Oligosaccharide synthesis by affinity separation based on molecular recognition between podand ether and ammonium ion

Article abstract of DOI:10.1055/s-2005-872269

We previously reported a new synthetic methodology termed 'synthesis based on affinity separation' (SAS) in which the desired tagged compound was separated from the reaction mixture by solid-phase extraction using specific molecular recognition of the tag. The interaction between a crown ether tag and polymer-supported ammonium ion was initially employed for SAS. In the present study, a new SAS method using a podand-type tag, a pseudo-benzo-31-crown-10 structure, was elaborated for oligosaccharide synthesis. The podand tag was much easier to synthesize than the corresponding crown ether. The podand moiety was attached to the monosaccharide residue via appropriate linkers. After glycosylation of the tagged monosaccharide with a glycosyl donor, the reaction mixture was subjected to the affinity separation. The desired compounds possessing the podand tag were effectively separated by the affinity between the podand and the ammonium ion. Continuous flow synthesis by integration of a microreactor and the present SAS system was applied for high throughput oligosaccharide synthesis. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2005-872269

2342
LETTER
Oligosaccharide Synthesis by Affinity Separation Based on Molecular
Recognition between Podand Ether and Ammonium Ion
Oligosaccharide
S
y
o
nthesis by
A
i
ffinity
c
S
eparationhi Fukase,* Mamoru Takashina, Yumiko Hori, Daizo Tanaka, Katsunori Tanaka, Shoichi Kusumoto
Department of Chemistry, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043, Japan
Fax +81(6)68505419; E-mail: koichi@chem.sci.osaka-u.ac.jp
Received 6 July 2005
were washed off. Subsequent desorption by CH2Cl2–Et3N
Abstract: We previously reported a new synthetic methodology
or CH2Cl2–MeOH (1:1) afforded the desired compound
with high purity.
termed ‘synthesis based on affinity separation’ (SAS) in which the
desired tagged compound was separated from the reaction mixture
by solid-phase extraction using specific molecular recognition of
Since the crown ether tag is not commercially available,
the tag. The interaction between a crown ether tag and polymer-
we then investigated the use of commercially available
supported ammonium ion was initially employed for SAS. In the
short chain polyethylene glycol (PEG) as a tag.5 Since
present study, a new SAS method using a podand-type tag, a
Triton X-100 is a detergent having a PEG chain and a
pseudo-benzo-31-crown-10 structure, was elaborated for oligosac-
hydrophobic moiety, the tagged compounds show good
solubility in many organic solvents. The binding of Triton
X-100 to the polymer-supported ammonium is, however,
somehow weaker than that of the crown ether. In addition,
the chain length of Triton X-100 is heterogeneous and
Triton X-100 with the shorter chain length only showed
weak binding.
charide synthesis. The podand tag was much easier to synthesize
than the corresponding crown ether. The podand moiety was
attached to the monosaccharide residue via appropriate linkers.
After glycosylation of the tagged monosaccharide with a glycosyl
donor, the reaction mixture was subjected to the affinity separation.
The desired compounds possessing the podand tag were effectively
separated by the affinity between the podand and the ammonium
ion. Continuous flow synthesis by integration of a microreactor and
the present SAS system was applied for high throughput oligo-
saccharide synthesis.
–
R
–
R
CO2
CO2
Key words: oligosaccharide synthesis, affinity separation, high
throughput synthesis, linker, glycosylation
CF3CO2
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
NH3
NH3
Phase tag strategy has been developed for high throughput
synthesis as a hybrid system that combines the merits of
solid-phase synthesis (easy separation) and solution-
phase synthesis (homogeneous reaction conditions). In
this strategy, a compound having a tag group is easily sep-
arated from untagged molecules. Various phase tags such
as soluble polymers, fluorous, hydrophobic, and basic
tags have been reported.1 We have developed a new ‘tag’
strategy, termed ‘synthesis based on affinity separation
(SAS)’, in which the desired tagged compound is separat-
ed from the reaction mixture by solid-phase extraction
using specific molecular recognition.2–5
nonpolar solvent
CO2
R
NH2
+
polar solvent
O
O
O
O
O
O
O
O
O
O
Figure 1 Synthesis based on affinity separation using podand tag
In the present study, we developed a podand-type ether
tag for SAS (Figure 1). The podand tag, a pseudo-benzo-
31-crown-10 structure, was much easier to synthesize
than the corresponding crown ether.6 The compounds
having the podand tag showed high affinity to the ammo-
nium ion on the solid support. The present SAS method
was then successfully applied to the synthesis of oligo-
saccharides.
We first employed the interaction between a crown ether
(32-crown-10) and the ammonium ion for SAS.2 Amino-
methylated polystyrene resins were used as a column sta-
tionary phase. The desired compounds possessing the
crown ether tag were readily isolated from the reaction
mixture by the following procedure. After each reaction
cycle, the reaction mixture was applied to the amino-
methylated polystyrene column [trifluoroacetic acid
(TFA) form]. By using non-polar eluents such as CH2Cl2
and toluene, the tagged compound was selectively ad-
sorbed on the column, whereas other untagged impurities
We first investigated a facile preparation of the tag
moiety. Since tetraethylene glycol monomethyl ether is
expensive, the tag 6 was prepared from inexpensive trieth-
ylene glycol momomethyl ether (1) in a straightforward
manner as shown in Scheme 1. Thus, mono-alkylation of
the mesylate 2 by ethylene glycol provided 3, which was
mesylated to give tetraethylene glycol derivative 4 in 78%
yield for three steps. Mesylate 4 was then reacted with the
SYNLETT 2005, No. 15, pp 2342–2346
1
9
.0
9
.2
0
0
5
Advanced online publication: 03.08.2005
DOI: 10.1055/s-2005-872269; Art ID: U21305ST
© Georg Thieme Verlag Stuttgart · New York

LETTER
Oligosaccharide Synthesis by Affinity Separation
2343
MsCl, Et3N
O O O O O
HO OH
O
O
O
O
O
OH
O
O
O O OMs
CH2Cl2
quant.
NaH, DMF
78%
COOH
6
(1.2 equiv)
affinity separation
1
2
Ph
O
O
O O
O O
O
O
MsCl, Et3N
HO
O
O
O
O
OMs
O
OH
CH2Cl2
quant.
TrocN
DIC, DMAP
CH2Cl2, r.t.
3
4
OAllyl
i) CH2Cl2
7
H
ii) CH2Cl2–MeOH (1:1)
93%
i) 4, NaI,
K2CO3, 50 °C
O
O
O
O
O O
HO
HO
Ph
O
O
O O O O O
O O O O O
HO
CO2H
TFA-H2O-CH2Cl2
CO2Me
O
ii) aq NaOH
88%
O
O
O
O O
DMF
TrocN
5
(1:1:10)
NH
6
OAllyl
O
84%
H
O
8
Scheme 1
AcO
O
AcO
AcO
CCl3
O
HO
phenol dihydroxyls of 5, which was subsequently hydro-
lyzed to give 6 in 88% yield for two steps. A 30-gram-
scale synthesis of 6 was possible by this route.
TrocNH
(1.1 equiv)
O
affinity separation
10
Tag
TrocN
OAllyl
TMSOTf, MS4Å
CH2Cl2, 0 °C
H
i) CH2Cl2
ii) CH2Cl2–MeOH (1:1)
O
9
We then introduced the tag 6 to glucosamine derivative 7,
and after the excess 6 was removed by silica gel column
chromatography, the adsorption ability of the tagged
monosaccharide 8 was tested to various solid-supported
amines [trifluoroacetic acid (TFA) form] (Scheme 2).7
Among the resins tested, i.e., aminomethylated polysty-
rene, tris-(2-aminoethyl)aminomethyl polystyrene, N,N-
(diisopropyl)aminomethyl polystyrene, and polyethylene
imine resins, the amino-methylated polystyrene resin
showed the best adsorption ability. The highly cross-
linked macroporous aminomethylated polystyrene resin
showed higher adsorption of 8 than the 1% cross-linked
gel-type resin. In the present study, we hence used the
commercially available macroporous amino-methylated
polystyrene resin ArgoPore-NH2 (Argonaut Technologies
Inc., amine loading: 1.16 mmol/g).
96%
AcO
AcO
AcO
O
O
O O O O O
O
HO
TrocNH
Tag
O
tag =
TrocN
OAllyl
H
O O O O O
O
11
Scheme 2
p-acylaminobenzyl linker has also been reported.11 We
therefore investigated oligosaccharide SAS by using p-
acylaminobenzyl and p-acylaminophenyl linkers, respec-
tively (Scheme 3 and Scheme 4).
Glycosyl acceptor 15 having the tag moiety via an acyl-
aminobenzyl linker was prepared from p-nitrobenzylated
glucose derivative 1211 (Scheme 3). The nitro group in 12
was reduced by Zn–Cu and acetylacetone to give 13.
Since the aniline amino group of 13 was not reactive
enough for direct acylation with the acid 6, acylation with
6 was carried out by using acid chloride prepared in situ
from 6 and triphosgene to give the desired tagged
monosaccharide 14 in a good yield after silica gel chroma-
tography.12 After removal of the benzylidene group of 14,
glycosylation of the resulting 15 with glycosyl donor 10
was effected by using TMSOTf. After the affinity separa-
tion, the resulting disaccharide 16 was further subjected to
the glycosylation with excess amount of the donor 10. Al-
though the affinity separation could not remove a small
amount of the unreacted disaccharide 16 from the desired
trisaccharide 17 (since both bear the tag moieties), subse-
quent separation by silica gel column chromatography af-
forded pure 17 in 61% yield from 15. In addition,
glycosylation of 16 with galactosyl donor 19 gave the
trisaccharide 20, which was also purified by the affinity
separation and subsequent silica gel column chromatogra-
phy (Scheme 3 in the bottom). Importantly, during the af-
finity separation, TFA was eluted from the affinity
column at the elution with CH2Cl2–MeOH (1:1). Since it
is difficult to remove TFA completely by only vacuum
evaporation, TFA should be removed by liquid–liquid
separation before the subsequent glycosylation reaction.
We then applied the developed podand tag 6 to oligosac-
charide synthesis (Scheme 2). The benzylidene group of 8
was removed by TFA to give the glycosyl acceptor 9.
Since contamination of TFA inhibits the following glyco-
sylation, TFA was completely removed by concentration
and subsequent liquid–liquid extraction with aqueous
NaHCO3. Glycosylation of 9 with N-trichloroethoxycar-
bonyl (Troc) glucosaminyl donor 10 was carried out by
using TMSOTf as an acid catalyst. The reaction mixture
was directly applied to the affinity separation. By using
CH2Cl2 as an eluent, the desired disaccharide 11 was
retained in the column, whereas other by-products such as
trichloroacetamide and the 1-hydroxy sugar formed by
hydrolysis of 10 were washed off. The pure 11 was
obtained by elution with CH2Cl2–MeOH (1:1). In such a
case, toluene was not suitable as an eluent for the affinity
separation; since 1-hydroxy sugar has latent aldehyde
structure, a considerable amount of 1-hydroxy sugar was
retained in the column when toluene was used.
The tag moiety was also introduced to the sugar moiety
via a variety of appropriate linkers. We previously report-
ed that p-acylaminobenzyl ether8,9 and p-acylaminophe-
nyl glycoside10 were selectively cleaved by DDQ and
cerium(IV) diammonium nitrate (CAN) oxidation, re-
spectively. Solid-phase oligosaccharide synthesis using a
Synlett 2005, No. 15, 2342–2346 © Thieme Stuttgart · New York

2344
K. Fukase et al.
LETTER
Ph
O
Ph
O
Zn–Cu
acetylacetone
Ph
O
Ph
O
O
O
O
O
O
O
BnO
BnO
O
O
THF
OMe
OMe
12
13
BzCl, pyridine
O
O
NO2
NO2
O
O
HO
BzO
CH2Cl2, r.t.
66%
NO2
NH2
HO
BzO
O O O O O
O O O O O
21
22
Ph
O
O
O
Ph
O
COOH
O
BnO
6
O
Zn–Cu
acetylacetone
OMe
O
(1.3 equiv)
6 (1.3 equiv)
14
O
BzO
NH2
O
N
Tag
THF
triphosgene (0.48 equiv)
collidine (0.91 equiv)
THF, 97% (2 steps)
triphosgene (1.3 equiv)
collidine (10 equiv)
THF
BzO
79%
H
O
NH
23
Ph
O
AcO
AcO
HO
AcO
O
CCl3
10
O
O
O
HO
BnO
TrocNH
i)
(1.1 equiv)
TFA–H2O–CH2Cl2
84% from 23
NH
TFA–H2O–CH2Cl2
H
OMe
O
N
Tag
O
TMSOTf, MS4Å
CH2Cl2, 0 °C
15
BzO
(3:2:10)
O
87%
(1:1:10)
BzO
24
N
H
Tag
ii) affinity separation
quant.
AcO
AcO
AcO
O
O
AcO
OH
O
CCl3
10
O
O
AcO
TrocNH
(1.1 equiv)
HO
BzO
O
O
AcO
i)
(3 equiv)
10
HO
BnO
i)
H
O
TrocNH
N
Tag
O
TMSOTf, MS4Å
CH2Cl2, 0 °C
OMe
TMSOTf, MS4Å
CH2Cl2, 0 °C
16
O
BzO
25
ii) affinity separation
ii) affinity separation
quant.
AcO
AcO
AcO
N
Tag
O
ii) silica gel column
chromatography
H
O
O
AcO
AcO
AcO
O
O
TrocNH
i) DDQ
CH2Cl2–H2O (18:1)
O
AcO
AcO
AcO
HO
O
BnO
O
TrocNH
H
O
N
Tag
O
O
BzO
26
OMe
ii) ascorbic acid buffer
iii) affinity separation
TrocNH
O
17
BzO
61% from 15
CH2Cl2
82%
N
Tag
H
O
AcO
AcO
AcO
i) CAN
MeCN–H2O
AcO
AcO
AcO
O
O
HO
O
O
(10:1)
TrocNH
OHC
O
TrocNH
ii) silica gel column
chromatography
O
HO
AcO
AcO
AcO
BzO
+
OH
O
BnO
O
27
BzO
N
H
Tag
OMe
O
TrocNH
18
Scheme 4
AcO
We then investigated the synthesis using the acylami-
nophenyl linker (Scheme 4). The p-nitrophenyl galacto-
side 21 was first benzoylated and the resulting benzoate
22 was reduced with Zn–Cu and acetylacetone to give 23.
The tag 6 was then introduced onto the amino group of 23
by in situ acid chloride method to give 24, after the sepa-
ration of the excess tag 6 by silica gel chromatography.
Subsequently, the benzylidene group of 24 was removed
by TFA. The acceptor 25 was then glycosylated with the
glucosaminyl donor 10, which was purified by affinity
separation to provide the pure disaccharide 26 in quantita-
tive yield. The tag moiety attached on 26 via p-acylami-
nophenyl glycoside linkage was successfully removed by
CAN oxidation. Since the desired product, disaccharide
27, was somehow retained in the ArgoPore-
AcO
AcO
O
OAc
O
AcO
NH
O
O
AcO
AcO
NHTroc
O
OAc
O
CCl3
O
AcO
19
BnO
AcO
(3 equiv)
i)
O
OMe
16
AcO
20
TMSOTf, MS4Å
CH2Cl2, 0 °C
N
Tag
45% from 15
H
ii) affinity separation
O
ii) silica gel column
chromatography
Scheme 3
Cleavage of the acylaminobenzyl linker in 17, thus ob-
tained, was achieved without affecting other protective
groups (Scheme 3 in the middle). Thus, when the reaction
completed, excess DDQ was quenched with ascorbic acid
buffer, and the produced dichlorodicyanohydroquinone
(DDHQ) was removed by liquid–liquid extraction. The
resulting CH2Cl2 solution of the mixture of the desired
trisaccharide 18 and the aldehyde derived from the tag
was then applied to the affinity column separation by elu-
tion with CH2Cl2. While the trisaccharide 18 passed
through the column, the aldehyde bearing the tag moiety
was adsorbed in the column. The trisaccharide 18 was
thus obtained in 82% yield.
+
NH3 ·CF3COO– column during affinity separation, 27
was further purified by silica gel column chromatography.
In addition to the p-acylaminobenzyl and p-acylami-
nophenyl linkers described above, a benzyloxycarbonyl-
type linker can be also applied to the SAS-based oligosac-
charide synthesis as shown in Scheme 5.13 For this pur-
pose, we have developed 29, which can be readily
prepared from 6 (the structure shown in Scheme 1),
Synlett 2005, No. 15, 2342–2346 © Thieme Stuttgart · New York

LETTER
Oligosaccharide Synthesis by Affinity Separation
2345
through LiAlH4 reduction (95%) followed by the reaction method has various advantages in terms of reaction
with p-nitrophenyl chloroformate (82%). After the po- control, such as reagent transfer, effective temperature
dand tag was introduced onto the C-6 hydroxyl of glu- control, fast mixing, and precise residence time control.
cosamine derivative 28 by the reaction with 29 in the Seeberger and co-workers have reported the first applica-
presence of DMAP, the tagged compound 30 was glyco- tion of glycosylation using a microfluidic-based device.20
sylated with the galactosyl donor 31 to provide 32 in al- In the present study, we combined a microreactor and the
most quantitative yield after the affinity separation. The present SAS system for high throughput oligosaccharide
azidechlorobenzyl protecting group of 32 was selectively synthesis. We used a combination of an IMM micromixer
removed in the presence of the benzyloxy-type podand and a stainless tube reactor (l = 2.0 m, a diameter of 500
tag, by the reaction with PPh3 followed by the oxidation mm), equipped with a stainless column as an affinity sep-
of the resulting benzylaniline with DDQ.14 Following the aration unit (Figure 2).21 The glycosylation was carried
affinity separation, the next fucosylation was effected by out by mixing the solution of donor 10 and acceptor 15 in
the reaction with 3-nitro-2-pyridyl donor 3415 in cyclo- CH2Cl2 and the solution of TMSOTf in CH2Cl2 under
pentylmethylether (CPME)16 using TMSOTf as a catalyst continuous flow. The reaction mixture was directly intro-
to provide trisaccharide 35, which was again purified by
the affinity separation.17
AcO
NH
O
AcO
AcO
O
CCl3
Continuous flow synthesis using a microreactor has
emerged as a new technology for both small-scale high
throughput synthesis and large-scale production.18,19 This
TrocNH
+
O
10
HO
HO
BnO
O
OMe
TMSOTf
in CH2Cl2
15
MeO
MeO
O
O
O
O
O
O
O
O
in CH2Cl2
HO
O
O
N
Tag
O
AllocNH
28
HO
Cl
O
NO2
H
O
O
29
IMM micromixer
DMAP/CH2Cl2
then
OAllyl
N3
58%
silica gel chromatography
OAc
OAc
0 °C
NH
O
O
i)
Tag
O
31
O
AcO
O
CCl3
AcO
O
HO
residence time =
1.1 min
(3 equiv)
O
AllocNH
TMSOTf, MS4Å
CH2Cl2, 0 °C
OAllyl
30
N3
Cl
ii) affinity separation
93%
washing and
desorption
adsorption
NH3
O
Tag
i) PPh3/THF
O
O
OAc
NH3
OAc
O
ii) DDQ, AcOH, H2O
O
CF3CO2
CF3CO2
O
iii) affinity separation
quant.
O
AcO
AcO
AllocNH
OAllyl
32
NO2
N3
Cl
i)
O
O
N
OBn
O
OBn
OBn
Tag
34 (2 equiv)
O
O
OAc
OAc
O
TMSOTf, MS4Å
CPME, 0 °C
O
O
HO
AcO
ii) affinity separation
23%
AcO
AllocNH
33
OAllyl
O
Tag
AcO
O
O
AcO
O
OAc
O
O
AcO
OAc
O
HO
BnO
O
O
O O O O
O
TrocNH
O
O
AcO
tag =
OMe
O
16
91%
AcO
AllocNH
OAllyl
O O
O O
O
N
Tag
OBn
H
35
O
OBn
OBn
Figure 2 Continuous flow synthesis using microreactor and SAS
system
Scheme 5
Synlett 2005, No. 15, 2342–2346 © Thieme Stuttgart · New York

2346
K. Fukase et al.
LETTER
(9) Fukase, K.; Yoshimura, T.; Hashida, M.; Kusumoto, S.
Tetrahedron Lett. 1991, 32, 4019.
(10) Fukase, K.; Yasukochi, T.; Nakai, Y.; Kusumoto, S.
Tetrahedron Lett. 1996, 37, 3343.
(11) Fukase, K.; Nakai, Y.; Egusa, K.; Porco, J. A.; Kusumoto, S.
Synlett 1999, 1074.
(12) Falb, F.; Yechezkel, T.; Salitra, Y.; Gilon, C. J. Peptide Res.
1999, 53, 507.
(13) Benzylcarbonyl and benzyl-type tags can be removed by
catalytic hydrogenolysis using Pd catalyst.
(14) Egusa, K.; Fukase, K.; Kusumoto, S. Synlett 1997, 675.
(15) Yasukochi, T.; Fukase, K.; Kusumoto, S. Tetrahedron Lett.
1999, 40, 6591.
duced to the stainless steel affinity column (4.6 mm × 250
mm) and the flow channel was switched to wash the
column with CH2Cl2. During this time, the desired disac-
charide 16 was trapped in the column, and then eluted
with CH2Cl2–MeOH (1:1); the product 16 was desorbed
and obtained in 91% yield.
As described above, the present SAS method using a
podand tag was successfully applied to oligosaccharide
synthesis.22 Because of the simplicity of the purification
procedure, SAS is expected to be useful for automated
synthesis, such as in combination with the continuous
flow system.
(16) a-Selective glycosylation in CPME: Tokimoto, H.;
Fujimoto, Y.; Fukase, K.; Kusumoto, S. Tetrahedron:
Asymmetry 2005, 16, 441.
Acknowledgment
(17) Glycosylation with nitropyridyl glycoside gave better results
than with glycosyl fluoride and thioglycoside. The
fucosylation stopped at 50% consumption of 33. The
reaction mixture was applied to SAS to give a mixture of 33
and trisaccharide 35. After TFA was removed by liquid–
liquid separation, the mixture was subjected to glycosylation
with fucosyl donor 34, again. This procedure was repeated
twice and the resulting compound 35 was finally purified by
silica gel chromatography.
The present work was conducted with the aid of the Micro-Chemi-
cal Plant Technology Union (MCPT) for the Project of Micro-Che-
mical Technology for Production, Analysis, and Measurement
Systems financially supported by NEDO. The present work was
also financially supported in part by Grant-in-Aid for Scientific
Research No. 15310149 from the Japan Society for the Promotion
of Science.
(18) Pennemann, H.; Hessel, V.; Loewe, H. Chem. Eng. Sci.
2004, 59, 4789.
(19) Jahnisch, K.; Hessel, V.; Loewe, H.; Baerns, M. Angew.
Chem. Int. Ed. 2004, 43, 406.
(20) Ratner, D. M.; Murphy, E. R.; Jhunjhunwala, M.; Snyder, D.
A.; Jensen, K. F.; Seeberger, P. H. Chem. Commun. 2005,
578.
(21) IMM micromixer: http://www.imm-main2.de/.
(22) Representative Procedure of SAS Method. Preparation
of 32.
References
(1) (a) Zhang, W. Curr. Opin. Drug Discov. Dev. 2004, 7, 784.
(b) Yoshida, J.; Itami, K. Chem. Rev. 2002, 102, 3693.
(c) Curran, D. P. Pure Appl. Chem. 2000, 72, 1649.
(d) Porco, J. A. Jr. Comb. Chem. High Throughput Screening
2000, 3, 93.
(2) Zhang, S.-Q.; Fukase, K.; Kusumoto, S. Tetrahedron Lett.
1999, 40, 7479.
To a solution of the acceptor 30 (77 mg, 76 mmol),
trichloroacetimidate 31 (112 mg, 227 mmol), and molecular
sieves 4 Å in CH2Cl2 (1.0 mL) was added TMSOTf (2.7 mL,
15 mmol) at 0 °C under Ar atmosphere. After the reaction
mixture was stirred for 1 h at r.t., the resulting mixture was
filtered to remove the molecular sieves before applying to
the affinity separation. The mixture was directly charged
(3) Zhang, S.-Q.; Fukase, K.; Izumi, M.; Fukase, Y.; Kusumoto,
S. Synlett 2001, 590.
(4) Fukase, Y.; Zhang, S.-Q.; Iseki, K.; Oikawa, M.; Fukase, K.;
Kusumoto, S. Synlett 2001, 1693.
(5) Fukase, K.; Zhang, S.-Q.; Fukase, Y.; Umesakao, N.;
Kusumoto, S. In New Discoveries in Agrochemicals; Clark,
J. M.; Ohkawa, H., Eds.; ACS Symposium Series 892,
American Chemical Society: Washington DC, 2005, 87–98.
(6) The podand tag with a shorter chain length showed weaker
affinity to the ammonium ion column, whereas the tag
having longer chain length, such as 6, showed comparable
affinity with the corresponding crown ether derivatives.
+
onto ArgoPore-NH3 ·CF3COO– filled in a syringe-like
column (Varian, Bond Elut empty cartridges with frits,
column size: 2.0 cm × 8.5 cm, resin 3.8 g), prepared
according to ref. 7. After untagged compounds were washed
off with CH2Cl2 (200 mL), the tagged product 32 was eluted
with CH2Cl2–MeOH (1:1, 50 mL). Evaporation of the
solvents afforded the desired product 32 as a yellow oil (95
mg, 93%): ESI-MS(positive): m/z = 1367.50 [M + Na]+. 1H
NMR (500 MHz, CDCl3): d = 7.32 (d, J = 1.5 Hz, 1 H,
ClAzb), 7.24 (d, J = 8.2 Hz, 1 H, ClAzb), 7.12 (d, J = 8.2 Hz,
1 H, ClAzb), 6.53 (d, J = 2.2 Hz, 2 H, –C6H3–CH2–OCO),
6.47 (t, J = 2.1 Hz, 1 H, –C6H3–CH2–OCO), 5.96–5.80 (m, 2
H, –CH2–CH=CH2 × 2), 5.31–5.16 (m, 6 H, H-4¢, –CH2–
CH=CH2 × 2, H-2¢), 5.09 (s, 2 H, –C6H3–CH2–OCO), 4.95
(dd, J = 3.4, 10.4 Hz, 1 H, H-3¢), 4.90 (d, J = 11.6 Hz, 1 H,
ClAzPh–CH2), 4.81 (d, J = 3.7 Hz, 1 H, H-1), 4.78 (d,
J = 10.0 Hz, 1 H, NH), 4.60 (d, J = 7.9 Hz, 1 H, H-1¢), 4.56–
4.48 (m, 4 H, ClAzPh–CH2, OCO–CH2-CH=CH2, H-6a),
4.23 (dd, J = 3.7, 11.5 Hz, 1 H, H-6b), 4.15–4.08 [m, 5 H, –
C6H3 (OCH2)2, –CH2–CH=CH2], 3.98–3.93 (m, 2 H, –CH2-
CH=CH2, H-2), 3.89–3.53 {m, 33 H, –C6H3[OCH2CH2–
(OCH2CH2)2–OCH2CH2OMe]2, H-4, H-5, H-5¢, H-6¢, H-3},
3.37 (s, 6 H, MeO × 2), 2.13, 2.05, 1.96 (s, 12 H, Ac × 4).
(7) The maximum adsorption of 8 to ArgoPore-NH3 ·CF3COO–
+
was determined as follows: the solid-phase extraction
column (Varian, Bond Elut empty cartridges with frits, 6 mL
capacity) was filled with ArgoPore®-NH2 (1.74 g, Argonout
Technologies, Inc). The resin column was washed with
CH2Cl2–MeOH (1:1) and CH2Cl2 (or toluene). The amino
groups on the resins were changed to ammonium ions with
10% TFA in CH2Cl2 (or toluene) and then excess TFA was
washed with CH2Cl2 (or toluene). A sufficient quantity of
the sample in CH2Cl2 (or toluene) was charged to the
+
ArgoPore-NH3 ·CF3COO– column and then the column was
washed with the same solvent to remove the excess sample.
Compound 8 adsorbed in the column was then eluted with
CH2Cl2–MeOH (1:1). The maximum adsorption of 8 was
determined to be 138 mg (6.9% to amino groups) in toluene
and 58.4 mg (2.9% to amino groups) in CH2Cl2.
(8) Fukase, K.; Tanaka, H.; Torii, S.; Kusumoto, S. Tetrahedron
Lett. 1990, 31, 389.
Synlett 2005, No. 15, 2342–2346 © Thieme Stuttgart · New York