24-6 Reduction of Monosaccharides to Alditols 一含堂 mnbergeroauhteertaioacensumedhdkatsthe 56e 24-7 Carbonyl Condensations with Amine Derivatives N-NHCH N-NHCJ 24-8 Ester and Ether Formation:Glycosides Williamson ether synthesis allows complete methylation of sugars Sugars can be esterfied and methylated. meric bd OH- 0 The aetafubeselctively hydrolid: 55 Exhaustive oxidation of a sugar with HIO4 results in a mixture of one carbon compounds. Analysis of this mixture is useful in the elucidation of the structure of the original sugar. The number of equivalents of HIO4 consumed indicates the number of carbon atoms in the sugar. Each one-carbon fragment produced carries the same number of hydrogen substituents as it did in the original sugar. CHO Î HCOOH C=O Î CO2 CHOH Î HCOOH CH2OH Î CH2O 24-6 Reduction of Monosaccharides to Alditols The same reagents used to reduce aldehydes and ketones to alcohols can be used to reduce aldoses and ketoses to polyhydroxy compounds called alditols. D-Glucitol is found in red seaweed in concentrations as high as 14%. It is also found in many berries, cherries, plums, pears and apples. 24-7 Carbonyl Condensations with Amine Derivatives The carbonyl function in aldoses and ketoses will undergo condensation reactions with amine derivatives. Treatment of a sugar with phenylhydrazine yields the corresponding hydrazone. A second molecule of phenylhydrazine then adds forming an osazone. Osazones are stable and no further molecules of phenylhydrazine react. Osazones, unlike their parent sugars, crystallize readily to form solids with well defined melting points, simplifying isolation and characterization of many sugars. 24-8 Ester and Ether Formation: Glycosides Sugars can be esterfied and methylated. Monosaccharides can be converted into esters by standard techniques. Excess reagent converts all hydroxyl groups, including the anomeric hydroxyl. Williamson ether synthesis allows complete methylation of sugars. The acetal function can be selectively hydrolized: