An efficient synthesis of Nα-protected amino and peptide acid aryl amides via iodine-mediated oxidative acylation of N α-protected amino and peptide thioacids

Article abstract of DOI:10.1055/s-0033-1339488

Thioacids derived from N-protected amino or dipeptide and tripeptide acids undergo facile N-acylation with aromatic amines to afford N-protected amino or peptide aryl amides in good to excellent yields and enantiopurities. The method also furnishes difficult-to-prepare N-Fmoc amino acid 4-nitroanilides in good yields. This simple oxidative N^α-acylation of thioacids with aromatic amines proceeds in the presence of iodine, 1-hydroxybenzotriazole and N,N-diisopropylethylamine at room temperature in tetrahydrofuran. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0033-1339488

PAPER
▌2727
α
paper
An Efficient Synthesis of N -Protected Amino and Peptide Acid Aryl Amides
via Iodine-Mediated Oxidative Acylation of Nα-Protected Amino and Peptide
Thioacids
Synthesis of Nα-Protected Amino and Peptide Acid Aryl Amides
Chilakapati Madhu, T. M. Vishwanatha, Vommina V. Sureshbabu*
#109, Peptide Research Laboratory, Department of Studies in Chemistry, Central College Campus, Bangalore University,
Dr. B. R. Ambedkar Veedhi, Bangalore 560 001, India
Fax +91(80)22292848; E-mail: sureshbabuvommina@rediffmail.com; E-mail: hariccb@gmail.com; E-mail: hariccb@hotmail.com
Received: 27.05.2013; Accepted after revision: 08.07.2013
not only because of their easy preparation, but also on ac-
Abstract: Thioacids derived from N-protected amino or dipeptide
count of the numerous advantages over their carboxylic
and tripeptide acids undergo facile N-acylation with aromatic
acid (RCOOH) counterparts, such as solubility, acidity
amines to afford N-protected amino or peptide aryl amides in good
to excellent yields and enantiopurities. The method also furnishes
and enhanced nucleophilicity.8 Thus, amino/peptide thio-
difficult-to-prepare N-Fmoc amino acid 4-nitroanilides in good acids have been the subject of major endeavors devoted
yields. This simple oxidative Nα-acylation of thioacids with aromat-
ic amines proceeds in the presence of iodine, 1-hydroxybenzotri-
azole and N,N-diisopropylethylamine at room temperature in
undergo acylation directly with amines; they need to be
tetrahydrofuran.
toward the chemical assembly of polypeptides and a vari-
ety of proteins.9 Thioacids, similar to oxo-acids, do not
activated prior to treatment with an amine. Importantly,
Key words: thioacids, acylation, aryl amides, iodine
the activation of a thioacid is very mild and does not re-
quire any coupling reagent,10 and sometimes not even a
base.11 Such inherent advantages of thioacids have been
explored for the preparation of amides12 and peptidomi-
metics.13
Amide bond formation is an important reaction in organic
synthesis as this moiety occurs widely in Nature.1 Hence,
there has been significant research on the development of
novel and efficient methods toward the formation of am-
ides.2 The most popular strategy for the generation of am-
ide bonds relies on the reactions of activated carboxylic
acids with amines.3 However, studies have also been di-
rected to the use of thioacids as efficient acylating agents.4
Thioacids have been used as precursors to thioesters,
which participate in ligation reactions in the chemical syn-
thesis of proteins.5,6 Due to the challenges in preparing
thioesters (especially in Fmoc chemistry),7 research has
focused on N-protected amino/peptide thioacids as alter-
natives to thioesters in native chemical ligation. This is
Among pharmaceutical compounds possessing amide
bonds, aryl amides are an example of carboxamides,
which have generated significant interest in varied appli-
cations.14,15
Substituted aniline derivatives, in particular those pos-
sessing electron-withdrawing groups, do not undergo
straightforward condensation with carboxylic acids.
Therefore, a number of strategies have been developed for
the synthesis of C-terminal amino acid or peptide acid aryl
amides (Scheme 1). Aryl amides of tert-butoxycarbonyl
(Boc) or benzyloxycarbonyl (Cbz) amino acids are pre-
pared from carboxylic acids via the mixed anhydride
O
PgHN Xaa
OH
+
ArNH2
oxo-acid activation via
coupling agents
O
O
Staudinger
reaction
H/Me/Bn
O
PgHN Xaa
O
PgHN Xaa
Se
Ar
PgHN Xaa
I2, HOBt
N
+
+
ArN3
enzyme
activation
H
ArNH2
O
ArNH2
+
PgHN Xaa
SH
Scheme 1 Retrosynthetic analysis of aryl amides through various approaches
SYNTHESIS 2013, 45, 2727–2736
Advanced online publication: 06.08.2013
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0033-1339488; Art ID: SS-2013-N0036-OP
© Georg Thieme Verlag Stuttgart · New York

2728
C. Madhu et al.
PAPER
method, or by using carbodiimides or other expensive We report herein a rapid, high-yielding and racemization-
coupling reagents.16 Alternative procedures include the free synthesis of aryl amides via iodine-mediated oxida-
Staudinger-type reaction in which azides are treated with tive acylation of N-protected thioacids with substituted
in situ generated N-protected amino acid selenocarboxyl- anilines. The protocol is compatible with the three com-
ates.17 However, the preparation of selenocarboxylates is monly employed peptide protecting groups (Fmoc, Boc
cumbersome. Liskamp’s group have developed an elegant and Cbz), as well as several bifunctional amino acids,
protocol for the acylation of N-Cbz protected amino peptides and a diverse range of substituted aniline deriva-
acids/esters with amines mediated by Alcalase-CLEA en- tives. In addition, N-protected amino acids such as serine,
zyme.18 Although enantiomerically pure products were threonine and tyrosine have been converted into the corre-
obtained, the long reaction times and high temperature sponding aryl amides without protection of the hydroxyl
were not suited to the general applicability of this proto- group. Iodine is a cheap and easily available reagent,
col. Many aniline derivatives, being the amine compo- which has been used extensively in a number of reac-
nents for the preparation of the title compounds, have tions.19 Danishefsky’s group have previously reported the
basicities in the range of pH 8–9, and thus are not suitable total chemical synthesis of complex glycoproteins via io-
for 9-fluorenylmethoxycarbonyl (Fmoc) chemistry at dine-mediated oxidative acylation of amino and peptide
high temperature. Some attempts have been made to pre- thioacids.9 In an earlier study, we prepared two dipep-
pare Fmoc-protected 4-nitroanilides,16f,g however, low tides, Fmoc-(L)-Phg-Ala-OMe and Fmoc-(D)-Phg-Ala-
yields of products were obtained.
OMe, and studied their enantiopurities.20 These results es-
tablished that thioacids could be employed to acylate aryl
amines at room temperature in the presence of iodine and
1-hydroxybenzotriazole (HOBt) (Scheme 2). On the basis
of these studies, we initiated an investigation on the reac-
tion of N-protected thioacids with aniline derivatives.
H2N
R2
R1
2
R1
H
The required N-protected amino and peptide thioacids 1
were prepared using our previously reported protocol.20
We have also reviewed the advantages of propanephos-
phonic acid anhydride (T3P®) over other traditional cou-
pling reagents in a variety of reactions.21 Hence, a
procedure involving T3P®-mediated activation of a car-
boxylic acid followed by treatment with sodium sulfide
(Na2S) was employed to prepare thioacids 1. Our study
began with the condensation of Fmoc-Ala-SH (1a, R1 =
Me) with aniline in the presence of iodine and HOBt at
room temperature in dimethyl sulfoxide (DMSO) as the
solvent (Table 1, entries 1 and 2). After five hours, the ex-
pected product 3a was isolated in a yield of 54–58%. Sol-
vents including acetonitrile, N,N-dimethylformamide,
dichloromethane and tetrahydrofuran were tested in this
reaction (Table 1, entries 3–7). Tetrahydrofuran was
found to be the best solvent, leading to the desired product
3a in 91% yield in 30 minutes. The use of N-methylmor-
pholine (NMM) as the tertiary base had no beneficial in-
fluence on the reaction rate, therefore we used N,N-
diisopropylethylamine (DIPEA) as the base (Table 1, en-
try 6). In order to ascertain the role of HOBt in the cou-
pling reaction, a control experiment was carried out in
which aniline was coupled to 1a in the absence of HOBt.
Under these conditions, the product yield was reduced
significantly to 58% (Table 2, entry 1), and the level of
epimerization increased to 12%. Thus, HOBt played a vi-
tal role in suppressing racemization as well as increasing
the yield. According to the mechanism established by
Danishefsky9 (Scheme 3), thioacylation can be achieved
in dimethyl sulfoxide, even in the absence of iodine. Con-
sequently, thioacid 1a was treated with aniline and HOBt
in dimethyl sulfoxide (Table 2, entry 2), however, it was
interesting to note that only 20% of the desired aryl amide
3a was detected after five hours. In contrast, thioacylation
of 1a with aniline mediated by iodine and HOBt in di-
I2, DIPEA, HOBt
N
SH
FmocHN
R2
FmocHN
THF, r.t., 30 min
O
O
3
1
Scheme 2 Synthesis of N-protected amino acid aryl amides 3
Table 1 Optimization of the Solvent for the Synthesis of 3aa
Entry
Solvent
Base
Timeb
Yield (%)c
1
2
3
4
5
6
7
DMSO
DMSO
MeCN
DMF
DIPEA
NMM
5 h
5 h
54
58
61
63
59
91
86
DIPEA
DIPEA
DIPEA
DIPEA
NMM
4 h
2 h
CH2Cl2
THF
4 h
30 min
45 min
THF
a Reactions were conducted at r.t.
b The reaction was monitored by TLC until thioacid 1a had been fully
consumed.
c Yield of isolated product after column chromatography.
Table 2 Investigation of the Coupling of 1a with Anilinea
Entry
Additive
Solvent
Yield (%)
1
2
3
4
none
I2, DMSO
DMSO
58
20
54
91
HOBt (2.0 equiv)
HOBt (2.0 equiv)
HOBt (2.0 equiv)
I2, DMSO
I2, THF
a Reactions were conducted at r.t. with DIPEA as the base.
Synthesis 2013, 45, 2727–2736
© Georg Thieme Verlag Stuttgart · New York

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Synthesis of Nα-Protected Amino and Peptide Acid Aryl Amides
2729
methyl sulfoxide, led to an increase in the yield of 3a (Ta- triazolyl (OBt) ester or amide product derived from the
ble 2, entry 3). Although, dimethyl sulfoxide assists in the diacyl disulfide.
formation of the intermediate diacyl disulfide, it is less ef-
ficient than tetrahydrofuran for formation of the O-benzo-
To demonstrate the scope of the optimized protocol, a
series of N-protected thioacids was acylated with aniline
Table 3 Synthesis of N-Protected Aryl Amides 3
Entry Aryl amide
Yield
(%)
Mp
(°C)
Entry Aryl amide
Yield
(%)
Mp (°C)
190–192
HO
H
N
H
N
FmocHN
FmocHN
1
91
88
191–193
8
87
83
O
O
O
O
3a
3h
H
N
H
N
FmocHN
FmocHN
2
179
9
213–215
N
O
O
3i
3b
BocHN
H
N
4
FmocHN
H
N
FmocHN
3
79
81
176–178
10
76
65
227–229
161–163
N
N
O
3c
3j
COOt-Bu
H
N
FmocHN
H
N
F
F
4
132
11
O
CbzHN
O
3d
3k
H
H
N
N
CbzHN
FmocHN
5
86
218
12
81
219–221
O
O
N
3l
3e
SMe
Cl
H
N
H
N
6
7
85
77
187–188
180–184
13
14
78
89
170
FmocHN
CbzHN
O
O
CN
3f
3m
H
N
H
N
FmocN
BocHN
O
O
154–155
Cl
Br
3g
3n
© Georg Thieme Verlag Stuttgart · New York
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2730
C. Madhu et al.
PAPER
derivatives containing electron-donating or electron-
withdrawing substituents. The results are summarized in
Table 3. It was found that the coupling of anilines with
electron-donating groups gave the corresponding prod-
ucts in higher yields than those possessing electron-with-
drawing groups. The aniline substrates containing ortho,
para, and meta substituents had no effect on the product
yield. Various Fmoc-, Boc- and Cbz-protected amino
thioacids were well-tolerated under the optimized reac-
tion conditions, leading to the desired aryl amides 3 in
good to excellent yields.
Table 4 Synthesis of N-Protected 4-Nitroanilides 4
Entry
1
4-Nitroanilide
Yield (%) Mp (°C)
H
N
FmocHN
O
81
75
181–183
185–187
NO2
4a
H
N
FmocHN
O
2
3
N-Protected amino acid 4-nitroanilides play a significant
role in biology and medicine.22 However, a number of the
reported methods for their synthesis result in low yields.
Despite the procedure employing phosphorus(V) oxy-
chloride (POCl3) giving 4-nitroanilides in almost 80%
yield,16g this reagent is not employed commonly as an ac-
ylating agent in peptide chemistry because of the inherent
disadvantages associated with sensitive protecting
groups. Thus, we focused our studies on the synthesis of
Fmoc-protected 4-nitroanilides 4a–f via the condensation
of Fmoc-protected amino thioacids with 4-nitroaniline.
The products were obtained in satisfactory yields after re-
crystallization from diethyl ether–THF (Table 4). Interest-
ingly, the reaction occurred efficiently with sterically
hindered amino thioacids such as Fmoc-Val, Fmoc-Pro
and Fmoc-Aib, affording the corresponding 4-nitroani-
lides in high purities (as confirmed by HPLC analysis).
Due to the wide functional group tolerance of the T3P®-
mediated thioacid preparation,20 we also addressed the
compatibility of the present protocol with unprotected bi-
functional amino acids. For this investigation, thioacids
derived from Fmoc-Ser, Fmoc-Thr, Fmoc-Tyr and Fmoc-
His were employed without protection of the side chain
functionalities. The aryl amides 5a–d derived from these
thioacids were obtained in good yields (Table 5).
NO2
4b
H
N
FmocHN
O
80
190
NO2
4c
H
N
FmocN
O
4
5
69
63
183–184
197–199
NO2
4d
H
N
FmocHN
O
NO2
4e
H
N
6
78
172–173
BocHN
O
In order to broaden the scope of the present methodology,
the synthesis of N-protected dipeptide and tripeptide acid
aryl amides was carried out (Scheme 4). The required
thioacids 6 were synthesized via T3P® activation of the re-
NO2
4f
O
O
R1NH2
R1
R
N
R
OBt
O
O
H
O
HOBt
R
I2
HOBt
S
R
R
SH
– HI
R
S
S
O
R
S
O
O
R
S
SH
Scheme 3 A plausible mechanism for the formation of an amide bond using thioacids
H2N
R3
R1
O
R1
O
2
H
R3
H
N
I2, DIPEA, HOBt
N
PgHN
SH
PgHN
N
H
O
R2
THF, r.t.
O
R2
6
7
Scheme 4 Synthesis of N-protected peptide acid aryl amides 7
Synthesis 2013, 45, 2727–2736
© Georg Thieme Verlag Stuttgart · New York

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Synthesis of Nα-Protected Amino and Peptide Acid Aryl Amides
2731
Table 5 Synthesis of Unprotected Bifunctional Amino Acid Aryl Amides 5
Entry
1
Thioacid
Aryl amide
Yield (%)
HO
HO
H
N
FmocHN
79
82
SH
SH
FmocHN
O
O
CN
O
O
5a
HO
HO
H
N
FmocHN
2
3
FmocHN
5b
OH
Cl
OH
H
N
88
75
FmocHN
SH
FmocHN
O
O
5c
HN
N
HN
N
H
N
4
FmocHN
SH
FmocHN
O
NO2
O
5d
N-Protected Amino/Peptide Thioacids; General Procedure
To a soln of the appropriate carboxylic acid (1.0 mmol) and T3P®
(2.2 mmol) in anhyd MeCN (8.0 mL) was added Et3N (1.5 mmol)
at 0 °C, followed by finely ground Na2S (3.0 mmol). The resulting
mixture was stirred for 2–3 h until the reaction was complete (TLC
monitoring), concentrated and then diluted with H2O. The mixture
was acidified with aq citric acid soln (10%) and the product was ex-
tracted with EtOAc (10 mL). The organic layer was washed with
H2O (2 × 10 mL) and brine (10 mL), and then dried over anhyd
Na2SO4. The solvent was evaporated in vacuo to afford the corre-
spective oxo-acids. In general, the reactions of peptide
thioacids 6 with aniline derivatives were satisfactory,
however, the reaction times were longer, taking up to an
hour. In all cases, the peptidyl aryl amides 7 were isolated
in moderate to good yields (Table 6).
In conclusion, a general and efficient synthesis of enantio-
pure N-protected amino/peptide aryl amides has been de-
scribed. The coupling of N-protected amino, dipeptide
and tripeptide thioacids with aniline derivatives occurs in sponding amino thioacid in quant. yield.
the presence of iodine, HOBt and N,N-diisopropylethyl-
N-Protected Amino/Peptide Acid Aryl Amides; General Proce-
amine at room temperature in tetrahydrofuran. The scope
of this new protocol has been demonstrated using a vari-
ety of N-urethane protecting groups, and side-chain func-
tionalized and sterically hindered amino acids.
dure
To a stirred suspension of thioacid (1.0 mmol) in THF (5 mL) were
added I2 (0.6 mmol, 152 mg), DIPEA (1.2 mmol, 0.156 mL) and
HOBt (2.0 mmol, 270 mg) at r.t., followed by the appropriate amine
(1.1 mmol). The reaction mixture was stirred for 0.5 to 1 h as ana-
lyzed by TLC (until complete disappearance of the thioacid was ob-
served). After the reaction was complete, the solvent was
evaporated under vacuum and diluted with EtOAc (20 mL). The or-
ganic phase was washed with 10% HCl (2 × 10 mL), 1 N Na2CO3
(3 × 10 mL), H2O (2 × 10 mL) and brine (10 mL) and then dried
over anhydrous Na2SO4. The solvent was filtered and evaporated
under reduced pressure. The crude reaction mixture was purified
under column chromatography using hexane–EtOAc (7:3) as the el-
uent to afford the desired product.
All solvents were freshly distilled before use. Amino acids were
used as received from Sigma-Aldrich. All the reactions were moni-
tored by TLC using Merck precoated silica gel plates. Column chro-
matography was performed with Merck silica gel (200–300 mesh)
at normal atmospheric pressure. Melting points were recorded on a
Kofler hot block in open capillary tubes and are uncorrected. IR
spectra were recorded on a Nicolet Impact 400D FT-IR spectropho-
tometer (KBr pellets, 3 cm–1 resolution). Optical rotation values
1
were recorded on a JASCO P-2000 digital polarimeter. H NMR
(400 MHz) and 13C NMR (75 MHz) were recorded on a Bruker
AMX 400 MHz instrument with tetramethylsilane (TMS) as the in-
ternal standard. HRMS analyses were recorded on a Q-Tof Micro-
mass spectrometer.
Fmoc-Ala-anilide (3a)
Yield: 0.355 g (91%); white solid; mp 191–193 °C; [α]D25 –27.5 (c
0.1, CHCl3).
IR (neat): 3359, 1689, 1528 cm–1.
© Georg Thieme Verlag Stuttgart · New York
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C. Madhu et al.
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Table 6 Synthesis of N-Protected Peptide Aryl Amides 7
Entry
Peptide aryl amide
Yield (%) Entry
Peptide aryl amide
Yield (%)
O
O
H
H
N
N
FmocHN
N
H
BocHN
N
H
O
1
83
86
5
6
76
80
O
7e
7a
Cl
N
O
O
H
H
N
N
FmocHN
N
H
2
BocHN
N
H
O
O
7b
7f
OMe
O
H
O
N
H
H
FmocHN
N
H
N
N
CbzHN
N
3
79
7
75
O
H
O
O
Cl
7c
7g
O
O
H
H
H
N
N
N
CbzHN
N
BocHN
N
H
4
81
8
76
H
O
Cl
O
O
7h
7d
1H NMR (400 MHz, DMSO-d6): δ = 1.27 (d, J = 7.6 Hz, 3 H), 4.13–
4.24 (m, 4 H), 6.90 (d, J = 7.6 Hz, 2 H), 7.25–7.81 (m, 12 H), 9.94
(s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 16.4, 45.9, 51.3, 69.2, 122.3,
124.1, 127.1, 128.1, 128.6, 129.3, 139.1, 141.2, 143.7, 156.2, 172.1.
IR (neat): 3353, 1663, 1530, 1251 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 1.23–1.27 (m, 2 H), 1.39 (s, 9
H), 1.62–1.67 (m, 2 H), 1.92–1.96 (m, 2 H), 2.25 (s, 3 H), 2.81–2.85
(m, 2 H), 4.35–4.41 (m, 1 H), 4.42 (t, J = 5.6 Hz, 1 H), 4.64 (d,
J = 6.8 Hz, 2 H), 6.90 (br s, 2 H), 7.08–7.55 (m, 12 H), 8.91 (s, 1 H).
HRMS (ESI): m/z [M + Na]+ calcd for C24H22N2O3Na: 409.1528;
found: 409.1531.
13C NMR (75 MHz, CDCl3): δ = 21.9, 22.9, 24.1, 28.9, 30.0, 30.2,
32.2, 47.6, 55.9, 67.7, 117.5, 120.5, 121.1, 125.5, 125.8, 127.6,
128.2, 129.3, 139.4, 141.8, 144.2, 156.7, 156.9, 168.2, 170.5.
HRMS (ESI): m/z [M + Na]+ calcd for C33H39N3O5Na: 580.2787;
found: 580.2789.
Fmoc-Leu-3-methylanilide (3b)
25
Yield: 0.39 g (88%); white solid; mp 179 °C; [α]D –35.1 (c 0.1,
CHCl3).
IR (neat): 3288, 1686, 1530, 1258 cm–1.
Fmoc-Asp(t-Bu)-3-methylanilide (3d)
25
Yield: 0.4 g (81%); white solid; mp 132 °C; [α]D –38.5 (c 0.1,
1H NMR (400 MHz, DMSO-d6): δ = 0.97 (d, J = 7.8 Hz, 6 H), 1.87–
1.92 (m, 3 H), 2.34 (s, 3 H), 4.28–4.33 (m, 2 H), 4.61 (d, J = 7.2 Hz,
2 H), 6.89 (d, J = 5.8 Hz, 1 H), 7.19–7.80 (m, 12 H), 9.29 (s, 1 H).
CHCl3).
IR (neat): 3288, 1656, 1535, 1258 cm–1.
13C NMR (75 MHz, DMSO-d6): δ = 21.9, 24.2, 40.3, 48.1, 51.7,
67.8, 119.1, 121.7, 123.9, 125.4, 127.8, 128.1, 128.7, 137.3, 138.1,
139.8, 143.3, 156.2, 171.8.
HRMS (ESI): m/z [M + Na]+ calcd for C28H30N2O3Na: 465.2154;
found: 465.2151.
1H NMR (400 MHz, CDCl3): δ = 1.46 (s, 9 H), 2.33 (s, 3 H), 2.95–
3.00 (m, J = 3.6 Hz, 2 H), 4.20 (t, J = 6.8 Hz, 1 H), 4.46 (d, J = 6.8
Hz, 2 H), 4.58–4.65 (m, 1 H), 6.10 (br s, 1 H), 6.94 (d, J = 7.6 Hz,
1 H), 7.20–7.70 (m, 11 H), 8.48 (s, 1 H).
13C NMR (75 MHz, CDCl3): δ = 22.0, 28.5, 38.0, 47.6, 52.2, 67.8,
82.7, 117.6, 120.6, 121.1, 125.5, 125.9, 127.6, 128.3, 129.3, 137.9,
139.4, 141.8, 144.1, 156.8, 169.0, 171.8.
Fmoc-Lys(Boc)-4-methylanilide (3c)
25
Yield: 0.44 g (79%); white solid; mp 176–178 °C; [α]D –25.3
HRMS (ESI): m/z [M + Na]+ calcd for C30H32N2O5Na: 523.2209;
found: 523.2212.
(c 0.1, CHCl3).
Synthesis 2013, 45, 2727–2736
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Synthesis of Nα-Protected Amino and Peptide Acid Aryl Amides
2733
Fmoc-Phg-3-methylanilide (3e)
13C NMR (75 MHz, DMSO-d6): δ = 17.4, 28.9, 44.7, 46.8, 57.4,
63.2, 68.1, 114.7, 121.3, 125.8, 127.3, 128.4, 128.7, 129.4, 140.1,
142.7, 144.4, 156.2, 170.7.
25
Yield: 0.4 g (86%); white solid; mp 218 °C; [α]D –32.1 (c 0.1,
CHCl3).
IR (neat): 3277, 1656, 1535, 1258 cm–1.
HRMS (ESI): m/z [M + Na]+ calcd for C30H33N3O4Na: 522.2369;
1H NMR (400 MHz, DMSO-d6): δ = 2.25 (s, 3 H), 4.22–4.28 (m, 3
H), 5.43 (d, J = 8.0 Hz, 1 H), 6.80 (d, J = 7.2 Hz, 1 H), 7.15–8.20
(m, 17 H), 10.24 (s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 24.2, 46.3, 66.1, 119.3, 120.9,
125.1, 126.3, 127.4, 128.3, 128.8, 129.1, 129.6, 138.3, 138.7, 156.2,
169.2.
found: 522.2364.
Fmoc-Ala-4-pyrazolo-anilide (3j)
Yield: 0.34 g (76%); white solid; mp 227–229 °C; [α]D –37.1
(c 0.1, CHCl3).
IR (neat): 3293, 1725, 1668, 1533 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 1.32 (d, J = 6.4 Hz, 3 H), 2.80–
2.86 (m, 1 H), 4.24 (t, J = 4.8 Hz, 1 H), 4.47 (d, J = 7.2 Hz, 2 H),
5.90 (br s, 1 H), 6.34 (d, J = 6.8 Hz, 1 H), 7.23–7.80 (m, 14 H), 8.92
(s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 16.5, 46.3, 66.9, 109.1, 121.3,
122.7, 125.9, 126.2, 127.8, 128.4, 133.4, 136.7, 140.4, 143.2, 156.6,
171.8.
25
HRMS (ESI): m/z [M + H]+ calcd for C30H27N2O3: 463.2022; found:
463.2019.
Fmoc-Met-2-chloroanilide (3f)
25
Yield: 0.41 g (85%); white solid; mp 187–188 °C; [α]D –29.2
(c 0.1, CHCl3).
IR (neat): 3295, 1678, 1532, 1256 cm–1.
HRMS (ESI): m/z [M + Na]+ calcd for C27H24N4O3Na: 475.1746;
found: 475.1748.
1H NMR (400 MHz, CDCl3): δ = 2.13 (s, 3 H), 2.65–2.61 (m, 2 H),
2.74 (t, J = 6.0 Hz, 2 H), 4.24 (t, J = 6.4 Hz, 1 H), 4.45–4.46 (m, 3
H), 5.60 (d, J = 8.0 Hz, 1 H), 6.10 (br s, 1 H), 7.05–7.70 (m, 11 H),
8.80 (s, 1 H).
13C NMR (75 MHz, CDCl3): δ = 16.9, 28.7, 32.3, 45.4, 55.1, 69.1,
123.8, 126.1, 126.8, 127.3, 128.4, 128.7, 129.6, 131.5, 137.3, 140.9,
144.7, 155.9, 169.7.
Cbz-Phe-3,4-difluoroanilide (3k)16i
Yield: 0.26 g (65%); white solid; mp 162–164 °C; [α]D –25.6
(c 0.1, CHCl3).
IR (neat): 3284, 1653, 1530, 1283 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 2.88 (d, J = 6.8 Hz, 2 H), 4.29
(t, J = 5.2 Hz, 1 H), 5.14 (s, 2 H), 6.92 (d, J = 7.2 Hz, 1 H), 7.20–
7.38 (m, 11 H), 7.60–7.80 (m, 2 H), 10.25 (br s, 1 H).
25
HRMS (ESI): m/z [M + Na]+ calcd for C26H25ClN2O3SNa:
503.1172; found: 503.1171.
Fmoc-Pro-3-chloroanilide (3g)
13C NMR (75 MHz, DMSO-d6): δ = 36.3, 55.1, 66.0, 110.4, 116.5,
118.2, 125.8, 126.7, 127.3, 128.1, 128.5, 129.4, 136.3, 138.8, 140.2,
146.2, 148.4, 156.7, 172.0.
25
Yield: 0.34 g (77%); white solid; mp 180–184 °C; [α]D –26.4
(c 0.1, CHCl3).
IR (neat): 3332, 1672, 1545, 1421 cm–1.
HRMS (ESI): m/z [M + Na]+ calcd for C23H20F2N2O3Na: 433.1340;
1H NMR (400 MHz, CDCl3): δ = 1.82–1.87 (m, 2 H), 2.01–2.07 (m,
2 H), 3.14 (t, J = 4.8 Hz, 2 H), 4.10 (t, J = 5.4 Hz, 1 H), 4.35 (t,
J = 5.0 Hz, 1 H), 4.89 (d, J = 7.4 Hz, 2 H), 6.93 (d, J = 7.2 Hz, 1 H),
7.23–7.56 (m, 11 H), 8.92 (s, 1 H).
13C NMR (75 MHz, CDCl3): δ = 25.2, 28.5, 47.6, 48.1, 61.5, 68.5,
118.1, 120.2, 120.5, 124.4, 125.4, 127.5, 127.6, 128.3, 130.2, 134.9,
139.7, 141.8, 144.1, 157.3, 170.0.
found: 433.1337.
Cbz-Leu-4-pyrrolylanilide (3l)16i
Yield: 0.33 g (81%); white solid; mp 219–221 °C; [α]D –27.1
(c 0.1, CHCl3).
IR (neat): 3284, 1685, 1594, 1531 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 0.84 (d, J = 7.2 Hz, 6 H), 1.14–
1.19 (m, 1 H), 1.44–1.52 (m, 2 H), 4.00 (t, J = 4.2 Hz, 1 H), 5.01 (s,
2 H), 5.58 (br s, 1 H), 6.22 (d, J = 6.4 Hz, 2 H), 7.12–7.65 (m, 11
H), 10.06 (s, 1 H).
25
HRMS (ESI): m/z [M + Na]+ calcd for C26H23ClN2O3Na: 469.1295;
found: 469.1291.
Fmoc-Ser-3-methylanilide (3h)
13C NMR (75 MHz, DMSO-d6): δ = 21.8, 22.3, 41.7, 50.3, 66.1,
110.3, 121.5, 122.2, 123.9, 127.0, 127.8, 129.4, 135.3, 137.1, 140.9,
156.2, 171.8.
25
Yield: 0.36 g (87%); white solid; mp 190–192 °C; [α]D –21.5
(c 0.1, CHCl3).
IR (neat): 3272, 1654, 1535, 1257 cm–1.
HRMS (ESI): m/z [M + Na]+ calcd for C24H27N3O3Na: 428.1950;
1H NMR (400 MHz, DMSO-d6): δ = 2.27 (s, 3 H), 3.64 (d, J = 6.0
Hz, 2 H), 4.21–4.30 (m, 4 H), 6.86 (d, J = 6.8 Hz, 1 H), 7.10–7.90
(m, 11 H), 8.10 (s, 1 H), 9.90 (s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 21.7, 47.1, 62.2, 116.9, 120.2,
120.6, 124.4, 125.8, 127.6, 128.1, 129.0, 138.3, 139.4, 141.2, 144.3,
144.4, 156.4, 172.6.
found: 428.1952.
Cbz-Phe-4-cyanoanilide (3m)18
Yield: 0.31 g (78%); white solid; mp 170 °C; [α]D –35.7 (c 0.1,
CHCl3).
IR (neat): 3325, 2235, 1530, 1251 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 2.87 (d, J = 7.2 Hz, 2 H), 3.05
(t, J = 4.4 Hz, 1 H), 4.97 (s, 2 H), 7.14–7.56 (m, 12 H), 7.79 (d,
J = 6.6 Hz, 2 H), 8.09 (br s, 1 H), 10.46 (br s, 1 H).
25
HRMS (ESI): m/z [M + Na]+ calcd for C25H24N2O4Na: 439.1634;
found: 439.1634.
Fmoc-Val-4-morpholino-anilide (3i)
13C NMR (75 MHz, DMSO-d6): δ = 37.2, 56.9, 65.3, 111.4, 118.5,
121.9, 123.8, 126.3, 126.9, 127.4, 127.6, 128.0, 128.2, 129.1, 130.1,
136.8, 137.5, 139.4, 155.9, 171.1.
25
Yield: 0.42 g (83%); white solid; mp 213–215 °C; [α]D –32.1
(c 0.1, CHCl3).
IR (neat): 3287, 1682, 1537, 1254 cm–1.
HRMS (ESI): m/z [M + Na]+ calcd for C24H21N3O3Na: 422.1481;
1H NMR (400 MHz, DMSO-d6): δ = 0.97 (d, J = 7.4 Hz, 6 H), 2.51–
2.58 (m, 1 H), 3.20 (t, J = 4.6 Hz, 4 H), 3.71 (t, J = 4.6 Hz, 4 H),
4.32 (t, J = 5.2 Hz, 1 H), 4.57 (d, J = 6.4 Hz, 2 H), 4.72–4.85 (m, 1
H), 6.57 (d, J = 7.2 Hz, 2 H), 6.80 (br s, 1 H), 7.28–7.78 (m, 10 H),
10.21 (s, 1 H).
found: 422.1483.
Boc-Val-3-bromoanilide (3n)
Yield: 0.33 g (89%); white solid; mp 154–155 °C; [α]D –33.4
(c 0.1, CHCl3).
25
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 2727–2736

2734
C. Madhu et al.
PAPER
IR (neat): 3314, 1683, 1532, 1249 cm–1.
Fmoc-Aib-4-nitroanilide (4e)
Yield: 0.28 g (63%); white solid; mp 197–199 °C.
1H NMR (400 MHz, DMSO-d6): δ = 1.03 (d, J = 7.2 Hz, 6 H), 1.37
(s, 9 H), 2.66–2.78 (m, 1 H), 4.04–4.07 (m, 1 H), 7.13–7.52 (m, 4
H), 7.92 (br s, 1 H), 9.80 (s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 17.8, 27.9, 32.4, 58.2, 78.5,
120.4, 120.9, 123.4, 127.1, 130.7, 139.2, 155.8, 172.3.
IR (neat): 3318, 1669, 1539, 1382 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 1.41 (s, 6 H), 4.30 (t, J = 4.2
Hz, 1 H), 4.55 (d, J = 4.9 Hz, 2 H), 5.11 (br s, 1 H), 7.11–8.15 (m,
12 H), 10.23 (br s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 24.7, 45.8, 47.1, 66.8, 121.2,
121.7, 126.4, 127.8, 128.0, 128.2, 139.5, 141.0, 143.6, 143.8, 155.1,
171.2.
HRMS (ESI): m/z [M + Na]+ calcd for C25H23N3O5Na: 468.1535;
found: 468.1522.
HRMS (ESI): m/z [M + Na]+ calcd for C16H23BrN2O3Na: 393.0790;
found: 393.0785.
Fmoc-Ala-4-nitroanilide (4a)16f
25
Yield: 0.35 g (81%); white solid; mp 181–183 °C; [α]D –30.5
(c 0.1, CHCl3).
IR (neat): 2983, 1737, 1372, 1234 cm–1.
Boc-Phe-4-nitroanilide (4f)16g
Yield: 0.3 g (78%); white solid; mp 172–173 °C; [α]D25 –42.6 (c 0.1,
1H NMR (400 MHz, DMSO-d6): δ = 1.31 (d, J = 4.2 Hz, 3 H), 4.11
(t, J = 6.0 Hz, 1 H), 4.43 (d, J = 5.6 Hz, 2 H), 4.65–4.70 (m, 1 H),
5.11 (br s, 1 H), 7.11–8.12 (m, 12 H), 10.80 (br s, 1 H).
CHCl3).
IR (neat): 3289, 1663, 1534, 1381 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 1.32 (s, 9 H), 2.85–2.91 (m, 2
H), 4.77–4.85 (m, 1 H), 5.08 (br s, 1 H), 7.01–8.05 (m, 9 H), 9.80
(br s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 16.5, 45.5, 49.6, 66.3, 120.4,
121.6, 125.8, 126.4, 127.1, 127.8, 140.1, 141.2, 143.2, 143.8, 155.8,
171.2.
13C NMR (75 MHz, DMSO-d6): δ = 27.5, 37.2, 54.1, 79.2, 121.1,
121.8, 125.7, 127.2, 128.1, 139.1, 144.0, 144.1, 155.7, 172.1.
HRMS (ESI): m/z [M + Na]+ calcd for C24H21N3O5Na: 454.1379;
found: 454.1368.
HRMS (ESI): m/z [M + Na]+ calcd for C20H23N3O5Na: 408.1535;
found: 408.1519.
Fmoc-Val-4-nitroanilide (4b)16g
25
Yield: 0.34 g (75%); white solid; mp 185–187 °C; [α]D –39.1
(c 0.1, CHCl3).
IR (neat): 3329, 1685, 1533, 1383 cm–1.
Fmoc-Ser-4-cyanoanilide (5a)
25
Yield: 0.34 g (79%); white solid; mp 173–175 °C; [α]D –34.5
(c 0.1, CHCl3).
IR (neat): 3312, 2225, 1672, 1542 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 0.96 (d, J = 7.2 Hz, 6 H), 2.45–
2.53 (m, 1 H), 4.21–4.28 (m, 2 H), 4.51 (d, J = 5.8 Hz, 2 H), 5.29
(br s, 1 H), 7.18–8.15 (m, 12 H), 9.80 (br s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 16.8, 30.5, 45.7, 58.5, 67.6,
121.2, 121.6, 125.5, 126.8, 127.4, 127.8, 140.0, 141.5, 143.3, 143.9,
155.0, 171.1.
1H NMR (400 MHz, DMSO-d6): δ = 3.80 (d, J = 5.6 Hz, 2 H), 4.24
(t, J = 8.0 Hz, 1 H), 4.48 (d, J = 6.4 Hz, 2 H), 4.68–4.75 (m, 1 H),
6.20 (br s, 1 H), 7.20–7.80 (m, 12 H), 9.80 (s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 45.3, 53.1, 60.8, 67.2, 108.9,
113.7, 121.8, 125.3, 127.4, 128.0, 128.6, 131.5, 140.2, 141.8, 143.2,
156.4, 172.8.
HRMS (ESI): m/z [M + Na]+ calcd for C26H25N3O5Na: 482.1692;
found: 482.1680.
HRMS (ESI): m/z [M + Na]+ calcd for C25H21N3O4Na: 450.1430;
found: 450.1427.
Fmoc-Leu-4-nitroanilide (4c)16f
25
Yield: 0.38 g (80%); white solid; mp 190 °C; [α]D –36.4 (c 0.1,
CHCl3).
Fmoc-Thr-2-methylanilide (5b)
25
IR (neat): 3299, 1635, 1538, 1372 cm–1.
Yield: 0.35 g (82%); white solid; mp 190 °C; [α]D –35.7 (c 0.1,
CHCl3).
1H NMR (400 MHz, DMSO-d6): δ = 0.98 (d, J = 8.4 Hz, 6 H), 1.75–
1.81 (m, 3 H), 4.22–4.31 (m, 2 H), 4.61 (d, J = 5.8 Hz, 2 H), 5.55
(br s, 1 H), 7.11–8.21 (m, 12 H), 10.60 (br s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 21.8, 22.0, 40.2, 46.5, 50.8,
66.8, 120.8, 121.5, 126.4, 126.8, 127.0, 128.0, 139.7, 141.0, 142.8,
143.4, 155.0, 170.7.
IR (neat): 3285, 1654, 1535, 1235 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 1.30 (d, J = 6.4 Hz, 3 H), 2.31
(s, 3 H), 3.91–4.01 (m, 1 H), 4.37 (t, J = 4.8 Hz, 1 H), 4.64–4.71 (m,
3 H), 5.86 (br s, 1 H), 6.87–7.03 (m, 3 H), 7.23–7.50 (m, 9 H), 9.95
(s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 14.7, 18.2, 46.9, 59.4, 66.9,
68.1, 121.8, 123.7, 125.9, 126.3, 127.8, 128.1, 128.5, 129.7, 133.8,
137.2, 140.3, 143.5, 155.8, 171.3.
HRMS (ESI): m/z [M + Na]+ calcd for C26H26N2O4Na: 453.1790;
found: 453.1735.
HRMS (ESI): m/z [M + Na]+ calcd for C27H27N3O5Na: 496.1848;
found: 496.1831.
Fmoc-Pro-4-nitroanilide (4d)16f
25
Yield: 0.32 g (69%); white solid; mp 183–184 °C; [α]D –53.4
(c 0.1, CHCl3).
IR (neat): 3315, 1658, 1543, 1425 cm–1.
Fmoc-Tyr-2-chloroanilide (5c)
25
Yield: 0.45 g (88%); white solid; mp 194–196 °C; [α]D –43.2
1H NMR (400 MHz, DMSO-d6): δ = 1.22–1.27 (m, 2 H), 1.85–1.94
(m, 2 H), 3.21–3.26 (m, 2 H), 4.12–4.18 (m, 1 H), 4.28 (t, J = 7.2
Hz, 1 H), 4.57 (d, J = 6.8 Hz, 2 H), 7.10–8.12 (m, 12 H), 9.60 (br s,
1 H).
13C NMR (75 MHz, DMSO-d6): δ = 21.8, 28.5, 46.8, 47.0, 61.5,
67.0, 121.5, 121.9, 127.2, 127.8, 128.0, 128.2, 139.9, 141.5, 143.1,
143.5, 155.2, 170.8.
(c 0.1, CHCl3).
IR (neat): 3159, 1657, 1538, 1446 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 3.10–3.18 (m, 2 H), 4.41 (t,
J = 5.2 Hz, 1 H), 4.63 (d, J = 6.2 Hz, 2 H), 4.78–4.85 (m, 1 H), 5.63
(br s, 1 H), 6.62 (s, 2 H), 6.85 (s, 2 H), 7.15–7.55 (m, 12 H), 10.25
(s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 36.3, 47.1, 53.8, 67.9, 114.3,
122.7, 125.1, 125.5, 126.5, 126.9, 127.8, 128.3, 128.9, 129.4, 130.2,
132.7, 137.4, 140.0, 142.5, 155.4, 156.2, 171.8.
HRMS (ESI): m/z [M + Na]+ calcd for C26H23N3O5Na: 480.1535;
found: 480.1530.
Synthesis 2013, 45, 2727–2736
© Georg Thieme Verlag Stuttgart · New York

PAPER
Synthesis of Nα-Protected Amino and Peptide Acid Aryl Amides
2735
HRMS (ESI): m/z [M + Na]+ calcd for C30H25ClN2O4Na: 535.1401;
found: 535.1408.
1H NMR (400 MHz, DMSO-d6): δ = 1.10 (d, J = 7.4 Hz, 6 H), 1.80–
1.83 (m, 2 H), 2.85 (d, J = 6.6 Hz, 2 H), 4.35–4.42 (m, 3 H), 5.27 (s,
2 H), 5.80 (br s, 1 H), 6.90–7.21 (m, 14 H), 7.42 (br s, 1 H), 9.72 (s,
1 H).
13C NMR (75 MHz, DMSO-d6): δ = 16.1, 21.3, 22.7, 36.8, 42.5,
50.4, 53.7, 123.7, 125.4, 125.9, 126.8, 127.1, 127.5, 127.9, 128.3,
128.8, 129.3, 131.2, 135.3, 139.1, 141.7, 156.3, 169.8, 171.4.
Fmoc-His-4-nitroanilide (5d)
25
Yield: 0.37 g (75%); white solid; mp 225–228 °C; [α]D –38.5
(c 0.1, CHCl3).
IR (neat): 3105, 2856, 1854, 1628 cm–1.
1H NMR (400 MHz, CDCl3): δ = 3.51 (d, J = 6.4 Hz, 2 H), 4.47 (t,
J = 5.4 Hz, 1 H), 4.63 (d, J = 7.2 Hz, 2 H), 4.80 (t, J = 6.2 Hz, 1 H),
6.30 (br s, 1 H), 6.75 (s, 1 H), 7.28–7.87 (m, 11 H), 8.15 (d, J = 6.8
Hz, 2 H), 9.70 (s, 1 H), 12.30 (br s, 1 H).
13C NMR (75 MHz, CDCl3): δ = 28.7, 46.4, 51.7, 66.9, 118.5,
120.9, 122.2, 126.7, 127.8, 128.6, 133.8, 135.1, 141.2, 143.0, 144.1,
144.8, 156.5, 172.1.
HRMS (ESI): m/z [M + Na]+ calcd for C29H32ClN3O4Na: 544.1979;
found: 544.1975.
Boc-Ala-Ile-4-methylanilide (7e)
Yield: 0.3 g (76%); white solid; mp 218–221 °C; [α]D25 –58.5 (c 0.1,
CHCl3).
IR (neat): 3292, 2916, 1613, 1529 cm–1.
HRMS (ESI): m/z [M + Na]+ calcd for C27H23N5O5Na: 520.1597;
found: 520.1591.
1H NMR (400 MHz, DMSO-d6): δ = 0.85 (t, J = 5.2 Hz, 3 H), 1.00
(d, J = 6.8 Hz, 3 H), 1.18–1.21 (m, 2 H), 1.37 (s, 9 H), 1.45 (d,
J = 7.4 Hz, 3 H), 2.25–2.34 (m, 1 H), 2.36 (s, 3 H), 4.40 (d, J = 6.2
Hz, 1 H), 5.61 (br s, 1 H), 6.80 (br s, 1 H), 7.15 (d, J = 5.6 Hz, 2 H),
7.62 (d, J = 5.6 Hz, 2 H), 8.63 (s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 13.1, 15.2, 18.4, 23.5, 24.6,
28.1, 35.4, 49.7, 54.1, 78.5, 120.8, 129.1, 133.5, 135.1, 156.7,
170.1, 172.3
Fmoc-Gly-Phe-3-methylanilide (7a)
25
Yield: 0.44 g (83%); white solid; mp 235–237 °C; [α]D –93.6
(c 0.1, CHCl3).
IR (neat): 3314, 2922, 1640, 1536 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 2.31 (s, 3 H), 3.05–3.16 (m, 2
H), 3.72 (s, 2 H), 4.32 (t, J = 5.4 Hz, 1 H), 4.42–4.61 (m, 3 H), 6.78
(d, J = 6.4 Hz, 1 H), 7.15–7.79 (m, 18 H), 9.10 (s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 24.1, 35.3, 41.7, 46.9, 53.4,
67.4, 119.4, 121.3, 123.4, 126.1, 126.5, 127.1, 127.8, 128.3, 128.7,
129.1, 137.9, 138.3, 139.8, 140.7, 143.2, 156.4, 169.6, 172.8.
HRMS (ESI): m/z [M + Na]+ calcd for C21H33N3O4Na: 414.2369;
found: 414.2372.
Boc-Gly-Val-4-pyrrolylanilide (7f)
25
Yield: 0.33 g (80%); white solid; mp 227–279 °C; [α]D –29.7
(c 0.1, CHCl3).
IR (neat): 3297, 2928, 1625, 1532 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 1.13 (d, J = 7.2 Hz, 6 H), 1.35
(s, 9 H), 2.31–2.37 (m, 1 H), 3.73 (d, J = 6.6 Hz, 2 H), 4.41 (d,
J = 7.0 Hz, 1 H), 5.57 (br s, 1 H), 6.13 (d, J = 5.8 Hz, 2 H), 6.83 (d,
J = 5.8 Hz, 2 H), 7.21 (d, J = 6.2 Hz, 2 H), 7.65 (d, J = 6.2 Hz, 2 H),
7.80 (br s, 1 H), 9.85 (s, 1 H).
HRMS (ESI): m/z [M + Na]+ calcd for C33H31N3O4Na: 556.2212;
found: 556.2222.
Fmoc-Val-Ala-4-chloroanilide (7b)
25
Yield: 0.45 g (86%); white solid; mp 243 °C; [α]D +79.3 (c 0.1,
CHCl3).
IR (neat): 3298, 2955, 1675, 1535 cm–1.
13C NMR (75 MHz, DMSO-d6): δ = 17.8, 27.3, 31.5, 46.1, 55.7,
78.9, 109.2, 121.7, 122.5, 124.1, 134.6, 135.4, 156.1, 170.3, 171.5.
HRMS (ESI): m/z [M + Na]+ calcd for C22H30N4O4Na: 437.2165;
found: 437.2158.
1H NMR (400 MHz, DMSO-d6): δ = 1.07 (d, J = 7.2 Hz, 6 H), 1.32
(d, J = 6.6 Hz, 3 H), 2.48–2.56 (m, 1 H), 4.43–4.50 (m, 2 H), 4.63
(d, J = 6.8 Hz, 2 H), 4.78–4.85 (m, 1 H), 6.80 (br s, 1 H), 7.25–7.90
(m, 13 H), 9.72 (s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 16.8, 17.4, 30.2, 46.8, 48.2,
58.7, 67.2, 123.7, 126.4, 127.8, 128.0, 128.3, 128.7, 129.4, 137.6,
139.5, 143.1, 156.5, 170.3, 171.7.
Cbz-Phe-Ile-Ala-4-chloroanilide (7g)
25
Yield: 0.45 g (75%); white solid; mp 235 °C; [α]D +23.4 (c 0.1,
CHCl3).
HRMS (ESI): m/z [M + Na]+ calcd for C29H30ClN3O4Na: 542.1823;
found: 542.1825.
IR (neat): 3311, 2954, 2925, 1631 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 1.03 (t, J = 7.2 Hz, 3 H), 1.15
(d, J = 6.6 Hz, 3 H), 1.32–1.40 (m, 2 H), 1.53 (d, J = 7.0 Hz, 3 H),
2.25–2.34 (m, 1 H), 2.85 (d, J = 5.8 Hz, 2 H), 3.84 (d, J = 5.4 Hz, 1
H), 4.45–4.53 (m, 1 H), 4.72–4.81 (m, 1 H), 5.21 (s, 2 H), 5.80 (br
s, 1 H), 6.64 (br s, 1 H), 7.18–7.52 (m, 14 H), 9.85 (s, 1 H).
Fmoc-Ala-Leu-4-methoxyanilide (7c)
25
Yield: 0.42 g (79%); white solid; mp 253–255 °C; [α]D +18.3
(c 0.1, CHCl3).
IR (neat): 3307, 2825, 1682, 1538 cm–1.
13C NMR (75 MHz, DMSO-d6): δ = 11.3, 15.1, 17.6, 26.1, 38.1,
38.6, 45.4, 53.1, 55.8, 64.3, 122.6, 125.4, 126.8, 127.4, 128.8,
129.5, 129.7, 134.5, 138.3, 140.2, 155.3, 168.8, 170.5, 142.3.
HRMS (ESI): m/z [M + Na]+ calcd for C32H37ClN4O5Na: 615.2350;
found: 615.2348.
1H NMR (400 MHz, DMSO-d6): δ = 0.95 (d, J = 7.2 Hz, 6 H), 1.39
(d, J = 6.2 Hz, 3 H), 1.81–1.87 (m, 3 H), 3.68 (s, 3 H), 4.42–4.53
(m, 3 H), 4.63 (d, J = 6.8 Hz, 2 H), 6.71 (d, J = 7.0 Hz, 2 H), 7.25–
7.51 (m, 12 H), 8.95 (s, 1 H).
13C NMR (75 MHz, DMSO-d6): δ = 17.5, 21.3, 22.4, 40.9, 48.4,
50.3, 50.8, 56.2, 68.1, 114.6, 122.3, 126.0, 127.6, 128.2, 131.4,
141.2, 143.1, 156.3, 156.7, 170.5, 172.4.
Boc-Gly-Ala-Ile-anilide (7h)
25
Yield: 0.33 g (76%); white solid; mp 241–243 °C; [α]D +68.3
HRMS (ESI): m/z [M + Na]+ calcd for C31H35N3O5Na: 552.2474;
found: 552.2471.
(c 0.1, CHCl3).
IR (neat): 3295, 2961, 2884, 1626 cm–1.
1H NMR (400 MHz, DMSO-d6): δ = 0.87 (t, J = 4.8 Hz, 3 H), 1.09
(d, J = 6.4 Hz, 3 H), 1.20–1.27 (m, 2 H), 1.34 (s, 9 H), 1.48 (d,
J = 6.8 Hz, 3 H), 2.80–2.89 (m, 1 H), 3.51 (s, 2 H), 4.43 (d, J = 7.6
Hz, 1 H), 4.78–4.85 (m, 1 H), 5.23 (br s, 1 H), 6.82 (br s, 1 H), 7.10–
7.35 (m, 5 H), 10.23 (s, 1 H).
Cbz-Phe-Leu-2-chloroanilide (7d)
25
Yield: 0.42 g (81%); white solid; mp 231–232 °C; [α]D –123.5
(c 0.1, CHCl3).
IR (neat): 3283, 2846, 1698, 1535 cm–1.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 2727–2736

2736
C. Madhu et al.
PAPER
13C NMR (75 MHz, DMSO-d6): δ = 12.1, 14.3, 16.8, 26.2, 28.4,
38.2, 43.2, 47.8, 56.5, 79.7, 120.6, 123.9, 129.4, 136.3, 155.72,
169.4, 171.5.
HRMS (ESI): m/z [M + Na]+ calcd for C22H34N4O5Na: 457.2427;
found: 457.2454.
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Thunnissen, M.; Trinh, L.; Whitlow, M.; Ye, B.; Ye, H.;
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Acknowledgment
We thank the Department of Science and Technology (DST) for the
financial assistance. C.M. thanks UGC for the award of SRF.
T.M.V. is grateful to the CSIR for the award of SRF.
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Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.SnuIomprifgtooatrinSugpIoi
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nfomartit
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Synthesis 2013, 45, 2727–2736
© Georg Thieme Verlag Stuttgart · New York