C O M M U N I C A T I O N S
Scheme 2 a
complete R-selectivity in 81% yield, although Kerns reported the
difficulty of activation of the 2,3-trans-oxazolidinone having
disaccharide.4a To the best of our understanding, this is the first
example of the preparation of two cis glycoside bonds in a one-
pot operation.
In conclusion, we have demonstrated N-benzyl 2,3-trans-oxazoli-
dinone having glycosyl donors exhibits high R-selectivities. Al-
though at this moment, the origin of high R-selectivity is not clear,
the glycosyl donors can be prepared in gram-scale, thus avoiding
the use of triflyl azide necessary for the preparation of the 2-azido-
2-deoxy sugar system or avoiding the low yields of the azido-nitra-
tion procedure. Furthermore, the 2,3-oxazolidinone can be cleaved
under basic conditions. In regard to the preparation, glycosylation,
and deprotection procedures, it is our belief that this novel donor
can serve as an ideal glycosyl donor for 1,2-cis glycosidic bond
formation. Furthermore, by using these novel glycosyl donors, the
sequential two-step glycosylation reaction in a one-pot operation
to form two cis bonds was successful. Application of such a donor
to polymer-supported or automated oligosaccharide synthesis can
also be promising because no severe low temperature is required
for R-selectivity.15 Further investigations of bioactive oligosaccha-
ride synthesis using these donors are currently underway.
a (i) 1 M NaOH, 1,4-dioxane; (ii) H2, 20% Pd(OH)2/C, 0.1 M HCl,
dioxane, H2O; (iii) Ac2O, pyridine, 92% (3 steps).
Scheme 3 a
Acknowledgment. We thank Dr. Teiji Chihara and his staff
for elemental analyses and Ms. Akemi Takahashi for her technical
assistance.
Supporting Information Available: Preparation of new compounds
and experimental details. This material is available free of charge via
a (i) Br2, CH2Cl2, 91%; (ii) NaOMe, MeOH/1,4-dioxane, 99%; (iii)
AgOTf, MS4A, di-tert-butylmethylpyridine, toluene/1,4-dioxane (3:1); (iv)
AgOTf, PhSCl, 81%.
References
dioxane at near room temperature9 dramatically increased the
R-selectivity. Under these reaction conditions, galactosamine donor
6 exhibited a slightly higher R-selectivity. This methodology using
either conditions B or C of the glycosylation reaction was applied
to various glycosyl acceptors. In the cases of the less-reactive
secondary hydroxyl group in the 4-position of glucose 10 and
glucosamine derivative 12 under condition B, complete R-selectivi-
ties were observed; the corresponding â-glycosides were undetect-
able after gel filtration of the crude mixture within the limits of
400 MHz 1H NMR analysis. Moreover, R-selectivity was observed
for the less-reactive secondary alcohol regardless of the solvent.
Although the hydroxy group at the 4-position of glucosamine is
known to be relatively unreactive, disaccharide 13 was obtained in
good yield.10 Similarly, high R-selectivities were observed for 15R11
and 17R,11 which are components of heparin, a drug for the
prevention and treatment of thromboembolic disorders.12
As shown in Scheme 2, disaccharide 8R was deprotected under
basic conditions, followed by the concomitant removal of the O-
and N-benzyl groups via hydrogenolysis. Acetylation of the
unprotected disaccharide afforded 18 in overall 92% yield. Sub-
sequently, the novel glycosyl donor was applied toward a one-pot
oligosaccharide synthetic strategy.13 Therefore, we proposed that
glycosyl donor 5 can form two 1,2-cis glycosidic bonds in a one-
pot operation (Scheme 3), where a component of the immune
system stimulating O-specific polysaccharide from Proteus mirabilis
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(9) Demchenko, A. V.; Stauchi, T.; Boons, G.-J. Synlett 1997, 818-820.
(10) When the azido donor, as indicated below, was coupled to 12 under
condition B at -40 °C, both R and â glycosides were obtained in 24%
and 10%, respectively.
(11) (a) Orgueira, H. A.; Bartolozzi, P. S.; Schell, P.; Seeberger, P. H. Angew.
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