Ecological base-conditioned preparation of dipeptides using unprotected α-amino acids containing hydrophilic side chains

Article abstract of DOI:10.1246/bcsj.20170035

The coupling reactions of 3-phenylpropanoic acid and Ncarboxybenzyl á-amino acids with unprotected á-amino acids containing hydrophilic side chains such as aliphatic alcohol, aromatic alcohol, thiol, carboxylic acid, and amide afforded the corresponding amides in 6696% yield without racemization via the corresponding mixed carbonic carboxylic anhydrides under basic conditions through an ecological green synthetic method.

Full text of DOI:10.1246/bcsj.20170035

Ecological Base-Conditioned Preparation of Dipeptides Using
Unprotected α-Amino Acids Containing Hydrophilic Side Chains
Tetsuya Ezawa, Seunghee Jung, Yuya Kawashima, Takuya Noguchi, and Nobuyuki Imai*
Faculty of Pharmacy, Chiba Institute of Science, 15-8 Shiomi-cho, Choshi, Chiba 288-0025
E-mail: nimai@cis.ac.jp
Received: January 25, 2017; Accepted: March 19, 2017; Web Released: May 10, 2017
Nobuyuki Imai
Nobuyuki Imai was born in 1959. He graduated from Shizuoka College of Pharmacy in 1982 and obtained
his Ph.D. from Shizuoka College of Pharmacy under Professor Kazuo Achiwa in 1987. After postdoctoral
work at University of Kentucky (with Professor David S. Watt), Harvard University (with Professor E. J.
Corey), and Sagami Chemical Research Institute (with Dr. Susumu Kobayashi), he joined Okayama
University of Science as an assistant professor. He is currently a professor at Chiba Institute of Science.
Abstract
pared via the azidation of Cbz-Ser-OH with hydrazine hydrate
and sodium nitrite under acidic conditions by the reaction with
Tyr-OBn. However, the yields of these dipeptides were moder-
ate. Furthermore, peptide syntheses using α-amino acids con-
taining unprotected side chains also have been developed, and
the native chemical ligation (NCL) method reported by Kent
is quite efficient.8 In NCL, the thioester at the C-terminal of a
peptide reacts initially with the cysteine residue at the N-
terminal of another peptide by ester transfer, followed by the
replacement of sulfur with nitrogen to form the corresponding
amide. Namely, the condensation by NCL is limited to the
peptide fragment oriented cysteine residue at the N-terminal,
and it is well known that peptides containing cysteine are rare.9
In addition, the preparations of the thioesters in the C-terminals
were obtained in poor yield in some cases.10 Li also has reported
the chemoselective synthesis of peptides using O-salicylalde-
hyde ester as a C-terminal fragment and L-serine or L-threonine
ester possessing free side chain as an N-terminus via the corre-
sponding N,O-benzylidene acetal.11 These methods have prob-
lems in terms of atom economy and substrate generality.
Recently, we have reported a green synthetic method for di-
peptides using unprotected α-amino acids via the mixed carbon-
ic carboxylic anhydrides in aqueous organic solvent.12a,12f,12g
In our method, dipeptides were synthesized from N-protected
α-amino acids and unprotected α-amino acids in good yields
in half aqueous organic solvent. Herein, we describe in detail
the convenient condensation of N-protected α-amino acids
with unprotected α-amino acids containing hydrophilic side
chains under basic conditions via the mixed carbonic carboxylic
anhydride under basic conditions as shown in Scheme 1.
The coupling reactions of 3-phenylpropanoic acid and N-
carboxybenzyl α-amino acids with unprotected α-amino acids
containing hydrophilic side chains such as aliphatic alcohol,
aromatic alcohol, thiol, carboxylic acid, and amide afforded the
corresponding amides in 66-96% yield without racemization
via the corresponding mixed carbonic carboxylic anhydrides
under basic conditions through an ecological green synthetic
method.
1. Introduction
Development of convenient and cheap synthetic methods
of peptides is quite important in industrial chemistry. α-Amino
acids are generally categorized on the basis of the properties of
their side chains into four groups, which are aliphatic, aromatic,
acidic, and basic amino acids.1 In particular, α-amino acids
containing nucleophilic side chains such as hydroxy, mercapto,
and carboxy groups also react easily with electrophiles in these
side chains as undesired side reactions. Therefore, it is neces-
sary for synthesis of peptides to protect not only the N-
terminals of α-amino acids and the C-terminals of the other
reactants but also the nucleophilic side chains in order to avoid
undesired side reactions.
A number of useful peptide synthetic methods have recently
been reported.2-6 In these reports, protections of functional
groups such as hydroxy, mercapto, amino, and carboxy groups
in the corresponding α-amino acids are necessary to avoid gen-
eration of by-products in most of the peptide synthetic methods.
Hofmann has reported that the synthesis of peptides related to α-
melanocyte-stimulating hormone (α-MSH) and corticotropins.7
In his study, Cbz-Met-Gln-OH was synthesized by the reaction
of the mixed carbonic carboxylic anhydride of Cbz-Met-OH
with aqueous solution of Gln, and Cbz-Ser-Tyr-OBn was pre-
2. Results and Discussion
In a preliminary investigation, a clear solution of 3-phenyl-
propanoic acid (1) and 1.5 equiv of unprotected α-amino acids
Bull. Chem. Soc. Jpn. 2017, 90, 689–696 | doi:10.1246/bcsj.20170035
© 2017 The Chemical Society of Japan | 689

O
O
O
R1
O
Table 2. Effect of additives on the amidation of 3-phenyl-
propanoic acid (1) with L-Glu-OH (2e)a)
ClCO2Et
Et3N
R1
O
OEt
Cbz-HN
OH
THF
Cbz-HN
O
O
COOH
O
1) ClCO2Et, Et3N, THF, 0 oC, 30 min
2) L-Glu-OH (2e), additive, H2O, 0 oC, 30 min
OH
Ph
Ph
N
R2
O
H
OH
O
R2
1
3e
R2
R1
O
H2N
OH
O
Entry
Additive
pHc)
Yieldb)/%
EtO
+
N
N
H
H
THF-H2O, base
OH
Cbz-HN
OH
1
2
3
4
5
6
7d)
HCl
Free
1.0
4.5
6.5
7.5
8.0
9.0
5
59
90
93
92
93
36
Scheme 1. Convenient condensation of N-protected α-amino
acids with unprotected α-amino acids containing hydro-
philic side chains under basic conditions.
NaHCO3
NaOH
Na2CO3
K2CO3
K2CO3
Table 1. Amidation of 3-phenylpropanoic acid (1) with
unprotected α-amino acids 2a-2ea)
12
O
R2
O
1) ClCO2Et, Et3N, THF, 0 oC, 30 min
a) All reactions were carried out with 0.50 mmol of 1, 0.70
mmol of ethyl chloroformate, and 1.5 mmol of triethylamine in
10 mL of THF. After stirring for 30 min at 0 °C, 0.75 mmol of
L-Glu-OH (2e) and 0.75 mmol of an additive in 10 mL of H2O
were added at 0 °C to the reaction mixture. b) Isolated yields.
c) The pH value of the solution of 2e and additive in 10 mL of
H2O was measured with pH-test paper. d) The reaction was
carried out with 20 mmol of K2CO3.
O
R2
O
Ph
OH
Ph
N
H
2)
, H2O, 0 oC, 30 min
OH
3
1
H2N
OH
2
Entry
1
Amide 3
Yieldb)/%
OH
O
O
3a
90
Ph
N
H
OH
SH
O
despite possession of hydrophilic side chains. A small amount
of N-ethoxycarbonyl α-amino acids 2a¤-2e¤ were observed as a
by-product on the basis of H NMR analysis in all entries of
O
2
3
3b
3c
87
19
Ph
N
H
OH
1
OH
Table 1.
O
O
O
Subsequently, we tried to resolve the problems in Entries 3
and 5 of Table 1. The amidation of 3-phenylpropanoic acid (1)
with L-Glu-OH (2e) was examined under acidic and basic con-
ditions and the results are summarized in Table 2. The reaction
of 1 with 2e in aqueous HCl gave the corresponding amide 3e
in 5% yield, which was obviously decreased (Entry 1). In con-
trast, 1 reacted with 2e under basic conditions in the presence
of NaHCO3 to afford 3e in 90% yield (Entry 3). The amide 3e
was obtained in 93% yield by the reaction using NaOH as a
base (Entry 4). The amidations in the presence of Na2CO3 and
K2CO3, which are stronger bases than NaHCO3, gave 3e in
92% and 93% yields, respectively (Entries 5 and 6). In the
presence of an excess amount of K2CO3, the reaction of 1 with
2e proceeded in 36% yield (Entry 7). We judged that NaHCO3
is better among these bases in the reaction by considering
safety and handling.
A possible pathway of the amidation via the mixed carbonic
carboxylic anhydride 4 is shown in Scheme 2. The carboxylic
anhydride intermediate 5 is generated under the neutral condi-
tions from the corresponding mixed carbonic carboxylic anhy-
dride 4 by the nucleophilic attack of α-amino acid 2. The free
amine of 5 works as a good nucleophile and the corresponding
product 3 is formed by the intramolecular reaction of 5 via the
five-membered transition state (Entries 3-6 in Table 2). The
reaction rate is very slow under the acidic conditions due to the
protonation of the nitrogen atom of 5-H+ (Entry 1 in Table 2).
Then, the mixed carbonic carboxylic anhydride 4 reacts directly
under the basic conditions with the amine part of 2 to give the
corresponding product 3.
O
Ph
Ph
Ph
N
H
OH
CONH2
O
4
5
3d
3e
85
59
N
H
OH
COOH
O
N
H
OH
a) All reactions were carried out with 0.50 mmol of 1, 0.70
mmol of ethyl chloroformate, and 1.5 mmol of triethylamine in
10 mL of the THF. After stirring for 30 min at 0 °C, 0.75 mmol
of 2 in 10 mL of H2O was added to the reaction mixtures.
b) Isolated yields.
2a-2e containing another hydrophilic moiety as a side chain
in aqueous tetrahydrofuran (THF) under neutral conditions was
reacted to afford the corresponding amides 3a-3e as indicated
in Table 1. The reactions of 1 with unprotected α-amino acids
2a and 2b containing hydroxy and mercapto groups afforded
the corresponding amides 3a and 3b in 90% and 87% yields,
respectively (Entries 1 and 2). The amide 3c was obtained by
the reaction of 1 with 2c containing aromatic hydroxy group in
19% yield due to low solubility of 2c in H2O (Entry 3). The
acid 1 smoothly reacted with 2d containing amide group to
give the corresponding amide 3d in 85% yield (Entry 4). In
contrast, the coupling reaction of 1 with 2e containing a car-
boxy group gave the corresponding amide 3e in moderate yield
(Entry 5). It is suggested that the amino group does not work
well as a nucleophile due to protonation by the carboxy group
of 2e. Unprotected α-amino acids 2a, 2b and 2d are easily
dissolved in H2O, but the solubility of 2c and 2e in H2O is low
Next, we tried to synthesize the amides 3 using 3-phenyl-
propanoic acid (1) with several kinds of unprotected α-amino
acids 2a-2e in an aqueous NaHCO3 solution as collected in
690 | Bull. Chem. Soc. Jpn. 2017, 90, 689–696 | doi:10.1246/bcsj.20170035
© 2017 The Chemical Society of Japan

R2
O
R2
O
O
R2
O
O
H+
HO-
ed that the solubility of 2c is improved by the production of
sodium phenoxide in an aqueous NaOH solution, and that 2c
works as a good nucleophile in the second step of the reaction.
The amide 3d was prepared from 1 with L-Gln-OH (2d) in 83%
yield (Entry 4), which is similar to that of the reaction under
the neutral conditions (Entry 4 of Table 1).
H3N
OH
H3N
H2N
2
O
O
slow
fast
fast
4
4
Ph
R2
O
4
OEt
O
O
O
O
R2
Then, we attempted to prepare dipeptides from Cbz-L-Phe-
OH (6a) and various unprotected α-amino acids 2 and these
results are displayed in Table 4. L-Asp-OH (2f), L-Tyr(3-OH)-
OH (2g), L-Tyr(3-I)-OH (2h), and L-Trp(5-OH)-OH (2i) were
added to the substrates containing aromatic alcohols as a side
chain. The dipeptide 7aa was synthesized from 6a and L-Ser-
OH (2a) containing a hydroxy group in 82% yield (Entry 1).
The reaction of 6a with L-Cys-OH (2b) containing a mercapto
group proceeded sufficiently to give the corresponding dipep-
tide 7ab in 86% yield (Entry 2). L-Tyr-OH (2c) containing a
phenolic hydroxy group reacted with the activated form of 6a
to afford 7ac in 73% yield (Entry 3). L-Gln-OH (2d) is most
soluble in H2O among them and was converted to produce 7ad
in 83% yield (Entry 4). Absence of racemization under the
reaction conditions was investigated using Cbz-L-Phe-OH (6a)
and Cbz-D-Phe-OH (6a¤) as follows. The dipeptides 7ae and
7a¤e were synthesized as a single diastereomer by the reactions
of 6a and 6a¤ with L-Glu-OH (2e) containing a carboxy group
in 87% and 85% yields, respectively (Entries 5 and 6). The
coupling reaction of 6a with L-Asp-OH (2f) gave the corre-
sponding dipeptide 7af in 74% yield (Entry 7), which is caused
by slightly lower solubility of 2f in H2O than that of 2e. Both
α-amino acids 6a and 2g containing a 3,4-dihydroxyphenyl
moiety condensed to give 7ag in 68% yield (Entry 8). The
formations of the dipeptides 7ah and 7ai by the reactions of 6a
from 2h containing 4-hydroxy-3-iodophenyl moiety and 2i
containing 5-hydroxyindole moiety succeeded via the activa-
tion of 6a by isobutyl chloroformate in 74% and 76% yields,
respectively (Entries 9 and 10). The dipeptides 7ah and 7ai
were easily separated from the N-isobutyloxycarbonyl by-
products 2h¤¤ and 2i¤¤ by silica gel chromatography. In the case
of using ethyl chloroformate for the activating agent, it was
difficult to isolate from the mixtures of the dipeptides 7ah, 7ai
and the N-ethoxycarbonyl derivatives 2h¤, 2i¤, respectively.
Finally, we examined application to synthesis of various di-
peptides 7ba-7dc under the reaction conditions, and the results
are shown in Table 5. Cbz-L-Ala-OH (6b), Cbz-L-Val-OH (6c)
and Cbz-L-Met-OH (6d) were selected as a N-protected α-
amino acid. The reaction of Cbz-L-Ala-OH (6b) with L-Ser-OH
(2a) was carried out to afford the corresponding dipeptide 7ba
in 79% yield (Entry 1). The reaction of 6b with L-Cys-OH (2b)
efficiently proceeded to give 7bb in 89% yield (Entry 2). The
dipeptide 7bc was synthesized from 6b and L-Tyr-OH (2c) in
71% yield (Entry 3), which was slightly lower than those of
7ba and 7bb. Cbz-L-Val-OH (6c) possessing a branched side
chain reacted with 2a, 2b, and 2c to provide the corresponding
dipeptides 7ca, 7cb, and 7cc in 81%, 75%, and 71% yields,
respectively (Entries 4-6). Cbz-L-Met-OH (6d) containing a
mercapto group as a side chain was converted by the reactions
of unprotected α-amino acids 2a, 2b, and 2c to the correspond-
ing dipeptides 7da, 7db, and 7dc in 77%, 78%, and 66%
yields, respectively (Entries 7-9). Then, we attempted to syn-
thesize the corresponding dipeptide from N-protected α-amino
O
Ph
O
Ph
O
Ph
N
H2N
H
NH3
O
O
5 H+
5
R2
slow
fast
R2
O
R2
O
O
O
Ph
N
Ph
N
H
H
OH
OH
3
3
Scheme 2. Possible pathway of the amidation via the mixed
carbonic carboxylic anhydride 5.
Table 3. Amidation of 3-phenylpropanoic acid (1) with un-
protected α-amino acids 2a-2e under the basic conditions
using NaHCO3
a)
O
O
R2
1) ClCO2Et, Et3N, THF, 0 oC, 30 min
O
R2
O
, NaHCO3, H2O, 0 oC, 30 min
Ph
OH
Ph
N
2)
H
OH
1
3
H2N
OH
2
Entry
Amide 3
Yieldb)/%
OH
O
O
1
2
3a
3b
93
Ph
N
H
OH
SH
O
O
96
Ph
N
H
OH
OH
25 (86)c)
O
O
O
3
3c
O
Ph
Ph
Ph
N
H
OH
CONH2
O
4
5
3d
3e
83
90
N
H
OH
COOH
O
N
H
OH
a) All reactions were carried out with 0.50 mmol of 1, 0.70
mmol of ethyl chloroformate, and 1.5 mmol of triethylamine in
10 mL of THF. After stirring for 30 min at 0 °C, 0.75 mmol of
unprotected α-amino acids 2 and 0.75 mmol of NaHCO3 in
10 mL of H2O were added at 0 °C to the reaction mixtures.
b) Isolated yields. c) NaOH was used instead of NaHCO3.
Table 3. The coupling reaction of 1 with L-Ser-OH (2a) pro-
ceeded smoothly to give the corresponding amide 3a in 93%
yield (Entry 1). L-Cys-OH (2b) was converted to the corre-
sponding amide 3b in 96% yield (Entry 2). Although the
amidation of 1 with L-Tyr-OH (2c) afforded the correspond-
ing amide 3c in 25% yield under the basic conditions using
NaHCO3 (Entry 3), 2c reacted efficiently with 1 to give 3c in
86% yield under the basic conditions using NaOH (parentheses
of Entry 3). In the case of using NaHCO3 as a base, 2c is hardly
dissolved in H2O as well as the neutral conditions. It is suggest-
Bull. Chem. Soc. Jpn. 2017, 90, 689–696 | doi:10.1246/bcsj.20170035
© 2017 The Chemical Society of Japan | 691

Table 4. Synthesis of dipeptides 7 with Cbz-L-Phe-OH (6a)
and unprotected α-amino acids 2a-2i under the basic
conditionsa)
Table 5. The coupling reaction of N-protected α-amino
acids 6b-6f and unprotected α-amino acids 2a-2c and 2e
under the basic conditionsa)
R2
Ph
O
R2
O
R1
O
1) ClCO2Et, Et3N, THF, 0 oC, 30 min
1) ClCO2Et, Et3N, THF, 0 oC, 30 min
Ph
O
R1
O
O
N
N
R2
O
, base, H2O, 0 oC, 30 min
R2
2)
O
2)
H
, base, H2O, 0 oC, 30 min
H
OH
Cbz-HN
OH
P-HN
Cbz-HN
OH
P-HN
OH
6a
7
7b-7f
6b-6f
H2N
OH
H2N
OH
2
2
Yieldb)/%
Entry Base
Dipeptide 7
Yieldb)/%
Entry Base
Dipeptide 7
OH
OH
Ph
O
O
O
1
2
NaHCO3
7aa
7ab
82
O
1
2
NaHCO3
NaHCO3
7ba
7bb
79
N
H
N
H
Cbz-HN
Ph
OH
SH
OH
SH
Cbz-HN
Cbz-HN
O
O
O
NaHCO3
86
73
O
N
H
89
71
N
H
OH
Cbz-HN
Ph
OH
OH
OH
OH
OH
O
O
O
O
3
NaOH
7ac
O
O
O
3
NaOH
7bc
O
O
N
H
N
H
Cbz-HN
Ph
OH
Cbz-HN
Cbz-HN
Cbz-HN
OH
OH
O
CONH2
O
4
5
NaHCO3
NaHCO3
7ad
7ae
7a¤e
7af
83
N
H
4
5
NaHCO3
NaHCO3
7ca
7cb
81
75
N
H
Cbz-HN
Ph
OH
OH
SH
COOH
O
87 (81)e)
85
N
H
O
Cbz-HN
Ph
OH
N
H
OH
COOH
O
6c) NaHCO3
N
H
Cbz-HN
Ph
OH
O
O
O
6
NaOH
7cc
71
COOH
O
O
O
O
O
N
H
7
8
NaHCO3
NaOH
74
Cbz-HN
OH
OH
N
H
Cbz-HN
OH
MeS
OH
OH
O
7
8
NaHCO3
NaHCO3
7da
7db
77
78
N
H
Cbz-HN
MeS
OH
SH
O
Ph
7ag
7ah
68
74
O
N
H
OH
Cbz-HN
N
H
OH
I
OH
Cbz-HN
9d) NaOH
Ph
O
MeS
N
H
O
O
9
10
11
NaOH
7dc
7ee
7fe
66
76
84
Cbz-HN
OH
O
N
H
H
N
Cbz-HN
BnO
OH
COOH
O
10d) NaOH
7ai
76
Ph
O
OH
NaHCO3
NaHCO3
N
H
O
N
H
Boc-HN
OH
Cbz-HN
OH
Cbz-HN
a) All reactions were carried out with 0.50 mmol of Cbz-L-Phe-
OH (6a), 0.70 mmol of ethyl chloroformate, and 1.5 mmol of
triethylamine in 10 mL of THF. After stirring for 30 min at
0 °C, 0.75 mmol of unprotected α-amino acids 2 and 0.75
mmol of base in 10 mL of H2O were added at 0 °C to the reac-
tion mixtures. b) Isolated yields. c) This reaction was carried
out with Cbz-D-Phe-OH (6a¤). d) Isobutyl chloroformate was
used instead of ethyl chloroformate. e) 5.0 mmol (1.5 g) of 6a
was used.
O
COOH
O
N
H
Boc-HN
OH
a) All reactions were carried out with 0.50 mmol of N-
protected α-amino acids 6b-6f, 0.70 mmol of ethyl chloro-
formate, and 1.5 mmol of triethylamine in 10 mL of THF. After
stirring for 30 min at 0 °C, 0.75 mmol of unprotected α-amino
acids 2 and 0.75 mmol of base in 10 mL of H2O were added at
0 °C to the reaction mixtures. b) Isolated yields.
acids containing hydrophilic side chains as the starting mate-
rials with L-Glu-OH (2e). The dipeptide 7ee was synthesized
from N-Boc-O-Bn-L-Ser-OH (6e) and 2e under basic condi-
tions in 76% yield (Entry 10). Nα-Boc-Nε-Cbz-L-Lys-OH (6f)
containing bulky side chain was effectively converted into the
corresponding dipeptide 7fe in 84% yield (Entry 11).
3. Conclusion
We have found that the dipeptides 7aa-7ai were conven-
iently synthesized in 68-87% yield from Cbz-L-Phe-OH (6a)
and unprotected α-amino acids 2a-2i containing other hydro-
philic moieties under the basic conditions. Additionally, we
692 | Bull. Chem. Soc. Jpn. 2017, 90, 689–696 | doi:10.1246/bcsj.20170035
© 2017 The Chemical Society of Japan

have also succeeded in the preparation of the dipeptides 7ba-
7fe in 66-89% yields without racemization by the reactions of
N-protected α-amino acids 6b-6f with unprotected α-amino
acids 2a-2c and 2e by the ecological green synthetic method.
N-(3-phenylpropanoyl)-L-Cys-OH (3b): 122 mg (96%),
28
colorless powder; mp: 132-133 °C; ½ꢀꢀD = ¹4.10 (c 1.01,
MeOH); 1H NMR (400 MHz, MeOD-d4): ¤ 2.58 (ddd, J = 1.2,
7.6, 7.6 Hz, 1H, CHACO), 2.58 (ddd, J = 1.2, 7.7, 7.7 Hz, 1H,
CHBCO), 2.79 (dd, J = 6.6, 14.0 Hz, 1H, CHASH), 2.86 (dd,
J = 4.6, 14.0 Hz, 1H, CHBSH), 2.93 (dd, J = 7.6, 7.7 Hz, 2H,
CH2C6H5), 4.58 (dd, J = 4.6, 6.6 Hz, 1H, CHCH2SH), 7.14-
7.19, 7.21-7.28 (m, m, 1H, 4H, C6H5); 13C NMR (100 MHz,
MeOD-d4): ¤ 26.8, 32.8, 38.6, 55.9, 127.3, 129.5, 129.5,
142.1, 173.1, 175.3; HRMS (ESI-TOF): Calcd for C12H16NO3S
(M+Na)+: 254.0854, found: 254.0856; IR (KBr, νmax/cm¹1):
3353 (OH), 2563 (SH), 1720 (CO2), 1589 (CON).
4. Experimental
General Information. All reagents were used without any
purification. The 1H NMR and 13C NMR spectra were measured
with a Bruker Ultrashield TM 400 Plus (400 MHz) spectrom-
eter. The chemical shifts are expressed in parts per million
downfield from tetramethylsilane (δ = 0.00) in MeOD-d4 or
dimethyl sulfoxide-d6 (δ = 2.50) as an internal standard.
13C NMR spectra were calibrated with tetramethylsilane (δ =
0.00) in MeOD-d4 or dimethyl sulfoxide-d6 (δ = 39.5). Chemi-
cal shifts (δ) are reported in ppm, and spin-spin coupling
constants (J) are given in hertz. Abbreviations to denote the
multiplicity of a particular signal are s (singlet), d (doublet),
t (triplet), q (quartet), m (multiplet), and br (broad). The high-
resolution mass spectra (HRMS) of the compounds with a high
molecular weight were recorded using a Waters LCT Premier
(ESI-TOF-MS) spectrometer. Reactions were monitored using
thin-layer chromatography with silica gel 60 F254. Purification
of the products was carried out by column chromatography
using silica gel (64-210 mesh). Melting points were determined
with a hot plate apparatus. Optical rotations were measured on
a digital polarimeter with a sodium lamp at room temperature.
Infrared (IR) spectra were recorded on HORIBA FT-IR Fourier
transform infrared spectrophotometer.
A Typical Procedure for the Amidation of 3-Phenyl-
propanoic Acid (1) Using Ethyl Chloroformate is as
Follows. To a colorless solution of 75 mg (0.50 mmol) of 3-
phenylpropanoic acid (1) in 10 mL of THF were added at 0 °C
67 ¯L (0.70 mmol, 1.4 equiv) of ethyl chloroformate and 209
¯L (1.5 mmol, 3.0 equiv) of triethylamine. After stirring for
30 min at 0 °C, a solution of 110 mg (0.75 mmol, 1.5 equiv) of
L-Glu-OH (2e) and 63 mg (0.75 mmol, 1.5 equiv) of NaHCO3
in 10 mL of H2O was added at 0 °C to the colorless suspension.
The mixture was stirred for 30 min at 0 °C and the resulting
colorless clear solution was concentrated in vacuo. The residue
was adjusted to pH 2 by addition of a 1.0 M aqueous solution
of HCl. The resulted suspension was diluted with 30 mL of
EtOAc. The aqueous layer was extracted with 20 mL of EtOAc.
The combined organic layer was washed with 10 mL of brine,
and dried over anhydrous MgSO4. The crude product was chro-
matographed on silica gel with EtOAc containing 1% AcOH to
afford 126 mg (90% yield) of N-(3-phenylpropanoyl)-L-Glu-
OH (3e).
N-(3-phenylpropanoyl)-L-Tyr-OH (3c): 135 mg (86%),
28
colorless powder; mp: 164-167 °C; ½ꢀꢀD = +16.8 (c 1.00,
MeOH); 1H NMR (400 MHz, MeOD-d4): ¤ 2.46 (ddd, J = 1.6,
8.1, 8.1 Hz, 1H, CHACO), 2.46 (ddd, J = 1.6, 8.2, 8.2 Hz, 1H,
CHBCO), 2.81 (dd, J = 8.1, 8.2 Hz, 2H, CH2C6H5), 2.82 (dd,
J = 8.8, 13.9 Hz, 1H, CHAC6H4), 3.05 (dd, J = 5.1, 13.9 Hz,
1H, CHBC6H4), 4.58 (dd, J = 5.1, 8.8 Hz, 1H, CHCH2C6H4),
6.67, 6.95 (d, d, J = 8.6, 8.6 Hz, 2H, 2H, C6H4), 7.13-7.16,
7.21-7.25 (m, m, 3H, 2H, C6H5); 13C NMR (100 MHz, MeOD-
d4): ¤ 32.8, 37.7, 38.6, 55.3, 116.2, 127.2, 129.1, 129.4, 129.5,
131.3, 142.2, 157.3, 174.9, 175.1; HRMS (ESI-TOF): Calcd for
C18H19NO4Na (M+Na)+: 336.1206, found: 336.1187; IR (KBr,
ν
max/cm¹1): 3309 (ArOH), 3197 (OH), 1745 (CO2), 1592 (CON).
N-(3-phenylpropanoyl)-L-Gln-OH (3d):12a 116 mg (83%),
colorless powder; 1H NMR (400 MHz, MeOD-d4): ¤ 1.83-1.93
(m, 1H, CHACH), 2.07-2.24 (m, 3H, CHBCH, CH2CH2CH),
2.55 (ddd, J = 1.5, 7.5, 7.5 Hz, 1H, CHACO), 2.55 (ddd, J =
1.5, 8.1, 8.1 Hz, 1H, CHBCO), 2.92 (dd, J = 7.5, 8.1 Hz, 2H,
CH2C6H5), 4.37 (dd, J = 4.5, 9.4 Hz, 1H, CHCO), 7.14-7.18,
7.21-7.28 (m, m, 1H, 4H, C6H5).
N-(3-phenylpropanoyl)-L-Glu-OH (3e):12a 126 mg (90%),
colorless powder; 1H NMR (400 MHz, MeOD-d4): ¤ 1.80-1.90
(m, 1H, CHACH), 2.07-2.15 (m, 1H, CHBCH), 2.22-2.26
(m, 2H, CH2CH2CH), 2.54 (ddd, J = 1.4, 7.4, 7.4 Hz, 1H,
CHACO), 2.54 (ddd, J = 1.4, 8.0, 8.0 Hz, 1H, CHBCO), 2.91
(dd, J = 7.4, 8.0 Hz, 2H, CH2C6H5), 4.40 (dd, J = 4.8, 9.8 Hz,
1H, CHCO), 7.15-7.18, 7.20-7.27 (m, m, 1H, 4H, C6H5).
A Typical Procedure of the Amidation of Cbz-L-Phenyl-
alanine (6a) Using Ethyl Chloroformate is as Follows. To a
colorless solution of 150 mg (0.50 mmol) of Cbz-L-phenyl-
alanine (6a) in 10 mL of THF were added at 0 °C 67 ¯L (0.70
mmol, 1.4 equiv) of ethyl chloroformate and 209 ¯L (1.5 mmol,
3.0 equiv) of triethylamine. After stirring for 30 min at 0 °C, a
solution of 110 mg (0.75 mmol, 1.5 equiv) of L-Glu-OH (2e)
and 63 mg (0.75 mmol, 1.5 equiv) of NaHCO3 in 10 mL of H2O
was added at 0 °C to the colorless suspension. The mixture was
stirred for 30 min at 0 °C and the resulting colorless clear solu-
tion was concentrated in vacuo. The residue was adjusted to
pH 2 by addition of a 1.0 M aqueous solution of HCl. The
colorless suspension was diluted with 10 mL of brine, extracted
with 25 ml © 3 of a 4:1 mixture of EtOAc and MeOH, and
dried over anhydrous MgSO4. The crude product was chroma-
tographed on silica gel with a 9:1 mixture of chloroform and
MeOH containing 1% AcOH to afford 187 mg (87% yield) of
Cbz-L-Phe-L-Glu-OH (7ae).
N-(3-phenylpropanoyl)-L-Ser-OH (3a): 111 mg (93%),
28
colorless powder; mp: 119-123 °C; ½ꢀꢀD = +6.70 (c 1.00,
MeOH); 1H NMR (400 MHz, MeOD-d4): ¤ 2.72 (ddd, J = 1.5,
7.6, 7.6 Hz, 1H, CHACO), 2.72 (ddd, J = 1.5, 8.3, 8.3 Hz, 1H,
CHBCO), 2.92 (dd, J = 7.6, 8.3 Hz, 2H, CH2C6H5), 3.77 (dd,
J = 4.3, 11.2 Hz, 1H, CHAOH), 3.86 (dd, J = 4.8, 11.2 Hz, 1H,
CHBOH), 4.48 (dd, J = 4.3, 4.8 Hz, 1H, CHCH2OH), 7.14-
7.18, 7.21-7.28 (m, m, 1H, 4H, C6H5); 13C NMR (100 MHz,
MeOD-d4): ¤ 32.8, 38.8, 56.1, 63.0, 127.2, 129.4, 129.5, 142.3,
173.5, 175.4; HRMS (ESI-TOF): Calcd for C12H15NO4Na
(M+Na)+: 260.0893, found: 260.0894; IR (KBr, νmax/cm¹1):
3305 (OH), 1716 (CO2), 1648 (CON).
Cbz-L-Phe-L-Ser-OH (7aa):
powder; mp; 156-159 °C; ½ꢀꢀD = +4.82 (c 1.00, MeOH);
158 mg (82%), colorless
30
Bull. Chem. Soc. Jpn. 2017, 90, 689–696 | doi:10.1246/bcsj.20170035
© 2017 The Chemical Society of Japan | 693

1H NMR (400 MHz, MeOD-d4): ¤ 2.85 (dd, J = 9.8, 13.8 Hz,
1H, CHAC6H5), 3.19 (dd, J = 4.7, 13.8 Hz, 1H, CHBC6H5), 3.83
(dd, J = 3.8, 11.2 Hz, 1H, CHAOH), 3.92 (dd, J = 4.5, 11.2 Hz,
1H, CHBOH), 4.46 (dd, J = 4.7, 9.8 Hz, 1H, CHCH2C6H5), 4.48
(dd, J = 3.8, 4.5 Hz, 1H, CHCH2OH), 4.98 (d, J = 12.6 Hz, 1H,
OCHAC6H5), 5.03 (d, J = 12.6 Hz, 1H, OCHBC6H5), 7.19-7.33
(m, 10H, C6H5 © 2); 13C NMR (100 MHz, MeOD-d4): ¤ 39.2,
56.2, 57.8, 63.0, 67.6, 127.8, 128.7, 129.0, 129.5, 129.5, 130.4,
138.2, 138.6, 158.4, 173.1, 174.2; HRMS (ESI-TOF): Calcd for
C20H23N2O6 (M+H)+: 387.1551, found: 387.1539; IR (KBr,
1H, CHBC6H5), 4.38 (dd, J = 6.6, 8.8 Hz, 1H, CHCH2C6H5),
4.40-4.44 (m, 1H, CHCH2CH2), 5.00 (d, J = 12.4 Hz, 1H,
OCHAC6H5), 5.05 (d, J = 12.4 Hz, 1H, OCHBC6H5), 7.19-7.33
(m, 10H, C6H5 © 2); 13C NMR (100 MHz, MeOD-d4): ¤ 27.8,
31.0, 39.5, 53.1, 58.0, 67.7, 127.9, 128.8, 129.0, 129.5, 129.6,
130.4, 138.2, 138.4, 158.2, 174.0, 174.6, 176.3; HRMS (ESI-
TOF): Calcd for C22H24N2O7Na (M+Na)+: 451.1476, found:
451.1488; IR (KBr, νmax/cm¹1): 3299 (OH), 1716 (CO2), 1670
(CON).
Cbz-L-Phe-L-Asp-OH (7af):
163 mg (74%), colorless
28
ν
max/cm¹1): 3298 (OH), 1732 (CO2), 1647 (CON).
Cbz-L-Phe-L-Cys-OH (7ab): 173 mg (86%), colorless
powder; mp; 178-179 °C; ½ꢀꢀD = ¹11.7 (c 1.01, MeOH);
1H NMR (400 MHz, MeOD-d4): ¤ 2.84 (dd, J = 9.7, 13.9 Hz,
1H, CHAC6H5), 2.84 (d, J = 5.6 Hz, 2H, CH2CO), 3.18 (dd,
J = 4.8, 13.9 Hz, 1H, CHBC6H5), 4.42 (dd, J = 4.8, 9.7 Hz,
1H, CHCH2C6H5), 4.73 (t, J = 5.6 Hz, 1H, CHCH2CO), 4.97
(d, J = 12.7 Hz, 1H, OCHAC6H5), 5.02 (d, J = 12.7 Hz, 1H,
OCHBC6H5), 7.18-7.33 (m, 10H, C6H5 © 2); 13C NMR (100
MHz, MeOD-d4): ¤ 36.8, 39.1, 50.2, 57.8, 67.6, 127.7, 128.7,
128.9, 129.5, 130.4, 138.2, 138.6, 158.3, 173.7, 173.9, 174.0;
HRMS (ESI-TOF): Calcd for C21H23N2O7 (M+H)+: 415.1500,
found: 415.1486; IR (KBr, νmax/cm¹1): 3305 (OH), 1716
(CO2), 1695 (CON), 1653 (CON).
29
powder; mp; 121-122 °C; ½ꢀꢀD = ¹9.32 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4): ¤ 2.87 (dd, J = 9.5, 13.9 Hz,
1H, CHAC6H5), 2.88 (dd, J = 4.6, 14.0 Hz, 1H, CHASH), 2.97
(dd, J = 4.6, 14.0 Hz, 1H, CHBSH), 3.16 (dd, J = 5.2, 13.9 Hz,
1H, CHBC6H5), 4.44 (dd, J = 5.2, 9.5 Hz, 1H, CHCH2C6H5),
4.60 (dd, J = 4.6, 4.6 Hz, 1H, CHCH2SH), 5.01 (s, 2H,
OCH2C6H5), 7.17-7.33 (m, 10H, C6H5 © 2); 13C NMR (100
MHz, MeOD-d4): ¤ 26.8, 39.0, 56.0, 57.8, 67.6, 127.8, 128.7,
129.0, 129.5, 130.4, 138.2, 138.6, 158.3, 172.8, 174.2; HRMS
(ESI-TOF): Calcd for C20H23N2O5S (M+H)+: 403.1322, found:
403.1296; IR (KBr, νmax/cm¹1): 3309 (OH), 2568 (SH), 1716
(CO2), 1656 (CON).
Cbz-L-Phe-L-Tyr(3-OH)-OH (7ag): 164 mg (68%), color-
28
less powder; mp; 132-134 °C; ½ꢀꢀD = ¹7.26 (c 1.00, MeOH);
Cbz-L-Phe-L-Tyr-OH (7ac):
169 mg (73%), colorless
1H NMR (400 MHz, MeOD-d4): ¤ 2.77 (dd, J = 9.8, 14.0 Hz,
1H, CHAC6H3), 2.87 (dd, J = 7.7, 14.0 Hz, 1H, CHAC6H5),
3.03 (dd, J = 5.5, 14.0 Hz, 1H, CHBC6H5), 3.09 (dd, J =
4.9, 14.0 Hz, 1H, CHBC6H3), 4.37 (dd, J = 4.9, 9.8 Hz, 1H,
CHCH2C6H3), 4.58 (dd, J = 5.5, 7.7 Hz, 1H, CHCH2C6H5),
4.96 (d, J = 12.7 Hz, 1H, OCHAC6H5), 5.03 (d, J = 12.7 Hz,
1H, OCHBC6H5), 6.53, 6.65-6.67 (d, m, J = 8.0 Hz, 1H, 2H,
C6H3), 7.16-7.32 (m, 10H, C6H5 © 2); 13C NMR (100 MHz,
MeOD-d4): ¤ 37.9, 39.0, 55.2, 57.8, 67.7, 116.4, 117.5, 121.9,
127.7, 128.7, 128.9, 129.4, 129.5, 130.4, 138.2, 138.6, 145.3,
146.2, 158.3, 173.9, 174.5; HRMS (ESI-TOF): Calcd for
C26H27N2O7 (M+H)+: 479.1813, found: 479.1796; IR (KBr,
28
powder; mp; 189-190 °C; ½ꢀꢀD = ¹4.90 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4): ¤ 2.77 (dd, J = 9.9, 14.0 Hz,
1H, CHAC6H4), 2.91 (dd, J = 8.0, 14.0 Hz, 1H, CHAC6H5),
3.09 (dd, J = 5.0, 14.0 Hz, 1H, CHBC6H4), 3.09 (dd, J =
5.3, 14.0 Hz, 1H, CHBC6H5), 4.36 (dd, J = 5.0, 9.9 Hz, 1H,
CHCH2C6H4), 4.58 (dd, J = 5.3, 8.0 Hz, 1H, CHCH2C6H5),
4.97 (d, J = 12.6 Hz, 1H, OCHAC6H5), 5.03 (d, J = 12.6 Hz,
1H, OCHBC6H5), 6.68, 7.02 (d, d, J = 8.4, 8.4 Hz, 2H, 2H,
C6H4), 7.16-7.32 (m, 10H, C6H5 © 2); 13C NMR (100 MHz,
MeOD-d4): ¤ 37.7, 39.0, 55.3, 57.8, 67.6, 116.3, 127.7, 128.7,
128.8, 129.0, 129.4, 129.5, 130.4, 131.5, 138.2, 138.6, 157.4,
173.9, 174.4; HRMS (ESI-TOF): Calcd for C26H27N2O6
(M+H)+: 463.1864, found: 463.1862; IR (KBr, νmax/cm¹1):
3433 (OH), 3334 (ArOH), 1734 (CO2), 1684 (CON), 1653 (CON).
Cbz-L-Phe-L-Gln-OH (7ad):12a 177 mg (83%), colorless
powder; 1H NMR (400 MHz, MeOD-d4): ¤ 1.91-1.98 (m,
1H, CHACH2CO), 2.16-2.35 (m, 3H, CHBCH2CO, CH2CO),
2.85 (dd, J = 9.7, 14.0 Hz, 1H, CHAC6H5), 3.16 (dd, J = 4.9,
14.0 Hz, 1H, CHBC6H5), 4.38-4.43 (m, 2H, CH © 2), 4.99
(d, J = 12.7 Hz, 1H, OCHAC6H5), 5.03 (d, J = 12.7 Hz, 1H,
OCHBC6H5), 7.17-7.33 (m, 10H, C6H5 © 2).
ν
max/cm¹1): 3487 (ArOH), 3325 (ArOH), 3033 (OH), 1724
(CO2), 1695 (CON), 1657 (CON).
Cbz-L-Phe-L-Tyr(3-I)-OH (7ah): 220 mg (74%), colorless
28
powder; mp; 182-185 °C; ½ꢀꢀD = ¹1.08 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4): ¤ 2.79 (dd, J = 9.7, 13.9 Hz,
1H, CHAC6H3), 2.88 (dd, J = 7.9, 13.9 Hz, 1H, CHAC6H5),
3.08 (dd, J = 5.1, 13.9 Hz, 1H, CHBC6H5), 3.08 (dd, J =
5.1, 13.9 Hz, 1H, CHBC6H3), 4.36 (dd, J = 5.1, 9.7 Hz, 1H,
CHCH2C6H3), 4.58 (dd, J = 5.1, 7.9 Hz, 1H, CHCH2C6H5),
4.97 (d, J = 12.6 Hz, 1H, OCHAC6H5), 5.03 (d, J = 12.6 Hz,
1H, OCHBC6H5), 6.74, 7.03, 7.54 (d, d, s, J = 8.0 Hz, 1H, 1H,
1H, C6H3), 7.17-7.32 (m, 10H, C6H5 © 2); 13C NMR (100
MHz, MeOD-d4): ¤ 37.0, 39.2, 55.1, 57.9, 67.7, 84.6, 115.7,
127.7, 128.7, 128.9, 129.5, 129.5, 130.4, 131.0, 131.6, 138.2,
138.6, 141.0, 157.0, 174.0, 174.2; HRMS (ESI-TOF): Calcd
for C26H26IN2O6 (M+H)+: 589.0830, found: 589.0835; IR
(KBr, νmax/cm¹1): 3359 (ArOH), 3280 (OH), 1735 (CO2), 1706
(CON), 1644 (CON), 1051 (ArI).
Cbz-L-Phe-L-Glu-OH (7ae):12a 187 mg (87%), colorless
1
powder; H NMR (400 MHz, MeOD-d4): ¤ 1.89-1.99 (m, 1H,
CHACH2CO), 2.15-2.23 (m, 1H, CHBCH2CO), 2.39 (dd, J =
7.6, 7.8 Hz, 2H, CH2CO), 2.84 (dd, J = 9.6, 14.0 Hz, 1H,
CHAC6H5), 3.15 (dd, J = 5.0, 14.0 Hz, 1H, CHBC6H5), 4.40-
4.47 (m, 2H, CH © 2), 4.99 (d, J = 13.0 Hz, 1H, OCHAC6H5),
5.03 (d, J = 13.0 Hz, 1H, OCHBC6H5), 7.18-7.33 (m, 10H,
C6H5 © 2).
Cbz-D-Phe-L-Glu-OH (7a¤e):
182 mg (85%), colorless
Cbz-L-Phe-L-Trp(5-OH)-OH (7ai): 192 mg (76%), color-
28
28
powder; mp; 169-172 °C; ½ꢀꢀD = +0.82 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4): ¤ 1.79-1.88 (m, 1H, CHACH2-
CO), 2.04-2.18 (m, 3H, CHBCH2CO, CH2CO), 2.88 (dd,
J = 8.8, 13.7 Hz, 1H, CHAC6H5), 3.09 (dd, J = 6.6, 13.7 Hz,
less powder; mp; 107-110 °C; ½ꢀꢀD = ¹14.2 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4): ¤ 2.72 (dd, J = 10.0, 14.0 Hz,
1H, CHA-indole), 3.08 (dd, J = 4.7, 14.0 Hz, 1H, CHB-indole),
3.14 (dd, J = 7.2, 14.1 Hz, 1H, CHAC6H5), 3.28 (dd, J =
694 | Bull. Chem. Soc. Jpn. 2017, 90, 689–696 | doi:10.1246/bcsj.20170035
© 2017 The Chemical Society of Japan

5.3, 14.1 Hz, 1H, CHBC6H5), 4.37 (dd, J = 4.7, 10.0 Hz, 1H,
CHCH2-indole), 4.69 (dd, J = 5.3, 7.2 Hz, 1H, CHCH2C6H5),
4.94 (d, J = 12.8 Hz, 1H, OCHAC6H5), 5.01 (d, J = 12.8 Hz,
1H, OCHBC6H5), 6.66, 6.95, 7.03, 7.13-7.29 (d, s, s, m, J =
8.6 Hz, 1H, 1H, 1H, 11H, indole, C6H5 © 2); 13C NMR (100
MHz, MeOD-d4): ¤ 28.6, 39.0, 54.7, 57.8, 67.6, 103.7, 110.0,
112.5, 112.8, 125.4, 127.7, 128.7, 128.9, 129.4, 129.5, 129.7,
130.3, 133.0, 138.2, 138.6, 151.3, 158.3, 174.0, 174.9; HRMS
(ESI-TOF): Calcd for C28H28N3O6 (M+H)+: 502.1973, found:
502.1957; IR (KBr, νmax/cm¹1): 3566 (NH), 3396 (ArOH),
3324 (OH), 1704 (CO2), 1654 (CON).
(100 MHz, MeOD-d4): ¤ 18.4, 19.8, 32.2, 56.1, 62.0, 63.1,
67.8, 128.9, 129.1, 129.5, 138.3, 158.7, 173.2, 174.3; HRMS
(ESI-TOF): Calcd for C16H22N2O6Na (M+Na)+: 361.1370,
found: 361.1388; IR (KBr, νmax/cm¹1): 3546 (OH), 3307 (OH),
1733 (CO2), 1645 (CON).
Cbz-L-Val-L-Cys-OH (7cb):
132 mg (75%), colorless
28
powder; mp; 152-154 °C; ½ꢀꢀD = ¹11.2 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4): ¤ 0.96 (d, J = 7.0 Hz, 3H,
CH3), 0.98 (d, J = 7.0 Hz, 3H, CH3), 2.03-2.12 (m, 1H,
CH(CH3)2), 2.88 (dd, J = 6.4, 13.9 Hz, 1H, CHASH), 2.96
(dd, J = 4.6, 13.9 Hz, 1H, CHBSH), 3.99 (d, J = 7.0 Hz, 1H,
CHCH(CH3)2), 4.62 (dd, J = 4.6, 6.4 Hz, 1H, CHCH2SH), 5.09
(s, 2H, OCH2C6H5), 7.26-7.37 (m, 5H, C6H5); 13C NMR (100
MHz, MeOD-d4): ¤ 18.6, 19.8, 26.7, 31.9, 55.9, 62.2, 67.8,
128.9, 129.0, 129.5, 138.3, 158.7, 172.8, 174.4; HRMS (ESI-
TOF): Calcd for C16H22N2O5SNa (M+Na)+: 377.1142, found:
372.1144; IR (KBr, νmax/cm¹1): 3356 (OH), 2575 (SH), 1736
(CO2), 1643 (CON).
Cbz-L-Ala-L-Ser-OH (7ba):
122 mg (79%), colorless
28
powder; mp; >300 °C; ½ꢀꢀD = +33.9 (c 1.00, DMSO);
1H NMR (400 MHz, DMSO-d6): ¤ 1.22 (d, J = 7.3 Hz, 3H,
CH3), 3.40 (dd, J = 6.2, 9.9 Hz, 1H, CHAOH), 3.60 (dd, J =
5.3, 9.9 Hz, 1H, CHBOH), 3.79 (ddd, J = 5.3, 6.2, 6.2 Hz,
1H, CHCH2OH), 4.04 (dd, J = 7.3, 7.6 Hz, 1H, CHCH3), 5.01
(d, J = 12.6 Hz, 1H, OCHAC6H5), 5.06 (d, J = 12.6 Hz, 1H,
OCHBC6H5), 5.34 (brs, 1H, OH), 7.31-7.38 (m, 5H, C6H5),
7.49 (d, J = 6.2 Hz, 1H, NHCHCH2), 7.60 (d, J = 7.6 Hz, 1H,
NHCHCH3); 13C NMR (100 MHz, DMSO-d6): ¤ 18.3, 50.4,
55.2, 62.5, 65.4, 127.7, 127.8, 128.4, 137.0, 155.7, 171.7,
173.9; HRMS (ESI-TOF): Calcd for C14H18N2O6Na (M+Na)+:
333.1057, found: 333.1073; IR (KBr, νmax/cm¹1): 3354 (OH),
3320 (OH), 1693 (CO2), 1666 (CON).
Cbz-L-Val-L-Tyr-OH (7cc):
147 mg (71%), colorless
27
powder; mp; 156-157 °C; ½ꢀꢀD = ¹4.70 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4): ¤ 0.88 (d, J = 7.1 Hz, 3H,
CH3), 0.89 (d, J = 7.1 Hz, 3H, CH3), 1.96-2.01 (m, 1H,
CH(CH3)2), 2.89 (dd, J = 8.2, 13.9 Hz, 1H, CHAC6H4), 3.08
(dd, J = 5.3, 13.9 Hz, 1H, CHBC6H4), 3.91 (d, J = 7.1 Hz, 1H,
CHCH(CH3)2), 4.60 (dd, J = 5.3, 8.2 Hz, 1H, CHCH2C6H4),
5.06 (d, J = 12.5 Hz, 1H, OCHAC6H5), 5.11 (d, J = 12.5 Hz,
1H, OCHBC6H5), 6.67, 7.03 (d, d, J = 8.4, 8.4 Hz, 2H, 2H,
C6H4), 7.26-7.37 (m, 5H, C6H5); 13C NMR (100 MHz, MeOD-
d4): ¤ 18.6, 19.7, 32.0, 37.8, 55.3, 62.1, 67.8, 116.2, 128.9,
129.0, 129.1, 129.6, 131.4, 138.3, 157.4, 158.6, 174.0, 174.6;
HRMS (ESI-TOF): Calcd for C22H26N2O6Na (M+Na)+:
437.1683, found: 437.1685; IR (KBr, νmax/cm¹1): 3301
(ArOH), 3307 (OH), 1716 (CO2), 1695 (CON), 1654 (CON).
Cbz-L-Ala-L-Cys-OH (7bb):
145 mg (89%), colorless
27
powder; mp; 164-166 °C; ½ꢀꢀD = ¹11.9 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4): ¤ 1.36 (d, J = 7.2 Hz, 3H,
CH3), 2.90 (dd, J = 5.8, 14.0 Hz, 1H, CHASH), 2.98 (dd, J =
4.6, 14.0 Hz, 1H, CHBSH), 4.21 (q, J = 7.2 Hz, 1H, CHCH3),
4.61 (dd, J = 4.6, 5.8 Hz, 1H, CHCH2SH), 5.09 (s, 2H,
OCH2C6H5), 7.26-7.37 (m, 5H, C6H5); 13C NMR (100 MHz,
MeOD-d4): ¤ 18.2, 26.8, 52.0, 55.9, 67.7, 128.9, 129.1, 129.5,
138.2, 158.3, 173.0, 175.6; HRMS (ESI-TOF): Calcd for
C14H18N2O5SNa (M+Na)+: 349.0829, found: 349.0847; IR
(KBr, νmax/cm¹1): 3346 (OH), 2565 (SH), 1733 (CO2), 1637
(CON).
Cbz-L-Met-L-Ser-OH (7da):
142 mg (77%), colorless
powder; mp; 158-161 °C; ½ꢀꢀD = +8.16 (c 1.00, DMSO);
1H NMR (400 MHz, MeOD-d4):
1.87-1.96 (m, 1H,
28
¤
CHACH2S), 2.04-2.13 (m, 1H, CHBCH2S), 2.08 (s, 3H, CH3),
2.51-2.63 (m, 2H, CH2S), 3.83 (dd, J = 3.9, 11.3 Hz, 1H,
CHAOH), 3.93 (dd, J = 4.3, 11.3 Hz, 1H, CHBOH), 4.32 (dd,
J = 5.3, 8.6 Hz, 1H, CHCH2CH2), 4.48 (dd, J = 3.9, 4.3 Hz,
1H, CHCH2OH), 5.10 (s, 2H, OCH2C6H5), 7.26-7.38, (m, 5H,
C6H5); 13C NMR (100 MHz, MeOD-d4): ¤ 15.2, 31.1, 33.0,
55.5, 56.2, 62.9, 67.8, 128.9, 129.1, 129.5, 138.2, 158.5, 173.2,
174.4; HRMS (ESI-TOF): Calcd for C16H23N2O6S (M+H)+:
371.1271, found: 371.1262; IR (KBr, νmax/cm¹1): 3289 (OH),
1743 (CO2), 1722 (CON), 1680 (CON).
Cbz-L-Ala-L-Tyr-OH (7bc):
137 mg (71%), colorless
28
powder; mp; 148-152 °C; ½ꢀꢀD = +10.6 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4): ¤ 1.28 (d, J = 7.1 Hz, 3H,
CH3), 2.93 (dd, J = 7.5, 14.0 Hz, 1H, CHAC6H4), 3.07 (dd, J =
5.4, 14.0 Hz, 1H, CHBC6H4), 4.14 (q, J = 7.1 Hz, 1H, CHCH3),
4.57 (dd, J = 5.4, 7.5 Hz, 1H, CHCH2C6H4), 5.05 (d, J = 12.5
Hz, 1H, OCHAC6H5), 5.09 (d, J = 12.5 Hz, 1H, OCHBC6H5),
6.68, 7.02 (d, d, J = 8.3, 8.3 Hz, 2H, 2H, C6H4), 7.28-7.35
(m, 5H, C6H5); 13C NMR (100 MHz, MeOD-d4): ¤ 18.2, 37.6,
51.9, 55.2, 67.8, 116.2, 128.8, 128.9, 129.1, 129.5, 131.5,
138.2, 157.4, 158.2, 174.6, 175.3; HRMS (ESI-TOF): Calcd
for C20H22N2O6Na (M+Na)+: 409.1370, found: 409.1386; IR
(KBr, νmax/cm¹1): 3401 (ArOH), 3300 (OH), 1733 (CO2), 1687
(CON), 1653 (CON).
Cbz-L-Met-L-Cys-OH (7db):
151 mg (78%), colorless
powder; mp; 142-144 °C; ½ꢀꢀD = ¹7.03 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4):
1.88-1.97 (m, 1H,
28
¤
CHACH2S), 2.03-2.12 (m, 1H, CHBCH2S), 2.07 (s, 3H,
CH3), 2.50-2.63 (m, 2H, CH2CH2S), 2.90 (dd, J = 6.0, 13.8
Hz, 1H, CHASH), 2.98 (dd, J = 4.5, 13.8 Hz, 1H, CHBSH),
4.30 (dd, J = 5.5, 8.5 Hz, 1H, CHCH2CH2), 4.62 (dd, J =
4.5, 6.0 Hz, 1H, CHCH2SH), 5.10 (s, 2H, OCH2C6H5), 7.27-
7.37 (m, 5H, C6H5); 13C NMR (100 MHz, MeOD-d4): ¤ 15.3,
26.7, 31.1, 32.8, 55.5, 55.9, 62.9, 67.8, 128.9, 129.1, 129.5,
138.2, 158.5, 172.8, 174.5; HRMS (ESI-TOF): Calcd for
C16H23N2O5S (M+H)+: 387.1043, found: 387.1062; IR (KBr,
Cbz-L-Val-L-Ser-OH (7ca):
138 mg (81%), colorless
28
powder; mp; 172-175 °C; ½ꢀꢀD = ¹4.24 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4): ¤ 0.94 (d, J = 6.8 Hz, 3H,
CH3), 0.99 (d, J = 6.8 Hz, 3H, CH3), 2.05-2.14 (m, 1H,
CH(CH3)2), 3.82 (dd, J = 4.2, 11.3 Hz, 1H, CHAOH), 3.91
(dd, J = 4.5, 11.3 Hz, 1H, CHBOH), 4.03 (d, J = 6.8 Hz, 1H,
CHCH(CH3)2), 4.49 (dd, J = 4.2, 4.5 Hz, 1H, CHCH2OH),
5.10 (s, 2H, OCH2C6H5), 7.26-7.38 (m, 5H, C6H5); 13C NMR
ν
max/cm¹1): 3313 (OH), 2584 (SH), 1736 (CO2), 1635 (CON).
Bull. Chem. Soc. Jpn. 2017, 90, 689–696 | doi:10.1246/bcsj.20170035
© 2017 The Chemical Society of Japan | 695

Cbz-L-Met-L-Tyr-OH (7dc):
148 mg (66%), colorless
powder; mp; 133-135 °C; ½ꢀꢀD = +0.26 (c 1.00, MeOH);
1H NMR (400 MHz, MeOD-d4):
1.78-1.87 (m, 1H,
of EtOAc and MeOH. The combined organic layer was dried
over anhydrous MgSO4. The crude product was recrystallized
from 50 mL of a 1:4 mixture of toluene and hexane to afford a
colorless solid, followed by recrystallization from 20 mL of a
4:1 mixture of EtOAc and hexane to afford 1.74 g (81% yield)
of Cbz-L-Phe-L-Glu-OH (7ae).
28
¤
CHACH2S), 1.93-2.04 (m, 1H, CHBCH2S), 2.04 (s, 3H, CH3),
2.41-2.54 (m, 2H, CH2S), 2.92 (dd, J = 8.0, 14.0 Hz, 1H,
CHAC6H4), 3.09 (dd, J = 5.1, 14.0 Hz, 1H, CHBC6H4), 4.23 (dd,
J = 5.7, 8.7 Hz, 1H, CHCH2CH2), 4.59 (dd, J = 5.1, 8.0 Hz,
1H, CHCH2C6H4), 5.06 (d, J = 12.4 Hz, 1H, OCHAC6H5), 5.10
(d, J = 12.4 Hz, 1H, OCHBC6H5), 6.68, 7.03 (d, d, J = 8.4,
8.4 Hz, 2H, 2H, C6H4), 7.28-7.35 (m, 5H, C6H5); 13C NMR
(100 MHz, MeOD-d4): ¤ 15.2, 31.0, 32.8, 37.5, 55.2, 55.5, 67.8,
116.3, 128.8, 128.9, 129.1, 129.5, 131.4, 138.2, 157.4, 158.4,
174.1, 174.5; HRMS (ESI-TOF): Calcd for C22H27N2O6S
(M+H)+: 447.1584, found: 447.1569; IR (KBr, νmax/cm¹1):
3302 (OH), 1716 (CO2), 1691 (CON), 1649 (CON).
This work was supported in part by the Scientific Research
Project by CIS (Chiba Institute of Science), Japan.
Supporting Information
1H NMR and 13C NMR spectra for all amides 3a-3e and
dipeptides 7aa-7fe are available on http://dx.doi.org/10.1246/
bcsj.20170035.
References
N-Boc-O-Bn-L-Ser-L-Glu-OH (7ee): 161 mg (76%), color-
19
1
less sticky oil; ½ꢀꢀD = ¹1.46 (c 1.00, MeOH); H NMR (400
MHz, MeOD-d4): ¤ 1.45 (s, 9H, CH3 © 3), 1.89-1.98 (m, 1H,
CHACH2CO), 2.15-2.25 (m, 1H, CHBCH2CO), 2.36-2.42 (m,
2H, CH2CO), 3.67 (dd, J = 4.5, 9.8 Hz, 1H, CHAOCH2C6H5),
3.74 (dd, J = 5.2, 9.8 Hz, 1H, CHBOCH2C6H5), 4.30 (dd, J =
4.5, 5.2 Hz, 1H, CHCH2O), 4.47-4.50 (m, 1H, CHCH2CH2),
4.52 (d, J = 11.5 Hz, 1H, OCHAC6H5), 4.55 (d, J = 11.5
Hz, 1H, OCHBC6H5), 7.26-7.33 (m, 5H, C6H5); 13C NMR
(100 MHz, MeOD-d4): ¤ 28.2, 28.7, 31.0, 53.0, 56.2, 71.1,
74.3, 81.0, 128.8, 129.0, 129.5, 139.3, 157.8, 172.9, 174.4,
176.4; HRMS (ESI-TOF): Calcd for C20H28N2O8Na (M+Na)+:
447.1743, found: 447.1756; IR (KBr, νmax/cm¹1): 3329 (OH),
1716 (CO2), 1652 (CON).
1
G. M. Cooper, R. E. Hausman, The Cell: A Molecular
Approach, ASM Press, Washington, D.C., 2004.
For selected reviews on peptide syntheses: a) M. A.
2
Blaskovich, Handbook on Syntheses of Amino Acids: General
Routes for the Syntheses of Amino Acids, Oxford University
Press, New York, 2010. b) C. A. G. N. Montalbetti, V. Falque,
Tetrahedron 2005, 61, 10827. c) T. Wieland, M. Bodanszky, The
World of Peptides: A Brief History of Peptide Chemistry, Springer-
Verlag, New York, 1991, 77. doi:10.1007/978-3-642-75850-8. For
selected reports for peptide syntheses using unprotected α-amino
acids: d) P. Gagnon, X. Huang, E. Therrien, J. W. Keillor,
Tetrahedron Lett. 2002, 43, 7717, and the references cited therein.
e) M. V. Anuradha, B. Ravindranath, Tetrahedron 1997, 53, 1123.
f) G. W. Anderson, J. E. Zimmerman, F. M. Callahan, J. Am.
Chem. Soc. 1964, 86, 1839.
Nα-Boc-Nε-Cbz-L-Lys-L-Glu-OH (7fe): 215 mg (84%),
18
1
colorless sticky oil; ½ꢀꢀD = ¹11.4 (c 1.00, MeOH); H NMR
(400 MHz, MeOD-d4): ¤ 1.39-1.55 (m, 13H, CH3 © 3, CH2-
(CH2)2N, CH2CH2N), 1.56-1.63 (m, 1H, CHA(CH2)3N), 1.70-
1.81 (m, 1H, CHB(CH2)3N), 1.91-1.98 (m, 1H, CHACH2CO),
2.14-2.23 (m, 1H, CHBCH2CO), 2.38-2.42 (m, 2H, CH2CO),
3.09-3.1.3 (m, 2H, CH2N), 3.99-4.03 (m, 1H, CH(CH2)4N),
4.42-4.44 (m, 1H, CHCH2CH2CO), 5.06 (s, 2H, OCH2C6H5),
7.28-7.34 (m, 5H, C6H5); 13C NMR (100 MHz, MeOD-d4):
¤ 24.1, 28.0, 28.8, 30.5, 31.1, 32.9, 41.5, 52.9, 56.0, 67.4,
81.0, 128.8, 129.0, 129.5, 138.5, 157.9, 159.0, 174.6, 175.4,
176.4; HRMS (ESI-TOF): Calcd for C24H35N3O9Na (M+Na)+:
532.2276, found: 532.2278; IR (KBr, νmax/cm¹1): 3329 (OH),
1716 (CO2), 1685 (CON), 1655 (CON).
A Typical Procedure of the Amidation of Cbz-L-Phenyl-
alanine (6a) in a Gram Scale is as Follows. To a colorless
solution of 1.50 g (5.0 mmol) of Cbz-L-phenylalanine (6a) in
100 mL of THF were added at 0 °C 0.67 mL (7.0 mmol, 1.4
equiv) of ethyl chloroformate and 2.09 mL (15 mmol, 3.0
equiv) of triethylamine. After stirring for 30 min at 0 °C, a
solution of 1.10 g (7.5 mmol, 1.5 equiv) of L-Glu-OH (2e) and
0.63 g (7.5 mmol, 1.5 equiv) of NaHCO3 in 100 mL of H2O was
added at 0 °C to the colorless suspension. The mixture was
stirred for 30 min at 0 °C and the resulting colorless clear
solution was concentrated in vacuo. The residue was adjusted
to pH 2 by addition of a 1.0 M aqueous solution of HCl. The
colorless suspension was diluted with 100 mL of brine, extract-
ed with 200 mL of a 9:1 mixture of EtOAc and MeOH. The
aqueous layer was extracted with 100 mL © 2 of a 9:1 mixture
3
A. Furka, F. Sebestyén, M. Asgedom, G. Dibó, Int. J. Pept.
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S. A. Kates, N. A. Solé, C. R. Johnson, D. Hudson, G.
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696 | Bull. Chem. Soc. Jpn. 2017, 90, 689–696 | doi:10.1246/bcsj.20170035
© 2017 The Chemical Society of Japan