Two sets of RNA phosphoramidites, carrying the (fluoride-labile) 2'-O-[(triisopropylsilyl)oxy]methyl (tom) group and the (photolabile) [(R)-1-(2-nitrophenyl)ethoxy]methyl ((R)-npeom) group, were prepd. The two protecting groups were completely orthogonal to each other. Three ribozyme-substrate constructs, protected each by a (R)-npeom group, were synthesized; on photolysis, efficient cleavage of this remaining protecting group occurred. It could be demonstrated that the presence of one (R)-npeom group within a RNA strand has only a minor influence on the pairing properties of corresponding duplexes. [on SciFinder (R)]