REGIOSELECTIVE 2'/3'-O-ALLYLATION OF PYRIMIDINE RIBONUCLEOSIDES USING PHASE-TRANSFER CATALYSIS

A short and convenient procedure for regiospecific O-allylation of uridine is reported by employing dibutyltin oxide as a mild base in conjunction with a phase transfer catalyst tetrabutylammonium bromide. The resulting isomeric 2'/3'-O-allyl uridines were separated after conversion into their corresponding 5'-O-DMT derivatives. The 2'-O-allyluridine 3 was then transformed into 2'-O-allylcytidine 7 and both were individually converted into the corresponding beta-cyanoethyl phosphoramidite monomers (9 and 10) and a phosphodiester monomer 11, required for oligonucleotide assembly. The utility of 11 is demonstrated by synthesis and characterization of a 2'-O-allyl ribodinucleotide UpU.