2-Nitrophenylcarbamoyl-(S)-prolyl-(S)-3-(2-naphthyl)alanyl-N-benzyl-N- methylamide (SDZ NKT 343), a potent human NK1 tachykinin receptor antagonist with good oral analgesic activity in chronic pain models

Article abstract of DOI:10.1021/jm970499g

A lead compound which had sub-micromolar affinity for the rabbit NK₁ receptor but negligible affinity for rat NK₁ receptors, 3a, was discovered by directed screening. 2-Substitution in the ring of the benzylthiourea substituent in the initial lead was found to be important, and halogens (Cl, Br) in this position were found to improve affinity for the human receptor. The activity of a series of 2-halo-substituted benzylthioureas was then optimized by modification of the proline diphenylmethyl amide, guided by a simple conceptual model based on structural overlay between these early antagonists and NK₁ selective peptides. In this way, aromatic amino acid amides were identified which had improved affinity with respect to the starting diphenylmethyl (DPM) amides. The first sub-nanomolar ligand for the human NK₁ receptor which arose from this series, 4af, combined a 2- chlorobenzylthiourea unit with a 2-naphthylalanine amide. Contemporaneously it was discovered that the benzylthiourea unit could be simplified to a phenylthiourea providing that an appropriate 2-substituent was also incorporated. Combination of these two series gave 2-NO₂ phenylthiourea analogues which led directly to the analogous urea, 5f (2- nitrophenylcarbamoyl-(S)-prolyl-(S)-3-(2-naphthyl)alanyl-N-benzy-N- methylamide, SDZ NKT 343), a highly potent ligand for the human NK₁ receptor (K(i) = 0.16 nM). In addition to its high in vitro potency, 5f proved to be a potent orally active analgesic in guinea pig models of chronic inflammatory and neuropathic pain. The nature of the 2-aryl substituent was found to be critical for oral activity in this series. Clinical evaluation of 5f as a novel analgesic agent is currently underway.

Full text of DOI:10.1021/jm970499g

J . Med. Chem. 1998, 41, 3159-3173
3159
2-Nitr op h en ylca r ba m oyl-(S)-p r olyl-(S)-3-(2-n a p h th yl)a la n yl-N-ben zyl-N-
m eth yla m id e (SDZ NKT 343), a P oten t Hu m a n NK1 Ta ch yk in in Recep tor
An ta gon ist w ith Good Or a l An a lgesic Activity in Ch r on ic P a in Mod els
C. Walpole,*,† S. Y. Ko,‡ M. Brown,§ D. Beattie, E. Campbell, F. Dickenson, S. Ewan, G. A. Hughes,
M. Lemaire,| J . Lerpiniere, S. Patel, and L. Urban
Novartis Institute for Medical Sciences, 5 Gower Place, London WC1E 6BN, U.K.
Received J uly 30, 1997
A lead compound which had sub-micromolar affinity for the rabbit NK1 receptor but negligible
affinity for rat NK1 receptors, 3a , was discovered by directed screening. 2-Substitution in the
ring of the benzylthiourea substituent in the initial lead was found to be important, and halogens
(Cl, Br) in this position were found to improve affinity for the human receptor. The activity of
a series of 2-halo-substituted benzylthioureas was then optimized by modification of the proline
diphenylmethyl amide, guided by a simple conceptual model based on structural overlay
between these early antagonists and NK1 selective peptides. In this way, aromatic amino acid
amides were identified which had improved affinity with respect to the starting diphenylmethyl
(DPM) amides. The first sub-nanomolar ligand for the human NK1 receptor which arose from
this series, 4a f, combined a 2-chlorobenzylthiourea unit with a 2-naphthylalanine amide.
Contemporaneously it was discovered that the benzylthiourea unit could be simplified to a
phenylthiourea providing that an appropriate 2-substituent was also incorporated. Combination
of these two series gave 2-NO2 phenylthiourea analogues which led directly to the analogous
urea, 5f (2-nitrophenylcarbamoyl-(S)-prolyl-(S)-3-(2-naphthyl)alanyl-N-benzyl-N-methylamide,
SDZ NKT 343), a highly potent ligand for the human NK1 receptor (Ki ) 0.16 nM). In addition
to its high in vitro potency, 5f proved to be a potent orally active analgesic in guinea pig models
of chronic inflammatory and neuropathic pain. The nature of the 2-aryl substituent was found
to be critical for oral activity in this series. Clinical evaluation of 5f as a novel analgesic agent
is currently underway.
In tr od u ction
pain (particularly those involving inflammatory hype-
ralgesia), however, NK1 receptors become increasingly
important.12 The role of the NK1 receptor in neuro-
pathic pain is less clear, but recent evidence in animal
models suggests that NK1 antagonists might be effec-
tive.13,14 One published report suggests that NK1
antagonists may show clinical efficacy in certain pain
states.15
Besides pain, the main indications forseen for these
antagonists are emesis, migraine, inflammation, and
chronic bronchitis.16-18
The tachykinins are a family of neuropeptides which
include substance P, neurokinin A, and neurokinin B
(SP, NKA, and NKB). These peptides exert their effects
through three G-protein-coupled receptor subtypes, the
NK1, NK2, and NK3 receptors.1 SP is the preferred
agonist at NK1 receptors.2
Several non-peptide antagonists at NK1 receptors,
mostly the products of screening and optimization
programs, have been described in recent years3-10 and
some are currently in clinical development.
The development of such agents as novel analgesics
is based on recent evidence that NK1 tachykinin recep-
tors are instumental in the development and mainte-
nance of the central component of pain and hyperalge-
sia. Substance P is an important mediator in nociceptive
pathways.11 NK1 receptor antagonists produce only a
weak inhibition of acute nociceptive responses in animal
models, suggesting that under normal physiological
conditions SP is less important than other excitatory
transmitters in this pathway. In models of pathological
Ch em istr y
The benzyl- and phenylthioureas and their derivatives
were prepared by reaction of the central intermediates
2 with a variety of reagents outlined in Scheme 1 by
routes A-G. The intermediates 2 were prepared by
reaction of an N-protected amino acid with the amines
1 using a variety of standard coupling agents, e.g.,
mixed anhydride method or DCCI and then deprotec-
tion, e.g., with HCl/dioxan. The amines 1 were either
commercially available or were amino acid derivatives
which were synthesized by reaction of N-protected
amino acids with amines using coupling agents, e.g.,
mixed anhydride method, by analogy with the prepara-
tion of intermediates 2, deprotection, and then isolation
of the free base.
† Current address: Astra Research Centre Montreal, 7171 Frederick
Banting, Saint-Laurent, Quebec H4S 1Z9, Canada.
‡ Current address: Samsung Advanced Institute of Technology, 103-
112 Moonji-Dong, Yusong-Gu, Taejon, Korea 305-380.
§ Current address: New England Nuclear, Dupont UK Ltd., Wedge-
wood Way, Stevenage, Hertfordshire SG1 4QN, U.K.
Current address: Pfizer Central Research, Sandwich, Kent CT13
9NJ , U.K.
Since the intermediates, 2, were prepared by standard
methods, their preparation is described in the Experi-
| Novartis Pharma, Basel, Switzerland.
S0022-2623(97)00499-8 CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/21/1998

3160 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Walpole et al.
Sch em e 1
mental Section as exemplified by one example of the
class. Full experimental details for the preparation of
the individual intermediates is included as Supporting
Information. Likewise the repetitive procedures, e.g.,
the formation of thioureas and ureas from these inter-
mediates, are exemplified by a single example where
the synthesis is described in detail and subsequent
compounds of the same class have been presented in
tabular format with full details included in the Sup-
porting Information.
prepared by route A using the appropriate O-TBDMS-
protected isocyanate and subsequent deprotection of the
intermediate urea using TBAF in THF. 5a l (R ) Ph-
2-NH2, Table 4) was prepared by catalytic reduction of
5f (R1 ) Ph-2-NO2) using H2/Pd on C. 5a m (R ) Ph-
2-NHCOCH3, Table 4) was prepared by acetylation of
5a l using acetic anhydride.
The benzyl N-cyanoguanidine compound 3q (X ) NH,
Y ) NCN, Table 1) was prepared by reaction of 2 with
the appropriately ring-substituted N-cyano-O-phenyli-
sourea (route B). The benzyl carbamate, 3r (X ) O, Y
) O, Table 1), and guanidine, 4l (Y ) NH, Table 2), were
prepared by reaction of 2 with the appropriate chloro-
formate and N-benzyl-S-methylthiouronium salt (routes
C and D respectively). The guanidines 4a j (Y ) NH,
R1 ) Cl, Table 2) and 5h (R1 ) NO2Ph, Y ) NH, Table
3) were prepared by a novel route19,20 using HgCl2
coupling of 2 with protected thioureas. In the former
case the bis-protected guanidine product of the coupling
reaction was deprotonated using NaH and then alky-
lated with the appropriately ring-substituted benzyl
bromide (route E), whereas the latter compound was
prepared by direct coupling with a ring-substituted
N-phenyl-N-Boc-thiourea intermediate (route F). The
3g (R1 ) NH2, Table 1) was prepared by catalytic
reduction of 3f (R1 ) NO2) using H2/Pd on C. 5a c (R )
Ph-CO2H, Table 4) was prepared by saponification of
5a b (R ) Ph-CO2CH3) using potassium hydroxide in
methanol. The acid 5a c was converted to the mixed
anhydride, under standard conditions, using isobutyl
chloroformate for 5a d , 5a e, and 5a f (R ) Ph-2-CO2NH2,
Ph-3-CO2NH2, Ph-2-CO2NHCH3, Table 4) and then
cleavage with ammonia and methylamine as required.
The hindered anhydride formed from isopropyl chloro-
formate was required to suppress opening of the inap-
propriate anhydride carbonyl when reacted with dim-
ethylamine, furnishing 5a g (Ph-2-CO2N(CH3)2, Table 4).
5a j and 5a k (Ph-2-CH2OH and Ph-2-OH, Table 4) were

Human NK1 Tachykinin Receptor Antagonist
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17 3161
Ta ble 1. Effect on Rabbit NK1 Receptor Binding Affinity of Simple Structural Modifications to 3a
rabbit NK1 receptor binding
Ki, µM, mean ( SEM (n g 3)
(IC50, µM, n ) 2)
compd
no.
R1
X
Y
*
Z
3a
OMe
H
Cl
F
Br
NO2
NH2
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
O
S
S
S
S
S
S
S
O
S
S
S
S
S
S
S
S
S
S
S
S
S
S
R
S
S
S
S
S
S
S
NHCH(Ph)2
NHCH(Ph)2
NHCH(Ph)2
NHCH(Ph)2
NHCH(Ph)2
NHCH(Ph)2
NHCH(Ph)2
NHCH(Ph)2
NHCH(Ph)2
NHCH (CH2Ph) 2
NHCH2CH(Ph)2
N(CH2Ph) 2
0.33 ( 0.11
(>5)
3b
3c
3d
3e
3f
3g
3h
3j
0.17 ( 0.06
1.27 ( 0.53
0.17 ( 0.08
1.56 ( 0.61
(>50)
(>50)
(>5)
3k
3l
(>50)
(>5)
3m
3n
3p
3q
3r
(>50)
NHCH(CH2Ph)CON(CH3)CH2Ph-(S)
NHCH(CH2Ph)CON(CH3)CH2Ph-(R)
NHCH(Ph)2
0.26 ( 0.09
1.28 ( 0.37
(>50)
NCN
O
NHCH(Ph)2
(>50)
Boc-protected guanidine in each case was then depro-
tected with TFA. Similar chemistry was employed in
the synthesis of the N-cyanoguanidine analogue, 5j,
starting from cyanamide (route G).
amides in a rabbit NK1 binding assay. 3a had sub-
micromolar affinity for the rabbit NK1 receptor (Ki )
0.33 µM) but negligible affinity for the rat receptor.
SAR of th e Lea d Str u ctu r e, 3a . Simple variation
of the aromatic ring substitution in this early lead
structure established that 2-substitution was important
(compare 3a and 3b, Table 1) for sub-micromolar
affinity at the rabbit NK1 receptor. 2-Substitution with
halogens (Cl and Br but not F) led to a 2-fold increase
in affinity. The nitro-substituted compound, 3f, was
5-fold less potent, and the amino compound, 3g, was
inactive.
Biology: Assa ys in Vitr o
The in vitro assessment of the compounds was carried
out in binding assays and in the guinea pig ileum organ
bath bioassay. Binding assays were carried out using
rabbit whole brain membranes, rat whole forebrain
membranes, and membranes from Cos-7 cells tran-
siently transfected with the human NK1 receptor.
Guinea pig ileum (GPI) contractions were evoked by the
potent NK1 selective peptide agonist [Sar9Met(O2)11]SP
(4.0 nM).
In such 2-methoxybenzylthioureas, replacement of the
thiourea substructure with urea, 3h , carbamate, 3r , or
the N-cyanoguanidine, 3q (sometimes considered a
thiourea “bioisostere”22), led to loss of affinity. The
chirality of the proline unit appeared to be important,
since the D-proline analogue of 3a , 3j, was much less
active. Several other amino acids (e.g., glycine) were
explored as replacements for L-proline but were without
activity, suggesting that the conformational constraint
afforded by L-proline was critical.
Full experimental details of these assays are pre-
sented in the Experimental Section.
P h a r m a cology: Assa ys in Vivo
Due to the marked species differences in receptor
affinity noted with this class of compounds, a model of
carrageenan-induced hyperalgesia in the guinea pig21
was used to assess the effects of NK1 antagonists on
inflammatory hyperalgesia in vivo. Carrageenan (1.0%,
100 µL) injected intraplantar into one hind paw induces
both a mechanical and thermal hyperalgesia which
persists for over 24 h. Subcutaneously administered
morphine potently and completely reverses hyperalgesia
whereas orally administered aspirin is less potent and
only produces a partial reversal of hyperalgesia, as do
other NSAIDs.
ED30 was calculated as the dose required to produce
a 30% inhibition of hyperalgesia, and the maximum
effect achieved was expressed as percentage reversal of
the predose hyperalgesia.
Full experimental details of this assay are presented
in the Experimental Section.
The nature of the hydrophobic prolinamide substitu-
ent (diphenylmethyl in 3a ) was then modified. SAR
from the initial lead finding established that a simple
benzyl substituent on the proline amide was insufficient
for significant rabbit NK1 receptor affinity: two aryl
rings were apparently required. The activity of other
substituents for the proline amide containing two aryl
rings was explored, e.g., dibenzylmethyl, diphenylethyl,
and N-dibenzyl (3k -m ), but none were found to be
active. It is now known that the majority of non-peptide
NK1 antagonists, whose structures have been published,
do not share binding determinants in common with
peptide agonists, i.e., they are not peptidomimetics.23
In the absence of such information, however, a simple
conceptual model, in which the diphenylmethyl moiety
in 3a was hypothesized to mimic the Phe-Phe side
chains in a panel of NK1 selective peptide ligands, was
used as a basis for design. The proline amide substitu-
Resu lts a n d Discu ssion
A lead compound, 3a (Table 1), was discovered by
directed screening of a proprietary library of amino acid

3162 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Walpole et al.
Ta ble 2. Optimization of a Series of Benzylthiourea Proline Amides for Human NK1 Receptor Binding Affinity
human NK1 receptor binding
Ki, nM, mean ( SEM (n g 3)
(IC50, nM, n ) 2)
compd
no.
R1
Y
R2
R3
R4
R5
3n
4a
4b
4c
4d
4e
4f
4g
4h
4j
4k
4l
4m
4n
4p
2-OMe
2-Cl
2-Br
S
S
S
S
S
S
S
S
S
S
O
NH
S
H
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
123.0 ( 34.0
29.9 ( 5.0
H
H
H
H
H
H
H
H
H
H
H
H
H
H
29.7 ( 15.0
2-F
(290, 480)
2-CF3
2-NO2
2-CH3
2-H
2,6-diCl
3,5-diCF3
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
27.2 ( 10.9
77.6 ( 23.2
(410, 330)
1010 ( 47
25.9 ( 9.6
78.6 ( 32.2
(590, 660)
18.5 ( 4.5
CH2CH2Ph
Ph
(2500, 1100)
(100,000, 11700)
8000 ( 250
S
S
N
4q
4r
4s
4t
4u
4v
4w
4x
4y
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
2-Cl
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
H
H
H
H
H
H
CH3
H
H
H
H
H
H
H
CH3
H
H
H
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH3
CH3
CH3
CH3
H
CH2-1-naphthyl
CH2-2-naphthyl
CH2(3,5-diCF3Ph)
CH2CH2(3-indolyl)
CH2CH2(3-indolyl)
CH2(4-pyridyl)
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
17.1 ( 4.1
36.0 ( 17.0
26.9 ( 13.0
48 ( 22
(3700, 6000)
(10000, 2500)
38 ( 11
(206, 543)
7.2 ( 1.9
5 ( 1
16.7 ( 5.3
4.7 ( 1.1
13.7 ( 3.6
0.7 ( 0.3
1.7 ( 0.7
7.4 ( 2.2
29.4 ( 11.7
2.3 ( 0.6
0.5 ( 0.2
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH2CH2Ph
CH2(4-Ph)Ph
4z
CH2(3,4-diCl)Ph
CH2(3-indolyl)
CH2(N-Me 3-indolyl)
CH2-(1-naphthyl)
CH2-(2-naphthyl)
CH2-(2-naphthyl)
CH2-(benzothienyl)
CH(Ph)2
4a a
4a b
4a c
4a d
4a e
4a f
4a g
4a h
4a j
S
O
NH
CH2-(2-naphthyl)
CH2-(2-naphthyl)
H
ent was therefore elaborated to the prolyl-phenylalanine
amide 3n . Phenylalanine benzyl amides overlayed the
two aryl moieties in the model particulary well and,
since N-methylbenzylamides had been found to confer
oral activity on a series of structurally related analogues
including FK 888,5 this substitution was therefore
introduced. The L-phenylalanine N-methylbenzylamide
analogue retained activity on the rabbit receptor with
respect to 3a , whereas the D-isomer, 3p , was 5-fold less
active than 3n .
Ben zylth iou r ea s: Ar om a tic Rin g Su bstitu tion in
P r olyl-P h en ylalan ylam ides. When the parent 2-meth-
oxybenzylthiourea in the prolyl-phenylalanylamide se-
ries, 3n , was tested in the human NK1 receptor binding
assay, it was found to be slightly more potent than at
the rabbit NK1 receptor (Table 2). As was the case with
the earlier studies on the rabbit receptor, the unsub-
stituted benzylthiourea (2-H, 4g) was less potent than
the 2-methoxy compound. Importantly, the 2-methoxy
to halogen substitution which in the proline diphenyl-
methyamide series retained affinity, resulted in a large
increase in affinity for the human receptor (compare 3v
with 4a -b). 2-CF3 aryl substitution (4d ) gave similarly
high affinity, while as before, 2-F substitution (4c) was
not so effective. Disubstitution was tolerated, as shown
by the equipotency of the 2,6-dichloro compound with
the 2-monochloro compound (compare 4h and 3n ). 3,5-
Bis-CF3 substitution (4j), which is known to improve
in vitro potency greatly in other structural series of NK1
antagonists,8 gave only a modest increase in potency
compared with 3n in this series. 2-Nitro substitution,
as in the diphenylmethylamides, was inferior to halogen
though it was superior to methoxy in this series
(compare 4e, 3n , and 4a ).
As with the prolyldiphenylmethyl amide series, the
urea analogue of 4a (the most potent thiourea), 4k , was
much less potent while the benzylguanidine, 4l, retained
or slightly increased activity and had improved solubil-
ity with respect to the thiourea.
Ben zylth iou r ea s: SAR of th e P r olyl P h en yla la -
n yl Am id e Su bstitu en t. The optimum substitution
of the phenylalanine amide was then explored. The
N-methyl-N-benzyl amide could be substituted by other
N-methyl-N-aralkyl substituents, e.g., 1- or 2-naphth-
ylmethyl, 4q, 4r (Table 2). 3,5-Bis(trifluoromethyl)
substitution of the benzyl ring in the N-methyl-N-benzyl

Human NK1 Tachykinin Receptor Antagonist
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17 3163
Ta ble 3. Optimization of a Series of Phenylthiourea Proline Amides and Their Derivatives for Human NK1 Receptor Binding
Affinity
human NK1 receptor binding
compd
no.
Ki, nM, mean ( SEM (n g 3)
R1
Y
*,#
R2
R3
(IC50, nM, n ) 2)
5a
5b
5c
5d
5e
5f
5g
5h
5j
5k
5l
5m
5n
5p
2-ClPh
2-HPh
2-NO2Ph
2-BrPh
S
S
S
S
S
O
O
NH
NCN
O
S,S
S,S
S,S
S,S
S,S
S,S
S,S
S,S
S,S
R,R
S,R
R,S
S,S
S,S
H
H
H
H
H
H
CH3
H
H
H
H
H
H
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2-2-naphthyl
CH2-2-naphthyl
CH2-2-naphthyl
CH2-2-naphthyl
CH2-2-naphthyl
CH2-2-naphthyl
CH2-2-naphthyl
CH2-2-naphthyl
CH2-3-indolyl
(3200, 2700)
80.0 ( 24.8
100.0 ( 35.0
(600, 1000)
0.8 ( 0.3
2-NO2Ph
2-NO2Ph
2-NO2Ph
2-NO2Ph
2-NO2Ph
2-NO2Ph
2-NO2Ph
2-NO2Ph
2-NO2Ph
2-NO2Ph
0.16 ( 0.07
0.14 ( 0.04
60.6 ( 20.6
2.7 ( 1.1
82.4 ( 12.4
7.1( 1.2
O
O
O
O
274 ( 63
0.41 ( 0.15
0.82 ( 0.20
H
CH2-3,4-dichlorophenyl
amide 4s was well tolerated but did not increase affinity
with respect to 4a . The incorporation of a heteroatom
into the benzyl ring, to give the 4-pyridyl analogue, 4v,
caused a large loss of affinity. Shortening the aralkyl
chain in such amides, e.g., benzyl to phenyl, 4n , was
not tolerated whereas lengthening this group to phe-
nylethyl, 4m , had less of a deleterious effect. The
related indolylethyl group in this position restored
affinity, 4t, although the analogous secondary amide,
4u , was much less active. In common with other
N-methyl amides described in this paper, two rotomeric
forms of 4t were observed by NMR (see the Experimen-
tal Section) but only one (presumably the trans amide)
was observed with the secondary amide, 4u . The much
higher affinity observed with 4t compared with 4u
suggests, therefore, that the conformer which binds to
the NK1 receptor was the cis amide. Constraint of the
N-methyl-N-benzyl amide into a tetrahydroisoquinolyl
amide, 4p , also had a deleterious effect on affinity. No
amide substitution which was markedly superior to the
N-methyl benzylamide was identified and so this sub-
structure was retained subsequently.
toxic in vivo (lethal within 30 min of systemic admin-
istration) and so were not pursued further.
In both the parent phenylalanine and naphthylala-
nine compounds, N-methylation of the central amide
NH was achieved without a significant loss of affinity
(compare 4a and 4w ; 4a d and 4a e, Table 2).
P h en ylu r ea s: An a logou s Str u ctu r a l Mod ifica -
tion s. The 2-chlorophenyl thiourea 5a (Table 3, in
which the benzyl methylene group has been omitted
with respect to 4a ) was much less potent than the
corresponding 2-chlorobenzyl compound. Interestingly,
however, the unsubstituted compound, 5b, retained
high affinity. In the case of this unsubstituted com-
pound, omission of the benzyl methylene group signifi-
cantly increased affinity with respect to the unsubsti-
tuted benzyl compound, 4g, but had the opposite effect
in the halo-substituted coupled pairs, 4a and 5a , 4b and
5d . The 2-nitro-substituted compound 5c, however,
retained affinity with respect to the unsubstituted
compound.
The SAR of the ring substitution is thus clearly
different in the phenyl series to that observed in the
benzyl series, with the rank order for potency being as
follows:
Ben zylth iou r ea s: Ela bor a tion of th e Cen tr a l
Am in o Acid Moiety. Ring substitution of the phenyl-
alanine side chain with hydrophobic substituents, as in
4y and 4z, gave a small increase in affinity. Modifica-
tion of the benzyl methylene group by inserting an
additional methylene group in the linker, as in 4x, led
to a decrease in affinity compared with 4a whereas
methylene branching (substitution with another phenyl
ring), as in 4a g, led to retention of potency. Bicyclic
aromatic groups, including heterocycles (4a a -a f), were
tolerated, and some resulted in a large increase in
affinity, especially the 2-naphthylalanine analogue, 4a d .
In this 2-naphthylalanine series, as noted previously for
phenylalanine analogues, the benzylurea analogue, 4a h ,
was somewhat less potent than the thiourea, 4a d ,
whereas the benzylguanidine, 4a j, was very potent and
had increased solubility with respect to the thiourea.
However, benzylguanidines of this type were acutely
benzyl:
phenyl:
Cl ) Br > OMe ≈ NO2 > F > H
NO2 ≈ H > Cl, Br
In a series of 2-nitrophenyl analogues, the SAR of the
central amino acid unit (phenylalanine in 5c) was
closely comparable to that observed in 2-chlorobenzyl-
thioureas. Bicyclic hydrophobic amino acids increased
affinity, particularly 2-naphthylalanine and tryptophan
(5e, 5n ), all of which had sub-nanomolar affinity, as did
3,4-dichlorophenylalanine, 5p . In a series of such
analogues, where 2-naphthylalanine was chosen as the
central amino acid substituent, the “linker group”, e.g.,
thiourea in 5e, was then varied. The N-cyanoguanidine,
5j, was active, although slightly less potent than the

3164 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Walpole et al.
Ta ble 4. Effect of Ring Substitution on in Vitro and in Vivo Activity of a Series of Phenylureas
human NK1 receptor binding
Ki, nM, mean ( SEM
(n g 3)
GPI NK1 IC50, nM,
mean ( SEM
(n ) 3)
% inhibn at 30 mg/kg po
(3 h after dosing)
compd
no.
R
(DR curve, n ) 3)
5q
5r
5f
Ph
3-pyridyl
Ph-2-NO2
0.88 ( 0.29
6.7 ( 1.5
5.0 ( 0.52
4.2 ( 2.56
1.6 ( 0.94
26
14 (1 h)
68.4 ( 1.3
(ED30 ) 1.1 ( 0.5)
0.16 ( 0.07
5s
5t
5u
Ph-3-NO2
Ph-4-NO2
Ph-2-CN
2.3 ( 0.53
1.0 ( 0.38
1.1 ( 0.37
NT
NT
1.0 ( 0.3
NT
NT
42
(ED30 ) 2.1)
38
32
NT
10
NT
NT
NT
NT
35
(ED30 ) 15.7)
NT
NT
NT
67.0 ( 1.7
(ED30 ) 1.2 ( 0.1)
NT
NT
NT
NT
5v
5w
5x
5y
5z
5a a
5a b
5a c
5a d
Ph-3-CN
Ph-4-CN
Ph-2-F
Ph-3-F
Ph-4-F
Ph-2-CF3
Ph-2-CO2CH3
Ph-2-CO2H
Ph-2-CO2NH2
4.2 ( 1.5
1.1 ( 0.4
3.5 ( 0.5
0.7 ( 0.1
2.2 ( 0.4
18.2 ( 2.2
0.3 ( 0.09
172 ( 58
0.8 ( 0.2
2.6 ( 0.9
2.4 ( 0.7
NT
6.8 ( 3.0
17.3 ( 5.1
NT
6.0 ( 3.0
NT
1.9 ( 0.42
5a e
5a f
5a g
5a h
Ph-3-CO2NH2
5.0 ( 1.2
3.8 ( 0.6
6.1 ( 1.5
1.0 ( 0.2
NT
3.0 ( 1.0
NT
Ph-2-CO2NHCH3
Ph-2-CO2N(CH3)2
Ph-2-CH2OCH3
1.2 ( 0.4
5a j
5a k
5a l
Ph-2-CH2OH
Ph-2-OH
Ph-2-NH2
1.7 ( 0.6
2.6 ( 0.9
19.7 ( 3.9
9.6 ( 3.1
NT
NT
21.0 ( 7.2
7.5 ( 3.2
5a m
Ph-2-NHCOCH3
thiourea, but the guanidine, 5h , was much less potent.
The urea 5f, however, had outstandingly high human
NK1 receptor binding affinity. This contrasts with the
benzyl series where the urea is less potent than the
thiourea and guanidine (compare 4a h , 4a d , and 4a j).
This rank order, like that for aromatic ring substitution,
is completely different from that seen in the benzylthio-
urea series:
ent basicity and preferred tautomeric forms, but the
most important feature responsible for modulating NK1
receptor binding affinity is not clearly understood at
present.
In 5f, the most potent of this series of compounds on
the human receptor, the position of the nitro group is
important for very high affinity (IC50 < 1 nM), compare
5f, 5s, and 5t (Table 4). The difference between the
affinities of the corresponding CN or F-substituted
positional isomers, 5u -z, however, was less apparent,
with all isomers having moderate to high affinity. The
2-methoxycarbonyl compound, 5a b, and the related
primary amide, 5a d , had high affinity, comparable to
5f, but the related carboxylic acid, 5a c, had 500-fold
lower affinity. As with the nitro compounds, previously
discussed, the 3-positional isomer of the 2-primary
amido compound 5a d , 5a e, was less potent. This SAR
suggested to us that H-bond acceptor function in the
2-position had some influence on affinity at the human
receptor, perhaps by stabilizing an intramolecular H-
bond with the anilide-like NH and a consequent influ-
ence on conformation.
benzyl:
guanidine ≈ thiourea > urea ) NCN guanidine
phenyl:
urea > thiourea ≈ NCN guanidine > guanidine
5f has a high “eudysmic ratio” with the (S,S) diaste-
reomer being the eutomer. Its enantiomer (5k , the R,R
diastereomer) is >500-fold less potent, and the other two
diastereoisomers also have lower affinity. In common
with the analogous substitution in the benzylthiourea
series, the N-methyl analogue of 5f, 5g, retains similarly
high affinity.
Discu ssion
In general the correlation between the human recep-
tor binding affinities and the guinea pig ileum bioassay
(GPI) potencies was good (R ) 0.85, Figure 1). Minor
species differences were, however, evident within this
data set, e.g., 5f, which is outstanding in its human
receptor affinity but is relatively less potent in the GPI.
The lower potency of the methyl ester, 5a b, in GPI may
Clear differences in the preferred ring substitution
and linking group (e.g., thiourea) are evident between
the two (benzyl and phenyl) series.
The difference in affinity between the phenyl- and
benzylguanidines, 5h and 4a j, is remarkable. The two
guanidines would be expected to have markedly differ-

Human NK1 Tachykinin Receptor Antagonist
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17 3165
Sch em e 2
F igu r e 1. Correlation between hNK1 receptor binding and
guinea pig ileum bioassay potencies.
not, however, represent a species difference but, rather,
some degree of enzymatic hydrolysis in the organ bath.
Ta ble 5. Effect of Ring Substitution on Physicochemical
Properties of a Series of Phenylureas
The guinea pig was, therefore, chosen as the species
in which to assess anti-hyperalgesic activity in vivo,
since activity in this model should predict efficacy in
humans. The compounds with highest potency in the
human assay in vitro and which retained acceptable
potency in the GPI were therefore tested in a guinea
pig model of persistent inflammatory hyperalgesia.
Compounds which gave significant reversal of hyperal-
gesia 3 h after oral aministration at 30 mg/kg po were
tested further, and dose-response data was generated.
The 2-nitro compound, 5f, gave a good reversal of
hyperalgesia (68.4 ( 1.3%) and had high potency 3 h
after oral administration (ED30 ) 1.1 ( 0.5 mg/kg, n )
3). Its enantiomer, 5k , was inactive in this model, in
agreement with its much lower in vitro potency. For
comparison, at the same time point, subcutaneously
administered morphine had a ED30 ) 0.5 mg/kg and an
efficacy of 79.8 ( 12.2% and orally administered aspirin
had a ED30 ) 71.6 mg/kg and an efficacy of 55.0 ( 6.8%.
compd
no.
chemical shift of urea
NHAr (δ, ppm, CDCl3)
HPLC
tR (min)
2-substituent
5f
2-NO2
9.95
8.82
10.75
6.40
30.91
30.42
26.75
29.56
5a h
5a d
5q
2-CH2OCH3
2-CONH2
2-H
data are suggestive of an H-bonded aromatic urea NH
group in 5f, 5a d , and 5a h , but not 5q (Table 5). Other
analogues with 2-substituents possessing H-bond ac-
ceptor function but lacking overtly polar groups were
therefore synthesized. The 2-methoxymethylurea, 5a h ,
retained high affinity in the human and guinea pig
assays and had comparable anti-hyperalgesic activity
to 5f by oral administration (Table 4). The downfield
shift observed with 5a h (2-methoxymethyl, an electron-
donating group) argues against these effects on chemical
shift being due, rather, to an inductive electron-
withdrawing effect.
Apart from the methyl ester 5a b (which was assumed
to be susceptible to rapid enzymatic hydrolysis in vivo
despite having reasonable potency in GPI), the most
promising compound other than 5f, 5a d , had rather
poor in vivo activity. We assumed this might relate to
the high polarity and H-bonding capacity of the primary
amide since such properties are known to restrict access
across the blood-brain barrier (BBB).24
The postulated ability of, for example, 5f to form an
intramolecular H-bond can be offered as an explanation
for the high analgesic potency and CNS penetration
after oral administration of this compound,25 in com-
parison with other closely related congeners, e.g., the
unsubstituted or carboxamido-substituted phenylurea
compounds, 5q and 5a d . Such an H-bond (shown
schematically in Scheme 2) has the effect of “masking”
the anilide-like NH. Despite the potential for 5a d to
form an intramolecular H-bond, the carboxamide NH2
is still exposed. Likewise, since 5q possesses no H-bond
acceptor functionality in the 2-position, the urea NH is
unmasked. The reversed phase HPLC retention time,
which is qualitatively related to overall hydrophobic-
ity,26 shows that 5f is less polar than 5q and that 5a d
is by far the most polar compound (Table 5).
Br a in Up ta k e of 5f a n d 5a h . The locus of action of
NK1 antagonists as anti-hyperalgesic agents lies in the
dorsal horn of the spinal cord,27 and so CNS penetration
is prerequisite for prospective drug candidates.
The BBB passage of 5f and 5a h was measured by the
brain uptake index (BUI) method in the rat.28 The brain
extraction of the drugs was determined after a rapid
carotid artery injection of [3H]-5f or [3H]-5a h together
with the diffusible reference [14C]butanol.
The brain extraction ratio (BER) of [3H]-5f is plasma
protein concentration dependent; 32.4 ( 2.7% in the
presence and 16.0 ( 5.0% in the absence of plasma
proteins. For comparison, 5a h has a BER of 20.2 (
4.0%, in the absence of plasma proteins.
These values are lower than the extraction of highly
diffusible substances, e.g., diazepam (56.3%29) and [3H]-
propranolol (66.4%30) but are higher than the brain
extraction of lovastatin (7%31), a drug showing a low,
but still significant brain penetration.
These, results thus indicate a relatively good brain
penetration of 5f and 5a h .
5f has fairly good oral bioavailability (25% in the
rat32) and good brain penetration. An observation that
5f is a potent inhibitor of P Glycoprotein33 (a transport
protein which is heavily expressed in membranes of
endothelial cells at the BBB and normally excludes
We have no direct evidence to support the above
hypothesis at present; however, NMR chemical shift

3166 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Walpole et al.
(1H, d, J ) 8 Hz, ArH3), 6.95 (1H, d, J ) 8 Hz, ArH5), 7.20-
7.40 (12H, m, ArH), 8.26 (1H, m, NHCH(Ph)2); FAB MS m/e
460 (MH+). Anal. (C27H29N3O2S) C, H, N.
hydrophobic molecules from the CNS) might explain its
unexpectedly good brain penetration.
In conclusion, 5f is a highly potent antagonist of
human NK1 receptors which has good oral activity in
animal models of persistent inflammatory pain and
penetrates the CNS. 5f is currently under clinical
evaluation as a novel therapy for chronic pain condi-
tions. The detailed pharmacology of this compound in
vitro and in vivo will be reported elesewhere.34
N -(2-Am in ob e n zyl)-a m in ot h ioca r b on yl-(S )-p r olin e
Dip h en ylm eth yla m id e, Tr iflu or oa ceta te, 3g. 3f (1.4 g,
2.95 mmol) was dissolved in MeOH (100 mL), and 10% Pd/C
(100 mg) was added under an inert atmosphere. The atmo-
sphere was replaced with H2, and the mixture was stirred for
24 h, after which time the reaction was complete by TLC. The
reaction mixture was evaporated and purified by flash column
chromatography (CH2Cl2/MeOH 100:1) and then by prepara-
tive reversed phase HPLC (CH3CN/0.1% aqueous TFA gradi-
ent 20-60%) to yield a colorless solid. The solid was recrys-
tallized from hexane/EtOAc and dried to give a colorless solid
(46 mg, 3%): mp 103-108 °C (glass); TLC (cyclohexane/EtOAc
Exp er im en ta l Section
Gen er a l In for m a tion . Routine NMR spectra were re-
corded using a Varian Gemini 200 instrument. All spectra
were recorded using tetramethylsilane (TMS) as an internal
standard, and chemical shifts are reported in parts per million
(δ) downfield from TMS. Coupling constants are reported in
hertz. Mass spectra were recorded in Novartis, Basle, using
a VG 70-SE spectrometer. A Perkin-Elmer 781 spectropho-
tometer was used to record IR spectra, either as liquid films
or as KBr disks. Elemental analyses were performed in
Novartis, Basel, and were within 0.4% of theory. Melting
points were determined using a Reichert hot stage microscope
and are uncorrected. TLC was performed using Merck Kie-
selgel 60 F254 silica plates, and components were visualized
using UV light, iodine vapor, or ammonium molybdate.
Compounds were purified by crystallization, flash column
chromatography using Merck Kieselgel 60 (230-400 mesh),
or preparative HPLC using a Waters Delta Prep 3000 pre-
parative chromatography system equipped with a Dynamax
300A C18 12 µm particle size column (83-243-C), dimensions
41.4 × 250 mm. Solvents were HLPC grade and were used
without further purification. Chemical yields were not opti-
mized.
Ben zyloxyca r bon yl-L-p r olin e Dip h en ylm eth yla m id e.
Benzyloxycarbonyl-L-proline (10 g, 40.2 mmol) was stirred in
CH2Cl2 (50 mL) under a N2 atmosphere. DCCI (9.13 g, 44.2
mmol) in CH2Cl2 (25 mL) and aminodiphenylmethane (7.4 g,
40.2 mmol) in CH2Cl2 (10 mL) were then added, and the
reaction mixture was stirred for 5 h. The solution was filtered
and the solvent evaporated to give a colorless solid which was
purified by flash column chromatography (cyclohexane/EtOAc
2:1). Pure fractions were concentrated to give a colorless solid,
12.5 g (75%). TLC (cyclohexane/EtOAc 2:1) Rf 0.25.
1
1:1) Rf 0.12; H NMR (CDCl3) δ 1.80-2.45 (4H, m, proline â-
and γ-CH2), 3.28-3.48 (2H, m, proline δ-CH2), 3.91 (2H, br,
aniline NH2) 4.57 (1H, ddABX, J AX ) 5.4 Hz, J AB ) 15 Hz,
PhCHAHB-NH), 5.13 (1H, ddABX, J BX ) 5.4 Hz, J BA ) 15 Hz,
PhCHAHB-NH), 5.28 (1H, m, proline R-CH), 5.57 (1H, br m, X
of ABX) 6.18 (1H, d, J ) 6.8 Hz, NHCH(Ph)2), 6.57 (1H, d, J
) 8 Hz, ArH3), 6.68 (1H, m, ArH5), 7.05-7.10 (2H, m, ArH4,6),
7.20-7.40 (10H, m, diphenylmethyl ArH), 7.96 (1H, m, NH-
CH(Ph)2); FAB MS m/e 445, 10% (MH+).
(C28H29N4F3O3S‚1.6H2O) C, H, N.
Anal.
Boc-(R)-p r olin e Dip h en ylm eth yla m id e. Boc-(R)-proline
(4.3 g, 20 mmol) was dissolved in dichloromethane (50 mL).
N-Methylmorpholine (2.03 g, 20 mmol) was added, and the
solution was cooled to ca. -10 °C on a salt-ice bath. Isobutyl
chloroformate (3.41 g, 25 mmol) was then added at such a rate
that the temperature did not rise. Once the addition was
complete the reaction mixture was stirred at -10 °C for 15
min. Aminodiphenylmethane (3.67 g, 20 mmol) was then
added, and the reaction mixture was stirred at room temper-
ature. The reaction was shown to be complete by TLC after 3
h. The solution was washed with 0.1M HCl(aq) (50 mL), water
(50 mL), and finally brine (50 mL). The organic layer was
dried over MgSO4 and filtered, and the solvent was removed
in vacuo. The product was purified by flash column chroma-
tography (cyclohexane/ethyl acetate 4:1) (5.14 g, 68%). TLC
(cyclohexane/ethyl acetate 1:1, Rf ) 0.36).
(R)-P r olin e Dip h en ylm eth yla m id e. Boc-(R)-proline di-
phenylmethylamide (5.00 g, 13.1 mmol) was dissolved in 4 M
HCl/dioxan (40 mL), and the reaction mixture was stirred at
room temperature for 1 h. The solvent was then removed in
vacuo, and the product was dissolved in water (50 mL). Then,
2 M NaOH(aq) (5 mL) was added, and the product was
extracted into ethyl acetate. The organic layer was dried over
MgSO4 and filtered, and the solvent was removed in vacuo to
give (R)-proline diphenylmethylamide (3.46 g, 94%): TLC
(cyclohexane/ethyl acetate 1:1, Rf ) 0.36); 1H NMR (CDCl3) δ
1.71 (2H, m, CH2 pyrrolidine), 1.98 (1H, m, CH2 pyrrolidine),
2.15 (1H, m, NH pyrrolidine), 2.97 (2H, m, NCH2 pyrrolidine),
3.80 (1H, m, CH pyrrolidine), 6.22 (1H, d, J ) 8.5 Hz. Ph2-
CH), 7.15-7.38 (10H, m, ArH), 8.41 (1H, d, J ) 8.5 Hz.
CONH).
L-P r olin e Dip h en ylm eth yla m id e Hyd r och lor id e. Ben-
zyloxycarbonyl-L-proline diphenylmethylamide (15 g, 36.2
mmol) was dissolved in methanol (200 mL), and Pd/C (10%)
was added under a N2 atmosphere. The flask was then filled
with H2, and the mixture was stirred for 24 h, after which
time the reaction was complete by TLC. The catalyst was
removed by filtration and the filtrate concentrated. The
residue was redissolved in diethyl ether/EtOAc 4:1. HCl gas
was introduced into the stirred solution, and the precipitated
salt was collected by filtration and washed with dry ether,
yielding a colorless solid, 8.0 g (70%), which was used without
further purification.
N-(2-Met h oxyb en zyl)-a m in ot h ioca r b on yl-(S)-p r olin e
Dip h en ylm eth yla m id e, 3a . L-Proline diphenylmethylamide
hydrochloride (2.26 g, 7.15 mmol) in dry DMF (10 mL)
containing triethylamine (1.12 mL, 7.9 mmol) was stirred at
room temperature. A solution of 2-methoxybenzyl isothiocy-
anate (1.28 g, 7.15 mmol) in DMF (5 mL) was added and the
solution stirred for 12 h. After removal of solvent in vacuo,
the crude product was purified by flash column chromatogra-
phy (cyclohexane/EtOAc 1:1). Pure fractions were concen-
trated to give a colorless glass which was recrystallized from
ethylene glycol dimethyl ether/water to give colorless
needles: 2.61 g (79.6%); mp 105-106 °C; TLC (cyclohexane/
EtOAc 1:1) Rf 0.22; 1H NMR (CDCl3) δ 1.80-2.45 (4H, m,
proline â- and γ-CH2), 3.28-3.55 (2H, m, proline δ), 3.82 (3H,
s, ArOCH3), 4.86 (1H, ddABX, J AX ) 5.4 Hz, J AB ) 15 Hz,
PhCHAHB-NH), 4.96 (1H, ddABX, J BX ) 5.4 Hz, J BA ) 15 Hz,
PhCHAHB-NH), 5.22 (1H, br d, proline R-CH) 6.10-6.22 (1H,
br, thiourea NH), 6.15 (1H, d, J ) 8.6 Hz, NHCH(Ph)2), 6.88
2-Me t h o x y b e n zy lt h io c a r b a m o y l-(R )-p r o ly l-N -(d i-
p h en ylm eth yl)a m id e, 3j. (R)-Prolyl-N-(diphenylmethyl)-
amide (0.39 g, 1.40 mmol) and 2-methoxybenzyl isothiocyanate
(0.25 g, 1.40 mmol) were dissolved in dioxan (50 mL), and the
reaction mixture was stirred at room temperature overnight.
The reaction was shown to be complete by TLC. The solvent
was removed in vacuo, and the product was purified by
recrystallization (n-hexane/ethyl acetate) to give a white solid,
mp112-113 °C (75%): TLC (cyclohexane/ethyl acetate 1:1, Rf
) 0.17); 1H NMR (CDCl3) δ 1.80-2.47 (4H, m, 2 × CH2
pyrrolidine), 3.41 (2H, m, NCH2 pyrrolidine), 3.85 (3H, s,
ArOCH3), 4.80 (1H, ddABX, J AB ) 15.0 Hz, J AX ) 5.0 Hz,
ArCHAHBNH), 4.95 (1H, ddABX, J AB ) 15.0 Hz, J BX ) 5.0 Hz,
ArCHAHBNH), 5.24 (1H, broad, CH pyrrolidine), 6.15 (2H,
broad, Ph2CH and thiourea NH), 6.91 (2H, m, ArH), 7.15-
7.40 (12H, m, ArH), 8.25 (1H, broad, CONH); FAB MS m/e
460 (MH+). Anal. (C27H29N3O2S) C, H, N.

Human NK1 Tachykinin Receptor Antagonist
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17 3167
N-[N(2)-Cya n o-N(1)-(2-m et h oxyb en zyl)a m id in o]-(S)-
p r olin e Dip h en ylm eth yla m id e, 3q. o-Methoxybenzylamine
(0.65 mL, 5 mmol) was added to a suspension of diphenyl
cyanocarbonimidate (1.19 g, 5 mmol) in 2-propanol (15 mL).
The mixture was stirred at room temperature overnight. A
white precipitate formed. TLC (hexane/EtOAc 2:1) indicated
the complete disappearance of the starting materials and the
formation of a new spot (Rf 0.18). The white precipitate was
filtered and washed with additional 2-propanol. It was identi-
fied to be the newly formed compound (808 mg, 57%).
O-[N(2)-Cyano-N(1)-(2-methoxybenzyl)amidino]phenol (400
mg, 1.4 mmol) thus obtained was treated with proline diphe-
nylmethylamide in 2-propanol (20 mL) under reflux for 5 days.
The mixture was concentrated and the crude product purified
by flash chromatography (hexane/EtOAc 1:7) to yield the title
compound (89 mg, 13%): mp 79-81 °C; TLC (hexane/EtOAc
1:7) Rf 0.5; 1H NMR(CDCl3) δ 1.7-2.26 (4H, m, CH2CH2),
3.28-3.54 (2H, m, NCH2), 3.81 (3H, s, OCH3), 4.62-4.7 (1H,
m, R-H), 4.73 (2H, d, J ) 5.8 Hz, ArCH2N), 5.50 (1H, br t,
NH), 6.13 (1H, d, J ) 7.4 Hz, CHPh2), 6.86-6.97 (2H, m, NH
and ArH), 7.2-7.41 (13H, m, ArH); IR 3269 (br), 2168 (s), 1669
(m), 1577 (s), 1543 (s), 1242 (s) cm-1; MS m/e (FAB) 468 (MH+),
167 (100%). Anal. (C28H29N5O2) C, H, N.
3.48-3.65 (1H, m, NCH2 pyrrolidine), 3.69-3.86 (1H, m, NCH2
pyrrolidine), 4.15-4.60 (4H, NCH2Ph, NHCH2Ar), 4.66-4.80
(1H, m, CH-pyrrolidine), 4.93-5.09 (1H, m, CHBn), 7.01-7.50
(15H, m, ArH), 7.73-7.94 (1H, m, ArH), 8.22-8.34 (1H, m,
ArH); IR(film) 3425-3106 m, br, 3064 m, 1672 s, 1633 s, 1202
s cm-1; MS m/e (FAB) 532 (MH)+ (100%). Anal. (C30H34
ClN5O2‚0.5H2O‚1.2C2HF3O2) C, H, N, F.
-
2-Ch lor ob en zylt h ioca r b a m oyl-(S)-p r olyl-(S)-p h en yl-
a la n yl-1,2,3,4-t et r a h yd r oisoq u in ol-2-yla m id e, 4p . Boc-
(S)-prolyl-(S)-phenylalanyl-1,2,3,4-tetrahydroisoquinol-2-yl-
amide36 was deprotected using the method exemplified in the
formation of (R)-prolyl-N-(diphenylmethyl)amide to give (S)-
phenylalanyl-N-dibenzylamide. The product was not purified
further.
(S)-Prolyl-(S)-phenylalanyl-1,2,3,4-tetrahydroisoquinol-2-
ylamide and 2-chlorobenzylisothiocyanate were coupled using
the method exemplified exemplified for 3a . The product was
purified by recrystallization (n-hexane/ethyl acetate) to give
a white solid, mp 87-89 °C (67%): TLC (cyclohexane/ethyl
acetate 1:1, Rf ) 0.09); 1H NMR (CDCl3) mixture of 2 rotamers
δ 1.95-2.22 (4H, m, 2 × CH2 pyrrolidine), 2.42 (0.3 × 2H, m,
ArCH2CH2N THIQ minor), 2.75 (0.7 × 2H, m, ArCH2CH2N
THIQ major), 3.06 (2H, m, PhCH2CH), 3.23 (0.3 × 2H, m,
ArCH2CH2N THIQ minor), 3.38-3.90 (0.7 × 2H + 2H, m,
ArCH2CH2N THIQ and NCH2 pyrrolidine), 4.05 (0.3H, dAB, J AB
N-(2-Meth oxyben zyloxyca r bon yl)-(S)-p r olin e Dip h en -
ylm eth yla m id e, 3r . A solution of o-methoxybenzyl alcohol
(0.4 mL, 3 mmol) in toluene (15 mL) was treated with phosgene
(1.93 M in toluene, 2.5 mL, 4.3 mmol) at 0 °C. The mixture
was stirred at 0 °C for 0.5 h and then warmed to room
temperature, where it was stirred for a further 2 h. The
mixture was concentrated to yield o-methoxybenzyl chlorofor-
mate.
) 15.0 Hz, ArCHACHBN THIQ minor), 4.52 (0.3H, dAB, J AB
15.0 Hz, ArCHACHBN THIQ minor), 4.58 (0.7H, dAB, J AB
)
)
15.0 Hz, ArCHACHBN THIQ major), 4.74 (0.7H, dAB, J AB ) 15.0
Hz, ArCHACHBN THIQ major), 4.90 (1H, ddABX, J AB ) 15.0
Hz, J AX ) 5.0 Hz, ArCHAHBNHC(S)N), 4.98 (1H, broad, CH
pyrrolidine), 5.02 (1H, ddABX, J AB ) 15.0 Hz, J BX ) 5.0 Hz,
ArCHAHBNHC(S)N), 5.19 (1H, m, PhCH2CH), 6.00 (1H, broad
t, J ) 5 Hz, thiourea NH), 6.85-7.27 (10H, m, ArH and
CONH), 7.37 (2H, m, ArH), 7.52 (1H, m, ArH); FAB MS m/e
561 (MH+). Anal. (C31H33N4O2SCl) C, H, N.
o-Methoxybenzyl chloroformate (1 mmol) thus prepared was
treated with proline diphenylmethylamide (280 mg, 1 mmol)
in CH2Cl2 (10 mL) in the presence of Et3N (0.17 mL, 1.2 mmol)
at 0 °C. The mixture was warmed to room temperature and
stirred for an additional 1.5 h. It was concentrated. The
residue was dissolved in EtOAc (100 mL) and washed with
aqueous NaHCO3 (50 mL) and then with brine (50 mL).
Drying (MgSO4) was followed by flash chromatographic puri-
fication (hexane/EtOAc 2:3). The product fractions were
concentrated and the product recrystallized (hexane/EtOAc)
to yield the title compound (230 mg, 52%): mp 99-101 °C;
2-Ch lor ob en zylt h ioca r b a m oyl-(S)-p r olyl-(S)-p h en yl-
a la n yl-N-[2-(in d ol-3-yl)eth yl]-N-m eth yla m id e, 4t. 2-Chlo-
robenzylthiocarbamoyl-(S)-prolyl-(S)-phenylalanyl-N-[2-(1-Boc-
indol-3-yl)ethyl]-N-methylamide was heated in a flask at ∼160
°C. The reaction was shown to be complete by TLC after 1 h.
The product was purified by flash column chromatography
(cyclohexane/ethyl acetate 1:1) to give a cream-colored solid,
mp 97-99 °C (65%): TLC (cyclohexane/ethyl acetate 1:4, Rf
) 0.38); 1H NMR (CDCl3) δ 1.80-2.22 (4H, m, 2 × CH2
pyrrolidine), 2.60-3.10 (7H, m, CH2CH2NCH3, PhCH2CH and
CH2CH2NCH3), 3.30-3.70 (4H, m, CH2CH2NCH3 and NCH2
pyrrolidine), 4.85-5.20 (4H, m, ArCH2NHC(S)N, CH pyrroli-
dine, and PhCH2CH), 6.00 (1H, m, thiourea NH), 6.90-7.70
(15H, m, ArH and CONH), 8.15 (1H, broad, ArH); FAB MS
m/e 602 (MH+). Anal. (C33H36N5O2SCl) C, H, N.
2-Ch lor ob en zylt h ioca r b a m oyl-(S)-p r olyl-(S)-p h en yl-
a la n yl-N-[2-(in d ol-3-yl)eth yl]a m id e, 4u . 2-Chlorobenzylth-
iocarbamoyl-(S)-prolyl-(S)-phenylalanyl-N-[2-(1-Boc-indol-3-yl-
)ethyl]amide was heated in a flask at ∼160 °C. The reaction
was shown to be complete by TLC after 1 h. The product was
purified by flash column chromatography (cyclohexane/ethyl
acetate 1:1) to give a cream-colored solid, mp 93-95 °C
(43%): TLC (cyclohexane/ethyl acetate 1:4, Rf ) 0.28); 1H NMR
(CDCl3) δ 1.40-2.10 (4H, m, 2 × CH2 pyrrolidine), 2.78-3.33
(6H, m, CH2CH2NH, PhCH2CH and NCH2 pyrrolidine), 3.57
(2H, m, CH2CH2NH), 4.70 (1H, m, PhCH2CH), 4.93 (3H, m,
ArCH2NHC(S)N and CH pyrrolidine), 5.99 (1H, m, thiourea
NH), 6.40 (1H, m, CH2CH2NH), 6.88 (1H, m, indole NH), 7.00-
7.68 (14H, m, ArH and CONH), 8.06 (1H, broad, ArH); FAB
MS m/e 588 (MH+). Anal. (C32H34N5O2SCl) C, H, N.
1
TLC (hexane/EtOAc 1:1) Rf 0.37; H NMR(CDCl3) δ 1.8-2.5
(4H, m, CH2CH2), 3.4-3.6 (2H, m, NCH2), 3.82 (3H, s, OCH3),
4.4-4.5 (1H, m, R-H), 5.05-5.33 (2H, m, ArCH2), 6.20 (1H, d,
J ) 8.4 Hz, CHPh2), 6.97-7.4 (14H, m, ArH), 7.77 (1H, br,
NH); IR 3330 (m), 1711 (s), 1692 (s), 1666 (s), 1539 (s), 1496
(s), 1416 (s), 1353 (s), 1243 (s) cm-1; MS m/e (FAB) 445 (MH+),
167 (100%). Anal. (C27H28N2O4) C, H, N.
[Am in o(2-ch lor o-b e n zyla m in o)m e t h yle n e ]m e t h yl-
su lfon iu m Iod id e. To (2-chlorobenzyl)thiourea35 (476 mg,
2.37 mmol) in ethyl acetate (20 mL) was added methyl iodide
(0.6 mL, 9.5 mmol). The reaction mixture was stirred at room
temperature for 1 h. A white solid was formed which was
isolated by filtration and washed with diethyl ether (50 mL),
to obtain [amino(2-chlorobenzylamino)methylene]methyl-
sulfonium iodide as a white solid (755 mg, 2.20 mmol, 93%):
1H NMR (CDCl3) δ 2.69 (3H, s, SCH3) 4.70 (2H, s, CH2Ar),
4.71 (2H, s, br, NH), 7.36-7.48 (3H, m, ArH), 7.47-7.56 (1H,
m, ArH); IR (KBr) 3202 m, 3049 s, 1633 s, 1589 s cm-1; MS
m/z (CI, CH4) 215 (MH)+ (92%), 125 (100%).
N-(2-Ch lor oben zylam idin o)-(S)-pr olyl-(S)-ph en ylalan yl-
N-ben zylm eth yla m id e, 4l. To [amino(2-chlorobenzylamino)-
methylene]methylsulfonium iodide (342 mg, 2.14 mmol) in
ethanol (10 mL) was added (S)-prolyl-(S)-phenylalanyl-N-
benzyl-N-methylamide. The reaction mixture was stirred at
room temperature for 16 days. Although the reaction had not
gone to completion, the reaction mixture was concentrated in
vacuo and purified by preparative HPLC to afford N-(2-
chlorobenzylamidino)-(S)-prolyl-(S)-phenylalanyl-N-benzylm-
ethylamide as a white solid (55 mg, 0.1 mmol, 5%): mp 68-
71 °C; 1H NMR (CDCl3) mixture of two rotamers δ 1.78-2.33
(4H, m, CH2 pyrrolidine), 2.72 (0.7 × 3H, s, NCH3 major), 2.81
(0.3 × 3H, s, NCH3 minor), 2.96-3.10 (2H, m, CHCH2Ph),
2-Ch lor ob e n zylca r b a m oyl-(S )-p r olyl-(S )-3-(2-n a p h -
th yl)a la n yl-N-ben zyl-N-m eth yla m id e, 4a h . To (S)-prolyl-
(S)-3-(2-naphthyl)alanyl-N-benzyl-N-methylamide (168 mg, 0.4
mmol) in dioxan (3 mL) was added crude 2-chlorobenzyl
isocyanate37 (354 mg, 1 mmol). The reaction mixture was
stirred at room temperature for 3 h. The reaction mixture was
concentrated in vacuo and purified by flash column chroma-
tography (hexane/EtOAc 1:4) to afford 145 mg (0.24 mmol,
62%): mp 69-73 °C; 1H NMR (CDCl3) mixture of two rotamers

3168 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Walpole et al.
δ 1.63-1.94 (3H, m, CH2 pyrrolidine), 2.08-2.25 (1H, m, CH2
pyrrolidine), 2.72 (0.6 × 3H, s, NCH3 major), 2.90 (0.4 × 3H,
s, NCH3 minor), 3.00-3.31 (4H, m, CH2Nap, NCH2 pyrroli-
dine), 4.28 (0.6 × 1H,, dAB, J AB ) 14 Hz, NCHAHBPh major),
4.25-4.56 (2.8 H, m, ArCH2NH, NCHAHBPh minor), 4.76 (0.6
× 1H, dAB, J AB ) 14 Hz, NCHAHBPh major), 4.82-4.98 (1H,
m, pyrrolidine), 5.16-5.32 (1H, m, CHCH2Nap), 6.92-7.05
(2H, m, ArH), 7.08-7.52 (11H, m, ArH), 7.54-7.83 (5H, m,
ArH); IR (KBr) 3630-3170s, br, 1636 s, 1533 m cm-1; MS m/e
(FAB) 583 (MH)+ (53%), 265 (93%), 122 (100%). Anal.
(C34H35N4O3Cl‚0.25H2O) C, H, N.
N-(N,N′-Di-ter t-bu toxycar bon ylam idin o)-(S)-pr olyl-(S)-
3-(2-n a p h th yl)a la n yl-N-ben zylm eth yla m id e. To (S)-pro-
lyl-(S)-3-(2-naphthyl)alanyl-N-benzyl-N-methylamide (207 mg,
0.5 mmol), 1,3-bis-tert-butoxycarbonylthiourea (138m mg, 0.5
mmol), and Et3N (0.17 mL, 1.25 mmol) in DMF (2 mL) cooled
in ice was added HgCl2 (150 mg, 0.55 mmol). The reaction
mixture was stirred in ice for 2 h. The reaction mixture was
poured into water and extracted with EtOAc (3 × 50 mL). The
combined organic extracts were dried (Na2SO4) and filtered
through silica. The colorless filtrate was concentrated to afford
a white solid (348 mg, 0.5 mmol, 100%): 1H NMR (CDCl3)
mixture of two rotamers δ 1.46 (0.3 × 18H, s, t-Bu major), 1.51
(0.7 × 18H, s, t-Bu minor), 1.68-2.01 (4H, m, CH2 pyrrolidine),
2.64 (0.7 × 3H, s, NCH3 major), 2.85 (0.3 × 3H, s, NCH3
minor), 3.17-3.36 (2H, m, NCH2 pyrrolidine), 3.36-3.63 (2H,
m, CH2Nap), 4.20-4.37 (1H, m, CH pyrrolidine), 4.55-4.81
(2H, m, CH2Ph), 5.12-5.38 (1H, m, CHCH2Nap), 6.83-6.96
(2H, m, ArH), 7.03-7.19 (3H, m, ArH), 7.46-7.52 (3H, m,
ArH), 7.52-7.65 (1H, m, ArH), 7.65-7.84 (4H, m), 10.12-10.28
(1H, s, NH); IR (KBr) 3350-3200 s, br, 2978 m, 2931 s, 1749
s, 1634 s, 1605 s cm-1; MS m/e (FAB) 658 (MH)+ (32%), 458
(100%).
MS m/e (FAB) 582 (MH)+ (100%). Anal. (C34H36N5O2‚
1.0H2O‚1.3C2HF3O2) C, H, N, F.
2-Ch lor op h en ylt h ioca r b a m oyl-(S)-p r olyl-(S)-p h en yl-
a la n yl-N-ben zylm eth yla m id e, 5a . H-Pro-Phe-benzylmethy-
lamide36 was treated with 2-chlorophenyl isothiocyanate as
described above for 3a . The title compound was obtained in
63% yield after crystallization (hexane/EtOAc): TLC (CH2Cl2/
MeOH 14:1) Rf 0.76; 1H NMR (CDCl3) mixture of two rotamers
δ 2.05-2.27 (4H, m, CH2CH2), 2.67 (0.7 × 3H, s, NCH3, major),
2.87 (0.3 × 3H, s, NCH3, minor), 3.07 (0.3 × 2H, d, J ) 9.5
Hz, PhCH2), 3.09 (0.7 × 2H, d, J ) 8.0 Hz, PhCH2), 3.65-3.83
(2H, m, NCH2), 4.30 (0.3 × 1H, dAB, J ) 17.4 Hz, PhCHAHBN,
minor), 4.39 (0.7 × 1H, dAB, J ) 14.7 Hz, PhCHAHBN, major),
4.60 (1H, dAB, J ) 14.7 Hz, PhCHAHBN, both), 5.02-5.27 (2H,
m, R-H, R-H), 6.98-7.52 (14H, m, ArH, NH, NH), 8.23 (1H, d,
J ) 9 Hz, ArH); IR 3327 (m), 3239 (br), 1629 (s), 1520 (s), 1383
(m), 1344 (m) cm-1; MS m/e (FAB) 535 (MH+), 269 (100%).
Anal. (C29H31N4O2SCl) C, H, N.
2-Nitr op h en ylca r ba m oyl-(S)-p r olyl-(S)-3-(2-n a p h th yl)-
a la n yl-N-ben zyl-N-m eth yla m id e, 5f. (S)-Prolyl-(S)-3-(2-
naphthyl)alanyl-N-benzyl-N-methylamide38 was treated with
2-nitrophenyl isocyanate as described for 3a . Flash chromato-
graphic purification (ethyl acetate/hexane 2:1) yielded the title
compound in 83% yield: TLC (EtOAc/hexane 1:1) Rf 0.1; mp
79-82 °C; 1H NMR (CDCl3) mixture of two rotamers δ 1.71-
2.05 (3H, m, CH2 pyrrolidine), 2.15-2.33 (1H, m, CH2 pyrro-
lidine), 2.78 (0.6 × 3H, s, NCH3 major), 2.94 (0.4 × 3H, s, NCH3
minor), 3.14-3.41 (4H, m, CH2Nap, NCH2 pyrrolidine), 4.32-
4.75 (3H, m, NCH2Ph. CH pyrrolidine), 5.36 (1H, q, J ) 7.55
Hz, CHCH2Nap), 7.05-7.74 (15H, m, ArH), 8.22 (1H, d, J )
8.5 Hz, ArH), 8.75 (1H, d, J ) 8.79 Hz, ArH), 9.90 (0.4 × 1H,
s, NH minor), 10.00 (0.6 × 1H, s, NH minor); IR (KBr) 3600-
3190 w, br, 1681 s, 1645 s, 1610 m, 1586 s, 1501 s, 1452 m,
1437 s, 1355 m cm-1; MS m/e (FAB) 580 (MH)+ (79%), 459
(8%), 416 (24%), 319 (24%), 262 (80%), 234 (91%), 170 (100%);
N-(N,N′-Di-ter t-b u t oxyca r b on yla m id in o-N-[2-ch lor o-
b en zyl])-(S)-p r olyl-(S)-3-(2-n a p h t h yl)a la n yl-N-b en zyl-
m eth yla m id e. To N-(N,N′-di-tert-butoxycarbonylamidino)-
(S)-prolyl-(S)-3-(2-naphthyl)alanyl-N-benzylmethylamide (165
mg, 0.25 mmol) dissolved in DMF (5 mL) was added NaH (12
mg, 0.3 mmol). The reaction was stirred at room temperature
for 5 min before 2-chlorobenzyl bromide (37 mL, 0.28 mmol)
was added. The reaction mixture was stirred at room tem-
perature for 2 h. The reaction mixture was poured into water
and extracted with EtOAc (3 × 50 mL). The combined organic
extracts were washed with brine, dried (MgSO4), and concen-
trated. The residue was purified by flash column chromatog-
raphy (hexane/EtOAc 1:2) to afford N-(N,N′-di-tert-butoxy-
carbonylamidino-N-[2-chlorobenzyl])-(S)-prolyl-(S)-3-(2-naph-
thyl)alanyl-N-benzylmethylamide (98 mg, 50%): 1H NMR-
(CDCl3) mixture of two rotamers δ 1.29-1.63 (18H, m, t-Bu),
1.63-1.97 (4H, m, CH2 pyrrolidine), 2.67 (0.3 × 3H, s, NCH3
minor), 2.82 (0.7 × 3H, s, NCH3 major), 2.97-3.48 (4H, m,
NCH2 pyrrolidine, CH2Nap), 4.15-4.37 (4H, m, NHCH2Ar,
NCH2Ph), 4.42-4.69 (1H, m, CH pyrrolidine), 4.88-5.29 (1H,
m, CHCH2Nap), 6.66-7.15 (6H, m, ArH), 7.15-7.31 (2H, m,
ArH), 7.31-7.56 (5H, m, ArH), 7.56-7.83 (4H, m, ArH); IR-
(KBr) 2977 m, 1722 s, 1680 s, 1653 s, 1600 s cm-1; MS m/e
(FAB) 782 (MH)+ (98%), 582 (100%).
23
[R]D -60.6° (c 0.53, CHCl3). Anal. (C33H33N5O5‚0.5H2O) C,
H, N.
N-Boc-N′-(2-n itr op h en yl)th iou r ea . To a solution of 2-ni-
trophenylthiourea (0.59 g, 3 mmol) in dry THF (60 mL) was
added NaH (180 mg, 4.5 mmol), causing a red coloration. The
mixture was cooled on ice, and di-tert-butyl dicarbonate (0.72
g, 3.3 mmol) in THF (10 mL) was added. After 12 h of stirring,
the reaction mixture was evaporated in vacuo and then
redissolved in EtOAc (100 mL). Then 2 M NaHCO3 (10 mL)
was added and the red aqueous layer removed. The aqueous
layer was acidified to pH 4 with 10% citric acid and extracted
with EtOAc (50 mL). The orange organic phase was separated,
washed with brine, and dried over MgSO4. The crude product
was purified by flash column chromatography (hexane/EtOAc
5:1) to give a yellow solid, 340 mg (38%): TLC (hexane/EtOAc
1:1) Rf 0.8; 1H NMR (CDCl3) δ 1.54 (9H, s, Boc), 7.37 (1H, t, J
) 8.2 Hz, ArH), 7.65 (1H, t, J ) 8.2 Hz, ArH), 8.08 (2H, d, J
) 8.2 Hz, ArH and NH), 8.43 (1H, d, J ) 8.2 Hz, ArH), 12.50
(1H, br s, NH); IR 3178 (s), 1722 (s), 1609 (m), 1584 (m), 1552
(s), 1520 (s), 1369 (s), 1339 (s) cm-1; MS m/e (FAB) 298 (MH+),
242 (100%).
N,N′-Bisbu tyloxyca r bon yl-N-(2-n itr op h en yla m id in o)-
(S )-p r olyl-(S )-3-(2-n a p h t h yl)a la n yl-N -b e n zylm e t h yl-
am ide. N-Boc-N′-(2-nitrophenyl)thiourea (130 mg, 0.44 mmol),
triethylamine (0.15 mL, 1 mmol), and (S)-prolyl-(S)-3-(2-
naphthyl)alanyl-N-benzyl-N-methylamide (183 mg, 0.44 mmol)
in DMF (5 mL) was cooled in an ice bath. Mercury(II) chloride
(130 mg, 0.48 mmol) was added and the mixture stirred for 1
h. After this time the reaction mixture was diluted with
EtOAc and washed with water. The organic phase was
separated, washed with brine, dried over Na2SO4, and then
filtered through a pad of Celite. Evaporation yielded a yellow
solid which was purified by flash column chromatography
(hexane/EtOAc 1:1) to give the title compound (269 mg, 90%):
N-Am idin o-N-[2-ch lor oben zyl]-(S)-pr olyl-(S)-3-(2-n aph -
th yl)a la n yl-N-ben zylm eth yla m id e, 4a j. N-(N,N′-di-tert-
butoxycarbonylamidino-N-[2-chlorobenzyl])-(S)-prolyl-(S)-3-(2-
naphthyl)alanyl-N-benzylmethylamide (181 mg, 0.23 mmol)
was treated with a mixture of trifluoroacetic acid (2 mL) and
CH2Cl2 (2 mL). The reaction mixture was stirred at room
temperature for 4 h. The reaction mixture was concentrated
and purified by preparative HPLC (gradient run (90:10-0:100
H2O:acetonitrile) to afford a cream-colored foam (63 mg, 0.1
1
mmol, 47%): mp 73-76 °C; H NMR (CDCl3) mixture of two
rotamers δ 1.84-2.32 (4H, m, CH2 pyrrolidine), 2.72 (0.7 ×
3H, s, NCH3 major), 2.82 (0.3 × 3H, s, NCH3 minor), 3.03-
3.25 (2H, m, CH2Nap), 3.38-3.81 (2H, m, NCH2 pyrrolidine),
4.20-4.81 (5H, m, NHCH2Ar, CH pyrrolidine, NCH2Ph), 5.02-
5.25 (1H, m, CHCH2Nap), 6.77-7.82 (18H, m, ArH, NH), 8.30-
1
TLC (hexane/EtOAc 1:1) Rf 0.3; H NMR (CDCl3) mixture of
two rotamers δ 1.34 and 1.43 (9H, s, Boc), 1.6-2.2 (4H, m,
CH2CH2), 2.85 and 2.9 (3H, s, NCH3), 3.2-3.7 (4H, m, ArCH2,
NCH2), 4.3-4.7 (3H, m, PhCH2 and R-H), 5.2 (1H, m, R-H),
6.9-7.2 (8H, m, ArH, NH), 7.3-7.5 (4H, m, ArH), 7.6-7.9 (6H,
8.45 (1H, ArH); IR (KBr) 3510-3100 w, br, 1663 s, 1632 s cm-1
;

Human NK1 Tachykinin Receptor Antagonist
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17 3169
m, ArH, NH); IR 3350 (br), 2978 (w), 1717 (m), 1643 (s), 1599
(s), 1520 (m), 1496 (m), 1453 (m), 1417 (m) cm-1; MS m/e (FAB)
679 (MH+), 261 (100%).
(4H, m, ArH), 7.33-7.56 (4H, m, ArH), 7.56-8.09 (4H, m,
ArH), 7.97-8.09 (1H, m, ArH), 8.21-8.33 (1H, m, ArH), 8.48-
8.58 (1H, m, ArH); IR (KBr) 3293 w, 2928 w, 1645 s, 1593 w,
1533 s, 1482 m, 1420 s cm-1; MS m/e (FAB) 536 (MH)+ (100%).
Anal. (C32H33N5O3‚HCl‚0.25H2O) C, H, N, Cl.
N -(2-Nit r op h e n yla m id in o)-(S )-p r olyl-(S )-3-(2-n a p h -
th yl)a la n yl-N-ben zylm eth yla m id e, 5h . To N,N′-bisbutyl-
oxycarbonyl-N-(2-nitrophenylamidino)-(S)-prolyl-(S)-3-(2-naph-
thyl)alanyl-N-benzylmethylamide (293 mg, 0.43 mmol) in CH2-
Cl2 (4 mL) was added TFA (2 mL). The reaction mixture was
stirred at room temperature for 10 min. The reaction mixture
was concentrated in vacuo. The pale yellow oil was partitioned
between ethyl acetate (50 mL) and saturated NaHCO3 (30 mL)
The organic phase was removed, and the aqueous phase was
reextracted twice with ethyl acetate. The combined organic
fractions were dried (MgSO4) and concentrated. The residue
was purified by flash column chromatography (5% methanol
in CH2Cl2), to afford the title compound as an orange foam
2-Ca r b oxyp h en ylca r b a m oyl-(S)-p r olyl-(S)-n a p h t h yl-
a la n yl-N-ben zyl-N-m eth yla m id e, 5a c. 2-Methoxycarbon-
ylphenylcarbamoyl-(S)-prolyl-(S)-naphthylalanyl-N-benzyl-N-
methylamide (250 mg, 0.44 mmol) was stirred in MeOH (60
mL) while an aqueous solution of sodium hydroxide (4.4 mL
of 5 M, 21.9 mmol) was added dropwise and thereafter for 12
h. After this time complete consumption of starting material
was demonstrated by TLC. The solution was evaporated in
vacuo and then dissolved in a minimum of water. The solution
was acidified to pH 1, causing precipitation of a white solid
which was collected by filtration and air-dried to give a
colorless solid, 136 mg (56%): mp 128-129 °C; 1H NMR
(CDCl3) mixture of two rotamers δ 1.25-2.28 (4H, m, proline
âγ-CH2), 2.86 (0.67 × 3H, s, NCH3 major), 2.97 (0.33 × 3H, s,
NCH3 minor), 3.08-3.46 (4H, m, naphthylAla-CH2CH, proline
δ), 4.22 (0.66 × 1H, dAB, J ) 14.5 Hz, ArCHAHBNCH3 major),
4.44-4.66 (1.33 × 1H, ArCHAHBNCH3 minor, proline R-CH),
4.92 (0.66 × 1H, m, dAB, J ) 14.5 Hz, ArCHAHBNCH3 major),
5.46 (1H, br m, naphthylalanine R-CH), 6.62-7.85 (15H, m,
ArH), 8.30 (0.33 × 1H, br d, CONH minor), 8.38 8.30 (0.66 ×
1H, br d, CONH major), 8.57 (1H, d, J ) 8 Hz, ArH3), 10.90-
11.00 (1H, br s, urea NH); FABMS m/e 579, 45% (MH+). Anal.
(C34H34N4O5‚0.2H2O) C, H, N.
2-Ca r boxa m id op h en ylca r ba m oyl-(S)-p r olyl-(S)-n a p h -
th yla la n yl-N-ben zyl-N-m eth yla m id e, 5a d . 5a c (500 mg,
0.86 mmol) was stirred in dry EtOAc (25 mL), under N2, at
-15 °C, and N-methylmorpholine (NMM, 104 µL, 0.95 mmol)
was added. A solution of isobutyl chloroformate (124 µL, 0.95
mmol) in dry EtOAc (25 mL) was added dropwise, such that
the temperature did not exceed -10 °C. The reaction mixture
was stirred for 15 min before dry ammonia gas was slowly
bubbled through the solution with efficient stirring for 30 min.
The reaction mixture was evaporated and the product purified
by flash column chromatography (cyclohexane/EtOAc 1:4 to
elute high Rf material, then changing to EtOAc/MeOH 1:1 to
elute the product). Concentration of the pure fractions and
then crystallization from cyclohexane/EtOAc gave a colorless
solid, 270 mg (54%): mp 109-115 °C; TLC (silica, cyclohexane/
EtOAc 1:4) Rf 0.10; 1H NMR (CDCl3) mixture of two rotamers
δ 1.60-2.29 (4H, m, proline âγ-CH2), 2.72 (0.67 × 3H, s, NCH3
major), 2.91 (0.33 × 3H, s, NCH3 minor), 3.08-3.55 (4H, m,
naphthylala-CH2CH, proline δ), 4.30 (0.66 × 1H, dAB, J ) 14.7
Hz, ArCHAHBNCH3 major), 4.36-4.61 (1.33 × 2H, proline
R-CH, ArCHAHBNCH3 minor), 4.71 (0.66 × 1H, dAB, J ) 14.7
Hz, ArCHAHBNCH3 major), 5.41 (1H, br m, naphthylalanine
R-CH), 6.00-6.20 (1H, br, CONH), 6.90-7.86 (16H, m, ArH),
8.54 (1H, d, J ) 8 Hz, ArH3), 10.11 (1H, s, CONH), 8.38 8.30
(0.66 × 1H, br d, CONH major), 8.57 (1H, d, J ) 8 Hz, ArH3),
10.78 (0.33 × 1H, br s, urea NH minor), 10.86 (0.66 × 1H, br
s, urea NH major); FABMS m/e 578, 10% (MH+). Anal.
(C34H35N5O4‚0.75H2O) C, H, N.
1
(198 mg, 0.34 mmol, 80%): mp 64-70 °C; H NMR (CDCl3)
mixture of two rotamers δ 1.62-2.30 (4H, m, CH2 pyrrolidine),
2.78 (0.6 × 3H, s, NCH3 major), 2.87 (0.4 × 3H, s, NCH3
minor), 3.18-3.45 (4H, m, CH2Nap, NCH2 pyrrolidine), 4.21-
4.73 (5H, m, NCH2Ph, CH pyrrolidine, 2 × NH), 5.22 (1H, q,
J ) 7.3 Hz, CHCH2Nap), 6.95-7.13 (7H, m, ArH), 7.32-7.48
(4H, m, ArH), 7.64-7.93 (6H, m, ArH); IR (KBr) 3628-3148
m, br, 1632 s, 1583 s, 1514 m, 1450 m, 1351 m cm-1; MS m/e
(FAB) 579 (MH)+ (45%), 261 (100%). Anal. (C33H34N6O4‚
0.5H2O) C, H, N.
N-(N-2-Nitr op h en yl-N′-cya n oa m id in o)-(S)-p r olyl-(S)-3-
(2-n a p h t h yl)a la n yl-N-b en zylm et h yla m id e, 5j. To cyan-
amide (44 mg, 1 mmol) in DMF (5 mL) was added potassium
tert-butoxide (1 mL, 1 M in THF, 1 mmol). A white precipitate
formed. The reaction mixture was stirred at room temperature
for 20 min. 2-Nitrophenyl isothiocyanate (180 mg, 1 mmol)
was added as a solid, and the reaction mixture was stirred at
room temperature for 10 min. The solution became dark
orange. The reaction mixture was cooled in ice, and triethy-
lamine (0.42 mL, 3 mmol) was added followed by (S)-prolyl-
(S)-3-(2-naphthyl)alanyl-N-benzyl-N-methylamide (415 mg, 1
mmol) and HgCl2 (300 mg, 1.1 mmol). After 3 h the reaction
mixture was diluted with ethyl acetate (50 mL) and filtered
through a pad of Celite. The filtrate was washed with water.
The aqueous extract was reextracted with ethyl acetate (2 ×
50 mL). The combined organic extracts were dried (MgSO4)
and concentrated in vacuo. The residue was purified by flash
column chromatography (ethyl acetate/hexane, 4:1) to afford
the title compound as a yellow foam (259 mg, 0.43 mmol,
43%): mp 92-96 °C; 1H NMR (CDCl3) mixture of two rotamers
δ 1.86-2.37 (4H, m, CH2 pyrrolidine), 2.68 (0.7 × 3H, s, NCH3
major), 2.88 (0.3 × 3H, s, NCH3 minor), 3.13-3.29 (2H, m,
CH2Nap), 3.49-3.71 (2H, m, NCH2 pyrrolidine), 4.14 (0.3 ×
1H, dAB, J AB ) 15.82 Hz, NCHAHBPh minor), 4.37 (0.7 × 1H,
dAB, J AB ) 14.57 Hz, NCHAHBPh major), 4.43 (0.3 × 1H, dAB,
J AB ) 15.78 Hz, NCHAHBPh minor), 4.56-4.75 (1H, m, CH
pyrrolidine), 4.66 (0.7 × 1H, dAB, J AB ) 14.49 Hz, NCHAHBPh
major), 5.21-5.38 (1H, m, CHCH2Nap), 6.88-7.50 (10H, m,
ArH), 7.51-7.82 (6H, m, ArH), 8.14 (1H, d, J ) 8.16 Hz, ArH),
9.38 (0.3 × 1H, s, NH minor), 9.41 (0.7 × 1H, s, NH major);
IR (KBr) 3610-3130 w, br, 2177 m, 1647 m, 1578 s, 1496 m
cm-1; MS m/z (FAB) 604 (MH)+ (100%), 319 (24%), 286 (32%).
Anal. (C34H33N7O4‚1.5H2O) C, H, N.
3-Meth oxyca r bon ylp h en yl Isocya n a te. Methyl 3-ami-
nobenzoate (1.0 g, 0.0066 mol) was dissolved in toluene (20
mL), containing phosgene (0.0265 mol), and stirred at 80 °C
for 3 h. The solvent was removed in vacuo, and the product
was used without characterization or purification.
3-P yr idylcar bam oyl-(S)-pr olyl-(S)-3-(2-n aph th yl)alan yl-
N-ben zylm eth yla m id e, 5r . To (S)-prolyl-(S)-3-(2-naphthyl)-
alanyl-N-benzyl-N-methylamide (645 mg, 1.55 mmol) in tolu-
ene (10 mL) was added 3-pyridyl azide (285 mg, 1.55 mmol).
The reaction mixture was heated to 90 °C for 5 h and then
stirred at room temperature overnight. The reaction mixture
was cooled and concentrated in vacuo. The mixture was
purified by flash column chromatography (MeOH/CH2Cl2, 1:10)
to afford a white foam (173 mg, 0.32 mmol, 21%): mp 84-87
°C; 1H NMR (CDCl3) mixture of two rotamers δ 1.69-2.27 (4H,
m, CH2 pyrrolidine), 2.78 (0.7 × 3H, s, NCH3 major), 2.93 (0.3
× 3H, s, NCH3 minor), 3.03-3.52 (2H, m, CH2Nap), 4.30-4.61
3-Met h oxyca r b on ylp h en ylca r b a m oyl-(S)-p r olyl-(S)-
n a p h th yla la n yl-N-ben zyl-N-m eth yla m id e. The title com-
pound was prepared from (S)-prolyl-(S)-phenylalanyl-N-benzyl-
N-methylamide and 3-methoxycarbonylphenyl isocyanate, using
the method exemplified in the formation of 3a . The product
was purified by flash column chromatography (cyclohexane/
EtOAc 1:2) to give a colorless glass, yield 50%: TLC (cyclo-
1
hexane/EtOAc 1:2) Rf 0.25; H NMR (CDCl3) mixture of two
rotamers δ 1.75-2.20 (4H, m, 2 × CH2 pyrrolidine), 2.79 (0.67
× 3H, s, NCH3 major), 2.92 (0.33 × 3H, s, NCH3 minor), 3.0-
3.4 (4H, m, ArCH2CH + CH2N pyrrolidine), 3.88 (3H, s, ArCO2-
CH3), 4.34 (0.67 × 1H, dAB, J AB ) 14.5 Hz, ArCHAHBNCH3
major), 4.48 (1.66H, m, ArCH2NCH3 minor + CH pyrrolidine),
(3.3H, m, NCH2 pyrrolidine, NCHAHBPh), 4.70 (0.7 × 1H, dAB
,
J AB ) 15 Hz, NCHAHBPh major), 5.18-5.35 (2H, m, CH
pyrrolidine, CHCH2Nap), 6.95-7.12 (3H, m, ArH), 7.12-7.33

3170 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Walpole et al.
4.73 (0.67 × 1H, dAB, J AB ) 14.6 Hz, ArCHAHBNCH3 major),
5.26 (1H, m, ArCH2CH), 7.00-8.00 (18H, m, 17 × ArH +
CONH).
1H, dAB, J ) 15.1 Hz, ArCHAHBNCH3 major), 5.29 (1H, br m,
naphthylalanine R-CH), 6.90-7.82 (16H, m, 15 × ArH, CONH),
8.26 (1H, d, J ) 8 Hz, ArH3), 8,79 (0.33 × 1H, br s, urea NH
minor); 8.85 (0.66 × 1H, br s, urea NH major); FABMS m/e
607, 70% (MH+). Anal. (C36H39N5O4‚0.9H2O) C, H, N.
3-Ca r b oxyp h en ylca r b a m oyl-(S)-p r olyl-(S)-n a p h t h yl-
a la n yl-N-ben zyl-N-m eth yla m id e. The title compound was
prepared from 3-methoxycarbonylphenylcarbamoyl-(S)-prolyl-
(S)-naphthylalanyl-N-benzyl-N-methylamide, in the method
exemplified in the formation of 2-carboxyphenylcarbamoyl-(S)-
prolyl-(S)-naphthylalanyl-N-benzyl-N-methylamide, to yield a
colorless foam (76%): TLC (silica, CH2Cl2/MeOH 10:1) Rf 0.45;
1H NMR (CDCl3) mixture of two rotamers δ 1.60-2.10 (4H,
m, 2 × CH2 pyrrolidine), 2.80 (0.67 × 3H, s, NCH3 major), 2.90
(0.33 × 3H, s, NCH3 minor), 3.30 (2H, m, ArCH2CH), 3.62 (2H,
m, CH2N pyrrolidine), 4.25 (0.67 × 1H, dAB, J AB ) 14.5 Hz,
ArCHAHBNCH3 major), 4.36 (0.33 × 1H, dAB, J AB ) 16.6 Hz,
ArCHAHBNCH3 minor), 4.58 (0.66H, m, CH pyrollidine), 4.71
(0.67 × 1H, dAB, J AB ) 14.6 Hz, ArCHAHBNCH3 major), 4.73
(0.33 × 1H, dAB, J AB ) 16.6 Hz, ArCHAHBNCH3 minor), 5.40
(1H, m, ArCH2CH), 7.00-7.85 (17H, m, 14 × ArH, NH, CO2H
+ CONH), 8.07 (1H, m, ArH), 8.19 (1H, d, J ) 9.7 Hz, ArH).
3-Ca r boxa m id op h en ylca r ba m oyl-(S)-p r olyl-(S)-n a p h -
th yla la n yl-N-ben zyl-N-m eth yla m id e, 5a e. The title com-
pound was prepared from 3-carboxyphenylcarbamoyl-(S)-
prolyl-(S)-naphthylalanyl-N-benzyl-N-methylamide, using the
method exemplified in the formation of the 2-carboxamidophe-
nyl analogue 5a d . The product was purified by crystallization
from EtOAc to give a colorless crystalline solid, yield 42%: mp
140-141 °C; TLC (silica, CH2Cl2/MeOH 10:1) Rf 0.75; 1H NMR
(CDCl3) mixture of two rotamers δ 1.70-2.20 (4H, m, 2 × CH2
pyrrolidine), 2.76 (0.67 × 3H, s, NCH3 major), 2.88 (0.33 ×
3H, s, NCH3 minor), 3.1-3.4 (4H, m, ArCH2CH + CH2N
pyrrolidine), 4.30 (0.67 × 1H, dAB, J AB ) 15.2 Hz, ArCHAHB-
NCH3 major), 4.46 (1.66H, m, CH pyrrolidine + ArCH2NCH3
minor), 4.67 (0.67 × 1H, dAB, J AB ) 14.0 Hz, ArCHAHBNCH3
major), 5.25 (1H, m, ArCH2CH), 7.03 (2H, m, ArH), 7.15-7.80
(16H, m, 14 × ArH + 2 × NH); FABMS m/e 578 (MH+). Anal.
(C34H35N5O4‚0.5H2O) C, H, N.
2-Meth oxym eth ylph en ylcar bam oyl-(S)-pr olyl-(S)-n aph -
th yla la n yl-N-ben zyl-N-m eth yla m id e, 5a h . The title com-
pound was prepared from (S)-prolyl-(S)-phenylalanyl-N-benzyl-
N-methylamide and 2-methoxymethylphenyl isocyanate,39 using
the method exemplified in the formation of 3a . The product
was purified by flash column chromatography (cyclohexane/
EtOAc 1:2) as a colorless glass, yield 71%: mp 62-66 °C; TLC
(silica, cyclohexane/EtOAc 1:2) Rf 0.26; 1H NMR (CDCl3)
mixture of two rotamers δ 1.60-2.30 (4H, m, proline âγ-CH2),
2.71 (0.67 × 3H, s, NCH3 major), 2.89 (0.33 × 3H, s, NCH3
minor), 3.00-3.35 (7H, m, naphthylala-CH2CH, proline δ,
ArCH2OCH3), 4.29 (0.66 × 1H, dAB, J ) 13.5 Hz, ArCHAHB-
NCH3 major), 4.38-4.59 (0.33 × 2H, m, ArCHAHBNCH3 minor,
3H, ArCH2OCH3, proline R-CH), 4.70 (0.66 × 1H, dAB, J ) 13.5
Hz, ArCHAHBNCH3 major), 5.29 (1H, br m, naphthylalanine
R-CH), 6.90-7.80 (16H, m, 15 × ArH, CONH), 8.26 (1H, d, J
) 8 Hz, ArH3), 8.79 (0.33 × 1H, br s, urea NH minor), 8.85
(0.66 × 1H, br s, urea NH major); FABMS m/e 579, 100%
(MH+). Anal. (C35H38N4O4) C, H, N.
ter t-Bu tyl(2-isocyan atoben zyloxy)dim eth ylsilan e. tert-
Butyl(2-aminobenzyloxy)dimethylsilane40 (400 mg, 0.0017 mol),
was dissolved in toluene (5 mL), and 20% phosgene in toluene
(3.5 mL) was added. The solution was stirred at 60 °C for 1
h, and was complete by TLC. The toluene was removed in
vacuo, and the isocyanate was used without purification or
characterization.
2-(t er t -B u t y ld i m e t h y ls i la n y lo x y m e t h y l)p h e n y l-
ca r ba m oyl-(S)-p r olyl-(S)-3-(2-n a p h th yl)a la n yl-N-ben zyl-
N-m eth yla m id e. The title compound was prepared from (S)-
prolyl-(S)-N-methyl-3-(2-naphthyl)alanyl-N-benzyl-N-methy-
lamide and tert-butyl(2-isocyanatobenzyloxy)dimethylsilane,
using the method exemplified in the formation of 3a . The
product was purified by flash column chromatography (cyclo-
hexane/EtOAc 1:1) to give a colorless amorphous solid, yield
42%: TLC (cyclohexane/EtOAc 1:1) Rf 0.30; 1H NMR (DMSO-
d6) mixture of two rotamers δ 0.07 (3H, s, SiCH3), 0.09 (3H, s,
SiCH3), 0.88 (9H, s, tBuSi), 1.70-2.00 (4H, m, 2 × CH2
pyrrolidine), 2.75 (0.33 × 3H, s, NCH3 major), 2.85 (0.67 ×
3H, s, NCH3 minor), 3.15 (2H, m, ArCH2CH), 3.45 (2H, m,
CH2N pyrrolidine), 4.30-4.80 (3H, m, ArCH2NCH3 + CH
pyrollidine), 5.10 (1H, m, ArCH2CH), 7.00-7.80 (17H, m, 17
× ArH + NH), 8.22 (1H, m, NH).
2-Ca r b oxym et h yla m id op h en ylca r b a m oyl-(S)-p r olyl-
(S)-n a p h th yla la n yl-N-ben zyl-N-m eth yla m id e, 5a f. The
title compound was prepared using the method exemplified
in the formation of 5a d from 5a c, using dry methylamine gas.
The reaction mixture was evaporated and the product purified
by flash column chromatography (cyclohexane/EtOAc 1:4).
Concentration of the pure fractions and then crystallization
from cyclohexane/EtOAc gave a colorless solid, 60% yield: mp
96-102 °C; TLC (cyclohexane/EtOAc 1:4) Rf 0.21; 1H NMR
(CDCl3) mixture of two rotamers δ 1.68-2.28 (4H, m, proline
âγ-CH2), 2.70 (0.67 × 3H, s, NCH3 major), 2.91 (0.33 × 3H, s,
NCH3 minor), 2.96 (3H, d, J ) 4 Hz, NHCH3), 3.21 (2H, m,
naphthylAla-CH2CH), 3.45 (2H, m, proline δ), 4.29 (0.66 × 1H,
2-Hyd r oxym eth ylp h en ylca r ba m oyl-(S)-p r olyl-(S)-3-(2-
n a p h th yl)a la n yl-N-ben zyl-N-m eth yla m id e, 5a j. 2-(tert-
Butyldimethylsilanyloxymethyl)phenylcarbamoyl-(S)-prolyl-
(S)-3-(2-naphthyl)alanyl-N-benzyl-N-methylamide (300 mg,
0.000 44 mol) was dissolved in dry THF (6 mL) with tetrabu-
tylammonium fluoride (155 mg, 0.000 49 mol), and stirred for
15 min. The reaction was poured into saturated aqueous
ammonium chloride and the product extracted into EtOAc (3
× 50 mL). The organic washes were combined, washed with
brine (25 mL), then dried over MgSO4, and filtered, and the
solvent was removed in vacuo. The product was purified by
flash column chromatography (silica, cyclohexane/EtOAc 1:4),
then precipitated from EtOAC in n-hexane, to give a white
powdered solid, yield 200 mg (80%): mp 83-86 °C; TLC (silica,
d
AB, J ) 14.7 Hz, ArCHAHBNCH3 major), 4.32-4.58 (0.33 ×
2H, ArCHAHBNCH3 minor, 1H, proline R-CH), 4.71 (0.66 ×
1H, dAB, J ) 14.7 Hz, ArCHAHBNCH3 major), 5.29 (1H, br m,
naphthylalanine R-CH), 6.52 (1H, br, CONHCH3), 6.90-7.84
(16H, m, 15 × ArH, CONH), 8.50 (1H, dd, J ) 8 Hz, J ′ ) 2 Hz
ArH3), 10.72 (0.33 × 1H, br s, urea NH minor), 10.79 (0.66 ×
1H, br s, urea NH major); FABMS m/e 592, 75% (MH+). Anal.
(C35H37N5O4) C, H, N.
2-Ca r boxyd im eth yla m id op h en ylca r ba m oyl-(S)-p r olyl-
(S)-n a p h th yla la n yl-N-ben zyl-N-m eth yla m id e, 5a g. The
title compound was prepared using the method exemplified
in the formation of 5a d from 5a c, using anhydrous dimethy-
lamine and isopropyl chloroformate. The reaction mixture was
evaporated and the product purified by flash column chroma-
tography (silica, EtOAc/MeOH 10:1). Evaporation of the pure
gave a colorless solid, 75% yield: mp 71-73 °C; TLC (silica,
1
cyclohexane/EtOAc 1:4) Rf 0.18; H NMR (CDCl3) mixture of
two rotamers δ 1.70-2.20 (4H, m, 2 × CH2 pyrrolidine), 2.79
(0.67 × 3H, s, NCH3 major), 2.94 (0.33 × 3H, s, NCH3 minor),
3.20 (4H, m, ArCH2CH + CH2N pyrrolidine), 4.37 (0.67 × 1H,
d
AB, J AB ) 14.5 Hz, ArCHAHBNCH3 major), 4.50 (1.66H, m,
1
ArCH2NCH3 minor + CH pyrollidine), 4.67 (0.67 × 1H, dAB
,
cyclohexane/EtOAc 1:4) Rf 0.07; H NMR (CDCl3) mixture of
J AB ) 14.7 Hz, ArCHAHBNCH3 major), 5.20 (1H, m, ArCH2CH),
7.00-7.80 (16H, m, ArH), 8.00 (1H, m, NH); FABMS m/e 565
(MH+). Anal. (C34H36N4O4‚0.33H2O) C, H, N.
two rotamers δ 1.65-2.16 (4H, m, proline âγ-CH2), 2.67 (0.67
× 3H, s, NCH3 major), 2.88 (0.33 × 3H, s, NCH3 minor), 3.08
(6H, s,, N(CH3)2), 3.22 (2H, m, naphthylAla-CH2CH), 3.39 (2H,
m, proline δ), 4.29 (0.66 × 1H, dAB, J ) 15.1 Hz, ArCHAHB-
NCH3 major), 4.39 (0.33 × 1H, dAB, J ) 10.1 Hz ArCHAHB-
NCH3 minor), 4.48 (0.33 × 1H, dAB, J ) 10.1 Hz ArCHAHB-
NCH3 minor), 4.52 (1H, m, 1H, proline R-CH), 4.71 (0.66 ×
2-(ter t-Bu t yld im et h ylsilyloxy)p h en ylca r b a m oyl-(S)-
p r o ly l-(S )-3-(2-n a p h t h y l)a la n y l-N -b e n zy l-N -m e t h y l-
a m id e. The title compound was prepared from (S)-prolyl-(S)-
N-methyl-3-(2-naphthyl)alanyl-N-benzyl-N-methylamide and

Human NK1 Tachykinin Receptor Antagonist
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17 3171
Ta ble 6. Characterization Data on Compounds Synthesized by Repetitive Methodsa
compd chromatography
crystallization
solvent
FABMS
no.
olvent
yield, % mp, °C
TLC
(MH+) m/e
anal.
3a
3b
3c
3d
3e
3f
3h
3k
3l
3m
3n
3p
4a
4b
4c
4d
4e
CHEX/EtOAc 1:1
HEX/EtOAc 2:3
EGDME/water
80
77
41
31
45
81
63
82
77
63
75
92
64
22
77
31
40
67
78
51
45
36
43
32
39
47
37
63
47
47
77
56
59
68
84
47
66
55
63
34
66
96
95
83
60
58
78
79
50
86
97
69
48
22
22
52
47
65
67
64
57
105-106 CHEX/EtOAc 1:1, Rf 0.22
460
430
465
449
508
475
444
488
474
474
545
545
549
593
533
583
560
529
515
583
651
533
563
535
599
599
685
550
563
563
625
588
602
599
599
613
605
613
535
501
546
579
596
580
594
580
580
580
569
598
535
580
580
560
560
560
553
553
553
603
593
(C27H29N3O2S) C, H, N
(C26H27N3OS) C, H, N
(C26H26N3ClOS) C, H, N
(C26H26N3FOS) C, H, N
(C26H26N3BrOS) C, H, N
(C26H26N4O3S) C, H, N
(C27H29N3O3) C, H, N
(C29H33N3O2S) C, H, N
(C28H31N3O2S) C, H, N
(C28H31N3O2S) C, H, N
(C31H36N4O3S) C, H, N
(C31H36N4O3S‚0.25H2O) C, H, N
(C30H33N4O2SCl) C, H, N
(C30H33N4O2BrS) C, H, N
(C30H33N4FO2S) C, H, N
(C31H33N4F3O2S) C, H, N
(C30H33N5O4S) C, H, N
(C31H36N4O2S‚0.25H2O) C, H, N
(C30H34N4O2S) C, H, N
(C30H32N4Cl2O2S) C, H, N
(C32H32N4F6O2S) C, H, N
(C30H33ClN4O3‚0.25H2O) C, H, N
(C31H35N4O2SCl) C, H, N
66-69 HEX/EtOAc 1:1, Rf 0.5
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
EtOAc
154-156 CHEX/EtOAc 1:1, Rf 0.24
136-138 CHEX/EtOAc 1:1, Rf 0.25
152-155 CHEX/EtOAc 1:1, Rf 0.3
143-145 CHEX/EtOAc 1:1, Rf 0.14
147-149 CHEX/EtOAc 1:2, Rf 0.4
CHEX/EtOAc 2:1
CHEX/EtOAc 1:1
HEX/EtOAc
HEX/EtOAc
MeOH/water
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
EtOAc
CHEX/EtOAc 1:1
CHEX/EtOAc 1:1
glass
66-67
166
82-83
68-69
165
CHEX/EtOAc 1:1, Rf 0.29
CHEX/EtOAc 1:1, Rf 0.24
CHEX/EtOAc 1:1, Rf 0.25
CHEX/EtOAc 1:1, Rf 0.14
CHEX/EtOAc 1:1, Rf 0.10
CHEX/EtOAc 1:1, Rf 0.14
CHEX/EtOAc 1:1
CHEX/EtOAc 1:1
CHEX/EtOAc 1:1
CHEX/EtOAc 1:1
CHEX/EtOAc 1:1
152-153 CHEX/EtOAc 1:1, Rf 0.16
174-175
152-153
173-175
160-161
4f
CHEX/EtOAc 2:1
CHEX/EtOAc 1:1
MeOH/EtOAc, 1:20
4 g
4h
4j
4k
4m
4n
4q
4r
89-92
CH2Cl2/MeOH 9:1, Rf 0.88
156-157 CHEX/EtOAc 1:1), Rf 0.10
172-173 CHEX/EtOAc 1:1, Rf 0.07
54-56
MeOH/EtOAc 1:50, Rf 0.5
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
132-134 CHEX/EtOAc 1:1, Rf ) 0.05
174-176 CHEX/EtOAc 1:1, Rf ) 0.06
154-156 CHEX/EtOAc 1:1, Rf ) 0.08
(C29H31N4O2SCl) C, H, N
(C34H35N4O2SCl‚0.2H2O) C, H, N
(C34H35N4O2SCl‚0.33H2O) C, H, N
(C32H31N4O2SClF6) C, H, N
(C29H32N5O2SCl‚0.6H2O) C, H, N
(C31H35N4O2SCl‚0.3H2O) C, H, N
(C31H35N4O2SCl) C, H, N
(C36H37N4O2SCl) C, H, N
(C32H34N5O2SCl) C, H, N
(C33H36N5O2SCl‚0.5H2O) C, H, N
(C34H35N4O2SCl‚0.33C4H8O2) C, H, N
(C34H37N4O2SCl) C, H, N
CHEX/EtOAc 1:1
CHEX/EtOAc 1:1
81-82
CHEX/EtOAc 1:1, Rf 0.13
109-111 CHEX/EtOAc 1:1, Rf ) 0.10
4s
4v
4w
4x
4y
4a a
4a b
4a c
4a d
4a e
4a f
4a g
5a
HEX/EtOAc
95-97
76-78
CH2Cl2/MeOH 25:1, Rf ) 0.23
CHEX/EtOAc 1:1, Rf ) 0.10
CHEX/EtOAc 1:1
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
HEX/CH2Cl2
HEX/EtOAc
138-139 CH2Cl2/MeOH 25:1, Rf 0.58
91-92 CHEX/EtOAc 1:1, Rf 0.34
101-103 CHEX/EtOAc 1:1, Rf 0.05
160-162 CHEX/EtOAc 1:1, Rf 0.06
126-127 CH2Cl2/MeOH 25:1, Rf 0.58
134-135 CHEX/EtOAc 1:4, Rf 0.44
CHEX/EtOAc 1:1
CHEX/EtOAc 1:1
CHEX/EtOAc 1:1
CHEX/EtOAc 1:1
84-85
CHEX/EtOAc 1:1, Rf 0.19
194-195 CH2Cl2/MeOH 25:1, Rf 0.60
(C35H37N4O2SCl) C, H, N
(C32H31N4O2S2Cl) C, H, N
(C36H37N4O2SCl‚0.33H2O) C, H, N
(C29H31N4O2SCl) C, H, N
92-93
glass
CH2Cl2/MeOH 25:1, Rf 0.59
CH2Cl2/MeOH 14:1, Rf 0.76
5b
5c
5d
5e
183-184
86-88
glass
(C29H32N4O2S) C, H, N, S
(C29H31N5O4S‚0.75H2O) C, H, N
(C29H31BrN4O2S‚H2O) C, H, N
(C33H33N5O4S‚0.5H2O) C, H, N
(C33H33N5O5‚0.5H2O) C, H, N
(C34H35N5O5‚0.33H2O) C, H, N
(C33H33N5O5‚0.33H2O) C, H, N
(C33H33N5O5‚0.33H2O) C, H, N
(C33H33N5O5‚0.5H2O) C, H, N
(C31H32N6O5‚0.25H2O) C, H, N
(C29H29N5O5Cl2) C, H, N
CHEX/EtOAc 1:1
HEX/EtOAc 1:1, Rf 0.2
HEX/EtOAc
118-121 CHEX/EtOAc 1:2, Rf 0.45
5f
HEX/EtOAc 1:2
CHEX/EtOAc 1:2
CHEX/EtOAc 1:2
CHEX/EtOAc 1:2
CHEX/EtOAc 1:2
CHEX/EtOAc 2:3
CHEX/EtOAc 1:2
CHEX/EtOAc 1:1
HEX/EtOAc 1:4
HEX/EtOAc 1:4
CHEX/EtOAc 1:2
CHEX/EtOAc 1:4
CHEX/EtOAc 1:4
HEX/EtOAc 1:2
HEX/EtOAc 1:2
HEX/EtOAc 1:2
HEX/EtOAc 1:3
CHEX/EtOAc 2:3
79-82
71-72
73-76
76-79
76-82
96-98
HEX/EtOAc, 1:1, Rf 0.1
CHEX/EtOAc 1:4, Rf 0.60
CHEX/EtOAc 1:2, Rf 0.47
CHEX/EtOAc 1:4, Rf 0.53
5g
5k
5l
5m
5n
5p
5q
5s
HEX/EtOAc
HEX/EtOAc
CHEX/EtOAc
HEX/EtOAc
151-152 CHEX/EtOAc 1:1, Rf 0.16
72-74
98-101 HEX/EtOAc 1:2, Rf 0.24
126-129
124-126 CH2 Cl2/ MeOH 25:1 Rf 0.36
105-107 CH2 Cl2/MeOH 25:1, Rf 0.32
150-152 CH2 Cl2/MeOH 25:1, Rf 0.21
(C33H34N4O3‚1.3H2O) C, H, N
(C33H33N5O5) C, H, N
HEX/CH2Cl2
HEX/EtOAc
5t
(C33H33N5O5‚0.25H2O) C, H, N
(C34H33N5O3‚0.2H2O) C, H, N
(C34H33N5O3) C, H, N
(C34H33N5O3‚0.25H2O) C, H, N
(C33H33N4O3F‚0.25H2O) C, H, N
(C33H33N4O3F‚0.25H2O) C, H, N
(C33H33N4O3F‚0.25H2O) C, H, N
(C34H33F3N4O3‚0.25H2O) C, H, N
(C35H36N4O5‚1.2H2O) C, H, N
5u
5v
5w
5x
5y
5z
HEX/EtOAc
HEX/EtOAc
HEX/EtOAc
67-70
82-85
85-87
66-69
52-56
CHEX/EtOAc 1:1, Rf 0.08
CHEX/EtOAc 1:4, Rf 0.68
CHEX/EtOAc 1:2, Rf 0.30
HEX/EtOAc 1:4, Rf 0.6
CHEX/EtOAc 1:2, Rf 0.22
5a a
5a b
a
Abbreviations: CHEX, cyclohexane; HEX, n-hexane; EGDME, ethylene glycol dimethyl ether.
2-(tert-butyldimethylsilanyloxy)phenyl isocyanate (prepared as
described above) using the method exemplified in the forma-
tion of 3a . The product was purified by flash column chro-
matography (hexane/EtOAc 4:1) to give the title compound in
73% yield: mp 56-58 °C; 1H NMR (CDCl3) mixture of two
rotamers δ 0.27 (3H, s, SiCH3), 0.30 (3H, s, SiCH3), 1.02 (9H,
s, SiC(CH3)3), 1.51-2.03 (3H, m, CH2 pyrrolidine), 2.10-2.32
(1H, m, CH2 pyrrolidine), 2.73 (0.7 × 3H, s, NCH3 major), 2.92
(0.3 × 3H, s, NCH3 minor), 3.04-3.36 (4H, m, CH2Nap, NCH2
pyrrolidine), 4.22-4.63 (2.3H, m, NCHAHBPh, CH pyrrolidine),
4.72 (0.7 × 1H, dAB, J AB ) 15 Hz, NCHAHBPh major), 5.18-
5.37 (1H, m, CHCH2Nap), 6.76-7.94 (17H, m, ArH), 8.28-
8.40 (1H, m, ArH); IR (KBr) 2954 w, 2929 w, 1650 s, 1598 m,
1521 s, 1450 s cm-1; MS m/e (FAB) 665 (MH)+ (100%). Anal.
(C39H48N4O4Si) C, H, N.
2-Hyd r oxyp h en ylca r b a m oyl-(S)-p r olyl-(S)-3-(2-n a p h -
th yl)a la n yl-N-ben zyl-N-m eth yla m id e, 5a k . To 2-(tert-bu-
tyldimethylsilyloxy)phenylcarbamoyl-(S)-prolyl-(S)-3-(2-naph-
thyl)alanyl-N-benzyl-N-methylamide (305 mg, 0.46 mmol) in
THF (5 mL) was added TBAF (158 mg, 0.5 mmol). The
reaction mixture was stirred at room temperature for 30 min.
The reaction mixture was poured into saturated NH4Cl and
extracted with EtOAc (3 × 50 mL). The combined organic
extracts were dried (MgSO4) and concentrated in vacuo. The
residue was purified by flash column chromatography (silica,
EtOAc/hexane 4:1) to afford a white foam (265 mg, 0.48 mmol,

3172 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Walpole et al.
100%): TLC (silica, EtOAc/Hexane, 2:1) Rf 0.1; mp 98-104
°C; 1H NMR (CDCl3) mixture of two rotamers δ 1.73-2.22 (4H,
m, CH2 pyrrolidine), 2.73 (0.7 × 3H, s, NCH3 major), 2.91 (0.3
× 3H, s, NCH3 minor), 3.08-3.46 (4H, m, CH2Nap, NCH2
pyrrolidine), 4.28-4.49 (2.3H, m, NCHAHBPh, CH pyrrolidine),
4.68 (0.7 × 1H, dAB, J AB ) 14 Hz, NCHAHBPh major), 5.18-
5.34 (1H, m, CHCH2Nap), 6.60 (0.3 × 1H, s, NH minor), 6.73
(0.7 × 1H, s, NH major), 6.93-7.58 (14H, m, ArH), 7.58-7.83
(3H, m, ArH), 9.23 (1H, s, br, OH); IR(KBr) 3269 w, 1637 s,
1600 m, 1531 s, 1498 s, 1452 s cm-1; MS m/e (FAB) 551 (MH)+
(100%). Anal. (C33H34N4O4‚0.5H2O) C, H, N.
2-Am in op h en ylca r b a m oyl-(S)-p r olyl-(S)-3-(2-n a p h t h -
yl)a la n yl-N-ben zyl-N-m eth yla m id e, 5a l. To 2-nitrophen-
ylcarbamoyl-(S)-prolyl-(S)-3-(2-naphthyl)alanyl-N-benzyl-N-
methylamide (1.15 g, 2 mmol) in ethanol (12 mL) and H2O (3
mL) were added CaCl2 (141 mg) and zinc dust (4.3 g). The
reaction mixture was heated to reflux for 5 h. The reaction
mixture was filtered through Celite to remove the zinc powder,
and the filtrate was concentrated in vacuo. The residue was
diluted with EtOAc (100 mL) and washed with water (50 mL)
and brine (50 mL). The organic phase was dried (MgSO4) and
concentrated in vacuo. The yellow solid was purified by flash
column chromatography (silica, EtOAc/MeOH 20:1) to afford
2-aminophenylcarbamoyl-(S)-prolyl-(S)-3-(2-naphthyl)alanyl-
N-benzyl-N-methylamide as a yellow foam (816 mg, 1.49 mmol,
74%): mp 92-96 °C; 1H NMR (CDCl3) mixture of two rotamers
δ 1.71-1.96 (3H, m, CH2 pyrrolidine), 1.98-2.22 (1H, m, CH2
pyrrolidine), 2.74 (0.7 × 3H, s, NCH3 major), 2.88 (0.3 × 3H,
s, NCH3 minor), 3.05-3.47 (4H, m, CH2Nap, NCH2 pyrroli-
dine), 4.24-4.49 (2.3H, m, NCHAHBPh, CH pyrrolidine), 4.67
(0.7 × 1H, dAB, J AB ) 14 Hz, NCHAHBPh major), 5.18-5.34
(1H, m, CHCH2Nap), 6.18 (0.3 × 1H, s, NH minor), 6.23 (0.7
× 1H, s, NH major), 6.69-6.86 (2H, m, ArH), 6.94-7.08 (3H,
m, ArH), 7.08-7.37 (6H, m, ArH), 7.37-7.58 (4H, m, ArH),
7.58-7.83 (4H, m, ArH); IR(KBr) 3401 m, 1640 s, 1506 m, 1453
m cm-1; MS m/e (FAB) 550 (MH)+ (100%). Anal. (C33H35N5O3‚
0.5H2O) C, H, N.
The software packages EBDA and LIGAND were used to
estimate binding parameters from the experimental data. Data
represent mean ( SEM of at least three separate experiments.
F u n ction a l Assa ys:34,38 Gu in ea P ig Ileu m Bioa ssa y.
Contractions were evoked by [Sar9Met(O2)11]SP (4.0 nM). The
application of the NK1 receptor agonist was repeated at least
five times to establish stable responses. Once the amplitude
of the contraction became stable, the NK1 agonist was admin-
istered in the presence of the selected NK1 receptor antagonist
(added 2 min prior to the agonist application to the bath). Each
antagonist concentration was tested three times. At least
three different concentrations of the antagonist were used.
log10 concentration was plotted against calculated responses,
and the IC50 value was determined from the curve. Data
represent the mean IC50 values ( SEM, calculated from three
separate experiments
In Vivo Mod els. A model of carrageenan-induced hyper-
algesia in the guinea pig was used to assess the effects of NK1
antagonists on inflammatory hyperalgesia in vivo.38,21 Car-
rageenan (1.0%, 100 µL) injected intraplantar into one hind
paw induces both a mechanical and thermal hyperalgesia
which persists over 24 h. To determine the analgesic effects
of drugs, 1% carrageenan (100 µL intraplantar) was injected
into the hind paw, and 24 h later mechanical hyperalgesia
assessed as above. Drug was then administered, and further
readings were taken at various times up to 6 h.
ED30 was calculated as the dose required to produce a 30%
inhibition of hyperalgesia, and the maximum effect achieved
was expressed as percentage reversal of the predose hyperal-
gesia.
Aspirin was administered orally in 1% tragacanth, and
morphine was injected subcutaneously in saline. Three hours
after drug administration, morphine completely reversed the
hyperalgesia, and the NSAID, aspirin, produced a partial
reversal:
morphine (sc): ED30 ) 0.5 mg/kg, 79.8 ( 12.2% efficacy
aspirin (po): ED30 ) 71.6 mg/kg, 55.0 ( 6.8% efficacy
2-Acetam idoph en ylcar bam oyl-(S)-pr olyl-(S)-3-(2-n aph -
t h yl)a la n yl-N-b en zyl-N-m et h yla m id e, 5a m . To 2-ami-
nophenylcarbamoyl-(S)-prolyl-(S)-3-(2-naphthyl)alanyl-N-benzyl-
N-methylamide (404 mg, 0.74 mmol) in CH2Cl2 (4 mL), cooled
in ice were added pyridine (0.06 mL, 0.74 mmol) and acetic
anhydride (0.07 mL, 0.74 mmol). The reaction mixture was
allowed to warm to room temperature and stirred at room
temperature overnight. The reaction mixture was poured into
water and extracted with CH2Cl2 (3 × 40 mL). The combined
organic extracts were dried (MgSO4) and concentrated in
vacuo. The residue was purified by flash column chromatog-
raphy (silica, EtOAc/MeOH 20:1) to afford an orange foam (150
mg, 0.25 mmol, 34%): mp 104-110 °C; 1H NMR (CDCl3)
mixture of two rotamers δ 1.73-2.30 (4H, m, CH2 pyrrolidine),
2.06 (3H, s, COCH3), 2.71 (0.7 × 3H, s, NCH3 major), 2.88 (0.3
× 3H, s, NCH3 minor), 3.04-3.51 (4H, m, CH2Nap, NCH2
pyrrolidine), 4.22-4.53 (2.3H, m, NCHAHBPh, CH pyrrolidine),
4.69 (0.7 × 1H, dAB, J AB ) 14 Hz, NCHAHBPh major), 5.18-
5.35 (1H, m, CHCH2Nap), 6.90-7.84 (18H, m, ArH), 8.14-
8.53 (1H, m, NH); IR (KBr) 3280 m, 3057 w, 1735 w, 1645 s,
1600 m, 1521 s, 1450 m, 1371 m cm-1; MS m/e (FAB) 592
(MH)+ (100%). Anal. (C35H36N5O4‚H2O) C, H, N.
The NK1 antagonists were given orally in 10% DMSO in
tragacanth (1%) or as a microemulsion.38 Three hours after
oral administration, 5f gave a good, though not complete,
reversal of hyperalgesia and had potency comparable to
subcutaneous morphine:
5f (10% DMSO/tragacanth po):
ED30 ) 0.7 ( 0.3 mg/kg, 68.9 ( 3.88% efficacy
5f (microemulsion po):
ED30 ) 1.1 ( 0.5 mg/kg, 68.4 ( 1.3% efficacy
Su p p or tin g In for m a tion Ava ila ble: Synthetic proce-
dures for the preparation of and characterization data for
compounds included in Table 6 (compounds synthesized by
repetitive procedures) (43 pages). Ordering information is
given on any current masthead page.
Biology. Recep tor Bin d in g Assa ys. Standard binding
assays were performed using the following membrane prepa-
rations and radioligands.34,38
Ra bbit NK1. Displacement of [3H][Sar9Met(O2)11]SP (1 nM)
binding to rabbit whole brain membranes; KD for SP ) 0.14 (
0.03 nM, Bmax ) 9.82 ( 1.47 fmol/mg of protein.
Ra t NK1. Displacement of [3H][Sar9Met(O2)11]SP (0.5 nM)
binding to rat whole forebrain membranes: KD for SP ) 0.23
( 0.09 nM, Bmax ) 14.6 ( 2.6 fmol/mg of protein.
Hu m a n NK1. Displacement of [3H]SP (0.6 nM) binding to
membranes from Cos-7 cells transiently transfected with the
hNK-1R. (KD for SP ) 85 ( 12 pM), Bmax ) 537 ( 139 fmol/
mg of protein.
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