Phosphoramidites of base-modified 2′-deoxyinosine isosteres and solid-phase synthesis of d(GCI*CGC) oligomers containing an ambiguous base

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Abstract
Novel phosphoramidites ( 1,2 ) of appropriately protected 2′-deoxyinosine isosteres (I * ) such as allopurinol 2′-deoxy-ribofuranoside ( 4a ) and 7-deaza-2′-deoxyinosine ( 4b ) have been synthesized. They were employed together with the phosphorami-dite of 2′-deoxyinosine in solid-phase synthesis of d(GCI * CGC) hexamers ( 12a-d ). From thermodynamic data of these alternating hexamers it was shown that allopurinol 2′-deoxyribofuranoside destabilizes such duplexes less strongly than 2′-deoxyinosine. Additionally, the phosphoramidite of 7-deaza-2′-deoxyinosine ( 2 ) exhibits an extraordinary stability of the N-glycosylic bond. Since the new phosphoramidites are structurally related to 2′-deoxyinosine, they can be used in the construction of hybridization probes containing an ambiguous base.