Cyclic dipeptides exhibit potency for scavenging radicals

Article abstract of DOI:10.1016/j.bmc.2012.01.050

Twenty kinds of cyclic dipeptides containing l-leucine were synthesized, and their antioxidant activity against ^.OH and O2·- was investigated. Compounds possessing polar amino acid residues, such as Asp, Cys, Glu, Lys, Pro, Ser, and Trp, exhibited higher antioxidant activity against ^.OH than vitamin E. However, only cyclo(l-Cys-l-Leu) scavenged O2·-.

Full text of DOI:10.1016/j.bmc.2012.01.050

Bioorganic & Medicinal Chemistry 20 (2012) 2002–2009
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Cyclic dipeptides exhibit potency for scavenging radicals
Tadashi Furukawa a, Takashi Akutagawa a, Hitomi Funatani a, Toshikazu Uchida a, Yoshihiro Hotta b,c
,
Masatake Niwa a, Yoshiaki Takaya a,
⇑
a Faculty of Pharmacy, Meijo University, 150 Yagotoyama, Tempaku, Nagoya 468-8503, Japan
b College of Pharmacy, Kinjo Gakuin University, Omori, Moriyama, Nagoya 463–8521, Japan
c Department of Pharmacology, Aichi Medical University, School of Medicine, Nagakute, Aichi 480–1195, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Twenty kinds of cyclic dipeptides containing
L
-leucine were synthesized, and their antioxidant activity
ꢀꢁ
Å
Received 7 January 2012
Revised 26 January 2012
Accepted 27 January 2012
Available online 3 February 2012
against OH and O2 was investigated. Compounds possessing polar amino acid residues, such as Asp,
Cys, Glu, Lys, Pro, Ser, and Trp, exhibited higher antioxidant activity against ÅOH than vitamin E. However,
only cyclo(L-Cys–L .
-Leu) scavenged O2ꢀꢁ
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Cyclic dipeptide
Antioxidant
ESR
Hydroxy radical
Superoide radical
1. Introduction
of cyclo(
L
-Leu-
L
-Tyr) against postischemic myocardial dysfunc-
tion.16 In this way, cyclic dipeptides can exhibit interesting biolog-
Cyclicpeptides play important roles in biology. Many drugs,
such as cyclosporine and colistin, contain a cyclicpeptide structure.
Cyclosporin is an immunosuppressant and is used for treatment of
autoimmune disease and rejection of internal organ transplants.
Colistin treats multiple-drug-resistant Pseudomonas aeruginosa.
RAs1 and trapoxin,2 which are cyclic hexapeptide and cyclic tetra-
peptide, respectively, were reported to exhibit antitumor activity.
Thus, cyclicpeptides indicate various biological activities. Among
them, cyclicdipeptides (CDPs) belong to a group of compounds
with the simplest structure.
ical activities. In this study, we synthesized CDPs containing L-Leu
and examined their antioxidant activity by using ESR to investi-
gate the amino acid contribution to the activity.
2. Chemistry
A general synthetic scheme for most cyclic dipeptides is shown
in Figure 1. A N-protected-L-amino acid and a L-amino acid methyl
ester were used as starting materials.17 They were treated with
´
N,N-dicyclohexylcarbodiimide (DCC) in the presence of triethyl-
CDPs are generated by cyclization of two amino acids, and they
characteristically contain a 2,5-diketopiperazine skeleton. CDPs are
found in various foods and beverages such as cocoa,3 roasted cof-
fee,4 beer5 and Japanese sake.6 Their bitter taste is unique. CDPs
were also isolated from marine fungus7–11 and were reported to
have biological activity, antimicrobacterial activity,12 antitumor
activity,13 platelet-activating factor inhibitory activity,14 etc.
We previously reported that several CDPs were contained in the
distillation residue of awamori spirits,15 and they exhibited
antioxidant activity by the bleomycin-Fe method. Most CDPs
amine (TEA) to give a N-protected-dipeptide methyl ester (1).
The dipeptides except for compounds 1P and 1Q were treated with
4 M HCl–1,4-dioxane followed by refluxing in 0.1 M acetic acid–2-
butanol with N-methylmorphorine (NMM) for 3 h to give CDPs (3).
N-Boc-
methyl ester by treatment with 4 M HCl–1,4-dioxane, then the es-
ter was refluxed in benzene for 3 days to afford cyclo( -Leu- -Pro)
-Leu methyl ester (1Q)
L-Leu-L-Pro methyl ester (1P) was converted into L-Leu-L-Pro
L
L
a
x
(3P). On the other hand, N -Z-N -Trt-L-Gln-L
was treated with Pd-C in methanol to remove the Z-group. The
resulting dipeptide methyl ester in 0.1 M acetic acid–2-butanol
x
contained of L-Leu and other amino acids, and exhibited nearly
identical activities. Moreover, we reported the protective effects
was refluxed 1 h with NMM to afford cyclo(N -Trt-
L
-Gln-
L
-Leu)
(2Q). Compound 2Q was further treated with 50% trifluoroacetic
acid-dichloromethane to give cyclo( -Gln-
-Leu) (3Q).18 Cyclo
-Cys- -His- -Glu- -Leu)
-Leu) (3C),19 cyclo( -Leu) (3H),20 cyclo(
(3E), cyclo( -Leu- -Lys) (3K) and cyclo( -Arg-
-Leu) (3R)21 were
L
L
(L
L
L
L
L
L
⇑
Corresponding author.
E-mail address: ytakaya@meijo-u.ac.jp (Y. Takaya).
L
L
L
L
0968-0896/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2012.01.050

T. Furukawa et al. / Bioorg. Med. Chem. 20 (2012) 2002–2009
2003
Figure 1. General scheme for preparation of cyclic dipeptides.
prepared by deprotection on the side chains, respectively, after
generation of diketopiperazines (2).
of these functional groups would contribute more to antioxidant
activity than the generation of radical on the carbon as men-
a
tioned above. We tried to identify products of the oxidation reac-
tion by hydroxyl radical. However, the amount of the products
were too small to discuss their structure. So the precise mechanism
for scavenging radicals on the side chain of the amino acid residue
is not clear yet, and its investigation is in progress. On the other
hand, only 3C exhibited antioxidant activity against Oꢀ2ꢁ (83.3%,
IC50 8.8 ꢂ 10ꢁ4 M) at a concentration of 2.5 ꢂ 10ꢁ5 M, but other
CDPs did not exhibit antioxidant activity. The potency of com-
pound 3C should due to the thiol group on the side chain to form
S–S linkage to exhibit the radical scavenging effect.
As mentioned above, the contribution of an amino acid residue
with highly polar functional groups in the side chains to the anti-
oxidant activity is critical. In addition to investigating the mecha-
nism of antioxidant activity, we are now examining the activity
of CDPs that consist of an amino acid with a highly polar side chain.
3. Antioxidant activity
Å
We investigated antioxidant activities of CDPs against OH and
Oꢀ2ꢁ using ESR spectra.22 Among the CDPs tested, some (3S, 3M,
3W, 3P, 3C, 3D, 3E and 3K) exhibited higher antioxidant activity
against ÅOH at a concentration of 2.5 ꢂ 10ꢁ5 M than vitamin E used
as a positive control (37.7% inhibition). In particular, 3D showed
the highest antioxidant activity (95.0%, IC50 4.0 ꢂ 10ꢁ6 M). On the
other hand, only 3C exhibited high activity against Oꢀ2ꢁ (83.3%,
8.8 ꢂ 10ꢁ4 M) at the same concentration, but other CDPs did not
exhibit antioxidant activity as shown in Table 1.
4. Discussion
We synthesized 20 kinds of CDPs, which all contain L-Leu, and
5. Experimental
5.1. General
investigated antioxidant activities by using ESR. Most of the CDPs
Å
scavenged OH. Radicals on the
a-position of the peptide carbonyl
group can be conveniently produced by H-atom abstraction from
Å
CDPs by OH.23 According to this theory, the antioxidant activity
Infrared spectra were recorded on the FT-IR-410 spectropho-
tometer. 1H and 13C NMR spectra were recorded on the JEOL
ECA-500 (1H: 500 MHz and 13C: 125 MHz) and JEOL JNM A-400
(1H: 400 MHz and 13C: 100 MHz) spectrometers. Chemical shifts
for 1H and 13C NMR are given in parts per million (d) relative to sol-
vent signal (methanol-d4; dH 3.30 and dC 49.0, and chloroform-d; dH
7.24 and dC 77.7) as the internal standard. FAB-MS were obtained
with a JEOL JMS HX-110 spectrometer, and m-nitrobenzyl alcohol
was used as a matrix. Analytical TLC was performed on silica gel
of CDPs is demonstrated by this mechanism, and CDP radicals
would become hydroxyL-CDPs or CDP dimers. Moreover the
potency of antioxidant activity against ÅOH should be almost iden-
tical. However, among the CDPs tested, some (3S, 3M, 3W, 3P, 3C,
Å
3D, 3E and 3K) exhibited higher antioxidant activity against OH
than vitamin E, and some did not. On the basis of the evidence that
most of the CDPs that possessed high antioxidant activity tend to
have the highly polar functional group on their side chains, such
as carboxylic group and amino group, the radical scavenging effect
Table 1
Radical scavenging activity of cyclic dipeptides
ÅOH
Oꢀ2ꢁ
Inhibition ratea (%)
IC50 (M)
Inhibition ratea (%)
IC50 (M)
Cyclo(Gly-
-Ala-
-Leu-
-Ile- -Leu) (3I)
L
-Leu) (3G)
-Leu) (3A)
-Val) (3V)
0.0 0.10
—
—
—
—
0.0 0.13
0.0 0.15
0.0 0.23
—
—
—
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
Cyclo(
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
12.3 0.12
9.7 0.09
26.0 0.14
95.2 0.04
0.0 0.11
79.0 0.11
88.9 0.02
23.5 0.12
L
-Leu-
-Leu-
-Leu-
-Leu-
L
L
L
L
-Leu) (3L)
-Ser) (3S)
-Thr) (3T)
-Met) (3M)
-Leu) (3C)
—
0.0 0.05
0.0 0.25
0.0 0.17
0.0 0.08
83.3 0.01
0.0 0.24
—
—
—
—
1.0 ꢂ 10ꢁ3
—
8.0 ꢂ 10ꢁ4
1.0 ꢂ 10ꢁ4
—
-Cys-
L
8.8 ꢂ 10ꢁ4
-Leu-
-Leu-
-Leu-
L
-Phe) (3F)
-Tyr) (3Y)
-Trp) (3W)
—
—
—
—
—
—
—
—
—
—
—
L
L
66.0 0.33
83.9 0.05
95.0 0.02
97.8 0.21
96.0 0.15
19.0 0.14
—
96.0 0.05
86.2 0.03
37.7
1.8 ꢂ 10ꢁ3
8.5 ꢂ 10ꢁ4
4.0 ꢂ 10ꢁ6
8.0 ꢂ 10ꢁ5
1.7 ꢂ 10ꢁ4
—
0.0 0.21
0.0 0.17
0.0
0.0 0.26
0.0 0.30
0.0 0.19
-His-
L-Leu) (3H)
-Asp-
L
-Leu) (3D)
-Glu-
L-Leu) (3E)
-Asn-
L
-Leu) (3N)
-Leu) (3Q)
-Leu) (3R)
-Gln-
-Arg-
L
L
-Leu-
-Leu-
L
-Lys) (3K)
1.6 ꢂ 10ꢁ4
1.1 ꢂ 10ꢁ3
0.0 0.25
0.0 0.02
32.3
L-Pro) (3P)
Vitamin E
a
At 2.5 ꢂ 10ꢁ3 M.

2004
T. Furukawa et al. / Bioorg. Med. Chem. 20 (2012) 2002–2009
60 F254 (Merck). Column chromatography was carried out on silica
gel BW-820MH (Fuji Silysia Chemicals, Co. Ltd, Seto, Japan).
5.2.4. N-Boc-5-benzyL-L-Glu-L-Leu methyl ester (1E)
Yield 94%; white powder; ½a D25
ꢃ
: ꢁ31.7 (c 0.20, MeOH); IR mmax
Develosil ODS MG-5 (
u
20 ꢂ 250 mm, Nomura Chemical, Seto,
(KBr): 3338, 2954, 1745, 1726, 1685, 1656 cmꢁ1 1H NMR
;
Japan) was used for preparative HPLC. ESR spectra were recorded
on the JEOL JES FR-30 spectrometer. The operated conditions for
the ESR to estimate the concentration of superoxide anion radicals
were as follows: magnetic field, 335.7 5 mT; power, 4 mW 9.414
GHz; modulation, 100 kHz 1 ꢂ 0.079 mT; response, 0.1 s; tempera-
ture, 25 °C; amplitude, 160; and sweep time, 2 min, respectively.
For the determination of hydroxy radicals, the magnetic field,
power, modulation, response, temperature, amplitude, and sweep
time were 335.7 5 mT, 4 mW 9.414 GHz, 100 kHz 1 ꢂ 0.079 mT,
0.1 s, 25 °C, 160 and 2 min, respectively. Hypoxantine, diethylene-
triaminepentaacetic acid (DETAPAC) and xantine oxidase from
bovine milk were purchased from Sigma–Aldrich Co. 5,5-Dime-
(500 MHz, CD3OD, dH): 0.89 (3H, d, J = 6.8 Hz), 0.93 (3H, d,
J = 6.8 Hz), 1.42 (9H, s), 1.59 (3H, m), 1.95 (1H, m), 2.06 (1H, m),
2.47 (2H, t, J = 7.4 Hz), 3.66 (3H, s), 4.12 (1H, t, J = 6.2 Hz), 4.45
(1H, dd, J = 5.7, 9.2 Hz), 5.12 (2H, s), 7.33 (5H, m); 13C NMR
(125 MHz, CD3OD, dC): 21.8, 23.3, 25.8, 28.5, 28.5, 28.7, 31.3,
34.8, 41.3, 52.1, 57.7, 64.9, 67.4, 80.6, 129.2, 129.5, 137.6, 157.7,
174.3, 174.4, 174.5; HRMS–FAB: m/z 465.2578 [M+H]+ calcd for
C
25H39N2O7 465.2601; FAB-MS (positive): m/z 465 [M+H]+.
5.2.5. N-Boc-L-Leu-L-Phe methyl ester (1F)
Yield 77%; white powder; ½a D25
ꢃ
: ꢁ17.3 (c 0.10, MeOH); IR mmax
(KBr): 3329, 3285, 2954, 1748, 1686, 1657 cmꢁ1
;
1H NMR
thy
L
-1-pyrroline N-oxide (DMPO) was purchased from Labotec
(400 MHz, CDCl3, dH): 0.86 (3H, d, J = 6.6 Hz), 0.89 (3H, d,
J = 6.6 Hz), 1.42 (9H, s), 1.61 (2H, m), 1.94 (1H, m), 3.06 (1H, dd,
J = 7.7, 13.6 Hz), 3.15 (1H, dd, J = 7.7, 13.6 Hz), 3.69 (3H, s), 4.05
(1H, br s), 4.74 (1H, br s), 4.82 (1H, dd, J = 5.8, 13.6 Hz), 6.43 (1H,
d, J = 9.7 Hz), 7.25 (5H, m); 13C NMR (125 MHz, CDCl3, dC): 21.9,
22.8, 24.7, 28.3, 33.9, 37.9, 41.2, 49.1, 52.3, 53.1, 80.0, 127.1,
128.5, 129.3, 135.7, 156.7, 171.6, 172.1; HRMS–FAB: m/z
393.2386 [M+H]+ calcd for C21H33N2O5 393.2389; FAB-MS (posi-
tive): m/z 393 [M+H]+.
(Tokyo). Other chemicals used were of analytical grade.
5.2. General procedure for the synthesis of N-Boc-dipeptide me
thyl ester (1)
To a solution of
dichloromethane, triethylamine (1 equiv) and N-Boc-
L-amino acid methyl ester hydrochloride in
L-amino acid
were added at ꢁ15 °C, and DCC was added as a dichloromethane
solution at 0 °C. The reaction mixture was stirred at 0 °C for 1 h.
Then the solution was stirred at room temperature for 3 h. The dicy-
clohexylurea was removed by filtration from the reaction mixture.
The solution was washed with 5% NaHCO3, 1 M HCl, and brine.
The organic layer was dried over anhydrous Na2SO4 and evaporated.
The product was purified by silica gel column chromatography.
5.2.6. N-Boc-Gly-L-Leu methyl ester (1G)
Yield: 83%; white powder; ½a D25
ꢃ
: ꢁ22.4 (c 0.06, MeOH); IR mmax
(KBr): 3261, 3237, 3067, 1690, 1625 cmꢁ1
;
1H NMR (500 MHz,
CD3OD, dH): 0.90 (3H, d, J = 5.6 Hz), 0.93 (3H, d, J = 5.6 Hz), 1.31
(1H, m), 1.44 (9H, s), 1.61 (2H, m), 3.69 (3H, s), 3.71 (2H, s), 4.48
(1H, m); 13C NMR (125 MHz, CDCl3, dC): 21.8, 22.7, 24.7, 28.2,
41.5, 44.3, 50.6, 52.3, 80.3, 156.0, 169.2, 173.2; HRMS–FAB: m/z
325.1746 [M+Na]+ calcd for C14H26N2O5Na 325.1739; FAB-MS (po-
sitive): m/z 325 [M+Na]+.
5.2.1. N-Boc-L-Ala-L-Leu methyl ester (1A)
Yield 97%; white powder; ½a D25
ꢃ
: ꢁ47.0 (c 0.10, MeOH); IR mmax
(Film): 3019, 2961, 1739, 1683 cmꢁ1
;
1H NMR (500 MHz, CDCl3,
dH): 0.83 (3H, d, J = 6.6 Hz), 0.85 (3H, d, J = 6.6 Hz), 1.19 (3H, d,
J = 7.3 Hz), 1.34 (9H, s), 1.51 (2H, m), 1.61 (m), 3.60 (3H, s), 3.99
(1H, br d, J = 6.4 Hz), 4.36 (1H, dd, J = 5.9, 9.2 Hz); 13C NMR
(125 MHz, CDCl3, dC); 17.9, 21.7, 22.7, 24.7, 28.2, 41.3, 49.3, 49.8,
50.6, 52.2, 80.0, 155.5, 172.4, 173.2: HRMS–FAB: m/z 317.2083
[M+H]+ calcd for C15H29N2O5 317.2076; FAB-MS (positive): m/z
317 [M+H]+.
a
p
5.2.7. N -Boc-N -BOM-L-His-L-Leu methyl ester (1H)
Yield 70%; white powder; ½a D25
ꢃ
: ꢁ20.2 (c 0.20, MeOH); IR mmax
(Film): 3422, 3330, 3214, 3015, 2959, 1742, 1678 cmꢁ1
;
1H NMR
(400 MHz, CDCl3, dH): 0.85 (3H, d, J = 6.6 Hz), 0.87 (3H, d,
J = 6.6 Hz), 1.39 (9H, s), 1.45 (3H, m), 3.04 (1H, dd, J = 7.7,
15.4 Hz), 3.10 (1H, dd, J = 7.6, 15.4 Hz), 3.68 (3H, s), 4.48 (1H, m),
4.50 (2H, s), 4.50 (2H, m), 6.92 (1H, br s), 7.30 (5H, m), 7.61 (br
s); 13C NMR (125 MHz, CDCl3, dC): 21.7, 22.7, 24.6, 26.6, 28.2,
41.2, 50.6, 52.2, 53.7, 69.9, 73.0, 80.2, 127.2, 128.1, 128.3, 128.7,
129.4, 135.9, 155.4, 170.6, 172.7; HRMS–EI: m/z 502.2773 [M]+
calcd for C26H38N4O6 502.2791; EI-MS: m/z 502 [M]+.
5.2.2. N-Boc-S-4-methoxybenzy -L-Cys-L-Leu methyl ester (1C)
Yield 82%; white powder; ½aꢃ2DL5: ꢁ25.9 (c 0.10, MeOH); IR mmax
(Film): 3314, 2956, 2932, 1744, 1682, 1657 cmꢁ1
;
1H NMR
(400 MHz, CDCl3, dH): 0.90 (3H, d, J = 6.6 Hz), 0.92 (3H, d,
J = 6.6 Hz), 1.30 (1H, m), 1.40 (9H, s), 1.55 (2H, m), 2.70 (1H, dd,
J = 7.0, 14.3 Hz), 2.83 (1H, dd, J = 5.5, 14.3 Hz), 3.69 (3H, s), 3.77
(3H, s), 4.20 (1H, br s), 4.57 (1H, dt, J = 4.8, 8.4 Hz), 5.24 (1H, br
s), 6.67 (1H, br s), 6.82 (2H, d, J = 9.6 Hz), 7.23 (2H, d, J = 9.6 Hz);
13C NMR (125 MHz, CDCl3, dC): 21.8, 22.8, 24.7, 28.2, 33.4, 33.9,
35.9, 41.4, 50.9, 52.2, 55.2, 80.3, 114.0, 129.8, 130.1, 155.3, 158.7,
170.4, 172.8; HRMS–FAB: m/z 469.2369 [M+H]+ calcd for
5.2.8. N-Boc-L-Ile-L-Leu methyl ester (1I)
Yield 44%; white powder; ½a D25
ꢃ
: ꢁ46.4 (c 0.10, MeOH); IR mmax
(KBr): 3330, 3276, 3078, 2963, 1756, 1685, 1648 cmꢁ1
;
1H NMR
(400 MHz, CDCl3, dH): 0.92 (12H, m), 1.42 (9H, s), 1.57 (5H, m),
1.84 (1H, br s), 3.70 (3H, s), 3.89 (1H, dd, J = 6.6, 8.8 Hz), 4.60
(1H, dt, J = 4.8, 8.6 Hz), 5.00 (1H, br d, J = 7.0 Hz), 6.16 (1H, br d,
J = 6.6 Hz); 13C NMR (125 MHz, CDCl3, dC): 11.3, 15.4, 21.8, 22.7,
24.7, 24.8, 37.1, 41.4, 50.6, 52.2, 59.2, 79.8, 155.7, 171.4, 173.1;
HRMS–FAB: m/z 359.2549 [M+H]+ calcd for C18H35N2O5
359.2546; FAB-MS (positive): m/z 359 [M+H]+.
C
23H37N2O6S 469.2372; FAB-MS (positive): m/z 469 [M+H]+.
5.2.3. N-Boc-4-benzyL-L-Asp-L-Leu methyl ester (1D)
Yield 89%; white powder; ½a D25
ꢃ
: ꢁ23.5 (c 0.10, MeOH); IR mmax
(KBr): 3416, 3332, 2959, 1739, 1684 cmꢁ1
;
1H NMR (400 MHz,
a
e
CDCl3, dH): 0.91 (3H, d, J = 6.0 Hz), 0.92 (3H, d, J = 6.0 Hz), 1.45
(9H, s), 1.54 (1H, m), 1.64 (2H, m), 2.72 (1H, dd, J = 6.4, 17.0 Hz),
3.02 (1H, dd, J = 4.5. 17.0 Hz), 3.70 (3H, s), 4.55 (1H, m), 5.14 (1H,
dd, J = 12.0, 17.0 Hz), 6.88 (1H, br d, J = 7.2 Hz), 7.34 (5H, m); 13C
NMR (125 MHz, CDCl3, dC): 21.8, 22.8, 24.7, 28.2, 36.0, 41.3, 50.5,
50.9, 52.0, 66.8, 80.5, 128.2, 128.3, 128.6, 135.4, 155.5, 170.5,
171.8, 172.9; HRMS–FAB: m/z 451.2407 [M+H]+ calcd for
5.2.9. N -Boc-N -Z-L-Lys-L-Leu methyl ester (1K)
Yield 44%; white powder; ½a D25
ꢃ
: ꢁ23.8 (c 0.10, MeOH); IR mmax
(Film): 3431, 3329, 3017, 2957, 1707, 1675 cmꢁ1
;
1H NMR
(500 MHz, CDCl3, dH): 0.85 (6H, d, J = 5.5 Hz), 1.36 (9H, s), 1.47
(3H, m), 1.61 (5H, m), 1.78 (m), 3.12 (2H, m), 3.61 (3H, s), 4.02
(m), 4.52 (m), 5.02 (2H, s), 7.37 (5H, m); 13C NMR (125 MHz, CDCl3,
dC): 21.7, 22.3, 22.9, 24.7, 24.9, 28.2, 29.3, 31.7, 40.3, 41.2, 50.7,
52.3, 54.1, 66.6, 80.0, 128.1, 128.4, 136.6, 155.7, 156.6, 171.9,
C
23H35N2O7 451.2444; FAB-MS (positive): m/z 451 [M+H]+.

T. Furukawa et al. / Bioorg. Med. Chem. 20 (2012) 2002–2009
2005
173.3; HRMS–FAB: m/z 508.3012 [M+H]+ calcd for C26H42N3O7
508.3023; FAB-MS (positive): m/z 508 [M+H]+.
[M+H]+ calcd for C18H35N6O7 447.2567; FAB-MS (positive): m/z
447 [M+H]+.
5.2.10. N-Boc-
L
-Leu-
L
-Leu methyl ester (1L)
5.2.16. N-Boc-L-Leu-L-Ser methyl ester (1S)
Yield 57%; white powder; ½a D25
ꢃ
: ꢁ44.1 (c 0.10, MeOH); IR mmax
Yield 57%; white powder; ½a D25
ꢃ
: ꢁ14.0 (c 0.10, MeOH); IR mmax
(Film): 3434, 3346, 3019, 2961, 1740, 1697, 1682 cmꢁ1
;
1H NMR
(Film): 3432, 3019, 1743, 1677 cmꢁ1 1H NMR (400 MHz, CDCl3,
;
(400 MHz, CDCl3, dH): 0.92 (12H, m), 1.24 (9H, s), 1.60 (6H, m),
3.71 (3H, s), 4.06 (1H, br s), 4.59 (1H, dt, J = 5.1, 9.2 Hz), 4.81 (1H,
br s), 6.37 (1H, br d, J = 7.0 Hz); 13C NMR (125 MHz, CDCl3, dC):
21.8, 22.1, 22.8, 24.7, 28.2, 33.9, 40.8, 41.5, 50.6, 52.2, 52.9, 80.0,
155.7, 172.2, 173.1; HRMS–FAB: m/z 359.2512 [M+H]+ calcd for
dH): 0.92 (3H, d, J = 6.6 Hz), 0.93 (3H, d, J = 6.6 Hz), 1.43 (9H, s),
1.48 (1H, m), 1.64 (2H, m), 3.77 (3H, s), 3.92 (2H, m), 4.07 (1H,
m), 4.62 (1H, dt, J = 3.7, 7.3 Hz), 4.99 (1H, d, J = 7.0 Hz), 6.93 (1H,
br d, J = 7.3 Hz); 13C NMR (125 MHz, CD3OD, dC): 21.9, 23.5, 25.9,
28.7, 42.0, 52.8, 54.5, 56.1, 62.8, 80.7, 157.9, 172.000, 175.8;
HRMS–FAB: m/z [M+H]+ 333.2014 calcd for C15H29N2O6
333.2026; FAB-MS (positive): m/z 333 [M+H]+.
C
18H35N2O5 359.2546; FAB-MS (positive): m/z 359 [M+H]+.
5.2.11. N-Boc-L-Met-L-Leu methyl ester (1M)
Yield 71%; white powder; ½a D25
ꢃ
: ꢁ27.0 (c 0.10, MeOH); IR mmax
5.2.17. N-Boc-L-Thr-L-Leu methyl ester (1T)
(Film): 3422, 3333, 3017, 2960, 1743, 1680 cmꢁ1
;
1H NMR
Yield 97%; white powder; ½a D25
ꢃ
: ꢁ37.7 (c 0.10, MeOH); IR mmax
(500 MHz, CDCl3, dH): 0.89 (6H, d, J = 5.5 Hz), 1.41 (9H, s), 1.52
(1H, m), 1.63 (2H, m), 1.90 (1H, m), 2.03 (1H, m), 2.03 (3H, s),
2.56 (2H, t, J = 7.3 Hz), 3.69 (3H, s), 4.27 (1H, m), 4.56 (1H, ddd,
J = 4.1, 8.7, 12.9 Hz), 5.19 (1H, d, J = 7.8 Hz), 6.58 (1H, d,
J = 6.9 Hz); 13C NMR (125 MHz, CDCl3, dC): 12.5, 21.7, 22.8, 24.7,
28.2, 30.0, 31.3, 50.7, 52.2, 53.1, 80.1, 156.5, 171.3, 173.0; HRMS–
FAB: m/z 377.2094 [M+H]+ calcd for C17H33N2O5S 377.2110; FAB-
MS (positive): m/z 377 [M+H]+.
(Film): 3329, 2960, 2872, 1744, 1700, 1654 cmꢁ1 1H NMR (400
;
MHz, CD3OD, dH): 0.91 (3H, d, J = 6.8 Hz), 0.93 (3H, d, J = 6.8 Hz),
1.19 (3H, d, J = 5.5 Hz), 1.45 (9H, s), 1.60 (2H, m), 1.70 (1H, m), 3.69
(3H, s), 4.02 (2H, m), 4.48 (1H, dd, J = 5.9, 9.2 Hz); 13C NMR (125
MHz, CD3OD, dC): 17.9, 21.6, 22.8, 24.7, 28.2, 41.0, 50.7, 52.3, 57.6,
66.7, 80.3, 156.4, 171.5, 173.1; HRMS–FAB: m/z 347.2197 [M+H]+
calcd for C16H31N2O6 347.2182; FAB-MS (positive): m/z 347 [M+H]+.
5.2.18. N-Boc-L-Leu-L-Val methyl ester (1V)
5.2.12. N-Boc-
L
-Asn-
L
-Leu methyl ester (1N)
Yield 67%; white powder; ½a D25
ꢃ
: ꢁ33.4 (c 0.1, MeOH); IR mmax
Yield 46%; white powder; ½a D25
ꢃ
: ꢁ35.3 (c 0.10, MeOH); IR mmax
(Film): 3436, 3328, 3070, 2964, 1739, 1686 cmꢁ1 1H NMR
;
(KBr): 3412, 3317, 3206, 2958, 1741, 1685, 1667 cmꢁꢁ1
;
1H NMR
(400 MHz, CDCl3, dH): 0.92 (12H, m), 1.42 (9H, s), 1.43 (1H, m),
1.65 (2H, m), 2.15 (1H, m), 3.71 (3H, s), 4.09 (1H, br s), 4.51 (1H,
dd, J = 4.9, 8.5 Hz), 4.82 (1H, br s), 6.52 (1H, br d, J = 4.8 Hz); 13C
NMR (125 MHz, CDCl3, dC): 17.5, 18.9, 22.1, 22.8, 24.7, 28.2, 31.2,
40.6, 52.1, 56.9, 80.0, 155.7, 172.1, 172.4; HRMS–FAB: m/z
345.2383 [M+H]+ calcd for C17H33N2O5 345.2389; FAB-MS (posi-
tive): m/z 345 [M+H]+.
(500 MHz, CD3OD, dH): 0.92 (3H, d, J = 6.4 Hz), 0.93 (3H, d,
J = 6.4 Hz), 1.43 (9H, s), 1.62 (2H, m), 1.71 (1H, m), 2.56 (1H, dd,
J = 7.8, 15.6 Hz), 2.65 (1H, dd, J = 5.0, 15.6 Hz), 3.69 (3H, s), 4.45
(2H, m); 13C NMR (125 MHz, CD3OD, dC): 21.8, 23.3, 25.8, 27.0,
28.5, 28.6, 38.1, 41.5, 52.2, 52.7, 52.7, 157.5, 174.0, 174.4, 175.0;
HRMS–FAB: m/z 360.2147 [M+H]+ calcd for C16H30N3O6
360.2135; FAB-MS (positive): m/z 360 [M+H]+.
5.2.19. N-Boc-L-Trp-L-Leu methyl ester (1W)
5.2.13. N-Boc-
L
-Leu-
L
-Pro methyl ester (1P)
Yield 94%; white powder; ½a D25
ꢃ
: ꢁ14.7 (c 0.10, MeOH); IR mmax
Yield 87%; white powder; ½a D25
ꢃ
: ꢁ85.1 (c 0.10, MeOH); IR mmax
(Film): 3329, 2960, 2872, 1744, 1700, 1654 cmꢁ1 1H NMR
;
(KBr): 3328, 2958, 1750, 1709, 1648 cmꢁ1
;
1H NMR (500 MHz,
(400 MHz, CDCl3, dH): 0.82 (3H, d, J = 6.7 Hz), 0.84 (3H, d,
J = 6.7 Hz), 1.41 (9H, s), 1.48 (3H, m), 3.16 (1H, dd, J = 6.3,
14.7 Hz), 3.26 (1H, dd, J = 5.1, 14.7 Hz), 3.61 (3H, s), 4.42 (1H, br
s), 4.48 (1H, m), 5.57 (1H, br s), 6.22 (1H, d, J = 8.1 Hz), 7.02 (1H,
br s), 7.09 (1H, t, J = 8.7 Hz), 7.16 (1H, t, J = 8.7 Hz), 7.32 (1H, d,
J = 8.7 Hz), 7.63 (1H, d, J = 8.7 Hz), 8.32 (s); 13C NMR (125 MHz,
CD3OD, dC): 21.9, 23.3, 25.7, 28.6, 34.8, 41.6, 52.0, 52.6, 56.7,
80.6, 110.9, 112.2, 119.4, 122.3, 124.6, 128.9, 138.0, 157.6, 174.3,
174.8; HRMS–FAB: m/z 432.2485 [M+H]+ calcd for C23H34N3O5
432.2498; FAB-MS (positive): m/z [M+H]+ 432.
CD3OD, dH): 0.92 (6H, d, J = 6.2 Hz), 1.38 (9H, s), 1.40 (m), 1.90
(5H, m), 2.22 (m), 3.57 (m), 3.65 (3H, s), 3.80 (1H, br dd, J = 5.8,
14.7 Hz), 4.33 (1H, br s), 4.42 (1H, m); 13C NMR (125 MHz, CD3OD,
dC): 21.9, 23.6, 25.8, 25.9, 29.9, 34.8, 41.3, 48.2, 50.9, 52.6, 60.4,
80.5, 158.0, 174.0, 174.1; HRMS–FAB: m/z 343.2222 [M+H]+ calcd
for C17H31N2O5 343.2233; FAB-MS (positive): m/z 343 [M+H]+.
a
x
5.2.14. N -Z-N -Trt-L-Gln-L-Leu methyl ester (1Q)
Yield 45%; white powder; ½a D25
ꢃ
: ꢁ1.9 (c 0.14, MeOH); IR mmax
(KBr): 3310, 3030, 2956, 1670 cmꢁ1
;
1H NMR (500 MHz, CD3OD,
dH): 0.88 (3H, d, J = 8.7 Hz), 0.90 (3H, d, J = 8.7 Hz), 1.57 (2H, t,
J = 6.8 Hz), 1.68 (1H, m), 1.85 (1H, m), 2.01 (1H, m), 2.44 (2H, m),
3.64 (3H, s), 4.14 (1H, dd, J = 5.7, 8.5 Hz), 4.42 (1H, t, J = 7.4 Hz),
5.07 (2H, d, J = 2.3 Hz), 7.22 (20H, m); 13C NMR (125 MHz, CD3OD,
dC): 21.8, 23.3, 25.9, 29.2, 33.6, 41.2, 49.9, 52.2, 52.7, 55.5, 67.7,
71.6, 127.8, 128.7, 128.9, 129.0, 130.0, 138.2, 145.9, 158.3, 174.3,
174.6; HRMS–FAB: m/z 650.7981 [M+H]+ calcd for C39H45N3O6
650.7974; FAB-MS (positive): m/z 650 [M+H]+.
5.2.20. N-Boc-L-Leu-L-Tyr methyl ester (1Y)
Yield 65%; white powder; ½a D25
ꢃ
: ꢁ16.5 (c 0.10, MeOH); IR mmax
(Film): 3323, 2960, 1746, 1697, 1657 cmꢁ1
;
1H NMR (400 MHz,
CD3OD, dH): 0.88 (3H, d, J = 6.6 Hz), 0.92 (3H, d, J = 6.6 Hz), 1.15
(1H, m), 1.42 (9H, s), 1.48 (3H, m), 2.91 (1H, dd, J = 7.7, 14.0 Hz),
3.02 (1H, dd, J = 5.5, 14.0 Hz), 3.66 (3H, s), 4.05 (1H, dd, J = 7.3,
16.1 Hz), 4.60 (1H, t, J = 7.3 Hz), 6.68 (2H, d, J = 8.4 Hz), 6.98 (2H,
d, J = 8.4 Hz); 13C NMR (125 MHz, CD3OD, dC): 22.5, 23.8, 29.2,
38.1, 42.6, 53.1, 55.9, 55.6, 81.1116.8, 128.9, 131.8, 157.9, 158.2,
173.8, 175.9; HRMS–FAB: m/z 409.2339 [M+H]+ calcd for
C21H33N2O6 409.2339; FAB-MS (positive): m/z 409 [M+H]+.
a
5.2.15. N -Boc-NG-nitro-
L
-Arg- -Leu methyl ester (1R)
Yield 86%; white powder; ½aLꢃD25: ꢁ6.3 (c 0.10, MeOH); IR mmax
(Film): 2959, 2871, 1741, 1651 cmꢁ1 1H NMR (500 MHz, CD3OD,
;
dH): 0.91 (3H, d, J = 6.0 Hz), 0.92 (3H, d, J = 6.0 Hz), 1.43 (9H, s),
1.67 (7H, m), 3.26 (2H, br s), 3.69 (3H, s), 4.09 (1H, br.t,
J = 7.3 Hz), 4.46 (1H, dd, J = 5.5, 9.6 Hz); 13C NMR (125 MHz,
CD3OD, dC): 21.8, 23.3, 25.8, 26.5, 27.0, 30.5, 41.4, 41.8, 52.1,
52.7, 80.7, 157.6, 161.0, 174.5, 174.8; HRMS–FAB: m/z 447.2565
5.3. General procedure for the synthesis of cyclic dipeptide (1 to
2 or 3)
N-Boc-dipeptide methyl ester was treated with 4 M HCl–1,4-
dioxane at room temperature for 30 min, and the reaction mixture

2006
T. Furukawa et al. / Bioorg. Med. Chem. 20 (2012) 2002–2009
was evaporated. The residue was dissolved in 0.1 M acetic acid–2-
butanol, and one equivalent N-methylmorpholine (NMM) was
added to the solution. The reaction mixture was refluxed for 3 h
under N2. The reaction mixture was concentrated in vacuo to a
small volume. Cyclic dipeptide was collected by filtration, and
was washed with small amounts of 2-butanol. The cyclic dipeptide
can be further obtained from the filtrate by silica gel column
chromatography.
13C NMR (125 MHz, DMSO-d6, dC): 14.3, 21.8, 22.9, 23.5, 28.9,
33.0, 42.9, 52.0, 53.0, 167.7, 168.4; HRMS–FAB: m/z 245.1324
[M+H]+ calcd for C11H21N2O2S 245.1324; FAB-MS (positive): m/z
245 [M+H]+.
5.3.7. Cyclo(L-Asn-L-Leu) (3N)
Yield 63%; white powder; ½a D25
ꢃ
: ꢁ23.2 (c 0.50, MeOH); IR mmax
1H NMR
(KBr): 3403, 3343, 3205, 3091, 2957, 1681 cmꢁ1
;
(400 MHz, CD3OD, dH): 0.94 (3H, d, J = 6.4 Hz), 0.96 (3H, d,
J = 6.4 Hz), 1.72 (2H, m), 1.86 (1H, m), 2.66 (1H, dd, J = 8.1,
15.8 Hz), 2.83 (1H, dd, J = 4.4, 15.8 Hz), 3.96 (1H, ddd, J = 1.1, 5.1,
8.1 Hz), 4.32 (1H, ddd, J = 1.1, 4.0, 8.1 Hz); 13C NMR (125 MHz,
DMSO-d6, dC): 21.7, 23.0, 23.5, 38.1, 42.1, 51.2, 52.4, 167.8, 168.4,
171.1; HRMS–FAB: m/z 228.1347 [M+H]+ calcd for C10H18N3O2
228.1348; FAB-MS (positive): m/z 228 [M+H]+.
5.3.1. Cyclo(L-Ala-L-Leu) (3A)
Yield 36%; white powder; ½a D25
ꢃ
: ꢁ25.1 (c 0.15, MeOH); IR mmax
1H NMR (500 MHz, DMSO-
(KBr): 3197, 3085, 2958, 1687 cmꢁ1
;
d6, dH): 0.86 (3H, d, J = 6.6 Hz), 0.88 (3H, d, J = 6.6 Hz), 1.26 (3H,
m), 1.45 (1H, m), 1.60 (1H, m), 1.81 (1H, m), 3.75 (1H, br s), 3.85
(1H, dd, J = 5.0, 11.9 Hz), 8.08 (1H, s), 8.10 (1H, s); 13C NMR
(125 MHz, DMSO-d6, dC): 19.5, 21.8, 22.9, 23.6, 4.6, 49.9, 52.6,
168.3, 168.8; HRMS–FAB: m/z 185.1290 [M+H]+ calcd for
C9H17N2O2 185.1264; FAB-MS (positive): m/z 185 [M+H]+.
5.3.8. Cyclo(L-Leu-L-Ser) (3S)
Yield 46%; white powder; ½a D25
ꢃ
: ꢁ286.5 (c 0.20, MeOH); IR mmax
1H NMR
(KBr): 3464, 3363, 3190, 3051, 2960, 1670 cmꢁ1
;
5.3.2. Cyclo(
L
-Leu-
L
-Phe) (3F)
(400 MHz, CD3OD, dH): 0.93 (3H, d, J = 6.9 Hz), 0.95 (3H, d,
J = 6.9 Hz), 1.80 (3H, m), 3.67 (1H, dd, J = 4.0, 12.4 Hz), 3.90 (3H,
m); 13C NMR (125 MHz, CD3OD, dC): 21.8, 23.6, 25.1, 54.6, 59.0,
63.9, 65.3, 168.8, 171.4; HRMS–FAB: m/z 201.1257 [M+H]+ calcd
for C9H17N2O3 201.1239; FAB-MS (positive): m/z 201 [M+H]+.
Yield 34%; white powder; ½a D25
ꢃ
: ꢁ98.2 (c 0.2, MeOH); IR mmax
1H NMR (400 MHz,
(KBr): 3247, 3209, 2957, 1667, 1459 cmꢁ1
;
CD3OD, dH) 0.06 (1H, ddd, J = 4.8, 9.9, 13.9 Hz), 0.67 (3H, d,
J = 6.6 Hz), 0.72 (3H, d, J = 6.6 Hz), 0.85 (1H, ddd, J = 4.4, 9.5,
13.9 Hz), 1.43 (1H, m), 2.93 (1H, dd, J = 4.8, 13.6 Hz), 3.27 (1H,
m), 3.65 (1H, ddd, J = 1.1, 4.4, 9.9 Hz), 4.23 (1H, ddd, J = 1.1, 4.0,
8.5 Hz):; 13C NMR (125 MHz, DMSO-d6, dC): 21.4, 22.9, 22.9, 38.5,
43.7, 52.3, 55.5, 126.8, 128.2, 130.5, 136.1, 166.2, 167.5; HRMS–
FAB: m/z 261.1607 [M+H]+ calcd for C15H21N2O2 261.1603; FAB-
MS (positive): m/z 261 [M+H]+.
5.3.9. Cyclo(L-Leu-L-Thr) (3T)
Yield 38%; white powder; ½a D25
ꢃ
: ꢁ56.5 (c 0.07, MeOH); IR mmax
1H NMR (400 MHz,
(KBr): 3323, 3201, 3058, 2963, 1677 cmꢁ1
;
CD3OD, dH): 0.91 (3H, d, J = 6.8 Hz), 0.93 (3H, d, J = 6.8 Hz), 1.23
(3H, d, J = 6.8 Hz), 1.38 (m), 1.85 (2H, m), 3.71 (1H, m), 3.85 (1H,
dd, J = 3.4, 9.5 Hz), 4.17 (1H, ddd, J = 2.4, 6.6, 13.4 Hz); 13C NMR
(125 MHz, DMSO-d6, dC): 20.1, 21.5, 23.1, 23.3, 45.0, 52.7, 60.5,
66.6, 166.7, 168.6; HRMS–FAB: m/z 215.1383 [M+H]+ calcd for
5.3.3. Cyclo(Gly-L-Leu) (3G)
Yield 50%; white powder; ½a D25
ꢃ
: ꢁ11.1 (c 0.07, MeOH); IR mmax
1H NMR
(KBr): 3237, 3067, 2956, 1688, 1625, 1558 cmꢁ1
;
C
10H19N2O3 215.1396; FAB-MS (positive): m/z 215 [M+H]+.
(500 MHz, D2O, dH): 0.63 (3H, d, J = 6.2 Hz), 0.67 (3H, d,
J = 6.2 Hz), 1.35 (3H, m), 3.58 (2H, d, J = 2.3 Hz), 3.95 (1H, t,
J = 6.8 Hz); 13C NMR (125 MHz, D2O, dC): 10.2, 11.9, 14.2, 30.0,
43.7, 156.0, 169.4; HRMS–FAB: m/z 171.1140 [M+H]+ calcd for
C8H15N2O2 171.1134; FAB-MS (positive): m/z 171 [M+H]+.
5.3.10. Cyclo(L-Leu-L-Val) (3V)
Yield 29%; white powder; ½a D25
ꢃ
: ꢁ71.2 (c 0.10, MeOH); IR mmax
1H NMR (500 MHz, DMSO-
(KBr): 3100, 3054, 2959, 1662 cmꢁ1
;
d6, dH): 0.85 (9H, m), 0.93 (3H, d, J = 6.9 Hz), 1.43 (1H, ddd,
J = 4.6, 8.6, 13.3 Hz), 1.82 (1H, m), 2.09 (1H, m), 3.60 (1H, t,
J = 2.8 Hz), 3.74 (1H, t, J = 4.1 Hz), 8.03 (1H, s), 8.16 (1H, s); 13C
NMR (125 MHz, DMSO-d6, dC): 17.3, 18.7, 21.7, 23.1, 23.5, 31.5,
43.9, 52.4, 59.5, 166.8, 168.4; HRMS–FAB: m/z 213.1603 [M+H]+
calcd for C11H21N2O2 213.1603; FAB-MS (positive): m/z [M+H]+.
5.3.4. Cyclo(L-Ile-L-Leu) (3I)
Yield quant.; white powder; ½a D25
ꢃ
: ꢁ56.5 (c 0.1, MeOH); IR mmax
1H NMR (400 MHz, CD3OD,
(KBr): 3191, 3054, 2960, 1661 cmꢁ1
;
dH): 0.96 (12H, m), 1.25 (m), 1.58 (2H, m), 1.74 (ddd, J = 4.4, 8.8,
13.6 Hz), 1.88 (m), 3.84 (dd, J = 1.1, 4.1 Hz), 3.94 (ddd, J = 1.1, 4.4,
9.2 Hz); 13C NMR (125 MHz, CD3OD, dC): 11.8, 15.1, 21.8, 23.1,
23.5, 24.3, 38.3, 43.7, 52.3, 58.8, 166.8, 168.4; HRMS–FAB: m/z
227.1759 [M+H]+ calcd for C12H23N2O2 227.1760; FAB-MS (posi-
tive): m/z 227 [M+H]+.
5.3.11. Cyclo(L-Leu-L-Trp) (3W)
Yield 73%; yellow powder; ½a D25
ꢃ
: ꢁ2.6 (c 0.14, MeOH); IR mmax
1H NMR (400 MHz, CD3OD,
(KBr): 3212, 3057, 2957, 1670 cmꢁ1
;
dH): 0.18 (1H, m), 0.45 (3H, d, J = 6.6 Hz), 0.58 (3H, d, J = 6.6 Hz),
0.65 (1H, m), 1.14 (1H, m), 3.47 (1H, dd, J = 3.7, 14.7 Hz), 3.57
(1H, dd, J = 1.1, 4.8 Hz), 4.48 (1H, s), 6.98 (1H, dt, J = 1.1, 8.8 Hz),
7.06 (1H, s), 7.06 (1H, dt, J = 1.1, 8.8 Hz), 7.31 (1H, d, J = 8.8 Hz),
7.58 (1H, d, J = 8.8 Hz); 13C NMR (125 MHz, DMSO-d6, dC): 21.3,
22.6, 22.8, 29.1, 43.6, 52.3, 55.5, 108.1, 111.1, 118.3, 118.9, 120.7,
124.6, 127.7, 135.9, 167.0, 167.4; HRMS–FAB: m/z 300.1708
[M+H]+ calcd for C17H22N3O2 300.1712; EI-MS: m/z 299 [M+H]+.
5.3.5. Cyclo(L-Leu-L-Leu) (3L)
Yield 63%; white powder; ½a D25
ꢃ
: ꢁ46.4 (c 0.10, MeOH); IR mmax
1H NMR (400 MHz, CD3OD,
(KBr): 3189, 3054, 2958, 1670 cmꢁ1
;
dH): 0.95 (6H, d, J = 6.6 Hz), 0.96 (6H, d, J = 6.6 Hz), 1.62 (2H, ddd,
J = 5.1, 8.8, 18.0 Hz), 1.71 (1H, ddd, J = 4.8, 8.8, 13.6 Hz), 1.83 (2H,
m), 3.89 (2H, dd, J = 4.8, 9.2 Hz); 13C NMR (100 MHz, CD3OD, dC):
21.9, 23.5, 25.3, 45.9, 65.1, 171.2; HRMS–FAB: m/z 227.1795
[M+H]+ calcd for C12H23N2O2 227.1760; FAB-MS (positive): m/z
227 [M+H]+.
5.3.12. Cyclo(L-Leu-L-Tyr) (3Y)
Yield 57%; white powder; ½a D25
ꢃ
: +222.3 (c 0.10, MeOH); IR mmax
1H NMR
(KBr): 3312, 3204, 3084, 2953, 1676, 1661 cmꢁ1
;
5.3.6. Cyclo(
L
-Leu-
L
-Met) (3M)
(400 MHz, DMSO-d6, dH): 0.14 (1H, ddd, J = 5.0, 9.2, 13.8 Hz), 0.63
(3H, d, J = 6.6 Hz), 0.65 (3H, d, J = 6.6 Hz), 0.76 (1H, ddd, J = 5.0,
11.9, 13.8 Hz), 1.42 (1H, m), 2.68 (1H, dd, J = 4.6, 13.3 Hz), 3.01
(1H, dd, J = 3.7, 13.8 Hz), 3.45 (1H, br dd, J = 4.1, 8.3 Hz), 4.06 (1H,
br s), 6.63 (2H, d, J = 8.3 Hz), 6.89 (2H, d, J = 8.3 Hz), 8.03 (1H, s),
8.04 (1H, s), 9.20 (1H, s); 13C NMR (125 MHz, DMSO-d6, dC): 21.3,
Yield 23%; white powder; ½a D25
ꢃ
: ꢁ47.1 (c 0.07, MeOH); IR mmax
1H NMR (500 MHz,
(KBr): 3321, 3199, 3095, 2958, 1681 cmꢁ1
CD3OD, dH): 0.96 (3H, d, J = 6.4 Hz), 0.98 (3H, d, J = 6.4 Hz), 1.61
(1H, m), 1.72 (1H, m), 1.85 (1H, m), 2.12 (3H, m), 2.61 (2H, m),
3.95 (1H, ddd, J = 0.9, 4.6, 8.7 Hz), 4.08 (1H, dd, J = 4.6, 8.7 Hz);
;

T. Furukawa et al. / Bioorg. Med. Chem. 20 (2012) 2002–2009
2007
22.8, 23.0, 37.8, 43.7, 52.3, 55.7, 114.9, 125.9, 131.3, 156.4, 166.3,
167.5; HRMS–FAB: m/z 277.1516 [M+H]+ calcd for C15H21N2O3
277.1552; FAB-MS (positive): m/z 277 [M+H]+.
J = 2.2 Hz), 8.19 (1H, d, J = 2.2 Hz); 13C NMR (125 MHz, DMSO-d6,
dC): 21.8, 23.0, 23.6, 24.2, 30.9, 40.2, 43.4, 52.6, 53.9, 159.3,
167.9, 168.4; HRMS–FAB: m/z 315.1789 [M+H]+ calcd for
C
12H23N6O4 315.1781; FAB-MS (positive): m/z 315 [M+H]+.
5.3.13. Cyclo(S-4-MeO-benzyL-L-Cys- -Leu) (2C)
Yield 55%; white powder; ½a D25
ꢃ
: ꢁL16.9 (c 0.10, MeOH); IR mmax
5.4. Preparation of cyclo(N -Trt-
L-Gln-
L-Leu) (2Q)
x
(Film): 3188, 3049, 2958, 2898, 1666 cmꢁ1 1H NMR (400 MHz,
;
CDCl3, dH): 0.92 (3H, d, J = 6.6 Hz), 0.94 (3H, d, J = 6.6 Hz), 1.62
(1H, m), 1.72 (1H, m), 1.85 (1H, m), 2.67 (1H, dd, J = 8.8, 13.9 Hz),
3.06 (1H, dd, J = 3.3, 13.9 Hz), 3.58 (2H, m), 3.78 (3H, s), 3.94 (2H,
m), 6.46 (1H, br s), 6.50 (1H, br s), 6.83 (2H, d, J = 9.8 Hz), 7.20
(2H, d, J = 9.8 Hz); 13C NMR (125 MHz, CDCl3, dC): 21.1, 23.3, 24.2,
35.7, 36.1, 43.3, 53.3, 54.0, 55.3, 114.2, 129.3, 130.0, 158.9, 166.8,
168.2; HRMS–FAB: m/z 337.1591 [M+H]+ calcd for C17H25N2O3S
337.1586; FAB-MS (positive): m/z 337 [M+H]+.
1Q (112 mg, 0.17 mmol) was dissolved in methanol (25 mL),
and Pd-C (10%) was added to the solution. The reaction mixture
was stirred at room temperature for 30 min under H2. Pd-C was re-
moved by filtration, and the solution was evaporated. The residue
was dissolved in 0.1 M acetic acid–2-butanol (5 mL), and NMM
(17 mg, 0.17 mmol) was added. The reaction mixture was refluxed
for 1 h under N2. The reaction mixture was concentrated in vacuo
to a small volume. Product was collected on a filter and washed
x
with small amounts of 2-butanol. Cyclo(N -Trt-
L
-Gln-L-Leu) (2Q)
5.3.14. Cyclo(4-benzy
L
-
L
-Asp-
L
-Leu) (2D)
was obtained (72 mg, 88%) as a white powder.
Yield 36%; white powder; ½a D25
ꢃ
: ꢁ55.6 (c 0.10, MeOH); IR mmax
Compound 2Q: ½a 2D5
ꢃ
: ꢁ17.7 (c 0.30, MeOH); IR
mmax (KBr): 3019,
(KBr): 3209, 3091, 3066, 2958, 1723, 1689 cmꢁ1
;
1H NMR
2962, 1680 cmꢁ1 1H NMR (500 MHz, CD3OD, dH): 0.93 (3H, d,
;
(400 MHz, DMSO-d6, dH): 0.84 (3H, d, J = 6.6 Hz), 0.85 (3H, d,
J = 6.6 Hz), 1.46 (1H, m), 1.63 (1H, m), 1.85 (1H, m), 2.76 (2H, d,
J = 5.5 Hz), 3.86 (1H, br dd, J = 4.8, 7.6 Hz), 4.25 (1H, br.t,
J = 5.4 Hz), 5.09 (2H, dd, J = 2.4, 15.3 Hz), 7.36 (5H, m), 8.11 (1H,
s), 8.16 (1H, s); 13C NMR (100 MHz, DMSO-d6, dC): 21.8, 22.9,
23.6, 36.6, 41.4, 50.9, 52.4, 65.6, 127.9, 128.0, 128.4, 136.0, 167.3,
166.7, 169.7; HRMS–FAB: m/z 319.1648 [M+H]+ calcd for
J = 6.8 Hz), 0.95 (3H, d, J = 6.8 Hz), 1.62 (1H, m), 1.75 (1H, m),
1.82 (1H, m), 2.02 (2H, m), 2.47 (2H, m), 3.83 (1H, t, J = 5.7 Hz),
3.89 (1H, dd, J = 4.5, 8.5 Hz), 7.24 (15H, m); 13C NMR (125 MHz,
CD3OD, dC): 18.4, 22.0, 23.5, 25.3, 31.7, 33.4, 33.4, 45.3, 54.5,
55.4, 58.3, 71.6, 127.8, 128.7, 130.0, 146.0, 170.1, 171.2, 174.0;
HRMS–FAB: m/z 484.6211 [M+H]+ calcd for C30H34N3O3
484.6204; FAB-MS (positive): m/z 484 [M+H]+.
C
17H23N2O4 319.1658; FAB-MS (positive): m/z 319 [M+H]+.
5.5. Preparation of cyclo(L-Leu-L-Pro) (3P)
5.3.15. Cyclo(5-benzyL-L-Glu-L-Leu) (2E)
Yield 20%; white powder; ½a D25
ꢃ
: ꢁ28.1 (c 0.10, MeOH); IR mmax
Compound 1P (362 mg, 1.06 mmol) was treated with 4 M HCl–
1,4-dioxane (20 mL) at room temperature for 30 min. The reaction
mixture was evaporated, and the residue was dissolved in benzene
(50 mL). The reaction mixture was refluxed with Molecular Sieves
4A for3 daysunderN2. MolecularSieve 4Awasremovedandthereac-
tion mixture was evaporated. The product was purified by silica gel
column chromatography eluting with chloroform–acetone (5:1). Cy-
(KBr): 3198, 3094, 3063, 2957, 1721, 1679 cmꢁ1
;
1H NMR
(400 MHz, CD3OD, dH): 0.94 (3H, d, J = 6.6 Hz), 0.95 (3H, d,
J = 6.6 Hz), 1.66 (2H, m), 1.83 (1H, m), 2.12 (2H, m), 2.57 (2H, m),
3.92 (1H, ddd, J = 3.7, 4.8, 8.8 Hz), 3.97 (1H, t, J = 5.9 Hz), 5.11
(2H, s), 7.32 (5H, m); 13C NMR (125 MHz, CD3OD, dC): 21.0, 23.1,
24.2, 28.9, 29.9, 43.0, 53.2, 54.1, 66.7, 128.3, 128.4, 128.6, 135.5,
167.9, 168.9, 172.6; HRMS–FAB: m/z 333.1815 [M+H]+ calcd for
clo(L-Leu-L-Pro) (3P) was obtained as a white powder (85 mg, 38%).
C
18H25N2O4 333.1814; FAB-MS (positive): m/z 333 [M+H]+.
Compound 3P: ½a 2D5
ꢃ
: ꢁ101.0 (c 0.10, MeOH); IR mmax (KBr):
3413, 1653, 1606, 1503 cmꢁ1
;
1H NMR (400 MHz, CD3OD, dH):
p
5.3.16. Cyclo(N -BOM-
L
-His-
L
-Leu) (2H)
ꢃ
0.95 (3H, d, J = 6.7 Hz), 0.96 (3H, d, J = 6.7 Hz), 1.51 (1H, m), 2.29
(1H, m), 3.50 (2H, m), 4.13 (1H, m), 4.25 (1H, m); 13C NMR
(125 MHz, CD3OD, dC): 22.2, 23.3, 23.6, 25.8, 29.0, 39.4, 46.4,
54.6, 60.3, 168.9, 172.8; HRMS–FAB: m/z 211.1453 [M+H]+ calcd
for C11H19N2O2 211.1447; FAB-MS (positive): m/z 211 [M+H]+.
Yield 32%; white powder; ½a D25
: ꢁ24.0 (c 0.14, MeOH); IR mmax
(KBr): 3193, 3057, 2959, 1668 cmꢁ1
;
1H NMR (500 MHz, CD3OD,
dH): 0.76 (1H, m), 0.82 (6H, d, J = 6.8 Hz), 1.29 (1H, m), 1.61 (1H,
m), 3.14 (1H, dd, J = 4.1, 15.6 Hz), 3.35 (1H, dd, J = 5.1, 15.6 Hz),
3.80 (1H, m), 4.26 (1H, m), 4.45 (2H, d, J = 1.4 Hz), 4.60 (1H, br s),
5.43 (1H, d, J = 11.0 Hz), 5.51 (1H, d, J = 11.0 Hz), 6.87 (1H, br s),
7.30 (5H, m), 7.78 (1H, br s); 13C NMR (125 MHz, CD3OD, dC): 22.2,
24.0, 25.5, 29.2, 46.0, 54.8, 56.7, 67.4, 71.9, 75.8, 128.5, 129.4,
129.6, 130.0, 130.8, 138.7, 140.4, 169.4, 171.2; HRMS–EI: m/z
370.2019 [M]+ calcd for C20H26N4O3 370.2005; EI-MS: m/z 370 [M]+.
5.6. Preparation of cyclo(L-Cis-L-Leu) (3C)
2C (143 mg, 0.43 mmol) was dissolved in trifluoroacetic acid
(30 mL). The reaction mixture was refluxed for 2 h under N2 and
the reaction mixture was evaporated. The product was purified
by silica gel column chromatography eluting with chloroform–ace-
e
5.3.17. Cyclo(
L
-Leu-N -Z-
L
-Lys) (2K)
tone. Cyclo(L-Cys-L-Leu) (3C) was obtained (75 mg, 81%) as a white
Yield 61%; white powder; ½a D25
ꢃ
: ꢁ25.3 (c 0.14, MeOH); IR mmax
powder.
(KBr): 3339, 3209, 3089, 2958, 1733, 1716, 1684, 1653 cmꢁ1
;
1H
Compound 3C: ½a 2D5
ꢃ
: ꢁ44.9 (c 0.05, MeOH); IR
mmax (KBr): 3192,
NMR (400 MHz, CDCl3, dH): 0.94 (3H, d, J = 7.3 Hz), 0.95 (3H, d,
J = 7.3 Hz), 1.65 (9H, m), 3.13 (2H, t, J = 6.6 Hz), 3.93 (2H, m), 5.05
(2H, s), 7.30 (5H, m); 13C NMR (125 MHz, DMSO-d6, dC): 21.7,
21.8, 22.9, 23.5, 29.0, 33.1, 43.2, 52.5, 54.0, 65.0, 127.6, 128.3,
137.2, 156.0, 167.8, 168.3; HRMS–FAB: m/z 376.2213 [M+H]+ calcd
for C20H30N3O4 376.2236; FAB-MS (positive): m/z 376 [M+H]+.
3054, 2959, 2894, 2561, 1669 cmꢁ1 1H NMR (400 MHz, CD3OD,
;
dH): 0.91 (3H, d, J = 6.7 Hz), 0.93 (3H, d, J = 6.7 Hz), 1.80 (2H, m),
1.88 (1H, m), 2.83 (1H, dd, J = 4.0, 14.3 Hz), 3.04 (1H, dd, J = 4.0,
14.3 Hz), 3.98 (1H, m), 4.26 (1H, m); 13C NMR (125 MHz, CD3OD,
dC): 22.0, 23.6, 25.1, 28.6, 45.6, 54.4, 57.6, 168.3, 171.1; HRMS–
FAB: m/z 217.1024 [M+H]+ calcd for C9H17N2O2S 217.1011; FAB-
MS (positive): m/z 217 [M+H]+.
5.3.18. Cyclo(NG-nitro-
L-Arg-L-Leu) (2R)
Yield 21%; white powder; ½a D25
ꢃ
: –43.7 (c 0.05, MeOH); IR mmax
5.7. Preparation of cyclo(L-His-L-Leu) (3H)
(KBr): 3201, 3103, 2960, 2928, 1687, 1659 cmꢁ1
;
1H NMR
(400 MHz, DMSO-d6, dH): 0.83 (3H, d, J = 6.8 Hz), 0.84 (3H, d,
J = 6.8 Hz), 1.57 (7H, m), 3.15 (2H, m), 3.75 (2H, m), 8.15 (1H, d,
Compound 2H (33 mg, 0.09 mmol) was dissolved in 80% acetic
acid aqueous solution (10 mL). The reaction mixture was stirred

2008
T. Furukawa et al. / Bioorg. Med. Chem. 20 (2012) 2002–2009
with 10% Pd-C at room temperature for 30 min under H2. Pd-C was
removed, and the reaction mixture was evaporated. The product
was purified by silica gel column chromatography eluting with
at room temperature under H2 with 10% Pd-C. Pd-C was removed
by filtration, and the reaction mixture was evaporated. Cyclo(
L-
Arg-L-Leu) (3R) was obtained as a white powder (15 mg, quant).
chloroform–acetone (4:1). Cyclo(
L
-His-L-Leu) (3H) was obtained
Compound 3R: ½a 2D5
ꢃ
: ꢁ43.7 (c 0.05, MeOH); IR
mmax (KBr): 3201,
as a white powder (9 mg, 40%).
3103, 2960, 2928, 1687, 1659 cmꢁ1
;
1H NMR (400 MHz, DMSO-d6,
Compound 3H: ½a 2D5
ꢃ
: ꢁ67.7 (c 0.10, MeOH); IR
m
max (KBr): 3195,
dH): 0.83 (3H, d, J = 6.8 Hz), 0.84 (3H, d, J = 6.8 Hz), 1.57 (7H, m),
3.15 (2H, m), 3.75 (2H, m), 8.15 (1H, d, J = 2.2 Hz), 8.19 (1H, d,
J = 2.2 Hz); 13C NMR (125 MHz, DMSO-d6, dC): 21.8, 23.0, 23.6,
24.2, 30.9, 40.2, 43.4, 52.6, 53.9, 159.3, 167.9, 168.4; HRMS–FAB:
m/z 315.1789 [M+H]+ calcd for C12H23N6O4 315.1781; FAB-MS (po-
sitive): m/z 315 [M+H]+.
2958, 1670 cmꢁ1 1H NMR (500 MHz, CD3OD, dH): 0.73 (1H, m),
;
0.82 (3H, d, J = 6.7 Hz), 0.84 (3H, d, J = 6.7 Hz), 1.26 (1H, m), 1.61
(1H, m), 3.00 (1H, dd, J = 4.6, 14.7 Hz), 3.19 (1H, dd, J = 5.0,
14.7 Hz), 3.79 (1H, m), 4.23 (1H, m), 6.89 (1H, br s), 7.62 (1H, br
s); 13C NMR (125 MHz, CD3OD, dC): 21.7, 23.5, 24.9, 32.2, 45.3,
54.3, 56.7, 120.0, 132.8, 136.3, 169.3, 170.7; HRMS–FAB: m/z
251.1509 [M+H]+ calcd for C12H19N4O2 251.1508; FAB-MS (posi-
tive): m/z 251 [M+H]+.
5.12. Preparation of cyclo(L-Leu-L-Lys) (3K)
Compound 2K (151 mg, 0.41 mmol) was dissolved in methanol
(50 mL). The reaction mixture was stirred for 4 h at room temper-
ature under H2 in the presence of 10% Pd-C. Pd-C was removed by
filtration, and the reaction mixture was evaporated. The product
was purified by silica gel column chromatography using chloro-
5.8. Preparation of cyclo(L-Asp-L-Leu) (3D)
Compound 2D (40 mg, 0.12 mmol) was dissolved in methanol
(10 mL). The reaction mixture was stirred for 30 min at room tem-
perature under H2 in the presence of 5% Pd-C. Pd-C was removed
form–methanol (3:1) to afford cyclo (
powder (36 mg, 41%).
L-Leu-L-Lys) (3K) as a white
by filtration, and the reaction mixture was evaporated. Cyclo(L-
Asp-
L
-Leu) (3D) was obtained as a white powder (28 mg, quant).
Compound 3K: ½a 2D5
ꢃ
: ꢁ46.7 (c 0.14, MeOH); IR
mmax (KBr): 3495,
Compound 3D: ½a 2D5
ꢃ
: ꢁ61.0 (c 0.10, MeOH); IR
mmax (KBr): 3441,
3316, 3201, 3094, 2958, 2870, 1772, 1682 cmꢁ1 1H NMR
;
3197, 3097, 3059, 2959, 1678 cmꢁ1
;
1H NMR (500 MHz, pyridine-
(500 MHz, CD3OD, dH): 0.95 (3H, d, J = 6.4 Hz), 0.96 (3H, d,
J = 6.4 Hz), 1.53 (5H, m), 1.79 (4H, m), 2.71 (2H, t, J = 6.9 Hz), 3.92
(2H, m); 13C NMR (125 MHz, DMSO-d6, dC): 21.7, 21.8, 23.0, 23.6,
32.4, 33.4, 41.1, 43.3, 52.5, 54.1, 167.9, 168.3; HRMS–FAB: m/z
242.1861 [M+H]+ calcd for C12H24N3O2 242.1869; FAB-MS (posi-
tive): m/z [M+H]+.
d5, dH): 0.90 (3H, d, J = 6.0 Hz), 0.91 (3H, d, J = 6.0 Hz), 2.13 (1H,
m), 2.15 (2H, m), 3.25 (dd, J = 8.2, 16.5 Hz), 3.57 (1H, dd, J = 3.7,
16.5 Hz), 4.31 (1H, m), 4.94 (1H, m), 9.30 (1H, s), 9.39 (1H, s); 13C
NMR (125 MHz, pyridine-d5, dC): 21.8, 24.7, 39.5, 43.8, 53.1, 65.2,
168.6, 169.5, 173.5; HRMS–FAB: m/z 229.1181 [M+H]+ calcd for
C
10H17N2O4 229.1188; FAB-MS (positive): m/z 229 [M+H]+.
ꢀꢁ
Å
5.13. Antioxidant assay for scavenging OH and O2
5.9. Preparation of cyclo( -Glu- -Leu) (3E)
L
L
Antioxidant assay against ÅOH and Oꢀ2ꢁ by ESR was carried out as
reported previously.15
Compound 2E (60 mg, 0.18 mmol) was prepared in the same
manner as that of 3D. The product was purified by HPLC equipped
with an ODS column by using methanol–water (50:50) as a mobile
Acknowledgment
phase. Cyclo(L-Glu-L-Leu) (3E) was obtained as a white powder
(21 mg, 58%).
This work was supported by the bounty for academic research
from the Research Institute of Meijo University.
Compound 3E: ½a 2D5
ꢃ
: ꢁ27.5 (c 0.14, MeOH); IR
mmax (KBr): 3326,
3196, 3055, 2956, 2929, 1719, 1673 cmꢁ1
;
1H NMR (400 MHz,
CD3OD, dH): 0.96 (3H, d, J = 6.6 Hz), 0.97 (3H, d, J = 6.6 Hz), 1.69
(2H, m), 1.85 (1H, ddd, J = 6.5, 8.4, 15.0 Hz), 2.02 (1H, m), 2.16
(1H, m), 2.36 (1H, m), 3.91 (1H, m), 3.95 (1H, m); 13C NMR
(125 MHz, DMSO-d6, dC): 21.8, 22.9, 23.6, 28.8, 29.5, 43.0, 52.5,
51.4, 167.7, 168.5, 173.9; HRMS–FAB: m/z 243.1371 [M+H]+ calcd
for C11H19N2O4 243.1345; FAB-MS (positive): m/z 243 [M+H]+.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmc.2012.01.050. These data
include MOL files and InChiKeys of the most important compounds
described in this article.
5.10. Preparation of cyclo(L-Gln-L-Leu) (3Q)
References and notes
Compound 2Q (72 mg, 0.15 mmol) was dissolved in 50% trifluoro-
acetic acid–dichloromethane (15 mL). The reaction mixture was re-
fluxed for 5 min under N2. The reaction mixture was evaporated.
1. Morita, H.; Kondo, K.; Hitotsuyanagi, Y.; Takeya, K.; Itokawa, H.; Tomioka, N.;
Itai, A.; Iitaka, Y. Tetrahedron 1991, 16(17), 2752.
2. Kijima, M.; Yoshida, M.; Sugita, K.; Horinouchi, S.; Beppu, T. J. Biol. Chem. 1993,
268, 22429.
3. Stark, T.; Hoffmann, T. J. Agric. Food Chem. 2005, 53, 7222.
4. Ginz, M.; Engelhardt, U. H. J. Agric Food Chem. 2000, 48, 3528.
5. Gautschi, K.; Schmid, J. P. J. Agric Food Chem. 1997, 45, 3183.
6. Takahashi, K.; Tadenuma, M.; Kitamoto, K.; Sato, S. Agric. Biol. Chem. 1974, 38,
927.
7. Li, Y.; Li, X.; Kim, S.; Kang, J. S.; Choi, H. D.; Rho, J. R.; Son, B. W. Chem. Pharm.
Bull. 2004, 52, 375.
8. Jayatilake, G. S.; Thornton, M. P.; Leonard, A. C.; Grimwade, J. E.; Baker, B. J. J.
Nat. Prod. 1996, 59, 293.
9. Hodge, R. P.; Harris, C. M.; Harris, T. M. J. Nat. Prod. 1988, 51, 66.
10. Deffieux, G.; Baute, M.-A.; Baute, R.; Filleau, M.-J. J. Antibiot. (Tokyo) 1978, 31,
1102.
Cyclo(L-Gln-L-Leu)(3Q)wasobtainedasawhitepowder(43 mg, 99%).
Compound 3Q: ½a 2D5
ꢃ
: ꢁ38.9 (c 0.14, MeOH); IR
mmax (KBr): 3395,
3199, 1683, 1653 cmꢁ1
;
1H NMR (600 MHz, CD3OD, dH): 0.97 (3H,
d, J = 6.5 Hz), 0.98 (3H, d, J = 6.5 Hz), 1.63 (2H, m), 1.85 (1H, m),
2.14 (2H, m), 2.36 (2H, t, J = 7.6 Hz), 3.93 (1H, dd, J = 4.0,
14.8 Hz), 3.96 (1H, t, J = 5.8 Hz); 13C NMR (125 MHz, CD3OD, dC):
22.0, 23.5, 25.3, 31.9, 48.9, 55.1, 55.6, 71.5, 170.1, 171.2, 177.4;
HRMS–FAB: m/z 242.1505 [M+H]+ calcd for C11H20N3O3
242.1541; FAB-MS (positive): m/z 242 [M+H]+.
11. Deffieux, G.; Filleau, M.-J.; Baute, R. J. Antibiot. (Tokyo) 1978, 31, 1106.
12. Byun, H.-G.; Zhang, H.; Mochizuki, M.; Adachi, K.; Shizuri, Y.; Lee, W.-J.; Kim, S.-
K. J. Antibiot. (Tokyo) 2003, 56, 102.
13. Takahashi, C.; Numata, A.; Ito, Y.; Matsumura, E.; Araki, H.; Iwaki, H.; Kushida,
K. J. Chem. Soc. Perkin Trans. II 1994, 1859.
5.11. Preparation of cyclo(L-Arg-L-Leu) (3R)
Compound 2R (17 mg, 0.06 mmol) was dissolved in 5% formic
acid–methanol (25 mL). The reaction mixture was stirred for 4 h

T. Furukawa et al. / Bioorg. Med. Chem. 20 (2012) 2002–2009
2009
14. Yoshida, K.; Okamoto, M.; Shimazaki, N.; Hemmi, K. Prog. Biochem. Pharmacol.
1988, 22, 66.
20. Brown, T.; Jones, J. H.; Richards, J. D. J. Chem. Soc. Perkin Trans. II 1982,
1553.
15. Takaya, Y.; Furukawa, T.; Miura, S.; Akutagawa, T.; Hotta, Y.; Ishikawa, N.;
Niwa, M. J. Agric. Food Chem. 2007, 55, 75.
21. ElAmin, B.; Anantharamaiah, G. M.; Royer, G. P.; Means, G. E. J. Org. Chem. 1979,
44, 3442.
16. Saitoh, K. M.; Furukawa, T.; Akutagawa, T.; Hasada, K.; Mizutani, H.; Sugimoto,
Y.; Yamada, J.; Niwa, M.; Hotta, Y.; Takaya, Y. Biol. Pharm. Bull. 2011, 34, 335.
17. Suzuki, K.; Sasaki, Y.; Endo, N.; Mihara, Y. Chem. Pharm. Bull. 1981, 29, 233.
18. Sieber, P.; Riniker, B. Tetrahedron Lett. 1991, 32, 739.
19. Akabori, S.; Sakakibara, S.; Shimonishi, Y.; Nobuhara, Y. Bull. Chem. Soc. Jpn.
1964, 37, 433.
22. Noda, Y.; Anzai, K.; Mori, A.; Kohno, M.; Shinmei, M.; Packer, L. Biochem. Mol.
Biol. Int. 1997, 42, 35.
23. Mieden, O. J.; Sonntag, C. J. Chem. Soc. Perkin Trans. II 1989, 2071.