CHEMISTRY OF RIBOSE AND DEOXYRIBOSE 27 



bromide, isomeric with that previously known. It was dextrorotatory and was con- 

 sidered to be the a-isomer. The new a-isomer could also be obtained in very low yield 

 (1.3%) when tri-0-benzoyl-/3-D-ribopyranosyl bromide was treated with hydrogen 

 bromide in glacial acetic acid. Most of the starting material (i.e., /3-isomer) (96%) 

 could be recovered unchanged. 



Treatment of /3-D-ribopyranose tetra-0-benzoate with titanium tetrachloride in 

 chloroform solution gives two crystalline products which are considered to be tri-O- 

 benzoyl-a- and -/3-D-ribopyranosyl chloride. The major product is the /3-anomer. Both 

 compounds react with methanol in the absence of an acid-acceptor to give methyl 

 tri-0-benzoyl-/3-D-ribopyranoside. 



Further evidence in favor of the assigned configurations for the triacylribopy- 

 ranosyl halides was obtained by studying their reactions with methanol in the pres- 

 ence and absence of acid-acceptors. As expected the triacyl-;8-D-ribopyranosyl halides 

 reacted with the alcohol in the presence of acid-acceptors to yield acid-labile dex- 

 trorotatory syrups which most probably contained ortho-ester derivatives, whereas 

 the a-halides gave acylated derivatives of methyl /3-D-ribopyranoside in good yield. 

 The latter result is in conformity with present ideas on the role of neighboring groups 

 in replacement reactions (see Remick'") since the a-halides, having a halogen on 

 C-1 in a czs-position relative to the benzoyloxy group on C-2 might be expected to 

 react with methanol with simple inversion to give methyl /S-D-riboside tri-0-benzoate. 

 The j3-halides, on the other hand, having a /rans-relationship between the groups at 

 C-1 and C-2, react with methanol, in part at least, by a different mechanism. (Cf. 

 Jeanloz and Fletcher* for further details.) The /rans-halide reacted more rapidly 

 with methanol than its cis-isomer as shown in Table III."^ It wasshown'"*^ that tri- 

 0-benzoyl-;3-D-ribopyranosyl bromide in dry benzene-ether solution could be con- 

 verted in high yield to the corresponding chloride by treatment with active silver 

 chloride"*' "' according to the method developed originally by Haworth et al.^^° 



Levene and Tipson"" found that tri-0-acetyl-/3-D-ribopyranosyl bromide reacts 

 with methanol in the presence of silver carbonate to give 3,4-di-O-acetyl-D-ribo- 

 pyranose methyl 1 ,2-orthoacetate. Klingensmith and Evans'"^ obtained an analogous 

 compound (i.e., di-O-acetyl-n-ribose l,2-ortho-3'-acetoxyacetonyl acetate) on con- 

 densing the same halide with dihydroxyacetone monoacetate. The structures of these 

 compounds have recently been discussed by Pacsu.'^' 



c. N -Glycosides 



A^-Ribosides occur naturally in important biological substances, as for 

 example ribonucleic acids, vitamin Bn and cozymase. Furthermore in the 

 ribityl derivatives which are found in Nature, C-1 of the reduced sugar 

 residue is linked to a nitrogen atom in a heterocyclic nucleus. Consequently 

 it is not surprising that a great deal of current interest in the chemistry of 

 D-ribose is centered on the A^-ribosides. The product from the condensation 

 of D-ribose (XXIV) with ammonia or a primary amine might be expected 



1" A. E. Remick, "Electronic Interpretations of Organic Chemistry," 2nd ed., p. 



339. J. Wiley & Sons, New York, 1949. 

 "8 H. H. Schlubach, Ber. 69, 840 (1926). 

 1" H. H. Schlubach and R. Gilbert, Ber. 63, 2292 (1930). 

 ISO W. N. Haworth, E. L. Hirst, and M. Stacey, J. Chem. Soc. 1931, 2864. 

 *^i E. Pacsu, Advances in Carbohydrate Chem. 1, 77 (1945). 



