Combined tachykinin receptor antagonist: Synthesis and stereochemical structure-activity relationships of novel morpholine analogues

Article abstract of DOI:10.1016/S0960-894X(00)00324-3

We report herein the synthesis and stereochemical structure-activity relationships of novel morpholine analogues 12 and 13 with regards to NK₁, NK₂ and NK₃ tachykinin receptor binding affinity. An essential requirement for more potent binding affinities was controlled by absolute configuration. (S,R)-12 and (S,R)-13 exhibited high binding affinities for NK₁, NK₂ and NK₃ receptors. (C) 2000 Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0960-894X(00)00324-3

Bioorganic & Medicinal Chemistry Letters 10 (2000) 1665±1668
Combined Tachykinin Receptor Antagonist: Synthesis and
Stereochemical Structure±Activity Relationships of Novel
Morpholine Analogues
Takahide Nishi,a,* Koki Ishibashi,a Toshiyasu Takemoto,a Katsuyoshi Nakajima,a
Tetsuya Fukazawa,a Yukiko Iio,a Kazuhiro Itoh,b Osamu Mukaiyamab
and Takeshi Yamaguchib
aMedicinal Chemistry Research Laboratories, Sankyo Co., Ltd., 1-2-58 Hiromachi, Shinagawa-ku, Tokyo 140±8710, Japan
bNeuroscience and Immunology Research Laboratories, Sankyo Co., Ltd., 1-2-58 Hiromachi, Shinagawa-ku, Tokyo 140±8710, Japan
Received 6 April 2000; accepted 22 May 2000
AbstractÐWe report herein the synthesis and stereochemical structure±activity relationships of novel morpholine analogues 12 and
13 with regards to NK1, NK2 and NK3 tachykinin receptor binding anity. An essential requirement for more potent binding
anities was controlled by absolute con®guration. (S,R)-12 and (S,R)-13 exhibited high binding anities for NK1, NK2 and NK3
receptors. # 2000 Elsevier Science Ltd. All rights reserved.
Introduction
already reported that a series of novel oxazolidine ana-
logues exhibited high binding anities for both NK1
and NK2 receptors.4
The tachykinins are a family of neuropeptides that share
the common C-terminal region, Phe-X-Gly-Leu-Met-
NH2. The main members are substance P (SP), neurokinin
A (NKA), and neurokinin B (NKB). They are di€erentially
distributed in both the central nervous system and periph-
ery, with a prominent location in the peripheral endings of
capsaicin-sensitive primary a€erent neurons. Tachykinin
actions are mediated by at least three distinct receptors
designated as NK1, NK2 and NK3. The endogenous
tachykinin ligands interact with all tachykinin receptors,
although there is a de®ned agonist rank order of potency
such that SP, NKA and NKB have the highest anities for
NK1, NK2 and NK3 receptors, respectively.1 SP, NKA
and NKB have been linked to several chronic diseases such
as asthma, chronic obstructive pulmonary disease,
in¯ammatory bowel disorders, rheumatoid arthritis, pain,
migraine, emesis, urinary incontinence, and psychiatric
disorders such as anxiety and schizophrenia.2 It is thus
expected that tachykinin receptor antagonists will prove
useful in the therapy of a wide variety of disorders. Based
on the speculation that combined tachykinin receptor
antagonist would be of greater bene®t in the treatment of
pulmonary diseases than selective antagonist,3 we have
We report herein the preparation of a series of novel
optically active morpholine analogues that possess spiro-
piperidine moiety. The key steps in the preparation of
novel morpholine analogues were Sharpless asymmetric
dihydroxylation (AD) and the Mitsunobu reaction.
These a€orded the intermediate 5 in good yield in which
the substituents at 2-position of the morpholine ring were
employed to introduce the required stereochemistry. The
intermediate 5 was also prepared using iodoetheri®cation
and optical resolution. In addition, all stereoisomers were
prepared to fully explore the stereochemical preferences of
compounds 12 and 13. Compared to all stereoisomers,
(S,R)-12 and (S,R)-13 showed the higher binding anities
to tachykinin receptors. These compounds exhibited
excellent high binding anities for NK1, NK2 and NK3
receptors.
Chemistry
The key intermediate 2-[(2R)-(3,4-dichlorophenyl)mor-
pholin-2-yl]ethanol ((R)-5) was prepared in a straight-
forward fashion as outlined in Scheme 1.5 As previously
described, ole®n 1 was treated with AD-mix-b in t-
BuOH±H2O to obtain (R)-diol 2 with high enantiomeric
*Corresponding author. Tel.: +81-3-3492-3131; fax: +81-3-5436-8563;
e-mail: takahi@shina.sankyo.co.jp
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00324-3

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T. Nishi et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1665±1668
Boc-aminoethanol and N-iodosuccinimide (NIS) in ace-
tonitrile at 70 ꢀC to obtain iodide 7 in good yield. Treat-
ment of 7 with NaH in DMF at 70 ꢀC cleanly provided 8,
and then deprotection of both the triphenylmethyl (Tr)
and Boc groups of 8 by 4N HCl proceeded smoothly in
good yield. Next, the resulting racemic (RS)-5 was
resolved with d-( )-tartaric acid in EtOH to give (R)-5
with high enantiomeric purity. (S)-5 was also resolved
with l-(+)-tartaric acid. This method is useful for the
synthesis of a variety of 2,2-disubstituted morpholine
derivatives from 1,1-disubstituted ole®ns.
Next, morpholine 5 was condensed with 3,4,5-trimeth-
oxybenzoyl chloride and the resulting primary alcohol
was converted to the methanesulfonate 9 in good yield.
In an earlier paper, we described the design rationale
that led to the 3,4-dichlorophenyl and 3,4,5-trimethoxy-
benzoyl groups as the best moiety in terms of combined
NK1 and NK2 receptor antagonistic activities.3 Our pre-
liminary studies on the e€ects of piperidine analogues
indicated that compounds possessing spiro-piperidine
analogues exhibited higher binding anities for both
receptors compared to structurally related compounds.
Scheme 1. Synthesis of key intermediate (R)-5 using the Sharpless AD
and Mitsunobu reaction.
purity (>97% ee). After selective formation of the pri-
mary tosylate, substitution with aminoethanol was per-
formed in the presence of LiClO4 in acetonitrile at
100 ꢀC, and the protection of the resulting secondary
amine with Boc2O and Et3N cleanly provided 3 in good
yield. Next, treatment of 3 with DEAD and Ph3P in
toluene for dehydration provided 4 in good yield. The
Boc and TBDMS groups of 4 were deprotected via
treatment with 4N HCl/dioxane at 60 ꢀC, and the sub-
sequent base treatment gave the enantiomerically pure
(R)-5. This synthesis also led to the synthesis of 2-[(2S)-
(3,4-dichlorophenyl)morpholin-2-yl]ethanol ((S)-5) with
the opposite con®guration by using AD-mix-a for the
Sharpless AD of 1.
Among the series of spiro-piperidine analogues, com-
pounds possessing properties such as spiro[benzo[c]
thiophene-1(3H),40-piperidine]-2-oxide (10) or spiro[(2-
hydroxy)indane-1,40-piperidine] (11) moiety were parti-
cularly ecacious in increasing the binding anities.
The synthetic methods for the preparation of optically
active 10 and 11 have already been reported.7,8 Heating 9
and spiro-piperidine analogues 10 or 11 in the presence
of NaHCO3 and KI at 80ꢀC in DMF a€orded the desired
compounds 12 or 13 (Scheme 3).9 Finally, all of the
stereoisomers were prepared to fully explore the stereo-
chemical preferences of compounds 12 and 13.
On the other hand, a versatile and short-step synthetic
method using iodoetheri®cation has also been achieved
(Scheme 2).6 Styrene derivative 6 was treated with N-
Scheme 2. Synthesis of key intermediate (R)-5 using the iodoetheri-
®cation and optical resolution.
Scheme 3. Synthesis of optically active 12 and 13.

T. Nishi et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1665±1668
1667
Results and Discussion
impact on the binding activity to the tachykinin recep-
tor, and thus that the (S)-con®guration is an essential
requirement for more potent binding anities. These
properties clearly appear to form an appropriately
positioned pocket in the binding site, probably through
their actions as hydrogen bond acceptors or donors, or
possibly due to the steric e€ect.
Compounds 12 and 13 were evaluated for their binding
anities, and the NK1, NK2 and NK3 receptor binding
anity data (IC50; nM) are summarized in Tables 1 and
2.10 As can be seen from the results, the (R)-con®guration
at the 2-position of the morpholine ring was crucial for
high anity (compound (S,R)- and (R,R)-12, 13 versus
(S,S)- and (R,S)-12, 13). (S,S)-12, 13 and (R,S)-12, 13
possessing the (S)-con®guration at the mopholine ring,
were both found to be inactive. The data con®rmed that
the (R)-con®guration is an essential requirement for
high binding anity. On the other hand, the stereo-
chemistry of the sulfoxide and hydroxy groups also had
e€ects on the activity. When we assessed the sulfoxide-
containing spiro-piperidine analogues, we found that
(S,R)-12 had 10-fold (NK1), 20-fold (NK2), and 15-fold
(NK3) higher levels than (R,R)-12. As shown in Table 2,
the inversion of stereochemistry of the hydroxy group
resulted in 7-fold (NK1), 6-fold (NK2), and 6-fold (NK3)
decreases in anity, bringing the anity down to the
same level seen with sulfoxide-containing analogues.
These results indicated that the stereochemistry of the
sulfoxide of 12 and the hydroxyl group of 13 has great
We also evaluated the in vivo potency of (S,R)-12 HCl salt
and its inhibitory e€ect on SP-induced tracheal vascular
hyperpermeability in anesthetized guinea pigs. (S,R)-12
HCl salt dose-dependently inhibited SP-induced plasma
protein extravasation (ID50; 0.1±0.33 mg/kg, iv) medi-
ated by NK1 receptors in guinea pig airways.11 It was also
evaluated for the inhibitory e€ects on bronchoconstriction
induced by NKA and NKB in anesthetized guinea pigs. It
dose-dependently inhibited NKA-induced bronchocon-
striction (ID50; 0.040 mg/kg, iv) and NKB-induced bron-
choconstriction (ID50; 0.063 mg/kg, iv), respectively.12
In conclusion, we have developed a synthetic route for
the preparation of the optically active novel morpholine
derivatives 12 and 13 and evaluated them as antagonists
for tachykinin NK1, NK2, and NK3 receptors. The
binding anity is highly dependent on the stereochemistry
of the compounds, showing (S,R)-12 and (S,R)-13 are
most potent in the in vitro assay. Furthermore, we also
evaluated the in vivo potency of (S,R)-12 HCl salt, and its
inhibitory e€ects on SP-induced tracheal vascular hyper-
permeability and NKA- and NKB-induced bronchocon-
striction in anesthetized guinea pigs. A more detailed
analysis of SAR and further work in elucidating biological
activities will be described in future publications.
Table 1. In vitro binding anity of compound 12 to NK1, NK2, and
NK3 receptors from the membrane of guinea pigs
Absolute con®guration
IC50 (nM)a
NK2
References and Notes
Compounds
Ã
ÃÃ
NK1
NK3
(S,R)-12
(R,R)-12
(S,S)-12
(R,S)-12
S
R
S
R
R
S
S
21
220
3.1
59
0.72
11
520
660
1. Regoli, D.; Boudon, A.; Fauchere, J.-L. Pharmacol. Rev.
1994, 46, 551 and references cited therein.
2. (a) Longmore, J.; Swain C. J.; Hill, R. G. Drug News Per-
spet. 1995, 8, 5. (b) Kucharczyk, N. Exp. Opin. Invest. Drugs.
1995, 4, 299. (c) Elliott, J.; Seward, E. M. Exp. Opin. Ther.
Patents. 1997, 7, 43 and references cited therein.
>1000 >1000
>1000 >1000
R
aEach value is the mean of at least three determinations.
3. (a) Maggi, C. A. Pharmacol. Res. 1990, 22, 527. (b)
Cheung, D.; Van Der Veen, H.; Den Hartigh, J.; Dijkman, J.
H.; Sterk, P. J. J. Appl. Physiol. 1994, 77, 1325. (c) Maggi, C.
A.; Patacchini, R.; Rovero, P.; Giachetti, A. J. Auton. Phar-
macol. 1993, 13, 23.
Table 2. In vitro binding anity of compound 13 to NK1, NK2, and
NK3 receptors from the membrane of guinea pigs
4. Nishi, T.; Fukazawa, T.; Ishibashi, K.; Nakajima, K.;
Sugioka, Y.; Iio, Y.; Kurata, H.; Itoh, K.; Mukaiyama, O.;
Satoh, Y.; Yamaguchi, T. Bioorg. Med. Chem. Lett. 1999, 9, 875.
5. Nishi, T.; Ishibashi, K.; Nakajima, K.; Iio, Y.; Fukazawa,
T. Tetrahedron: Asymmetry 1998, 9, 3251.
6. Takemoto, T.; Iio, Y.; Nishi, T. Tetrahedron Lett. 2000, 41,
1785.
7. Nishi, T.; Nakajima, K.; Iio, Y.; Ishibashi, K.; Fukazawa,
T. Tetrahedron: Asymmetry 1998, 9, 2567.
8. Takemoto, T.; Nakajima, K.; Iio, Y.; Tamura, M.; Nishi,
T. Tetrahedron: Asymmetry 1999, 10, 1787.
9. All new compounds are fully characterized by their spec-
troscopic and analytical data.
10. NK1 IC50 determined using [3H]-SP and NK1 receptors
from lung membrane of male Hartley guinea pigs. NK2 IC50
determined using [3H]-SR-48968 and NK2 receptors from
Absolute con®guration
IC50 (nM)a
NK2
Compounds
Ã
ÃÃ
NK1
NK3
2.7
17
>1000
>1000
(S,R)-13
(R,R)-13
(S,S)-13
(R,S)-13
S
R
S
R
R
S
S
40
270
6.8
45
>1000 >1000
>1000 >1000
R
aEach value is the mean of at least three determinations.

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T. Nishi et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1665±1668
ileum membrane of male Hartley guinea pigs. NK3 IC50
determined using [3H]-senktide and NK3 receptors from brain
membrane of male Hartley guinea pigs. Each value is the
mean of at least three determinations.
11. Compounds were administered intravenously just before
intravenous injection of SP (1 mg/kg). The amount of Evans
blue dye extracted from the trachea was used as the index of
plasma protein leakage. The trachea was isolated from the
Evans blue-treated animal 15 min after SP injection.
12. The assessment of the inhibitory e€ect was based on air-
way pressure as an index of bronchoconstriction according to
the modi®ed method of Konzett-Rossler. Compounds were
administered intravenously 5 min before intravenous injection
of NKA (4 mg/kg) or NKB (4 mg/kg).