Ethers and Acetal Nucleosides

The 2 -hydroxy group of adenosine can be selectively blocked as a 4-methoxybenzyl ether, a new protecting group, by treatment with 4-methoxybenzyl bromide and sodium hydride. A mixture of the 2 -and 3 -ethers results if p-methoxyphenyl diazomethane is used in presence of stannous chloride. The ether protecting group was rapidly cleaved with trityl tetraf luoroborate.  

Tetrahydrofuranyl derivatives of uridine and 2 -deoxycytidine, either partially or completely O- and/or N-substituted, have been prepared from the nucleoside with dihydrofuran. The protecting group may be removed either by dilute acid or by treatment with microsomal non-specific oxidases. 3 -0-tetrahydrofuranyl-N-benzoyladenosine and a 5 -0-dimethoxytrityl-arabinosyl-adenine derivative have been prepared conventionally for use in ribo-oiigonucieotide synthesis. 

Boron trichloride selectively cleaves benzyl ether groups on the sugar in the presence of 6-methoxy or 6-methylthio substituents in the base moiety of 7-deaza-purine nucleosides.  

Good yields of 2 -O-methyl or 2 -0-tertbutyldimethylsilyl derivatives of uridine result on standard sugar-base condensation synthesis of these unsymmetrically substituted nucleosides, B-products forming in spite of the absence of an ester participating group at C-2.  

Selective 2 -0-silylation of ribonucleosides occurs in presence of nitrate or perchlorate ion, whereas 1,4-diazobicycloL2,2,2]-octane and silver ion lead to selective reaction at o-3. in this way 2, 5 and 3, 5 -disilylated nucleosides can be prepared with high selectivity. ° 2 - and 3 -Mono-tetbutyldimethylsilyl 

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