Chemistry Letters 2002
393
ture, respectively (entries 1–4). In situ generated strong protic
acids9 such as HClO4 and HB(C6F5)4 were further examined and
HB(C6F5)4 proved to be an effective catalyst (entries 5, 6).
Various Lewis acids such as [TrB(C6F5)4,10 TMSOTf] and
thioglycoside 5 was used, on the other hand, the same
glycosylation gave the corresponding disaccharide in moderate
yield along with the transglycosylated compound, ethyl 2,3,4,6-
tetra-O-benzoyl-ꢁ-D-glucopyranosyl thioglycoside, in 20% yield
(entry 1).
12
combinations of SnCl2 and AgClO4,11 or AgB(C6F5)4 also
promoted the reaction smoothly. (entries 7–10).
The typical experimental procedure is as follows: to a stirred
ꢀ
suspension of MS 5 A (178 mg), 1 (56.7 mg, 0.059 mmol) and 2
Table 2. Glycosylation using various catalysts
(25.0 mg, 0.049 mmol) in CH2Cl2 (2.0 mL) was added TfOH
(0.44 mg, 3.0 ꢂmmol) in toluene solution (ca. 0.1 mL) at 0 ꢀC.
The reaction mixture was stirred for 1 h at 0 ꢀC and was quenched
by adding saturated aqueous NaHCO3. The mixture was filtered
through the pad of celite, and aqueous layer was extracted with
CH2Cl2. The combined organic layer was washed with brine, and
dried over Na2SO4. After filtration and evaporation, the resulted
residue was purified by preparative TLC (toluene/MeCN 9 : 1) to
give the desired product 3 (51.4 mg, 96%, ꢁ-only).
Thus, catalytic and stereoselective glycosylation of several
glycosyl acceptors with a novel glycosyl donor was efficiently
ꢀ
performed in the presence of 5 mol% TfOH and MS 5 A in
CH2Cl2. Further study on the alternative activation method of thio
group involved in the leaving group of the present glycosyl donor
with thiophilic reagents is now in progress.
The present research is partially supported by Grant-in-Aids
for Scientific Research from Ministry of Education, Science,
Sports and Culture.
References and Notes
1
Reviews: K. Toshima and K. Tatsuta, Chem. Rev., 93, 1503
(1993);K. Suzuki and T. Nagasawa, J. Synth. Org. Chem. Jpn.,
50, 378 (1992).
2
3
4
A. Varki, Glycobiology, 3, 97 (1993).
P. J. Garegg, Adv. Carbohydr. Chem. Biochem., 52, 179 (1997).
R. R. Schmidt and W. Kinzy, Adv. Carbohydr. Chem. Biochem.,
50, 21 (1994).
5
6
7
M. Shimizu, H. Togo, and M. Yokoyama, Synthesis, 1998, 799;
K. Toshima, Carbohydr. Res., 327, 15 (2000).
S. J. Danishefsky and M. T. Bilodeau, Angew. Chem., Int. Ed.
Engl., 35, 1380 (1996).
D. Kahne, S. Walker, Y. Cheng, and D. V. Engen, J. Am. Chem.
Soc., 111, 6881, (1989);J. Gildersleeve, R. A. Pascal, Jr., and D.
Kahne, J. Am. Chem. Soc., 120, 5961 (1998).
B. Fraser-Reid and R. Madsen, in ‘‘Preparative Carbohydrate
Chemistry,’’ ed. by S. Hanessian, Marcel Dekker, New York
(1997), p 339.
Table 3. Glycosylation using various acceptors
8
9
H. Jona, H. Mandai, and T. Mukaiyama, Chem. Lett., 2001, 426,
and related references are also sited.
10 J. C. W. Chien, W.-M. Tsai, and M. D. Rausch, J. Am. Chem.
Soc., 113, 8570 (1991).
11 K. C. Nicolaou, T. J. Caulfield, H. Kataoka, and N. A.
Stylianides, J. Am. Chem. Soc., 112, 3693 (1990);K. C.
Nicolaou, N. J. Bockovich, and D. R. Carcanague, J. Am. Chem.
Soc., 115, 8843 (1993).
12 T. Mukaiyama, H. Maeshima, and H. Jona, Chem. Lett., 2001,
388;Silver tetrakis(pentafluorophenyl)borate [AgB(C 6F5)4]
was prepared by adding an ethereal solution of LiB(C6F5)4
(purchased from Tokyo Chemical Industry Co., Ltd.) to an
aqueous solution of AgNO3. After azeotropic removal of water
and diethyl ether with toluene, AgB(C6F5)4 was obtained as a
brown solid containing 1–3 mol of toluene.
Finally, glycosylation of various glycosyl acceptors includ-
ing 7 having secondary alcohol with the present donor proceeded
smoothly within 30 min in CH2Cl2 at 0 ꢀC to give the
corresponding disaccharides in high yields without activating
the armed glycosyl fluoride 6 (Table 3, entries 2, 3). When