198 ASCORBIC ACID 



(LXI) l)y a Claisen type of condensation thus: 



Attempts have been made to extend this reaction to the synthesis of 

 hydroxy tetronic acid having the ascorbic acid side chain. '"^ 



E. STRUCTURE AND ANTISCORBUTIC ACTIVITY OF 

 ANALOGS OF l-ASCORBIC ACID 



The methods outlined above have enabled a number of analogs of l- 

 ascorbic acid to be made. Although their structures have not all been de- 

 termined, the work on two of them, namely D-glucoascorbic acid** and 

 D-araboascorbic acid,^* • ^"^ strongly suggests that all have the same dienolic 

 five-atom ring found in L-ascorbic acid. 



The antiscorbutic activity of these analogs has been compared with that 

 of L-ascorbic acid (see Tables I, II, and III below). 



Inspection of these formulas reveals the interesting fact that for anti- 

 scorbutic activity (see Table I) the five-atom lactone ring must lie to the 

 right of the carbon chain when the formula is written according to the 

 Fischer convention. Apparently no exception to this rule has been brought 

 to light. Methyl 2-keto-L-gulonate has been reported to have antiscorbutic 

 activity,^' but presumably this is due to the fact that it undergoes conver- 

 sion into L-ascorbic acid in the animal. It has also been observed that, 

 although dehydroascorbic acid or 2,3-diketo-L-gulono-7-lactone (II) is full}'' 



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