2 -deoxy-p-disaccharide

Scheme 13. Synthesis of a 2 -deoxy-P-disaccharide with a glycal epoxide as glycosyl donor.

When the donor is correctly adjusted to the acceptor, yields are high (64-97%). However, acidic conditions of the glycosylation reaction may induce partial anomerization at the reducing end of the obtained disaccharide. In that case, more reactive A -phthaloylglucosamine donors can be used a sequential treatment converts then the A -phthaloyl group into the required Af-formyl substituent. Radical deamination at C-2 through an isonitrile delivered 2 -deoxy-P-disaccharides 132 in 65 89% overall yields (Scheme 29). 

Insoluble silver salts such as silver silicate favor direct Sn displacement of an anomeric bromide by alcohols [88]. When applied to 2-deoxy-pyranosyl bromides, this procedure can lead to 2 -deoxy-P-disaccharides with a good stereoselectivity. For instance (Scheme 32), bromide 141, where an ester group at 0-4 can also favor [85] P-glycoside formation, reacted with the sugar alcohol 142 in the presence of silver silicate to give the disaccharide 143 in 85% yield (P a 5.4 1) [89]. 

Kiso, M, Anderson, L, Synthesis of disaccharides by the ferric chloride-catalyzed coupling of 2-acylamido-2-deoxy-P-D-glucopyranose 1-acetates to protected sugar acceptors, Carbohydr. Res., 72, C15-C17, 1979. 

C-methyl-substituted 2-acetamido-2-deoxy- P-D-glucopyranosyl mono-and disaccharides... 

Acetamido-4-amino-2,4,6-trideoxy-D-galactopyranosyl precursors such as trichltHoacetimidate 76, were prepared from ethyl 1-thio-a-D-mannopyranoside. Key steps were stereoselective reduction of oxine 74 (available in 5 steps), and azidonitration of glycal 75 (Scheme 23). Their application in the synthesis of disaccharides is covered in Chapter 3. Benzyl 2,4-diacetamido-3-6>-benzyl-2,4,6-trideoxy-P-D-galactopyranoside has been synthesized in 5 steps from benzyl 2-acetamido-3-6>-benzyl-2-deoxy-P-D-galactopyranoside. ... 

Hyaluronic acid is a poly(saccharide) electrolyte having ->4)- p-D-glucopyranosyluronic acid)- (l->3)-(2-acetamido-2-deoxy-p-D-glucopyrano-syl)-(l as the repeating disaccharide unit (Figure 4). 

This glycosaminoglycan consists of a linear chain of the repeating disaccharide units of [-> 4)-P-D-glucopyranosyl uronic acid-(l—>3)-A -acetyl-2-amino-2-deoxy-p-D-glucopyranosyl-(l-> ] (see Fig. 6.14A). It is composed of 500-50,000 monosaccharide residues per molecule [130]. 

Simple alkoxides react upon these a-adducts to give 2-deoxy-P-glycosides according to a Sn mechanism [97]. Activation by thiophilic promoters such as silver perchlorate in acetonitrile [96], or NIS in dichloromethane, or IDCP in acetonitrile [98] leads with alcohols mainly to 2-deoxy-a-glycosides. 2 -Deoxy-a-disaccharides (147) can thus be prepared in good yields, but with a p ratios better than 9 I only in a few eases (sugar alcohol 146). 

The H- and C-n.m.r. spectra of sucrose, methyl a-D-fructofuranoside (20) and methyl P D-fhictofuranoside (21) with single sites of C-substitution at C-1, C-2, C-3-, or C-6 of the furanose moieties have been analysed to assess the conformations of the their furanose rings, and of the glycosidic linkages in aqueous solution. In addition, spin-couplings in 20 and 21 were compared with those of a-(22) and p-D-r/jrco-pentulofuranose (23), respectively, to study the effect of glycosidation and hydroxymethyl substitution on the solution conformations. The conformations of 2-mono- and 2,2 -di-G-substituted a,a-trehalose derivatives 25 have been shown by n.m.r. spectroscopy in combination with molecular mechanics calculations, to differ from that of the 2,2 -unsubstituted disaccharide 24, both in solution and in the solid state. N.O.e. experiments on the 6 -deoxy-, 6 -thio-, and 6 -0-THP derivatives of methyl 2-acetamido-2-deoxy-P-lactoside, potential inhibitors of (2- 6)-a-sialyltransferase, proved that they adopt the same conformation as the parent compound. ... 

Roush WR, Lin X-F. Studies on the synthesis of aureolic acid antibiotics highly stereoselective synthesis of aryl 2-deoxy-p-glycosides via the Mitsunobu reaction and synthesis of the olivomycin A-B disaccharide. J. Am. Chem. Soc. 1995 117 2236 2250. 

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