The use of 2-deoxy-2-trichloroacetamido-d-glucopyranose derivatives in syntheses of oligosaccharides

From Polymer to Size‐Defined Oligomers: An Expeditious Route for the Preparation of Chondroitin Oligosaccharides

“…To overcome this problem, the trichloromethyl oxazoline 22 (Scheme 4) was prepared directly from 3 by using a protocol reported for the dgluco series. [8] Indeed, reaction of 22 with 4-methoxyphenol in the presence of TMSOTf at 0 8C gave exclusively the bglycoside 23 in excellent yield. It is to be noted that the NAPsubstituted glycoside 9 could be obtained from 3 in 80 % overall yield via 22.…”

“…This product contains a number of attractive features. Besides its backbone, which still possesses d-GlcA and d-GalNH 2 arranged in the correct manner, there is an interesting possibility to substitute the free amine group with a powerful stereocontrolling auxiliary such as a trichloroacetyl group, [8] a process that was used successfully for the synthesis of chondroitin sulfate oligosaccharides.…”

“…Further coupling of 18 with imidate 6 or 16 under the same conditions gave hexasaccharide derivatives 19 and 20, respectively, in 65 % yield. Deprotection of 19 was achieved through transformation of the N-trichloroacetyl groups into their N-acetyl congeners by radical reduction with tributylstannane [8] followed by a two-step saponification with lithium hydroperoxide [16] and sodium hydroxide, to give the target hexasaccharide glycoside 21 in good yield. Thus, an efficient route is now open for the preparation of size-defined chondroitin oligomers containing a fluorescent glycoside as useful probes for the study of the biosynthesis as well as the polymerization of chondroitin sulfate chains.…”

Synthesis of Pentasaccharide Fragments Related to the O‐Specific Polysaccharide of Shigella flexneri Serotype 1a

“…However, commonly used N-protecting groups like N-dichlorophthaloyl, [71] Ntetrachlorophthaloyl, [72][73][74] N-chloroacetyl, [75] N-trichloroacetyl, [76,77] N-trichloroethoxycarbonyl, [78,79] or N,N-diacetyl [80] were not applicable here due to their high sensibility under conditions required for saponification of the tether. The use of 2-azido-2-deoxy glucose derivatives as starting materials appeared impractical as well, because this avenue would require employment of triflyl azide which is, however, inconvenient on a large scale.…”

New Diacylamino Protecting Groups for Glucosamine

“…In addition, O-glycosylation of acetamido groups, that is, intermolecular imidate formation, has also been observed as a side-reaction. [5] Therefore, the replacement of the N-acetyl group by strongly electron-withdrawing groups, such as the trifluoroacetyl, trichloroacetyl, [6,7] and trichloroethoxycarbonyl groups, [8][9][10][11][12] respectively, have been investigated in order to avoid the formation of stable cyclic imidate intermediates which impede glycoside bond formation. However, similar to the N-acetyl group, the structural assignment of these groups by NMR spectroscopy can be hampered when rotation around the amidic CN bond is hindered.…”