Aldoses from aldonolactones

The results of inhibition studies with aldonolactones and 5-amino-5-deoxyaldonolactams may be summarized as follows y -D-glycosidases are inhibited by 1,5-lactones and the lactams some 100- to > 10,000-fold better than by the parent aldoses, with Kj values from 200 //Mto <0.1 nM. Al-dono-1,4-lactones are probably no better inhibitors than aldoses or polyols of comparable structure, with the possible exception s of 2-acetamido-2-deoxy-D-glucono-1,4-lactone. 

He himself found that aldonolactones could be reduced with sodium amalgam to the aldoses. Thus, the way was opened to proceed from any pentose to the next higher aldose, which, as he soon showed, always arose in two stereoisomeric forms because of the introduction of a new asymmetric center. Another novel method created was the epimerization of aldonic... 

The anomeric forms derived from equilibration of aldoses give rise to multiple peaks when trimethylsilylated and gas chromatographed [311]. A method of overcoming this problem, assuming that mutarotation itself is not under study, is to modify the aldose. It can be oxidised and lactonised to the aldonolactone, for example, and characterised as its TMS derivative [322]. Alternatively for the identification of aldoses and alditols, more use may be made in the future of the separations achievable on open tubular columns of the poly-0-acetylaldonic nitriles (18) produced from aldoses and the poly-acetyl esters from alditols [323]. Figure 1.18 shows the separation of 32 assorted polyols and aldoses. 

Esters of fatty acids are only to some extent reduced to the alcohols by sodium amalgam. Aldonolactones and their esters, however, are reduced to aldoses by Na(Hg) [99]. Optimal conditions are found at pH 3-3.5 and temperatures below 15°C 2.5-3 atoms of Na [as 2.5% Na(Hg)] are used per mole of lactone. Yields of different aldoses range from 50 to 84% [100,101]. 

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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