Synthesis of Selectively 15N‐Labeled 2′‐O‐{[(Triisopropylsilyl)oxy]methyl}(=tom)‐Protected Ribonucleoside Phosphoramidites and Their Incorporation into a Bistable 32Mer RNA Sequence

Abstract

AbstractWe 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 4, 6, 12, and 18, respectively (Schemes 1–4). On a DNA synthesizer, the resulting 15N‐labeled 2′‐O‐tom‐protected phosphoramidite building blocks 19–22 were efficiently incorporated into five selected positions of a bistable 32mer RNA sequence 23 (known to adopt two different structures) (Fig. 1). By 2D‐HSQC and HNN‐COSY experiments 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 23.