Nucleosides of Unsaturated Sugars, Ketosugars, and Uronic Acids

8 Nucleosides of Unsaturated Sugars, Ketosugars and Uronic Acids 

As in previous volumes, 2, 3 -didehydro-2, 3 -dideoxyfuranosyl nucleosides (d4 systems) are discussed in Section 3, together with their saturated analogues. 

When the 3 -mesylate 141 was treated with secondary amines, enamines of type 142 were obtained, as anomeric mixtures. The authors theorise that a 2 -ketonucleoside is involved, formed by a hydride shift under metal-free conditions for a similar reaction starting from a D-/yxo-precursor see Vol. 28, p. 273. Hydrolysis of the a-anomer of 142 (-NR2 = morpholinyl) gave the a-2 -ketonucleoside 143, the structure of which was secured by crystallography of a derivative, and some earlier structural assignments were revised.  

An improved route has been developed for the synthesis of adenosine receptor agonists of type 145, involving the high-yield oxidation of 2, 3 -0-isopropylidene-adenosine with KMn04 at pH 12. Esters and amides of adenosine-5 -carboxylic acid have also been prepared for investigation as inhibitors of S-adenosylhomocysteine hydrolase. 

Anomeric 2,3-dideoxy-D-erythro-hex-2-enopyranosyl nucleosides have been synthesized by Lewis-acid-catalysed condensation of triacetyl- 

The alkene (39), produced by Wittig reaction, gave exclusively 0-anomers (40) on cyclization and hydrolysis. The a-chloroacid was 

5-(0-D-Ribofuranosyl)-l,2,3,4-tetrahydrophthalazine-l,4-diones have been prepared by means of cycloaddition to derivatives of 2- 

A series of 2 -deoxyribofuranosyl C-nucleosides of imidazo-fused bridgehead nitrogen systems, typified by (45), have been prepared starting from tri-O-benzoyl-2,5-anhydro-D-allonic acid.  

---