Lead tetraacetate glycosides

The spiroacetal morpholine work of Scheme 38 subsequently inspired research on the preparation of a novel family of morpholino-glycosides from sucrose via lead tetraacetate cleavage and reductive amination (Scheme 40). Significantly, the latter work, which was done with the present author, unveiled a completely new structural class of sweeteners, more intense than sucrose but having a similar taste profile. 

A glycoside containing two cis-glycol groups was not available for comparison with the other types examined, but 1-0-benzoyl-D-talopyran-ose122 123 has been oxidized123 under similar conditions (as a representative of this class of pyranose compounds) and found to consume two moles of lead tetraacetate per mole very rapidly. 

LVIII) yields much more formic acid than does maltose (LIX), and its lead tetraacetate consumption is proportionately higher.166 Other disaccharides were examined142 166 under the latter conditions, and also in 98% acetic acid without potassium acetate.166 Each position of the glycosidic... 

One fraction was obtained in the crystalline state in a yield of 20%. It was assigned the structure (42), which was based not only on elemental and methoxyl analyses but also on the following observations. The two -d-glycosidic linkages were indicated by a high dextrorotation ([a]o + 262°). It was hydrolyzed at a rate comparable with that of furanosides, and methylation followed by hydrolysis and borohydride reduction gave 2,5-di-O-methyl-D-mannitol (43). The structure of (43) was established by synthesis and by lead tetraacetate oxidation it consumed one mole of oxidant, with the formation of 2-0-methyl-D-glyceraldehyde (44). 

Oxidation of 1 mol of the anomeric methyl aldopentopyranosides with 2 mol of periodate or lead tetraacetate yields one of a pair of dialdehydes, a dextrorotatory product 48 being derived from a-D- or p-L-glycosides and levo-rotatory 49 from p-D or a-L isomers. In turn, hypobromite oxidation affords either dicarboxylic acid 47 or 50. Additional possibilities for configurational correlation accrue from the fact that a methyl aldotetrofuranoside similarly yields 48 or 49, whereas a methyl aldopentofuranoside gives 44 or 45 as the final product. 

J. M. Grosheintz, Oxidation of glycosides by means of lead tetraacetate in aqueous solution, J. Am. Chem. Soc., 61 (1939) 3379-3381. 

Saccharides linked glycosidically to an a-hydroxy carbonyl compound cleave readily on treatment with hydrazine. Such glycosides are commonly encountered following periodate or lead tetraacetate cleavage of oligosaccharides. 

Glycol cleavage by oxidation with sodium periodate, lead tetraacetate, or sodium bismuthate, is a useful method for determination of the ring size of glycosides as well as for the assignment of anomeric configuration and position of substituents on the ring. (See Chapters VI and I.)... 

L-Ascorbic acid, an enediol, has been oxidized by sodium hypoiodite and by potassium permanganate to L-threonic acid (9). Such oxidation of double bonds does not occur in the enols alone, for D-arabinal is oxidized by H2O2 and OSO4 in er butanol to D-erythronic acid in addition to D-arabinose (10). Periodic acid and lead tetraacetate are useful for the cleavage of hexitols and glycosides to glyceraldehyde and glycolaldehyde (see Chapter... 

The steric requirements for tetraacetate oxidations are higher than for periodate oxidations. As the common C-1 ring conformation (Chapter I) of glycosides does not allow for true cis relationships, many of the glycosides are not oxidized by lead tetraacetate (225a). 

Differences in the degree of reaction that follow changes in histochemical conditions may eventually offer clues to the spatial relations of the adjacent hydroxyls, the positions of the 1,2-glycols in the carbon chains, and the position of glycosidic linkages. Boric acid added to lead tetraacetate in glacial acetic is said to selectively inhibit the oxidation of cis hydroxyls under histochemical conditions (69b). 

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