RNA synthesis using monomers containing the 2’-O-TriisopropylsilylOxyMethyl (TOM) group (TOM-Protecting- Group™) is characterized by very high coupling efficiency along with fast, simple deprotection. High coupling efficiency is achieved because the TOM-Protecting-Group exhibits lower steric hindrance than the 2’-O-t-butyldimethylsilyl (tBDMS) group used in our previous RNA monomers. Indeed, the TOM-Protecting-Group is similar sterically to the 2’-OMe group and exhibits high efficiency similar to 2’-OMe-RNA monomers.
Fast and reliable deprotection is achieved using ammonium hydroxide/methylamine (AMA) or methylamine in ethanol/water (EMAM). AMA works best for regular oligos while EMAM is optimal for long oligos. A further feature of the TOM-Protecting-Group is that during basic steps it cannot undergo 2’ to 3’ migration. This migration under basic conditions leads to non-biologically active 2’-5’ linkages when using the tBDMS group. These features allow the TOM-Protected monomers to produce longer oligonucleotides and, for this reason, we offer only 1000Å supports. TOM-Protected RNA monomers are also fully compatible with minor bases with 2’-O-tBDMS protection.