Nucleoside 3 ,5 -cyclic

Azauridine was also synthesized using the knowledge of the course of alkylation of 6-azauracil 2-methylmercapto derivatives (e.g., Section II,B,4,b). The 1-ribofuranosyl derivative obtained by reaction of the mercury salt of the 2-methylmercapto derivative with tri-O-benzoyl-jS-D-ribofuranosyl chloride on removal of the methyl-mercapto and then benzoyl groups yielded crystalline 6-azauridine, The main difference between uracil and 6-azauracil nucleosides consists in the preparation of cyclic nucleosides. It is known that uridine can be readily converted to cyclic nucleosides by the reaction of 2 (50-O-mesyl derivatives with nucleophilic agents, Analogous... 

RhH(PPh3)4 (1 mol%) exhibited higher catalytic activity and promoted a complete reversal in stereoselectivity to provide the trans isomer of 24 and 25 as the major reaction product. The czs-cyclopentane 29, derived from optically active 28, was converted to the differentially protected cyclopentane triol 29, which, in turn, converted to the differentially protected tetrad 30, a key intermediate in the synthesis of enantiopure bioactive carbo-cyclic nucleosides [19]. 

The formation of the adduct between 86 and the nitrile, i.e., 89, occurs more readily than that between 86 and ketones, since an activated nitrile is a better nucleophile than a ketone. Since the ce-proton in the adduct 89 is more acidic than the ce-proton in the ketonic adduct, also the ring opening will occur more easily. The interchange of a nitrile carbon with the ring carbon of a pyrimidine ring was also observed with the 3-benzyloxymethyl-l-ribosyl-5-cyanouracil. With a series of activated nitriles, the protected bi-cyclic nucleosides are formed. After deprotection, the corresponding bi-cyclic nucleosides are obtained (Scheme IV.35). 

Intramolecular cyclization of appropriately substituted nucleosides is a general approach to the preparation of cyclic nucleosides, such as (170) and (171), which are derivatives of the parent system (58) <71JOC4105, 75JOC2372, 78JPR157, 81CJC468, 85CPB3689). 

De Clercq E (2011) The clinical potential of the acyclic (and cyclic) nucleoside phosphonates the magic of the phosphonate bond. Biochem Pharmacol 82 99-109... 

Yamamoto, M., M. Masaka, K. Yamada, Y. Hayashi, H. Hirai, and A. Kumagai Stimulatory Effect of Ginsenosides on DNA, Protein and Lipid Synthesis in Rat Bone Marrow and Participation of Cyclic Nucleosides. Arzneim. Forsch. (Drug Res.) 28,2238 (1978), and reference cited therein. 

Figure 20 Praziquantel and cyclic nucleoside phosphonates as antischistosomal agents.

Little is known of the mechanism by which ribose is reduced. It has been suggested on the basis of chemical analogy (97) that the process could occur by displacement of the hydroxyl on C-2 of ribose to form the cyclonucleotide (IX). This could be followed bya reductive cleavage of theCj—O bond to form the deoxyribonucleotide. Cyclic nucleoside formation might be assisted by a preliminary phosphorylation of the 2 -hydroxyl group. H H... 

In the area of cyclic nucleosides, a new route to derivatives of cAMP has been described, proceeding via a 3 -,S -cyclic phosphite, and treatment of cAMP with benzyl bromide and Ag20 in MeCN-DMSO gives the D-benzyl cyclic triester as an epimeric mixture in good yield. 

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