Chemistry Letters 2000
1179
armed’ glycosides proceeded smoothly to give the correspond-
ing disaccharides in good yields without damaging ‘disarmed’
thioglycosidic linkage of the reducing end (Entries 3–5).
at –15 °C. After the reaction mixture was stirred for 14 h at –15
°C, 3 (72.4 mg, 0.16 mmol) in dichloromethane (2.5 mL) and
NIS (33.8 mg, 0.15 mmol) were successively added at –23 °C.
The reaction mixture was stirred for additional 1h at –23 °C and
was quenched by adding saturated aqueous NaHCO . The mix-
3
ture was filtered through Celite and extracted with
dichloromethane (3 times). The combined organic layer was
washed with 10% aqueous Na S O , H O and brine. Then the
2
2
3
2
organic layer was dried over Na SO . After being filtered and
2
4
evaporated, the resulting residue was purified by preparative
TLC (silica gel) to give the desired product 10 (114 mg, 75.5 %,
αβ/ββ = 10/90).
Finally, one pot sequential glycosylation was attempted
according to the above method. In the first step, 1 was treated
with ethylthio glycosides 7 or 9 in the presence of a catalytic
amount of TrB(C F ) and 1.2 equivalent of PhthNSEt in a
The present research is partially supported by Grant-in-
Aids for Scientific Research from Ministry of Education,
Science, Sports and Culture.
6
5 4
t
mixed solvent ( BuCN/BTF/CH Cl ), where thioglycosides
2
2
References and Notes
were almost completely consumed after 14 h. These were all
confirmed by TLC monitoring. Next, the second glycosylation
of thus formed disaccharide with glycosyl acceptor 3 was tried
1
P. J. Garegg, Adv. Carbohydr. Chem. Biochem., 52, 179
(1997).
2
K. Toshima and K. Tatsuta, Chem. Rev., 93, 1503 (1993); K.
Suzuki and T. Nagasawa, J. Synth. Org. Chem. Jpn., 50, 378
(1992).
12
and the desired trisaccharides were obtained stereoselectively in
3
good yields by successive addition of NIS in one-pot operation.
3
4
K. Takeuchi, T. Tamura and T. Mukaiyama, Chem. Lett.,
It is noteworthy that the sequential reactions were thoroughly car-
ried out without adding further TrB(C F ) , a promoter, and that
2
000, 124.
6
5 4
J. C. W. Chien, W.-M. Tsai, M. D. Rausch, J. Am. Chem.
Soc., 113, 8570 (1991).
trisaccharide including 2-deoxy-2-amino sugar moiety was
obtained also in high yield with good stereoselectivity.
5
6
H. Shimizu, Y. Ito and T. Ogawa, Synlett, 1994, 535.
K. Fukase, Y. Nakai, T. Kanoh, and S. Kusumoto, Synlett,
Thus, a useful glycosylation method of armed thioglycoside
by using a combination of easy-to-handle PhthNSEt and catalytic
amount of TrB(C F ) was developed. It is interesting to note
1
998, 84.
M. Behforouz and J. E. Kerwood, J. Org. Chem., 34, 51
1969).
7
8
9
6
5 4
(
that trityl borate interacts with thiophthalimides to generate an
active ethylsulfenyl cation which is stabilized by the borate anion
and that the above cation oxidizes only the armed thioglycoside
to afford the corresponding disaccharides in high yields and
stereoselectivities. Then, this procedure was thus applied to the
coupling of armed and disarmed thioglycosides in ‘armed–dis-
armed’ sequential trisaccharide syntheses by one-pot procedure.
Further study on the application of the present method to
the naturally occurring oligosaccharide synthesis is now in
progress.
D. R. Mootoo, P. Konradsson, U. Udodong, and B. Fraser-
Reid, J. Am. Chem. Soc., 110, 5583 (1988).
A. Ogawa and D. P. Curran, J. Org. Chem., 62, 450 (1997).
10 Since the melting point of pivalonitrile is 15 °C, the reaction
was carried out in the mixed solvent of pivalonitrile and (tri-
fluoromethyl)benzene at 0 °C, K. Takeuchi and T.
Mukaiyama, Chem. Lett., 1998, 555.
1
1
2
H. Uchiro and T. Mukaiyama, Chem. Lett., 1997, 121.
1
1
NMR date of 10 and 11; 10 (major : Glcβ1–6Glcβ–6Glc): H
NMR (500 MHz, CDCl ) δ 4.47 (d, 1H, J = 3.4 Hz, H-1),
3
4.51 (d, 1H, J = 8.1 Hz, H-1' or H-1''), 4.52 (d, 1H, J = 8.1
Hz, H-1' or H-1''), 13C NMR (CDCl ) δ 97.9 (C-1), 100.5 (C-
The typical experimental procedure is as follows: to a
3
1
1
'), 103.9 (C-1''); 11 (major : Glcβ1–4GlcNβ–6Glc): H
stirred suspension of Drierite (500 mg), 1 (70.5 mg, 0.12 mmol)
NMR (400 MHz, CDCl ) δ 4.34 (d, 1H, J = 3.4 Hz, H-1),
t
3
and 7 (59.1 mg, 0.10 mmol) in BuCN/BTF/CH Cl (5/5/1, total
2
2
4.35 (d, 1H, J = 8.3 Hz, H-1''), 5.38 (d, 1H, J = 8.5 Hz, H-1'),
1
.0 mL) was successively added TrB(C F ) (9.2 mg, 10 µmol)
13
6
5 4
C NMR (CDCl ) δ 97.7 (C-1), 98.4 (C-1'), 102.7 (C-1'').
3