26 W. G. OVEREND AND M. STAGEY 



Hence it was 2,3,5-tri-O-methyl-D-ribonolactone rather than the corresponding 

 2,3,4-derivative, and therefore the original glycoside must have had a furanose 

 structure. 



Syntheses of alkyl ribosides by treatment of triacylribopyranosyl halides with 

 alcohols have been frequently reported. Levene and Tipson"" prepared a crystalline 

 methyl 2,3,4-tri-O-acetyl-D-riboside by reacting tri-0-acetyl-D-ribopyranosyl bro- 

 mide with methanol in the presence of silver carbonate. The tri-O-acetyl-o-ribo- 

 pyranosyl bromide was made by acting on crystalline D-ribose 1,2,3,4-tetra-O-acetate 

 with hydrogen bromide. The halide derivative was obtained in crystalline form and 

 showed a value of —209.3° in chloroform solution for its specific rotation, and so 

 presumably belongs to the /3-series. It is markedly unstable and is reconverted to 

 ribose tetra-0-acetate by shaking with silver acetate. The corresponding tri-0-acetyl- 

 /3-D-ribopyranosyl chloride has been prepared in crystalline form,'^^ but the ace- 

 tylated D-ribofuranosyl halides are very unstable, and although both the chlo- 

 i.i(jgi4i-i43 and the bromide"' ■ '^^ have been handled in various researches, neither has 

 been adequately characterized. The benzoylated D-ribopyranosyl halides apparently 

 are more stable than the acetyl analogues. Jeanloz et aZ.'" obtained 2,3,4-tri-O- 

 benzoyl-D-ribopyranosyl bromide in crystalline form through the action of hydrogen 

 bromide on /3-D-ribopyranose 1,2,3,4-tetra-O-benzoate in glacial acetic acid. The 

 compound could be stored at 5° indefinitely if kept over calcium chloride and caustic 

 potash. The j3-configurational assignment was based on optical rotation measure- 

 ments, and the pyranose structure follows from the observation that on reaction with 

 methanol in the absence of an acid-acceptor the ribose halide derivative is converted 

 to methyl 2,3,4-tri-0-benzoyl-/3-D-ribopyranoside,"* identical with the product 

 obtained by benzoylation of methyl /3-D-riboside (XXI) prepared according to Min- 

 saas, the structure of which was established as described above. Since tri-0-benzoyI- 

 /3-D-ribopyranosyl bromide may be obtained from D-ribose in 68% of the theoretical 

 yield and will react with methanol to give the benzoylated methyl riboside in high 

 yield (88%) and since debenzoylation can be carried out in nearly quantitative yield, 

 Jeanloz and Fletcher* claim that this route for the synthesis of alkyl ribopyranosides 

 is rather more attractive than that involving direct condensation of the sugar with 

 an alcohol, particularly as the latter procedure leads to mixtures from which it is 

 often difficult to obtain the required product in crystalline form. Furthermore it is 

 not absolutely necessary to isolate the lialogenated sugar in syntheses of alkyl ribo- 

 sides. Ethyl /8-D-ribopyranoside has been prepared by both routes.'" The pyranose 

 structure was confirmed by periodate titration. 



Treatment of 2,3,4-tri-0-benzoyl-/8-D-ribopyranosyl bromide with methanol in 

 the presence of an acid-acceptor (i.e., silver carbonate) yielded an amorphous mixture 

 from which no crystalline material could be obtained.'" Reinvestigation of this 

 reaction and also of the reaction between /3-D-ribopyranose tetra-0-benzoate and 

 hydrogen bromide in glacial acetic acid, by Ness, Fletcher and Hudson,'" led to the 

 isolation in low yield (5.2%) of a new crystalline tri-O-benzoyl-D-ribopyranosyl 



"' H. Zinner, Chem. Ber. 83, 153 (1950). 



»« G. A. Howard, A. C. McLean, G. T. Newbold, F. S. Spring, and A. R. Todd, /. 



Chem. Soc. 1949, 232. 

 1" J. Davoll, B. Lythgoe, and A. R. Todd, J. Chem. Soc. 1948, 967. 

 '" G. A. Howard, B. Lythgoe, and A. R. Todd, J. Chem. Soc. 1947, 1052. 

 '" R. Jeanloz, H. G. Fletcher, Jr., and C. S. Hudson, J. Am. Chem. Soc. 70, 4055 



(1948). 

 '" R. K. Ness, H. G. Fletcher, Jr., and C. S. Hudson, J. Am. Chem. Soc. 73, 959 (1951). 



