groups e g n6 benzoyl adenosine n4 acetyl cytidine and n2 isobutyryl guanosine alternately 2 u2032 o silyl ethers can be used in conjunction with acid labile 2 u2032 o orthoester protecting groups in the synthesis of rna as described by scaringe supra differing 2 u2032 chemistries can require different protecting groups for example 2 u2032 deoxy 2 u2032 amino nucleosides can utilize n phthaloyl protection as described by usman et al u s pat no 5 631 360 incorporated by reference herein in its entirety during solid phase synthesis each nucleotide is added sequentially 3 u2032 to 5 u2032 direction to the solid support bound oligonucleotide the first nucleoside at the 3 u2032 end of the chain is covalently attached to a solid support e g controlled pore glass or polystyrene using various linkers the nucleotide precursor a ribonucleoside phosphoramidite and activator are combined resulting in the coupling of the second nucleoside phosphoramidite onto the 5 u2032 end of the first nucleoside the support is then washed and any unreacted 5 u2032 hydroxyl groups are capped with a capping reagent such as acetic anhydride to yield inactive 5 u2032 acetyl moieties the trivalent phosphorus linkage is then oxidized to a more stable phosphate linkage at the end of the nucleotide addition cycle the 5 u2032 o protecting group is cleaved under suitable conditions e g acidic conditions for trityl based groups and fluoride for silyl based groups the cycle is repeated for each subsequent nucleotide modification of synthesis conditions can be used to optimize coupling efficiency for example.