Synthesis of 2'(R)-substituted neplanocin A's (nucleosides and nucleotides. XXXVII).

Neplanocin A (I) was treated with 1, 3-dichloro-1, 1, 3, 3-tetraisopropyldisiloxane to give 3', 5'-O-(tetraisopropyldisiloxane-1, 3-diyl) neplanocin A (II), which was converted to the 2'-O-trifluoromethanesulfonyl derivative (III). Nucleophilic substitution of III with a number of nucleophiles (AcO-, AcS-, N3-, Cl-, Br-, I-) in hexamethylphosphoric triamide afforded the respective 2' (R)-substituted derivatives in high yield. The halogenated derivatives were reduced with tri-n-butyltin hydride to the 2'-deoxy compound. 2'-O-Thiocarbonylimidazoyl-3', 5'-O-(tetraisopropyldisiloxane-1, 3-diyl) neplanocin A was also reduced to the 2'-deoxy derivative. The deprotection of the bifunctional silyl group with tetra-n-butylammonium fluoride afforded 2' (R)-AcO, -AcS, -N3, -Cl, -Br, -I, and 2'-deoxy neplanocin A's, respectively. Physical data of these compounds including nuclear magnetic resonance, mass spectrum, and circular dichroism were given.