Saccharinic acids configuration

This mechanism is illustrated in Scheme 4. The reaction occurred in 0.2 M methanolic sodium hydroxide, and the isosaccharinic acid derivatives 78a and 78b obtained constitute the first saccharinic acid nucleosides reported. The configuration of the isomers at the branch-point was established by spectroscopic58 and chemical59 means. 

If the two lowest asymmetric carbon atoms possess the D-erythro configuration, a -D-glucosaccharinic acid must be either 2-C-methyl-o-arabmo-pentonic acid or 2-C-methyl-D-ribo-pentonic acid. The initial choice between these two possibilities was made by Nef, who chose the D-arabino configuration because of similarities between certain alkaloid salts of the saccharinic acid and the corresponding salts of n-arabinonic acid. However, subsequent developments make the D-ribo configuration appear the more... 

The saccharinic acids formed from some of the pentoses and hexoses have been the objects of study by Nef and his students. Glattfeld and Hanke reported in 1918 that, during the oxidation of maltose in alkaline solution, an acid had been produced whose phenylhydrazide had an analysis agreeing perfectly with that calculated for a four-carbon saccharinic acid. Furthermore, the properties of the free aeid were those which would be expected of one of these acids. Its configuration could not, however, be reported at that time because of the absence of data as to the properties and constants of the four-carbon saccharinic acids. Nef had also referred to the handicap which this lack of information had imposed on the work with sugars in alkaline solution. Consequently, with this in mind, Glattfeld began in 1920 the systematic synthesis of the four-carbon saccharinic acids. 

Although Nef had prepared the dl form of this saccharinic acid and had converted it to 2-deoxy-j)h-glycero-tetr vic acid (nL-malic acid), Glattfeld and Miller succeeded in separating the dl compound into its enantio-morphous forms and thus established the absolute configuration of the optical isomers. 

The nucleosides (261) and (371) (analogues of gougerotin) were obtained from branched-chain amino-sugars described in Chapter 15. The assignment of configuration at the branch-point of nucleosides containing a saccharinic acid component is reported in a later section (see p. 156). 

---