Stepwise enzymatic oligoribonucleotide synthesis including modified nucleotides.

A method has been developed for the routine synthesis of 2'(3')-o-monoacyl ribonucleoside 5'-diphosphates for stepwise synthesis of oligoribonucleotides with Escherichia coli polynucleotide phosphorylase. The use of triethyl orthoisovalerate allows the facile preparation of 2'(3')-o-isovaleryl-UDP, -CDP, -ADP, -GDP, -IDP, -EPLISON-APD, eplison-CDP, and N6-isopentenyl-ADP. The synthesis of N6-isopentenyl-ADP from ADP by N1-alkylation and the Dimroth rearrangement to N6 is reported. The effects of several factors including the nature of the divalent cation, pH, SALT CONCENTRATION, AND TIME ON THE EFFICIENCY OF THE POLYNUCLEOTIDE PHPSPHORYLASE CATALYZED SINGLE ADDITIONS OF THE 2'(3')-O-ISOVALERYL RIBONUCLEOSIDE 5'-DIPHOSPHATES TO AN OLIGORIBONUCLEOTIDE PRIMER ARE REPORTED. The syntheses of many tetranucleoside triphosphates and two pentanucleoside tetraphosphates in yields of 20-75 per cent are reported. The 2'(3')-o-isovaleryl derivatives of IDP, eplison-ADP, eplison-CDP, and N6-isopentenyl-ADP were all accepted by polynucleotide phosphorylase as substrates for the monoaddition reaction. The extension of the method to include the syntheses of oligoribonucleotides containing modified nucleosides offers a means of studying the role s of these modification by the use of relatively simple model compounds.