Nucleic-Acid Analogs with Restricted Conformational Flexibility in the Sugar-Phosphate Backbone (`Bicyclo-DNA'), Part 7, Synthesis and Properties of Oligodeoxynucleotides Containing [(3′S,5′S,6′R)-6′-Amino-2′-deoxy-3′,5′-ethano-β-D-ribofuranosyl]thymine (=(6′R)-6′-Amino-bicyclo-thymidine)
作者:Roland Meier、Sabine Grüschow、Christian Leumann
DOI:10.1002/(sici)1522-2675(19991110)82:11<1813::aid-hlca1813>3.0.co;2-0
日期:1999.11.10
We describe the synthesis of the acetamido- and trifluoroacetamido-functionalized bicyclo-thymidines 11 and 12, starting from the silyl enol ether 1, in 6 steps. These nucleosides were converted to the corresponding cyanoethyl phosphoramidite building blocks 16 and 17 and subsequently incorporated into the homothymidylate decamers 18-22. Upon deprotection of the oligomers, the trifluoroacetamido functions were cleaved, leaving behind a free amino function in the sugar-phosphate backbone that is protonated at neutral pH, giving rise to partially zwitterionic oligonucleotides. Pairing properties with the complementary DNA oligomer d(A(10)), as determined by UV/melting curves, revealed a slightly increased stability of the duplex d(A(10)) . 20, in which the decathymidylate sequence shows an alternating arrangement of natural thymidine and amino-bicyclo-thymidine residues, relative to the natural reference duplex. The dependence of T-m on the salt concentration of the medium is reduced in this case. Duplex destabilization occurs if the amino-bicyclo-thymidine residues are replaced by the charge-neutral acetamido-bicyclo-nucleosides (e.g., d(A(10)) . 22), most probably due to steric interference of the acetamido substituent with the backbone P-O(5') bond.