- Nucleotides. LXXIV* synthesis of α-D-arabino-oligonucleotides
-
□ The 5 α-D-arabinofuranosylnucleosides α-araU (15), α-araT (18), α-araC (22), α-araA (25), and α-araG (28) have been synthesized by the modified silyl-method. The amino groups at the nucleobases and the 2′-hydroxy group at the sugar moiety were protected by the 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) group (37-40) and the amide function in α-araG was additionally blocked by the 2-(4-nitrophenyl)ethyl group (63) to improve solubility in organic solvents. Mono-and dimethoxytritylation of the 5′-OH group was performed in the usual manner to give 41-48, 64, and 65 in high yields and further substitution of the 3′-OH group led to the monomeric building blocks 66-75 as well as the 3′-O-succinoyl derivatives 76-85 functioning as starting units in solid-support oligonucleotide synthesis. A large number of oligo-α- arabinonucleotides have been prepared on modified CPG-material applying the npeoc/npe strategy as a very efficient synthetic tool for highly purified, homogenous oligomers. Hybridizations between α-arabinonucleotide strands revealed in analogy to earlier findings an antiparallel orientation whereas the combination of an oligo-α-D-arabinonucleotide with a complementary oligo-2′-deoxy-β-D-ribofuranosylnucleotide showed base-pairing only if a parallel polarity was present. The advantages in oligo-α-arabino- nucleotide synthesis were furthermore demonstrated by the synthesis of the tα-ANAhis a structural analog of the natural tRNAhis of the phage T5. Copyright Taylor & Francis Group, LLC.
- Henke, Christoph,Pfleiderer, Wolfgang
-
p. 1665 - 1706
(2007/10/03)
-
- Recognition of RNA by tripler formation: Divergent effects of pyrimidine C-5 methylation
-
In DNA triple helices, methylation at C-5 of thymine or cytosine is reported to have similar stabilizing effects for both bases. Here we show, however, that methylation of the same positions in RNA triplexes has distinctly different effects than in DNA. We have previously described the use of circular triplex-forming RNA oligonucleotides to recognize RNA sequences. Here it is shown that addition of C-5 methyl groups to uracils in these compounds very significantly increases not only affinity but also sequence selectivity in binding a purine-rich RNA target, as measured by thermal denaturation with various target RNAs. Surprisingly, however, addition of C-5 methyl groups to cytosines actually decreases affinity in binding RNA, while the same substitution in DNB is thermally stabilizing. Possible sources of this divergent behavior are discussed. A synthesis of 5-methylcytidine ribonucleoside 2'-O-silyl-3'-O-phosphoramidite is also described.
- Wang, Shaohui,Xu, Yanzheng,Kool, Eric T.
-
p. 1043 - 1050
(2007/10/03)
-