ABSTRACT2'-O-Methyl oligoribonucleotides have recently been introduced as antisense probes for studying RNA processing and for affinity purification of RNA-protein complexes. To identify RNA analogues with improved properties for antisense analysis, 2'--alkyl oligoribonucleotides were synthesized in which the alkyl moiety was either the threecarbon linear allyl group or the five-carbon branched 3,3-dimethylallyl group. Both these analogues were found to be completely resistant to degradation by either DNA-or RNAspecific nucleases. Use of biotinylated derivatives of the probes to affinity-select ribonucleoprotein particles from crude HeLa cell nuclear extracts showed that the presence of the bulky

The synthesis of base protected 5'-O-dimethoxytrityl-2'-O-[1-(2- fluorophenyl)-4-methoxypiperidin-4-yl]-3'-O-(2-cyanoethyl N,N-diisopropylphosphoramidites) is described, using phenoxyacetyl protection for the exocyclic amino groups of guanosine and adenosine and acetyl protection of the amino group of cytidine. High yield assembly of these building blocks into oligoribonucleotides on aminopropyl controlled pore glass was achieved using 5-(4-nitrophenyl)-1H-tetrazole as activator. Mixed sequences containing selected 2'-O-methylation were also synthesised and their significance for the study of RNA biochemistry is discussed.