5-Phosphoribonic acid

This conciusion was confirmed " by an investigation of the rate of lactone formation of the phosphoribonic acid. (Levene and Simms had previously shown that if hydroxyls (4) and (5) are both free the formation of both the y- and the 5-lactone can be detected if position (4) is substituted and (5) is free, the 5-lactone is formed at a relatively rapid rate if position (5) is substituted and (4) is free, the y-lactone is slowly formed.) The transformation of the phosphoribonic acid to its lactone in aqueous solution was found to proceed smoothly and very slowly, a property of sugar acids so substituted that they can only give rise to 7-lactones. The formation of 5-lactone was not observed, as was to be expected if position (5) of the sugar is substituted. 

O, phosphoribonic acid from xanthylic acid x, 5-phosphoribonic acid. (Taken from P A Levene end S. A. Harria, /. Bid. Ckem. 95, 763 (1932)). 

In the first place, cautious oxidation gives a phosphoribonic acid which lactonizes at a different rate, and from which the phosphoryl group is hydrolyzed twice as rapidly as from 5-phosphoribonic acid (see Fig. 2). Secondly, on condensation with methanol in the presence of dry hydrogen chloride it gives rise to both the furanoside and pyranoside forms of glycoside (see Fig. 3). Hence the phosphoryl group cannot be attached at either position (4) or (5), but must be at (2) or (3). 

This conclusion was confirmed by an investigation of the rate of lactone formation of the phosphoribonic acid. (LevenC and Simms had previously shown that if hydroxyls (4) and (5) are both free the formation of both the y- and the i-lactone can be detected if position... 

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