Synthesis and properties of RNA constrained by a 2'-O-disulfide bridge.

We recently reported the properties of RNA hairpins constrained by a dimethylene (DME) disulfide (S-S) linker incorporated between two adjacent nucleosides in the loop and showed that this linker locked the hairpin conformation thus disturbing the duplex/hairpin equilibrium. We have now investigated the influence of the length of the linker and synthesized oligoribonucleotides containing diethylene (DEE) and dipropylene (DPE) S-S bridges. This was achieved via the preparation of building blocks, namely 2'-O-acetylthioethyl (2'-O-AcSE) and 2'-O-acetylthiopropyl (2'-O-AcSP) uridine phosphoramidites, which were successfully incorporated into RNA sequences. Thermal denaturation analysis revealed that the DEE and DPE disulfide bridges destabilize RNA duplexes but do not disrupt the hairpin conformation. Furthermore, our investigation of the duplex/hairpin equilibrium indicated that sequences modified with DME and DEE S-S linkers predominantly lock the hairpin form, whereas the DPE S-S linker provides flexibility. These findings highlight the potential of S-S linkers to study RNA interactions.