| Abstract: | Oligodeoxyribonucleotides containing 1-deaza-2′-deoxyadenosine ( = 7-amino-3-(2-deoxy-β-D -erythro-pentofuranosyl)-3H-imidazo4, 5-b]pyridine; 1b ) form Hoogsteen duplexes. Watson-Crick base pairs cannot be built up due to the absence of N(1). For these studies, oligonucleotide building blocks – the phosphonate 3a and the phosphoramidite 3b – were prepared from 1b via 4a and 5 , as well as the Fractosil-linked 6b , and used in solid-phase synthesis. The applicability of various N-protecting groups (see 4a – c ) was also studied. The Hoogsteen duplex d(c1A)20] · d(T20) ( 11 · 13 ; Tm 15°) is less stable than d(A20) · d(T20) ( 12 · 13 ; Tm 60°). The block oligomers d(c1A)10–;T10] ( 14 ) and dT10–(c1A)10] ( 15 ) containing purine and pyrimidine bases in the same strand are also able to form duplexes with each other. The chain polarity was found to be parallel. |
