Aldoses relative configurations

Notwithstanding the various intellectual and practical challenges involved, the correct relative configurations were assigned to the family of aldoses (and hence ketoses), and a major milestone... 

The term carbohydrate diacids as used in this report represents that class of compoimds know as aldaric acids, i.e., simple diacids derived from oxidation of the terminal carbons of aldoses. As a class of compounds aldaric acids have been known for more than a century and some of these diacids played an important role in Emil Fischer s assignment of the relative configurations of naturally occurring D-aldoses (1). Surprisingly, these molecules have seen very little chemical application over the past century but their time may have arrived to be considered as valuable and versatile synthons for preparation of specialty chemicals and polyamides. The material in this report presents an overview of... 

Larger sugars can be made from smaller ones and vice versa, by chain lengthening and chain shortening. These transformations can also be used to structurally correlate various sugars, a procedure applied by Fischer to prove the relative configuration of all the stereocenters in the aldoses shown in Figure 24-1. 

RELATIVE CONFIGURATIONS OF THE ALDOSES AN EXERCISE IN STRUCTURE DETERMINATION... 

As shown for the aldotetroses an aldose belongs to the d or the l series accord mg to the configuration of the chirality center farthest removed from the aldehyde func tion Individual names such as erythrose and threose specify the particular arrangement of chirality centers within the molecule relative to each other Optical activities cannot be determined directly from the d and l prefixes As if furns ouf bofh d eryfhrose and D fhreose are levorofafory buf d glyceraldehyde is dexfrorofafory... 

The reaction is used for the chain extension of aldoses in the synthesis of new or unusual sugars In this case the starting material l arabinose is an abundant natural product and possesses the correct configurations at its three chirality centers for elaboration to the relatively rare l enantiomers of glucose and mannose After cyanohydrin formation the cyano groups are converted to aldehyde functions by hydrogenation m aqueous solution Under these conditions —C=N is reduced to —CH=NH and hydrolyzes rapidly to —CH=0 Use of a poisoned palladium on barium sulfate catalyst prevents further reduction to the alditols... 

Aldose Polyhydroxy aldehyde witli three or more carbon atoms. When of sufficient length will form flve-or six-membered ring (furanose or pyranose) hemiac-etals. Designated d- or l- based on the configuration of the asymmetric center furthest from the carbonyl group relative to glyceraldehyde. 

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