Use of a dipeptide chemical library in the development of non-peptide tachykinin NK3 receptor selective antagonists

Article abstract of DOI:10.1021/jm950892r

The use of a dipeptide library as the source of a micromolar chemical lead compound for the human tachykinin NK₃ receptor is described. The screening of a dipeptide library through a cloned human NK₃ receptor binding assay resulted in the identification of Boc(S)Phe(S)PheNH₂ (1), which has subsequently been developed, following a 'peptoid' design strategy, into a series of high-affinity NK₃ receptor selective antagonists. The structure- activity relationship of the C-terminal portion of this dipeptide lead was first explored and led to the identification of the urea derivative Boc(S)Phe(R)αMePheNH(CH₂)₇NHCONH₂ (41, PD157672). This modified dipeptide has a K(o) of 7 nM in blocking senktide-induced increases in intracellular calcium levels in human NK₃ receptors stably expressed in CHO cells. Subsequent optimization of the N-terminal BocPhe group and the αMePhe residue side chain of 41 led to the identification of [S-(R*,S*)]-[2-(2,3- difluorophenyl)-1-methyl-1-[(7-ureidoheptyl)carbamoyl]ethyl]carbamic acid 2- methyl-1-phenylpropyl ester (60, PD161182), a non-peptide NK₃ receptor selective antagonist. Compound 60 blocks the senktide-evoked increases in intracellular calcium levels in cloned human NK₃ receptors stably expressed in CHO cells with K(e) of 0.9 nM.

Full text of DOI:10.1021/jm950892r

1664
J . Med. Chem. 1996, 39, 1664-1675
Use of a Dip ep tid e Ch em ica l Libr a r y in th e Develop m en t of Non -P ep tid e
Ta ch yk in in NK3 Recep tor Selective An ta gon ists
Phil Boden, J on M. Eden, J ulie Hodgson, David C. Horwell, J ohn Hughes, Alexander T. McKnight,
Russell A. Lewthwaite, Martyn C. Pritchard, J enny Raphy,* Ken Meecham, Giles S. Ratcliffe,
Nirmala Suman-Chauhan, and Geoffrey N. Woodruff
Parke-Davis Neuroscience Research Centre, Cambridge University Forvie Site, Robinson Way, Cambridge CB2 2QB, U.K.
Received December 6, 1995X
The use of a dipeptide library as the source of a micromolar chemical lead compound for the
human tachykinin NK3 receptor is described. The screening of a dipeptide library through a
cloned human NK3 receptor binding assay resulted in the identification of Boc(S)Phe(S)PheNH2
(1), which has subsequently been developed, following a ‘peptoid’ design strategy, into a series
of high-affinity NK3 receptor selective antagonists. The structure-activity relationship of the
C-terminal portion of this dipeptide lead was first explored and led to the identification of the
urea derivative Boc(S)Phe(R)RMePheNH(CH2)7NHCONH2 (41, PD157672). This modified
dipeptide has a Ke of 7 nM in blocking senktide-induced increases in intracellular calcium
levels in human NK3 receptors stably expressed in CHO cells. Subsequent optimization of the
N-terminal BocPhe group and the RMePhe residue side chain of 41 led to the identification of
[S-(R*,S*)]-[2-(2,3-difluorophenyl)-1-methyl-1-[(7-ureidoheptyl)carbamoyl]ethyl]carbamic acid
2-methyl-1-phenylpropyl ester (60, PD161182), a non-peptide NK3 receptor selective antagonist.
Compound 60 blocks the senktide-evoked increases in intracellular calcium levels in cloned
human NK3 receptors stably expressed in CHO cells with Ke of 0.9 nM.
In tr od u ction
ties of the amino acids was used to select a library of
256 N-protected dipeptides.
The medicinal chemistry community has been quick
to recognize, and subsequently exploit, the concept of
large combinatorial chemical libraries as a means of
rapid chemical lead identification. Since Houghton,1
Hruby,2 and Fodor’s3 key initial publications in this
area, the scope of this technology has been significantly
broadened to encompass the rapid synthesis of arrays
of both peptide1-3 and non-peptide4-8 compound collec-
tions generated by resin or solution phase chemical
techniques.
Subsequent hits obtained from the screening of this
library in neuropeptide receptor assays were found to
contain predominantly lipophilic amino acids (unpub-
lished data). A second library of 64 dipeptides enriched
in lipophilic side chains was therefore prepared in order
to exploit this observation. These compounds are a set
of Boc-protected dipeptide amides constructed from all
combinations of the lipophilic amino acids Trp, Phe, Tyr,
Val, Leu, Met, Ala, and Thr.
Active interest in the tachykinin research area13-15
is reflected in the large number of recent publications
describing non-peptide receptor antagonists. The ma-
jority of these describe NK1 and NK2 receptor selective
ligands.16 Recently the first non-peptide NK317 receptor
selective antagonist has been revealed. Our interest in
this field has been illustrated by the rational design of
both NK1 and NK2 receptor antagonists following a
‘peptoid’ design strategy. This ‘peptoid’ design strategy
therefore became the starting point for our NK3 receptor
program and is summarized in Scheme 1.
Whichever library type is chosen, it must serve to
provide a collection of compounds which are capable of
interacting with the biological target of interest at a
detectable level. The compounds must also provide
suitable starting points for subsequent optimization into
a credible drug candidate. With these points in mind,
we have recently described a dipeptide library.9 The
construction of such a library was considered useful as
a potential source of novel lead structures since: (a)
dipeptides have been shown, by us10 and other groups,11
to be an excellent starting point for drug design, (b)
sufficient quantity of compound, even for in vivo profil-
ing, can easily be prepared at relatively low cost, (c) no
specialized equipment is required for the synthesis of
such a library, (d) a library containing only 256 com-
pounds can provide a data set that spans a broad
spectrum of physicochemical properties in a minimum
number of compounds, and (e) no deconvolution is
required to identify the lead structures.
18
19
In the development of our NK1 and NK2 receptor
antagonists, a key step in the ‘peptoid’ design strategy
was the identification of a dipeptide lead. In the case
of our NK3 receptor program, we took the opportunity
to investigate whether the initial steps in our ‘peptoid’
design strategy, i.e., the preparation of N- and C-
terminal deletions, and the alanine scan could be
superseded by the screening of our dipeptide libraries.
The key requirement of the library so constructed was
that the greatest possible diversity of physical properties
should be contained in a minimum set of compounds.
For this purpose a factorial design using the minimum
analogue peptide sets (MAPS)12 in the principal proper-
This paper describes the implementation of the dipep-
tide libraries in the identification of a micromolar
affinity NK3 receptor lead. The subsequent develop-
ment of this dipeptide lead into high-affinity modified
dipeptide20 and non-peptide21 nanomolar NK3 selective
receptor antagonists is reported.
X Abstract published in Advance ACS Abstracts, March 15, 1996.
0022-2623/96/1839-1664$12.00/0 © 1996 American Chemical Society

Dipeptide Library for NK3 Receptor Lead Development
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8 1665
Sch em e 3. Synthesis of Intermediate 16a
Sch em e 1. Peptoid Design Strategy
a
(i) 2-Bromoacetamide, K2CO3, 2-butanone, 80 °C, 4 h; (ii)
p-toluenesulfonyl chloride, DMAP, DCM, pyridine, 16 h (81%); (iii)
NaN3, DMF, 75 °C, 2 h (77%); (iv) Lindlar catalyst, MeOH, H2, 44
psi, 25 °C, 18 h.
zyl)oxy]carbonyl moiety is introduced by coupling the
p-nitrophenyl carbonate of the 2-methyl-1-phenyl-1-
propanol to the appropriate amino acid methyl ester.
In the case of the side-chain-substituted RMePhe resi-
dues, the resulting diastereoisomers were separated at
this stage by column chromatography. The esters were
then hydrolyzed with lithium hydroxide, and the (7-
aminoheptyl)urea moiety was coupled to the acids using
HBTU activation.
Sch em e 2. Synthesis of Intermediate 12a
Biology
The human CHO NK3 receptor binding assay was
carried out as described previously,23 as were the NK1
and NK2 binding assays.18,19 The procedures employed
in the in vitro functional assays have been published
and are referenced in Table 8.
Resu lts a n d Discu ssion
Screening of the dipeptide libraries in a cloned human
NK3 receptor binding assay resulted in the identification
of a number of micromolar hits (Table 1). All hits with
>10 µM affinity for the NK3 receptor contain two
aromatic amino acid residues and as a consequence
came predominantly from the 64-membered lipophilic
dipeptide library described above. From these hits Boc-
(S)Phe(S)PheNH2 (1) with an IC50 of 1550 nM was
selected as the lead compound. This compound is
selective for the NK3 receptor over the NK1 and NK2
receptors, for which the IC50 values are >10 µM in both
cases.
Following the identification of a dipeptide lead, the
next step in our peptoid design strategy is the explora-
tion of the spatial arrangement of the amino acid side
chains and protecting groups. Conformational con-
straint can be built into the peptide backbone by the
strategic placement of methyl groups. This approach
has been successful in the improvement of the binding
affinity of initial leads in our NK1,18 NK2,19 and CCK10
receptor programs. Compounds were therefore pre-
pared in which single methyl groups were appended on
the nitrogen atom or R-carbon of the amino acid residues
(Table 2).
a
(i) KOH, N2H4, diethylene glycol, 180 °C, 2 h (71%); (ii) 48%
HBr, AcOH, 116 °C, 6 h (91%); (iii) DCCI, pentafluorophenol,
EtOAc, 4 h, NH3, 12 h (82%); (iv) 2 M borane-methyl sulfide
complex in THF, 65 °C, 6 h (23%).
Ch em istr y
The Boc dipeptides 1-4 were purchased from Neo-
system Laboratoire. The dipeptide library compounds
5 and 6 and the N- and R-methyl dipeptides 1a -j were
prepared by standard peptide-coupling procedures using
pentafluorophenyl ester or 2-(1H-benzotriazol-1-yl)-
1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU)
activation. Schemes 2 and 3 describe the syntheses of
the C-terminal fragments 12 and 16 which were sub-
sequently coupled to Boc(S)Phe(R)RMePheOH22 using
HBTU activation. The sulfonamide derivative 39 was
prepared by the treatment of Boc(S)Phe(R)RMePheNH-
(CH2)7NH2 with methanesulfonyl chloride and pyridine
in dichloromethane as outlined in Scheme 4. The (7-
aminoheptyl)urea was prepared from 1,7-diaminohep-
tane and then coupled to Boc(S)Phe(R)RMePheOH22 as
shown in Scheme 5. Scheme 6 depicts the synthesis of
the monoamino acid compounds. The [(isopropylben-
Unfortunately, no increase in binding affinity was
observed as a result of the methylations. The C-
terminal R-methyl compound Boc(S)Phe(RS)RMePheNH2

1666 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8
Sch em e 4. Synthesis of 39a
Boden et al.
a
(i) (a) EtOCOCl, NMM, THF, 0 °C, 1 h, (b) LiBH4, THF, 3 h (96%); (ii) (a) TFA, DCM, 1 h, (b) Boc(S)Phe(R)RMePheOH, DCCI, HOBt,
DMF, 15 h (67%); (iii) p-toluenesulfonyl chloride, NEt3, DCM, DMAP, 15 h; (iv) NaN3, DMF, 60 °C, 3 h (69%); (v) Lindlar catalyst, EtOH,
H2, 40 psi, 30 °C, 6 h (76%); (vi) methanesulfonyl chloride, pyridine, DCM, 15 h (21%).
Sch em e 5. Synthesis of 41a
Ta ble 1. Micromolar Hits Identified from Screening the
Dipeptide Library against the Human NK3 Receptor
compd no.
structure
IC50, nMa
1
2
3
4
5
6
Boc(S)Phe(S)PheNH2
Boc(S)Trp(S)PheNH2
Boc(S)Phe(S)TrpNH2
Boc(S)Phe(S)TyrNH2
(CH3)2CH(CH2)2COTrpTrpNH2
(CH3)2CH(CH2)2COPheTrpNH2
1550
2080
9610
8620
1760
3270
a
(i) Trimethylsilyl isocyanate, THF, 2 h (90%); (ii) Boc(S)-
Phe(R)RMePheOH, HBTU, DIPEA, DMF, 2 h (47%).
a
IC50 is the concentration (nM) producing half-maximal inhibi-
tion of the specific binding of [125I][MePhe7]NKB to NK3 binding
sites in cloned NK3 receptors stably expressed in CHO cells.
Values shown represent the geometric mean of three to six
experiments.23
Sch em e 6. Synthesis of 54-61a
Ta ble 2. Methylation of the Dipeptide Lead
Boc(S)Phe(S)PheNH2
compd no.
R1
R2
R3
R4
b
9
IC50, nMa
1
H
H
H
H
S
S
1550
1a
1b
1c
1d
1e
1f
1g
1h
1i
CH3
H
H
H
CH3
H
H
H
H
H
H
CH3
H
H
H
CH3
H
H
H
H
H
H
CH3
H
H
H
CH3
H
H
H
H
H
H
CH3
H
H
H
CH3
CH3
CH3
RS
RS
S
S
S
RS
RS
R
>10 000
>10 000
>10 000
1520
>10 000
>10 000
>10 000
>10 000
1490
S
RS
RS
R
R
S
R
RS
RS
S
1j
S
R
1830
a
See footnote a, Table 1.
a
(i) p-Nitrophenyl chloroformate, pyridine, DCM, 24 h (92%);
(ii) (R)-RMePheOCH3, 46 or 47, DMF, 3 days (26-78%); (iii) LiOH,
THF/H2O, 48 h (86-93%); (iv) RNH2, HBTU, DIPEA, DMF, 2-18
h (29-70%).
(1d , IC50 ) 1520 nM) did however display similar
binding affinity to that of the parent compound. This
compound was selected as the new lead on the basis that
the R-methyl may impart some in vivo stability.24
The next step in our strategy is the optimization of
the N- and C-terminal groups. In order to identify
suitable binding moieties for N- and C-terminal modi-
fications of Boc(S)Phe(RS)RMePheNH2 (1d ), we consid-
ered the hypothesis that the PhePhe sequence in our
ligand mimics the binding characteristics of the same
sequence in [(4-hydroxyphenyl)acetyl]PhePheGlyLeu-
MetNH2 (7),25 NKB, and senktide (Figure 1). If this
hypothesis is valid, it should be possible to increase the
binding affinity of the dipeptide 1d by appending
binding groups and/or side chain moieties from these
peptides.
F igu r e 1. Structure of 1d , 7, neurokinin B, and senktide.
The smallest of these peptides (7), i.e., the compound
containing the smaller number of residues, was chosen
as a template. The affinity of this pentapeptide deriva-
tive for the NK3 receptor (IC50 ) 112 nM23) has been
attributed to a specific binding interaction of the N-
terminal (4-hydroxyphenyl)acetyl group, as the pen-
tapeptide itself has been shown to have significantly
lower affinity (IC50 ) 10 000 nM). This moiety was
therefore appended to the N- and C-termini of the
dipeptide 1d (Table 3).
Appending the (4-hydroxyphenyl)acetyl moiety to the
N-terminal of 1d led to a significant drop in NK3
receptor binding affinity (8, IC50 ) 5890 nM). In
contrast appending this group at the C-terminal re-

Dipeptide Library for NK3 Receptor Lead Development
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8 1667
Ta ble 4. NK3 Receptor Binding Affinities
Ta ble 3. NK3 Receptor Binding Affinities
compd no.
structure
IC50, nMa
compd
no.
IC50,
structure
nMa
1d
8b
17
18
19
20
21
22
23
Boc(S)Phe(RS)RMePheNH2
1520
5890
425
39
1080
162
111
92
106
1690
40
439
229
101
Ph(4-OH)CH2CO(S)Phe(RS)RMePheNH2
Boc(S)Phe(RS)RMePheNHCH2Ph(4-OH)
Boc(S)Phe(R)RMePheNH(CH2)4Ph(4-OH)
Boc(S)Phe(RS)RMePheNHCH2Ph
Boc(S)Phe(RS)RMePheNH(CH2)4Ph
Boc(S)Phe(RS)RMePheNH(CH2)7OH
Boc(S)Phe(RS)RMePheNH(CH2)8OH
Boc(S)Phe(RS)RMePheNH(CH2)9OH
Boc(S)Phe(S)RMePheNH(CH2)8OH
Boc(S)Phe(R)RMePheNH(CH2)8OH
Boc(S)Phe(RS)RMePheNH(CH2)8CH3
Boc(S)Phe(RS)RMePheNH(CH2)7CO2H
Boc(S)Phe(RS)RMePheNH(CH2)8OMe
25b Boc(S)Phe(R)RMePheNH(CH2)8OH
40
4310
39
18
28
28
31
16
67
29
Boc(S)Phe(RS)PheNH(CH2)8OH
30b Boc(S)Phe(R)RMePheNH(CH2)8CONH2
31b Boc(S)Phe(R)RMePheNH(CH2)8CONHCH3
32
Boc(S)Phe(R)RMePheNH(CH2)8CON(CH3)2
33b Boc(S)Phe(R)RMePheNH(CH2)8SO2Me
39
41
Boc(S)Phe(R)RMePheNH(CH2)7NHSO2Me
Boc(S)Phe(R)RMePheNH(CH2)7NHCONH2
24
42b Boc(S)Phe(R)RMePheNH(CH2)2Ph(4-OCH2CONH2)
25b
26
43
Boc(S)Phe(R)RMePheNH(CH2)2Ph(2-OCH2CONH2) 119
a
b
See footnote a, Table 1. Synthesis as described in ref 22.
27b
28b
a
b
See footnote a, Table 1. Synthesis as described in ref 22.
sulted in an ca. 3-fold increase in NK3 receptor binding
affinity (17, IC50 ) 425 nM). Increasing the methylene
chain length in compounds of this nature led to an
improvement in binding affinity, with four methylenes
being optimal (18, IC50 ) 39 nM). As the replacement
of the phenol moiety with a phenyl group in both cases
(19 and 20) led to a decrease in affinity, the hydroxyl
moiety was considered to be important in the binding
interaction of these ligands. A series of alkyl alcohols
with varying chain lengths were therefore prepared. The
optimum chain length for these compounds was identi-
fied in 22, the 8-amino-1-octanol derivative which has
an IC50 of 92 nM; the shorter 7-amino-1-heptanol (21)
and the longer 9-amino-1-nonanol (23) derivatives have
slightly lower affinities (111 and 106 nM, respectively).
F igu r e 2. Structure of [2-(1H-indol-3-yl)-1-methyl-1-[(1-phe-
nylethyl)carbamoyl]ethyl]carbamic acid 2-methyl-1-phenyl-
propyl ester (44).
In order to reduce the chain flexibility of these poly-
(methylene) compounds, we prepared analogues in
which a phenyl ring was introduced within the alkyl
chain. Although the analogues prepared showed no
improvement in binding affinity, a preference for the
para substitution (42) over the ortho substitution (43)
was observed. This result suggests that the C-terminal
segment may bind in an extended conformation (Table
4).
The contribution to receptor binding affinity of the
R-methylation at the C-terminal phenylalanine residue
was re-examined by the preparation of the non-R-methyl
compound 29. The binding affinity of this ligand is 4310
nM, which compares to 92 nM for the R-methylated
analogue 22. In these compounds where the C-terminal
group plays a major role in the binding affinity of the
ligand, the presence of the R-methyl group is crucial,
presumably in restricting the number of conformations
available to these ligands.27
Having optimized the C-terminal portion of our
dipeptide lead, our next objective as outlined in our
‘peptoid’ design strategy was to examine the N-terminal
portion of our compounds. A key consideration was to
convert these modified dipeptides into non-peptide
derivatives, and to this end the replacement of the
N-terminal Boc(S)Phe moiety was investigated. An
interesting lead in this area came in the form of 44
(Figure 2) which was prepared as part of our NK1
receptor program. In addition to having the targeted
NK1 receptor affinity (IC50 ) 1400 nM), this monoamino
acid derivative was noted to also have micromolar
affinity for the NK3 receptor (IC50 ) 1200 nM). The
possible relationship between this monoamino acid
derivative and our modified dipeptides was investigated
by the substitution of the (R)RMeTrp residue in 44 by
the (R)RMePhe residue found in the dipeptide ligands
(Table 5). In order to determine which stereochemistry
is required at the N-terminal [(isopropylbenzyl)oxy]-
carbonyl moiety for NK3 receptor affinity, both stereoi-
somers at this center were prepared. The compound
The compounds so far described with the exception
of 18 are all equal mixtures of two diastereoisomers
having a racemic center at the RMePhe residue. The
individual stereoisomers of 22 were prepared to deter-
mine the stereochemical preference of these ligands with
respect to NK3 receptor affinity. The preferred stere-
ochemistry was found to be S,R at the two centers,
respectively. The dipeptide with this stereochemistry
(25) has an IC50 of 40 nM in comparison to the
equivalent S,S-isomer 24 which has an IC50 of 1690 nM
(Table 3).
The hydroxyl moiety in the amino alcohol series is
strongly implicated in participating in the binding
interaction with the NK3 receptor as the alkyl derivative
26 shows much reduced binding affinity (IC50 ) 439 nM;
cf. 22, IC50 ) 92 nM; Table 3). In order to optimize the
binding interaction of the hydroxyl group, the nature
of this interaction was investigated with the preparation
of the corresponding hydrogen bond-accepting methyl
ether and hydrogen bond-donating carboxylic acid de-
rivatives (Table 3). The methyl ether 28 was found to
have a similar binding affinity (IC50 ) 101 nM) to the
alcohol 22, while the carboxylic acid analogue 27 binds
with a lower affinity (IC50 ) 229 nM). These observa-
tions led to the postulation that the hydroxyl group is
interacting as a hydrogen bond acceptor in these
ligands. A series of derivatives were therefore prepared
in which the hydroxyl function is replaced with selected
hydrogen bond-accepting groups.26 A number of such
compounds which bind to the human NK3 receptor with
IC50 values in the 20-30 nM range were identified.
Among these compounds, the urea derivative 41, Boc-
(S)Phe(R)RMePheNH(CH2)7NHCONH2, displays the
highest binding affinity (IC50 ) 16 nM).

1668 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8
Ta ble 5. NK3 Receptor Binding Affinities
Boden et al.
Ta ble 7. Tachykinin Receptor Selectivity
binding affinities (IC50, nM)
c
d
compd
no.
NK3
(GP)
NK3
(CHO)
NK1a(IM9) NK2b(HUB)
NK3e(rat)
NKB
98
3.6
2
9.7
senktide >10 000
12
22
22
40
11
2790
25
41
59
60
>10 000
>10 000
2200
6160
(3840-9990) (12-51) (26-61) (2000-3700)
6540 16 1730
(4100-9700) (5-13) (8-24) (1100-2200)
1500 14 16 83
compd no.
b
R
IC50, nMa
9
54
55
56
57
58
R
S
R
S
S
-(S)CH(CH3)Ph
-(S)CH(CH3)Ph
-(CH2)8OH
-(CH2)8OH
-(CH2)7NHCONH2
74
>10 000
350
52
(750-3700) (1300-1700) (8-18) (14-20) (44-156)
3000
790
4
7
30
(2900-3100) (480-1100) (1-6)
(6-9)
(13-78)
57
a
a
Values shown represent the geometric mean of three separate
See footnote a, Table 1.
experiments carried out using [125I]Bolton-Hunter substance P to
label NK1 binding sites in human lymphoma IM9 cells.18 Values
b
Ta ble 6. NK3 Receptor Binding Affinities
shown represent the geometric mean of three separate experi-
ments carried out using [125I]NKA to label NK2 binding sites in
membranes prepared from hamster urinary bladder.19 c Values
shown represent the geometric mean of three to six separate
experiments carried out using [125I][MePhe7]NKB to label NK3
binding sites in guinea pig cortical membranes.23 See footnote
d
a, Table 1. e Values shown represent the geometric mean of three
to six separate experiments carried out using [125I][MePhe7]NKB
to label NK3 binding sites in rat cortical membranes.23
compd no.
b
R
IC50, nMa
58
59
60
61
R
R
R
S
-CH2Ph
-CH2Ph(2-F)
-CH2Ph(2,3-diF)
-CH2Ph(2,3-diF)
57
16
7
Ta ble 8. In Vitro Functional Data
1400
in vitro functional assays (Ke, nM)
a
compd
no.
See footnote a, Table 1.
CHOa cells
GPb ileum
GPc hab
rat habd
with the R stereochemistry at the [(isopropylbenzyl)-
oxy]carbonyl moiety (54) is clearly preferred, having an
IC50 value of 74 nM, in comparison to the S-isomer 55,
which has an IC50 value of >10 000 nM. Encouraged
by this increase in NK3 receptor affinity with compound
54, we went on to append the C-terminal groups
identified as optimum in our modified dipeptides. Ap-
pending the 8-amino-1-octanol moiety found in 25
results in a marginal increase in NK3 receptor affinity
(57, IC50 ) 52 nM). The observed binding affinity of
57 is very similar to that of 25 (IC50 ) 40 nM),
suggesting that the (S)-[(isopropylbenzyl)oxy]carbonyl
group is a good replacement for the N-terminal Boc(S)-
Phe moiety in the dipeptide ligands. Interestingly,
when the C-terminal R-methylbenzylamine is replaced
by the 8-amino-1-octanol group, a switch in the pre-
ferred stereochemistry at the N-terminal for optimal
NK3 receptor binding affinity is observed. In these
compounds the S,R isomer has highest affinity for the
NK3 receptor. The replacement of the 8-amino-1-octanol
group with the (7-aminoheptyl)urea group found in 41
results in no further increase in NK3 receptor affinity
(58, IC50 ) 57 nM).
The final stage in our peptoid design strategy is the
optimization of the amino acid side chains. The central
RMePhe phenyl ring structure-activity relationship
(SAR) was investigated using a Topliss28 type approach.
This lead to the identification of a 2-chlorinated com-
pound with a 2-fold increase in NK3 receptor affinity.
The 2-position was further investigated by the prepara-
tion of a number of halogen and alkyl 2-substituted
RMePhe derivatives. Substitution in this position with
fluorine increases NK3 receptor affinity just over 3-fold
(59, IC50 ) 16 nM); see Table 6. Affinity is further
increased in the 2,3-difluoro analogue 60 (IC50 ) 7 nM).
The stereochemistry at the two chiral centers was
confirmed as S,R from an X-ray crystallographic struc-
ture of compound 50a .
25
41
59
60
29 (25-35)
7 (2-22)
14 (8-40)
54 (34-108)
42 (26-130) 16 (12-21)
13 (5-21)
2 (2-11)
0.9 (0.5-1.5)
6 (4-7)
19 (10-34)
a
Inhibition of senktide-evoked increases in intracellular calcium
levels in cloned human NK3 receptors stably expressed in CHO
cells measured using the fluorescent indicator Fura2.29 Equilib-
rium constants shown represent the mean of at least three
b
separate experiments. Isomeric contractions were recorded from
longitudinal muscle myenteric plexus preparations with responses
to the NK3 receptor selective agonist senktide.30 Data represent
the geometric means of individual values in at least three separate
experiments. c Inhibition of senktide-induced increases in spon-
taneous firing of guinea pig habenula neurons in vitro.31 Values
d
are the mean of at least three separate experiments. Inhibition
of senktide-induced increases in spontaneous firing of rat habenula
neurons in vitro.31 Values are the mean of at least three separate
experiments.
selectivity for the NK3 receptor over NK1 and NK2
receptors in human and hamster preparations, respec-
tively (Table 7). It is interesting to note that while the
dipeptide ligands 25 and 41 have low affinity for the
rat NK3 receptor (IC50 ) 2790 and 1730 nM, respec-
tively), the non-peptide ligands 59 and 60 have ap-
preciable affinity for the rat NK3 receptor (IC50 ) 83
and 30 nM, respectively).
Selected ligands were tested in human and guinea pig
in vitro functional assays. The ability of these ligands
to inhibit senktide-evoked increases in intracellular
calcium levels in cloned human NK3 receptors stably
expressed in CHO cells and senktide-induced increases
in spontaneous firing of guinea pig habenula neurons
in vitro was examined (Table 8). These functional
assays show potent and competitive NK3 receptor selec-
tive antagonism with these compounds. The non-
peptide 60 has Ke values of 0.9 and 6 nM in these two
assays, respectively. As 60 had been shown to have
moderate affinity for the rat NK3 receptor, its ability to
inhibit the senktide-induced increase in the spontaneous
firing of rat medial habenula neurons in vitro was
investigated. The Ke for antagonism of senktide by 60
Both the modified dipeptide ligands, e.g., 25 and 41,
and the non-peptide ligands 59 and 60 show good

Dipeptide Library for NK3 Receptor Lead Development
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8 1669
2H), 4.50-4.60 (m, 1H), 4.65-4.85, (m, 1H), 6.90-7.00 (m, 1H),
7.10-7.25 (m, 10H), 7.40-7.50 (m, 1H); IR (film) 3331, 2978,
1665 cm-1; MS m/ e (CI) 426 (M + H) (5), 326 (100). Anal.
(C24H31N3O4‚0.1H2O) C, H, N.
in this assay is 19 nM, only some 3-fold lower than that
seen in the guinea pig habenula.
Con clu sion
[1-[(1-Ca r ba m oyl-2-p h en yleth yl)ca r ba m oyl]-1-m eth yl-
2-p h en yleth yl]ca r ba m ic Acid ter t-Bu tyl Ester (1b). Boc-
(RS)RMePheOH (213 mg, 0.76 mmol) was dissolved in DMF
(10 mL), and DCCI (157 mg, 0.76 mmol) and pentafluorophenol
(140 mg, 0.76 mmol) were added. The reaction mixture was
stirred for 2 h, after which the precipitate was removed by
filtration. The H-PheNH2 (138 mg, 0.84 mmol) in EtOAc (10
mL) was added, and the reaction mixture was stirred for 3
days. The solvent was removed in vacuo, and the residue was
redissolved in EtOAc (25 mL) and washed with aqueous
NaHCO3 (3 × 10 mL), 1 M HCl (2 × 10 mL), and water (3 ×
10 mL). The organic layer was separated, dried over MgSO4
and evaporated. The residue was purified by column chro-
matography, 50% EtOAc/hexane, to afford a white solid: mp
In this paper we have described the development of
a novel series of high-affinity non-peptide NK3 receptor
selective antagonists. The initial lead compound in this
program was identified from the screening of a dipeptide
chemical library through a human NK3 receptor binding
assay. Optimization of the C-terminal portion of this
dipeptide lead resulted in the identification of a series
of modified dipeptides. These compounds bind selec-
tively to the human NK3 receptor with comparable
binding affinity to the peptide ligands neurokinin B and
senktide. The C-terminal urea derivative 41 has the
highest affinity for the NK3 receptor in this series of
compounds (IC50 ) 16 nM).
These modified dipeptide ligands were then further
developed following our ‘peptoid’ design strategy (Scheme
1). Modification of the N-terminal portion and substitu-
tion of the RMePhe residue side chain led to the
identification of 60, a true non-peptide NK3 receptor
selective antagonist. 60 has an affinity of 7 nM for the
human NK3 receptor and has been shown to be a
competitive antagonist in human, guinea pig, and rat
functional assays with Ke values of 0.9, 6, and 19 nM,
respectively.
80-85 °C; 127 mg (39%); [R]21 ) -40.4° (c ) 0.5, MeOH);
D
1H-NMR (DMSO-d6) δ 0.93, 1.08 (2 × s, 3H), 1.38, 1.41 (2 × s,
9H), 2.83-3.25 (m, 4H), 4.30-4.53 (m, 1H), 6.74-6.95 (m, 3H),
7.14-7.26 (m, 10H), 7.79-7.89 (m, 1H); IR (film) 3400-3200,
1675, 1608, 1520, 1369 cm-1. Anal. (C24H31N3O4‚0.3H2O), C,
H, N.
[1-[(1-Ca r ba m oyl-2-p h en yleth yl)m eth ylca r ba m oyl]-2-
p h en yleth yl]ca r ba m ic Acid ter t-Bu tyl Ester (1c). Boc-
(S)PheOH (124 mg, 0.47 mmol) was dissolved in DMF (5 mL),
and HBTU (177 mg, 0.47 mmol) and DIPEA (362 mg, 2.79
mmol) were added. The reaction mixture was stirred for 10
min, and TFA‚H-(S)-NMePheNH2 (150 mg, 0.51 mmol) was
added. The reaction mixture was stirred for 30 min, and the
solvent was then removed in vacuo and the residue redissolved
in EtOAc (25 mL) and washed with aqueous NaHCO3 (3 × 10
mL), 1 M HCl (2 × 10 mL), and water (3 × 10 mL). The
organic layer was separated, dried over MgSO4, and evapo-
rated. The residue was purified by reverse phase column
chromatography, 65-95% MeOH in water, to afford a white
To our knowledge this is the first published example
in which an initial hit obtained from the screening of a
synthetic peptide chemical library has been developed
into a high-affinity non-peptide ligand for a membrane-
bound receptor. With these non-peptide NK3 receptor
antagonists now in hand, we can begin to determine
whether such ligands will be of therapeutic value in
such areas as analgesia,32 schizophrenia,17 and Parkin-
son’s disease.33
solid: mp 113-117 °C; 42 mg (21%); [R]20 ) -29.0° (c ) 0.5,
D
MeOH); 1H-NMR (DMSO-d6) δ 1.27-1.30 (m, 9H), 2.19-2.44
(m, 1H), 2.69-3.02 (m, 4H), 3.14-3.34 (m, 1H), 4.20-4.50 (m,
1H), 4.81-4.99, 5.20-5.29 (m, 1H), 6.83-7.36 (m, 13H); IR
(film) 3412, 3079, 1690, 1680, 1641, 1632, 1496 cm-1. Anal.
(C24H31N3O4‚1.5H2O) C, H; N: calcd, 9.29; found, 8.84.
Exp er im en ta l Section
[1-[(1-Ca r ba m oyl-1-m eth yl-2-p h en yleth yl)ca r ba m oyl]-
Melting points were determined with a Mettler FP80 or a
Reichert Thermovar hot-stage apparatus. Proton NMR were
recorded on a Bruker AM300 or a Varian Unity +400 spec-
trometer; chemical shifts are recorded in ppm downfield from
tetramethylsilane. IR spectra were recorded with the com-
pound neat on a sodium chloride disk on a Perkin-Elmer
System 2000 Fourier transform spectrophotometer. Optical
rotations were determined with a Perkin-Elmer 241 polarim-
eter. Mass spectra were recorded with a Finnigan MAT
TSQ70 or Fisons VG Trio-2A instrument. Elemental analyses
are within (0.4% of theoretical values and were determined
by Medac Ltd., Uxbridge, U.K. Normal Phase silica gel used
for chromatography was Merck no. 9385 (230-400 mesh), and
reverse phase silica gel used was Lichroprep RP-18 (230-400
mesh); both were supplied by E. Merck, A.G., Darmstadt,
Germany. Anhydrous solvents were purchased in septum-
capped bottles from Fluka Chemicals Ltd., Glossop, U.K.
[1-[(1-Ca r ba m oyl-2-p h en yleth yl)ca r ba m oyl]-2-p h en yl-
eth yl]m eth ylca r ba m ic Acid ter t-Bu tyl Ester (1a ). Boc-
(RS)NMePheOH (150 mg, 0.54 mmol) was dissolved in DMF
(5 mL), and DCCI (111 mg, 0.54 mmol) and HOBt (83 mg, 0.54
mmol) were added. The reaction mixture was stirred for 4 h,
after which H-PheNH2 (90 mg, 0.55 mmol) was added and
stirring was continued for a further 12 h. The solvent was
removed in vacuo, and the residue was redissolved in EtOAc
(100 mL) and washed with aqueous NaHCO3 (3 × 50 mL), 1
M HCl (3 × 50 mL), and water (3 × 50 mL). The organic layer
was separated, dried over MgSO4, and evaporated. The
residue was purified by reverse phase column chromatography
2-p h en yleth yl]ca r ba m ic Acid ter t-Bu tyl Ester (1d ). The
compound was prepared by the method described for 1c in 47%
1
yield: mp 141-143 °C; [R]21 ) -32.0° (c ) 0.5, MeOH); H-
D
NMR (DMSO-d6) δ 1.30 (s, 9H), 1.42 (s, 3H), 2.73-3.39 (m,
4H), 4.03-4.18 (m, 1H), 7.08-7.26, (m, 13H), 7.57 (s, 1H); IR
(film) 3300-3200, 1676, 1497 cm-1. Anal. (C24H31N3O4‚0.1H2O)
C, H, N.
[1-[(1-Ca r ba m oyl-2-p h en yleth yl)ca r ba m oyl]-2-p h en yl-
eth yl]m eth ylca r ba m ic Acid ter t-Bu tyl Ester (1e). The
compound was prepared by the method described for 1b in
35% yield: mp 98-106 °C; 1H-NMR (DMSO-d6, 340 K) δ 1.19
(s, 9H), 2.41 (d, J ) 14.2 Hz, 1H), 2.60-3.08 (m, 6H), 4.40-
4.58 (m, 1H), 4.60-4.91 (m, 1H), 7.12-7.50 (m, 12H), 7.72-
7.98 (m, 1H); IR (film) 3300-3000, 2930, 1667, 1516 cm-1
Anal. (C24H31N3O4‚0.6H2O) C, H, N.
.
[1-[(1-Ca r ba m oyl-2-p h en yleth yl)ca r ba m oyl]-1-m eth yl-
2-p h en yleth yl]ca r ba m ic Acid ter t-Bu tyl Ester (1f). The
compound was prepared by the method described for 1b in
49% yield: mp 60-62 °C; [R]21 ) +49.3° (c ) 0.5, MeOH);
D
1H-NMR (DMSO-d6) δ 0.93, 1.08 (2 × s, 3H), 1.40 (s, 9H), 2.82-
3.25 (m, 4H), 4.30-4.53 (m, 1H), 6.74-6.95 (m, 3H), 7.14-
7.28 (m, 10H), 7.78-7.85 (m, 1H); IR (film) 3307, 2981, 1671,
1496 cm-1. Anal. (C24H31N3O4‚0.3H2O) C, H, N.
[1-[(1-Ca r ba m oyl-2-p h en yleth yl)ca r ba m oyl]-2-p h en yl-
eth yl]ca r ba m ic Acid ter t-Bu tyl Ester (1g). The compound
was prepared by the method described for 1c in 33%
yield: mp 47-50 °C; 1H-NMR (DMSO-d6) δ 1.10-1.37 (m,
9H), 2.19-2.42 (m, 1H), 2.59-3.04 (m, 5H), 3.13-3.40 (m,
1H), 4.20-4.70 (m, 1H), 4.82-5.28 (m, 1H), 6.88-7.39 (m,
to afford a white solid: mp 55-60 °C; 125 mg (54%); [R]20
)
D
-22.2° (c ) 0.5, MeOH); 1H-NMR (DMSO-d6, 340 K) δ 1.26 (s,
13H); IR (film) 3308, 3196, 1680, 1640, 1496 cm-1
. Anal.
9H), 2.46, 2.62 (2 × s, 3H), 2.65-2.95 (m, 2H), 3.00, 3.10 (m,
(C24H31N3O4‚0.25H2O) C, H, N.

1670 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8
Boden et al.
[1-[(1-Ca r ba m oyl-1-m eth yl-2-p h en yleth yl)ca r ba m oyl]-
2-p h en ylet h yl]ca r b a m ic Acid ter t-Bu t yl E st er (1h ).
The compound was prepared by the method described for 1c
in 41% yield: mp 138-143 °C; [R]21D ) +52.7° (c ) 0.5, MeOH);
1H-NMR (DMSO-d6) δ 1.29 (s, 9H), 1.37 (s, 3H), 2.67-2.78
(m, 1H), 2.93-3.08 (m, 1H), 3.18-3.37 (m, 1H), 3.98-4.18
(m, 1H), 7.07 (d, J ) 5.9 Hz, 1H), 7.17-7.28, (m, 12H), 7.74
adjusted to 10 with solid Na2CO3, and the mixture was then
extracted with EtOAc (3 × 100 mL). The organic layer was
dried, and the solvent was evaporated to give a solid: 105 mg
1
(23%); H-NMR (DMSO-d6) δ 1.28 (m, 2H), 1.46 (t, 2H), 2.39
(t, 2H), 3.50 (m, 2H), 6.60 (d, 2H), 6.90 (d, 1H); IR (film) 3313,
2924, 1576, 1462 cm-1
.
2-[2-(2-Hyd r oxyeth yl)p h en oxy]a ceta m id e (13). Potas-
sium carbonate (1.20 g, 8.7 mmol) was added to a solution of
2-(2-hydroxyethyl)phenol (1.20 g, 8.7 mmol) and 2-bromoac-
etamide (1.32 g, 8.7 mmol) in 2-butanone (25 mL). The
suspension was heated under reflux for 4 h and stirred at room
temperature for 15 h. The solid was removed by filtration,
and the filtrate was concentrated in vacuo. Purification by
column chromatography, 5% MeOH/EtOAc, gave a white
(s, 1H); IR (film) 3306, 2980, 1664, 1498 cm-1
.
Anal.
(C24H31N3O4‚0.5H2O) C, H, N.
[S-(R*,R*)]-[1-[(1-Ca r ba m oyl-1-m eth yl-2-p h en yleth yl)-
ca r ba m oyl]-2-p h en yleth yl]ca r ba m ic Acid ter t-Bu tyl Es-
ter (1i). The compound was prepared by the method described
for 1c in 64% yield: mp 160-162 °C; [R]21 ) +60.0° (c ) 0.5,
D
MeOH); 1H-NMR (DMSO-d6) δ 1.27 (s, 9H), 1.20 (s, 3H), 2.73-
2.96 (m, 2H), 3.23-3.37 (m, 2H), 3.98 (m, 1H), 7.07 (d, J ) 6.2
Hz, 2H), 7.19-7.28 (m, 11H), 7.77 (s, 1H); IR (film) 3306, 2980,
1665, 1498 cm-1. Anal. (C24H31N3O4) C, H, N.
1
solid: 1.50 g (88%); H-NMR (DMSO-d6) δ 2.75 (t, 2H), 3.55
(m, 2H), 4.38 (s, 2H), 4.57 (m, 1H), 6.75-7.15 (m, 4H), 7.30
(br s, 1H), 7.37 (br s, 1H); IR (film) 3377, 1682, 1590, 1040
cm-1
.
[R-(R*,S*)]-[1-[(1-Ca r ba m oyl-1-m eth yl-2-p h en yleth yl)-
ca r ba m oyl]-2-p h en yleth yl]ca r ba m ic Acid ter t-Bu tyl Es-
ter (1j). The compound was prepared by the method described
Tolu en e-4-su lfon ic Acid 2-[2-(Ca r b a m oylm et h oxy)-
p h en yl]eth yl ester (14). p-Toluenesulfonyl chloride (1.77 g,
9.3 mmol) in DCM (25 mL) was added dropwise over 2 h to a
solution of the alcohol 13 (1.45 g, 7.4 mmol) and DMAP (1.13
g, 9.3 mmol) in DCM (75 mL) at 0 °C. The reaction mixture
was stirred at room temperature for 16 h and then washed
with 10% citric acid (2 × 50 mL) and water (50 mL). The
organic layer was dried over MgSO4, and the solvent was
removed in vacuo to give a residue which was purified by
column chromatography, 60% EtOAc/hexane, to give an oil:
2.10 g (81%); 1H-NMR (DMSO-d6) δ 2.36 (s, 3H), 2.91 (t, 2H),
4.18 (t, 2H), 4.29 (s, 2H), 6.72-7.62 (m, 10H); IR (film) 3330,
for 1c in 58% yield: mp 191-195 °C; [R]21 ) +4.0° (c ) 0.5,
D
MeOH); 1H-NMR (DMSO-d6) δ 1.16, 1.28 (2 × s, 9H), 1.36,
1.50 (2 × s, 3H), 2.58-2.79 (m, 1H), 3.13-3.35 (m, 3H), 4.08-
4.17 (m, 1H), 7.08-7.26 (m, 13H), 7.73 (s, 1H); IR (film) 3172,
1674, 1655, 1541 cm-1. Anal. (C24H31N3O4) C, H, N.
4-(4-Meth oxyp h en yl)bu tyr ic Acid (9). 4-(4-Methoxyphe-
nyl)-4-oxobutyric acid34 (3.46 g, 16.6 mmol), hydrazine mono-
hydrate (1.61 mL, 33 mmol), and KOH pellets (3.77 g, 66
mmol) were heated under reflux in diethylene glycol (20 mL)
for 1.5 h. The temperature was increased to 180 °C for 2 h,
during which time the hydrazine and water distilled over. On
cooling additional hydrazine (1.61 mL) was added, and the
process was repeated; 10% citric acid solution (130 mL) was
added, and the mixture was extracted with ether (3 × 200 mL).
The organic layer was washed with water and dried over
MgSO4, the solvent was evaporated, and the residue was
purified by column chromatography, ether/hexane (2:3), to give
2916, 1684, 1585, 1357, 1175 cm-1
.
2-[2-(2-Azid oeth yl)p h en oxy]a ceta m id e (15). 14 (2.05 g,
5.9 mmol) and NaN3 (0.42 g, 6.5 mmol) were dissolved in DMF
(20 mL), and the reaction mixture was heated to 75 °C for 2
h. The solution was cooled to room temperature and poured
onto ice (120 mL). The aqueous phase was then extracted with
ether (3 × 100 mL) and dried over MgSo4, and the solvent was
removed in vacuo to give a white solid which was used without
purification: 0.99 g (77%); 1H-NMR (DMSO-d6) δ 2.88 (t, 2H),
3.50 (t, 2H), 4.42 (s, 2H), 6.80-7.40 (m, 6H); IR (film) 2924,
2104, 1694 cm-1; MS m/ e (CI) 221 (M + H), 107 (100).
2-[2-(2-Am in oeth yl)p h en oxy]a ceta m id e (16). A solution
of the azide 15 (205 mg, 0.9 mmol) in MeOH (40 mL) was
treated with Lindlar catalyst (100 mg) and hydrogen gas at
44 psi, 25 °C, for 18 h. After removal of the catalyst by
filtration through Kieselguhr, the solvent was removed in
vacuo to give a gum (182 mg), which was used without
purification: 1H-NMR (DMSO-d6) δ 2.60-2.80 (m, 4H), 4.39
(s, 2H), 6.80-7.20 (m, 4H), 7.36 (br s, 1H), 7.42 (br s, 1H); IR
1
a white solid: 2.30 g (71%); H-NMR (CDCl3) δ 1.93 (q, 2H),
2.35 (t, 2H), 2.61 (t, 2H), 3.78 (s, 3H), 6.82 (d, 2H), 7.08 (d,
2H); IR (film) 2936, 1707 cm-1
(100).
. MS m/ e (CI) 194 (M), 177
4-(4-Hyd r oxyp h en yl)bu tyr ic Acid (10). 9 (1.0 g, 5 mmol)
was dissolved in 48% HBr (50 mL) and glacial acetic acid (80
mL), and the solution was heated under reflux for 6 h. The
solution was poured onto ice (300 mL) and stirred for a further
12 h. The mixture was extracted with ether (3 × 300 mL),
and the combined extracts were washed with water (3 × 200
mL). The organic layer was dried over MgSO4, and the solvent
was evaporated to given an oil which was purified by reverse
phase chromatography, 10-80% methanol/water. A white
(film) 3297, 2927, 1682 cm-1
.
1
solid was obtained: 0.82 g (91%); H-NMR (CDCl3) δ 1.77 (q,
[1-[[1-[(4-Hyd r oxyben zyl)ca r ba m oyl]-1-m eth yl-2-p h e-
n yleth yl]ca r ba m oyl]-2-p h en yleth yl]ca r ba m ic Acid ter t-
Bu tyl Ester (17). The compound was prepared by coupling
p-hydroxybenzylamine35 to Boc(S)Phe(RS)RMPheOH22 by
the procedure described for 1a . The product was purified
by column chromatography, 50% EtOAc/hexane, to give the
compound: 97 mg (37%); mp 86-90 °C; 1H-NMR (CDCl3)
δ 1.26, 1.28 (2 × s, 9H), 1.50, 1.59 (2 × s, 3H), 2.73-3.08
(m, 3H), 3.32-3.41 (m, 1H), 3.98-4.39 (m, 3H), 4.88, 4.99 (2
× d, J ) 5.2 Hz, 1H), 5.89, 6.27 (2 × s, 1H), 6.72-7.32 (m,
2H), 2.16 (t, 2H), 2.45 (t, 2H), 6.63 (d, 2H), 6.86 (d, 2H), 8.16
(s, 1H); MS m/ e (CI) 181 (M + H), 163 (100).
4-(4-Hyd r oxyp h en yl)bu tyr a m id e (11). 4-(4-Hydroxyphe-
nyl)butyric acid 10 (0.80 g, 4.4 mmol), DCCI (0.92 g, 4.4 mmol),
and pentafluorophenyl (0.82 g, 4.4 mmol) were dissolved in
EtOAc (80 mL), and the solution was stirred for 4 h. The
precipitate was removed by filtration, and the filtrate was
concentrated in vacuo. The residue was dissolved in DCM (60
mL), and ammonia gas was bubbled through the solution for
1 h. Stirring was continued for a further 12 h, and the solvent
was then evaporated. The residue was purified by column
chromatography, 6% MeOH/DCM, to give a white solid: 0.70
g (82%); 1H-NMR (DMSO-d6) δ 1.66 (m, 2H), 1.98 (t, 2H), 2.39
(t, 2H), 6.20 (m, 3H), 6.91 (d, 2H), 7.17 (s, 1H), 9.05 (s, 1H); IR
14H); IR (film) 3329, 1689, 1673, 1650, 1516 cm-1
. Anal.
(C24H31N3O4‚0.1H2O) C, H, N.
[R-(R*,S*)]-[1-[[1-[[4-(4-Hyd r oxyp h en yl)bu tyl]ca r ba m -
oyl]-1-m eth yl-2-p h en yleth yl]ca r ba m oyl]-2-p h en yleth yl]-
ca r ba m ic Acid ter t-Bu tyl Ester (18). The amine 12 was
coupled to Boc(S)Phe(SR)RMePheOH22 using HOBt activation
as described for 1a . The compound was purified by column
chromatography, 5% MeOH/DCM, to give a white solid: 105
(film) 3357, 3183, 1676, 1608 cm-1
.
4-(4-Am in obu tyl)p h en ol (12). BSM (2 M) in THF (3.23
mL, 6.5 mmol) was added dropwise to a solution of 11 (0.50 g,
2.8 mmol) in THF (25 mL) under N2. The reaction mixture
was heated under reflux for 6 h and then cooled to room
temperature. MeOH (3 mL) was added, and the solution was
stirred overnight. Dry HCl gas was bubbled through the
solution for 20 min, and the solution was then reheated under
reflux for 1 h. The solvent was removed in vacuo, and the
residue was dissolved in EtOAc (100 mL) and washed with 2
M HCl (2 × 60 mL). The pH of the aqueous phase was
mg (61%); mp 66-71 °C; [R]23 ) +10.4° (c ) 1.0, MeOH); 1H-
D
NMR (DMSO-d6) δ 1.04-1.45 (m, 16H), 2.40 (t, J ) 6.8 Hz,
2H), 2.60-3.18 (m, 6H), 4.08-4.15 (m, 1H), 6.60-7.22 (m,
15H), 7.51 (s, 1H), 7.71 (s, 1H), 9.02 (s, 1H); IR (film) 3347,
2927, 1693, 1652, 1515 cm-1; MS m/ e (CI) 574 (M + H), 474,
166, 134 (100). Anal. (C34H43N3O5) C, H, N.
[1-[[1-(Ben zylca r ba m oyl)-1-m eth yl-2-p h en yleth yl]ca r -
ba m oyl]-2-p h en yleth yl]ca r ba m ic Acid ter t-Bu tyl Ester

Dipeptide Library for NK3 Receptor Lead Development
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8 1671
(19). The compound was prepared by coupling benzylamine
to Boc(S)Phe(RS)RMePheOH22 using DCCI/pentafluorophenol
as described for 1b. The crude material was purified by
reverse phase chromatography to give the required compound
in 89% yield: mp 60-62 °C; 1H-NMR (DMSO-d6) δ 1.73, 1.80
(2 × s, 9H), 1.32, 1.36 (2 × s, 3H), 2.60-2.34 (m, 4H), 4.06-
4.36 (m, 1H), 6.92-7.30 (m, 15H), 7.89, 7.93 (2 × s, 1H), 8.15
(m, 1H); MS m/ e (CI) 516 (M + H), 416, 309, 281, 134 (100).
Anal. (C31H36N3O‚0.3H2O) C, H, N.
[1-[[1-[(8-Hyd r oxyoctyl)ca r ba m oyl]-2-p h en yleth yl]ca r -
ba m oyl]-2-p h en yleth yl]ca r ba m ic Acid ter t-Bu tyl Ester
(29). 8-Amino-1-octanol22 was coupled to Boc(S)Phe(RS)-
PheOH36 using DCCI/HOBt as described for 1a . The crude
product was purified by reverse phase chromatography to
give a white solid: 20 mg (47%); mp 98-105 °C; [R]21
)
D
-5.1° (c ) 0.5, MeOH); 1H-NMR (CDCl3) δ 1.41-1.65 (m,
22H), 2.79-3.40 (m, 6H), 3.61-3.66 (t, J ) 6.5 Hz, 2H), 4.01
(m, 2H), 4.97-5.07 (m, 1H), 5.70-6.62 (m, 2H), 6.97-7.36 (m,
10H); IR (film) 3291, 2929, 1695, 1645, 1538 cm-1
. Anal.
[1-[[1-Meth yl-2-p h en yl-1-[(4-p h en ylbu tyl)ca r ba m oyl]-
eth yl]ca r ba m oyl]-2-p h en yleth yl]ca r ba m ic Acid ter t-Bu -
tyl Ester (20). The compound was prepared by coupling
4-phenylbutylamine to Boc(S)Phe(RS)RMePheOH22 using HBTU
activation as described for 1c. The compound was purified
by column chromatography, 50% EtOAc/hexane, to give a
white solid: 180 mg (65%); mp 66-70 °C; 1H-NMR (CDCl3)
δ 1.28 (m, 2H), 1.31, 1.35 (2 × s, 9H), 1.48, 1.57 (2 × s, 3H),
1.52 (m, 2H), 2.61 (t, J ) 8 Hz, 2H), 2.75-3.40 (m, 6H),
4.05 (m, 1H), 4.83, 4.92 (2 × d, J ) 7 Hz, 1H), 5.86, 6.18 (2 ×
s, 1H), 6.50, 6.66 (2 × s, 1H), 6.94 (br s, 2H), 7.10-7.35
(C31H45N3O5‚0.55H2O) C, H, N.
[R-(R*,S*)]-[1-[[1-[[8-(Dim et h ylca r b a m oyl)oct yl]ca r -
b a m oyl]-1-m et h yl-2-p h en ylet h yl]ca r b a m oyl]-2-p h en yl-
eth yl]ca r ba m ic Acid ter t-Bu tyl Ester (32). The compound
was prepared by coupling dimethylamine to Boc(S)Phe-
(R)RMePheOH22 using HBTU as described for 1c. A glass was
1
obtained: 180 mg (88%); [R]22 ) +8.8° (c ) 1.0, MeOH); H-
D
NMR (CDCl3) δ 1.20-1.65 (m, 24H), 2.30 (t, 2H), 2.75-3.44
(m, 12H), 4.03 (m, 1H), 4.95 (br s, 1H), 5.92 (br s, 1H), 6.65
(br s, 1H), 6.95-7.00 (m, 2H), 7.20-7.40 (m, 8H); IR (film)
(m, 13H); IR (film) 3327, 1688, 1652, 1497 cm-1
.
Anal.
. Anal. (C35H52N4O5‚0.2H2O) C,
3326, 2930, 1692, 1652 cm-1
H, N.
(C34H43N3O4‚0.5H2O) C, H, N.
[1-[[1-[(7-Hyd r oxyh ep tyl)ca r ba m oyl]-1-m eth yl-2-p h e-
n yleth yl]ca r ba m oyl]-2-p h en yleth yl]ca r ba m ic Acid ter t-
Bu tyl Ester (21). The compound was prepared as described
for 35 using Boc(S)Phe(RS)RMePheOH22 to give a white
(7-Hyd r oxyh ep tyl)ca r ba m ic Acid ter t-Bu tyl Ester (34).
(tert-Butoxycarbonyl)-7-aminoheptanoic acid (0.45 g, 1.8 mmol)
and N-methylmorpholine (0.22 mL, 2 mmol) were dissolved
in THF (10 mL). The solution was cooled to 0 °C, and ethyl
chloroformate (0.2 mL, 2 mmol) in THF (10 mL) was added
dropwise over 10 min. The solution was stirred for 1 h, and
the precipitate was then removed by filtration. The filtrate
was recooled to 0 °C, and 1 M LiBH4 in THF (3 mL, 6 mmol)
was added dropwise over 5 min. The solution was stirred with
slow warming to room temperature over 3 h, and the solvent
was then removed in vacuo. The residue was dissolved in
EtOAc (50 mL), washed with water (3 × 50 mL) and brine (50
mL), and then dried over MgSO4. The solvent was removed
in vacuo to given an oil, 0.40 g (96%), which was used without
purification: 1H-NMR (CDCl3) δ 1.28-1.60 (m, 19H), 3.10 (m,
2H), 3.64 (m, 12H), 4.50 (br s, 1H); IR (film) 33.44, 2931, 2858,
1
solid: 80 mg (59%); H-NMR (CDCl3) δ 1.18-1.56 (m, 22H),
2.75-3.49 (m, 6H), 3.63 (t, J ) 6.5 Hz, 2H), 3.98-4.12 (m, 1H),
4.84, 4.92 (2 × d, J ) 7 Hz, 1H), 5.87, 6.18 (2 × s, 1H), 6.50,
6.64 (2 × s, 1H), 6.95 (m, 2H), 7.16-7.36 (m, 8H); IR (film)
3339, 2931, 1687, 1648, 1533 cm-1; MS m/ e (FAB) 540 (M+),
440, 134. Anal. (C31H45N3O5‚0.35H2O) C, H, N.
[1-[[1-[(8-H yd r oxyoct yl)ca r b a m oyl]-1-m et h yl-2-p h e-
n yleth yl]ca r ba m oyl]-2-p h en yleth yl]ca r ba m ic Acid ter t-
Bu tyl Ester (22). 8-Amino-1-octanol22 was coupled to Boc-
(S)Phe(RS)RMePheOH22 by the method described for 1c to give
a white solid: 60 mg (22%); mp 46-48 °C; 1H-NMR (CDCl3) δ
1.32-1.66 (m, 25H), 2.75-3.43 (m, 6H), 3.63 (t, J ) 6.5 Hz,
2H), 4.00-4.10 (m, 2H), 4.86, 4.96 (2 × d, J ) 7 Hz, 1H),
5.86, 6.20 (2 × s, 1H), 6.52, 6.65 (2 × s, 1H), 6.95 (m, 2H),
7.16-7.34 (m, 8H); IR (film) 3340, 2931, 1690, 1650, 1530
cm-1; MS m/ e (FAB) 555 (M + H), 454, 307, 28. Anal.
(C32H47N3O5‚0.8H2O) C, H, N.
1689, 1531 cm-1
.
[R-(R*,S*)]-[1-[[1-[(7-Hydr oxyh eptyl)car bam oyl]-1-m eth -
yl-2-ph en yleth yl]car bam oyl]-2-ph en yleth yl]car bam ic Acid
ter t-Bu tyl Ester (35). (7-Hydroxyheptyl)carbamic acid tert-
butyl ester (34) (0.4 g, 1.7 mmol) was dissolved in DCM (10
mL)/TFA (10 mL), and the solution was stirred for 1 h. The
solvent was then removed in vacuo, and the residue was added
to a mixture of Boc(S)Phe(R)RMePheOH22
[1-[[1-[(9-Hydr oxyn on a n yl)ca r ba m oyl]-1-m eth yl-2-ph e-
n yleth yl]ca r ba m oyl]-2-p h en yleth yl]ca r ba m ic Acid ter t-
Bu tyl Ester (23). 9-Amino-1-nonanol was coupled to Boc(S)-
Phe(RS)RMePheOH22 by the method described for 1c to give
a white solid: 189 mg (55%); mp 58-63 °C; 1H-NMR (CDCl3)
δ 1.20-1.65 (m, 26H), 2.75-3.40 (m, 6H), 3.63 (t, J ) 7 Hz,
2H), 4.05 (m, 1H), 4.83, 4.93 (2 × br s, 1H), 5.88, 6.21 (2 × s,
1H), 6.49, 6.63 (2 × s, 1H), 6.96 (m, 2H), 7.15-7.35 (m, 8H);
(0.64 g, 1.5 mmol),
DCCI (0.31 g, 1.5 mmol), and HOBt (0.2 g, 1.5 mmol) in DMF
(3 mL). DIPEA (0.7 mL, 4 mmol) was added, and the reaction
mixture was stirred for 15 h. The precipitate was removed
by filtration, and the solvent was concentrated in vacuo. The
residue was dissolved in EtOAc (100 mL), and the solution
was washed with 1 M HCl (3 × 50 mL), saturated NaHCO3 (3
× 50 mL), water (3 × 50 mL), and brine (50 mL). The organic
layer was dried over MgSO4, and the solvent was removed
in vacuo to give a residue which was purified by reverse
phase chromatography, 0-100% MeOH/water. A white solid
was obtained: 0.54 g (67%); 1H-NMR (CDCl3) δ 1.29-1.58 (m,
22H), 2.75-3.45 (m, 6H), 3.63 (t, J ) 6.8 Hz, 2H), 4.00 (m,
1H), 4.96 (br d, 1H), 5.85 (br s, 1H), 6.65 (br s, 1H), 6.96-6.98
(m, 2H), 7.19-7.35 (m, 8H); IR (film) 3324, 3029, 2929, 1661,
1516 cm-1; MS m/ e (CI) 540 (M + H), 440, 134. Anal.
(C31H45N3O5‚0.25H2O) C, H, N.
[R-(R*,S*)]-Tolu en e-4-su lfon ic Acid 7-[[2-[[2-[(ter t-Bu -
toxyca r bon yl)a m in o]-3-p h en ylp r op ion yl]a m in o]-2-m eth -
yl-3-p h en ylp r op ion yl]a m in o]h ep tyl Ester (36). The al-
cohol 35 (267 mg, 0.5 mmol) was dissolved in DCM (3 mL),
and p-toluenesulfonyl chloride (105 mg, 0.55 mmol), NEt3 (0.08
mL, 0.6 mmol), and DMAP (catalytic) were added. The
reaction mixture was stirred for 15 h and then diluted with
DCM (50 mL). The solution was washed with 1 M HCl (3 ×
20 mL), saturated aqueous NaHCO3 (3 × 20 mL), water (3 ×
20 mL), and brine (20 mL). The organic layer was dried over
MgSO4, and the solvent was removed in vacuo to give a white
solid (359 mg) which was used without purification: 1H-NMR
(CDCl3) δ 1.21-1.66 (m, 22H), 2.45 (s, 3H), 2.75-3.45 (m, 6H),
4.01 (m, 3H), 4.90 (br d, 1H), 5.85 (br s, 1H), 6.70 (br s, 1H),
IR (film) 3339, 2929, 2836, 1682, 1651, 1531 cm-1
. Anal.
(C33H49N3O5‚0.2H2O) C, H, N.
[S-(R*,R*)]-[1-[[1-[(8-Hyd r oxyoctyl)ca r ba m oyl]-1-m eth -
yl-2-ph en yleth yl]car bam oyl]-2-ph en yleth yl]car bam ic Acid
ter t-Bu tyl Ester (24). 8-Amino-1-octanol22 was coupled to
Boc(S)Phe(S)RMePheOH36 using HBTU as described for 1c to
give a white solid: 460 mg (42%); mp 108-114 °C; [R]20
)
D
+49.9° (c ) 0.5, MeOH); 1H-NMR (CDCl3) δ 1.30-1.58 (m,
26H), 2.85-3.95 (m, 6H), 3.64 (t, J ) 6.4 Hz, 2H), 4.10 (m,
1H), 4.85 (m, 1H), 6.15 (s, 1H), 6.50 (s, 1H), 6.95 (m, 2H), 7.16-
7.33 (m, 8H); IR (film) 3326, 2978, 2856, 1678, 1651, 1532 cm-1
;
MS m/ e (CI) 555 (M + H), 554, 454, 146, 134 (100). Anal.
(C32H47N3O5) C, H, N.
[1-[[1-Met h yl-1-(n on ylca r b a m oyl)-2-p h en ylet h yl]ca r -
ba m oyl]-2-p h en yleth yl]ca r ba m ic Acid ter t-Bu tyl Ester
(26). The compound was prepared by coupling nonylamine
to Boc(S)Phe(RS)RMePheOH22 using HBTU as described for
1c. The crude material was purified by column chromatog-
raphy to give a white solid: 134 mg (48%); mp 63-68 °C; 1H-
NMR (CDCl3) δ 0.88 (t, J ) 7 Hz, 3H), 1.25 (m, 14H), 1.33,
1.37 (2 × s, 9H), 1.45, 1.55 (2 × s, 3H), 2.70-3.20 (m, 5H),
3.37 (m, 1H), 4.05 (m, 1H), 4.85 (m, 1H), 5.85, 6.20 (2 × s,
1H), 6.45, 6.60 (2 × s, 1H), 6.95 (m, 2H), 7.15-7.40 (m, 8H);
IR (film) 3307, 2927, 2855, 1671, 1645, 1531 cm-1
(C33H49N3O4) C, H, N.
. Anal.

1672 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8
Boden et al.
6.96-6.98 (m, 2H), 7.12-7.35 (m, 10H), 7.70 (d, J ) 8.4 Hz,
m/ e (FAB) 605 (M + Na), 582 (M + H), 482, 335. Anal.
(C31H47N5O5‚0.4H2O) C, H, N.
2H); IR (film) 3351, 2978, 2935, 1687, 1657, 1521, 1598, 1366,
1175 cm-1
.
[R-(R*,S*)]-[1-[[1-[[2-(Ca r ba m oylm eth oxy)p h en yl]eth -
yl]car bam oyl]-1-m eth yl-2-ph en yleth yl]car bam oyl]-2-ph e-
n yleth yl]ca r ba m ic Acid ter t-Bu tyl Ester (43). The amine
16 was coupled to Boc(S)Phe(R)RMePheOH22 by the procedure
described for 1a . The crude product was purified by reverse
phase chromatography, 60-80% MeOH/water, to give a white
[R-(R*,S*)]-[1-[[1-[(7-Azid oh ep tyl)ca r ba m oyl]-1-m eth -
yl-2-ph en yleth yl]car bam oyl]-2-ph en yleth yl]car bam ic Acid
ter t-Bu tyl Ester (37). The tosylate 36 (317 mg, 0.46 mmol)
was dissolved in DMF (5 mL), and sodium azide (33 mg, 0.51
mmol) was added. The reaction mixture was heated to 60 °C,
stirred for 3 h, and then cooled to room temperature and
stirred for a further 15 h. The solution was poured onto ice
and extracted with DCM (3 × 100 mL). The combined extracts
were washed with water (3 × 100 mL) and brine (100 mL)
and then dried over MgSO4, and the solvent was removed in
vacuo. The residue was purified by column chromatography,
50% ether/hexane, to give a white solid: 179 mg (69%); 1H-
NMR (CDCl3) δ 1.30-1.60 (m, 22H), 2.75-3.45 (m, 8H), 4.00
(m, 1H), 4.90 (br d, 1H), 5.85 (br s, 1H), 6.70 (br s, 1H), 6.97-
6.99 (m, 2H), 7.20-7.36 (m, 8H); IR (film) 3322, 2932, 2095,
solid: 180 mg (34%); mp 98-103 °C; [R]23 ) +8.1° (c ) 1.0,
D
MeOH); 1H-NMR (DMSO-d6) δ 1.21 (s, 3H), 1.26 (s, 9H), 2.60-
3.27 (m, 8H), 4.15 (m, 1H), 4.40 (s, 2H), 6.80-7.23 (m, 15H),
7.41 (s, 1H), 7.50 (s, 1H), 7.70 (m, 1H), 7.76 (s, 1H); IR (film)
3328, 2979, 1694, 1683, 1652 cm-1. Anal. (C34H42N4O6) C, H,
N.
[2-(1H-In d ol-3-yl)-1-m eth yl-1-[(1p h en yleth yl)ca r ba m -
oyl]eth yl]ca r ba m ic Acid 2-Meth yl-1-p h en ylp r op yl Ester
(44). (R,S)-2-Methyl-1-phenyl-1-propanol p-nitrophenyl car-
bonate (184 mg, 0.3 mmol) was added to a stirred solution of
R-amino-R-methyl-N-(1-phenylethyl)-[R-(R*,S*)]-1H-indole-3-
1683, 1651, 1517 cm-1
.
propanamide18 (94 mg, 0.6 mmol) in EtOAc (20 mL).
A
[R-(R*,S*)]-[1-[[1-[(7-Am in oh ep tyl)ca r ba m oyl]-1-m eth -
yl-2-ph en yleth yl]car bam oyl]-2-ph en yleth yl]car bam ic Acid
ter t-Bu tyl Ester (38). A solution of the azide 37 (275 mg,
0.49 mmol) in EtOH (20 mL) was treated with Lindlar catalyst
(60 mg) and hydrogen gas at 40 psi, 30 °C, for 6 h. After
removal of the catalyst by filtration through Kieselguhr, the
solvent was removed in vacuo to give a white solid (266 mg).
The product was dissolved in MeOH containing 1 M HCl and
purified by reverse phase chromatography, 50-100% MeOH/
water, to give a white solid: 215 mg (76%); mp 94-102 °C;
1H-NMR (CDCl3) δ 1.20-1.50 (m, 20H), 2.84 (br t, 2H), 2.75-
3.33 (m, 8H), 4.00 (m, 1H), 5.20 (br s, 1H), 6.24 (br s, 1H),
6.79 (br t, 1H), 6.97-6.99 (m, 2H), 7.18-7.33 (m, 8H), 8.34
catalytic amount of DMAP was added, and the reaction
mixture was stirred for 4 days. The solution was diluted with
Et2O (25 mL) and washed with 5% citric acid (3 × 25 mL) and
brine (25 mL). The organic layer was dried over MgSO4 and
filtered and the solvent evaporated. The residue was purified
by column chromatography, 33% EtOAc/hexane, to give a
solid: 36 mg (25%); mp 65-75 °C; 1H-NMR (CDCl3) δ 0.76
(m, 3H), 0.93 (m, 3H), 1.16-1.43 (m, 3H), 1.55 (m, 3H), 2.03
(m, 1H), 3.17-3.50 (m, 2H), 4.87-4.99 (m, 1H), 5.29-5.42 (m,
2H), 6.42 (br, 1H), 6.52, 6.75 (2 × s, 1H), 7.04-7.33 (m, 13H),
7.55 (m, 1H), 7.88, 8.07 (2 × s, 1H); IR (film) 3339, 2965, 1707,
1655, 1494, 1069 cm-1. Anal. (C31H35N3O3‚0.2H2O) C, H, N.
(R)-Car bon ic Acid 2-Meth yl-1-ph en ylpr opyl Ester 4-Ni-
tr op h en yl Ester (45a ). A solution of pyridine (8.8 mL, 0.1
mmol) in anhydrous DCM (20 mL) was added dropwise over
30 min to a stirred solution of p-nitrophenyl chloroformate
(22.2 g, 0.11 mmol) and S-(-)-2-methyl-1-phenyl-1-propanol
(15.0 g, 0.1 mmol) in anhydrous DCM (200 mL) cooled to 0
°C. The solution was stirred for 24 h with slow warming to
room temperature. The reaction mixture was diluted with
DCM (200 mL) and washed with 10% HCl (3 × 100 mL) and
brine (100 mL). The organic layer was dried over MgSO4, the
solvent was removed in vacuo, and the residue was purified
by column chromatography, 10% EtOAc/heptane, to give a
(br s, 3H); IR (film) 3322, 2933, 1689, 1652, 1520 cm-1
.
[R-(R*,S*)]-[1-[[1-[[7-[(-Meth ylsu lfon yl)a mino]h ep tyl]-
ca r b a m oyl]-1-m et h yl-2-p h en ylet h yl]ca r b a m oyl]-2-p h e-
n yleth yl]ca r ba m ic Acid ter t-Bu tyl Ester (39). The amine
38 (100 mg, 0.2 mmol) was dissolved in pyridine, and meth-
anesulfonyl chloride (16 µL, 0.2 mmol) in pyridine/DCM (2 mL)
was added dropwise over 10 min. The solution was stirred
for 15 h, and then diluted with aqueous NaHCO3 (20 mL). The
mixture was extracted with DCM (3 × 20 mL), and the
combined extracts were washed with water (50 mL) and dried
over MgSO4. The solvent was removed in vacuo, and the
residue was purified by column chromatography, 5% MeOH/
1
gum: 28.87 g (92%); H-NMR (CDCl3) δ 0.85 (d, J ) 6.8 Hz,
1
DCM, to give a white solid: 25 mg (21%); mp 55-59 °C; H-
3H), 1.09 (d, J ) 6.8 Hz, 3H), 2.25 (m, 1H), 5.38 (d, J ) 7.6
Hz, 1H), 7.26-7.41 (m, 7H), 8.24 (d, J ) 9.2 Hz, 2H); IR (film)
3362, 1764, 1526, 1224, 1218 cm-1. Anal. (C17H17NO5) C, H,
N.
NMR (CDCl3) δ 1.20-1.60 (m, 22H), 2.95 (s, 3H), 2.72-3.45
(m, 8H), 4.00 (m, 1H), 4.84 (m, 1H), 5.02 (br d, 1H), 5.82 (br s,
1H), 6.70 (br s, 1H), 6.95-6.98 (m, 2H), 7.19-7.36 (m, 8H); IR
(film) 3340, 2932, 2859, 1688, 1652, 1520 cm-1
.
Anal.
(S)-Car bon ic Acid 2-Meth yl-1-ph en ylpr opyl Ester 4-Ni-
tr op h en yl Ester (45b). The compound was prepared as
described for 45a ; purification by column chromatography, 10%
(C32H48N4O6S‚0.3H2O) C, H, N.
(7-Am in oh ep t yl)u r ea (40). A solution of trimethylsilyl
isocyanate (0.35 mL, 2.6 mmol) in anhydrous THF (75 mL)
was added dropwise over 30 min to a stirred solution of 1,7-
diaminoheptane (1.0 g, 7.7 mmol) in THF (25 mL). The
reaction mixture was stirred at room temperature for 2 h, and
water (10 mL) was then added. After stirring for a further 2
h, the solvent was removed in vacuo. The residue was slurried
with hot EtOAc, and the solid was collected by filtration. The
solid was then slurried with water (25 mL) and filtered and
the solvent evaporated to give a white solid: 398 mg (90%);
1
ether/hexane, gave an oil: 1.50 g (82%); H-NMR (CDCl3) δ
0.85 (d, J ) 6.8 Hz, 3H), 1.09 (d, J ) 6.8 Hz, 3H), 2.23 (m,
1H), 5.37 (d, J ) 6.8 Hz, 1H), 7.31-7.41 (m, 7H), 8.24 (d, 2H);
IR (film) 3424, 3088, 2968, 1746, 1526, 1347, 1255, 1218 cm-1
.
2-Am in o-3-(2-flu or op h en yl)-2-m et h ylp r op ion ic Acid
Meth yl Ester (46). To a suspension of (S)-alanine methyl
ester hydrochloride (5.0 g, 36 mmol), 4-chlorobenzaldehyde (5.1
g, 36 mmol), and MgSO4 (2 g) in DCM (60 mL) was added NEt3
(5 mL, 36 mmol). The reaction mixture was stirred for 20 h,
filtered, and concentrated in vacuo. The resulting gum was
triturated with ether, and the precipitate was removed by
filtration. The filtrate was concentrated to give an oil (7.9 g,
98%). The Schiff base (2 g, 8.9 mmol) was dissolved in THF
(20 mL) under an atmosphere of N2, and the solution was
cooled to -78 °C; 1 M LHMDS in THF (9.8 mL, 9.8 mmol)
was added dropwise, and the reaction mixture was stirred for
1 h. 2-Fluorobenzyl bromide (1.7 g, 8.9 mmol) was added
dropwise in THF (5 mL), and the solution was stirred for 20 h
with slow warming to room temperature. HCl (1 M, 200 mL)
was then added, and stirring was continued for 2 h. The
solvent was removed in vacuo, and the residue was partitioned
between 1 M HCl (200 mL) and EtOAc (200 mL). The pH of
the aqueous layer was adjusted to 8 with Na2CO3, and the
mixture was extracted with EtOAc (3 × 100 mL). The
1
mp 108-114 °C; H-NMR (DMSO-d6) δ 1.24-1.35 (m, 10H),
2.48-2.52 (m, 2H), 2.90-2.95 (m, 2H), 5.32 (s, 2H), 5.87 (s,
1H); IR (film) 3326, 2928, 2856, 1649, 1561, 1155 cm-1; MS
m/ e (CI) 174, 157, 144, 131, 114. Anal. (C8H19N3O4‚0.25H2O)
C, H, N.
[R-(R*,S*)]-[1-[[1-Meth yl-2-p h en yl-1-[(7-u r eid oh ep tyl)-
ca r b a m oyl]et h yl]ca r b a m oyl]-2-p h en ylet h yl]ca r b a m ic
Acid ter t-Bu tyl Ester (41). (7-Aminoheptyl)urea (40) was
coupled to Boc(S)Phe(R)RMePheOH22 using HBTU as de-
scribed for 1c. Purification by column chromatography, 5%
MeOH/DCM, gave a white solid: 66 mg (47%); mp 65-72
°C; 1H-NMR (CDCl3) δ 1.21-1.52 (m, 22H), 2.75-3.22 (m,
8H), 4.02 (m, 1H), 4.55 (br s, 2H), 5.05, 5.15 (2 × br s, 2H),
5.95 (br s, 1H), 6.80 (br s, 1H), 6.97-6.99 (m, 2H), 7.18-7.34
(m, 8H); IR (film) 3344, 2931, 1693, 1651, 1539 cm-1
. MS

Dipeptide Library for NK3 Receptor Lead Development
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8 1673
combined extracts were washed with water (3 × 100 mL) and
dried over MgSO4, and the solvent was removed in vacuo to
give an oil: 1.54 g (82%); 1H-NMR (CDCl3) δ 1.39 (s, 3H), 2.93
(d, J ) 13.6 Hz, 1H), 3.09 (d, J ) 13.6 Hz, 1H), 3.72 (s, 3H),
2961, 1739, 1720, 1493, 1260 cm-1; MS m/ e (CI) 406 (M + H),
230, 133. Anal. (C22H25NO4F2) C, H, N.
[R-(R*,R*)]-2-Meth yl-2-[[(2-m eth yl-1-p h en ylp r op oxy)-
ca r bon yl]a m in o]-3-p h en ylp r op ion ic Acid Meth yl Ester
(51a ). The ester 48a (0.74 g, 2 mmol) was dissolved in THF
(20 mL), and LiOH monohydrate (0.16 g, 4 mmol) in water (4
mL) was added. The reaction mixture was heated under reflux
for 48 h, and the solvent was then removed in vacuo. The
residue was partitioned between 2 M HCl (100 mL) and EtOAc
(100 mL), the aqueous layer was re-extracted with EtOAc (3
× 100 mL), and the combined extracts were dried over MgSO4.
7.00-7.25 (m, 4H); IR (film) 2952, 1735 cm-1
.
2-Am in o-3-(2,3-diflu or oph en yl)-2-m eth ylpr opion ic Acid
Meth yl Ester (47). The compound was prepared following
the procedure described for 46. The product was obtained as
1
an oil: 0.38 g (73%); H-NMR (CDCl3) δ 1.40 (s, 3H), 2.96 (d,
J ) 13 Hz, 1H), 3.12 (d, J ) 13 Hz, 1H), 3.72 (s, 3H), 6.92-
7.08 (m, 3H); IR (film) 3378, 2954, 1735, 1491, 1206 cm-1
.
The solvent was removed to give a white solid: 0.6 g (86%);
[R-(R*,R*)]-2-Meth yl-2-[[(2-m eth yl-1-p h en ylp r op oxy)-
ca r bon yl]a m in o]-3-p h en ylp r op ion ic Acid Meth yl Ester
(48a ). The carbonate 45a (3.00 g, 9.5 mmol) and (R)RMe-
PheOMe (1.84 g, 9.5 mmol) were dissolved in anhydrous DMF
(20 mL), and the solution was stirred for 3 days. The solvent
was removed in vacuo, and the residue was dissolved in EtOAc
(100 mL) and washed with 10% aqueous K2CO3 (5 × 75 mL)
and brine (75 mL). The organic layer was dried over MgSO4,
and the solvent was concentrated. The residue was purified
by column chromatography, 10% ether/heptane, to give a white
1
[R]23 ) +44° (c ) 0.4, MeOH); H-NMR (CDCl3) δ 0.82 (d, J
D
) 6.8 Hz, 3H), 0.99 (d, J ) 6.8 Hz, 3H), 1.55 (s, 3H), 2.10 (m,
1H), 3.29 (m, 2H), 5.27 (s, 1H), 5.42 (d, J ) 7.2 Hz, 1H), 6.99
(m, 2H), 7.17-7.38 (m, 8H); IR (film) 3409, 2969, 1713, 1497,
1452, 1052 cm-1; MS m/ e (CI) 356 (M + H), 302, 266, 180,
133.
[S-(R*,S*)]-2-Met h yl-2-[[(2-m et h yl-1-p h en ylp r op oxy)-
ca r bon yl]a m in o]-3-p h en ylp r op ion ic Acid Meth yl Ester
(51b). The compound was prepared from the ester 48b as
described for 51a . A white solid was obtained: 1.32 g (93%);
solid: 2.5 g (70%); mp 118-120 °C; [R]23 ) +46° (c ) 0.5,
D
1
[R]23 ) +14° (c ) 0.4, MeOH); H-NMR (CDCl3) δ 0.81 (d, J
acetone); 1H-NMR (CDCl3) δ 0.83 (d, J ) 6.8 Hz, 3H), 0.99 (d,
J ) 6.8 Hz, 3H), 1.55 (s, 3H), 2.06-2.11 (m, 1H), 3.19 (d, J )
13.4 Hz, 1H), 3.39 (d, J ) 13.4 Hz, 1H), 3.75 (s, 3H), 5.41 (m,
2H), 6.96-6.98 (m, 2H), 7.18-7.37 (m, 8H); IR (film) 3353,
2959, 1732, 1714, 1497, 1451 cm-1; MS m/ e (CI) 370 (M + H),
238, 194, 133.
D
) 6.8 Hz, 3H), 0.99 (d, J ) 6.8 Hz, 3H), 1.67 (s, 3H), 2.10 (m,
1H), 3.13-3.42 (d × d, 2H), 5.37 (d, J ) 7 Hz, 1H), 5.42 (s,
1H), 6.87 (m, 2H), 7.11-7.39 (m, 8H); IR (film) 3414, 2964,
1711, 1498, 1452, 1053 cm-1; MS m/ e (CI) 356 (M + H), 224,
180, 133.
[S-(R*,S*)]-3-(2-F lu or op h en yl)-2-m eth yl-2-[[(2-m eth yl-
1-p h en ylp r op oxy)ca r bon yl]a m in o]p r op ion ic Acid (52).
The compound was prepared as described for 51a from ester
49. A white solid was obtained: 127 mg (97%); 1H-NMR
(CDCl3) δ 0.81 (d, J ) 6.8 Hz, 3H), 0.98 (d, J ) 6.8 Hz, 3H),
1.52 (s, 3H), 2.07 (m, 1H), 3.34 (m, 2H), 5.22 (s, 1H), 5.39 (d,
J ) 7 Hz, 1H), 6.85-7.38 (m, 9H); IR (film) 2964, 1714, 1494
[S-(R*,S*)]-2-Met h yl-2-[[(2-m et h yl-1-p h en ylp r op oxy)-
ca r bon yl]a m in o]-3-p h en ylp r op ion ic Acid Meth yl Ester
(48b). The compound was prepared as described for 48a using
carbonate 45b. Column chromatography gave an oil: 1.4 g
1
(78%); [R]23 ) +21° (c ) 0.25, acetone); H-NMR (CDCl3) δ
D
0.81 (d, J ) 6.8 Hz, 3H), 0.98 (d, J ) 6.8 Hz, 3H), 1.66 (s, 3H),
2.03-2.10 (m, 1H), 3.05 (d, J ) 13.6 Hz, 1H), 3.40 (d, J ) 13.4
Hz, 1H), 3.72 (s, 3H), 5.35 (d, J ) 6.8 Hz, 1H), 5.55 (s, 1H),
6.76-6.77 (m, 2H), 7.08-7.40 (m, 8H); IR (film) 3423, 2960,
1740, 1721, 1496, 1451 cm-1; MS m/ e (CI) 370 (M + H), 238,
194, 133.
cm-1
.
[S-(R*,S*)]-3-(2,3-Diflu or oph en yl)-2-m eth yl-2-[[(2-m eth -
yl-1-ph en ylpr opoxy)car bon yl]am in o]pr opion ic Acid (53a).
The compound was prepared as described for 51a from ester
50a . A white solid was obtained: 94 mg (94%); 1H-NMR
(CDCl3) δ 0.80 (d, J ) 6.8 Hz, 3H), 0.98 (d, J ) 6.8 Hz, 3H),
1.52 (s, 3H), 2.08 (m, 1H), 3.35 (d, J ) 14 Hz, 1H), 3.42 (d, J
) 14 Hz, 1H), 5.21 (s, 1H), 5.38 (d, J ) 6.8 Hz, 1H), 6.57 (m,
1H), 6.82 (m, 1H), 7.02 (m, 1H), 7.26-7.38 (m, 5H); IR (film)
[S-(R*,S*)]-3-(2-F lu or op h en yl)-2-m eth yl-2-[[(2-m eth yl-
1-p h en ylp r op oxy)ca r bon yl]a m in o]p r op ion ic Acid Meth -
yl Ester (49). The compound was prepared as described for
48a using carbonate 45b and 2-fluoro-(RS)RMePheOMe (46).
The two diastereoisomers were separated by column chroma-
tography, 10% ether/heptane, and the desired product (the
3418, 3035, 2965, 1715, 1493 cm-1
.
[S-(R*,R*)]-3-(2,3-Diflu or oph en yl)-2-m eth yl-2-[[(2-m eth -
yl-1-ph en ylpr opoxy)car bon yl]am in o]pr opion ic Acid (53b).
The compound was prepared as described for 51a from ester
50b. A white solid was obtained: 67 mg (90%); 1H-NMR
(CDCl3) δ 0.81 (d, J ) 6.8 Hz, 3H), 0.98 (d, J ) 6.8 Hz, 3H),
1.62 (s, 3H), 2.08 (m, 1H), 3.37 (s, 2H), 5.36 (m, 2H), 6.62 (m,
1H), 6.79 (m, 1H), 7.02 (m, 1H), 7.26-7.36 (m, 5H); IR (film)
1
more polar isomer) was isolated as an oil: 165 mg (26%); H-
NMR (CDCl3) δ 0.81 (d, J ) 6.8 Hz, 3H), 0.97 (d, J ) 6.8 Hz,
3H), 1.54 (s, 3H), 2.08 (m, 1H), 3.25 (d, J ) 13.6 Hz, 1H), 3.40
(d, J ) 13.4 Hz, 1H), 3.73 (s, 3H), 5.39 (m, 2H), 6.86-7.36 (m,
9H); IR (film) 3354, 2960, 1739, 1717 cm-1
.
[S-(R*,S*)]-3-(2,3-Diflu or oph en yl)-2-m eth yl-2-[[(2-m eth -
yl-1-p h en ylp r op oxy)ca r b on yl]a m in o]p r op ion ic Acid
Met h yl E st er (50a ). The compound was prepared as
described for 48a using carbonate 45b and 2,3-difluoro-
(RS)RMePheOMe (47). The two diastereomers were separated
by column chromatography, 10% ether/heptane, and the
desired product (the more polar isomer) was isolated as a white
2965, 1715, 1492, 1290, 1258, 1071 cm-1
.
[1-Meth yl-2-p h en yl-1-[(1-p h en yleth yl)ca r ba m oyl]eth -
yl]ca r ba m ic Acid 2-Meth yl-1-p h en ylp r op yl Ester (54).
The compound was prepared by coupling (S)-R-methylbenzy-
lamine to acid 51a by the method described for 1a . A white
solid was obtained: 41 mg (70%); mp 151-161 °C; [R]20
)
D
solid: 111 mg (35%); mp 112-115 °C; [R]23 ) +36° (c ) 0.1,
1
D
+10° (c ) 0.5, acetone); H-NMR (CDCl3) δ 0.81 (d, J ) 6.8
Hz, 3H), 0.98 (d, J ) 6.8 Hz, 3H), 1.32 (d, J ) 6.8 Hz, 3H),
1.48 (s, 3H), 2.02-2.11 (m, 1H), 3.14 (d, J ) 14 Hz, 1H), 3.28
(d, J ) 14 Hz, 1H), 4.93-5.00 (m, 1H), 5.26 (m, 1H), 5.38 (d,
J ) 7.6 Hz, 1H), 6.39 (d, J ) 7.1 Hz, 1H), 6.99-7.01 (m, 2H),
7.14-7.36 (m, 13H); IR (film) 3326, 3031, 2930, 1721, 1694,
1645, 1485, 1078 cm-1; MS m/ e (CI) 459 (M + H), 327, 283,
133. Anal. (C29H34N2O3‚0.25H2O) C, H, N.
1
MeOH); H-NMR (CDCl3) δ 0.81 (d, J ) 6.8 Hz, 3H), 0.98 (d,
J ) 6.8 Hz, 3H), 1.54 (s, 3H), 2.07 (m, 1H), 3.29 (d, J ) 14 Hz,
1H), 3.46 (d, J ) 14 Hz, 1H), 3.76 (s, 3H), 5.38 (m, 2H), 6.65
(m, 1H), 6.85 (m, 1H), 7.02 (m, 1H), 7.26-7.36 (m, 5H); IR
(film) 3343, 2957, 1735, 1713, 1492, 1268, 1071 cm-1; MS m/ e
(CI) 406 (M + H), 130, 133. Anal. (C22H25NO4F2) C, H, N.
[S-(R*,R*)]-3-(2,3-Diflu or oph en yl)-2-m eth yl-2-[[(2-m eth -
yl-1-p h en ylp r op oxy)ca r b on yl]a m in o]p r op ion ic Acid
Meth yl Ester (50b). The compound was prepared as de-
scribed for 50a . The two diastereoisomers were separated by
column chromatography, 10% ether/heptane, and the desired
product (the less polar isomer) was isolated as an oil: 87 mg
(27%); [R]23D ) -105° (c ) 0.2, MeOH); 1H-NMR (CDCl3) δ 0.83
(d, J ) 6.8 Hz, 3H), 0.98 (d, J ) 6.8 Hz, 3H), 1.65 (s, 3H), 2.07
(m, 1H), 3.26 (d, J ) 14 Hz, 1H), 3.38 (d, J ) 14 Hz, 1H), 3.72
(s, 3H), 5.34 (d, J ) 6.8 Hz, 1H), 5.55 (s, 1H), 6.46 (m, 1H),
6.68 (m, 1H), 6.97 (m, 1H), 7.26-7.38 (m, 5H); IR (film) 3350,
[1-Meth yl-2-p h en yl-1-[(1-p h en yleth yl)ca r ba m oyl]eth -
yl]ca r ba m ic Acid 2-Meth yl-1-p h en ylp r op yl Ester (55).
The compound was prepared by coupling (S)-R-methylbenzy-
lamine to acid 51b by the method described for 1a . A white
solid was obtained: 51 mg (50%); mp 183-189 °C; [R]20
)
D
+6° (c ) 0.5, acetone); 1H-NMR (CDCl3) δ 0.78 (d, J ) 6.8 Hz,
3H), 0.94 (d, J ) 6.8 Hz, 3H), 1.38 (d, J ) 6.8 Hz, 3H), 1.44 (s,
3H), 2.01-2.10 (m, 1H), 3.07 (d, J ) 14 Hz, 1H), 3.33 (d, J )
14 Hz, 1H), 5.01-5.08 (m, 1H), 5.15 (s, 1H), 5.38 (d, J ) 7.8
Hz, 1H), 6.41 (d, J ) 7.3 Hz, 1H), 6.92 (d, J ) 6.8 Hz, 2H),

1674 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8
Boden et al.
7.09-7.36 (m, 13H); IR (film) 3331, 2960, 1692, 1647, 1524,
1455, 1081 cm-1; MS m/ e (CI) 459 (M + H), 327, 283, 133.
Anal. (C29H34N2O3) C, H, N.
3.35 (m, 6H), 4.43 (s, 2H), 4.82 (br, 1H), 5.35 (d, J ) 7.2 Hz,
1H), 5.42 (br, 1H), 6.12 (m, 1H), 6.68 (m, 1H), 6.87 (m, 1H),
7.04 (m, 1H), 7.26-7.34 (m, 5H); IR (film) 3351, 2932, 2858,
1709, 1651, 1540 cm-1; MS m/ e (APCI) 547 (M), 504. Anal.
(C29H40N4O4F2‚0.2H2O) C, H, N.
[R-(R*,R*)]-[1-[(8-Hyd r oxyooctyl)ca r ba m oyl]-1-m eth yl-
2-p h en yleth yl]ca r ba m ic Acid 2-Meth yl-1-p h en ylp r op yl
Ester (56). The compound was prepared by coupling 8-ami-
nooctanol22 to acid 51a by the method described for 1a .
Purification by column chromatography, 33-50% EtOAc/
Ack n ow led gm en t. The authors wish to thank Miss
H. Chilvers, Mrs. R. Franks, Miss P. Grimson, Mrs. L.
Webdale, and Dr. P. D. McDonnel for their excellent
technical assistance.
hexane, gave a gum: 23 mg (34%); [R]20 ) +9° (c ) 0.8,
D
acetone); 1H-NMR (CDCl3) δ 0.81 (d, J ) 6.8 Hz, 3H), 0.99 (d,
J ) 6.8 Hz, 3H), 1.19-1.42 (m, 10H), 1.52-1.59 (m, 3H), 2.04-
2.14 (m, 1H), 3.06-3.23 (m, 3H), 3.27 (d, J ) 14 Hz, 1H), 3.64
(t, J ) 6.6 Hz, 2H), 5.24 (m, 1H), 5.38 (d, J ) 7.6 Hz, 1H),
6.01 (br, 1H), 7.00-7.02 (m, 2H), 7.18-7.36 (m, 8H); IR (film)
3366, 3031, 2930, 1720, 1649, 1488, 1078 cm-1; MS m/ e (CI)
483 (M + H), 307, 266, 133. Anal. (C29H42N2O4‚0.5H2O) C,
H, N.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic coordinates and experimental parameters for com-
pound 50a (22 pages). Ordering information is given on any
current masthead page.
Refer en ces
[S-(R*,S*)]-[1-[(8-Hyd r oxyooctyl)ca r ba m oyl]-1-m eth yl-
2-p h en yleth yl]ca r ba m ic Acid 2-Meth yl-1-p h en ylp r op yl
Ester (57). The compound was prepared by coupling 8-ami-
nooctanol22 to acid 51b by the method described for 1a .
Purification by column chromatography, 33-50% EtOAc/
(1) Houghten, R. A.; Pinilla, C.; Blondelle, S. E.; Appel, J . R.; Dooley,
C. T.; Cuervo, J . H. Generation and use of synthetic peptide
combinatorial libraries for basic research and drug discovery.
Nature 1991, 354, 84-86.
(2) Lam, K. S.; Salmon, S. E.; Hersh, E. M.; Hruby, V. J .; Kazmier-
ski, W. M.; Knapp, R. J . A new type of synthetic peptide library
for identifying ligand-binding activity. Nature 1991, 354, 82-
84.
(3) Fodor, S. P. A.; Read, J . L.; Pirrung, M. C.; Stryer, L.; Tsai Lu,
A.; Solas, D. Light-directed, spatially addressable parallel
chemical synthesis. Science 1991, 251, 767-773.
(4) Bunin, B. A.; Ellman, J . A general and expedient method for
the solid-phase synthesis of 1,4-benzodiazepine derivatives. J .
Am. Chem. Soc. Soc. 1992, 114, 10997-10998.
(5) Hobbs, DeWitt, S.; Kiely, J . S.; Stankovic, C. J .; Schroeder, M.
C.; Reynolds Cody, D. M.; Pavia, M. R. “Diversomers”: An
approach to nonpeptide, nonoligomeric chemical diversity. Proc.
Natl. Acad. Sci. U.S.A. 1993, 90, 6909-6913.
(6) Gordon, D. W.; Steele, J . Reductive alkylation on a solid phase:
Synthesis of a piperazinedione combinatorial library. Bioorg.
Med. Chem. Lett. 1995, 5, 47-50.
(7) Kurth, M. J .; Ahlberg Randall, L. A.; Chen, C.; Melander, C.;
Miller, R. B.; McAlister, K.; Reitz, G.; Kang, R.; Nakatsu, T.;
Green, C. Library-based lead compound discovery: Antioxidants
by an analogous synthesis/deconvolutive assay strategy. J . Org.
Chem. 1994, 59, 5862-5864.
(8) Smith, P. W.; Lai, J . Y. Q.; Whittington, A. R.; Cox, B.; Houston,
J . G.; Stylli, C. H.; Banks, M. N.; Tiller, P. R. Synthesis and
biological evaluation of a library containing potentiall 1600
amides/esters. A strategy for rapid compound generation and
screening. Bioorg. Med. Chem. Lett. 1994, 4, 2821-2824.
(9) Horwell, D. C.; Howson, W.; Ratcliffe, G. S.; Rees, D. C. The
design of a dipeptide library for screening at peptide receptor
sites. Bioorg. Med. Chem. Lett. 1993, 3, 799-802.
hexane, gave a gum: 24 mg (39%); [R]20 ) +7° (c ) 1.0,
D
acetone); 1H-NMR (CDCl3) δ 0.80 (d, J ) 6.8 Hz, 3H), 0.98 (d,
J ) 6.8 Hz, 3H), 1.19-1.42 (m, 10H), 1.50-1.62 (m, 3H), 2.08
(m, 1H), 3.08 (d, J ) 14 Hz, 1H), 3.17-3.22 (m, 2H), 3.33 (d,
J ) 14 Hz, 1H), 3.64 (t, J ) 6.6 Hz, 2H), 5.11 (m, 1H), 5.39 (d,
J ) 7.6 Hz, 1H), 6.17 (br, 1H), 6.94-6.95 (m, 2H), 7.14-7.38
(m, 8H); IR (film) 3363, 3031, 2856, 1719, 1649, 1494, 1079
cm-1; MS m/ e (CI) 483 (M + H), 307, 266, 133. Anal.
(C29H42N2O4‚0.5H2O) C, H, N.
[S-(R*,S*)]-[1-Meth yl-2-p h en yl-1-[(7-u r eid oh ep tyl)ca r -
ba m oyl]eth yl]ca r ba m ic Acid 2-Meth yl-1-p h en ylp r op yl
Ester (58). The compound was prepared by coupling the
amino urea 40 to acid 51b by the method described for 1c.
Purification by column chromatography, 80% EtOAc/heptane,
gave a white solid: 30 mg (43%); mp 54-57 °C; 1H-NMR
(CDCl3) δ 0.79 (d, J ) 6.8 Hz, 3H), 0.98 (d, J ) 6.8 Hz, 3H),
1.21-1.60 (m, 13H), 2.07 (m, 1H), 3.05 (d, J ) 14 Hz, 1H),
3.32 (d, J ) 14 Hz, 1H), 3.14-3.22 (m, 4H), 4.42 (br, 2H), 4.85
(s, 1H), 5.09 (s, 1H), 5.37 (d, J ) 7.6 Hz, 1H), 6.28 (br, 1H),
6.92-7.38 (m, 10H); IR (film) 3347, 2931, 1713, 1651, 1538
cm-1; MS m/ e (APCI) 511 (M + H). Anal. (C29H42N4O4‚0.6H2O)
C, H, N.
[S -(R *,S *)]-[2-(2-F lu or op h e n yl)-1-m e t h yl-1-[(7-u r e -
id oh ep tyl)ca r ba m oyl]eth yl]ca r ba m ic Acid 2-Meth yl-1-
p h en ylp r op yl Ester (59). The compound was prepared by
coupling the amino urea 40 to acid 52 by the method described
for 1c. Purification by column chromatography, 5% MeOH/
DCM, gave a white solid: 17 mg (29%); mp 67-72 °C; 1H-
NMR (CDCl3) δ 0.81 (d, J ) 6.8 Hz, 3H), 1.00 (d, J ) 6.8 Hz,
3H), 1.20-1.58 (m, 13H), 2.10 (m, 1H), 3.10-3.30 (m, 6H), 4.48
(br, 2H), 4.98 (s, 1H), 5.38 (m, 2H), 6.22 (br, 1H), 6.82-7.36
(10) Horwell, D. C.; Hughes, J .; Hunter, J . C.; Pritchard, M. C.;
Richardson, R. S.; Roberts, E.; Woodruff, G. N. Rationally
designed “dipeptoid” analogues of CCK. R-Methyltryptophan
derivatives as highly selective and orally active gastrin and
CCK-B antagonists with potent anxiolytic properties. J . Med.
Chem. 1991, 34, 404-414.
(11) Ondetti, M. D.; Rubin, B.; Cushman, D. W. Design of specific
inhibitors of angiotensin-converting enzyme: new class of orally
active antihypertensive agents. Science 1977, 196, 441-444.
(12) Hellberg, S.; Eriksson, L.; J onsson, J .; Lindgren, F.; Sjostrom,
M.; Skagerberg, B.; Wold, S.; Andrews, P. Minimimum analogue
peptide sets (MAPS) for quantitative structure-activity relation-
ships. Int. J . Pept. Protein Res. 1991, 37, 414-424.
(13) Maggi, C. A.; Patacchini, R.; Rovero, P.; Giachetti, A. Tachykinin
receptors and tachykinin antagonists. J . Auton. Pharmacol.
1993, 13, 23-93.
(m, 9H); IR (film) 3343, 2932, 2858, 1713, 1651, 1539 cm-1
.
Anal. (C29H41N4O4F‚0.2H2O) C, H, N.
[S-(R*,S*)]-[2-(2,3-Diflu or op h en yl)-1-m eth yl-1-[(7-u r e-
id oh ep tyl)ca r ba m oyl]eth yl]ca r ba m ic Acid 2-Meth yl-1-
p h en ylp r op yl Ester (60). The compound was prepared by
coupling the amino urea 40 to acid 53a by the method
described for 1c. Purification by column chromatography, 5%
MeOH/DCM, gave a white solid: 39 mg (55%); mp 59-64 °C;
1H-NMR (CDCl3) δ 0.80 (d, J ) 6.8 Hz, 3H), 0.99 (d, J ) 6.8
Hz, 3H), 1.26-1.57 (m, 13H), 2.09 (m, 1H), 3.19 (m, 4H), 3.26
(d, J ) 14 Hz, 1H), 3.36 (d, J ) 14 Hz, 1H), 4.40 (br, 2H), 4.80
(s, 1H), 5.28 (br, 1H), 5.37 (br, 1H), 6.25 (br, 1H), 6.55 (m, 1H),
6.76 (br, 1H), 7.00 (br, 1H), 7.26-7.38 (m, 5H); IR (film) 3363,
(14) Regoli, D.; Boudon, A.; Fauchere, J .-L. Receptors and antagonists
for substance P and related peptides. Pharmacol. Rev. 1994,
46, 551-599.
(15) Pritchard, M. C.; Boden, P. Tachykinin NK3 receptors: biology
and development of selective peptide and nonpeptide ligands.
Drugs Future 1995, 20, 1163-1173.
(16) Watling, K. J .; Krause, J . E. The rising sun shines on substance
P and related peptides. Trends Pharmacol. Sci. 1993, 14, 81-
84.
2932, 2864, 1709, 1651, 1539 cm-1; MS m/ e (APCI) 1050 (M2+
547 (M), 504. Anal. (C29H40N4O4F2‚0.75H2O) C, H, N.
)
(17) Emonds-Alt, X.; Bichon, D.; Ducoux, J . P.; Heaulme, M.; Miloux,
B.; Poncelet, M.; Proietto, V.; Van Broeck, D.; Vilain, P.; Neliat,
G.; Soubrie, P.; Le Fur, G.; Breliere, J . S. SR 142801 The first
potent non-peptide antagonist of the tachykinin NK3 receptor.
Life Sci. 1995, 56, 27-32.
(18) Boyle, S.; Guard, S.; Higginbottom, M.; Horwell, D. C.; Howson,
W.; McKnight, A. T.; Martin, K.; Pritchard, M. C.; O’Toole, J .;
Raphy, J .; Rees, D. C.; Roberts, E.; Watling, K. J .; Woodruff, G.
N.; Hughes, J . Rational design of high affinity tachykinin NK1
receptor antagonists. Biorg. Med. Chem. 1994, 2, 357-370.
[S-(R*,R*)]-[2-(2,3-Diflu or op h en yl)-1-m eth yl-1-[(7-u r e-
id oh ep tyl)ca r ba m oyl]eth yl]ca r ba m ic Acid 2-Meth yl-1-
p h en ylp r op yl Ester (61). The compound was prepared by
coupling the amino urea 40 to acid 53b by the method
described for 1c. Purification by column chromatography, 5%
MeOH/DCM, gave a white solid: 54 mg (62%); mp 56-61 °C;
1H-NMR (CDCl3) δ 0.81 (d, J ) 6.8 Hz, 3H), 1.00 (d, J ) 6.8
Hz, 3H), 1.17-1.49 (m, 8H), 1.56 (m, 5H), 2.08 (m, 1H), 3.14-

Dipeptide Library for NK3 Receptor Lead Development
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8 1675
(19) Boyle, S.; Guard, S.; Hodgson, J .; Horwell, D. C.; Howson, W.;
Hughes, J .; McKnight, A. T.; Martin, K.; Pritchard, M. C.;
Watling, K. J .; Woodruff, G. N. Rational design of high affinity
tachykinin NK2 receptor antagonists. Bioorg. Med. Chem. 1994,
2, 101-113.
(20) Boden, P.; Eden, J . M.; Hodgson, J .; Horwell, D. C.; Howson,
W.; Hughes, J .; McKnight, A. T.; Meecham, K.; Pritchard, M.
C.; Raphy, J .; Ratcliffe, G. S.; Suman-Chauhan, N.; Woodruff,
G. N. The rational development of small molecule tachykinin
NK3 receptor selective antagonists-The utilisation of a dipeptide
chemical library in drug design. Bioorg. Med. Chem. Lett. 1994,
4, 1679-1684.
(21) Boden, P.; Eden, J . M.; Hodgson, J .; Horwell, D. C.; Pritchard,
M. C.; Raphy, J .; Suman-Chauhan, N. The development of a
novel series of non-peptide tachykinin NK3 receptor selective
antagonists. Bioorg. Med. Chem. Lett. 1995, 5, 1773-1778.
(22) Patent publication no. US 228236, Apr. 15, 1994.
(23) Suman-Chauhan, N.; Grimson, P.; Gaurd, S.; Madden, Z.; Chung,
F.-Z.; Watling, K.; Pinnock, R.; Woodruff, G. Characterisation
of [125I][MePhe7]neurokinin B binding to tachykinin NK3 recep-
tors: evidence for interspecies variance. Eur. J . Pharmacol.
1994, 269, 65-72.
(24) Horwell, D. C.; Ratcliffe, G.; Roberts, E. Stabilities of typtopha-
nylphenylethylamides to acid and alkaline conditions. Bioorg.
Med. Chem. Lett. 1991, 1, 169-172.
(25) Michelot, R.; Mayer, M.; Magneney, S.; Pham, Van Chuong, P.;
Schmitt, P.; Potier, P. Activity of the C-terminal part of
substance P on guinea pig ileum and trachea preparations 1.
N-Acylated pentapeptides SP(7-11). Eur. J . Med. Chem. 1988,
23, 243-247.
(26) Abraham, M. H.; Duce, P. P.; Prior, D. V.; Barratt, D. G.; Morris,
J . J .; Taylor, P. J . Hydrogen bonding. Part 9. Solute proton
donor and proton acceptor scales for use in drug design. J .
Chem. Soc., Perkin Trans. II 1989, 1355-1375.
(27) Higginbottom, M.; Kneen, C.; Ratcliffe, G. S. Rationally designed
“dipeptoid” analogues of CCK. A Free-Wilson/Fujita-Ban analy-
sis of some R-methyltryptophan derivatives as CCK-B antago-
nists. J . Med. Chem. 1992, 35, 1572-1577.
(28) Topliss, J . G. Utilization of operational schemes for analog
synthesis in drug design. J . Med. Chem. 1972, 15, 1006-1011.
(29) Suman-Chauhan, N.; Daum, P.; Hill, D. R.; Woodruff, G. CCK/
Gastrin receptor-mediated changes in intracellular calcium in
AR42J cells. Br. J . Pharmacol. 1992, 107, 149P.
(30) Guard, S.; Boyle, S. J .; Tang, K. W.; Watling, K. J .; McKnight,
A. T.; Woodruff, G. N. The interaction of the NK1 receptor
antagonist CP-96,345 with L-type calcium channels and its
functional consequences. Br. J . Pharmacol. 1993, 110, 385-
391.
(31) Boden, P.; Woodruff, G. N. Presence of NK3-sensitive neurones
in different proportions in the medial habenula of guinea-pig,
rat and gerbil. Br. J . Pharmacol. 1994, 112, 717-719.
(32) Laneuville, O.; Dorais, J .; Couture, R. Characterization of the
effects produced by neurokinins and three agonists selective for
neurokinin subtypes in a spinal nociceptive reflex of the rat. Life
Sci. 1988, 42, 1295-1305.
(33) Bannon, M. J .; Brownschidle, L. A.; Tian, Y.; Whitty, C. J .;
Poosch, M. S.; D’sa, C.; Moody, C. A. Neurokinin-3 receptors
modulate dopamine cell function and alter the effects of 6-hy-
droxydopamine. Brain Res. 1995, 695, 19-24.
(34) Thomas, D. G.; Nathan, A. H. 6-Methoxy-1-tetralone. J . Am.
Chem. Soc. 1948, 70, 331-334.
(35) Witkop, B.; Beiler, T. W. Studies on Schiff bases in connection
with the mechanism of transamination. J . Am. Chem. Soc. 1954,
76, 5589-5597.
(36) Boc(S)Phe(S)RMePheOH and Boc(S)Phe(RS)PheOH were pre-
pared as described for Boc(S)Phe(R)RMePheOH in ref 22.
J M950892R