Kiliani-Fischer synthesis extending aldose chain

The Kiliani—Fischer synthesis extends chains of monosaccharides using the formation of a cyanohydrin to generate the additional stereogenic center. In the first step, one enantiomeric form of an aldose reacts with HCN to give a mixture of diastereomeric cyanohydrins. We recall that the formation of an additional stereogenic center in a chiral compound results in some stereoselectivity. A mixture results, but because diastereomers have different physical properties, the reaction mixture can be separated to give two cyanohydrins. 

A sequence known as the Kiliani-Fischer synthesis was developed primarily for extending an aldose chain by one carbon, and was one way in which configurational relationships between different sugars could be established. A major application of this sequence nowadays is to employ it for the synthesis of " C-labelled sugars, which in turn may be used to explore the role of sugars in metabolic reactions. 

In 1885, Heinrich Kiliani (Freiburg, Germany) discovered that an aldose can be converted to the epimeric aldonic adds having one additional carbon through the addition of hydrogen cyanide and subsequent hydrolysis of the epimeric cyanohydrins. Fischer later extended this method by showing that aldonolactones obtained from the aldonic acids can be reduced to aldoses. Today, this method for lengthening the carbon chain of an aldose is called the Kiliani-Fischer synthesis. 

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