42 W. G. OVEREND AND M. STACEY 



of D-ribose as the sugar component of yeast nucleic acid, several other pentose phos- 

 phates were prepared. Interest in xylose phosphate stemmed from Robinson's"* 

 suggestion that xylose might be a primary constituent of nucleic acids and that 

 ribose might result by hydrolysis of xylose-3-phosphate with Walden inversion. This 

 possibility does not apply to ribose-5-phosphate isolated from inosinic acid because 

 a Walden inversion at the primary hydroxyl group would not affect the configuration 

 of the sugar. Attempts by Levene and Raymond"* to prepare xylose-3-phosphate for 

 testing the validity of Robinson's hypothesis, were unsuccessful. Phosphorylation 

 of xylose derivatives with only the hydroxyl group at C-3 free, .gave xylose-5-phos- 

 phate derivatives, and obviously migration occurred at some stage of the preparation 

 via an intermediate cyclic diester structure. The only 3-phosphate derivative which 

 they were able to isolate was l,2-0-isopropylidine-3-phosphate-5-0-methylxylose. 

 Owing to the difficulty of removing the methyl group, this derivative was of little 

 value for comparison with the phosphopentose derived from nucleic acid. The rate 

 of dephosphorylation for this compound was many times greater than that of xylose- 

 5-phosphate. 



Xylopyranose-1 -phosphate (isolated as the barium or dipotassium salt) was pre- 

 pared by reacting bromoacetylxylose and trisilver phosphate and subsequent partial 

 hydrolysis."' 



Generally pentose phosphate esters are stronger acids than free phosphoric acid 

 and the values of pKi' and pKi' are smaller. For example, the dissociation constants 

 of xylose-1 -phosphate calculated by means of Van Slyke's"' formula and the Hen- 

 derson-Hasselbach equation are pKi' = 1.25 and pK^' = 6.15. Comparative values 

 for phosphoric acid are pKi' = 1.95-2.00 and pKi' = 6.83-6.93.2"-23o 



D-Arabinose-5-phosphate was synthesized by Levene and Christman.'*' 



(e) Ethers, Esters, Acetals and Anhydrides. 



(1) Ethers. Reference has already been made to the complete methyla- 

 tion of methyl D-ribf)side and to the fact that acidic hydrolysis of the 

 product yields crystalline 2,3,4-tri-O-methyl-D-ribose.^^^' ^^^ Proof of struc- 

 ture followed from nitric acid oxidation which gave f-trimethoxyglutaric 

 acid. An isomeric tri-0-methyl-D-ribose was obtained by Levene and 

 Tipson by subjecting either adenosine^'" or guanosine^^" to methylation 

 and subsequent hydrolysis. The amorphous product reacted more rapidly 

 with acidic methanol than the 2,3,4-isomer and could be converted to a 

 7-lactone. Nitric acid oxidation afforded i-dimethoxysuccinic acid, and on 

 the basis of these results the sugar was considered to be 2 , 3 , 5-tri-O-methyl- 

 D-ribose, a conclusion subsequently confirmed by synthesis studies.^^'' 

 Methyl 2 , 3-0-isopropylidene-5-0-methyl-D-ribofuranoside was prepared by 

 successive acetonation and methylation of methyl D-ribofuranoside. Hy- 

 dolysis, further methylation and rehydrolysis furnished 2,3,5-tri-O- 



226 R. A. Robinson, Nature 120, 44 (1927). 



2" D. D. Van Slyke, J. Biol. Chem. 52, 525 (1922). 



228 O. Meyerhof and J. Suranyi, Biochem. Z. 178, 427 (1926). 



229 C. F. Cori, S. P. Colowick, and Gerty T. Cori, J. Biol. Chem. 121, 465 (1937). 



230 H. T. S. Britton and R. A. Robinson, Trans. Faraday Soc. 28, 531 (1932). 

 2" P. A. Levene and J. Compton, J. Biol. Chem. 116, 169 (1936). 



