Ribofuranose anomeric forms

The two anomeric forms are called a- and P-ribofuranose. Again, in solution there exists an equilibrium between the open chain carbonyl form and the two anomeric hemiacetal forms. Ribose also forms six-membered pyranose anomers, and... 

The synthesis of corresponding pyrimidine nucleosides was not possible by the mercuric chloride method. The syntheses succeeded, however, on application of the Hilbert—Johnson procedure. Tetra-O-acetyl-4-thio-D-ribofuranose was transformed with ethereal hydrogen chloride into the glycosyl chloride derivative 254, and this was directly heated for five days with 2,4-diethoxy-5-methylpyrimidine. The anomeric forms of 4-ethoxy-5-methyl-l-(2,3,5-tri-0-acetyl-4-thio-D-ribofuranosyl)-2(lH)-pyrimidinone obtained could be separated... 

Hydantocidin. Hydantocidin (182), C2H2QN2O3, is elaborated by S. hygroscopicus (278). It is unique in that the anomeric carbon of the ribosyl moiety forms the spHo bond of hydantoin (279). The ribofuranose moiety which has been reported to be in a Q -endo conformation (279) has been synthesized (280,281). Hydantocidin is a herbicidal nucleoside with activity against monocotyledenous and dicotyledenous plants. 

Draw a structural formula for the 3-A/-glycoside formed between D-ribofuranose and cytosine. Label the anomeric carbon and the A/-glycosidic bond. 

C-glycosides (32) and (33) using a Wittig reaction. The j8-glycoside (32) is formed initially, but it anomerizes to the a-glycoside (33) under the basic conditions of the reaction. Similar reactions were carried out with 2,3 5,6-di>0-iso-propylidene-D-manno- and -allo-furanose. Condensation of 2,3,5-tri-< -benzyl-D-ribofuranose with carbomethoxymethylenetriphenylphosphorane produced a... 

A route to ketose-derived nucleosides relies upon the 1-deoxy-l-nitro-ribofuranose derivative (18) as an important intermediate. Henry reaction of this was the key to the synthesis of psicouridine (20) outlined in Scheme 3, anomer (19) being the major kinetic product initially formed. Alternatively, Michael reactions of (18) with, for example, acrylonitrile, permitted the introduction of 3-carbon chains at the anomeric position. l... 

---