Design and synthesis of new orally active inhibitors of human neutrophil elastase

Article abstract of DOI:10.1016/S0968-0896(01)00007-4

To identify new orally active inhibitors, further modification of 1 (ONO-6818) was performed. Peptidic derivatives 4b, 4c and 4n showed more potent inhibitory activity than nonpeptidic derivatives 3a-c. As a result, a series of peptidic inhibitors, 4a-s a

Full text of DOI:10.1016/S0968-0896(01)00007-4

Bioorganic & Medicinal Chemistry 9 (2001) 1307±1323
Design and Synthesis of New Orally Active Inhibitors
of Human Neutrophil Elastase
Kazuyuki Ohmoto, Motohiro Okuma, Tetsuya Yamamoto, Hideomi Kijima,
Tomohiko Sekioka, Kanji Kitagawa, Shigeki Yamamoto, Kenji Tanaka,
Kazuhito Kawabata, Atsushi Sakata, Haruo Imawaka, Hisao Nakai* and Masaaki Toda
Minase Research Institute, Ono Pharmaceutical Co., Ltd., Shimamoto, Mishima, Osaka 618-8585, Japan
Received 20 November 2000; accepted 29 December 2000
AbstractÐTo identify new orally active inhibitors, further modi®cation of 1 (ONO-6818) was performed. Peptidic derivatives 4b, 4c
and 4n showed more potent inhibitory activity than nonpeptidic derivatives 3a±c. As a result, a series of peptidic inhibitors, 4a±s
and 5a±v, were discovered. Among these N-aryl derivatives 5a±g, 5i, 5m and 5o±v showed oral activity. Their oral activity showed
good correlation with their metabolic stability. Compounds 5h and 5j±l, which were extremely metabolically unstable in hamster
plasma, did not show oral activity. Oral activity was considered to be determined by a combination of at least two factors: oral
absorption and metabolic stability. # 2001 Elsevier Science Ltd. All rights reserved.
Introduction
this report, we describe the discovery of peptidyl a-keto-
1,3,4-oxadiazolin-2-ones, which possess excellent oral
activity.
Human neutrophil elastase (HNE) has been implicated
in initiation or exacerbation of a number of pathologi-
cal conditions such as pulmonary emphysema,1 cystic
®brosis,2 chronic bronchitis,3 adult respiratory distress
syndrome,4 chronic bowel disease,5,6 myocarditis7,8 and
arthritis.9 Several classes of orally active, nonpeptidic
inhibitors of HNE have been described including tri-
¯uoromethyl ketones,10À12 b-lactams13,14 and pyrrolo-
pyrrolones.15 An attempt has also been made to identify
peptidic inhibitors with the desired level of in vivo activ-
ity following oral administration.16 However, orally
active inhibitors with clinical potential are very rare.
Chemistry
Compounds 4a±s, 5a±t and 5v were synthesized by the
peptide formation of aminoalcohols 14a±s, 19a±t and 25
with carboxylic acid 16 followed by oxidation of the
formed alcohols 15a±s, 20a±t and 26, respectively.
The common intermediate 10a was prepared as described
in Scheme 1. Ring-opening reaction of N-protected
aminoepoxide 618 a€orded 7. The newly formed
hydroxyl group was protected by formation of an aceto-
nide to a€ord 8. Methanolysis of O-acetate of 8 pro-
vided 9, which was oxidized in good yield to a€ord car-
boxylic acid 10a.
Our studies to ®nd a low molecular weight inhibitor of
HNE resulted in the discovery of the orally active non-
peptidic inhibitor 1 (ONO-6818).17 An orally active pepti-
dic inhibitor 2 (ZD8321) was also indenti®ed by Zeneca.16
In the process of our own screening program for an
orally active inhibitor of HNE, a new series of inhibitors,
3a±c, 4b, 4c and 4n, were obtained by further chemical
modi®cation of a-keto-1,3,4-oxadiazole 1 (Chart 1). In
Compounds 4a±s were prepared as described in Scheme
2. The compound 10b, which was prepared by esteri-
®cation of 10a, was converted to acid hydrazide 11 by
condensation reaction with hydrazine hydrate. Cycliza-
tion of the acid hydrazide function of 11 was accom-
plished by reaction with carbonyldiimidazole (CDI) in
the presence of triethylamine to a€ord 1,3,4-oxadiazo-
lin-2-one 12.
*Corresponding author. Tel.: +81-75-961-1151; fax: +81-75-962-9314;
e-mail: hi.nakai@ono.co.jp
0968-0896/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(01)00007-4

1308
K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
3N-Alkylation of the newly formed 1,3,4-oxadiazolin-2-
one with alkyl halide in the presence of a base or with
alkyl alcohol in the presence of diethyl azodicarboxylate
(DEAD)/triphenylphosphine gave 13a±s. Deprotection
of the acetonide of 13a±s under acidic conditions pro-
vided amino-alcohols 14a±s, which were converted to
the corresponding 15a±s, respectively, by condensation
with 16.19 Swern oxidation of the alcohols 15a±s a€orded
4a±s.
Synthesis of 5a±u was carried out as described in
Schemes 3 and 4. N-Aryl-N0-acylhydrazide 17a±t were
prepared by condensation reaction of 10a with the cor-
.
responding aryl hydrazine in the presence of EDC HCl.
Cyclization reaction of 17a±t using CDI a€orded 18a±t,
deprotection of which under acidic conditions provided
19a±t, respectively. Peptide formation of 19a±t with 16
provided 20a±t, oxidation of which provided 5a±t,
respectively. Hydrogenolysis of the benzyl group of 5n
gave the phenol derivative 5u (Scheme 4).
Chart 1. a-Keto-1,3,4-oxadiazolin-2-one as a new right half.
3-(4-Anilino)-1,3,4-oxadiazolin-2-one 5v was prepared
as described in Scheme 5. The acid hydrazide 21 was
obtained from 10a by the conventional method using
4-nitrophenylhydrazine. Cyclization of 21 using CDI was
carried out by the same procedure as described above to
a€ord 22. Catalytic hydrogenation of 22 a€orded 23,
which was alkylated to give 24. Acidic deprotection of
24 provided the amino-alcohol 25, peptide formation of
which with 16 gave 26. Swern oxidation of 26 a€orded
5v. Compounds 3a±c were prepared as described in Scheme
6(a) and (b). Peptide formation of the aminoketones
14b,c with 27a a€orded 28a,b, respectively, which were
converted to the corresponding ketones 29a,b by Swern
oxidation. Subsequent deprotection of 29a,b by catalytic
hydrogenation a€orded 3a,b, respectively (Scheme 6(a)).
Replacement of the N-benzyloxycarbonyl group of 27b,
Scheme 1. Preparation of the common intermediate 10a. Reagent:
(a) AcOH, Li2CO3, DMF; (b) 2-methoxypropene, 10-camphorsulfonic
.
acid, DMF; (c) K2CO3, MeOH; (d) RuCl3 nH2O, NaIO4, CCl4,
CH3CN, H2O.
.
Scheme 2. Preparation of 3-alkyl-1,3,4-oxadiazolin-2-ones 4a±s. Reagent: (a) CH2N2±Et2O, EtOAc; (b) NH2NH2 H2O, MeOH; (c) CDI, triethyla-
.
mine, THF; (d) RX, K2CO3, DMF; (e) ROH, DEAD, Ph3P, THF; (f) TFA±MeOH or TFA±H2O, then HCl±EtOAc; (g) TsOH H2O, EtOH; (h) 16,
.
EDC HCl, HOBt H2O, N-methylmorpholine, DMF; (i) oxalyl chloride, DMSO, N-methylmorpholine, CH2Cl2.
.

K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
1309
Scheme 3. Preparation of 3-Aryl-1,3,4-oxadiazolin-2-ones 5a±t. Ar-: a, Ph-; b, 2-Me-Ph-; c, 3-Me-Ph-; d, 4-Me-Ph-; e, 2-MeO-Ph-; f, 4-MeO-Ph-; g,
2-CF3-Ph-; h, 4-CF3-Ph-; i, 4-F-Ph-; j, 4-Cl-Ph-; k, 4-CN-Ph-; l, 4-CF3O-Ph-; m, 4-EtO-Ph-; n, 4-BnO-Ph-; o, 2-Me-4-MeO-Ph-; p, 2,4-diMeO-Ph-;
.
q, 2-Me-4-F-Ph-; r, 2-MeO-4-F-Ph-; s, 2,4-diF-Ph-; t, 2,4-diMe-Ph-. Reagent: (a) ArNHNH2, EDC HCl, HOBt H2O, DMF; (b) ArNHNH2 HCl,
.
.
.
.
.
.
.
EDC HCl, HOBt H2O, N-methylmorpholine, DMF; (c) CDI, triethylamine, THF; (d) TsOH H2O, EtOH; (e) 16, EDC HCl, HOBt H2O,
N-methylmorpholine, DMF; (f) oxalyl chloride, DMSO, N-methylmorpholine, CH2Cl2.
prepared from 27a, with a N-tert-butoxycarbonyl group
was carried out by the conventional method to give 27c.
Peptide formation of 27c with 14n a€orded 28c, which
was converted to 29c by Swern oxidation. Acidic
deprotection of 29c provided 3c (Scheme 6(b)).
This assay evaluates the ability of an orally adminis-
tered inhibitor to protect the lungs from hemorrhage
induced by a subsequent intratracheal challenge of a
10U/lung dose of HNE.
As shown in Table 1, replacement of 5-tert-butyl-1,3,4-
oxadiazole of 1 with 3-alkyl-1,3,4-oxadiazolin-2-ones
a€orded 3a±c with marked reduction of the inhibitory
activity. Conversion of 3a±c to their corresponding
peptidic inhibitors 4b, 4c and 4n restored the potent in
vitro activity (Table 2). Based on these experimental results,
a series of peptidic inhibitors, 4a±s, were discovered to
exhibit moderate to potent in vitro activity. More
detailed chemical modi®cation of this series of com-
pounds was continued to obtain orally active inhibitors.
Biological data of 3-alkyl-1,3,4-oxadiazolin-2-ones are
shown in Table 2(a). Among the compounds tested, 4c
demonstrated the most potent in vitro activity, although
it was not orally active. 3-Alkyl derivatives 4b±m
exhibited potent inhibitory activity, while 3-methyl
derivative 4a did not. Clear-cut SARwas not obtained
within the chemical modi®cations described in Table 2(a).
Unfortunately, none of the 3-alkyl-1,3,4-oxadiazolin-2-
ones described in Table 2(a) was orally active despite
their potent in vitro activities. The same extent of in
vitro potency was obtained in the series of compounds
Results and Discussion
The compounds listed in Tables 1±5 were tested
both in vitro and in vivo for their ability to inhibit
elastase activity. In vitro testing consisted of determi-
nation of the Ki value corresponding to the compounds'
ability to inhibit hydrolysis of the synthetic substrate
MeO-Suc-Ala-Ala-Pro-Val-pNa.20 In vivo testing was
performed by acute hemorrhagic assay in hamsters.
Scheme 4. Hydrogenolysis of benzyl group of 5n. Reagent: (a) H2,
10% Pd(OH)2/C, MeOH.
.
Scheme 5. Preparation of 3-(4-anilino)-1,3,4-oxadiazolin-2-one 5v. Reagent: (a) 4-nitrophenylhydrazine, EDC HCl, HOBt H2O, DMF; (b) CDI,
.
.
triethylamine, THF; (c) H2, 10% Pd(OH)2/C, MeOH, dioxane; (d) HCHOaq, NaBH3CN, AcOH, MeCN; (e) TsOH H2O, EtOH; (f) 16, EDC HCl,
.
.
HOBt H2O, N-methylmorpholine, DMF; (g) oxalyl chloride, DMSO, N-methylmorpholine, CH2Cl2.

1310
K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
.
.
Scheme 6. (a) Preparation of 3a±b. a, R=isoPr; b, R =n-Bu. Reagent: (a) 14b or 14c, EDC HCl, HOBt H2O, N-methylmorpholine, DMF; (b)
oxalyl chloride, DMSO, N-methylmorpholine, CH2Cl2; (c) H2, 10% Pd/C (wet), HCl±EtOAc, MeOH; (b) preparation of 3c. Reagent: (a) CH2N2,
.
.
Et2O, MeOH; (b) H2, 10% Pd/C (wet), HCl±EtOAc, MeOH; (c) Boc2O, THF re¯ux; (d) NaOHaq, MeOH; (e) 14n, EDC HCl, HOBt H2O,
N-methylmorpholine, DMF; (f) oxalyl chloride, DMSO, N-methylmorpholine, CH2Cl2; (g) HCl±EtOAc.
4n±s as described in Table 2(b). None of the compounds
possessing a 3-arylalkyl-1,3,4-oxadiazolin-2-one moiety
were orally active, although they showed potent Ki
values. Replacement of the phenyl moiety of 4n with a
3-thienyl or 2-thienyl moiety a€orded 4o and 4p,
respectively, with slightly lower in vitro activities.
Insertion of another methylene group in benzyl moiety
a€orded the phenethyl derivative 4q with ca. 5-fold
lower activity. Substitution of the phenyl moiety of 4n
with a 4-¯uoro or 3,4-methylenedioxy group produced 4r
and 4s with no marked changes on inhibitory activity.
Biological data of 3-(2,4-disubstituted-phenyl)-1,3,4-
oxadiazolin-2-ones 5o±t are shown in Table 5. All of
these compounds were orally active. Asymmetrical sub-
stitution of the 3-phenyl moiety was speculated to
improve their physicochemical properties such as water-
solubility.
In summary, the compounds reported here could be
clearly classi®ed into two classes: orally active and
inactive compounds. 3-Aryl-1,3,4-oxadiazolin-2-ones
showed oral activity, while the other 3-alkyl and 3-aryl-
alkyl-1,3,4-oxadiazolin-2-ones did not.
Biological data of 3-phenyl-1,3,4-oxadiazolin-2-ones are
shown in Table 3. Among the compounds tested, 5a±g
exhibited oral activity at a dose of 30 mg/kg, while 5h
was not orally active at the same dose. All the com-
pounds retained potent inhibitory activity. The sub-
stitution pattern (ortho, meta, para) did not a€ect the in
vitro or in vivo activity.
Tables 3±5 also demonstrate the results of in vitro
metabolic study.
Table 3 shows the results of an in vitro study of meta-
bolism of 5a±h. Metabolic stability of the orally active
inhibitors was investigated. Compounds 5a±h were treated
with hamster liver microsomes (MS) in the presence of
NADPH for 30 min. All of these compounds except for
5c were quite stable against in vitro metabolism with
hamster liver MS. These compounds were also treated
with hamster plasma for 60 min. Introduction of an
ortho- or para-substituent to the phenyl group usually
provided an increase in stability, while meta-substitution
decreased the metabolic stability relative to 5a as illu-
strated by 5c. The order of stability was 5b>5e>5f>
5a, 5g>5h. Among the compounds tested, 5b exhibited
the most potent activity after oral administration. The
other compounds also showed oral activity. This result
indicated that meta-substitution reduced the metabolic
stability against both hamster liver MS and plasma rela-
tive to the corresponding para- and ortho-substitutions.
Biological data of other 3-(4-substituted-phenyl)-1,3,4-
oxadiazolin-2-ones 5i±n, 5u and 5v are shown in Table
4. Most of the compounds 5i, 5m, 5n, 5u and 5v were
orally active. Their potencies, however, did not show
the expected correlation with their in vitro potencies.
Especially, 5j and 5n did not show oral activity despite
their potent in vitro activity. Again, clear-cut colleration
was not obtained between their structure and activities.
Table 1. Biological data of 3-amino-6-phenylaminopyrimidinone-
1,3,4-oxadiazolin-2-ones 3a±c
Table 4 shows the in vitro experimental results of the
metabolic study of para-substituted phenyl derivatives.
The same experiment as described above was carried
out using para-substituted phenyl derivatives 5i±n, 5u
and 5v. Compounds 5h and 5j±l, which were not orally
active, were extremely unstable in hamster plasma.
Compound
R
Ki (nM)a
3a
3b
3c
isoPr
n-Bu
Bn (HCl salt)
264
42.8
111
The rest of the compounds 5i, 5m, 5u and 5v, which
were orally active, showed metabolic stability against
both hamster liver MS and the hamster plasma. Among
the compounds tested, 5v exhibited the most potent oral
1 (ONO-6818)
12.2
aInhibition of HNE-catalyzed hydrolysis of the synthetic substrate
MeO-Suc-Ala-Ala-Pro-Val-pNa.

K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
1311
activity. Metabolic stability showed good correlation
with respect to oral activity. Especially, polar groups
such as 2-OMe, 4-OMe, 4-OH and 4-NMe2 groups were
e€ective for metabolic stabilization of the inhibitors.
These results demonstrated that at least two factors,
metabolic stability and oral absorption, are required to
obtain good oral activity.
Table 2. Biological data of (a) 3-alkyl-1,3,4-oxadiazolin-2-ones 4a±m;
(b) 3-arylalkyl-1,3,4-oxadiazolin-2-ones 4n±s
Compound
R
Ki (nM)a
Table 5 shows the results of the in vitro study of the
metabolic stability of 3-(2,4-disubstituted-phenyl) deri-
vatives. Combination of the above-mentioned results
produced ortho, para-disubstituted inhibitors 5o±t with
good metabolic stability and good oral activity. The
compounds 5o and 5p showed the most potent oral
activity, while 5s was less orally active despite its potent
inhibitory activity because of its unstability in hamster
plasma.
a.
4a
40.8
4.73
0.85
1.87
4b
4c
4d
4e
4f
5.09
10.4
Conclusion
A series of tripeptidyl 3-phenyl-1,3,4-oxadiazolin-2-one
derivatives have been identi®ed as orally active inhibi-
tors of HNE that exhibited good in vivo activity fol-
lowing oral administration in the HNE-induced lung
injury model. Within the series of 3-phenyl-1,3,4-oxadi-
azolin-2-ones, the oral pro®le could be controlled by
substitutions of the 3-phenyl group of the 1,3,4-oxadi-
azolin-2-ones. By replacing 3-phenyl group of 5a with a
4-N,N-dimethylaminophenyl group or 2,4-disubstituted
phenyl group, compounds with excellent oral potency
were obtained. Our results demonstrated that oral
activity of the inhibitors indicates good SARwith
metabolic stability and oral absorption.
4g
8.10
4h
4i
5.00
1.47
4j
6.04
4k
4l
6.63
14.7
Experimental
4m
4.01
General directions
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
b.
Analytical samples were homogeneous as con®rmed by
TLC, and a€orded spectroscopic results consistent with
the assigned structures. All 1H NMRspectra were
obtained using a Varian Gemini-200, VXR-200s or
Mercury300 spectrometer. Mass spectra were obtained
on a Hitachi M1200H, JEOL JMS-DX303HF or Per-
Septive Voyager Elite spectrometer. IRspectra were
measured on a Perkin-Elmer FT-IR1760X or Jasco FT/
IR-430 spectrometer. Melting points were uncorrected.
Elemental analyses for carbon, hydrogen, nitrogen and
sulfur were carried out by the Analytical Section of Ono
Pharmaceutical Co., Ltd. on a Perkin-Elmer PE2400
SeriesII CHNS/O analyzer. Optical rotations were
measured using a Jasco DIP-1000 polarimeter. Column
chromatography was carried out on silica gel (Merck
silica gel 60 (0.063ꢀ0.200 mm) or Fuji Silysia FL60D).
Thin layer chromatography was performed on silica gel
(Merck TLC or HPTLC plates, silica gel 60 F254).
HPLC analyses were performed with an Alliance (2690
Separations Module, 486 Detector: Waters): (Capcell
PAK C18 UG-120 (4.6Â150 mm), 40 ꢁC, 20 mM
KH2PO4(pH 3)/CH3CN, 1.0 mL/min, UV 220ꢀ245 nm).
The following abbreviations are used: DME, ethylene
4n
4o
4p
4q
1.67
4.27
4.79
8.45
4r
2.50
4s
3.45
aInhibition of HNE-catalyzed hydrolysis of the synthetic substrate
MeO-Suc-Ala-Ala-Pro-Val-pNa.

1312
K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
Table 3. Biological data and in vitro metabolic stability of 3-(unsubstituted or monosubstitutedphenyl)-1,3,4-oxadiazolin-2-ones 5a±h
Acute hemorrhagic assay
% Inhibition at 30 mg/kg, pob ED50 (mg/kg)b
Remaining % of parent compoundc
MS+NADPH (after 30 min) Plasma (after 60 min)
36 19
Compound
X
Ki (nM)a
5a
5b
5c
5d
5e
5f
H
2-Me
3-Me
4-Me
2-OMe
4-OMe
2-CF3
4-CF3
3.41
1.70
4.10
1.60
3.20
1.50
4.90
11.0
64
87
65
58
68
87
83
0
18.7
11.7
NDd
NDd,e
21.5
11.0
NDd,e
NDd
32
15
36
56
69
61
65
90
7
48
74
65
18
0
5g
5h
1 (ONO-6818)
12.2
100
5.1
82
100
aInhibition of HNE-catalyzed hydrolysis of the synthetic substrate MeO-Suc-Ala-Ala-Pro-Val-pNa.
bInhibition of HNE-induced lung hemorrhage in hamsters (n=6±10). Test compounds were administered orally (as a solution in PEG400/distilled
water/ethanol=51/33/16) 1 h before intratracheal instillation of HNE (10 U/lung).
cDetermined based on HPLC analysis: see Experimental.
dND, not determined.
eDose dependency was not observed.
Table 4. Biological data and in vitro metabolic stability of 3-(4-substituted phenyl)-1,3,4-oxadiazolin-2-ones 5i±n and 5u±v
Acute hemorrhagic assay
Remaining % of parent compoundc
MS+NADPH (after 30 min) Plasma (after 60 min)
63 24
Compound
X
Ki (nM)a
% Inhibition at 30 mg/kg, pob
ED50 (mg/kg)b
5i
5j
F
Cl
CN
OCF3
OEt
OBn
OH
2.00
2.20
1.90
9.90
8.90
4.60
4.20
6.40
63
32 (NS)f
NDd,e
NDd
NDd
NDd
NDd
NDd
NDd
7.5
37
30
67
37
39
49
51
3
0
0
78
60
73
100
5k
5l
5m
5n
5u
5v
0
20 (NS)f
72
24 (NS)f
60
96
NMe2
aInhibition of HNE-catalyzed hydrolysis of the synthetic substrate MeO-Suc-Ala-Ala-Pro-Val-pNa.
bInhibition of HNE-induced lung hemorrhage in hamsters (n=6±10). Test compounds were administered orally (as a solution in PEG400/distilled
water/ethanol=51/33/16) 1 h before intratracheal instillation of HNE (10 U/lung).
cDetermined based on HPLC analysis: see Experimental.
dND, not determined.
eDose dependency was not observed.
fNS, not signi®cant.
heated at 100 ꢁC for 17 h. The reaction mixture was
poured into ice-cooled 10% citric acid, and extracted
with EtOAc. The organic layer was washed with H2O,
saturated NaHCO3, brine, dried over anhydrous Na2SO4,
and concentrated in vacuo. The residue was puri®ed by
silica gel column chromatography (Merck7734, EtOAc/
n-hexane (1/9!1/1)) to a€ord 7 (31.0 g, 59%): TLC
.
glycol dimethyl ether; EDC HCl, 1-[3-(dimethylamino)-
.
propyl]-3-ethylcarbodiimide hydrochloride; HOBt H2O,
N-hydroxybenzotriazole hydrate; DEAD, diethyl azodi-
carboxylate; CDI, carbonyldiimidazole; m-NBA, 3-nitro-
benzylalcohol.
(3S,2R)-3-(tert-Butoxycarbonylamino)-2-hydroxy-4-meth-
ylpentyl acetate (7). A mixture of tert-butoxy-N-[(1S)-1-
1
Rf=0.24, EtOAc/n-hexane (1/3); H NMR(300 MHz,
((2R)-oxiran-2-yl)-2-methylpropyl]carboxamide
(6)18
CDCl3) d 4.86±4.75 (m, 1H), 4.20±3.96 (m, 4H), 3.31±
3.20 (m, 1H), 2.10 (s, 3H), 2.00±1.86 (m, 1H), 1.44 (s,
9H), 0.98 and 0.96 (dÂ2, J=6.9 Hz, 3HÂ2).
(41.3 g, 192 mmol), acetic acid (32.9 mL, 575 mmol) and
Li2CO3 (42.6 g, 576 mmol) in DMF (384 mL) was

K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
1313
Table 5. Biological Data and In vitro metabolic Stability of 3-(2,4-disubstitutedphenyl)-1,3,4-oxadiazolin-2-ones 5o±t
Acute hemorrhagic assay
Remaining % of parent compoundc
Compound
X
Y
Ki (nM)a % Inhibition at 30 mg/kg, pob ED50 (mg/kg)b MS+NADPH (after 30 min) Plasma (after 60 min)
5o
5p
5q
5r
5s
5t
OMe Me
OMe OMe
5.00
5.10
3.10
3.30
1.70
4.60
92
92
71
77
74
58
7.8
11.9
NDd
NDd
16.9
17.3
57
66
61
62
59
67
91
76
96
69
9
F
F
F
Me
Me
OMe
F
Me
96
aInhibition of HNE-catalyzed hydrolysis of the synthetic substrate MeO-Suc-Ala-Ala-Pro-Val-pNa.
bInhibition of HNE-induced lung hemorrhage in hamsters (n=6±10). Test compounds were administered orally (as a solution in PEG400/distilled
water/ethanol=51/33/16) 1 h before intratracheal instillation of HNE (10 U/lung).
cDetermined based on HPLC analysis: see Experimental.
dND, not determined.
[(4S,5R)-3-(tert-Butoxycarbonyl)-2,2-dimethyl-4-(methyl-
ethyl)-1,3-oxazolidin-5-yl]methyl acetate (8). To a stirred
solution of 7 (9.66 g, 35.1 mmol) in DMF (40 mL) was
added 2-methoxypropene (10.1 mL, 105 mmol) and 10-
camphorsulfonic acid (405mg, 1.75mmol). After stirring
at rt for 2 h, the reaction mixture was poured into ice-
cooled saturated NaHCO3, and extracted with EtOAc.
The organic layer was washed with brine, dried over
anhydrous MgSO4, concentrated in vacuo, and puri®ed
by silica gel column chromatography (FL60D, EtOAc/
n-hexane (1/40!1/2)) to a€ord 8 (10.0 g, 90%): TLC
Rf=0.72, EtOAc/n-hexane (1/3); MS (MALDI, Pos.)
m/z=216 (MÀBoc+H)+; 1H NMR(200 MHz, CDCl 3)
d 4.20±4.02 (m, 3H), 3.80±3.40 (m, 1H), 2.34±2.12 (m,
1H), 2.10 (s, 3H), 1.59 and 1.54 (sÂ2, 3HÂ2), 1.48 (s,
9H), 0.92 and 0.91 (dÂ2, J=6.8 Hz, 3HÂ2).
CH2Cl2. The ®ltrate was washed with H2O, and dried
over anhydrous Na2SO4. Concentration followed by
trituration with n-hexane, gave 10a (17.6 g, 68%). The
resulting n-hexane solution was concentrated in vacuo,
and puri®ed by column chromatography on silica gel
(FL60D, EtOAc/n-hexane (1/4!1/2)) to a€ord addi-
tional 10 (1.40 g, 5%) as an o€-white powder: total
19.0 g, 73%: TLC Rf=0.33, MeOH/CHCl3 (1/9); 1H
NMR(300 MHz, CDCl 3) d 4.38 (d, J=2.4 Hz, 1H),
4.26±4.18 (m, 1H), 2.34±2.18 (m, 1H), 1.63 and 1.62
(sÂ2, 3HÂ2), 1.47 (s, 9H), 0.97 and 0.95 (dÂ2, J=
7.2 Hz, 3HÂ2).
Methyl (4S,5R)-3-(tert-butoxycarbonyl)-2,2-dimethyl-4-
(methylethyl)-1,3-oxazolidine-5-carboxylate (10b).
A
solution of 10aꢁ(16.0 g, 55.7 mmol) in EtOAc (100 mL)
was treated at 0 C with CH2N2/Et2O21 until the evolution
of gas subsided. The resulting solution was concentrated
in vacuo to a€ord 10b (17.5 g, quant) as a yellow oil: 1H
NMR(300 MHz, CDCl 3) d 4.36 (d, J=2.4 Hz, 1H),
4.28±4.05 (m, 1H), 3.78 (s, 3H), 2.38±2.10 (m, 1H), 1.58
(s, 6H), 1.47 (s, 9H), 0.95 and 0.93 (dÂ2, J=6.9 Hz,
3HÂ2).
tert-Butyl
(4S,5R)-5-(hydroxymethyl)-2,2-dimethyl-4-
(methylethyl)-1,3-oxazolidine-3-carboxylate (9). A mix-
ture of 8 (10.0 g, 31.8 mmol) and K2CO3 (4.83 g,
35.0 mmol) in MeOH (50 mL) was stirred at rt for 3 h.
The reaction mixture was poured into crushed ice, and
extracted with EtOAc. The organic layer was washed
with H2O, brine, dried over anhydrous MgSO4, and
concentrated in vacuo to a€ord 9 (8.74 g, quant). The
product was used for the next reaction without further
puri®cation: TLC Rf=0.50, EtOAc/n-hexane (1/2); MS
tert-Butyl (4S,5R)-5-(N-aminocarbamoyl)-2,2-dimethyl-
4-(methylethyl)-1,3-oxazolidine-3-carboxylate (11).
A
.
mixture of 10b (17.1 g, 55.7 mmol) and NH2NH2 H2O
(55.7 g, 1.11 mol) in MeOH (30 mL) was stirred at rt for
1 h. The reaction mixture was poured into ice water, and
extracted with CH2Cl2. The organic layer was washed
with H2O (Â2), brine, and dried over anhydrous
Na2SO4. Concentration gave 11 (17.1 g, quant) as a
beige solid: TLC Rf=0.51, EtOAc; 1H NMR(300 MHz,
CDCl3) d 7.63 (m, 1H), 4.30 (d, J=3.0 H, 1H), 4.28±4.22
(m, 1H), 2.37±2.17 (m, 1H), 1.59 and 1.58 (sÂ2, 3HÂ2),
1.46 (s, 9H), 0.98 and 0.94 (dÂ2, J=6.9 Hz, 3HÂ2).
1
(APCI, Pos. 20 V) m/z=174 (MÀBoc+H)+; H NMR
(300 MHz, CDCl3) d 4.07±4.00 (m, 1H), 3.66±3.56 (m,
3H), 2.38±2.20 (m, 1H), 1.93 (m, 1H), 1.61 and 1.54
(sÂ2, 3HÂ2), 1.47 (s, 9H), 0.91 and 0.90 (dÂ2,
J=6.9 Hz, 3HÂ2); optical rotation [a]2D5 À2.6, (c 1.7,
CHCl3).
(4S,5R)-3-(tert-Butoxycarbonyl)-2,2-dimethyl-4-(methyl-
ethyl)-1,3-oxazolidine-5-carboxylic acid (10a). To a stirred
solution of 9 (24.8 g, 90.8 mmol) in CCl4/CH3CN/H2O
(2/2/3, 840 mL) were added NaIO4 (58.3 g, 273 mmol)
tert-Butyl (4S,5R)-2,2-dimethyl-4-(methylethyl)-5-(2-oxo-
1,3,4-oxadiazolin-5-yl)-1,3-oxazolidine-3-carboxylate (12).
To a stirred solution of 11 (369 mg, 1.22 mmol) in THF
(25 mL) was added triethylamine (0.21 mL, 1.51 mmol)
.
and then RuCl3 nH2O (248mg, 1 wt%) at rt. After stirring
overnight, the reaction mixture was ®ltered through Celite
to remove an insoluble material, which was washed with

1314
K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
and CDI (239 mg, 1.47 mmol) at 0 ꢁC. The reaction
mixture was stirred at rt overnight, then poured into ice
water, and extracted with EtOAc. The organic layer was
washed with brine, dried over anhydrous Na2SO4, and
concentrated in vacuo. The residue was puri®ed by silica
gel column chromatography (FL60D, CHCl3/MeOH
(1/100)) to a€ord 12 (367 mg, 91%) as a white powder:
TLC Rf=0.27, EtOAc/n-hexane (1/3); 1H NMR
(200 MHz, CDCl3) d 9.40±9.10 (m, 1H), 4.75 (d,
J=4.2 Hz, 1H), 4.50±4.15 (m, 1H), 2.46±2.15 (m, 1H),
1.59 and 1.53 (sÂ2, 3HÂ2), 1.49 (s, 9H), 0.96 and 0.92
(dÂ2, J=6.6 Hz, 3HÂ2).
(130 mg, quant) as a white amorphous powder: TLC
Rf=0.51, CHCl3/MeOH (9/1); 1H NMR(300 MHz,
DMSO-d6) d 7.74 (d, J=9.6 Hz, 1H), 7.23 (d, J=8.7 Hz,
1H), 5.99 (d, J=5.7 Hz, 1H), 4.69±4.63 (m, 1H), 4.41±
4.33 (m, 1H), 4.02±3.92 (m, 1H), 3.76±3.44 (m, 5H), 3.51
(s, 3H), 2.04±1.67 (m, 6H), 1.66±1.53 and 1.34±1.20
(mÂ2, 4H), 1.01±0.74 (m, 12H).
N-[(1S)-2-((2S)-2-{N-[(1S)-2-(3-Butyl-2-oxo-1,3,4-oxa-
diazolin-5-yl)-1-(methylethyl)-2-oxoethyl]carbamoyl}pyrro-
lidinyl)-1-(methylethyl)-2-oxoethyl]methoxycarboxamide
(4c). To a stirred solution of oxalyl chloride (0.045 mL,
0.51 mmol) in CH2Cl2 (0.5 mL) was added dropwise a
solution of DMSO in CH2Cl2 (1 M, 1.02 mL) at À70 ꢁC.
After 30 min, a solution of 15c (130 mg, 0.26 mmol) in
CH2Cl2 (1 mL) was added dropwise at À70 ꢁC. After
stirring at À70 ꢁC for 2 h, the reaction mixture was
treated with N-methylmorpholine (0.23 mL, 2.09 mmol),
then stirred at À20 ꢁC for 30 min. The reaction was
quenched with ice-cooled 1 N HCl, and extracted with
EtOAc. The organic layer was washed with saturated
NaHCO3 and brine, dried over anhydrous Na2SO4, and
concentrated in vacuo. The residue was puri®ed by column
chromatography on silica gel (FL60D, CHCl3/MeOH
(100/1)) to a€ord 4c (688 mg, 70%) as a white amor-
phous powder: TLC Rf=0.23, EtOAc/n-hexane (2/1);
MS (APCI, Pos. 20V) m/z=496 (M+H)+; IR(KBr)
1793, 1717, 1685, 1633, 1525 cmÀ1; 1H NMR(300 MHz,
CDCl3) d 7.39 (d, J=7.2 Hz, 1H), 5.36 (d, J=9.0 Hz,
1H), 5.14 (dd, J=7.2, 5.4 Hz, 1H), 4.61 (dd, J=8.1,
3.0 Hz, 1H), 4.31 (dd, J=9.0, 6.9 Hz, 1H), 3.83 (t,
J=7.2 Hz, 2H), 3.79±3.56 (m, 2H), 3.68 (s, 3H), 2.38±
1.85 (m, 6H), 1.85±1.72 and 1.46±1.31 (mÂ2, 4H), 1.08±
0.88 (m, 15H); optical rotation [a]2D5 À61.6 (c 0.3,
tert-Butyl (4S,5R)-5-(3-butyl-2-oxo-1,3,4-oxadiazolin-5-yl)-
2,2-dimethyl-4-(methylethyl)-1,3-oxazolidine-3-carboxylate
(13c). To a stirred solution of 12 (304 mg, 0.93 mmol)
in DMF (1 mL) was added K2CO3 (143 mg, 1.03 mmol)
followed by n-BuI (0.12 mL, 1.03 mmol) at rt. The reac-
tion mixture was stirred at rt for 2.5 h, then poured into
ice water, and extracted with EtOAc. The organic layer
was washed with 10% citric acid, saturated NaHCO3,
brine, dried over anhydrous Na2SO4, and concentrated
in vacuo. The residue was puri®ed by silica gel column
chromatography (FL60D, EtOAc/n-hexane (1/20)) to
a€ord 13c (347 mg, 97%) as a white solid: TLC
1
Rf=0.58, EtOAc/n-hexane (1/4); H NMR(300 MHz,
CDCl3) d 4.74 (d, J=3.0 Hz, 1H), 4.42±4.11 (m, 1H),
3.71 (t, J=7.2 Hz, 2H), 2.44±1.80 (m, 1H), 1.78±1.66
(m, 2H), 1.59 and 1.53 (sÂ2, 3HÂ2), 1.48 (s, 9H), 1.43±
1.26 (m, 2H), 0.95 and 0.93 (dÂ2, J=7.0 Hz, 3HÂ2),
0.94 (t, J=7.0 Hz, 3H).
5-[(2S,1R)-2-Amino-1-hydroxy-3-methylbutyl]-3-butyl-1,3,4-
oxadiazolin-2-one p-toluenesulfonate (14c). A solution of
ꢂ
.
13c (337 mg, 0.88 mmol) and TsOH H2O (234 mg,
MeCN). Anal. calcd for C23H37N5O7 0.2H2O: C, 55.34;
1.23 mmol) in EtOH (18 mL) was stirred at 80 ꢁC over-
night, and then concentrated in vacuo to a€ord 14c
(428 mg) as TsOH salt quantitatively. The product was
used for the next coupling reaction without further
puri®cation: TLC Rf=0.29, CHCl3/MeOH (9/1); 1H
NMR(300 MHz, DMSO- d6) d 8.04±7.82 (m, 3H), 7.48
(d, J=8.1 Hz, 2H), 7.11 (d, J=8.1 Hz, 2H), 7.01±6.90
(m, 1H), 4.80±4.76 (m, 1H), 3.65 (t, J=6.6 Hz, 2H),
3.29±3.16 (m, 1H), 2.29 (s, 3H), 2.01±1.86 (m, 1H),
1.57±1.39 and 1.39±1.22 (mÂ2, 4H), 0.99 and 0.94 (dÂ2,
J=6.9 Hz, 3H), 0.90 (t, J=7.5 Hz, 3H).
H, 7.55; N, 14.03; found: C, 55.10; H, 7.59; N, 13.83.
Preparation of 4a±b, 4d±f, 4j±n and 4q±s. The following
compounds were prepared according to the same pro-
cedures as described for the preparation of 4c.
N-[(1S)-2-((2S)-2-{N-[(1S)-1-(Methylethyl)-2-(3-methyl-2-
oxo-1,3,4-oxadiazolin-5-yl)-2-oxoethyl]carbamoyl}pyrro-
lidinyl)-1-(methylethyl)-2-oxoethyl]methoxycarboxamide
(4a). Derived from 12 and methyl iodide: white amor-
phous powder; TLC Rf=0.22, CHCl3/MeOH (50/1);
MS (APCI, Pos. 20 V) m/z=454 (M+H)+; IR(KBr)
1795, 1714, 1684, 1635, 1526 cmÀ1; 1H NMR(300 MHz,
CDCl3) d 7.45 (d, J=7.2 Hz, 1H), 5.37 (d, J=9.3 Hz,
1H), 5.10 (dd, J=7.2, 5.7 Hz, 1H), 4.61 (dd, J=8.4,
2.7 Hz, 1H), 4.31 (dd, J=9.3, 7.2 Hz, 1H), 3.81±3.56 (m,
2H), 3.68 (s, 3H), 3.54 (s, 3H), 2.37±1.83 (m, 6H), 1.07±
0.89 (m, 12 H); optical rotation [a]2D6 À60.0, (c 0.3,
N-[(1S)-2-((2S)-2-{N-[(1S,2R)-2-(3-Butyl-2-oxo-1,3,4-ox-
adiazolin-5-yl)-2-hydroxy-1-(methylethyl)ethyl]carbamoyl}
pyrrolidinyl)-1-(methylethyl)-2-oxoethyl]methoxycarbox-
amide (15c). To a stirred solution of (2S)-1-[(2S)-2-
(methoxycarbonylamino)-3-methylbutanoyl]pyrrolidine-
2-carboxylic acid (16)19 (70 mg, 0.26 mmol), 14c (TsOH
ꢂ
.
salt: 126 mg, ca. 0.26 mmol) and HOBt H2O (49 mg,
MeCN). Anal. calcd for C20H31N5O7 0.3H2O: C, 52.35;
.
0.32 mmol) in DMF (2 mL) was added EDC HCl
H, 6.94; N, 15.26; found: C, 52.56; H, 7.01; N, 14.86.
(60 mg, 0.31 mmol) and then N-methylmorpholine
(0.055 mL, 0.50 mmol) at 0 ꢁC. The reaction mixture was
stirred at rt for 7 h, then poured into ice-cooled 10%
citric acid, and extracted with EtOAc. The organic layer
was washed with H2O, saturated NaHCO3, brine, dried
over anhydrous Na2SO4, and concentrated in vacuo.
The residue was puri®ed by silica gel column chroma-
tography (FL60D, MeOH/CHCl3 (1/100)) to a€ord 15c
N-{(1S)-2-[(2S)-2-(N-{(1S)-1-(Methylethyl)-2-[3-(methyl-
ethyl)-2-oxo-1,3,4-oxadiazolin-5-yl]-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (4b). Derived from 12 and isopropyl
iodide: white amorphous powder; TLC Rf=0.24,
EtOAc/n-hexane (2/1); MS (APCI, Pos. 20 V) m/z=482
À1
(M+H)+; IR(KBr) 1791, 1718, 1686, 1632, 1529 cm
;

K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
1315
1H NMR(300 MHz, CDCl ) d 7.36 (d, J=7.8 Hz, 1H),
white amorphous powder; TLC Rf=0.36, EtOAc/
n-hexane (2/1); MS (APCI, Pos. 20 V) m/z=522
3
5.36 (d, J=9.6 Hz, 1H), 5.19 (dd, J=7.8, 5.4 Hz, 1H),
4.61 (dd, J=8.1, 3.0 Hz, 1H), 4.49±4.37 (m, 1H), 4.32
(dd, J=9.6, 6.6 Hz, 1H), 3.82±3.57 (m, 2H), 3.68 (s,
3H), 2.38±1.85 (m, 6H), 1.43 and 1.42 (dÂ2, J=6.9 Hz,
3HÂ2), 1.01, 0.97 and 0.91 (dÂ3, J=6.9 Hz, 12H).
À1
(M+H)+; IR(KBr) 1789, 1715, 1685, 1633, 1525 cm
;
1H NMR(300 MHz, CDCl ) d 7.35 (d, J=7.5 Hz, 1H),
3
5.35 (d, J=9.6 Hz, 1H), 5.18 (dd, J=7.5, 4.8 Hz, 1H),
4.60 (dd, J=8.1, 3.0 Hz, 1H), 4.32 (dd, J=9.6, 7.2 Hz,
1H), 4.10±3.94 (m, 1H), 3.83±3.52 (m, 2H), 3.67 (s, 3H),
2.37±1.03 (m, 16H), 1.01, 0.96 and 0.91 (dÂ3,
J=6.9 Hz, 12H); optical rotation [a]2D5 À38.6 (c 0.2,
ꢂ
Anal. calcd for C22H35N5O7 0.4H2O: C, 54.06; N, 7.38;
N, 14.33; found: C, 53.74; H, 7.29; N, 14.01.
ꢂ
N-{(1S)-2-[(2S)-2-(N-{(1S)-1-(Methylethyl)-2-[3-(2-methyl-
propyl)-2-oxo-1,3,4-oxadiazolin-5-yl]-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (4d). Derived from 12 and 1-bromo-2-
methylpropane: white amorphous powder; TLC
Rf=0.64, EtOAc; MS (MALDI, Pos.) m/z=534
(M+K)+, 518 (M+Na)+, 496 (M+H)+; IR(KBr)
1793, 1716, 1685, 1633, 1525 cmÀ1; 1H NMR(300 MHz,
CDCl3) d 7.40 (d, J=7.5 Hz, 1H), 5.38 (d, J=9.2 Hz,
1H), 5.14 (dd, J=7.5 and 5.4 Hz, 1H), 4.60 (dd, J=8.1
and 2.7 Hz, 1H), 4.31 (dd, J=9.2 and 6.6 Hz, 1H), 3.84±
3.51 (m, 4H), 3.67 (s, 3H), 2.40±1.80 (m, 7H), 1.08±0.84
(m, 18H); optical rotation [a]2D6 À48.3 (c 0.26, MeCN).
MeCN). Anal. calcd for C25H39N5O7 0.1H2O: C, 57.37;
H, 7.55; N, 13.38; found: C, 56.99; H, 7.68; N, 13.05.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(Cyclohexylmethyl)-2-
oxo-1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}-
carbamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}meth-
oxycarboxamide (4k). Derived from 12 and bromo-
methylcyclohexane: clear viscous syrup; TLC Rf=0.64,
EtOAc; MS (MALDI, Pos.) m/z=574 (M+K)+, 558
(M+Na)+, 536 (M+H)+; IR(KBr) 1792, 1717, 1685,
1633, 1524 cmÀ1; 1H NMR(300 MHz, CDCl 3) d 7.38 (d,
J=7.5 Hz, 1H), 5.37 (d, J=9.5 Hz, 1H), 5.14 (dd,
J=7.5 and 5.7 Hz, 1H), 4.61 (dd, J=8.4 and 3.0 Hz,
1H), 4.32 (dd, J=9.5 and 6.9 Hz, 1H), 3.85±3.55 (m,
4H), 3.68 (s, 3H), 2.43±1.48 (m, 12H), 1.40±0.75 (m,
17H); optical rotation [a]2D6 À38.9 (c 0.2, MeCN). Anal.
calcd for C26H41N5O7: C, 58.30; H, 7.71; N, 13.08;
found: C, 57.93; H, 7.88; N, 12.73.
ꢂ
Anal. calcd for C23H37N5O7 0.2H2O: C, 55.34; H, 7.55;
N, 14.03; found: C, 55.10; H, 7.60; N, 13.83.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(Cyclopropylmethyl)-2-
oxo-1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}-
carbamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}meth-
oxycarboxamide (4e). Derived from 12 and cyclopro-
pylmethyl bromide: white amorphous powder; TLC
Rf=0.50, EtOAc; MS (MALDI, Pos.) m/z=532
(M+K)+, 516 (M+Na)+, 494 (M+H)+; IR(KBr)
1791, 1715, 1685, 1633, 1526 cmÀ1; 1H NMR(200 MHz,
CDCl3) d 7.39 (d, J=7.1 Hz, 1H), 5.38 (d, J=9.0 Hz,
1H), 5.17 (dd, J=7.1 and 5.0 Hz, 1H), 4.61 (dd, J=8.2
and 3.4 Hz, 1H), 4.32 (dd, J=9.0 and 6.6 Hz, 1H), 3.88±
3.50 (m, 4H), 3.68 (s, 3H), 2.45±1.70 (m, 6H), 1.40±1.10
(m, 1H), 1.10±0.82 (m, 12H), 0.72±0.53 and 0.53±0.34
(mÂ2, 2HÂ2); optical rotation [a]2D6 À58.7 (c 0.3,
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(2-Methoxyethyl)-2-oxo-
1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}car-
bamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (4l). Derived from 12 and 2-bromo-1-
methoxyethane: white amorphous powder; TLC
Rf=0.50, EtOAc; MS (APCI, Pos. 20 V) m/z=498
À1
(M+H)+; IR(KBr) 1793, 1715, 1684, 1633, 1526 cm
;
1H NMR(300 MHz, CDCl ) d 7.39 (d, J=7.2 Hz, 1H),
3
5.35 (d, J=9.6 Hz, 1H), 5.15 (dd, J=7.2, 5.1 Hz, 1H),
4.60 (dd, J=8.1, 2.7 Hz, 1H), 4.31 (dd, J=9.6, 6.6 Hz,
1H), 4.05±3.97 (m, 2H), 3.82±3.55 (m, 4H), 3.67 (s, 3H),
3.36 (s, 3H), 2.35±1.80 (m, 6H), 1.01, 0.96 and 0.91
(dÂ3, J=6.9 Hz, 12H); optical rotation [a]2D5 À55.8 (c 0.5,
.
MeCN). Anal. calcd for C23H35N5O7 0.2H2O: C, 55.57;
H, 7.18; N, 14.09; found: C, 55.29; H, 7.21; N, 13.89.
ꢂ
MeCN). Anal. calcd for C22H35N5O8 0.2H2O: C, 52.73;
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(3-Methylbutyl)-2-oxo-
1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (4f). Derived from 12 and 1-bromo-3-
methylbutane: white amorphous powder; TLC
Rf=0.60, EtOAc; MS (MALDI, Pos.) m/z=548
(M+K)+, 532 (M+Na)+, 510 (M+H)+; IR(KBr)
1793, 1717, 1685, 1633, 1525 cmÀ1; 1H NMR(300 MHz,
CDCl3) d 7.39 (d, J=7.1 Hz, 1H), 5.36 (d, J=9.2 Hz,
1H), 5.14 (dd, J=7.1 and 5.4 Hz, 1H), 4.61 (dd, J=8.1
and 3.0 Hz, 1H), 4.31 (dd, J=9.2 and 6.6 Hz, 1H), 3.85
(t, J=6.9 Hz, 2H), 3.84±3.54 (m, 2H), 3.68 (s, 3H), 2.40±
1.80 (m, 6H), 1.75±1.48 (m, 3H), 1.10±0.83 (m, 18H);
optical rotation [a]2D6 À51.5 (c 0.3, MeCN). Anal. calcd
for C24H39N5O7: C, 56.57; H, 7.71; N, 13.74; found: C,
56.30; H, 7.94; N, 13.37.
H, 7.12; N, 13.97; found: C, 52.42; H, 7.16; N, 13.69.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(Ethoxymethyl)-2-oxo-
1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (4m). Derived from 12 and chloromethyl
ethyl ether: white amorphous powder; TLC Rf=0.55,
EtOAc; MS (APCI, Pos. 20 V) m/z=498 (M+H)+; IR
(KBr) 1798, 1718, 1685, 1633, 1625 cmÀ1 1H NMR
;
(300 MHz, CDCl3) d 7.46 (d, J=6.9 Hz, 1H), 5.34 (d,
J=9.6 Hz, 1H), 5.21 (s, 2H), 5.12 (dd, J=6.9, 5.1 Hz,
1H), 4.62 (dd, J=8.1, 3.0 Hz, 1H), 4.31 (dd, J=9.6,
6.9 Hz, 1H), 3.81±3.55 (m, 4H), 3.68 (s, 3H), 2.39±1.80
(m, 6H), 1.24 (t, J=6.9 Hz, 3H), 1.02, 1.00, 0.96 and
0.93 (dÂ4, J=6.9Hz, 3HÂ4); optical rotation [a]2D7 À55.4
(c 0.3, MeCN). Anal. calcd for C22H35N5O8: C, 53.11; H,
7.09; N, 14.08; found: C, 52.72; H, 7.18; N, 13.81.
N-[(1S)-2-((2S)-2-{N-[(1S)-2-(3-Cyclohexyl-2-oxo-1,3,4-
oxadiazolin-5-yl)-1-(methylethyl)-2-oxoethyl]carbamoyl}-
pyrrolidinyl)-1-(methylethyl)-2-oxoethyl]methoxycarbox-
amide (4j). Derived from 12 and cyclohexyl iodide:
N-{(1S)-2-[(2S)-2-(N-{(1S)-1-(Methylethyl)-2-oxo-2-(2-
oxo-3-benzyl-1,3,4-oxadiazolin-5-yl)}ethyl)carbamoyl]-
pyrrolidinyl}-1-(methylethyl)-2-oxoethyl}methoxycarbox-

1316
K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
amide (4n). Derived from 12 and benzyl bromide: white
amorphous powder; mp 58±63 ꢁC; TLC Rf=0.46,
CHCl3/MeOH (19/1), MS (APCI, Pos.) m/z=530
tert-Butyl (4S,5R)-5-[3-(2-cyclopropylethyl)-2-oxo-1,3,4-
oxadiazolin-5-yl]-2,2-dimethyl-4-(methylethyl)-1,3-oxazoli-
dine-3-carboxylate (13i). To a stirred solution of 12
(374 mg, 1.14 mmol), 2-cyclopropylethanol (296 mg,
3.44 mmol) and triphenylphosphine (898 mg, 3.42 mmol) in
THF (11.5 mL) was added dropwise DEAD (0.54 mL,
3.43 mmol) at rt. After 15 min, the reaction mixture was
concentrated in vacuo. The residue was puri®ed by column
chromatography on silica gel (FL60D, EtOAc/n-hexane
(1/19)) to a€ord 13i (416 mg, 92%): TLC Rf=0.50,
EtOAc/n-hexane (1/4); MS (MALDI, Pos.) 418
(M+H)+; IR(KBr) 1791, 1718, 1684, 1613, 1527 cm À1
;
1H NMR(200 MHz, CDCl ) d 7.47±7.30 (m, 1H), 7.37
3
(m, 5H), 5.39 (d, J=9.2 Hz, 1H), 5.10 (dd, J=7.2 Hz,
5.4 Hz, 1H), 4.97 (s, 2H), 4.62±4.52 (m, 1H), 4.30 (dd,
J=9.2 Hz, 7.0 Hz, 1H), 3.83±3.47 (m, 2H), 3.67 (s, 3H),
2.37±1.75 (m, 6H), 1.07±0.84 (m, 12H); optical rotation
[a]2D7 À49.8 (c 0.6, MeCN). Anal. calcd for C26H35N5O7
.
0.6H2O: C, 57.79; H, 6.75; N, 12.96; found: C, 57.41;
1
H, 6.63; N, 12.78.
(M+Na)+, 296 (MÀBoc+H)+; H NMR(300 MHz,
CDCl3) d 4.74 (d, J=3.3 Hz, 1H), 4.42±4.08 (m, 1H),
3.80 (t, J=6.9 Hz, 1H), 2.42±2.17 (m, 1H), 1.70±1.57
(m, 2H), 1.59 and 1.54 (sÂ2, 3HÂ2), 1.48 (s, 9H), 0.95
and 0.92 (dÂ2, J=6.9 Hz, 3HÂ2), 0.75±0.59 (m, 1H),
0.50±0.41 and 0.07±0.02 (mÂ2, 2HÂ2).
N-{(1S)-2-[(2S)-2-(N-{(1S)-1-(Methylethyl)-2-oxo-2-[2-
oxo-3-(2-phenylethyl)-1,3,4-oxadiazolin-5-yl]ethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (4q). Derived from 12 and phenethyl
bromide: clear viscous syrup; TLC Rf=0.58, EtOAc;
MS (APCI, Pos. 40 V) m/z=544 (M+H)+, 386, 354,
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(2-Cyclopropylethyl)-2-
oxo-1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}-
carbamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}meth-
oxycarboxamide (4i). Prepared from 13i according to
the same procedures as described for the preparation of
4c: white amorphous powder; TLC Rf=0.31, EtOAc/
n-hexane (2/1); MS (APCI, Pos. 20V) m/z=508
À1
255, 229; IR(KBr) 1793, 1716, 1684, 1633, 1524 cm
;
1H NMR(300 MHz, CDCl ) d 7.39 (d, J=7.2 Hz, 1H),
3
7.38±7.09 (m, 5H), 5.35 (d, J=8.9 Hz, 1H), 5.09 (dd,
J=7.2, 5.4 Hz, 1H), 4.60 (dd, J=8.1, 3.0 Hz, 1H), 4.31
(dd, J=8.9, 7.2 Hz, 1H), 4.23±3.96 (m, 2H), 3.86±3.47
(m, 2H), 3.68 (s, 3H), 3.11 (t, J=7.2 Hz, 2H), 2.41±2.23
(m, 1H), 2.23±1.78 (m, 5H), 1.12±0.75 (m, 12H). Anal.
À1
(M+H)+; IR(KBr) 1793, 1716, 1685, 1633, 1525 cm
;
calcd for C27H37N5O7 0.2H2O: C, 59.26; H, 6.89; N,
12.80; found: C, 58.90; H, 6.97; N, 12.43.
1H NMR(300 MHz, CDCl ) d 7.39 (d, J=7.5 Hz, 1H),
ꢂ
3
5.35 (d, J=9.6 Hz, 1H), 5.13 (dd, J=7.5, 5.4 Hz, 1H),
4.60 (dd, J=8.1, 2.7 Hz, 1H), 4.31 (dd, J=9.6, 6.9 Hz,
1H), 3.92 (t, J=6.9 Hz, 2H), 3.82±3.56 (m, 2H), 3.68 (s,
3H), 2.38±1.80 (m, 6H), 1.73±1.63 (m, 2H), 1.01, 0.96
and 0.92 (dÂ3, J=6.9 Hz, 12H), 0.76±0.60 (m, 1H),
0.52±0.43 and 0.10±0.03 (mÂ2, 2HÂ2); optical rotation
[a]2D5 À53.5, (c 0.3, MeCN). Anal. calcd for C24H37N5O7
ꢂ 0.1H2O: C, 56.59; H, 7.36; N, 13.75; found: C, 56.23;
H, 7.41; N, 13.41.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(4-Fluorophenyl)methyl-
2-oxo-1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}
carbamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}meth-
oxycarboxamide (4r). Derived from 12 and 4-¯uoro-
benzyl bromide: white amorphous powder; TLC
Rf=0.56, CHCl3/MeOH (19/1), MS (MALDI, Pos.) m/z=
586 (M+K)+, 570 (M+Na)+, 548 (M+H)+; IR(KBr)
1792, 1716, 1684, 1633, 1513 cmÀ1; 1H NMR(300 MHz,
CDCl3) d 7.44±7.38 (m, 1H), 7.37 (dd, J=8.4, 4.8 Hz,
1H), 7.06 (t, J=8.4 Hz, 1H), 5.37 (d, J=9.0 Hz, 1H),
5.09 (dd, J=7.2, 5.7 Hz, 1H), 4.96 and 4.91 (dÂ2,
J=15.9 Hz, 1HÂ2), 4.57 (dd, J=8.1, 3.0 Hz, 1H), 4.30
(dd, J=9.0, 6.9 Hz, 1H), 3.73±3.54 (m, 2H), 3.67 (s,
3H), 2.34±1.81 (m, 6H), 1.00, 0.97, 0.96 and 0.89 (dÂ4,
J=6.9 Hz, 3HÂ4); optical rotation [a]2D5 À43.7 (c 0.8,
Preparation of 4g±h and 4o±p
The following compounds were prepared according to the
same procedures as described for the preparation of 4i.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(2,2-Dimethylpropyl)-2-
oxo-1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}-
carbamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}meth-
oxycarboxamide (4g). Derived from 12 and 2,2-dime-
thyl-1-propanol: white amorphous powder; TLC Rf=
0.58, EtOAc; MS (MALDI, Pos.) m/z=548 (M+K)+,
ꢂ
MeCN). Anal. calcd for C26H34FN5O7 H2O: C, 55.21;
H, 6.42; N, 12.38; found: C, 54.90; H, 6.09; N, 12.28.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(2H-benzo[3,4-d]1,3-dioxo-
lan-5-ylmethyl)-2-oxo-1,3,4-oxadiazolin-5-yl]-1-(methylethyl)
-2-oxoethyl}carbamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxo-
ethyl}methoxycarboxamide (4s). Derived from 12 and 5-
(bromomethyl)-2H-benzo[3,4-d]1,3-dioxolene:22 white
amorphous powder; TLC Rf=0.63, EtOAc; MS (APCI,
Pos. 40 V) m/z=574 (M+H)+, 386, 255, 229; IR(KBr)
1791, 1715, 1685, 1632, 1505 cmÀ1; 1H NMR(300 MHz,
CDCl3) d 7.39 (d, J=7.5 Hz, 1H), 6.90±6.83 (m, 2H),
6.78 (d, J=8.7 Hz, 1H), 5.97 (s, 2H), 5.36 (d, J=9.2 Hz,
1H), 5.10 (dd, J=7.5, 5.4 Hz, 1H), 4.86 (s, 2H), 4.58
(dd, J=7.5, 2.7 Hz, 1H), 4.31 (dd, J=9.2, 6.9 Hz, 1H),
3.84±3.50 (m, 2H), 3.67 (s, 3H), 2.40±1.80 (m, 6H),
1.08±0.80 (m, 12H); optical rotation [a]2D6 À43.8 (c 0.3,
532 (M+Na)+, 510 (M+H)+; IR(KBr) 1793, 1716,
1
1685, 1633, 1525 cmÀ1; H NMR(300 MHz, CDCl ) d
3
7.39 (d, J=7.1 Hz, 1H), 5.36 (d, J=9.3 Hz, 1H), 5.15
(dd, J=7.1, 5.1 Hz, 1H), 4.60 (dd, J=8.1, 2.7 Hz, 1H),
4.31 (dd, J=9.3, 6.6 Hz, 1H), 3.83±3.52 (m, 2H), 3.68 (s,
3H), 3.66 and 3.58 (dÂ2, J=14.1 Hz, 1HÂ2), 2.40±1.79
(m, 6H), 1.10±0.78 (m, 12H), 1.01 (s, 9H); optical rota-
tion [a]2D6 À50.0 (c 0.2, MeCN). Anal. calcd for
ꢂ
C24H39N5O7 0.1H2O: C, 56.37; H, 7.73; N, 13.69;
found: C, 56.06; H, 7.81; N, 13.41.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(Cyclobutylmethyl)-2-oxo-
1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}carbam-
oyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxycarbox-
amide (4h). Derived from 12 and cyclobutanemethanol:
.
MeCN). Anal. calcd for C27H35N5O9 0.9H2O: C, 54.98;
H, 6.29; N, 11.87; found: C, 54.67; H, 6.04; N, 11.58.

K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
1317
white amorphous powder; TLC Rf=0.62, EtOAc; MS
(MALDI, Pos.) m/z=546 (M+K)+, 530 (M+Na)+,
508 (M+H)+; IR(KBr) 1792, 1715, 1685, 1633,
TLC Rf=0.32, EtOAc/n-hexane (1/3); MS (APCI, Pos.
1
40 V) m/z=422 (M+H)+, 366; H NMR(300 MHz,
CDCl3) d 8.18 (d, J=5.4 Hz, 1H), 6.78 (d, J=8.1 Hz,
1H), 6.71±6.63 (m, 2H), 5.90 (d, J=5.4 Hz, 1H), 4.38 (d,
J=3.0 Hz, 1H), 4.32±4.20 (m, 1H), 3.74 (s, 3H), 2.40±
2.18 (m, 1H), 2.28 (s, 3H), 1.68 and 1.64 (sÂ2, 3HÂ2),
1.46 (s, 9H), 0.96 and 0.94 (dÂ2, J=6.9 Hz, 3HÂ2).
1525 cmÀ1 1H NMR(300 MHz, CDCl 3) d 7.38 (d,
;
J=6.9 Hz, 1H), 5.37 (d, J=8.9 Hz, 1H), 5.14 (dd,
J=6.9, 5.1 Hz, 1H), 4.60 (dd, J=8.1, 3.0 Hz, 1H), 4.31
(dd, J=8.9, 6.9 Hz, 1H), 3.95±3.48 (m, 4H), 3.67 (s,
3H), 2.88±2.69 (m, 1H), 2.40±1.71 (m, 12H), 1.10±0.80
(m, 12H); optical rotation [a]2D6 À48.4 (c 0.3, MeCN).
Anal. calcd for C24H37N5O7: C, 56.79; H, 7.35; N,
13.80; found: C, 56.40; H, 7.44; N, 13.50.
tert-Butyl (4S,5R)-5-[3-(4-Methoxy-2-methylphenyl)-2-
oxo-1,3,4-oxadiazolin-5-yl]-2,2-dimethyl-4-(methylethyl)-
1,3-oxazolidine-3-carboxylate (18o). A mixture of 17o
(804 mg,
1.91 mmol),
triethylamine
(0.80 mL,
N-{(1S)-2-[(2S)-2-(N-{(1S)-1-(Methylethyl)-2-oxo-2-[2-
oxo-3-(3-thienylmethyl)-1,3,4-oxadiazolin-5-yl]ethyl}car-
bamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (4o). Derived from 12 and 3-thiophene-
methanol: white amorphous powder; mp 58.1±59.9 ꢁC;
TLC Rf=0.13 EtOAc/n-hexane (1/1); MS (APCI, Pos.
20 V) m/z=536 (M+H)+; IR(KBr) 1791, 1714, 1683,
1632, 1526 cmÀ1; 1H NMR(300 MHz, DMSO- d6) d 8.37
(d, J=6.9 Hz, 1H), 7.57±7.54 (m, 2H), 7.26 (d,
J=8.4 Hz, 1H), 7.12±7.10 (m, 1H), 5.01 (s, 2H), 4.81 (t,
J=6.9 Hz, 1H), 4.43 (dd, J=8.4, 4.2 Hz, 1H), 3.98 (t,
J=8.4 Hz, 1H), 3.76±3.67 and 3.55±3.45 (mÂ2, 5H),
2.26±2.14 and 2.02±1.66 (mÂ2, 6H), 0.92±0.84 (m,
12H); optical rotation [a]2D6 À52.2 (c 0.5, CHCl3). Anal.
5.72 mmol) and CDI (1.54 g, 9.54 mmol) in THF
(19 mL) was stirred at 80 ꢁC for 15 h, then poured into
1N HCl, and extracted with EtOAc. The organic layer
was washed with saturated NaHCO3, H2O, brine, dried
over anhydrous MgSO4, and concentrated in vacuo.
The residual solid was washed with n-hexane containing
a small amount of EtOAc to a€ord 18o (501 mg, 59%)
as a pale brown viscous syrup: TLC Rf=0.42, EtOAc/
n-hexane (1/3); MS (MALDI, Pos.) m/z=486 (M+K)+,
1
470 (M+Na)+; H NMR(300 MHz, CDCl ) d 7.25 (d,
3
J=9.0 Hz, 1H), 6.85±6.76 (m, 2H), 4.82 (d, J=3.0 Hz,
1H), 4.50±4.27 (m, 1H), 3.82 (s, 3H), 2.50±2.14 (m, 1H),
2.25 (s, 3H), 1.62 and 1.60 (sÂ2, 3HÂ2), 1.48 (s, 9H),
0.98 and 0.95 (dÂ2, J=6.0 Hz, 3HÂ2).
.
calcd for C24H33N5O7S 0.3H2O: C, 53.28; H, 6.26; N,
12.94; S, 5.93; found: C, 53.00; H, 6.23; N, 12.66; S,
6.18.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(4-Methoxy-2-methyl-
phenyl)-2-oxo-1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-
oxoethyl}carbamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxo-
ethyl}methoxycarboxamide (5o). Prepared from 18o
according to the same procedures as described for the
preparation of 4c: white amorphous solid; TLC
Rf=0.25, EtOAc/n-hexane (3/1); MS (APCI, Pos. 20 V)
m/z=560 (M+H)+, 386; IR(KBr) 1793, 1717, 1685,
1635, 1508 cmÀ1; 1H NMR(300 MHz, CDCl 3) d 7.46 (d,
J=7.1 Hz, 1H), 7.32±7.25 (m, 1H), 6.88±6.79 (m, 2H),
5.36 (d, J=9.5 Hz, 1H), 5.14 (dd, J=7.1, 5.7 Hz, 1H),
4.63 (dd, J=8.4, 3.0 Hz, 1H), 4.31 (dd, J=9.5, 6.9 Hz,
1H), 3.85±3.53 (m, 2H), 3.84 (s, 3H), 3.68 (s, 3H), 2.44±
1.82 (m, 6H), 2.28 (s, 3H), 1.03, 0.99, 0.95 and 0.94
(dÂ4, J=6.9 Hz, 3HÂ4); optical rotation [a]2D5 À41.2, (c
N-{(1S)-2-[(2S)-2-(N-{(1S)-1-(Methylethyl)-2-oxo-2-[2-
oxo-3-(2-thienylmethyl)-1,3,4-oxadiazolin-5-yl]ethyl}carb-
amoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (4p). Derived from 12 and 2-thiophene-
methanol: white amorphous powder; mp 59.4±61.2 ꢁC;
TLC Rf=0.34, CHCl3/MeOH (20/1); MS (APCI, Neg.
20 V) m/z=534 (MÀH)À; IR(KBr) 1793, 1715, 1684,
1632, 1525 cmÀ1; 1H NMR(300 MHz, DMSO- d6) d 8.39
(d, J=7.0 Hz, 1H), 7.54 (dd, J=5.0, 1.0 Hz, 1H), 7.27
(d, J=8.5 Hz, 1H), 7.18 (d, J=3.5 Hz, 1H), 7.02 (dd,
J=5.0, 3.5 Hz, 1H), 5.21 (s, 2H), 4.80 (t, J=7.0 Hz,
1H), 4.44 (dd, J=7.5, 4.0 Hz, 1H), 3.97 (t, J=8.5 Hz,
1H), 3.75±3.67 and 3.58±3.46 (mÂ2, 5H), 2.25±2.14 and
2.02±1.65 (mÂ2, 6H), 0.92±0.85 (m, 12H); optical rota-
tion [a]2D6 À58.3 (c 0.5, CHCl3). Anal. calcd for
ꢂ
0.3, MeCN). Anal. calcd for C27H37N5O8 0.3H2O: C,
57.40; H, 6.71; N, 12.40; found: C, 57.54; H, 6.76; N,
12.01.
.
C24H33N5O7S 0.4H2O: C, 53.10; H, 6.28; N, 12.90; S,
5.91; found: C, 52.75; H, 6.23; N, 12.72; S, 6.16.
Preparation of 5a±n and 5p±t. The following com-
pounds were prepared according to the same procedures
as described for the preparation of 5o.
tert-Butyl
(4S,5R)-5-{N-[(4-methoxy-2-methylphenyl)
amino]carbamoyl}-2,2-dimethyl-4-(methylethyl)-1,3-oxazo-
lidine-3-carboxylate (17o). To a stirred mixture of 10a
(678 mg, 2.36 mmol), 4-methoxy-2-methylphenylhy-
N-[(1S)-2-((2S)-2-{N-[(1S)-1-(Methylethyl)-2-oxo-2-(2-
oxo-3-phenyl-1,3,4-oxadiazolin-5-yl)ethyl]carbamoyl}pyr-
rolidinyl)-1-(methylethyl)-2-oxoethyl]methoxycarboxamide
(5a). Derived from 10a and phenylhydrazine: white
amorphous powder; TLC Rf=0.40, EtOAc; MS (APCI,
Pos. 20 V) m/z=516 (M+H)+; IR(KBr) 1794, 1717,
drazine23 (445 mg, 2.36 mmol), HOBt H2O (433 mg,
.
.
2.83 mmol) and EDC HCl (905 mg, 4.72 mmol) in DMF
(5 mL) was added dropwise N-methylmorpholine
(0.29 mL, 2.60 mmol) at 0 ꢁC. After stirring at rt for 7 h,
the reaction mixture was poured into ice-cooled 1N
HCl, and extracted with EtOAc. The organic layer was
washed with 1 N HCl, saturated NaHCO3, H2O, brine,
dried over anhydrous MgSO4, and concentrated in
vacuo. The residue was puri®ed by silica gel column
chromatography (FL60D, EtOAc/n-hexane (1/5!1/3))
to a€ord 17o (813 mg, 82%) as a yellow viscous syrup:
1685, 1632, 1598, 1570, 1524, 1503 cmÀ1 1H NMR
;
(300 MHz, CDCl3) d 7.89 (d, J=8.4 Hz, 2H), 7.56±7.44
(m, 3H), 7.39±7.31 (m, 1H), 5.35 (d, J=8.7 Hz, 1H),
5.21 (dd, J=7.5, 5.7 Hz, 1H), 4.63 (dd, J=7.8, 3.0 Hz,
1H), 4.32 (dd, J=8.7, 6.9 Hz, 1H), 3.85±3.53 (m, 2H),
3.68 (s, 3H), 2.40±1.82 (m, 6H), 1.06 and 1.01 (dÂ2,
J=6.6 Hz, 3HÂ2), 0.97 (d, J=6.9 Hz, 6H); optical

1318
K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
rotation [a]2D7 À46.7 (c 0.5, MeCN). Anal. calcd for
m/z=546 (M+H)+, 386; IR(KBr) 1799, 1717, 1684,
1
1634, 1507 cmÀ1; H NMR(300 MHz, CDCl ) d 7.52±
ꢂ
C25H33N5O7 0.2H2O: C, 57.84; H, 6.48; N, 13.49;
found: C, 57.52; H, 6.50; N, 13.15.
3
7.35 (m, 3H), 7.11±7.01 (m, 2H), 5.37 (d, J=9.2 Hz,
1H), 5.18 (dd, J=7.2, 5.4 Hz, 1H), 4.62 (dd, J=8.4,
3.0 Hz, 1H), 4.31 (dd, J=9.2, 7.2 Hz, 1H), 3.87 (s, 3H),
3.84±3.54 (m, 2H), 3.68 (s, 3H), 2.40±1.81 (m, 6H), 1.03,
0.99, 0.95 and 0.94 (dÂ4, J=6.9 Hz, 3HÂ4); optical
rotation [a]2D6 À47.8 (c 0.3, MeCN). Anal. calcd for
N-{(1S)-2-[(2S)-2-(N-{(1S)-1-(Methylethyl)-2-[3-(2-methyl-
phenyl)-2-oxo-1,3,4-oxadiazolin-5-yl]-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (5b). Derived from 10a and 2-methyl-
phenylhydrazine: white amorphous powder; TLC Rf=
0.29, EtOAc/n-hexane (2/1); MS (APCI, Pos. 20 V) m/z=
530 (M+H)+; IR(KBr) 1795, 1718, 1685, 1634,
ꢂ
C26H35N5O8 0.5H2O: C, 56.31; H, 6.54; N, 12.63;
found: C, 56.65; H, 6.55; N, 12.26.
1523 cmÀ1
;
1H NMR(300 MHz, CDCl 3) d 7.48 (d,
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(4-Methoxyphenyl)-2-oxo-
1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (5f). Derived from 10a and 4-methoxy-
phenylhydrazine: white amorphous powder; TLC
Rf=0.38, EtOAc/n-hexane (2/1); MS (APCI, Pos. 20 V)
m/z=516 (M+H)+; IR(KBr) 1793, 1716, 1684, 1633,
1568, 1504 cmÀ1; 1H NMR(300 MHz, CDCl 3) d 7.89 (d,
J=7.8 Hz, 2H), 7.56±7.44 (m, 3H), 7.35 (t, J=7.8 Hz,
1H), 5.38 (d, J=9.0 Hz, 1H), 5.22 (dd, J=7.2, 5.4 Hz,
1H), 4.63 (dd, J=8.1, 2.7 Hz, 1H), 4.32 (dd, J=9.0,
7.2 Hz, 1H), 3.84±3.56 (m, 2H), 3.68 (s, 3H), 2.40±1.82
(m, 6H), 1.06 and 1.01 (dÂ2, J=6.6 Hz, 3HÂ2), 0.97
(d, J=6.9 Hz, 6H); optical rotation [a]2D7 À41.1 (c 0.8,
J=7.2 Hz, 1H), 7.43±7.31 (m, 4H), 5.36 (d, J=9.3 Hz,
1H), 5.15 (dd, J=7.2, 5.4 Hz, 1H), 4.63 (dd, J=8.4,
3.0 Hz, 1H), 4.31 (dd, J=9.3, 6.9 Hz, 1H), 3.82±3.55 (m,
2H), 3.68 (s, 3H), 2.41±1.82 (m, 6H), 2.33 (s, 3H), 1.03,
0.99 and 0.95 (dÂ3, J=6.9 Hz, 12H); optical rotation
[a]2D6 À44.8 (c 0.8, MeCN). Anal. calcd for C26H35N5O7
ꢂ H2O: C, 57.03; H, 6.81; N, 12.79; found: C, 56.70; H,
6.51; N, 12.44.
N-{(1S)-2-[(2S)-2-(N-{(1S)-1-(Methylethyl)-2-[3-(3-methyl-
phenyl)-2-oxo-1,3,4-oxadiazolin-5-yl]-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (5c). Derived from 10a and 3-methyl-
phenylhydrazine: white amorphous powder; TLC
Rf=0.30, EtOAc/n-hexane (2/1); MS (APCI, Pos. 20 V)
ꢂ
MeCN). Anal. calcd for C26H35N5O8 0.2H2O: C,
56.86; H, 6.50; N, 12.75; found: C, 56.54; H, 6.54; N,
12.47.
m/z=530 (M+H)+; IR(KBr) 1793, 1718, 1685, 1633,
1
1523 cmÀ1; H NMR(300 MHz, CDCl ) d 7.69 (s, 1H),
3
7.68 (d, J=7.5 Hz, 1H), 7.51 (d, J=7.2 Hz, 1H), 7.36 (t,
J=7.5 Hz, 1H), 7.16 (d, J=7.5 Hz, 1H), 5.37 (d,
J=9.0 Hz, 1H), 5.23 (dd, J=7.2, 5.4 Hz, 1H), 4.63 (dd,
J=8.1, 3.0 Hz, 1H), 4.32 (dd, J=9.0, 7.2 Hz, 1H), 3.85±
3.55 (m, 2H), 3.68 (s, 3H), 2.43 (s, 3H), 2.40±1.83 (m,
6H), 1.06, 1.01, 0.97 and 0.96 (dÂ4, J=6.9 Hz, 3HÂ4);
optical rotation [a]2D5 À45.6 (c 0.2, MeCN). Anal. calcd
N-((1S)-2-{(2S)-2-[N-((1S)-1-(Methylethyl)-2-oxo-2-{2-
oxo-3-[2-(tri¯uoromethyl)phenyl]-1,3,4-oxadiazolin-5-yl}
ethyl)carbamoyl]pyrrolidinyl}-1-(methylethyl)-2-oxoethyl)
methoxycarboxamide (5g). Derived from 10a and 2-(tri-
¯uoromethyl)phenylhydrazine: white amorphous powder;
TLC Rf=0.25, EtOAc/n-hexane (3/1); MS (APCI, Pos.
40 V) m/z=584 (M+H)+, 386, 255, 229; IR(KBr)
1805, 1719, 1685, 1635, 1520 cmÀ1; 1H NMR(300 MHz,
CDCl3) d 7.86 (dd, J=7.2, 1.2 Hz, 1H), 7.80±7.58 (m,
3H), 7.51 (d, J=6.8 Hz, 1H), 5.35 (d, J=9.3 Hz, 1H),
5.06 (dd, J=6.8, 5.7 Hz, 1H), 4.63 (dd, J=7.8, 2.7 Hz,
1H), 4.30 (dd, J=9.3, 6.9 Hz, 1H), 3.83±3.51 (m, 2H),
3.67 (s, 3H), 2.42±1.80 (m, 6H), 1.09±0.87 (m, 12H);
optical rotation [a]2D7 À38.8 (c 0.3, MeCN). Anal. calcd
for C26H32F3N5O7: C, 53.51; H, 5.53; N, 12.00; found:
C, 53.21; H, 5.50; N, 11.66.
.
for C26H35N5O7 0.5H2O: C, 57.98; H, 6.74; N, 13.00;
found: C, 57.60; H, 6.63; N, 12.74.
N-{(1S)-2-[(2S)-2-(N-{(1S)-1-(Methylethyl)-2-[3-(4-methyl-
phenyl)-2-oxo-1,3,4-oxadiazolin-5-yl]-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (5d). Derived from 10a and 4-methyl-
phenylhydrazine: white amorphous powder; TLC
Rf=0.30, EtOAc/n-hexane (2/1); MS (APCI, Pos. 20 V)
m/z=530 (M+H)+; IR(KBr) 1796, 1718, 1685, 1632,
1515 cmÀ1
;
1H NMR(300 MHz, CDCl 3) d 7.74 (d,
N-((1S)-2-{(2S)-2-[N-((1S)-1-(Methylethyl)-2-oxo-2-{2-
oxo-3-[4-(tri¯uoromethyl)phenyl]-1,3,4-oxadiazolin-5-yl}
ethyl)carbamoyl]pyrrolidinyl}-1-(methylethyl)-2-oxoethyl)
methoxycarboxamide (5h). Derived from 10a and 4-(tri-
¯uoromethyl)phenylhydrazine: white amorphous powder;
TLC Rf=0.42, EtOAc/n-hexane (2/1); MS (APCI, Pos.
20 V) m/z=584 (M+H)+; IR(KBr) 1801, 1720, 1685,
1618, 1521 cmÀ1; 1H NMR(300 MHz, CDCl 3) d 8.08 (d,
J=8.7 Hz, 2H), 7.76 (d, J=8.7 Hz, 2H), 7.63 (d,
J=6.6 Hz, 1H), 5.35 (d, J=9.3 Hz, 1H), 5.16 (dd,
J=6.6, 5.7 Hz, 1H), 4.64 (dd, J=8.4, 2.7 Hz, 1H),
4.32 (dd, J=9.3, 6.9 Hz, 1H), 3.84±3.56 (m, 2H), 3.68 (s,
3H), 2.41±1.83 (m, 6H), 1.06, 1.01, 0.98 and 0.97 (dÂ4,
J=6.9 Hz, 3HÂ4); optical rotation [a]2D7 À41.9 (c 0.7,
J=8.4 Hz, 2H), 7.51 (d, J=7.2 Hz, 1H), 7.28 (d,
J=8.4 Hz, 2H), 5.37 (d, J=9.3 Hz, 1H), 5.22 (dd,
J=7.2, 5.4 Hz, 1H), 4.63 (dd, J=7.8, 2.7 Hz, 1H), 4.32
(dd, J=9.3, 6.9 Hz, 1H), 3.82±3.55 (m, 2H), 3.68 (s,
3H), 2.39 (s, 3H), 2.38±1.83 (m, 6H), 1.05, 1.01, 0.97
and 0.96 (dÂ4, J=6.9 Hz, 3HÂ4); optical rotation [a]D27
À44.6, (c 0.5, MeCN). Anal. calcd for C26H35N5-O7
ꢂ 0.5H2O: C, 57.98; H, 6.74; N, 13.00; found: C, 57.63;
H, 6.56; N, 12.73.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(2-Methoxyphenyl)-2-oxo-
1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (5e). Derived from 10a and 2-methoxy-
phenylhydrazine: white amorphous powder; TLC
Rf=0.21, EtOAc/n-hexane (2/1); MS (APCI, Pos. 20 V)
ꢂ
MeCN). Anal. calcd for C26H32F3N5O7 0.6H2O: C,
52.54; H, 5.63; N, 11.78; found: C, 52.27; H, 5.36; N,
11.61.

K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
1319
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(4-Fluorophenyl)-2-oxo-
1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (5i). Derived from 10a and 4-¯uoro-
phenylhydrazine: white amorphous powder; TLC
Rf=0.39, EtOAc/n-hexane (2/1); MS (APCI, Pos. 20 V)
m/z=534 (M+H)+; IR(KBr) 1800, 1719, 1685, 1636,
1H), 4.32 (dd, J=9.0, 6.6 Hz, 1H), 3.83±3.56 (m, 2H),
3.68 (s, 3H), 2.41±1.82 (m, 6H), 1.05, 1.01 and 0.97
(dÂ3, J=6.9 Hz, 12H); optical rotation [a]2D7 À43.5 (c
0.7, MeCN). Anal. calcd for C26H32F3N5O8: C, 52.09;
H, 5.38; N, 11.68; found: C, 51.73; H, 5.33; N, 11.48.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(4-Ethoxyphenyl)-2-oxo-
1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (5m). Derived from 10a and 4-ethoxy-
phenylhydrazine, which was prepared from ethoxy-
benzene according to the method described for pre-
paration of 4-methoxy-2-methylphenylhydrazine: pale
yellow amorphous powder; TLC Rf=0.32, EtOAc/
n-hexane (2/1); MS (APCI, Pos. 20 V) m/z=560
1511 cmÀ1 1H NMR(300 MHz, CDCl 3) d 7.87 (dd,
;
J=9.3, 4.5 Hz, 2H), 7.56 (d, J=6.9 Hz, 1H), 7.18 (d,
J=9.3, 8.4 Hz, 2H), 5.35 (dd, J=9.3 Hz, 1H), 5.18 (dd,
J=6.9, 5.7 Hz, 1H), 4.63 (dd, J=7.8, 2.7 Hz, 1H), 4.32
(dd, J=9.3, 6.9 Hz, 1H), 3.82±3.56 (m, 2H), 3.68 (s,
3H), 2.40±1.83 (m, 6H), 1.05, 1.01 and 0.97 (dÂ3,
J=6.9 Hz, 12H); optical rotation [a]2D7 À38.4 (c 0.5,
ꢂ
MeCN). Anal. calcd for C25H32FN5O7 0.3H2O: C,
À1
;
55.71; H, 6.10; N, 12.99; found: C, 55.40; H, 5.99; N,
12.61.
(M+H)+; IR(KBr) 1791, 1718, 1685, 1634, 1514 cm
1H NMR(300 MHz, CDCl ) d 7.74 (d, J=9.3 Hz, 2H),
3
7.50 (d, J=6.9 Hz, 1H), 6.97 (d, J=9.3 Hz, 2H), 5.37 (d,
J=9.3 Hz, 1H), 5.21 (dd, J=6.9, 5.4 Hz, 1H), 4.63 (dd,
J=8.1, 3.0 Hz, 1H), 4.32 (dd, J=9.3, 6.9 Hz, 1H), 4.07
(q, J=6.9 Hz, 2H), 3.82±3.57 (m, 2H), 3.68 (s, 3H),
2.40±1.82 (m, 6H), 1.44 (t, J=6.9 Hz, 3H), 1.05, 1.01,
0.97 and 0.96 (dÂ4, J=6.9 Hz, 3HÂ4); optical rotation
[a]2D6 À38.0 (c 0.2, MeCN). Anal. calcd for
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(4-Chlorophenyl)-2-oxo-
1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (5j). Derived from 10a and 4-chloro-
phenylhydrazine: white amorphous powder; TLC
Rf=0.30, EtOAc/n-hexane (2/1); MS (APCI, Pos. 20 V)
m/z=550 (M+H)+; IR(KBr) 1797, 1718, 1685, 1632,
ꢂ
C27H37N5O8 1.4H2O: C, 55.45; H, 6.86; N, 11.98;
1523 cmÀ1
;
1H NMR(300 MHz, CDCl 3) d 7.86 (d,
found: C, 55.34; H, 6.74; N, 11.58.
J=9.3 Hz, 2H), 7.57 (d, J=7.2 Hz, 1H), 7.46 (d,
J=9.3 Hz, 2H), 5.36 (d, J=9.3 Hz, 1H), 5.17 (dd,
J=7.2, 6.0 Hz, 1H), 4.63 (dd, J=8.1, 3.0 Hz, 1H), 4.32
(dd, J=9.3, 6.6 Hz, 1H), 3.83±3.57 (m, 2H), 3.68 (s,
3H), 2.40±1.82 (m, 6H), 1.05, 1.01 and 0.97 (dÂ3,
J=6.9 Hz, 12H); optical rotation [a]2D6 À38.7 (c 0.6,
MeCN). Anal. calcd for C25H32ClN5O7: C, 54.59; H,
5.86; N, 12.73; found: C, 54.37; H, 5.86; N, 12.41.
N-((1S)-2-{(2S)-2-[N-((1S)-1-(Methylethyl)-2-oxo-2-{3-
[4-(benzyloxy)phenyl]-2-oxo-1,3,4-oxadiazolin-5-yl}ethyl)
carbamoyl]pyrrolidinyl}-1-(methylethyl)-2-oxoethyl)meth-
oxycarboxamide (5n). Derived from 10a and 4-benzyl-
oxyphenylhydrazine: pale yellow amorphous powder;
TLC Rf=0.38, EtOAc/n-hexane (2/1); MS (APCI, Pos.
20 V) m/z=660 (M+K)+, 644 (M+Na)+, 622
À1
(M+H)+; IR(KBr) 1791, 1715, 1684, 1632, 1512 cm
;
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(4-Cyanophenyl)-2-oxo-
1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}carba-
moyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}methoxy-
carboxamide (5k). Derived from 10a and 4-cyano-
phenylhydrazine: white amorphous powder; mp 97.3±
99.8 ꢁC; TLC Rf=0.60, CHCl3/MeOH (10/1); MS
(APCI, Pos. 20 V) m/z=541 (M+H)+; IR(KBr) 1802,
1H NMR(300 MHz, CDCl ) d 7.76 (d, J=9.3 Hz, 2H),
3
7.50 (d, J=6.9 Hz, 1H), 7.47±7.30 (m, 5H), 7.05 (d,
J=9.3 Hz, 2H), 5.36 (d, J=9.0 Hz, 1H), 5.19 (dd,
J=6.9, 5.7 Hz, 1H), 5.10 (s, 2H), 4.63 (dd, J=8.1,
2.7 Hz, 1H), 4.32 (dd, J=9.0, 6.6 Hz, 1H), 3.82±3.56 (m,
2H), 3.68 (s, 3H), 2.40±1.83 (m, 6H), 1.05, 1.01, 0.97
and 0.96 (dÂ4, J=6.9 Hz, 3HÂ4); optical rotation [a]D26
1719, 1685, 1635, 1513 cmÀ1
;
1H NMR(300 MHz,
À34.3 (c 0.5, MeCN). Anal. calcd for C32H39N5O8
ꢂ
DMSO-d6) d 8.49 (d, J=6.9 Hz, 1H), 8.10±7.98 (m, 4H),
7.21 (d, J=8.4 Hz, 1H), 4.92 (t, J=6.9 Hz, 1H), 4.47
(dd, J=8.1, 4.8 Hz, 1H), 3.98 (t, J=8.4 Hz, 1H), 3.78±
3.68 and 3.58±3.50 (mÂ2, 5H), 2.40±2.28 and 2.08±1.70
(mÂ2, 6H), 1.00±0.83 (m, 12H); optical rotation [a]D26
À15.2 (c 0.3, CHCl3). Anal. calcd for C26H32N6O7
ꢂ 0.5H2O: C, 56.82; H, 6.05; N, 15.29; found: C, 56.56;
H, 5.89; N, 15.04.
H2O: C, 60.08; H, 6.46; N, 10.95; found: C, 59.71; H,
6.16; N, 10.83.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(2,4-Dimethoxyphenyl)-
2-oxo-1,3,4-oxadiazolin-5-yl]}-1-(methylethyl)-2-oxoethyl)
carbamoyl]pyrrolidinyl}-1-(methylethyl)-2-oxoethyl}meth-
oxycarboxamide (5p). Derived from 10a and 2,4-dime-
thoxyphenylhydrazine, which was prepared from 1,3-
dimethoxybenzene according to the method described
for preparation of 4-methoxy-2-methylphenylhydrazine:
white amorphous powder; TLC Rf=0.22, EtOAc/
n-hexane (3/1); MS (APCI, Pos. 20 V) m/z=576
(M+H)+, 386; IR(KBr) 1798, 1717, 1685, 1634,
N-((1S)-2-{(2S)-2-[N-((1S)-1-(Methylethyl)-2-oxo-2-{2-
oxo-3-[4-(tri¯uoromethoxy)phenyl]-1,3,4-oxadiazolin-5-
yl}ethyl)carbamoyl]pyrrolidinyl}-1-(methylethyl)-2-oxo-
ethyl)methoxycarboxamide (5l). Derived from 10a and
4-(tri¯uoromethoxy)phenylhydrazine: white amorphous
powder; TLC Rf=0.45, EtOAc/n-hexane (2/1); MS
(APCI, Pos. 20 V) m/z=600 (M+H)+; IR(KBr) 1797,
;
1719, 1685, 1634, 1511 cmÀ1 1H NMR(300 MHz,
CDCl3) d 7.96 (d, J=9.0 Hz, 2H), 7.59 (d, J=6.9 Hz,
1H), 7.34 (d, J=9.0 Hz, 2H), 5.35 (d, J=9.0 Hz, 1H),
5.16 (dd, J=6.9, 5.7 Hz, 1H), 4.63 (dd, J=8.1, 3.0 Hz,
1518 cmÀ1 1H NMR(200 MHz, CDCl 3) d 7.40 (d,
;
J=7.3 Hz, 1H), 7.31 (d, J=9.2 Hz, 1H), 6.61±6.51 (m,
2H), 5.37 (d, J=9.0 Hz, 1H), 5.18 (dd, J=7.3, 5.4 Hz,
1H), 4.62 (dd, J=8.2, 3.4 Hz, 1H), 4.31 (dd, J=9.0,
7.0 Hz, 1H), 3.91±3.48 (m, 2H), 3.86 and 3.83 (sÂ2,
3HÂ2), 3.68 (s, 3H), 2.46±1.77 (m, 6H), 1.02, 0.99, 0.95
and 0.93 (dÂ4, J=6.6 Hz, 3HÂ4); optical rotation [a]D26

1320
K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
ꢂ
À44.2 (c 0.2, MeCN). Anal. calcd for C27H37N5O9
0.3H2O: C, 55.82; H, 6.52; N, 12.05; found: C, 55.48; H,
6.40; N, 11.67.
oxycarboxamide (5t). Derived from 10a and 2,4-dime-
thylphenylhydrazine: white amorphous powder; TLC
Rf=0.34, EtOAc/n-hexane (2/1); MS (APCI, Pos. 20 V)
m/z=544 (M+H)+; IR(KBr) 1795, 1718, 1685, 1633,
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(4-Fluoro-2-methylphenyl)-
2-oxo-1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}
carbamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}meth-
oxycarboxamide (5q). Derived from 10a and 4-¯uoro-2-
methylphenylhydrazine, which was prepared from
4-¯uoro-2-methylphenylamine according to the method
described for preparation of 4-¯uoro-2-methoxyphenyl-
hydrazine described below: white amorphous powder;
TLC Rf=0.37, EtOAc/n-hexane (2/1); MS (MALDI,
Pos.) m/z=586 (M+K)+, 570 (M+Na)+, 548
1509 cmÀ1 1H NMR(300 MHz, CDCl 3) d 7.47 (d,
;
J=7.2 Hz, 1H), 7.25 (d, J=8.7 Hz, 1H), 7.15 (s, 1H),
7.12 (d, J=8.7 Hz, 1H), 5.37 (d, J=9.0 Hz, 1H), 5.15
(dd, J=7.2, 5.4 Hz, 1H), 4.62 (dd, J=8.4, 3.0 Hz, 1H),
4.31 (dd, J=9.0, 6.6 Hz, 1H), 3.82±3.55 (m, 2H), 3.68 (s,
3H), 2.45±1.84 (m, 6H), 2.38 and 2.28 (sÂ2, 3HÂ2),
1.03, 0.99, 0.95 and 0.94 (dÂ4, J=6.9 Hz, 3HÂ4); opti-
cal rotation [a]2D7 À42.6 (c 0.7, MeCN). Anal. calcd for
ꢂ
C27H37N5O7 0.9H2O: C, 57.93; H, 6.99; N, 12.51;
found: C, 57.56; H, 6.62; N, 12.26.
(M+H)+; IR(KBr) 1798, 1718, 1684, 1633, 1504 cm À1
;
1H NMR(300 MHz, CDCl ) d 7.51 (d, J=6.9 Hz, 1H),
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(4-Hydroxyphenyl)-2-
oxo-1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}-
carbamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}meth-
3
7.37 (dd, J=8.7, 5.4 Hz, 1H), 7.09±6.98 (m, 2H), 5.35
(d, J=9.3 Hz, 1H), 5.12 (dd, J=6.9, 5.4 Hz, 1H), 4.63
(dd, J=8.4, 3.0 Hz, 1H), 4.31 (dd, J=9.3, 6.9 Hz, 1H),
3.82±3.55 (m, 2H), 3.68 (s, 3H), 2.41±1.83 (m, 6H), 2.32
(s, 3H), 1.03, 0.99 and 0.95 (dÂ3, J=6.9 Hz, 12H);
optical rotation [a]2D6 À41.8 (c 0.7, MeCN). Anal. calcd
oxycarboxamide (5u).
A mixture of 5n (338 mg,
0.54 mmol) and 10% Pd-C (71 mg, 10 wt%) in MeOH
(5.5 mL) was stirred under an atmosphere of H2 gas at
rt. After 7 h, the reaction mixture was ®ltered through
Celite to remove the catalyst, and concentrated in
vacuo. The residue was puri®ed by column chromato-
graphy on silica gel (FL60D, CHCl3/MeOH (100/
0!100/1)) to a€ord 5u (283 mg, 98%) as a pale yellow
amorphous powder: TLC Rf=0.24, EtOAc/n-hexane (2/
1); MS (MALDI, Pos.) m/z=570 (M+K)+, 554
(M+Na)+, 532 (M+H)+; IR(KBr) 1789, 1713, 1631,
.
for C26H34FN5O7 H2O: C, 55.21; H, 6.42; N, 12.38;
found: C, 54.81; H, 6.15; N, 12.21.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(4-Fluoro-2-methoxy-
phenyl)-2-oxo-1,3,4-oxadiazolin-5-yl]}-1-(methylethyl)-2-
oxoethyl)carbamoyl]pyrrolidinyl}-1-(methylethyl)-2-oxo-
ethyl}methoxycarboxamide (5r). Derived from 10a and
4-¯uoro-2-methoxyphenylhydrazine:24 white amorphous
powder; TLC Rf=0.37, EtOAc/n-hexane (3/1); MS
(FAB, Pos. Glycerol+m-NBA) m/z=564 (M+H)+; IR
1518 cmÀ1 1H NMR(300 MHz, CDCl 3) d 7.61 (d,
;
J=9.3 Hz, 2H), 7.50 (d, J=7.2 Hz, 1H), 6.89 (d,
J=9.3 Hz, 2H), 6.41 (s, 1H), 5.36 (d, J=9.3 Hz, 1H),
5.20 (dd, J=7.2, 5.4 Hz, 1H), 4.67±4.60 (m, 1H), 4.32
(dd, J=9.3, 7.2 Hz, 1H), 3.85±3.57 (m, 2H), 3.68 (s,
3H), 2.39±1.86 (m, 6H), 1.05, 1.02 and 0.97 (dÂ3,
J=6.9 Hz, 12H); optical rotation [a]2D5 À40.0 (c 0.6,
(KBr) 1802, 1717, 1685, 1618, 1515 cmÀ1 1H NMR
;
(300 MHz, CDCl3) d 7.44 (d, J=7.5 Hz, 1H), 7.38 (dd,
J=9.2, 5.9 Hz, 1H), 6.82±6.71 (m, 2H), 5.36 (d,
J=9.0 Hz, 1H), 5.15 (dd, J=7.5, 5.4 Hz, 1H), 4.62 (dd,
J=8.1, 2.7 Hz, 1H), 4.31 (dd, J=9.0, 6.6 Hz, 1H), 3.86
(s, 3H), 3.85±3.54 (m, 2H), 3.68 (s, 3H), 2.40±1.83 (m,
6H), 1.03, 0.99, 0.95 and 0.94 (dÂ4, J=6.6 Hz, 3HÂ4);
optical rotation [a]2D6 À41.8 (c 0.4, MeCN). Anal. calcd
ꢂ
MeCN). Anal. calcd for C25H33N5O8 0.3C4H10O2: C,
56.40; H, 6.39; N, 12.55; found: C, 56.09; H, 6.41; N,
12.20.
ꢂ
for C26H34FN5O8 0.1H2O: C, 55.23; H, 6.10; N, 12.39;
tert-Butyl (4S,5R)-5-[3-(4-aminophenyl)-2-oxo-1,3,4-ox-
adiazolin-5-yl]-2,2-dimethyl-4-(methylethyl)-1,3-oxazoli-
dine-3-carboxylate (23). Under an atmosphere of H2
gas, a mixture of 22 (350 mg, 0.78 mmol), which was
prepared from 10a and 4-nitrophenylhydrazine according
to the same procedures as described for preparation of
18o, and 20% Pd(OH)2/C (wet, 70mg) in MeOH/dioxane
(1/2, 6.9 mL) was stirred at rt for 2.5 h. The reaction
mixture was ®ltered to remove the catalyst, and con-
centrated in vacuo to a€ord 23 (353 mg, quant) as a pale
yellow viscous syrup. The product was used for the next
reaction without further puri®cation: TLC Rf=0.13,
EtOAc/n-hexane (1/3); MS (MALDI, Pos.) m/z=457
(M+K)+, 441 (M+Na)+, 418 (M+H)+; 1H NMR
(300 MHz, CDCl3) d 7.56 and 6.73 (dÂ2, J=8.7 Hz,
2HÂ2), 4.82 (d, J=3.0 Hz, 1H), 4.60±4.15 (m, 1H),
2.52±2.16 (m, 1H), 1.61 and 1.59 (sÂ2, 3HÂ2), 1.49 (s,
9H), 0.98 and 0.96 (dÂ2, J=6.6 Hz, 3HÂ2).
found: C, 55.02; H, 6.10; N, 12.01.
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(2,4-Di¯uorophenyl)-2-
oxo-1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}-
carbamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}meth-
oxycarboxamide (5s). Derived from 10a and 2,4-di¯uoro-
phenylhydrazine: white amorphous solid; mp 80.7±
82.2 ꢁC; TLC Rf=0.55, CHCl3/MeOH (10/1); MS
(APCI, Pos. 20 V) 552 (M+H)+; IR(KBr) 1806, 1718,
1684, 1633, 1520 cmÀ1; 1H NMR(300 MHz, DMSO- d6)
d 8.47 (d, J=6.9 Hz, 1H), 7.84±7.77 (m, 1H), 7.65±7.58
(m, 1H), 7.37±7.29 (m, 1H), 7.25 (d, J=8.4 Hz, 1H),
4.80 (t, J=6.9 Hz, 1H), 4.43 (dd, J=8.1, 4.5 Hz, 1H),
3.98 (t, J=8.4 Hz, 1H), 3.77±3.68 and 3.58±3.50 (mÂ2,
5H), 2.34±2.24 and 2.08±1.71 (mÂ2, 6H), 0.96±0.83 (m,
12H); optical rotation [a]2D7 À18.5 (c 0.3, CHCl3). Anal.
ꢂ
calcd for C25H31F2N5O7 H2O: C, 52.72; H, 5.84; N,
12.30; found: C, 52.45; H, 5.47; N, 12.09.
tert-Butyl (4S,5R)-5-{3-[4-(dimethylamino)phenyl]-2-oxo-
1,3,4-oxadiazolin-5-yl}-2,2-dimethyl-4-(methylethyl)-1,3-
oxazolidine-3-carboxylate (24). To a stirred solution of
23 (340 mg, 0.78 mmol) in CH3CN (15 mL) was added
N-{(1S)-2-[(2S)-2-(N-{(1S)-2-[3-(2,4-Dimethylphenyl)-2-
oxo-1,3,4-oxadiazolin-5-yl]-1-(methylethyl)-2-oxoethyl}-
carbamoyl)pyrrolidinyl]-1-(methylethyl)-2-oxoethyl}meth-

K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
1321
35% HCHOaq (0.4 mL) and NaBH3CN (78 mg,
1.25 mmol). After stirring at rt for 30 min, the reaction
mixture was acidi®ed to pH 4ꢀ5 with acetic acid, and stir-
red for 1 h. The reaction mixture was poured into saturated
NaHCO3, and extracted with EtOAc. The organic layer
was washed with H2O, brine, dried over anhydrous
MgSO4, and concentrated in vacuo. The residue was pur-
i®ed by silica gel column chromatography (FL60D,
EtOAc/n-hexane, (1/9)) to a€ord 24 (219 mg, 63%) as a
beige solid: TLC Rf=0.47, EtOAc/n-hexane (1/3); MS
N-[(1S)-2-(3-Butyl-2-oxo-1,3,4-oxadiazolin-5-yl)-1-(methyl-
ethyl)-2-oxoethyl]-2-[5-(benzyloxycarbonylamino)-6-oxo-
2-phenylhydropyrimidinyl]acetamide (29b). To a stirred
solution of oxalyl chloride (0.031 mL, 0.36 mmol) in
CH2Cl2 (0.5 mL) was added dropwise a solution of
DMSO in CH2Cl2 (1 M, 0.71 mL) at À70 ꢁC. After 30 min,
a solution of 28b (107 mg, 0.18 mmol) in DMSO/CH2Cl2
(1/5, 1.2 mL) was added dropwise at À70 ꢁC. After stirring
at À70 ꢁC for 2 h, the reaction mixture was treated with
N-methylmorpholine (0.16 mL, 1.45 mmol), then stirred
at À20 ꢁC for 30 min. The reaction mixture was poured
into ice-cooled 1N HCl, and extracted with EtOAc. The
organic layer was washed with saturated NaHCO3,
brine, dried over anhydrous Na2SO4, and concentrated
in vacuo. The residue was puri®ed by column chromato-
graphy on silica gel (FL60D, MeOH/CHCl3 (1/100)) to
1
(APCI, Pos. 40 V) m/z=447 (M+H)+, 391; H NMR
(300 MHz, CDCl3) d 7.60 and 6.75 (dÂ2, J=9.0 Hz,
2HÂ2), 4.83 (d, J=2.7 Hz, 1H), 4.57±4.16 (m, 1H), 2.97
(s, 6H), 2.57±2.10 (m, 1H), 1.61 and 1.59 (sÂ2, 3HÂ2),
1.49 (s, 9H), 0.98 and 0.96 (dÂ2, J=6.6 Hz, 3HÂ2).
N-((1S)-2-{(2S)-2-[N-((1S)-2-{3-[4-(Dimethylamino)phenyl]-
2-oxo-1,3,4-oxadiazolin-5-yl}-1-(methylethyl)-2-oxoethyl)
carbamoyl]pyrrolidinyl}-1-(methylethyl)-2-oxoethyl)meth-
oxycarboxamide (5v). Prepared from 24 according to the
same procedures as described for preparation of 4c:
orange amorphous solid; TLC Rf=0.29, EtOAc/n-hexane
(3/1); MS (APCI, Pos. 20 V) m/z=559 (M+H)+, 386;
a€ord 29b (104 mg, 98%): TLC Rf=0.50, EtOAc/
1
n-hexane (1/1), H NMR(300 MHz, CDCl ) d 8.79 (br
3
s, 1H), 7.61±7.30 (m, 11H), 6.47 (d, J=8.7 Hz, 1H), 5.34
(dd, J=8.7, 5.1 Hz, 1H), 5.23 (s, 2H), 4.63 and 4.56
(dÂ2, J=15.6 Hz, 1HÂ2), 3.84 (t, J=7.2 Hz, 2H), 2.35±
2.20 (m, 1H), 1.85±1.72 and 1.46±1.32 (mÂ2, 4H), 1.04
and 0.86 (dÂ2, J=6.9 Hz, 3HÂ2), 0.97 (t, J=7.2 Hz,
3H).
1
IR(KBr) 1789, 1717, 1685, 1633, 1523 cm À1; H NMR
(200 MHz, CDCl3) d 7.64 (d, J=9.2 Hz, 2H), 7.45 (d,
J=7.4 Hz, 1H), 6.75 (d, J=9.2 Hz, 2H), 5.39 (d,
J=9.0 Hz, 1H), 5.23 (dd, J=7.4, 5.4 Hz, 1H), 4.63 (dd,
J=8.0, 2.8 Hz, 1H), 4.32 (dd, J=9.0, 6.6 Hz, 1H), 3.84±
3.52 (m, 2H), 3.68 (s, 3H), 3.00 (s, 6H), 2.45±1.79 (m,
6H), 1.04, 1.01, 0.97 and 0.95 (dÂ4, J=6.6 Hz, 3HÂ4);
optical rotation [a]2D5 À30.7 (c 0.3, MeCN). Anal. calcd
N-[(1S)-2-(3-Butyl-2-oxo-1,3,4-oxadiazolin-5-yl)-1-(methyl-
ethyl)-2-oxoethyl]-2-(5-amino-6-oxo-2-phenylhydropyr-
imidinyl)acetamide (3b). A mixture of 29b (102 mg,
0.17 mmol), 1 N HCl±EtOAc (0.017 mL) and 10% Pd-C
(50% wet, 21 mg) in MeOH (1.7 mL) was stirred under
an atmosphere of H2 gas for 3.5 h. The reaction mixture
was ®ltered through Celite to remove the catalyst, and
then concentrated in vacuo. The residual product was
dissolved in EtOAc, washed with saturated NaHCO3,
H2O, brine, dried over anhydrous Na2SO4, con-
centrated in vacuo, and puri®ed by column chromato-
graphy on silica gel (FL60D, CHCl3/MeOH (100/1)) to
a€ord 3b (67 mg, 85%) as a pale yellow amorphous
solid: TLC Rf=0.39, EtOAc; MS (APCI, Pos. 20 V) 469
ꢂ
for C27H38N6O7 0.4H2O: C, 57.31; H, 6.91; N, 14.85;
found: C, 57.64; H, 6.91; N, 14.46.
N-[(1S,2R)-2-(3-Butyl-2-oxo-1,3,4-oxadiazolin-5-yl)-2-
hydroxy-1-(methylethyl)ethyl]-2-[5-(benzyloxycarbonyl-
amino)-6-oxo-2-phenylhydropyrimidinyl]acetamide (28b).
A solution of 13c (95 mg, 0.25 mmol) in MeOH/TFA
(1/6, 3.5 mL) was stirred at rt for 18 h and at 40 ꢁC for
2 h, then concentrated in vacuo. The residue was treated
with 4 N HCl±EtOAc, followed by azeotropic removal of
water with toluene to give 14c (82 mg) as HCl salt
quantitatively. The product was used for the next coupl-
ing reaction without further puri®cation.
1
(M+H)+; IR(KBr) 1791, 1663, 1610, 1530 cm À1; H
NMR(300 MHz, CDCl ) d 7.60±7.35 (m, 6H), 6.68 (d,
3
J=8.4 Hz, 1H), 5.33 (dd, J=8.4, 5.1 Hz, 1H), 4.63 and
4.56 (dÂ2, J=15.3 Hz, 1HÂ2), 4.05 (m, 2H), 3.85 (t,
J=7.2 Hz, 2H), 2.36±2.18 (m, 1H), 1.85±1.72 and 1.47±
1.32 (mÂ2, 4H), 1.05 and 0.88 (dÂ2, J=6.9 Hz, 3HÂ2),
0.98 (t, J=7.2 Hz, 3H). Anal. calcd for C23H28N6O5: C,
58.96; H, 6.02; N, 17.94; found: C, 58.60; H, 5.96; N,
17.62.
To a mixture of 14c (82 mg, ca. 0.25 mmol), 27a (76 mg,
.
0.20 mmol) and HOBt H2O (40 mg, 0.26 mmol) in DMF
.
(2 mL) was added EDC HCl (50 mg, 0.26 mmol) and
N-methylmorpholine (0.035 mL, 0.32 mmol) at 0 ꢁC. The
reaction mixture was stirred at rt for 18 h, then poured
into ice-cooled 10% citric acid, and extracted with
EtOAc. The organic layer was washed with saturated
NaHCO3, brine, and dried over anhydrous Na2SO4.
Concentration gave 28b (109 mg, 90%) as a white solid.
The product was used for the next reaction without
further puri®cation: TLC Rf=0.73, MeOH/CHCl3 (1/9);
1H NMR(300 MHz, DMSO- d6) d 8.74 (s, 1H), 8.44 (s,
1H), 8.05 (d, J=9.3 Hz, 1H), 7.55±7.30 (m, 10H), 6.06
(d, J=5.7 Hz, 1H), 5.19 (s, 2H), 4.65±4.59 (m, 1H), 4.50
and 4.43 (br dÂ2, J=16.2 Hz, 1HÂ2), 3.82±3.72 (m,
1H), 3.62±3.54 (m, 2H), 1.82±1.67 (m, 1H), 1.63±1.47
and 1.30±1.14 (mÂ2, 4H), 0.90 and 0.78 (dÂ2,
J=6.6 Hz, 3HÂ2), 0.83 (t, J=7.2 Hz, 3H).
N-{(1S)-1-(Methylethyl)-2-[3-(methylethyl)-2-oxo-1,3,4-
oxadiazolin-5-yl]-2-oxoethyl}-2-(5-amino-6-oxo-2-phenyl-
hydropyrimidinyl)acetamide (3a). This compound was
prepared from 27a and 14b according to the same proce-
dures as described for the preparation of 3b: pale yellow
powder; TLC Rf=0.40, EtOAc; MS (APCI, Pos. 20 V)
m/z=455 (M+H)+; IR(KBr) 1785, 1664, 1612,
1530 cmÀ1; 1H NMR(200 MHz, CDCl 3) d 7.57±7.37 (m,
6H), 6.84 (d, J=8.4 Hz, 1H), 5.36 (dd, J=8.4, 5.0 Hz,
1H), 4.67 and 4.56 (dÂ2, J=15.6 Hz, 1HÂ2), 4.57±4.36
(m, 1H), 4.10±3.10 (m, 2H), 2.38±2.16 (m, 1H), 1.44 (d,
J=6.8 Hz, 6H), 1.04 and 0.87 (dÂ2, J=7.0 Hz, 3HÂ2).
ꢂ
Anal. calcd for C22H26N6O5 0.4C6H14: C, 59.94; H,
6.51; N, 17.19; found: C, 60.02; H, 6.17; N, 16.86.

1322
K. Ohmoto et al. / Bioorg. Med. Chem. 9 (2001) 1307±1323
Methyl 2-[5-(tert-butoxycarbonylamino)-6-oxo-2-phenyl-
hydropyrimidinyl]acetate (27b). solution of 27a
J=7.8 Hz, 1H), 7.55±7.24 (m, 11H), 5.03 (s, 2H), 4.93
(dd, J=7.8, 5.4 Hz, 1H), 4.53 (s, 2H), 2.29±2.11 (m,
1H), 0.86 and 0.79 (dÂ2, J=6.9 Hz, 3HÂ2). Anal. calcd
for C26H27ClN6O5: C, 57.94; H, 5.05; N, 15.59; found:
C, 57.92; H, 4.95; N, 15.49.
A
(1.76 g, 4.64 mmol) in MeOH (4 mL) was treated at 0 ꢁC
with CH2N2/Et2O until the evolution of gas subsided.
The resulting solution was concentrated in vacuo to a€ord
the methyl ester (1.83g, quant) as a white amorphous
solid. The product was used for the next reaction without
further puri®cation: TLC Rf=0.30, EtOAc/n-hexane (1/1);
MS (APCI, Pos. 40V) m/z=394 (M+H)+, 260; 1H
References
NMR(200 MHz, CDCl ) d 8.78 (br s, 1H), 7.56±7.30
(m, 11H), 5.24 (s, 2H), 4.63 (s, 2H), 3.76 (s, 3H).
3
1. Jano€, A. Am. Rev. Repir. Dis. 1985, 132, 417.
2. Jackson, A. H.; Hill, S. L.; A€ord, S. C.; Stockley, R. A. J.
Respir. Dis. 1984, 65, 114.
A mixture of the methyl ester (1.83 g, 4.64 mmol), 10%
Pd-C (367 mg) and 1 N HCl±EtOAc (0.5 mL) in MeOH
(50 mL) was stirred under an atmosphere of H2 gas at rt.
After 2 h, the reaction mixture was ®ltered through Celite
to remove the catalyst. The ®ltrate was treated with 4 N
HCl±EtOAc (10 mL), and concentrated in vacuo. The
residue was partitioned between EtOAc and saturated
NaHCO3. The organic layer was washed with brine, dried
over anhydrous Na2SO4, and concentrated to give the
amine (1.15 g, 95%) as a yellow solid. The product was
used for the next reaction without further puri®cation:
3. Piccioni, P. D.; Kramps, J. A.; Rudolphus, A.; Bulgheroni,
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TLC Rf=0.82, MeOH/CHCl3 (1/4); MS (APCI, Pos.
40V) m/z=260 (M+H)+; H NMR(300 MHz, CDCl )
1
3
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d 7.51 (s, 1H), 7.50±7.38 (m, 5H), 4.63 (s, 2H), 3.77 (s, 3H).
A mixture of the amine (879 mg, 3.39 mmol) and
(Boc)2O (4.68 mL, 20.4 mmol) in THF (15 mL) was
re¯uxed for 5 days, and then evaporated under reduced
pressure. The residue was puri®ed by column chroma-
tography on silica gel (FL60D, EtOAc/n-hexane (1/4))
to a€ord 27b (1.14 g, 93%) as a clear viscous syrup:
TLC Rf=0.53, EtOAc/n-hexane (1/1); MS (APCI, Pos.
40V) m/z=360 (M+H)+, 304, 260; 1H NMR
(200 MHz, CDCl3) d 8.72 (br s, 1H), 7.48 (m, 6H), 4.63
(s, 2H), 3.77 (s, 3H), 1.53 (s, 9H).
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pyrimidinyl]acetic acid (27c). To a stirred solution of
27b (1.11 g, 3.09 mmol) in MeOH (5 mL) was added 2N
NaOH (1.85 mL, 3.70 mmol) at 0 ꢁC. After stirring at rt
for 2 h, the reaction mixture was cooled to 0 ꢁC, then
acidi®ed with 1 N HCl, and extracted with EtOAc. The
organic layer was washed with H2O, brine, dried over
anhydrous Na2SO4, and concentrated in vacuo to a€ord
27c (1.07 g, quant) as a white amorphous solid: TLC
Rf=0.21, MeOH/CHCl3 (1/4); 1H NMR(200 MHz,
CDCl3+several drops of CD3OD) d 8.70 (br s, 1H),
7.60±7.33 (m, 6H), 4.42 (s, 2H), 1.52 (s, 9H).
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N-[(1S)-1-(Methylethyl)-2-oxo-2-(2-oxo-3-benzyl-1,3,4-
oxadiazolin-5-yl)ethyl]-2-(5-amino-6-oxo-2-phenylhydro-
pyrimidinyl)acetamide hydrochloride (3c). A mixture of
29c (60 mg, 0.10 mmol), which was prepared from 13n
and 27c according to the same procedures as described
for preparation of 29b, and 4 N HCl±EtOAc (1 mL) in
EtOAc (1 mL) was stirred at rt for 2 h, and then con-
centrated in vacuo. The residual product was washed
with Et2O to a€ord 3c (47 mg, 88%) as a pale yellow
powder: TLC Rf=0.48, EtOAc; MS (APCI, Pos. 20 V)
m/z=503 (M+H)+; IR(KBr) 1790, 1694, 1661,
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