chemistry of ribose and deoxyribose 55 



3. Physical Properties 



Deriaz et alP"^ investigated the mutarotation in aqueous solution of 2- 

 deoxyribose. The velocity constants for the mutarotations of both the 

 D- and L-forms of this sugar were calculated, and the values obtained were 

 2 to 3 times greater than those for L-arabinose. In the presence of 0.01 A'^ 

 hydrochloric acid or 0.01 A^ sodium hydroxide, 2-deoxyribose reached the 

 equilibrium value for the specific rotation immediately on dissolution. 

 Values of the physical constants of 2-deoxyribose and its derivatives are 

 listed in the Appendix (Table VIII.) 



4. Properties and Reactions of Derivatives 

 a. -Glycosides 



Early in the development of deoxysugar chemistry it was noted that the rates of 

 formation and hydrolysis of deoxysugar glj^cosides greatly exceeded those of the 

 corresponding normal pentose or hexose. When 2-deoxj'-L-ribose was treated with 1% 

 methanolic hydrogen chloride it afforded a methyl 2-deoxyriboside mixture which 

 was separated into crystalline a- and /3-isomers (A and B, respectively).^*' If 0.1% 

 methanolic hydrogen chloride was used then a third methyl 2-deo.\ypentoside (C) 

 was obtained. The glycoside C was much more rapidly hydrolyzed by acids than 

 were the glycosides A and B,^*! thereby indicating that C was probably a glycofur- 

 anoside. The glycosides A, B and C were separately mechanically shaken with acetone 

 and anhydrous copper sulfate. Glycosides A and B readily formed mono-0-isopro- 

 pylidene derivatives whereas C was recovered unchanged. ^^^ Since it is usual for 

 acetone to condense with adjacent cis-hydroxyl groups, this would imply that A and 

 B had pyranose structures and C a furanose structure. 



When the glycosides B and C were treated with p-toluenesulfonyl chloride in dry 

 pyridine, they both yielded a di-p-toluenesulfonyl derivative. That from the gly- 

 coside C readil}' underwent exchange with one mole of sodium iodide when heated 

 at 105-110° for 3 hours with excess sodium iodide in acetone, whereas the derivative 

 from B was unaffected by this treatment, indicating that only in glycoside C was 

 there a primary hydroxyl group. From this it follows that B had a pyranose and C a 

 furanose structure. Results of oxidation of the glycosides A, B and C with lead tetra- 

 acetate confirmed these conclusions.-*' Final proof of the structures of the glycosides 

 B and C was obtained by methylation, hydrolysis, oxidation and comparison of the 

 rates of hydrolysis of the lactones so obtained. From the glycoside B a 1,5-lactone 

 was obtained'*' whereas a 1,4-lactone was derived from C, showing that the glycoside 

 B had a 1,5-pyranose lactol ring and C a 1,4-furanose lactol ring. Since A and B were 

 a- and /3-anomers, it followed that A also had a pyranose structure. 



Independent proof of the structure of B was furnished by the fact that it could 

 be obtained from methyl 2,3-anhydro-/3-D-ribopyranoside by a series of transforma- 

 tions which did not affect the lactol ring structure or configuration at carbon atom 1 

 of the initial material or intermediates in the conversion. 2^' Further, this synthesis 

 served to establish the a,)3-relationship in the pyranose series, since the product was 

 the optical enantiomorph of the glycoside B designated as methyl 2-deoxy-/3-L-ribo- 

 pyranoside. Davoll and Lythgoe'"^ have pointed out that configurational assignments 



'"^ J. Davoll and B. Lythgoe, /. Chem. Soc. 1949, 2526. 



