Building‐Block Approach for the Straightforward Incorporation of a New FRET (Fluorescence‐Resonance‐Energy Transfer) System into Synthetic DNA

The synthesis of the two new phosphoramidites 5 and 8 bearing a carbostyril (=quinolin‐2(1 H )‐one) chromophore used as donor entity in our recently developed new FRET (fluorescence‐resonance‐energy transfer) system is described ( Schemes 1 and 2 ) The high stability of the chromophore to basic conditions enables the incorporation of the phosphoramidites directly into DNA during solid‐phase synthesis ( Schemes 3 and 4 ). Since this is also possible for the (bathophenanthroline)ruthenium(II) complex used as acceptor ( Scheme 4, Steps d and e ), the whole labelling procedure to insert the FRET system into synthetic DNA is straightforward and represents a major improvement to our previous strategy.