Synthesis of a series of 3,4-methanoarginines as side-chain conformationally restricted analogues of arginine

Article abstract of DOI:10.1016/j.bmc.2011.08.049

A series of optically active stereoisomers of 3,4-methanoarginine (1-4 and ent-1-ent-4) with trans/cis, d/l, and syn/anti stereochemical diversity, the side-chains of which were restricted in various special arrangements, was designed as biologically usef

Full text of DOI:10.1016/j.bmc.2011.08.049

Bioorganic & Medicinal Chemistry 19 (2011) 5984–5988
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Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis of a series of 3,4-methanoarginines as side-chain
conformationally restricted analogues of arginine
Mizuki Watanabe a,b, Kazuya Yamaguchi a, Wei Tang b, Keisuke Yoshida a, Richard B. Silverman b,c
,
Mitsuhiro Arisawa a, Satoshi Shuto a,
⇑
a Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12, Nishi-6, Kita-ku, Sapporo 060-0812, Japan
b Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113, USA
c Department of Molecular Biosciences, Chemistry of Life Processes Institute, and Center for Molecular Innovation and Drug Discovery,
Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of optically active stereoisomers of 3,4-methanoarginine (1–4 and ent-1–ent-4) with trans/cis,
, and syn/anti stereochemical diversity, the side-chains of which were restricted in various special
arrangements, was designed as biologically useful arginine mimetics. These conformationally restricted
arginine analogues were synthesized effectively by using a series of chiral 3,4-methanoamino acid equiv-
alents (7–10 and ent-7–ent-10) as the key synthetic units. Their biological evaluation with three isoforms
Received 1 August 2011
Revised 20 August 2011
Accepted 22 August 2011
Available online 27 August 2011
D/L
of nitric oxide synthase showed that trans-3,4-methano-
L
-syn-arginine (2) was a good substrate, having
Keywords:
Cyclopropane
Conformational restriction
Stereochemical diversity
Arginine analogue
Nitric oxide synthase
close potency to -arginine, and isoforms selectivities were also similar to those of
L
L
-arginine.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
useful compounds by this strategy, which have high affinity for tar-
get proteins such as histamine receptor subtypes or the protea-
some.3–7 Thus, we applied this strategy to arginine to design and
synthesize a series of cyclopropane-based conformationally re-
stricted arginine analogues with stereochemical diversity. These
analogues are of importance in medicinal chemistry, for example,
as potentially selective ligands for the isoforms of nitric oxide syn-
thase (NOS, EC 1.14.13.39) and also as side-chain conformationally
restricted amino acid mimetics of biologically active peptides.
The cyclopropane-based conformationally restricted arginine
analogues have been reported,8,9 which are two isomers of 3,
The conformational restriction of backbone or side-chains of
biologically active peptides to the bioactive conformation can be
a
promising approach in the development of small useful
peptidomimetics.1 A cyclopropane is very effective for restricting
the conformations of molecule because of its rigid and
a
small structural properties. In fact, conformationally restricted
analogues of various amino acids containing a cyclopropane, which
have improved the biological potency and selectivity of lead
molecules depending on the conformations, are known.2 Therefore,
the development of useful synthetic methods of conformationally
restricted amino acid analogues is important for peptidomimetics
studies.
4-methaonoarginines, that is, trans-3,4-methano-L-anti- and
-syn-arginines (1 and 2), shown in Figure 1, of which the carboxylic
group is oriented anti or syn to the cyclopropane moiety, respec-
Based on the characteristic conformational restriction of cyclo-
propanes, we devised a stereochemical diversity-oriented confor-
mational restriction strategy for compounds that bind selectively
to a target protein.3–5 In this strategy, a series of cyclopropane-based
conformationally restricted analogues of a conformationally flexible
lead compound, which has stereochemical diversity, is designed and
synthesized, and the compounds that selectively bind to the target
protein can be identified. In fact, we have successfully developed
tively. We decided to synthesize all of the stereoisomeric
-3,4-methanoarginine analogues including known 1 and 2, which
have trans/cis, , and syn/anti stereochemical diversity (1–4 and
L- and
D
D/L
ent-1–ent-4, Fig. 1).
To prepare various cyclopropane derivatives effectively, we
have designed chiral cyclopropane units, which are composed of
four stereoisomeric cyclopropanes, 5 and 6, and their enantiomers,
ent-5 and ent-6, bearing two adjacent carbon substituents in a
trans or cis relationship (Fig. 2).3,5 These units are generally useful
for synthesizing
a series of optically active stereoisomeric
cyclopropane derivatives having an asymmetric trans- or cis
⇑
Corresponding author. Tel./fax: +81 11 706 3769.
E-mail address: shu@pharm.hokudai.ac.jp (S. Shuto).
-cyclopropane structure.3–7,10,11
0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2011.08.049

M. Watanabe et al. / Bioorg. Med. Chem. 19 (2011) 5984–5988
5985
trans
cis
L-form
D
-form
L-form
D
-form
CO2H
CO2H
H
N
H
N
NH
NH2
NH
NH2
-anti)
H
N
H
N
CO2H
CO2H
NH2
NH2
NH2
anti
syn
H2N
H2N
H2N
H2N
H2N
H2N
NH
NH
1 (trans-
L
-anti)
ent-1 (trans-
D
-anti)
3 (cis-
L
-anti)
ent-3 (cis-D
CO2H
CO2H
H
N
H
NH
N
NH
NH2
-syn)
H
N
H
N
CO2H
CO2H
NH2
H2N
ent-2 (trans-
NH2
H2N
ent-4 (cis-D
NH
-syn)
NH
2 (trans-
L
D
-syn)
4 (cis-
L
-syn)
Figure 1. A series of optically active cyclopropane-based conformationally restricted analogues of
L
- and D-arginine with stereochemical diversity.
Chiral cyclopropane units
O
S
O
S
O
S
R
R
O
S
R
R
t-Bu
N
H
R
R
t-Bu
N
H
R
t-Bu
N
H
L
t-Bu
N
H
OHC
OHC
R
7 (trans-
L
-anti)
-syn)
ent-7 (trans-
D
-anti)
9 (cis-
-anti)
-syn)
ent-9 (cis-D-anti)
5
6
O
S
O
S
O
S
O
S
R
R
OHC
OHC
R
t-Bu
N
H
t-Bu
N
H
R
t-Bu
N
H
L
t-Bu
N
H
ent-5
ent-6
8 (trans-
L
ent-8 (trans-
D
-syn)
10 (cis-
ent-10 (cis-
D
-syn)
R = CH2OTBDPS
R = CH2OTBDPS
Figure 2. Chiral cyclopropane units and chiral 3,4-methanoamino acid equivalents as the key units for the synthesis of conformationally restricted
L
- and
D-amino acid
analogues.
Also, we recently developed an efficient method for the system-
atic synthesis of a series of 3,4-methanoamino acid equivalents
(7–10 and ent-7–ent-10), shown in Figure 2, with trans/cis, D/L,
nylimine 11 in a high yield. 3,4-Methanoamino acid equivalent 7
was obtained in a very high yield by a highly diastereoselective
addition of a vinyl group to imine 11 using a Grignard reaction
with CH2@CHMgBr.6 The spectral data of 7 was consistent with
that of ent-7, which is the enantiomer of 7 reported previously
by us.6 The removal of the N-sulfinyl and the O-silyl groups of 7 un-
der acidic conditions, followed by protection of the resulting free
amino group with a Cbz group provided alcohol 12. The Mitsunobu
reaction of 12 with N,N0-bis-Cbz-guanidine13 gave compound 13
contaminated with an inseparable by-product derived from diiso-
propyl azodicarboxylate. However, oxidation of the mixture with
a mixture of NaIO4/KMnO4/NaHCO3 in aqueous acetone worked
well, and pure carboxylic acid 14 was obtained in a good yield
for the two steps after silica gel column chromatography. Finally,
the Cbz-protecting groups were removed by catalytic hydrogena-
and syn/anti stereochemical diversity from the chiral cyclopropane
units 5, 6, ent-5, and ent-6.6 This series has an optically active
CH2@CHC⁄H(NH–)- moiety in the structures. These compounds
can be considered to be equivalents of D- or L-methanoamino acids
because a vinyl group is stable under various reaction conditions
and can be converted easily to a carboxyl group.7,12
Herein, we report the systematic synthesis of a series of
optically active cyclopropane-based conformationally restricted
arginine analogues (1–4 and ent-1–ent-4) using our 3,4-methan-
oamino acid equivalents as key intermediates.
2. Results and discussion
2.1. Chemistry
tion to produce trans-
The other -arginine analogues, trans-
-anti-isomer 3, and cis- -syn-isomer 4, were synthesized from cor-
L-anti-isomer 1.
L
L-syn-isomer 2, cis-L
L
responding chiral cyclopropane units ent-5, 6, or ent-6 by the same
procedure for the synthesis of compound 1 described above, via
corresponding 3,4-methanoamino acid equivalents 8, 9, or 10,
The synthesis of trans-3,4-methano-
L-anti-arginine analogue 1
from chiral cyclopropane unit via 3,4-methanoamino acid
5
equivalent 7 as a key intermediate is shown in Scheme 1. Chiral
trans-cyclopropane aldehyde 53 was treated with (S)-tert-butane-
sulfinamide in the presence of CuSO4 to give (S)-tert-butanesulfi-
respectively. The four
ent-1, trans- -syn-isomer ent-2, cis-
cis- -syn-isomer ent-4, were also synthesized from corresponding
D-arginine analogues, trans-
D-anti-isomer
D
D
-anti-isomer ent-3, and
D
Scheme 1. Reagents and conditions: (a) (S)-t-BuSONH2, CuSO4, CH2Cl2, 94%; (b) CH2@CHMgBr, toluene, 110 °C, 97%; (c) (i) HCl, AcOEt/MeOH; (ii) Cbz-Cl, Na2CO3, aq THF, 75%
for two steps; (d) N,N0-bis-Cbz-guanidine, PPh3, DIAD, THF, 0 °C to rt; (e) NaIO4, KMnO4, NaHCO3, aq acetone, 68% for two steps; (f) H2, Pd/C, HCl, EtOH, 48%.

5986
M. Watanabe et al. / Bioorg. Med. Chem. 19 (2011) 5984–5988
3,4-methanoamino acid equivalents ent-7, ent-8, ent-9, or ent-10,
which were prepared from chiral cyclopropane units ent-5, 5, ent-
6, or 6, respectively, by the procedure using (R)-tert-butanesulfina-
mide instead of (S)-tert-butanesulfinamide described above.14
These results demonstrate that the series of 3,4-methanoamino
acid equivalents, 7–10 and ent-7–ent-10, is useful for the system-
atic synthesis of conformationally restricted amino acid analogues
with stereochemical diversity.
found to be substrates for all isoforms of NOS, as shown in Table 2.
The Km values of 2 for all NOS isoforms were only about a factor of
three higher than the corresponding Km values of
(7.6 M vs 2.7 M for nNOS; 20 M vs 9.5 M for iNOS; 3.6
1.1 M for eNOS, respectively). The kcat/Km values of 2 for all NOSiso-
forms were comparable to those of -arginine. The selectivities of 2
L
-arginine
l
l
l
l
lM vs
l
L
for nNOS and eNOS over iNOS on the basis of Km values were 2.6-
and 5.6-fold, respectively, and those tendencies were also similar
to those of
show that trans-
each isoform of NOS are comparable to those of
L
-arginine (3.5- and 8.6-fold, respectively). These results
-syn-isomer 2, whose affinities and potencies with
-arginine, is a good
2.2. Evaluation as NOS ligands
L
L
NOS is a family of enzymes that catalyzes the production of
-citrulline and nitric oxide (NO) from L-arginine with O2 and
substrate for all NOS isoforms, although 2 shows little selectivity.
Compound 3 was identified as a less effective substrate for all
three isoforms of NOS than 2, having Km values of 29- to 45-times
greater than those of 2 and kcat/Km values less than 33-times those
of 2. The selectivities of 3 for nNOS and eNOS over iNOS on the ba-
sis of Km values were 2.3- and 3.6-fold, respectively, and were both
L
NADPH.15 The family of NOS consists of three isoforms: neuronal
NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS).16
Two of these isoforms, nNOS and eNOS, are constitutively
expressed mainly on neurons or vascular endothelial cells, respec-
tively. On the other hand, iNOS is transcriptionally activated by
stimulating factors such as cytokines and bacterial lipopolysaccha-
ride in a wide range of cell types. These different NOS isoforms
generate NO, which is an important signaling molecule that
regulates a variety of physiological functions in the nervous,
cardiovascular, and immune systems.17 Overproduction of NO in
these systems induces various pathological states such as stroke,18
hypertension,19 and septic shock.20 Therefore, NOS isoform-selec-
tive ligands are useful as biological tools and/or drug leads for
NOS isoform-selective therapeutic agents for NO-related diseases.21
Thus, to examine the biological activity of the synthesized con-
formationally restricted analogues of arginine, we evaluated them
as ligands for three isoforms of NOS: rat nNOS, murine iNOS, and
bovine eNOS using known methods.22
less than those of
cis- -anti-isomer 3 was a weak and non-selective substrate for all
NOS isoforms. These results suggest that the binding orientation
of the side-chain of -arginine would prefer an extended form to
a folded one with all three isoforms of NOS.
While trans- -syn-isomer worked as
trans- -anti-isomer 1 was only a very poor inhibitor of all NOS
2 (2.6- and 5.6-fold, respectively). Thus,
L
L
L
2
a good substrate,
L
isoforms. The structural difference between 2 and 1 is only the
orientation of the cyclopropane to the carboxylic acid moiety,
but their functions and affinities for NOS isoforms are totally chan-
ged. When the stereochemistry of the amino acid moiety is in the
D-form, all of the analogues (ent-1–ent-4) were very poor ligands
irrespective of the orientation of the cyclopropane moiety, that
is, trans/cis and syn/anti.
As a result, the six analogues, 1, 4, and ent-1–ent-4, did not act
as substrates for all NOS isoforms but were weak inhibitors with
As described, only one of these analogues, trans-
was as good of a substrate as -arginine for all three NOS isoforms.
These results indicate that -arginine binds to all NOS isoforms
L-syn-isomer 2,
L
IC50 values greater than 300
lM (Table 1). There was very little
L
selectivity among the isoforms of NOS, although their inhibitory ef-
fects were slightly different among them (for example, inhibitory
with the extended form of its side-chain and the stereochemistry
of the amino acid moiety in arginine is important to work as the
effects of 1 at 300
lM were 16% for nNOS; 26% for iNOS; 45% for
NOS substrate. Thus, the binding sites for L-arginine on all three
eNOS).
isoforms of NOS recognize the conformation and configuration of
the substrates and the tolerance range of the active sites are very
similar. Indeed, the crystal structures of the catalytic domains of
all three NOS isoforms show that the substrate binding sites are
nearly identical and that the NOS substrate requires both a guanid-
On the other hand, two analogues, trans-
L-syn-isomer 2 and
cis- -anti-isomer 3, did not inhibit any of the NOS isoforms but were
L
Table 1
Inhibitory activities for three NOS isoformsa
inium group and an
a-amino acid group that make specific H-
bonding networks in the first hydroxylation step.24–28 These re-
sults in this study are consistent with the ligand-binding structural
information from the crystal structures.
Compound
Configuration
Inhibitionb (%)
nNOS
iNOS
eNOS
1
trans-
trans-
trans-
L
-anti
-anti
-syn
16
5
13
30
10
30
26
19
19
22
24
14
45
23
4
16
4
ent-1
ent-2
4
ent-3
ent-4
D
3. Conclusion
D
cis-
cis-
cis-
L
-syn
-anti
-syn
In summary, we systematically synthesized eight optically ac-
tive cyclopropane-based conformationally restricted analogues of
D
D
27
L
- and D-arginine (1–4 and ent-1–ent-4) with trans/cis, D/L, and
a
nNOS from rat, iNOS from murine, eNOS from bovine, respectively: See Ref. 22.
Inhibitory effects of the compounds (300 lM) against L-arginine (10 lM).
b
syn/anti stereochemical diversity using a series of 3,4-methanoami-
no acid equivalents as key intermediates. Evaluation of the
Table 2
Kinetic constants for substrate activity of compounds 2 and 3 and L-arginine for three NOS isoformsa
Compound
Configuration
nNOS
iNOS
eNOS
Selectivityc
Km
(lM)
kcat/Km (sꢀ1 mMꢀ1
)
Km
(lM)
kcat/Km (sꢀ1 mMꢀ1
)
Km
(l
M)
kcat/Km (sꢀ1 mMꢀ1
)
n/i
e/i
2
3
trans-
L
-syn
7.6
256
2.7
317
8.6
180
20
582
9.5
99
3.0
110
3.6
163
1.1
42
0.92
73
2.6
2.3
3.5
5.6
3.6
8.6
cis-
L
-anti
L
-Arginineb
–
a
b
c
nNOS from rat, iNOS from murine, eNOS from bovine, respectively: See Ref. 22.
Data taken from Ref. 23.
Ratio of the inverse of the Km values.

M. Watanabe et al. / Bioorg. Med. Chem. 19 (2011) 5984–5988
5987
analogues as ligands for NOS isoforms provided useful information
of the binding mode of -arginine for the enzymes. Thus, the stereo-
cyclopropyl-CH), 1.04 (9H, s, tBu), 1.21 (9H, s, tBu), 3.20–3.26
(2H, m), 3.42 (1H, dd, J = 7.0, 10.7 Hz, CH2OTBDPS), 3.69 (1H, dd,
J = 5.4, 10.7 Hz, CH2OTBDPS), 5.14 (1H, d, J = 10.4 Hz, CH2@CH–),
5.33 (1H, d, J = 17.7 Hz, CH2@CH–), 5.90 (1H, m, CH2@CH-),
7.35–7.44 (6H, m, aromatic), 7.64–7.66 (4H, m, aromatic); 13C
NMR (100 MHz, CDCl3) d 9.8, 18.7, 19.4, 21.4, 22.7, 27.0, 55.6,
61.7, 66.5, 116.2, 127.5, 129.4, 133.7, 135.4, 138.6; HRMS (FAB)
L
chemical diversity-oriented approach can be an effective strategy
to reveal three-dimensional information of the active site of the tar-
get protein in relation to the ligands. Since an arginine residue often
occurs in active sites of peptides and proteins due to its effective io-
nic and hydrogen bond-forming properties, the conformationally
restricted analogues of arginine with the stereochemical diversity
developed in this study can be effectively used as tools to be intro-
calcd for
C
27H40NO2SSi: 470.2549 [(M+H)+], found 470.2540
[(M+H)+].
duced into biologically active peptides instead of L-arginine. This
strategy, employing a series of 3,4-methanoamino acid equivalents
as key intermediates, can be applicable to the side-chain-conforma-
tional restriction of various amino acids other than arginine.
4.1.3. (1R,2R)-1-[(1R)-1-(Benzyloxycarbonylamino)-2-
propenyl]-2-hydroxymethylcyclopropane (12)
To a solution of 7 (147 mg, 0.313 mmol) in MeOH (3.1 mL) was
added HCl (4 M in AcOEt, 0.31 mL), and the mixture was stirred at
rt for 1.5 h. After the mixture was evaporated, the residue was dis-
solved in THF/H2O (3/2, 5.0 mL). To the mixture were added ben-
zyloxycarbonyl chloride (2.91 M soln in toluene, 0.118 mL,
0.344 mmol) and sodium carbonate (66 mg, 0.67 mmol) at rt, and
the resulting mixture was stirred at rt for 12 h. After dilution with
AcOEt, the mixture was washed with H2O, brine, dried (Na2SO4),
and evaporated. The residue was purified by silica gel column chro-
matography (hexane/AcOEt = 4/1–1/1) to give 12 (62 mg, 75% for
4. Experimental section
4.1. General methods
1H NMR and 13C NMR spectra were obtained on JEOL JNM-AL-400
or JEOL JMM-ECA-500 spectrometers with tetramethylsilane as an
internal standard and the resonance patterns are reported with
notations as followings: br (broad), s (singlet), d (double), t (triplet)
and m (multiplet). All 1H NMR assignments described were in agree-
ment with COSY spectra. Mass spectra were obtained using a JEOL
JMS-700TZ, JMS-HX110, or JEOL FABmate. Specific rotations were
obtained using a JASCO P-1030 polarimeter. Thin-layer chromatog-
raphy was done on Merck 60F254 plates. Silica gel and reverse phase
chromatographies were done on silica gel 5715 (Merck) and Fuji
Silysia ODS Chromatorex, respectively. HPLC purifications were per-
formed with a JASCO 875-UV (detector), JASCO PU-2087 plus (pump
and system controller), and JASCO 807-IT (recorder). Reactions were
carried out under an argon atmosphere.
two steps) as an amorphous solid: ½a D21
ꢁ
+15.60 (c 0.92, CHCl3);
1H NMR (500 MHz, CDCl3) d 0.46 (1H, m, cyclopropyl-CH2), 0.65
(1H, br s, cyclopropyl-CH2), 0.85 (1H, br s, cyclopropyl-CH), 1.05
(1H, br s, cyclopropyl-CH), 1.76 (1H, br s, CH2OH), 3.38 (1H, dd,
J = 7.4, 11.4 Hz, CH2OH), 3.55 (1H, dd, J = 6.3, 11.4 Hz, CH2OH),
3.79 (1H, m, –CHNH), 5.00 (1H, br s, NH), 5.09–5.24 (4H, m,
CH2@CH– and CH2 of Cbz), 5.80 (1H, m, CH2@CH–), 7.29–7.36
(5H, m, aromatic); 13C NMR (125 MHz, CDCl3) d 8.0, 18.9, 21.4,
55.7, 65.9, 66.8, 115.4, 128.1, 128.5, 136.4, 137.0, 155.8; HRMS
(EI) calcd for C15H19NO3: 261.1365 (M+), found 261.1350 (M+).
a
x
4.1.4. (3R,4R)-3,4-Methano-N ,Nd,N -tri-Cbz-
A mixture of 12 (80 mg, 0.31 mmol), N,N0-bis-Cbz-guanidine
(200 mg, 0.612 mmol), and triphenylphosphine (96 mg,
L-arginine (14)
4.1.1. (1R,2R)-2-tert-Butyldiphenylsiloxymethyl-1-[((S)-tert-
butylsulfinyl)iminomethyl]cyclopropane (11)
A mixture of trans-cyclopropane aldehyde 53 (339 mg, 1.00
mmol), (S)-(ꢀ)-tert-butanesulfinamide (97%, 187 mg, 1.50 mmol),
and copper sulfate (638 mg, 4.00 mmol) in CH2Cl2 (10 mL) was stir-
red at room temperature until the aldehyde disappeared by TLC.
The resulting mixture was filtered through Celite and the filtrate
was evaporated. The residue was purified by silica gel column
chromatography (hexane/AcOEt = 20/1–15/1) to give 11 (414 mg,
0.37 mmol) in toluene (3 mL) was stirred at 0 °C for 10 min. To
the mixture was added a solution of diisopropyl azodicarboxylate
(72 lL, 0.37 mmol) in toluene (3 mL) at 0 °C, and the resulting mix-
ture was stirred at rt for 2 h. After being evaporated, the residue
was purified by short silica gel column chromatography (hexane/
AcOEt = 7/1–2/1) to give a crude product of 13 as a colorless oil.
To a solution of the crude product of 13 in acetone/H2O (2/1,
9 mL) were added sodium periodate (326 mg, 1.53 mmol), potas-
sium permanganate (34 mg, 0.21 mmol), and sodium bicarbonate
(25 mg, 0.31 mmol) at rt, and the mixture was stirred at rt for
2 h. After dilution with AcOEt, the resulting mixture was washed
with aqueous HCl (1 M, four times), brine, dried (Na2SO4), and
evaporated. The residue was purified by silica gel column chroma-
tography (0–10% MeOH in CHCl3) to give 14 (141 mg, 78% for two
94%) as a colorless oil: ½a D22
ꢁ
+57.59 (c 1.03, CHCl3); 1H NMR
(400 MHz, CDCl3) d 1.04 (9H, s, tBu), 1.01–1.14 (2H, m, cyclopro-
pyl-CH2), 1.19 (9H, s, tBu), 1.64 (1H, m, cyclopropyl-CH), 1.92
(1H, m, cyclopropyl-CH), 3.53 (1H, dd, J = 6.2, 10.8 Hz, CH2OTBDPS),
3.83 (1H, dd, J = 4.7, 10.8 Hz, CH2OTBDPS), 7.36–7.45 (6H, m, aro-
matic), 7.53 (1H, d, J = 7.7 Hz, –N@CH), 7.63–7.65 (4H, m, aro-
matic); 13C NMR (100 MHz, CDCl3) d 13.0, 19.4, 22.4, 22.9, 24.8,
26.9, 56.8, 64.8, 127.6, 129.6, 133.4, 135.4, 170.3; HRMS (EI) calcd
for C25H35NO2SSi: 441.2158 (M+), found 441.2158 (M)+.
steps) as a colorless amorphous solid: ½a D17
ꢁ
+24.27 (c 0.96, CHCl3);
1H NMR (400 MHz, CD3OD) d 0.54–0.60 (2H, m, cyclopropyl-CH2),
1.27 (1H, m, cyclopropyl-CH), 1.36 (1H, m, cyclopropyl-CH), 3.43
(1H, d, J = 9.0 Hz, CHNH), 3.77 (1H, dd, J = 8.6, 14.0 Hz, CH2-guani-
dine), 4.07 (1H, dd, J = 5.4, 14.0 Hz, CH2-guanidine), 5.05–5.33
(6H, m, CH2 of Cbz ꢂ3), 7.25–7.45 (15H, m, aromatic); 13C NMR
(100 MHz, CD3OD) d 9.8, 18.5, 21.1, 58.7, 67.5, 68.2, 70.0, 79.5,
128.8, 128.8. 128.9, 129.4, 129.6, 129.7, 129.7, 136.4, 138.1,
138.5, 157.0, 158.4, 162.2, 164.9, 175.2; HRMS (FAB) calcd for
4.1.2. (1R,2R)-2-tert-Butyldiphenylsiloxymethyl-1-[(1R)-1-((S)-
tert-butylsulfinylamino)-2-propenyl]cyclopropane (7)
To a solution of 11 (44 mg, 0.10 mmol) in toluene (10 mL) was
added vinylmagnesium bromide (1.0 M soln in THF, 0.11 mL,
0.11 mmol) at 110 °C, and the mixture was stirred at 110 °C until
11 disappeared by TLC. After the addition of MeOH, the resulting
mixture was evaporated, and the residue was partitioned between
AcOEt and aqueous HCl (1 M). The organic layer was washed with
brine, dried (Na2SO4), and evaporated. The residue was purified by
silica gel column chromatography (hexane/AcOEt = 3/1) to give 7
C
31H33N4O8: 589.2298 [(M+H)+], found 589.2303 [(M+H)+].
4.1.5. (3R,4R)-3,4-Methano- -arginine dihydrochloride (1)
L
Compound 14 (141 mg, 0.239 mmol) was dissolved in a solu-
tion of HCl in EtOH (1 M, 15 mL), and Pd/C (10%, 141 mg) was
added to the mixture. The resulting mixture was stirred under an
atmospheric pressure of H2 gas at rt for 6 h. The mixture was
(45 mg, 97%) as a light yellow oil: ½a D18
ꢁ
+26.48 (c 0.98, CHCl3); 1H
NMR (400 MHz, CDCl3) d 0.54 (1H, m, cyclopropyl-CH2), 0.61 (1H,
m, cyclopropyl-CH2), 0.83 (1H, m, cyclopropyl-CH), 0.98 (1H, m,

5988
M. Watanabe et al. / Bioorg. Med. Chem. 19 (2011) 5984–5988
filtered through Celite with MeOH, and the filtrate was evaporated.
The residue was mixed into H2O, and evaporated. The residue was
purified by C18 reverse phase silica gel column chromatography
(10% MeOH in H2O) to give a crude product of 1 (59 mg) as an
amorphous solid. After the crude product of 1 was purified by
RP-HPLC (0.1% TFA in H2O, 10 mL/min, rt, detected at 202 nm) with
Mightysil RP-18 (250 ꢂ 20 mm, Kanto Chemical Co.), the obtained
compound was treated with aqueous HCl (2 M) and the mixture
was evaporated (this process was repeated three times.) to give 1
Memorial Foundation (to M.W.). The authors are grateful to Sanyo
Fine Co., Ltd for the gift of the chiral epichlorohydrins.
A. Supplementary data
Supplementary data (experimental details for the synthesis of 2,
3, 4, ent-1, ent-2, ent-3, and ent-4) associated with this article can
be found, in the online version, at doi:10.1016/j.bmc.2011.08.049.
(30 mg, 48%) as an amorphous solid: ½a D23
ꢁ
+33.68 (c 0.77, H2O);
References and notes
1H NMR (400 MHz, D2O) d 0.72–0.79 (2H, m, cyclopropyl-CH2),
1.13 (1H, m, cyclopropyl-CH), 1.46 (1H, m, cyclopropyl-CH), 2.87
(1H, dd, J = 8.6, 14.5 Hz, CH2-guanidine), 3.30 (1H, dd, J = 5.9,
14.5 Hz, CH2-guanidine), 3.35 (1H, d, J = 9.9 Hz, –CHNH); 13C
NMR (100 MHz, D2O) d 9.9, 17.9, 18.1, 44.3, 57.1, 157.3, 172.2;
HRMS (FAB) calcd for C7H15N4O2: 187.1195 [(M+H)+], found
187.1200 [(M+H)+]. Anal. (C7H16Cl2N4O2ꢃ0.8H2O) C, 30.74; H,
6.49; N, 20.48. Found: C, 30.70; H, 6.31; N, 20.52.
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l
l
Nitric oxide-mediated oxidation of hemoglobin-A0 was monitored
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Acknowledgments
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This study was supported by the Japan Society for the
Promotion of Science (Grant-in-Aid for Young Scientists
20890002 to M.W. and Grant 21390028 to S.S.) and the Uehara