Glycosides ring size

This reaction has been used m an imaginative way to determine the ring size of glycosides Once all the free hydroxyl groups of a glycoside have been methylated the glycoside is subjected to acid catalyzed hydrolysis Only the anomeric methoxy group IS hydrolyzed under these conditions—another example of the ease of carbocation for matron at the anomeric position... 

In glycosides derived from ketoaldonic acids, the ending is -ulosidonic acid , with appropriate ring-size infix, e.g. -ulopyranosidonic acid . 

The direct comparison of 1 and 2 in a variety of RCM reactions also indicates a presumably close relationship between these catalysts (Table 1) [6]. Both of them give ready access to cycloalkenes of almost any ring size > 5, including medium sized and macrocyclic products. Only in the case of the 10-membered jasmine ketolactone 16 was the yield obtained with 2a lower than that with lc this result may be due to a somewhat shorter lifetime of the cationic species in solution. However, the examples summarized in Table 1 demonstrate that the allenylidene species 2 exhibit a remarkable compatibility with polar functional groups in the substrates, including ethers, esters, amides, sulfonamides, ketones, acetals, glycosides and even free hydroxyl groups. 

Problem 34.27 The crystalline methyl a- and jS-o-glycosides we have discussed are usually prepared using methanolic HCl at 120 . When D-(+)-glucose is methylated at room temperature, there is obtained a liquid methyl D-glucoside. When this so called V -glucoside is methylated, hydrolyzed, and oxidized by nitric acid, there is obtained a dimethoxysuccinic acid, (a) What ring size is indicated for this... 

The ring size in cardiac glycosides is not well established. Methylation and other experiments designed to differentiate between furanoid and pyranoid rings have been performed in only a few instances. < > A tentative differentiation mainly depends on the rates of hydrolysis of the glycosides. 

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