Expeditious synthesis of nicotianamine and 2′-deoxymugineic acid

Article abstract of DOI:10.1016/S0040-4020(01)00215-0

A simple and efficient method of synthesizing nicotianamine 4 and 2′-deoxymugineic acid 3 was devised. We employed thioamide as an intermediate and the title compounds (4 and 3) were afforded via chemoselective reduction of the thioamides in 33% overall yield through 7 steps and 30% overall yield through 8 steps, respectively.

Full text of DOI:10.1016/S0040-4020(01)00215-0

TETRAHEDRON
Pergamon
Tetrahedron 57 -2001) 3355±3360
Expeditious synthesis of nicotianamine and 20-deoxymugineic acid
Katsuhiro Miyakoshi, Jun Oshita and Takeshi Kitaharap
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi,
Bunkyo-ku, Tokyo 113-8657, Japan
Received 30 December 2000; accepted 21 February 2001
AbstractÐA simple and ef®cient method of synthesizing nicotianamine 4 and 20-deoxymugineic acid 3 was devised. We employed
thioamide as an intermediate and the title compounds -4 and 3) were afforded via chemoselective reduction of the thioamides in 33%
overall yield through 7 steps and 30% overall yield through 8 steps, respectively. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
intermediates to afford structurally diverse phytosidero-
phores in suf®cient amount for biological studies. Our
synthetic strategy toward 3 and 4 is illustrated in Scheme
1. In our previous work,2d we prepared tripeptide D by twice
amide coupling, C with B, then with A. On the other hand,
we have been interested in the biological activities of
various analogues related to 3 and 4. If these analogues
show high iron-chelating and uptake-promoting ability,
phytosiderophores would be applicable for practical use.
One dif®culty, which impedes their practical use, is the
particular structure of l-azetidine-2-carboxylic acid -see
C), so we intended to synthesize analogues without an
azetidine ring. In order to afford the related analogues
ef®ciently, it should be better to prepare the dipeptide
from the righthand side. Thus, preparation of A and B and
then coupling with C should give the target molecule. By
changing the residue C with other amino acid derivatives, it
would be possible to afford any type of phytosiderophore
analogues very ef®ciently.
Phytosiderophores 1±4 produced in higher plants as iron-
chelating amino acids promote the uptake of iron from soil.
The role of phytosiderophores is signi®cant in plant
physiology and has led several groups to synthesize them.
20-Deoxymugineic acid 3 -Fig. 1) has been isolated from the
washing of wheat -Triticum aestivum L.) under iron-
de®cient conditions.1 It has been synthesized four times2
and the syntheses have established its absolute con®guration
as depicted in Fig. 1. Nicotianamine 4 was ®rst isolated from
the leaves of Nicotiana tabacum L. and the ®rst structure
proposal was reported by Noma et al.3a Later, the structure
was slightly corrected to 4 by Kristensen and Larsen.3b
Nicotianamine 4 is now known as a key biosynthetic pre-
cursor of phytosiderophores. Various studies have proved
that nicotianamine plays a signi®cant role in plants as an
iron transporter4 and, therefore, nicotianamine also has
become a synthetic target compound.2c,d,4b,5 A comprehen-
sive review of the previous syntheses of phytosiderophores
has been published.6
With this plan in mind, we ®rst examined the synthesis of
20-deoxymugineic acid 3 and nicotianamine 4. Here we
describe the synthesis of 3 and 4 in detail.
The aim of the present work is to attempt a novel approach
for an ef®cient synthesis of these compounds via peptide
2. Results and discussion
CO2H
N
CO2H
CO2H
Z
The synthesis of nicotianamine 4 was carried out as shown
in Scheme 2. Coupling of the known amine 57 and
carboxylic acid 68 by use of DCC gave dipeptide 7 in
89% yield. The dipeptide 7 was hydrogenated, and the
resulting carboxylic acid 8 was coupled with the amine 99
by use of DCC to give tripeptide 10 in 75% yield. Thio-
amidation of 10 with Lawesson's reagent10 gave thioamide
11 in 71% yield, which was converted to the fully protected
nicotianamine 12 by reaction with excess amount of Raney-
Ni11 in 75% yield. Final deprotection with 4N HCl±EtOAc
and Dowex puri®cation afforded nicotianamine 4 in 94%
yield. The spectral data were identical with those
Y
N
H
X
1 Mugineic acid : X=Z=OH, Y=H
2 3-Epihydroxymugineic acid : X=Y=Z=OH
3 2'-Deoxymugineic acid : X=Y=H, Z=OH
4 Nicotianamine : X=Y=H, Z=NH2
Figure 1.
Keywords: phytosiderophores; thioamidation; chemoselective reduction.
Corresponding author. Tel.: 181-3-5841-5119; fax: 181-3-5841-8019;
e-mail: atkita@mail.ecc.u-tokyo.ac.jp
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020-01)00215-0

3356
K. Miyakoshi et al. / Tetrahedron 57 /2001) 3355±3360
Amide coupling with
CO2R1
CO2R1
Y
CO2R1
Y
CO2R1
XR3
HO2C
NHR2
CO2R1
XR3
B
3
or
4
Deprotection
HO2C
N
N
then with
H
Chemoselective
Reduction
X = O or NH
A
CO2R1
Y = O or S
( X= O or NH )
C
D
NH
Scheme 1. Revised strategy.
CO2But
O
CO2But
NHBoc
CO2But
CO2But
NHBoc
Pd/C, H2
DCC, HOBt
+
BnO2C
BnO2C
HO2C
NH2
N
EtOAc, 99%
CH2Cl2, 89%
H
5
7
6
CO2But
CO2But
O
CO2But CO2But
O
CO2But CO2But
O
9
NH
Lawesson's reagent
benzene, reflux, 71%
HO2C
N
H
NHBoc
N
H
10
NHBoc
N
DCC, HOBt
CH2Cl2, 75%
8
CO2But CO2But
CO2But
N
CO2But CO2But
S
CO2But
S
Raney-Ni (W-2)
THF, 75%
N
H
N
NHBoc
NHBoc
N
H
11
12
CO2H
N
CO2H
CO2H
NH2
1) 4N HCl-EtOAc
N
H
2) Dowex purification
94%
Nicotianamine 4
Scheme 2.
reported3a -33.2% overall yield in 7 steps). Especially,
the agreement of the value of optical rotation showed
that no epimerization occurred through thioamidation
and desulfurization steps.
desulfurization because of the same reason for the synthesis
of nicotianamine.
In conclusion, we have achieved an ef®cient synthesis of nico-
tianamine 4 and 20-deoxymugineic acid 3 by a simple and
straightforward method. By this procedure, we are now able
to afford 4 and 3 on several gram scale, which enables ®eld
study to be carried out. This method will be applied to synth-
esis of other phytosiderophores and analogues and, in fact, we
already established the synthesis of avenic acid, also a natural
congenerofphytosiderophore, andother interestinganalogues
with signi®cant biological activity as that of phytosidero-
phores. These results will be reported in the near future.
The synthesis of 20-deoxymugineic acid 3 was realized
according to Scheme 3. Amide coupling of the known
amine 5 and carboxylic acid 1312 by use of DCC afforded
dipeptide 14 in 95% yield. The dipeptide 14 was subjected
to hydrogenation, and the resulting carboxylic acid 15 was
coupled with amine 9 to give tripeptide 16 in 71% yield. The
tripeptide 16 was converted to thioamide 17 with
Lawesson's reagent in 95% yield, and the successive
desulfurization was achieved with Raney-Ni to afford
protected 20-deoxymugineic acid 18 in 51% yield. Finally,
treatment with TFA and 1% methanolic KOH solution
followed by Dowex puri®cation gave 20-deoxymugineic
acid 3 in 93% yield. The spectral data were in agreement
with the literature values1 -29.5% overall yield in 8 steps),
and no epimerization occurred through thioamidation and
3. Experimental
3.1. General
Infrared spectra -IR) were measured on a Jasco FT/IR-230

K. Miyakoshi et al. / Tetrahedron 57 /2001) 3355±3360
3357
CO2But
O
CO2Me
OAc
CO2But
NH2
CO2Me
OAc
Pd/C, H2
DCC, HOBt
BnO2C
+
HO2C
BnO2C
N
H
EtOAc, 96%
CH2Cl2, 95%
13
5
14
CO2But CO2Me
O
CO2But CO2Me
O
CO2But
O
9, DCC, HOBt
Lawesson's reagent
benzene, reflux, 95%
HO2C
N
H
OAc
N
H
OAc
N
CH2Cl2, 71%
15
16
CO2But CO2Me
CO2But
N
CO2But CO2Me
S
CO2But
S
Raney-Ni (W-2)
THF, 51%
N
H
N
OAc
OAc
N
H
17
18
CO2H
CO2H
CO2H
OH
1) TFA
N
H
N
2) 1% KOH-MeOH
3) Dowex purification
93%
2'-Deoxymugineic acid 3
Scheme 3.
spectrometer. Proton magnetic resonance spectra -1H NMR)
were recorded at 300 MHz on JEOL JNM-AL 300 spectro-
meter. Chemical shifts -d) are reported in parts per million
relative to internal chloroform -d 7.24). Optical rotations
were measured on a Jasco DIP-1000 polarimeter. Analytical
thin-layer chromatography -TLC) was carried out using
0.25 mm Merck silica gel 60 F254 precoated glass-backed
plates. Column chromatography was performed on Merck
silica gel 60 and Cica silica gel 60N -neutral). All solvents
used were of reagent grade. Tetrahydrofuran was distilled
over benzophenone and sodium prior to use. Dichloro-
white foam; FT-IR -nujol cm21) 3314, 1747, 1729, 1692,
25
1
1655; [a]D ˆ25.8 -c 0.98, CHCl3); H NMR -300 MHz,
CDCl3) d -ppm) 1.42 -27H, s, ±CO2But, Boc), 2.63 -1H, dd,
Jˆ4.5, 15.9 Hz, H-3), 2.81 -2H, m, H-20), 2.98 -1H, dd,
Jˆ4.2, 15.9 Hz, H-3), 4.36 -1H, m, H-30), 4.67 -1H, ddd,
Jˆ4.2, 4.5, 7.5 Hz, H-2), 5.09 -2H, m,± CH2Ph), 5.64 -1H,
d, Jˆ8.4 Hz, N0-H), 6.45 -1H, d, Jˆ7.5 Hz, N-H), 7.34 -5H,
m, ±CH2Ph). Anal. calcd for C28H42N2O9: C, 61.07; H, 7.69;
N, 5.09. Found: C, 61.02; H, 7.66; N, 5.11.
3.1.2. +3S,30S)-3-+3-t-Butoxycarbonyl-3-t-butoxycarbonyl-
aminopropanamido)-3-t-butoxycarbonylpropionic acid
+8). To a solution of dipeptide 7 -4.40 g, 7.99 mmol) in
EtOAc -20 ml) was added 10% Pd/C -1.0 g) and the mixture
was stirred for 3 h under hydrogen at rt. The reaction
mixture was ®ltered through celite and the ®ltrate was
concentrated under reduced pressure. The residue was
puri®ed by chromatography on silica gel -hexane/
EtOAcˆ1:1) to give carboxylic acid 8 -3.63 g, 7.88 mmol,
98.6%) as a white solid; FT-IR -nujol cm21) 3313, 1731,
Ê
methane and benzene were dried and stored over 4 A
molecular sieves.
3.1.1. +2S,30S)-2-+3-t-Butoxycarbonyl-3-t-butoxycarbonyl-
aminopropanamido)-3-benzyloxycarbonylpropionic acid
t-butyl ester +7). To a solution of HOBt -3.47 g,
25.7 mmol) in CH2Cl2 -31 ml) was added successively a
solution of amine 5 -5.39 g, 19.3 mmol) in CH2Cl2
-10 ml),
a solution of carboxylic acid 6 -5.59 g,
25
19.3 mmol) in CH2Cl2 -15 ml) and a solution of DCC
-5.30 g, 25.7 mmol) in CH2Cl2 -10 ml) under argon at 08C
and the mixture was stirred for 15 h at rt. The reaction
mixture was ®ltered through celite and the ®ltrate was
concentrated under reduced pressure. The residue was
diluted with EtOAc and ®ltered through celite again. The
®ltrate was washed with sat. NaHCO3, 1N aq. HCl, sat.
NaHCO3 and brine, dried over MgSO4 and concentrated
under reduced pressure. The residue was diluted with
EtOAc and ®ltered through celite. The ®ltrate was concen-
trated under reduced pressure and the residue was puri®ed
by chromatography on silica gel -hexane/EtOAcˆ4:1) to
give the dipeptide 7 -9.44 g, 17.1 mmol, 88.6%) as a
1698, 1654; [a]D ˆ120.4 -c 1.01, CHCl3); 1H NMR
-300 MHz, CDCl3) d -ppm) 1.42 -27H, s, ±CO2But, Boc),
2.69 -1H, dd, Jˆ3.6, 15.5 Hz, H-3), 2.76±2.92 -2H, m,
H-20), 2.99 -1H, dd, Jˆ4.5, 15.5 Hz, H-3), 4.38 -1H, m,
H-30), 4.70 -1H, m, H-2), 5.72 -1H, d, Jˆ8.4 Hz, N0-H),
6.62 -1H, d, Jˆ8.4 Hz, N-H). Anal. calcd for C21H36N2O9:
C, 54.77; H, 7.88; N, 6.08. Found: C, 54.77; H, 7.96; N,
5.68.
3.1.3. +2S,30S,300S)-N-[3-+3-t-Butoxycarbonyl-3-t-butoxy-
carbonylaminopropanamido)-3-t-butoxycarbonylpropa-
noyl]azetidine-2-carboxylic acid t-butyl ester +10). To a
solution of HOBt -1.42 g, 10.5 mmol) in CH2Cl2 -7 ml) was

3358
K. Miyakoshi et al. / Tetrahedron 57 /2001) 3355±3360
[a]D ˆ242.2 -c 1.60, CHCl3); 1H NMR -300 MHz,
CDCl3) d -ppm) 1.30 -9H, s, ±CO2But or Boc), 1.33 -9H,
s, ±CO2But or Boc), 1.35 -9H, s, ±CO2But or Boc), 1.40
-9H, s, ±CO2But or Boc), 1.56±1.84 -4H, m, H-10, H-100),
2.00±2.23 -2H, m, H-3), 2.34±2.42 -2H, m, H-20 or H-200),
2.55±2.70 -2H, m, H-20 or H-200), 3.00 -1H, dd, Jˆ7.6,
5.6 Hz, H-300), 3.26 -1H, td, Jˆ7.4, 2.4 Hz, H-30), 3.38
-1H, t, Jˆ8.3 Hz, H-2), 4.08 -2H, br, H-4), 5.61 -1H, d,
Jˆ7.5 Hz, N00-H); HRFAB: [M1H]1 calcd for
C29H54N3O8 572.3911, found 572.3925.
21
added successively a solution of amine 9 -1.27 g,
8.08 mmol) in CH2Cl2 -5 ml), a solution of carboxylic
acid 8 -3.71 g, 8.06 mmol) in CH2Cl2 -10 ml) and a solution
of DCC -2.16 g, 10.5 mmol) in CH2Cl2 -5 ml) under argon
at 08C and the mixture was stirred for 20 h at rt. The reaction
mixture was ®ltered through celite and the ®ltrate was
concentrated under reduced pressure. The residue was
diluted with EtOAc and ®ltered through celite again. Then
the ®ltrate was washed with sat. NaHCO3, 1N aq. HCl, sat.
NaHCO3 and brine, dried over MgSO4 and concentrated
under reduced pressure. The residue was diluted with
EtOAc, ®ltered through celite. The ®ltrate was concentrated
under reduced pressure and the residue was puri®ed by
chromatography on silica gel -hexane/EtOAcˆ4:1±2:1) to
give tripeptide 10 -3.64 g, 6.07 mmol, 75.3%) as a white
3.1.6. Nicotianamine +4). To the amine 12 -519 mg,
0.908 mmol) was added 15 ml of 4N HCl in EtOAc under
argon at 08C and the mixture was stirred for 10 h at rt. The
reaction mixture was concentrated under reduced pressure
and puri®ed by ion exchange resin -Dowex 50W-X8, H2O
then 2N aq. NH3) to give nicotiamanine 4 -260 mg,
foam; FT-IR -nujol cm21
)
3340, 1742, 1660;
[a]D ˆ244.0 -c 1.00, CHCl3); 1H NMR -300 MHz,
CDCl3) d -ppm) 1.41 -9H, s, ±CO2But or Boc), 1.43 -9H,
s, ±CO2But or Boc), 1.45 -9H, s, ±CO2But or Boc), 1.48
-9H, s, ±CO2But or Boc), 1.89 -1H, br, H-3), 2.10±2.23 -1H,
m, H-3), 2.43±2.91 -4H, m, H-20, H-200), 3.85±4.20 -2H, m,
H-4), 4.38 -1H, br, H-2 or H-30 or H-300), 4.51±4.72 -2H, m,
H-2 or H-30 or H-300), 5.67 -1H, br, N00-H), 6.67 -0.5H, d,
Jˆ6.9 Hz, N0-H), 6.93 -0.5H, d, Jˆ7.7 Hz, N0-H). Anal.
calcd for C29H49N3O10: C, 58.08; H, 8.24; N, 7.01. Found:
C, 57.64; H, 8.19; N, 6.95.
25
0.857 mmol, 94.4%) as a white solid; FT-IR -nujol cm21
)
34
3410, 1617; [a]D ˆ256.4 -c 0.81, H2O), [lit.
23
1
[a]D ˆ260.5 -c 2.7, H2O)]; H NMR -300 MHz, D2O)
-ppm) 1.91±2.21 -4H, m, H-20, H-200), 2.32±2.46 -1H, m,
H-3), 2.59 -1H, qd, Jˆ9.3, 4.3 Hz, H-3), 3.12 -2H, t,
Jˆ6.9 Hz, H-100), 3.15±3.35 -2H, m, H-10), 3.66 -1H, dd,
Jˆ4.4, 8.3 Hz, H-30), 3.74 -1H, t, Jˆ5.7 Hz, H-300), 3.83
-1H, t, Jˆ9.6 Hz, H-4), 3.95 -1H, td, Jˆ9.8, 6.6 Hz, H-4),
4.75 -1H, t, Jˆ9.6 Hz, H-2); HRFAB: [M1H]1 calcd for
C12H22N3O6 304.1509, found 304.1512.
3.1.4. +2S,30S,300S)-N-[3-+3-t-Butoxycarbonyl-3-t-butoxy-
carbonylaminopropanethioamido)-3-t-butoxycarbonyl-
propanethioyl]azetidine-2-carboxylic acid t-butyl ester
+11). To a solution of tripeptide 10 -4.92 g, 8.20 mmol) in
benzene -82 ml) was added Lawesson's reagent -3.65 g,
9.02 mmol) and the mixture was stirred for 2 h under
argon at 808C. The reaction mixture was ®ltered through
celite and the ®ltrate was concentrated under reduced pres-
sure. The residue was puri®ed twice by chromatography on
silica gel -CH2Cl2/EtOAcˆ1:0±10:1, hexane/EtOAcˆ
20:1±10:1) to give thioamide 11 -3.68 g, 5.82 mmol,
71.0%) as a white foam; FT-IR -nujol cm21) 3304, 1729;
3.1.7. +2S,30S)-2-+3-Acetoxy-3-methoxycarbonylpropan-
amido)-3-benzyloxycarbonylpropionic acid t-butyl ester
+14). To a solution of HOBt -7.01 g, 51.9 mmol) in CH2Cl2
-155 ml) was added successively a solution of amine 5
-11.5 g, 41.2 mmol) in CH2Cl2 -10 ml), a solution of
carboxylic acid 13 -7.83 g, 41.2 mmol) in CH2Cl2 -15 ml)
and a solution of DCC -10.7 g, 51.9 mmol) in CH2Cl2
-10 ml) under argon at 08C and the mixture was stirred for
6 h at rt. The reaction mixture was ®ltered through celite and
the ®ltrate was concentrated under reduced pressure. The
residue was diluted with EtOAc and ®ltered through celite
again. Then the ®ltrate was washed with sat. NaHCO3, 1N
aq. HCl, sat. NaHCO3 and brine, dried over MgSO4 and
concentrated under reduced pressure. The residue was
diluted with EtOAc and ®ltered through celite. The ®ltrate
was concentrated under reduced pressure and the residue
was puri®ed by chromatography on silica gel -hexane/
EtOAcˆ1:1) to give dipeptide 14 -17.7 g, 39.3 mmol,
95.3%) as a white foam; FT-IR -nujol cm21) 3320, 1747,
[a]D ˆ17.3 -c 1.17, CHCl3); 1H NMR -300 MHz, CDCl3)
29
d -ppm) 1.42 -9H, s, ±CO2But or Boc), 1.44 -9H, s,
±CO2But or Boc), 1.46 -9H, s, ±CO2But or Boc), 1.52
-9H, s, ±CO2But or Boc), 2.15±2.27 -1H, m, H-3), 2.45±
2.70 -1H, m, H-3), 3.03±3.23 -4H, m, H-20, H-200), 4.09±
4.37 -2H, m, H-4), 4.48±4.58 -1H, m, H-30 or H-300), 4.75±
4.85 -1H, m, H-30 or H-300), 5.24 -0.5H, dt, Jˆ4.2, 7.9 Hz,
H-2), 5.39 -0.5H, dt, Jˆ4.2, 8.1 Hz, H-2), 5.75 -1H, d,
Jˆ8.4 Hz, N00-H), 8.73 -0.5H, d, Jˆ7.5 Hz, N0-H), 8.89
-0.5H, d, Jˆ7.5 Hz, N0-H); HRFAB: [M]1 calcd for
C29H49N3O8S2 631.2961, found 631.2933.
26
1650; [a]D ˆ132.4 -c 1.07, CHCl3); 1H NMR -300 MHz,
CDCl3) d -ppm) 1.38 -9H, s, ±CO2But), 2.08 -3H, s, ±OAc),
2.72 -1H, d, Jˆ7.5 Hz, H-20), 2.74 -1H, d, Jˆ4.8 Hz, H-20),
2.84 -1H, dd, Jˆ4.2, 17.0 Hz, H-3), 2.99 -1H, dd, Jˆ4.2,
17.0 Hz, H-3), 3.74 -3H, s, ±CO2Me), 4.70 -1H, dd, Jˆ4.2,
7.8 Hz, H-2), 5.10 -2H, q, Jˆ12.0 Hz, ±CH2Ph), 5.40 -1H,
dd, Jˆ4.8, 7.5 Hz, H-30), 6.55 -1H, d, Jˆ7.8 Hz, N-H), 7.33
-5H, m, ±CH2Ph). Anal. calcd for C22H29NO9: C, 58.53; H,
6.47; N, 3.10. Found: C, 58.59; H, 6.47; N, 3.21.
3.1.5. +2S,30S,300S)-N-[3-+3-t-Butoxycarbonyl-3-t-butoxy-
carbonylaminopropylamino)-3-t-butoxycarbonylpropyl]-
azetidine-2-carboxylic acid t-butyl ester +12). To a
solution of thioamide 11 -1.05 g, 1.66 mmol) in THF
-10 ml) was added 10 ml of THFsuspension of Raney-Ni
-W-2) -0.5 g/ml) and the mixture was stirred for 4 h under
argon at rt. The reaction mixture was ®ltered through celite
by washing with hot THFand the ®ltrate was concentrated
under reduced pressure. The residue was puri®ed by chro-
matography on silica gel -hexane/EtOAcˆ3:2±0:1) to give
amine 12 -712 mg, 1.25 mmol, 75.3%) as a yellow oil;
FT-IR -neat cm21) 3355, 2977, 2932, 1730, 1708;
3.1.8. +3S,30S)-3-+3-Acetoxy-3-methoxycarbonylpropan-
amido)-3-t-butoxycarbonylpropionic acid +15). To a
solution of dipeptide 14 -7.22 g, 16.0 mmol) in EtOAc
-20 ml) was added 10% Pd/C -2.0 g) and the mixture was
stirred for 2.5 h under hydrogen at rt. The reaction mixture
was ®ltered through celite and the ®ltrate was concentrated

K. Miyakoshi et al. / Tetrahedron 57 /2001) 3355±3360
3359
to give carboxylic acid 15 -5.55 g, 15.4 mmol, 96.0%) as a
white solid; FT-IR -nujol cm21) 3354, 1754, 1668;
3.68 -3H, s, ±CO2Me), 4.04±4.32 -2H, m, H-4), 4.79 -1H,
m, H-2), 5.16 -0.5H, dt, Jˆ4.2, 6.6 Hz, H-30), 5.40 -0.5H, dt,
Jˆ4.8, 7.8 Hz, H-30), 5.48 -0.5H, dd, Jˆ3.9, 8.4 Hz, H-300),
5.57 -0.5H, dd, Jˆ4.2, 8.4 Hz, H-300), 8.78 -0.5H, d,
Jˆ6.6 Hz, N0-H), 9.12 -0.5H, d, Jˆ7.8 Hz, N0-H);
HRFAB: [M1H]1 calcd for C23H37N2O8S2 533.1991,
found 533.1971.
[a]D ˆ121.1 -c 1.01, CHCl3); 1H NMR -300 MHz,
26
CDCl3) d -ppm) 1.42 -9H, s, ±CO2But), 2.10 -3H, s,
±OAc), 2.79 -1H, d, Jˆ7.2 Hz, H-20), 2.80 -1H, d,
Jˆ5.1 Hz, H-20), 2.83 -1H, dd, Jˆ4.5, 17.0 Hz, H-2), 2.98
-1H, dd, Jˆ4.5, 17.0 Hz, H-2), 3.69 -3H, s, ±CO2Me), 4.70
-1H, dt, Jˆ4.5, 7.5 Hz, H-3), 5.40 -1H, dd, Jˆ5.1, 7.2 Hz,
H-30), 6.88 -1H, d, Jˆ7.5 Hz, N-H), 9.86 -1H, br, ±CO2H).
Anal. calcd for C15H23NO9: C, 49.86; H, 6.42; N, 3.88.
Found: C, 49.93; H, 6.43; N, 3.92.
3.1.11. +2S,30S,300S)-N-[3-+3-Acetoxy-3-methoxycarbo-
nylpropylamino)-3-t-butoxycarbonylpropyl]azetidine-2-
carboxylic acid t-butyl ester +18). To a solution of thio-
amide 17 -5.00 g, 9.39 mmol) in THF-15 ml) was added
100 ml of THFsuspension of Raney-Ni -W2) -0.5 g/ml) and
the mixture was stirred for 4 h under argon at rt. The reac-
tion mixture was ®ltered through celite by washing with hot
THFand the ®ltrate was concentrated under reduced pres-
sure. The residue was puri®ed by chromatography on silica
gel -hexane/EtOAcˆ1:3±0:1) to give amine 18 -2.28 g,
3.1.9. +2S,30S,300S)-N-[3-+3-Acetoxy-3-methoxycarbonyl-
propanamido)-3-t-butoxycarbonylpropanoyl]azetidine-
2-carboxylic acid t-butyl ester +16). To a solution of HOBt
-10.4 g, 76.6 mmol) in CH2Cl2 -230 ml) was added succes-
sively a solution of amine 9 -9.56 g, 60.8 mmol) in CH2Cl2
-10 ml),
a solution of carboxylic acid 15 -22.0 g,
4.82 mmol, 51.4%) as a yellow oil; FT-IR -neat cm21
)
60.8 mmol) in CH2Cl2 -10 ml) and a solution of DCC
-15.8 g, 76.6 mmol) in CH2Cl2 -10ml) under argon at 08C
and the mixture was stirred for 6 h at rt. The reaction
mixture was ®ltered through celite and the ®ltrate was
concentrated under reduced pressure. The residue was
diluted with EtOAc and ®ltered through celite again. Then
the ®ltrate was washed with sat. NaHCO3, 1N aq. HCl, sat.
NaHCO3 and brine, dried over MgSO4 and concentrated
under reduced pressure. The residue was diluted with
EtOAc and ®ltered through celite. The ®ltrate was concen-
trated under reduced pressure and the residue was puri®ed
by chromatography on silica gel -hexane/EtOAcˆ1:3±0:1)
to give tripeptide 16 -21.6 g, 43.2 mmol, 71.2%) as a white
foam; FT-IR -nujol cm21) 3315, 1770, 1739, 1687, 1639;
3454, 1731; [a]D ˆ276.6 -c 1.13, CHCl3); 1H NMR
-300 MHz, CDCl3) d -ppm) 1.43 -18H, s, ±CO2But),
1.37±1.54 -3H, m, H-20, N0-H), 1.96 -2H, q, Jˆ6.3 Hz,
H-200), 2.01±2.11 -1H, m, H-3), 2.10 -3H, s, ±OAc), 2.23
-1H, dt, Jˆ8.4, 9.0 Hz, H-3), 2.41±2.56 -2H, m, H-10 or
H-100), 2.61±2.78 -3H, m, H-4, H-10 or H-100), 3.08 -1H,
m, H-4), 3.32 -1H, t, Jˆ6.6 Hz, H-30), 3.46 -1H, t,
Jˆ8.4 Hz, H-2), 3.70 -3H, s, ±CO2Me), 5.09 -1H, t,
Jˆ6.3 Hz, H-300); HRFAB: [M1H]1 calcd for
C23H41N2O8 473.2863, found 473.2848.
21
3.1.12. 20-Deoxymugineic acid +3). To the amine 18
-670 mg, 1.42 mmol) was added 10 ml of TFA under
argon at 08C and the reaction mixture was stirred for 3 h
at rt. To this was added 1% KOH±MeOH and the mixture
was stirred overnight at rt. The mixture was concentrated
and puri®ed by ion exchange resin -Dowex 50W-X8, H2O
then 1N aq. NH3) to give 20-deoxymugineic acid 3 -400 mg,
[a]D ˆ253.9 -c 0.99, CHCl3); 1H NMR -300 MHz,
25
CDCl3) d -ppm) 1.45 -18H, s, ±CO2But), 2.10 -3H, s,
±OAc), 2.06±2.14 -1H, m, H-3), 2.42±2.60 -2H, m, H-3,
H-20), 2.69 -0.5H, dd, Jˆ4.2, 16.5 Hz, H-20), 2.74 -0.5H, d,
Jˆ6.0 Hz, H-200), 2.75 -0.5H, d, Jˆ5.1 Hz, H-200), 2.76
-0.5H, d, Jˆ6.6 Hz, H-200), 2.77 -0.5H, d, Jˆ8.4 Hz,
H-200), 2.80 -0.5H, dd, Jˆ4.2, 16.5 Hz, H-20), 3.69-3H, s,
±CO2Me), 3.91±4.18 -2H, m, H-4), 4.55 -0.5H, dd, Jˆ4.2,
8.7 Hz, H-2), 4.58 -0.5H, dd, Jˆ4.8, 8.1 Hz, H-2), 4.63
-0.5H, dt, Jˆ5.1, 6.9 Hz, H-30), 4.75 -0.5H, dt, Jˆ4.2,
8.4 Hz, H-30), 5.41 -0.5H, dd, Jˆ6.0, 8.4 Hz, H-300), 5.44
-0.5H, dd, Jˆ5.1, 6.6 Hz, H-300), 6.77 -0.5H, d, Jˆ6.9 Hz,
N0-H), 7.07 -1H, d, Jˆ8.4 Hz, N0-H). Anal. calcd for
C23H36N2O10: C, 55.19; H, 7.25; N, 5.60. Found: C, 55.19;
H, 7.23; N, 5.69.
1.31 mmol, 93.0%) as a white solid; FT-IR -nujol cm21
)
29
3441, 1703, 1605; [a]D ˆ274.5 -c 0.74, H2O), [lit.
34
1
[a]D ˆ270.5 -c 0.31, H2O)]; H NMR -300 MHz, D2O)
d -ppm) 1.83 -2H, m, H-20 or H-200), 2.09 -1H, m, H-20 or
H-200), 2.38 -2H, H-3, H-20 or H-200), 2.58 -1H, m, H-3), 3.01
-1H, m, H-100), 3.25 -3H, m, H-10, H-100), 3.75 -1H, q,
Jˆ9.0 Hz, H-30), 3.92 -1H, m, H-4), 4.21 -1H, dd, Jˆ5.7,
9.0 Hz, H-4), 4.33 -1H, t, Jˆ9.0 Hz, H-300), 4.58 -1H, t,
Jˆ9.3 Hz, H-2); HRFAB: [M1H2H2O]1 calcd for
C12H19N2O6 287.1243, found 287.1266.
3.1.10. +2S,30S,300S)-N-[3-+3-Acetoxy-3-methoxycarbonyl-
propanethioamido)-3-t-butoxycarbonylpropanethioyl]-
azetidine-2-carboxylic acid t-butyl ester +17). To a
solution of tripeptide 16 -8.01 g, 16.0 mmol) in benzene
-70 ml) was added Lawesson's reagent -7.12 g,
17.6 mmol) and the mixture was stirred for 3 h under
argon at 808C. The reaction mixture was ®ltered through
celite and the ®ltrate was concentrated under reduced pres-
sure. The residue was puri®ed by chromatography on silica
gel -CH2Cl2/EtOAcˆ1:0±10:1) to give thioamide 17
-8.06 g, 15.1 mmol, 94.6%) as a white foam; FT-IR -nujol
References
1. Nomoto, K.; Yoshioka, H.; Arima, M.; Fushiya, S.; Takagi, S.;
Takemoto, T. Chimia 1981, 249.
2. -a) Ohfune, Y.; Tomiya, M.; Nomoto, K. J. Am. Chem. Soc.
1981, 103, 2409. -b) Fushiya, S.; Sato, Y.; Nakatsuyama, S.;
Kanuma, N.; Nozoe, S. Chem. Lett. 1981, 909. -c) Matsuura,
F.; Hamada, Y.; Shioiri, T. Tetrahedron 1994, 50, 9457.
-d) Klair, S. S.; Mohan, H. R.; Kitahara, T. Tetrahedron
Lett. 1998, 39, 89.
cm21) 3285, 1759, 1737, 1711; [a]D ˆ225.8 -c 1.06,
27
3. -a) Noma, M.; Noguchi, M.; Tamaki, E. Tetrahedron Lett.
1971, 22, 2017. -b) Kristensen, I.; Larsen, P. O. Phyto-
chemistry 1974, 13, 2791.
1
CHCl3); H NMR -300 MHz, CDCl3) d -ppm) 1.49 -18H,
s, ±CO2But), 2.11 -3H, s, ±OAc), 2.09±2.20 -1H, m, H-3),
2.50±2.60 -1H, m, H-3), 3.01±3.26 -4H, m, H-20, H-200),
Á Â Â
4. -a) Budesõnsky, M.; Budzikiewicz, H.; Prochazka, Z.;

3360
K. Miyakoshi et al. / Tetrahedron 57 /2001) 3355±3360
È
Ripperber, H.; Romer, A.; Scholz, G.; Schreiber, K. Phyto-
chemistry 1980, 19, 2295. -b). Ripperger, H.; Schreiber, K.
Heterocycles 1982, 17, 447.
9. Shioiri, T.; Hamada, Y.; Matsuura, F. Tetrahedron 1993, 49,
8211.
10. Clausen, K.; Thosen, M.; Lawesson, S. O. Tetrahedron 1981,
37, 3635.
5. Fushiya, S.; Nakatsuyama, S.; Sato, Y.; Nozoe, S. Hetero-
cycles 1981, 15, 819.
11. Dener, J. M.; Hart, D. J.; Ramesh, S. J. Org. Chem. 1988, 53,
6022.
6. Shioiri, T.; Hamada, Y.; Matsuura, F. Tetrahedron 1995, 14,
3939.
12. Henrot, S.; Larcheveque, M.; Petit, Y. Synth. Commun. 1986,
16, 183.
7. Roeske, R. W. J. Org. Chem. 1963, 28, 1251.
8. Ramsamy, K.; Olsen, R. K.; Emery, T. Synthesis 1982, 42.