Hz, 1H, lactam NH), 7.51-
7.47 (m, 2H, trifluoromethoxyphenyl-2H, -6H), 7.19-7.13 (m,
4H, indanyl-arylH), 6.94-6.90 (m, 2H, trifluoromethoxyphe-
nyl-3H, -5H), 6.00 (s, 1H, NHCMe3), 5.30 (s, 1H, NCHtrifluo-
romethoxyphenyl), 4.04-3.95 (m, 2H, NCHisobutyl, NCHin-
danyl), 3.16-2.29 (m, 3H, indanyl-3H, -1H), 2.92-2.79 (m, 2H,
indanyl-2H, indanyl-1H), 1.85-1.64 (m, 2H, CHHCHMe2,
CH2CHMe2), 1.35-1.24 (m, 10H, CHHCHMe2, NHCMe3), 0.82
and 0.74 (2d, J ) 7.0 Hz, 3H, CH2CHMe2); LCMS m/z 560
(MH+) single component, gradient 2 (tR ) 3.65 min); HRMS
calcd for CxxHxxN3O3 (MH+) 560.2736, found 560.2736; HPLC
100% (tR ) 15.75 min).
(2R)-2-[3-(Acetylamino)phenyl]-N-(tert-butyl)-2-[(3R,6R)-
3-(2,3-dihydro-1H-inden-2-yl)-6-isobutyl-2,5-dioxopiper-
azin-1-yl]ethanamide (40). Compound 8 was reacted with
3-acetamidobenzaldehyde and tert-butylisonitrile as described
for compound 15 to give 40 as a colorless solid (11%). 1H NMR
(CDCl3) δ 7.87-7.80 (m, 2H, AcNH, acetamidophenyl-4H), 7.56
(s, 1H, acetamidophenyl-2H), 7.36 (pseudo-t, J ) 8.0 Hz,
acetamidophenyl-5H), 7.22-7.09 (m, 5H, indanyl-arylH, ac-
etamidophenyl-5H), 6.71 (d, J ) 4.0 Hz, lactamNH), 5.75 (s,
1H, NHCMe3), 5.06 ((s, 1H, NCHacetamidophenyl), 3.98-3.90
The diastereomer 36 (31%) was isolated as a white solid.
1H NMR (CDCl3) δ 8.36 (d, J ) 3.5 Hz, 1H, lactam NH), 7.51-
7.47 (m, 2H, trifluoromethoxyphenyl-2H, -6H), 7.19-7.13 (m,

6968 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22
Borthwick et al.
(m, 2H, NCHisobutyl, NCHindanyl), 3.19-3.00 (m, 3H, inda-
nyl-3H, -1H), 2.95-2.78 (m, 2H, indanyl-2H, indanyl-1H), 2.15
(s, 3H, MeCO), 1.82-1.65 (m, 2H, CHHCHMe2, CH2CHMe2),
1.45-1.37 (m, 1H, CHHCHMe2), 1.33 (s, 9H, NHCMe3), 0.80
and 0.74 (2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS m/z 533
(MH+) single component, gradient 2 (tR ) 3.21 min); HRMS
calcd for C31H40N4O4 (MH+) 533.3128, found 533.3130; HPLC
100% (tR ) 12.69 min).
(2R)-2-[(3R,6R)-3-(2,3-Dihydro-1H-inden-2-yl)-6-(2-meth-
ylpropyl)-2,5-dioxo-1-piperazinyl]-N-(1,1-dimethylethyl)-
2-[4-(4-methyl-1-piperazinyl)phenyl]ethanamide (41).
Compound 8 was reacted with 4-(4-methyl-1-piperazinyl)-
benzaldehyde and tert-butylisonitrile as described for com-
pound 15 to give 41 as a colorless solid (11%). 1H NMR (CDCl3)
δ 7.32-7.14 and 6.95-6.90 (2m, 8H, arylH), 6.13 (d, J ) 4.5
Hz, lactamNH), 5.52 (s, 1H, NHCMe3), 5.14 (s, 1H, NCHpip-
erazinophenyl), 3.97-3.90 (m, 2H, NCHisobutyl, NCHindanyl),
3.45-2.54 (4m, 13H, indanyl-3H, -1H, -2H, piperazine 4 ×
CH2), 2.36 (s, 3H, NMe), 1.78-1.50 (m, 3H, CH2HCHMe2), 1.31
(s, 9H, NHCMe3), 0.77 and 0.69 (2d, J ) 6.5 Hz, 6H, CH2-
CHMe2); LCMS m/z 574 (MH+) single component, gradient 2
(tR ) 2.48 min); HRMS calcd for C34H48N5O3 (MH+) 574.3757,
found 574.3751; HPLC 100% (tR ) 10.21 min).
(2R)-2-[(3R,6R)-3-(2,3-Dihydro-1H-inden-2-yl)-6-(2-meth-
ylpropyl)-2,5-dioxo-1-piperazinyl]-N-(1,1-dimethylethyl)-
2-[3-(4-methyl-1-piperazinyl)phenyl]ethanamide (42).
Compound 8 was reacted with 3-(4-methyl-1-piperazinyl)-
benzaldehyde and tert-butylisonitrile as described for com-
pound 15 to give 42 as a colorless solid (14%). 1H NMR (CDCl3)
δ 7.30-7.15 and 7.00-6.85 (2m, 8H, arylH), 6.07 (d, J ) 4.0
Hz, lactamNH), 5.56 (s, 1H, NHCMe3), 5.24 ((s, 1H, NCHpip-
erazinophenyl), 4.03-3.94 (m, 2H, NCHisobutyl, NCHindanyl),
3.25-2.55 (4m, 13H, indanyl-3H, -1H, -2H, piperazine 4 ×
CH2), 2.36 (s, 3H, NMe), 1.65-1.30 (m, 3H, CH2HCHMe2), 1.32
(s, 9H, NHCMe3), 0.76 and 0.68 (2d, J ) 6.5 Hz, 6H, CH2-
CHMe2); LCMS m/z 574 (MH+) single component, gradient 2
(tR ) 2.53 min); HRMS calcd for C34H48N5O3 (MH+) 574.3757,
found 574.3761; HPLC 100% (tR ) 10.57 min).
(2R)-2-[(3R,6R)-3-(2,3-Dihydro-1H-inden-2-yl)-6-(2-meth-
ylpropyl)-2,5-dioxo-1-piperazinyl]-N-methyl-N-(1-methyl-
ethyl)-2-phenylethanamide (43). Compound 15 (60 mg) and
methyl iodide (0.016 mL) were dissolved in dry tetrahydrofu-
ran (1 mL), and the solution was stirred at -20 °C under dry
nitrogen. A solution of lithium hexamethyldisilazide (1.0 M
in tetrahydrofuran, 0.100 mL) was added via syringe. The
mixture was kept between -20 and -10 °C for 3 h and then
allowed to warm to room temperature. The reaction was
quenched with saturated aqueous ammonium chloride (0.5
mL). The quenched reaction mixture was diluted with ethyl
acetate (50 mL) and dried over anhydrous sodium sulfate. The
mixture was evaporated under reduced pressure, and the crude
product was purified by preparative layer chromatography on
silica (eluted with 3% 2-propanol in dichloromethane) to give
the title compound as a colorless solid (20 mg, 32%). 1H NMR
(CDCl3) (rotameric forms present) δ 7.45-7.39 and 7.25-7.13
(m, 9H, phenyl-arylH, indanyl-arylH), 6.85-6.79 (broad m, 1H,
lactamNH), 6.63 and 6.37 (2s, 1H, NCHphenyl), 494 (septet,
1H, NMeCHMe2), 4.20-4.06 (dd, J ) 12.1 Hz, 4.0 Hz, 1H,
NCHisobutyl), 3.99 (dd, J ) 10.5 Hz, 4.5 Hz, 1H, NMeCHMe2),
3.21-3.03 and 2.93-2.73 (2m, 5H, indanyl-3H, -1H, -2H), 2.82
and 2.60 (2s, 3H, NMeCHMe2), 1.53-1.35 (m, 2H, CHHCHMe2,
CH2CHMe2), 1.22, 1.10, 1.00 and 0.68 (4d, J ) 6.5 Hz, 6H,
NMeCHMe2), 0.62-0.53 (m, 4H, CH2CHMeMe, CHHCHMe2),
0.35 (d, J ) 6.5 Hz, 3H, CH2CHMeMe); LCMS m/z 476 (MH+)
major component, gradient 2 (tR ) 3.54 min). HRMS calcd for
C29H38N3O3 (MH+) 476.2913, found 476.2907; HPLC 95% (tR
) 14.36 min).
syringe. The mixture was allowed to warm to room tempera-
ture over 2 h, then stirred at room temperaure for 30 min.
The solution was cooled to -30 °C. Then the reaction was
quenched with saturated aqueous ammonium chloride (2 mL).
The reaction mixture was diluted with ethyl acetate (50 mL)
and dried over anhydrous sodium sulfate. The mixture was
evaporated under reduced pressure, and the crude product was
purified by preparative layer chromatography on silica (eluted
with 2% 2-propanol in dichloromethane) to give the title
compound as a colorless solid (16 mg, 35%). 1H NMR (CDCl3)
δ 7.41 (s, 5H, phenyl-arylH), 7.28-7.14 (m, 4H, indanyl-arylH),
5.76-5.65 (m, 1H, CHdCH2), 5.46 (d, J ) 7.8 Hz, 1H,
NHCHMe2), 5.22 (s, 1H, NCHphenyl), 5.20 (broad d, J ) 11.3
Hz, 1H, CHdCHH (cis to CHdCH2)), 5.09 (broad d, J ) 17.3
Hz, 1H, CHdCHH (trans to CHdCH2)), 4.85-4.78 (m, 1H,
CHHCHdCH2), 4.16-4.06 (m, 1H, NHCHMe2), 4.05 (dd, J )
10.8 Hz, 4.0 Hz, 1H, NCHisobutyl), (d, J ) 9.0 Hz, 1H,
NCHindanyl), 3.42-3.35 (m, 1H, CHHCHdCH2), 3.20-2.84
(m, 5H, indanyl-3H, -1H, -2H), 1.81-1.66 (m, 2H, CHHCHMe2,
CH2CHMe2), 1.34-1.26 (m, 1H, CHHCHMe2), 1.12 and 1.09
(2d, J ) 6.5 Hz, 6H, NHCHMe2), 0.80 and 0.75 (2d, J ) 6.5
Hz, 6H, CH2CHMe2); LCMS m/z 502 (MH+) major component,
gradient 2 (tR ) 3.57 min). HRMS calcd for C31H40N3O3 (MH+)
502.3070, found 502.3065; HPLC 100% (tR ) 14.74 min).
(2R)-2-[(3R,6R)-3-(2,3-Dihydro-1H-inden-2-yl)-6-(2-meth-
ylpropyl)-2-oxo-1-piperazinyl]-N-(1-methylethyl)-2-phenyl-
ethanamide (45). Compound 15 (70 mg) was dissolved in dry
tetrahydrofuran (3 mL), and the solution was stirred at room
temperature under dry nitrogen. A solution of borane (1.0 M
in tetrahydrofuran, 0.84 mL) was added via syringe over 1 min
(effervescence was observed). The mixture was left at room
temperature overnight, and then the excess borane was
destroyed by addition of 0.5 M hydrochloric acid (2 mL,
effervescence). After the mixture was stirred at room temper-
ature for 2 h, the reaction mixture was evaporated under
reduced pressure and the residue was partitioned between
saturated aqueous sodium hydrogen carbonate (5 mL) and
dichloromethane (10 mL). The organic extract was separated
using a hydrophobic frit and evaporated under reduced pres-
sure. The crude product was purified by preparative layer
chromatography on silica (eluted with 2.5% 2-propanol in
dichloromethane) to give the title compound as a colorless gum
(21 mg, 31%). 1H NMR (CDCl3) δ 7.43-7.32 and 7.23-7.11
(2m, 9H, phenyl-arylH, indanyl-arylH), 5.90 (d, J ) 7.5 Hz,
1H, NHCHMe2), 5.37 (s, 1H, NCHphenyl), 4.15-4.05 (m, 1H,
NHCHMe2), 3.77 (d, J ) 4.5 Hz, 1H, NCHindanyl), 3.46-3.36
(m, 1H, NHCHHCHisobutyl), 3.17-2.88 (m, 7H, NCHisobutyl,
NHCHHCHisobutyl, indanyl-3H, -1H, -2H),1.89-1.67 (m, 2H,
CHHCHMe2, CH2CHMe2), 1.35-1.25 (m, 1H, CHHCHMe2),
1.13 and 1.10 (2d, J ) 6.5 Hz, 6H, NHCHMe2), 0.74 and 0.58
(2d, J ) 6.5 Hz, 6H, CH2CHMe2); LCMS m/z 448 (MH+) major
component, gradient 2 (tR ) 3.02 min); HRMS calcd for
C28H38N3O2 (MH+) 448.2964, found 448.2972; HPLC 94% (tR
) 11.55 min).
X-ray Crystallographic Analysis of 17. Crystals of 17
grew as colorless prisms by slow evaporation of 1,2-dimethoxy-
ethane. The data crystal was a prism with approximate
dimensions of 0.90 × 0.22 × 0.14 mm3. Crystal data are the
following: empirical formula, C31H42N3O4; M ) 520.68; mono-
clinic; space group P21; a ) 12.7167(7) Å; b ) 19.3272(11) Å;
c ) 13.8360(8) Å; R ) 90°; â ) 117.124(2)°; γ ) 90°; volume,
3026.6(3) Å3; Z ) 4; Dc ) 1.143 g/cm3; F(000) ) 1124. The data
were collected at 160(2) K on a Bruker SMART 1K CCD
diffractometer using Mo KR, radiation (λ ) 0.710 73 Å). Data
reduction was performed using SAINT, version 6.63 (from
Bruker AXS). The structure was solved by direct methods
using SHELXTL and refined by full-matrix least-squares on
F2 with anisotropic displacement parameters for the non-H
atoms using SHELXTL. The structure was refined to R )
(2R)-2-[(3R,6R)-3-(2,3-Dihydro-1H-inden-2-yl)-6-(2-meth-
ylpropyl)-2,5-dioxo-4-(2-propen-1-yl)-1-piperazinyl]-N-(1-
methylethyl)-2-phenylethanamide (44). Compound 15 (42
mg) and allyl bromide (0.060 mL) were dissolved in dry
tetrahydrofuran (2 mL), and the solution was stirred at -78
°C under dry nitrogen. A solution of lithium hexamethyldisi-
lazide (1.0 M in tetrahydrofuran, 0.100 mL) was added via
0.0474 (10 899 reflections with F2 > 2σ(Fo)]), wR2 ) 0.1048,
o
and a goodness of fit ) 1.055 for 714 refined parameters. The
absolute structure parameter, Flack, was refined to -0.1(8);
this was not sufficient to assign the absolute stereochemistry.
Neutral atom scattering factors and values used to calculate

2,5-Diketopiperazines Oxytocin Antagonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22 6969
Identification of potent and selective oxytocin antagonists. Part
2: further investigation of benzofuran derivatives. Bioorg. Med.
Chem. Lett. 2002, 12, 1405-1411.
the linear absorption coefficient are from the International
Tables for X-ray Crystallography. The crystal structure has
been deposited at the Cambridge Crystallographic Data Cen-
tre, and the allocated deposition number is CCDC 272988.
(16) Wood, S. P.; Tickle, I. J.; Treharne, A. M.; Pitts, J. E.; Mas-
carenhas, Y.; Li, J. Y.; Husain, J.; Cooper, S.; Blundell, T. L.;
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Acknowledgment. We thank Sean M. Lynn, Ana-
lytical Sciences, Discovery Research, GlaxoSmithKline
Research and Development, Stevenage, U.K., and Pro-
fessor William Clegg of the University of Newcastle
upon Tyne for their help with the crystallographic
aspects of the paper.
(19) Melin, P.; Trojnar, J.; Johansson, B.; Vilhardt, H.; Akerlund, M.
Synthetic antagonists of the myometrial response to vasopressin
and oxytocin. J Endocrinol. 1986, 111, 125-131.
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M. Inhibitory effect of O-alkylated analogues of oxytocin and
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(21) Chromatographic hydrophobicity index (CHI) utilizes the gradi-
ent retention time from rapid gradient reverse-phase elution to
measure lipophilicity. See the following. Valko, K.; Du, C. M.;
Bevan, C.; Reynolds, D. P.; Abrahams, M. H. Rapid method for
the estimation of octanol/water partition coefficient (log Poct) from
gradient RP-HPLC retention and a hydrogen bond acidity term
(∑R2H). Curr. Med. Chem. 2001, 8, 1137-1146.
(22) Valko, K. Separation Methods in Drug Synthesis and Purifica-
tion. In Handbook of Analytical Separations; Valko, K., Ed.;
Elsevier: Amsterdam, 2000; Vol. 1, Chapter 12, pp 535-583.
(23) For HSA and RSA binding methods using Chromtech im-
mobilized HSA and RSA HPLC columns, see the following.
Valko, K.; Nunhuck, S.; Bevan, C.; Abraham, M. H.; Reynolds,
D. P. Fast gradient HPLC method to determine compounds
binding to human serum albumin. Relationships with octanol/
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Supporting Information Available: Details of the X-ray
crystallographic determination of 17 and the CD spectra of
17, 18, and 37. This material is available free of charge via
the Internet at http://pubs.acs.org.
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V1a, V1b, and V2 binding assay method is identical to the hOT
method except 10 µg of V1a-CHO membrane was used and 0.5
nM [3H]vasopressin was used as ligand (Kd ) 0.79 nM), 10 µg of
V1b-CHO membrane was used and 1 nM [3H]vasopressin was
used as ligand (Kd ) 3.9nM), and 10 µg of V2-CHO membrane
was used and 0.5 nM [3H]vasopressin was used as ligand (Kd
3.8 nM).
)
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JM050557V