Nucleotides, Part LXVIII , Acetals as New 2′-O-Protecting Functions for the Synthesis of Oligoribonucleotides: Synthesis of Monomeric Building Units and Oligoribonucleotides
✍ Scribed by Stefan Matysiak; Wolfgang Pfleiderer
- Publisher
- John Wiley and Sons
- Year
- 2001
- Tongue
- German
- Weight
- 232 KB
- Volume
- 84
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
For the efficient synthesis of oligoribonucleotides by the 5'-O-(4,4'-dimethoxytrityl) phosphoramidite approach, the 2'-O-[1-(benzyloxy)ethyl]acetals 56 ± 67 were investigated. Studies with the 2'-O-[1-(benzyloxy)ethyl]-5'-O-(dimethoxytrityl)ribonucleoside 3'-phosphoramidites 56 ± 59 gave, however, only reasonable results. The oligoribonucleotides obtained showed some impurities since the acid stabilities of the acetal and dimethoxytrityl functions are too close to guarantee a high selectivity. A combination of new acid-labile protected 2'-O-protecting groups with the 2-(4-nitrophenyl)ethyl/[2-(4-nitrophenyl)ethoxy]carbonyl (npe/ npeoc) strategy for base protection was more successful. The synthesis and physical properties of the monomeric building units and their intermediates 8 ± 67 and the conditions for the automated generation of homo-and mixed oligoribonucleotides is described. The new 2'-acetal protecting group could be cleaved off in a two step procedure and was designed for levelling their stability with regard to the attached nucleobase as well. Therefore, we used the 1-{{3-fluoro-4-{{[2-(4-nitrophenyl)ethoxy]carbonyl}oxy}benzyl}oxy}ethyl (fnebe) moiety for the protection of 2'-OH of uridine, and for that of 2'-OH of A, C, and G, the 1-{{4-{{[2-(4nitrophenyl)ethoxy]carbonyl}oxy}benzyl}oxy}ethyl (nebe) residue. After selective deprotection by b-elimination induced by a strong organic base like DBU, the remaining activated acetal was hydrolyzed under very mild acidic protic conditions, which reduced 2'-3' isomerization and chain cleavage. Also storage, handling, and purification of the chemically and enzymatically sensitive oligomers was simplified by this approach.