In 1885,Heinrich Killiani developed a method for the conversion of an aldose to next higher epimeric aldonic acids through the cyanohydrin formation followed by hydrolysis. In1890, Fisher reported that the reduction of aldonic acid via the intermediate formation of aldolactone can be controlled to yield the corresponding aldose. Thus the Killiani Fisher synthesis involves the conversion of an aldose to next higher epimeric aldoses. We can illustrate the Killiani-Fisher synthesis with the synthesis of D-erythrose and D-threose (aldotetroses) from D-glyceraldehyde (an aldotriose) in the following way--
Decreasing the length of the aldose chain by Wohl degradation-----
An aldose can be degraded to another aldose with one loss carbon atom. In this degradation the aldehyde carbon is removed and carbon 2 of the original sugar becomes the aldehyde carbon of the lower sugar.In this process we degraded D-glucose to D-arabinose.
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