Selective Biocatalytic Acylation Studies on 5'-O-(4,4'-Dimethoxytrityl)-2',3'-Secouridine: An Efficient Synthesis of UNA Monomer

Lipozyme® TL IM (Theremomyces lanuginosus lipase immobilized on silica) in toluene catalyzes the acylation of the 2( )'-OH over the 3( )'-OH group in 5( )'-O-(4,4( )'-dimethoxytrityl)-2( )',3( )'-secouridine (5( )'-O-DMT-2( )',3( )'-secouridine) in a highly selective fashion in moderate to almost quantitative yields. The turn over during benzoyl transfer reactions mediated by vinyl benzoate or benzoic anhydride was faster than in acyl transfer reactions with vinyl acetate or C(1) to C(5) acid anhydrides; except in the case of butanoic anhydride. The 2( )'-O-benzoyl-5( )'-O-DMT-2( )',3( )'-secouridine obtained by Lipozyme® TL IM catalyzed benzoylation of 5( )'-O-DMT-2( )',3( )'-secouridine was successfully converted into its 3( )'-O-phosphoramidite derivative in satisfactory yield, which is a building block for the preparation of oligonucleotides containing the uracil monomer of UNA (unlocked nucleic acid).