Oligosaccharide synthesis on controlled-pore glass as solid phase material

Article abstract of DOI:10.1055/s-1998-3127

Mercaptopropyl-functionalized controlled-pore glass (MP-CPG, 2) was employed as a solid phase material for the synthesis of α(1-2)-connected trimannoside 16. As a glycosyl donor O-(3,4,6-tri-O-benzyl-2-O-phenoxyacetyl-α-D-mannopyranosyl) trichloroacetimid

Full text of DOI:10.1055/s-1998-3127

February 1998
SYNLETT
171
1
Oligosaccharide Synthesis on Controlled-Pore Glass as Solid Phase Material
Alexander Heckel, Elmar Mross, Karl-Heinz Jung, Jörg Rademann, and Richard R. Schmidt
*
Fakultät Chemie, Universität Konstanz, Fach M 725, D-78457 Konstanz, Germany
FAX +49/7531/88 3135
Received 30 September 1997
Abstract: Mercaptopropyl-functionalized controlled-pore glass (MP-
CPG, 2) was employed as a solid phase material for the synthesis of
α(1-2)-connected trimannoside 16. As a glycosyl donor O-(3,4,6-tri-O-
benzyl-2-O-phenoxyacetyl-α-D-mannopyranosyl)trichloroacetimidate
(6) was employed which was readily obtained from D-mannose.
Glycosylation of 2 and of intermediates 9 and 13 was performed with
excess 6 in CH Cl at -40 °C in the presence of TMSOTf as the catalyst
2
2
(→ 7, 11, 15). For the removal of the temporary phenoxyacetyl (PA)
protective group guanidine in DMF was used (→ 9, 13). Cleavage of
products 7, 9, 11, 13 and 15 from MP-CPG was carried out with N-
bromosuccinimide (NBS) in THF/MeOH in the presence of 2,6-di-tert-
butylpyridine (DTBP) affording 8, 10, 12, 14, and methyl trimannoside
16, respectively.
Progress has recently been made in solid phase supported
2,3
oligosaccharide synthesis based on the use of the Merrifield resin. In
order to permit reactions, this resin requires swelling by the solvent.
However, because resin swelling is highly solvent and temperature
dependent, anomer control (and sometimes also regioselectivity) is
often limited. Therefore, we investigated 'controlled-pore glass' (CPG)
as a solid support, because it does not require swelling. Although this
Scheme 1
alcoholysis or aminolysis of this group under mild basic conditions is
much faster than the common O-acetyl protective group. Therefore,
from D-mannose via the known intermediate 3 we synthesized the bis-
12
13
4
material is extensively employed in oligonucleotide synthesis, the
phenoxyacetyl derivative 4 which is selectively 1-O-deacylated with
hydrazinium acetate (→ 5) and then transformed into
trichloroacetimidate 6 with trichloroacetonitrile in the presence of
promises for its uselfulness in oligosaccharide synthesis were not high
2,5,6
according to previous work;
the ubiquitous presence of hydroxy
14
groups at the surface of this material and the sensitivity to aqueous base
could be major drawbacks. Yet, CPG could be recently successfully
employed as solid phase material for enzymatic glycosylation
DBU.
7
reactions.
Our first goal was to find a linker system for ligation to CPG and for the
attachment of the first sugar residue. In order to gain high loading of the
8
CPG surface with the linker system, we selected 250 Å CPG. After
investigating
various
linker
systems,
3-mercaptopropyl-
9
trimethoxysilane (1, Scheme 1) was chosen because it provides
mercaptopropyl functionalized MP-CPG 2. Thus, a thioglycosidic
10
linkage is available to the first sugar residue; it is compatible with the
mild acid catalysis required for the O-glycosyl trichloroacetimidate
3a
methodology which will be used for further chain extension reactions;
additionally, after completion of the reaction sequence at the polymer, it
offers the possibility of selective cleavage by thiophilic reagents which
3a
do not affect O-glycosides. Loading of MP-CPG 2 was determined by
reaction with dithiodinitrobenzoate (DTNB) following known
10,11
procedures.
Thus, 0.3 mmol of free mercapto groups/g CPG was
found as mean value on 2. In order to remove traces of methanol, 2 had
to be heated to 150 °C in vacuo for 6 h. (Monomethoxytritylation of this
material with monomethoxytrityl (MMT) chloride, silylation of the
remaining free hydroxyl groups, and then selective removal of the MMT
groups did not result in higher glycosylation yields as later found).
Scheme 2
Linking the first mannosyl residue to the mercapto group of 2 with 6 as
mannosyl donor was performed essentially under standard conditions;
i.e. the reaction was carried out in CH Cl as solvent at -40 °C with
TMSOTf as catalyst. In order to get complete glycosylation yielding 7
two times three equivalents of glycosyl donor 6 were employed. The
reaction was followed by gravimetry and by MALDI-TOF analysis of
small samples, from which the thiomannoside was cleaved with NBS in
THF/MeOH in the presence of 2,6-di-tert-butylpyridine (DTBP); thus,
For the glycosylation studies, α(1-2)-linked oligomannose was chosen
as model, because this glycosidic connection is often found in nature
and short oligosaccharides of this type have been already successfully
2
2
15
3a
synthesized on other supports. In order to ease cleavage of the
temporary protective group at the 2-O-position of the required mannosyl
donor, the phenoxyacetyl group was chosen (6, Scheme 2), because

172
LETTERS
SYNLETT
Scheme 3
methyl α-mannoside 8 was obtained and could be easily identified by
comparison with independently obtained material.
can be removed under nonaqueous conditions, success in solid phase
oligosaccharide synthesis.
16
The temporary phenoxyacetyl group at 2-O of 7 was best cleaved with
References and Notes
two times two equivalents of guanidine in DMF; after extensive
(1) This
work
was
supported
by
the
Deutsche
washing with DMF and then with CH Cl /HOAc and with dry EtOAc,
2
2
Forschungsgemeinschaft and the Fonds der Chemischen Industrie.
− The helpful discussions with Dr. Rademann, J. are gratefully
acknowledged.
CH Cl , and acetone, evaporation in vacuo afforded 2-O-unprotected
2
2
17
9. Application of the cleavage procedure gave the corresponding
16
methyl mannoside 10,
thus confirming the successful 2-O-
(2) For a review of early work in this field, see: Fréchet, J.M.J. In
Polymer-supported Reactions in Organic Chemistry; Hodge, P.;
Sherrington, D.C., Eds.; Chichester, 1980; Chapter 8, p. 407.
deprotection.
Chain extension with glycosyl donor 6 under the conditions described
above gave disaccharide 11; the reaction was monitored by MALDI-
(3) For more recent chemical glycosylations on solid phase:
(a) Rademann, J.; Schmidt, R.R. Tetrahedron Lett. 1996, 37,
3989-3990; J. Org. Chem. 1997, 62, 3650-3653. (b) Randolph,
J.T.; Danishefsky, S.J. Angew. Chem. 1994, 106, 1538-1541;
Angew. Chem. Int. Ed. Engl. 1994, 33, 1470-1473; Danishefsky,
S.J.; McClure, K.F.; Randolph, J.T.; Ruggeri, R.B. Science 1993,
260, 1307-1309. (c) Yan, L.; Taylor, C.M.; Goodnow, R.; Kahne,
D. J. Am. Chem. Soc. 1994, 116, 6953-6954; Liang, R.; Yan, L.;
Loebach, J.; Ge, M.; Uozumi, Y.; Sekanina, K.; Horan, N.;
Gildersleeve, J.; Thompson, C.; Smith, A.; Biswas, K.; Still,
W.C.; Kahne, D. Science, 1996, 274, 1520-1522. (d) Hunt, J.A.,
Roush, W.R. J. Am. Chem. Soc. 1996, 118, 9998-9999.
(e) Andinolfi, M.; Barone, G.; De Napoli, L.; Iadonisi, A.;
Piccialli, G. Tetrahedron Lett. 1996, 37, 5007-. (f) Veenemann,
G.H.; Notermans, S.; Liskamp, R.M.J.; van der Marel, G.A.; van
15
TOF analysis and product formation was confirmed after cleavage also
1
16,18
by H NMR, thus proving the synthesis of methyl dimannoside 12.
Removal of the phenoxyacetyl group, applying the same procedure as
17
described above, gave 2β-O-unprotected 13; application of the
16
cleavage process led to the corresponding dimannoside 14. In order to
demonstrate the success with MP-CPG 2 as solid phase material, 13 was
15
again glycosylated with 6, thus affording 15, which was again
characterized by cleavage with NBS/MeOH/DTBP and by MALDI-
16,18
TOF analysis affording α(1-2)-linked trimannoside 16
contained small traces of 8 and 12.
which
In conclusion, mercaptopropyl-functionalized CPG (MP-CPG, 2) offers
with reactive glycosyl donors and temporary protective groups, which

February 1998
SYNLETT
173
Boom, J.H. Tetrahedron Lett. 1987, 28, 6695-6698. (g) Nicolaou,
33:3:1 solution of dry THF, dry methanol and DTBP for 2 h. This
mixture is suitable for MALDI-TOF analysis. For preparative
cleavage triethylsilane is then added to remove excess NBS. The
product is isolated by filtration, followed by washing the CPG
K.C.; Winssinger, N.; Pastor, J.; DeRoose, F. J. Am. Chem. Soc.
1997, 119, 449-450. (h) Ito, Y.; Kanie, O.; Ogawa, T. Angew.
Chem. 1996, 108, 2691-2693; Angew. Chem. Int. Ed. Engl. 1996,
35, 2510-2512
with dry CH Cl and dry acetone, 40 mL each. After evaporation
2
2
of the solvent the product is pre-purified by column
chromatography. Pure product is finally obtained by HPLC with a
silica gel column and hexane/ethyl acetate as eluent.
(4) Geckeler, K.E.; Wacker, R. Naturwiss. 1996, 83, 498-513.
(5) Eby, R.; Schuerch, C. Carbohydr. Res. 1975, 39, 151-155.
(6) Veeneman, G.H.; Brugghe, H.F.; van den Elst, H.; van Boom, J.H.
(17) General procedure for the synthesis of 9 and 13: Guanidine is
prepared by reaction of guanidinium chloride (61.9 mg, 0.648
mmol) with sodium methoxide (35 mg, 0.648 mmol) in dry
methanol under argon, followed by filtration and evaporation of
the solvent. The guanidine is then dissolved in dry DMF (1 mL)
and added to a suspension of 7 (1.330 g, 0.324 mmol) in dry DMF
(5 mL). After shaking for 16 h the product is isolated by filtration,
followed by washing with dry DMF and dry acetone, 20 mL each.
The product is dried in a stream of dry argon and then in vacuo
with gentle warming. To complete the reaction, the treatment with
guanidine was usually repeated once more. For the final
purification the product is washed with dry DMF (60 mL), a 10%
Carbohydr. Res. 1990, 195, C1-C4.
(7) Halmcomb, R.L.; Huang, H.; Wong, C.-H. J. Am. Chem. Soc.
1994, 116, 11315-11322; Schuster, M.; Wang, P.; Paulson, J.C.;
Wong, C.-H. J. Am. Chem. Soc. 1994, 116, 1135-1136.
(8) Type 332, pore diameter 250 Å, particle size 20-45 µm, Fa. Grace
GmbH (in der Hollerecke 1, D-67547 Worms); CPG with a pore
diameter of 1500 Å was employed with similar success.
(9) Commercially available from Aldrich.
(10) Badley, R.; Ford, W. J. Org. Chem. 1989, 54, 5437-5443.
(11) Ellman, G.L., Arch. Biochem. Biophys. 1959, 82, 70-77.
(12) Reese, C.B.; Stewart, J.M.C.; van Boom, J.H.; de Leeuw, H.P.M.;
Nagel, J.; de Rooy, J.F.M. J. Chem. Soc., Perkin Trans. II, 1974,
293-297; Reese, C.B.; Stewart, J.M.C. Tetrahedron Lett. 1968,
4273-4276.
solution of acetic acid in dry CH Cl (20 mL), dry ethyl acetate
2
2
(40 mL), dry CH Cl (40 mL) and finally dry acetone (40 mL).
2
2
Then the product is dried as described, affording 9 (1.2809 g) as a
slightly yellow powder; yield: > 90%; MALDI-TOF analysis did
not show any phenoxyacetylated material.
(13) Mayer, T.G.; Kratzer, B.; Schmidt, R.R. Angew. Chem. 1994, 106,
2289-2293; Angew. Chem. Int. Ed. Engl. 1994, 33, 2177-2181.
1
(18) NMR data: 12: H NMR (600 MHz, CDCl ): δ 3.23 (H C-O),
3
3
1
(14) H NMR data (250 MHz, CDCl ): δ 3.70-4.06 (m, 5 H, H-
3
3.64 (4b-H), 3.68 (6b-H, 6b-H'), 3.69 (5a-H), 3.71 (6a-H, 6a-H'),
3.80 (4a-H), 3.87 (3a-H), 3.91 (5b-H), 3.96 (3b-H), 3.96 (2a-H),
3,4,5,6,6'), 4.41-4.79 [m, 8 H, 3 CH (Bn), CH (PA)], 5.62 (dd, 1
2
2
3
3
H, J = 2.1, J = 3.1 Hz, H-2), 6.33 (d, 1 H, H-1), 6.87-6.98
1,2
2,3
4.39-4.84 [6 CH (Bn)], 4.64 [CH (PA)], 4.74 (1a-H), 5.07 (1b),
2
2
and 7.13-7.35 (m, 20 H, 3 Bn, PA), 8.7 (s, 1 H, NH).
13
5.62 (2b). – C NMR (150.9 MHz, CDCl ): 54.88 [H C-O],
3
3
(15) General procedure for the synthesis of 7, 11, and 15: MP-CPG (2:
65.13 [CH (PA)], 68.96 (C-6b), 69.25 (C-6a), 69.51 (C-2b),
2
1.22 g, 0.366 mmol SH) was suspended in 6 mL of dry CH Cl
under an argon atmosphere and cooled to -45 °C in a three-mantle
71.67 (C-5a), 71.83 (C-5b), 72.09 (Bn), 72.14 (Bn), 73.32 (Bn),
73.41 (Bn), 74.25 (C-4b), 74.58 (C-4a), 74.65 (C-2a), 75.07 (2
Bn), 78.10 (C-3b), 79.77 (C-3a), 99.19 (C-1b), 99.65 (C-1a),
2
2
flask. Then 6 (800 mg, 1.098 mmol) in dry CH Cl (2 mL) was
2
2
added and the suspension was horizontally shaken (300 times/
min) for 10 min. The reaction was finally started by adding
TMSOTf (30 µL, 0.16 mmol). After gentle shaking for 1 h the
reaction mixture was brought to room temp. Then the product was
isolated by filtration and subsequently washed with dry CH Cl
114.76-138.37 [Bn, PA], 157 (PA), 168.24 (C=O).
1
NMR data 16: H NMR (600 MHz, CDCl ): δ 2.97 (5c-H), 3.07
3
(H C-O), 3.31 (3c-H), 3.49 (6c-H), 3.5 (4b-H), 3.54 (6b-H), 3.55
3
(6c-H') 3.57 (5b-H, 6a-H), 3.58 (5a-H), 3.62 (6b-H'), 3.66 (4c-H),
3.68 (4a-H), 3.76 (3a-H), 3.78 (3b-H), 3.8 (6a-H), 4.0 (2a-H), 4.2-
2
2
and dry acetone, 60 mL each. Finally the product was dried in a
stream of dry argon and then in vacuo with gentle warming,
affording 7 (1.3829 g; ~ 80%) as a slightly yellowish powder. In
order to prevent the contamination of unreacted materials, each
glycosylation reaction was usually performed twice, thus
increasing the yield to over 95%. Similar results were obtained for
the synthesis of 11 and 15.
4.7 [9 CH (Bn)], 4.32 (2b-H), 4.39 (1c-H), 4.62 [CH , (PA)], 4.79
2
2
13
(1a-H), 5.02 (1b-H), 5.45 (2c-H). – C NMR (150.9 MHz,
CDCl ): 54.6 (CH O), 64.9 [CH (PA)], 68.9 (C-2c), 68.8 (C-4b),
3
3
2
69.2 (C-6b), 69.9 (C-6c), 70.9 (C-2b), 71.5 (C-6a), 74.0 (C-2a),
74.2 (C-4c), 74.9 (C-4a), 74.9 (C-5c), 77.5 (C-3b), 79.2 (C-3c),
80.3 (C-3a), 95.3 (C-1c), 99.2 (C-1b), 99.9 (C-1a), 114.5-157.6
(Bn, PA).
(16) General procedure for the synthesis of 8, 10, 12, 14, and 16:
Glycosylated MP-CPG is shaken with 3 equivalents of NBS in a