A new synthetic method for dipeptides containing α,β- didehydroamino acids utilizing an α-tosylglycine residue

Article abstract of DOI:10.1246/bcsj.77.2219

The reaction of peptides containing an N-Boc- or N-Z-α-tosylglycine residue at the N-terminus with a variety of excess nitro compounds under basic conditions to give the nitro compound-adducts in good yields, followed by the elimination of nitrous acid fr

Full text of DOI:10.1246/bcsj.77.2219

Ó 2004 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 77, 2219–2229 (2004) 2219
A New Synthetic Method for Dipeptides Containing
ꢀ,ꢁ-Didehydroamino Acids Utilizing an ꢀ-Tosylglycine Residue
ꢀ
Yohsuke Shiraishi, Hiroshi Yamauchi, Takashi Takamura, and Hideki Kinoshita
Department of Chemistry, Faculty of Science, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192
Received May 10, 2004; E-mail: kinosita@cacheibm.s.kanazawa-u.ac.jp
The reaction of peptides containing an N-Boc- or N-Z-ꢀ-tosylglycine residue at the N-terminus with a variety of
excess nitro compounds under basic conditions to give the nitro compound-adducts in good yields, followed by the elim-
ination of nitrous acid from the adducts to afford the corresponding dipeptide containing ꢀ,ꢁ-didehydroamino acids with
(Z)-configuration predominantly. Treatment of the same starting materials with aldehydes in the presence of base and
tributylphosphine also gave a dipeptide containing ꢀ,ꢁ-didehydroamino acids with high (Z)-selectivity in satisfactory
yields. The present method can be successfully applied to the synthesis of a protected leucine enkephalin analog.
ꢀ,ꢁ-Didehydroamino acid residues are common compo-
nents of naturally occurring peptides that remarkably affect
the physiological activity of peptides,1 as well as their confor-
mations,2 and their resistance to enzyme-catalyzed degrada-
tion.3 Consequently, there are many reports related to methods
for the syntheses of peptides containing ꢀ,ꢁ-didehydroamino
acid residues.4
In previous papers, we already reported that N-t-butoxycar-
bonyl (Boc)- or N-benzyloxycarbonyl (Z)-ꢀ-tosylglycine ester
was reacted with either a variety of nitroalkanes in the pres-
ence of base5a or various kinds of aldehydes in the presence
of base and tributyl phosphine5b to afford the corresponding
ꢀ,ꢁ-didehydroamino acid derivatives with high (Z)-selectivity
in good yields. The latter procedure was successfully applied
to the syntheses of optically active 4-hydroxyprolines.5b
In the light of our results mentioned above, we now wish to
report a convenient method for the preparation of dipeptides
17–31 containing an ꢀ,ꢁ-didehydroamino acid residue starting
from dipeptides containing ꢀ-tosylglycine residue at N-termi-
nus 2. Z- and Boc-ꢀ-tosylglycines, 1a and 1b, were prepared
by the reaction of sodium sulfinate, glyoxylic acid, and Z- or
Boc-carbamate in 99% or 50% formic acid in 84% and 69%
yields, respectively (Scheme 1).
First, dipeptide 2a was obtained as a mixture of diastereom-
ers in a 71% yield by the coupling reaction of methyl L-leuci-
nate and N-Z-ꢀ-tosylglycine (1a) using the dicyclohexylcarbo-
diimide (DCC)–N-hydroxysuccinimide (HONSu) method. Di-
peptides 2b–d were obtained in moderate yields, respectively
(Entries 2–4 in Table 1). Similarly, N-Boc protected dipeptides
.
TsNa 4H2O (2.0 mol. amt.)
Ts
.
OHCCO2H H2O (3.0 mol. amt.)
R
NH2
R
NH CH
CO2H
HCO2H, r.t., 36 - 48 h
R = Z
1a: R = Z 84%
R = Boc
1b: R = Boc 69%
Scheme 1. Preparation of Z- and Boc-ꢀ-tosylglycine.
Table 1. Preparation of Dipeptides 2a–i Containing Tosylglycine Residue
Ts
NH CH
1a , 1b
H-AA-OMe (1.0 mol. amt.)
DCC (1.0-1.5 mol. amt.)
Ts
R
NH CH
R
CO AA OMe
CO2H
Additive (1.0 - 2.0 mol. amt.)
r.t., 2 d, THF
2a-i
Ratio of
diastereomeraÞ
Entry
R
AA
Additive
Product/%
1
2
3
4
5
6
7
8
9
Z
Z
Z
Z
Boc
Boc
Boc
Boc
Boc
Leu
Ala
Gly
Val
Leu
Ala
Gly
Val
Ile
HONSu
HOBt
HOBt
HOBt
HOBt
HOBt
HOBt
HONSu
HOBt
2a 71
2b 51
2c 65
2d 56
56/44
55/45
56/44
67/33
54/46
2e
2f
78
74
2g 76
2h 45
53/47
68/32
2i
62
a) Determined by NMR spectrum.
Published on the web December 10, 2004; DOI 10.1246/bcsj.77.2219

2220 Bull. Chem. Soc. Jpn., 77, No. 12 (2004)
Dipeptide Containing Dehydroamino Acid
2e–i were also prepared from N-Boc-ꢀ-tosylglycine (1b)
with the corresponding amino acid esters in moderate yields
(Entries 5–9 in Table 1).
As preliminary experiments, compound 2a was treated with
2 molar amounts of 2-nitropropane in the presence of 3 molar
amounts of potassium t-butoxide (KOtBu) in tetrahydrofuran
(THF) at 0 ꢁC for 2 h. Contrary to our previous studies,5a
the reaction did not give the expected dipeptide 17 containing
an ꢀ,ꢁ-didehydroamino acid residue, but the nitro compound-
adduct 3 in 50% yield, as shown in Table 2 (Entry 1).6 Al-
though 3 molar amounts of sodium hydride were used instead
of KOtBu, only 3 was obtained in a 44% yield (Entry 2 in
Table 2). The usage of 3 molar amounts of 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU) as a base at 50 ꢁC for 6 h afford-
ed both 3 and the desired product 17 in 18% and 42% yields,
respectively (Entry 3 in Table 2).
After isolation of the nitro compound-adduct 3, the conver-
sion of 3 into 17 was examined under various conditions.
Eventually, the slow addition of 2a into a mixture of 3 molar
amounts of KOtBu and 6 molar amounts of 2-nitropropane at
ꢁ
ꢂ40 C in THF succeeded in forming 3 in quantitative yield,
as shown in Table 3 (Method A, Entry 1). In the same way,
N-protected ꢀ-tosylglycine derivatives 2a–g were successfully
converted into the corresponding nitro compound-adducts 4–
14 in high yields. The results are listed in Table 3. Moreover,
in order to reduce the quantity of nitro compound used for the
preparation of nitro compound-adduct, various reaction condi-
tions were examined. The reaction of 2a with 2 molar amounts
of 2-nitropropane in the presence of 2 molar amounts of
KOtBu in THF at ꢂ40 ꢁC for 1 h proceeded to afford the
desired compound 3 in 61% yield (Method B, Entry 2 in
Table 3). Similarly, compounds 4–6 and 13–16 were furnished
in good yields according to method B (Table 3).
Table 2. Reaction of Dipeptide 2a with 2-Nitropropane
(CH3)2CHNO2 (2.0 mol. amt.)
Ts
Base (3.0 mol. amt.)
Z-NH-CH-CO-Leu-OMe
Temp., Time, THF
2a
Z-NH-CH-CO-Leu-OMe
H3C-C-CH3
Z-NH
CO-Leu-OMe
CH3
+
NO2
H3C
3
17
Time/h
Entry
Base
Temp.
ꢁ
3/%
17/%
Next, the elimination of the nitrous acid from the nitrocom-
pound-adduct to form a dipeptide containing an ꢀ,ꢁ-didehy-
droamino acid residue was performed. Compound 16 was
readily converted into methyl N-Boc-dehydrovalyl-L-isoleuci-
1
2
3
KOtBu
NaH
DBU
0 C
r.t.
2
2
6
50
44
18
0
0
42
ꢁ
r.t. ! 50 C
Table 3. Reaction of a Variety of Dipeptides with Nitro Compounds
Ts
Method A or B
R
CH CO AA OMe
NH
R1
(R1R2CHNO2, KOtBu)
C
R2
R
NH CH CO AA OMe
NO2
2a-f
3 -16
Entry
Substrate
R
AA
MethodaÞ
R1
R2
Product
Yield/%
dsbÞ
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
2a
2a
2a
2a
2b
2b
2c
2c
2d
2d
2e
2e
2e
2e
2f
Z
Z
Z
Z
Z
Z
Z
Z
Z
Leu
Leu
Leu
Leu
Ala
Ala
Gly
Gly
Val
Val
Leu
Leu
Leu
Leu
Ala
Ala
Gly
Gly
Ala
Ile
A
B
A
B
A
B
A
B
A
A
A
A
A
A
A
B
A
B
B
B
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Ph
Me
Me
H
3
3
4
4
5
5
6
6
7
quant.
61
90
82
83
83
80
89
99
95
95
95
71
94
95
99
96
89
83
94
50/50
cÞ
—
—
dÞ
dÞ
H
—
53/47
Me
Me
Me
Me
Me
H
Me
H
H
Me
Me
Me
Me
Me
Me
Me
cÞ
—
51/49
dÞ
Z
8
9
—
55/45
55/45
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Boc
10
11
12
13
13
14
14
15
16
dÞ
—
—
55/45
dÞ
Et
Me
Me
Me
Me
Me
Me
cÞ
2f
—
2g
2g
2h
2i
cÞ
—
53/47
a) Method A: the reaction was peꢁrformed utilizing 6 equimolar amounts of nitro compound and 3 equimolar
amounts KOtBu in THF at ꢂ40 C to room temperature for 1–3 h. Method B: the reaction was performed
utilizing 2 equimolar amounts of nitro compound and KOtBu in THF at ꢂ40 ꢁC for 1 h. b) Means the ratio
of diastereomers determined by NMR spectrum. c) Not determined. d) Consisted of four diastereomers.

Y. Shiraishi et al.
Bull. Chem. Soc. Jpn., 77, No. 12 (2004) 2221
Table 4. Preparation of Dipeptides Containing Dehydroamino Acid Residue
R
NH CH CO AA OMe
R1
R2
NO2
3 - 6, 9 -16
NH
R1
CO AA
R2
R
OMe
DBU (2.0-3.0 mol. amt.)
r.t., 1-2 d, CH2Cl2
C
17 - 28
Entry
Substrate
R
R1
R2
AA
Product
Yield/%
E=ZaÞ
1
2
3
4
5
6
7
3
4
5
6
9
10
11
11
12
13
14
15
16
Z
Z
Z
Z
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Boc
Me
Me
Me
Me
Me
Me
Ph
Ph
Et
Me
Me
Me
Me
Me
H
Me
Me
Me
H
Leu
Leu
Ala
Gly
Leu
Leu
Leu
Leu
Leu
Ala
Gly
Val
Ile
17
18
19
20
21
22
23
23
24
25
26
27
28
70
48
53
47
84
66
34
62
55
67
81
70
91
—
0/100
—
—
—
0/100
0/100
0/100
14/86
—
H
H
8bÞ
9
Me
Me
Me
Me
Me
10
11
12
13
—
—
—
a) Determined by NOE measurement. b) 7.0 equimolar amounts of 1,4-diazabicyclo[2.2.2]octane (DABCO)
were used instead of DBU.
Table 5. Reaction of Dipeptides Containing Tosylglycine Residue with Aldehydes
Ts
CO AA
H
BocNH
OMe
RCHO (4.0 mol. amt.), Bu P (1.5 mol. amt.)
3
DBU (1.2 mol. amt.)
BocNH CH CO AA OMe
o
N , 0
2
C
r.t., 1.5-2.5 h, THF
R'
2e, 2g
Entry
Substrate
AA
RCHO
R0
Product
Total yield/%
E=Z
(Z)-22
(E)-220
1
2
3
2e
2e
2e
Leu
Leu
Leu
MeCHO
PhCHO
EtCHO
Me
Ph
Et
89
64
97
5/95aÞ
23
0/100aÞ
(Z)-29
(E)-290
10/90aÞ
6/94bÞ
6/94aÞ
(Z)-30
(E)-300
4
5
2g
2g
Gly
Gly
MeCHO
EtCHO
Me
Et
82
(Z)-31
(E)-310
quant.
a) Determined by NOE measurement. b) The major product was assigned to be (Z)-isomer by comparison
with the authentic sample.
nate (28) in 91% yield utilizing 2 molar amounts of DBU in
dichloromethane at room temperature for 2 days under nitro-
gen. Although the yield in Entry 7 was not so high, it was im-
proved by using 7 molar amounts of 1,4-diazabicyclo[2.2.2]oc-
tane (DABCO) instead of DBU (Entry 8 in Table 4). In the
cases of Entries 2 and 6–8 (Table 4), the products 18, 22,
and 23 were obtained with only (Z)-configuration. The elimi-
nation reaction of the nitrous acid proceeded smoothly with
high (Z)-selectivity to afford the products 17–28 in good yields
(Table 4). The stereochemistry was assigned by NOE measure-
ment.
We furthermore examined the direct conversion of a dipep-
tide containing an ꢀ-tosylglycine residue to a dipeptide contain-
ing an ꢀ,ꢁ-didehydroamino acid residue. Namely, compounds
2e and 2g were treated with 4 equimolar amounts of aldehyde
in the presence of 1.5 molar amounts of tributylphosphine
(Bu3P) and 1.2 molar amounts of DBU. Accordingly, the reac-
tion proceeded through a Wittig-type reaction5b to afford di-
peptides; the (Z)-isomer of 22, 23, and 29–31 as major prod-
ucts in good yields accompanied by a small amount of (E)-iso-
mer, except for Entry 2 (Table 5). The results are summarized
in Table 5. The stereochemistry of the major product 30 in
Entry 4 was assigned to be (Z)-configuration by comparison
with the authentic sample prepared by the coupling reaction
of (Z)-2-(t-butoxycarbonylamino)-2-butenoic acid and methyl
glycinate.
Moreover, it was found that treatment of isolable (E)-isomer
220 with a catalytic amount of iodine in dichloromethane at
room temperature resulted in the isomerization to the corre-
sponding (Z)-isomer in an 83% yield (Entry 1 in Table 6).
In a similar way, 290, 300, and 310 were also isomerized to their
(Z)-isomers in good yields (Table 6).

2222 Bull. Chem. Soc. Jpn., 77, No. 12 (2004)
Table 6. Isomerization of (E)- to (Z)-isomer by Iodine
Dipeptide Containing Dehydroamino Acid
BocNH
CO AA OMe
H
BocNH
CO AA OMe
cat. I2
r.t., overnight
CH2Cl2
R
R
H
22', 29', 30', 31'
Entry
Substrate
R
AA
Yield/%
E=Z
1
2
3
4
220
290
300
310
Me
Et
Me
Et
Leu
Leu
Gly
Gly
83
90
83
80
5/95
20/80
5/95
2/98
Ts
Ts
a
b
Boc-NH-CH-CO-Leu-OtBu
Boc-NH-CH-CO-Leu-OtBu
Boc-NH-CH-CO H
2
32
1b
Ph
C
H
NO
2
33
c
d
CO-Leu-OtBu
Boc-Gly-NH-CH-CO-Leu-OtBu
Boc-Gly-NH
Ph
C
H
NO
2
Ph
H
35
36
e
Boc-Tyr(Boc)-Gly-Gly-∆Phe-Leu-OtBu
39
Scheme 2. Synthesis of protected ꢀPhe4-leucine enkephalin analog. a) H-Leu-OtBu (1.0 mol. amt.), DCC (1 mol. amt.), HOBt (1
ꢁ
mol. amt.) in THF, r.t., 23 h. 32 77%. b) PhCH2NO2 (2 mol. amt.), KOtBu (2 mol. amt.) in THF, ꢂ40 C ! r.t., 33 70%. c) 1)
CH3COCl (17 mol. amt.), MeOH (17 mol. amt.) in AcOEt, r.t., 8 h. HCl salt 34 quant. 2) Boc-Gly-OH (1.1 mol. amt.), IBCF
ꢁ
(1.0 mol. amt.), NMM (1.1 mol. amt.) in THF, ꢂ15 C, 8 min; 34 (1 mol. amt.), NMM (1.1 mol. amt.) in THF/DMF (2/1),
ꢂ15 ꢁC to r.t., 5 h. 35 76%. d) DABCO (7 mol. amt.) in CH2Cl2, r.t., 8 h. 36 81%. e) 1) CH3COCl (17 mol. amt.), MeOH
(17 mol. amt.) in AcOEt, r.t., 8 h. HCl salt 37 quant. 2) Boc-Tyr(Boc)-Gly-OH (38) (1 mol. amt.), IBCF (1.1 mol. amt.),
ꢁ
ꢁ
NMM (1.1 mol. amt.) in THF, ꢂ15 C, 15 min; 37 (1 mol. amt.), NMM (1.1 mol. amt.) in THF/DMF (2/1), ꢂ15 C to r.t.,
overnight. 39 72%. DCC = dicyclohexylcarbodiimide, HOBt = 1-hydroxybenzotriazole, IBCF = isobutyl chloroformate,
NMM = 4-methylmorpholine, DABCO = 1,4-diazabicyclo[2.2.2]octane.
As nitro compound-adducts (3–6 and 9–16) could be easily
converted to the corresponding dipeptide containing an ꢀ,ꢁ-di-
dehydroamino acid residue under basic conditions in moderate
to good yields (Table 4), the present method was applied to the
synthesis of protected analog 39 of the opioid peptide, leucine-
enkephalin, according to Scheme 2.7 Initially, N-Boc-ꢀ-tosyl-
glycine (1b) was coupled with t-butyl L-leucinate using the
DCC–HOBt method to afford the dipeptide 32 in 77% yield,
which was treated with (nitromethyl)benzene in the presence
of 2 molar amounts of KOtBu to give t-butyl N-Boc-(ꢁ-nitro)-
phenylalanyl-L-leucinate 33 in 70% yield. Next, selective de-
protection of the N-Boc protecting group in compound 33
was examined under various acidic conditions. Eventually, it
was found that N-deprotection of 33 with hydrogen chloride
in MeOH4o gave the hydrogen chloride salt 34 in quantitative
yield. Compound 34 was mediated with N-Boc-glycine by
means of the mixed anhydride method using isobutyl chloro-
dormate to afford the tripeptide 35 in 76% yield, which was
treated with 2 molar amounts of DBU in dichloromethane at
room temperature for 2 days under nitrogen to afford the de-
sired Boc-Gly-ꢀPhe-Leu-OtBu (36) with (Z)-configuration in
only 34% yield. The conditions used for the preparation of
compound 23 (Entry 8 in Table 4) were then applied. Namely,
the treatment of 35 with 7 molar amounts of DABCO in dichlo-
romethane at room temperature for 8 h afforded 36 in 81%
yield. The stereochemistry of the ꢀ,ꢁ-dehydrophenylalanine
residue of 36 were determined by NOE measurement. Finally,
after N-deprotection of 36 with hydrogen chloride under the
same reaction conditions as described for compound 33 the
resulting amine hydrogen chloride salt 37 was condensed with
N,O-diBoc-L-tyrosylglycine (38) using the mixed anhydride
method to give the desired protected leucine-enkephalin analog

Y. Shiraishi et al.
Bull. Chem. Soc. Jpn., 77, No. 12 (2004) 2223
The insoluble substances were filtered off, and the filtrate was suc-
cessively washed with 10% citric acid, 10% NaHCO3, and brine,
dried over anhydrous MgSO4, and evaporated under reduced pres-
sure to afford methyl N-Z-ꢀ-tosylglycyl-L-leucinate (2a) as an in-
separable mixture of diastereomers in 71% yield (1.39 g). Mp
105.0–106.0 ꢁC (ethyl acetate–hexane); IR (KBr) 3284, 3033,
2957, 2871, 1737, 1717, 1669, 1628, 1597, 1523, 1456, 1328,
(39) in 72% yield.
As mentioned above, the ꢀ-tosylglycine residue proved to
be a very useful precursor for the ꢀ,ꢁ-didehydroamino acid
residue. The utility of the present method was demonstrated
by the synthesis of the protected leucine-enkephalin analog.
Experimental
1232, 1181, 1147, 1083, 1058, 816, 771, 741, 698, 670 cmꢂ1
;
All of the melting points were determined with a micro melting
apparatus (Yanagimoto Seisakusho) and were uncorrected. The
1H NMR, IR, and MS spectra were recorded on JEOL JNM-LA
400FT (400 MHz) and LA 300FT (300 MHz) NMR spectrome-
ters, a JASCO FT/IR-230 infrared spectrometer, and a JEOL
SX-102A mass spectrometer, respectively. The chemical shifts
of the NMR spectra are reported in ꢂ relative to TMS as an inter-
nal standard. All of the solvents were distilled and stored over a
drying agent. Thin-layer chromatography (TLC) and flash-column
chromatography were performed using Merck’s silica-gel 60
PF254 (Art. 7749) and Cica-Merck’s silica-gel 60 (No. 9385-5B),
respectively.
1H NMR (400 MHz, CDCl3) (major product = M) ꢂ 0.97 (d, J ¼
6:1 Hz, 6H), 1.64–1.73 (m, 2H), 1.83–1.94 (m, 1H), 2.40 (s, 3H),
3.74 (s, 3H), 4.69 (dd, J ¼ 7:6, 7.6 Hz, 1H), 4.86 (d, J ¼ 12:2 Hz,
1H), 4.94–4.97 (m, 1H), 5.65 (d, J ¼ 9:3 Hz, 1H), 6.20 (d, J ¼ 8:8
Hz, 1H), 7.12 (d, J ¼ 7:8 Hz, 1H), 7.18–7.38 (m, 7H), 7.74 (d,
J ¼ 8:8 Hz, 2H). (Minor product = m) ꢂ 0.90–0.94 (m, 6H),
1.64–1.73 (m, 2H), 1.83–1.94 (m, 1H), 2.40 (s, 3H), 3.79 (s,
3H), 4.60–4.68 (m, 1H), 4.96 (d, J ¼ 12:4 Hz, 1H), 5.04 (d, J ¼
12:2 Hz, 1H), 5.68 (d, J ¼ 10:5 Hz, 1H), 6.15 (d, J ¼ 8:8 Hz, 1H),
7.18–7.38 (m, 7H), 7.41 (d, J ¼ 7:3 Hz, 1H), 7.76 (d, J ¼ 8:5 Hz,
2H). Found: C, 58.97; H, 6.22; N, 5.85%. Calcd for
C24H30N2O7S: C, 58.76; H, 6.16; N, 5.71%.
N-Z-ꢀ-Tosylglycine (1a). A solution of benzyl carbamate
(1.51 g, 17 mmol), glyoxylic acid monohydrate (1.84 g, 20 mmol),
and sodium p-toluenesulfinate tetrahydrate (7.50 g, 30 mmol) in
99% formic acid (9 mL) was allowed to stir for 48 h at room tem-
perature under air. The solution was then poured into a large
amount of water. The crystalline product was collected, washed
with water, and dried to afford the desired product 1a in 84% yield
(3.17 g). Mp 81.0–82.0 ꢁC (ethyl acetate–hexane); IR (KBr) 3289,
2372, 2338, 1687, 1655, 1552, 1436, 1300, 1258, 1110, 1062, 976,
The physical and spectral data of compounds 2b–2i are shown
in the following. The products, except for 2c and 2g, were ob-
tained as an inseparable mixture of diastereomers.
Methyl N-Z-ꢀ-Tosylglycyl-L-alaninate (2b):
Mp 150.5–
151.0 ꢁC (ethyl acetate); IR (KBr) 3343, 3278, 3033, 2953,
1738, 1663, 1597, 1524, 1454, 1380, 1356, 1324, 1305, 1265,
1227, 1180, 1146, 1083, 1056, 982, 912, 833, 818, 772, 741,
1
698, 669 cmꢂ1; H NMR (400 MHz, CDCl3) (M) ꢂ 1.47 (d, J ¼
7:3 Hz, 3H), 2.41 (s, 3H), 3.81 (s, 3H), 4.54–4.68 (m, 1H),
4.93–5.03 (m, 2H), 5.62 (d, J ¼ 8:5 Hz, 1H), 7.22–7.35 (m,
8H), 7.76 (d, J ¼ 8:3 Hz, 2H). (m) ꢂ 1.51 (d, J ¼ 7:3 Hz, 3H),
2.41 (s, 3H), 3.76 (s, 3H), 4.54–4.68 (m, 1H), 4.89–5.00 (m,
2H), 5.62 (d, J ¼ 8:5 Hz, 1H), 6.16 (d, J ¼ 8:9 Hz, 1H), 7.22–
7.35 (m, 7H), 7.52 (d, J ¼ 6:1 Hz, 1H), 7.73 (d, J ¼ 8:5 Hz,
2H). Found: C, 54.07; H, 6.82; N, 6.31%. Calcd for
C20H30N2O7S: C, 54.28; H, 6.83; N, 6.33%.
1
757, 698 cmꢂ1; H NMR (400 MHz, CDCl3) ꢂ 2.43 (s, 3H), 5.01
(s, 2H), 5.58 (d, J ¼ 9:7 Hz, 1H), 6.26 (d, J ¼ 9:9 Hz, 1H), 7.25–
7.36 (m, 7H), 7.80 (d, J ¼ 8:3 Hz, 2H). One proton of the carbox-
ylic acid was not assigned. 1a was converted to the corresponding
methyl ester by means of diazomethane for elementary analysis.
ꢁ
Mp 127.0–127.5 C (ethyl acetate–hexane). Found: C, 57.34; H,
5.05; N, 3.60%. Calcd for C18H19NO6S: C, 57.28; H, 5.07; N,
3.71%.
Methyl N-Z-ꢀ-Tosylglycylglycinate (2c): Mp 153.0–154.0
ꢁC (ethyl acetate); IR (KBr) 3312, 3283, 3033, 2947, 2853,
1739, 1704, 1674, 1658, 1597, 1523, 1439, 1386, 1323, 1268,
N-Boc-ꢀ-Tosylglycine (1b). A solution of t-butyl carbamate
(3.98 g, 34 mmol), glyoxylic acid monohydrate (6.26 g, 68 mmol),
and p-toluenesulfinate tetrahydrate (25.50 g, 102 mmol) in 50%
aqueous formic acid (15 mL) was allowed to stir for 36 h at room
temperature under air. The solution was then poured into 800 mL
of water. The crystalline product was collected, washed with wa-
ter, and dried to afford the desired product 1b in 69% yield (7.73
g). Mp 142.0–144.0 ꢁC (ethyl acetate–hexane); IR (KBr) 3354,
2960, 1727, 1698, 1595, 1517, 1467, 1429, 1366, 1325, 1227,
1233, 1181, 1135, 1107, 1083, 1051, 983, 873, 742, 699 cmꢂ1
;
1H NMR (400 MHz, CDCl3) ꢂ 2.41 (s, 3H), 3.79 (s, 3H), 4.09
(dd, J ¼ 5:7, 18.1 Hz, 1H), 4.20 (dd, J ¼ 5:7, 18.1 Hz, 1H),
4.93 (d, J ¼ 12:2 Hz, 1H), 4.99 (d, J ¼ 12:4 Hz, 1H), 5.65 (d, J ¼
8:8 Hz, 1H), 6.14 (d, J ¼ 8:8 Hz, 1H), 7.23–7.35 (m, 7H), 7.78 (d,
J ¼ 8:3 Hz, 2H). Found: C, 55.25; H, 5.12; N, 6.46%. Calcd for
C20H22N2O7S: C, 55.29; H, 5.10; N, 6.45%.
1
1162, 1146, 1082, 1056, 923, 854, 815, 778, 659 cmꢂ1; H NMR
Methyl N-Z-ꢀ-Tosylglycyl-L-valinate (2d): Mp 117.0–118.0
ꢁC (ethyl acetate–diethyl ether–hexane); IR (KBr) 3338, 3270,
3065, 2962, 1745, 1725, 1672, 1598, 1534, 1455, 1438, 1375,
1327, 1265, 1234, 1182, 1147, 1084, 1020, 840, 815, 737, 714,
(400 MHz, CDCl3) ꢂ 1.31 (s, 9H), 2.44 (s, 3H), 3.64 (br, 1H), 5.66
(d, J ¼ 9:8 Hz, 1H), 5.81 (d, J ¼ 9:8 Hz, 1H), 7.36 (d, J ¼ 8:1
Hz, 2H), 7.83 (d, J ¼ 8:1 Hz, 2H). One proton of the carboxylic
acid was not assigned. Found: C, 51.09; H, 5.86; N, 4.09%. Calcd
for C14H19NO6S: C, 51.05; H, 5.81; N, 4.25%.
A General Procedure for the Preparation of Dipeptides
Containing a Tosylglycine Residue (2a–i). To a suspension
of methyl leucinate hydrochloride (927 mg, 5.10 mmol) in dry
THF (15 mL) was added a solution of triethylamine (526 mg,
5.20 mmol) in dry THF (2 mL) at 0 ꢁC under nitrogen. After stir-
ring for 2 h at room temperature, 1a (151 g, 4.00 mmol), DCC
(825 mg, 4.00 mmol), and N-hydroxysuccinimide (460 mg, 4.00
mmol) were added. The mixture was stirred for 2 d at room tem-
perature under air. After filtration, the filtrate was concentrated in
vacuo to give a residue, which was redissolved into ethyl acetate.
697, 669 cmꢂ1 1H NMR (400 MHz, CDCl3) (M) ꢂ 0.96 (dd,
;
J ¼ 2:1, 7.0 Hz, 6H), 2.18–2.34 (m, 1H), 2.41 (s, 3H), 3.80 (s,
3H), 4.65 (dd, J ¼ 4:6, 8.8 Hz, 1H), 4.95 (d, J ¼ 11:2 Hz, 1H),
5.03 (d, J ¼ 12:2 Hz, 1H), 5.65 (d, J ¼ 9:0 Hz, 1H), 6.17 (d, J ¼
8:8 Hz, 1H), 7.13 (d, J ¼ 8:8 Hz, 1H), 7.16–7.38 (m, 7H), 7.75 (d,
J ¼ 8:3 Hz, 2H). (m) ꢂ 1.04 (dd, J ¼ 2:1, 7.0 Hz, 6H), 2.18–2.34
(m, 1H), 2.41 (s, 3H), 3.76 (s, 3H), 4.53 (dd, J ¼ 4:9, 8.1 Hz, 1H),
4.85 (d, J ¼ 12:4 Hz, 1H), 4.93 (d, J ¼ 12:2 Hz, 1H), 5.63 (d, J ¼
9:0 Hz, 1H), 6.17 (d, J ¼ 9:0 Hz, 1H), 7.16–7.38 (m, 7H), 7.40 (d,
J ¼ 8:1 Hz, 1H), 7.75 (d, J ¼ 8:3 Hz, 2H). Found: C, 57.75; H,
5.90; N, 5.85%. Calcd for C23H28N2O7S: C, 57.97; H, 5.92; N,
5.88%.

2224 Bull. Chem. Soc. Jpn., 77, No. 12 (2004)
Methyl N-Boc-ꢀ-Tosylglycyl-L-leucinate (2e):
Dipeptide Containing Dehydroamino Acid
Mp 84.0–
Hz, 1H), 7.34 (d, J ¼ 8:3 Hz, 2H), 7.81 (d, J ¼ 8:3 Hz, 2H).
(m) ꢂ 0.95 (t, J ¼ 7:3: Hz, 3H), 1.05 (d, J ¼ 6:8 Hz, 3H), 1.20
(s, 9H), 1.30–1.37 (m, 2H), 1.46–1.56 (m, 1H), 2.42 (s, 3H),
3.80 (s, 3H), 4.61 (dd, J ¼ 4:6, 7.8 Hz, 1H), 5.51 (d, J ¼ 8:8
Hz, 1H), 5.91 (d, J ¼ 9:3 Hz, 1H), 7.35 (d, J ¼ 8:3 Hz, 1H),
7.37–7.40 (br, 1H), 7.81 (d, J ¼ 8:3 Hz, 2H). EI-MS m=z 456
(Mþ, 0.12%).
86.0 ꢁC (diethyl ether–hexane); IR (KBr) 3309, 2957, 2871,
1729, 1703, 1681, 1655, 1597, 1556, 1521, 1453, 1393, 1367,
1287, 1256, 1147, 1084, 1056, 1019, 977, 867, 817, 732, 708,
670 cmꢂ1
;
1H NMR (400 MHz, CDCl3) (M) ꢂ 0.99 (d, J ¼ 6:3
Hz, 6H), 1.21 (s, 9H), 1.64–1.78 (m, 2H), 1.82–1.92 (m, 1H),
2.42 (s, 3H), 3.76 (s, 3H), 4.71 (dt, J ¼ 7:7, 7.7 Hz, 1H), 5.49
(d, J ¼ 8:8 Hz, 1H), 5.92 (d, J ¼ 8:5 Hz, 1H), 6.97 (d, J ¼ 8:1
Hz, 1H), 7.34 (d, J ¼ 7:3 Hz, 2H), 7.80 (d, J ¼ 7:8 Hz, 2H).
(m) ꢂ 0.95 (d, J ¼ 5:9 Hz, 3H), 0.96 (d, J ¼ 5:9 Hz, 3H), 1.26
(s, 9H), 1.64–1.78 (m, 2H), 1.82–1.92 (m, 1H), 2.42 (s, 3H),
3.80 (s, 3H), 4.62–4.68 (m, 1H), 5.49 (d, J ¼ 8:8 Hz, 1H), 5.87
(d, J ¼ 9:0 Hz, 1H), 7.24 (d, J ¼ 7:8 Hz, 1H), 7.34 (d, J ¼ 7:8
Hz, 2H), 7.82 (d, J ¼ 7:8 Hz, 2H). Found: C, 55.02; H, 7.26; N,
6.19%. Calcd for C21H32N2O7S: C, 55.25; H, 7.06; N, 6.14%.
Methyl N-Boc-ꢀ-Tosylglycyl-L-alaninate (2f): Mp 144.5 ꢁC
(ethyl acetate); IR (KBr) 3420, 3331, 3278, 2979, 2953, 1742,
1684, 1650, 1597, 1518, 1455, 1366, 1345, 1322, 1308, 1291,
1254, 1224, 1152, 1085, 1050, 1021, 975, 866, 831, 768, 715,
A General Procedure for the Preparation of Dipeptides
Containing a ꢁ-Nitro-ꢀ-amino Acid Residue 3–16. Method
A: To a solution of KOtBu (270 mg, 2.4 mmol) in dry THF
(1 mL) was added a solution of 2-nitropropane (428 mg, 4.8
mmol) in dry THF (2 mL) at ꢂ40 ꢁC under nitrogen. After 5
min, a solution of 2a (392 mg, 0.80 mmol) in dry THF (2 mL)
was added over 60 min. The reaction mixture was gradually
warmed to room temperature, and then quenched with a saturated
aqueous solution of NH4Cl. The THF was removed in vacuo to
give a residue, which was partitioned between ethyl acetate and
water. The aqueous layer was extracted with ethyl acetate. The
combined extracts were washed with brine and dried over anhy-
drous MgSO4. Removal of the solvent gave methyl N-Z-ꢁ-nitro-
valyl-L-leucinate 3 as an inseparable mixture of diastereomers in
quantitative yield (335 mg). Mp 92.0–93.0 ꢁC (ethyl acetate–hex-
ane); IR (KBr) 3291, 3068, 2960, 1713, 1692, 1652, 1551, 1455,
667 cmꢂ1 1H NMR (400 MHz, CDCl3) (M) ꢂ 1.23 (s, 9H),
;
1.53 (d, J ¼ 7:1 Hz, 3H), 2.43 (s, 3H), 3.78 (s, 3H), 4.67 (dq,
J ¼ 7:1, 7.3 Hz, 1H), 5.52 (d, J ¼ 8:8 Hz, 1H), 5.94 (d, J ¼ 8:8
Hz, 1H), 7.16 (d, J ¼ 7:3 Hz, 1H), 7.35 (d, J ¼ 7:6 Hz, 2H),
7.80 (d, J ¼ 7:6 Hz, 2H). (m) ꢂ 1.26 (s, 9H), 1.50 (d, J ¼ 7:1
Hz, 3H), 2.43 (s, 3H), 3.81 (s, 3H), 4.64 (dq, J ¼ 7:1, 7.3 Hz),
5.50 (d, J ¼ 9:0 Hz, 1H), 5.92 (d, J ¼ 9:0 Hz, 1H), 7.35 (d, J ¼
8:3 Hz, 2H), 7.46 (d, J ¼ 6:6 Hz, 1H), 7.82 (d, J ¼ 8:3 Hz, 2H).
Found: C, 51.91; H, 6.31; N, 6.63%. Calcd for C18H26N2O7S: C,
52.16; H, 6.32; N, 6.76%.
1390, 1360, 1288, 1248, 1153, 1052, 748, 697 cmꢂ1 1H NMR
;
(400 MHz, CDCl3) (M) ꢂ 0.89 (d, J ¼ 6:1 Hz, 3H), 0.91 (d, J ¼
6:1 Hz, 3H), 1.50–1.67 (m, 3H), 1.57 (s, 3H), 1.71 (s, 3H), 3.70 (s,
3H), 4.49–4.56 (m, 1H), 4.96 (d, J ¼ 8:3 Hz, 1H), 5.11–5.17 (m,
2H), 5.97–6.01 (m, 1H), 6.66 (d, J ¼ 7:8 Hz, 1H), 7.32–7.36 (m,
5H). (m) ꢂ 0.89–0.92 (m, 6H), 1.50–1.67 (m, 3H), 1.60 (s, 3H),
1.71 (s, 3H), 3.72 (s, 3H), 4.49–4.56 (m, 1H), 4.98 (d, J ¼ 8:8
Hz, 1H), 5.11–5.17 (m, 2H), 5.97–6.01 (m, 1H), 6.68–6.74 (br,
1H), 7.32–7.36 (m, 5H). Found: C, 56.57; H, 6.90; N, 9.92%.
Calcd for C20H29N3O7: C, 56.73; H, 6.90; N, 9.92%.
Methyl N-Boc-ꢀ-Tosylglycylglycinate (2g): Mp 158.0–159.5
ꢁC (ethyl acetate); IR (KBr) 3356, 3306, 2977, 1743, 1720, 1683,
1599, 1545, 1517, 1442, 1404, 1375, 1338, 1315, 1300, 1256,
1227, 1209, 1162, 1133, 1081, 1040, 974, 934, 869, 841, 813,
767, 706, 692 cmꢂ1
;
1H NMR (400 MHz, CDCl3) ꢂ 1.24 (s,
Method B: To a suspension of KOtBu (185 mg, 1.65 mmol)
in dry THF (6 mL) was added a solution of 2-nitropropane (1.453
g, 1.63 mmol) in THF (2 mL) at ꢂ40 ꢁC under nitrogen. After 15
min, a solution of 2a (402 mg, 0.82 ꢁmmol) in THF (4 mL) was
added dropwise over 30 min at ꢂ40 C. The mixture was stirred
for 1 h and then quenched with a saturated aqueous solution of
NH4Cl. The THF was removed in vacuo to give a residue, which
was partitioned between ethyl acetate and water. The aqueous lay-
er was extracted with ethyl acetate. The combined extracts were
washed with brine and dried over anhydrous MgSO4. Removal
of the solvent and recrystallization from AcOEt–hexane gave 3
as an inseparable mixture of diastereomers in 61% yield (211 mg).
Methyl 2-(Benzyloxycarbonylamino)-3-nitrobutanoyl-L-leu-
9H), 2.43 (s, 3H), 3.80 (s, 3H), 4.10 (dd, J ¼ 5:9, 18.3 Hz, 1H),
4.26 (dd, J ¼ 4:9, 18.3 Hz, 1H), 5.56 (d, J ¼ 9:0 Hz, 1H), 5.92
(d, J ¼ 9:0 Hz, 1H), 7.26–7.30 (br, 1H), 7.35 (d, J ¼ 8:3 Hz,
2H), 7.81 (d, J ¼ 8:3 Hz, 2H). Found: C, 50.75; H, 6.01; N,
6.95%. Calcd for C17H24N2O7S: C, 50.99; H, 6.04; N, 7.00%.
Methyl N-Boc-ꢀ-Tosylglycyl-L-valinate (2h): Mp 135.0–
136.0 ꢁC (ethyl acetate–diethyl ether–hexane); IR (KBr) 3341,
3069, 2965, 2882, 1737, 1720, 1679, 1597, 1551, 1513, 1440,
1366, 1334, 1320, 1307, 1255, 1223, 1166, 1140, 1081, 1058,
1021, 983, 908, 864, 845, 819, 774, 729, 708 cmꢂ1 1H NMR
;
(400 MHz, CDCl3) (M) ꢂ 1.03 (d, J ¼ 7:0 Hz, 3H), 1.08 (d, J ¼
7:0 Hz, 3H), 1.20 (s, 9H), 2.20–2.36 (m, 1H), 3.78 (s, 3H), 4.67
(dd, J ¼ 4:8, 8.8 Hz, 1H), 5.50 (d, J ¼ 8:8 Hz, 1H), 5.93 (d, J ¼
8:8 Hz, 1H), 7.05 (d, J ¼ 8:8 Hz, 1H), 7.34 (d, J ¼ 8:6 Hz, 2H),
7.81 (d, J ¼ 8:6 Hz, 2H). (m) ꢂ 0.98 (d, J ¼ 7:0 Hz, 6H), 1.26 (s,
9H), 2.20–2.36 (m, 1H), 3.81 (s, 3H), 4.56 (dd, J ¼ 5:0, 8.1 Hz,
1H), 5.50 (d, J ¼ 8:8 Hz, 1H), 5.87 (d, J ¼ 9:0 Hz, 1H), 7.29–
7.31 (br, 1H), 7.34 (d, J ¼ 8:6 Hz, 2H), 7.81 (d, J ¼ 8:6 Hz,
2H). Found: C, 54.07; H, 6.82; N, 6.31%. Calcd for
C20H30N2O7S: C, 54.28; H, 6.83; N, 6.33%.
ꢁ
cinate (4): Mp 85.0–86.0 C (ethyl acetate–hexane); IR (KBr)
3287, 3076, 2959, 1748, 1713, 1693, 1658, 1555, 1455, 1389,
1361, 1285, 1244, 1153, 1056, 1030, 873, 739, 698 cmꢂ1. Com-
pound 4 was found to be a mixture of four diastereomers based
on the NMR spectrum. Found: C, 55.94; H, 6.62; N, 10.16%.
Calcd for C19H27N3O7: C, 55.74; H, 6.65; N, 10.26%.
Methyl N-Z-ꢁ-Nitrovalyl-L-alaninate (5): Mp 110.0–112.0
ꢁC (ethyl acetate–hexane); IR (KBr) 3328, 3269, 3070, 3002,
2953, 1754, 1736, 1715, 1665, 1540, 1457, 1400, 1383, 1345,
1324, 1289, 1262, 1213, 1152, 1061, 1016, 912, 859, 797, 757,
Methyl N-Boc-ꢀ-Tosylglycyl-L-isoleucinate (2i): A solid; IR
(KBr) 3343, 2971, 2879, 1739, 1680, 1597, 1495, 1458, 1439,
1368, 1327, 1305, 1253, 1211, 1164, 1146, 1083, 1057, 1020,
741, 728, 698, 677 cmꢂ1 1H NMR (400 MHz, CDCl3) (M) ꢂ
;
980, 900, 864, 814, 768, 733, 707, 660 cmꢂ1
;
1H NMR (400
1.37 (d, J ¼ 7:1 Hz, 3H), 1.61 (s, 9H), 1.73 (s, 3H), 3.73 (s,
3H), 4.42–4.58 (m, 1H), 4.93 (d, J ¼ 9:8 Hz, 1H), 5.10–5.19
(m, 2H), 5.97 (d, J ¼ 7:8 Hz, 1H), 6.76–6.90 (br, 1H), 7.30–
7.40 (m, 5H). (m) ꢂ 1.37 (d, J ¼ 7:1 Hz, 3H), 1.57 (s, 3H), 1.72
(s, 3H), 4.42–4.58 (m, 1H), 4.97 (d, J ¼ 9:5 Hz, 1H), 5.10–5.19
MHz, CDCl3) (M) ꢂ 0.96 (t, J ¼ 7:6 Hz, 3H), 1.05 (d, J ¼ 6:8
Hz, 3H), 1.20 (s, 9H), 1.30–1.37 (m, 2H), 1.46–1.56 (m, 1H),
2.42 (s, 3H), 3.77 (s, 3H), 4. 71 (dd, J ¼ 4:6, 8.8 Hz, 1H), 5.52
(d, J ¼ 8:8 Hz, 1H), 5.94 (d, J ¼ 8:8 Hz, 1H), 7.11 (d, J ¼ 8:8

Y. Shiraishi et al.
Bull. Chem. Soc. Jpn., 77, No. 12 (2004) 2225
(m, 2H), 5.99 (d, J ¼ 8:8 Hz, 1H), 6.76–6.90 (br, 1H), 7.30–7.40
(m, 5H). Found: C, 53.43; H, 6.13; N, 11.09%. Calcd for
C17H23N3O7: C, 53.54; H, 6.08; N, 11.02%.
Methyl N-Boc-(ꢁ-nitro)phenylalanyl-L-leucinate (11): Mp
169.0–170.0 ꢁC (ethyl acetate–hexane); IR (KBr) 3302, 3089,
2959, 2871, 1726, 1693, 1657, 1557, 1525, 1458, 1438, 1369,
1329, 1289, 1249, 1208, 1168, 1050, 1024, 863, 801, 750, 719
cmꢂ1. Compound 11 was found to be a mixture of four diaster-
eomers based on the NMR spectrum. Found: C 57.53; H, 7.17;
N, 9.60%. Calcd for C21H31N3O7: C, 57.65; H, 7.14; N, 9.60%.
ꢁ
Methyl N-Z-ꢁ-Nitrovalylglycinate (6): Mp 140.5–141.5 C
(ethyl acetate); IR (KBr) 3303, 3067, 2954, 2851, 1745, 1717,
1665, 1540, 1499, 1455, 1439, 1393, 1376, 1345, 1323, 1259,
1223, 1137, 1105, 1057, 1012, 981, 902, 856, 794, 778, 742,
697 cmꢂ1
;
1H NMR (400 MHz, CDCl3) ꢂ 1.63 (s, 3H), 1.73 (s,
Methyl N-Boc-ꢁ-Nitroisoleucyl-L-leucinate (12):
Mp
3H), 3.73 (s, 3H), 3.89 (dd, J ¼ 5:6, 18.3 Hz, 1H), 4.07 (dd,
J ¼ 5:6, 18.3 Hz, 1H), 5.01 (d, J ¼ 9:8 Hz, 1H), 5.10 (d, J ¼
12:2 Hz, 1H), 5.15 (d, J ¼ 12:0 Hz, 1H), 6.03 (d, J ¼ 9:8 Hz,
1H), 6.94 (br, 1H), 7.31–7.38 (m, 5H). Found: C, 52.54; H,
5.83; N, 11.51%. Calcd for C16H21N3O7: C, 52.31; H, 5.76; N,
11.44%.
143.5–145.0 ꢁC (ethyl acetate); IR (KBr) 3326, 2979, 2883,
1750, 1688, 1655, 1548, 1461, 1380, 1369, 1350, 1323, 1275,
1254, 1212, 1156, 1061, 1012, 985, 881, 857, 769, 669 cmꢂ1
.
Compound 12 was found to be a mixture of four diastereomers
based on the NMR spectrum. Found: C, 53.57; H, 8.23; N,
10.41%. Calcd for C18H33N3O7: C, 53.58; H, 8.24; N, 10.42%.
Methyl N-Boc-ꢁ-Nitrovalyl-L-alaninate (13): Mp 152.5–
154.0 ꢁC (ethyl acetate); IR (KBr) 3279, 3089, 2982, 2955,
1753, 1696, 1665, 1546, 1456, 1381, 1369, 1347, 1328, 1281,
1254, 1218, 1162, 1052, 1013, 877, 856, 835, 806, 751, 669
Methyl N-Z-ꢁ-Nitrovalyl-L-alaninate (7): Mp 110.0–112.0
ꢁC (ethyl acetate–hexane); IR (KBr) 3328, 3269, 3070, 2953,
1754, 1736, 1715, 1665, 1540, 1457, 1400, 1383, 1345, 1324,
1289, 1262, 1213, 1152, 1061, 1016, 912, 859, 797, 757, 741,
728, 698, 677 cmꢂ1
;
1H NMR (400 MHz, CDCl3) (M) ꢂ 1.37
cmꢂ1
;
1H NMR (400 MHz, CDCl3) (M) ꢂ 1.39 (d, J ¼ 7:1 Hz,
(d, J ¼ 7:1 Hz, 3H), 1.61 (s, 9H), 1.73 (s, 3H), 3.73 (s, 3H),
4.42–4.58 (m, 1H), 4.93 (d, J ¼ 9:8 Hz, 1H), 5.10–5.19 (m,
2H), 5.97 (d, J ¼ 8:8 Hz, 1H), 7.30–7.40 (m, 5H). (m) ꢂ 1.37
(d, J ¼ 7:1 Hz, 3H), 1.57 (s, 3H), 1.72 (s, 3H), 3.73 (s, 3H),
4.42–4.58 (m, 1H), 4.97 (d, J ¼ 9:5 Hz, 1H), 5.10–5.19 (m,
2H), 5.99 (d, J ¼ 8:8 Hz, 1H), 6.76–6.90 (br, 1H), 7.30–7.40
(m, 5H). Found: C, 53.43; H, 6.13; N, 11.09%. Calcd for
C17H23N3O7: C, 53.54; H, 6.08; N, 11.02%.
3H), 1.47 (s, 9H), 1.62 (s, 3H), 1.74 (s, 3H), 3.74 (s, 3H), 4.46–
4.58 (m, 1H), 4.80 (d, J ¼ 9:8 Hz, 1H), 5.69 (d, J ¼ 9:3 Hz,
1H), 6.71 (d, J ¼ 5:9 Hz, 1H). (m) ꢂ 1.40 (d, J ¼ 7:3 Hz, 3H),
1.47 (s, 9H), 1.59 (s, 3H), 1.75 (s, 3H), 3.75 (s, 3H), 4.46–4.58
(m, 1H), 4.84 (d, J ¼ 10:0 Hz, 1H), 5.69 (d, J ¼ 9:3 Hz, 1H),
6.70–6.82 (m, 1H). Found: C, 48.26; H, 7.31; N, 12.00%. Calcd
for C14H25N3O7: C, 48.41; H, 7.25; N, 12.10%.
Methyl N-Boc-ꢁ-Nitrovalylglycinate (14): Mp 173.0–180.0
ꢁC (ethyl acetate); IR (KBr) 3281, 3096, 3005, 2984, 1762, 1697,
1668, 1549, 1456, 1438, 1405, 1394, 1381, 1370, 1350, 1322,
1282, 1258, 1209, 1179, 1100, 1059, 1038, 1015, 982, 931, 877,
Methyl 2-(Benzyloxycarbonylamino)-3-nitrobutanoyl-L-ala-
ninate (8): Mp 131.5–134.0 ꢁC (ethyl acetate–hexane); IR (KBr)
3287, 3068, 3035, 2966, 2934, 2878, 2851, 2786, 1957, 1744,
1715, 1664, 1539, 1456, 1437, 1376, 1346, 1258, 1146, 1115,
1102, 1087, 1059, 1014, 911, 857, 787, 754, 739, 699, 686
855, 791, 706, 662 cmꢂ1 1H NMR (400 MHz, CDCl3) ꢂ 1.47
;
(s, 9H), 1.62 (s, 3H), 1.77 (s, 3H), 3.75 (s, 3H), 3.97 (dd,
J ¼ 5:6, 18.3 Hz, 1H), 4.05 (dd, J ¼ 5:6, 18.3 Hz, 1H), 4.83 (d,
J ¼ 9:8 Hz, 1H), 5.68 (d, J ¼ 9:8 Hz, 1H), 6.62 (br, 1H). Found:
C, 46.75; H, 6.98; N, 12.56%. Calcd for C13H23N3O7: C, 46.84; H,
6.95; 12.61%.
cmꢂ1
;
1H NMR (400 MHz, CDCl3) (M) ꢂ (d, J ¼ 6:8 Hz, 3H),
0.89 (d, J ¼ 6:8 Hz, 3H), 1.60 (s, 3H), 1.72 (s, 3H), 2.10–2.20
(m, 1H), 3.72 (s, 3H), 4.43 (dd, J ¼ 4:9, 8.3 Hz, 1H), 4.96 (d, J ¼
9:8 Hz, 1H), 5.15 (s, 2H), 6.04 (d, J ¼ 9:8 Hz, 1H), 6.73–6.75 (br,
1H), 7.32–7.38 (m, 5H). (m) ꢂ 0.86 (d, J ¼ 6:8 Hz, 3H), 0.89 (d,
J ¼ 6:8 Hz, 3H), 1.58 (s, 3H), 1.72 (s, 3H), 2.10–2.20 (m, 1H),
3.72 (s, 3H), 4.46 (dd, J ¼ 4:7, 8.4 Hz, 1H), 5.00 (d, J ¼ 8:8
Hz, 1H), 5.15 (s, 2H), 5.98 (d, J ¼ 8:8 Hz, 1H), 6.64–6.66 (br,
1H), 7.32–7.38 (m, 5H). Found: C, 55.59; H, 6.74; N, 10.28%.
Calcd for C19H27N3O7: C, 55.74; H, 6.65; N, 10.26%.
Methyl N-Boc-ꢁ-Nitrovalyl-L-valinate (15): Mp 143.0 ꢁC
(benzene–hexane); IR (KBr) 3326, 2971, 2935, 2879, 1749,
1691, 1653, 1549, 1457, 1392, 1379, 1369, 1351, 1327, 1278,
1255, 1216, 1157, 1062, 1012, 981, 953, 881, 858, 792, 769,
1
752, 662 cmꢂ1; H NMR (400 MHz, CDCl3) (M) ꢂ 0.89 (d, J ¼
7:1 Hz, 3H), 0.93 (d, J ¼ 7:1 Hz, 3H), 1.47 (s, 9H), 1.61 (s,
3H), 1.75 (s, 3H), 2.13–2.23 (m, 1H), 4.44 (dd, J ¼ 4:6, 8.8 Hz,
1H), 4.77 (d, J ¼ 9:5 Hz, 1H), 5.78 (d, J ¼ 9:5 Hz, 1H), 6.56–
6.58 (br, 1H). (m) ꢂ 0.87 (d, J ¼ 7:1 Hz, 3H), 0.89 (d, J ¼ 7:1
Hz, 3H), 1.47 (s, 9H), 1.59 (s, 3H), 1.74 (s, 3H), 2.13–2.20 (m,
1H), 3.74 (s, 3H), 4.46 (dd, J ¼ 4:6, 10.0 Hz, 1H), 4.85 (d, J ¼
9:5 Hz, 1H), 5.69 (d, J ¼ 9:5 Hz, 1H), 6.53–6.56 (br, 1H). Found:
C, 51.00; H, 7.81; N, 11.07%. Calcd for C16H29N3O7: C, 51.19; H,
7.79; N, 11.19%.
Methyl N-Boc-ꢁ-Nitrovalyl-L-leucinate (9):
Mp 141.0–
144.0 ꢁC (ethyl acetate–hexane); IR (KBr) 3280, 3105, 2957,
2874, 1743, 1692, 1655, 1546, 1457, 1435, 1394, 1369, 1345,
1332, 1272, 1163, 1099, 1060, 1020, 984, 879, 854, 803, 754,
715 cmꢂ1
;
1H NMR (400 MHz, CDCl3) (M) ꢂ 0.93 (d, J ¼ 5:3
Hz, 6H), 1.43–1.68 (m, 3H), 1.47 (s, 9H), 1.59 (s, 3H), 1.74 (s,
3H), 3.72 (s, 3H), 4.40–4.60 (m, 1H), 4.81 (d, J ¼ 9:7 Hz, 1H),
5.66–5.76 (br, 1H), 6.55 (d, J ¼ 7:9 Hz, 1H). (m) ꢂ 0.91 (d, J ¼
5:5 Hz, 6H), 1.43–1.68 (m, 3H), 1.46 (d, J ¼ 5:5 Hz, 6H), 1.62 (s,
3H), 1.74 (s, 3H), 3.72 (s, 3H), 4.40–4.60 (m, 1H), 4.80 (d, J ¼
7:9 Hz, 1H), 5.66–5.76 (br, 1H), 6.55 (d, J ¼ 7:9 Hz, 1H). Found:
C, 52.39; H, 8.04; N, 10.58%. Calcd for C17H31N3O7: C, 52.43; H,
8.02; N, 10.79%.
Methyl N-Boc-ꢁ-Nitrovalyl-L-isoleucinate (16): Mp 123.0–
123.5 ꢁC (benzene–hexane); IR (KBr) 3326, 2979, 2883, 1750,
1688, 1655, 1548, 1461, 1380, 1369, 1350, 1323, 1275, 1254,
1212, 1156, 1061, 1012, 881, 857, 769 cmꢂ1 1H NMR (400
;
MHz, CDCl3) (M) ꢂ 0.89 (t, J ¼ 9:3 Hz, 3H), 0.90 (d, J ¼ 11:0
Hz, 3H), 1.11–1.21 (m, 1H), 1.35–1.42 (m, 1H), 1.47 (s, 9H),
1.61 (s, 3H), 1.74 (s, 3H), 1.82–1.96 (m, 1H), 3.73 (s, 3H), 4.48
(m, 1H), 4.80 (d, J ¼ 9:8 Hz, 1H), 5.77 (d, J ¼ 9:3 Hz, 1H),
6.63–6.66 (m, 1H). (m) ꢂ 0.90 (d, J ¼ 11:0 Hz, 3H), 0.90 (t, J ¼
9:3 Hz, 3H), 1.11–1.21 (m, 1H), 1.35–1.42 (m, 1H), 1.47 (s, 9H),
1.59 (s, 3H), 1.74 (s, 3H), 1.82–1.96 (m, 1H), 3.73 (s, 3H), 4.41
(dd, J ¼ 4:6, 8.5 Hz, 1H), 4.85 (d, J ¼ 9:3 Hz, 1H), 5.70 (d, J ¼
Methyl 2-(t-Butoxycarbonylamino)-3-nitrobutanoyl-L-leuci-
nate (10): Mp 161.0–164.0 ꢁC (ethyl acetate–hexane); IR (KBr)
3342, 3278, 3088, 2976, 1755, 1687, 1655, 1554, 1520, 1455,
1392, 1369, 1305, 1253, 1204, 1160, 1112, 1055, 874, 755
cmꢂ1. Compound 10 was found to be a mixture of four diaster-
eomers based on the NMR spectrum. Found: C 51.12; H, 7.83;
N, 11.18%. Calcd for C16H29N3O7: C, 51.19; H, 7.79; N, 11.19%.

2226 Bull. Chem. Soc. Jpn., 77, No. 12 (2004)
Dipeptide Containing Dehydroamino Acid
9:3 Hz, 1H), 6.60–6.63 (m, 1H). Found: C, 52.18; H, 8.01; N,
10.59%. Calcd for C17H31N3O7: C, 52.43; H, 8.02; N, 10.79%.
A General Procedure for the Preparation of Dipeptide Con-
taining an ꢀ,ꢁ-Didehydroamino Acid Residue (17–28). To a
solution of compound 16 (164 mg, 0.42 mmol) in dry CH2Cl2
(4 mL) was added aꢁsolution of DBU (128 mg, 0.42 mmol) in
CH2Cl2 (2 mL) at 0 C under nitrogen. After stirring for 24 h at
room temperature, the solvent was removed in vacuo to afford a
residue, which was partitioned between ethyl acetate and water.
The aqueous layer was extracted with ethyl acetate, and the com-
bined extracts were washed with 10% citric acid, 10% NaHCO3,
and brine, dried over anhydrous MgSO4, and evaporated under re-
duced pressure to afford a residue, which was subjected to prepa-
rative TLC (SiO2, hexane:ethyl acetate = 2/1, v/v) to afford
methyl N-Boc-ꢀ,ꢁ-didehydrovalyl-L-isoleucinate (28) in 91%
Methyl N-Boc-ꢀ,ꢁ-Didehydrovalyl-L-leucinate (21):
Mp
25
133.0 C (ethyl acetate–hexane); ½ꢀꢃD ¼ ꢂ37:5ꢁ (0.36, MeOH);
IR (KBr) 3279, 2960, 2868, 1757, 1699, 1624, 1541, 1492,
1458, 1370, 1333, 1251, 1232, 1201, 1162, 1053, 1031, 986,
ꢁ
897, 698 cmꢂ1 1H NMR (400 MHz, CDCl3) ꢂ 0.90–0.92 (m,
;
6H), 1.46 (s, 9H), 1.54–1.73 (m, 3H), 1.79 (s, 3H), 2.05 (s, 3H),
3.73 (s, 3H), 4.63 (dt, J ¼ 4:8, 8.8 Hz, 1H), 5.68 (br, 1H),
6.54–6.65 (br, 1H). Found: C, 59.42; H, 8.91; N, 8.04%. Calcd
for C17H30N2O5: C, 59.63; H, 8.83; N, 8.18%.
Methyl (Z)-2-(t-Butoxycarbonylamino)-2-butenoyl-L-leuci-
25
nate (22): Mp 110.0–112.0 ꢁC (ethyl acetate) ½ꢀꢃD ¼ ꢂ33:7ꢁ
(1.00, MeOH) IR (KBr) 3334, 3220, 3049, 2964, 2868, 1759,
1688, 1670, 1626, 1548, 1488, 1453, 1371, 1344, 1304, 1252,
1233, 1201, 1159, 1096, 1053, 1031, 989, 905, 859, 785, 711,
666 cmꢂ1
;
1H NMR (400 MHz, CDCl3) ꢂ 0.94 (d, J ¼ 6:3 Hz,
25
yield (131 mg). Mp 78.0–79.0 ꢁC (hexane); ½ꢀꢃD ¼ ꢂ7:1ꢁ
3H), 0.95 (d, J ¼ 6:1 Hz, 3H), 1.46 (s, 9H), 1.57–1.71 (m, 3H),
1.76 (d, J ¼ 7:1 Hz, 3H), 3.73 (s, 3H), 4.67 (m, 1H), 6.25 (s,
1H), 6.53 (q, J ¼ 7:1 Hz, 1H), 6.69 (d, J ¼ 8:3 Hz, 1H). HRMS
(FAB) (Mþ þ 1): Found: m=z 329.2068. Calcd for C16H29N2O5:
329.2076. When the carbamate NH proton was irradiated, 3.3%,
2.5%, and 2.2% of the NOE were observed for the Bu protons
of the Boc group, the methyl protons at the double bond, and
the amide NH proton, respectively.
(0.27, MeOH); IR (KBr) 3319, 3060, 2973, 1745, 1691, 1670,
1629, 1549, 1458, 1368, 1348, 1254, 1201, 1168, 1055, 856
cmꢂ1
;
1H NMR (400 MHz, CDCl3) ꢂ 0.92 (t, J ¼ 7:3 Hz, 3H),
0.93 (d, J ¼ 6:8 Hz, 3H), 1.14–1.30 (m, 1H), 1.40–1.50 (m,
1H), 1.46 (s, 9H), 1.79 (s, 3H), 1.87–1.97 (m, 1H), 2.04 (s, 3H),
3.73 (s, 3H), 4.61 (dd, J ¼ 4:9, 8.5 Hz, 1H), 5.95 (s, 1H), 6.85
(br, 1H). Found; C, 59.39; H, 8.87; N, 7.93%. Calcd for
C17H30N2O5: C, 59.63; H, 8.83; N, 8.18%.
t
Methyl (Z)-N-Boc-ꢀ,ꢁ-Didehydrophenylalanyl-L-leucinate
25
The physical and spectral data of compounds 17–27 are shown
in the following.
(23):
Mp 104.0–105.0 ꢁC (ethyl acetate–hexane); ½ꢀꢃD
¼
23
ꢂ43:0ꢁ (1.00, MeOH) [Lit. mp 99–101.0 ꢁC, ½ꢀꢃD ¼ ꢂ41:8ꢁ
(1.00, MeOH)];4l IR (KBr) 3230, 3056, 2957, 2871, 1743, 1680,
1658, 1629, 1550, 1504, 1489, 1446, 1391, 1366, 1342, 1304,
1250, 1201, 1164, 1078, 1061, 1029, 962, 938, 882, 841, 783,
Methyl N-Z-ꢀ,ꢁ-Didehydrovalyl-L-leucinate (17):
Mp
25
128.0–129.0 ꢁC (ethyl acetate–hexane); ½ꢀꢃD ¼ ꢂ24:4ꢁ (0.59,
MeOH); IR (KBr) 3284, 3048, 2956, 2869, 1756, 1703, 1626,
1
1559, 1509, 1250, 1229, 1202, 1157, 1060, 738 cmꢂ1; H NMR
754, 689 cmꢂ1; H NMR (400 MHz, CDCl3) ꢂ 0.59 (d, J ¼ 5:7
1
(400 MHz, CDCl3) ꢂ 0.87–0.96 (br, 6H), 1.51–1.72 (m, 3H),
1.78 (s, 3H), 2.06 (s, 3H), 4.60–4.67 (br, 1H), 5.15 (s, 2H), 5.95
(s, 1H), 6.45–6.55 (br, 1H), 7.35–7.52 (m, 5H). Found: C,
63.59; H, 7.53; N, 7.36%. Calcd for C20H28N2O5: C, 63.81; H,
7.50; N, 7.44%.
Hz, 3H), 0.97 (d, J ¼ 5:7 Hz, 3H), 1.40 (s, 9H), 1.58–1.79 (m,
3H), 3.73 (s, 3H), 4.70–4.78 (m, 1H), 6.29 (s, 1H), 6.90 (d, J ¼
8:1 Hz, 1H), 7.21 (s, 1H), 7.27–7.46 (m, 5H). Found: C, 64.38;
H, 7.79; N, 7.04%. Calcd for C21H30N2O5: C, 64.60; H, 7.74;
N, 7.17%. When the carbamate NH proton was irradiated, 2.4%
and 8.9% of the NOE were observed for the amide NH proton
and the ortho protons of the phenyl group, respectively.
Methyl (Z)-2-Benzyloxycarbonylamino-2-butenoyl-L-leuci-
25
nate (18): Mp 77.5–78.0 ꢁC (ethyl acetate); ½ꢀꢃD ¼ ꢂ27:8ꢁ
(0.50, MeOH); IR (KBr) 3244, 3042, 2956, 2870, 1752, 1698,
1671, 1630, 1551, 1507, 1252, 1232, 1202, 1158, 1099, 740,
Methyl (E,Z)-N-Boc-ꢀ,ꢁ-Didehydroisoleucyl-L-leucinate
(24): A mixture of (Z)- and (E)-isomers. Mp 108.0–108.5 ꢁC
(ethyl acetate); IR (KBr) 3349, 3058, 2938, 2740, 2344, 1758,
696 cmꢂ1 1H NMR (400 MHz, CDCl3) ꢂ 0.90–0.92 (m, 2H),
;
1.51–1.66 (m, 2H), 1.74 (d, J ¼ 7:0 Hz, 3H), 3.71 (s, 3H),
4.62–4.70 (m, 1H), 5.14 (s, 2H), 6.53 (q, J ¼ 7:0 Hz, 1H), 6.57
(d, J ¼ 8:3 Hz, 1H), 7.31–7.38 (br, 5H). Found: C, 61.25; H,
1690, 1637, 1491, 1386, 1332, 1252, 1201, 1093, 1030 cmꢂ1
;
1H NMR (400 MHz, CDCl3) (Z)-isomer ꢂ 0.93 (d, J ¼ 5:9 Hz,
3H), 0.94 (d, J ¼ 5:9 Hz, 3H), 1.03 (t, J ¼ 7:6 Hz, 3H), 1.45 (s,
9H), 1.55–1.73 (m, 3H), 2.01 (s, 3H), 2.15 (q, J ¼ 7:6 Hz, 2H),
3.72 (s, 3H), 4.62–4.68 (m, 1H), 5.89 (s, 1H), 7.30 (br, 1H).
(E)-isomer ꢂ 0.93 (d, J ¼ 5:9 Hz, 3H), 0.94 (d, J ¼ 5:9 Hz,
3H), 1.08 (t, J ¼ 7:6 Hz, 3H), 1.45 (s, 9H), 1.55–1.73 (m, 3H),
1.76 (s, 3H), 2.15 (q, J ¼ 7:6 Hz, 2H), 3.72 (s, 3H), 4.62–4.68
(m, 1H), 7.30 (br, 1H). Found: C, 60.45; H, 9.06; N, 7.78%. Calcd
for C18H32N2O5: C, 60.65; H, 9.05; N, 7.86%.
7.21; N, 7.32%. Calcd for C19H26N2O5 1/2H2O: C, 61.42; H,
ꢄ
7.33; N, 7.54%.
Methyl N-Z-ꢀ,ꢁ-Didehydrovalyl-L-alaninate (19):
Mp
25
83.0–84.0 ꢁC (benzene–hexane); ½ꢀꢃD ¼ ꢂ7:8ꢁ (0.83, MeOH);
IR (KBr) 3276, 2987, 2951, 1745, 1687, 1631, 1543, 1507,
1257, 1219, 1161, 1042, 860, 755, 732, 698 cmꢂ1 1H NMR
;
(400 MHz, CDCl3) ꢂ 1.32–1.50 (br, 3H), 1.77 (s, 3H), 2.05 (s,
3H), 3.72 (s, 3H), 4.50–4.70 (br, 1H), 5.14 (s, 2H), 6.22 (s, 1H),
6.60–6.80 (br, 1H), 7.28–7.40 (br, 5H). Found: C, 61.02; H,
6.64; N, 8.22%. Calcd for C17H22N2O5: C, 61.07; H, 6.63; N,
8.38%.
Methyl N-Boc-ꢀ,ꢁ-Didehydrovalyl-L-alaninate (25): Mp
25
118.5–119.0 ꢁC (ethyl acetate–hexane); ½ꢀꢃD ¼ ꢂ14:4ꢁ (0.73,
MeOH); IR (KBr) 3282, 3060, 2982, 1753, 1688, 1665, 1635,
1542, 1457, 1367, 1339, 1278, 1252, 1210, 1164, 1055, 1029,
Methyl N-Z-ꢀ,ꢁ-Didehydrovalylglycinate (20): Mp 107.0–
108.0 ꢁC (ethyl acetate–hexane); IR (KBr) 3298, 2947, 1764,
1707, 1663, 1499, 1446, 1388, 1356, 1329, 1208, 1186, 1118,
689 cmꢂ1
;
1H NMR (400 MHz, CDCl3) ꢂ 1.43 (d, J ¼ 7:1 Hz,
3H), 1.46 (s, 9H), 1.79 (s, 3H), 2.05 (s, 3H), 3.75 (s, 3H), 4.63
(dq, J ¼ 7:1, 7.3 Hz, 1H), 5.83 (s, 1H), 6.75 (br, 1H). Found: C,
56.04; H, 8.13; N, 9.13%. Calcd for C14H24N2O5: C, 55.99; H,
8.05; N, 9.33%.
1011, 961, 928, 915, 787, 765, 752, 718, 698 cmꢂ1 1H NMR
;
(400 MHz, CDCl3) ꢂ 1.78 (s, 3H), 2.07 (s, 3H), 3.74 (s, 3H),
4.03–4.17 (br, 2H), 5.13 (s, 2H), 6.17 (s, 1H), 6.50–6.78 (br,
1H), 7.35–7.40 (m, 5H). Found: C, 59.93; H, 6.31; N, 8.60%.
Calcd for C16H20N2O5: C, 59.99; H, 6.29; N, 8.74%.
Methyl N-Boc-ꢀ,ꢁ-Didehydrovalylglycinate (26):
Mp
164.0–165.0 ꢁC (ethyl acetate–hexane); IR (KBr) 3335, 3189,
2985, 1761, 1691, 1659, 1634, 1540, 1456, 1435, 1397, 1365,

Y. Shiraishi et al.
Bull. Chem. Soc. Jpn., 77, No. 12 (2004) 2227
1333, 1288, 1258, 1202, 1175, 1135, 1085, 1058, 1034, 1013, 981,
1
Methyl (Z)-2-(t-Butoxycarbonylamino)-2-butenoylglycinate
900, 831, 779, 658 cmꢂ1; H NMR (400 MHz, CDCl3) ꢂ 1.46 (s,
(30):
Mp 116.0–118.0 ꢁC (ethyl acetate); IR (KBr) 3324,
3207, 2973, 1762, 1691, 1674, 1631, 1536, 1498, 1456, 1436,
1405, 1367, 1298, 1273, 1254, 1208, 1173, 1097, 1050, 1010,
9H), 1.80 (s, 3H), 2.07 (s, 3H), 3.76 (s, 3H), 4.11 (d, J ¼ 5:7 Hz,
2H), 5.74 (br, 1H), 6.70 (br, 1H). Found: C, 54.39; H, 7.76; N,
9.79%. Calcd for C13H22N2O5: C, 54.53; H, 7.74; N, 9.78%.
1
986 cmꢂ1; H NMR (400 MHz, CDCl3) ꢂ 1.46 (s, 9H), 1.77 (d,
Methyl N-Boc-ꢀ,ꢁ-Didehydrovalyl-L-valinate (27):
Mp
J ¼ 7:1 Hz, 3H), 3.75 (s, 3H), 4.10 (d, J ¼ 5:4 Hz, 2H), 5.70–
5.85 (br, 1H), 6.52 (q, J ¼ 7:1 Hz, 1H), 6.50–6.60 (br, 1H).
Found: C, 52.86; H, 7.51; N, 10.21%. Calcd for C12H20N2O5:
C, 52.93; H, 7.40; N, 10.29%. In order to confirm the stereochem-
istry of the major product 30, an authentic sample was prepared as
follows: (Z)-2-(t-butoxycarbonylamino)butenoic acid and methyl
glycinate were condensed by the DCC–HOBt method (57%).
The NMR spectrum of the product was consistent with that of 30.
Methyl (E)-2-(t-Butoxycarbonylamino)-2-butenoylglycinate
(300): A solid: IR (KBr) 3326, 3195, 2928, 2850, 1756, 1687,
1662, 1640, 1552, 1519, 1433, 1397, 1364, 1284, 1258, 1205,
25
120.5–121.0 ꢁC (hexane); ½ꢀꢃD ¼ ꢂ9:7ꢁ (0.48, MeOH); IR
(KBr) 3299, 2976, 2364, 1750, 1686, 1638, 1543, 1510, 1365,
1
1273, 1252, 1174, 1057, 900 cmꢂ1; H NMR (400 MHz, CDCl3)
ꢂ 0.92 (d, J ¼ 6:8 Hz, 3H), 0.97 (d, J ¼ 6:8 Hz, 3H), 1.46 (s, 9H),
1.80 (s, 3H), 2.05 (s, 3H), 2.16–2.24 (m, 1H), 3.73 (dd, J ¼ 4:8,
8.7 Hz, 1H), 5.95 (s, 1H), 5.76 (br, 1H), 6.77 (br, 1H). Found;
C, 58.39; H, 8.65; N, 8.32%. Calcd for C16H28N2O5: C, 58.52;
H, 8.59; N, 8.53%.
Reaction of N-Boc-ꢀ-Tosylglycylamino Acid Methyl Ester
with Aldehydes. To a solution of Bu3P (124 mg, 0.61 mmol)
and DBU (73 mg, 0.48 mmol) in dry THF (3 mL) was added
1165, 1122, 1050, 1033, 1017, 982 cmꢂ1 1H NMR (400 MHz,
;
ꢁ
0.12 mL of propanal (95 mg, 1.6 mmol) at 0 C under nitrogen.
CDCl3) ꢂ 1.46 (s, 9H), 2.02 (d, J ¼ 7:5 Hz, 3H), 3.79 (s, 3H),
4.16 (d, J ¼ 6:3 Hz, 2H), 6.20–6.30 (br, 1H), 6.30–6.40 (br,
1H), 6.45–6.60 (m, 1H). HRMS (FAB) (Mþ þ 1); Found: m=z
273.1434. Calcd for C12H21N2O5: 273.1450.
A solution of 2e (187 mg, 0.41 mmol) in dry THF (1 mL) was
added to the solution over 10 min at 0 ꢁC under nitrogen. The mix-
ture was allowed to stir for 5.5 h at room temperature. After re-
moval of the solvent, a residue was partitioned between ethyl ace-
tate and water. The aqueous layer was extracted with ethyl acetate.
The combined extracts were washed with brine, dried over anhy-
drous MgSO4, and concentrated under reduced pressure. The re-
sidual oil was subjected to preparative TLC (SiO2, hexane:ethyl
acetate = 4/1, v/v) to afford (Z)-isomer 29 (132 mg, 88%) and
(E)-isomer 290 (13 mg, 9%) in 97% yields, respectively. (Z)-iso-
Methyl
(Z)-2-(t-Butoxycarbonylamino)-2-pentenoylglyci-
nate (31): A solid: IR (KBr) 3265, 3060, 3006, 2978, 2937,
2875, 1763, 1748, 1704, 1683, 1666, 1639, 1513, 1460, 1434,
1414, 1392, 1366, 1319, 1279, 1254, 1213, 1173, 1124, 1107,
;
1059, 1039, 1020, 984 cmꢂ1 1H NMR (400 MHz, CDCl3) ꢂ
1.07 (t, J ¼ 7:6 Hz, 3H), 1.47 (s, 9H), 2.18 (dq, J ¼ 7:3, 7.6
Hz, 2H), 3.77 (s, 3H), 4.12 (d, J ¼ 5:1 Hz, 2H), 5.80 (br, 1H),
6.41 (br, 1H), 6.62 (br, 1H). HRMS (FAB) (Mþ þ 1): Found:
m=z 287.1614. Calcd for C13H23N2O5: 287.1607. When the meth-
ylene protons of the ethyl group were irradiated, 9.7%, 6.7%, and
2.7% of the NOE were observed for the methyl protons of the eth-
yl group, the olefinic proton, and the carbamate NH proton, re-
spectively.
25
mer 29: Mp 136.5–137.5 ꢁC (ethyl acetate); ½ꢀꢃD ¼ ꢂ34:4ꢁ
(1.00, MeOH); IR (KBr) 3350, 3224, 3053, 2965, 2870, 1759,
1690, 1667, 1631, 1549, 1485, 1368, 1324, 1296, 1249, 1230,
1159, 1096, 1053, 1020, 981, 903, 857, 825, 790, 752, 669
cmꢂ1
;
1H NMR (400 MHz, CDCl3) ꢂ 0.94 (d, J ¼ 5:9 Hz, 3H),
0.95 (d, J ¼ 5:6 Hz, 3H), 1.06 (t, J ¼ 7:6 Hz, 3H), 1.46 (s, 9H),
1.54–1.74 (m, 2H), 2.17 (dq, J ¼ 7:3, 7.6 Hz, 2H), 3.73 (s, 3H),
4.69 (dt, J ¼ 4:6, 8.5 Hz, 1H), 5.95 (s, 1H), 6.40–6.43 (m, 1H),
6.57 (d, J ¼ 8:1 Hz, 1H). Found: C, 59.34; H, 8.86; N, 8.13%.
Calcd for C17H30N2O5: C, 59.36; H, 8.83; N, 8.18%. When the
carbamate NH proton of the major product 29 was irradiated,
2.2% and 4.4% of the NOE were observed for the amide NH pro-
ton and methylene protons of the ethyl group, respectively.
Methyl
(E)-2-(t-Butoxycarbonylamino)-2-pentenoylglyci-
nate (310): A solid: IR (film) 3323, 2929, 2850, 1749, 1732,
1716, 1697, 1684, 1521, 1506, 1489, 1457, 1369, 1211, 1160,
1
1144, 1069, 1047, 1021, 984 cmꢂ1; H NMR (400 MHz, CDCl3)
ꢂ 1.10 (t, J ¼ 7:6 Hz, 3H), 1.46 (s, 9H), 2.45 (dq, J ¼ 7:3, 7.6 Hz,
2H), 3.78 (s, 3H), 4.14 (d, J ¼ 5:1 Hz, 2H), 6.12 (br, 1H), 6.37 (br,
1H), 6.52 (br, 1H). HRMS (FAB) (Mþ þ 1): Found: m=z
287.1600. Calcd for C13H23N2O5: 287.1607.
25
(E)-isomer 290: A solid; ½ꢀꢃD ¼ ꢂ45:5ꢁ (0.40, MeOH); IR
(KBr) 3255, 3058, 3009, 2964, 2935, 2870, 2365, 1760, 1693,
1655, 1636, 1545, 1503, 1457, 1384, 1369, 1329, 1251, 1232,
Isomerization of the (E)- to (Z)-Isomer by Iodine. To a so-
lution of 220 (105 mg, 0.32 mmol) in dry CH2Cl2 (2 mL) was add-
ed a solution of a catalytic amount of iodine in dry CH2Cl2 (2 mL)
at room temperature under a nitrogen. The solution was allowed to
stand overnight with stirring, and was then concentrated in vacuo
to give a residue, which was redissolved into AcOEt. The solution
was washed with NaHSO3, NaHCO3, and brine, dried over
MgSO4, and concentrated in vacuo to afford a residue, which
was subjected to preparative TLC (SiO2, hexane:AcOEt = 2:1,
v/v); (Z)-isomer 83 mg, (E)-isomer 5 mg.
Compounds 290, 300, and 310 were isomerized to their (Z)-iso-
mer in the same way. The results are summarized in Table 6.
Synthesis of Protected Leucine-Enkephalin Analog (39). t-
Butyl N-Boc-ꢀ-Tosylglycyl-L-leucinate (32): To a suspension of
t-butyl L-leucinate hydrochloride (985 mg, 44 mmol) in dry THF
(2 mL) was added dropwise a solution of 4ꢁ-methylmorpholine
(546 mg, 5.4 mmol) in dry THF (2 mL) at 0 C under air. After
stirring for 1 h at room temperature, 16 (1.472 g, 4.5 mmol),
DCC (927 mg, 4.5 mmol), and HOBt (608 mg, 4.5 mmol) were
added. After the mixture was stirred for 23 h at room temperature,
1
1197, 1158, 1050, 1022, 985 cmꢂ1; H NMR (400 MHz, CDCl3)
ꢂ 0.95 (d, J ¼ 5:6 Hz, 3H), 0.96 (d, J ¼ 5:9 Hz, 3H), 1.10 (t, J ¼
7:6 Hz, 3H), 1.46 (s, 9H), 1.57–1.71 (m, 3H), 2.44 (dq, J ¼ 7:3,
7.6 Hz, 2H), 3.75 (s, 3H), 4.70 (dt, J ¼ 4:9, 8.3 Hz, 1H), 6.16
(br, 1H), 6.32–6.46 (m, 2H). HRMS (FAB) (Mþ þ 1): Found:
m=z 343.2247. Calcd for C17H31N2O5: 343.2233.
The physical and spectral data of compounds 220, 30, 300, 31,
and 310 are shown in the following.
Methyl (E)-2-(t-Butoxycarbonylamino)-2-butenoyl-L-leuci-
25
nate (220): A solid; ½ꢀꢃD ¼ ꢂ15:8ꢁ (0.18, MeOH); IR (KBr)
3336, 3225, 3060, 3014, 2965, 2927, 2869, 2367, 2346, 1761,
1693, 1663, 1631, 1555, 1504, 1455, 1386, 1371, 1252, 1199,
1
1158, 1130, 1048, 1024, 987 cmꢂ1; H NMR (400 MHz, CDCl3)
ꢂ 0.95 (d, J ¼ 6:3 Hz, 3H), 0.97 (d, J ¼ 6:1 Hz, 3H), 1.45 (s, 9H),
1.55–1.85 (m, 3H), 2.01 (d, J ¼ 7:6 Hz, 3H), 3.75 (s, 3H), 4.71
(dt, J ¼ 5:1, 8.5 Hz, 2H), 6.28 (br, 1H), 6.38 (q, J ¼ 7:6 Hz,
1H). HRMS (FAB) (Mþ þ 1): Found: m=z 329.2077. Calcd for
C16H29N2O5: 329.2076.

2228 Bull. Chem. Soc. Jpn., 77, No. 12 (2004)
Dipeptide Containing Dehydroamino Acid
the insoluble substances were filtered off and washed with AcOEt.
The filtrate was concentrated in vacuo to afford a residue, which
was dissolved into AcOEt. The AcOEt solution was successively
washed with 10% citric acid, 10% NaHCO3, and brine, dried over
anhydrous MgSO4, and concentrated under reduced pressure to
give the desired product as a mixture of diastereomers, which
was recrystallized from ethyl acetate–hexane (1.726 g, 77%).
ter. The aqueous layer was extracted with AcOEt and the com-
bined extracts were successively washed with 10% citric acid,
10% NaHCO3, and brine, dried over anhydrous MgSO4, and con-
centrated under reduced pressure. The residue was subjected to
preparative TLC (SiO2, hexane:ethyl acetate = 2/1, v/v) to give
35 as a mixture of diastereomers in 76% yield (82 mg). Mp 114.0–
116.0 ꢁC (ethyl acetate–hexane); IR (KBr) 3308, 3068, 2961,
2872, 1732, 1699, 1657, 1556, 1471, 1456, 1368, 1280, 1247,
1152, 1047, 947, 847, 718, 694 cmꢂ1. Found: C, 57.53; H, 7.17;
N, 9.55%. Calcd for C24H37N3O7: C, 57.65; H, 7.14; N, 9.60%.
t-Butyl N-Boc-Glycyl-ꢀ,ꢁ-didehydrophenylalanyl-L-leuci-
nate (36): To a solution of 35 (29 mg, 0.06 mmol) in CH2Cl2
(0.5 mL) was added a solid of DABCO (7 mg, 0.06 mmol) at 0
ꢁC under air. After stirring for 5 h at room temperature, an addi-
tional DABCO (42 mg, 0.36 mmol) was added. The solution was
stirred for 18 h and quenched with a phosphate buffer solution
(pH ¼ 7). The solvent was removed in vacuo to afford a residue,
which was partitioned between AcOEt and water. The aqueous
layer was extracted with AcOEt, and the combined extracts were
washed with brine, dried over anhydrous MgSO4, and concentrat-
ed under reduced pressure. The residue was subjected to prepara-
tive TLC (SiO2, chloroform:methanol = 15/1, v/v) to afford 36
25
Mp 143.0–146.0 ꢁC (ethyl acetate–hexane); ½ꢀꢃD ¼ ꢂ29:1ꢁ
(1.00, MeOH); IR (KBr) 3421, 3377, 2967, 2871, 1719, 1698,
1596, 1549, 1499, 1394, 1367, 1317, 1289, 1255, 1227, 1148,
;
1084, 1054, 950, 871, 848, 818, 737, 708, 666 cmꢂ1 1H NMR
(400 MHz, CDCl3) (M) ꢂ 0.99 (d, J ¼ 6:6 Hz, 6H), 1.21 (s,
9H), 1.48 (s, 9H), 1.64–1.71 (m, 2H), 1.80–1.92 (m, 1H), 2.42
(s, 3H), 4.49–4.63 (m, 1H), 5.46 (d, J ¼ 3:5 Hz, 1H), 5.91 (d, J ¼
8:8 Hz, 1H), 7.18 (d, J ¼ 7:5 Hz, 1H), 7.35 (d, J ¼ 3:5 Hz, 2H),
7.79 (d, J ¼ 5:3 Hz, 2H). (m) ꢂ 0.95 (d, J ¼ 4:6 Hz, 6H), 1.26 (s,
9H), 1.52 (s, 9H), 1.64–1.71 (m, 2H), 1.80–1.92 (m, 1H), 2.42 (s,
3H), 4.49–4.62 (m, 1H), 5.43 (d, J ¼ 3:5 Hz, 1H), 5.85 (d, J ¼ 9:4
Hz, 1H), 6.92 (d, J ¼ 7:5 Hz, 1H), 7.32 (d, J ¼ 3:7 Hz, 2H), 7.82
(d, J ¼ 5:5 Hz, 2H). Found: C, 57.68; H, 7.68; N, 5.55%. Calcd
for C24H38N2O7S: C, 57.81; H, 7.68; N, 5.62%.
t-Butyl N-Boc-(ꢁ-Nitro)phenylalanyl-L-leucinate (33): To a
suspension of KOtBu (169 mg, 1.5 mmol) in dry THF (1.5 mL)
was added dropwise a solution of (nitromethyl)benzene5a (384
mg, 2.8 mmol) in dry THF (2 mL) at ꢂ40 ꢁC under nitrogen. After
10 min, a solution of 32 (249 mg, 0.5 mmol) in dry THF (3 mL)
was added dropwise over 40 min. The reaction mixture was grad-
ually warmed to room temperature and then quenched with a satu-
rated aqueous solution of NH4Cl. The THF was removed in vacuo
to afford a residue, which was partitioned between AcOEt and wa-
ter. The aqueous solution was extracted with AcOEt. The com-
bined extracts were washed with brine, dried over anhydrous
MgSO4, and concentrated under reduced pressure. The residue
was subjected to preparative TLC (SiO2, hexane:ethyl acetate =
10/1, v/v) to give 33 as a mixture of diastereomers in 70% yield
(168 mg). Mp 131.0–136.0 ꢁC (ethyl acetate–hexane); IR (KBr)
3317, 2979, 2871, 2352, 1726, 1696, 1658, 1556, 1529, 1457,
1393, 1369, 1327, 1283, 1249, 1168, 1049, 1023, 947, 849, 803,
743, 717, 695 cmꢂ1. The product was found to be a mixture of
four diastereomers based on the NMR spectrum. Found: C,
59.92; H, 7.83; N, 8.71%. Calcd for C24H37N3O7: C, 60.11; H,
7.78; N, 8.76%.
t-Butyl N-Boc-Glycyl-(ꢁ-nitro)phenylalanyl-L-leucinate (35):
A mixed solution of AcOEt (3 mL), abs. methanol (122 mg =
0.15 mL, 3.8 mmol), and acetyl chloride (299 mg = 0.27 mL,
3.8 mmol) was stirred for 30 min at room temperature under nitro-
gen. The solid 33 (108 mg, 0.22 mmol) was added to the resulting
solution at 0 ꢁC, and the solution was then stirred for 8 h at room
temperature to afford the hydrogen chloride salt 34 in quantitative
yield, which was used in the subsequant coupling reaction without
further purification.
To a solution of N-Boc-Gly-OH (40 mg, 0.23 mmol) in dry
THF (0.5 mL) was added a solution of isobutylꢁ chloroformate
(30 mg, 0.22 mmol) in dry THF (1.5 mL) at ꢂ15 C under nitro-
gen, followed by the addition of a solution of NMM (24 mg, 0.23
mmol) in dry THF (1.5 mL). After 3 min, a solution of 34 and
NMM (24 mg, 0.23 mmol) in dry DMF (1.5 mL) was added to
the mixed-anhydride solution prepared above. The mixture was
kept at ꢂ15 ꢁC for 30 min and then stirred for 2 h at room temper-
ature. After the insoluble substances were filtered off and washed
with AcOEt, the filtrate was concentrated under reduced pressure
to afford a residue, which was partitioned between AcOEt and wa-
25
in 81% yield (22 mg). Mp 114.0–116.0 ꢁC; ½ꢀꢃD ¼ ꢂ8:9ꢁ
(0.42, MeOH); IR (KBr) 3365, 3290, 3056, 2976, 2932, 2871,
1725, 1687, 1657, 1623, 1523, 1457, 1391, 1367, 1274, 1253,
1
1153, 1050, 1030, 969, 946, 849, 764, 689 cmꢂ1; H NMR (400
MHz, CDCl3) ꢂ 0.94 (d, J ¼ 6:6 Hz, 6H), 1.42 (s, 9H), 1.46 (s,
9H), 1.62 (dd, J ¼ 7:1, 7.1 Hz, 2H), 1.75 (tq, J ¼ 6:6, 6.6 Hz,
1H), 3.86 (d, J ¼ 5:1 Hz, 2H), 4.53 (dt, J ¼ 7:3, 7.3 Hz, 1H),
5.48 (t, J ¼ 5:1 Hz, 1H), 7.06 (d, J ¼ 6:8 Hz, 1H), 7.20 (s, 1H),
7.28–7.42 (m, 5H), 8.10 (s, 1H). EI-MS m=z 447 (Mþ: 18.4%).
When the amide NH proton of the ꢀ,ꢁ-didehydrophenylalanine
residue was irradiated, 3.2%, 2.1%, 1.4%, and 1.8% of the NOE
were observed for the ortho-protons of the phenyl group, the
NH and the methylene protons of the glycine residue, and the
NH proton of the leucine residue.
N,O-(DiBoc)-L-Tyrosylglycine (38): A mixed solution of Boc-
Tyr(Boc)-OH10 (2.830 g, 7.43 mmol), HONSu (941 mg, 8.17
mmol), and DCC (1.533 g, 7.43 mmol) in dry THF (40 mL)
was stirred for 4 h at room temperature under air. After filtration,
the filtrate was treated with an aqueous solution (3 mL) of H-Gly-
OH (837 mg, 11.5 mmol) and NaHCO3 (937 mg, 11.15 mmol) at
room temperature overnight. The THF was removed in vacuo to
give a residue, which was diluted with a small amount of water
and extracted with AcOEt. The aqueous layer was acidified with
10% citric acid. After salting out, the liberated oil was extracted
with AcOEt. The organic solution was washed with brine, dried
over anhydrous MgSO4, and concentrated under reduced pressure
to afford the desired product, which was recrystallized from ethyl
25
acetate (2.51 g, 77%). Mp 147.0–148.5 ꢁC; ½ꢀꢃD ¼ ꢂ1:2ꢁ (1.0,
MeOH); IR (KBr) 3310, 2935, 2981, 2602, 2345, 1760, 1655,
1532, 1510, 1455, 1394, 1369, 1335, 1280, 1257, 1225, 1152,
1
1105, 1049, 1019, 897, 846, 834, 782, 671 cmꢂ1; H NMR (400
MHz, CDCl3) ꢂ 1.39 (s, 9H), 1.55 (s, 9H), 3.04 (br, 2H), 3.98
(br, 2H), 4.50 (br, 1H), 5.22 (br, 1H), 6.65 (br, 1H), 7.08 (d, J ¼
8:5 Hz, 2H), 7.21 (d, J ¼ 8:5 Hz, 2H). One proton of the carbox-
ylic acid was not assigned. Found: C, 57.32; H, 6.97; N, 6.34%.
Calcd for C21H30N2O8: C, 57.52; H, 6.90; N, 6.39%.
t-Butyl N,O-(DiBoc)-L-Tyrosylglycylglycyl-ꢀ,ꢁ-didehydro-
phenylalanyl-L-leucinate (39): To 1.5 mL of AcOEt was added
methanol (60 mg = 0.076 mL, 1.87 mmol) followed by the addi-
tion of acetyl chloride (147 mg = 0.134 mL, 1.87 mmol) at room

Y. Shiraishi et al.
Bull. Chem. Soc. Jpn., 77, No. 12 (2004) 2229
temperature under nitrogen. The solution was stirred for 80 min at
room temperature, and a solution of 36 (54 mg, 0.11 mmol) in eth-
yl acetate (2 mL) was then added at 0 ꢁC. The solution was grad-
ually warmed to room temperature and then stirred for 20 h. The
solvent was removed under reduced pressure to afford the hydro-
gen chloride salt 37 in quantitative yield (47 mg), which was then
used in the subsequent reaction. To a solution of 38 (44 mg, 0.10
mmol) in dry THF (2 mL) was added a solution of NMM (11 mg,
0.11 mmol) in dry THF (1 mL) followed by the addition of IBCF
(15 mg, 0.11 mmol) in dry THF (1 mL) at ꢂ15 ꢁC under nitrogen.
After 30 min, a solution of the hydrogen chloride salt prepared
above and NMM (12 mg, 0.12 mmol) in dry DMF (1 mL) was
J. M. Schmidt, and H. J. Kizu, J. Am. Chem. Soc., 111, 5015
(1989). h) E. D. de Silva, D. E. Williams, R. J. Anderson, H. Klix,
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2
a) D. E. Palmer, C. Pattaroni, K. Nunami, R. K. Chadha,
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Formaggio, C. Toniolo, T. Yoshikawa, and T. Wakamiya, J.
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ꢁ
added while the solution was kept ꢂ15 C for 15 min, and then
gradually warmed to room temperature. After stirring overnight,
the THF was removed in vacuo to afford a residue, which was par-
titioned between ether and water. The aqueous layer was extracted
with ether. The combined extracts were successively washed with
10% citric acid, 10% NaHCO3, and brine, dried over anhydrous
MgSO4, and concentrated under reduced pressure. The residual
oil was subjected to preparative TLC (SiO2, chloroform:ethyl
acetate:ethanol = 40:8:1, v/v). Yield, 64 mg (a solid, 72%);
3 M. L. English and C. H. Stammer, Biochem. Biophys. Res.
Commun., 85, 1464 (1978).
4
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1466 (1976). c) N. Izumiya, S. Lee, T. Kanmera, and H. Aoyagi,
J. Am. Chem. Soc., 99, 8346 (1977). d) A. Srinivasan, R. W.
Stephenson, and R. K. Olsen, J. Org. Chem., 42, 2253 (1977).
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S. Nomoto, A. Sano, and T. Shiba, Tetrahedron Lett., 20, 521
(1979). g) C. Shin, Y. Yonezawa, and J. Yoshimura, Tetrahedron
Lett., 20, 4085 (1979). h) Y. Yonezawa, C. Shin, Y. Ono, and J.
Yoshimura, Bull. Chem. Soc. Jpn., 53, 2905 (1980). i) C. Shin,
Y. Yonezawa, M. Takahashi, and J. Yoshimura, Bull. Chem.
Soc. Jpn., 54, 1132 (1981). j) C. Shin, T. Yamada, and Y.
Yonezawa, Tetrahedron Lett., 24, 2175 (1983). k) C. Shin, N.
Takamatsu, and Y. Yonezawa, Agric. Biol. Chem., 50, 797
(1986). l) C. Shin, Y. Yonezawa, and M. Ikeda, Bull. Chem.
Soc. Jpn., 59, 3573 (1986). m) D. Ranganathan, K. Shah, and
N. Vaish, J. Chem. Soc., Chem. Commun., 1992, 1145. n) U.
Schmidt, H. Griesser, V. Leitenberger, A. Lieberknecht, R.
Mangold, R. Meyer, and B. Riedl, Synthesis, 1992, 487. o) P.
A. Goghlan and C. J. Easton, Tetrahedron Lett., 40, 4745
(1999). p) F. Yokokawa and T. Shioiri, Tetrahedron Lett., 43,
8673 (2002). q) F. Yokokawa and T. Shioiri, Tetrahedron Lett.,
43, 8679 (2002). r) H. Saito, T. Yamada, K. Okumura, Y.
Yonezawa, and C. Shin, Chem. Lett., 2002, 1098.
25
½ꢀꢃD ¼ ꢂ1:4ꢁ (0.41, MeOH); IR (film) 3314, 3059, 2960, 2933,
2872, 2354, 1759, 1667, 1510, 1392, 1369, 1275, 1256, 1223,
1150, 1048, 1019, 970, 896, 846, 758, 693 cmꢂ1; selected
1H NMR (400 MHz, CDCl3) ꢂ 1.36 (s, 9H), 1.45 (s, 9H), 1.55
(s, 9H); HRMS (FAB) (Mþ þ 1): Found: m=z 810.4253. Calcd
for C42H60N5O11: 810.4289. Amino acid analysis showed the
presence of tyrosine, glycine, and leucine in the ratio of
0.61:2.00:1.10.
The authors express their sincere thanks to Prof. N. Sakura
and Assistant Prof. K. Okimura of the Faculty of Pharmaceut-
ical Science, Hokuriku University, for their kind help in the
amino acid analysis.
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