A synthetic method for the N-alkyloxycarbonylation of adenine and guanine nucleosides was developed and used for the prepn. of RNA-phosphoramidites carrying photolabile sugar and nucleobase protecting groups. From these building blocks, a heptameric oligoribonucleotide was prepd. by automated synthesis, followed by detachment form the solid support and photolytic deprotection under mild conditions. The presented strategy allows a simple prepn. of 3'-O-aminoacylated RNA-sequences. [on SciFinder (R)]