Studies on chemical modification of monensin VIII. Synthesis of 7-O-substituted-25-carboxymonensins and their Ca2+ ion transport activity

Article abstract of DOI:10.1016/S0040-4020(01)00154-5

Monensin (1), an ionophore antibiotic agent, was converted to 25-carboxymonensin (2) and 7-O-substituted-25-carboxyl derivatives (3a-d), which have two carboxyl groups at both ends of the molecule. Ca²⁺ ion transport activity of the dicarboxylic monensins was evaluated by the CHCl₃ liquid membrane method, and 25-carboxymonensins (2 and 3a-d) were shown to transport the Ca²⁺ ion through the CHCl₃ liquid membrane.

Full text of DOI:10.1016/S0040-4020(01)00154-5

TETRAHEDRON
Pergamon
Tetrahedron 57 )2001) 3005±3012
Studies on chemical modi®cation of monensin VIII. Synthesis of
7-O-substituted-25-carboxymonensins and their Ca21 ion
transport activity
Rie Tanaka, Akito Nagatsu,p Hajime Mizukami, Yukio Ogihara and Jinsaku Sakakibara
Faculty of Pharmaceutical Sciences, Nagoya City University, Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan
Received 22 December 2000; accepted 5 February 2001
AbstractÐMonensin )1), an ionophore antibiotic agent, was converted to 25-carboxymonensin )2) and 7-O-substituted-25-carboxyl
derivatives )3a±d), which have two carboxyl groups at both ends of the molecule. Ca21 ion transport activity of the dicarboxylic monensins
was evaluated by the CHCl3 liquid membrane method, and 25-carboxymonensins )2 and 3a±d) were shown to transport the Ca21 ion through
the CHCl3 liquid membrane. q 2001 Elsevier Science Ltd. All rights reserved.
Monensin )1, Fig. 1), isolated from Streptomyses
cinnamonensis, is a representative of polyether antibiotics
such as X-206, nigericin and septamycin, and is well known
as a Na1 ionophore.1 Monensin has attracted much attention
because of its unique structure with 17 asymmetric centers
and contiguous tetrahydrofuran and tetrahydropyran rings.
X-Ray crystal structure analysis of the free acid and many
cation complexes clari®ed that monensin )1) formed a
lipophilic exterior and a hydrophilic cavity lined with
oxygen atoms which serve as ligands for the encapsulated
Na1 ion.2 The molecule as a whole is, therefore, lipophilic
enough to transport the Na1 ion across lipophilic biological
membranes depending on the density gradient.3 This ability
results in a variety of biological activities such as antibiotic4
and anticoccidial5 activities. In spite of such chemically and
biologically unique features, monensin is now used only for
veterinary medicine.
duction across membranes. There are only few natural
ionophores such as lasalocid A and A-23187, which
transport one Ca21 ion by two molecules. Some synthetic
`non-cyclic crown ethers' having carboxyl groups at both
terminals were reported to form a 1:1 complex with the
Ca21 ion.7 As a diameter of the Na1 ion )0.97 A) is close
Ê
to that of the Ca21 ion )0.99 A), we expected the trans-
Ê
formation of monensin )1) to the divalent molecule led to
a Ca21 ionophore, which transports one Ca21 ion by one
molecule utilizing the structural nature of monensin.
We reported that 7-O-benzylmonensins8 were more lipo-
philic and much more potent Na1 ionophores than monensin
)1), indicating that lipophilicity of the molecule is an
important factor for ion transport through the membrane.
Furthermore, in a previous communication we described
the conversion of monensin )1) to 25-carboxymonensin
)2), and clari®ed that the Ca21 ion transport activity of 2
was about threefold higher than that of lasalocid A.9
This current work in our laboratory led us to plan the
preparation of more lipophilic 25-carboxymonensin
Calcium ionophores6 are widely used as important reagents
in the ®eld of biological research in order to clarify the
mechanisms of various phenomena including signal trans-
Figure 1. Chemical structure of monensin and its derivatives.
Keywords: monensin; calcium ionophore; ion transport activity; 25-carboxymonensin.
Corresponding author. Tel./fax: 181-52-836-3437; e-mail: anagatsu@phar.nagoya-cu.ac.jp
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020)01)00154-5

3006
R. Tanaka et al. / Tetrahedron 57 /2001) 3005±3012
derivatives, 7-O-substituted-25-carboxymonensins )3a±d),
to obtain potent calcium ionophores. In this paper, we
describe the preparation of 7-O-substituted-25-carboxy-
monensins )3a±d) together with 25-carboxymonensin )2)
in detail and the evaluation of their calcium ion transport
activity.
the second carboxyl group appeared at dc175.9 in the 13C
NMR spectrum. The FABMS of 6 also supported the struc-
ture. Then the methyl ester was hydrolyzed in aqueous
alkaline to give 25-O-methyl-25-carboxymonensin. The
exchange of 25-OMe with OH was achieved by adsorption
on a precoated SiO2 plate for a week, followed by elution
and puri®cation to give the desired dicarboxylic monensin
derivative )2).
1. Result and discussion
1.1. Chemistry
The course to 3a±d is indicated in Scheme 2. Compound 4
was treated with benzyl iodide in the presence of NaH to
1
give a 7-O-benzyl derivative in 57% yield. In the H NMR
spectrum of the resulting compound, the signals due to the
benzyl position appeared at d 4.45 and 4.66. The FABMS of
this compound also supported the structure. After cleavage
of the silyl group to give 7a, stepwise oxidation of the
resulting OH group at C-26 of 7a was carried out in the
same manner as 5 to yield a 25-carboxyl derivative )8a).
In the 13C NMR spectrum of 8a, the signal due to the
25-carboxyl group appeared at 168.9 ppm. Then the methyl
ester was hydrolyzed in aqueous alkaline to give 7-O-
benzyl-25-O-methyl-25-carboxymonensin. The conversion
of 25-OMe to OH was achieved in the same manner to 2,
yielding the desired compound 3a. In the 1H NMR spectrum
of 3a, the signal due to 25-OMe disappeared. The high-
resolution )HR) FABMS spectrum of 3a also supported
the structure. Other 7-O-susbstituted-25-carboxymonensins
The synthetic course to 2 is summarized in Scheme 1. The
hydroxy group at 25-C and the carboxyl group were
protected as methyl ether and methyl ester, respectively,10
followed by silylation of 26-OH to yield 4. Then, 7-OH in 4
was converted to acetate, followed by cleavage of silyl ether
to give 5. In the 1H NMR spectrum of 5, the methyl signals
due to the acetyl group )d 2.06) and two methoxy groups )d
3.28, 3.35) appeared. The signal of 7-H appeared at d 4.72
which shifted down®eld relative to monensin )1).
Compound 5 was treated with PDC to give the aldehyde.
1
The H NMR spectrum of the resulting compound showed
the signal of the formyl proton at d 9.38. The aldehyde was
further oxidized successively to the carboxylic acid )6) by
1
Lindgren's method.11 In the H NMR spectrum of 6, the
signal due to the formyl group disappeared and a signal of
Scheme 1.
Scheme 2.

R. Tanaka et al. / Tetrahedron 57 /2001) 3005±3012
3007
Figure 2. U-Tube system for measurement of ion transport activity through
CHCl3 liquid membrane. The tube contained 1 mL of 10 mM calcium or
sodium chloride in 25 mM tricine buffer )A), 3.5 mL of 0.25 mM test
compound solution in water-saturated CHCl3 )B) and 1 mL of 50 mM citric
acid solution )pH 5, C). The pH of the aqueous phases were adjusted by
addition of Me4NOH.
)3b±d) were similarly prepared from monensin as 3a. Thus,
we established an ef®cient method for the preparation of
25-carboxymonensin )2) and 7-O-substituted-25-carboxy-
monensins )3a±d) by a combination of mild and essential
reactions. We obtained 25-formyl derivatives as the
intermediate, and the formyl derivative will probably
become a synthetically useful intermediate of 26-substituted
monensins.
Figure 3. Ca21 and Na1 ion transport activity of 2 in the different pH.
ion than higher lipophilicity due to the substituents on the
7-O-position.
1.2. Ca21 ion transport activity
We also measured Na ion transport activity of 2 and 3a±d
using the same system. The Na1 ion transport activity of 2
and 3a±d was much lower than that of monensin )1), but 2
and 3a±d transported Na1 ions more than Ca21 ions in this
condition. The ratio of Ca21/Na1 ion transport of 3a±d was
less than that of 2. These data imply that 7-O-substitution
could not contribute to the increase of Ca21 ion transport
activity and should reduce the Ca21 ion selectivity.
Ca21 ion transport activity of the monensin derivatives )2,
3a±d) was evaluated by a CHCl3 liquid membrane method
using a U-tube system )Fig. 2). In the previous letter, the
ion transport activity was evaluated using a calcium or
sodium picrate solution as ion donor aqueous phase )A)
and distilled water as the receiving aqueous phase )C).
This time, we used the buffer solutions to set the pH of
the donor phase )A) containing CaCl2 or NaCl and the
receiving phase )C) at 7.4 and 5.0, respectively. The amount
of Ca21 ion transported from phase A to phase C through the
CHCl3 liquid membrane )B) for 2.0 h at 318C was
0.53 mmol for 3a, 0.55 mmol for 3b, 0.52 mmol for 3c,
0.58 mmol for 3d and 0.61 mmol for 2, while monensin
)1) showed no Ca21 ion transport activity )Table 1). These
data indicate that the introduction of the second carboxyl
group at C-25 gave the Ca21 ion transport activity to the
molecules. Ca21 ion transport activity of 2 and 3a±d was
1.6±1.8-fold higher than that of lasalocid A, a well-known
calcium ionophore. Judging from the Rf values in TLC, the
lipophilicities of 3a±d were higher than, or similar to, that
of 2. Nevertheless, the Ca21 ion transport activities of 3a±d
were similar to or less than that of 2. This fact suggested that
the 7-OH group is important for trapping and releasing of
Ca21 ion and/or stability of the resulting complex with Ca21
We evaluated the Ca21 ion transport activity of 2 by setting
the pH of the ionic water phase at 6.0 and 10.0. Compound 2
transported no ions at pH 6.0, while 2 transported 0.80 mmol
at pH 10.0, which was 1.3-fold larger than the value at pH
7.4. )Fig. 3). The Na1 ion transport activity of 2 at pH 6.0
and 10.0 was also measured. Compound 2 transported
0.30 mmol at pH 6.0 and 0.82 mmol at pH 10 which is the
same as the value at pH 7.4. These data suggested that 2
transported Ca21 ion mainly as the dicarboxylate form and
Na1 ion as the monocarboxylate form.
In summary, 25-carboxymonensin )2) and its 7-O-substi-
tuted derivatives )3a±d) were prepared and were shown to
transport the Ca21 ion through the CHCl3 liquid membrane
in much higher ef®ciency with lower activity for Na1 than
monensin, but the ratio of Ca21 and Na1 ion transport
activity was less than 1 at pH 7.4 in this condition. As 2
transported more Ca21 ions at pH 10 than at pH 7.4, the
dicarboxylic compounds were suggested to transport the
Ca21 ions as the dicarboxylate form. The investigation of
the conformations of dicarboxyl derivatives in the solvent
together with Job's method is now in progress.
Table 1. Ca21 and Na1 ion transport activities of monensin and its deriva-
tives at pH 7.4 )mmol, mean^SE, nˆ3)
Ca21
Na1
1 h
2 h
2 h
Monensin )1)
2
3a
3b
3c
0.01^0.00
0.61^0.04
0.53^0.01
0.55^0.06
0.52^0.02
0.58^0.02
0.33^0.02
2.73^0.07
0.80^0.03
1.05^0.06
1.01^0.05
0.93^0.11
0.95^0.08
0.21^0.00
2. Experimental
2.1. General
0.36^0.04
0.25^0.03
0.26^0.02
0.26^0.04
0.24^0.02
0.15^0.02
3d
Lasalocid A
All the melting points were determined on a Yanagimoto
micro melting point apparatus and are uncorrected. The

3008
R. Tanaka et al. / Tetrahedron 57 /2001) 3005±3012
FABMS and high-resolution )HR) FABMS were measured
with JEOL JMS DX-505 or SX-102 mass spectrometer, and
silylmonensin methyl ester )325 mg) and TBAF´3H2O
)240 mg) in THF )8.5 mL) was stirred under Ar atmosphere
at room temperature for 3.5 h. The reaction mixture was
poured into brine, and extracted with EtOAc. The organic
layer was dried over Na2SO4, and evaporated under reduced
pressure. The residue was chromatographed on silica gel
)hexane/EtOAcˆ3:1) to give 5 )273 mg, 97%) as a colorless
1
the IR spectra with a JASCO IRA-2 spectrometer. The H
NMR spectra were measured with a JEOL EX-270,
Lambda-400 or 500 spectrometer using tetramethylsilane
as an internal standard. The following abbreviations are
used: s, singlet; d, doublet; t, triplet; dd, doublet-of-
doublets; td, triplet-of-doublets; qd, quartet of doublets;
ddd, doublet-of-doublets-of-doublets; m, multiplet; br,
broad. Optical rotations were measured on a JASCO DIP-
140 or DIP-1000 digital polarimeter. TLC was carried out
on precoated plates )Kieselgel 60 F254, 0.25 mm thick,
Merck no. 5715), and spots were detected by illumination
with an ultraviolet lamp or by spraying 1% Ce)SO4)2±10%
H2SO4, followed by heating. Column chromatography was
performed on Silica gel BW-200 )Fuji Devison Chemicals).
25
syrup: [a]D ˆ181 )c 0.23, CHCl3); IR )CHCl3,
cm21):1732 )CvO); H NMR )CDCl3, d): 2.06 )3H, s,
1
CH3CO), 2.63 )1H, quintet-like, Jˆ6.8 Hz, 2-H), 3.28
)3H, s, 25-OCH3), 3.35 )4H, 3-OCH3 and 3-H, overlapped),
3.45 )1H, dd, Jˆ3.5, 9.6 Hz, 21-H), 3.54 )1H, dd, Jˆ6.8,
11.1 Hz, 26-Ha), 3.55 )1H, dd, Jˆ6.6, 8.3 Hz, 13-H), 3.70
)1H, dd, Jˆ5.0, 11.2 Hz, 26-Hb), 3.74 )3H, s, CO2CH3), 3.88
)1H, dd, Jˆ2.0, 9.9 Hz, 5-H), 3.95 )1H, d, Jˆ4.2 Hz, 17-H),
4.26 )1H, ddd, Jˆ3.5, 6.6, 11.7 Hz, 20-H), 4.72 )1H, dd,
Jˆ2.7, 5.6 Hz, 7-H). Anal )%): Calcd for C40H68O12: C,
64.84; H, 9.25. Found: C, 64.59; H, 9.29.
2.1.1. 25-O-Methyl-26-O-t-butyldimethylsilylmonensin
methyl ester ,4). A solution of 25-O-methylmonensin
methyl ester10 )1807 mg), imidazole )1409 mg) and
TBDMS±Cl )2540 mg) in THF )80 mL) was stirred under
Ar atmosphere at room temperature for 22 h. The mixture
was poured into brine and extracted with EtOAc. The
organic layer was dried over Na2SO4, and concentrated
under reduced pressure. The residue was chromatographed
on silica gel )hexane/EtOAcˆ6:1) to give 4 )2069 mg, 98%)
2.1.4. 7-O-Acetyl-25-O-methyl-25-formylmonensin methyl
ester. To a solution of 5 )221 mg) in CH2Cl2 )9.0 mL) was
added PDC )280 mg), MS4A )160 mg), and Celite
)400 mg). The mixture was stirred under Ar atmosphere at
room temperature for 4.5 h. The resulting mixture was
®ltered through Celite and the ®ltrate was evaporated
under reduced pressure. The residue was chromatographed
on silica gel )hexane/EtOAcˆ6:1) to give the aldehyde
25
as a colorless syrup: [a]D ˆ157 )c 0.30, CHCl3); IR
1
25
)CHCl3, cm21): 1735 )CvO); H NMR )CDCl3, d): 0.00
)200 mg, 91%) as a colorless syrup: [a]D ˆ1100 )c
1
)6H, s, Si)CH3)2), 0.88 )9H, s, SiC)CH3)3), 2.64 )1H, qd,
Jˆ6.9, 3.5 Hz, 2-H), 3.20 )3H, s, 25-OCH3), 3.33 )3H, s,
3-OCH3), 3.41 )1H, dd, Jˆ4.7, 3.5 Hz, 3-H), 3.52 )1H, t,
Jˆ5.0 Hz, 13-H), 3.64 )1H, m, 21-H), 3.71 )3H, s,
CO2CH3), 3.66±3.75 )1H, m, 7-H), 3.93 )1H, dd, Jˆ2.0,
9.6 Hz, 5-H), 4.02 )1H, d, Jˆ4.3 Hz, 17-H), 4.24 )1H, td,
Jˆ3.0, 6.3 Hz, 20-H). FABMS )m/z): 835 )M1Na)1.
HRFABMS: Calcd for C44H80O11SiNa: 835.5368
)M1Na)1. Found: 835.5355.
0.21, CHCl3); IR )CHCl3, cm21):1730 )CvO); H NMR
)CDCl3, d): 2.06 )3H, s, CH3CO), 2.64 )1H, quintet-like,
Jˆ6.8 Hz, 2-H), 3.27 )3H, s, 25-OMe), 3.35 )1H, t,
Jˆ5.5 Hz, 13-H), 3.47 )1H, dd, Jˆ3.5, 10.1 Hz, 21-H),
3.54 )1H, dd, Jˆ6.8, 8.4 Hz, 3-H), 3.74 )3H, s, CO2CH3),
3.88 )1H, dd, Jˆ1.8, 9.9 Hz, 5-H), 3.97 )1H, d, Jˆ3.9 Hz,
17-H), 4.30 )1H, ddd, Jˆ3.5, 8.7, 8.5 Hz, 20-H), 4.72 )1H,
d, Jˆ2.9 Hz, 7-H), 9.38 )1H, s, CHO). FABMS )m/z): 738
)M)1, 762 )M1Na11)1, HRFABMS: Calcd for
C40H66O12Na: 761.4452 )M1Na)1. Found: 761.4435.
2.1.2. 7-O-Acetyl-25-O-methyl-26-O-t-butyldimethylsilyl-
monensin methyl ester. To a solution of 4 )631 mg) in
pyridine )3.0 mL) and benzene )5.0 mL) was added Ac2O
)3.0 mL) and DMAP )9.4 mg). The mixture was stirred
under Ar atmosphere at room temperature for 15 h. The
reaction mixture was poured into water and extracted with
EtOAc. The organic layer was washed with 5% HCl, 10%
NaHCO3, and brine, dried over Na2SO4, and evaporated in
vacuo. The residue was chromatographed on silica gel
)hexane/EtOAcˆ9:1) to give 7-O-acetyl derivative
CHCl3); IR )CHCl3, cm21):1732 )CvO); 1H NMR )CDCl3,
d): 0.04 )6H, s, Si)CH3)2), 0.88 )9H, s, C)CH3)3), 2.06 )3H,
s, CH3CO), 2.64 )1H, quintet-like, Jˆ6.8 Hz, 2-H), 3.21
)3H, s, 25-OMe), 3.35 )3H, s, 3-OMe), 3.36 )1H, t,
Jˆ4.4 Hz, 13-H), 3.41 )1H, dd, Jˆ3.2, 9.5 Hz, 21-H),
3.55 )1H, dd, Jˆ6.8, 8.2 Hz, 3-H), 3.60 )2H, s, 26-H2),
3.74 )3H, s, CO2CH3), 3.89 )1H, dd, Jˆ2.0, 9.8 Hz, 5-H),
4.00 )1H, d, Jˆ4.2 Hz, 17-H), 4.23 )1H, ddd, Jˆ3.6, 6.5,
9.5 Hz, 20-H), 4.73 )1H, d, Jˆ2.9 Hz, 7-H). FABMS )m/z):
855 )M11)1, 878 )M1Na11)1. HRFABMS: Calcd for
C46H82O12SiNa: 877.5473 )M1Na)1. Found: 877.5519.
2.1.5. 7-O-Acetyl-25-O-methyl-25-carboxymonensin methyl
ester ,6). To a solution of 7-O-acetyl-25-O-methyl-25-
formylmonensin methylester )148 mg) in t-BuOH±H2O
)1:1, 15.0 mL), NaH2PO4´2H2O )47 mg) in H2O )1.0 mL)
and NaClO2 )136 mg) in H2O )2.0 mL) were added. The
mixture was stirred at room temperature for 2 h, poured
into water, and extracted with EtOAc. The organic layer
was washed with brine, dried over Na2SO4, and evaporated
under reduced pressure. The residue was chromatographed
on silica gel )hexane/EtOAcˆ1:1) to give 6 )150 mg, 99%)
25
)630 mg, 95%) as a colorless syrup: [a]D ˆ190 )c 0.26,
25
as a colorless syrup: [a]D ˆ193 )c 0.26, CHCl3); IR
)CHCl3, cm21):1732 )CvO); H NMR )CDCl3, d): 2.06
1
)3H, s, CH3CO), 2.64 )1H, qd, Jˆ7.0, 6.4 Hz, 2-H), 3.30
)3H, s, 25-OCH3), 3.35 )3H, s, 3-OCH3), 3.36 )1H, t-like,
Jˆ4.3 Hz, 13-H), 3.52 )1H, dd, Jˆ3.8, 10.2 Hz, 21-H), 3.56
)1H, dd, Jˆ6.4, 8.5 Hz, 3-H), 3.75 )3H, s, CO2CH3), 3.89
)1H, dd, Jˆ2.0, 9.9 Hz, 5-H), 3.94 )1H, d, Jˆ4.3 Hz, 17-H),
4.31 )1H, m, 20-H), 4.72 )1H, dd, Jˆ2.9, 5.9 Hz, 7-H), 13C
NMR )CDCl3, d): 169.0, 170.8, 175.9 )CvO). FABMS )m/
z): 777 )M1Na)1. HRFABMS: Calcd for C40H66O13Na:
777.4401 )M1Na)1. Found: 777.4393.
2.1.3. 7-O-Acetyl-25-O-methylmonensin methyl ester ,5).
A mixture of 7-O-acetyl-25-O-methyl-26-O-t-butyldimethyl-
2.1.6. 25-O-Methyl-25-carboxymonensin. To a solution of
6 )46 mg) in MeOH±THF )1:1, 4.0 mL) was added 5 mol/L

R. Tanaka et al. / Tetrahedron 57 /2001) 3005±3012
3009
NaOH )1.0 mL). The mixture was stirred at room tempera-
ture for 4 h, neutralized with 5% aquerous citric acid, and
extracted with EtOAc. The organic layer was washed with
brine, dried over Na2SO4, and concentrated under reduced
pressure. The residue was chromatographed on silica gel
)CHCl3/MeOHˆ100:1) to give 25-O-methyl-25-carboxy-
)c 0.28, CHCl3); IR )CHCl3, cm21):1720, 1745 )CvO); 1H
NMR )CDCl3, d): 2.66 )1H, qd, Jˆ6.8, 6.1 Hz, 2-H), 3.33
)3H, s, 25-OMe), 3.38 )3H, s, 3-OMe), 3.47 )1H, br, 13-H),
3.54 )1H, dd, Jˆ2.8, 10.1 Hz, 21-H), 3.72 )1H, dd, Jˆ6.1,
8.5 Hz, 3-H), 3.77 )1H, br, 7-H), 3.91 )1H, d, Jˆ4.1 Hz, 17-
H), 4.01 )1H, dd, Jˆ1.6, 9.9 Hz, 5-H), 4.32 )1H, td, Jˆ2.8,
7.8 Hz, 20-H). HRFABMS: Calcd for C37H62O12Na:
721.4139 )M1Na)1. Found: 721.4164.
)CDCl3, d): 0.04 )6H, s, Si)CH3)2), 0.88 )9H, s, SiC)CH3)3),
2.64 )1H, qd, Jˆ7.0, 6.3 Hz, 2-H), 3.21 )3H, s, 25-OCH3),
3.29 )1H, dd, Jˆ2.6, 6.3 Hz, 3-H), 3.31 )3H, s, 7-OCH3),
3.32 )3H, s, 3-OCH3), 3.41 )1H, dd, Jˆ3.3, 9.4 Hz, 7-H),
3.51 )1H, t, Jˆ5.0 Hz, 13-H), 3.60 )2H, s, 26-H2), 3.67 )1H,
dd, Jˆ6.3, 8.9 Hz, 21-H), 3.70 )3H, s, CO2CH3), 3.92 )1H,
dd, Jˆ1.7, 10.3 Hz, 5-H), 3.99 )1H, d, Jˆ4.0 Hz, 17-H),
4.24 )1H, ddd, Jˆ3.4, 7.3, 8.9 Hz, 20-H); FABMS )m/z):
850 )M1Na11)1. HRFABMS: Calcd for C45H82O11SiNa:
849.5524 )M1Na)1. Found: 849.5518.
25
monensin )39 mg, 91%) as a colorless syrup: [a]D ˆ140
7-O-p-Ethylbenzyl-25-O-methyl-26-O-t-butyldimethyl-
silylmonensin methyl ester. Colorless syrup, yield; 62%;
[a]D ˆ187 )c 0.32, CHCl3); IR )CHCl3, cm21):1730
25
1
)CvO); H NMR )CDCl3, d): 0.04 )6H, s, Si)CH3)2), 0.89
)9H, s, SiC)CH3)3), 2.58±2.67 )3H, m, 2-H, CH3CH2Ar),
3.21 )3H, s, 25-OCH3), 3.33 )3H, s, 3-OCH3), 3.41±3.49
)2H, m, 13-H and 26-Ha), 3.54 )3H, s, CO2CH3), 3.61±
3.71 )3H, m, 7-H, 21-H and 26-Hb), 4.02 )1H, dd, Jˆ2.0,
8.9 Hz, 5-H), 4.03 )1H, d, Jˆ4.0 Hz, 17-H), 4.25 )1H, m,
20-H), 4.41, 4.62 )each 1H, both d, Jˆ12.0 Hz, OCH2Ar),
7.11±7.32 )4H, m, Ar); FABMS )m/z): 953 )M1Na)1.
HRFABMS: Calcd for C53H90O11SiNa: 953.6150
)M1Na)1. Found: 953.6202.
2.1.7. 25-Carboxymonensin ,2). 25-O-Methyl-25-carboxy-
monensin )52 mg) was adsorbed on a silica gel plate for
7
days. The silica gel was eluted with CHCl3/
MeOHˆ10:1. The ef¯uent was evaporated under reduced
pressure. The residue was chromatographed on silica gel
)CHCl3/MeOHˆ80:1) to give 2 )25 mg, 50%) with recovery
25
)50%) as colorless syrup: [a]D ˆ195 )c 0.20, CHCl3); IR
1
)CHCl3, cm21):1730 )CvO); H NMR )CDCl3, d): 2.63
)1H, qd, Jˆ6.6, 10.0 Hz, 2-H), 3.13 )1H, dd, Jˆ1.8,
10.0 Hz, 3-H), 3.37 )3H, s, 3-OMe), 3.52 )1H, dd, Jˆ4.6,
10.7 Hz, 13-H), 3.84 )1H, d, Jˆ3.1 Hz, 17-H), 3.87 )1H, dd,
Jˆ4.0, 10.4 Hz, 21-H), 3.90 )1H, dd, Jˆ2.0, 11.4 Hz, 5-H),
3.95 )1H, d, Jˆ1.5 Hz, 7-H), 4.39 )1H, m, 20-H). 13C NMR
)CDCl3, d): 173.7, 180.4 )CvO). HRFABMS: Calcd for
C36H60O12Na: 707.3982 )M1Na)1. Found: 707.3952.
7-O-p-Chlorobenzyl-25-O-methyl-26-O-t-butyldimethyl-
silylmonensin methyl ester. Colorless syrup, yield; 50%;
25
[a]D ˆ144 )c 0.27, CHCl3); IR )CHCl3, cm21):1730
1
)CvO); H NMR )CDCl3, d): 0.03 )6H, s, Si)CH3)2), 0.87
)9H, s, SiC)CH3)3), 2.61 )1H, qd, Jˆ6.6, 6.6 Hz, 2-H), 3.20
)3H, s, 25-OCH3), 3.32 )3H, s, 3-OCH3), 3.40±3.45 )3H, m,
13-H, 26-Ha and 3-H), 3.51 )3H, s, CO2CH3), 3.53±3.69
)3H, m, 21-H, 7-H and 26-Hb), 3.99 )1H, br d, Jˆ7.3 Hz,
5-H), 4.01 )1H, d, Jˆ3.6 Hz, 17-H), 4.23 )1H, td, Jˆ6.3,
3.3 Hz, 20-H), 4.40, 4.60 )each 1H, both d, Jˆ12.0 Hz,
OCH2Ar), 7.20±7.36 )4H, m, Ar); FABMS )m/z): 959
)M1Na)1. HRFABMS: Calcd for C51H85O11ClSiNa:
959.5447 )M1Na)1. Found: 959.5454.
2.1.8. 7-O-Substituted-25-O-methyl-26-O-t-butyldimethyl-
silylmonensin methyl ester. To a solution of 4 )352 mg) in
THF )7.5 mL), NaH )26 mg), benzyl bromide )0.36 mL)
and n-Bu4NI )160 mg) were added. The mixture was stirred
under N2 atmosphere at room temperature for 2 h, quenched
by the addition of NH4Cl solution and diluted with EtOAc.
The organic layer was washed with brine, dried over
Na2SO4, ®ltered, and evaporated to dryness. The residue
was chromatographed on silica gel )hexane/EtOAcˆ10:1)
to give 7-O-benzyl derivative )231 mg, 57%) as colorless
syrup. 7-O-methyl, 7-O-p-ethylbenzyl and 7-O-p-chloro-
benzyl derivatives were similarly prepared from 4, using
the corresponding bromide instead of benzyl bromide.
2.1.9. 7-O-Substituted-25-O-methylmonensin methyl ester
,7a±d). A mixture of 7-O-benzyl-25-O-methyl-26-O-t-
butyldimethylsilylmonensin methyl ester )207 mg) and
TBAF´3H2O )140 mg) in THF )5.0 mL) was stirred under
Ar atmosphere at room temperature for 4 h. The reaction
mixture was poured into brine, and extracted with EtOAc.
The organic layer was dried over Na2SO4, and evaporated
under reduced pressure. The residue was chromatographed
on silica gel )hexane/EtOAcˆ5:1) to give 7a )175 mg, 99%)
as a colorless syrup. Compounds 7b±d were similarly
obtained from the corresponding 26-O-silyl derivatives.
7-O-Benzyl-25-O-methyl-26-O-t-butyldimethylsilylmonen-
25
sin methyl ester. [a]D1 ˆ156 )c 0.23, CHCl3); IR )CHCl3,
cm21):1735 )CvO); H NMR )CDCl3, d): 0.04 )6H, s,
Si)CH3)2), 0.88 )9H, s, SiC)CH3)3), 2.64 )1H, qd, Jˆ6.9,
5.6 Hz, 2-H), 3.21 )3H, s, 25-OCH3), 3.33 )3H, s, 3-
OCH3), 3.37±3.49 )3H, m, 3-H, 13-H and 26-H2), 3.54
)3H, s, CO2CH3), 3.57±3.71 )2H, m, 7-H and 26-H2), 3.67
)1H, dd, Jˆ4.3, 6.3 Hz, 21-H), 4.03 )1H, d, Jˆ4.0 Hz, 17-
H), 4.04 )1H, dd. Jˆ1.7, 4.5 Hz, 5-H), 4.25 )1H, td, Jˆ4.3,
3.6 Hz, 20-H), 4.45, 4.66 )each 1H, both d, Jˆ12.0 Hz,
OCH2Ar), 7.19±7.42 )5H, m, Ar); FABMS )m/z): 926
)M1Na11)1. HRFABMS: Calcd for C51H86O11SiNa:
925.5837 )M1Na)1. Found: 925.5830.
7a. [a]D ˆ134 )c 0.27, CHCl3); IR )CHCl3, cm21):1730
25
)CvO); 1H NMR )CDCl3, d): 2.63 )1H, qd, Jˆ6.8, 6.2 Hz,
2-H), 3.28 )3H, s, 25-OCH3), 3.33 )3H, s, 3-OCH3), 3.47±
3.58 )3H, m, 3-H and 13-H, 26-Ha), 3.54 )3H, s, CO2CH3),
3.64±3.74 )3H, m, 26-Hb, 7-H and 21-H), 3.96 )1H, d,
Jˆ4.0 Hz, 17-H), 4.02 )1H, dd, Jˆ1.8, 9.9 Hz, 5-H), 4.27
)1H, ddd, Jˆ3.7, 6.2, 9.2 Hz, 20-H), 4.45, 4.65 )each 1H,
both d, Jˆ12.0 Hz, OCH2Ar), 7.19±7.42 )5H, m, Ar);
FABMS )m/z): 811 )M1Na)1. HRFABMS: Calcd for
C45H72O11Na: 811.4972 )M1Na)1. Found: 811.4969.
7-O-Methyl-25-O-methyl-26-O-t-butyldimethylsilylmonen-
25
sin methyl ester. Colorless syrup, yield; 63%; [a]D ˆ175
)c 0.27, CHCl3); IR )CHCl3, cm21):1740 )CvO); 1H NMR
25
7b. Colorless syrup, yield; 99%; [a]D ˆ183 )c 0.22,

3010
R. Tanaka et al. / Tetrahedron 57 /2001) 3005±3012
CHCl3); IR )CHCl3, cm21):1735 )CvO); 1H NMR )CDCl3,
d): 2.63 )1H, qd, Jˆ6.9, 5.1 Hz, 2-H), 3.27 )3H, s, 25-
OCH3), 3.30 )3H, s, 7-OCH3), 3.32 )3H, s, 3-OCH3),
3.46±3.57 )3H, m, 13-H, 26-Ha, 7-H), 3.64±3.72 )2H, m,
21-H, 26-Hb), 3.70 )3H, s, CO2CH3), 3.91 )1H, dd, Jˆ1.7,
10.0 Hz, 5-H), 3.94 )1H, d, Jˆ4.3 Hz, 17-H), 4.27 )1H, ddd,
Jˆ3.6, 4.8, 9.6 Hz, 20-H); FABMS )m/z): 735 )M1Na)1.
HRFABMS: Calcd for C39H68O11Na: 735.4659 )M1Na)1.
Found: 735.4698.
IR )CHCl3, cm21):1740 )CvO); 1H NMR )CDCl3, d): 2.64
)1H, qd, Jˆ6.9, 6.1 Hz, 2-H), 3.28 )3H, s, 25-OMe), 3.30
)3H, s, 7-OMe), 3.33 )3H, s, 3-OMe), 3.45±3.52 )2H, m, 13-
H and 7-H), 3.66 )1H, dd, Jˆ6.6, 8.3 Hz, 21-H), 3.71 )3H, s,
CO2CH3), 3.91 )1H, br d, Jˆ9.9 Hz, 5-H), 3.97 )1H, d,
Jˆ3.3 Hz, 17-H), 4.30 )1H, m, 20-H), 9.38 )1H, s, 26-
CHO). HRFABMS: Calcd for C39H66O11Na: 733.4503
)M1Na)1. Found: 733.4487.
7-O-p-Ethylbenzyl-25-O-methy-25-formylmonensin
25
13
7c. Colorless syrup, yield; 95%; [a]D ˆ157 )c 0.38,
methyl ester. Colorless syrup, yield; 85%; [a]D ˆ171 )c
1
CHCl3); IR )CHCl3, cm21):1730 )CvO); 1H NMR
)CDCl3, d): 2.63 )2H, q, Jˆ7.6 Hz, CH3CH2Ar), 2.65 )1H,
m, 2-H), 3.28 )3H, s, 25-OCH3), 3.33 )3H, s, 3-OCH3), 3.46
)1H, m, 13-H), 3.48 )1H, dd, Jˆ4.1, 8.7 Hz, 7-H), 3.54 )3H,
s, CO2CH3), 3.56 )1H, m, 26-Ha), 3.68 )1H, dd, Jˆ6.2,
8.4 Hz, 21-H), 3.70 )1H, dd, Jˆ5.1, 10.5 Hz, 26-Hb), 3.97
)1H, d, Jˆ4.0 Hz, 17-H), 4.01 )1H, br d, Jˆ9.9 Hz, 5-H),
4.27 )1H, ddd, Jˆ3.4, 9.5, 6.2 Hz, 20-H), 4.41, 4.62 )each
1H, both d, Jˆ11.9 Hz, OCH2Ar), 7.11±7.32 )4H, m, Ar);
FABMS )m/z): 840 )M1Na11)1. HRFABMS: Calcd for
C47H76O11Na: 839.5285 )M1Na)1. Found: 839.5274.
0.33, CHCl3); IR )CHCl3, cm21):1740 )CvO); H NMR
)CDCl3, d): 2.59±2.67 )3H, m, 2-H, CH3CH2Ar), 3.28
)3H, s, 25-OCH3), 3.33 )3H, s, 3-OCH3), 3.45±3.51 )2H,
m, 13-H and 3-H), 3.54 )3H, s, CO2CH3), 3.64±3.71 )2H, m,
21-H and 7-H), 3.99±4.15 )2H, m, 17-H, 5-H), 4.32 )1H, m,
20-H), 4.41, 4.61 )each 1H, both d, Jˆ11.9 Hz, OCH2Ar),
7.11±7.32 )4H, m, Ar), 9.39 )1H, s, 26-CHO). HRFABMS:
Calcd for C47H74O11Na: 837.5129 )M1Na)1. Found:
837.5141.
7-O-p-Chlorobenzyl-25-O-methy-25-formylmonensin
13
methyl ester. Colorless syrup, yield; 69%; [a]D ˆ151 )c
0.24, CHCl3); IR )CHCl3, cm21): 1740 )CvO); H NMR
25
1
7d. Colorless syrup, yield; 97%; [a]D ˆ145 )c 0.26,
CHCl3); IR )CHCl3, cm21):1735 )CvO); 1H NMR
)CDCl3, d): 2.62 )1H, qd, Jˆ6.3, 6.5 Hz, 2-H), 3.28 )3H,
s, 25-OCH3), 3.33 )3H, s, 3-OCH3), 3.44 )1H, dd, Jˆ4.6,
6.1 Hz, 13-H), 3.46 )1H, dd, Jˆ4.9, 8.1 Hz, 7-H), 3.53 )3H,
s, CO2CH3), 3.55 )1H, dd, Jˆ6.6, 11.2 Hz, 26-Ha), 3.63 )1H,
dd, Jˆ6.3, 8.8 Hz, 21-H), 3.70 )1H, dd, Jˆ4.6, 11.0 Hz, 26-
Hb), 3.95 )1H, d, Jˆ4.0 Hz, 17-H), 4.00 )1H, dd, Jˆ2.0,
10.0 Hz, 5-H), 4.27 )1H, ddd, Jˆ3.4, 6.3, 9.3 Hz, 20-H),
4.42, 4.60 )each 1H, both d, Jˆ12.0 Hz, OCH2Ar), 7.21±
7.38 )4H, m, Ar); FABMS )m/z): 845 )M1Na)1.
HRFABMS: Calcd for C45H71O11ClNa: 845.4583
)M1Na)1. Found: 845.4577.
)CDCl3, d): 2.62 )1H, qd, Jˆ6.6, 6.8 Hz, 2-H), 3.27 )3H, s,
25-OCH3), 3.33 )3H, s, 3-OCH3), 3.42±3.55 )3H, m, 3-H, 7-
H and 13-H), 3.53 )3H, s, CO2CH3), 3.62 )1H, dd, Jˆ6.6,
8.6 Hz, 21-H), 3.97 )1H, d, Jˆ3.6 Hz, 17-H), 4.00 )1H, br d,
Jˆ7.9 Hz, 5-H), 4.30 )1H, m, 20-H), 4.41, 4.59 )each 1H,
both d, Jˆ12.0 Hz, OCH2Ar), 7.25±7.37 )4H, m, Ar), 9.38
)1H, s, 26-CHO). HRFABMS: Calcd for C45H69O11ClNa:
843.4426 )M1Na)1. Found: 843.4426.
2.1.11. 7-O-Substituted-25-O-methyl-25-carboxymonen-
sin methyl ester ,8a±d). To a solution of 7-O-benzyl-25-
O-methyl-25-formylmonensin methyl ester )164 mg) in
t-BuOH±H2O )1:1, 5.0 mL), NaH2PO4´2H2O )23 mg) in
H2O )1.0 mL) and NaClO2 )95 mg) in H2O )2.0 mL) were
added. The mixture was stirred at room temperature for 2 h,
poured into water, and extracted with EtOAc. The organic
layer was washed with brine, dried over Na2SO4, ®ltered and
evaporated under reduced pressure. The residue was chro-
matographed on silica gel )hexane/EtOAcˆ1:1) to give 8a
)162 mg, 97%). Compounds 8b±d were similarly obtained
from the corresponding 25-formyl derivatives.
2.1.10. 7-O-Substituted-25-O-methy-25-formylmonensin
methyl ester. To a solution of 7a )197 mg) in CH2Cl2
)9.0 mL), PDC )141 mg), MS4A )140 mg), and Celite
)350 mg) were added. The mixture was stirred under Ar
atmosphere at room temperature for 4.5 h. The resulting
mixture was ®ltered through Celite and the ®ltrate was
evaporated under reduced pressure. The residue was chro-
matographed on silica gel )hexane/EtOAcˆ8:1) to give the
aldehyde )164 mg, 84%) as colorless syrup. Compounds
7b±d were similarly converted to the corresponding 25-
folmyl derivatives.
8a. [a]D ˆ170 )c 0.20, CHCl3); IR )CHCl3, cm21):1735
25
)CvO); 1H NMR )CDCl3, d): 2.63 )1H, qd, Jˆ5.9, 6.9 Hz,
2-H), 3.29 )3H, s, 25-OCH3), 3.33 )3H, s, 3-OCH3), 3.45±
3.57 )2H, m, 13-H, 3-H), 3.54 )3H, s, CO2CH3), 3.64±3.71
)2H, m, 21-H and 7-H), 3.95 )1H, d, Jˆ4.3 Hz, 17-H), 4.02
)1H, dd, Jˆ2.0, 9.9 Hz, 5-H), 4.31 )1H, m, 20-H), 4.45, 4.64
)each 1H, both d, Jˆ12.0 Hz, OCH2Ar), 7.19±7.41 )5H, m,
Ar); 13C NMR )CDCl3, d): 168.9 )25-CO2H), 176.0
)CO2CH3); FABMS )m/z): 826 )M1Na11)1, 848
)M12Na)1. HRFABMS: Calcd for C45H70O12Na:
825.4765 )M1Na)1. Found: 825.4795.
7-O-Benzyl-25-O-methy-25-formylmonensin methyl ester.
13
[a]D ˆ166 )c 0.38, CHCl3); IR )CHCl3, cm21):1740
)CvO); 1H NMR )CDCl3, d): 2.63 )1H, qd, Jˆ6.3,
6.6 Hz, 2-H), 3.28 )3H, s, 25-OMe), 3.33 )3H, s, 3-OMe),
3.47±3.50 )3H, m, 13-H, 3-H and 7-H), 3.54 )3H, s,
CO2CH3), 3.65 )1H, dd, Jˆ4.3, 6.3 Hz, 21-H), 3.98 )1H,
d, Jˆ3.6 Hz, 17-H), 4.02 )1H, br d, Jˆ10.0 Hz, 5-H), 4.31
)1H, m, 20-H), 4.45, 4.64 )each 1H, both d, Jˆ12.0 Hz,
CH2±Ar), 7.19±7.41 )5H, m, benzyl), 9.39 )1H, s, 26-
CHO). HRFABMS: Calcd for C45H70O11Na: 809.4816
)M1Na)1. Found: 809.4786.
25
8b. Colorless syrup, yield; 83%; [a]D ˆ163 )c 0.40,
CHCl3); IR )CHCl3, cm21):1735 )CvO); 1H NMR
)CDCl3,d): 2.64 )1H, qd, Jˆ7.1, 5.1 Hz, 2-H), 3.28 )1H,
dd, Jˆ2.6, 7.1 Hz, 3-H), 3.30 )3H, s, 25-OCH3), 3.31 )3H,
s, 7-OCH3), 3.33 )3H, s, 3-OCH3), 3.49±3.54 )2H, m, 13-H,
7-O-Methyl-25-O-methy-25-formylmonensin methyl ester.
13
Colorless syrup, yield; 85%; [a]D ˆ156 )c 0.37, CHCl3);

R. Tanaka et al. / Tetrahedron 57 /2001) 3005±3012
3011
7-H), 3.65±3.74 )1H, m, 21-H), 3.71 )3H, s, CO2CH3), 3.90
)1H, dd, Jˆ1.8, 9.0 Hz, 5-H), 3.94 )1H, d, Jˆ4.4 Hz, 17-H),
4.32 )1H, m, 20-H); 13C NMR )CDCl3, d): 169.3 )25-
CO2H), 176.1 )CO2CH3); FABMS )m/z): 749 )M1Na)1,
771 )M12Na21)1. HRFABMS: Calcd for C39H66O12Na:
749.4452 )M1Na)1. Found: 749.4427.
)1H, br s, 17-H), 3.97 )1H, br d, Jˆ10.6 Hz, 5-H), 4.30 )1H,
m, 20-H), FABMS )m/z): 735 )M1Na)1, 757
)M12Na2H)1. HRFABMS: Calcd for C38H64O12Na:
735.4295 )M1Na)1. Found: 735.4240.
7-O-p-Ethylbenzyl-25-O-methyl-25-carboxymonensin.
25
Colorless syrup, yield; 58%; [a]D ˆ151 )c 0.26, CHCl3);
25
8c. Colorless syrup, yield; 84%; [a]D ˆ155 )c 0.39,
IR )CHCl3, cm21):1730 )CvO); 1H NMR )CDCl3, d):
2.59±2.76 )3H, m, 2-H, CH3CH2Ar), 3.30 )3H, s, 25-
OCH3), 3.33±3.55 )3H, m, 3-H, 13-H and 7-H), 3.37 )3H,
s, 3-OCH3), 3.67 )1H, dd, Jˆ6.6, 8.3 Hz, 21-H), 3.95 )1H, d,
Jˆ4.0 Hz, 17-H), 4.12 )1H, br d, Jˆ9.7 Hz, 5-H), 4.30 )1H,
br s, 20-H), 4.46, 4.57 )each 1H, both d, Jˆ12.0 Hz,
OCH2Ar), 7.13±7.30 )4H, m, Ar); FABMS )m/z): 839
)M1Na)1, 861 )M12Na2H)1. HRFABMS: Calcd for
C46H72O12Na: 839.4921 )M1Na)1. Found: 839.4902.
CHCl3); IR )CHCl3, cm21):1730 )CvO); 1H NMR
)CDCl3, d): 2.62 )1H, m, 2-H), 2.63 )2H, q, Jˆ7.6 Hz,
CH3CH2Ar), 3.29 )3H, s, 25-OCH3), 3.32 )1H, m, 3-H),
3.33 )3H, s, 3-OCH3), 3.45±3.59 )1H, m, 13-H), 3.55 )3H,
s, CO2CH3), 3.67 )1H, dd, Jˆ6.3, 8.6 Hz, 21-H), 3.69±3.78
)1H, m, 7-H), 3.95 )1H, d, Jˆ4.0 Hz, 17-H), 4.01 )1H, dd,
Jˆ2.0, 9.6 Hz, 5-H), 4.32 )1H, m, 20-H), 4.42, 4.61 )each
1H, both d, Jˆ12.0 Hz, OCH2Ar), 7.12±7.38 )4H, m, Ar);
13C NMR )CDCl3, d): 169.2 )25-CO2H), 176.0 )CO2CH3);
FABMS )m/z): 853 )M1Na)1. HRFABMS: Calcd for
C47H74O12Na: 853.5078 )M1Na)1. Found: 853.5093.
7-O-p-Chlorobenzyl-25-O-methyl-25-carboxymonensin.
25
Colorless syrup, yield; 50%; [a]D ˆ136 )c 0.37, CHCl3);
IR )CHCl3, cm21):1720 )CvO); 1H NMR )CDCl3, d): 2.67
)1H, m, 2-H), 3.29 )3H, s, 25-OCH3), 3.37 )3H, s, 3-OCH3),
3.45±3.52 )3H, m, 3-H, 13-H and 7-H), 3.65 )1H, dd, Jˆ6.3,
4.5 Hz, 21-H), 3.94 )1H, d, Jˆ4.3 Hz, 17-H), 4.12 )1H, br d,
Jˆ7.9 Hz, 5-H), 4.30 )1H, m, 20-H), 4.45, 4.56 )each 1H,
both d, Jˆ11.9 Hz, OCH2Ar), 7.26±7.35 )4H, m, Ar);
FABMS )m/z): 846 )M1Na11)1, 868 )M12Na)1.
HRFABMS: Calcd for C44H67O12ClNa: 845.4219
)M1Na)1. Found: 845.4172.
25
8d. Colorless syrup, yield; 90%; [a]D ˆ153 )c 0.33,
CHCl3); IR )CHCl3, cm21):1735 )CvO); 1H NMR
)CDCl3, d): 2.62 )1H, qd, Jˆ6.6, 6.6 Hz, 2-H), 3.29 )3H,
s, 25-OCH3), 3.33 )3H, s, 3-OCH3), 3.55±3.58 )2H, m, 13-
H, 21-H), 3.53 )3H, s, CO2CH3), 3.63 )1H, dd, Jˆ4.3,
6.6 Hz, 3-H), 3.94 )1H, d, Jˆ4.3 Hz, 17-H), 3.99 )1H, dd,
Jˆ2.0, 9.9 Hz, 5-H), 4.31 )1H, td, Jˆ9.3, 3.0 Hz, 20-H),
4.41, 4.59 )each 1H, both d, Jˆ12.0 Hz, OCH2Ar), 7.21±
7.37 )4H, m, Ar); 13C NMR )CDCl3, d): 169.2 )25-CO2H),
176.0 )CO2CH3); FABMS )m/z): 860 )M1Na11)1.
HRFABMS: Calcd for C45H69O12ClNa: 859.4375
)M1Na)1. Found: 859.4363.
2.1.13. 7-O-Substituted-25-carboxymonensin ,3a±d).
7-O-Benzyl-25-O-methyl-25-carboxymonensin )54 mg) was
adsorbed on a silica gel plate for 7 days. The silica gel was
eluted with CHCl3/MeOHˆ10:1. The ef¯uent was evapo-
rated under reduced pressure. The residue was chromato-
graphed on silica gel )CHCl3/MeOHˆ80:1) to give 3a
)21 mg, 40%) with recovery of the starting material
)55%). Compounds 3b±d were similarly obtained from
corresponding 25-O-methyl derivatives, respectively.
2.1.12. 7-O-Alkyl-25-O-methyl-25-carboxymonensin. To
a solution of 8a )134 mg) in MeOH±THF )1:1, 4.0 mL) was
added 5 mol/L NaOH )1.0 mL). The mixture was stirred at
room temperature for 4 h, neutralized with 5% aqueous
citric acid, and extracted with EtOAc. The organic layer
was washed with brine, dried over Na2SO4, and concen-
trated under reduced pressure. The residue was chromato-
graphed on silica gel )CHCl3/MeOHˆ100:1) to give 7-O-
benzyl-25-O-methyl-25-carboxylmonensin )50 mg, 57%).
7-O-methyl, 7-O-ethylbenzyl and 7-O-chlorobenzyl deriva-
tives were similarly obtained from 8b±d, respectively.
3a. [a]D ˆ147 )c 0.21, CHCl3); IR )CHCl3, cm21):1720,
25
1
1735 )CvO); H NMR )CDCl3, d): 2.67 )1H, qd, Jˆ6.7,
10.1 Hz, 2-H), 3.17 )1H, dd, Jˆ1.5, 10.1 Hz, 3-H), 3.38)1H,
dd, Jˆ2.1, 4.6 Hz, 7-H), 3.40 )3H, s, 3-OCH3), 3.43 )1H, dd,
Jˆ4.6, 10.1 Hz, 21-H), 3.58 )1H, dd, Jˆ6.1, 9.7 Hz, 13-H),
3.90 )1H, dd, Jˆ2.1, 11.6 Hz, 5-H), 3.93 )1H, m, 20-H),
4.03 )1H, d, Jˆ3.4 Hz, 17-H), 4.51, 5.91 )each 1H, both
d, Jˆ15.8 Hz, OCH2Ar), 7.35±7.37 )5H, m, Ar).
HRFABMS: Calcd for C43H65O12Na2: 819.4271
)M12Na2H)1. Found: 819.4252.
25
7-O-Benzyl-25-O-methyl-25-carboxymonensin. [a]D
ˆ
145 )c 0.27, CHCl3); IR )CHCl3, cm21): 1600 )CvO),
1
1700 )CvO); H NMR )CDCl3, d): 2.92 )1H, dd, Jˆ2.3,
10.2 Hz, 3-H), 3.16 )3H, s, 25-OCH3), 3.27±3.39 )1H, m,
13-H), 3.46 )1H, br s, 7-H), 3.50 )3H, s, 3-OCH3), 3.65±
3.69 )1H, m, 21-H), 4.04 )1H, br s, 5-H), 4.09 )1H, d,
Jˆ4.3 Hz, 17-H), 4.34 )1H, m, 20-H), 4.31, 4.87 )each
1H, both d, Jˆ14.3 Hz, OCH2Ar), 7.26±7.41 )5H, m, Ar);
FABMS )m/z): 811 )M1Na)1, 833 )M12Na21)1.
HRFABMS: Calcd for C44H67O12Na2: 833.4428
)M12Na2H)1. Found: 833.4412.
25
3b. Colorless syrup, yield; 45%; [a]D ˆ139 )c 0.30,
1
CHCl3); IR )CHCl3, cm21):1720, 1730 )CvO); H NMR
)CDCl3, d): 2.61)1H, qd, Jˆ6.6, 10.5 Hz, 2-H), 3.10 )1H,
dd, Jˆ1.5, 10.5 Hz, 3-H), 3.28 )1H, t-like, Jˆ2.2 Hz, 7-H),
3.38 )3H, s, 3-OCH3), 3.45 )1H, dd, Jˆ5.7, 10.1 Hz, 13-H),
3.65 )3H, s, 7-OMe), 3.77 )1H, dd, Jˆ2.0, 11.2 Hz, 5-H),
3.90 )1H, dd, Jˆ4.5, 10.1 Hz, 21-H), 4.03 )1H, d, Jˆ3.2 Hz,
17-H), 4.39 )1H, ddd, Jˆ4.6, 7.3, 9.0 Hz, 20-H); FABMS
)m/z): 722 )M1Na11)1, 744 )M12Na)1. HRFABMS:
Calcd for C37H61O12Na2: 743.3958 )M12Na2H)1. Found:
743.3983.
7-O-Methyl-25-O-methyl-25-carboxymonensin. Color-
25
less syrup, yield; 64%; [a]D ˆ153 )c 0.50, CHCl3); IR
1
)CHCl3, cm21):1740 )CvO); H NMR )CDCl3, d): 2.66
)1H, br s, 2-H), 3.31 )6H, s, 7-OCH3, 25-OCH3), 3.36
)3H, s, 3-OCH3), 3.09±3.36 )1H, m, 3-H), 3.42±3.53 )2H,
m, 7-H and 13-H), 3.67 )1H, dd, Jˆ6.3, 8.6 Hz, 21-H), 3.95
25
3c. Colorless syrup, yield; 50%; [a]D ˆ149 )c 0.22,

3012
R. Tanaka et al. / Tetrahedron 57 /2001) 3005±3012
1
CHCl3); IR )CHCl3, cm21):1720, 1735 )CvO); H NMR
)CDCl3, d): 2.59±2.70 )3H, m, 2-H, CH3CH2-Ar), 3.16 )1H,
d-like, Jˆ9.9 Hz, 3-H), 3.40 )3H, s, 3-OCH3), 3.45±3.77
)3H, m, 13-H, 7-H and 21-H), 3.89 )1H, dd, Jˆ1.7,
11.3 Hz, 5-H), 4.03 )1H, d, Jˆ3.0 Hz, 17-H), 4.21 )1H, m,
20-H), 4.47, 5.83 )each 1H, both d, Jˆ15.8 Hz, OCH2Ar),
7.16±7.34 )4H, m, Ar). HRFABMS: Calcd for
C45H69O12Na2: 847.4584 )M12Na2H)1. Found: 847.4561.
in part by the Ministry of Education, Science, Sports and
Culture of Japan for a Grant-in-Aid for Scienti®c Research
and for a High-Tech Research Center Project, and Aburahi
laboratory of Shionogi Pharmaceutical.
References
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25
3d. Colorless syrup, yield; 55%; a]D ˆ135 )c 0.20,
1
CHCl3); IR )CHCl3, cm21):1720, 1735 )CvO); H NMR
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)CDCl3, d): 2.66 )1H, qd, Jˆ6.2, 10.2 Hz, 2-H), 3.14 )1H,
d-like, Jˆ10.2 Hz, 3-H), 3.32 )1H, t-like, Jˆ2.2 Hz, 7-H),
3.39 )3H, s, 3-OCH3), 3.43 )1H, dd, Jˆ4.4, 10.0 Hz, 21-H),
3.57 )1H, dd, Jˆ6.2, 9.9 Hz, 13-H), 3.88 )1H, dd, Jˆ2.0,
11.5 Hz, 5-H), 3.98 )1H, m, 20-H), 4.03 )1H, d, Jˆ2.9 Hz,
17-H), 4.47, 5.83 )each 1H, both d, Jˆ15.9 Hz, CH2Ar),
7.26±7.64 )5H, m, Ar); FABMS )m/z): 832 )M1Na11)1,
854 )M12Na)1. HRFABMS: Calcd for C43H65O12ClNa:
831.4062 )M1Na)1. Found: 831.4077.
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York, 1982; Vol. 1, pp 304±314.
2.1.14. Ion transport activity. The experiment was
performed essentially according to the method reported by
Pressman12a using a glass cell as shown in Fig. 2. The
3.5 mL of 0.25 mM test compound solution in water-
saturated CHCl3 was placed in the bottom of the cell )B).
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taken, diluted 2.5 times for Ca21 ion and 10 times for Na1
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Shimadzu AA-660 spectrometer at 422.7 nm for Ca21 ion
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and Na1 ions was determined from the calibration lines
made by measurement of the absorption of 1.0, 10, 20, 50,
80 and 100 mM CaCl2 and NaCl solutions, respectively.
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Acknowledgements
We thank Ms. T. Naito, Ms. S. Kato and Ms. K. Iwasawa of
this faculty for elemental analysis and measurement of
NMR and MS spectra. This work was ®nancially supported