Abstract
The replication of Moloney murine leukaemia virus relies on the formation of a stable homodimeric ‘kissing complex’ of a GACG tetraloop interacting through only two C⋅G base pairs flanked of 5′‐adjacent unpaired adenosines A9. Previous NMR investigations of a model stem loop 1 has not permitted to reveal the origin of this interaction. Therefore, with the aim of deeper comprehension of the phenomena, the model sequence 10 was prepared where position 9 has been substituted for a nucleoside offering a wider π‐stacking. In this context, the wyosine phosphoramidite building block 2 was prepared and incorporated by adapting the conditions of the automated synthesis and developing original templated enzymatic ligation. However, no ‘kissing interaction’ has been observed for this model sequence 10 due to steric hindrance as confirmed by computational simulation. Consequently, several other model sequences, 18, 23–26, containing modified nucleosides were prepared. Finally, the importance of the cross‐loop H‐bond between G8 and G11 nucleobases was revealed by preparing a 18mer RNA hairpin 27, where the guanosine G8 has been substituted for inosine. The latter, which does not possess a C^3^ amino function compared to guanosine, is unable to form any ‘kissing complex’ demonstrating the importance of this secondary interaction in the formation of the complex.