Glycosyl glycosidation

Disaccharides which can be regarded as formed by reaction of the two glycosidic (anomeric) hydroxy groups with one another are named, systematically, as glycosyl glycosides. The parent (cited as the glycoside component) is chosen according to 2-Carb-2.1. Both anomeric descriptors must be included in the name. 

Glycosylation. Glycosidation with tin phenoxides and silyl ethers may use SnCl4 as catalyst. It is interesting that either a- or 3-glucosides are accessible from the same glycosyl donor by slight variation of conditions. 

Typical Aldehydo-aldose or Glycosyl-glycose Typical Ketose or Glycosyl-glycoside... 

It was concluded that acetolyses of the pyranosides that give rise to both cyclic and acyclic products involve reaction from the /3-rather than the a-anomer. Attempts to glycosylate glycosides of polyethyleneglycol monomethyl ether did not lead to disaccharide products but rather to products of glycosyl exchange on the ether. ... 

Glycosidic thiol groups can be introduced into glycosyl bromides by successive reactions with thiourea and aqueous sodium disulfite (D. Horton, 1963 M. Cemy, 1961, 1963). Such thiols are excellent nucleophiles in weakly basic media and add to electrophilic double bonds, e.g., of maleic esters, to give Michael adducts in high yields. Several chiral amphiphiles have thus been prepared without any need for chromatography (J.-H. Fuhrhop, 1986 A). 

Halide derivatives may be fluorides, chlorides, or bromides. Fluorides are best prepared by the reaction of hydroxy groups with (diethylamino)sulfur trilluoride ( DAST M. Sharma, 1977) or of glycosyl thioethers with DAST/NBS (K.C. Nicolaou, 1990 B). The other halides are usually only introduced at the glycosidic position, where treatment with hydrogen chloride... 

Trichloroacetonitrile reacts with glycosidic hydroxy groups of protected sugars to form glycosyl trichloroacetimidates (R. R. Schmidt, 1980, 1984,1985,1986 B. Wegmann, 1988). The imidate is substituted by alcohols in the presence of trimethylsilyl trifluoromethanesulfonate... 

A combination of Cp nCX —A CXC) (where = cyclopentadienyl) effectively promotes the Friedel-Crafts coupling of glycosyl fluorides with aromatic compounds, such as trimethoxyben2ene or methoxynaphthalenes. The derived C-aryl glycosides are potent antitumor agents (39). 

Dondoni has elaborated this methodology to include C-glycosylated dihydro-pyrimidines/ The sugar residue can be a subunit in the aldehyde, 1,3-dicarbonyl, or urea consequently, substitution of the DHPM ring may occur in one of three places depending on which component originally contains the glycosidic residue. In the example... 

Now with the two requisite coupling partners available, the next step is the elaboration of the AE ring system (see Scheme 11). Through the application of previously developed conditions for activation of glycosyl fluorides,24 the convergent union of compounds 19 and 20 can be achieved, giving a 4.5 1 mixture of axial and equatorial isomers in favor of the desired axial glycoside 60 (ca. 70 % yield). 

The glycal epoxide method turned out to be useful for the construction of complex 2-branched [3-aryl glycosides, which are salient features of the potent antibiotic vancomycin [75a]. Glycal epoxide glycosylation with sodium salts of indoles pro-... 

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