| Abstrakt: |
A series of new base-protected and 5'-O-(4-monomethoxytrityl)- or 5'-O-(4,4'-dimethoxytrityl)-substituted 3'-(2-cyanoethyl diisopropylphosphoramidites) and 3'-[2-(4-nitrophenyl)ethyl diisopropylphosphoramidites] 52 66 and 67 82, respectively, are prepared as potential building blocks for oligonucleotide synthesis (see Scheme). Thus, 3',5'-di-O-acyl- and N 2,3'-O,5'-O-triacyl-2'-deoxyguanosines can easily be converted into the corresponding O6-alkyl derivatives 6, 8, 10, 12, 14, and 16 by a Mitsunobu reaction using the appropriate alcohol. Mild hydrolysis removes the acyl groups from the sugar moiety (→ 9, 11, 13, 15, and 19 (via 18), resp.) which can then be tritylated (→ 38 42) and phosphitylated (→ 57 61) in the usual manner. N 2-[2-(4-nitrophenyl)ethoxycarbonyl]-substituted and N 2-[2-(4-nitrophenyl)ethoxycarbonyl]-O6-[2-(4-nitrophenyl)ethyl]-substituted 2'-deoxyguanosines 5 and 7, respectively, are synthesized as new starting materials for tritylation (→ 28, 35, and 37) and phosphitylation (→ 54, 56, 70, and 78). Various O4-alkylthymidines (see 20 24) are also converted to their 5'-O-dimethoxytrityl derivatives (see 43 47) and the corresponding phosphoramidites (see 62 66 and 79 82). |
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