We report an optimized synthesis of all canonical 2'-O-TOM protected ribonucleoside phosphoramidites and solid supports containing [13C5]-labeled ribose moieties, their sequence-specific introduction into very short RNA sequences and their use for the structure determination of two protein–RNA complexes. These specifically labeled sequences facilitate RNA resonance assignments and are essential to assign a high number of sugar–sugar and intermolecular NOEs, which ultimately improve the precision and accuracy of the resulting structures. This labeling strategy is particularly useful for the study of protein–RNA complexes with single-stranded RNA in solution, which is rapidly an increasingly relevant research area in biology.