Synthesis and properties of 2′-O-Methyl-2-thiouridine and oligoribonucleotides containing 2′-O-Methyl-2-thiouridine

A new method for the synthesis of 2′-O-methyl-2-thiouridine (s2Um) found in thermophilic bacterial tRNA was developed. Structural properties of s2Um and s2UmpU were studied by using 1H NMR spectroscopy. A modified nonaribonucleotide (RNA*: 5′-CGUUs2UmUUGC-3′) was synthesized to study the base-recognition ability of s2Um in formation of RNA–RNA and RNA–DNA duplexes. The UV melting experiments revealed that RNA*–RNA and RNA*–DNA duplexes having an s2U-A base pair are more stable than those having a U-A base pair. On the contrary, the thermal stability of RNA*–RNA and RNA*–DNA duplexes having an s2U-G wobble base pair was much lower than that of the unmodified duplexes having a natural U-G base pair. It is concluded that s2Um has higher selectivity toward A over G than unmodified U.