Sugar organometallic

Although simple solutions can be examined by these electrospray techniques, often for a single substance dissolved in a solvent, straightforward evaporation of the solvent outside the mass spectrometer with separate insertion of the sample is sufficient. This situation is not true for all substances. Peptides, proteins, nucleotides, sugars, carbohydrates, mass organometallics, and many... 

As a rule of thumb, one can say that the efficiency of separation of mixtures and the simplicity of operating and maintaining apparatus are much greater for GC than for LC. Hence, other things being equal, GC is most often the technique of first choice and can be used with a very wide variety of compound types. However, for nonvolatile or thermally labile substances like peptides, proteins, nucleotides, sugars, carbohydrates, and many organometallics, GC may be ruled out completely... 

FAB has been used with a wide variety of substances, including thermally labile compounds such as peptides, sugars, carbohydrates, and organometallics. 

Another recent example of a Michael addition of organometallic reagents to sugar nitroolefins consists of the addition of vinyl magnesium bromide to nitroolefin 83, that afforded nitro sugar 84 (Scheme 27).64... 

The addition of organometallic reagents to the carbonyl group of conveniently substituted aldonolactones constitutes a viable chain-extension method. The reaction leads to the formation of hemiacetals of glyculoses, 1-methylene sugars, and C-glycosyl compounds, which are precursors of, or occur as subunits of, a variety of natural products. 

The application of high temperatures to increase the speed of HPLC separation extends to ion chromatography and to inorganic analysis. Le et al. [18,19] reported a 50% reduction in analysis time when a number of selenium and arsenic species including inorganic forms, organometallics, and compounds with amino acids and sugars were analyzed at 70°C. 

The C-glycosylation procedures generally exploit the electrophilic character of the anomeric carbon of the sugar. The new C-C bond can be formed by reaction of the aldehydic function of the sugar with an organometallic or a Wittig... 

Organometallic methods, with the possible exception of those involving the stoichiometric generation of enolates and other stabilized carbanionic species 140], have seldom been used in carbohydrate chemistry for the synthesis of cyclohexane and cyclopentane derivatives. The present discussion will not cover these areas. The earliest of the examples using a catalytic transition metal appears in the work of Trost and Runge [41], who reported the Pd-catalyzed transformation of the mannose-derived intermediate 22 to the functionalized cyclopentane 23 in 98% yield (Scheme 10). Under a different set of conditions, the same substrate gives a cycloheptenone 24. Other related reactions are the catalytic versions of the Ferrier protocol for the conversion of methylene sugars to cyclohexanones (see Chap. 26) [40,42,43]. 

The reactions of carbohydrate derivatives with certain organometallic reagents (Grignard and Friedel-Crafts processes) have been reviewed in this Series and elsewhere.87 The attempted application of a Chugaev reaction to sugar xanthates was reported by Wolfram and Foster.88 It was found,... 

Decarbonylation of sugars.1 Aldoses undergo decarbonylation when treated with this organometallic in N-methylpyrrolidin-2-one (NMP) at 130°. Thus glucose is converted into arabinitol in 88% yield (equation I). 

In contrast, the Barbier reactions of 2-acetamido-2-deoxy sugars with ketones showed a preference for the formation of 1,2-m-C-glycoside products (Scheme 7.39). This was attributed to the complexation of the C2-acetamido group to the glycosyl samarium, thereby reducing the configurational lability of the organometallic species.78,80,81... 

The nucleophilicity of the aromatic system can alternatively be increased by using organometallic aromatic compounds, which also solves the problem of regioselectivity. This method was applied by Sulikowski et al., who reacted a variety of sugar lactones with aryl lithiums to afford intermediate lactols which were subsequently reduced to the C-glycosides by cyanoboro hydride [137]. For example, selective orfho-bromination of monobenzylated napthalene diol 174 affords the bromide 175 which is converted into the dianion with three equivalents of n-BuLi. Treatment with the benzylated lactone 176 afforded lactol 177 (Scheme 45, the D-dideoxygluconolactone 176 was erroneously drawn as the... 

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