Analysis of crucial structural requirements of 2-substituted pyrimido[4,5-b][1,5]oxazocines as NK1 receptor antagonist by axially chiral derivatives

Article abstract of DOI:10.1016/j.bmc.2007.05.040

This study aimed to identify the crucial structural features of 2-substituted 8-methylpyrimido[4,5-b][1,5]oxazocine derivatives. Axially chiral 8-methylpyrimido[4,5-b][1,5]oxazocines bearing a substituent at the C-2 position were synthesized and evaluated

Full text of DOI:10.1016/j.bmc.2007.05.040

Bioorganic & Medicinal Chemistry 15 (2007) 5083–5089
Analysis of crucial structural requirements of 2-substituted
pyrimido[4,5-b][1,5]oxazocines as NK1 receptor antagonist
by axially chiral derivatives
Shigeki Seto* and Jun Asano
Discovery Research Laboratories, Kyorin Pharmaceutical Co., Ltd, 2399-1, Nogi, Nogi-machi, Shimotsuga-gun,
Tochigi 329-0114, Japan
Received 8 April 2007; revised 12 May 2007; accepted 15 May 2007
Available online 18 May 2007
Abstract—This study aimed to identify the crucial structural features of 2-substituted 8-methylpyrimido[4,5-b][1,5]oxazocine deriv-
atives. Axially chiral 8-methylpyrimido[4,5-b][1,5]oxazocines bearing a substituent at the C-2 position were synthesized and evalu-
ated as NK1 antagonists. The results revealed that (aR, 8S)-stereochemistry and the substituent at the C-2 position are important for
NK1 receptor recognition.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
phenyl rings (Fig. 1). The eight-membered ring system
is known to be an effective core region9 and it fits well
with the NK1 receptor; however, occasionally slow ring
flipping occurs causing analytical and pharmaceutical
complications.9
Neurokinin receptors exist as three subtypes, NK1,
NK2, and NK3, which have selective affinities for Sub-
stance P (SP), neurokinin A, and neurokinin B, respec-
tively.1 Among them, SP exhibits a wide variety of
biological responses, both centrally and peripherally.2
SP has been implicated in the transmission of pain and
stress signals, inflammation, and the contraction of
smooth muscle because it binds to the NK1 receptor.
Therefore, NK1 antagonists may be efficacious in the
treatment of a wide range of diseases. Since Pfizer dis-
covered CP-96345 and CP-99994, the first non-peptide
NK1 antagonists, extensive research among several
other structural classes of NK1 receptor antagonists
has been on-going.3–6
Takeda et al.9 reported that introducing an asymmetric
methyl group to the eight-membered ring of TAK-637
could resolve the ring flipping problem. As a result, its
preparation as a single diastereomer (C-9 and axial)
was successful because the axial chirality of the eight-
membered lactam carbonyl moiety is triggered by intro-
ducing a C-9 asymmetric methyl group. In addition,
(aR, 9R) stereochemistry is important for the com-
pound’s activity as an NK1 antagonist.9,10
We have previously reported on pyrimido[4,5-
b][1,5]oxazocine derivatives11 such as KRP-103 (3), a
new structural class of potent and selective NK1 antag-
onists. On the basis of the report by Takeda et al.,9 we
synthesized compounds represented by the general
structure A , shown in Figure 2. This work led to an
analysis of the structural requirements of the pyrimi-
do[4,5-b][1,5]oxazocine skeleton in two key regions; (1)
the axial chirality of eight-membered lactam carbonyl
moiety and (2) the C-2 substituent on the pyrimi-
do[4,5-b][1,5]oxazocine ring. Here, we report on the syn-
thesis and structure–activity relationships (SAR) of this
new class of compounds focusing on the axially chiral
2-substituted pyrimido[4,5-b][1,5]oxazocines.
Most NK1 antagonists have a common pharmacophore
that contains two phenyl rings and a linkage that
incorporates either an ester- or amide-moiety.7 The
interactions of these parts with the receptor can be
examined using mutagenesis studies.8 Some potent
NK1 antagonists9–11 have an eight-membered lactam
moiety as an amide-based linkage between the two
Keywords: 2-substituted 8-methylpyrimido[4,5-b][1,5]oxazocine; Axial
chirality; NK1 antagonist.
*
Corresponding author. Fax: +81 (0)280 57 1293; e-mail: shigeki.
seto@mb.kyorin-pharm.co.jp
0968-0896/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2007.05.040

5084
S. Seto, J. Asano / Bioorg. Med. Chem. 15 (2007) 5083–5089
O
O
Me
N
O
O
N
N
N
N
Me
Me
N
9
R
3S
CF3
CF3
CF3
CF3
CF3
CF3
aR
aR
N
N
N
N
Me
O
O
O
Me
1 (TAK-637)
2
3 (KRP-103)
Figure 1. Examples of NK1 antagonist including eight-membered lactam moiety.
derivatives produced the desired compounds (14b–d,
15b–d, and 16b–d).
R2
N
O
R1
2
8
CF3
CF3
N
5
N
The stereochemistry of axial chirality was revealed by
NMR analysis using 15a. The NOE correlation of 15a
was observed between the C-8 proton and one of the
benzylic protons and was similar to that of TAK-637
(Fig. 3).9b These results indicate that 15a has (aR, 8S)
stereochemistry. Therefore, the stereochemistry of 14a–
d and 15a–d is (aS, 8R) and (aR, 8S), respectively. In
addition, the diastereomer of 14a–d or 15a–d could
Me
O
A
Figure 2. General structure of target compounds.
1
not be determined by the H NMR spectrum.
2. Chemistry
The synthesis of the pyrimido[4,5-b][1,5]oxazocine deriv-
atives bearing a functionalized amine moiety at the C-2
position is shown in Scheme 1. Treatment of 4 with thio-
nyl chloride, followed by amide formation with 3-
aminopropanol derivatives and subsequent cyclization
using potassium carbonate, led to the bicyclic com-
pounds 5–7. Palladium coupling reactions of 5–7 with
o-tolylboronic acid produced biaryl compounds, C-2
methylthio groups of which were oxidized to give meth-
anesulfonyl derivatives 11–13. Sodium borohydride
reduction12 of 11–13 gave rise to the C-2 non-substituted
derivatives (14a–16a). Substitution reactions of the C-2
methanesulfonyl group of 11–13 with various amine
O
Me
H
N
8
N
N
Ha
Hb
Me
O
F3C
CF3
Figure 3. NOE correlation between C-8 proton and benzylic methy-
lene proton of 15a.
Cl
N
O
O
O
MeS
N
R1
MeS
Me
N
R1
MeO2S
Me
N
R1
8
8
8
CO2H
Cl
N
CF3
CF3
CF3
CF3
CF3
CF3
a, b, c
N
d
N
e
N
N
N
N
MeS
Cl
O
O
O
5: R1 = (
6: R1 = (
R
S
)-Me
)-Me
8: R1 = (
9: R1 = (
R)-Me
11: R1 = (
12: R1 = (
S
R)-Me
4
S)-Me
)-Me
7: R1 = H
10: R1 = H
13: R1 = H
R2
N
R1
R2
N
R2
N
N
O
O
O
Me
Me
8
R
8S
2
8
2
2
CF3
CF3
CF3
CF3
CF3
CF3
f or g
N
N
N
aS N
aR N
Me
Me
Me
O
O
O
14a−d: R1 = (
15a−d: R1 = (
R
)-Me
(aS, 8R)-14a−d
(aR, 8S)-15a−d
S)-Me
16a−d: R1 = H
Scheme 1. Reagents: (a) SOCl2; (b) (2R)- or (2S)-3-[3,5-bis(trifluoromethyl)benzylamino]-2-methyl-1-propanol or 3-[3,5-bis(trifluoromethyl)ben-
zylamino]-1-propanol, Et3N, THF; (c) K2CO3, DMF (53–66%, 3 steps); (d) o-tolylboronic acid, Pd(PPh3)4, Na2CO3 (73–95%); (e) mCPBA, THF
(89–100%); (f) R3R4NH, diisopropylethylamine, dioxane (60–89%); (g) NaBH4, CHCl3-MeOH (37–65%).

S. Seto, J. Asano / Bioorg. Med. Chem. 15 (2007) 5083–5089
5085
3. Results and discussion
(aR, 8S)-isomers, 15a–d. In this case, the axially chiral
compound is not advantageous from a pharmaceutical
perspective. These results are in accord with the NMR
studies,13,14 which indicate that equilibrium between
(aR)-16 and (aS)-16 is freely interchangeable at room
temperature.
The results of the NK1 antagonist activity for the newly
synthesized compounds 14a–d, 15a–d, and 16a,b,d, and
the representative compound 16c are shown in Table
1. In addition, the stereochemistry at C-8 and the axial
chirality for 14a–d, 15a–d are shown.
Some other interesting trends are notable in the data.
The difference in activities between the (aR, 8S)- and
(aS, 8R)-isomers depends on the type of substituent at
the C-2 position. Those compounds bearing a small sub-
stituent at C-2 position, e.g., a hydrogen or dimethyla-
mino group, showed clear differences in their activities
(12–120 times) between the (aR, 8S)- and the (aS, 8R)-
isomers (14a vs 15a, KB = 162, 12.6 nM, respectively;
14d vs 15d, KB = 52.9, 0.427 nM, respectively). In con-
trast, in the case of compounds bearing a terminal acetyl
group as the 2-substituent, there were only slight differ-
ences in the activities between the two (14c vs 15c,
KB = 0.345, 0.139 nM, respectively; 14d vs 15d, KB =
0.545, 0.217 nM, respectively). From these results, the
substituent at the C-2 position, such as an acetylpipera-
zinyl group, was effective in the key region for NK1
receptor recognition, regardless of the axial chirality of
the carbonyl moiety on the eight-membered lactam.
The compounds bearing the 8S-methyl group showed
more potent NK1 antagonist activity than the corre-
sponding compounds bearing the 8R-methyl group
(14a–d vs 15a–d, respectively). These results indicate
that (aR, 8S)-stereochemistry is important for NK1
receptor recognition which is similar to that reported
by Takeda on pyrido[4,5-b]-1,5-oxazocine derivatives.10
Interestingly, the NK1 antagonist activities of 15a–d are
comparable to those of 16a–d (e.g., 15c, KB = 0.139 nM;
16c, KB = 0.105 nM). These data indicate that the bind-
ing conformation of 16a–d to the NK1 receptor is simi-
lar to that of 15a–d, that is, the equilibrium between
(aR)-16 and (aS)-16 is completely biased toward (aR)-
16 (Fig. 4) which has the same conformation as the
Table 1. NK1 antagonist activity of pyrimido[4,5-b][1,5]oxazocine
derivatives
R2
N
R1
O
4. Conclusion
2
8
CF3
N
*
On the basis of the SAR study, we have clarified the
structural requirements for NK1 antagonists in two
key regions: (1) the stereochemistry of the axially chiral
eight-membered lactam carbonyl group and (2) the C-2
substituent. The (aR, 8S)-stereochemistry is important
for NK1 antagonist activity. However, in the case of
the pyrimido[4,5-b][1,5]oxazocine skeleton, an axially
chiral compound is not always pharmaceutically advan-
tageous compared with a non-chiral compound, which
can interchange between possible atropisomers. In addi-
tion, the substituent at the C-2 position is effective in the
key region for NK1 receptor recognition, regardless of
axial chirality. These SAR studies can be used to explore
new types of NK1 receptor antagonists.
N
Me
O
CF3
Compound R1
R2
H
Stereo
a
KB (nM)
C-8 Axial (*)
14a
15a
16a
Me
Me
H
R
S
S
162
R
—
12.6
11.6
—
14b
15b
16b
Me
Me –NMe2
H
R
S
S
52.9
0.427
0.679
R
—
—
14c
15c
16c
Me
R
S
S
0.345
0.139
0.105
Me
H
R
—
N
N
NAc
Me
—
5. Experimental
5.1. Chemistry
14d
15d
16d
Me
Me
H
R
S
S
52.9
0.217
0.679
R
—
NAc
—
Me
a Data present means of KB value of guinea pig ileum contraction assay
(n = 3–5). Compounds were screened for antagonist activity on gui-
nea pig ileum as described in the text.
Melting points were determined with a Yamato MP-500
melting point apparatus and are uncorrected. H NMR
spectra were measured in CDCl3 or DMSO-d6 with
1
R2
N
R2
N
O
O
2
2
CF3
CF3
CF3
CF3
N
aR
N
aS
N
N
Me
Me
O
O
(aR)-16
(aS)-16
Figure 4. Proposed equilibrium of 16.

5086
S. Seto, J. Asano / Bioorg. Med. Chem. 15 (2007) 5083–5089
TMS and the solvent peak as internal standards, on a
JEOL ECA-400 (400 MHz) spectrometer. Mass spectra
(MS) were obtained on a Hitachi M-2000 mass spec-
trometer. Column chromatography was carried out on
Merck silica gel 60. Analytical thin-layer chromatogra-
phy (TLC) was performed on Merck precoated silica
gel 60F254 plates, and the compounds were visualized
by UV illumination (254 nm) or by heating after spray-
ing with phosphomolybdic acid in ethanol. The data for
elemental analysis are within 0.4% of theoretical values
and were determined by a Yanaco CHN corder MT-5.
temperature, and diluted with ethyl acetate, then washed
with 2 M Na2CO3 and brine, and dried over Na2SO4, fil-
tered, then concentrated in vacuo. Flash chromatography
(AcOEt/Hexane = 1:1) of the residue gave 8 as a pale yel-
25
low foam (581 mg, 76%). ½aꢀ
= ꢁ9.96° (c 1.02, CHCl3).
D
1H NMR (400 MHz, CDCl3) d 1.16 (3H, d, J = 6.7 Hz),
2.16–2.29 (1H, m), 2.28 (3H, s), 2.56 (3 H, s), 3.18 (1H,
dd, J = 15.3 and 4.9 Hz), 3.45 (1H, dd, J = 14.7 and
12.7 Hz), 3.90 (1H, d, J = 14.7 Hz), 4.19 (1H, dd,
J = 13.4 and 3.1 Hz), 4.52 (1H, dd, J = 13.4 and 1.8 Hz),
5.31 (1H, d, J = 14.7 Hz), 6.87–6.93 (1H, m), 6.99–7.05
(1H, m), 7.17–7.25 (2H, m), 7.58 (2H, s), 7.81 (1H, s).
HRMS (EI) for C26H23F6N3O2S (M+): calcd, 555.1415;
found, 555.1396. Anal. Calcd for C26H23F6N3O2S: C,
56.21; H, 4.17; N, 7.56. Found: C, 56.36; H, 4.14; N, 7.19.
5.1.1. (8R)-6-[3,5-Bis(trifluoromethyl)benzyl]-4-chloro-8-
methyl-2-methylthio-6,7,8,9-tetrahydro-5H-pyrimido[4,
5-b][1,5]oxazocin-5-one (5). A mixture of 4,6-dichloro-2-
(methylthio)pyrimidine-5-carboxylic acid (4)11 (645 mg,
2.70 mmol) and thionyl chloride (5.0 mL) was refluxed
for 0.5 h and concentrated. A solution of the residue in
THF (5 mL) was added dropwise to a solution of (2R)-
3-[[3,5-bis(trifluoromethyl)benzyl]amino]-2-methyl-1-
propanol10 (850 mg, 2.70 mmol) and triethylamine
(2.0 mL) in THF (20 mL) at 0 °C. The mixture was stirred
for 1 h at 0 °C and then for 2 h at room temperature. After
concentration in vacuo, to a solution of the residue in
DMF (10 mL) was added potassium carbonate (750 mg,
5.43 mmol) and the mixture was stirred for 1 h at 80 °C.
The resulting mixture was diluted with ethyl acetate, then
washed with water and brine. The organic layer was dried
over anhydrous Na2SO4, filtered, and then concentrated
in vacuo. Flash chromatography (hexane/AcOEt = 2:1)
5.1.4. (8S)-6-[3,5-Bis(trifluoromethyl)benzyl]-8-methyl-2-
methylthio-4-(2-methylphenyl)-6,7,8,9-tetrahydro-5H-
pyrimido[4,5-b][1,5]oxazocin-5-one (9). The compound 9
(950 mg, 73%) was prepared from 6 (1.12 g, 2.24 mmol)
and o-tolylboronic acid (366 mg, 2.69 mmol) in a man-
ner similar to that described for the preparation of 8.
1
25
Pale yellow foam. ½aꢀ
= +11.7° (c 1.08, CHCl3). H
D
NMR spectrum was identical with that of 8. HRMS
(EI) for C26H23F6N3O2S (M+): calcd, 555.1415; found,
555.1437. Anal. Calcd for C26H23F6N3O2S: C, 56.21;
H, 4.17; N, 7.56. Found: C, 56.22; H, 4.13; N, 7.41.
5.1.5. (8R)-6-[3,5-Bis(trifluoromethyl)benzyl]-8-methyl-2-
methylsulfonyl-4-(2-methylphenyl)-6,7,8,9-tetrahydro-
5H-pyrimido[4,5-b][1,5]oxazocin-5-one (11). To a solution
of 8 (560 mg, 1.01 mmol) in THF (3 mL) was added
mCPBA (435 mg, 2.52 mmol) portionwise under ice cool-
ing. The mixture was stirred for 30 min at 0 °C and then
for 2 h at room temperature. The resulting mixture was di-
luted with ethyl acetate, then washed with saturated so-
dium hydrogen carbonate. The organic layer was dried
over anhydrous Na2SO4, filtered, and then concentrated
in vacuo. Flash chromatography (hexane/AcOEt 1:1) of
the residue gave 11 as a white solid (528 mg, 89%). Mp:
of the residue gave 5 as a pale yellow foam (717 mg,
23
53%). ½aꢀ
= ꢁ33.9° (c 1.05, CHCl3). 1H NMR
D
(400 MHz, CDCl3) d 1.14 (3H, d, J = 6.7 Hz), 2.17–2.29
(1H, m), 2.56 (3H, s), 3.15 (1H, dd, J = 15.3 and
5.5 Hz), 3.35 (1H, dd, J = 15.3 and 13.5 Hz), 4.05 (1H,
d, J = 15.3 Hz), 4.21 (1H, dd, J = 13.4 and 2.4 Hz), 4.59
(1H, dd, J = 13.4 and 1.8 Hz), 5.61 (1H, d, J =
15.3 Hz), 7.83 (3H, s). HRMS (EI) for C19H16ClF6N3O2S
(M+): calcd, 499.0556; found, 499.0592. Anal. Calcd for
C19H16ClF6N3O2S: C, 45.65; H, 3.23; N, 8.41. Found:
C, 45.27; H, 3.04; N, 8.36.
1
25
204–205 °C. ½aꢀ
= ꢁ13.6° (c 0.680, CHCl3). H NMR
D
(400 MHz, CDCl3) d 1.20 (3H, d, J = 7.3 Hz), 2.23 (3H,
s), 2.25–2.36 (1H, m), 3.25–3.45 (2H, m), 3.34 (3H, s),
3.94 (1H, d, J = 14.7 Hz), 4.31 (1H, dd, J = 13.5 and
2.4 Hz), 4.63 (1H, dd, J = 13.5 and 1.8 Hz), 5.29 (1H, d,
J = 14.7 Hz), 6.86 (1H, d, J = 7.9 Hz), 6.99 (1H, dd,
J = 7.9 and 7.9 Hz), 7.21–7.30 (2H, m), 7.57 (2H, s),
7.84 (1H, s). HRMS (ESI+) for C26H24F6N3O4S
(M++1): calcd, 588.13917; found, 588.14095.
5.1.2. (8S)-6-[3,5-Bis(trifluoromethyl)benzyl]-4-chloro-8-
methyl-2-methylthio-6,7,8,9-tetrahydro-5H-pyrimido[4,5-
b][1, 5]oxazocin-5-one (6). The compound 6 (1.16 g, 66%)
was prepared from 4 (835 mg, 3.49 mmol) and (2S)-3-
[[3,5-bis(trifluoromethyl)benzyl]amino]-2-methyl-1-pro-
panol10 (1.10 g, 3.49 mmol) in a manner similar to that
described for the preparation of 5. Pale yellow foam.
1
24
½aꢀ
= +36.8° (c 1.02, CHCl3). H NMR spectrum was
D
identical with that of 5. HRMS (EI) for C19H16ClF6N3
O2S (M+): calcd, 499.0556; found, 499.0579. Anal. Calcd
for C19H16ClF6N3O2S: C, 45.65; H, 3.23; N, 8.41. Found:
C, 45.47; H, 3.00; N, 8.38.
Anal. Calcd for C26H23F6N3O4S: C, 53.15; H, 3.95; N,
7.15. Found: C, 52.96; H, 3.76; N, 7.06.
5.1.6. (8S)-6-[3,5-Bis(trifluoromethyl)benzyl]-8-methyl-2-
methylsulfonyl-4-(2-methylphenyl)-6,7,8,9-tetrahydro-5H-
pyrimido[4,5-b][1,5]oxazocin-5-one (12). The compound
12 (862 mg, 93%) was prepared from 9 (875 mg,
1.58 mmol) and mCPBA (682 mg, 3.95 mmol) in a man-
ner similar to that described for the preparation of 11.
White solid. Mp: 202–205 °C.
5.1.3.
(8R)-6-[3,5-Bis(trifluoromethyl)benzyl]-8-methyl-2-
methylthio-4-(2-methylphenyl)-6,7,8,9-tetrahydro-5H-pyrimi-
do[4,5-b][1,5]oxazocin-5-one (8). To a mixture of 5
(690 mg, 1.38 mmol) and o-tolylboronic acid (225 mg,
1.65 mmol) in toluene (4 mL) and 1,4-dioxane (4 mL)
were added 2 M Na2CO3 (4 mL) and Pd(PPh3)4
(160 mg, 0.138 mmol), and the mixture was stirred under
reflux for 6 h. The reaction mixture was cooled to room
25
½aꢀ
= +16.2° (c 0.830, CHCl3). 1H NMR spectrum
D
was identical with that of 11. HRMS (ESI+) for

S. Seto, J. Asano / Bioorg. Med. Chem. 15 (2007) 5083–5089
5087
C26H24F6N3O4S (M++1): calcd, 588.13917; found,
588.13874.
(3H, d, J = 6.7 Hz), 2.10–2.28 (1H, m), 2,13 (3H, s),
2.25 (3H, s), 3.13 (1H, dd, J = 15.3 and 5.5 Hz),
3.45–3.56 (3H, m), 3.61–3.72 (2H, m), 3.80–3.95 (5H,
m), 4.13 (1H, dd, J = 13.4 and 3.1 Hz), 4.46 (1H, dd,
J = 13.5 and 2.4 Hz), 5.32 (1H, d, J = 15.3 Hz),
6.90–6.96 (1H, m), 6.99–7.07 (1H, m), 7.17–7.28 (2H,
m), 7.56 (2H, s), 7.80 (1H, s). HRMS (FAB+) for
C31H32F6N5O3 (M++1): calcd, 636.2409; found,
636.2378. Anal. Calcd for C31H31F6N5O30.3H2O: C,
58.09; H, 4.87; N, 10.93. Found: C, 57.93; H, 4.75; N,
10.84.
Anal. Calcd for C26H23F6N3O4S: C, 53.15; H, 3.95; N,
7.15. Found: C, 53.02; H, 3.78; N, 7.08.
5.1.7. (8R)-6-[3,5-Bis(trifluoromethyl)benzyl]-8-methyl-4-
(2-methylphenyl)-6,7,8,9-tetrahydro-5H-pyrimido[4,5-
b][1,5]oxazocin-5-one (14a). To a solution of 11 (70.0 mg,
0.119 mmol) in CHCl3-EtOH (1 mL; 1:1 v/v) was added
NaBH4 (23.0 mg, 0.608 mmol) at room temperature and
the mixture was stirred at same temperature for 1 h. To
the resulting mixture was added water and the mixture
was stirred at room temperature for 0.5 h, diluted with
ethyl acetate, and then washed with water and brine.
The organic layer was dried over anhydrous Na2SO4, fil-
tered, and then concentrated in vacuo. Flash chromatog-
5.1.10. (8R)-2-(4-Acetyl-3,5-dimethyl-1-piperazinyl)-6-[3,5-
bis(trifluoromethyl)benzyl]-8-methyl-4-(2-methylphenyl)-
6,7,8,9-tetrahydro-5H-pyrimido[4,5-b][1,5]oxazocin-5-one
(14d). The compound 14d (56.6 mg, 63%) was prepared
from 11 (80.0 mg, 0.136 mmol) and 1-acetyl-2,6-dimeth-
ylpiperazine (25.5 mg, 0.163 mmol) in a manner similar
to that described for the preparation of 14b. White foam.
raphy (AcOEt/hexane = 2:1) of the residue gave 14a as a
26
white foam (22.6 mg, 37%). ½aꢀ
= +13.9° (c 1.05,
D
1
1
26
CHCl3). H NMR (400 MHz, CDCl3) d 1.17 (3H, d,
J = 7.3 Hz), 2.17–2.30 (1H, m), 2.21 (3H, s), 3.20 (1H,
dd, J = 15.3 and 4.9 Hz), 3.42 (1H, dd, J = 15.3 and
12.2 Hz), 3.92 (1H, d, J = 15.3 Hz), 4.22 (1H, dd,
J = 13.4 and 3.1 Hz), 4.56 (1H, dd, J = 13.5 and 1.8 Hz),
5.33 (1H, d, J = 15.3 Hz), 6.92 (1H, d, J = 7.9 Hz), 7.00–
7.08 (1H, m), 7.20–7.28 (2H, m), 7.56 (2H, s), 7.82 (1H,
s), 8.87 (1H, s). HRMS (EI) for C25H21F6N3O2 (M+):
calcd, 509.1538; found, 509.1492. Anal. Calcd for
C25H21F6N3O2: C, 58.94; H, 4.15; N, 8.25. Found: C,
58.64; H, 4.03; N, 8.21.
½aꢀ
= +3.99° (c 1.01, CHCl3). H NMR (400 MHz,
D
CDCl3) d 1.15 (3H, d, J = 6.7 Hz), 1.20–1.35 (6H, m),
2.10–2.23 (1H, m), 2.14 (3H, s), 2.26 (3H, s), 3.01–3.09
(3H, m), 3.47–3.57 (1H, m), 3.90 (1H, d, J = 15.3 Hz),
4.09–4.16 (1H, m), 4.46 (1H, dd, J = 13.4 and 1.8 Hz),
4.62–4.79 (3H, m), 5.30 (1H, d, J = 15.3 Hz), 6.87–6.96
(1H, m), 6.98–7.08 (1H, m), 7.18–7.26 (2H, m), 7.57
(2H, s), 7.80 (1H, s). HRMS (EI) for C33H35F6N5O3
(M+): calcd, 663.2644; found, 663.2626. Anal. Calcd for
C33H35F6N5O3 0.5H2O: C, 58.92; H, 5.24; N, 10.41.
Found: C, 58.86; H, 5.33; N, 10.06.
5.1.8. (8R)-6-[3,5-Bis(trifluoromethyl)benzyl]-2-(dimeth-
ylamino)-8-methyl-4-(2-methylphenyl)-6,7,8,9-tetra-
hydro-5H-pyrimido[4,5-b][1,5]oxazocin-5-one (14b). To a
solution of 11 (88.2 mg, 0.150 mmol) in THF (0.5 mL)
was added dimethylamine (1.0 mL, 2.0 mmol, 2 M solu-
tion in methanol) at room temperature and the mixture
was stirred at 80 °C for 3 h. The resulting mixture was
diluted with ethyl acetate, then washed with water and
brine. The organic layer was dried over anhydrous
Na2SO4, filtered, and then concentrated in vacuo. Flash
chromatography (AcOEt/hexane = 2:1) of the residue
5.1.11. (8S)-6-[3,5-Bis(trifluoromethyl)benzyl]-8-methyl-
4-(2-methylphenyl)-6,7,8,9-tetrahydro-5H-pyrimido[4,5-
b][1,5]oxazocin-5-one (15a). The compound 15a
(45.7 mg, 60%) was prepared from 12 (88.2 mg,
0.150 mmol) and NaBH4 (29.0 mg, 0.767 mmol) in a
manner similar to that described for the preparation of
1
26
14a. White foam. ½aꢀ
= ꢁ11.5° (c 1.06, CHCl3). H
D
NMR spectrum was identical with that of 14a. HRMS
(EI) for C25H21F6N3O2 (M+): calcd, 509.1538; found,
509.1510. Anal. Calcd for C25H21F6N3O2: C, 58.94; H,
4.15; N, 8.25. Found: C, 58.65; H, 4.05; N, 8.14.
gave 14b as
25
a
white foam (68.0 mg, 82%).
1
½aꢀ
= +20.4° (c 1.08, CHCl3). H NMR (400 MHz,
5.1.12. (8S)-6-[3,5-Bis(trifluoromethyl)benzyl]-2-(dimeth-
ylamino)-8-methyl-4-(2-methylphenyl)-6,7,8,9-tetrahydro-
D
CDCl3) d 1.13 (3H, d, J = 6.7 Hz), 2.12–2.24 (1H, m),
2.26 (3H, s), 3.10 (1H, dd, J = 15.3 and 4.9 Hz), 3.19
(6H, s), 3.47–3.56 (1H, m), 3.88 (1H, d, J = 14.7 Hz),
4.11 (1H, dd, J = 13.5 and 3.1 Hz), 4.44 (1H, dd,
J = 13.5 and 2.4 Hz), 5.32 (1H, d, J = 14.7 Hz), 6.90–
6.96 (1H, m), 6.98–7.06 (1H, m), 7.16–7.24 (2H, m),
7.56 (2H, s), 7.79 (1H, s). HRMS (FAB+) for
C27H27F6N4O2 (M++1): calcd, 533.2038; found,
533.2004. Anal. Calcd for C27H26F6N4O2: C, 58.69; H,
4.74; N, 10.14. Found: C, 58.49; H, 4.67; N, 10.00.
5H-pyrimido[4,5-b][1,5]oxazocin-5-one
(15b).
The
compound 15b (69.2 mg, 83%) was prepared from 12
(88.2 mg, 0.150 mmol) and dimethylamine (1.0 mL,
2.0 mmol, 2 M solution in methanol) in a manner similar
to that described for the preparation of 14b. White solid.
1
26
Mp: 83–86 °C. ½aꢀ
= ꢁ18.3° (c 1.04, CHCl3). H NMR
D
spectrum was identical with that of 14b. HRMS (FAB+)
for C27H27F6N4O2 (M++1): calcd, 533.2038; found,
533.2078. Anal. Calcd for C27H26F6N4O2: C, 58.69; H,
4.74; N, 10.14. Found: C, 58.59; H, 4.67; N, 9.95.
5.1.9. (8R)-2-(4-Acetyl-1-piperazinyl)-6-[3,5-bis(trifluoro-
methyl)benzyl]-8-methyl-4-(2-methylphenyl)-6,7,8,9-tetra-
hydro-5H-pyrimido[4,5-b][1,5]oxazocin-5-one (14c). The
compound 14c (79.7 mg, 84%) was prepared from 11
(88.2 mg, 0.150 mmol) and 1-acetylpiperazine (23.0 mg,
5.1.13. (8S)-2-(4-Acetyl-1-piperazinyl)-6-[3,5-bis(trifluo-
romethyl)benzyl]-8-methyl-4-(2-methylphenyl)-6,7,8,9-tetra-
hydro-5H-pyrimido[4,5-b][1,5]oxazocin-5-one (15c). The
compound 15c (85.2 mg, 89%) was prepared from 12
(88.2 mg, 0.150 mmol) and 1-acetylpiperazine (23.0 mg,
0.179 mmol) in a manner similar to that described for
25
the preparation of 14b. White foam. ½aꢀ
= +9.94° (c
0.179 mmol) in a manner similar to that described for
26
D
1.09, CHCl3). 1H NMR (400 MHz, CDCl3) d 1.15
the preparation of 14b. White foam. ½aꢀ
= ꢁ8.51°
D

5088
S. Seto, J. Asano / Bioorg. Med. Chem. 15 (2007) 5083–5089
1
(c 1.03, CHCl3). H NMR spectrum was identical with
that of 14c. HRMS (FAB+) for C31H32F6N5O3 (M++1):
calcd, 636.2409; found, 636.2412. Anal. Calcd for
C31H31F6N5O30.3H2O: C, 58.09; H, 4.87; N, 10.93.
Found: C, 57.88; H, 4.74; N, 10.81.
d, J = 15.1 Hz), 6.95 (1H, br d, J = 7.3 Hz), 7.05 (1H, br
dd, J = 7.3 and 7.3 Hz), 7.20–7.25 (2H, m), 7.57 (2H, s),
7.81 (1H, s). HRMS (EI) for C30H29F6N5O3 (M+): calcd,
621.217500; found, 621.2192. Anal. Calcd for
C30H29F6N5O3: C, 57.97; H, 4.70; N, 11.27. Found: C,
57.90; H, 4.70; N, 11.33.
5.1.14. (8S)-2-(4-Acetyl-3,5-dimethyl-1-piperazinyl)-6-[3,5-
bis(trifluoromethyl)benzyl]-8-methyl-4-(2-methylphenyl)-
6,7,8,9-tetrahydro-5H-pyrimido[4,5-b][1,5]oxazocin-5-one
(15d). The compound 15d (60.2 mg, 60%) was prepared
from 12 (88.2 mg, 0.150 mmol) and 1-acetyl-2,6-dimeth-
ylpiperazine (28.0 mg, 0.179 mmol) in a manner similar
5.1.18. 2-(4-Acetyl-3,5-dimethyl-1-piperazinyl)-6-[3,5-bis(tri-
fluoromethyl)benzyl]-4-(2-methylphenyl)-6,7,8,9-tetra-
hydro-5H-pyrimido[4,5-b][1,5]oxazocin-5-one (16d). The
compound 16d (203 mg, 62%) was prepared from 13
(281 mg, 0.500 mmol) and 1-acetyl-2,6-dimethylpipera-
zine (86.0 mg, 0.550 mmol) in a manner similar to that
described for the preparation of 14b. White solid. Mp:
to that described for the preparation of 14b. White foam.
26
½aꢀ
= ꢁ2.84° (c 1.01, CHCl3). 1H NMR spectrum
D
1
was identical with that of 14d. HRMS (EI) for
C33H35F6N5O3 (M+): calcd, 663.2644; found, 663.2626.
Anal. Calcd for C33H35F6N5O3 0.5H2O: C, 58.92; H,
5.24; N, 10.41. Found: C, 58.96; H, 5.38; N, 10.08.
130–133 °C. H NMR (400 MHz, CDCl3) d 1.28 (6H,
s), 1.90–2.03 (1H, m), 2.09–2.20 (1H, m), 2.14 (3H, s),
2.27 (3H, s), 3.04–3.16 (2H, m), 3.30 (1H, dd, J = 15.8
and 5.5 Hz), 3.75–3.90 (1H, m), 3.87 (1H, d,
J = 14.6 Hz), 4.30–4.42 (2H, m), 4.63–4.80 (2H, m),
5.30 (1H, d, J = 14.6 Hz), 6.90–6.98 (1H, m), 7.02–7.08
(1H, m), 7.20–7.30 (2H, m), 7.58 (2H, s), 7.81 (1H, s).
HRMS (FAB+) for C32H34F6N5O3 (M+H+): calcd,
650.2566; found, 650.2588. Anal. Calcd for
C32H33F6N5O3 1H2O: C, 57.57; H, 4.98; N, 10.49.
Found: C, 57.42; H, 5.11; N, 10.10.
5.1.15. 6-[3,5-Bis(trifluoromethyl)benzyl]-4-(2-methylphe-
nyl)-6,7,8,9-tetrahydro-5H-pyrimido[4,5-b][1,5]oxazocin-
5-one (16a). The compound 16a (48.6 mg, 65%) was
prepared from 1311 (86.0 mg, 0.150 mmol) and NaBH4
(28.5 mg, 0.753 mmol) in a manner similar to that de-
scribed for the preparation of 14a. White solid. Mp:
1
171–172 °C. H NMR (400 MHz, CDCl3) d 1.97–2.10
(1H, m), 2.15–2.27 (1H, m), 2.21 (3H, s), 3.35 (1H, ddd,
J = 15.3, 5.5 and 1.2 Hz), 3.67–3.78 (1H, m), 3.89 (1H,
d, J = 15.3 Hz), 4.43–4.50 (2H, m), 5.32 (1H, d,
J = 15.3 Hz), 6.93 (1H, d, J = 7.3 Hz), 7.06 (1H, t,
J = 7.3 Hz), 7.20–7.31 (2H, m), 7.56 (2H, s), 7.82 (1H,
s), 8.87 (1H, s). HRMS (EI) for C24H19F6N3O2 (M+):
calcd, 495.1381; found, 495.1350. Anal. Calcd for
C24H19F6N3O2: C, 58.18; H, 3.87; N, 8.48. Found: C,
58.06; H, 3.74; N, 8.45.
5.2. Biology
5.2.1. NK1 receptor antagonist test15. Guinea pigs were
stunned by a blow on the head and then exsanguinated
from the carotid artery and the ileum was isolated. The
ileum was mounted in an organ bath containing Tyrode’s
solution, which was maintained at 32 °C and gased with
95% O2 and 5% CO2. The ileum was subjected to a resting
tension of 1 g and allowed to equilibrate for 20 min before
the experiment was started. As a control, a concentration-
response curve for substance P obtained in the absence of
test compounds was used. The NK1 receptor antagonist
activity of each test compound was determined from a
concentration-response curve obtained by pretreatment
with at least three concentrations of a test compound in
DMSO solution for 10 min and subsequently applying
substance P in a cumulative manner. The activity was ex-
pressed as a KB value determined by the Schild method.16
5.1.16. 6-[3,5-Bis(trifluoromethyl)benzyl]-2-(dimethylami-
no)-4-(2-methylphenyl)-6,7,8,9-tetrahydro-5H-pyrimido[4,5-
b][1,5]oxazocin-5-one (16b). The compound 16b (38.7 mg,
72%) was prepared from 13 (57.4 mg, 0.100 mmol) and
dimethylamine (1 mL; 2 M solution in methanol) in a
manner similar to that described for the preparation
of 14b. White foam. 1H NMR (400 MHz, CDCl3) d
1.90–2.02 (1H, m), 2.07–2.18 (1H, m), 2.27 (3H, s), 3.19
(6H, s), 3.26 (1H, dd, J = 15.3 and 4.3 Hz), 3.75–3.88
(1H, m), 3.84 (1H, d, J = 14.7 Hz), 4.29–4.41 (2H, m),
5.33 (1H, d, J = 14.7 Hz), 6.95 (1H, d, J = 7.3 Hz),
7.02–7.08 (1H, m), 7.19–7.25 (2H, m), 7.57 (2H, s), 7.80
(1H, s). HRMS (ESI+)for C26H25F6N4O2 (M+H+): calcd,
539.18817; found, 539.18740. Anal. Calcd for
C26H24F6N4O2: C, 57.99; H, 4.49; N, 10.40. Found: C,
57.74; H, 4.57; N, 10.21.
Acknowledgments
We thank Mr. Asao Tanioka, Mr. Makoto Ikeda, Mr.
Tetsuharu Takatsuka, and Ms Sayako Nakazawa for
their technical support. We also thank Dr. Yasushi
Kohno, Dr. Takayoshi Ishizaki, and Dr. Kazuhiko
Iwase for their helpful discussions and encouragement.
Furthermore we express our thanks to Professor Hide-
aki Natsugari, presently at Teikyo University, for his
many valuable suggestions.
5.1.17. 2-(4-Acetyl-1-piperazinyl)-6-[3,5-bis(trifluorometh-
yl)benzyl]-4-(2-methylphenyl)-6,7,8,9-tetrahydro-5H-pyrim-
ido[4,5-b][1,5]oxazocin-5-one (16c). The compound 16c
(60.7 mg, 65%) was prepared from 13 (86.0 mg,
0.150 mmol) in a manner similar to that described for the
preparation of 14b. White solid. Mp: 162–164 °C. 1H
NMR (400 MHz, CDCl3) d 1.92–2.04 (1H, m), 2.10–2.20
(1H, m), 2.13 (3H, s), 2.25 (3H, s), 3.30 (1H, dd, J = 15.1
and 4.4 Hz), 3.50 (2H, dd, J = 4.4 and 4.4 Hz), 3.63–3.70
(2H, m), 3.76–3.95 (6H, m), 4.30–4.43 (2H, m), 5.32 (1H,
References and notes
1. Guard, S.; Watson, S. P. Neurochem. Int. 1991, 18, 149.
2. Von Euler, U. S.; Gaddum, J. H. J. Physiol. 1931, 72, 74.
3. Swain, C.; Rupniak, N. M. J. Annu. Rep. Med. Chem.
1999, 34, 51.

S. Seto, J. Asano / Bioorg. Med. Chem. 15 (2007) 5083–5089
5089
4. Gerspacher, M.; Von Sprecher, A. Drugs Future 1999, 24,
883.
5. Gao, Z.; Peet, N. P. Curr. Med. Chem. 1999, 6, 375.
6. Sakurada, T.; Sakurada, C.; Tan-No, K.; Kisara, K. CNS
Drugs 1997, 8, 436.
Natsugari, H.; Ikeura, Y.; Kamo, I.; Ishimaru, T.; Ishichi,
Y.; Fujishima, A.; Tanaka, T.; Kasahara, F.; Kawada, M.;
Doi, T. J. Med. Chem. 1999, 42, 3982.
10. Ishichi, Y.; Ikeura, Y.; Natsugari, H. Tetrahedron 2004,
60, 4481.
7. Swain, C. J.; Seward, E. M.; Cascieri, M. A.; Fong, T. M.;
Herbert, R.; MacIntyre, D. E.; Merchant, K. J.; Owen, S.
N.; Owens, A. P.; Sabin, V.; Teall, M.; VanNiel, M. B.;
Williams, B. J.; Sadowski, S.; Strader, C.; Ball, R. G.;
Baker, R. J. Med. Chem. 1995, 38, 4793.
8. (a) Fong, T. M.; Cascieri, M. A.; Yu, H.; Bansal, A.;
Swain, C.; Strader, C. D. Nature 1993, 362, 350; (b) Fong,
T. M.; Cascieri, M. A.; Yu, H.; Underwood, D.; Swain,
C.; Strader, C. D. J. Biol. Chem. 1994, 269, 2728; (c) Fong,
T. M.; Yu, H.; Cascieri, M. A.; Underwood, D.; Swain,
C.; Strader, C. D. J. Biol. Chem. 1994, 269, 14957.
9. (a) Ikeura, Y.; Ishichi, Y.; Tanaka, T.; Fujishima, A.;
Murabayashi, M.; Kawada, M.; Ishimaru, T.; Kamo, I.;
Doi, T.; Natsugari, H. J. Med. Chem. 1998, 41, 4232; (b)
11. Seto, S.; Tanioka, A.; Ikeda, M.; Izawa, S. Bioorg. Med.
Chem. 2005, 13, 5717.
12. Yamaguchi, H.; Ishikawa, F. Chem. Pharm. Bull. 1982, 30,
326.
13. Gilman, N. W.; Rosen, P.; Earley, J. V.; Cook, C.;
Todaro, L. J. J. Am. Chem. Soc. 1990, 112, 3969.
14. The same trend holds true in the studies on high-
temperature 1H NMR spectrum of KRP-103 including
pyrimido[4,5-b][1,5]oxazocine skeleton.11,13
15. Dion, S.; D’Orleans-Juste, P.; Drapeau, G.; Rhaleb,
N.-E.; Rouissi, N.; Tousignant, C.; Regoli, D. Life
Sci. 1987, 41, 2269.
16. Arunlakshana, O.; Schild, H. O. Br. J. Pharmacol. 1959,
14, 48.