Conformationally Constrained 2'-N,4'-C-Ethylene-Bridged Thymidine (Aza-ENA-T): Synthesis, Structure, Physical, and Biochemical Studies of Aza-ENA-T-Modified Oligonucleotides
2006 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 47, 15173-15187 p.Article in journal (Refereed) Published
The 2'-deoxy-2'-N,4'-C-ethylene-bridged thymidine (aza-ENA-T) has been synthesized using a key cyclization step involving 2'-ara-trifluoromethylsufonyl-4'-cyanomethylene 11 to give a pair of 3',5'-bis-OBn- protected diastereomerically pure aza-ENA-Ts (12a and 12b) with the fused piperidino skeleton in the chair conformation, whereas the pentofuranosyl moiety is locked in the North-type conformation (7 < P < 27 degrees, 44 degrees < phi(m) < 52 degrees). The origin of the chirality of two diastereomerically pure aza-ENA-Ts was found to be due to the endocyclic chiral 2'-nitrogen, which has axial N-H in 12b and equatorial N-H in 12a. The latter is thermodynamically preferred, while the former is kinetically preferred with E-a 25.4 kcal mol(-1), which is thus far the highest observed inversion barrier at pyramidal N-H in the bicyclic amines. The 5'-O-DMTr-aza-ENA-T-3'-phosphoramidite was employed for solid-phase synthesis to give four different singly modified 15-mer antisense oligonucleotides (AONs). Their AON/RNA duplexes showed a T m increase of 2.5-4 degrees C per modification, depending upon the modification site in the AON. The relative rates of the RNase H1 cleavage of the aza-ENA-T-modified AON/RNA heteroduplexes were very comparable to that of the native counterpart, but the RNA cleavage sites of the modified AON/RNA were found to be very different. The aza-ENA-T modifications also made the AONs very resistant to 3' degradation (stable over 48 h) in the blood serum compared to the unmodified AON (fully degraded in 4 h). Thus, the aza-ENA-T modification in the AON fulfilled three important antisense criteria, compared to the native: (i) improved RNA target affinity, (ii) comparable RNase H cleavage rate, and (iii) higher blood serum stability.
Place, publisher, year, edition, pages
2006. Vol. 128, no 47, 15173-15187 p.
Biochemistry and Molecular Biology
IdentifiersURN: urn:nbn:se:uu:diva-96272DOI: 10.1021/ja0634977ISI: 000242216100046PubMedID: 17117869OAI: oai:DiVA.org:uu-96272DiVA: diva2:170791