We present optimized reaction conditions for the conversion of 2'-O-{[(triisopropylsilyl)oxy]methyl}(tom) protected uridine and adenosine nucleosides into the corresponding protected (3-15N)-labeled uridine and cytidine and (1-15N)-labeled adenosine and guanosine nucleosides. On a DNA synthesizer, the resulting 15N-labeled 2'-O-tom-protected phosphoramidite building blocks were efficiently incorporated into five selected positions of a hairpin bi-stable 32mer RNA sequence. By 2D-HSQC and HNN-COSY expts. in H2O/D2O 9:1, the 15N-signals of all base-paired 15N-labeled nucleotides could be identified and attributed to one of the two coexisting structures of 32mer RNA sequence. [on SciFinder (R)]