Nucleotides - LXIII - New 2-(4-nitrophenyl)ethyl(npe)- and 2-(4-nitrophenyl)ethoxycarbonyl(npeoc)-protected 2 '-deoxyribonucleosides and their 3 '-phosphoramidites - Versatile building blocks for oligonucleotide synthesis

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 oligonucleo tide synthesis (see Scheme). Thus, 3',5'-di-O-acyl- and N-2,3'-O,5'-O-triac yl-2'-deoxyguanosines can easily be converted into the corresponding O-6-al kyl 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 trity lated (--> 38-42) and phosphitylated (--> 57-61) in the usual manner. N-2-[ 2-(4-nitrophenyl)ethoxycarbonyl]-substituted and N-2-[2-(4-nitrophenyl)etho xycarbonyl]-O-6-[2-(4-nitrophenyl)ethyl]-substituted 2'-deoxyguanosines 5 a nd 7, respectively, are synthesized as new starting materials for tritylati on (--> 28, 35, and 37) and phosphitylation (--> 54, 56, 70, and 78). Vario us O-4-alkylthymidines (see 20-24) are also converted to their 5'-O-dimetho xytrityl derivatives (see 43-47) and the corresponding phosphoramidites (se e 62-66 and 79-82).