A new catch-and-release purification method using a 4-azido-3-chlorobenzyl group

Article abstract of DOI:10.1055/s-2001-14623

Products that possess 4-azido-3-chlorobenzyl group were selectively isolated from reaction mixtures by using a solid-supported phosphine. Successive treatment with 2,3-dichloro-5,6-dicyanobenzoquinone readily liberated purified products. Application of this method to several oligosaccharide syntheses is described.

Full text of DOI:10.1055/s-2001-14623

LETTER
777
A New Catch-and-Release Purification Method Using a 4-Azido-3-
chlorobenzyl Group
Kenji Egusa, Shoichi Kusumoto, Koichi Fukase*
Department of Chemistry, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043, Japan
Fax +81 6 6850 5419; E-mail: koichi@chem.sci.osaka-u.ac.jp
Received 10 April 2001
IRA-68, and then filtered. To the filtrate was added triph-
enylphosphine-polystyrene resin to catch the ClAzb-dis-
accharide 3 onto the resin. The reagents and by-products
without the ClAzb moiety were removed by simple rins-
Abstract: Products that possess 4-azido-3-chlorobenzyl group
were selectively isolated from reaction mixtures by using a solid-
supported phosphine. Successive treatment with 2,3-dichloro-5,6-
dicyanobenzoquinone readily liberated purified products. Applica-
tion of this method to several oligosaccharide syntheses is de- ing with dichloromethane and the solid-supported disac-
scribed.
charide 4 was obtained. The disaccharide part of the resin
4 was finally released by treatment with DDQ. Excess
DDQ was removed by ion-exchange resin Amberlite®
IRA-68 after conversion of DDQ to the corresponding hy-
droquinone using L-ascorbic acid. After passing the solu-
tion of the product through a silica gel short column (1 × 2
cm) to remove 4-amino-3-chlorobenzaldehyde derived
from the ClAzb group, pure disaccharide 5 was obtained
in 72% yield.4 Disaccharide 5, which has a free hydroxy
group, can be used as a glycosyl acceptor for the subse-
quent glycosylation.
Key words: azides, combinatorial chemistry, glycosylations, phos-
phines, polymer-supported synthesis
In organic synthesis, the isolation of products is some-
times a tedious and time-consuming procedure. Especial-
ly in the area of combinatorial chemistry, a simple and
effective isolation method is necessary because many
compounds are handled at the same time. For instance,
chromatography is a quite popular method for the isola-
tion of products of organic synthesis. However, it is some-
what tedious and consumes a considerable amount of
solvents and optimization of the conditions of the separa-
tion sometimes requires much time. Therefore, techniques
for polymer-supported synthesis such as polymer-bound
reagents, scavenger resins, catch-and-release purification
have been developed recently.1
HO
BnO
BnO
O
N3
2
O
BnO
OMe
Cl
O
BzO
BzO
SPh
NBS, Sn(OTf)2
MS4A / CH2Cl2
BzO
1
We have already reported the use of the 4-azido-3-chlo-
robenzyl (ClAzb) group for practical protection of hy-
droxy functions.2,3 The ClAzb group is stable under
various conditions but is readily removed by a safety
catch procedure, i.e., conversion of the azido function to
the corresponding iminophosphorane followed by oxida-
N3
Ph
P
O
1)
Cl
O
BzO
BzO
O
Ph
BzO
O
BnO
BnO
2) rinse
tion
using
2,3-dichloro-5,6-dicyanobenzoquinone
BnO
3
OMe
(DDQ). We thought that the ClAzb group could be used
not only as a protecting group but also as a tag of the prod-
uct for catch-and-release purification. A compound pos-
sessing the ClAzb group can be selectively caught by a
solid-supported phosphine based on the specific reaction
between the azido function and the phosphine, separated
from the other compounds by simple rinsing, and then re-
leased from the solid-support by treatment with DDQ.
This method was examined in several oligosaccharide
syntheses.
+ by-products
Ph
P
N
O
Ph
Cl
O
BzO
BzO
O
BzO
O
BnO
BnO
4
BnO
OMe
HO
O
As shown in Scheme 1, ClAzb-thioglycoside 1 was react-
ed with 3 equiv of glycosyl acceptor 2 using N-bromosuc-
cineimide (NBS) and Sn(OTf)2 as activating reagents in
the presence of molecular sieves 4Å. In this reaction,
MS4A and excess amount of the acceptor were used to
avoid formation of the hydrolyzate of the thioglycoside 1.
The reaction mixture was neutralized with Amberlite®
BzO
BzO
O
DDQ, AcOH, H2O
CH2Cl2
BzO
BnO
BnO
O
BnO
5
OMe
72% from 1
Scheme 1 Glycosylation using ClAzb-thioglycoside
Synlett 2001 No. 6, 777–780 ISSN 0936-5214 © Thieme Stuttgart · New York

778
K. Egusa et al.
LETTER
We then carried out disaccharide synthesis using a glyco-
syl acceptor having the ClAzb group. As shown in
Scheme 2, 1-O-ClAzb-glycoside 7 was glycosylated with
3 equiv of thioglycoside 6 as above. The reaction mixture
containing disaccharide 8 was neutralized and treated
with triphenylphosphine-polystyrene similarly to give
solid-supported disaccharide 9. After the treatment with
DDQ and the operation described above, disaccharide 10
was obtained in 61% yield in a pure state. Disaccharide 10
can be used as a glycosyl donor for the subsequent glyco-
sylation after conversion of the 1-hydroxy group to a
proper functional group such as trichloroacetimidate.
HO
O
BzO
BzO
BzO
NH
SPh 12
O
BzO
BzO
BzO
O
CCl3
Sn(OTf)2, MS4A / CH2Cl2
BzO
11
HO
N3
O
BnO
BnO
7
O
BnO
Cl
NBS
BzO
O
BzO
BzO
O
+ by-products
BzO
BzO
BzO
O
HO
O
N3
O
BzO
BnO
N3
O
BnO
BnO
BnO
BzO
O
13
BnO
O
7
O
BnO
BzO
BzO
Cl
SPh
Cl
BzO
Sn(OTf)2, MS4A / CH2Cl2
6
1) triphenylphosphine-polystyrene
2) rinse
3) DDQ, AcOH, H2O / CH2Cl2
Ph
P
BzO
BzO
O
1)
BzO
BzO
O
O
BzO
BzO
Ph
O
BzO
BnO
BnO
N3
O
BzO
BzO
BzO
O
O
2) rinse
O
BnO
Cl
BzO
BnO
O
8
+ by-products
14
BnO
OH
BzO
BnO
55% from 7
O
BzO
BzO
O
Ph
P
Scheme 3 One-pot trisaccharide synthesis
BzO
BnO
BnO
N
O
BnO
O
Ph
Cl
9
BzO
compound, and such impurities must be removed. As
shown in Scheme 4, a glycosyl acceptor bound to a
macroporous polystyrene (ArgoPore™-NH2 ) 15 was gly-
O
BzO
BzO
DDQ, AcOH, H2O
CH2Cl2
O
7
BzO
BnO
BnO
O
cosylated with thioglycoside 1 using NBS and Sn(OTf)2
in the presence of MS4A to give a mixture of disaccharide
16 and unreacted 15.8 The resin was treated with sodium
methoxide in methanol to cleave the linker, and a mixture
of disaccharide 17, monosaccharide 18 derived from 15
and other by-products was obtained. Then, the mixture
was treated with triphenylphosphine-(polyethylenegly-
col-polystyrene-copolymer) resin9 in methanol instead of
the triphenylphosphine-polystyrene resin employed
above. This was because disaccharide 17 was insoluble in
dichloromethane and the polystyrene resin does not swell
in methanol. The solid-supported disaccharide 19 ob-
tained was treated with DDQ. Excess DDQ was then
quenched with L-ascorbic acid. The mixture was treated
with ion exchange resins Amberlyst® A-26 (OH- form, to
remove hydroquinone) and Amberlyst® 15 (H+ form, to
remove 4-amino-3-chlorobenzaldehyde derived from the
ClAzb group) to afford highly pure disaccharide 20 in
38% yield from 15.
OH
10
BnO
61% from 7
Scheme 2 Glycosylation using 1-O-ClAzb-glycoside
Next, we examined one-pot trisaccharide synthesis.5 One
problem in this approach is the separation of the desired
products from the reaction mixtures containing by-prod-
ucts derived from excess glycosyl donors. As shown in
Scheme 3, glycosyl trichloroacetoimidate 11 was reacted
with thioglycoside 12 using Sn(OTf)2 in the presence of
molecular sieves 4Å at r.t. for 30 min and then 1-ClAzb-
glycoside 7 and NBS were added. The reaction was con-
tinued at r.t. for 30 min. to give a complex reaction mix-
ture containing trisaccharide 13. The mixture was first
treated with triphenylphosphine-polystyrene resin and
then with DDQ to give the pure trisaccharide 14 in 55%
yield from 7.
Thus, the products possessing the ClAzb group were se-
lectively isolated from the reaction mixture using triphe-
nylphosphine-resin, and the successive treatment with
DDQ readily afforded purified products. Since a new free
Finally, we examined a combined application of this
method with solid-phase glycosylation.6 In the final cleav-
age step of solid-phase synthesis, solid-bound impurities
formed in each reaction step are released with the desired
Synlett 2001, No. 6, 777–780 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
A New Catch-and-Release Purification Method Using
779
O
N3
NBS, Sn(OTf)2
MS4A / CH2Cl2
NH
BnO
O
O
+
O
Cl
O
BnO
HO
BzO
O
O
SPh
BnO
BzO
BzO
BzO
15
1
O
N3
NH
NaOMe / MeOH
O
O
+ 15
O
Cl
BnO
O
BzO
BzO
O
O
O
BzO
BzO
16
N3
BnO
OH
BnO
O
O
OH
BnO
HO
+ by-products
+
O
O
Cl
BnO
O
HO
HO
O
O
OH
OH
OH
17
18
Ph
Ph
P
1)
P
N
BnO
BnO
O
Ph
Ph
OH
O
Cl
O
HO
HO
O
2) rinse with MeOH
O
OH
OH
19
BnO
HO
OH
DDQ, AcOH, H2O
MeOH
O
BnO
O
HO
HO
O
O
38% from 15
20
OH
OH
Scheme 4 Solid-phase saccharide synthesis
hydroxyl function is generated through this purification
procedure, this method can be regarded as a combination
of purification and deprotection.
Tetrahedron Lett. 1999, 40, 7479. (d) Purification of
anthracene-tagged compounds: Wang, X.; Parlow, J. J.;
Porco, Jr., J. A. Org. Lett. 2000, 22, 3509. (e) The use of trityl
chloride resin for rapid isolation of an amine: Hidai, Y.; Kan,
T.; Fukuyama, T. Tetrahedron Lett. 1999, 40, 4711.
(f) Purification of compounds having barbituric acid tag by
using hydrogen bond interaction: Zhang, S.-Q; Fukase, K.;
Izumi, M.; Fukase, Y.; Kusumoto, S. Synlett 2001, in press.
(g) Other catch-and-release purification techniques and
polymer-bound reagents: Thompson, L. A. Curr. Opin. Chem.
Biol. 2000, 4, 324.
In conclusion, the catch-and-release purification using the
ClAzb group was proved to be simple but quite effective.
This method offers a new approach to the purification of
products in organic synthesis, especially in the field of
combinatorial synthesis.
(2) (a) Fukase, K.; Egusa, K.; Nakai, Y.; Kusumoto, S. Molecular
Diversity 1996, 2, 182. (b) Egusa, K.; Fukase, K.; Kusumoto,
S. Synlett 1997, 675.
(3) 4-Azido-3-chlorobenzyl bromide is commercially available
from Wako Pure Chemicals Industries, Ltd., http://
www.wako-chem.co.jp/.
(4) Representative procedure: Preparation of 2,3,4-tri-O-benzoyl-
β-D-glucopyranosyl-2,3,4-tri-O-benzyl-β-D-glucopyranoside
5. After a mixture of ClAzb-thioglycoside 1 (50 mg, 67 µmol),
glycosyl acceptor 2 (93 mg, 200 µmol), Sn(OTf)2 (6 mg, 13
µmol) and molecular sieves 4 Å (ca. 500 mg) in 2 mL of
dichloromethane was stirred at r.t. for 15 min., the reaction
was started by addition of NBS (13 mg, 70 µmol). The mixture
was stirred at r.t. for 30 min. and then ion exchange resin
Amberlite® IRA-68 (ca. 200 mg) was added and filtered. To
the filtrate was added triphenylphosphine-polystyrene resin
(278 mg, 333 µmol), and the mixture was stirred at r.t. for 3 h,
and filtered. The resin was washed with dichloromethane
twice and suspended in 2 mL of dichloromethane. DDQ
Acknowledgement
The present work was financially supported in part by Special Coor-
dination Funds of the Science and Technology Agency of the Japa-
nese Government, Grants-in-Aid for Scientific Research
No.11558080 from the Ministry of Education, Science, Sports and
Culture of Japan and "Research for the Future" Program
No.97L00502 from the Japan Society for the Promotion of Science.
We thank Prof. Yasuhiro Uozumi for helpful discussions on phos-
phine resins.
References and Notes
(1) (a) Affinity purification of biotinylated peptides synthesized
by solid-phase method: Funakoshi, S.; Fukuda, H.; Fujii, N. J.
Chromatogr. 1993, 638, 21. (b) "Fishing Out" method for
purification of β-amino alcohols: Hori, M.; Janda, K. D. J.
Org. Chem. 1998, 63, 889. (c) Purification of crown-ether-
tagged compounds: Zhang, S.-Q; Fukase, K.; Kusumoto, S.
Synlett 2001, No. 6, 777–780 ISSN 0936-5214 © Thieme Stuttgart · New York

780
K. Egusa et al.
LETTER
D. J. Am. Chem. Soc. 1994, 116, 6953. (d) Douglas, S. P.;
Whitfield, D. M.; Krepinsky, J. J. J. Am. Chem. Soc. 1995,
117, 2116. (e) Randolph, J. T.; McClure, K. F.; Danishefsky,
S. J. J. Am. Chem. Soc. 1995, 117, 5712. (f) Ito, Y.; Kanie, O.;
Ogawa, T. Angew. Chem., Int. Ed. Engl. 1996, 35, 2510.
(g) Rademann, J.; Schmidt, R. R. Tetrahedron Lett. 1996, 37,
3989. (h) Nicolaou, K. C.; Winssinger, N.; Pastor, J.;
DeRoose, F. J. Am. Chem. Soc. 1997, 119, 449. (i) Rademann,
J.; Schmidt, R. R. J. Org. Chem. 1997, 62, 3650.
(91 mg, 400 µmol), acetic acid (100 µL) and water (100 µL)
were added and the mixture was shaken at r.t. for 3 h, then
filtered. To the filtrate was added a solution of L-ascorbic acid
(70 mg, 400 µmol) in methanol and the mixture was stirred at
r.t. for 5 min. After passing through a column of ion exchange
resin Amberlite® IRA-68 (2 × 5 cm), the mixture was
concentrated in vacuo. The residue was dissolved in
dichloromethane and charged on a short silica gel column
(1 × 2 cm). After flushing the column with 5 mL of
dichloromethane, the product was eluted with hexane/ethyl
acetate 1:1 and the solvent was removed in vacuo to give
disaccharide 5 (45 mg, 48 µmol, 72% yield) as a colorless oil.
HPLC (column: Inertsil ODS-2 5 µm, 4.6 × 150 mm, 30 °C,
mobile phase: acetonitrile/water 85:15, flow rate: 1.0 mL/min,
detection: UV210 nm) Rt = 6.2 min., purity: 96% (calcd. from
the peak area); 1H NMR (270 MHz, CDCl3): δ = 7.95-7.80 (m,
6H), 7.56-7.49 (m, 1H), 7.44-7.20 (m, 21H), 7.09-7.05 (m,
2H), 5.89 (t, 1H, J = 9.57 Hz), 5.84 (dd, 1H, J = 9.57, 7.92
Hz), 5.50 (t, 1H, J = 9.57 Hz), 4.90 (d, 1H, J = 10.89 Hz), 4.81
(d, 1H, J = 7.59 Hz), 4.73 (d, 1H, J = 12.21 Hz), 4.70 (d, 1H,
J = 10.89 Hz), 4.60 (d, 1H, J = 12.21 Hz), 4.85 (d, 1H,
J = 9.21), 4.52 (d, 1H, J = 3.63 Hz), 4.33 (d, 1H, J = 11.21),
4.13-4.08 (m, 1H), 3.90 (t, 1H, J = 9.24), 3.78-3.70 (m, 5H),
3.45 (dd, 1H, J = 9.57, 3.63 Hz), 3.42 (t, 1H, J = 9.90), 3.23 (s,
3H), 2.50 (broad, 1H); ESI-MS m/z: Calcd for C55H54NaO14
[(M+Na)+] 961.3, found 961.4.
(j) Rodebaugh, R.; Joshi, S.; Fraser-Reid, B.; Geysen, H. M. J.
Org. Chem. 1997, 62, 5660. (k) Zheng, C.; Seeberger, P. H.;
Danishefsky, S. J. J. Org. Chem. 1998, 63, 1126. (l) Zheng, C.;
Seeberger, P. H.; Danishefsky, S. J. Angew. Chem., Int. Ed.
Engl. 1998, 37, 786. (m) Heckel, A.; Mross, E.; Jung, K.-H.;
Rademann, J.; Schmit, R. R. Synlett 1998, 171. (n) Rademann,
J.; Geyer A.; Schmidt, R. R. Angew. Chem., Int. Ed. Engl.
1998, 37, 1241. (o) Nicolaou, K. C.; Watanabe, N.; Li, J.;
Pastor, J.; Winssinger, N. Angew. Chem., Int. Ed. Engl. 1998,
37, 1559. (p) Doi, T.; Sugiki, M.; Yamada, H.; Takahashi, T;
Porco, Jr., J. A. Tetrahedron Lett. 1999, 40, 2141. (q) Fukase,
K.; Nakai, Y.; Egusa, K.; Porco, Jr., J. A.; Kusumoto, S.
Synlett 1999, 1074. (r) Egusa, K.; Fukase, K.; Nakai, Y.;
Kusumoto, S. Synlett 2000, 27.
(7) Commercially available from Argonaut Technologies, http://
www.argotech.com.
(8) The macroporous resin, ArgoPore™, is heterogeneous in the
pore size. It was thought that the glycosylation in smaller
pores was interfered by steric hindrance of the resin itself and
some of the glycosyl acceptors remained unchanged.
(9) Commercially available from Wako Pure Chemicals
Industries, Ltd., http://www.wako-chem.co.jp/.
(5) (a) Takahashi, T.; Adachi, M.; Matsuda, A.; Doi, T.
Tetrahedron Lett. 2000, 41, 2599. (b) Zhang, Z.; Ollmann, I.
R.; Ye, X.-S.; Wischnat, R.; Baasov, T.; Wong, C.-H. J. Am.
Chem. Soc. 1999, 121, 734.
(6) For recent advances in solid phase chemical synthesis of
oligosaccharide see: (a) Verduyn, R.; van der Klein, P. A. M.;
Douwes, M.; van der Marel, G. A.; van Boom, J. H. Recl.
Trav. Chim. Pays-Bas 1993, 112, 464. (b) Danishefsky, S. J.;
McClure, K. F.; Randolph, J. T.; Ruggeri, R. B. Science 1993,
260, 1307. (c) Yan, L.; Taylor, C. M.; Goodnow, R.; Kahne,
Article Identifier:
1437-2096,E;2001,0,06,0777,0780,ftx,en;Y07801ST.pdf
Synlett 2001, No. 6, 777–780 ISSN 0936-5214 © Thieme Stuttgart · New York